TECHNICAL FIELD
[0001]
The present invention relates to techniques for manufacturing, by hot forging, a
crankshaft (hereinafter also referred to as a "forged crankshaft") for a three-cylinder
engine. In particular, the present invention relates to an apparatus for forming, in the
process of manufacturing a forged crankshaft, a blank for finish forging to be subjected
to finish forging by which a final shape of the forged crankshaft is obtained, and a
method for manufacturing a forged crankshaft for a three-cylinder engine including
preforming steps using such forming apparatus.
BACKGROUND ART
[0002]
In engines of passenger cars, motorcycles, agricultural machines, and the like,
a crankshaft is required for taking out power by converting reciprocating motion of
pistons to rotary motion. Generally, there are two types of crankshafts: those that are
manufactured by forging and those that are manufactured by casting, and the former
forged crankshafts superior in terms of strength and stiffness are more widely used. In
recent years, in order to improve fuel economy performance and meet emission
regulations, downsizing of engine displacement becomes popular, and a three-cylinder
engine is attracting wide attention.
[0003]
In general, forged crankshafts for three-cylinder engines are manufactured by
using, as a starting material, a billet having a circular or square cross section and having
a constant cross-sectional area along the entire length, and subjecting the billet to the
steps of preforming, die forging, trimming and coining in order. The preforming step
includes roll forming and bending (so called "preforming"), and the die forging step
includes block forging and finish forging.
[0004]
FIG 1 is a schematic diagram illustrating a typical conventional process for
manufacturing a forged crankshaft for a three-cylinder engine. A crankshaft 1
illustrated in FIG 1 is to be mounted in a three-cylinder engine. It is a three-cylinder
four-counterweight crankshaft that includes: four journals Jl to J4; three crank pins PI
to P3; a front part Fr; a flange Fl; and six crank arms (hereinafter referred to as "arms"
to be simple) Al to A6 that alternatively connect the journals Jl to J4 and the crank pins
PI to P3 to each other, wherein among the six arms Al to A6, first and second arms Al
and A2, and fifth and sixth arms A5 and A6 respectively connecting to first and third
crank pins PI and P3 at opposite ends, have balance weights. Hereinafter, when the
journals Jl to J4, the crank pins PI to P3, and the arms Al to A6 are each collectively
referred to, a reference character "J" is used for the journals, a reference character "P"
for the crank pins, and a reference character "A" for the arms.
[0005]
According to the manufacturing method shown in FIG 1, the forged crankshaft
1 is manufactured in the following manner. Firstly, a billet 2 shown in FIG 1(a),
which has been previously cut to a predetermined length, is heated by an induction
heater or a gas atmosphere furnace and then is subjected to roll forming. In the roll
forming step, the billet 2 is rolled and reduced in cross section by grooved rolls, for
example, to distribute its volume in the longitudinal direction, whereby a rolled blank
103, which is an intermediate material, is formed (see FIG 1(b)). In the bending step,
the rolled blank 103 obtained by the roll forming is partially pressed in a press in a
direction perpendicular to the longitudinal direction to distribute its volume, whereby a
bent blank 104, which is a secondary intermediate material, is formed (see FIG 1(c)).
[0006]
Then, in the block forging step, the bent blank 104 obtained by bending is press
forged with a pair of upper and lower dies, whereby a forged blank 105 having a general
shape of a crankshaft (forged final product) is formed (see FIG 1(d)). Then, in the
finish forging step, the block forged blank 105 obtained by the block forging is further
3
processed by press forging the block forged blank 105 with a pair of upper and lower
dies, whereby a forged blank 106 having a shape in agreement with the shape of the
crankshaft is formed (see FIG. 1(e)). In the block forging and the finish forging,
excess material flows out as a flash from between the parting surfaces of the dies that
oppose each other. Thus, the block forged blank 105 and the finish forged blank 106
have large flashes 105a and 106a, respectively, around the formed shape of the
crankshaft.
[0007]
In the trimming step, the finish forged blank 106 with the flash 106a, obtained
by the finish forging, is held by dies from above and below and the flash 106a is
trimmed by a cutting die. In this manner, the forged crankshaft 1 is obtained as shown
in FIG 1(f). In the coining step, principal parts of the forged crankshaft 1, from which
the flash has been removed, e.g., shaft parts such as the journals J, the crank pins P, the
front part Fr, and the flange Fl, and in some cases the arms A, are slightly pressed with
dies from above and below and formed into a desired size and shape. Finally, the
forged crankshaft 1 is manufactured.
[0008]
The manufacturing process shown in FIG. 1 is applicable not only to a
three-cylinder four-counterweight crankshaft as exemplified, but also to a three-cylinder
six-counterweight crankshaft in which, all six arms A have balance weights. It should
be noted that, when adjustment of a placement angle of the crank pins is necessary, a
step of twisting is added after the trimming step.
[0009]
With such a manufacturing method, however, it is inevitable that material
utilization decreases since large amounts of unnecessary flash, which is not a part of the
end product, are generated. Thus, in the manufacturing of a forged crankshaft, it has
been so far an important object to inhibit the generation of flash to the extent possible
and achieve improvement of material utilization. Examples of conventional
techniques that address this object are as follows.
[0010]
For example, Patent Literature 1 discloses a technique for manufacturing a
crankshaft, the technique including: using, as a blank, a stepped round bar having
reduced diameter regions at portions to be formed into journals and crank pins of a
crankshaft; holding, with dies, a pair of the portions to be formed into journals, between
which a portion to be formed into a crank pin is disposed and, in this state, axially
moving the opposing dies toward each other to compressively deform the round bar
blank; pressing punches against the portion to be formed into a crank pin in a direction
perpendicular to the axial direction to place the portion to be formed into a crank pin
into an eccentric position; and repeating the above operations in succession for all crank
throws, whereby the journals and the crank pins are shaped and the arms are roughly
shaped.
[0011]
Further, Patent Literature 2 discloses a technique for manufacturing a
crankshaft, the technique including: using, as a blank, a simple round bar; holding one
end of the two ends of the round bar with a stationary die and the other end thereof with
a movable die, and holding portions to be formed into journals with journal dies and
portions to be formed into crank pins with crank pin dies; in this state, axially moving
the movable die, the journal dies, and the crank pin dies toward the stationary die to
compressively deform the round bar blank; and moving the crank pin dies in an
eccentric direction perpendicular to the axial direction to place the portion to be formed
into the crank pin into an eccentric position, whereby the journals and the crank pins are
shaped and the arms are roughly shaped.
[0012]
With both the techniques disclosed in Patent Literatures 1 and 2, no flash will
be generated, and therefore a significant improvement in material utilization can be
expected.
CITATION LIST
PATENT LITERATURE
[0013]
Patent Literature 1: Japanese Patent Application Publication No. 2008-155275
Patent Literature 2: Japanese Patent Application Publication No. 2011-161496
SUMMARY OF INVENTION
-*5
TECHNICAL PROBLEM
[0014]
As described above, according to the techniques disclosed in Patent Literatures
1 and 2, a round bar blank is directly processed into a crankshaft shape. However,
forged crankshafts are required to have high strength and high stiffness, thus blanks for
the forged crankshaft are not easily deformable. As such, crankshafts that would be
practically manufacturable are inevitably limited to the ones having arms of large
thickness and crank pins with a small amount of eccentricity, and therefore having a
relatively gentle crankshaft shape. Moreover, the shape of the arms is limited to a
simple one without a balance weight.
[0015]
In addition, according to the techniques disclosed in Patent Literatures 1 and 2,
the shape of arms is formed by free expansion of a round bar blank in a direction
perpendicular to the axial direction in conjunction with its axial compressive
deformation and by tensile deformation of the round bar blank in conjunction with the
movement of portions to be formed into crank pins in an eccentric direction. Because
of this, the contour shape of the arms tend to be unstable, and thus dimensional accuracy
cannot be ensured.
[0016]
The present invention has been made in view of the above-mentioned problems.
Accordingly, in order to manufacture forged crankshafts for three-cylinder engines with
high material utilization and also with high dimensional accuracy regardless of their
shapes, it is an object of the present invention to provide an apparatus for use in forming
a blank for finish forging to be subjected to finish forging on the premise that, in the
process of manufacturing the forged crankshaft, finish forging for forming its final
shape is performed. Further, it is another object of the present invention to provide a
method for manufacturing forged crankshafts for three-cylinder engines with high
material utilization and also with high dimensional accuracy regardless of their shapes.
SOLUTION TO PROBLEM
[0017]
In order to achieve the above object, the present invention is directed to an
apparatus for forming a blank for finish forging for a forged crankshaft for a
three-cylinder engine as set forth in (1) and (2) below and a method for manufacturing a
forged crankshaft for a three-cylinder engine as set forth in (3) to (6) below.
[0018]
A forming apparatus according to one embodiment of the present invention is
an apparatus for forming, in the process of manufacturing the forged crankshaft for a
three-cylinder engine, the blank for finish forging to be subjected to finish forging by
which a final shape of the forged crankshaft is formed, from a preform blank including:
rough journal portions having an axial length equal to an axial length of journals of the
forged crankshaft; rough crank pin portions having an axial length equal to an axial
length of crank pins of the forged crankshaft; and rough crank arm portions having an
axial thickness greater than an axial thickness of crank arms of the forged crankshaft.
The apparatus has a configuration described below.
[0019]
(1) The rough crank pin portions in the preform blank have a smaller amount of
eccentricity in the direction perpendicular to the axial direction than an amount of
eccentricity of the crank pins of the forged crankshaft.
The forming apparatus according to one embodiment of the present invention
includes a reference crank pin die, movable crank pin dies, and journal dies, described
below.
The reference crank pin die is disposed at a location of one rough crank pin
portion among the rough crank pin portions, configured to be brought into contact with
such rough crank pin portion, and configured to move in the direction perpendicular to
the axial direction, but be constrained from moving in the axial direction, while being in
contact with side surfaces of rough crank arm portions through which the rough crank
arm portions connect with such rough crank pin portion.
The movable crank pin dies are disposed at locations of the corresponding
rough crank pin portions except the one being in contact with the reference crank pin
die, configured to be brought into contact with such rough crank pin portions, and
configured to move axially toward the reference crank pin die and in the direction
perpendicular to the axial direction, while being in contact with side surfaces of the
rough crank arm portions through which the rough crank arm portions connect with
such rough crank pin portions.
The journal dies are disposed at locations of the corresponding rough journal
portions, configured to hold and retain such rough journal portions therebetween in the
direction perpendicular to the axial direction, and configured to move axially toward the
reference crank pin die while being in contact with side surfaces of the rough crank arm
portions through which the rough crank arm portions connect with such rough journal
portions.
The forming apparatus is configured such that in a state that the rough journal
portions are held and retained by the journal dies and the rough crank pin portions are
contacted with the reference crank pin die and the movable crank pin dies, the journal
dies are moved axially, the movable crank pin dies are moved axially and in the
direction perpendicular to the axial direction, and the reference crank pin die is moved
in the direction perpendicular to the axial direction, thereby compressing the rough
crank arm portions in the axial direction so as to reduce the thickness thereof to the
thickness of crank arms of the forged crankshaft, and pressing the rough crank pin
portions in the direction perpendicular to the axial direction so as to increase the amount
of eccentricity thereof to the amount of eccentricity of the crank pins of the forged
crankshaft.
[0020]
In the above forming apparatus in (1), it is preferred that the reference crank
pin die and the movable crank pin dies each includes an auxiliary crank pin die disposed
at a location outside of the corresponding rough crank pin portion, opposite to the side
where the reference crank pin die and the movable crank pin dies are contacted, and in
conjunction with the axial movement of the journal dies as well as that of the movable
crank pin dies and the auxiliary crank pin dies forming pairs therewith, a movement of
the crank pin dies in the direction perpendicular to the axial direction is controlled in a
manner that the rough crank pin portions to be deformed by pressing reach to the
auxiliary crank pin dies after spaces between the journal dies, the reference crank pin
die, the movable crank pin dies, and the auxiliary crank pin dies are filled.
[0021]
This forming apparatus preferably has a configuration such that, provided that
a total length of movement of the reference crank pin die and the movable crank pin
dies in the direction perpendicular to the axial direction is a 100% length of movement
thereof, when the axial movement of the journal dies that are adjacent to such crank pin
dies is completed, a length of movement of such crank pin dies in the direction
perpendicular to the axial direction is 90% or less of the total length of movement, and
thereafter, the movement of such crank pin dies in the direction perpendicular to the
axial direction is completed.
[0022]
Further, the above forming apparatus in (1) may have a configuration such that
the reference crank pin die, the movable crank pin dies, and the journal dies are
mounted on a press machine that is capable of being moved downward along the
direction perpendicular to the axial direction and, by the downward movement of the
press machine, the journal dies are caused to hold and retain the rough journal portions
therebetween while the reference crank pin die and the movable crank pin dies are
brought into contact with the rough crank pin portions, and with continued downward
movement of the press machine, the journal dies are moved axially by wedge
mechanisms, and the movable crank pin dies are caused to move axially by the
movement of the journal dies.
[0023]
In case of this forming apparatus, it is preferred that the wedge mechanisms
have different wedge angles for each journal die. Furthermore, it is preferred that the
reference crank pin die and the movable crank pin dies are coupled to hydraulic
cylinders and caused to move in the direction perpendicular to the axial direction by
driving the hydraulic cylinders.
[0024]
(2) Among the rough crank pin portions in a preform blank, first and third
rough crank pin portions at opposite ends have an amount of eccentricity in a direction
perpendicular to an axial direction in the opposite direction to each other, the amount of
eccentricity thereof being less than a V3/2 of an amount of eccentricity of the crank pins
of the forged crankshaft, and a second rough crank pin portion in the center has an
amount of eccentricity in the direction perpendicular to the axial direction of zero or has
the same amount of eccentricity in a direction perpendicular to an eccentric direction of
the first and third rough crank pin portions as an amount of eccentricity of the crank pin
of the forged crankshaft.
The forming apparatus according to one embodiment of the present invention
includes a reference crank pin die, movable crank pin dies, and journal dies, described
below.
The reference crank pin die is disposed at a location of the second rough crank
pin portion, configured to be brought into contact with the second rough crank pin
portion, and configured to be constrained from moving in the axial direction while,
being in contact with side surfaces of rough crank arm portions through which the rough
crank arm portions connect with the second rough crank pin portion.
The movable crank pin dies are disposed at locations of the corresponding first
and third rough crank pin portions, configured to be brought into contact with the first
and third rough crank pin portions, and configured to move axially toward the reference
crank pin die and in the direction perpendicular to the axial direction, while being in
contact with side surfaces of the rough crank arm portions through which the rough
crank arm portions connect with the first and third rough crank pin portions.
The journal dies are disposed at locations of the corresponding rough journal
portions, configured to hold and retain such rough journal portions therebetween in the
direction perpendicular to the axial direction, and configured to move axially toward the
reference crank pin die while being in contact with side surfaces of the rough crank arm
portions through which the rough crank arm portions connect with such rough journal
portions.
The forming apparatus is configured such that in a state that the rough journal
portions are held and retained by the journal dies and the rough crank pin portions are
contacted with the reference crank pin die and the movable crank pin dies, the journal
dies are moved axially and the movable crank pin dies are moved axially and in the
direction perpendicular to the axial direction, thereby compressing the rough crank arm
portions in the axial direction so as to reduce the thickness thereof to the thickness of
crank arms of a forged crankshaft, and pressing the first and third rough crank pin
portions in the direction perpendicular to the axial direction, but in the opposite
direction to each other, so as to increase the amount of eccentricity thereof to theV3/2 of
the amount of eccentricity of crank pins of the forged crankshaft.
[0025]
to
(3) A method for manufacturing a forged crankshaft for a three-cylinder engine
includes the following successive steps comprising a first preforming step, a second
preforming step, and a finish forging step.
The first preforming step forms, as the preform blank to be supplied to the
above forming apparatus in (1), a preform blank in which first and third rough crank pin
portions at opposite ends among the rough crank pin portions have an amount of
eccentricity in a direction perpendicular to an axial direction in the opposite direction to
each other, the amount of eccentricity thereof being equal to a V3/2 of an amount of
eccentricity of crank pins of the forged crankshaft, and a second rough crank pin portion
in the center has a smaller amount of eccentricity in the direction perpendicular to the
axial direction in the direction perpendicular to an eccentric direction of the first and
third rough crank pin portions than an amount of eccentricity of the crank pin of the
forged crankshaft.
The second preforming step forms, as the blank for finish forging, a blank for
finish forging in which a final shape of the forged crankshaft is formed including a
placement angle of the crank pins using the above forming apparatus described in (1).
In the finish forging step, finish forging is performed on the blank for finish
forging to form a forged product having the final shape of the forged crankshaft
including the placement angle of the crank pins.
[0026]
(4) A method for manufacturing a forged crankshaft for a three-cylinder engine
includes the following successive steps comprising a first preforming step, a second
preforming step, a finish forging step, and a twisting step.
The first preforming step forms, as the preform blank to be supplied to the
above forming apparatus in (1), a preform blank in which first and third rough crank pin
portions at opposite ends among the rough crank pin portions have a smaller amount of
eccentricity in a direction perpendicular to an axial direction in the same direction than
an amount of eccentricity of crank pins of the forged crankshaft, and a second rough
crank pin portion in the center has a smaller amount of eccentricity in the direction
perpendicular to the axial direction in the direction opposite to an eccentric direction of
the first and third rough crank pin portions than an amount of eccentricity of the crank
pin of the forged crankshaft.
The second preforming step forms, as the blank for finish forging, a blank for
finish forging in which a final shape of the forged crankshaft is formed excluding a
placement angle of the crank pins using the above forming apparatus in (1).
In the finish forging step, finish forging is performed on the blank for finish
forging to form a forged product having the final shape of the forged crankshaft
excluding the placement angle of the crank pins.
In the twisting step, the placement angle of the crank pins of the forged product
is adjusted to the placement angle of the crank pins of the forged crankshaft.
[0027]
(5) A method for manufacturing a forged crankshaft for a three-cylinder engine
includes the following successive steps comprising a first preforming step, a second
preforming step, and a finish forging step.
The first preforming step forms, as the preform blank to be supplied to the
above forming apparatus in (2), a preform blank in which first and third rough crank pin
portions at opposite ends among the rough crank pin portions have an amount of
eccentricity in a direction perpendicular to an axial direction in the opposite direction to
each other, the amount of eccentricity thereof being less than a V3/2 of an amount of
eccentricity of the crank pins of the forged crankshaft, and a second rough crank pin
portion in the center has an amount of eccentricity in the direction perpendicular to the
axial direction of zero.
The second preforming step forms, using the above forming apparatus
described in (2), as the blank for finish forging, a blank for finish forging in which the
first and third rough crank pin portions at opposite ends among the rough crank pin
portions have an amount of eccentricity in the direction perpendicular to the axial
direction in the opposite direction to each other, the amount of eccentricity thereof being
equal to the V3/2 of the amount of eccentricity of the crank pins of the forged crankshaft,
and the second rough crank pin portion in the center remains the same amount of
eccentricity in the direction perpendicular to the axial direction as the preform blank.
In the finish forging step, finish forging is performed on the blank for finish
forging in a state that the first and third rough crank pin portions at opposite ends are
horizontally placed, whereby all the rough crank pin portions are pressed in the
direction perpendicular to the axial direction to form a forged product having a final
shape of the forged crankshaft including a placement angle of the crank pins.
[0028]
(6) A method for manufacturing a forged crankshaft for a three-cylinder engine
includes the following successive steps comprising a first preforming step, a second
preforming step, and a finish forging step.
The first preforming step forms, as the preform blank to be supplied to the
above forming apparatus in (2), a preform blank in which first and third rough crank pin
portions at opposite ends among the rough crank pin portions have an amount of
eccentricity in a direction perpendicular to an axial direction in the opposite direction to
each other, the amount of eccentricity thereof being less than a V3/2 of an amount of
eccentricity of the crank pins of the forged crankshaft, and a second rough crank pin
portion in the center has an amount of eccentricity in the direction perpendicular to the
axial direction in the direction perpendicular to an eccentric direction of the first and
third rough crank pin portions, the amount of eccentricity thereof being the same as an
amount of eccentricity of the crank pin of the forged crankshaft.
The second preforming step forms, using the above forming apparatus
described in (2), as the blank for finish forging, a blank for finish forging in which the
first and third rough crank pin portions at opposite ends among the rough crank pin
portions have an amount of eccentricity in the direction perpendicular to the axial
direction in the opposite direction to each other, the amount of eccentricity thereof being
equal to the V3/2 of the amount of eccentricity of the crank pins of the forged crankshaft,
and the second rough crank pin portion in the center remains the same amount of
eccentricity in the direction perpendicular to the axial direction as the preform blank.
In the finish forging step, finish forging is performed on the blank for finish
forging in a state that the first and third rough crank pin portions at opposite ends are
horizontally placed, whereby the first and third rough crank pin portions are pressed in
the direction perpendicular to the axial direction to form a forged product having a final
shape of the forged crankshaft including a placement angle of the crank pins.
ADVANTAGEOUS EFFECTS OF INVENTION
[0029]
With the forming apparatus of the present invention and the manufacturing
method including the preforming steps in which such apparatus is used, it is possible to
form, from a preform blank without a flash, a blank for finish forging without a flash
which has a shape generally in agreement with a shape of a forged crankshaft for a
three-cylinder engine having thin arms. When such a blank for finish forging without
a flash is subjected to finish forging, it is possible to obtain a final shape of a forged
crankshaft including the contour shape of arms although some minor amount of flash is
generated. Thus, forged crankshafts for three-cylinder engines can be manufactured
with high material utilization and also with high dimensional accuracy regardless of
their shapes.
BRIEF DESCRIPTION OF DRAWINGS
[0030]
[FIG 1] FIG. 1 is a schematic diagram illustrating a typical conventional
process for manufacturing a forged crankshaft for a three-cylinder engine.
[FIG 2] FIG 2 is a diagram schematically showing the shapes of a preform
blank to be processed by the forming apparatus, a blank for finish forging formed
therefrom, and a forged product after finish forging, in the manufacturing method of a
first embodiment of the present invention.
[FIG 3] FIG. 3 is a schematic diagram illustrating a process for manufacturing
a forged crankshaft for a three-cylinder engine according to the first embodiment of the
present invention.
[FIG 4] FIG 4 is a longitudinal sectional view showing a configuration of the
forming apparatus according to the first embodiment of the present invention.
[FIG. 5] FIG. 5 is a longitudinal sectional view illustrating a process for
forming a blank for finish forging using the forming apparatus according to the first
embodiment of the present invention shown in FIG 4, with a forming state at an initial
stage shown therein.
[FIG. 6] FIG. 6 is a longitudinal sectional view illustrating a process for
forming a blank for finish forging using the forming apparatus according to the first
embodiment of the present invention shown in FIG. 4, with a forming state at the
completion shown therein.
[FIG. 7] FIG. 7 is a diagram illustrating how fin flaws occur in forming a blank
for finish forging using the forming apparatus of the present invention.
[FIG 8] FIG 8 is a diagram illustrating how fin flaws are prevented by taking a
measure in forming a blank for finish forging using the forming apparatus of the present
invention.
[FIG 9] FIG 9 is a diagram schematically showing the shapes of a preform
blank to be processed by the forming apparatus, a blank for finish forging formed
therefrom, a forged product after finish forging, and a twisted product after twisting, in
the manufacturing method of a second embodiment of the present invention.
[FIG 10] FIG 10 is a schematic diagram illustrating a process for
manufacturing a forged crankshaft for a three-cylinder engine according to the second
embodiment of the present invention.
[FIG 11] FIG 11 is a longitudinal sectional view showing a configuration of
the forming apparatus according to the second embodiment of the present invention.
[FIG 12] FIG 12 is a longitudinal sectional view illustrating a process for
forming a blank for finish forging using the forming apparatus according to the second
embodiment of the present invention shown in FIG 11, with a forming state at an initial
stage shown therein.
[FIG 13] FIG 13 is a longitudinal sectional view illustrating a process for
forming a blank for finish forging using the forming apparatus according to the second
embodiment of the present invention shown in FIG 11, with a forming state at the
completion shown therein.
[FIG 14] FIG 14 is a diagram schematically showing the shapes of a preform
blank to be processed by the forming apparatus, a blank for finish forging formed
therefrom, and a forged product after finish forging, in the manufacturing method of a
third embodiment of the present invention.
[FIG 15] FIG 15 is a schematic diagram illustrating a process for
manufacturing a forged crankshaft for a three-cylinder engine according to the third
embodiment of the present invention.
[FIG. 16] FIG. 16 is a longitudinal sectional view showing a configuration of
the forming apparatus according to the third embodiment of the present invention.
[FIG 17] FIG 17 is a longitudinal sectional view illustrating a process for
forming a blank for finish forging using the forming apparatus according to the third
embodiment of the present invention shown in FIG 16, with a forming state at an initial
stage shown therein.
[FIG 18] FIG 18 is a longitudinal sectional view illustrating a process for
forming a blank for finish forging using the forming apparatus according to the third
embodiment of the present invention shown in FIG 16, with a forming state at the
completion shown therein.
[FIG 19] FIG 19 is a diagram schematically showing the shapes of a preform
blank to be processed by the forming apparatus, a blank for finish forging formed
therefrom, and a forged product after finish forging, in the manufacturing method of a
fourth embodiment of the present invention.
[FIG 20] FIG 20 is a schematic diagram illustrating a process for
manufacturing a forged crankshaft for a three-cylinder engine according to the fourth
embodiment of the present invention.
DESCRIPTION OF EMBODIMENTS
[0031]
The present invention is based on the premise that, in manufacturing a forged
crankshaft for a three-cylinder engine, finish forging is performed in the manufacturing
process. The forming apparatus of the present invention is used for forming, in a step
prior to finish forging, a blank for finish forging to be subjected to the finish forging,
from a preform blank. With regard to the apparatus for forming a blank for finish
forging for a forged crankshaft for a three-cylinder engine and the method for
manufacturing a forged crankshaft for a three-cylinder engine including the preforming
steps using such apparatus, of the present invention, embodiments thereof are described
in detail below.
[0032]
1. First Embodiment
1-1. Preform Blank To Be Processed, Blank For Finish Forging Formed Therefrom, and
Forged Product After Finish Forging
FIG 2 is a diagram schematically showing the shapes of a preform blank to be
processed by the forming apparatus, a blank for finish forging formed therefrom, and a
forged product after finish forging, in the manufacturing method of the first embodiment
of the present invention. FIG 2 illustrates how a three-cylinder four-counterweight
crankshaft is manufactured as an example and displays plane views showing an outside
appearance of the crankshaft and drawings depicting an arrangement of crank pins with
a view along an axial direction side by side to facilitate understanding of the shapes of
the blanks in each step.
[0033]
As shown in FIG 2, a preform blank 4 of the first embodiment has a crankshaft
shape that is approximate to a shape of a forged crankshaft 1 for a three-cylinder
four-counterweight shown in FIG 1 (f) but is generally in a rough shape. The preform
blank 4 includes: four rough journal portions Jla to J4a; three rough crank pin portions
PI a to P3a; a rough front part portion Fra; a rough flange portion Fla; and six rough
crank arm portions Ala to A6a (hereinafter also referred to simply as "rough arm
portions") that alternatively connect the rough journal portions Jla to J4a, and the rough
crank pin portions PI a to P3a to each other. The preform blank 4 has no flash.
Hereinafter, when the rough journal portions Jla to J4a, the rough crank pin portions
PI a to P3a, and the rough arm portions Ala to A6a, of the preform blank 4, are each
collectively referred to, a reference character "Ja" is used for the rough journal portions,
a reference character "Pa" for the rough crank pin portions, and a reference character
"Aa" for the rough arm portions.
[0034]
A blank for finish forging 5 of the first embodiment is formed from the preform
blank 4 described above using a forming apparatus, details of which will be provided
later. The blank for finish forging 5 includes four rough journal portions Jib to J4b,
three rough crank pin portions Plb to P3b, a rough front part portion Frb, a rough flange
portion Fib, and six rough crank arm portions Alb to A6b (hereinafter also referred to
simply as "rough arm portions") that alternatively connect the rough journal portions
Jib to J4b, and the rough crank pin portions Plb to P3b to each other. The blank for
finish forging 5 has no flash. Hereinafter, when the rough journal portions Jib to J4b,
the rough crank pin portions Plb to P3b, and the rough arm portions Alb to A6b, of the
blank for finish forging 5, are each collectively referred to, a reference character "Jb" is
used for the rough journal portions, a reference character "Pb" for the rough crank pin
portions, and a reference character "Ab" for the rough arm portions.
[0035]
A forged product 6 of the first embodiment is obtained from the blank for
finish forging 5 described above by finish forging. The forged product 6 includes four
journals Jlc to J4c, three crank pins Pic to P3c, a front part Frc, a flange Flc, and six
crank arms Ale to A6c (hereinafter also referred to simply as "arms") that alternatively
connect the journals Jlc to J4c, and the crank pins Pic to P3c to each other.
Hereinafter, when the journals Jlc to J4c, the crank pins Pic to P3c, and the arms Ale
to A6c, of the forged product 6, are each collectively referred to, a reference character
"Jc" is used for the journals, a reference character "Pc" for the crank pins, and a
reference character "Ac" for the arms.
[0036]
The forged product 6 has a shape that is in agreement with a shape of a
crankshaft (forged final product) including a placement angle of the crank pins Pc and
corresponds to a forged crankshaft 1 shown in FIG. 1(f). Specifically, the journals Jc
of the forged product 6 have an axial length equal to that of journals J of the forged
crankshaft having the final shape. The crank pins Pc of the forged product 6 have an
axial length equal to that of crank pins P of the forged crankshaft having the final shape.
Further, the crank pins Pc of the forged product 6 have the same amount of eccentricity
in a direction perpendicular to an axial direction and the same placement angle of 120°
as the crank pins P of the forged crankshaft having the final shape, thus they are placed
at the specified positions. The arms Ac of the forged product 6 have an axial thickness
equal to that of arms A of the forged crankshaft having the final shape.
[0037]
The blank for finish forging 5 has a shape that is generally in agreement with
the shape of the forged product 6 and corresponds exactly to a block forged blank 105
shown in FIG. 1(d) with a difference therebetween being a flash 105a. Specifically, the
rough journal portions Jb of the blank for finish forging 5 have an axial length equal to
that of the journals J of the forged crankshaft having the final shape (journals Jc of
forged product 6). The rough crank pin portions Pb of the blank for finish forging 5
have an axial length equal to that of the crank pins P of the forged crankshaft having the
final shape (crank pins Pc of forged product 6). Further, the crank pins Pb of the blank
for finish forging 5 have the same amount of eccentricity in the direction perpendicular
to the axial direction and the same placement angle of 120° as the crank pins P of the
forged crankshaft having the final shape, thus they are placed at the specified positions.
The rough arm portions Ab of the blank for finish forging 5 have an axial thickness
equal to that of the arms A of the forged crankshaft having the final shape (arms Ac of
forged product 6).
[0038]
In contrast, the rough journal portions Ja of the preform blank 4 have an axial
length equal to that of the rough journal portions Jb of the blank for finish forging 5, i.e.,
that of the journals J of the forged crankshaft (journals Jc of forged product 6). The
rough crank pin portions Pa of the preform blank 4 have an axial length equal to that of
the rough crank pin portions Pb of the blank for finish forging 5, i.e., that of the crank
pins P of the forged crankshaft (crank pins Pc of forged product 6), but have a smaller
amount of eccentricity than that of the rough crank pin portions Pb of the blank for
finish forging 5. Specifically, the first and third rough crank pin portions PI a and P3a
at opposite ends among the rough crank pin portions Pa of the preform blank 4 have an
amount of eccentricity in the opposite direction to each other, the amount of eccentricity
thereof being equal to a V3/2 of an amount of eccentricity in the crank pins P of the
forged crankshaft. On the other hand, the second rough crank pin portion P2a in the
center is configured to have an amount of eccentricity in the direction perpendicular to
an eccentric direction of the first and third rough crank pin portions Pla and P3a, the
amount of eccentricity thereof being approximately equal to a half of an amount of
eccentricity in the crank pin P of the forged crankshaft.
[0039]
The rough arm portions Aa of the preform blank 4 have an axial thickness
greater than that of the rough arm portions Ab of the blank for finish forging 5, i.e., that
of the arms A of the forged crankshaft (arms Ac of forged product 6). Essentially, in
comparison with the blank for finish forging 5 (forged crankshaft and forged product 6,
having final shape), the preform blank 4 has an overall length that is relatively long by
the additional thickness of the rough arm portions Aa, and has a smaller amount of
eccentricity of the rough crank pin portions Pa. Thus, the preform blank 4 has a
relatively gentle crankshaft shape.
[0040]
J**
However, strictly speaking, the blank for finish forging 5 has such a
configuration that, with respect to the final shapes of the forged crankshaft and the
forged product 6, the rough arm portions Ab are made slightly thinner and therefore the
axial lengths of the rough journal portions Jb and the rough crank pin portions Pb are
accordingly slightly greater. This is intended to ensure that the blank for finish forging
5 can be easily received by the dies when finish forging is performed and thereby
prevent the occurrence of scoring. Correspondingly, the preform blank 4, too, has such
a configuration that, with respect to the final shapes of the forged crankshaft and the
forged product 6, the axial lengths of the rough journal portions J' and the rough crank
pin portions P' are accordingly slightly greater.
[0041]
1-2. Process For Manufacturing Forged Crankshaft For Three-Cylinder Engine
FIG 3 is a schematic diagram illustrating a process for manufacturing a forged
crankshaft for a three-cylinder engine according to the first embodiment of the present
invention. As shown in FIG. 3, the process for manufacturing the forged crankshaft for
the three-cylinder engine of the first embodiment includes a first preforming step, a
second preforming step, and a finish forging step, and also includes a trimming step and
a coining step as necessary.
[0042]
The first preforming step is a step in which the preform blank 4 described
above is obtained. In the first preforming step, such a preform blank 4 can be obtained
by using a round billet having a circular cross section as a starting material and applying
a preforming operation to the round billet after it is heated by an induction heater or a
gas atmosphere furnace. For example, the preform blank 4 can be obtained in a
manner such that: the round billet is subjected to roll forming in which it is
reduction-rolled by grooved rolls to distribute its volume in the longitudinal direction;
and the resulting rolled blank is repeatedly subjected to bending in which it is partially
pressed in a press from a direction perpendicular to the longitudinal direction to
distribute its volume. Also, the preform blank 4 may be obtained by using the
techniques disclosed in Patent Literatures 1 and 2. Furthermore, cross roll forging or
fully-enclosed die forging may also be employed.
[0043]
The second preforming step is a step in which the blank for finish forging 5
described above is obtained. In the second preforming step, the blank for finish
forging 5 having the final shape of the forged crankshaft including the placement angle
of crank pins can be obtained from the preform blank 4 described above by using a
forming apparatus described in FIG 4 below.
[0044]
The finish forging step is a step in which the forged product 6 described above
is obtained. In the finish forging step, the blank for finish forging 5 is supplied to be
processed by press forging with a pair of upper and lower dies, whereby the forged
product 6 having a shape in agreement with the shape of the crankshaft of the forged
crankshaft having the final shape including the placement angle of the crank pins can be
obtained.
[0045]
1-3. Apparatus For Forming Blank For Finish Forging
FIG 4 is a longitudinal sectional view showing a configuration of the forming
apparatus according to the first embodiment of the present invention. FIG. 3 illustrates,
as an example, a forming apparatus that is used in manufacturing a three-cylinder
four-counterweight crankshaft, i.e., a forming apparatus configured to form the blank
for finish forging 5 from the preform blank 4 shown in FIG. 2. It should be noted that
in the longitudinal sectional view shown in FIG 4, the first and third rough crank pin
portions are in reality extended in a front-back direction, where either one of them is
located in the front side of the paper and the other one is located in the back side of the
paper, however they are illustrated on the same plane for convenience.
[0046]
As shown in FIG 4, the forming apparatus is configured to utilize a press
machine and includes a stationary lower pressure pad 20 serving as a base and an upper
pressure pad 21, which is lowered by driving a ram of the press machine. A lower die
holder 22, located over the lower pressure pad 20, is resiliently supported via a resilient
member 24. This lower die holder 22 is vertically movable. As the resilient member
24, disc springs, coil springs, air springs, or the like may be employed, or a hydraulic
spring system may be employed. An upper die holder 23 is secured under the upper
pressure pad 21 via support posts 25. This upper die holder 23 is lowered together
with the upper pressure pad 21 by driving the press machine (ram).
[0047]
In the forming apparatus shown in FIG 4, the preform blank 4 is placed in the
dies in a manner such that the first and third rough crank pin portions PI a and P3a are
horizontally positioned and the second rough crank pin portion P2a is positioned in a
lower side in the vertical direction, whereby the preform blank 4 is formed into the
blank for finish forging. Thus, vertically forming pairs, i.e., the journal dies 10U and
10B, the reference crank pin die 11 and the auxiliary crank pin die 13, and the movable
crank pin dies 12 and the auxiliary crank pin dies 13, are apart from each other in the
axial direction of the preform blank 4, and the lower and upper ones are respectively
mounted on the lower die holder 22 and the upper die holder 23.
[0048]
The reference crank pin die 11 and the auxiliary crank pin die 13, vertically
forming a pair, are disposed at a location of one rough crank pin portion Pa serving as a
reference among the rough crank pin portions Pa of the preform blank 4, e.g., the
location of the second rough crank pin portion P2a in the center in FIG. 4, with the
upper one mounted on the upper die holder 23 and the lower one mounted on the lower
die holder 22. The reference crank pin die 11 of the first embodiment is disposed on
the opposite side of a specified position of one of the rough crank pin portions Pa
serving as a reference, whereas its counterpart, the auxiliary crank pin die 13 is disposed
in the same side of the specified position of such rough crank pin portion Pa in the
outside. For example, at the location of the second rough crank pin portion P2a, the
second rough crank pin portion P2a is positioned in the lower side, thus the specified
position thereof is located in the lower side, as a result, the reference crank pin die 11 is
mounted on the upper die holder 23, and its counterpart, the auxiliary crank pin die 13 is
mounted on the lower die holder 22.
[0049]
Particularly, the reference crank pin die 11 and the auxiliary crank pin die 13,
i.e., both the upper and lower dies, are constrained from moving in the axial direction on
the upper die holder 23 and the lower die holder 22, respectively. Only the reference
crank pin die 11 is movable in the direction perpendicular to the axial direction, i.e., the
direction toward the specified position of the rough crank pin portion Pa (downward
direction in FIG 4).
[0050]
The reference crank pin die 11 and the auxiliary crank pin die 13 respectively
have impressions 11a and 13a having a semi-cylindrical shape. The length of the
impressions 11a and 13a is equal to the axial length of the rough crank pin portion P2b
of the blank for finish forging 5.
[0051]
By the lowering of the upper die holder 23 caused by driving the press machine,
i.e., the downward movement of the press machine, the impression 11a is brought into
contact with the second rough crank pin portion P2a, bringing into a state in which the
reference crank pin die 11 at both side surfaces are in contact with the third and fourth
rough arm portions A3 a and A4a at the second rough crank pin portion P2a-side side
surfaces through which the third and fourth rough arm portions A3 a and A4a and the
second rough crank pin portion P2a are connected.
[0052]
The movable crank pin dies 12 and the auxiliary crank pin dies 13, vertically
forming pairs with each other, are disposed at locations of the corresponding rough
crank pin portions Pa excluding the one with which the reference crank pin die 11 is in
contact, e.g., the locations of the first and third rough crank pin portions Pla and P3a in
FIG 4, with the upper ones mounted on the upper die holder 23 and the lower ones
mounted on the lower die holder 22. The movable crank pin dies 12 of the first
embodiment are disposed on the opposite side of specified positions of the
corresponding rough crank pin portions Pa, whereas their counterparts, the auxiliary
crank pin dies 13 are disposed on the same side of the specified positions of the
corresponding rough crank pin portions Pa in the outside. For example, at the location
of the first rough crank pin portion Pla, the specified position of the first rough crank
pin portion Pla is located in the upper side, thus the corresponding movable crank pin
die 12 is mounted on the lower die holder 22, and its counterpart, the auxiliary crank pin
die 13 is mounted on the upper die holder 23.
[0053]
Particularly, all the movable crank pin dies 12 and the auxiliary crank pin dies
13, i.e., both the upper and lower dies, are axially movable toward the reference crank
pin die 11 on the lower die holder 22 and the upper die holder 23, respectively. Only
the movable crank pin dies 12 are movable in the direction perpendicular to the axial
direction, i.e., the direction toward the specified positions of the rough crank pin
portions Pa (upward direction in FIG 4).
[0054]
The movable crank pin dies 12 and the auxiliary crank pin dies 13 respectively
have impressions 12a and 13a having a semi-cylindrical shape. The length of the
impressions 12a and 13a is equal to the axial length of the rough crank pin portions Pb
of the blank for finish forging 5.
[0055]
The journal dies 10U and 10B are disposed at locations of the corresponding
rough journal portion Ja of the preform blank 4, with the upper ones mounted on the
upper die holder 23 and the lower ones mounted on the lower die holder 22.
Particularly, the journal dies 10U and 10B, i.e., both the upper and lower dies, are
axially movable toward the reference crank pin die 11 on the upper die holder 23 and
the lower die holder 22, respectively.
[0056]
The journal dies 10U and 10B respectively have first impressions lOUa and
lOBa having a semi-cylindrical shape and respectively have second impressions lOUb
and lOBb, located adjacent to the first impressions lOUa and lOBa at the front and back
(right and left as seen in FIG 4). The length of the first impressions lOUa and lOBa is
equal to the axial length of the rough journal portions Jb of the blank for finish forging 5.
The length of the second impressions lOUb and lOBb is equal to the axial thickness of
the rough arm portions Ab connecting to the rough journal portions Jb of the blank for
finish forging 5.
[0057]
By the lowering of the upper die holder 23 caused by driving a press machine,
i.e., the downward movement of the press machine, the journal dies 10U and 10B are
caused to hold and retain the rough journal portions Ja from the upper and lower sides
with the first impressions lOUa and lOBa. Concurrently, the journal dies 10U and 10B
are brought into a state in which the second impressions lOUb and lOBb, at their first
impression lOUa and lOBa-side surfaces, are in contact with the rough arm portions Aa,
J** i
at their rough journal portion Ja-side side surfaces through which the rough arm
portions Aa and the rough journal portions Ja are connected.
[0058]
In this operation, by the lowering of the upper die holder 23 caused by driving
the press machine, i.e., the downward movement of the press machine, the reference
crank pin die 11 and the movable crank pin dies 12 are placed in a state in which the
impressions 11a and 12a are brought into contact with the rough crank pin portions Pa,
and both side surfaces of the reference crank pin die 11 and the movable crank pin dies
12 are in contact with the rough arm portions Aa at their rough crank pin portion Pa-side
side surfaces through which the rough arm portions Aa and rough crank pin portions Pa
are connected.
[0059]
The journal dies 10U and 10B disposed at locations of the corresponding first
and fourth rough journal portions Jla and J4a at opposite ends have end surfaces, which
are respectively referred to as inclined surfaces 14U and 14B. In relation to this, on
the lower pressure pad 20, there are provided first wedges 26, each located
correspondingly to the location of the inclined surfaces 14U and 14B of the journal dies
10U and 10B for the first and fourth rough journal portions Jla and J4a. Each of the
first wedges 26 extends upward penetrating through the lower die holder 22. The
inclined surfaces 14B of the lower journal dies 10B, among the journal dies 10U and
10B for the first and fourth rough journal portions Jla and J4a, are in contact with the
slopes of the first wedges 26 in the initial condition. On the other hand, the inclined
surfaces 14U of the upper journal dies 10U are brought into contact with the slopes of
the first wedges 26 by the lowering of the upper die holder 23 caused by driving the
press machine, i.e., the downward movement of the press machine.
[0060]
The journal dies 10U and 10B disposed at locations of the corresponding
second and third rough journal portions J2a and J3a, which are closer to the center, are
provided with blocks, not shown, secured at side sections (front and back sides of the
paper in FIG 4) apart from the first impressions lOUa and lOBa and the second
impressions lOUb and lOBb, the blocks having inclined surfaces 15U and 15B. In
relation to this, on the lower pressure pad 20, there are provided second wedges 27, each
located correspondingly to the location of the inclined surfaces 15U and 15B of the
journal dies 10U and 10B for the second and third rough journal portions J2a and J3a.
Each of the second wedges 27 extends upward penetrating through the lower die holder
22. The inclined surfaces 15B of the lower journal dies 10B, among the journal dies
10U and 10B for the second and third rough journal portions J2a and J3a, are in contact
with the slopes of the second wedges 27 in the initial condition. On the other hand, the
inclined surfaces 15U of the upper journal dies 10U are brought into contact with the
slopes of the second wedges 27 by the lowering of the upper die holder 23 caused by
driving the press machine, i.e., the downward movement of the press machine.
[0061]
Then, with continued downward movement of the press machine, the upper
journal dies 10U are pressed downwardly together with the lower journal dies 10B.
This allows the movable journal dies 10U and 10B for the first and fourth rough journal
portions Jla and J4a, i.e., both the upper and lower ones, to move axially toward the
reference crank pin die 11 for the second rough crank pin portion P2a serving as a
reference, as their inclined surfaces 14U and 14B slide along the slopes of the first
wedges 26. Concurrently, the journal dies 10U and 10B for the second and third rough
journal portions J2a and J3a, i.e., both the upper and lower ones, are allowed to move
axially toward the reference crank pin die 11 for the second rough crank pin portion P2a
serving as a reference as their inclined surfaces 15U and 15B slide along the slopes of
the second wedges 27. Essentially, the journal dies 10U and 10B are all capable of
being moved axially by the wedge mechanisms.
[0062]
Then, the movable crank pin dies 12 and the auxiliary crank pin dies 13 are
pressed downwardly together with continued downward movement of the press
machine. Accordingly, with the axial movement of the journal dies 10U and 10B as
described above, the movable crank pin dies 12 and the auxiliary crank pin dies 13 are
moved axially along with them toward the reference crank pin die 11 for the second
rough crank pin portion P2a serving as a reference. The movement of the reference
crank pin die 11 and the movable crank pin die 12 in the direction perpendicular to the
axial direction is accomplished by driving the hydraulic cylinders 16 coupled to the
crank pin dies 11 and 12.
[0063]
It should be noted that the axial movement of the movable crank pin dies 12
and the auxiliary crank pin dies 13 may be forcibly caused using a wedge mechanism
similar to the one for the journal dies 10U and 1 OB or a separate mechanism such as a
hydraulic cylinder or a servo motor. The auxiliary crank pin dies 13 may be integral
with one of their adjacent journal dies 10U and 10B forming pairs.
[0064]
In the initial condition shown in FIG 4, spaces are secured between the axially
arranged journal dies 10U and 10B, the reference crank pin die 11, the movable crank
pin dies 12, and the auxiliary crank pin dies 13, so as to allow the axial movement of the
journal dies 10U and 10B as well as that of the movable crank pin dies 12 and the
auxiliary crank pin dies 13. The size of the spaces represents the difference between
the thickness of the rough arm portions Ab of the blank for finish forging 5 and the
thickness of the rough arm portions Aa of the preform blank 4.
[0065]
Next, descriptions are given as to how the blank for finish forging is formed
using the thus configured forming apparatus.
FIG. 5 and FIG 6 are longitudinal sectional views illustrating a process for
forming a blank for finish forging using the forming apparatus of the first embodiment
of the present invention shown in FIG 4, with FIG. 5 showing a forming state at the
initial stage and FIG. 6 showing a forming state at the completion.
[0066]
The preform blank 4 is placed in the lower journal die 10B, the movable crank
pin dies 12, and the auxiliary crank pin dies 13, shown in FIG. 4, and then lowering of
the press machine is started. Then, as shown in FIG 5, the upper journal dies 10U are
brought into contact with the corresponding lower journal dies 10B.
[0067]
Thus, the preform blank 4 is brought into a state in which the rough journal
portions Ja are held by the journal dies 10U and 10B from above and below, and the
rough crank pin portions Pa are contacted by the reference crank pin die 11 and the
movable crank pin dies 12. In this state, in the preform blank 4, the rough arm
portions Aa, at their rough journal portion Ja-side side surfaces, are in contact with the
^7
journal dies 10U and 10B, and the rough arm portions Aa, at their rough crank pin
portion Pa-side side surfaces, are in contact with the reference crank pin die 11 and the
movable crank pin dies 12. Further, in this state, the inclined surfaces 14U and 14B of
the journal dies 10U and 10B for the first and fourth rough journal portions Jla and J4a
are in contact with the slopes of the first wedges 26, and the inclined surfaces 15U and
15B of the journal dies 10U and 10B for the second and third rough journal portions J2a
and J3a are in contact with the slopes of the second wedges 27.
[0068]
In this state, the lowering of the press machine is continued. Accordingly, the
inclined surfaces 14U and 14B of the journal dies 10U and 10B for the first and fourth
rough journal portions Jla and J4a slide along the slopes of the first wedges 26, and by
this wedge mechanism, these journal dies 10U and 10B are allowed to move axially
toward the reference crank pin die 11 for the second rough crank pin portion P2a.
Concurrently, the inclined surfaces 15U and 15B of the journal dies 10U and 10B for
the second and third rough journal portions J2a and J3a slide along the slopes of the
second wedges 27, and by this wedge mechanism, these journal dies 10U and 10B are
also allowed to move axially toward the reference crank pin die 11 for the second rough
crank pin portion P2a. By such axial movement of the journal dies 10U and 10B
caused by the wedge mechanism, the movable crank pin dies 12 and the auxiliary crank
pin dies 13 are also allowed to move axially toward the reference crank pin die 11.
[0069]
Accordingly, the spaces between the journal dies 10U and 10B, the reference
crank pin die 11, the movable crank pin dies 12, and the auxiliary crank pin dies 13 are
gradually narrowed, and finally filled. In this process, in the preform blank 4, the
rough arm portions Aa are axially compressed by the journal dies 10U and 10B, the
reference crank pin die 11, and the movable crank pin dies 12, while the axial lengths of
the rough journal portions Ja and the rough crank pin portions Pa are maintained, so that
the thickness of the rough arm portions Aa is reduced to the thickness of the rough arm
portions Ab of the blank for finish forging 5 (see FIG. 6).
[0070]
Also, in coordination with the axial movement of the journal dies 10U and 10B
as well as that of the movable crank pin dies 12 and the auxiliary crank pin dies 13, each
of the hydraulic cylinders 16 for the reference crank pin die 11 and the movable crank
pin dies 12 is operated. Accordingly, the crank pin dies 11 and 12 press the
corresponding rough crank pin portions Pa of the preform blank 4 in the direction
perpendicular to the axial direction. Thus, the rough crank pin portions Pa of the
preform blank 4 are displaced in the vertical direction perpendicular to the axial
direction, and an amount of eccentricity thereof is increased to an amount of eccentricity
of the rough crank pin portions Pb of the blank for finish forging 5, bringing into a state
in which all the rough crank pin portions Pb are disposed in their specified positions
(see FIGS. 2 and 6).
[0071]
In this manner, it is possible to form, from the preform blank 4 without a flash,
the blank for finish forging 5 without a flash, which has a shape generally in agreement
with the shape of the forged crankshaft for the three-cylinder engine having thin arms A
(forged final product). By supplying such a blank for finish forging 5 without a flash
for finish forging, and performing finish forging with it, it is possible to obtain the final
shape of the forged crankshaft for the three-cylinder engine including the contour shape
of arms and the placement angle of the crank pins, although some minor amount of
flash is generated. Therefore, forged crankshafts for three-cylinder engines can be
manufactured with high material utilization and also with high dimensional accuracy
regardless of their shapes. If, at the stage of preparing the preform blank, the arm
portions are shaped so as to include portions for forming balance weights, it is even
possible to manufacture forged crankshafts having balance weights.
[0072]
In the forming apparatus shown in FIGS. 4 to 6, the inclined surfaces 14U and
14B of the journal dies 10U and 10B for the first rough journal portion Jla and its
contacting slope of the first wedge 26, and the inclined surfaces 14U and 14B of the
journal dies 10U and 10B for the fourth rough journal portion J4a and its contacting
slope of the first wedge 26 are angled in a reverse relationship relative to a vertical
plane. Also, the inclined surfaces 15U and 15B of the journal dies 10U and 10B for
the second rough journal portion J2a and its contacting slope of the second wedge 27,
and the inclined surfaces 15U and 15B of the journal dies 10U and 10B for the third
rough journal portion J3a and its contacting slope of the second wedge 27 are angled in
a reverse relationship relative to a vertical plane. Furthermore, the angle of the slopes
of the first wedges 26 (the angle of the inclined surfaces 14U and 14B of the journal
dies 10U and 10B for the first and fourth rough journal portions Jla and J4a) is greater
than the angle of the slopes of the second wedges 27 (the angle of the inclined surfaces
15U and 15B of the journal dies 10U and 10B for the second and third rough journal
portions J2a and J3a). The purpose of varying, for each of the journal dies 10U and
10B, the wedge angle of the wedge mechanism, which causes the axial movement of the
journal dies 10U and 10B, is to ensure that the rate of deformation at which the rough
arm portions Aa are axially compressed to reduce the thickness thereof stays constant
for all the rough arm portions Aa.
[0073]
In the preform blank 4, which is processed by the forming apparatus shown in
FIGS. 4 to 6, the rough journal portions Ja have a cross-sectional area that is equal to or
greater than that of the rough journal portions Jb of the blank for finish forging 5, i.e.,
that of the journals J of the forged crankshaft. Similarly, the rough crank pin portions
Pa of the preform blank 4 have a cross-sectional area that is equal to or greater than that
of the rough crank pin portions Pb of the blank for finish forging 5, i.e., that of the crank
pins P of the forged crankshaft. Even when the cross-sectional area of the rough
journal portions Ja of the preform blank 4 is greater than the cross-sectional area of the
rough journal portions Jb of the blank for finish forging 5, and the cross-sectional area
of the rough crank pin portions Pa of the preform blank 4 is greater than the
cross-sectional area of the rough crank pin portions Pb of the blank for finish forging 5:
the cross-sectional area of the rough journal portions Ja can be reduced to the
cross-sectional area of the rough journal portions Jb of the blank for finish forging 5 by
the holding and retaining of the rough journal portions Ja by the journal dies 10U and
10B, and by the subsequent axial movement of the journal dies 10U and 10B; and the
cross-sectional area of the rough crank pin portions Pa can be reduced to the
cross-sectional area of the rough crank pin portions Pb of the blank for finish forging 5
by the movement in the direction perpendicular to the axial direction of the reference
crank pin die 11, and also by the axial movement and the movement in the direction
perpendicular to the axial direction of the movable crank pin dies 12.
[0074]
2^
An issue to be addressed regarding the forming of the blank for finish forging
described above is local formation of fin flaws. The following describes how fin flaws
are formed and how they can be prevented.
[0075]
FIG 7 is a diagram illustrating how fin flaws occur in forming a blank for
finish forging using the forming apparatus of the present invention, and FIG 8 is a
diagram illustrating how fin flaws are prevented by taking a measure. In FIGS. 7 and
8, there are shown (a) a forming state at an initial stage, (b) a forming state during the
process, (c) a forming state at the completion, and (d) a blank for finish forging, which
is removed from the forming apparatus after the completion of forming.
[0076]
As shown in FIG. 7(a), upon the start of the forming operation, the journal dies
10U and 10B move axially, and the movable crank pin dies 12 and the auxiliary crank
pin dies 13 move axially and in the direction perpendicular to this direction. Then, as
shown in FIG 7(b), if the rough crank pin portions Pa to be processed for deformation
by pressing in the direction perpendicular to the axial direction reach the auxiliary crank
pin dies 13 before the completion of the axial movement of the journal dies 10U and
10B, the movable crank pin dies 12, and the auxiliary crank pin dies 13, i.e., before the
spaces between the journal dies 10U and 10B, the reference crank pin die 11, the
movable crank pin dies 12, and the auxiliary crank pin dies 13, are filled, the fillings of
the rough crank pin portions Pa flow into the spaces between the auxiliary crank pin
dies 13 and the journal dies 10U and 10B. Although the fillings that have flowed
thereinto are thinned with the progress of the forming operation, they stay there even
after the forming operation is completed as shown in FIG. 7(c). Thus, as shown in FIG
7(d), fin flaws 5a, coming out of the rough crank pin portions Pb of the blank for finish
forging 5, are formed locally at the boundaries with adjacent rough arm portions Aa.
[0077]
In the subsequent finish forging step, the fin flaws 5a will be struck into the
finished product, resulting in causing overlaps. Therefore, in order to ensure product
quality, it is necessary to prevent the formation of the fin flaws.
[0078]
One measure to prevent the formation of the fin flaws may be to control the
movement of the reference crank pin die 11 and the movable crank pin dies 12 in the
direction perpendicular to the axial direction so that the rough crank pin portions Pa to
be processed for deformation by pressing reach the auxiliary crank pin dies 13 after the
spaces between the journal dies 10U and 10B, the reference crank pin die 11, the
movable crank pin dies 12, and the auxiliary crank pin dies 13, are filled. Specifically,
it may be configured such that the axial movement of the journal dies 10U and 10B as
well as that of the movable crank pin dies 12 and the auxiliary crank pin dies 13
forming pair with the movable crank pin dies 12 is completed, thereafter the movement
of the reference crank pin die 11 and the movable crank pin dies 12 in the direction
perpendicular to the axial direction is completed. For example, when the total length
of movement of the reference crank pin die 11 and the movable crank pin dies 12 in the
direction perpendicular to the axial direction is designated as a 100% length of
movement thereof, it is preferred that, when the axial movement of the journal dies 10U
and 10B that are adjacent to the crank pin dies 11 and 12 is completed, the length of
movement of the crank pin dies 11 and 12 in the direction perpendicular to the axial
direction is 90% or less (more preferably 83% or less, and even more preferably 60% or
less) of the total length of movement, and thereafter, the movement of the crank pin dies
11 and 12 in the same direction is completed.
[0079]
That is, the forming operation is started as shown in FIG. 8(a), and then, as
shown in FIG 8(b), the axial movement of the journal dies 10U and 10B as well as that
of the movable crank pin dies 12 and the auxiliary crank pin dies 13 are completed
before the length of movement of the reference crank pin die 11 and the movable crank
pin dies 12 in the direction perpendicular to the axial direction reaches 90% of the total
length of movement. Consequently, by this time, the spaces between the journal dies
10U and 10B, the reference crank pin die 11, the movable crank pin dies 12, and the
auxiliary crank pin dies 13 have been filled, whereas the rough crank pin portions Pa to
be processed for deformation by pressing have not reached the auxiliary crank pin dies
13. Subsequently, along with the movement of the crank pin dies 11 and 12 in the
direction perpendicular to the axial direction, the rough crank pin portions Pa reach the
auxiliary crank pin dies 13, and with the completion of the movement, the forming is
completed as shown in FIG. 8(c). Thus, no such problem occurs as the fillings of the
2>v
rough crank pin portions Pa flow into the spaces between the auxiliary crank pin dies 13
and the journal dies 10U and 10B. As a result, as shown in FIG 8(d), a high quality
blank for finish forging 5 without the fin flaws can be obtained.
[0080]
The process of movement of the crank pin dies in the direction perpendicular to
the axial direction before the completion of the axial movement of the journal dies may
be varied as desired. For example, the movement of the crank pin dies in the direction
perpendicular to the axial direction may be started simultaneously with the start of the
axial movement of the journal dies or in advance of that, or conversely, it may be started
after the axial movement of the journal dies has progressed to some extent. Also, the
movement of the crank pin dies in the direction perpendicular to the axial direction may
be stopped temporarily after its start, at positions a certain distance away from their
initial positions, and it may be resumed after the completion of the axial movement of
the journal dies.
[0081]
2. Second Embodiment
A second embodiment is based on the configuration of the first embodiment
described above and includes a twisting step in a process of manufacturing a forged
crankshaft for a three-cylinder engine as well as modifications of the configuration
related to this step.
[0082]
2-1. Preform Blank To Be Processed, Blank For Finish Forging Formed Therefrom,
Forged Product After Finish Forging, and Twisted Product After Twisting
FIG 9 is a diagram schematically showing the shapes of a preform blank to be
processed by the forming apparatus, a blank for finish forging formed therefrom, a
forged product after finish forging, and a twisted product after twisting, in the
manufacturing method of the second embodiment of the present invention. FIG 9
illustrates how a three-cylinder six-counterweight crankshaft is manufactured as an
example and displays, as seen in FIG. 2, plane views showing an outside appearance of
the crankshaft and drawings depicting an arrangement of crank pins with a view along
an axial direction side by side. It is noted that the descriptions of the matters that
overlap with the first embodiment shall be appropriately omitted. This is also the case
31
for third and fourth embodiments described later.
[0083]
As shown in FIG 9, a preform blank 4 of the second embodiment has a
crankshaft shape that is approximate to the shape of a forged crankshaft 1 for a
three-cylinder six-counterweight, but is generally in rough shape. The preform blank 4
includes four rough journal portions Ja, three rough crank pin portions Pa, a rough front
part portion Fra, a rough flange portion Fla, and six rough arm portions Aa. A blank
for finish forging 5 of the second embodiment is formed from the preform blank 4
described above using a forming apparatus, details of which will be provided later.
The blank for finish forging 5 includes four rough journal portions Jb, three rough crank
pin portions Pb, a rough front part portion Frb, a rough flange portion Fib, and six rough
arm portions Ab. A forged product 6 of the second embodiment is obtained from the
blank for finish forging 5 described above by finish forging. The forged product 6
includes four journals Jc, three crank pins Pc, a front part Frc, a flange Flc, and six arms
Ac.
[0084]
A twisted product 7 of the second embodiment is obtained from the forged
product 6 described above by twisting. The twisted product 7 includes four journals
Jld to J4d, three crank pins Pld to P3d, a front part Frd, a flange Fid, and six crank
arms Aid to A6d (hereinafter also referred to simply as "arms") that alternatively
connect the journals Jld to J4d, and the crank pins Pld to P3d to each other.
Hereinafter, when the journals Jld to J4d, the crank pins Pld to P3d, and the arms Aid
to A6d, of the twisted product 7, are each collectively referred to, a reference character
"Jd" is used for the journals, a reference character "Pd" for the crank pins, and a
reference character "Ad" for the arms.
[0085]
The twisted product 7 has a shape that is in agreement with a shape of a
crankshaft (forged final product) including a placement angle of the crank pins Pd.
Specifically, the journals Jd of the twisted product 7 have an axial length equal to that of
the journals J of the forged crankshaft having the final shape. The crank pins Pd of
twisted product 7 have an axial length equal to that of the crank pins P of the forged
crankshaft having the final shape. Further, the crank pins Pd of the twisted product 7
have the same amount of eccentricity in the direction perpendicular to the axial
direction and the same placement angle of 120° as the crank pins P of the forged
crankshaft having the final shape, thus they are placed at the specified positions. The
arms Ad of the twisted product 7 have an axial thickness equal to that of arms A of the
forged crankshaft having the final shape.
[0086]
The forged product 6 has a shape that is in agreement with the shape of the
crankshaft (forged final product) excluding the placement angle of the crank pins Pc.
Specifically, the journals Jc of the forged product 6 have an axial length equal to that of
the journals J of the forged crankshaft having the final shape. The crank pins Pc of the
forged product 6 have an axial length equal to that of the crank pins P of the forged
crankshaft having the final shape, and an amount of eccentricity in the direction
perpendicular to the axial direction is the same between them. However, the
placement angle of the crank pins Pc of the forged product 6 is deviated from specified
positions. Specifically, among the crank pins Pc of the forged product 6, the first and
third crank pins Pic and P3c at opposite ends are eccentric in the direction
perpendicular to the axial direction in the same direction, whereas the second crank pins
P2c in the center is eccentric in the direction opposite to an eccentric direction of the
first and third crank pins Pic and P3c. The arms Ac of the forged product 6 have an
axial thickness equal to that of arms A of the forged crankshaft having the final shape.
[0087]
The blank for finish forging 5 has a shape that is generally in agreement with
the shape of the forged product 6. Specifically, the rough journal portions Jb of the
blank for finish forging 5 have an axial length equal to that of the journals J of the
forged crankshaft having the final shape (journals Jc of forged product 6). The rough
crank pin portions Pb of the blank for finish forging 5 have an axial length equal to that
of the crank pins P of the forged crankshaft having the final shape (crank pins Pc of
forged product 6), and the amount of eccentricity in the direction perpendicular to the
axial direction is the same between them. However, the placement angle of the blank
for finish forging 5 is, like the forged product 6, deviated from the specified positions.
The rough arm portions Ab of the blank for finish forging 5 have an axial thickness
equal to that of the arms A of the forged crankshaft having the final shape (arms Ac of
forged product 6).
[0088]
In contrast, the rough journal portions Ja of the preform blank 4 have an axial
length equal to that of the rough journal portions Jb of the blank for finish forging 5, i.e.,
that of the journals J of the forged crankshaft (journals Jc of forged product 6). The
rough crank pin portions Pa of the preform blank 4 have an axial length equal to that of
the rough crank pin portions Pb of the blank for finish forging 5, i.e., that of the crank
pins P of the forged crankshaft (crank pins Pc of forged product 6), but have a smaller
amount of eccentricity than that of the rough crank pin portions Pb of the blank for
finish forging 5. Specifically, among the rough crank pin portions Pa of the preform
blank 4, the first and third rough crank pin portions Pla and P3a at opposite ends are
eccentric in the same direction with an amount of eccentricity thereof equal to about a
half of an amount of eccentricity in the crank pins P of the forged crankshaft. On the
other hand, the second rough crank pin portion P2a in the center is eccentric in a
direction opposite to an eccentric direction of the first and third rough crank pin
portions Pla and P3a with an amount of eccentricity equal to about a half of an amount
of eccentricity in the crank pin P of the forged crankshaft. The rough arm portions Aa
of the preform blank 4 have an axial thickness greater than that of the rough arm
portions Ab of the blank for finish forging 5, i.e., that of the arms A of the forged
crankshaft (arms Ac of forged product 6).
[0089]
2-2. Process For Manufacturing Forged Crankshaft For Three-Cylinder Engine
FIG 10 is a schematic diagram illustrating a process for manufacturing a
forged crankshaft for a three-cylinder engine according to the second embodiment of the
present invention. As shown in FIG. 10, the process for manufacturing the forged
crankshaft for the three-cylinder engine of the second embodiment includes a first
preforming step, a second preforming step, a finish forging step, and a twisting step, and
also includes a trimming step before the twisting step and a coining step after the
twisting step as necessary.
[0090]
The first preforming step is a step in which the preform blank 4 described
above is obtained. The second preforming step is a step in which the blank for finish
forging 5 described above having the final shape of the forged crankshaft excluding the
placement angle of crank pins is obtained from the preform blank 4 described above by
using a forming apparatus described in FIG 11 below. The finish forging step is a step
in which the blank for finish forging 5 is supplied to be processed by finish forging,
whereby the forged product 6 described above having the final shape of the forged
crankshaft excluding the placement angle of crank pins is obtained.
[0091]
The twisting step is a step in which the twisted product 7 described above is
obtained. In the twisting step, in a state in which the journals and the crank pins of the
forged product 6 described above are held and retained, the journals are twisted around
these axial centers in order to adjust the placement angle of the crank pins of the forged
product 6 to the placement angle of the crank pins of the forged crankshaft, so that the
twisted product 7 having a final shape that is in agreement with the shape of the
crankshaft of the forged crankshaft including the placement angle can be obtained.
[0092]
2-3. Apparatus For Forming Blank For Finish Forging
FIG. 11 is a longitudinal sectional view showing a configuration of the forming
apparatus according to the second embodiment of the present invention. FIG 11
illustrates, as an example, the forming apparatus that is used in manufacturing a
three-cylinder six-counterweight crankshaft, i.e., the forming apparatus configured to
form the blank for finish forging 5 from the preform blank 4 shown in FIG 9. It
should be noted that in the longitudinal sectional view shown in FIG 11, all parts of the
rough crank pin portions are actually on the same plane.
[0093]
In the forming apparatus of the second embodiment shown in FIG 11, the
preform blank 4 is placed in the dies in a manner such that an eccentric direction of the
rough crank pin portions Pa is in the vertical direction, e.g., with the first and third
rough crank pin portions Pla and P3a positioned in the upper side and the second rough
crank pin portion P2a positioned in the lower side, so that the preform blank 4 is formed
into the blank for finish forging 5. Other than this, the same configuration is shared
with the forming apparatus of the first embodiment shown in FIG. 4, thus the detailed
description thereof will be omitted.
[0094]
FIGS. 12 and 13 are longitudinal sectional views illustrating a process for
forming the blank for finish forging using the forming apparatus according to the
second embodiment of the present invention shown in FIG 11. FIGS. 12 and 13
respectively show a forming state at an initial stage and a forming state at the
completion.
[0095]
As shown in FIG 12, the preform blank 4 is placed in the lower journal die
10B, the movable crank pin dies 12, and the auxiliary crank pin dies 13, and then
lowering of the press machine is performed. This allows the journal dies 10U and 10B
holding and retaining the rough journal portions Ja to move axially toward the reference
crank pin die 11 in contact with the second rough crank pin portion P2a. Concurrently,
the movable crank pin dies 12 and the auxiliary crank pin dies 13 in contact with the
first and third rough crank pin portions Pla and P3a are moved axially toward the
reference crank pin die 11. By this operation, in the preform blank 4, the rough arm
portions Aa are axially compressed by the journal dies 10U and 10B, the reference
crank pin die 11, and the movable crank pin dies 12, while the axial length of the rough
journal portions Ja and the rough crank pin portions Pa is maintained, so that the
thickness of the rough arm portions Aa is reduced to the thickness of the rough arm
portions Ab of the blank for finish forging 5 (see FIG 13).
[0096]
Also, in coordination with the axial movement of the journal dies 10U and 10B
as well as that of the movable crank pin dies 12 and the auxiliary crank pin dies 13, the
reference crank pin dies 11 and the movable crank pin dies 12 press the rough crank pin
portions Pa of the preform blank 4 in the direction perpendicular to the axial direction
by the operation of each hydraulic cylinders 16. By this operation, the rough crank pin
portions Pa of the preform blank 4 are displaced in the direction perpendicular to the
axial direction, thus despite that the placement angle of the rough crank pin portions Pa
is deviated from the specified positions, the amount of eccentricity thereof is increased
to the amount of eccentricity of the rough crank pin portions Pb of the blank for finish
forging 5 (see FIGS. 9 and 13).
[0097]
In this manner, it is possible to form, from the preform blank 4 without a flash,
the blank for finish forging 5 without a flash, which has a shape generally in agreement
with the shape of the forged crankshaft for the three-cylinder engine having thin arms A
(forged final product) excluding the placement angle of the crank pins P. By supplying
such a blank for finish forging 5 without a flash for finish forging, and performing finish
forging with it, it is possible to obtain the forged product 6 having the final shape of the
forged crankshaft for the three-cylinder engine including the contour shape of arms but
excluding the placement angle of the crank pins, although some minor amount of flash
is generated. Then, by performing the twisting on the forged product 6, it is possible
to obtain the final shape of the forged crankshaft for the three-cylinder engine including
the placement angle of the crank pins. Therefore, forged crankshafts for three-cylinder
engines can be manufactured with high material utilization and also with high
dimensional accuracy regardless of their shapes.
[0098]
3. Third Embodiment
A third embodiment is based on the configuration of the first and second
embodiments described above, but includes modifications in the relevant parts of the
configuration, so that a final shape of a forged crankshaft can be formed as desired in
finish forging step without applying the twisting step in a process of manufacturing the
forged crankshaft for a three-cylinder engine.
[0099]
3-1. Preform Blank To Be Processed, Blank For Finish Forging Formed Therefrom, and
Forged Product After Finish Forging
FIG 14 is a diagram schematically showing the shapes of a preform blank to be
processed by the forming apparatus, a blank for finish forging formed therefrom, and a
forged product after finish forging, in the manufacturing method of the third
embodiment of the present invention. FIG. 14 illustrates how a three-cylinder
four-counterweight crankshaft is manufactured as an example.
[0100]
As shown in FIG. 14, the preform blank 4 of the third embodiment has a
crankshaft shape that is approximate to the shape of a forged crankshaft 1 for the
three-cylinder four-counterweight, but is generally in a rough shape. The preform
blank 4 includes four rough journal portions Ja, three rough crank pin portions Pa, a
rough front part portion Fra, a rough flange portion Fla, and six rough arm portions Aa.
The blank for finish forging 5 of the third embodiment is formed from the preform
blank 4 described above using a forming apparatus, details of which will be provided
below. The blank for finish forging 5 includes four rough journal portions Jb, three
rough crank pin portions Pb, a rough front part portion Frb, a rough flange portion Fib,
and six rough arm portions Ab. The forged product 6 of the third embodiment is
obtained from the blank for finish forging 5 described above by finish forging and
includes four journals Jc, three crank pins Pc, a front part Frc, a flange Flc, and six arms
Ac.
[0101]
The forged product 6 has a shape that is in agreement with the shape of the
crankshaft (forged final product) including a placement angle of the crank pins Pc.
Specifically, the journals Jc of the forged product 6 have an axial length equal to that of
the journals J of the forged crankshaft having the final shape. The crank pins Pc of the
forged product 6 have an axial length equal to that of the crank pins P of the forged
crankshaft having the final shape. Further, the crank pins Pc of the forged product 6
have the same amount of eccentricity in a direction perpendicular to an axial direction
and the same placement angle of 120° as the crank pins P of the forged crankshaft
having the final shape, thus they are placed at the specified positions. The arms Ac of
the forged product 6 have an axial thickness equal to that of arms A of the forged
crankshaft having the final shape.
[0102]
In contrast, the rough journal portions Jb of the blank for finish forging 5 have
an axial length equal to that of the journals Jc of forged product 6, i.e., that of the
journals J of the forged crankshaft. The rough crank pin portions Pb of the blank for
finish forging 5 have an axial length equal to that of the crank pins Pc of forged product
6, i.e., that of the crank pins P of the forged crankshaft, but both the amount of
eccentricity and the placement angle of the rough crank pin portions Pb are deviated
from the specified positions. Specifically, among the rough crank pin portions Pb of
the blank for finish forging 5, the first and third rough crank pin portions Plb and P3b at
opposite ends are eccentric in the opposite direction to each other with an amount of
eccentricity equal to a V3/2 of an amount of eccentricity in the crank pins P of the
forged crankshaft. On the other hand, the second rough crank pin portion P2b is not
eccentric and has an amount of eccentricity of zero. The rough arm portions Ab of the
blank for finish forging 5 have an axial thickness equal to that of the arms A of the
forged crankshaft having the final shape (arms Ac of forged product 6).
[0103]
Also, the rough journal portions Ja of the preform blank 4 have an axial length
equal to that of the rough journal portions Jb of the blank for finish forging 5, i.e., that
of the journals J of the forged crankshaft (journals Jc of forged product 6). The rough
crank pin portions Pa of the preform blank 4 have an axial length equal to that of the
rough crank pin portions Pb of the blank for finish forging 5, i.e., that of the crank pins
P of the forged crankshaft (crank pins Pc of forged product 6). However, among the
rough crank pin portions Pa of the preform blank 4, the first and third rough crank pin
portions Pla and P3a have a smaller amount of eccentricity than that of the rough crank
pin portions Pb of the blank for finish forging 5, and are eccentric in the opposite
direction to each other with an amount of eccentricity less than the V3/2 of the amount
of eccentricity in the crank pins P of the forged crankshaft. On the other hand, the
second rough crank pin portion P2a has a amount of eccentricity of zero, similar to the
second rough crank pin portion P2b in the blank for finish forging 5. The rough arm
portions Aa of the preform blank 4 have an axial thickness greater than that of the rough
arm portions Ab of the blank for finish forging 5, i.e., that of the arms A of the forged
crankshaft (crank arms Ac of forged product 6).
[0104]
3-2. Process For Manufacturing Forged Crankshaft For Three-Cylinder Engine
FIG. 15 is a schematic diagram illustrating a process for manufacturing the
forged crankshaft for the three-cylinder engine according to the third embodiment of the
present invention. As shown in FIG. 15, the process for manufacturing the forged
crankshaft for the three-cylinder engine of the third embodiment includes a first
preforming step, a second preforming step, and a finish forging step, and also includes a
trimming step and a coining step as necessary.
[0105]
The first preforming step is a step in which the preform blank 4 described
above is obtained. The second preforming step is a step in which the blank for finish
forging 5 described above having the final shape of the forged crankshaft is obtained
from the preform blank 4 described above excluding the amount of eccentricity and the
placement angle of all the crank pins, by using a forming apparatus described in FIG 16
below.
[0106]
The finish forging step is a step in which the forged product 6 described above
is obtained. In the finish forging step, the blank for finish forging 5 described above is
supplied to be processed by press forging with a pair of upper and lower dies in a state
in which the first and third rough crank pin portions are horizontally positioned,
whereby all rough crank pin portions are pressed in the vertical direction perpendicular
to the axial direction. By this operation, the forged product 6 having a shape in
agreement with the shape of the crankshaft of the forged crankshaft having the final
shape can be obtained including the placement angle of the crank pins.
[0107]
3-3. Apparatus For Forming Blank For Finish Forging
FIG 16 is a longitudinal sectional view showing a configuration of the forming
apparatus according to the third embodiment of the present invention. FIG 16
illustrates, as an example, the forming apparatus that is used in forming the blank for
finish forging 5 from the preform blank 4 shown in FIG 14. It should be noted that in
the longitudinal sectional view shown in FIG. 16, all parts of the rough crank pin
portions are actually on the same plane.
[0108]
The forming apparatus of the third embodiment shown in FIG 16 differs from
the forming apparatus of the first embodiment shown in FIG. 4 and the forming
apparatus of the second embodiment shown in FIG. 11 largely in the following. In the
forming apparatus of the third embodiment, the preform blank 4 is placed in the dies in
a manner such that the first and third rough crank pin portions PI a and P3a which are
eccentric in the opposite direction to each other are vertically positioned, whereby the
preform blank 4 is formed into the blank for finish forging 5. In this forming
apparatus, the reference crank pin die 11 disposed in the location of the second rough
crank pin portion P2a is constrained from moving not only in the axial direction but also
in the direction perpendicular to the axial direction. For this reason, the reference
crank pin die 11 of the third embodiment is, unlike the one in the first and second
embodiments, not coupled to a hydraulic cylinder, instead, directly mounted to one of
the upper die holder 23 and the lower die holder 22. To the other one, the auxiliary
crank pin die 13 forming a pair with the reference crank pin die 11 is directly mounted.
FIG 16 shows a mode in which the reference crank pin die 11 is mounted to the upper
die holder 23 while the auxiliary crank pin die 13 is mounted to the lower die holder 22.
[0109]
Further, in the forming apparatus of the third embodiment, the movable crank
pin dies 12 and the auxiliary crank pin dies 13 are disposed at locations of the rough
crank pin portions Pla and P3a. However since the first and third rough crank pin
portions Pla and P3a are eccentric in the opposite direction to each other in the vertical
direction, a vertical arrangement of the movable crank pin dies 12 and the auxiliary
crank pin dies 13 is reversed between the locations of the first and third rough crank pin
portions Pla and P3a. FIG 16 shows a mode in which the auxiliary crank pin die 13 at
the location of the first rough crank pin portion Pla and the movable crank pin die 12 at
the location of the third rough crank pin portion P3a are disposed on the upper side
while the movable crank pin die 12 at the location of the first rough crank pin portion
Pla and the auxiliary crank pin die 13 at the location of the third rough crank pin
portion P3a are disposed on the lower side.
[0110]
FIGS. 17 and 18 are longitudinal sectional views illustrating a process for
forming a blank for finish forging using the forming apparatus according to the third
embodiment of the present invention shown in FIG 16. FIGS. 17 and 18 respectively
show a forming state at an initial stage and at the completion.
[0111]
As shown in FIG. 17, the preform blank 4 is placed in the lower journal die
10B, the movable crank pin dies 12, and the auxiliary crank pin dies 13, and then
lowering of the press machine is performed. Then, the journal dies 10U and 10B are
caused to hold and retain the rough journal portions Ja of the preform blank 4
therebetween from above and below, and concurrently, the reference crank pin die 11
and the auxiliary crank pin die 13 are caused to hold and retain the second rough crank
hi
pin portion P2a therebetween from above and below, bringing into a state in which the
first and third rough crank pin portions Pla and P3a are in contact with the movable
crank pin dies 12. In this state, the lowering of the press machine is continued. This
allows the journal dies 10U and 10B holding and retaining each rough journal portion Ja
to move axially toward the reference crank pin die 11 holding and retaining the second
rough crank pin portion P2a. Concurrently, the movable crank pin dies 12 and the
auxiliary crank pin dies 13 in contact with the first and third rough crank pin portions
Pla and P3a are moved axially toward the reference crank pin die 11. By this
operation, in the preform blank 4, the rough arm portions Aa are axially compressed by
the journal dies 10U and 10B, the reference crank pin die 11, and the movable crank pin
dies 12, while the axial length of the rough journal portions Ja and the rough crank pin
portions Pa is maintained, so that the thickness of the rough arm portions Aa is reduced
to the thickness of the rough arm portions Ab of the blank for finish forging 5 (see FIG
18).
[0112]
Also, in coordination with the axial movement of the journal dies 10U and 10B
as well as that of the movable crank pin dies 12 and the auxiliary crank pin dies 13, the
movable crank pin dies 12 press the first and third rough crank pin portions Pla and P3a
of the preform blank 4 in the vertical direction perpendicular to the axial direction by
the operation of each hydraulic cylinders 16. By this operation, the first and third
rough crank pin portions Pla and P3a of the preform blank 4 are displaced in the
vertical direction perpendicular to the axial direction, thus the amount of eccentricity
thereof in the opposite direction to each other is increased to an amount of eccentricity
equal to a V3/2 of an amount of eccentricity in the crank pins P of the forged crankshaft
(see FIGS. 14 and 18). On the other hand, the location of the second rough crank pin
portion P2b of the preform blank 4 in the vertical direction perpendicular to the axial
direction remains unchanged before and after the forming, thus the amount of
eccentricity thereof remains zero.
[0113]
In this manner, it is possible to form, from the preform blank 4 without a flash,
the blank for finish forging 5 without a flash, which has a shape generally in agreement
with the shape of the forged crankshaft for the three-cylinder engine having thin arms A
(forged final product) excluding the amount of eccentricity and the placement angle of
all the crank pins P. Such a blank for finish forging 5 without a flash is supplied for
finish forging, and finish forging is performed with it in a state in which the first and
third rough crank pin portions PI a and P3a are horizontally positioned. In this process,
by pressing all the rough crank pin portions of the blank for finish forging 5 in the
vertical direction perpendicular to the axial direction so as to displace them to the
specified positions, it is possible to obtain the final shape of the forged crankshaft for
the three-cylinder engine including the contour shape of arms, and the amount of
eccentricity and the placement angle of the crank pins, although some minor amount of
flash is generated. Therefore, forged crankshafts for three-cylinder engines can be
manufactured with high material utilization and also with high dimensional accuracy
regardless of their shapes.
[0114]
4. Fourth Embodiment
A fourth embodiment includes modifications of the configuration of the third
embodiment.
[0115]
4-1. Preform Blank To Be Processed, Blank For Finish Forging Formed Therefrom, and
Forged Product After Finish Forging
FIG 19 is a diagram schematically showing the shapes of a preform blank to be
processed by the forming apparatus, a blank for finish forging formed therefrom, and a
forged product after finish forging, in the manufacturing method of the fourth
embodiment of the present invention.
[0116]
As shown in FIG. 19, the forged product 6 of the fourth embodiment maintains
the same shape as the forged product 6 of the third embodiment shown in FIG. 14.
[0117]
In contrast, the blank for finish forging 5 of the fourth embodiment differs from
the blank for finish forging 5 of the third embodiment shown in FIG. 14 in the following.
As shown in FIG 19, central second rough crank pin portion P2b of the blank for finish
forging 5 of the fourth embodiment is configured to be eccentric in a direction
perpendicular to an eccentric direction of the first and third rough crank pin portions
Plb and P3b at opposite ends with an amount of eccentricity equal to that of the crank
pin Pc of the forged product 6, i.e., that of the crank pin P of the forged crankshaft.
[0118]
Further, the preform blank 4 of the fourth embodiment differs from the preform
blank 4 of the third embodiment shown in FIG 14 in the following. As shown in FIG
19, central second rough crank pin portion P2b of the preform blank 4 of the fourth
embodiment is configured to be eccentric in a direction perpendicular to an eccentric
direction of first and third rough crank pin portions Plb and P3b at opposite ends with
an amount of eccentricity equal to that of the crank pin P of the forged crankshaft (crank
pin Pc of forged product 6), the configuration similar to that of the blank for finish
forging 5.
[0119]
4-2. Process For Manufacturing Forged Crankshaft For Three-Cylinder Engine
FIG. 20 is a schematic diagram illustrating a process for manufacturing a
forged crankshaft for a three-cylinder engine according to the fourth embodiment of the
present invention. As shown in FIG 20, the process for manufacturing the forged
crankshaft of the fourth embodiment, similar to the third embodiment shown in FIG 15,
includes a first preforming step, a second preforming step, and a the finish forging step,
and also includes a trimming step and a coining step as necessary.
[0120]
The first preforming step is a step in which the preform blank 4 described
above is obtained.
[0121]
The second preforming step is a step in which the blank for finish forging 5
described above is obtained. In the second preforming step, the same forming
apparatus used in the third embodiment shown in FIGS. 16-18 is used. It should be
noted that in the longitudinal sectional view shown in FIG. 16, the second rough crank
pin portion in the fourth embodiment is in reality located either in the front or back side
of the paper.
[0122]
In the second preforming step of the fourth embodiment, as similarly found in
the third embodiment shown in FIGS. 16-18, the preform blank 4 is placed in the lower
journal die 10B, the movable crank pin dies 12, and the auxiliary crank pin dies 13, and
then lowering of the press machine is performed. In the preform blank 4, this allows
the journal dies 10U and 10B holding and retaining each rough journal portion Ja, and
the movable crank pin dies 12 and the auxiliary crank pin dies 13 in contact with the
first and third rough crank pin portions PI a and P3a to move axially toward the
reference crank pin die 11 holding and retaining the second rough crank pin portion P2a.
In conjunction with this movement, the rough arm portions Aa are axially compressed
while the axial length of the rough journal portions Ja and the rough crank pin portions
Pa is maintained, so that the thickness of the rough arm portions Aa is reduced to the
thickness of the rough arm portions Ab of the blank for finish forging 5.
[0123]
Further, the first and third rough crank pin portions Pla and P3a are pressed by
the movable crank pin dies 12 in the vertical direction perpendicular to the axial
direction, so that the first and third rough crank pin portions Pla and P3a of the preform
blank 4 become eccentric in the opposite direction to each other with an amount of
eccentricity increased to a V3/2 of an amount of eccentricity in the crank pins P of the
forged crankshaft. On the other hand, the location of the second rough crank pin
portion P2b of the preform blank 4 in the direction perpendicular to the axial direction
remains unchanged before and after the forming, thus an amount of eccentricity thereof
remains the same as that of the crank pin P of the forged crankshaft.
[0124]
In this manner, it is possible to form, from the preform blank 4 without a flash,
the blank for finish forging 5 without a flash, which has a shape generally in agreement
with the shape of the forged crankshaft for the three-cylinder engine having thin arms A
(forged final product) excluding the amount of eccentricity and the placement angle of
the first and third crank pins PI and P3.
[0125]
The finish forging step is a step in which the forged product 6 described above
is obtained. In the finish forging step, the blank for finish forging 5 is supplied to be
processed for finish forging in a state that in which the first and third rough crank pin
portions are horizontally positioned. In this process, by pressing the first and third
rough crank pin portions Plb and P3b of the blank for finish forging 5 in the vertical
direction perpendicular to the axial direction so as to displace them to the specified
positions, it is possible to obtain the forged product 6 having a shape in agreement with
the shape of the crankshaft of the forged crankshaft for the three-cylinder engine having
the final shape including the contour shape of arms, and the amount of eccentricity and
the placement angle of the crank pins, although some minor amount of flash is
generated.
[0126]
The present invention is not limited to the embodiments described above, and
various modifications may be made without departing from the spirit and scope of the
present invention. For example, the mechanism for causing the journal dies to move
axially is not limited to the one described in the above embodiments, in which a wedge
mechanism of a press machine is employed. Alternatively, a link mechanism may be
employed, or a hydraulic cylinder or a servo motor may be employed in place of the
press machine. Furthermore, the mechanism for causing the crank pin dies to move in
the direction perpendicular to the axial direction is not limited to a hydraulic cylinder,
and it may be a servo motor.
[0127]
Furthermore, the embodiments described above have such a configuration that
the upper die holder is secured to the upper pressure pad while the lower die holder is
resiliently supported on the lower pressure pad on which the wedges are installed, and
the upper and lower journal dies are allowed to move by the wedges, but alternatively,
the functions of the upper section and the lower section may be reversed. The
configuration may also be such that the upper and lower die holders are resiliently
supported on the corresponding pressure pads, and that wedges are installed on both
pressure pads so that the upper and lower journal dies are caused to move by their
corresponding wedges.
[0128]
Furthermore, in the above embodiments, the auxiliary crank pin dies are
movable only axially, but additionally, they may be made to be movable also in a
direction toward the crank pin dies forming pairs, so that the crank pin dies and the
auxiliary crank pin dies can hold and retain the rough crank pin portions Pa
therebetween from above and below and meanwhile move in the direction perpendicular
to the axial direction cooperatively with each other.
[0129]
Furthermore, the embodiments described above have such a configuration that
the rough crank pin portions Pa are pressed in the vertical direction by moving the crank
pin dies in the direction perpendicular to the axial direction, however the configuration
may also be such that the locations of the crank pin dies and the journal dies are
changed so as to horizontally press the rough crank pin portions Pa.
INDUSTRIAL APPLICABILITY
[0130]
The present invention is useful in manufacturing forged crankshafts for
three-cylinder engines.
REFERENCE SIGNS LIST
[0131]
1: forged crankshaft, J, Jl to J5: journals,
P, PI to P4: crank pins, Fr: front part,
Fl: flange, A, Al to A8: crank arms,
2: billet,
4: preform blank, Ja, Jla to J5a: rough journal portions,
Pa, Pla to P4a: rough crank pin portions,
Fra: rough front part portion, Fla: rough flange portion,
Aa, Ala to A8a: rough crank arm portions,
5: blank for finish forging,
Jb, Jib to J5b: rough journal portions of blank for finish forging,
Pb, Plb to P4b: rough crank pin portions of blank for finish forging,
Frb: rough front part portion of blank for finish forging,
Fib: rough flange portion of blank for finish forging,
Ab, Alb to A8b: rough crank arm portions of blank for finish forging,
5a: fin flaws,
6: forged product, Jc, Jlc to J5c: journals of forged product,
Pc, Pic to P4c: crank pins of forged product,
4?
Frc: front part of forged product, Flc: flange of forged product,
Ac, Ale to A8c: crank arms of forged product,
7: twisted product,
Jd, Jld to J5d: journals of twisted product,
Pd, Pld to P4d: crank pins of twisted product,
Frd: front part of twisted product,
Fid: flange of twisted product,
Ad, Aid to A8d: crank arms of twisted product,
10U, 1 OB: journal dies,
11: reference crank pin die, 11a: impression
12: movable crank pin die, 12a: impression,
13: auxiliary crank pin die, 13 a: impression,
lOUa, lOBa: first impression of journal die,
lOUb, lOBb: second impression of journal die,
14U, 14B: inclined surfaces of journal dies for first and fourth rough journal portions,
15U, 15B: inclined surfaces of journal dies for second and third rough journal portions,
16: hydraulic cylinder,
20: lower pressure pad, 21: upper pressure pad,
22: lower die holder, 23: upper die holder,
24: resilient member, 25: support post,
26: first wedge, 27: second wedge

We claim:
1. An apparatus for forming a blank for finish forging for a forged crankshaft for
a three-cylinder engine, the apparatus configured to form, in a process of manufacturing
the forged crankshaft, the blank for finish forging to be subjected to finish forging by
which a final shape of the forged crankshaft is obtained, characterized in that:
the apparatus configured to form the blank for finish forging from a preform
blank, the preform blank including: rough journal portions having an axial length equal
to an axial length of journals of the forged crankshaft; rough crank pin portions having
an axial length equal to an axial length of crank pins of the forged crankshaft; and rough
crank arm portions having an axial thickness greater than an axial thickness of crank
arms of the forged crankshaft,
the rough crank pin portions of the preform blank having a smaller amount of
eccentricity in a direction perpendicular to an axial direction than an amount of
eccentricity of the crank pins of the forged crankshaft, and
the apparatus comprises:
reference crank pin die disposed at a location of one rough crank pin portion
among the rough crank pin portions, the reference crank pin die configured to be
brought into contact with such one rough crank pin portion, the reference crank pin die
configured to move in the direction perpendicular to the axial direction, but be
constrained from moving axially, while being in contact with side surfaces of rough
crank arm portions through which the rough crank arm portions connect with such one
rough crank pin portion;
movable crank pin dies disposed at locations of the corresponding rough crank
pin portions excluding the rough crank pin portion being in contact with the reference
crank pin die, the movable crank pin dies configured to be brought into contact with
such rough crank pin portions, the movable crank pin dies configured to move axially
toward the reference crank pin die and in the direction perpendicular to the axial
direction, while being in contact with side surfaces of the rough crank arm portions
through which the rough crank arm portions connect with such rough crank pin
portions; and
journal dies disposed at locations of the corresponding rough journal portions,
the journal dies configured to hold and retain such rough journal portions therebetween
in the direction perpendicular to the axial direction, the journal dies configured to move
axially toward the reference crank pin die while being in contact with side surfaces of
the rough crank arm portions through which the rough crank arm portions connect with
such rough journal portions,
wherein, in a state where the rough journal portions are held and retained by
the journal dies, and the rough crank pin portions are contacted by the reference crank
pin die and the movable crank pin dies, the journal dies are moved axially, the movable
crank pin dies are moved axially and in the direction perpendicular to the axial direction,
and the reference crank pin die is moved in the direction perpendicular to the axial
direction, thereby compressing the rough crank arm portions in the axial direction so as
to reduce the thickness thereof to the thickness of the crank arms of the forged
crankshaft, and pressing the rough crank pin portions in the direction perpendicular to
the axial direction so as to increase the amount of eccentricity thereof to the amount of
eccentricity of the crank pins of the forged crankshaft.
2. The apparatus for forming the blank for finish forging for the forged crankshaft
for the three-cylinder engine according to claim 1, characterized in that:
the reference crank pin die and the movable crank pin dies each includes an
auxiliary crank pin die disposed at a location outside of the corresponding rough crank
pin portion, opposite to the side where the reference crank pin die and the movable
crank pin dies are contacted, and
in conjunction with the axial movement of the journal dies as well as that of the
movable crank pin dies and the auxiliary crank pin dies forming pairs therewith, a
movement of the reference crank pin die and the movable crank pin dies in the direction
perpendicular to the axial direction is controlled in a manner that the rough crank pin
portions to be deformed by pressing reach the auxiliary crank pin dies after spaces
between the journal dies, the reference crank pin die, the movable crank pin dies, and
the auxiliary crank pin dies are filled.
3. The apparatus for forming the blank for finish forging for the forged crankshaft
for the three-cylinder engine according to claim 2, characterized in that:
provided that a total length of movement of the reference crank pin die and the
movable crank pin dies in the direction perpendicular to the axial direction is a 100%
length of movement thereof, when the axial movement of the journal dies that are
adjacent to such crank pin dies is completed, a length of movement of such crank pin
dies in the direction perpendicular to the axial direction is 90% or less of the total length
of movement, and thereafter, the movement of such crank pin dies in the direction
perpendicular to the axial direction is completed.
4. The apparatus for forming the blank for finish forging for the forged crankshaft
for the three-cylinder engine according to any one of claims 1 to 3, characterized in that:
the reference crank pin die, the movable crank pin dies, and the journal dies are
mounted on a press machine that is capable of being moved downward along the
direction perpendicular to the axial direction, and
by downward movement of the press machine, the journal dies are caused to
hold and retain the rough journal portions therebetween, and the reference crank pin die
and the movable crank pin dies are brought into contact with the rough crank pin
portions, and with continued downward movement of the press machine, the journal
dies are moved axially by wedge mechanisms, and the movable crank pin dies are
caused to move axially by the movement of the journal dies.
5. The apparatus for forming the blank for finish forging for the forged crankshaft
for the three-cylinder engine according to claim 4, characterized in that:
the wedge mechanisms have different wedge angles for each of the journal
dies.
6. The apparatus for forming the blank for finish forging for the forged crankshaft
for the three-cylinder engine according to claim 4 or 5, characterized in that:
the reference crank pin die and the movable crank pin dies are coupled to
hydraulic cylinders and caused to move in the direction perpendicular to the axial
direction by driving the hydraulic cylinders.
7. An apparatus for forming a blank for finish forging for a forged crankshaft for
a three-cylinder engine, the apparatus configured to form, in a process of manufacturing
the forged crankshaft, the blank for finish forging to be subjected to finish forging by
which a final shape of the forged crankshaft is obtained, characterized in that:
the apparatus configured to form the blank for finish forging from a preform
blank, the preform blank including: rough journal portions having an axial length equal
to an axial length of journals of the forged crankshaft; rough crank pin portions having
an axial length equal to an axial length of crank pins of the forged crankshaft; and rough
crank arm portions having an axial thickness greater than an axial thickness of crank
arms of the forged crankshaft,.
among the rough crank pin portion in the preform blank, first and third rough
crank pin portions at opposite ends having an amount of eccentricity in a direction
perpendicular to an axial direction in the opposite direction to each other, the amount of
eccentricity thereof being less than a V3/2 of an amount of eccentricity of the crank pins
of the forged crankshaft, a second rough crank pin portion in the center having an
amount of eccentricity of zero in the direction perpendicular to the axial direction or
having an amount of eccentricity in a direction perpendicular to an eccentric direction of
the first and third rough crank pin portions, the amount of eccentricity thereof being
equal to the amount of eccentricity of the crank pins of the forged crankshaft, and
the apparatus comprises:
reference crank pin die disposed at a location of the second rough crank pin
portion, the reference crank pin die configured to be brought into contact with the
second rough crank pin portion, the reference crank pin die configured to be constrained
from moving axially while being in contact with side surfaces of rough crank arm
portions through which the rough crank arm portions connect with the second rough
crank pin portion;
movable crank pin dies disposed at locations of the corresponding first and
third rough crank pin portions, the movable crank pin dies configured to be brought into
contact with the first and third rough crank pin portions, the movable crank pin dies
configured to move axially toward the reference crank pin die and in the direction
perpendicular to the axial direction, while being in contact with side surfaces of the
rough crank arm portions through which the rough crank arm portions connect with the
first and third rough crank pin portions; and
journal dies disposed at locations of the corresponding rough journal portions,
the journal dies configured to hold and retain such rough journal portions therebetween
in the direction perpendicular to the axial direction, the journal dies configured to move
axially toward the reference crank pin die while being in contact with side surfaces of
the rough crank arm portions through which the rough crank arm portions connect with
such rough journal portions,
wherein, in a state where the rough journal portions are held and retained by
the journal dies, and the rough crank pin portions are contacted by the reference crank
pin die and the movable crank pin dies, the journal dies are moved axially and the
movable crank pin dies are moved axially and in the direction perpendicular to the axial
direction, thereby compressing the rough crank arm portions in the axial direction so as
to reduce the thickness thereof to the thickness of the crank arms of the forged
crankshaft, and pressing the first and third rough crank pin portions in the direction
perpendicular to the axial direction but in the opposite direction to each other, so as to
increase the amount of eccentricity thereof to the V3/2 of the amount of eccentricity of
the crank pins of the forged crankshaft. -
8. The apparatus for forming the blank for finish forging for the forged crankshaft
for the three-cylinder engine according to claim 7, characterized in that:
the reference crank pin die and the movable crank pin dies each includes an
auxiliary crank pin die disposed at a location outside of the corresponding rough crank
pin portion, opposite to the side where the reference crank pin die and the movable
crank pin dies are contacted, and
in conjunction with the axial movement of the journal dies as well as that of the
movable crank pin dies and the auxiliary crank pin dies forming pairs therewith, a
movement of the movable crank pin dies in the direction perpendicular to the axial
direction is controlled in a manner that the rough crank pin portions to be deformed by
pressing reach the auxiliary crank pin dies after spaces between the journal dies, the
reference crank pin die, the movable crank pin dies, and the auxiliary crank pin dies are
filled.
9. The apparatus for forming the blank for finish forging for the forged crankshaft
for the three-cylinder engine according to claim 8, characterized in that:
provided that a total length of movement of the movable crank pin dies in the
direction perpendicular to the axial direction is a 100% length of movement thereof,
when the axial movement of the journal dies that are adjacent to such movable crank pin
dies is completed, a length of movement of such movable crank pin dies in the direction
perpendicular to the axial direction is 90% or less of the total length of movement, and
thereafter, the movement of such movable crank pin dies in the direction perpendicular
to the axial direction is completed.
10. The apparatus for forming the blank for finish forging for the forged crankshaft
for the three-cylinder engine according to any one of claims 7 to 9, characterized in that:
the reference crank pin die, the movable crank pin dies, and the journal dies are
mounted on a press machine that is capable of being moved downward along the
direction perpendicular to the axial direction, and
by downward movement of the press machine, the journal dies are caused to
hold and retain the rough journal portions therebetween, and the reference crank pin die
and the movable crank pin dies are brought into contact with the rough crank pin
portions, and with continued downward movement of the press machine, the journal
dies are moved axially by wedge mechanisms, and the movable crank pin dies are
caused to move axially by the movement of the journal dies.
11. The apparatus for forming the blank for finish forging for the forged crankshaft
for the three-cylinder engine according to claim 10, characterized in that:
the wedge mechanisms have different wedge angles for each of the journal
dies,
12. The apparatus for forming the blank for finish forging for the forged crankshaft
for the three-cylinder engine according to claim 10 or 11, characterized in that:
the movable crank pin dies are coupled to hydraulic cylinders and caused to
move in the direction perpendicular to the axial direction by driving the hydraulic
cylinders.
^si.
13. A method for manufacturing a forged crankshaft for a three-cylinder engine,
characterized in comprising the successive steps of:
a first preforming step for forming, as the preform blank to be supplied to the
forming apparatus according to any one of claims 1 to 6, a preform blank in which first
and third rough crank pin portions at opposite ends among the rough crank pin portions
have an amount of eccentricity in a direction perpendicular to an axial direction in the
opposite direction to each other, the amount of eccentricity thereof being equal to a V3/2
of an amount of eccentricity of the crank pins of the forged crankshaft, and a second
rough crank pin portion in the center has an amount of eccentricity in the direction
perpendicular to the axial direction, in a direction perpendicular to an eccentric direction
of the first and third rough crank pin portions, the amount of eccentricity thereof being
smaller than the amount of eccentricity of the crank pin of the forged crankshaft;
a second preforming step for forming, as the blank for finish forging, a blank
for finish forging in which a final shape of the forged crankshaft is formed including a
placement angle of the crank pins using the forming apparatus according tp any one of
claims 1 to 6; and
a finish forging step for, by performing finish forging on the blank for finish
forging, forming a forged product having the final shape of the forged crankshaft
including the placement angle of the crank pins.
14. A method for manufacturing a forged crankshaft for a three-cylinder engine,
characterized in comprising the successive steps of:
a first preforming step for forming, as the preform blank to be supplied to the
forming apparatus according to any one of claims 1 to 6, a preform blank in which first
and third rough crank pin portions at opposite ends among the rough crank pin portions
have an amount of eccentricity in a direction perpendicular to an axial direction in the
same direction, the amount of eccentricity thereof being smaller than an amount of
eccentricity of the crank pins of the forged crankshaft, and a second rough crank pin
portion in the center has an amount of eccentricity in the direction perpendicular to the
axial direction, in the opposite direction of an eccentric direction of the first and third
rough crank pin portions, the amount of eccentricity thereof being smaller than the
amount of eccentricity of the crank pin of the forged crankshaft,
S^
a second preforming step for formings as the blank for finish forging, a blank
for finish forging in which a final shape of the forged crankshaft is formed excluding a
placement angle of the crank pins using the forming apparatus according to any one of
claims 1 to 6;
a finish forging step for, by performing finish forging on the blank for finish
forging, forming a forged product having the final shape of the forged crankshaft
excluding the placement angle of the crank pins; and
a twisting step for adjusting the placement angle of the crank pins of the forged
product to the placement angle of the crank pins of the forged crankshaft.
15. A method for manufacturing a forged crankshaft for a three-cylinder engine,
characterized in comprising the successive steps of:
a first preforming step for forming, as the preform blank to be supplied to the
forming apparatus according to any one of claims 7 to 12, a preform blank in which first
and third rough crank pin portions at opposite ends among the rough crank pin portions
have an amount of eccentricity in a direction perpendicular to an axial direction in the
opposite direction to each other, the amount of eccentricity thereof being smaller than a
V3/2 of an amount of eccentricity of the crank pins of the forged crankshaft, and a
second rough crank pin portion in the center has the amount of eccentricity of zero in
the direction perpendicular to the axial direction,
a second preforming step for forming, using the forming apparatus according to
any one of claims 7 to 12, as the blank for finish forging, a blank for finish forging in
which the first and third rough crank pin portions at opposite ends among the rough
crank pin portions have an amount of eccentricity in the direction perpendicular to the
axial direction in the opposite direction to each other, the amount of eccentricity thereof
being equal to the V3/2 of the amount of eccentricity of the crank pins of the forged
crankshaft, and the second rough crank pin portion in the center remains the same
amount of eccentricity in the direction perpendicular to the axial direction as the
preform blank; and
a finish forging step for forming a forged product having a final shape of the
forged crankshaft including a placement angle of the crank pins by performing finish
forging on the blank for finish forging in a state in which the first and third rough crank
^r^g
pin portions at opposite ends are horizontally positioned whereby all the rough crank
pin portions are pressed in the direction perpendicular to the axial direction.
16. A method for manufacturing a forged crankshaft for a three-cylinder engine,
characterized in comprising the successive steps of:
a first preforming step for forming, as the preform blank to be supplied to the
forming apparatus according to any one of claims 7 to 12, a preform blank in which first
and third rough crank pin portions at opposite ends among the rough crank pin portions
have an amount of eccentricity in a direction perpendicular to an axial direction in the
opposite direction to each other, the amount of eccentricity thereof being smaller than a
V3/2 of an amount of eccentricity of the crank pins of the forged crankshaft, and a
second rough crank pin portion in the center has an amount of eccentricity in the
direction perpendicular to the axial direction, in a direction perpendicular to an eccentric
direction of the first and third rough crank pin portions, the amount of eccentricity
thereof being equal to the amount of eccentricity of the crank pin of the forged
crankshaft,
a second preforming step for forming, using the forming apparatus according to
any one of claims 7 to 12, as the blank for finish forging, a blank for finish forging in
which the first and third rough crank pin portions at opposite ends among the rough
crank pin portions have an amount of eccentricity in the direction perpendicular to the
axial direction in the opposite direction to each other, the amount of eccentricity thereof
being equal to the V3/2 of the amount of eccentricity of the crank pins of the forged
crankshaft, and the second rough crank pin portion in the center remains the same
amount of eccentricity in the direction perpendicular to the axial direction as the
preform blank; and
a finish forging step for forming a forged product having a final shape of the
forged crankshaft including a placement angle of the crank pins by performing finish
forging on the blank for finish forging in a state in which the first and third rough crank
pin portions at opposite ends are horizontally positioned whereby the first and third
rough crank pin portions are pressed in the direction perpendicular to the axial direction.