TECHNICAL FIELD
[0001]
The present invention relates to a method for producing a crankshaft
by hot forging.
BACKGROUND ART
[0002]
A reciprocating engine to be employed in a motor vehicle, a motorcycle,
an agricultural machine, a marine vessel or the like requires a crankshaft to
extract power· by converting reciprocating motions of pistons to rotational
motion. There are two types of crankshafts: the type manufactured by die
forging and the type manufactured by casting. Especially when high
strength and high stiffness are required, forged crankshafts manufactured by
die forging are often employed.
[0003]
A forged crankshaft is generally produced by using a billet as a
starting material. The billet is circular or square in cross section, and the
cross-sectional area is constant throughout the length .. · A method for
producing a forged crankshaft includes a preforming step, a die forging step,
and a trimming step that are to be executed in this order. After the trimming
step, a coining step may be executed if needed. Typically, the preforming step
includes a rolling step and a bending step, and the die forging step includes a
rough forging step and a finish forging step.
[0004]
FIGS. 1A to 1F are schematic diagrams showing a conventional
method for producing a common forged crankshaft. A crankshaft 1 shown in
FIG. 1F is a four-cylinder eight-counterweight crankshaft to be mounted in a
four-cylinder engine. The crankshaft 1 includes five journals J1 to J5, four
·j
pins PI to P4, a front part Fr, a flange Fl, and eight crank arms (hereinafter
referred to simply as "arms") AI to AS. The eight arms AI to AS connect the
journals JI to J5 respectively to the pins PI to P4. All ofthe eight arms AI to
AS have counterweights (hereinafter referred to simply as "weights") WI to
WS, which are integrated with the arms AI to AS, respectively.
[0005]
In the following paragraphs, when the journals JI to J5, the pins PI to
P 4, the arms AI to A8, and the weights WI to W8 are each collectively
referred to, a reference character "J" is used for the journals, a reference
character "P" for the pins, a reference character "A" for the arms, and a
reference character "W" for the weights.
[0006]
In the production method shown in FIGS. IA to IF, the forged
crankshaft I is produced as follows. First, a billet 2 with a specified length as
shown in FIG. IA is heated in a heating furnace (for example, an induction
heating furnace, a gas atmosphere heating furnace or the like), and the heated
billet undergoes a rolling step. In the rolling step, the billet 2 is rolled and
reduced, for example, by grooved rolls. This is to distribute the volume of the
billet 2 in the axial direction, and thereby, a rolled blank 3, which is an
in-process material, is obtained (see FIG. IB). Next, in a bending step, the
rolled blank 3 is partly reduced from a direction perpendicular to the length
direction. This is to distribute the volume of the rolled blank 3, and thereby,
a bent blank 4, which is a next in-process material, is obtained (see FIG. IC).
[0007]
Next, in a rough forging step, the bent blank 4 is reduced by a pair of
an upper die and a lower die, and thereby, a rough forged blank 5 is obtained
(see FIG. ID). The rough forged blank 5 is roughly in the shape of a
crankshaft (finished product). In a finish forging step, the rough forged
blank 5 is reduced by a pair of an upper die and a lower die, and thereby, a
finish forged blank 6 is obtained (see FIG. IE). The finish forged blank 6 has
a shape in agreement with the shape of the finished crankshaft. During the
rough forging and the finish forging, excess material flows out through a space
between the mutually facing parting faces of the dies, which results in
3'
·(
formation of flash. Accordingly, the rough forged blank 5 and the finish
forged blank 6 have great flash B on the periphery.
[0008]
In a trimming step, for example, while the finish forged blank 6 is
nipped and held by a pair of dies, the finish forged blank 6 is punched by a
cutting die. Thereby, the flash B is removed from the finish forged blank 6,
and a forged blank with no flash is obtained. The forged blank with no flash
has substantially the same shape as the forged crankshaft 1 shown in FIG. 1F.
[0009]
In a coining step, main parts of the forged blank with no flash are ·
slightly pressed by dies from above and below so that the forged blank with no
flash can have the exact size and shape of the finished product. The main
parts of the forged blank with no flash are, for example, shaft parts such as
the journals J, the pins P, the front part Fr, the flange Fl and the like, and
further, the arms A and the weights W In this way, the forged crankshaft 1
is produced.
[0010]
The production method shown in FIGS. 1A to 1F is applicable not only
to production of a four-cylinder eight-counterweight crankshaft as shown in
FIGS. 1F but also to production of any other crankshaft. For example, the
production method is applicable to a four-cylinder four-counterweight
crankshaft.
[0011]
In a four-cylinder four-counterweight crankshaft, only some of the
eight arms A1 to A8 incorporate a weight W. For example, the front first arm
A1, the rearmost eighth arm A8 and the central two arms (the fourth arm A4
and the fifth arm A5) incorporate a weight W. The other arms, namely, the
second, the third, the sixth and the seventh arms A2, A3, A6 and A 7 do not
have a weight. Such arms without a weight will hereinafter referred to as
"unweighted arms". These unweighted arms are oval.
[0012]
Other crankshafts, for example, crankshafts to be mounted in
three-cylinder engines, in-line six-cylinder engines, V-type six-cylinder
4-
I
engines, eight-cylinder engines and others can be produced by the same
production method. It is noted that, when adjustment of the placement
angles of the pins is necessary, a twisting step is added after the trimming
step.
[0013]
In recent years, there has been a need for weight reduction of
reciprocating engines, particularly those for motor vehicles, in order to
improve the fuel economy. Accordingly, there is also an ever-increasing
demand for weight reduction of crankshafts to be mounted in reciprocating
engines. Techniques to reduce the weight of a crankshaft are disclosed in
Japanese Patent Application Publication No. 2012-7726 (Patent Literature 1)
and Japanese Patent Application Publication No. 2010-230027 (Patent
Literature 2).
[0014]
Patent Literatures 1 and 2 teach an arm having a hole made in the
journal-facing surface and teach a method for producing a crankshaft with the
arm. The hole of the arm is made to lie on a straight line connecting the axis
of the journal and the axis of the pin (which will be hereinafter referred to as
an "arm centerline"), and the hole extends large and deep toward the pin.
This arm is reduced in weight by the weight corresponding to the volume of
the hole. The weight reduction of the arm leads to a weight reduction of the
weight paired with the arm, thereby resulting in a reduction in weight of the
whole forged crankshaft. Regarding the arm having a hole,- in a region near
the pin, both side portions across the arm centerline are thick, which ensures
stiffness (torsional stiffness and bending stiffness ) .
[0015]
Forming a recessed portion in the journal-facing surface of the arm
while keeping both side portions of the arm thick as described above leads to
weight reduction and ensuring of stiffness.
[0016]
It is, however, difficult to produce such a forged crankshaft with such
uniquely shaped arms by a conventional production method. The reason is
as follows. When a recess is to be formed in the surface of an arm in the die
I
forging step, the draft of the die will become a reverse draft at the site of the
recess, and therefore, the forged blank will not be able to be removed from the
die.
[0017]
To avoid such situations, in the production methods disclosed in
Patent Literatures 1 and 2, the following process is carried out. In the die
forging step, the arm is shaped to be small with no recess formed in the
surface of the arm, and after the trimming step, a punch is pushed into the
surface of the arm so that the imprint made by the punch forms a recess.
[0018]
In the crankshaft shown in FIG. 1F, all of the arms A and the weights
W integrated therewith have the same shape. Practically, however, the arms
A and the weights W integrated therewith may be different from one another
in shape as needed. Japanese Patent Application Publication No.
2007-71227 (Patent Literature 3) and Japanese Patent Application
Publication No. 2014-40856 (Patent Literature 4) disclose techniques for this.
[0019]
Patent Literature 3 discloses a four-cylinder eight-counterweight
crankshaft including a flywheel disposed at an end. In the crankshaft, the
arms incorporating a weight are different from one another in the thickness
and the center of gravity of the arm and in the mass of the weight.
Accordingly, it is possible to reduce the thicknesses of the arms that need' to
have only low stiffness while ensuring the minimum necessary stiffness to
each of the arms, thereby resulting in a reduction in weight.
[0020]
Patent Literature 4 discloses a crankshaft for a multicylinder engine,
the crankshaft including a flywheel disposed at an end. In the crankshaft,
an arm that is less distant from the flywheel has higher bending stiffness and
higher torsional stiffness than an arm that is more distant from the flywheel.
Also, it is preferred that the arms are different from one another in the
bending stiffness and in the torsional stiffness. Accordingly, it is possible to
attain a· reduction in weight while suppressing flexural vibration and
torsional vibration.
I
[0021]
In a case where the arms incorporating a weight have different arm
shapes and different weight shapes, what portion of the arm needs to have
high stiffness differs from arm to arm, depending on the shape. Specifically,
an arm may need to have high stiffness in the region near the pin, while
another arm may need to have high stiffness in the region near the journal.
CITATION LIST
PATENT UTERATURE
[0022]
Patent Literature 1: Japanese Patent Application Publication No.
2012-7726
Patent Literature 2: Japanese Patent Application Publication No.
2010-230027
Patent Literature 3: Japanese Patent Application Publication No.
2007-71227
Patent Literature 4: Japanese Patent Application Publication No.
2014-40856
SUMMARY OF INVETION
TECHNICAL PROBLEMS
[0023]
The production methods disclosed in Patent Literatures 1 and 2 make
it possible to make a hole in the journal-facing surface of an arm while
keeping both side portions of the arm thick. Accordingly, the production
methods allow production of a forged crankshaft with a reduced weight and
assured stiffness.
[0024]
In the production methods, however, in making a hole, the surface of
an arm is strongly punched and is deformed entirely, and a great force is
necessary for the punching. Therefore, a special facility including a die for
supplying a great force to a punch is required, and it is also necessary to give
attention to the durability of the punch.
-I
[0025]
It is an object of the present invention to provide a method for
producing a forged crankshaft with both a reduced weight and assured
stiffness by a simple process.
SOLUTION TO PROBLEMS
[0026]
A production method according to an embodiment of the present
invention is a method for producing a forged crankshaft including journals
serving as a center of rotation, pins decentered from the journals, and crank
arms connecting the journals and the pins. The forged crankshaft further
includes counterweights integrated with all or some of the crank arms. The
method includes a die forging step of obtaining a forged blank with flash
having a crankshaft shape, and a trimming step of removing the flash from
the forged blank while nipping the forged blank with a pair of holding dies.
The forged blank includes rough journals, rough pins, rough crank arms, and
rough counterweights, which correspond to the journals, the pins, the crank
arms, and the counterweights of the forged crankshaft, respectively. At least
one of the rough crank arms has, in a region near an adjacent one of the rough
pins, a first excess portion protruding from an outer periphery of a side
portion of the rough crank arm. When the forged blank is nipped with the
pair of holding dies in the trimming step, the first excess portion is deformed
by the pair of holding dies to bulge toward an adjacent one of the rough
journals.
ADVANTAGEOUS EFFECTS OF INVENTION
[0027]
In the forged crankshaft production method according to the present
invention, all or some of the rough crank arms have, in a region near an
adjacent one of the rough pins, at least one first excess portion protruding
from an outer periphery of at least one side portion of the rough crank arm.
When the forged blank is nipped with the pair of holding dies in the trimming
step, the first excess portion is deformed by the pair of holding dies to bulge
ftoward
an adjacent one of the rough journals_ This allows thickening of the
side portions of the arm in the region near the adjacent rough pin and
formation of a recess in the journal-facing surface of the arm_ The forged
crankshaft produced thereby has a reduced weight and assured stiffness.
Also, since the excess portion is deformed by the pair of holding dies, the
deformation can be carried out in a simple manner by use of an existing
equipment.
BRIEF DESCRIPTION OF DRAWINGS
[0028]
[FIG. IA] FIG. IA is a schematic diagram of a billet during a
conventional process of producing a common forged crankshaft.
[FIG. IB] FIG. IB is a schematic diagram of a rolled blank during the
conventional process of producing a common forged crankshaft.
[FIG. IC] FIG. IC is a schematic diagram of a bent blank during the
conventional process of producing a common forged crankshaft.
[FIG. ID] FIG. ID is a schematic diagram of a rough forged blank
during the conventional process of producing a common forged crankshaft.
[FIG. IE] FIG. IE is a schematic diagram of a finish forged blank
during the conventional process of producing a common forged crankshaft.
[FIG. IF] FIG. IF is a schematic diagram of a crankshaft during the
conventional process of producing a common forged crankshaft.
[FIG. 2A] FIG. 2A is a perspective view of an arm after trimming for a
crankshaft having a first exemplary configuration according to the present
invention, schematically showing the journal-facing surface of the arm.
[FIG. 2B] FIG. 2B is a diagram showing the journal-facing surface of
the arm shown in FIG. 2A.
[FIG. 2C] FIG. 2C is a diagram showing a side surface of the arm
shown in FIG. 2A.
[FIG. 2D] FIG. 2D is a sectional view along the line IID-IID in FIG.
2B.
[FIG. 3A] FIG. 3A is a diagram of a rough arm before trimming (of a
forged blank with flash) for the crankshaft having the first exemplary
·I
configuration, showing the rough-journal-facing surface of the rough arm.
[FIG. 3B] FIG. 3B is a diagram showing a side surface of the rough
arm shown in FIG. 3A.
[FIG. 3C] FIG. 3C is a sectional view along the line IIIC-IIIC in FIG.
3A.
[FIG. 4A] FIG. 4Ais a perspective view of an arm after trimming for a
crankshaft having the second exemplary configuration, showing the
rough-journal-facing surface of the arm.
[FIG. 4B] FIG. 4B is a diagram showing the pin-facing surface of the
arm shown in FIG. 4A.
[FIG. 4C] FIG. 4C is a diagram showing a side surface of the arm
shown in FIG. 4A.
[FIG. 4D] FIG. 4D is a sectional view along the line IVD-IVD in FIG.
4B.
[FIG. 5A] FIG. 5A is a diagram of a rough arm before trimming (of a
forged blank with flash) for the crankshaft having the second exemplary
configuration, showing the pin-facing surface of the rough arm.
[FIG. 5B] FIG. 5B is a diagram showing a side surface of the rough
arm shown in FIG. 5A.
[FIG. 5C] FIG. 5C is a sectional view along the line VC-VC in FIG. 5A.
[FIG. 6A] FIG. 6A is a diagram of an arm after trimming for a
crankshaft having a third exemplary configuration according to the present
invention, showing the pin -facing surface of the arm.
[FIG. 6B] FIG. 6B is a sectional view along the line VIB-VIB in FIG.
6A.
[FIG. 7A] FIG. 7A is a diagram of a rough arm before trimming (of a
forged blank with flash) for the crankshaft having the third exemplary
configuration, showing the rough-pin-facing surface of the rough arm.
[FIG. 7B] FIG. 7B is a sectional view along the line VIIB-VIIB in FIG.
7A.
[FIG. 8A] FIG. 8A is a sectional view showing the time when the
forged blank has been placed in dies in an exemplary process flow of the
trimming step according to the present invention.
\0 I
-(
[FIG. SB] FIG. 8B is a sectional view showing a state where the forged
blank is held by the dies in the exemplary process flow of the trimming step
according to the present invention.
[FIG. SC] FIG. 8C is a sectional view showing the time when a cutting
die has come into contact with the forged blank in the exemplary process flow
of the trimming step according to the present invention.
[FIG. SD] FIG. 8D is a sectional view showing the time when a
downward movement of the cutting die has been completed in the exemplary
process flow of the trimming step according to the present invention.
[FIG. 9A] FIG. 9A is a sectional view showing an example of a step in
an exemplary process flow of the trimming step according to the present
invention.
[FIG. 9B] FIG. 9B is a sectional view showing an example of a next
step after the step shown in FIG. 9A in the exemplary process flow of the
trimming step according to the present invention.
[FIG. 9C] FIG. 9C is a sectional view showing an example of a next
step after the step shown in FIG. 9B in the exemplary process flow of the
trimming step according to the present invention.
[FIG. 9D] FIG. 9D is a sectional view showing an example of a next
step after the step shown in FIG. 9C in the exemplary process flow of the
trimming step according to the present invention.
[FIG. 10] FIG. 10 is a view showing an exemplary holder arrangement
in the trimming step according to the present invention.
DESCRIPTION OF EMBODIMENTS
[0029]
An embodiment of the present invention will hereinafter be described.
However, the present invention is not limited to the embodiment to be
described below.
[0030]
(Forged Crankshaft Production Method)
A production method according to the present invention is a method
for producing a forged crankshaft. The forged crankshaft includes journals
-I
serving as a center of rotation, pins decentered from the journals, and crank
arms connecting the journals to the pins. The forged crankshaft further
includes counterweights integrated with all or some of the crank arms.
[0031]
The production method according to the present invention includes a
die forging step and a trimming step to be executed in this order. The die
forging step is to obtain a forged blank with flash having a crankshaft shape.
The forged blank has roughly the same shape as the crankshaft. The forged
blank includes rough journals, rough pins, rough crank arms and rough
counterweights corresponding to the journals, the pins, the crank arms and
the counterweights of the forged crankshaft, respectively. The forged blank
further includes flash and first excess portions which will be described later.
There is no limit to the die forging step, and the die forging step may include a
rough forging step and a finish forging step as described above with reference
to FIGS. lD and IE.
[0032]
In the trimming step, while the forged blank is nipped and held by a
pair of holding dies, the flash is removed from the forged blank. At least one
of the rough crank arms has, in a region near the adjacent rough pin, a first
excess portion protruding from the outer periphery of at least one of the two
side portions. In short, at least one of the rough crank arms has a first excess
portion. In the trimming step, when the forged blank is nipped with the pair
of holding dies, the first excess portion is deformed by the holding dies to bulge
toward the adjacent rough journaL
[0033]
All of the rough crank arms may include a first excess portion.
Alternatively, all or some of the rough crank arms incorporating a rough
counterweight may include a first excess portion. Also, only the rough crank
arms incorporating a rough counterweight may include a first excess portion.
Also, all or some of the crank arms not incorporating a rough counterweight
may include a first excess portion. Also, only the crank arms not
incorporating a rough counterweight may include a first excess portion.
[0034]
·f
At least one of the rough crank arms has, in the region near the
adjacent rough pin, two first excess portions protruding respectively from the
outer peripheries of the two side portions of the crank arm. This structure
ensures stiffness of both side portions of the crank arm in the region near the
adjacent pin. Between the two first excess portions, an area As (area with a
recess) is present. The surface of the recess may be convex and bulge in the
center with respect to the width direction as will be described later.
[0035]
In the trimming step, the first excess portion may be deformed to
bulge toward the rough journal while a holder is holding the lower surface of
the flash. Since the first excess portion is deformed by the pair of holding
dies, at the initial stage of the trimming step, the shape of the o/st excess
portion does not fit in the shape of the pair of holding dies. Therefore, if the
forged blank having a first excess portion before being deformed is held by
only the lower holding die, the forged blank will be in an unstable posture.
This problem is noticeable especially when only some of the rough crank arms
have the first excess portion. By using the holder, it is possible to apply
trimming to the forged blank while keeping the forged blank in a stable
posture. Specifically, trimming can be performed with the flash of the forged
blank kept in a horizontal posture. Further, the forged blank may be kept in
the center between the upper die and the lower die by the holder.
[0036]
The holder may move to keep holding the lower surface of the flash
along with movements of the holding dies. The flash may move up and down
along with movements of the holding dies. In this case, it is preferred that
the holder moves (up and down) following the flash.
[0037]
The edge of the holder (the edge to contact the lower surface of the
flash) may have a shape that fits in the edge of the cutting die to remove the
flash. For example, the edge of the holder may have a shape corresponding
to the parting line of the finished product. The lower surface of the flash may
be held by a plurality of holders. For example, three or more (for example,
four or more) holders may be used. Using four or more holders allows the
t3
rough forged blank to be kept in a more stable posture. When the holders
hold the lower surface of the flash at a plurality of points, the holders
preferably hold the portions that are great in mass (for example, the portions
around the rough counterweights). The plurality of holders may be located
on different levels such that the forged blank at the start of trimming is in a
stable posture. For example, in producing a three-cylinder or six-cylinder
crankshaft, the flash may not be formed on a level. In this case, the holders
shall be placed on levels as appropriate according to the respective levels
where the portions are to be kept.
[0038]
The holders are moved to and kept in proper positions to serve the
above function. There is no limit as to the mechanism for moving and
keeping the holders, and any conventional mechanism can be used. For
example, a hydraulic cylinder, a motor, an elastic member (spring) or the like
can be used to move and keep the holders. The holders may be moved and
kept by a conventional mechanism used for a blank holder.
[0039]
In the trimming step, the deformation of the first excess portion may
be carried out by crushing or bending.
[0040]
At least one of the rough crank arms may have, in a region near the
adjacent rough journal, a second excess portion protruding from the outer
periphery of a side portions. In this case, in the trimming step, when the
forged blank is nipped with the pair of holding dies, the second excess portion
is deformed by the holding dies to bulge toward the adjacent rough pin. All of
the rough crank arms may include a second excess portion. Alternatively, all
or some of the rough crank arms incorporating a rough counterweight may
include a second excess portion. Also, only the rough crank arms
incorporating a rough counterweight may include a second excess portion.
Also, all or some of the crank arms not incorporating a rough counterweight
may include a second excess portion. Also, only the crank arms not
incorporating a rough counterweight may include a second excess portion.
[0041]
' (LfAt
least one of the rough crank arms has, in the region near the
adjacent rough journal, two second excess portions protruding respectively
from the outer peripheries of the two side portions of the crank arm. This
structure ensures stiffness of both side portions of the crank arm in the region
near the adjacent journal. Between the two second excess portions, an area
As (area with a recess), which will be described later, is present. The surface
of the recess may be convex and bulge in the center with respect to the width
direction as will be described later.
[0042]
The rough crank arm having a second excess portion may be the rough
crank arm incorporating a rough counterweight.
[0043]
The rough crank arm having a second excess portion may be the rough
crank arm not incorporating a rough counterweight.
[0044]
In the trimming step, the deformation of the second excess portion
may be carried out by crushing or bending.
[0045]
In an aspect, the present invention provides an exemplary method for
producing a forged crankshaft. The exemplary production method is
intended to produce a forged crankshaft including journals serving as a center
of rotation, pins decentered from the journals, and crank arms connecting the
journals to the pins. In the forged crankshaft, all or some of the crank arms
incorporate a counterweight. The exemplary production method includes a
die forging step of obtaining a forged blank with flash having a crankshaft
shape, the forged blank including a crank arm (rough crank arm) having, in a
region near an adjacent pin (rough pin), first excess portions protruding
respectively from outer peripheries of both side portions, and a trimming step
of removing the flash from the forged blank while nipping the forged blank
with a pair of holding dies. In the exemplary production method, in the
trimming step, when the forged blank is nipped with the pair of holding dies,
the first excess portions are deformed by the pair of holding dies, whereby
both side portions of the crank arm (rough crank arm) in the region near the
-radjacent
pin (rough pin) are thickened.
[0046]
The above paragraph describes a case where the forged blank
necessarily includes first excess portions. However, the production method
according to the present invention is applicable to a case where the forged
blank does not include any first excess portions but include at least one second
excess portion. In this case, as mentioned above, in the trimming step, when
the forged blank is nipped with the pair of holding dies, the second excess
portion is deformed by the pair of holding dies to bulge toward the adjacent
rough pin.
[0047]
A forged crankshaft production method according an embodiment of
the present invention will hereinafter be described with reference to the
drawings. In the following paragraphs, descriptions of the matters already
described with reference to FIGS. lA to lF may not be repeated.
[0048]
1. Shape of Crankshaft
A forged crankshaft to be produced by a method according to the
present embodiment includes journals serving as a center of rotation, pins
decentered from the journals, and arms connecting the journals to the pins.
The forged crankshaft further includes counterweights integrated with all or
some of the crank arms.
[0049]
In an aspect, the forged crankshaft to be produced by the method
includes a number of units (which are also referred to as "slots")
corresponding to the number of cylinders of the engine. One unit includes a
pin, and two arms located to hold the pin therebetween. On both sides of one
unit, two journals are located. Two adjacent units are connected to each
other via a journal. In a crankshaft for a V-type six-cylinder engine, two pins
and an arm therebetween define a small unit, and one small unit and two
arms on both sides thereof define a large unit. Further, journals are located
on both sides of the large unit.
[0050]
-I
The forged crankshaft production method according to the present
embodiment is applicable to production of a four-cylinder eight-counterweight
crankshaft and production of a four-cylinder four-counterweight crankshaft,
for example. The forged crankshaft production method is applicable also to
production of other types of crankshafts, such as crankshafts to be mounted in
three-cylinder engines, in-line six-cylinder engines, V-type six-cylinder
engines, eight-cylinder engines and others.
[0051]
More specifically, the forged crankshaft production method according
to the present embodiment is applicable to production of a forged crankshaft
having a first exemplary configuration as shown in FIGS. 2A to 2D,
production of a forged crankshaft having a second exemplary configuration as
shown in FIGS. 4A to 4D, and production of a forged crankshaft having a third
exemplary configuration as shown in FIGS. 6A and 6B.
[0052]
In either of the crankshafts having the first, the second and the third
exemplary configurations, all of the arms, whether incorporating a weight or
not, have a recess in the journal-facing surface. As will be described later, at
least one of the arms may have a recess in the journal-facing surface. In the
crankshaft having the second' exemplary configuration, the arms
incorporating a weight further have a recess in the pin-facing surface. The
crankshaft having the third exemplary configuration includes arms
incorporating no weight. In the crankshaft having the third exemplary
configuration, the arms incorporating no weight have a recess in the
pin-facing surface in addition to the recess in the journal-facing surface.
[0053]
According to the present embodiment, in order to form recesses in the
arms, the crankshaft production method includes a die forging step of
obtaining a forged blank with flash, and a trimming step of removing the flash
from the forged blank. The rough arms of the forged blank have first excess
portions, and in the trimming step, the first excess portions are deformed to
bulge toward the journals. The shapes of the arms of the forged crankshaft
(finished product) and the rough arms of the forged blank will hereinafter be
described.
[0054]
FIGS. 2A to 2D are diagrams showing an arm after the trimming step
for the crankshaft having the first exemplary configuration according to the
present invention. FIG. 2A is a perspective view, FIG. 2B is a view showing
the journal-facing surface, and FIG. 2C is a side view. FIG. 2D is a sectional
view along the line IID-IID in FIG. 2B. FIGS. 2A to 2D show one ofthe arms
(incorporating a weight) of the crankshaft. FIG. 2C is a view from the
direction indicated by the dashed arrow in FIG. 2B.
[0055]
As shown in FIGS. 2A to 2D, in the first exemplary configuration, each
of the arms A has a recess in the journal(J)-facing surface, in a region near the
adjacent pin P, in an area As inside of both side portions (two side portions) Aa
and Ab. The side portions Aa and Ab in the region near the pin P bulge
toward the journal J, and the thicknesses of the side portions (Aa, Ab) are
greater than the thickness of the recess. The side portions mean surfaces
and portions there around at the edges of the· arm A in the width direction (a
direction perpendicular to the decentering direction of the pins), that is, the
end portions of the arm A in the width direction. The area As is on the
surface opposite to the pin P, that is, on the journal(J)-facing surface.
[0056]
In the crankshaft having the first exemplary configuration, the side
portions Aa and Ab of each arm A are kept as thick as an arm without a recess.
In·terms of results, a recess is formed in the journal(J)-facing surface of the
arm A. Accordingly, the forged crankshaft having the first exemplary
configuration can achieve a reduction of weight by the recesses formed in the
arms A. Additionally, the maintained thicknesses of the side portions Aa and
Ab of the arm A ensure stiffness. In other words, the greater thicknesses of
the side portions Aa and Ab in the region near the adjacent pin P than the
thickness of the recess ensure stiffness.
[0057]
The sectional shape of the area As inside of the side portions Aa and
Ab (the bottom shape of the recess) is preferably convex and bulges in the
·0·
center with respect to the width direction as shown in FIG. 2D. In other
words, it is preferred that the thickness of the area As gradually decreases
with increasing distance from the center with respect to the width direction.
Since the bottom shape of the recess is convex and bulges in the center with
respect to the width direction, the bending stiffness can be improved. It is
possible to form a recess with this bottom shape by making the sectional
shape of the central portion with respect to the width direction arc-shaped,
semi-elliptic or parabolic, for example.
[0058]
FIGS. 3A to 3C are diagrams showing a rough arm before undergoing
the trimming step (a rough arm of a forged blank with flash) for the
crankshaft having the first exemplary configuration. FIG. 3A is a view
showing the rough-journal-facing surface. FIG. 3B is a side view. FIG. 3C
is a sectional view along the line IIIC·IIIC in FIG. 3A. FIGS. 3A to 3C show
one of the rough arms (incorporating a rough weight W') for the crankshaft.
FIG. 3B is a view from the direction indicated by the dashed arrow in FIG. 3A.
[0059]
As shown in FIGS. 3A to 3C, each of the rough arms A' before the
trimming step has a surface shape in agreement with the bottom shape of the
recess after the trimming step, in the rough-journal(J')-facing surface, in a
region near the adjacent rough pin P', in an area As' inside of the side portions
Aa' and Ab'. The surface shape extends smoothly to the side portions Aa' and
Ab' in the region near the rough pin P'. Accordingly, the thicknesses of the
side portionsAa' andAb' are smaller than those after the trimming step.
[0060]
Each of the rough arm A' has, in the region near the adjacent rough
pin P', first excess portions Aaa and Aba on the outer peripheries of the side
portions Aa' and Ab'. The first excess portions Aaa and Aba protrude
respectively from the outer peripheries of the side portions Aa' and Ab' in the
region near the adjacent rough pin P'. The first excess portions Aaa and Aba
are plate-shaped, and extend along the outer peripheries of the side portions
Aa' and Ab' in the region near the adjacent rough pin P'. The thicknesses of
the first excess portions Aaa and Aha are substantially equal to or smaller
-Ithan
the thicknesses of the bases thereof, that is, the side portions Aa' and Ab' _
[0061]
FIGS. 4A to 4D are diagrams showing an arm after the trimming step
for the crankshaft having the second exemplary configuration according to the
present invention. FIG. 4A is a perspective view, FIG. 4B is a view showing
the pin-facing surface, and FIG. 4C is a side view. FIG. 4D is a sectional view
along the line IVD-IVD in FIG. 4B. FIGS. 4A to 4D show one of the arms
(incorporating a weight) of the crankshaft. FIG. 4C is a view from the
direction indicated by the dashed arrow in FIG. 4B.
[0062]
In the second exemplary configuration, as in the first exemplary
configuration, each of the arms A has thick side portions in a region near the
adjacent pin P, and has a recess in the journal(J)-facing surface. Further, in
the second exemplary configuration, each of the arms A incorporating a weight
has a recess in the pin(P)-facing surface, in a region near the adjacent journal
J, in an area At inside of both side portions (two side portions) Ac and Ad, as
shown in FIGS. 4A to 4D. The side portions Ac and Ad in the region near the
journal J bulge toward the adjacent pin P, and the thicknesses of the side
portions Ac and Ad are greater than the thickness of the recess. The area At
is on the surface opposite to the journal J.
[0063]
In the crankshaft having the second exemplary configuration,
regarding all the arms A, the side portions in the region near the adjacent pin
P ·are thick, and a recess is formed in the journal(J)-facing surface.
Regarding the arms A incorporating a weight, further, the side portions Ac
and Ad in the region near the adjacent journal J are kept as thick as those of
an arm A without a recess, and in terms of results, a recess is formed also in
the pin(P)-facing surface.
[0064]
Accordingly, the forged crankshaft having the second exemplary
configuration can achieve a reduction of weight by the recesses formed in the
respective journal(J)-facing surfaces of all the arms A and the recesses formed
in the respective pin(P)-facing surfaces of the arms A incorporating a weight.
-r-
Additionally, the maintained thicknesses of the side portions Aa and Ab in the
region near the adjacent pin P and the side portions Ac and Ad in the region
near the adjacent journal J ensure stiffness. In other words, the greater
thicknesses of the side portions Aa and Ab in the region near the adjacent pin
P and the greater thicknesses of the side portions Ac and Ad in the region near
the adjacent journal J than the thicknesses of the recesses ensure stiffness.
[0065]
Regarding the arms A incorporating a weight, the sectional shape of
the area At inside of the side portions Ac and Ad (the bottom shape of the
recess) is preferably convex and bulges in the center with respect to the width
direction as shown in FIG. 4D. In other words, it is preferred that the
thickness of the area At gradually decreases with increasing distance from the
center with respect to the width direction. Since the bottom shape of the
recess is convex and bulges in the center with respect to the width direction,
the bending stiffness can be improved. It is possible to form a recess with
this bottom shape by making the sectional shape of the central portion with
respect to the width direction arc-shaped, semi -elliptic or parabolic, for
example.
[0066]
FIGS. 5A to 5C are diagrams showing a rough arm before the
trimming step (a rough arm of a forged blank with flash) for the crankshaft
having the second exemplary configuration. FIG. 5A is a view showing the
rough-pin-facing surface. FIG. 5B is a side view. FIG. 5C is a sectional view
along the line VC-VC in FIG. 5A. FIGS. 5A to 5C show one of the rough arms
(incorporating a rough weight) for the crankshaft. FIG. 5B is a view from the
direction indicated by the dashed arrow in FIG. 5A.
[0067]
In the second exemplary configuration, as in the first exemplary
configuration, each of the rough arms A' before the trimming step has a
surface shape in agreement with the bottom shape of the recess after the
trimming step, in the rough-journal(J')-facing surface, in a region near the
adjacent rough pin P', in an area As' inside of the side portions Aa' and Ab'.
Also, as in the first exemplary configuration, each of the rough arms A' has, in
2--z/
the region near the adjacent rough pin P', first excess portions Aaa and Aha on
the outer peripheries of the side portions Aa' and Ab'. The first excess
portions Aaa and Aha protrude respectively from the outer peripheries of the
side portions Aa' and Ab' in the region near the adjacent rough pin P'.
[0068]
Additionally, each of the rough arms A' incorporating a rough weight
has a surface shape in agreement with the bottom shape of the recess after the
trimming step, in the rough-pin(P')-facing surface, in a region near the
adjacent rough journal J', in an area At' inside of the side portions Ac' and Ad'.
The surface shape extends smoothly to the side portions Ac' and Ad' in the
region near the adjacent rough journal J'. Accordingly, the thicknesses of the
side portions Ac' and Ad' are smaller than those after the trimming step.
[0069]
Each of the rough arms A' incorporating a rough weight further has,
in the region near the adjacent rough journal J', second excess portions Aca
and Ada on the outer peripheries of the side portions Ac' and Ad'. The second
excess portions Aca and Ada protrude respectively from the outer peripheries
of the side portions Ac' and Ad' in the region near the adjacent rough journal J'.
The second excess portions Aca and Ada shown in FIGS. 5A to 5C are
plate-shaped, and extend along the outer peripheries of the side portions Ac'
and Ad' in the region near the adjacent rough journal J'. The thicknesses of
the second excess portions Aca and Ada are substantially equal to or smaller
than the thicknesses of the bases thereof, that is, the side portions Ac' and Ad'.
[0070]
FIGS. 6A and 6B are diagrams showing an arm after the trimming
step for the crankshaft having the third exemplary configuration according to
the present invention. FIG. 6A is a view showing the pin-facing surface.
FIG. 6B is a sectional view along the line VIB-VIB in FIG. 6A. The
crankshaft having the third exemplary configuration includes a plurality of
arms, and at least one of the arms incorporate a weight. FIGS. 6A and 6B
show one of the arms not incorporating a weight, that is, one of the
unweighted arms of the crankshaft.
[0071]
In the third exemplary configuration, as m the first exemplary
configuration, each of the arms, whether incorporating a weight or not, has
thick side portions in a region near the adjacent pin P and has a recess in the
journal-facing surface, though it is not shown in the drawings. In the third
exemplary configuration, as shown in FIGS. 6A and 6B, each of the
unweighted arms A further has a recess in the pin P-facing surface, in a region
near the adjacent journal J, in an area At inside of side portions Ac and Ad.
The side portions Ac and Ad in the region near the adjacent journal J bulge
toward the adjacent pin P, and the thicknesses of the side portions Ac and Ad
are greater than the thickness of the recess.
[0072]
In the crankshaft having the third exemplary configuration, regarding
all the arms A, the side portions Aa and Ab in the region near the adjacent pin
P are thick, and a recess is formed in the journal J -facing surface. Regarding
the unweighted arms A, further, the side portions Ac and Ad in the region
near the adjacent journal J are kept as thick as those of an arm A without a
recess. Also, in terms of results, each of the unweighted arms A obtains a
recess in the pin P-facing surface.
[0073]
Accordingly, the forged crankshaft having the third exemplary
configuration can achieve a reduction of weight by the recesses formed in the
respective journal J -facing surfaces of all the arms A and the recesses formed
in the respective pin P-facing surfaces of the unweighted arms A.
Additionally, the maintained thicknesses of the side portions Aa and Ab in the
region near the adjacent pin P and the side portions Ac and Ad in the region
near the adjacent journal J ensure stiffness. In other words, the greater
thicknesses of the side portions Aa and Ab in the region near the adjacent pin
P and the greater thicknesses of the side portions Ac and Ad in the region near
the adjacent journal J than the thicknesses of the recesses ensure stiffness.
[0074]
Regarding the unweighted arms A, the sectional shape of the area At
inside of the side portions Ac and Ad (the bottom shape of the recess) is
preferably convex and bulges inthe center with respect to the width direction
-Ias
shown in FIG. 6B. In other words, it is preferred that the thickness of the
area At gradually decreases with increasing distance from the center with
respect to the width direction. Since the bottom shape of the recess is convex
and bulges in the center with respect to the width direction, the bending
stiffness can be improved. It is possible to form a recess with this bottom
shape by making the sectional shape of the central portion with respect to the
width direction arc-shaped, semi-elliptic or parabolic, for example.
[0075]
FIGS. 7A and 7B are diagrams showing a rough arm before the
trimming step (a rough arm of a forged blank with flash) for the crankshaft
having the third exemplary configuration. FIG. 7A is a view showing the
rough-pin-facing surface. FIG. 7B is a sectional view along the line
VIIB-VIIB in FIG. 7A. FIGS. 7A to 7B show one of the rough unweighted
arms of the forged blank.
[0076]
In the third exemplary configuration, as in the first exemplary
configuration, each of the rough arms A' before the trimming step, whether
incorporating a rough weight or not, has a surface shape in agreement with
the bottom shape of the recess after the trimming step, in the
rough·journal(J')-facing surface, in a region near the adjacent rough pin P', in
an area inside of the side portions, though it is not shown in the drawings.
Also, as in the first exemplary configuration, each of the rough arms A' has, in
the region near the adjacent rough pin P', first excess portionsAaa andAba on
the outer peripheries of the side portions. The first excess portions Aaa and
Aba protrude respectively from the outer peripheries of the side portions in
the region near the adjacent rough pin P'.
[0077]
Additionally, each of the rough unweighted arms A' before the
trimming step has a surface shape in agreement with the bottom shape of the
recess after the trimming step, in the rough-pin(P')-facing surface, in a region
near the adjacent rough journal J', in an area At' inside of the side portions Ac'
and Ad'. The surface shape extends smoothly to the side portions Ac' and Ad'
in the region near the adjacent rough journal J'. Accordingly, the thicknesses
-z/
of the side portions Ac' and Ad' are smaller than those after the trimming step.
[0078]
Each of the unweighted rough arms A' further has, in the region near
the adjacent rough journal J', second excess portionsAca and Ada on the outer
peripheries of the side portions Ac' and Ad'. The second excess portions Aca
and Ada protrude respectively from the outer peripheries of the side portions
Ac' and Ad' in the region near the adjacent rough journal J' The second
excess portions Aca and Ada are plate-shaped, and extend along the outer
peripheries of the side portions Ac' and Ad' in the region near the adjacent
rough journal J'. The thicknesses of the second excess portions Aca and Ada
are substantially equal to or smaller than the thicknesses of the bases thereof,
that is, the side portions Ac' and Ad'.
[0079]
2. Production Process of Forged Crankshaft
A forged crankshaft production method according to the present
embodiment includes a die forging step and a trimming step. Before the die
forging step, for example, a preforming step may be executed. After the
trimming step, for example, a coining step may be executed. When
adjustment of placement angles of the pins is necessary, a twisting step is
executed after the trimming step. These steps are to apply hot working and
are to be executed sequentially. The forged crankshaft production method
according to the present embodiment may employ a conventional production
method in the parts other than the distinctive features· of the present
invention. For example, the production process according to the present
invention may include at least one of the steps shown in FIGS. lA to lF or one
or more steps adapted from those shown in FIG. lA to lF for the present
invention as steps other than the distinctive features of the present invention.
[0080]
The preforming step includes a rolling step and a bending step, for
example. In the rolling step and the bending step, the volume of a billet
(starting material) is distributed, whereby a bent blank is obtained.
[0081]
The die forging step is to obtain a forged blank with flash as shown in
·zj·
FIGS. 3A to 3C. The obtained forged blank with flash is roughly in the shape
of a crankshaft, and specifically, the forged blank with flash includes rough
journals J', rough pins P', rough arms A' and others. Additionally, each of the
rough arms A' of the forged blank with flash has, in a region near the adjacent
rough pin P', first excess portions Aaa and Aha protruding from the outer
peripheries of side portions Aa' and Ab'. Accordingly, in the die forging step,
dies that permit formation of such excess portions (first excess portions or
second excess portions, or first and second excess portions) are used for the die
forging.
[0082]
The die forging step to obtain such a forged blank with flash may
include, for example, a rough forging step and a finish forging step.
[0083]
In the die forging step, the draft never becomes a reverse draft.
Specifically, the draft of the dies never becomes a reverse draft at any portions
corresponding to the bottom surfaces of the recesses to be formed in the
rough-journal(J')-facing surfaces of the rough arms (inner areas As') and at
any portions corresponding to the first excess portions Aaa and Aha. In other
words, the forged blank having the above-described shape can be produced by
use of dies having no reverse draft. Therefore, the die forging, whether it is
rough forging or finish forging, can be carried out with no trouble, and a
forged blank with flash as shown in FIGS. 3A to 3C can be obtained. Also, in
producing a forged blank with flash as shown in FIGS. 5A to 5C and in
producing a forged blank with flash as shown in FIGS. 7A and 7B, the draft
never becomes a reverse draft at any portions corresponding to the bottom
surfaces of the recesses to be formed in the rough-journal(P')-facing surfaces of
the rough arms A' (inner areas At') and at any portions corresponding to the
second excess portions Aca and Ada. In other words, the forged blank having
the above-described shape can be produced by use of dies having no reverse
draft. Therefore, the die forging, whether it is rough forging or finish forging,
can be carried out with no trouble.
[0084]
In the trimming step, for example, while the forged blank with flash is
-¥-
nipped and held by a pair of holding dies, the flash is removed from the forged
blank. Thereby, a forged blank with no flash is obtained. In the trimming
step, when the forged blank is nipped with the pair of holding dies, the first
excess portions are deformed by the pair of holding dies to bulge toward the
rough journals. Thereby, the thicknesses of the side portions of the rough
arms in the region near the rough pins are increased. The deformation of the
first excess portions may be performed, for example, by crushing or bending.
The details of the trimming step will be described later.
[0085]
In the coining step, the forged blank with no flash obtained by the
trimming step may be processed to have the exact size and shape of the
finished product. When adjustment of the placement angles of the pins is
necessary, the placement angles of the pins is adjusted in the twisting step.
[0086]
3. Exemplary Process Flow of Trimming Step
FIGS. 8A to 8D are sectional views showing an exemplary process flow
of the trimming step of the crankshaft production method according to the
present invention. FIG. 8A shows the time when the forged blank has been
placed in a pair of dies. FIG. 8B shows a state where the forged blank is held
by the pair of dies. FIG. 8C shows the time when a cutting die has come into
contact with the forged blank. FIG. 8D shows the time when a downward
movement of the cutting die has been completed. FIGS. 8A to 8D are
sectional views at a position corresponding to the position indicated by the line
rue-nrc in FIG. 3A.
[0087]
In FIGS. 8A to 8D, a forged blank 30, a pair of holding dies 10, and a
cutting die 20 are shown. The shape of the forged blank 30 with flash is the
same as the shape of the forged blank 30 with flash shown in FIGS. 3A to 3C.
FIG. 8A shows one of the rough pins P' and two rough arms A' connected to
the rough pin P', which are extracted from the forged blank 30.
[0088]
The pair of holding dies 10 includes an upper die 11 and a lower die 12.
The upper die 11 and the lower die 12 are movable to separate from each other
21
and movable to come close to each other. While the forged blank 30 is
positioned between the upper die 11 and the lower die 12, the upper die 11 and
the lower die 12 are moved toward each other, and thereby, the forged blank
30 is nipped and held between the upper die 11 and the lower die 12.
[0089]
The upper die 11 and the lower die 12 have impressions to nip and
hold the forged blank 30 and to deform the protruding excess portions. The
impressions reflect the shape of the finished crankshaft. The cutting die 20
has a proper shape for removal of flash B along the outline of the finished
product. In other words, the edge of the cutting die 20 has a shape
corresponding to the parting line of the finished product.
[0090]
In the process flow using the pair of holding dies 10, first, the upper
die 11 and the lower die 12 are separated from each other, and the cutting die
20 is moved up and retracted. In this state, as shown in FIG. 8A, the forged
blank 30 with flash is placed between the upper die 11 and the lower die 12.
[0091]
Next, the upper die 11 and the lower die 12 are moved toward each
other. More specifically, the upper die 11 is moved down. Thereby, as shown
in FIG. 8B, the upper die 11 and the lower die 12 come into contact with the
forged blank 30, and the forged blank 30 is nipped and held between the
upper die 11 and the lower die 12.
[0092]
In the forged crankshaft production method according to the present
embodiment, when the forged blank 30 is nipped with the pair of holding dies
10, the first excess portions Aaa and Aha are reduced and deformed by the
pair of holding dies 10. For example, the first excess portions Aaa and Aha
are crushed by the pair of holding dies 10 or are bent toward the rough
journals along the pair of holding dies 10. Thereby, the first excess portions
Aaa and Aha are formed into shapes corresponding to the impressions of the
pair of holding dies 10 and are caused to bulge toward the rough journals.
Consequently, the thicknesses of the side portions Aa' and Ab' of each of the
rough arms A in the region near the adjacent rough pin P are increased.
r-
Accordingly, in the finished crankshaft, each of the arms A has thick side
portionsAa andAb in a region near the adjacent pin p_ In the state shown in
FIG. 8B, each part of the forged blank 30 has a shape substantially same as
the corresponding part of the finished forged crankshaft. Therefore, in FIG.
8B, each part of the forged blank 30 is denoted by the same reference symbols
used for the corresponding part of the finished forged crankshaft. (The same
applies to FIG. 9B.)
[0093]
While the forged blank 30 is kept held by the pair of holding dies 10,
the cutting die 20 is moved in the reducing direction. More specifically, the
cutting die 20 is moved down. Thereby, as shown in FIG. 8C, the cutting die
20 comes into contact with the flash B of the forged blank 30, and the flash B
is cut and removed from the forged blank 30 as shown in FIG. 8D.
Consequently, a forged blank 30a with no flash is obtained.
[0094]
After completion of the downward movement of the cutting die 20, the
cutting die 20 is moved up and retracted, and the upper die 11 and the lower
die 12 of the pair of holding dies 10 are separated from each other. Then, the
forged blank 30a with no flash is taken out.
[0095]
In the forged blank 30 with flash, as shown in FIG. 8A, each of the
rough arms A' has a surface shape in agreement with the bottom surface of
the recess after the trimming step in the rough-journal-facing surface, in the
region near the adjacent rough pin P', in the area As' inside of the side
portions Aa' and Ab'. The surface shape of the inner area As' is kept during
the trimming step. Meanwhile, when the forged blank 30 is nipped with the
pair of holding dies 10, the side portions Aa' and Ab' in the region near the
adjacent rough pin P' are thickened. Consequently, each of the arms A
obtains a recess in the journal-facing surface.
[0096]
The forged crankshaft production method according to the present
embodiment allows production of a crankshaft, wherein each of the arms A
has thickened side portions Aa and Ab in the region near the adjacent pin P
-~-
and has a recess in the journal(J)-facing surface. Accordingly, the forged
crankshaft production method according to the present embodiment allows
production of a forged crankshaft having a reduced weight and assured
stiffness.
[0097]
In the forged crankshaft production method according to the present
embodiment, the first excess portions Aaa and Aha are deformed by the pair of
holding dies, whereby the thicknesses of the side portions of each rough arm
in the region near the adjacent rough pin are increased. In consequence, the
recess is formed in the journal(J)-facing surface of the arm A. Thus, any
special tool, such as a punch or the like, is not necessary for the deformation of
the first excess portions, and the deformation can be carried out in a simple
manner by use of the existing equipment.
[0098]
In the forged crankshaft production method according to the present
embodiment, the first excess portions are deformed when the forged blank is
nipped with the pair of holding dies 10 in the trimming step, whereby the
thicknesses of the side portions of each rough arm in the region near the
adjacent rough pin are increased. Therefore, it is not necessary to make any
changes to the conventional production process.
[0099]
The forged crankshaft production method according to the present
embodiment is applicable to production of the forged crankshaft having the
second exemplary configuration as shown in FIGS. 4A to 4D. In this case,
the forged blank with flash preferably has second excess portions Aca and Ada
in each of the rough arms incorporating a rough weight as shown in FIGS. 5A
to 5C. The second excess portions Aca and Ada protrude respectively from
the outer peripheries of the side portions Ac' and Ad' of the rough arm A' in the
region near the adjacent rough journal J'.
[0100]
When the forged blank is nipped with the pair of holding dies in the
trimming step, not only are the first excess portions Aaa and Aha deformed by
the pair of holding dies, but the second excess portions Aca and Ada provided
to each of the rough arms A' incorporating a rough weight shall be also
deformed by the pair of holding dies to bulge toward the adjacent rough pin.
Thereby, regarding each of the rough arms A' incorporating a rough weight,
the thicknesses of the side portions Ac' and Ad' in the region near the adjacent
rough journal J' are increased. The deformation of the second excess portions
may be performed, for example, by crushing or bending. Consequently, a
crankshaft with a more reduced weight and assured stiffness as shown in
FIGS. 4A to 4D can be obtained.
[0101]
The forged crankshaft production method according to the present
embodiment is applicable to the forged crankshaft having _the third exemplary
configuration as shown in FIGS. 6A and 6B. In the forged crankshaft, only
some of the arms A incorporate a weight, and the other arms A are
unweighted arms which incorporate no weight.
[0102]
In this case, the forged blank with flash preferably has second excess
portions Aca and Ada in each of the unweighted arms A' as shown in FIGS. 7 A
and 7B. The second excess portions Aca and Ada protrude respectively from
the outer peripheries of the side portions Ac' and Ad' of each of the rough
unweighted arms A' in the region near the adjacent rough journal J'.
[0103]
When the forged blank is nipped with the pair of holding dies in the
trimming step, not only are the first excess portions Aaa andAba deformed by
the pair of holding dies, but the second excess portions Aca and Ada provided
to each of the rough unweighted arms A' shall be also deformed by the pair of
holding dies to bulge toward the adjacent rough pin. Thereby, regarding each
of the rough unweighted arms A', the thicknesses of the side portions Ac' and
Ad' in the region near the adjacent rough journal J' are increased. The
deformation of the second excess portions may be performed, for example, by
crushing or bending. Consequently, a crankshaft with a more reduced
weight and assured stiffness as shown in FIGS. 6A and 6B can be obtained.
[0104]
According to the present embodiment, the above-described holder may
31
be used in combination with the pair of holding dies in the trimming step.
An example of the trimming step in which the holder is used in combination
with the pair of holding dies is described with reference to FIGS. 9A to 9D.
The states shown in FIGS. 9A to 9D correspond to the states shown in FIGS.
8A to 8D, respectively. The matters already described with reference to FIGS.
8A to 8D may not be described repeatedly.
[0105]
In the example to be described below, the trimming is applied to a
forged blank 30 for the first exemplary configuration shown in FIGS. 3A to 3C.
However, the trimming by use of the holder can be applied to other blanks (for
example, a forged blank for the second exemplary configuration and a forged
blank for the third exemplary configuration).
[0106]
In this example, a plurality of holders (for example, four holders) 40
are used to hold the lower surface of the flash 40. The drawings to be
described below show only a part of the forged blank, and therefore, only two
holders 40 are shown in the drawings. The holders 40 are movable up and
down.
[0107]
First, a forged blank 30 with flash and dies are placed. Specifically,
the forged blank 30 is placed between the upper die 11 and the lower die 12.
At this time, the cutting die 20 is retracted in the upper position. The lower
surface of the flash B is held and kept in a stable posture by the holders 40.
The holders 40 hold the forged blank 30 such that the flash B is kept in a
horizontal posture. In the state shown in FIG. 9A, the forged blank 30is not
in contact with the pair of holding dies 10.
[0108]
Next, the upper die 11 and the lower die 12 are moved toward each
other. Specifically, the upper die 11 is moved down. Thereby, as shown in
FIG. 9B, the upper die 11 and the lower die 12 come into contact with the
forged blank 30, and the forged blank 30 is nipped and held between the
upper die and 11 and the lower die 12.
[0109]
-?j-
In the production method according to the present embodiment, as
described above, when the forged blank 30 is nipped with the pair of holding
dies 10, the first excess portions Aaa and Aba provided to each of the rough
arms of the forged die 30 are reduced and deformed. Specifically, the first
excess portions are formed into shapes corresponding to the impressions of the
holding dies 10 and are caused to bulge toward the rough journaL
Consequently, the thicknesses of the side portions Aa' and Ab' of each of the
rough arms A' in the region near the adjacent rough pin P' are increased.
[0110]
In a case where the upper die 11 is moved down to hold the forged
blank 30, the upper die 11 first comes into contact with the forged blank 30,
and thereafter, the lower die 12 comes into contact with the forged blank 30
along with the downward movement of the forged blank 30. As the upper die
11 is moving further down, the forged blank 30 is deformed. In this case,
along with the movement of the pair of holding dies 10 (downward movement
of the upper die 11), the flash B moves down. Accordingly, the holders 40
move down along with the downward movement of the flash B while keeping
holding the lower surface of the flash B. In other words, the holders 40
moves following the flash B which changes its position along with the
movement of the pair of holding dies 10.
[0111]
The first excess portions Aaa and Aba of the forged blank 30 are
deformed by the pair of holding dies 10. Accordingly, at the initial stage of
the trimming step, the shapes of the first excess portions Aaa and Aba do not
fit in the shapes of the holding dies 10. Therefore, if the forged blank 30 is
held by only the lower die 12 without use of the holder 40 at the stage shown
in FIG_ 9A, the forged blank 30 may be in an unstable posture. The unstable
posture of the forged blank 30 will cause unstable performance of the holding
dies 10 for holding and shaping and unstable performance of the cutting die
20 for trimming_ Hence, it is preferred to use the holder 40 in the trimming
step to carry out a stable process_
[0112]
Next, the cutting die 20 is moved down while the forged blank 30 is
35
held by the pair of holding dies 10. Then, the cutting die 20 first comes into
contact with the flash Bas shown in FIG. 9C. Thereafter, as shown in FIG.
9D, the flash B is cut and removed from the forged blank 30. In this way, a
forged blank 30a with no flash is obtained.
[0113]
The holders 40 move down along with the downward movement of the
flash B. After completion of the deformation of the forged blank 30 by the
pair of holding dies 10, the forged blank 30 comes in a stable position and a
stable posture. Therefore, after completion of the deformation of the forged
blank 30 by the pair of holding dies 10 and before the start of trimming, only
the holders 40 may be moved down.
[0114]
The holders 40 which moved down to the positions shown in FIG. 9D
may be kept in the lower positions until a specified time even after the cutting
die 20 has moved back in the upper position. For example, until the trimmed
forged blank 30a has been taken out from between the upper die 11 and the
lower die 12, the holders 40 may be stopped at the lower positions. There is
no limit as to the mechanism to stop the holders 40 at the lower position, and
a conventional mechanism may be used.
[0115]
After the cutting die 20 is moved down, the cutting die 20 is retracted
to the upper position, and the upper die 11 and the lower die 12 of the holding
dies 10 are separated from each other. Then, the forged blank with no flash
30a is taken out.
[0116]
An example of the trimming step in which the holder 40 is used for
trimming of a forged blank 30 for the first exemplary configuration has been
described with reference to FIGS. 9A to 9D. The trimming may be applied to
other forged blanks 30 in the same manner. Fig. 10 shows an exemplary
holder arrangement when a forged blank 30 for the second exemplary
configuration is to be trimmed by use of the holder 40. The state shown in
FIG. 10 corresponds to the state shown in FIG. 9A.
[0117]
When a forged blank 30 for the second exemplary configuration is to
be trimmed, first, the forged blank 30 with flash is held by the holder 40 as
shown in FIG. 10. The lower surface of the forged blank 30 is held by a
plurality of holders 40. Thereafter, trimming is performed following the
steps shown in FIGS. 9B to 9D. In this way, the forged blank 30 for the
second exemplary configuration is trimmed by use of the holders 40. It is
possible to trim a forged blank 30 for the third exemplary configuration in the
same manner.
[0118]
In either of the crankshafts having the first, the second and the third
configurations, all of the arms, whether incorporating a weight or not, have a
recess in the journal-facing surface, in a region near the adjacent pin. In a
crankshaft to be produced by the crankshaft production method according to
the present embodiment, some of the arms may have a recess in the
journal-facing surface, in a region near the adjacent pin. In other words, all
or some of the rough arms of a forged blank have first excess portions. Which
of the rough arms are to be provided with the first excess portions shall be
determined as appropriate according to the bending stiffness and the torsional
stiffness required in each arm of the crankshaft and in what portions the
crankshaft is required to have high stiffness.
[0119]
As described above, an arm incorporating a weight (which will be
referred to as a "weighted arm") preferably has a recess in the pin-facing
surface, in a region near the adjacent journal. In a crankshaft including a
plurality of weighted arms, all of the weighted arms may have a recess in the
pin-facing surface, in a region near the adjacent journal. Alternatively, some
of the weighted arms may have a recess in the pin-facing surface. In other
words, all or some of the rough weighted arms of a rough forged blank may
have second excess portions. Which of the rough arms are to be provided
with the second excess portions shall be determined as appropriate according
to the bending stiffness and the torsional stiffness required in each arm of the
crankshaft and in what portions the crankshaft is required to have high
stiffness.
[0120]
As described above, an unweighted arm preferably has a recess in the
pin-facing surface, in a region near the adjacent journal. In a crankshaft
including a plurality of unweighted arms, all of the unweighted arms may
have a recess in the pin-facing surface, in a region near the adjacent journal.
Alternatively, some of the unweighted arms may have a recess in the
pin-facing surface. In other words, all or some of the rough unweighted arms
of a rough forged blank may have second excess portions. Which of the rough
arms are to be provided with the second excess portions shall be determined
as appropriate according to the bending stiffness and the torsional stiffness
required in each arm of the crankshaft and in what portions the crankshaft is
required to have high stiffness.
[0121]
The rough arm may have first excess portions on both sides in the
region near the adjacent rough pin as has been described in connection with
the first to the third exemplary configurations, or alternatively, the rough arm
may have a first excess portion only on one side in the region near the
adjacent rough pin. Even in a case where the rough arm has a first excess
portion only on one side in the region near the adjacent rough pin, the
trimming step to cause the first excess portion to bulge toward the rough
journal provides an increase in the thickness of the side portion. This
ensures stiffness while reducing the weight. Which side of the rough arm is
to be provided with the first excess portion shall be determined as appropriate
according to the bending stiffness and the torsional stiffness required in the
arm and in what portion the arm is required to have high stiffness.
[0122]
As has been described in connection with the second exemplary
configuration, the rough weighted arm may have second excess portions on
both sides in the region near the adjacent rough journal. Alternatively, the
rough weighted arm may have a second excess portion on only one side in the
region near the rough journal. Even in a case where the rough arm has a
second excess portion only on one side in the region near the adjacent rough
pin, the trimming step to cause the second excess portion to bulge toward the
rough pin provides an increase in the thickness of the side portion. This
ensures stiffness while reducing the weight. Which side of the rough arm is
to be provided with the second excess portion shall be determined as
appropriate according to the bending stiffness and the torsional stiffness
required in the arm and in what portion the arm is required to have high
stiffness.
[0123]
As has been described in connection with the third exemplary
configuration, the rough unweighted arm may have second excess portions on
both sides in the region near the adjacent rough journal. Alternatively, the
rough unweighted arm may have a second excess portion on only one side in
the region near the rough journal. Even in a case where the rough arm has a
second excess portion only on one side in the region near the adjacent rough
pin, the trimming step to cause the second excess portion to bulge toward the
rough pin provides an increase in the thickness of the side portion. This
ensures stiffness while reducing the weight. Which side of the rough arm is
to be provided with the second excess portion shall be determined as
appropriate according to the bending stiffness and the torsional stiffness
required in the arm and in what portion the arm is required to have high
stiffness.
INDUSTRIALAPPLICABIUTY
[0124]
The present invention is efficiently utilized in a method for producing
a forged crankshaft to be mounted in a reciprocating engine.
LIST OF REFERENCE SYl\ffiOLS
[0125]
1: forged crankshaft
J, J1 to J5: journal
P, P1 to P4: pin
Fr: front part
Fl: flange
. -.
A, A1 to AS: crank arm
W, W1 to ws: counterweight
J': rough journal
p•: rough pin
A': rough crank arm
w·: rough counterweight
-IAa,
Ab: side portion of an arm in a region near a pin
Aa', Ab': side portion of a rough arm in a region near a rough pin
Aaa, Aha: first excess portion
Ac, Ad: side portion of an arm in a region near a journal
Ac', Ad': side portion of a rough arm in a region near a rough journal
Aca, Ada: second excess portion
As: inner area of a journal-facing surface of an arm, inside of side
portions
As': inner area of a rough-journal-facing surface of a rough arm, inside
of side portions
At: inner area of a pin-facing surface of an arm, inside of side portions
At': inner area of a rough-pin-facing surface of a rough arm, inside of
side portions
B: flash
10: pair of holding dies
11: upper die
12: lower die
20: cutting die
30, 30a: forged blank
40: holder

We claim:
1. A method for producing a forged crankshaft including journals serving
as a center of rotation, pins decentered from the journals, and crank arms
connecting the journals and the pins, wherein
the forged crankshaft further includes counterweights integrated with
all or some of the crank arms,
the method comprising:
a die forging step of obtaining a forged blank with flash having a
crankshaft shape; and
a trimming step of removing the flash from the forged blank while
nipping the forged blank with a pair ofholding dies, wherein:
the forged blank includes rough journals, rough pins, rough crank
arm_s, and rough counterweights, which correspond to the journals, the pins,
the crank arms, and the counterweights ofthe forged crankshaft, respectively;
-
at least one of the rough crank arms has, in a region near an adjacent
one of the rough pins, a first excess portion protruding from an outer
periphery of a side portion of the rough crank arm; and
when the forged blank is nipped with the pair of holding dies in the
trimming step, the first excess portion is deformed by the pair of holding dies
to bulge toward an adjacent one of the rough journals.
2. The method for producing a forged crankshaft according to claim 1,
•.
wherein
the rough crank arm has, in the region near the adjacent rough pin,
first excess portions respectively protruding from outer peripheries of two side
portions of the rough crank arm.
3. The method for producing a forged crankshaft according to claim 1 or
2, wherein °
in the trimming step, the first excess portion is deformed by the pair of
holding dies to bulge toward the adjacent rough journal while a holder is
holding a lower surface of the flash; and
-y
the holder moves along with a movement of the pair holding dies
while keeping holding the lower surface of the flash.
4. The method for producing a forged crankshaft according to any one of
claims 1 to 3, wherein
in the trimming step, the first excess portion is deformed by crushing
or bending.
5. The method for producing a forged crankshaft according to any one of
claims 1 to 4, wherein
at least one of the rough crank arms has, in a region near an adjacent
one of the rough journals, a second excess portion protruding from an outer
periphery of a side portion of the rough crank arm; and
when the forged blank is nipped with the pair of holding dies in the
trimming step, the second excess portion is deformed by the pair of holding
dies to bulge toward the adjacent rough pin.
6. The method for producing a forged crankshaft according to claim 5,
wherein
the rough crank arm has, in the region near the adjacent rough
journal, second excess portions respectively protruding from outer peripheries
of two side portions of the rough crank arm.
7.- The method for producing a forged crankshaft according to claim 5 or
6, wherein
the rough crank arm having the second excess portion is the rough
crank arm incorporating a rough counterweight.
8. The method for producing a forged crankshaft according to claim 5 or
6, wherein
the rough crank arm having the second excess portion is the rough
crank arm not incorporating a rough counterweight.
l{-b'
9. The method for producing a forged crankshaft according to any one of
claims 5 to 8, wherein
in the trimming step, the second excess portion 1s deformed by
crushing or bending.