DESCRIPTION
METHOD FOR MANUFACTURING NUT FOR BALL SCREW AND BALL SCREW
Technical 5 al Field
[0001]
The present invention relates to a method for
manufacturing a nut constituting a ball screw. The present
invention also relates to a ball screw.
10
Background Art
[0002]
A ball screw is provided with: a nut having an inner
circumferential surface on which a spiral groove is formed;
15 a threaded shaft having an outer circumferential surface on
which a spiral groove is formed; balls loaded in a raceway
between the spiral groove of the nut and that of the threaded
shaft; and a ball return passage for returning the balls from
an end point of the raceway to a start point thereof.
20 The ball screw is a device such that the balls are rolling
in the raceway to make the nut relatively move with respect
to the threaded shaft.
Such ball screws are used in not only positioning devices
of general industrial machinery but also electrical actuators
25 mounted on vehicles such as automobiles, motorcycles, or
vessels.
[0003]
3
As to the ball return passage in the ball screw, there
are a circulation tube type of the ball return passage and
a deflector type thereof. In the case of the deflector type,
a deflector having a concave constituting the ball return
passage is fit in a through hole of the nut. In 5 contrast,
Patent Document 1 listed below describes that the concave
(circulation groove) constituting the ball return passage is
directly arranged on the inner circumferential surface of the
nut blank by plastic working. The method for forming it will
10 be described with reference to FIG. 19.
[0004]
Firstly, prepared is a died provided with a cylindrical
working head 30 having convexes 37 and 38 each having a letter
S shape to correspond to the shape of a circulation groove.
15 Then, a nut blank 1 is disposed on a table 200 with its axial
direction set to the horizontal, the working head 30 is
disposed inside the nut blank 1, the convexes 37 and 38 are
faced upwardly, and a base end portion 30a and a front end
portion 30b are secured. Next, in this state, pressure is
20 applied onto a top member 20 of the die to press it down. The
convexes 37 and 38 are pressed against an inner
circumferential surface 11 of the nut blank 1 to plastically
deform the inner circumferential surface 11 of the nut blank
1.
25
Prior Art Documents
Patent Documents
[0005]
4
Patent Document 1: JP 2008-281063 A
Patent Document 2: JP 2010-87071 A
Patent Document 3: JP 2010-275706 A
Patent Document 4: JP 2003-307263 A
Patent Document 5: 5 JP 2000-297854 A
Patent Document 6: JP 2005-321059 A
Patent Document 7: JP 2008-267523 A
Patent Document 8: JP 2007-146874 A
Patent Document 9: JP 2004-108538 A
10 Patent Document 10: JP 2003-166616 A
Patent Document 11: JP 2004-3631 A
Patent Document 12: JP 2008-281064 A
Summary of the Invention
15 Problem to be Solved
[0006]
It is to be noted, however, that the method described
in Patent Document 1 has a problem in that when the axial
dimension of the nut is long and the inner diameter is small,
20 the working head of the die is elongated and the strength is
insufficient and it is easily damaged.
An object of the present invention is to provide a method
of forming the concave without damaging a die, and a ball screw
provided with a nut obtained by the method, as a method for
25 forming a concave constituting a ball return passage directly
on an inner circumferential surface of a nut blank by plastic
working, even in a case where a nut having a long axial
dimension and a small diameter is manufactured.
5
Solution to the Problem
[0007]
In order to solve the above problems, embodiments of
the present invention have the following 5 ing configurations.
That is, according to an aspect of the present invention,
there is provided a method for manufacturing a nut for a ball
screw, the ball screw comprising: the nut having an inner
circumferential surface on which a spiral groove is formed;
10 a threaded shaft having an outer circumferential surface on
which a spiral groove is formed; balls loaded in a raceway
between the spiral groove of the nut and that of the threaded
shaft; and a ball return passage arranged as a concave on the
inner circumferential surface of the nut for returning the
15 balls from an end point of the raceway to a start point of
the raceway, the balls being rolling in the raceway to make
the nut relatively move with respect to the threaded shaft,
wherein the concave is formed on the inner circumferential
surface of the nut blank by plastic working in a pressing
20 method by use of a die of a cam mechanism, the cam mechanism
comprising: a cam driver inserted into a cylindrical nut blank
and moving in an axial direction of the nut blank at the time
of processing; and a cam slider disposed between the nut blank
and the cam driver and provided with a convex corresponding
25 to the concave, a movement of the cam driver causing the convex
to move in a radial direction of the nut.
[0008]
6
In the method for manufacturing the nut for the ball screw
according to an aspect of the present invention, preferably,
a plurality of the concaves are formed on the inner
circumferential surface of the nut, and at least one of a
plurality of the convexes corresponding to 5 the plurality of
the concaves is formed on the cam slider.
In addition, preferably, as the die, the cam driver
includes a load receiving surface parallel to the axial
direction of the nut blank, and pressing is performed by use
10 of the die having another member, other than the cam driver,
provided with a load receiving surface to be in contact with
the load receiving surface. In this situation, more
preferably, as the die, the cam slider is held by a holding
member, disposed between the cam driver and the nut blank,
15 and pressing is performed by use of the die in which the holding
member is provided with the load receiving surface.
[0009]
Furthermore, according to an aspect of the present
invention, in the method for manufacturing the nut for the
20 ball screw, the plurality of the concaves are formed in a
uniform manner by changing a movement amount of the plurality
of the convexes, formed on a plurality of the cam sliders,
moving outwardly in the radial direction of the nut blank.
Moreover, according to an aspect of the present invention,
25 in the method for manufacturing the nut for the ball screw,
by pressing method by use of the die of the cam mechanism
including the cam driver, the cam slider, and a restraining
member for restraining both end surfaces in the axial
7
direction and an outer circumferential surface of the nut
blank and having a depressed portion to correspond to the
convex on an inner circumferential surface that receives the
outer circumferential surface, the concave is formed on the
inner circumferential surface of the nut blank by pressin5 g
the inner circumferential surface of the nut blank with the
convex to protrude the outer circumferential portion of the
nut blank into the depressed portion of the restraining member.
In the nut manufactured in the above method, a projection may
10 be arranged at a position corresponding to the concave of the
outer circumferential surface of the nut. It is possible to
produce a screw with the use of the above nut.
[0010]
In addition, according to an aspect of the present
15 invention, preferably, in the method for manufacturing the
nut for the ball screw, a part of an outer circumferential
surface of the nut is formed at a position having a distance
from a central axis of the nut to be shorter than a radius
of another part having a circular shape on the outer
20 circumferential surface of the nut, the convex is pressed into
the inner circumferential surface of the nut to form a concave
so as to form a projection projecting on the outer
circumferential of the nut on the part of the outer
circumferential surface of the nut, and in the part of the
25 outer circumferential surface, the projection is arranged
such that the distance from the central axis of the nut to
be shorter than a radius of said another part having a circular
shape.
8
[0011]
Furthermore, preferably, forming of the concave permits
a material in the nut to flow and flowing of the material is
adjusted in accordance with a shape of the concave. In this
situation, preferably, the flowing of the material to an 5 outer
circumference side or flowing of the material to an end
portion side in the axial direction of the nut is adjusted
in accordance with the shape of the concave.
[0012]
10 Moreover, according to an aspect of the present invention,
preferably, in the method for manufacturing the nut for the
ball screw, the convex is pressed into the inner
circumferential surface of the nut to form the concave, and
a concave for shear droop for reducing the shear droop in the
15 concave generated by plastic working with the convex is formed
around the concave in the inner circumferential surface of
the nut. In this situation, preferably, the concave for shear
droop is formed adjacent to a part where the concave curves.
Additionally, preferably, a shape and a depth of the concave
20 for shear droop are determined in accordance with an amount
of the shear droop.
[0013]
Furthermore, according to an aspect of the present
invention, preferably, in the method for manufacturing the
25 nut for the ball screw, an excess material portion for
reducing shear droop of the concave is provided to protrude
from the inner circumferential surface having a circular
shape of the nut, and the convex is pressed into the excess
9
material portion to form the concave. In this situation,
preferably, the excess material portion has a shape
corresponding to that of the concave.
Moreover, according to an aspect of the present invention,
after a base concave to be included 5 uded in a cross-sectional arc
of the concave is formed at a position where the concave is
to be formed on the inner circumferential surface of the
cylindrical nut blank, the cam slider inserted into the nut
blank is moved outwardly in the radial direction of the nut
10 blank with restraining the outer circumferential surface and
an end surface in the axial direction of the nut blank to form
the concave.
[0014]
In addition, according to an aspect of the present
15 invention, preferably, there is provided a method for
manufacturing the nut for the ball screw, the method
comprising: a ball return passage forming process of forming
the concave in the method as described above; a spiral groove
forming process of forming the spiral groove to be in contact
20 with an end portion of the concave on the inner
circumferential surface of the nut; and a burr removing
process of removing burr by performing at least one of
brushing and blasting at a boundary portion between the
concave and the spiral groove.
25 [0015]
Furthermore, according to another aspect of the present
invention, there is provided a first ball screw comprising:
a nut having an inner circumferential surface on which a
10
spiral groove is formed; a threaded shaft having an outer
circumferential surface on which a spiral groove is formed;
balls loaded in a raceway between the spiral groove of the
nut and that of the threaded shaft; and a ball circulation
groove for returning the balls from an end point of the ra5 ceway
to a start point of the raceway, the balls being rolling in
the raceway to make the nut relatively move with respect to
the threaded shaft, wherein the nut may be manufactured in
the method for manufacturing the nut according to one aspect
10 of the present invention, and wherein at least one of corner
portions defined by both of side surfaces of the ball
circulation passage and a surface axially extending and
continuous with each of the side surfaces is rounded.
[0016]
15 Moreover, according to another aspect of the present
invention, there is provided a second ball screw comprising:
a threaded shaft having an outer circumferential surface on
which a spiral groove is formed; a nut having an inner
circumferential surface on which a spiral groove opposing the
20 spiral groove of the threaded shaft is formed; a plurality
of balls rotatably loaded in a ball rolling passage having
a spiral shape provided by both of the spiral grooves; and
a ball circulation passage for returning the balls from an
end point of the ball rolling passage to a start point of the
25 ball rolling passage, wherein the nut may be manufactured in
the method for manufacturing the nut according to one aspect
of the present invention, wherein the ball circulation
passage includes a concaved groove formed by concaving a
11
groove on a part of the inner circumferential surface of the
nut, and a lubricant reservoir capable of holding a lubricant,
and wherein the lubricant reservoir is made of a dented
portion by concaving a groove on a part of an inner surface
of 5 the concaved groove.
[0017]
In the second ball screw according to another aspect of
the present invention, preferably, the ball circulation
passage includes both of end portions that are connecting
10 portions with the ball rolling passage and a middle portion
between both of the end portions, and wherein as to a
cross-sectional area of the lubricant reservoir cut along a
plane perpendicular to a lengthwise direction of the ball
circulation passage, the cross-sectional area of a part
15 adjacent to the middle portion is larger than that of a part
adjacent to each of the end portions.
[0018]
In addition, preferably, the ball circulation passage
is curved, and as to a cross-sectional area of the lubricant
20 reservoir cut along a plane perpendicular to a lengthwise
direction of the ball circulation passage, the
cross-sectional area of the lubricant reservoir arranged on
the inside in a radial direction of a curve of the ball
circulation passage is larger than that of the lubricant
25 reservoir arranged on the outside in the radial direction of
the curve of the ball circulation passage.
Furthermore, preferably, the concaved groove
constituting the ball circulation passage and the dented
12
portion constituting the lubricant reservoir are formed at
the same time by forging.
[0019]
Moreover, according to another aspect of the present
invention, there is provided a third ball screw comprisin5 g
the nut manufactured in the method for manufacturing the nut
for the ball screw as described above, wherein at least a part
of a lengthwise direction of the ball return passage has a
substantially letter V shaped cross-section, when the ball
10 return passage is cut along a plane perpendicular to the
lengthwise direction.
Furthermore, according to another aspect of the present
invention, there is provided a fourth ball screw comprising
the nut manufactured in the method for manufacturing the nut
15 for the ball screw as described above, wherein a flange
protruding inwardly in the radial direction from a marginal
edge portion of the concave at a connecting part of the spiral
groove of the nut and the concave is provided.
[0020]
20 In the fourth ball screw according to another aspect of
the present invention, preferably, both end portions of the
concave that is a connecting part with the spiral groove of
the nut constitutes a straight shaped ball entering portion,
and the flange is arranged at least at a marginal edge portion
25 of the straight shaped ball entering portion.
Additionally, preferably, a distance H between an end
of the flange and a radial center of the nut is equal to or
smaller than 1/2 of ball circle diameter (BCD), and the flange
13
is arranged not to be in contact with the outer
circumferential surface of the threaded shaft.
Advantageous Effects of the Invention
5 [0021]
According to a method of the present invention, it is
possible to form a concave without damaging a die, even in
a case where a nut having a long axial dimension and a small
diameter is manufactured, as a method of directly forming a
10 ball return passage directly on an inner circumferential
surface of a nut blank by plastic working.
Brief Description of the Drawings
[0022]
15 FIG. 1 is a view illustrative of a first example of a
first embodiment of the present invention;
FIG. 2A is a plan view illustrative of a fitting state
of a cam slider and a cam driver used in the first example
of the first embodiment; FIG. 2B is a perspective view
20 illustrative of the cam slider; and FIG. 2C is a perspective
view illustrative of the cam driver;
FIG. 3 is a view illustrative of a modification of the
first example of the first embodiment of the present
invention;
25 FIG. 4 is a view illustrative of a second example of the
first embodiment of the present invention;
FIG. 5A is a plan view illustrative of a cam slider used
in the second example of the first embodiment; FIG. 5B is a
14
perspective view illustrative of the cam slider; and FIG. 5C
is a perspective view illustrative of the cam driver;
FIG. 6 is a view illustrative of a modification of the
second example of the first embodiment of the present
5 invention;
FIG. 7 is a view illustrative of a third example of the
first embodiment of the present invention;
FIG. 8 is a perspective view illustrative of a cam driver
used in the third example of the first embodiment;
10 FIG. 9A is a plan view illustrative of a cylindrical
member used in the third example of the first embodiment; FIG.
9B is a cross-sectional view taken along line A-A; and FIG.
9C is a plan view illustrative of the cam slider;
FIG. 10A is a view illustrative of a first modification
15 of the third example of the first embodiment; FIG. 10B is a
plan view illustrative of a holding member of the cam slider;
FIG. 11 is a view illustrative of a second modification
of the third example of the first embodiment;
FIG. 12 is a view illustrative of a third modification
20 of the third example of the first embodiment;
FIG. 13 is a view illustrative of a fourth modification
of the third example of the first embodiment;
FIG. 14 is a view illustrative of a fourth example of
the first embodiment of the present invention;
25 FIG. 15A is a perspective view illustrative of a cam
driver used in the fourth example of the first embodiment;
FIG. 15B is a view when viewed in arrow A; and FIG. 15C is
a cross-sectional view taken along line B-B;
15
FIG. 16A is a plan view illustrative of a cylindrical
member used in the fourth example of the first embodiment;
FIG. 16B is a cross-sectional view taken along line A-A; and
FIG. 16C is a plan view illustrative of the cam slider;
FIG. 17 is a view illustrative of a modification of 5 the
fourth example of the first embodiment; FIG. 17A is a plan
view illustrative of a holding member of the cam slider; and
FIG. 17B is a cross-sectional view taken along line A-A;
FIG. 18 is a view illustrative of a modification of the
10 fourth example of the first embodiment of the present
invention;
FIG. 19 is a view illustrative of a method of Patent
Document 1;
FIG. 20 is a view illustrative of a first example of a
15 second embodiment of the present invention;
FIG. 21 is a view illustrative of a second example of
the second embodiment of the present invention;
FIG. 22 is a view illustrative of an example of a third
embodiment of the present invention;
20 FIG. 23A is a perspective view illustrative of a cam
driver used in the third embodiment; FIG. 23B is a plan view
illustrative of the cam slider; and FIG. 23C is a perspective
view;
FIG. 24A is a plan view illustrative of a divided body
25 constituting a restraining member used in the third
embodiment; and FIG. 24B is a perspective view taken along
line A-A;
16
FIG. 25A is a front view illustrative of a nut blank in
which a letter S shaped concave and projection are provided
in a method of the third embodiment; FIG. 25B is a
cross-sectional view taken along line A-A; FIG. 25C is a view
when viewed in arrow B; and FIG. 25D 5 5D is a perspective view;
FIG. 26 is a view illustrative of a shape of a nut blank
constituting a S groove in the method for manufacturing the
ball screw nut in the fourth embodiment;
FIG. 27 is a view illustrative of the method of
10 manufacturing the ball screw nut in the fourth embodiment,
that is a method of forming a letter S shaped circulation
groove on an inner circumferential surface of the nut blank
by plastic working with a punch;
FIG. 28 is a view illustrative of a shape of the nut blank
15 in the method for manufacturing the ball screw nut in the
fourth embodiment;
FIG. 29 is a cross-sectional view illustrative of the
ball screw;
FIG. 30 is a view illustrative of a shape of the nut blank
20 in which the letter S shaped circulation groove is formed;
FIG. 31 is a front view and a longitudinal
cross-sectional view illustrative of the shape of the nut
blank in which the letter S shaped groove is formed in a
modification of the method for manufacturing the ball screw
25 nut in the fourth embodiment;
FIG. 32 is a front view and a longitudinal
cross-sectional view illustrative of the shape of the nut
blank in which the letter S shaped groove has been formed in
17
a modification of the method for manufacturing the ball screw
nut in the fourth embodiment;
FIG. 33 is a front view and a longitudinal
cross-sectional view illustrative of the shape of the nut
blank in which the letter S shaped groove is formed in 5 another
modification of the method for manufacturing the ball screw
nut in the fourth embodiment;
FIG. 34 is a front view and a longitudinal
cross-sectional view illustrative of the shape of the nut
10 blank in which the letter S shaped groove has been formed in
another modification of the method for manufacturing the ball
screw nut in the fourth embodiment;
FIG. 35 is a front view and a longitudinal
cross-sectional view illustrative of the shape of the nut
15 blank in which the letter S shaped groove is formed in another
modification of the method for manufacturing the ball screw
nut in the fourth embodiment;
FIG. 36 is a front view and a longitudinal
cross-sectional view illustrative of the shape of the nut
20 blank in which the letter S shaped groove has been formed in
another modification of the method for manufacturing the ball
screw nut in the fourth embodiment;
FIG. 37 is a front view and a longitudinal
cross-sectional view illustrative of the shape of the nut
25 blank in which the letter S shaped groove has been formed in
another modification of the method for manufacturing the ball
screw nut in the fourth embodiment;
18
FIG. 38 is a front view and a longitudinal
cross-sectional view illustrative of the shape of the nut
blank in which the letter S shaped groove has been formed in
another modification of the method for manufacturing the ball
screw nut 5 ut in the fourth embodiment;
FIG. 39 is a view illustrative of the method of
manufacturing the letter S shaped circulation groove on the
inner circumferential surface of the nut by plastic working
with a punch;
10 FIG. 40 is a view illustrative of a mechanism of
generating shear droop;
FIG. 41 is another view illustrative of a mechanism of
generating the shear droop;
FIG. 42 is a view illustrative of a configuration of
15 realizing the method of manufacturing the ball screw nut in
a fifth embodiment;
FIG. 43 is a view illustrative of a material flowing
portion arranged on an inner circumferential surface of a
restraining block;
20 FIG. 44 is a cross-sectional view illustrative of a ball
screw;
FIG. 45 is a cross-sectional view illustrative of a nut;
FIG. 46 is a view illustrative of operations and effects
of the fifth embodiment;
25 FIG. 47 is a view illustrative of a modification of the
fifth embodiment;
19
FIG. 48 is a view illustrative of a configuration of
realizing the method of manufacturing the ball screw nut in
a sixth embodiment;
FIG. 49 is a view illustrative of an inner
circumferential surface of the nut blank, in which a let5 ter
S shaped circulation groove and a dent are formed;
FIG. 50 is a view illustrative of functions and effects
of the sixth embodiment;
FIG. 51 is a view illustrative of a modification of the
10 sixth embodiment;
FIG. 52 is a view illustrative of a configuration of a
nut blank constituting an S groove in the method of
manufacturing the ball screw nut in a seventh embodiment;
FIG. 53 is a view illustrative of a configuration of a
15 nut blank constituting an S groove in the method of
manufacturing the ball screw nut in the seventh embodiment;
FIG. 54 is a cross-sectional view illustrative of a ball
screw;
FIG. 55 is a view illustrative of a shape of a nut blank
20 constituting the S groove to be formed in the method of
manufacturing the ball screw nut in a modification of the
seventh embodiment;
FIG. 56 is a view illustrative of a shape of a nut blank
constituting the S groove that has been formed in the method
25 of manufacturing the ball screw nut in a modification of the
seventh embodiment;
FIG. 57A is a cross-sectional view illustrative of a ball
screw of a first example in accordance with an eighth
20
embodiment; and FIG. 57B is a cross-sectional view
illustrative of a letter S shaped circulation passage in the
inner circumferential surface of the nut;
FIG. 58A is a perspective view illustrative of a jig
constituting the letter S shaped circulation passage, FIG5 .
58B is a top view of the jig; and FIG. 58C is a side view of
the jig;
FIG. 59A is a side view illustrative of a relationship
between the nut and the jig; and FIG. 59B is a front view
10 illustrative of a relationship between the nut and the jig;
FIG. 60 is a cross-sectional view illustrative of a
letter S shaped circulation passage on the inner
circumferential surface of the nut in the ball screw in a
second example of the eighth embodiment;
15 FIG. 61 is a perspective view illustrative of a jig for
forming a letter S shaped circulation passage in the ball
screw in the second example of the eighth embodiment;
FIG. 62 is a side view illustrative of a relationship
between a height of a flange and BCD in the ball screw in the
20 third example of the eighth embodiment;
FIG. 63A is a top view illustrative of a jig constituting
the letter S shaped circulation passage in the ball screw in
a fourth example of the eighth embodiment; FIG. 63B is a
cross-sectional view taken along line E-E in FIG. 63A; and
25 FIG. 63C is an enlarged cross-sectional view of substantial
parts in FIG. 63B;
FIG. 64A is a top view illustrative of a jig constituting
the letter S shaped circulation passage in the ball screw in
21
a fifth example of the eighth embodiment; FIG. 64B is a
cross-sectional view taken along line F-F in FIG. 64A; and
FIG. 64C is an enlarged cross-sectional view of substantial
parts in FIG. 64B;
FIG. 65A is a front view illustrative of a nut 5 ut provided
with plural letter S shaped circulation passages in a
conventional ball screw; FIG. 65B is a cross-sectional view
taken along line C-C in FIG. 65A; and FIG. 65C is a
cross-sectional view taken along line B-B in FIG. 65A;
10 FIG. 66A is a front view illustrative of a nut provided
with the letter S shaped circulation passages at an identical
phase in a conventional ball screw; and FIG. 66B is a
cross-sectional view taken along line D-D in FIG. 66A;
FIG. 67 is a cross-sectional view illustrative of a
15 configuration of a ball screw in accordance with a ninth
embodiment;
FIG. 68 is a cross-sectional view of substantial parts;
FIG. 69 is an enlarged cross-sectional view of the ball
circulation passage;
20 FIG. 70 is an enlarged view of a concaved groove of the
nut in FIG. 68 when viewed in a direction of arrow A;
FIG. 71 is a cross-sectional view of a concaved groove
illustrative of a cross-sectional shape of an end portion of
the ball circulation passage;
25 FIG. 72 is a cross-sectional view of a concaved groove
illustrative of a cross-sectional shape of a middle portion
of the ball circulation passage;
22
FIG. 73 is a cross-sectional view of a thread groove
illustrative of a cross-sectional shape of the ball rolling
passage;
FIG. 74 is a process drawing illustrative of a process
for manufacturing 5 the ball screw;
FIG. 75 is a cross-sectional view of a nut illustrative
of a boundary portion between the ball circulation passage
and the ball rolling passage;
FIG. 76 is a view illustrative of a first method in a
10 tenth embodiment;
FIG. 77 is a view illustrative of the method of forming
a single ball circulation groove in a method of forging with
a punch, employed in the first method in the tenth embodiment;
FIG. 78 is a view illustrative of the method of forming
15 plural ball circulation grooves in the method of forging with
a punch, in one shot employed in the first method in the tenth
embodiment;
FIG. 79 is a view illustrative of a second method in the
tenth embodiment;
20 FIG. 80 is a side view illustrative of a ball screw in
a first example of an eleventh embodiment;
FIG. 81 is a perspective view illustrative of a deflector
constituting the ball screw of FIG. 80;
FIG. 82 is a cross-sectional view taken along line A-A
25 of FIG. 80;
FIG. 83 is a side view illustrative of a ball screw in
a second example of the eleventh embodiment;
23
FIG. 84 is a cross-sectional view taken along line A-A
of FIG. 83;
FIG. 85 is a perspective view illustrative of components
of a die used in an example of the method for manufacturing
the 5 nut of FIG. 84;
FIG. 86 is a view illustrative of functions of a ball
circulation groove;
FIG. 87 is a view illustrative of movements of the balls
at part A and part B of FIG. 86;
10 FIG. 88 is a view illustrative of a configuration of a
ball screw in a first example of a twelfth embodiment, and
is an enlarged view when a concaved groove and a concave are
viewed in arrow A of FIG. 68;
FIG. 89 is a cross-sectional view taken along line B-B
15 of the concaved groove of FIG. 88;
FIG. 90 is an enlarged view when the concaved groove and
the concave in a second example of the twelfth embodiment are
viewed in arrow A of FIG. 68;
FIG. 91 is a cross-sectional view taken along line C-C
20 of the concaved groove and the concave of FIG. 90;
FIG. 92 is a cross-sectional view taken along line D-D
of the concaved groove and the concave of FIG. 90;
FIG. 93 is an enlarged view when a concaved groove and
a concave in a third example of the twelfth embodiment are
25 viewed in arrow A of FIG. 68;
FIG. 94 is a view illustrative of a configuration of a
ball screw in a thirteenth embodiment, and is an enlarged view
24
of the nut illustrative of a boundary from which burr has been
removed;
FIG. 95 is a view illustrative of a burr removing process
by brushing;
FIG. 96 is a view illustrative of a burr removing 5 ng process
by blasting;
FIG. 97 is an enlarged view illustrative of a step
generated at a boundary portion between the nut and the
deflector in a conventional deflector type of ball screw; and
10 FIG. 98 is a partial cross-sectional view of a steering
gear of an electric power steering apparatus.
Description of Embodiments
[0023]
15 Embodiments of method of manufacturing a nut for a ball
screw and those of the ball screw will be described in detail
with reference to drawings.
(First Embodiment)
(First Example)
20 The die described in a first example is, referring to
FIG. 1, provided with: a blank holder 2 having a concave 21
for holding a nut blank 1; and a cam slider 3 and a cam driver
4 disposed at the inside of the nut blank 1.
[0024]
25 Referring now to FIG. 2A and FIG. 2B, the cam slider 3
is a substantially semicircular column shaped member having
an outer circumferential surface 31 and a plane 32 parallel
to the axial direction. The diameter of a circle constituted
25
with the outer circumferential surface 31 is slightly smaller
than that of a circle 11a constituted with an inner
circumferential surface 11 of the nut blank 1. There is
provided an inclined surface 33, extending in the axial
direction at the midpoint of the radial 5 al direction, at the
plane 32 of the cam slider 3. The inclined surface 33
corresponds to a plane connecting a bottom surface line 34a
of a concave 34 at one end (upper end) in the axial direction
with a line 32d forming a lower end of the plane 32.
10 Additionally, a letter S shaped convex 35 corresponding to
the letter S shaped concave constituting the ball return
passage is arranged on the outer circumferential surface 31
of cam slider 3.
[0025]
15 Referring now to FIG. 2C, the cam driver 4 is a long plate
shaped member having one side surface 41 that is an inclined
surface having the same inclination with that of the inclined
surface 33 of cam slider 3. The other side surface 42 is a
circumferential surface along the circle 11a forming the
20 inner circumferential surface 11 of the nut blank 1. The
axial dimension of the cam driver 4 is greater than that of
cam slider 3. Additionally, the cam driver 4 is slightly
thinner than the thickness corresponding to an opening width
(size between both side surfaces of the inclined surface 33)
25 of the concave 34 of cam slider 3.
[0026]
26
The inclined surface 31 of the cam slider 3 and the
inclined surface 41 of the cam driver 4 constitute a cam
mechanism of the die.
By using this die, the letter S shaped concave
constituting the ball return passage is formed 5 on the inner
surface of the nut blank 1 in the following method.
Firstly, the nut blank 1 is disposed in the concave 21
of the blank holder 2, and the cam slider 3 is inserted into
the inner circumferential surface 11 of the nut blank 1 with
10 the concave 34 facing upwardly and the letter S shaped convex
35 facing the inner circumferential surface 11. Next, the
cam driver 4 is inserted between the cam slider 3 and the nut
blank 1. On this occasion, the side surface 41 of the cam
driver 4 is fit into the concave 34 of the cam slider 3, so
15 that the inclined surface 33 of the cam slider 3 and the
inclined side surface 41 of the cam driver 4 are brought into
contact with each other. FIG. 1A illustrates this state.
[0027]
Then, the cam driver 4 is pressed under pressure from
20 the top thereof, a force is transmitted from the inclined side
surface 41 of the cam driver 4 to the inclined surface 33 of
the cam slider 3. In accordance with this, a downward force
of the cam driver 4 is transformed into a force of moving the
cam slider 3 outwardly in the radial direction, and then the
25 letter S shaped convex 35 arranged in the cam slider 3 pushes
the inner circumferential surface 11 of the nut blank 1 for
plastic deformation. FIG. 1B illustrates this state.
[0028]
27
Thus, a letter S shaped concave 15 constituting the ball
return passage is formed on the inner circumferential surface
11 of the nut blank 1.
Therefore, according to the method of the present
embodiment, it is possible to arrange 5 the letter S shaped
concave 15 without breaking the cam driver 4, even when a nut
that has a long axial dimension and a small diameter.
[0029]
Further, when two letter S shaped concaves are arranged
10 on the inner circumferential surface 11 of the nut blank 1,
one letter S shaped concave 15 is arranged in the
above-described method. Then, after the cam driver 4 and the
cam slider 3 are pulled out, another cam slider 3 having the
letter S shaped convex 35 arranged at a different position
15 in the axial direction is used, the cam driver 4 is inserted
again, and the above-described method is performed. This
will be repeated in a case where three or more letter S shaped
concaves are arranged. Thus, multiple letter S shaped
concaves are arranged at different positions in the axial
20 direction of the nut blank 1 and in the circumferential
direction of the inner circumferential surface 11.
[0030]
In addition, the provision of multiple letter S shaped
convexes on the outer circumferential surface of the cam
25 slider 3 enables the formation of multiple letter S shaped
concaves by performing a one-time operation of pressing the
cam driver 4 from the top thereof. In the example of FIG.
3, two letter S shaped convexes 35 and 36 are provided on the
28
outer circumferential surface of the cam slider 3 so that they
are different in the axial direction of the nut blank 1 and
are same in the circumferential direction of the inner
circumferential surface 11. Thus, two letter S shaped
concaves 15 and 16 are formed at different positions 5 itions in the
axial direction of the inner circumferential surface 11 of
the nut blank 1 and at same positions in the circumferential
direction thereof.
[0031]
10 (Second Example)
The die described in a second example is, referring to
FIG. 4, provided with: the blank holder 2 having the concave
21 for holding the nut blank 1; a pair of cam sliders 3 disposed
at the inside of the nut blank 1; and the cam driver 4
15 interposed between both of the cam sliders 3.
[0032]
Each cam slider 3, referring now to FIG. 5A and FIG. 5B,
is a substantially semicircular column shaped member having
the outer circumferential surface 31 with a diameter slightly
20 smaller than an inner diameter of the nut blank 1, and a line
32 forming an opposite surface of the outer circumferential
surface 31 is smaller than the inner diameter of the nut blank
1. Accordingly, as illustrated in FIG. 5A, when the outer
circumferential surfaces 31 of both of the cam sliders 3 are
25 arranged to correspond to a circle 11a forming the inner
circumferential surface 11 of the nut blank 1, a gap 32a is
generated between the lines 32 of both of the cam sliders 3.
[0033]
29
There is provided the inclined surface 33 extending in
the axial direction, at the middle of the line 32, on opposing
surfaces 32b (surfaces along the lines 32) of both of the cam
sliders 3. Grooves 39 extending in the axial direction are
arranged on both sides of the inclined surface 33. 5 The
inclined surface 33 corresponds to a plane connecting the
bottom surface line 34a of the concave 34 at one end (upper
end) in the axial direction and the line 32 at the lower end.
Additionally, the letter S shaped convexes 35 and 36
10 respectively corresponding to the letter S shaped concaves
of the two ball return passages are respectively arranged on
the outer circumferential surfaces 31 of the cam sliders 3,
respectively.
[0034]
15 Referring now to FIG. 5C, the cam driver 4 has a shape
such that an inclined surface 41a inclined in the axial
direction and a parallel surface 42a parallel in the axial
direction are formed to have a concave shape at a pair of side
surfaces parallel to each other of a long square pole, and
20 side plate portions 43 each having a plate shape remain on
both sides in the width direction of the inclined surface 41a
and the parallel surface 42a. The inclined surface 41a of
the cam driver 4 has an inclination and a width same with those
of the cam slider 3. The plate thickness of the side plate
25 portion 43 is slightly smaller than the width of the groove
39 in the cam slider 3.
[0035]
30
That is, the cam driver 4 includes: a wedge shaped portion
41 composed of a pair of the inclined surfaces 41a; a plate
shaped portion 42 composed of a pair of the parallel surfaces
42a; and a pair of the side plate portions 43. Since the
thickness of the end portions on 5 the plate shaped portion 42
side of the wedge shaped portion 41 (the size between the
inclined surfaces 41a) is larger than that of the plate shaped
portion 42, a step surface 44 exists at the boundary of the
both. The end portion of the cam driver 4 has a letter H shape
10 due to the plate shaped portion 42 and the side plate portions
43 on the both sides thereof.
[0036]
The inclined surface 33 of the cam slider 3 and the
inclined surface 41a of the cam driver 4 constitute a cam
15 mechanism of the die.
There is arranged a through hole 22 having a letter H
shape into which the letter H shaped end portion of the cam
driver 4 is inserted at the middle of the bottom plate portion
of the blank holder 2. In the letter H shaped through hole
20 22, the plate shaped portion 42 at the end portion of the cam
driver 4 is inserted between wall surfaces 22a corresponding
the lateral bar of the letter H, and the side plate portion
43 of the cam driver 4 is inserted between wall surfaces 22b
corresponding to longitudinal bars of the letter H.
25 [0037]
By using the above-described die, the letter S shaped
concave of the ball return passage on the inner surface of
the nut blank 1 will be formed in the following method.
31
Firstly, the nut blank 1 is arranged at the concave 21
of the blank holder 2, and the pair of cam sliders 3 are
inserted into the nut blank 1 so that both of the inclined
surfaces 33 are opposed to each other. Next, the cam driver
4 is inserted between the concaves 34 of both of the cam s5 liders
3 from the plate shaped portion 42 side so as to insert the
end of the plate shaped portion 42 into the through hole 22.
FIG. 4A illustrates this state.
[0038]
10 Subsequently, when the cam driver 4 is pushed under
pressure from the top thereof, a force is transmitted from
the inclined surface 41a of the cam driver 4 to the inclined
surface 33 of the cam slider 3. In accordance with this, a
downward force of the cam driver 4 is converted into a force
15 of moving each cam slider 3 outwardly in the radial direction,
and the letter S shaped convexes 35 and 36 respectively
provided on the cam sliders 3 pushes the inner circumferential
surface 11 of the nut blank 1 for plastic deformation. FIG.
4B illustrates this state.
20 [0039]
Thus, the letter S shaped concaves 15 and 16 of two ball
return passages are provided on the inner circumferential
surface 11 of the nut blank 1. In such a situation, the letter
H shaped end portion of the cam driver 4 is guided to the letter
25 H shaped through hole 22 of the blank holder 2. In addition,
the reactive force of the force in the radial direction
transmitted to the cam slider 3 is received by the contact
between the wall surfaces 22a of the blank holder 2 and the
32
parallel surface 42a of the plate shaped portion 42, the
contact between the wall surfaces 22b of the blank holder 2
and an end surface 43a of the plate width direction of the
side plate portion 43, and the contact between a groove bottom
portion 39a of the groove 39 in the cam slider 5 lider 3 and the end
surface 43a of the plate width direction of the side plate
portion 43 in the cam driver 4 (received by surfaces vertical
to the reactive force). Thus, the reactive force is received
by an extension of the reactive force and in the vicinity in
10 the axial direction thereof, thereby making a bending moment
received by the cam driver 4 smaller. Furthermore, the
reactive force of the force in the radial direction
transmitted to the cam slider 3 does not work on the nut blank
1.
15 [0040]
Therefore, according to the method in the second example,
even when the nut having a long axial dimension and a small
diameter is produced, the two letter S shaped concaves 15 and
16 can be formed at the same time without damaging the cam
20 driver 4.
Moreover, since the structure of the die is simple and
robust, it is suitable as a method for producing a large volume
of the same products. Specifically, in the second example,
a single letter S shaped convex 35 or 36 is arranged on the
25 outer circumferential surface of each of the pair of the cam
sliders 3. However, plural letter S shaped convexes may be
arranged. In the example of FIG. 6, two letter S shaped
convexes 35 and 35a are arranged on the outer circumferential
33
surface of one cam slider 3A, whereas two letter S shaped
convexes 36 and 36a are arranged on the outer circumferential
surface of the other cam slider 3B.
[0041]
The arrangements of the two letter S 5 shaped convexes 35
and 35a of the cam slider 3A are different in the axial
direction the nut blank 1, but are same in the circumferential
direction of the inner circumferential surface 11. The
arrangements of the two letter S shaped convexes 36 and 36a
10 of the cam slider 3B are different in the axial direction the
nut blank 1, but are same in the circumferential direction
of the inner circumferential surface 11. Additionally, the
arrangements of the four letter S shaped convexes 35, 35a,
36, and 36a are all different in the axial direction of the
15 nut blank 1.
[0042]
Thus, it is made possible to form four letter S shaped
concaves 15, 15a, 16, and 16a on the inner circumferential
surface 11 of the nut blank 1, by a one-time operation of
20 pushing the cam driver 4 from the top thereof. In this example,
the arranged positions of the four letter S shaped concaves
15, 15a, 16, and 16a are all different in the axial direction
of the nut blank 1, but every two of them are same in the
circumferential direction of the inner circumferential
25 surface 11.
[0043]
(Third Example)
34
The die described in a third example is, referring to
FIG. 7, provided with: the blank holder 2 having the concave
21 for holding the nut blank 1; a cylindrical member 5 (holding
member of the cam slider) inserted into the nut blank 1; a
cam driver 6 inserted into a center hole 51 of the cylin5 drical
member 5; and cam sliders 7 and 8 arranged in through holes
52 and 53, respectively.
[0044]
Referring now to FIG. 8, the cam driver 6 includes: a
10 main body 61 formed to have a long plate shape; and a column
shaped end portion 62. One side surface of the main body 61
is composed of, sequentially arranged from the end portion
62 side, a first parallel surface 61a parallel to the axial
direction, an inclined surface 61b inclined with respect to
15 the axial direction, and a second parallel surface 61c. The
other side surface of the main body 61 is composed of,
sequentially arranged from the end portion 62 side, an
inclined surface 61d inclined with respect to the axial
direction and a parallel surface 61e parallel to the axial
20 direction. The boundary between the inclined surface 61d and
the parallel surface 61e of the other side surface lies
slightly on the end portion 62 side from the boundary between
the parallel surface 61a and the inclined surface 61b of one
side surface. The diameter of the column forming the end
25 portion 62 is same as the width of the lower end (on the end
portion 62 side) of the main body 61.
[0045]
35
The cylindrical member 5 has an outer circumferential
surface slightly smaller than the inner circumferential
surface of the nut blank 1. As illustrated in FIG. 9A and
FIG. 9B, the center hole 51 of the cylindrical member 5 has
a rectangular cross-section changing its shape in 5 the axial
direction. As surfaces forming the center hole 51, there are
provided parallel surfaces 51a to 51e parallel to the axial
direction.
The parallel surfaces 51a to 51c are surfaces on which
10 one side surface of the cam driver 6 is arranged, and a step
portion 51f is provided between the parallel surface 51a and
the parallel surface 51b. The through hole 52 penetrates
through in the radial direction of the cylindrical member 5
with the step portion 51f set as the lower end. The parallel
15 surfaces 51d and 51e are surfaces on which the other side
surface of the cam driver 6 is arranged, and the through hole
53 that penetrates through in the radial direction of the
cylindrical member 5 is provided at a position opposing the
parallel surface 51c of the parallel surface 51d. A step
20 portion 51g forming the boundary between the parallel surface
51d and the parallel surface 51e is the lower end of the through
hole 53.
[0046]
The cam sliders 7 and 8 are members each having a
25 trapezoid column shape, and have inclined surfaces 71 and 81
corresponding to the inclined surfaces 61b and 61d of the cam
driver 6. The opposite sides of the inclined surfaces 71 and
81 are, as illustrated in FIG. 9C, circumferential surfaces
36
72 and 82, respectively, corresponding to the circle 11a of
the inner circumferential surface 11 in the nut blank 1. On
the circumferential surfaces 72 and 82, arranged are letter
S shaped convexes 73 and 83, respectively, corresponding to
the letter S shaped concaves 5 s of the ball return passage.
[0047]
The axial dimension of the main body 61 of the cam driver
6 is longer than the axial dimension of the cylindrical member
5.
10 The inclined surface 71 of the cam slider 7 and the
inclined surface 61b of the cam driver 6, and the inclined
surface 81 of the cam slider 8 and the inclined surface 61d
of the cam driver 6 constitute a cam mechanism of the die.
The parallel surface 61c of the cam driver 6 and the
15 parallel surface 51a of the cylindrical member 5, the parallel
surface 61a of the cam driver 6 and the parallel surface 51c
of the cylindrical member 5, and the parallel surface 61e of
the cam driver 6 and the parallel surface 51d of the
cylindrical member 5 are load receiving surfaces in contact
20 with each other.
[0048]
At the middle of the bottom plate portion, there are
provided with: a circular hole 22b into which the end portion
62 of the cam driver 6 is inserted; and a rectangular hole
25 22c into which the end portion 62 side of the main body 61
in the cam driver 6 is inserted, which are arranged to be
continuous through holes.
37
By using this die, the letter S shaped concave of the
ball return passage on the inner surface of the nut blank 1
in the following method.
[0049]
Firstly, after the nut blank 1 is disposed in the co5 ncave
21 of the blank holder 2, the cylindrical member 5 is inserted
into the nut blank 1 such that the cam sliders 7 and 8 are
held in the through holes 52 and 53 with the letter S shaped
convexes 73 and 83 facing outward. Then, the cam driver 6
10 is inserted into the center hole 51 of the cylindrical member
5 from the end portion 62 side, and the end portion 62 of the
cam driver 6 is inserted into the through holes 22b and 22c
of the blank holder 2. FIG. 7A illustrates this state.
[0050]
15 Subsequently, when the cam driver 6 is pressed from the
top thereof under pressure, a force is respectively
transmitted from the inclined surface 61b of the cam driver
6 to the inclined surface 71 of the cam slider 7, and from
the inclined surface 61d of the cam driver 6 to the inclined
20 surface 81 of the cam slider 8. In accordance with this, the
downward force of the cam driver 6 is converted into the force
to move the cam sliders 7 and 8 outwardly in the radial
direction. The letter S shaped convexes 73 and 83 formed on
the cam sliders 7 and 8, respectively, push the inner
25 circumferential surface 11 of the nut blank 1 for plastic
deformation. FIG. 7B illustrates this state.
[0051]
38
Thus, the letter S shaped concaves 15 and 16 forming the
two ball return passages, respectively, are formed on the
inner circumferential surface 11 of the nut blank 1. In this
situation, the end portion 62 of the cam driver 6 is guided
to the through hole 22b of the bottom member 22 in the 5 he blank
holder 2. In addition, the reactive force of the force in
the radial direction transmitted to the cam slider 7 is
received by the parallel surface 51d of the cylindrical member
5 and the parallel surface 61e of the cam driver 6 brought
10 into contact with each other (received by a surface
perpendicular to the reactive force on the extension thereof).
Furthermore, the reactive force of the force in the radial
direction transmitted to the cam slider 8 is received by the
contact between the parallel surface 51c of the cylindrical
15 member 5 and the first parallel surface 61a of the cam driver
6, and the contact between the parallel surface 51a of the
cylindrical member 5 and the parallel surface 61c of the cam
driver 6 (received by a surface perpendicular to the reactive
force on the extension thereof). It is therefore possible
20 to make smaller the bending moment received by the cam driver
6.
[0052]
Therefore, according to the method of the third example,
even when a nut having a long axial dimension and a small inner
25 diameter, the two letter S shaped concaves 15 and 16 can be
formed at the same time without damaging the cam driver 6.
In addition, if the nut blank 1 has the same diameter, the
cylindrical member 5 and the cam driver 6 can be used as common
39
parts. The preparation of the cam sliders 7 and 8 having
different letter S shaped convexes 73 and 83, respectively,
enables various types of the letter S shaped concaves having
different shapes. This is suitable as a method of producing
various types of parts in small amounts. Furthermore, 5 ermore, only
the cam sliders 7 and 8 can be replaced for replacing the letter
S shaped convexes most likely subject to abrasion or
deformation. This is an advantage of maintenance.
[0053]
10 Moreover, in the third example, the cylindrical member
5 illustrated in FIG. 9A and FIG. 9B is used as a holding member
of the cam slider. However, in order to alleviate the force
extending outwardly in the radial direction, applied to the
cylindrical member 5, when the cam sliders 7 and 8 are pushed
15 out, it is preferable to provide an incision that reaches the
center hole 51 from the outer circumference of the cylindrical
member 5 and extends in the entire axial direction.
[0054]
In the example of FIG. 10, two incisions 54 are provided
20 in parallel to the parallel surface 51a to parallel surface
51e along the diameter of the outer circumference of the
cylindrical member 5. That is, the holding member of the cam
slider illustrated in FIG. 10A and FIG. 10B is composed of
divided bodies 5A and 5B, which are divided into two parts
25 by a surface along the diameter of the outer circumference.
By use of such a member including the divided bodies 5A and
5B, as a holding member of the cam slider, it is made possible
40
to be hardly damaged, as compared to a case of using the
cylindrical member 5.
[0055]
In addition, in the third example, as illustrated in FIG.
7, there are provided the cam sliders 5 ders 7 and 8, each having
a letter S shaped convex 73 or 83, respectively, at the outer
circumference. However, the cam slider having plural letter
S shaped convexes at the outer circumference may be employed,
or three or more cam sliders each having one letter S shaped
10 convex may be employed.
In the example of FIG. 11, two letter S shaped convexes
73 and 73a are provided at the outer circumference of one cam
slider 7, whereas two letter S shaped convexes 83 and 83a are
provided at the outer circumference of the other cam slider
15 8. The axial dimension of the cam sliders 7 and 8 are longer
than those illustrated in FIG. 7, so that through holes 52
and 53 of the cylindrical member 5 are arranged to correspond
to the above sizes. Furthermore, inclined surfaces 61b and
61d of the cam driver 6 are arranged to correspond to the
20 inclined surfaces 71 and 81 of the cam sliders 7 and 8,
respectively.
[0056]
The dispositions of two letter S shaped convexes 73 and
73a in the cam slider 7 are different in the axial direction
25 of the nut blank 1 and same in the circumferential direction
of the inner circumferential surface 11. The dispositions
of two letter S shaped convexes 83 and 83a in the cam slider
8 are different in the axial direction of the nut blank 1 and
41
same in the circumferential direction of the inner
circumferential surface 11. Then, the dispositions of the
four letter S shaped convexes 73, 73a, 83, and 83a are all
different in the axial direction of the nut blank 1.
5 [0057]
Thus, in the example of FIG. 11, it is made possible to
form four letter S shaped concaves 15, 15a, 16, and 16a on
the inner circumferential surface 11 of the nut blank 1, by
a one-time operation of pushing the cam driver 6 from the top
10 thereof. In this example, the arranged positions of the four
letter S shaped concaves 15, 15a, 16, and 16a are all different
in the axial direction of the nut blank 1, whereas two of them
are same in the circumferential direction of the inner
circumferential surface 11, respectively.
15 Moreover, in the example of FIG. 11, the reactive force
of the force in the radial direction transmitted to the cam
slider 7 is received, by the parallel surface 51d of the
cylindrical member 5 and the parallel surface 61e of the cam
driver 6 brought into contact with each other, at the position
20 of the letter S shaped convex 73 in the axial direction
(received by a surface perpendicular to the reactive force
on the extension thereof). The reactive force of the force
in the radial direction applied to the letter S shaped convex
73a is received by the two letter S shaped convexes 83 and
25 83a of the cam slider 8 and a contact point with the inner
circumferential surface 11 of the nut blank 1.
[0058]
42
The reactive force of the force in the radial direction
transmitted to the cam slider 8 and then applied to the letter
S shaped convex 83a is received by the two letter S shaped
convexes 73 and 73a of the cam slider 7 and a contact point
with the inner circumferential surface 11 of the nut bla5 nk
1. The reactive force of the force in the radial direction
applied to the letter S shaped convex 83 is received by the
parallel surface 51c of the cylindrical member 5 and the first
parallel surface 61a of the cam driver 6 brought into contact
10 with each other (received by a surface perpendicular to the
reactive force in the vicinity in the axial direction on the
extension thereof). Therefore, a bending moment received by
the cam driver 6 can be made smaller.
[0059]
15 In the example of FIG. 12, four cam sliders, each having
one letter S shaped convex, are used. Specifically, a cam
slider 7B is disposed at the same position in the
circumferential direction as that of the cam slider of FIG.
7 but at a different portion in the axial direction from that
20 of the cam slider 7 of FIG. 7, and a cam slider 8B is disposed
at the same position in the circumferential direction as that
of the cam slider 8 but at a different portion in the axial
direction from that of the cam slider 8.
In addition to the inclined surfaces 61b and 61d
25 corresponding to the inclined surfaces 71 and 81 of the cam
sliders 7 and 8, respectively, the cam driver 6 is provided
with inclined surfaces 61f and 61g corresponding to inclined
surfaces 71B and 81B of the cam sliders 7B and 8B, respectively.
43
In addition to the through holes 52 and 53 for arranging the
cam sliders 7 and 8, the cylindrical member 5 is provided with
through holes 52a and 53a for arranging the cam sliders 7B
and 8B.
5 [0060]
The die of FIG. 12 is provided with step surfaces 61i
and 61j between the inclined surfaces 61b and 61f and the
inclined surfaces 61g and 61d of the cam driver 6. Therefore,
it is necessary to assemble the cam driver 6 and all the cam
10 sliders into the cylindrical member 5 and then insert the cam
driver 6 into the nut blank 1.
The arrangements of the letter S shaped convexes 73, 83,
73b, and 83b arranged at the four cam sliders 7, 8, 7B, and
8B are all different in the axial direction of the nut blank
15 1, and the arrangements of two of them are same respectively
in the circumferential direction of the inner circumferential
surface 11.
[0061]
Accordingly, in the example of FIG. 12, it is possible
20 to form the four letter S shaped concaves 15, 15a, 16, and
16a on the inner circumferential surface 11 of the nut blank
1, by performing a one-time operation of pressing the cam
driver 6 from the top thereof. In this example, the formed
positions of the four letter S shaped concaves 15, 15a, 16,
25 and 16a are all different in the axial direction of the nut
blank 1, and two of them are same respectively in the
circumferential direction of the inner circumferential
surface 11.
44
Moreover, FIG. 13 illustrates an example of forming one
letter S shaped concave 15 by use of a die with a cylindrical
member (holding member of cam slider) 50 similar to the
cylindrical member 5 of FIG. 7 and one cam slider 7.
5 [0062]
In the example of FIG. 13, one cam slider 7 is held by
the cylindrical member 50 and the through hole 52 is arranged
in the cylindrical member 50, but the through hole 53 is not
arranged. The cam driver 6 does not include the inclined
10 surface 61d, but the parallel surface (load receiving
surface) 61e extends near the end portion 62 and includes a
step surface 61h. Additionally, the parallel surface (load
receiving surface) 51d in contact with the parallel surface
61e of the cam driver 6 is provided in the cylindrical member
15 50.
[0063]
Therefore, when the cam driver 6A is pushed from the top
thereof to transmit the force from the inclined surface 61b
of the cam driver 6A to the inclined surface 71 of the cam
20 slider 7 and move the cam slider 7 outwardly in the radial
direction, the reactive force of the force in the radial
direction transmitted to the cam slider 7 is received by the
parallel surface 51d of the cylindrical member 50 and the
parallel surface 61e of the cam driver 6A brought into contact
25 (received by a surface perpendicular to the reactive force
on the extension thereof). Specifically, in the first
embodiment, the inner circumferential surface 11 of the nut
45
blank 1 is the surface perpendicular to the reactive force
on the extension thereof.
[0064]
In the example of FIG. 13, as compared to the case where
the cylindrical member 50 is not provided 5 ided as in the first
example, the cylindrical member 50 and the cam driver 6A can
be used as a common part if the inner diameter of the nut blank
1 is same. Since the preparation of the cam slider 7 having
a different letter S shaped convex 73 enables various types
10 of the letter S shaped concaves having different shapes, this
is suitable as a method of producing various types of parts
in small amounts. Furthermore, only the cam slider 7 can be
replaced for replacing the letter S shaped convex most likely
subject to abrasion or deformation. This is an advantage in
15 the maintenance.
[0065]
Also in the examples FIG. 11 to FIG. 13, a member
including the divided bodies 5A and 5B is used as a cam slider
holding member instead of the cylindrical members 5 and 50,
20 it is made possible to be hardly damaged. In a case where
the cam sliders are arranged at plural positions in the
circumferential direction, it is preferable to provide an
incision 54 to separate the portions (the through holes 52
and 53 in FIG. 10) where the sliders are arranged from each
25 other. That is, for example, in a case where the cam sliders
arranged at three parts in the circumferential direction, it
is preferable to use a divided body having a shape of three
divisions.
46
[0066]
(Fourth Example)
The die used in the fourth example is, as illustrated
in FIG. 14, provided with: a blank holder 2 having a concave
21 for holding the nut blank 1; a cylindrical 5 rical member (holding
member of cam slider) 9 inserted into the nut blank 1; a cam
driver 60 inserted into a center hole 91 of the cylindrical
member 9; and cam sliders 7A and 8A provided at through holes
92 and 93 of the cylindrical member 9, respectively. There
10 is provided a concave 21a for holding an end portion of the
cylindrical member 9 at the middle of the concave 21 of the
blank holder 2.
[0067]
Referring to FIG. 15, the cam driver 60 is provided with:
15 a main body 63 shaped in a long square pole; and a column shaped
end portion 62. Recess portions 66 and 67 are formed at the
column shaped end portion 62 side of both side surfaces 64
and 65 of the main body 63, respectively. There are provided,
from the column shaped end portion 62 side, a parallel surface
20 66a parallel to the axial direction and an inclined surface
66b inclined in the axial direction, at the concave 66 of one
side surface 64. There is provided an inclined surface 67a
inclined in the axial direction, at the concave 67 of the other
side surface 65.
25 [0068]
The start position of the concave 67 (the boundary
between the side surface 65 and the inclined surface 67a) of
the other side surface 65 is arranged slightly on the column
47
shaped end portion 62 side from the boundary between the
parallel surface 66a and the inclined surface 66b of one side
surface. The diameter of the column forming the column shaped
end portion 62 is same as a gap between the bottom surface
of the concave 66 and the 5 bottom surface of the concave 67
(on the column shaped end portion 62 side) at the lower end
of the side surface 63. These arrangements are not essential,
but such arrangements enhance the strength of the column
shaped end portion 62 and a part in the vicinity of the column
10 shaped end portion 62 of the side surface 63.
[0069]
The cylindrical member 9 has an outer circumferential
surface slightly smaller than the inner circumferential
surface of the nut blank 1. Referring to FIG. 16A and FIG.
15 16B, a center hole 91 of the cylindrical member 9 has a
cross-sectional shape corresponding to the main body 63 of
the cam driver 60. Parallel surfaces 91a and 91b parallel
to the axial direction in which the center hole 91 is arranged
are the surfaces (load receiving surfaces) of receiving the
20 side surfaces 64 and 65 parallel to the axial direction of
the cam driver 60.
[0070]
Referring to FIG. 16C, the cam sliders 7A and 8A are
members, each having an arched column shaped portion, with
25 the circumferential surfaces 72 and 82, on the outside of a
substantially trapezoidal column shaped portion provided
with inclined surfaces 71 and 81, respectively. Letter S
shaped convexes 73 and 83, corresponding to the letter S
48
shaped concaves constituting the ball return passages, are
provided at the circumferential surfaces 72 and 82. The
inclined surfaces 71 and 81 have the same inclination with
the inclined surfaces 66b and 67a of the cam driver 60,
respectively, and the circumferential surfaces 72 and 82 ar5 e
almost the same with the inner circumferential surface 11,
of the nut blank 1, as indicated by the circle 11a.
[0071]
The axial dimension of the main body 63 of the cam driver
10 60 is longer than that of the cylindrical member 9.
The inclined surface 71 of the cam slider 7A and the
inclined surface 66b of the cam driver 60, and the inclined
surface 81 of the cam slider 8A and the inclined surface 67a
of the cam driver 60 constitute a cam mechanism of the die.
15 There is provided a circular through hole 23 into which the
column shaped end portion 62 of the cam driver 60 is inserted,
at the middle of the bottom plate portion of the blank holder
2.
[0072]
20 By use of this die, the letter S shaped concave of the
ball return passage is provided on the inner surface of the
nut blank 1 in the following method.
Firstly, after the nut blank 1 is arranged at the concave
21 of the blank holder 2, the cam sliders 7A and 8A insert
25 the cylindrical member 9 held by the through holes 92 and 93
with the letter S shaped convex 73 and the letter S shaped
convex 83 facing outwardly, so that its end portion is
disposed at the concave 21a. Next, the cam driver 60 is
49
inserted into the center hole 91 of the cylindrical member
9 from the column shaped end portion 62 side to insert the
column shaped end portion 62 of the cam driver 60 into the
circular through hole 23 of the blank holder 2. FIG. 14A
illustrates 5 ates this state.
[0073]
Subsequently, when the cam driver 60 is pressed under
pressure from the top thereof, forces are transmitted from
the inclined surface 66b of the cam driver 60 to the inclined
10 surface 71 of the cam slider 7A, and from the inclined surface
67a of the cam driver 60 to the inclined surface 81 of the
cam slider 8A, respectively. In accordance therewith, the
downward force of the cam driver 60 is converted to the forces
of moving the cam sliders 7A and 8A outwardly in the radial
15 direction, and then the letter S shaped convexes 73 and 83
formed at the cam sliders 7A and 8A push the inner
circumferential surface 11 of the nut blank 1 for plastic
deformation. FIG. 14B illustrates this state.
[0074]
20 Thus, the letter S shaped concaves 15 and 16 of the two
ball return passages are formed on the inner circumferential
surface 11 of the nut blank 1. In such a situation, the column
shaped end portion 62 of the cam driver 60 is guided to the
circular through hole 23 of the blank holder 2. In addition,
25 the reactive force of the force in the radial direction
transmitted to the cam slider 7A is received by the parallel
surface 91b of the cylindrical member 9 and the side surface
65 of the cam driver 60 brought into contact with each other
50
(received by a surface perpendicular to the reactive force
on the extension thereof). Furthermore, the reactive force
of the force in the radial direction transmitted to the cam
slider 8A is received by the parallel surface 91a of the
cylindrical member 9 and the parallel surface 5 e 66a of the side
surface 64 brought into contact with each other (received,
at the same position in the axial direction with the reactive
force, in the vicinity of the extension of the reactive force
and by a surface perpendicular to the reactive force). Thus,
10 it is made possible to make smaller the bending moment
received by the cam driver 60.
[0075]
Therefore, according to the method in the fourth example,
even in a case where a nut having a long axial dimension and
15 a small diameter, the two letter S shaped concaves 15 and 16
can be formed at the same time without damaging the cam driver
60. In addition, since the cam driver 60 and the cylindrical
member 9 used in the method of the fourth example has a larger
area of the load receiving surface than that of the cam driver
20 6 and the holding member 5 used in the third example, the cam
driver is hardly damaged as compared to the method of the third
example.
[0076]
Furthermore, the load receiving surface (the parallel
25 surfaces 91a and 91b of the cylindrical member 9 and the side
surfaces 63 and 64 of the cam driver 60) is arranged on the
entire axial direction. Even if the gap is narrow in the axial
direction of the two letter S shaped concaves 15 and 16
51
provided in the nut blank 1, it is possible to sufficiently
receive the reactive force of the force in the radial
direction transmitted to the cam sliders.
Moreover, when the inner diameter of the nut blank 1 is
same, the cylindrical member 5 mber 9 and the cam driver 60 can be
used as a common part. The preparation of the cam sliders
7A and 8A having the letter S shaped convexes 73 and 83,
different from each other, enables various types of the letter
S shaped concaves having different shapes. This is suitable
10 as a method of producing various types of parts in small
amounts. Additionally, only the cam sliders 7A and 8A can
be replaced for replacing the letter S shaped convexes most
likely subject to abrasion or deformation. This is an
advantage of maintenance.
15 [0077]
Moreover, in the fourth example, the cylindrical member
9 illustrated in FIG. 16A and FIG. 16B is used as a holding
member of cam slider. However, in order to alleviate the
force of extending outwardly in the radial direction applied
20 to the cylindrical member 9 when the cam sliders 7A and 8A
are pushed out, it is preferable to provide an incision that
reaches the center hole 91 from the outer circumference of
the cylindrical member 9 and extends in the entire axial
direction.
25 [0078]
In the example of FIG. 17, two incisions 94 are provided
in parallel with the parallel surfaces 91a and 91b along the
diameter of the outer circumference of the cylindrical member
52
9. That is, the holding member of cam slider illustrated in
FIG. 17A and FIG. 17B is composed of divided bodies 9A and
9B, each having a shape where the cylindrical member 9 is
divided into two parts by a surface along the diameter of the
outer circumference. By use of such a member including 5 ding the
divided bodies 9A and 9B, as a holding member of cam slider,
it is made possible to be hardly damaged, as compared to a
case of using the cylindrical member 9.
[0079]
10 In addition, in the fourth example, as illustrated in
FIG. 14, there are provided the cam sliders 7A and 8A, each
having a letter S shaped convex 73 or 83, respectively, at
the outer circumference. However, the cam slider having
plural letter S shaped convexes at the outer circumference
15 may be employed, or three or more cam sliders each having one
letter S shaped convex may be employed.
In the example of FIG. 18, two letter S shaped convexes
73 and 73a are provided at the outer circumference of one cam
slider 7A, whereas two letter S shaped convexes 83 and 83a
20 are provided at the outer circumference of the other cam
slider 8A. The axial dimension of the cam sliders 7A and 8A
are longer than those illustrated in FIG. 14, so that through
holes 92 and 93 of the cylindrical member 9 are arranged to
correspond to the above dimensions. Furthermore, inclined
25 surfaces 66b and 67a of the cam driver 60 are arranged to
correspond to the inclined surfaces 71 and 81 of the cam
sliders 7A and 8A, respectively.
[0080]
53
The arrangements of two letter S shaped convexes 73 and
73a in the cam slider 7A are different in the axial direction
of the nut blank 1 and same in the circumferential direction
of the inner circumferential surface 11. The arrangements
of two letter S shaped convexes 83 and 83a in the cam slide5 r
8A are different in the axial direction of the nut blank 1
and same in the circumferential direction of the inner
circumferential surface 11. Then, the arrangements of the
four letter S shaped convexes 73, 73a, 83, and 83a are all
10 different in the axial direction of the nut blank 1.
[0081]
Accordingly, in the example of FIG. 18, it is made
possible to form four letter S shaped concaves 15, 15a, 16,
and 16a on the inner circumferential surface 11 of the nut
15 blank 1, by a one-time operation of pushing the cam driver
60 from the top thereof. In this example, the arranged
positions of the four letter S shaped concaves 15, 15a, 16,
and 16a are all different in the axial direction of the nut
blank 1, whereas two of them are same in the circumferential
20 direction of the inner circumferential surface 11,
respectively.
[0082]
Moreover, in the example of FIG. 18, the reactive force
of the force in the radial direction transmitted to the cam
25 slider 7A is received, by the parallel surface 91b of the
cylindrical member 9 and the side surface 65 of the cam driver
60 brought into contact with each other, at any position of
the letter S shaped convexes 73 and 73a (received by a surface
54
perpendicular to the reactive force on the extension thereof).
Furthermore, the reactive force of the force in the radial
direction transmitted to the cam slider 8A is received by the
parallel surface 91a of the cylindrical member 9 and a both
side part of the parallel surface 66a in the side surface 5 64
of the cam driver 60 brought into contact with each other,
at any position of the letter S shaped convexes 83 and 83a
(received, at the same position in the axial direction with
the reactive force, in the vicinity of the extension of the
10 reactive force and by a surface perpendicular to the reactive
force). Thus, it is made possible to make smaller the bending
moment received by the cam driver 60.
[0083]
Additionally, when the example of FIG. 11 and the example
15 of FIG. 18 are compared, the example of FIG. 11 has an advantage
in the simpler structure of the die than that in the example
of FIG. 18, whereas the example of FIG. 18 has an advantage
in the smaller bending moment received by the cam driver than
that in the example of FIG. 11.
20 [0084]
(Second Embodiment)
A second embodiment relates to a method for manufacturing
a nut included in a ball screw.
The ball screw is provided with: a nut having an inner
25 circumferential surface on which a spiral groove is formed;
a threaded shaft having an outer circumferential surface on
which a spiral groove is formed; balls loaded in a raceway
between the spiral groove of the nut and that of the threaded
55
shaft; and a ball return passage for returning the balls from
an end point of the raceway to a start point thereof. The
ball screw is a device such that the balls are rolling in the
raceway to make the nut relatively move with respect to the
5 threaded shaft.
Such ball screws are used in not only positioning devices
of general industrial machinery but also in electrical
actuators mounted on vehicles such as automobiles,
motorcycles, or vessels.
10 [0085]
As to the ball return passage in the ball screw, there
are a circulation tube type of the ball return passage and
a deflector type thereof. In the case of the deflector type,
a deflector having a concave included in the ball return
15 passage is fitted in a through hole of the nut. In contrast,
Patent Document 1 describes that the concave (circulation
groove) of the ball return passage is directly arranged on
the inner circumferential surface of the nut blank by plastic
working. The method for arranging it has been described with
20 reference to FIG. 19. Hence, the description thereof is
omitted here.
[0086]
In the method described in Patent Document 1, when the
axial dimension of the nut is long and the inner diameter is
25 small, the working head of the die is elongated.
This causes a problem that the strength is insufficient and
easily damaged.
56
An object of the second embodiment is to provide a method
of forming multiple concaves without damaging a die, as a
method of forming multiple ball return passages directly on
the inner circumferential surface of the nut blank by plastic
working, even in a case where the nut 5 having a long axial
dimension and a small inner diameter.
[0087]
In order to achieve the above object, in the second
embodiment, there is provided a method of manufacturing a nut
10 for a ball screw, ball screw comprising having an inner
circumferential surface on which a spiral groove is formed;
a threaded shaft having an outer circumferential surface on
which a spiral groove is formed; balls loaded in a raceway
between the spiral groove of the nut and that of the threaded
15 shaft; and plural ball return passages, for returning the
balls from an end point of the raceway to a start point thereof,
formed as plural concaves on the inner circumferential
surface of the nut, wherein the nut of the ball screw is that
the balls are rolling in the raceway to make the nut relatively
20 move with respect to the threaded shaft. With a pressing
method by use of a die of a cam mechanism including: a cam
driver inserted into the nut blank having a cylindrical shape
and moving in its axial direction; and plural cam sliders
arranged between the nut blank member and the cam driver, at
25 least one of plural convexes corresponding to the plural
concaves, and the convexes moving in the radial direction of
the nut due to the movement of the cam driver, whereby the
57
plural concaves are formed at the same time on the inner
circumferential surface of the nut blank by plastic working.
[0088]
According to the method in the second embodiment, in the
pressing method by use of the die, the movement in the axia5 l
direction of the cam driver on the inclined surface forming
the cam mechanism changes the direction to the radial
direction to be transmitted to plural cam sliders. The plural
convexes formed on the plural cam sliders push the inner
10 circumferential surface of the nut blank for plastic
deformation, so that the plural concaves are arranged on the
inner circumferential surface of the nut blank. Then, even
in a case where a nut having a long axial dimension and a small
inner diameter is manufactured, the die is hardly damaged as
15 compared to the method described in Patent Document 1.
[0089]
In the method according to the second embodiment, it is
possible to operate the press working, as the die, the cam
driver has a load receiving surface in parallel to the axial
20 direction of the nut blank, whereas a load receiving surface,
at another member other than the cam driver (an example is
the bottom of a nut blank holding member or a cam slider holding
member), to be in contact with the above-described load
receiving surface. This enables the reactive force of the
25 force in the radial direction transmitted to the cam slider
to be received by both of the load receiving surfaces to be
in contact with each other (received by the surface
perpendicular to the reactive force). Accordingly, even if
58
the cam driver has an elongated shape, the bending moment
received by the cam driver can be made smaller.
[0090]
According to the method in the second embodiment, as the
die, it is possible to perform the press working by 5 use of
the die having the plural cam sliders held by the holding
member disposed between the cam driver and the nut blank, the
holding member having the load receiving surface.
In the method according to the second embodiment, the
10 movement amount (pushing amount), outwardly on the radial
direction of the nut blank, of the convexes formed at the
plural cam sliders, is changed to correspond to the difference
in the plastic flow of the portion where the plural concaves
of the nut blank are formed (the pushing amount of the portion
15 easily subject to the plastic flow is reduced, whereas the
pushing amount of the portion hardly subject to the plastic
flow). This enables the shapes and dimensions of the plural
concaves to be uniform.
[0091]
20 By changing the angles of inclination of plural inclined
surfaces where the plural cam sliders and the cam drivers are
in contact with each other, it is possible to change the
movement amount outwardly in the radial direction of the nut
blank of the convex arranged at each cam slider.
25 According to the method in the second embodiment, as a
method of forming plural ball return passages directly on the
inner circumferential surface of the nut blank as plural
concaves by the plastic working, even in a case of producing
59
a nut having a long axial dimension and a small inner diameter,
it is possible to form the plural concaves without damaging
the die.
[0092]
5 (First Example)
In the method of the second example of the first
embodiment, as illustrated in FIG. 4, by use of the pair of
cam sliders 3 having the same angles of inclination of the
inclined surface 33 and having the same protruding dimensions
10 in the radial direction of the convexes 35 and 36, the timings
when the convexes 35 and 36 start to push the inner
circumferential surface 11 of the nut blank 1 are made to be
the same. This forms the letter S shaped concaves 15 and 16
with the same pushing amounts (the movement amount in the
15 radial direction of the nut blank 1) against the convexes 35
and 36.
[0093]
In a case where the blank holder 2 is used, as a
restraining block of the nut blank 1, for restraining the
20 lower end surface in the axial direction and the outer
circumferential surface of the nut blank 1, since the lower
portion in the axial direction of the nut blank 1 close to
an end surface restrained by a concave 21 of the blank holder
2, plastic flow hardly occurs as compared to the upper portion
25 in the axial direction of the nut blank 1 is close to an end
surface not restrained by the concave 21. Accordingly, as
the method according to the first embodiment, when the pushing
amounts of the convexes 35 and 36 are same, it is difficult
60
to form the upper letter S shaped concave 15 and the lower
letter S shaped concave 16 in a uniform shape and dimension.
[0094]
In contrast, according to the first example in the second
embodiment, referring to FIG. 20, cam sliders 5 iders 103A and 103B
are employed such that the angles of inclination of inclined
surfaces are same but protruding dimensions in the radial
direction of convexes 135 and 136 are different (the convex
135 forming an upper letter S shaped concave 115 is smaller
10 than the convex 136 forming a lower letter S shaped concave
116).
Except for the above aspect, the die used in the first example
of the second embodiment is same with that used in the second
example of the first embodiment.
15 [0095]
For that reason, as illustrated in FIG. 20, in a state
where outer end portions in the radial direction of the
convexes 135 and 136 of the cam sliders 103A and 103B are in
contact with an inner circumferential surface of a nut blank
20 101, and an inclined surface 133 of the cam slider 103B is
in contact with an inclined surface 141a of the cam driver,
that is, in a state immediately before the convex 136 of the
cam slider 103B is pushed into the inner circumferential
surface 111 of the nut blank 101, the inclined surface 141a
25 of the cam driver 104, the inclined surface 141a of the cam
driver 104 and the inclined surface 133 of the cam slider 103A
oppose each other with a gap. Accordingly, when the cam
driver 104 is pushed from the top thereof in this state, the
61
cam slider 103B having the convex 136 moves outwardly in the
radial direction earlier than the cam slider 103A having the
convex 135 moves, and the convex 136 starts pushing the inner
circumferential surface 111 of the nut blank 101 earlier than
the 5 convex 135 pushes.
[0096]
Then, after the inclined surface 141a of the cam driver
104 and the inclined surface 133 of the cam slider 103A are
in contact with each other in accordance with the movement
10 of the cam driver 104, the cam sliders 103A and 103B
respectively move outwardly in the radial direction. At this
point of time, since the angles of inclination of the inclined
surfaces 133 of the cam sliders 103A and 103B (the pair of
the inclined surfaces 141a of the cam driver 104) are same,
15 the movement amount outwardly in the radial direction of the
convex 135 is smaller than that of the convex 136, which is
later in the timing of starting pushing the inner
circumferential surface 111 of the nut blank 101. The
difference in the protruding dimension in the radial
20 direction between the convexes 135 and 136 corresponds to the
difference in the movement amount.
[0097]
As described heretofore, according to the first method
of the second embodiment, by changing the timings when the
25 convexes 135 and 136 start to push the inner circumferential
surface 111 of the nut blank 101 to change the pushing amounts
of the convexes 135 and 136 into the inner circumferential
surface 111 of the nut blank 101, it is made easier to form
62
the upper letter S shaped concave 115 and the lower letter
S shaped concave 116 in a uniform shape and dimension than
the second method of the first embodiment.
[0098]
Specifically, in FIG. 20B, the upper 5 pper letter S shaped
concave 115 and the lower letter S shaped concave 116 seem
to have different depths corresponding to the protruding
dimensions of the corresponding convexes 135 and 136,
respectively. However, the drawing is merely an explanatory
10 one. In the implementation of the first method of the second
embodiment, in reality, the upper letter S shaped concave 115
and the lower letter S shaped concave 116 are formed in a
uniform shape and dimension.
[0099]
15 Additionally, the first method of the second embodiment
(that is the method of varying the pushing amount of each
convex by changing the timings when a pair of cam sliders start
to push the inner circumferential surface of the nut blank)
is applicable to the third and fourth examples of the first
20 embodiment.
[0100]
(Second Example)
In a second example of the second embodiment, referring
to FIG. 21, the same die of FIG. 7, used in the third example
25 of the first embodiment is used except for the following
points. That is, as to the die used in the second example,
the convex dimension in the radial direction of a convex 173
of a cam slider 107 having an upper letter S shaped concave
63
115 is smaller than a convex 183 of a cam slider 108 having
a lower letter S shaped concave 116. The angle of inclination
of an inclined surface 171 of the cam slider 107 is smaller
than that of an inclined surface 181 of the cam slider 108.
To correspond to this, the angle of inclination of an 5 inclined
surface 161b in the cam driver 106 is smaller than that of
the inclined surface 161d.
[0101]
For that reason, when pushing the cam driver 106 from
10 the top thereof, the cam sliders 107 and 108 move outwardly
in the radial direction of the nut blank 101 at the same time,
and then the convexes 173 and 183 start pushing the inner
circumferential surface of the nut blank 101. Subsequently,
the cam sliders 107 and 108 are moving outwardly in the radial
15 direction in accordance with the movement of the cam driver
106, respectively. Since the angle of inclination of the
inclined surface 171 in the cam slider 107 is smaller than
that of the inclined surface 181 of the cam slider 108, the
movement amount of the cam slider 107 outwardly in the radial
20 direction is smaller than that of the cam slider 108. The
difference in the convex dimension in the radial direction
between the convexes 173 and 183 corresponds to the difference
in the movement amount.
[0102]
25 As described above, according to the second example of
the second embodiment, although the timings when the convexes
173 and 183 start pushing the inner circumferential surface
111 of the nut blank 101 are same, the pushing amounts of the
64
convexes 173 and 183 into the inner circumferential surface
111 of the nut blank 101 are varied by changing the angles
of inclination of the inclined surfaces 171 and 181 where the
cam driver 106 is in contact with the cam sliders 107 and 108,
respectively. Thus, it is made possible to form the lette5 r
S shaped concaves 115 and 116 in a uniform shape and dimension
more easily than the method in the third example of the first
embodiment.
[0103]
10 Specifically, in FIG. 21B, the upper letter S shaped
concave 115 and the lower letter S shaped concave 116 seem
to be formed to have different depths to correspond to the
protruding dimensions of the convexes 173 and 183,
respectively. However, this drawing is merely provided for
15 description. In the implementation of the method according
to the second example in the second embodiment, in fact, the
letter S shaped concaves 115 and 116 are formed in a uniform
shape and dimension.
[0104]
20 In addition, in the method of the second example of the
second embodiment, the pushing amounts of the convexes 173
and 183 into the inner circumferential surface 111 of the nut
blank 101 may be changed in combination the fact that the
angles of inclination of the inclined surfaces 171 and 181
25 where the cam driver 106 is in contact with the cam sliders
107 and 108 are made different and the fact that the timings
when the convexes 173 and 183 start pushing the inner
65
circumferential surface 111 of the nut blank 101 (the fourth
example of the first embodiment).
[0105]
Furthermore, in the first example and second example of
the second embodiment, in order to form the 5 e letter S shaped
concaves 115 and 116 to have a uniform shape and dimension,
the pushing amounts of the pair of cam sliders are varied to
correspond to the difference in the plastic flow of the nut
blank 101 due to the difference in the restraint state. Other
10 than the example in which there is a difference in the plastic
flow in accordance with the difference in the restraint state
of the nut blank, even in a case where a flange is provided
at the outer circumference of the nut blank, it is possible
to easily form plural concaves in a uniform manner by changing
15 the pushing amount, of the convexes of the plural cam sliders,
into the inner circumferential surface of the nut blank.
[0106]
Moreover, in the first example of the second embodiment
and the second example of the second embodiment, the pushing
20 amount of the upper convex is larger than that of the lower
convex. However, the pushing amount of the upper convex may
be larger than that of the lower convex in accordance with
the restraint state or the outer circumferential shape of the
nut blank.
25 Additionally, in the second example, the third example,
and the fourth example of the first embodiment, the first
example and the second example of the second embodiment, the
description has been given of case where two letter S shaped
66
concaves (concaves forming the ball return passage) 15 (115)
and 16 (116) are arranged on inner circumferential surface
11 (111) of the nut blank 1 (101). However, it is to be
understood that the method of the second embodiment may be
applicable to a case where three or more concaves 5 forming the
ball return passage are may be arranged on the circumferential
surface of the nut blank.
[0107]
(Third Embodiment)
10 A third embodiment relates to a method for manufacturing
a ball screw and a ball screw manufactured by the method.
A ball screw is provided with: a nut having an inner
circumferential surface on which a spiral groove is formed;
a threaded shaft having an outer circumferential surface on
15 which a spiral groove is formed; balls loaded in a raceway
between the spiral groove of the nut and that of the threaded
shaft; and a ball return passage for returning the balls from
an end point of the raceway to a start point thereof. The
ball screw is a device such that the balls are rolling in the
20 raceway to make the nut relatively move with respect to the
threaded shaft.
[0108]
Such ball screws are used in not only positioning devices
of general industrial machinery but also electrical actuators
25 mounted on vehicles such as automobiles, motorcycles, or
vessels.
As to the ball return passage in the ball screw, there
are a circulation tube type of the ball return passage and
67
a deflector type thereof. In the case of the deflector type,
a deflector having a concave of the ball return passage is
fitted in a through hole of the nut. In contrast, Patent
Document 1 describes that the concave (circulation groove)
of the ball return passage is directly formed 5 ed on the inner
circumferential surface of the nut blank by plastic working.
The method of forming it has been described with reference
to FIG. 19. Therefore, the description thereof is omitted
here.
10 [0109]
It is to be noted, however, that the method described
in Patent Document 1 has a problem in that when the axial
dimension of the nut is long and the inner diameter is small,
the working head of the die is elongated and the strength is
15 insufficient and it is easily broken. Besides, the flow of
the material in accordance with the formation of the concave
cannot be controlled. Since the material flows towards the
axial direction of the nut blank, both end surfaces in the
axial direction of the nut blank deform to have a convex shape.
20 The end surface in the axial direction of the nut blank is
a reference surface for working in the next process of forming
a spiral groove. If the convex shape is formed and remains,
there is a problem that the accuracy in the forming process
of the spiral groove is degraded.
25 [0110]
An object of the third embodiment is to provide a method
of forming the concave without damaging the die and
suppressing deformation of both end surfaces in the axial
68
direction of the nut blank, as a method of directly forming
the concave, of the ball return passage, on the inner
circumferential surface of the nut blank, even in a case where
the nut having a long axial dimension and a small inner
5 diameter.
[0111]
In order to achieve the above object, in the third
embodiment, there are provided a method of manufacturing a
nut for a ball screw, the ball screw comprising: the nut having
10 an inner circumferential surface on which a spiral groove is
formed; a threaded shaft having an outer circumferential
surface on which a spiral groove is formed; balls loaded in
a raceway between the spiral groove of the nut and that of
the threaded shaft; and ball return passages, for returning
15 the balls from an end point of the raceway to a start point
thereof, formed as concaves on the inner circumferential
surface of the nut, wherein the ball screw is that the balls
are rolling in the raceway to make the nut relatively move
with respect to the threaded shaft. The die of cam mechanism
20 comprising: a cam driver inserted into a cylindrical nut blank
and moving in an axial direction of the nut blank; a cam slider
disposed between the nut blank and the cam driver and provided
with a convex corresponding to the concave, a movement of the
cam driver causing the convex to move in a radial direction
25 of the nut; and a restraining member, for restraining both
end surfaces in the axial direction and an outer
circumferential surface of the nut blank, provided with a
depressed portion corresponding to the convex, at the inner
69
circumferential surface for receiving the outer
circumferential surface. The concave is formed on the inner
circumferential surface of the nut, by pressing the inner
circumferential surface of the nut blank with the convex, in
a pressing method by use of a die of the cam mechanism, 5 echanism, so
as to protrude the outer circumferential surface of the nut
blank into the depressed portion of the restraining member.
[0112]
According to the method of the third embodiment, by use
10 of the pressing method with the die, the movement of the cam
driver in the axial direction on an inclined surface of the
cam mechanism is changed to the movement in the radial
direction and transmitted to the cam sliders. The convex
arranged on the cam sliders pushes the inner circumferential
15 surface of the nut blank for plastic deformation, whereby the
concave is formed on the inner circumferential surface of the
nut blank. Then, even in a case where a nut having a long
axial dimension and a small inner diameter is manufactured,
the die is hardly damaged as compared to the method described
20 in Patent Document 1.
[0113]
In addition, the restraining member restrains both end
surfaces in the axial direction and the outer circumferential
surface of the nut blank, and the outer circumference portion
25 of the nut blank protrudes in a depressed portion of the
restraining member. Hence, the material is prevented from
flowing in the axial direction of the nut blank in accordance
with the formation of the concave. Accordingly, both end
70
surfaces in the axial direction of the nut blank are hardly
deformed at the time of forming the concave. Since the end
surface in the axial direction of the nut blank serves as the
reference surface for working in the next process of forming
the spiral groove, the accuracy in the forming 5 ming process of the
spiral groove is improved when they are used without change.
[0114]
The ball screw manufactured in the method of the third
embodiment is provided with a projection at a position
10 corresponding to the concave on the outer circumferential
surface of the nut.
According to the method in the third embodiment, it is
made possible to form the concave without damaging the die
and suppress deformation of both end surfaces in the axial
15 direction of the nut blank, as a method of directly forming
the concave, of the ball return passage, on the inner
circumferential surface of the nut blank, even in a case where
the nut having a long axial dimension and a small inner
diameter.
20 [0115]
Hereinafter, the third embodiment will be described.
The die used in the present embodiment is provided with,
referring to FIG. 22 to FIG. 24: a cam driver 202 inserted
into a nut blank 201; cam sliders 203A to 203D disposed between
25 the nut blank 201 and the cam driver 202; a stand 204 having
a top surface with the midpoint where a concave 241 having
an inner diameter same with that of the nut blank 201; a
restraining member 205 for restraining an upper end surface
71
and an outer circumferential surface of the nut blank 201;
and an outside member 206 for regulating the movement of the
restraining member 205 outwardly.
[0116]
Referring to FIG. 23A, the cam driver 202 is a rod sh5 aped
member having a square cross-section, and is provided with:
a base end portion 221 having a square cross-section that does
not change in the axial direction; and a main body portion
222 having a square cross-section that becomes smaller as
10 getting closer to an end. In other words, four side surfaces
221a to 221d of the base end portion 221 each are parallel
to each other in the front and back and in the left and right,
and four side surfaces 222a to 222b of the main body portion
222 each have the same angle of inclination.
15 [0117]
Referring to FIG. 23B and FIG. 23C, the cam sliders 203A
to 203D are members each having a shape in which a cylinder,
having an outer circumferential surface 231 with a diameter
slightly smaller than the inner diameter of the nut blank 201,
20 is divided into four parts in the circumferential direction.
On the opposite side of the outer circumferential surface 231,
there are provided inclined surfaces 233 having the same
angles of inclination with those of the four side surfaces
222a to 222b of the cam driver 202. When the cam sliders 203A
25 to 203D are disposed so that the outer circumferential surface
231 matches a circle 211a constituting an inner
circumferential surface 211 of the nut blank 201, a space is
arranged by the four inclined surfaces 233 of the circle 211a
72
so that the cam driver 202 is inserted thereinto. In addition,
four letter S shaped convexes 235A to 235D are provided to
correspond to the four letter S shaped concaves of the ball
return passage, on the outer circumferential surfaces 231 of
the cam sliders 203A 5 03A to 203D, respectively.
[0118]
The side surfaces 222a to 222d of the cam driver 202 and
the inclined surface 233 of the cam slider 203 constitute the
cam mechanism of the die.
10 Referring to FIG. 24A, the restraining member 205 is
provided with divided bodies 251 to 254, in which a
cylindrical body having an outer circumferential circle
changing in a tapered shape in the axial direction is divided
into four parts in the circumferential direction. Referring
15 to FIG. 24B, the inner circumferential surfaces of the divided
bodies 251 to 254 are formed to have large diameter portions
251a to 254a to correspond to the outer diameters of the nut
blank 201, respectively, on the large diameter side of the
outer circumferential surface. The inner circumferential
20 surfaces of the divided bodies 251 to 254 are formed to have
small diameter portions 251b to 254b slightly larger than the
inner diameters (but smaller than the outer diameters) of the
nut blank 201, respectively, on the small diameter side of
the outer circumferential surface.
25 [0119]
Thus, restraining surfaces 251c to 254c to be in contact
with a top end surface of the nut blank 201 are provided at
the boundaries between the large diameter portions 251a to
73
254a and the small diameter portions 251b to 254b,
respectively. Additionally, depressed portions 251d to 254d
corresponding to the letter S shaped convexes 235A to 235D
of the cam slider 203 are provided at the large diameter
portions 251a to 254a of the inner circumferential surface5 s
of the divided bodies 251 to 254, respectively. The large
diameter portions 251a to 254a of the inner circumferential
surfaces of the divided bodies 251 to 254 respectively
correspond to the inner circumferential surfaces for
10 receiving the outer circumferential surface of the nut blank
201.
[0120]
The outside member 206 is a cylindrical body having an
inner circumferential surface 261 corresponding to the
15 tapered outer circumferential surface of the restraining
member 205, and the same outer surface with the outer surface
shape of the stand 204.
By using this die, the letter S shaped concaves of the
four ball return passages on the inner surface of the nut blank
20 201 are formed in the following method.
Firstly, the nut blank 201 is disposed at the center of
the stand 204 so that the inner circumferential surface of
the nut blank 201 matches the inner circumferential surface
of the concave 241. Next, the divided bodies 251 to 254 of
25 the restraining member 205 are disposed on the stand 204 so
that the large diameter portions 251a to 254a of the inner
circumferential surface are brought into contact with the
outer circumferential surface of the nut blank 201 and the
74
restraining surfaces 251c to 254c are brought into contact
with the upper end surface of the nut blank 201. Then, the
outside member 206 is disposed on the stand 204 so that the
inner circumferential surface 261 is brought into contact
with the tapered outer circumferential 5 l surface of the
restraining member 205.
In this state, the outside member 206 is secured to the stand
204.
[0121]
10 Thus, the movements of the divided bodies 251 to 254
forming the restraining member 205 outwardly in the radial
direction are regulated at the outside member 206, and both
end surfaces in the axial direction and the outer
circumferential surface of the nut blank 201 are brought into
15 the restraining state at the restraining member 205 and the
stand 204.
Subsequently, the cam sliders 203A to 203D are inserted
into the nut blank 201 with the outer circumferential surfaces
231 facing the inner circumferential surface of the nut blank
20 201. Thus, a space is formed by the four inclined surfaces
233 of the cam sliders 203A to 203D so that the cam driver
202 is inserted thereinto. Then, an end of the main body
portion 222 of the cam driver 202 is inserted into this space.
FIG. 22A illustrates this state.
25 [0122]
Next, the cam driver 202 is pressed from the top thereof
under pressure, a force is transmitted from the inclined side
surfaces 222a to 222d of the cam driver 202 to the inclined
75
surfaces 233 of the cam sliders 203A to 203D. In accordance
with this, a downward force of the cam driver 202 is converted
into forces of moving the cam sliders 203A to 203D outwardly
in the radial direction, and then the letter S shaped convexes
235A to 235D arranged in the cam sliders 203A 5 A to 203D push
the inner circumferential surface 211 of the nut blank 201
for plastic deformation, respectively. In accordance with
this, the material existing in the outer circumferential
portion of the nut blank 201 is pushed into the depressed
10 portions 251d to 254d of the divided bodies 251 to 254
constituting the restraining member 205. FIG. 22B
illustrates this state.
[0123]
Thus, the letter S shaped concaves 212A to 212D of the
15 four ball return passages are formed on the inner
circumferential surface 211 of the nut blank 201,
respectively. Additionally, the outer circumferential
portion of the nut blank 201 protrudes into the depressed
portions 251d to 254d of the divided bodies 251 to 254
20 constituting the restraining member 205, and projections 213A
to 213D are formed.
FIG. 25 illustrates the nut blank 201 where the letter
S shaped concaves 212A to 212D and the projections 213A to
213D are provided in this method. FIG. 25A is a front view,
25 FIG. 25B is a cross-sectional view taken along line A-A; FIG.
25C is a view when viewed in arrow B, and FIG. 25D is a
perspective view. The nut of the ball screw is manufactured
76
by arranging a spiral groove and a seal attaching groove in
the nut blank 201.

CLAIMS
1. A method for manufacturing a nut for a ball screw,
the ball screw comprising: the nut having an inner
circumferential surface on which a spiral groove is formed5 ;
a threaded shaft having an outer circumferential surface on
which a spiral groove is formed; balls loaded in a raceway
between the spiral groove of the nut and that of the threaded
shaft; and a ball return passage arranged as a concave on the
10 inner circumferential surface of the nut for returning the
balls from an end point of the raceway to a start point of
the raceway, the balls being rolling in the raceway to make
the nut relatively move with respect to the threaded shaft,
wherein the concave is formed on the inner
15 circumferential surface of the nut blank by plastic working
in a pressing method by use of a die of a cam mechanism, the
cam mechanism comprising: a cam driver inserted into a
cylindrical nut blank and moving in an axial direction of the
nut blank at the time of processing; and a cam slider disposed
20 between the nut blank and the cam driver and provided with
a convex corresponding to the concave, a movement of the cam
driver causing the convex to move in a radial direction of
the nut.
25 2. The method for manufacturing the nut for the ball
screw according to claim 1,
wherein a plurality of the concaves are formed on the
inner circumferential surface of the nut, and at least one
220
of a plurality of the convexes corresponding to the plurality
of the concaves is formed on the cam slider.
3. The method for manufacturing the nut for the ball
screw according to 5 claim 1,
wherein, as the die, the cam driver includes a load
receiving surface parallel to the axial direction of the nut
blank, and pressing is performed by use of the die having
another member, other than the cam driver, provided with a
10 load receiving surface to be in contact with the load
receiving surface.
4. The method for manufacturing the nut for the ball
screw according to claim 3,
15 wherein, as the die, the cam slider is held by a holding
member, disposed between the cam driver and the nut blank,
and pressing is performed by use of the die in which the holding
member is provided with the load receiving surface.
20 5. The method for manufacturing the nut for the ball
screw according to claim 2, wherein the plurality of the
concaves are formed in a uniform manner by changing a movement
amount of the plurality of the convexes, formed on a plurality
of the cam sliders, moving outwardly in the radial direction
25 of the nut blank.
6. The method for manufacturing the nut for the ball
screw according to claim 1, wherein by pressing method by use
221
of the die of the cam mechanism including the cam driver, the
cam slider, and a restraining member for restraining both end
surfaces in the axial direction and an outer circumferential
surface of the nut blank and having a depressed portion to
correspond to the convex on an inner circumferential surfac5 e
that receives the outer circumferential surface, the concave
is formed on the inner circumferential surface of the nut
blank by pressing the inner circumferential surface of the
nut blank with the convex to protrude the outer
10 circumferential portion of the nut blank into the depressed
portion of the restraining member.
7. The method for manufacturing the nut for the ball
screw according to claim 1,
15 wherein a part of an outer circumferential surface of
the nut is formed at a position having a distance from a central
axis of the nut to be shorter than a radius of another part
having a circular shape on the outer circumferential surface
of the nut,
20 wherein the convex is pressed into the inner
circumferential surface of the nut to form a concave so as
to form a projection projecting on the outer circumferential
of the nut on the part of the outer circumferential surface
of the nut, and
25 wherein in the part of the outer circumferential surface,
the projection is arranged such that the distance from the
central axis of the nut to be shorter than a radius of said
another part having a circular shape.
222
8. The method for manufacturing the nut for the ball
screw according to claim 1, wherein forming of the concave
permits a material in the nut to flow and flowing of the
material is adjusted in accordance 5 ordance with a shape of the
concave.
9. The method for manufacturing the nut for the ball
screw according to claim 8, wherein the flowing of the
10 material to an outer circumference side is adjusted in
accordance with the shape of the concave.
10. The method for manufacturing the nut for the ball
screw according to claim 8, wherein flowing of the material
15 to an end portion side in the axial direction of the nut is
adjusted in accordance with the shape of the concave.
11. The method for manufacturing the nut for the ball
screw according to claim 1, wherein the convex is pressed into
20 the inner circumferential surface of the nut to form the
concave, and a concave for shear droop for reducing the shear
droop in the concave generated by plastic working with the
convex is formed around the concave in the inner
circumferential surface of the nut.
25
12. The method for manufacturing the nut for the ball
screw according to claim 11, wherein the concave for shear
droop is formed adjacent to a part where the concave curves.
223
13. The method for manufacturing the nut for the ball
screw according to claim 11, wherein a shape and a depth of
the concave for shear droop are determined in accordance with
an amount 5 nt of the shear droop.
14. The method for manufacturing the nut for the ball
screw according to claim 1, wherein an excess material portion
for reducing shear droop of the concave is provided to
10 protrude from the inner circumferential surface having a
circular shape of the nut, and the convex is pressed into the
excess material portion to form the concave.
15. The method for manufacturing the nut for the ball
15 screw according to claim 14, wherein the excess material
portion has a shape corresponding to that of the concave.
16. The method for manufacturing the nut for the ball
screw according to claim 1, wherein after a base concave to
20 be included in a cross-sectional arc of the concave is formed
at a position where the concave is to be formed on the inner
circumferential surface of the cylindrical nut blank, the cam
slider inserted into the nut blank is moved outwardly in the
radial direction of the nut blank with restraining the outer
25 circumferential surface and an end surface in the axial
direction of the nut blank to form the concave.
224
17. A method for manufacturing the nut for the ball
screw, the method comprising:
a ball return passage forming process of forming the
concave in the method according to claim 1;
a spiral groove forming process of forming 5 orming the spiral
groove to be in contact with an end portion of the concave
on the inner circumferential surface of the nut; and
a burr removing process of removing burr by performing
at least one of brushing and blasting at a boundary portion
10 between the concave and the spiral groove.
18. A ball screw comprising the nut for the ball screw
manufactured in the method according to claim 6, wherein a
projection is arranged at a position corresponding to the
15 concave of the outer circumferential surface of the nut.
19. A ball screw comprising:
a nut having an inner circumferential surface on which
a spiral groove is formed;
20 a threaded shaft having an outer circumferential surface
on which a spiral groove is formed;
balls loaded in a raceway between the spiral groove of
the nut and that of the threaded shaft; and a ball circulation
groove for returning the balls from an end point of the raceway
25 to a start point of the raceway, the balls being rolling in
the raceway to make the nut relatively move with respect to
the threaded shaft,
225
wherein the nut is manufactured in the method for
manufacturing the nut according to claim 1, and
wherein at least one of corner portions defined by both
of side surfaces of the ball circulation passage and a surface
axially extending and continuous 5 nuous with each of the side
surfaces is rounded.
20. A ball screw comprising:
a threaded shaft having an outer circumferential surface
10 on which a spiral groove is formed;
a nut having an inner circumferential surface on which
a spiral groove opposing the spiral groove of the threaded
shaft is formed;
a plurality of balls rotatably loaded in a ball rolling
15 passage having a spiral shape provided by both of the spiral
grooves; and
a ball circulation passage for returning the balls from
an end point of the ball rolling passage to a start point of
the ball rolling passage,
20 wherein the nut is manufactured in the method for
manufacturing the nut according to claim 1,
wherein the ball circulation passage includes a concaved
groove formed by concaving a groove on a part of the inner
circumferential surface of the nut, and a lubricant reservoir
25 capable of holding a lubricant, and
wherein the lubricant reservoir is made of a dented
portion by concaving a groove on a part of an inner surface
of the concaved groove.
226
21. The ball screw according to claim 20,
wherein the ball circulation passage includes both of
end portions that are connecting portions with the ball
rolling passage and a middle portion 5 rtion between both of the end
portions, and
wherein as to a cross-sectional area of the lubricant
reservoir cut along a plane perpendicular to a lengthwise
direction of the ball circulation passage, the
10 cross-sectional area of a part adjacent to the middle portion
is larger than that of a part adjacent to each of the end
portions.
22. The ball screw according to claim 20,
15 wherein the ball circulation passage is curved, and
wherein as to a cross-sectional area of the lubricant
reservoir cut along a plane perpendicular to a lengthwise
direction of the ball circulation passage, the
cross-sectional area of the lubricant reservoir arranged on
20 the inside in a radial direction of a curve of the ball
circulation passage is larger than that of the lubricant
reservoir arranged on the outside in the radial direction of
the curve of the ball circulation passage.
25 23. The ball screw according to claim 20, wherein the
concaved groove constituting the ball circulation passage and
the dented portion constituting the lubricant reservoir are
formed at the same time by forging.
227
24. A ball screw comprising the nut manufactured in
the method for manufacturing the nut for the ball screw
according to claim 1, wherein at least a part of a lengthwise
direction of the ball return 5 n passage has a substantially
letter V shaped cross-section, when the ball return passage
is cut along a plane perpendicular to the lengthwise
direction.
10 25. A ball screw comprising the nut manufactured in
the method for manufacturing the nut for the ball screw
according to claim 1, wherein a flange protruding inwardly
in the radial direction from a marginal edge portion of the
concave at a connecting part of the spiral groove of the nut
15 and the concave is provided.
26. The ball screw according to claim 25,
wherein both end portions of the concave that is a
connecting part with the spiral groove of the nut constitutes
20 a straight shaped ball entering portion, and
wherein the flange is arranged at least at a marginal
edge portion of the straight shaped ball entering portion.
27. The ball screw according to claim 25,
25 wherein a distance H between an end of the flange and
a radial center of the nut is equal to or smaller than 1/2
of ball circle diameter (BCD), and
228
wherein the flange is arranged not to be in contact with
the outer circumferential surface of the threaded shaft.