U.S. patent application number 14/895123 was filed with the patent office on 2016-04-28 for method for manufacturing rack and hollow rack bar.
The applicant listed for this patent is NETUREN CO., LTD.. Invention is credited to Kenichi AOKI, Ryosuke SUZUKI, Takashi YAMAWAKI.
Application Number | 20160116049 14/895123 |
Document ID | / |
Family ID | 51059512 |
Filed Date | 2016-04-28 |
United States Patent
Application |
20160116049 |
Kind Code |
A1 |
YAMAWAKI; Takashi ; et
al. |
April 28, 2016 |
METHOD FOR MANUFACTURING RACK AND HOLLOW RACK BAR
Abstract
Method of fabricating a rack including: supporting a first rack
bar 12A having a first toothed part 12a on a shaft of the first
rack bar; supporting a second rack bar 12B having a second toothed
part 12b on a shaft of the second rack bar such that an axial
center line of the second rack bar coincides with an axial center
line of the first rack bar; supporting a joint member 15 between
the first and second rack bars such that an axial center line of
the joint member coincides with the axial center lines of the first
and second rack bars; rotating the joint member 15 about the axial
center lines of the first and second rack bars relative to the
first and second rack bars; and simultaneously bringing an end of
the first rack bar and an end of the second rack bar into friction
pressure welding with the joint member.
Inventors: |
YAMAWAKI; Takashi;
(Shinagawa-ku, Tokyo, JP) ; SUZUKI; Ryosuke;
(Shinagawa-ku, Tokyo, JP) ; AOKI; Kenichi;
(Shinagawa-ku, Tokyo, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
NETUREN CO., LTD. |
Tokyo |
|
JP |
|
|
Family ID: |
51059512 |
Appl. No.: |
14/895123 |
Filed: |
May 30, 2014 |
PCT Filed: |
May 30, 2014 |
PCT NO: |
PCT/JP2014/065024 |
371 Date: |
December 1, 2015 |
Current U.S.
Class: |
74/422 ;
228/114.5 |
Current CPC
Class: |
B23K 20/129 20130101;
F16H 55/26 20130101; B23K 37/0443 20130101; B23K 20/12 20130101;
B23K 20/1205 20130101; B23K 2103/04 20180801 |
International
Class: |
F16H 55/26 20060101
F16H055/26; B23K 20/12 20060101 B23K020/12 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 3, 2013 |
JP |
2013-117096 |
Claims
1. A method of fabricating a rack, the method comprising:
supporting a first rack bar having a first toothed part on a shaft
of the first rack bar; supporting a second rack bar having a second
toothed part on a shaft of the second rack bar such that an axial
center line of the second rack bar coincides with an axial center
line of the first rack bar; supporting a joint member between the
first and second rack bars such that an axial center line of the
joint member coincides with the axial center lines of the first and
second rack bars; rotating the joint member about the axial center
lines of the first and second rack bars relative to the first and
second rack bars; and simultaneously bringing an end of the first
rack bar and an end of the second rack bar into friction pressure
welding with the joint member.
2. The method according to claim 1, wherein a rotation of the joint
member is performed by a jig for providing a rotating force and an
engaging part provided for the engagement with the jig so as to
prevent a sliding motion of the joint member about the axial center
line of the joint member.
3. A hollow rack bar comprising: a first rack bar that has a first
toothed part on a hollow shaft of the first rack bar; a second rack
bar that has a second toothed part on a hollow shaft of the second
rack bar, wherein an axial center line of the second rack bar
coincides with an axial center line of the first rack bar; and a
joint member that is disposed between the first and second rack
bars such that an axial center line of the joint member coincides
with the axial center lines of the first and second rack bars and
one end surface of the joint member is engaged with the first rack
bar and the other end surface of the joint member is engaged with
the second rack bar.
4. The hollow rack bar according to claim 3, wherein the first and
second rack bars have different outer diameters.
Description
TECHNICAL FIELD
[0001] The present invention relates to a method of forming a rack
to fabricate a rack bar used for a steering device for a vehicle
and a rack bar having the rack, which method is adapted
particularly to an electric power steering device, in which a
steering wheel is steered by a slide motion of a rack shaft to be
geared with a steering pinion connected to the steering side and at
the same time, the output of a motor to be controlled by steering
torque is transmitted to an auxiliary pinion which is spaced apart
from the steering pinion and is geared with the rack shaft, thereby
accessorily supporting the steering operation.
BACKGROUND ART
[0002] An electric power steering device has been known to include
a double-type mechanism (referred hereinafter to as a
`double-pinion type`) in which two rack and pinions are provided.
In the meantime, it is general that the two racks provided at two
sites have different rotational phases with respect to the central
line of a shaft.
[0003] In the rack bar for use in such a double-pinion type, the
two-part racks have been formed by the following method.
Specifically, a solid rack bar made of a material, such as e.g. JIS
S45C carbon steel, is tooth-cut at two sites by a broaching
machine. The rotational phases are controlled by numerical control
(NC).
[0004] In addition, in a case of a hollow rack bar, rotational
phases of toothed parts are NC-controlled at the time when
flat-crushing machining is carried out. Further, in a case of a
frictional press joined rack bar, solid or hollow materials having
toothed parts are jointed together by means of frictional
press-joining (see e.g. JP 3772110 B2).
SUMMARY OF INVENTION
[0005] The fabrication method for the rack bar for use in the
double-pinion type however has problems as follows: That is, in the
case of the solid rack bar, the toothed parts are provided on
either axial side of the rack bar, so that machining such as gun
drilling or the like cannot be carried out and the whole weight of
the rack bar increases as well. In addition, in case of the hollow
rack bar, while it is possible to make the rack bar lighter, the
rotational phases of the toothed parts can be dislocated during
post tooth-formation and annealing processes, even though a
difference between the rotational phases of the toothed parts was
previously determined at the time when the flat crushing machining
was carried out. Further, in the case of the frictional
press-joined rack bar, two-way taking or drilling is required
because of the positioning in a rotational direction. Furthermore,
degradation in precision of a position, which occurs due to
deviation of rotational direction or centering, is not appropriate
to the electric power steering device.
[0006] Accordingly, an object of the present invention is to
provide a method of forming a rack which is capable of precisely
positioning two toothed parts at a specified degree of phase
difference, and a hollow rack bar having the rack.
[0007] In order to accomplish the object, the present invention
provides a method of fabricating a rack and a hollow rack bar
having the rack.
[0008] In a method of fabricating a rack, the method includes:
supporting a first rack bar having a first toothed part on a shaft
of the first rack bar; supporting a second rack bar having a second
toothed part on a shaft of the second rack bar such that an axial
center line of the second rack bar coincides with an axial center
line of the first rack bar; supporting a joint member between the
first and second rack bars such that an axial center line of the
joint member coincides with the axial center lines of the first and
second rack bars; rotating the joint member about the axial center
lines of the first and second rack bars relative to the first and
second rack bars; and simultaneously bringing an end of the first
rack bar and an end of the second rack bar into friction pressure
welding with the joint member.
[0009] A hollow rack bar includes first and second rack bars and a
joint member. The first rack bar has a first toothed part on a
hollow shaft of the first rack bar. The second rack bar has a
second toothed part on a hollow shaft of the second rack bar. An
axial center line of the second rack bar coincides with an axial
center line of the first rack bar. The joint member is disposed
between the first and second rack bars such that an axial center
line of the joint member coincides with the axial center lines of
the first and second rack bars. One end surface of the joint member
is engaged with the first rack bar and the other end surface of the
joint member is engaged with the second rack bar.
[0010] According to the present invention, it is possible to
position two toothed parts at a specified degree of phase
difference in high precision (with respect to
deviation/bending/inclination or the like of shaft center).
BRIEF DESCRIPTION OF DRAWINGS
[0011] FIG. 1 is a view showing a rack and pinion mechanism having
a double-pinion rack bar, which is fabricated by a method of
fabricating a rack according to an embodiment of the present
invention.
[0012] FIG. 2 is a plan view showing the double-pinion rack
bar.
[0013] FIG. 3 is a perspective view showing a joint member provided
in the double-pinion rack bar.
[0014] FIG. 4 is a view showing a procedure of manufacturing the
double-pinion rack bar.
[0015] FIG. 5 is a view showing a procedure of manufacturing the
double-pinion rack bar.
[0016] FIG. 6 is a view showing a procedure of manufacturing the
double-pinion rack bar.
[0017] FIG. 7 is a view showing a procedure of manufacturing the
double-pinion rack bar.
[0018] FIG. 8 is a view showing a procedure of manufacturing the
double-pinion rack bar.
[0019] FIG. 9 is a view showing a procedure of manufacturing the
double-pinion rack bar.
[0020] FIG. 10 is a view showing a procedure of manufacturing the
double-pinion rack bar.
[0021] FIG. 11 is a view showing a procedure of manufacturing the
double-pinion rack bar.
[0022] FIG. 12 is a plan view showing a double-pinion rack bar
using a joint member according to a modified embodiment of the
present invention.
[0023] FIG. 13 is a perspective view showing the joint member.
DESCRIPTION OF EMBODIMENTS
[0024] FIG. 1 is a view showing a rack and pinion mechanism having
a double-pinion rack bar 12, which is fabricated by a method of
fabricating a rack according to a first embodiment of the present
invention, FIG. 2 is a plan view showing the double-pinion rack bar
12, FIG. 3 is a perspective view showing a joint member provided in
the double-pinion rack bar 12, and FIGS. 4 to 11 are views showing
a procedure of manufacturing the double-pinion rack bar 12.
[0025] The rack and pinion mechanism 10 includes a substantially
cylindrical rack housing 11 which extends in a transverse direction
of a vehicle, and the double-pinion rack bar 12 is accommodated in
the rack housing 11 in such a way as to be slidably movable in a
transverse axial direction of the rack housing.
[0026] The double pinion rack bar 12 extends outwards from opposite
end-openings of the rack housing 11, and tie rods 13 and 13 are
respectively coupled to both ends of the double pinion rack bar via
respective joints, wherein the tie rods 13 and 13 extend laterally
from boots 14 and 14 which respectively cover the joints. In
operation, a motion of the double pinion rack bar 12 causes a
motion of the tie rods 13 and 13, which in turn allows a steering
wheel of a vehicle to be steered by a steering device.
[0027] A steering gear box 20 is provided at a right-side end of
the rack housing 11. An input shaft 21, which is connected to a
steering shaft, to which a steering wheel is integrally attached,
via a joint, is supported by the steering gear box such that the
input shaft is able to pivot by means of a bearing. The input shaft
21 is provided with a steering pinion (not shown).
[0028] The steering pinion is geared with a rack-toothed part (a
first toothed part) 12a of the double pinion rack bar 12. The
steering force transmitted to the input shaft 21 according to the
turning manipulation of the steering wheel rotates the steering
pinion having a diagonally toothed part engaged with the toothed
part 12a, allowing the double pinion rack bar 12 to be slidably
moved in a transverse axial direction.
[0029] An auxiliary gear box 30 is provided on a left-side end of
the rack housing 11. The auxiliary gear box 30 includes a pinion
cylinder part 31, which extends in a slightly tilted vertical
direction with respect to the rack housing 11, and a rack guide
cylinder part 32 extending perpendicular to the vertical
direction.
[0030] An auxiliary pinion (not shown) is accommodated in the
pinion cylinder part 31 such that the auxiliary pinion is geared
with a rack-toothed part (a second toothed part) 12b of the double
pinion rack bar 12. A motor 33 is attached to the auxiliary gear
box 30, such that a driving shaft of the motor 33 rotates the
auxiliary pinion having a diagonally toothed part meshed with the
rack-toothed part 12b of the double pinion rack bar 12, allowing
the double pinion rack bar 12 to be slidably moved in a transverse
axial direction.
[0031] The motor 33 is controlled depending upon steering torque of
the steering wheel detected through the input shaft 21. The
steering action is performed in such a manner that an input
steering force is transmitted to the double pinion rack bar 12 via
the steering pinion, and the driving force of the motor 33 to be
controlled by the steering torque is applied to the same double
pinion rack bar 12 via the auxiliary pinion, thereby performing
steering action while supporting the input.
[0032] FIG. 2 is a plan view showing the double rack bar 12. The
double rack bar 12 has first and second toothed parts 12a and 12b,
which respectively have angular positions (phases) with respect to
an axis of the double pinion rack bar, which are different from
each other by approximately 0 to 90 degrees.
[0033] In addition, the double pinion rack bar 12 consists of a
first rack bar 12A which is formed with a hollow shaft and has the
first toothed part 12a, a second rack bar 12B which is formed with
a hollow shaft and has the second toothed part 12b, and a joint
member 15, wherein the first and second rack bars and the joint
member are coupled together with respective axial center lines
aligned with each other.
[0034] The joint member 15 includes a cylindrical joint body 15a
and opposite planar parts (engaging parts) 15b on opposite sides
thereon. The planar parts 15b form so called two-way taking
engaging parts. In FIG. 2, reference signs 15c and 15d respectively
indicate one-side end and another-side end, which are provided for
the connection with friction pressure welding surfaces Qa and Qb
which will be described later. In addition, the joint body 15a may
have a cylindrical shape.
[0035] The joint member 15 may be composed of the same material as
the first and second rack bars 12A and 12B or other metal material
which is suitable for friction pressure welding working.
Specifically, S34C carbon steel or the like, which has been widely
used as an industrial material, may be proper because the steel is
cost-effective, is easily available, is easily cut-processed, and
has a proper strength.
[0036] The double pinion rack par 12 having the above-mentioned
construction is fabricated in the following manner. As shown in
FIG. 4, first and second rack bars 12A and 12B on which the rack
toothed parts 12a and 12b are respectively previously formed are
prepared. In FIG. 4, reference signs Qa and Qb indicate friction
pressure welding surfaces for a joint member 15. Here, before the
friction pressure welding, the first and second toothed parts 12a
and 12b of the first and second rack bars 12A and 12B, and the
friction pressure welding surfaces Qa and Qb are cut to have the
squareness, so that the straightness of the entire rack bar after
friction pressure welding can be secured in high precision
degree.
[0037] Next, as shown in FIG. 5, a joint member 15 is arranged
between the first and second rack bars 12A and 12B with its axial
center line aligned with those of the first and second rack bars
12A and 12B. Meanwhile, opposite-side surfaces 15c and 15d of the
joint member 15 maintain high-leveled parallelization.
[0038] Next, as shown in FIG. 6, the first and second rack bars 12A
and 12B are fixed such that the rack bars are not rotated about the
axial center line.
[0039] Next, as shown in FIG. 7, the planar parts 15b of the joint
member 15 are engaged with a jig 100. Then, as shown in FIG. 8, the
jig 100 is rotated about the axial center line. Then, as shown in
FIG. 9, the first rack bar 12A is axially pressed against one-side
surface of the joint member 15 and at the same time, the second
rack bar 12B are axially pressed against the other-side surface of
the joint member 1. Reference sign P in FIG. 9 indicates a joint
part.
[0040] Accordingly, fiction heat is generated to cause a metal
structure to change, and pressure is applied as well, so that the
first rack bar 12A and the second rack bar 12B are respectively
bonded to the joint member 15.
[0041] Further, as shown in FIG. 10, the rotation of the jig 100 is
stopped. Here, a phase difference with respect to axial center line
between the first and second rack bars 12A and 12B is set to a
predetermined value. In the meantime, the degree of precision in
determining a phase is about .+-.0.1.degree., which does not cause
a problem in practical use
[0042] Next, as shown in FIG. 11, the first rack bar 12A and the
second rack bar 12B are decoupled from each other, thereby forming
a double pinion rack bar 12.
[0043] In the method of fabricating the double pinion rack bar, two
rack bars can be fabricated in a conventional working manner.
Further, since the two rack bars are simultaneously coupled at both
surfaces in a friction pressure welding manner using the joint
member 15, it is possible to secure peripheral position-precision,
and coaxiality/straightness of the rack toothed parts 12a and 12b
at two sites in high precision. Accordingly, a double pinion rack
bar adaptable to an electric power steering device can be
obtained.
[0044] In addition, since it is possible to use a hollow shaft
member, in a case of 26 mm diameter member, the hollow shaft member
can be reduced in weight by about 40% to 50% compared to a solid
shaft member.
[0045] Meanwhile, the joint member 15 may be cut to have an outer
diameter to suit an outer diameter of the first and second rack
bars 12A and 12B.
[0046] FIG. 12 is a plan view showing a double pinion rack bar 12
using a joint member 16 modified from the above embodiment. FIG. 13
is a perspective view showing the joint member 16. In FIG. 12, the
same functional parts as in FIGS. 1 and 2 are assigned as the same
reference signs as in FIG. 3, and a detailed description thereof
will be omitted.
[0047] The joint member 15 is formed into a cylindrical shape which
is provided with a central through-hole (engaging hole) 16b. A jig
100 is engaged with the through-hole 16b. In addition, reference
signs 16c and 16d in FIG. 13 indicate opposite-side ends for the
engagement with the friction pressure welding surfaces Qa and Qb,
respectively.
[0048] The case using the modified joint member 16 may also have
the same effects as the case of fabricating the double pinion rack
bar 12 using the above-mentioned joint member 15.
[0049] In the meantime, although the present embodiment illustrates
that the rack bar having the hollow shaft and the rack bar having
the hollow shaft are engaged together, it is possible to accomplish
other combination such as a rack bar having a solid shaft and a
rack bar having a solid shaft, or a rack bar having a hollow shaft
and a rack bar having a solid shaft, which can be arranged opposite
the combination of a rack bar having a hollow shaft and a rack bar
having a solid shaft. Thus, hollow or solid shafts can be selected
and bonded together depending upon a desired function, so the
degree of freedom in designing the double pinion rack bar can be
increased.
[0050] Further, since the rack bar disposed on either steering-side
or assist-side side is subjected to a cold sequential forming
suitable for forming a complex shaped toothed part such as VGR or
the like while forming a toothed part having a shape in which a
sufficient tooth width or tooth height is simply required, a shape
such as CGR or the like may be set to have a combination of tooth
shapes capable of implementing desired performance.
[0051] Furthermore, the first and second rack bars 12A and 12B may
have different outer diameters.
[0052] Of course, the present invention is not limited to the
above-mentioned embodiment, but may be modified into a variety of
forms without departing from the scope of the present
invention.
[0053] This application is based on Japanese Patent Application No.
2013-117096 filed on Jun. 3, 2013, the entire content of which is
incorporated herein by reference.
* * * * *