U.S. patent application number 09/972234 was filed with the patent office on 2002-04-04 for power roller bearing of toroidal-type continuously variable transmission unit.
This patent application is currently assigned to NSK Ltd.. Invention is credited to Goto, Nobuo, Imanishi, Takashi, Itoh, Hiroyuki, Murakami, Yasuo, Yoshikawa, Tomonobu.
Application Number | 20020039949 09/972234 |
Document ID | / |
Family ID | 26439950 |
Filed Date | 2002-04-04 |
United States Patent
Application |
20020039949 |
Kind Code |
A1 |
Itoh, Hiroyuki ; et
al. |
April 4, 2002 |
Power roller bearing of toroidal-type continuously variable
transmission unit
Abstract
A power roller bearing of a toroidal-type continuously variable
transmission unit that is used for a transmission of an automobile
or the like comprises a power roller, an outer race, balls, a
retainer, etc. Annular raceway grooves are formed individually on
the respective opposite end faces of the outer race and the power
roller. Treated-surface layers for enhancing the endurance of the
power roller bearing are formed individually on the respective
surfaces of the raceway grooves. The treated-surface layers include
super-finished surfaces with the surface roughness of 0.05 Ra or
less, formed individually on the raceway grooves, and low-friction
layers formed individually on the super-finished surfaces.
Alternatively, the treated-surface layers include residual
compression stress layers formed on the respective surface layer
portions of the raceway grooves by shot-peening.
Inventors: |
Itoh, Hiroyuki;
(Fujisawa-shi, JP) ; Imanishi, Takashi;
(Yokohama-shi, JP) ; Goto, Nobuo; (Fujisawa-shi,
JP) ; Murakami, Yasuo; (Hadano-shi, JP) ;
Yoshikawa, Tomonobu; (Yamato-shi, JP) |
Correspondence
Address: |
CHRISTENSEN O'CONNOR JOHNSON & KINDNESS PLLC
Suite 2800
1420 Fifth Avenue
Seattle
WA
98101-2347
US
|
Assignee: |
NSK Ltd.
|
Family ID: |
26439950 |
Appl. No.: |
09/972234 |
Filed: |
October 5, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
09972234 |
Oct 5, 2001 |
|
|
|
PCT/JP00/02201 |
Apr 5, 2000 |
|
|
|
Current U.S.
Class: |
476/46 ;
476/40 |
Current CPC
Class: |
F16C 2240/54 20130101;
F16C 19/10 20130101; Y02T 10/86 20130101; F16C 33/585 20130101;
F16C 33/64 20130101; Y02T 10/865 20130101; F16C 2361/65 20130101;
F16H 15/38 20130101 |
Class at
Publication: |
476/46 ;
476/40 |
International
Class: |
F16H 015/38 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 6, 1999 |
JP |
11-098841 |
Apr 6, 1999 |
JP |
11-098842 |
Claims
What is claimed is:
1. In a power roller bearing of a toroidal-type continuously
variable transmission unit, which is provided for swinging motion
between an input disc capable of being rotated by means of a drive
source and an output disc opposed to said input disc, the power
roller bearing of the toroidal-type continuously variable
transmission unit comprising: an outer race; a power roller in
rolling contact with said input disc and output disc; and balls
provided for rolling motion between said outer race and said power
roller, said outer race and said power roller having annular
raceway grooves in which said balls roll individually, at least one
of the respective raceway grooves of said outer race, heat-treated
and ground, and said power roller being formed having
treated-surface layers including super-finished surfaces with the
surface roughness of 0.05 Ra or less and residual compression
stress layers shot-peened so that the residual compression stress
therein ranges from -20 kgf/mm.sup.2 to -100 kgf/mm.sup.2.
2. In a power roller bearing of a toroidal-type continuously
variable transmission unit, which is provided for swinging motion
between an input disc capable of being rotated by means of a drive
source and an output disc opposed to said input disc, the power
roller bearing of the toroidal-type continuously variable
transmission unit comprising: an outer race; a power roller in
rolling contact with said input disc and output disc; and balls
provided for rolling motion between said outer race and said power
roller, said outer race and said power roller having annular
raceway grooves in which said balls roll individually, both of the
respective raceway grooves of said outer race and said power roller
being formed having super-finished surfaces with the surface
roughness of 0.05 Ra or less and low-friction layers on at least
one of the super-finished surfaces, the low-friction layers being
formed of at least one of lubricative substances including gold,
silver, lead, molybdenum disulfide, tungsten disulfide, and
fluoroplastics.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This is a Continuation Application of PCT Application No.
PCT/JP00/02201, filed Apr. 5, 2000, which was not published under
PCT Article 21(2) in English.
[0002] This application is based upon and claims the benefit of
priority from the prior Japanese Patent Applications No. 11-098841,
filed Apr. 6, 1999; and No. 11-098842, filed Apr. 6, 1999, the
entire contents of both of which are incorporated herein by
reference.
BACKGROUND OF THE INVENTION
[0003] 1. Field of the Invention
[0004] The present invention relates to a power roller bearing of a
toroidal-type continuously variable transmission unit adapted to be
used for a transmission of, for example, an automobile, general
industrial machine, transportation equipment, etc.
[0005] 2. Description of the Related Art
[0006] A toroidal-type continuously variable transmission unit
adapted to be used for a transmissions of, for example, an
automobile, general industrial machine, transportation equipment,
etc. comprises an input disc and an output disc opposed to each
other, a power roller provided between the input and output discs,
a loading cam mechanism for pushing the input and output discs
toward each other, etc.
[0007] The input disc can be rotated by means of a drive source
such as an engine. Power that is based on the rotation of the input
disc is transmitted to the output disc through the power roller.
The power roller is provided for swinging motion between the input
disc and the output disc. The power roller is provided with
traction portions that are in rolling contact with the two discs,
individually. The power roller is rotatably supported by means of a
power roller bearing that functions as a thrust bearing.
[0008] The power roller bearing is provided with an end portion of
the power roller that functions as an inner race, an outer race,
balls provided for rolling motion between the outer race and the
power roller, etc. The power roller is supported for swinging
motion between the input disc and the output disc by means of a
trunnion. The gear ratio of the toroidal-type continuously variable
transmission unit can be changed by changing the angle of
inclination of the power roller.
[0009] The power roller bearing constructed in this manner hardly
apparently differs from a conventional thrust ball bearing that is
used to support a rotating shaft on which thrust load acts except
for the arrangement of the power roller. Accordingly, a study has
been made to produce power roller bearings at low cost by using
parts that are designed for existing thrust ball bearings.
[0010] Although a power roller bearing apparently resembles a
thrust ball bearing, however, its power roller functions quite
differently from the inner race of the conventional thrust ball
bearing. More specifically, the distribution of load that acts on
the power roller itself and the behavior of the balls in contact
with the outer race and the power roller considerably differ from
those of the conventional thrust ball bearing, so that improvement
must inevitably be made in consideration of those differences.
[0011] While the inner race of the conventional thrust ball bearing
is a member that simply supports a shaft, for example, the power
roller functions as a power transmitting member for transmitting
torque from the input disc to the output disc. This power roller is
equivalent to a transmission gear in a gear-type multistage
transmission. The power roller of this type rotates at high speed
under heavy forces of pressure from the input disc and the output
disc, so that it generates intense heat. The heat from the power
roller serves to heat the balls and the like. Thus, it is essential
to use high-viscosity traction oil, which is developed for the
purpose of power transmission, as lubricating oil to be supplied
between the outer race and the power roller.
[0012] The traction portions of the power roller that touch the
input disc and the output disc face each other at a circumferential
distance of 180.degree. on the outer peripheral edge of the power
roller. The heavy forces of pressure from the input disc and the
output disc intensively act on the traction portions of the power
roller as a resultant force that combines radial load and thrust
load. Thus, a very high contact pressure develops in the traction
portions of the power roller that touch the input disc and the
output disc.
[0013] A conventional bearing is used under a contact pressure of 2
to 3 GPa (gigapascals) or less, for example. In the case of a power
roller bearing that is used in a toroidal-type continuously
variable transmission unit for a vehicle, on the other hand, the
contact pressure ranges from 2.5 to 3.5 GPa in a normal
deceleration mode. In some cases, the contact pressure may even
reach 4 GPa in a maximum deceleration mode.
[0014] Further, the heavy forces of pressure from the input disc
and the output disc intensively act as a radial load in positions
at a distance of 180.degree. from each other on the traction
portions of the power roller. This radial load causes the power
roller to undergo compressive deformation in the radial direction.
Since this compressive deformation causes the power roller to warp,
it is hardly possible to allow a plurality of balls between the
power roller and the outer race uniformly to share thrust load that
acts on the power roller. Thrust load that acts on these balls
increases in positions at an angular distance of 90.degree. from
the positions of contact (traction portions of the power roller)
between the power roller and the input and output discs. In
consequence, pressures of contact between the individual balls and
raceway grooves vary, so that some of the balls roll in the raceway
grooves under very high contact pressures.
[0015] In order to prevent high contact pressures from lowering the
life performance, it is essential specially to adjust the
materials, surface hardness, and surface roughness of the traction
portions of the power roller in contact with the input and output
discs and the respective raceway grooves of the power roller and
the outer race that are touched by the balls.
[0016] In order to lengthen the life of the power roller bearing,
based on this background, the applicant hereof proposed a technique
in which balls are formed of medium-carbon steel or high-carbon
steel and the hardness and strength of the ball surface are
adjusted by carburizing-nitriding treatment or quenching and
tempering treatments (see Jpn. Pat. Appln. KOKAI Publication No.
7-208568).
[0017] The applicant hereof also proposed a technique in which an
input disc, an output disc, and a power roller in contact with them
are subjected to ground finish after they are subjected to
carburizing treatment. Further, the applicant hereof proposed a
technique in which input and output discs and a power roller are
subjected to ground finish after they are subjected to
carburizing-nitriding treatment so that the hardness and effective
case depth of the respective surfaces of these members can be
adjusted to appropriate values (2 mm to 4 mm) that stand locally
high contact pressures (see Jpn. Pat. Appln. KOKAI Publication No.
7-71555).
[0018] Although the hardness, effective case depth, and surface
roughness of the power roller and balls are rationalized by using
traction oil for power roller bearings, use of appropriate
materials for the individual members, and surface treatments, as
mentioned before, the endurance of the power roller bearing can be
improved only limitedly by it alone.
[0019] In some cases, the molecular structure of the traction oil,
synthetic oil, may be decomposed as the power roller is heated, in
particular. In these cases, the traction coefficient worsens, and
the safety factor for gloss slip also lowers. If the traction oil
is degenerated, moreover, it is hard to form oil films on the
respective surfaces of the power roller, balls, etc. Accordingly,
there is a possibility of the traction portions of the power roller
and the surfaces of the respective raceway grooves of the power
roller and the outer race undergoing early flaking. These phenomena
cause the life performance of the power roller bearing to
lower.
[0020] Since the power roller bearing is originally designed for
power transmission, it is important to minimize loss of the dynamic
torque of the bearing itself, thereby improving the torque
transmissibility. Despite the aforesaid improvement, however, a
substantial dynamic torque loss may be caused to lower the torque
transmissibility, depending on the dimensions of the balls and the
respective raceway grooves of the power roller and the outer race.
If the hardness and effective case depth of the respective surfaces
of the power roller and the like are adjusted in the aforesaid
manner, moreover, the edges of the raceway grooves or the balls
sometimes may be broken early, or the respective contact surfaces
of the raceway grooves and the balls may be marred, so that the
life performance of the power roller bearing may be lowered.
BRIEF SUMMARY OF THE INVENTION
[0021] Accordingly, the object of the present invention is to
provide a power roller bearing of a toroidal-type continuously
variable transmission unit, of which the life performance can be
restrained from lowering.
[0022] A power roller bearing of a toroidal-type continuously
variable transmission unit of the present invention is provided for
swinging motion between an input disc capable of being rotated by
means of a drive source and an output disc opposed to the input
disc, and comprises an outer race, a power roller in rolling
contact with the input disc and output disc, and balls provided for
rolling motion between the outer race and the power roller, the
outer race and the power roller having annular raceway grooves in
which the balls roll individually, at least one of the respective
raceway grooves of the outer race and the power roller being formed
having treated-surface layers for enhancing the endurance
thereof.
[0023] The treated-surface layers based on a first aspect of the
present invention include super-finished surfaces with the surface
roughness of 0.05 Ra or less, formed on both the respective raceway
grooves of the outer race and the power roller, and low-friction
layers formed on at least one of the super-finished surfaces.
[0024] According to this invention, heat generated in the power
roller bearing can be reduced by lessening friction that is
produced as the balls roll in the respective raceway grooves of the
outer race and the power roller. Thus, the respective surfaces of
the raceway grooves are not liable to flaking, so that the life of
the power roller bearing can be lengthened. According to this
invention, the dynamic torque of the power roller bearing is
lessened, and the general power transmission efficiency of the
toroidal-type continuously variable transmission unit is improved.
If the transmission unit is applied to an automobile, therefore,
the fuel consumption ratio can be improved at the same time.
[0025] Preferably, the low-friction layers are formed of
lubricative substances selected from at least one of materials
including gold, silver, lead, molybdenum disulfide (MoS.sub.2),
tungsten disulfide (WS.sub.2), and fluoroplastics. Among these
substances, some of the lubricative substances including gold,
silver, lead, or fluoroplastic are gradually scraped from the
low-friction layers by means of frictional force that is produced
as the bearing rotates. As the particles of the scraped lubricative
substances are transferred to a fellow surface that is touched by
the balls, thin films of the lubricative substances are formed on
the fellow surface, whereby the bearing is lubricated. Since layers
of molybdenum disulfide and tungsten disulfide as the lubricative
substances have their own lubricative surfaces, these lubricative
surfaces wear little by little as they develop lubricating
properties. The layer of molybdenum disulfide or tungsten disulfide
is formed on the surface of each ball or the surface of the raceway
groove of the power roller or the outer race by sputtering.
According to the power roller bearing using these low-friction
layers, heat can be restrained more securely, so that the life of
this bearing can be lengthened.
[0026] In order to achieve the above object, the treated-surface
layers of the power roller bearing of the present invention based
on a second aspect include residual compression stress layers
formed by shot-peening on at least one of the respective raceway
grooves of the outer race and the power roller. These residual
compression stress layers serve to ease stress that is generated as
the balls roll in the raceway grooves. Thus, the fatigue life of
the power roller bearing can be improved.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING
[0027] FIG. 1 is a longitudinal sectional view showing a part of a
single-cavity half-toroidal-type continuously variable transmission
unit according to a first embodiment of the present invention;
[0028] FIG. 2 is a sectional view showing a power roller bearing of
the same embodiment;
[0029] FIG. 3A is a plan view of an outer race of the power roller
bearing of the same embodiment;
[0030] FIG. 3B is a sectional view of the outer race taken along
line III-III of FIG. 3A;
[0031] FIG. 4A is a plan view of a plan view of a power roller of
the power roller bearing of the same embodiment;
[0032] FIG. 4B is a sectional view of the power roller taken along
line IV-IV of FIG. 4A;
[0033] FIG. 5 is a sectional view showing a ball of the power
roller bearing of the same embodiment;
[0034] FIG. 6 is a flowchart showing some of manufacturing
processes for an outer race and a power roller according to a
second embodiment of the present invention;
[0035] FIG. 7 is an enlarged sectional view schematically showing
the surface of a raceway groove of the outer race or the power
roller obtained in the manufacturing processes shown in FIG. 6;
[0036] FIG. 8 is a flowchart showing some of manufacturing
processes for an outer race and a power roller according to a third
embodiment of the present invention; and
[0037] FIG. 9 is an enlarged sectional view schematically showing
the surface of a raceway groove of the outer race or the power
roller obtained in the manufacturing processes shown in FIG. 8.
DETAILED DESCRIPTION OF THE INVENTION
First Embodiment
[0038] A first embodiment of the present invention will now be
described with reference to FIGS. 1 to 5.
[0039] FIG. 1 is a partial sectional view of an automotive
transmission 21 that uses a single-cavity half-toroidal-type
continuously variable transmission unit 20 as an example of a
toroidal-type continuously variable transmission unit. FIG. 2 is a
sectional view of a power roller bearing 11 that functions as a
thrust bearing of the toroidal-type continuously variable
transmission unit 20.
[0040] As shown in FIG. 1, the single-cavity half-toroidal-type
continuously variable transmission unit 20 that is used in the
transmission 21 comprises an input shaft 1 capable of being rotated
by means of a drive source E that includes an engine or the like,
an input disc 2, an output disc 3, a power roller 10, and a loading
cam mechanism 6 for use as push means.
[0041] The input disc 2 is supported on the input shaft 1 and can
rotates in association with the input shaft 1. The output disc 3 is
rotatably supported on the input shaft 1 so as to face the input
disc 2. The output disc 3 can rotates integrally with an output
transmitting member 3a for fetching power that is based on the
rotation of the input shaft 1. This output transmitting member 3a
can rotate in association with an output shaft (not shown).
[0042] The power roller 10 is provided for swinging motion between
the input disc 2 and the output disc 3, and is in rolling contact
with both the discs 2 and 3. The loading cam mechanism 6 is located
on the backside of the input disc 2.
[0043] The loading cam mechanism 6 is provided with a cam disc 4
and a cam roller 5. The cam disc 4 rotates integrally with the
input shaft 1 in a manner such that it is fitted on a spline
portion 1a that is formed on the input shaft 1. A cam face 22 that
is formed of a circumferential recess and projection are formed on
that surface of the cam disc 4 which faces the input disc 2. The
cam disc 4 can rotates in association with the drive source E.
[0044] The cam roller 5 is located between the cam disc 4 and the
input disc 2. The cam roller 5 is provided for rotation around an
axis Q in the radial direction with respect to an axis P of the
input shaft 1. A plurality of cam rollers 5 are arranged around the
axis P of the input shaft 1.
[0045] When the cam disc 4 is rotated by means of the drive source
E that includes the engine, in the loading cam mechanism 6 with the
configuration described above, the cam rollers 5 is pushed toward
the input disc 2 by means of the cam face 22. Then, the input disc
2 is pushed toward the output disc 3 by means of the cam rollers 5.
A push force generating mechanism such as a hydraulic piston may be
used in place of the loading cam mechanism 6 that functions as the
push means.
[0046] A trunnion 8 is provided between the input disc 2 and the
output disc 3. The trunnion 8 can swing around a pivot 7 in the
direction indicated by arrow R in FIG. 1. A displacement shaft 9 is
provided in the central portion of the trunnion 8. The power roller
10 is rotatably supported on the displacement shaft 9.
[0047] The power roller 10 includes a traction portion 10a that is
in rolling contact with the input disc 2 and the output disc 3.
Between the input disc 2 and output disc 3, the power roller 10
changes its angle of inclination in accordance with the gear ratio
of the toroidal-type continuously variable transmission unit 20. An
end portion 10b of the power roller 10 functions as an inner race
of the power roller bearing 11, which will be mentioned later.
[0048] The power roller bearing 11 for use as a thrust bearing is
provided between the trunnion 8 and the power roller 10. As shown
in FIG. 2, the power roller bearing 11 is provided with the end
portion 10b of the power roller 10 that serves as the inner race,
an outer race 13, a plurality of balls 12 as rolling elements, and
a retainer 14.
[0049] As shown in FIG. 3A, the outer race 13 has an annular shape.
The outer race 13 is supported on the trunnion 8. The balls 12 have
a spherical shape each. The balls 12 are arranged individually for
rolling motion between the power roller 10 and the outer race 13.
The retainer 14, which has an annular shape, is located between the
outer race 13 and the power roller 10. The retainer 14 holds the
balls 12 for rolling motion.
[0050] The power roller bearing 11 with the aforementioned
configuration is provided for swinging motion between the input
disc 2 and the output disc 3. When the input disc 2 is pushed
toward the output disc 3 by means of the loading cam mechanism 6,
the turning force of the input disc 2 that is rotated by means of
the drive source E is transmitted to the output disc 3 through the
power roller 10. As the output transmitting member 3a rotates
integrally with the output disc 3, the rotation of the input disc 2
is fetched as power.
[0051] Since the loading cam mechanism 6 pushes the input disc 2
toward the output disc 3 in the aforesaid manner so that the power
roller 10 comes into rolling contact with both the input and output
discs 2 and 3, load in the thrusting direction acts on the power
roller 10. The power roller bearing 11 supports the load in the
thrusting direction the input disc 2 and the output disc 3 apply to
the power roller 10, and allows the power roller 10 to rotate.
[0052] As shown in FIGS. 3A and 3B, a raceway groove 15 is formed
on an end face 17 of the outer race 13. As shown in FIGS. 4A and
4B, a raceway groove 16 is formed on an end face 18 of the power
roller 10 in a position opposite to the raceway groove 15 of the
outer race 13. The raceway grooves 15 and 16 are formed like rings
on their corresponding end faces 17 and 18. As shown in FIGS. 3B
and 4B, the raceway grooves 15 and 16 have an arcuate cross section
each.
[0053] Base materials that individually constitute the outer race
13 and the power roller 10 have super-finished surfaces 23a and 24a
that are formed by super-finishing the respective surfaces of the
raceway grooves 15 and 16. The surface roughness of these
super-finished surfaces 23a and 24a is adjusted to 0.05 Ra or less.
Low-friction layers 23b and 24b are formed on the super-finished
surfaces 23a and 24a, respectively. The super-finished surfaces 23a
and 24a and the low-friction layers 23b and 24b constitute
treated-surface layers 23 and 24. As shown in FIG. 5, a
treated-surface layer 25 including a low-friction layer 25b is
formed also on the surface of each ball 12. These low-friction
layers 23b, 24b and 25b are formed individually of lubricative
substances selected from at least one of materials including gold,
silver, lead, molybdenum disulfide (MOS.sub.2), tungsten disulfide
(WS.sub.2), and fluoroplastics. In the low-friction layers 23b, 24b
and 25b that are formed of lubricative substances including gold,
silver, lead, and fluoroplastics, among those substances, their
lubricative substances are gradually scraped from the respective
surfaces of the base materials as the power roller bearing 11
rotates. As the particles of the scraped lubricative substances are
transferred to a fellow surface that is touched by the balls 12,
thin films of the lubricative substances are formed also on the
fellow surface. The films of these lubricative substances serve to
lubricate the power roller bearing 11.
[0054] Since films of molybdenum disulfide and tungsten disulfide
have their own lubricative surfaces, these lubricative surfaces
wear little by little as they develop lubricating properties. The
films of molybdenum disulfide and tungsten disulfide are formed on
the respective surfaces of the balls 12 and the raceway grooves 15
and 16 by sputtering.
[0055] According to the arrangement described above, the
super-finished surfaces 23a and 24a with the surface roughness of
0.05 Ra or less are formed on the respective raceway grooves 15 and
16 of the outer race 13 and the power roller 10, and the
low-friction layers 23b and 24b of molybdenum disulfide or the like
are further formed on the super-finished surfaces. The low-friction
layer 25b is formed also on the surface of each ball 12.
Accordingly, the value of heat developed as the balls 12 roll in
the raceway grooves 15 and 16 can be lowered. Thus, the respective
surfaces of the raceway grooves 15 and 16 are not liable to
flaking, so that the life of the power roller bearing 11 of the
toroidal-type continuously variable transmission unit 20 can be
lengthened.
[0056] In the embodiment described above, the low-friction layers
23b and 24b are formed on both the raceway groove 15 of the outer
race 13 and the raceway groove 16 of the power roller 10.
Alternatively, however, the low-friction layer 23b or 24b may be
formed on one of the raceway grooves 15 and 16. In this case, the
life of the power roller bearing 11 can be also lengthened. Thus,
lowering of the life performance of the power roller bearing 11 of
the toroidal-type continuously variable transmission unit 20 can be
restrained by forming the low-friction layer 23b or 24b on at least
one of the respective raceway grooves 15 and 16 of the outer race
13 and the power roller 10.
[0057] According to the present invention, the dynamic torque of
the power roller bearing 11 is lessened, and the general power
transmission efficiency of the toroidal-type continuously variable
transmission unit 20 is improved. If the transmission unit is
applied to an automobile, therefore, the fuel consumption ratio can
be improved at the same time.
Second Embodiment
[0058] A toroidal-type continuously variable transmission unit of
this embodiment, like the embodiment shown in FIG. 1, comprises an
input disc 2, an output disc 3, a loading cam mechanism 6, a power
roller 10, a power roller bearing 11, etc. The power roller bearing
11 is composed of an end portion 10b of the power roller 10 that
functions as an inner race, a plurality of balls 12, an outer race
13, etc.
[0059] The respective surface regions of a raceway groove 15 of the
outer race 13 and a raceway groove 16 of the power roller 10 are
formed having treated-surface layers 23 and 24 that include
residual compression stress layers 23c and 24c (schematically shown
in FIG. 7), respectively. The treated-surface layers 23 and 24 that
include the residual compression stress layers 23c and 24c are
formed by shot-peening the surfaces of the raceway grooves 15 and
16, respectively. These treated-surface layers 23 and 24 that
include the residual compression stress layers 23c and 24c
individually have residual compression stresses within the range
from -20 kgf/mm.sup.2 to -100 kgf/mm.sup.2.
[0060] The outer race 13 and the power roller 10 with the
aforementioned configurations are obtained according to the
following processes. First, in Step S1 in FIG. 6, a workpiece as a
material is forged. After the workpiece is formed into the shape of
a nearly finished product by this forging work, the process
advances to Step S2. After the workpiece is cut in Step S2, the
process advances to Step S3. After the workpiece is subjected to
heat treatment such as carburizing treatment or
carburizing-nitriding treatment in Step S3, the process advances to
Step S4.
[0061] After the workpiece is ground into the same shape as a
product in Step S4, the process advances to Step S5. After the
respective surfaces of the raceway grooves 15 and 16 and the like
are subjected to super-finishing work and the like in Step S5, the
process advances to Step S6. In Step S6, the respective surfaces of
the raceway grooves 15 and 16 and the like are shot-peened to
obtain the outer race 13 and the power roller 10 that have desired
shapes and the residual compression stress layers 23c and 24c.
[0062] As is schematically shown in FIG. 7, depressions 45 and
protuberances 46 are formed on the respective surfaces of the
raceway grooves 15 and 16, that is, the respective surfaces of the
residual compression stress layers 23c and 24c, by shot-peening.
Since a lubricant such as traction oil or the lubricative
substances described in connection with the first embodiment are
held in the depressions 45, the power roller bearing 11 can be
prevented from being lubricated unsatisfactorily. Thus, the life of
the power roller bearing 11 can be lengthened.
[0063] In the present embodiment, shot-peening is carried out in
Step S6 after the raceway grooves 15 and 16 are ground in Step S4.
Accordingly, the outer race 13 and the power roller 10 can be
completed without removing the residual compression stress layers
23c and 24c from the respective surfaces of the raceway grooves 15
and 16 of the outer race 13 and the power roller 10. The residual
compression stress layers 23c and 24c serve to ease stress that is
generated as the balls 12 roll in the raceway grooves 15 and 16.
Thus, the fatigue life of the power roller bearing 11 can be
improved.
Third Embodiment
[0064] FIG. 8 shows processes according to a third embodiment of
the present invention that are used to form an outer race 13 and a
power roller 10. In the processes shown in FIG. 8, the respective
surfaces of raceway grooves 15 and 16 are shot-peened in Step ST5
after cutting work is carried out in Step S4. Thereafter, the
respective surfaces of the raceway grooves 15 and 16 are
super-finished in Step ST6. In FIG. 8, like symbols are used to
designate like processes of FIG. 6, and a description of those
processes is omitted.
[0065] If the outer race 13 and the power roller 10 are formed in
the processes shown in FIG. 8, residual compression stress layers
23c and 24c and super-finished surfaces 23a and 24a are formed on
the respective surfaces of the raceway grooves 15 and 16 as is
schematically shown in FIG. 9. More specifically, the protuberances
46 shown in FIG. 7 are removed by super-finishing work (Step ST6),
whereupon the depressions 45 remain on the respective surfaces of
the residual compression stress layers 23c and 24c. Since the
aforesaid lubricant is held in these depressions 45, the power
roller bearing 11 can be lubricated satisfactorily. In this case,
therefore, the life of the power roller bearing 11 can be
lengthened also.
[0066] In order to ascertain the function of the power roller
bearing 11 according to the present invention, the inventors hereof
conducted an endurance test on the toroidal-type continuously
variable transmission unit 20 that is provided with the outer race
13 and the power roller 10 described above. TABLE 1 shows results
of this test.
1 TABLE 1 Life Defect Invention 100 hours None product A or more
Invention 100 hours None product B or more Invention 100 hours None
product C or more Comparative 65 hours Separation of raceway
example A groove surfaces Comparative 68 hours Separation of
raceway example B groove surfaces Comparative 59 hours Separation
of raceway example C groove surfaces
[0067] In the test described above, the rotational frequency of the
input shaft 1 was set at 4,000 rpm, and input torque form the drive
source E at 390 Nm. Further, the endurance test was conducted with
use of synthetic traction oil as lubricating oil and with the
temperature of this lubricating oil at 100.degree. C.
[0068] In Table 1, a product A of the present invention and a
product B of the present invention uses outer races and power
rollers that were formed individually in the processes shown in
FIG. 8. A product C of the present invention uses a outer race and
a power roller that were formed in the processes shown in FIG. 6.
Comparative examples A, B and C use outer races and power rollers
in which the respective surfaces of their raceway grooves were not
shot-peened.
[0069] According to the test results shown in Table 1, none of the
shot-peened products A, B and C of the present invention was broken
in a test time of 100 hours. In all of the comparative examples A,
B and C, the respective surfaces of the raceway grooves underwent
flaking in a test time of about 60 hours.
[0070] Thus, power roller bearings 11 of high life performance were
able to be obtained in a manner such that the respective surfaces
of the raceway grooves 15 and 16 were shot-peened to form the
treated-surface layers 23 and 24 including the residual compression
stress layers 23c and 24c.
[0071] In order to apply a relatively high residual compression
stress of, e.g., -100 kgf/mm.sup.2 to the residual compression
stress layers 23c and 24c, shots must be struck hard against the
respective surfaces of the raceway grooves 15 and 16. In this case,
fine cracks sometimes may be formed in the surfaces of the raceway
grooves 15 and 16. These fine cracks can be removed by effecting
super-finishing work (Step ST6) after carrying out shot-peening
operation (Step ST5) in the processes shown in FIG. 8.
[0072] In the second and third embodiments described above, the
residual compression stress layers 23c and 24c are formed on both
the respective raceway grooves 15 and 16 of the outer race 13 and
the power roller 10. Alternatively, however, the residual
compression stress layer 23c or 24c may be formed on one of the
raceway grooves 15 and 16. In this case, the life of the power
roller bearing 11 can be lengthened also. Further, the low-friction
layer 25b described in connection with the first embodiment may be
formed on the surface of each ball 12. In this case, the residual
compression stress layers 23c and 24c is formed on the raceway
grooves 15 and 16 by shot-peening. Alternatively, the low-friction
layer 23b or 24b may be formed on one of the raceway grooves 15 and
16. In this case, the residual compression stress layer 23c or 24c
is formed on the other by shot-peening. Thus, the life of the power
roller bearing 11 of the toroidal-type continuously variable
transmission unit 20 can be lengthened by forming the
treated-surface layers 23 and 24 on at least one of the respective
surfaces of the raceway groove 15 of the outer race 13 and the
raceway groove 16 of the power roller 10.
[0073] It is to be understood, moreover, that any other portions
than the raceway grooves 15 and 16 may be shot-peened. The
aforesaid residual compression stress layers 23c and 24c may be
formed by barreling or the like instead of shot-peening.
[0074] The improvement of the rolling fatigue life by the aforesaid
shot-peening is also applicable to individual traction surfaces of
the toroidal-type continuously variable transmission unit 20. Thus,
conditions for these traction surfaces, including high temperature,
high speed, high contact pressure, presence of spins, and use of
traction oil, etc., are similar to those for the power roller
bearing 11. The technique of the present invention is also
effective for the traction surfaces. The results of the experiment
shown in Table 1 indicate that this technique is also effective for
the traction surfaces. More specifically, the life of the discs 2
and 3 or the power roller 10 can be lengthened by shot-peening at
least one of the respective traction surfaces of the discs and the
power roller.
[0075] As is evident from the above description, the power roller
bearing of the present invention can be suitably used for a
transmission of, for example, a general industrial machine or
transportation equipment, as well as a power transmission system of
an automobile. The present invention is applicable to
full-toroidal-type continuously variable transmission units as well
as to half-toroidal-type continuously variable transmission
units.
[0076] Additional advantages and modifications will readily occur
to those skilled in the art. Therefore, the invention in its
broader aspects is not limited to the specific details and
representative embodiments shown and described herein. Accordingly,
various modifications may be made without departing from the spirit
or scope of the general inventive concept as defined by the
appended claims and their equivalents.
* * * * *