U.S. patent application number 09/886378 was filed with the patent office on 2001-10-18 for tapered roller bearings and gear shaft support devices.
Invention is credited to Maeda, Kikuo, Okamoto, Yuji, Tsujimoto, Takashi.
Application Number | 20010031105 09/886378 |
Document ID | / |
Family ID | 27531239 |
Filed Date | 2001-10-18 |
United States Patent
Application |
20010031105 |
Kind Code |
A1 |
Tsujimoto, Takashi ; et
al. |
October 18, 2001 |
Tapered roller bearings and gear shaft support devices
Abstract
A tapered roller bearing and an automotive gear shaft support
device can ensure a long endurance life even in the state in which
debris is mixed. On the surfaces of an outer ring, inner ring, and
tapered rollers formed from carburized bearing steel having an
oxygen content of 9 ppm or less, carbo-nitrided layers having a
carbon content of 0.80 wt % or over, a Rockwell hardness HRC of 58
or over, and a residual austenite content of 25-35 vol % are formed
to increase mechanical properties and fatigue characteristics of
the parts and to stably maintain the carbo-nitrided layers on the
surfaces of the parts to a quality having suitable toughness,
thereby markedly improving the endurance life of the tapered roller
bearing in a state in which debris is mixed.
Inventors: |
Tsujimoto, Takashi; (Mie,
JP) ; Okamoto, Yuji; (Mie, JP) ; Maeda,
Kikuo; (Mie, JP) |
Correspondence
Address: |
WENDEROTH, LIND & PONACK, L.L.P.
2033 K STREET N. W.
SUITE 800
WASHINGTON
DC
20006-1021
US
|
Family ID: |
27531239 |
Appl. No.: |
09/886378 |
Filed: |
June 22, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
09886378 |
Jun 22, 2001 |
|
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09448941 |
Nov 24, 1999 |
|
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Current U.S.
Class: |
384/450 ;
384/571 |
Current CPC
Class: |
F16H 48/08 20130101;
F16C 19/364 20130101; F16C 2240/54 20130101; F16C 2202/04 20130101;
F16C 2240/50 20130101; F16C 2240/40 20130101; F16C 33/62 20130101;
B60K 17/16 20130101; F16C 33/30 20130101; F16C 33/366 20130101;
F16C 19/225 20130101; F16H 57/037 20130101; F16C 33/585 20130101;
F16C 2240/70 20130101; F16C 2361/61 20130101 |
Class at
Publication: |
384/450 ;
384/571 |
International
Class: |
F16C 033/58 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 27, 1998 |
JP |
10-337396 |
Nov 27, 1998 |
JP |
10-337493 |
Nov 30, 1998 |
JP |
10-339409 |
Dec 1, 1998 |
JP |
10-341953 |
Dec 3, 1998 |
JP |
10-344140 |
Claims
What is claimed is:
1. A tapered roller bearing comprising an outer ring having a
conical raceway, an inner ring having a conical raceway and formed
with a large rib surface on the large diameter side of said conical
raceway, a plurality of tapered rollers rollably arranged between
said raceway of said outer ring and said raceway of said inner
ring, and a retainer for keeping said tapered rollers
circumferentially spaced a predetermined distance from each other,
characterized in that said outer ring, said inner ring and said
tapered rollers are all formed from a steel having an oxygen
content of 9 ppm or less, and that a carbo-nitrided layer having a
carbon content of 0.80 wt % or more and a Rockwell hardness HRC of
58 or more is formed on surfaces of said outer ring, said inner
ring and said tapered rollers, and that the retained austenite
content of said carbo-nitrided layer is 25 to 35 vol %.
2. A tapered roller bearing comprising an outer ring having a
conical raceway, an inner ring having a conical raceway and formed
with a large rib surface on the large diameter side of said conical
raceway, a plurality of tapered rollers rollably arranged between
said raceway of said outer ring and said raceway of said inner
ring, and a retainer for keeping said tapered rollers
circumferentially spaced a predetermined distance from each other,
characterized in that a carbo-nitrided layer having a carbon
content of 0.80 wt % or more and a Rockwell hardness HRC of 58 or
more is formed on surfaces of said outer ring, said inner ring and
said tapered rollers, that the retained austenite content of said
carbo-nitrided layer is 25 to 35 vol %, and crownings are formed at
both ends of said raceway of said inner ring, and that the width of
each said crowning is 20% or less of the width of said raceway of
said inner ring.
3. The tapered roller bearing as claimed in claim 2 wherein a
crowning having a moderate curvature is formed on a portion of said
raceway of said inner ring except both ends thereof at which said
crownings are formed.
4. A tapered roller bearing comprising an outer ring having a
conical raceway, an inner ring having a conical raceway and formed
with a large rib surface on the large diameter side of said conical
raceway and a small rib surface on the small diameter side thereof,
a plurality of tapered rollers rollably arranged between said
raceway of said outer ring and said raceway of said inner ring, and
a retainer for keeping said rapered rollers circumferentially
spaced a predetermined distance from each other, wherein during
use, said tapered rollers are guided with large end faces thereof
in contact with the large rib surface of said inner ring,
characterized in that the small rib surface of said inner ring is
formed by a surface parallel to small end faces of said tapered
rollers, and that the ratio R/R.sub.base is 0.75 to 0.87, wherein R
is the radius of curvature of the large end faces of said tapered
rollers, and R.sub.base is the distance from the apex of the cone
angle of said tapered rollers to said large rib surface of said
inner ring, wherein a gap .delta. formed between the small rib
surface of said inner ring and the small end faces of said tapered
rollers when the large end faces of said tapered rollers are in
contact with the large rib surface of said inner ring is not more
than 0.4 mm.
5. The tapered roller bearing as claimed in claim 4 wherein the
small rib surface of said inner ring is formed by grinding or
turning.
6. A tapered roller bearing comprising an outer ring having a
conical raceway, an inner ring having a conical raceway and formed
with a large rib surface on the large diameter side of said conical
raceway and a small rib surface on the small diameter side thereof,
a plurality of tapered rollers rollably arranged between said
raceway of said outer ring and said raceway of said inner ring, and
a retainer for keeping said rapered rollers circumferentially
spaced a predetermined distance from each other, wherein during
use, said tapered rollers are guided with large end faces thereof
in contact with the large rib surface of said inner ring,
characterized in that the small rib surface of said inner ring is
formed by a surface parallel to small end faces of said tapered
rollers, and that the ratio R/R.sub.base is 0.75 to 0.87, wherein R
is the radius of curvature of the large end faces of said tapered
rollers, and R.sub.base is the distance from the apex of the cone
angle of said tapered rollers to said large rib surface of said
inner ring, wherein the small rib surface of said inner ring is
formed by grinding or turning.
7. A tapered roller bearing comprising an outer ring having a
conical raceway, an inner ring having a conical raceway and formed
with a large rib surface on the large diameter side of said conical
raceway, a plurality of tapered rollers rollably arranged between
said raceway of said outer ring and said raceway of said inner
ring, and a retainer for keeping said tapered rollers
circumferentially spaced a predetermined distance from each other,
characterized in that said inner ring has a large rib surface made
up of a conical surface brought into contact with large end faces
of said tapered rollers, and a flank smoothly connecting with said
conical surface and curving in a direction away from the large end
faces of said tapered rollers.
8. The tapered roller bearing as claimed in claim 7 wherein said
flank has a circular section.
9. The tapered roller bearing as claimed in claim 8 wherein a
circular recess is provided on the central portion of each of the
large end faces of said tapered rollers, and the outer peripheral
end of said recess extends to near the boundary between said
conical surface and said flank of said large rib surface of said
inner ring.
10. The tapered roller bearing as claimed in claim 9 wherein the
boundary between said conical surface and said flank of said large
rib surface of said inner ring is provided near the outer edge of
the maximum contact oval produced by the contact between the large
end faces of said tapered rollers and the large rib surface of said
inner ring under the maximum permissible axial load of said tapered
roller bearing.
11. The tapered roller bearing as claimed in claim 7 wherein a
circular recess is provided on the central portion of each of the
large end faces of said tapered rollers, and the outer peripheral
end of said recess extends to near the boundary between said
conical surface and said flank of said large rib surface of said
inner ring.
12. The tapered roller bearing as claimed in claim 11 wherein the
boundary between said conical surface and said flank of said large
rib surface of said inner ring is provided near the outer edge of
the maximum contact oval produced by the contact between the large
end faces of said tapered rollers and the large rib surface of said
inner ring under the maximum permissible axial load of said tapered
roller bearing.
13. The tapered roller bearing as claimed in claim 7 wherein the
boundary between said conical surface and said flank of said large
rib surface of said inner ring is provided near the outer edge of
the maximum contact oval produced by the contact between the large
end faces of said tapered rollers and the large rib surface of said
inner ring under the maximum permissible axial load of said tapered
roller bearing.
14. A gear shaft support device for a vehicle in which a gear shaft
is rotatably supported by tapered roller bearings in a housing in
which is sealed gear oil, characterized in that said tapered roller
bearings each have an outer ring, an inner ring and tapered rollers
formed from a steel having an oxygen content of 9 ppm or less, and
that a carbo-nitrided layer having a carbon content of 0.80 wt % or
more and a Rockwell hardness HRC of 58 or more is formed on
surfaces of said inner ring, said outer ring and said tapered
rollers, said carbo-nitrided layer having a retained austenite
content of 25 to 35 vol %.
15. A gear shaft support device for a vehicle in which a gear shaft
is rotatably supported by tapered roller bearings in a housing in
which is sealed gear oil, said tapered roller bearings each having
an outer ring, an inner ring and tapered rollers, characterized in
that a carbo-nitrided layer having a carbon content of 0.80 wt % or
more and a Rockwell hardness HRC of 58 or more is formed on each of
the surfaces of said outer ring, said inner ring and said tapered
rollers, that said carbo-nitrided layer has retained austenite
content of 25 to 35 vol %, and that crownings are formed at both
ends of said raceway of said inner ring, the width of each said
crowning being 20% or less of the width of said raceway of said
inner ring.
16. The gear shaft support device as claimed in claim 15 wherein a
crowning having a moderate curvature is formed on a portion of said
raceway of said inner ring except both ends thereof at which said
crownings are formed.
17. A gear shaft support device for a vehicle in which a gear shaft
is rotatably supported by tapered roller bearings in a housing in
which is sealed gear oil, said tapered roller bearings each having
an outer ring, an inner ring and tapered rollers, characterized in
that a small rib surface of said inner ring is formed by a surface
parallel to small end faces of said tapered rollers, and that the
ratio R/R.sub.base is 0.75 to 0.87, wherein R is the radius of
curvature of large end faces of said tapered rollers, and
R.sub.base is the distance from the apex of the cone angle of said
tapered rollers to a large rib surface of said inner ring, wherein
a gap .delta. formed between the small rib surface of said inner
ring and the small end faces of said tapered rollers when the large
end faces of said tapered rollers are in contact with the large rib
surface of said inner ring is not more than 0.4 mm.
18. The gear shaft support device as claimed in claim 17 wherein
the small rib surface of said inner ring is formed by grinding or
turning.
19. A gear shaft support device for a vehicle in which a gear shaft
is rotatably supported by tapered roller bearings in a housing in
which is sealed gear oil, said tapered roller bearings each having
an outer ring, an inner ring and tapered rollers, characterized in
that a small rib surface of said inner ring is formed by a surface
parallel to small end faces of said tapered rollers, and that the
ratio R/R.sub.base is 0.75 to 0.87, wherein R is the radius of
curvature of large end faces of said tapered rollers, and
R.sub.base is the distance from the apex of the cone angle of said
tapered rollers to a large rib surface of said inner ring, wherein
the small rib surface of said inner ring is formed by grinding or
turning.
20. A gear shaft support device for a vehicle in which a gear shaft
is rotatably supported by tapered roller bearings in a housing in
which is sealed gear oil, said tapered roller bearings each having
an outer ring, an inner ring, and tapered rollers, characterized in
that said inner ring has a large rib surface made up of a conical
surface brought into contact with large end faces of said tapered
rollers, and a flank smoothly connecting with said conical surface
and curving in a direction away from the large end faces of said
tapered rollers.
21. The gear shaft support device as claimed in claim 20 wherein
said flank has a circular section.
22. The gear shaft support device as claimed in claim 21 wherein a
circular recess is provided on the central portion of each of the
large end faces of said tapered rollers, and the outer peripheral
end of said recess extends to near the boundary between said
conical surface and said flank of said large rib surface of said
inner ring.
23. The gear shaft support device as claimed in claim 21 wherein
the boundary between said conical surface and said flank of said
large rib surface of said inner ring is provided near the outer
edge of the maximum contact oval produced by the contact between
the large end faces of said tapered rollers and the large rib
surface of said inner ring under the maximum permissible axial load
of said tapered roller bearing.
24. The gear shaft support device as claimed in claim 20 wherein a
circular recess is provided on the central portion of each of the
large end faces of said tapered rollers, and the outer peripheral
end of said recess extends to near the boundary between said
conical surface and said flank of said large rib surface of said
inner ring.
25. The gear shaft support device as claimed in claim 24 wherein
the boundary between said conical surface and said flank of said
large rib surface of said inner ring is provided near the outer
edge of the maximum contact oval produced by the contact between
the large end faces of said tapered rollers and the large rib
surface of said inner ring under the maximum permissible axial load
of said tapered roller bearing.
26. The gear shaft support device as claimed in claim 20 wherein
the boundary between said conical surface and said flank of said
large rib surface of said inner ring is provided near the outer
edge of the maximum contact oval produced by the contact between
the large end faces of said tapered rollers and the large rib
surface of said inner ring under the maximum permissible axial load
of said tapered roller bearing.
Description
[0001] This application is a divisional application of application
Ser. No. 09/448,941, filed Nov. 24, 1999.
BACKGROUND OF THE INVENTION
[0002] This invention relates to tapered roller bearings and gear
shaft support devices for vehicles.
[0003] Tapered roller bearings are suitable to support radial load,
axial load and combined load. Because of their large load capacity,
they are used to support gear shafts of power transmission devices
such as differentials and transmissions in automobiles and
construction machines.
[0004] FIG. 1 shows an automotive differential in which a gear
shaft is supported by tapered roller bearings which is one of the
embodiments of the present invention. It basically comprises a
drive pinion 4 rotatably supported in a housing 1 by two tapered
roller bearings 2, 3, a ring gear 5 meshing with the drive pinion
4, a differential gear case 7 carrying the ring gear 5 and
rotatably supported in the housing 1 by a pair of tapered roller
bearings 6, pinions 8 mounted in the differential gear case 7, and
a pair of side gears 9 meshing with the pinions 8. These members
are mounted in the housing 1 in which is sealed gear oil. The gear
oil also serves as a lubricating oil for the tapered roller
bearings 2, 3, 6.
[0005] FIG. 10 shows one conventional type of tapered roller
bearing. It comprises an outer ring 52 having a conical raceway 51,
an inner ring 56 having a conical raceway 53, a large rib surface
54 on the large-diameter side of the raceway 53 and a small rib
surface 55 on its small-diameter side, a plurality of tapered
rollers 57 rollably arranged between the raceway 51 of the outer
ring 52 and the raceway 53 of the inner ring 56, and a retainer 58
keeping the tapered rollers 57 circumferentially spaced a
predetermined distance from each other. The distance between the
large rib surface 54 and the small rib surface 55 of the inner ring
is designed to be slightly longer than the length of the tapered
rollers 57.
[0006] The tapered rollers 57 are designed to come into line
contact with the raceways 51 and 53 of the outer ring 52 and the
inner ring 56 with the cone apexes of the tapered rollers 57 and
the raceways 51, 53 converging on a point O on the centerline of
the tapered roller bearing. By this arrangement, the tapered
rollers 57 can roll along the raceways 51, 53.
[0007] With such a tapered roller bearing, the raceways 51, 53 have
different cone angles, so that the combined force of loads applied
to the tapered rollers 57 from the raceways 51, 53 acts in such a
direction as to push the tapered rollers 57 toward the large rib
surface 54 of the inner ring 56. Thus, during use of the bearing,
the tapered rollers 57 are guided with their large end faces 59
pressed against the large rib surface 54, so that the large end
faces 59 and the large rib surface 54 are in sliding contact with
each other.
[0008] On the other hand, since the distance between the large rib
surface 54 and the small rib surface 55 is designed to be slightly
longer than the length of the tapered rollers 57, as shown enlarged
in FIG. 11, the small rib surface 55 does not contact the small end
faces 60 of the tapered rollers 57 such that small clearances exist
therebetween. Also, the small rib surface 55 is formed by a surface
inclined outwardly relative to the small end faces 60 of the
tapered rollers 57. In the bearing manufacturing steps, the small
rib surface 55 and the small end faces 60, which are kept out of
contact with each other, are not finished by grinding.
[0009] In mounting such a tapered roller bearing in a mounting
position, as shown in FIG. 12A, the assembly comprising the inner
ring 56, the tapered rollers 57 and the retainer 58 is inserted
into the raceway 51 of the outer ring 52 from above with the large
end faces 59 of the tapered rollers 57 facing up. At this time,
since the tapered rollers 57 have freedom relative to the inner
ring 56 and the retainer 58, they will not seat in position, and
their small end faces 60 are brought into contact with the small
rib surface 55. This is an initial assembled state in which
clearance .delta. is present between the large end faces 59 and the
large rib surface 54 of the inner ring 56.
[0010] Next, the tapered roller bearing in the initial assembled
state is temporarily mounted on a mounting position of a mating
device. As shown in FIG. 12B, when break-in is carried out at a low
speed of about 50-100 rpm while applying an axial load Fa to the
end face of the inner ring 56, the tapered rollers 57 will move a
distance equal to the gap .delta. toward the large rib surface 54,
until as shown in FIG. 12C, the large end faces 59 come into
contact with the large rib surface 54 of the inner ring 56, so that
they settle at a regular position during use of the bearing where a
gap .delta. exists between the small end face 60 and the small rib
surface 55.
[0011] Thereafter, the tapered roller bearing is preloaded axially
under a predetermined load. This preloading is carried out to
prevent axial movement of the tapered rollers 57 during use of the
bearing, and to stably bring the tapered rollers into line contact
with the raceways 51, 53 of the outer ring 52 and the inner ring
56. The control of preloading force is carried out by measuring the
shaft torque, and preloading ends when the shaft torque reaches a
predetermined value.
[0012] Since the power transmission device such as a differential
has many gear meshing portions and sliding portions of rotary
members, foreign matter such as metallic powder produced by wear at
these portions can enter gear oil sealed in the housing. Such
powder will penetrate into tapered roller bearings for supporting
gear shafts, which are rotating under high load, thus shortening
the working life of the tapered roller bearings.
[0013] Also, when such tapered roller bearings are used to support
gear shafts of a differential which rotates at high speed under
high load, since the large end faces of the tapered rollers are
brought into sliding contact with the large rib surface of the
inner ring, torque due to the slide contact increases. Further, due
to frictional heat buildup, the temperature of the bearing portion
will rise, thus lowering the viscosity of gear oil. This may cause
shortage of oil film.
[0014] Further, in mounting the tapered roller bearing on a
mounting portion, if the gap between the large end faces 59 of the
tapered rollers 57 and the large rib surface 54 is large in the
initial assembled state shown in FIG. 12A, break-in time tends to
be long until the tapered rollers 57 settle in their regular
positions shown in FIG. 12C. As shown in FIG. 11, since the small
rib surface 55 of the inner ring 56 is formed inclined outwardly
relative to the the small end faces 60 of the tapered rollers 57,
variation in the gap between the large end faces 59 and the large
rib surface 54 in the initial assembled state is large for the
following reasons, and the abovementioned break-in time until all
the tapered rollers 57 settle in their regular positions tends to
become even longer.
[0015] Generally, the small end faces of the tapered rollers remain
as forged surfaces, so that chamfer dimensions and shape are large
in variation. Variations in chamfer dimension and shape are present
not only between tapered rollers but in a circumferential direction
of one tapered roller. As shown by solid and chain lines in FIG.
11, if the chamfer dimension and shape of the small end faces 60
differ from each other, the following will result. In the case of
the small end faces 60 shown by solid line, in the initial
assembled state, point P1 on the small end face 60 comes into
contact with point Q1 on the small rib surface 55, so that the gap
.delta. when the tapered rollers 57 settle will be .delta..sub.1.
On the other hand, in the case of the small end face 60 shown by
chain line, in the initial assembled state, point P2 comes into
contact with point Q2, so that the gap .delta. when the tapered
rollers 57 settle will be .delta..sub.2. Thus, due to differences
in chamfer dimension and shape of the small end faces 60, the time
until each tapered roller 57 settles in position tends to vary, so
that longer break-in time is required.
[0016] An object of this invention is to ensure a long endurance
life for a tapered roller bearing and a gear shaft support device
for a vehicle.
[0017] Another object is to reduce torque loss and heat buildup due
to friction.
[0018] A further object is to shorten break-in time.
SUMMARY OF THE INVENTION
[0019] According to this invention, there is provided a tapered
roller bearing comprising an outer ring having a conical raceway,
an inner ring having a conical raceway and formed with a large rib
surface on the large diameter side of the conical raceway, a
plurality of tapered rollers rollably arranged between the raceway
of the outer ring and the raceway of the inner ring, and a retainer
for keeping the tapered rollers circumferentially spaced a
predetermined distance from each other, characterized in that the
outer ring, the inner ring and the tapered rollers are all formed
from a steel having an oxygen content of 9 ppm or less, and that a
carbo-nitrided layer having a carbon content of 0.80 wt % or more
and a Rockwell hardness HRC of 58 or more is formed on surfaces of
the outer ring, the inner ring and the tapered rollers, and that
the retained austenite content of the carbo-nitrided layer is 25 to
35 vol %.
[0020] The outer ring, inner ring and tapered rollers are formed
from a steel having an oxygen content of 9 ppm or less in order to
minimize any nonmetallic inclusions formed by oxides in the steel,
improve the mechanical characteristics and fatigue properties, and
to sufficiently ensure bearing life under clean lubricating oil. A
steel having an oxygen content of 9 ppm or less can be obtained
e.g. by a method of degassing molten steel.
[0021] Carbo-nitrided layers are formed on the surfaces of the
outer ring, inner ring and tapered rollers for the following
reasons. Retained austenite in a carburized layer obtained by
normal carburizing has high toughness and work hardening
properties. Thus a proper amount of retained austenite ensures
hardness of the carburized layer and suppresses initiation and
progression of cracks. But it is unstable against heat.
[0022] In contrast, if these parts are subjected to carbo-nitriding
treatment under suitable conditions, nitrogen atoms will solid
soluted in retained austenite, and thus serve to stabilize the
retained austenite against heat and also properly keep the
properties of the carbo-nitrided layer against a temperature rise
due to temperature rise at the bearing portion. In a carbo-nitrided
layer obtained by such carbo-nitriding treatment, a greater
compressive residual stress is formed, so that it is also possible
to further increase fatigue strength.
[0023] The retained austenite content should be set at 25-35 vol %
to give the carbo-nitrided layer proper toughness, and to relieve
excessive increase in stress due to biting of debris. If the
retained austenite content is less than 25 vol %, toughness would
be insufficient. If over 35 vol %, the hardness would be too low,
thus resulting in deterioration in surface roughness due to plastic
deformation.
[0024] The structure of such a carbo-nitrided layer as mentioned
above can be formed by the following treatment steps. After heating
and holding the part for a predetermined time period while keeping
the carbon potential at 0.8% or over in a carburizing atmosphere,
it is quenched in oil and is subjected to hardening. Thereafter it
is heated and held for a predetermined time period in ammonia gas
for nitriding. It is also possible to employ a method in which
nitriding is carried out during carburizing. In order to adjust the
retained austenite content, sub-zero treatment or tempering may be
carried out.
[0025] According to this invention, a carbo-nitrided layer having a
carbon content of 0.80 wt % or over and a Rockwell hardness HRC of
58 or over may be formed on the surfaces of the outer ring, inner
ring and tapered rollers, the retained austenite amount of this
carbo-nitrided layer being 25 to 35 vol %, and crownings may be
formed at both ends of the raceway of the inner ring, the width of
the crowning at each end being 20% or less of the width of the
raceway of the inner ring.
[0026] The crowning is formed at each end of the raceway of the
inner ring in order to prevent excessive edge loads from acting on
the rollers and the raceway of the inner ring. The width of these
crownings should be 20% or less of the width of the raceway of the
inner ring because if it exceeds 20%, the contact surface pressure
at the central portion of the raceway would be excessive.
[0027] By forming a crowning having a moderate curvature on a
portion of the raceway of the inner ring except both ends at which
the crownings are formed, the surface pressure distribution on the
raceway can be made more uniform.
[0028] According to this invention, the small rib surface of the
inner ring may be formed by a surface parallel to the small end
faces of the tapered rollers, the value R/R.sub.BASE being 0.75 to
0.87, where R is the radius of curvature of the large end faces of
the tapered rollers, and R.sub.BASE is the distance from the apex
of the cone angle of the tapered rollers to the large rib surface
of the inner ring.
[0029] The small rib surface of the inner ring is formed by a
surface parallel to the small end faces of the tapered rollers for
the following reasons. As shown enlarged in FIG. 6B, by forming the
small rib surface 34 of the inner ring 35 from a surface parallel
to the small end faces 39 of the tapered rollers 36, it is possible
to minimize the influence of variations in chamfer dimension and
shape of the small end faces 39 of the tapered rollers 36 against
the gap between the large end faces 38 of the tapered rollers 36
and the large rib surface 33 of the inner ring 35 in the initial
assembled state (which is equal to the gap between the small end
faces 39 of the tapered rollers 36 and the small rib surfaces 34 of
the inner ring 35 when the tapered rollers 36 have settled in
position). As shown by chain line in FIG. 6B, even if the chamfer
dimensions and shapes of the small end faces 39 differ, in the
initial assembled state, since the mutually parallel small end
faces 39 and small rib surface 34 are brought into surface contact,
the gap between the large end faces 38 and the large rib surface 33
is always constant. Thus it is possible to reduce differences in
time required until each tapered roller settles and thus to shorten
the break-in time.
[0030] The ratio of the radius of curvature R of the large end
faces of the tapered rollers to the distance R.sub.base from the
apex of the cone angle of the tapered rollers to the large rib
surface of the inner ring, R/R.sub.base should be set at 0.75 to
0.87 for the following reasons.
[0031] FIG. 7 shows the results of calculation using the Karna's
equation, where t is the thickness of oil film formed between the
large rib surface of the inner ring and the large end faces of the
tapered rollers. The ordinate shows the ratio t/to, which is the
ratio to oil film thickness to when R/R.sub.base=0.76. The oil film
thickness t is the maximum when R/R.sub.base=0.76, and decreases
sharply when R/R.sub.BASE e x c e e d s 0.9.
[0032] FIG. 8 shows the results of calculation for determining the
maximum hertz stress p between the large rib surface of the inner
ring and the large end faces of the tapered rollers. The ordinate
shows, like FIG. 7, the ratio p/po, which is the ratio to maximum
hertz stress po when R/R.sub.base=0.76. The maximum hertz stress p
monotonously decreases with an increase in R/R.sub.base.
[0033] In order to reduce torque loss and heat buildup due to
sliding friction between the large rib surface of the inner ring
and the large end faces of the tapered rollers, it is desirable to
increase the oil film thickness t and reduce the maximum hertz
stress p. Based on the calculation results of FIGS. 7 and 8 and the
below-mentioned seizure resistance test results, the present
inventors determined the suitable range of R/R.sub.base at
0.75-0.87. For conventional tapered roller bearings, the
R/R.sub.base value is designed at a range of 0.90-0.97.
[0034] By forming the surface roughness Ra of the large rib surface
of the inner ring in the range of 0.05-0.20 .mu.m, the oil film
thickness t between the large rib surface of inner ring and the
large end faces of the tapered rollers, and the lubricating
condition between these surfaces can be maintained in a proper
state.
[0035] The surface roughness Ra should be 0.05 .mu.m or over for
the following reasons. As shown in FIG. 12B, when the tapered
roller bearing is mounted, break-in is carried out at a low speed
of 50-100 rpm while applying an axial load Fa to the end face of
the inner ring 56. If the surface roughness Ra is less than 0.05
.mu.m, the lubricating state between the large rib surface 54 of
the inner ring 56 and the large end faces 59 of the tapered rollers
57 will involve a mixture of fluid lubrication and boundary
lubrication during break-in, so that the friction coefficient
varies considerably and the measured shaft torque varies widely.
This worsens the preload control accuracy. If Ra is 0.05 .mu.m or
over, the lubricating state will be boundary lubrication, so that
the friction coefficient stabilizes and thus preload control is
possible with high accuracy. Under normal bearing use conditions
where speed exceeds 100 rpm, sufficient oil film is formed between
the large rib surface 54 and the large end faces 59, so that the
lubricating state between these surfaces becomes fluid lubrication,
and the friction coefficient decreases.
[0036] The surface roughness Ra should be 0.20 .mu.m or under
because if Ra is over 0.20 .mu.m, the temperature will rise at the
bearing portion in the high-speed rotation region, so that when the
viscosity of lubricating oil decreases, the oil film thickness
tends to be insufficient and seizure tends to occur.
[0037] By restricting the gap 6 formed between the small rib
surface of the inner ring and the small end faces of the tapered
rollers when the large end faces of the tapered rollers are in
contact with the large rib surface of the inner ring to not more
than 0.4 mm, it is possible to reduce the number of revolutions
required for the tapered rollers to settle in position during the
break-in, and to shorten the break-in time. The permissible maximum
value of the gap 6, that is, 0.4 mm, was determined based on the
results of the below-described break-in test.
[0038] By forming the small rib surface of the inner ring by
grinding or turning, it is possible to accurately control the gap
between the small rib surface of the inner ring and the small end
faces of the tapered rollers.
[0039] The tapered roller bearing of this invention may have the
large rib surface of the inner ring made up of a conical surface in
contact with the large end faces of the tapered rollers, and a
flank smoothly connecting with the conical surface and curving in a
direction away from the large end faces of the tapered rollers.
[0040] By smoothly connecting the curved flank to the conical
surface of the large rib surface of inner ring in contact with the
large end faces of the tapered rollers and forming an acute-angle,
wedge-shaped gap near the outer edge of the contact region, it is
possible to increase the function of drawing lubricating oil into
the contact region and to form a good oil film. Also, by the
formation of the smooth flank, it is possible to prevent damage due
to abutment with the large rib surface of inner ring when the
tapered roller skews.
[0041] By employing an arc as the sectional shape of the flank, it
is possible to easily form a flank that is superior in the
lubricating oil drawing function.
[0042] By providing a circular recess on the central portion of the
large end faces of the tapered rollers, and extending the outer
peripheral end of the recess to near the boundary between the
conical surface and the flank of the large rib surface of the inner
ring, it is possible to guide lubricating oil to near the
wedge-shaped gap and to supply a sufficient amount of lubricating
oil into the wedge-shaped gap, and also to further increase the
permissible skew angle of the tapered rollers.
[0043] By providing the boundary between the conical surface and
the flank of the large rib surface of inner ring near the outer
edge of the maximum contact oval produced by the contact between
the large end faces of the tapered rollers and the large rib
surface of the inner ring under the maximum permissible axial load
of the tapered roller bearing, it is possible to suitably form the
wedge-shaped gap for drawing the lubricating oil in the entire load
range of the tapered roller bearing.
[0044] Also, in this invention, in a gear shaft support device for
a vehicle in which a gear shaft is rotatably supported by a tapered
roller bearing in a housing in which is sealed gear oil, the outer
ring, inner ring and tapered rollers of the tapered roller bearings
are formed from a steel having an oxygen content of 9 ppm or less,
and a carbo-nitrided layer having a carbon content of 0.80 wt % or
more and a Rockwell hardness HRC of 58 or more is formed on each of
their surfaces, the carbo-nitrided layer having a retained
austenite amount of 25 to 35 vol %. Thus it is possible to markedly
prolong the maintenance cycle of differentials and transmissions,
etc.
[0045] Other features and objects of the present invention will
become apparent from the following description made with reference
to the accompanying drawings, in which:
BRIEF DESCRIPTION OF THE DRAWINGS
[0046] FIG. 1 is a vertical sectional view of a differential in
which is assembled a gear shaft support device of a first
embodiment;
[0047] FIG. 2A is a vertical sectional view of a tapered roller
bearing of a first embodiment;
[0048] FIG. 2B is a partially enlarged sectional view of the
same;
[0049] FIG. 3 is a partially enlarged sectional view of a tapered
roller bearing of a second embodiment;
[0050] FIG. 4A is a vertical sectional view of a tapered roller
bearing of a third embodiment;
[0051] FIG. 4B is a partially enlarged sectional view of the
same;
[0052] FIG. 5 is a sectional view explaining the design
specifications of the tapered roller bearing of FIG. 4;
[0053] FIG. 6A is a vertical sectional view of a tapered roller
bearing of a fourth embodiment;
[0054] FIG. 6B is a partially enlarged sectional view of the
same;
[0055] FIG. 7 is a graph showing the relation between the radius of
curvature of the large end face of the tapered roller and an oil
film thickness;
[0056] FIG. 8 is a graph showing the relation between the radius of
curvature of the large end face of the tapered roller and a maximum
hertz stress;
[0057] FIG. 9 is a partially enlarged sectional view of a tapered
roller bearing of a fifth embodiment;
[0058] FIG. 10 is a partially omitted vertical sectional view of a
conventional tapered roller bearing;
[0059] FIG. 11 is a partially enlarged sectional view of FIG. 10;
and
[0060] FIGS. 12A-12C are sectional views showing how the tapered
roller bearing is mounted.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0061] With reference to FIGS. 1 and 9, embodiments of this
invention are described. FIG. 1 shows, as described above, a
differential of an automobile, in which for the support of the
drive pinion 4 and the differential gear case 7 on which is mounted
the ring gear 5, the gear shaft support device using the tapered
roller bearings 2, 3, 6 of the embodiments is adopted.
[0062] FIG. 2A shows a tapered roller bearing 6 as a typical
example. It has an outer ring 11 having a conical raceway 10, an
inner ring 15 having a conical raceway 12, a large rib surface 13
on the large-diameter side of the raceway 12, and a small rib
surface 14 on its small-diameter side, a plurality of tapered
rollers 16 rollably arranged between the respective raceways 10, 12
of the outer ring 11 and the inner ring 15, and a retainer 17 for
retaining the tapered rollers 16 at predetermined circumferential
intervals.
[0063] The outer ring 11, inner ring 15 and tapered rollers 16 are
all formed from carburized bearing steel (SCr 435) having an oxygen
content of 9 ppm or less, and as shown in FIG. 2B, carbo-nitrided
layers 11a, 15a, 16a having a carbon content of 0.80 wt % or more
and a Rockwell hardness HRC of 58 or more, and the retained
austenite content of 25 to 35 vol % are formed on the surfaces of
these parts 11, 15 and 16. Though not shown, the tapered roller
bearings 2, 3 have the same structure.
[0064] Hereinbelow, the Examples of the first embodiment and its
Comparative Examples are described.
EXAMPLES
[0065] Tapered roller bearings (Examples 11-15 in Table 1) in which
a carbo-nitrided layer having a carbon content of 0.80 wt % or more
and a Rockwell hardness HRC of 58 or more and the retained
austenite content of 25-35 vol % was formed on each of the outer
ring, inner ring and tapered rollers formed from carburized bearing
steel (SCr435) having an oxygen content of 9 ppm or less were
prepared. The bearing dimensions were all 40 mm in inner diameter
and 68 mm in outer diameter.
Comparative Examples
[0066] Tapered roller bearings (Comparative Examples 11-15 in Table
1) in which, similar to the Examples, a carbo-nitrided layer having
a carbon content of 0.80 wt % or over and a Rockwell hardness HRC
of 58 or over and the retained austenite content of 25-35 vol % was
formed on each of the outer ring, inner ring and tapered rollers
formed from carburized bearing steel (SCr435) having an oxygen
content exceeding 9 ppm, and tapered roller bearings (Comparative
Examples 16, 17 in Table 1) in which the outer ring, inner ring and
tapered rollers were formed from carburized bearing steel (SCr435)
having an oxygen content of 9 ppm or less but the carbo-nitrided
layer formed thereon had a retained austenite content outside the
range as claimed in the present invention were prepared. Also, a
tapered roller bearing (Comparative Example 18 in Table 1) in which
carburized bearing steel (SCr435) having an oxygen content
exceeding 9 ppm was used and heat treatment with only ordinary
carburizing was prepared. The dimensions of each bearing were the
same as in Examples of the invention.
[0067] A debris contamination life test in which the tapered roller
bearings of the Examples of the invention and Comparative Examples
were mounted on a rotary shaft arranged in a case in which was
sealed a lubricating oil in which was mixed debris, and a clean oil
life test in which they were mounted on a rotary shaft arranged in
a case in which clean lubricating oil was circulated were
conducted.
[0068] The test conditions are as shown below.
[0069] Debris Contamination Life Test
[0070] Load: 11.76 kN
[0071] Revolutional speed: 1500 rpm
[0072] Lubricating oil: turbine oil VG56 (oil bath)
[0073] Debris: gas atomized metallic powder (particle diameter:
100-180 .mu.m, hardness: HV 700-800, mixed amount: 1 g/liter)
[0074] Clean Oil Life Test
[0075] Load: 21.56 kN
[0076] Revolutional speed: 2000 rpm
[0077] Lubricating oil: turbine oil VG 56 (circulation oil
supply)
[0078] The test results are shown in Table 1. In the debris
contamination life test and the clean oil life test, the lives were
evaluated in terms of L10 life (time period during which 90% of the
bearings were not destroyed and usable). Also, for the life ratios,
the endurance life of the bearing of Comparative Example 18, which
was manufactured under ordinary conditions both in material and
heat treatment, was used as a reference value.
[0079] It is apparent that the tapered roller bearings of the
Examples show excellent results both in the debris contamination
life test and clean oil life test. On the other hand, Comparative
Examples 11-15, in which the retained austenite content was in the
range of 25-35 vol % but the oxygen content of the steel was high,
showed good results in the debris contamination life test, but
inferior results in the clean oil life test. Also, for Comparative
Examples 16-17, in which the retained austenite content was out of
the range of the present application, the endurance life in the
clean oil life test was a relatively high value, but that of the
debris contamination life test was inferior.
[0080] FIG. 3 shows in enlarged scale a portion of the tapered
roller bearing of the second embodiment. It has edge crownings 20
having a width Wc which is 20% or less of the width W of the
raceway 19, at both ends of the raceway 19 of the inner ring 18. At
the central portion between these respective crownings 20, a center
crowning 21 having an extremely moderate curvature is formed. The
drop amount D of the crownings 20 is 20 .mu.m, and outside the
crownings 20, recesses 22 are provided.
[0081] This tapered roller bearing, too, is used to support a
differential gear case 7 like the one shown in FIG. 1, and each
part is formed from carburized bearing steel (SCr 435), and like
the tapered roller bearing 6 shown in FIG. 2, carbo-nitrided layers
having a carbon content of 0.8 wt % or over and a Rockwell hardness
HRC of 58 or over, and the retained austenite content of 25-35 vol
%, are formed on their surfaces.
[0082] Hereinbelow, the Examples of the second embodiment and its
Comparative Examples are described.
EXAMPLES
[0083] Tapered roller bearings (Examples 21-25 in Table 2) in which
a carbo-nitrided layer having a carbon content of 0.80 wt % or
over, a Rockwell hardness HRC of 58 or over and a retained
austenite content of 25-35 vol % was formed on each of the outer
ring, inner ring and tapered rollers formed from carburized bearing
steel (SCr435), and edge crownings having a width Wc which was 20%
or less of the width W of the inner ring raceway were formed at
both ends of the raceway were prepared. The tapered roller bearings
of Examples 21 through 23 were formed with a center crowning having
a crowning amount C of 2 .mu.m at the center of the inner ring
raceway, while the tapered roller bearings of Examples 24 and 25
were not. The bearing dimensions are the same as in the first
embodiment.
Comparative Examples
[0084] Tapered roller bearings (Comparative Examples 21-24 in Table
2) in which, similar to the Examples, a carbo-nitrided layer having
a carbon content of 0.80 wt % or over and a Rockwell hardness HRC
of 58 or over was formed on each of the outer ring, inner ring and
tapered rollers formed from carburized bearing steel (SCr435), but
the retained austenite content in the carbo-nitrided layers was out
of the range as claimed in the present application, and tapered
roller bearings (Comparative Examples 25-27 in Table 2) in which
the retained austenite content was within the range of the present
application, but the width of edge crownings exceeded the range of
the present application, or full crowning was formed over the
entire width of the inner ring raceway were prepared. In
Comparative Examples 22 and 24, the width of edge crowning also
exceeded the range of the present application. Also, a tapered
roller bearing (Comparative Example 28 in Table 2) in which the
retained austenite content and the width of edge crowning were
within the range of the present application, and the heat treatment
was ordinary carburizing hardening was prepared. Dimensions of each
bearing were the same as in the Examples.
[0085] For the tapered roller bearings of the Examples and
Comparative Examples, a debris contamination life test was
conducted. The test conditions were the same as those in the first
embodiment, and the endurance life was evaluated in terms of L10
life.
[0086] The test results are shown in Table 2. For the life ratios
in the table, the endurance life of Comparative Example 28, in
which the heat treatment was only carburizing hardening, was used
as a reference value. For any of the articles so indicated in the
Table, seizure occurred at the central portion of the raceway.
[0087] For each of the tapered roller bearings of the Examples, the
life ratio was more than four-fold and showed an excellent
endurance life. Also, no seizure occurred at the central portion of
the raceway. On the other hand, Comparative Examples 21-24, in
which the retained austenite content was out of the range of the
present application, had only about half the life ratio of the
tapered roller bearings of the Examples. For Comparative Examples
22 and 24, which were large in crowning width, seizure occurred at
the central portion of the raceway. Also, for Comparative Examples
25 and 26, in which the retained austenite content was in the range
of the present application, but the crowning width was large, the
life ratio was good, but seizure occurred at the central part of
the raceway. For Comparative Example 27, which was extremely small
in drop amount D, peeling occurred at the ends of the raceway, and
the life ratio improved little.
[0088] FIGS. 4A and 4B show the third embodiment. This tapered
roller bearing was also used for the support of a differential gear
case 7 like the one shown in FIG. 1, and their parts, that is, the
outer ring 23, inner ring 24 and tapered rollers 25, were formed
from carburized bearing steel (SCr435), and carbo-nitrided layers
23a, 24a, 25a having a carbon content of 0.80 wt % or over and a
Rockwell hardness HRC of 58 or over were formed on the surfaces of
these parts as shown in FIG. 4B.
[0089] As shown in FIG. 5, the cone angle apex of the tapered
rollers 25, and the respective raceways 26, 27 of the outer ring 23
and inner ring 24 converge at one point on the centerline of the
tapered roller bearing, and it is manufactured such that the ratio
of the radius of curvature R of the large end faces 28 of the
tapered rollers 25 to the distance R.sub.base from point O to the
large rib surface 29 of the inner ring 24, i.e. R/R.sub.base is in
the range of 0.75-0.87. Also, the large rib surface 29 is ground to
the surface roughness Ra of 0.12 .mu.m.
[0090] Hereinbelow, the Examples of the third embodiment and its
Comparative Examples are described.
EXAMPLES
[0091] Tapered bearings (Examples 31-34 in Table 3) shown in FIGS.
4A, 4B and 5, were prepared in which a carbo-nitrided layer having
a carbon content of 0.8 wt % or over and a Rockwell hardness HRC of
58 or over was formed on the surface of each of the outer ring,
inner ring and tapered rollers, which were formed from carburized
bearing steel SCr435, in which the radius of curvature R of the
large end faces of the tapered rollers was in the range of
R/R.sub.base=0.75 to 0.87, and in which the surface roughness Ra of
the large rib surface of the inner ring was 0.12 .mu.m. Dimensions
of the bearings were the same as in the first and second
embodiments.
Comparative Examples
[0092] Tapered bearings (Comparative Examples 31-33 in Table 3)
were prepared in which, like the Examples, a carbo-nitrided layer
having a carbon content of 0.8 wt % or over and a Rockwell hardness
HRC of 58 or over was formed on the surface of each of the outer
ring, inner ring and tapered rollers which were formed from
carburized bearing steel SCr435, but the R/R.sub.base ratio was out
of the range of the present application, and a tapered roller
bearing (Comparative Example 34 in Table 4) in which the heat
treatment was only carburized and hardening, and the R/R.sub.base
ratio was also out of the range of the present application was
prepared. Dimensions of the bearings are the same as in the
Examples.
[0093] For the Examples and Comparative Examples, a seizure
resistance test using a rotary tester, and the same debris
contamination life test as in the first and second embodiments were
conducted.
[0094] The test conditions of the seizure resistance test were as
follows.
[0095] Load: 19.61 kN
[0096] Revolutional speed: 1000-3500 rpm
[0097] Lubricating oil: turbine oil VG 56 (oil supply rate: 40
mililiters/minute, oil temperature: 40.degree. C..+-.3.degree.
C.)
[0098] The test results are shown in Table 3. For the life ratios
in the debris contamination life test, the endurance life (L10
life) of Comparative Example 34 was used as a reference value.
Also, seizure in the seizure resistance test occurred between the
large rib surface of the inner ring and the large end faces of the
tapered rollers.
[0099] For each of the tapered roller bearings of the Examples, the
endurance life was good with the life ratio in the debris
contamination life test being four or more. Also, it is apparent
that the limit revolving speed at which seizure occurred in the
seizure resistance test was 2700 rpm or over. On the other hand,
for Comparative Examples 31-33, in which carbo-nitrided layers were
formed, but the R/R.sub.base ratio was out of the range of the
present application, although the life ratio was good, the limit
revolving speed for the occurrence of seizure was 2500 rpm or
under, and the possibility that seizure may occur under normal use
conditions such as in a differential was high. For Comparative
Example 33, in which the surface roughness Ra of the large rib
surface was rough, it showed a limit revolving speed that was lower
than in Comparative Example 32 having the same radius of curvature.
For Comparative Example 34, in which heat treatment was ordinary
carburizing, and also R/R.sub.base ratio was a conventional value,
any of the test results were inferior.
[0100] In the above embodiments, SCr435 was used as a material for
each part, but it is possible to use such bearing steels as SCM420,
SCM430, SCM435, SCr420, SCr430, SAE5130, and SAE8620.
[0101] FIGS. 6A and 6B show the fourth embodiment. This tapered
roller bearing is also used for the support of a differential gear
case 7 as in FIG. 1, and comprises an outer ring 31 having a
conical raceway 30, an inner ring 35 having a conical raceway 32
and provided with a large rib surface 33 on the large-diameter side
of the raceway 32 and a small rib surface 34 on its small-diameter
side, a plurality of tapered rollers 36 arranged between the
respective raceways 30, 32 of the outer ring 31 and the inner ring
35, and a retainer 37 retaining the tapered rollers 36 at
predetermined circumferential intervals.
[0102] The small rib surface 34 of the inner ring 35, as shown
enlarged in FIG. 6B, is finished to a ground surface parallel to
the small end faces 39 of the tapered rollers 36 arranged on the
raceway 32. It is in surface contact with the small end faces 39 of
the tapered rollers 36 in the initial assembled state shown by
one-dot chain line in FIG. 6B, and the gap .delta. with respect to
the small end faces 39 of the tapered rollers 36 in the state in
which the tapered rollers 36 have settled in position as shown by
solid line is in the range of not more than 0.4 mm. The small rib
surface 34 may be finished by turning to reduce the cost.
[0103] The cone angle apexes of the tapered rollers 36, and the
respective raceways 30, 32 of the outer ring 31 and inner ring 35
converge, like the third embodiment shown in FIG. 5, at one point O
on the centerline of the tapered roller bearing, and it is
manufactured such that the ratio of the radius of curvature R of
the large end faces 38 of the tapered rollers 36 to the distance
R.sub.BASE from point O to the large rib surface 33 of the inner
ring 35, i.e. R/R.sub.base, is in the range of 0.75-0.87. Also, the
large rib surface 33 is ground to the surface roughness Ra of 0.12
.mu.m.
[0104] The Examples of the fourth embodiment and its Comparative
Examples are described below.
EXAMPLES
[0105] Tapered roller bearings (Examples 41-44 in Table 4) were
prepared in which the radius of curvature R of the large end faces
of the tapered rollers was such that the ratio R/R.sub.base was
0.75-0.87, the surface roughness Ra of the large rib surface of the
inner ring was 0.12 .mu.m, its small rib surface was formed as a
ground surface parallel to the small end faces of the tapered
rollers, and the gap .delta. was in the range of not more than 0.4
mm. Bearing dimensions were the same as in each of the
abovementioned embodiments.
Comparative Examples
[0106] Tapered roller bearings (Comparative Examples 41-43 in Table
4) were prepared in which the R/R.sub.base value was out of the
range of the present application, the small rib surface of the
inner ring was inclined outwardly relative to the small end faces
of the tapered rollers, and the gap .delta. exceeded 0.4 mm.
[0107] For the tapered roller bearings of the Examples of and
Comparative Examples, a seizure resistance test was conducted under
the same conditions as in the third embodiment. Also, for the
tapered roller bearings of Example 42 and Comparative Example 42, a
break-in test was also conducted. Sample numbers for the break-in
test were 66 for Example 42 and 10 for Comparative Example 42.
[0108] The results of the test are shown in Table 4. Seizure in the
seizure resistance test occurred between the large rib surface of
the inner ring and the large end faces of the tapered rollers.
[0109] For any of the tapered roller bearings of the Examples, the
limit revolving speed in the seizure resistance test was 2700 rpm
or over. This shows that the frictional resistance between the
large rib surface of the inner ring and the large end faces of the
tapered rollers is small. On the other hand, for the tapered roller
bearings of the Comparative Examples, the seizure occurrence limit
revolving speed was 2500 rpm or under, and a problem may arise
under normal use conditions such as in a differential. For
Comparative Example 43, in which the surface roughness Ra of the
large rib surface was rough, it showed a lower seizure occurrence
limit revolving speed than in Comparative Example 42 having the
same radius of curvature R.
[0110] For the break-in test results, in the Comparative Examples,
the average value of the number of revolutions until the tapered
rollers settled in position was six, whereas in the Examples, this
value was about half, i.e. 2.96. In the Examples of the invention,
the standard deviation of variation in the number of revolutions
was also small. Thus, this shows that it is possible to stably
shorten the break-in time.
[0111] FIG. 9 shows a portion of the tapered roller bearing of the
fifth embodiment. This tapered roller bearing was also used for the
support of a differential gear case 7 as shown in FIG. 1. The large
rib surface 41 of the inner ring 40 comprises a conical surface
41a, and a flank 41b smoothly connecting with the conical surface
41 and having an arcuate section, and a chamfer 41c connecting with
the flank 41b. The conical surface 41a is, like the tapered roller
bearing shown in FIG. 5, formed with point O as its center. The end
faces 43 of the tapered rollers 42 are each formed as a spherical
surface 43a having a radius of curvature R that is smaller than the
distance Ro from point O to the large rib surface 41 of the inner
ring 40. A recess 44 of a circular shape is formed at the center of
the spherical surface 43a. The outer peripheral end of the recess
44 extends to near the boundary between the conical surface 41a and
the flank 41b of the large rib surface 41.
[0112] As mentioned above, during use of the bearing, the tapered
rollers 42 roll with their large end faces 43 pressed against the
large rib surface 41, and the spherical surface 43a is partially
brought into contact with the conical surface 41a, so that a
contact oval 45 is produced between these two curved surfaces. The
boundary between the flank 41b and the conical surface 41a is
provided near the outer edge of the contact oval 45, and an acute
wedge-shaped gap is defined by the flank 41b and the spherical
surface 43a at a position near the contact oval 45.
[0113] The contact oval 45 grows larger as the axial load during
use of the bearing increases. With this tapered roller bearing,
assuming the maximum contact oval under the permissible maximum
axial load, the boundary between the flank 41b and the conical
surface 41a is designed to be near the outer edge of the maximum
contact oval, so that the wedge-shaped gap for drawing the
lubricating oil will be formed over the entire load range.
[0114] The present invention is applicable to various types of
tapered roller bearings.
[0115] As described above, for the tapered roller bearing of this
invention, each of its parts, i.e. outer ring, inner ring and
tapered rollers are formed from steel having an oxygen content of 9
ppm or less, and a carbo-nitrided layer having a carbon content not
less than 0.80 wt % and a Rockwell hardness HRC of 58 or over and
the retained austenite content of 25-35 vol % is formed on the
surface of these parts. Thus it is possible to enhance the
mechanical properties and fatigue strength of the parts, stably
maintain the carbo-nitrided layers on the surfaces of the parts to
a quality having suitable toughness, and markedly improve the
endurance life in debris contamination conditions.
[0116] According to this invention, an edge crowning having a width
that is 20% or less of the width of the raceway is formed at both
ends of the inner ring raceway. This prevents seizure by making the
contact surface pressure at the raceway uniform, maintains the
carbo-nitrided layers on the surfaces of the parts stably to a
quality having suitable toughness, and markedly improves the
endurance life in debris contamination conditions.
[0117] According to this invention, the radius of curvature R of
the large end faces of the tapered rollers is such that the ratio
R/R.sub.base will be 0.75-0.87, and the small rib surface of the
inner ring is formed into a surface parallel to the small end faces
of the tapered rollers to prevent seizure by reducing torque loss
and heat buildup due to sliding friction between the large rib
surface of the inner ring and the end faces of the tapered rollers,
and to shorten the break-in time to improve efficiency of mounting
of the bearing.
[0118] Further, according to this invention, a curved flank is
smoothly connected to the conical surface of the large rib surface
of the inner ring in contact with the large end faces of the
tapered rollers to form an acute wedge-shaped gap to increase the
lubricating oil drawing function into this contact region, prevent
seizure by reducing torque loss and heat buildup due to the sliding
friction, and prevent seizure due to abutment with the large rib
surface of the inner ring during tapered roller skew.
[0119] With the gear shaft support device of this invention, since
its gear shaft is supported by the tapered roller bearing of this
invention, endurance life improves even under use conditions in
which foreign matter mixes into gear oil, so that it is possible to
extremely prolong the maintenance cycle of a power transmission
device such as a differential.
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