Bearings – Rotary bearing – Antifriction bearing
Reexamination Certificate
1999-11-24
2001-12-11
Footland, Lenard A. (Department: 3682)
Bearings
Rotary bearing
Antifriction bearing
C384S564000, C384S565000, C384S569000, C384S571000
Reexamination Certificate
active
06328477
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to tapered roller bearings and gear shaft support devices for vehicles.
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.
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
.
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
.
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
.
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 slide contact with each other.
On the other hand, since the distance between the large rib surface
54
and the small rib surface
55
are 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
with small clearance existing 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.
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 &dgr; is present between the large end faces
59
and the large rib surface
54
of the inner ring
56
.
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 &dgr; 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 &dgr; exists between the small end face
60
and the small rib surface
55
.
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.
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 worn powder produced at these portions can enter gear oil sealed in the housing. Such worn 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.
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.
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 surfaces
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 regular position shown in FIG.
12
C. 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 regular position tends to become further long.
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 P
1
on the small end face
60
comes into contact with point Q
1
on the small rib surface
55
, so that the gap &dgr; when the tapered rollers
57
settle will be &dgr;
1
. On the other hand, in the case of the small end face
60
shown by chain line, in the initial assembled state, point P
2
comes into contact with point Q
2
, so that the gap &dgr; when the tapered rollers
57
settle will be &dgr;
2
. Thus, due to differences in chamfer dimension and shape of the small end fa
Maeda Kikuo
Okamoto Yuji
Tsujimoto Takashi
Footland Lenard A.
NTN Corporation
Wenderoth , Lind & Ponack, L.L.P.
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