Bearings – Rotary bearing – Antifriction bearing
Reexamination Certificate
1999-12-13
2001-07-17
Hannon, Thomas R. (Department: 3682)
Bearings
Rotary bearing
Antifriction bearing
C074S339000
Reexamination Certificate
active
06261004
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a main shaft gear mechanism for automobile (passenger car, truck, bus or the like) speed changers, and a tapered roller bearing used therefor.
For example, an automobile speed changer has a role to change the speed change ratio to meet widely varying travel conditions, thereby changing the engine torque so as to make smooth comfortable travel possible. Generally, the speed changer has to satisfy such requirements as proper speed change ratio, sufficient strength, durability, reliability, high power transmission efficiency, silence, and small-size and lightweight.
An example of this speed changer is a synchromesh type speed changer shown in FIG.
12
. In this speed changer, a main shaft
11
and an auxiliary shaft
12
which are disposed parallel with each other with a predetermined spacing therebetween are supported for rotation in a mission case (not shown), said main shaft
11
being operatively connected to an output shaft (associated with the driving wheels), the auxiliary shaft
12
being operatively connected to an input shaft (associated with the engine).
The auxiliary shaft
12
is integrally provided with an auxiliary shaft gear
13
, while the main shaft
11
has a main shaft gear
16
(which serves also as a bearing outer ring) rotatably mounted thereon through a bearing inner ring
14
and needle rollers
15
and constantly meshing with the auxiliary shaft gear
13
. One side of the main shaft gear
16
is formed with spline teeth
17
and a cone
18
, and a hub
19
is disposed close to the end surface of the cone
18
and integrally engagingly connected to the main shaft
11
. A synchromechanism
20
is interposed between the hub
19
and the cone
18
, and the outer periphery of the hub
19
has a sleeve
21
axially movably spline-connected thereto.
In the state shown in this figure, receiving the rotation of the auxiliary shaft gear
13
, the main shaft gear
16
is idling with respect to the main shaft
11
. On the other hand, when the sleeve
21
is moved axially rightward from the state shown in the figure, it meshes with the spline teeth
17
of the main shaft gear
16
through the synchromechanism
20
, whereby the connection between the main shaft gear
16
and the main shaft
11
is established. Thereby, the rotation of the auxiliary shaft gear
13
is reduced by the main shaft gear
16
with a predetermined speed ratio and transmitted to the main shaft
11
. During this speed change, the main shaft gear
16
rotates in synchronism with the main shaft
11
and the bearing inner ring
14
.
In this connection, during speed change, the synchronous rotation of the main shaft gear
16
and the bearing inner ring
14
causes the needle rollers
15
to assume a stopped position on the raceway surfaces of the two members
14
and
16
. On the other hand, repetitive action of external vibrations or the like could cause repetitive slight slippage between the needle rollers
15
and the raceway surfaces, so that the phenomenon called fretting in which the contact surface wears due to the relative repetitive slight slippage may become a problem.
In an arrangement intended to prevent fretting, the Parker process (phosphating) is applied to the raceway surfaces of the main shaft gear
16
and the bearing inner ring
14
, and the rolling contact surfaces of the needle rollers
15
to reduce the wear resistance between the needle rollers
15
and the raceway surfaces. However, wear of Parker process coatings may make it impossible to expect a long-term satisfactory fretting-preventive effect.
I have previously proposed, as means capable of long-term prevention of fretting on the raceway surfaces of the main shaft gear and the bearing inner ring and on the rolling contact surface of rolling element, an imbalance means in the form of the irregular circumferential disposition of rolling element, the circumferential weight imbalance of a cage holding rolling element, or rolling element weight inequality (Japanese Kokai Patent Publication Heisei 9-292008). Depending on the size of variation in rotation (variation in speed) or vibration, however, it might be difficult to attain a satisfactory fretting-preventive effect.
SUMMARY OF THE INVENTION
An object of the invention is to be capable of exerting the intended fretting-preventive effect without being influenced by the size of rotative variation (variation in speed) or vibration.
A main shaft gear mechanism for automobile speed changers according to the present invention comprises an auxiliary shaft operatively connected to an input shaft associated with an automobile engine, auxiliary shaft gear mounted on an auxiliary shaft, a main shaft operatively connected to an output shaft associated with the driving wheels, a main shaft gear which has a toothed portion integrally formed on its outer peripheral surface and constantly meshing with the auxiliary shaft gear and which has a raceway surface on its inner peripheral surface, a tapered roller bearing interposed between the main shaft and the main shaft gear, an imbalance means which produces a circumferential weight imbalance in the assembly of the tapered rollers and cage of the tapered roller bearing, a clutch gear connected to the main shaft gear, and a synchromechanism which effects or interrupts transmission of engine torque between the main shaft gear and the main shaft through the clutch gear by the action of a selector, wherein at least one of the roughness of the cone back face of the bearing inner ring and the roughness of the large end faces of the tapered rollers of the tapered roller bearing is not more than 0.05 &mgr;mRa.
Further, a tapered roller bearing according to the present invention comprises a bearing outer ring having a raceway surface on its inner peripheral surface, a bearing inner ring having a raceway surface on its outer peripheral surface, tapered rollers interposed between the raceway surfaces of the bearing outer and inner rings and held at predetermined circumferential intervals by a cage, and an imbalance means for producing a circumferential weight imbalance in the assembly of tapered rollers and cage, wherein at least one of the roughness of the cone back face of the bearing inner ring and the roughness of the large end faces of the tapered rollers is not more than 0.05 &mgr;mRa.
In addition, in the main shaft gear mechanism for automobile speed changers and in the tapered roller bearing according to the present invention, it is preferable that the radius of the large end faces be worked such that the maximum value thereof including the working precision is substantially equal to the reference radius, and that the roughness of the cone back face of the bearing inner ring be 0.01-0.04 &mgr;mRa and that the roughness of the large end faces of the tapered rollers be 0.01-0.05 &mgr;mRa.
According to the present invention, in an arrangement having an imbalance means in the form of the irregular circumferential disposition of tapered rollers, the circumferential weight imbalance of a cage holding tapered rollers, or the rolling body weight inequality imbalance, the setting of the roughness of the cone back face of the bearing inner ring and the roughness of the large end faces of the tapered rollers in the aforesaid predetermined allowable range makes it possible to reduce sliding friction resistance between the raceway surface of the main shaft gear or bearing outer ring, or the raceway surface of the bearing inner ring and the rolling contact surfaces of the tapered rollers. Further, setting the radius of the large end faces such that the maximum value thereof including the working precision is substantially equal to the reference radius, makes it possible to reduce sliding friction resistance by increasing the radius of the large end faces of tapered rollers and reducing the contract surface pressure. In addition, if the surfaces of the tapered rollers are formed with coating films of the MoS
2
type it is easier to reduce sliding friction resistance.
Application of full crowning to
Mizutani Mamoru
Tsujimoto Takashi
Arent, Fox, Kintner Plotkin & Kah, PLLC
Hannon Thomas R.
NTN Corporation
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