Constant velocity universal joint

Details Constant velocity universal joint Constant velocity universal joint

2000-12-22

2002-12-03

Brown, Lynne H. (Department: 3679)

Rotary shafts, gudgeons, housings, and flexible couplings for ro

Coupling accommodates drive between members having...

Coupling transmits torque via radially spaced ball

C464S906000

Reexamination Certificate

active

06488588

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates to a constant velocity universal joint that is suited to applications where rotation backlash is undesirable, and is particularly preferable for the steering apparatus of an automobile.
In the steering apparatus of an automobile, for example as shown schematically in
FIG. 34
, rotation torque imparted to a steering wheel
20
is transmitted via a main shaft
21
of a steering column and an intermediate shaft
22
to a gear shaft (pinion shaft or the like)
24
of a steering gear
23
, while being converted to a linear motion by the mechanism of the steering gear
23
thereby to be transmitted via a link mechanism (knuckle or the like)
25
to wheels
26
as steering force. The steering gear
23
may be one of various types including rack and pinion type, ball screw type and worm roller type, while the rack and pinion type is predominantly used for the reason of high rigidity and light weight thereof. The intermediate shaft
22
is disposed at an angle to the main shaft
21
and the gear shaft
24
, and is connected to the main shaft
21
and the gear shaft
24
via universal joints
27
,
28
, for the purpose of absorbing the impact energy in case of collision.
While the Cardan joint (universal joint employing cross yokes) has been predominantly used for the universal joints (
27
,
28
) of the steering apparatus, constant velocity universal joints are being increasingly employed instead of the Cardan joint in order to allow a larger angle in the joint (in conjunction with the layout of vehicle components) and improve the movement of the joint (feel of the steering operation).
Meanwhile a constant velocity universal joint of ordinary constitution has a small clearance (inner gap) between torque transmitting ball and a ball track, which inevitably results in rotation backlash (play in the circumferential direction) taking place in the joint when the direction of rotation changes. Thus use of the constant velocity universal joint of the ordinary constitution in the steering apparatus leads to such problems as the loss of stability in steering, and loss of sharp or direct feel of steering.
In the field of automobile, constant velocity universal joints have many records of applications to the drive shaft, and the constant velocity universal joint of the ordinary constitution is normally designed to such specifications that satisfy the requirements of the drive shaft. In the case of the steering apparatus, however, since less load torque is applied to the joint and the joint rotates at lower speeds than the drive shaft, the constant velocity universal joint of the ordinary constitution has rather excessively higher specifications compared to the required characteristics, and therefore improvements are required for the reduction of joint weight and manufacturing cost.
The ball fixed type constant velocity universal joint of this type also requires the complicated assembly process as described above, and therefore has such disadvantages as follows.
(1) The assembly work requires skilled technique and is difficult to mechanize (automate).
(2) It is necessary to make the guide grooves of the inner and outer joint members longer (in the axial direction) than the length required for the function, in order to facilitate the assembly of the balls, thus resulting in larger joint dimension.
(3) It is necessary to make the size of the pocket of the cage in the circumferential direction larger, in order to facilitate the assembly of the balls (because the balls move in the circumferential direction in the pocket of the cage when the inner and outer joint members are caused to make angular displacement). This makes a disadvantage in the design of the cage in terms of strength.
(4) It is necessary to prepare the inner joint member and the shaft separately (in case the inner joint member and the shaft are prepared as an integral part, the shaft interferes with the outer joint member when assembling the balls, thus making it impossible to secure the amount of angular displacement required for the assembly). This leads to increases in the number of parts and in the number of assembly steps.
SUMMARY OF THE INVENTION
An object of the present invention is to solve the problem of rotation backlash in the ball fixed type constant velocity universal joint, and provide a simpler, light weight, compact and low-cost ball fixed type constant velocity universal joint that can be assembled in an improved process.
Another object of the present invention is to ensure good feel of rotation (smoothness of rotation) and, when applied to the steering apparatus in particular, improve the performance such as the feel of steering, while maintaining the constant velocity characteristics of this type of constant velocity universal joint.
Yet another object of the present invention is to reduce the resistance to the rotation in the constant velocity universal joint of this type and ensure good feel of rotation (smoothness of rotation) and, when used in a steering apparatus in particular, improve the performance such as the steering force, auto-centering of the steering wheel and the feel of steering.
In order to achieve the objects described above, the present invention provides a ball fixed type constant velocity universal joint comprising an outer joint member having a curved guide groove formed in the axial direction on a spherical inner circumferential surface thereof, an inner joint member having a curved guide groove formed in the axial direction on a spherical outer circumferential surface thereof, ball disposed in a ball track formed by the coordination of the guide groove of the outer joint member and the guide groove of the inner joint member, and a cage that holds the ball, with the center of the guide groove of the outer joint member and the center of the guide groove of the inner joint member being offset to the opposite sides to each other by equal distances in the axial direction with respect to the center plane of the joint that include the centers of the ball, the ball track being gradually reduced toward the opening or the innermost side of the joint, wherein the inner joint member is allowed to make relative displacement in the axial direction with respect to the cage, and elastic pressing means having a spherical surface that makes fitting contact with the outer circumferential surface of the inner joint member is interposed between the outer circumferential surface of the inner joint member and the inner circumferential surface of the cage, so that the elastic force of the elastic pressing means presses the outer circumferential surface of the inner joint member toward the side opposite to the offset direction of center of the guide groove thereof.
The inner joint member makes a relative displacement in the axial direction opposite to the offset direction under the urging pressure of the elastic pressing means, thereby to press the ball, and stops at a position where the inner gap between the balls and the guide grooves of the inner and outer joint members disappears. As a result, a certain amount of preload is applied in the axial direction to the ball, thus eliminating the rotation backlash (play in the circumferential direction). Also because the spherical surface of the elastic pressing means presses the outer circumferential surface of the inner joint member, the surface pressure in the portion of contact between both members is reduced and the outer circumferential surface of the inner joint member can be guided by the spherical surface.
In the constitution described above, the ball track may have such a configuration that is gradually reduced toward the opening side of the joint, at least the region on the opening side of the inner circumferential surface of the cage is a cylindrical surface that fits with the outer circumferential surface of the inner joint member, and the elastic pressing means is disposed on the cylindrical surface. This configuration makes it possible to assemble the inner joint member into the inner circumferentia

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