Constant velocity universal joint

Details Constant velocity universal joint Constant velocity universal joint

1999-11-15

2001-11-20

Browne, Lynne H. (Department: 3629)

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

06319133

ABSTRACT:

BACKGROUND OF THE INVENTION
Description
The invention relates to a constant velocity universal joint for transmitting torque, having an outer joint part with outer ball tracks, an inner joint part with inner ball tracks, torque transmitting balls guided by pairs of outer and inner ball tracks positioned in corresponding meridian planes, and a ball cage which lodges the balls in circumferentially distributed windows and holds the balls in a common plane and guides the balls on to the angle-bisect-ing plane when the joint is articulated, with the center lines of the outer and inner ball tracks being composed of at least two differently curved portions adjoining one another.
Joints of this type are known as Rzeppa fixed joints (RF) or undercut-free fixed joints (UF). The latter are described in DE-PS 22 52 827. For a certain size of such joints, and especially as regards the axial length of such joints, there exists a mutual interdependence between the maximum articulation angle and the thickness of the shaft to be connected to the inner joint part. On the one hand, the articulation angle is limited in that the balls must be prevented from leaving the track ends, or, to be more precise, as far as edge loads at the track ends are concerned, it has to be ensured that there exists a sufficient safety distance between the point of contact of the ball in the track and the track end edge. Furthermore, the articulation angle is limited by the thickness of the connecting shaft which, upon articulation of the inner joint part, abuts against an inner cone of the outer joint part and thus prevents further articulation. It makes sense to adapt the thickness of the connecting shaft and the shape and position of the inner cone to one another in such a way that said abutment of the connecting shaft coincides with the safety distance between the point of contact of the ball and the track end edge.
Developments in automotive engineering are such that said constant velocity universal joints are expected to have an ever increasing performance, which means that with a predetermined available space and mass, the service life and functional scope have to be increased, or, vice versa, with a predetermined service and functional scope, space and mass have to be reduced.
With prior art joint designs, any improvements on the one side, for example in respect of the articulation angle, can only be achieved by shortening the service life and reducing the breaking strength.
SUMMARY OF THE INVENTION
It is the object of the present invention to provide a joint of the initially mentioned type whose performance is improved in such a way that space and mass can be reduced without adversely affecting the remaining parameters.
In accordance with the invention, the objective is achieved in that the center lines S of the ball tracks of the outer joint part each comprise convexly curved inner portions S
1
and, towards the open end, oppositely curved concave first end portions S
2
and that the center lines of the ball tracks of the inner joint part each comprise curved outer portions and, towards the base end of the outer joint part, oppositely curved, second end portions wherein the inner portions S
1
and the outer portions each extend in a curved way around a center Z
1
inside the outer joint part, and the first end portions S
2
and the second end portions each extend in a curved way around a center Z
2
outside the outer joint part. This means that the inner portions S
1
extend at least partially in a curved way around a joint center C and that the first end portions S
2
positioned towards the open end are curved in the opposite direction, i.e. outwardly. In general, the result is that the distance of the center lines of the ball tracks in the outer joint part from the axis A
A
in the first end portions S
2
increases towards the open end of the outer joint part.
The shape of the outer joint part is hence characterised in that the ends of the ball tracks widen and radially move away from one another towards the open end of the outer joint part.
Preferred embodiments of the invention are described in further sub-claims to which special reference is hereby made.
Due to general conditions of symmetry, the ball tracks in the inner joint part widen and move away from one another in an end portion at the axially opposite end, i.e. towards the base of the outer joint part, again with reference to the center lines of the ball tracks whose distance from the axis A
I
of the inner joint part is thus greatest at said end.
In accordance with certain lines of curvature, said first end portions S
2
can extend as circular arcs for example, but the end portions of the tracks can also extend in straight lines at an angle relative to the longitudinal axis A
A
.
The effect achieved by the track shape in accordance with the invention consists in that—in contrast to joints in accordance with the state of the art wherein the points of contact of the balls in the tracks are positioned approximately in radial planes extending through the respective centers of the balls—there is achieved an axial distance between the points of contact of the balls in the tracks with reference to the radial planes through the joint centers, with the points of contact being offset towards the central joint plane. In this way, it is possible to achieve improvements regarding the relationships of the parameters of joint length/joint mass, maximum articulation angle and thickness of the connecting shaft. As far as further explanations of the inventive measures and effects are concerend, reference has to be made to the following drawings. In the embodiment illustrated, the inventive joint is shown as a UF joint. However, to put the technical teaching in accordance with the invention into effect, it is not necessary for the ball tracks to be undercut-free.


REFERENCES:
patent: 4185476 (1980-01-01), Krude
patent: 4459122 (1984-07-01), Rehfeld
patent: 5376052 (1994-12-01), Jacob et al.
patent: 42 08 786 C1 (1993-07-01), None
patent: 43 02 432 A1 (1993-08-01), None
patent: 42 30 639 C1 (1993-10-01), None
patent: 2 081 748 (1996-03-01), None
patent: 2 115 520 A (1983-09-01), None
patent: 54-125342 (1979-09-01), None

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