Description of Invention

This invention relates to constant velocity ratio (homokinetic) universal joints, for uniform torque transmission between first and second members whose respective rotational axes may be inclined to one another.

Various forms of constant velocity ratio universal joint are well known. One such known type of joint comprises an outer joint member which is of hollow configuration, and an inner joint member disposed within the outer joint member. The inner joint member is provided with a plurality of circumferentially spaced, axially extending grooves which face corresponding grooves provided on the inside of the outer joint member. A number of balls are provided, one in each facing pair of grooves in the two joint members for torque transmission between the joint members. For the transmitted torque to be equally shared between the balls, the grooves in the inner joint member must be in perfect angular registration with the grooves in the outer joint member. This is difficult to achieve, and, because clearance between balls and grooves has to be provided to allow assembly, it is not unknown for some of the balls to be lightly loaded or even not loaded at all. This can cause noisy operation of the joint.

In this type of joint, when the rotational axes of the two joint members are inclined to one another, i.e. when the joint is articulated, uniform transmission of rotary motion between the joint members requires the centres of all the balls to lie in a plane (herein called the bisector plane) which bisects the angle between the rotational axes of the two joint members and which is normal to the plane in which the axes lie. To constrain the balls so that they occupy such a plane, it is usual to employ a ball-retaining cage interposed between the inner and outer joint members, the cage or the grooves being configured so as to bring the

balls into the bisector plane. The forces involved in such control of the balls bring the disadvantage of frictional losses in use of the joint.

In another known form of joint, the driving and driven members both have a number of similar axially extending projections, which are circurnferentially spaced apart within an annular envelope. The members fit together axially so that projections on one are interposed between the projections of the other with a clearance, and axially extending facing surfaces of the projections are provided with grooves in each facing pair of which a ball is received. Thus if each of the joint members has N projections, there are 2N balls in the complete universal joint.

This form of joint is subject to the aforementioned disadvantages with respect to the need for accurate manufacture in order that torque can be shared equally between the balls, but it will also be appreciated that only half the total number of balls partake in torque transmission in each direction. In other words, of the total of 2N balls in the joint a set of N alternate balls transmits torque only in one direction and the remaining N balls are able to transmit torque only in the other direction. This is because each ball is located in one groove in an axial plane on one joint member and in one groove in the co-acting axial plane on the other joint member.

It is an object of the present invention to provide a constant velocity ratio universal joint which overcomes or reduces the above described disadvantages associated with the provision of a ball-retaining cage in a joint, and of unequal sharing of transmitted torque between balls in a joint.

According to one aspect of the present invention, we provide a constant velocity ratio universal joint, comprising first and second joint members having respective rotational axes, and first and second balls arranged for torque transmission between said joint members, each of said balls being transversely confined by formations in the first joint member and also being transversely confined by formations in the second joint member.

By "transversely confined", we mean that at each position a ball assumes, in use, with respect to the formations in a respective joint member, the ball at such position is constrained against movement, other than that which may be permitted by operating clearances and manufacturing tolerances, in a plane normal to the rotational axis of the respective joint member.

The formations in each joint member for transversely confining each of the balls relative thereto may comprise a respective pair of groove formations engaging the ball at portions of the ball's surface substantially diametrically opposed to one another with respect to the ball. Then, in the complete joint, each of the balls is confined between a pair of groove formations in one joint member and a pair of groove formations in the other joint member.

Preferably the first and second joint members are substantially identical to one another.

The groove formations in each pair thereof may substantially comprise approximately diametrically opposite zones of an imaginary cylinder. In other words, the groove formations of each pair are substantially in the form of respective parts of a cylindrical surface, approximately diametrically opposed to one another relative to the central longitudinal axis of such cylinder which will herein be referred to as the axis of the groove pair. In practice, the groove formations of each pair may differ slightly from being exactly parts of a single cylindrical surface associated with the pair of groove formations. For example, in cross section of the groove pair, each formation may be of slightly increased radius of curvature with the centres of curvature of the two groove formations offset from another so that the maximum size of the circle which can be inscribed between the groove formations is equal to the ball diameter plus any required operating clearance. Each groove formation then provides for substantially point contact with a ball constrained thereby, instead of line contact. Such configuration of the groove formations, or any other desired variation from cylindrical surface portions, is intended to be within the scope of the present invention and to be embraced by the terminology used herein.

As described above, each of the joint members has a first pair of groove formations which constrains the first ball, and a second pair of groove formations which constrain the second ball, so that each of the joint members has associated therewith a first imaginary cylinder and a second imaginary cylinder. In each of the joint members, the longitudinal axes of the first and second groove pairs are parallel to one another, and lie in a plane which also contains the rotational axis of the joint member.

In one embodiment of joint according to the invention described hereafter, the axes of the groove pairs of each joint member are inclined to the rotational axis of the joint member. In a transverse view of the complete joint, the axes of the groove pairs of the second joint member are inclined to the rotational axis of such second joint member at the same angle as the inclination of the axes of the groove pairs of the first joint member but in the opposite sense, so that the axes of the groove pairs would appear to cross one another. Thus each ball is constrained to a position where its centre lies at the point of crossing of the axes of the groove pairs.

In another embodiment of joint according to the invention described hereafter, the axes of the groove pairs in each joint member are parallel to the respective rotational axes of the joint members. When such a joint is in the aligned (non-articulated) condition, such that the rotational axes of the two joint members are the same, the axes of the corresponding groove pairs of the joint members also would be the same so that, in the absence of any constraint, each ball would be free to move axially relative to both joint members.

In the first embodiment in which the axes of the groove pairs are inclined to the rotational axes of the joint members, such disposition of the axes of the groove pairs means that when the joint is articulated a line joining the centres of the two balls to one another passes through the centre of articulation of the joint (i.e. the point at which the rotational axes of the two joint members intersect) and, as the joint rotates, such line always lies in the bisector plane. Thus, the joint is a constant velocity ratio umversal joint. If the joint is never

articulated to an angle greater than twice the angle at which the axes of the groove pairs of each joint member are inclined to the rotational axis of the joint member, no further constraint upon the balls is necessary since the balls never are released from their constraint by the groove formations in the joint members.

The joint may comprise centering means operative between the two joint members, to constrain the joint members axially relative to one another and define the centre about which the joint members can undergo relative articulation.

Such centering means may comprise ball and socket means, comprising a ball element associated with one of the joint members and a socket element associated with the other joint member.

In the other embodiment of joint described hereafter, wherein the axes of the groove pairs of the joint members are parallel to the rotational axes of the joint members, this also is a constant velocity ratio universal joint since when the joint is articulated the axes of the groove pairs of the two joint members intersect one another and constrain the balls as aforesaid. When the joint is in the aligned (non-articulated) condition, however, each ball would not be so constrained and therefore, in this embodiment of the joint, there has to be provided ball-centering means, for centering the balls axially between the two joint members.

Such ball-centering means may comprise resilient means operable on the balls to centre them. Resilient elements may be operative between each ball and each of the joint members to centre the balls between the joint members.

In the embodiment described hereafter, such resilient elements comprise compression springs disposed on opposite sides of each ball and reacting axially against the joint members, the compression springs engaging the balls through the intermediary of abutment elements.

If the joint members of a joint according to the invention are connected to one another only by the torque-transmitting balls and without any other means such as a ball and socket device, the two joint members are able to undergo plunge, i.e. axial movement relative to one another, as well as relative articulation. The ability of a joint to accept plunge is useful for application to

a drive shaft in, for example, a motor vehicle where changes in the overall length of the shaft take place in use.

Each of the joint members in each embodiment of joint according to the invention described hereafter may take the form of a body having projections extending axially therefrom, the groove formations for confining the balls comprising cylindrically concave bevels formed on edge portions of the projections.

The invention will now be described by way of example with reference to the accompanying drawings, of which

Figure 1 is a three dimensional view of one joint member, with two balls transversely confined therein, of a first embodiment of joint according to the invention;

Figure 2 is a side view of the joint member of Figure 1, with two balls transversely confined therein, looking in the direction of arrow A in Figure 1;

Figure 3 is an axial view of the joint member, with two balls transversely confined therein, looking in the direction of arrow B in Figure 1;

Figure 4 is a view of the joint member, with two balls transversely confined therein, looking in the direction of arrow C in Figure 2;

Figure 5 is a transverse cross section through the joint member, on the plane containing point "P" in Figure 2;

Figure 6 is a side view of the complete universal joint; Figure 7 is a transverse cross section through the complete universal joint, on the plane containing point "P" in Figure 6;

Figure 8 is a transverse cross section similar to Figure 7 but showing a method of incorporating a conventional ball and socket joint in the joint;

Figure 9 is a three dimensional view of one joint member, with two balls transversely confined therein, of a further embodiment of joint according to the invention;

Figure 10 is a side view of the joint member of Figure 9, with two balls transversely confined therein, looking in the direction of arrow A in Figure 9;

Figure 11 is a side view of the joint member, with two balls transversely confined therein, looking in the direction opposite to arrow A in Figure 9;

Figure 12 is a view of the joint member with two balls transversely confined therein, looking in the direction of arrow B in Figure 10;

Figure 13 is a view in the direction of arrow B of Figure 10, with the balls omitted;

Figure 14 is a side view of the complete universal joint of Figures 9-12 with the right-hand half in axial cross-section;

Figure 15 is a transverse cross section through the complete universal joint, on the plane containing point "P" in Figure 14; and

Figure 16 is a schematic diagram showing how the position of the point of articulation "P" can be maintained relative to the main joint members.

Referring firstly to Figures 1 to 8 of the drawings, each of the main joint members of a first embodiment of joint according to the invention has a body portion 1 with an axis of rotation 2. The lateral surface of the body portion is cylindrical and concentric with the axis of rotation.

Integral with the body portion 1 are a first projection 3 and a second projection 4, both of which extend in a direction generally parallel to the axis of rotation. The lateral surfaces of first projection 3 are a plane face 5 and an axially extending oval section surface 6 as shown in Figure 5. Face 5 is parallel to and at a distance from the axis of rotation 2, that is to say, it is a portion of a chordal plane. The curved surface 6 is generally symmetrical about an axial plane which is perpendicular to face 5.

The lateral surfaces of second projection 4 are a part of a circular cylindrical surface 7, part of an oval cylindrical surface 8 and two plane faces 9 and 10 which are parts of a chordal plane as shown in Figure 5. The part- cylindrical surface 7 is a continuation of the lateral cylindrical surface of the body portion 1.

Faces 9 and 10 are parallel to the axis of rotation and at a distance therefrom in the direction opposite to that of face 5. Faces 9 and 10 are parallel to face 5. The curved surface 8 is generally symmetrical about an axial plane which is perpendicular to faces 9 and 10.

The shape of first projection 3 further comprises cylindrically concave groove formations in the form of bevels 11 and 12 along all or part of the length of the corner edges formed by the intersections of face 5 and the curved surface 6. The shape of second projection 4 further comprises concave groove formations in the form of bevels 13 and 14 along all or part of the length of the corner edges formed by the intersections of the curved surface 8 and faces 9 and 10 respectively.

Referring to Figure 5, the concave groove formation 11 on first projection 3 and adjacent groove formation 13 on second projection 4 are approximately diametrically opposite parts of the surface of a first imaginary circular cylinder, the central longitudinal axis 16 of which lies in the plane of the paper in Figure 2; that is to say, axis 16 is parallel to faces 5, 9 and 10. The concave groove formation 12 on first projection 3 and the adjacent groove formation 14 on second projection 4 are approximately diametrically opposite parts of the surface of a second imaginary circular cylinder the central longitudinal axis 17 of which lies in the same axial plane as the first imaginary cylinder, Le. in the plane of the paper in Figure 2.

Referring to Figure 2, the axes 16 and 17 of first and second imaginary cylinders of the two pairs of groove formations respectively are parallel to one another but are inclined to the axis of rotation 2 by an angle G.

The diameter of each of the two imaginary cylinders is such that the pair of proximate groove formations 11 and 13 and the pair of proximate groove formations 12 and 14 can each lightly transversely confine a respective ball 15 as shown in Figures 1, 2, 3, 4 and 7. Thus, at all positions of each ball along the groove formations, the ball is constrained against movement, other than what may be permitted by operating clearances and manufacturing tolerances, in directions

normal to the rotational axis of the joint member. The balls do, of course, move transversely of the joint member axis as they roll along the groove formations.

In the complete universal joint according to a first embodiment of the invention, two joint members 1 as above described are fitted together axially to one another as shown in Figures 6 and 7. The first projection 3 of each of the joint members is accommodated, with clearance, within the hollow defined by the curved wall 8 of the other joint member.

With reference to Figure 6, the lower joint member 1 shown in that figure has the axes of its ball-confining groove pairs oriented as shown by arrow C in Figure 2. Since the two joint members are identical to one another, the upper joint member in Figure 6 has the axes of its groove pairs oriented as indicated by the arrow D in Figure 6. Thus, in lateral view of the complete joint, the ball-confining groove pairs of the two joint members cross one another.

The universal joint of Figure 6 is assembled by positioning the respective balls 15 in the grooves of the lowermost joint member 1, to form a sub-assembly as shown in Figure 2. The uppermost joint member 1 is then positioned above the sub-assembly, oriented as shown in Figure 6, and pushed downwardly on to the sub-assembly in the direction of arrow D. Thus the balls are received in the groove pairs 11, 13 and 12, 14 of both the joint members.

The above described "crossing" configuration of the groove pairs in the two joint members has the effect that when the joint is articulated and the joint members rotated above their respective axes 2, the centres of the balls 15 always lie in the bisector plane. The centre of articulation of the joint, i.e. the point where the axes 2 intersect as indicated by P in Figure 6, also lies in such plane. Thus the universal joint is a constant velocity ratio (homokinetic) joint.

The axes of the groove pairs in each joint member are equally spaced from the point P. From consideration of the transverse section through the joint, in the plane containing the point P, shown in Figure 7, it will be noted that since each ball is transversely confined in the opposed groove pairs of both joint members, the balls transmit equally in torque transmission between the joint

members. Further, the balls do not have to be constrained by a cage or other means, since the guidance thereof is deteπnined by the configuration of the groove pairs in the joint members.

In use of a joint as above described, articulation angles up to twice the angle G at which the groove pairs in each joint member are inclined relative to the rotational axis of the joint member are possible, without the possibility that the balls may escape from their confinement in the groove pairs of the joint members.

Centering means operative between the joint members may be provided to constrain the joint members axially relative to one another and define the centre of articulation P of the joint. One possible configuration of such centering means is shown in Figure 8: it comprises a ball and socket device 20 having a ball element and a socket element associated respectively with one of the joint members and the other of the joint members. Such ball and socket elements may be assembled relative to one another by fitting them to the joint members through bores extending transversely through the projections 3 of the joint members, as shown in Figure 8.

If such centering means is not provided, the joint members may be disassembled axially from one another. However, it will be appreciated that if, in use, the joint members are associated with rotary components whose relative spatial position is fixed, such centering means need not be provided.

For strengthening purposes, the main body portion of each joint member may be thickened at its junction with the projection 3 extending therefrom. This is shown at 18 in Figure 6. This necessitates a complementary cutting away of the projection 4 of the joint member, as indicated at 19 in Figure 6, to maintain freedom of articulation between the joint members.

Referring now to Figures 9 to 16 of the drawings, each of the main joint members of a second embodiment of joint according to the invention has a body portion 101 with an axis of rotation 102. The lateral surface of the body portion is cylindrical and concentric with the axis of rotation.

Integral with the body portion 101 are a first projection 103 and a second projection 104, both of which extend in a direction generally parallel to the axis of rotation. In transverse cross-section the basic shape of projection 103 is a sector of a circle, that is to say it is bounded by two axial planes 105 and a part cylindrical surface which is a continuation of the lateral surface of the body portion 101. The zone at the intersection of the two axial planes is truncated symmetrically by a plane face 106 which is parallel to the axis of rotation, thus forming two straight parallel corner edges 107 seen clearly in Figure 13.

In transverse cross section the basic shape of projection 104 is a segment of a circle, that is to say it is bounded by a chordal plane 108 and a part cylindrical surface which is a continuation of the lateral surface of the body portion 101. Planes 106 and 108 are nominally parallel and approximately equi-distant from the axis of rotation. A slot having plane parallel sides 109, shown in Figure 11, is cut symmetrically and transversely through projection 104. The planes of sides 109 intersect plane 108 perpendicularly to form two straight parallel corner edges 110, Figure 13.

The shape of projection 103 is further characterised by the provision of groove formations in the form of cylindrically concave bevels 111 and 112 along all or part of the corner edges 107. The shape of second projection 104 is further characterised by the provision of groove formations in the form of cylindrically concave bevels 113 and 114 along all or part of corner edges 110.

Referring to Figure 13, the concave bevel surface 111 on first projection 103 and the adjacent bevel surface 113 on second projection 104 are approximately diametrically opposite parts of the surface of a first imaginary cylinder. Likewise, the concave bevel surface 112 on first projection 103 and the adjacent bevel surface 114 on second projection 104 are approximately diametrically opposite parts of the surface of a second imaginary cylinder. The central longitudinal axes of these imaginary cylinders are co-planar with, parallel to, and equi-distant from the axis of rotation.

The diameter of each of the two imaginary cylinders is such that the groove pairs provided by the bevel surfaces 111, 113 and the bevel surfaces 112, 114 can each lightly transversely confine a respective ball 115 as shown in Figures 9-12.

In a complete universal joint according to the second embodiment of the invention, two joint members, identical to one another and as described above, are assembled axially relative to one another as shown in Figure 14. The projection 103 of each of the joint members generally extends into the region between the planar sides 109 of the slot in projection 104 of the other joint member. Each ball is confined between the groove pairs of both joint members, as shown in Figure 15. In projection 104 of each joint member, the corner edges of the intersection of the outer cylindrical surface and the faces 109 are hollowed away in the form of a chamfer 116 (clearly shown in Figure 15), and the outer form of the basic sector shape of projection 103 is cut away in the form of bevels 117, 118 (Figure 9). Thus it is possible for projection 103 to be accommodated in the hollow of projection 104 with sufficient clearance to enable rotational motion to be transmitted when the axes of driving and driven members are inclined relative to one another.

As above described in relation to the first embodiment of joint according to the invention, it will be appreciated that such confinement of the balls relative to both joint members means that torque transmission between the joint members is shared equally by the two balls.

When the joint is rotated with the rotational axes 102 of the two joint members inclined to one another, the configuration of the grooves in the joint members is such that, analogously to the manner above described in relation to the first embodiment of joint according to the invention, the centres of the balls lie in the bisector plane so that the joint is a constant velocity ratio joint.

In the absence of any constraint between the two joint members, they are able readily to move axially relative to one another, i.e. the joint is a plunging joint. To maintain the position of the articulation centre P of the joint between

the two joint members, and to centralise the balls between the joint members when the joint is in the aligned (non-articulated) condition, each of the balls is centred between the two joint members by resilient ball-centering means, in the form of respective compression springs 119 which are operative between opposite sides of each ball and the two joint members. Such springs may operate on the balls through abutment elements 120 as shown in Figure 16.

The features disclosed in the foregoing description, or the following claims, or the accompanying drawings, expressed in their specific forms or in terms of a means for performing the disclosed function, or a method or process for attaining the disclosed result, as appropriate, may, separately or in any combination of such features, be utilised for realising the invention in diverse forms thereof.