This invention relates to Hookes universal joints.

A Hookes universal joint comprises two yokes with spaced limbs, and a cross member having four arms each . opposed pair of which is pivotably received in aligned apertures in the limbs of a respective yokej so that the yokes are connected together for torque transmission and articulation relative to one another. One common construction of Hookes joint has bearing cups received in the apertures in the yoke limbs, the bearing cups being held in position by means such as circlips. ^' The bearing ^' cups present internal hardened bearing surfaces, and rolling bearing members, usually needle roller bearings, are interposed between the arms of .the cross member and the bearing cups. Such a joint construction is relatively complex and expensive because of incorporating a large number of separate parts. Further , in assembly, measures must be taken to ensure that manufacturing tolerances are taken up with respect to elimination of undesirable free play axially of a pair of cross member arms relative to the respective yoke. For example, selective assembly; using circlips of different thicknesses, may be employed for this purpose.

A further construction of Hookes universal joint has been proposed, e.g. in GB PS 925322, wherein each aperture in a yoke limb is closed by a cover plate secured to the limb by bolts, with a thrust bearing disposed between the cover plate and the end of the cross member arm. Adjustment of the arm and thrust bearing axially of the arm is effected by use of shims of

appropriate thicknesses beneath the cover plates. Thus, this construction of joint also requires selective assembly during manufacture, with consequent increased costs.

It is an object of the present invention to provide a Hookes universal joint wherein this disadvantage is overcome or reduced. Further advantages of the invention will become apparent from the following description.

According to the invention, we provide a Hookes universal joint wherein at least one pair of arms of the cross member is retained in the apertures in the limbs of the respective yoke by closure members welded to the limbs in such a manner as to take up clearances and position the cross member relative to the yoke in the direction lengthwise of said arms. Preferably the closure members are projection welded to the yoke limbs.

Projection welding is an electric resistance welding technique wherein the components to be welded together make contact over a relatively small surface area defined by a projection or projections on at least one of the components. The components are pressed together while welding current passes between them, and when fusion occurs at the projection or projections the components will displace relative to orie another. Therefore, the projection welding of the closure members to the yoke limbs provides the possibility of eliminating clearances due to production tolerances of the joint components.

A further advantage of a joint according to the invention is that, by virtue of welding between the closure members and yoke limbs, effective sealing is achieved therebetween, to retain lubricant in the

bearings of the joint and exclude dirt therefrom. It becomes possible, if desired, to design the universal joint such that the needle roller bearings thereof run directly against the internal surface of the apertures in the yoke limbs , without any intervening sleeve or cup-like member.

Preferably a thrust washer is interposed between the end of each cross member arm and its respective closure member. With a thrust washer of suitable material, it is not then necessary for the closure members to be hardened.

The projection for welding may be of annular configuration^ provided on each closure member, or alternatively the closure members may be flat and an annular projection for welding may be provided on each yoke limb.

These and other features of the invention will now be described by way of example with reference to the accompanying drawings, of which:-

Figure 1 is a diagrammatic section through part of a Hookes joint according to the invention;

Figure 2 is a section through part of a further embodiment of joint according to the invention;

Figures 3 and 4 are sections showing further modifications of the invention.

Referring firstly to Figure 1 of the drawings, this shows the end portion 10 of one arm of the cross member of a Hookes universal joint. A lubricant channel 11

extends through the arm and opens frustoconically at 12 at the free end of the arm. Part of one limb of one of the yokes of the joint is indicated at 13 _> with an aperture 14 therein. The surface of the yoke limb in the aperture 14 is hardened, e.g. induction hardened, as is the external peripheral surface of the arm 10 of the cross member. A plurality of needle roller bearings 15 are disposed between the arm 10 and limb 13« Seals are provided for retaining lubricant in the needle roller bearings 15 and excluding dirt therefrom, comprising a first seal 16 fitted on arm 10 and engaging the limb 13 and a second seal 17 fitted in aperture 14 in limb 13 and engaging the arm 10.

A closure member 18 is fitted to the yoke limb 13, to close the aperture 14 therein and position the arm 10 lengthwise thereof. The closure member 18 is projection ^* _, welded to the limb \ > and the welding projection, which is annular and is provided on the closure member 18., is indicated at 19* A thrust washer 20 is disposed between the closure member 18 and the end of arm 10., the thrust washer having a conical projection 21 which fits within the frustoconical passage portion 12 at the end of the arm, to centralise the thrust washer relative to the arm.

In a projection welding operation, electrodes are applied to the closure member 18 and to an appropriate part of the yoke; and welding current passed therebetween. Fusion occurs at the relatively small area of contact between these components afforded by the projection^ and the components moved together if suitable pressure is applied. Thus any clearance between the end of arm 10; thrust washer 20 and closure member 18 is taken up.

The use of closure member 18 provides a sealed bearing assembly for the cross member of the Hookes joint, without requiring the use of a bearing cup and means such as a circlip to hold a bearing cup in position. The use of projection welding for securing the closure member ensures that production tolerances are taken up and the cross member is located accurately relative to the yoke of the joint. In the particular construction described, the elimination of the bearing cup wall between the needle roller bearings and the aperture in the yoke limb means that rollers of larger diameter can be utilised compared with those in the conventional construction. The capacity of the joint is thus increased for the same overall size of joint.

It is not, however, an essential part of the

^• invention that the needle roller bearings engage directly with the yoke limb. In the embodiment shown in Figure 2 of the drawings, a bearing shell 25 is provided within the yoke limb aperture, which may be stepped as shown or parallel in shape. The rest of the assembly is the same as that of Figure 1.

Referring now to Figure 3, this shows a modification wherein the annular projection (26) for projection welding is provided on the yoke limb rather than on the closure member. This enables the closure member to be a simple flat component. Figure 4 shows a modification in which the welding projection (27) on the closure member is provided in a pressing operation thereon forming an annular recess 28 on the other side of the closure member. Again, however, the principle of assembly is the same as that of the embodiment shown in Figure 1.