Description of Invention

This invention relates to constant velocity ratio (homokinetic) universal joints of the tripode joint, such a joint comprising an outer joint member in the form of a hollow body with a rotational axis; three tracks circumferentially spaced about its rotational axis and extending lengthwise of the joint member; an inner joint member having a rotational axis and three arms circumferentially spaced about such axis and extending outwardly into the tracks of the first joint member; and respective roller assemblies on the arms of the inner joint member, each roller assembly comprising a roller element with a periphery engaging opposed sides of the respective track in the outer joint member, an inner roller element and bearing means, e.g. needle roller bearings, operative between the roller element and the inner roller element to permit free rotation of the roller element relative to the inner roller element about an axis of the two elements, the roller assembly being able to tilt to change its orientation relative to the arm, and including means engaging a guide surface of the track for holding the roller element in a substantially constant orientation relative to the track. The guide surface of the track preferably is a surface generally perpendicular to a line extending radially of the outer joint member through the centre of the track, and conveniently is a base portion of the track. When such a joint, which will hereafter be referred to as a tripode type joint of the kind specified, is articulated, i.e. the rotational axes of the two joint members are inclined to one another, the roller elements of the roller assemblies roll along the tracks in the outer joint member, and tilt relative to the arms of the inner joint member.

Various construction of roller assembly have been proposed for joints of the kind specified, differing in respect of the way the inner roller element is supported on the associated arm of the inner joint member in such a way that it is able to tilt relative to the arm when the joint is articulated. For example, the inner roller element may have a cylindrical internal surface portion and the arm have a part-spherical surface portion which engages directly in the cylindrical

internal surface portion of the inner roller element. The present invention has been devised in relation to a joint with this type of roller assembly, but it is to be appreciated that it is applicable more broadly to joints of the kind specified.

A constant velocity ratio universal joint of the kind specified includes, in each roller assembly, means engaging a base portion of the track for holding the roller element in a substantially constant orientation relative to the track. It has been proposed that the roller element itself should have an end surface which engages the track base portion, or in a joint as immediately above described the inner roller element may have an end surface engaging the base portion of the track. Such an end surface, whether on the roller element or inner roller element, usually has to be provided on a portion of such element in the form of an extension projecting radially outwardly with respect to the outer joint member, which makes such element a component of more complex shape and heavier, and since such component usually is of steel, as is the outer joint member, both it and the track base portion engaged thereby must be of a surface finish and hardness suitable to provide low-friction sliding therebetween and resistance to wear.

It is broadly the object of the present invention to simplify a joint of the kind specified in one or more of such respects.

According to the invention, we provide a constant velocity ratio universal joint of the kind specified wherein each roller assembly comprises a retaining element connected to one of the roller element and inner roller element and cooperating with the other thereof and/or the bearing means, said retaining element comprising, at least on a surface portion thereof, a low friction polymeric material and also engaging a guide surface of the track to hold the roller element in said substantially constant orientation.

Preferably the retaining element is connected to the roller element. The retaining element may comprise a separate component removably fitted to the roller element. Preferably the retaining element is in the form of a resilient generally annular member, having a circumferential gap or the like to enable it to be radially contracted to be engaged with the roller element.

In this case, the retaining element could be entirely of polymeric material or could be of a metal or other suitable material having a surface coating of the low-friction, polymeric material.

Alternatively, the retaining element could be permanently secured to the roller element e.g. by being moulded in situ on to the roller element. In this case, the retaining element preferably is entirely of the low-friction polymeric material.

Examples of suitable materials are referred to hereafter.

In a joint according to the invention, the retaining element fulfils the function both of providing a retaining function between the roller element and the inner roller element and/or bearing means interposed between the inner roller element and roller element, and also engages the base portion of the track to provide guidance to hold the roller element in the required substantially constant orientation relative to the track. The configuration of the roller element or inner roller element is simplified as compared with the provision of an extension thereon to engage the track base portion, and the roller element or inner roller element is a relatively smaller and lighter component than one with such an extension.

Further, the material of the retaining element or of the surface thereof leads to reduced friction between it and the track base portion, and thus a reduced resistance to rolling of the roller element along the track when the joint articulates and/or plunges. The track base portion may not have to be hardened or provided with such a good surface finish as when it is engaged by an extension of the roller element or inner roller element.

The invention will now be described by way of example with reference to the accompanying drawing, which is a diagrammatic, partly sectioned, axial view of a joint in accordance with the invention.

Referring to the drawing, there is shown part of a tripode type of constant velocity joint of the kind specified, in accordance with the present invention. The joint comprises an outer joint member 10 of hollow configuration,

whose axis of rotation is perpendicular to the plane of the drawing, at the position indicated at 11. Equally circumferentially spaced about its axis 11, the outer joint member is provided in its interior with three tracks extending parallel to its axis, one of such tracks being indicated generally at 12. The track comprises opposed side portions 13 and a base portion 14 constituting a guide surface.

The joint further comprises an inner joint member 15 which is illustrated with its rotational axis coincident with the axis 11, the inner joint member 15 comprising an annular body with a central bore 16 for torque- transmitting reception of a drive shaft element, and three arms 17, equally circumferentially spaced about its axis, extending radially outwardly into the respective tracks 12.

A roller assembly is provided on each arm 17. Only one of such roller assemblies is shown in detail in the drawing, the others being shown in outline only. The roller assembly comprises a roller element 18 with a generally toroidal external surface 19 engaging the opposed side portions 13 of the track 12, and with a cylindrical internal surface 20. There is an inner roller element 21 with an external cylindrical surface 22 facing the internal surface 20 of the roller element 18, and a needle roller bearing assembly comprising a plurality of rollers 23 is interposed between the surfaces 20, 22. The inner roller element 21 has a cylindrical internal surface 24 engaged by a part-spherical external surface 25 on the arm 17, to enable the necessary tilting of the roller assembly relative to the arm to take place when the joint articulates, and also the necessary relative motion in the direction radially of the joint.

At the part of the roller element 18 which lies radially outermost having regard to the axis 11, there is provided a retaining element 26. This fulfils two functions, namely it engages the ends of the needle rollers 23 and an outermost end face of the inner roller element 21 to provide for retention of the needle rollers and the inner roller element in one direction relative to the roller element, and also it engages the base portion 14 of the track 12 so as to maintain the roller assembly in a constant or substantially constant orientation relative to

the track. At the innermost part of the roller assembly, having regard to the axis 11, there is a retaining snap ring 27 which may be a conventional steel snap ring engaging in a groove in the roller 18, which contacts faces of the needle rollers 23 and inner roller element 21 opposite those contacted by the retaining element 26.

The retaining element 26 has a cross-sectional shape which interfits with that of the roller element 18 to secure these two components together. As illustrated, the retaining element 26 includes an annular groove 29 and the roller element an annular projecting surface 30. The retaining element may have snap engagement with the roller element; i.e. the retaining element may be in the form of an incomplete annulus with a gap or other formation enabling the retaining element to be radially contracted against its resilience, and then expanded when correctly positioned relative to the roller element. Alternatively, the retaining element may be moulded in .situ on to the roller element, and thus be a permanent attachment thereto.

Suitable low-friction hardwearing polymeric materials for the retaining element include, by way of example, Nylon 46, Nylon 66, PPS (Polyphenylsulphide), Polyphthalamide. Such a material may, especially if it is in the form of a snap ring to be secured to the roller element, be fibre filled, e.g. with glass or preferably carbon fibres.

Yet a further possibility, in the case of a retaining element moulded in situ on to the roller element, is that the retaining element may be of a reaction injection moulded (e.g. "Nyrim") material.

Yet a further possibility is that the retaining element could be of metal with a covering of the low-friction polymeric material, e.g. the nylon type of material applied by a powder-coating process and known as Rilsan.

In the case where the retaining element is moulded in situ on the roller element, a different configuration of the annular groove 29 and projection 30 may be adopted. For example, these formations may be deeper, or possibly

include an undercut or the like to provide a high degree of security of fixing of the retaining element to the roller.

It may be desirable to arrange for the ends of the needle rollers to bear against a steel shoulder or washer rather than against a surface of polymeric material.

In use of a joint as above described, the retaining element cooperates with the base portion of the track in the outer joint member to maintain the roller assembly in a substantially constant orientation in the track. When the joint is articulated, the roller assembly tilts relative to the arm of the inner joint member on which it is carried, such tilting taking place between the cylindrical internal surface 24 of the inner roller element and the part-spherical external surface 25 of the arm. These latter surfaces also allow for the necessary relative movement between roller assembly and arm in the direction radially of the joint. By virtue of the material of which the retaining element is made, there is low friction between roller assembly and track base portion, enabling the roller to roll along the track in relative freedom. In constructional terms, the roller is a relatively lightweight and simple component, as compared with previously proposed configurations of rollers in joints as described.

Whilst it is preferred that the retaining element should be connected, as above described, to the roller element, it would be possible for the retaining element to be connected to the inner roller element.

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.