Title: Bearing Assembly for Drive Shaft

Description of Invention

This invention relates to a bearing assembly, for supporting an element for rotation about an axis. The invention has been devised in relation to a so- called centre bearing assembly, for supporting an intermediate universal joint between the ends of a universally-jointed drive shaft (although it is to be appreciated that the intermediate universal joint and bearing assembly for supporting it might not be exactly nor even approximately midway between the ends of the drive shaft). Drive shafts with centre bearing assemblies are widely used in the automotive field.

The conventional arrangement for the centre bearing assembly of an automotive drive shaft (propeller shaft) is to utilise a deep groove ball bearing whose inner race has a shaft part fitted within it and whose outer race is resiliently supported relative to the structure of the vehicle. The inner race is fitted on the shaft part, typically on a bearing-receiving portion of a member of or associated with the intermediate universal joint. The inner race of the bearing is an interference fit on a mounting surface of the shaft part, this interference fit causing the bearing inner race to be slightly expanded when it is fitted, so the correct running clearance is established in the bearing. To provide the correct interference fit between the mounting surface of the shaft part and the inner bearing race, the mounting surface of the shaft part has to have a fine surface finish and its size has to be very closely controlled: these characteristics are normally achieved by a grinding operation, which has to be carried out subsequent to heat treatment of the shaft part as such treatment typically causes distortion of components. The necessity for carrying out a grinding operation undesirably increases production costs.

It is broadly the object of the present invention to provide an arrangement wherein the need for a grinding operation subsequent to heat treatment is eliminated.

According to one aspect of the invention, we provide a bearing comprising an inner race, an outer race, and rolling elements operatively interposed between the bearing races, characterised in that a resilient material is provided inside the inner bearing race.

The resilient material may be an elastomeric material, for example a rubber material or an elastomeric plastics material.

The resilient material may be provided in spaced regions in the interior of the inner bearing race. Preferably the spaced regions comprise a plurality of axially extending regions spaced circumferentially around the interior of the inner race.

According to another aspect of the invention, we provide a bearing assembly for supporting an element for rotation about an axis, characterised in that the bearing assembly comprises a bearing according to the first aspect of the invention with its inner race adapted to be received on a mounting surface of the element and its outer race provided in a support structure.

The support structure may include a flexible, e.g. elastomeric, element enabling the bearing to be resiliently supported relative to a further element.

In a bearing assembly in accordance with the invention, the provision of the resilient material within the bearing inner race means that the requirement for highly accurate dimensioning of the mounting surface of the element, to achieve the correct interference fit with the inner bearing race, is reduced.

This means the need for grinding of the mounting surface, subsequent to heat treatment, can be eliminated: the surface can be turned to size as part of other manufacturing operations, prior to heat treatment, and the subsequent heat treatment does not disadvantageously affect the fit between the inner bearing race and mounting surface. When the inner race of the bearing is fitted to the rotary element, the resilient material is compressed between the inner race and the mounting surface of the rotary element, Because the inner bearing race is not expanded by being fitted tightly on the mounting surface, the bearing has to have the correct running clearance provided in it initially rather than have its running clearance determined by fitting the inner race on the mounting surface.

According to yet a further aspect of the invention, we provide a drive shaft including a bearing assembly according to the second aspect of the invention for supporting a rotational element of the shaft.

The bearing assembly may be a centre bearing assembly, in the vicinity of a universal joint of the shaft.

The mounting surface on which the bearing inner race is fitted may be provided on a part of a universal joint component.

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 diagrammatically illustrates a universally-jointed drive shaft and a possible disposition of a centre bearing assembly in relation thereto;

Figure 2 is a longitudinal section through a known form of centre bearing assembly and part of a drive shaft;

Figure 3 is a longitudinal section through a centre bearing assembly in accordance with the invention.

Referring firstly to figure 1 of the drawings, this illustrates, diagrammatically, a drive shaft 10 having universal joints indicated at 12, 14 at its ends and an intermediate universal joint 16, with respective shaft parts 18, 20 extending between the joints 12, 16 and 14, 16 respectively. The universal joints may be constant velocity ratio universal joints or Hooke's (Cardan) joints. The shaft part 18 or 20 may incorporate a sliding spline assembly or other arrangement to enable some variation in distance between torque transmitting components to which it is connected at its ends: possibly a plunging constant velocity ratio universal joint may be used as one of the joints for this purpose. Such a drive shaft arrangement requires to be supported in the vicinity of the intermediate universal joint 16, by a so-called centre bearing assembly, for example, where indicated at 22 in figure 1 , although it is to be appreciated that it need not be exactly midway between the joints 12, 14.

Such a drive shaft typically is used in motor vehicles for transmitting power between an engine at one end of the vehicle and driving wheels at the other end.

Figure 2 shows a known arrangement of centre bearing assembly. In this figure is shown part of the drive shaft in the vicinity of the immediate universal joint thereof, the arrangement including a shaft part 24 which lies within a bearing assembly indicated generally at 26. The shaft part 24 has a circumferential mounting surface 28 ending a shoulder 30 beyond which the shaft part 24 is formed into a somewhat cup-shaped connecting portion 32 connected to a tubular shaft element, not shown. In the opposite direction, the shaft part 24 extends into a part 34 for connection to a torque transmitting assembly such as a plunging constant velocity ratio universal joint:: a protective boot for such an assembly is partially shown, diagrammatically, at

36.

The bearing assembly 26 includes a deep groove ball-bearing having an inner race 36, an outer race 38 and a plurality of balls 40 therebetween, circumferentially spaced from one another by a cage. The bearing is a sealed bearing. The inner race 36 is an interference fit on the mounting surface 28, being pressed onto the surface 28 until it abuts a shoulder 30. In doing this, the diameter of inner race 40 is expanded slightly so that the correct running clearance is established in the bearing, the mounting surface 28 being ground to a fine finish and close tolerances so that the correct fit of the inner race 36 thereon is established. Such a grinding operation is carried out subsequent to heat treatment of the shaft part 24. A pressed thrower ring 42 also is fitted on the mounting surface 28 beyond the inner race 36.

The outer race 38 of the bearing 26 is received within a support structure including a carrier ring 44 which is of rubber or other suitable elastomeric material with a cylindrical metal strengthening ring 46 therein. From the exterior surface of the carrier ring 44 an elastomeric diaphragm 48 of concentrically convoluted form extends outwardly, into an annular exterior part 50 within a tubular metal support ring 52. The ring 52 is held within a support membrane which is adapted to be secured to the structure of a motor vehicle, for example, wherein the shaft assembly is to be used, being provided with mounting brackets or other formations, not shown, for this purpose.

Referring now to figure 3 of the drawings, this shows a bearing assembly in accordance with the invention, without the shaft part 24 and its associated components. The above description is to be taken as applying to figure 3 with the sole difference that the inner race 36 of the bearing 26 is, in its interior, coated with a suitable type of rubber or elastomeric plastics material indicated generally at 60. This covering is applied to the interior of the inner race 36 in a moulding process, in the form of a plurality of circumferentially spaced axially extending portions 62 of the elastomeric material, so that the inner race interior

has the appearance of internal splines. The bearing is manufactured so that it has the correct running clearance between its inner and outer races and balls from the start.

When the bearing race is to be fitted onto the mounting surface 28 of the shaft part 24, it is pressed thereon and the spaced portions 62 of the elastomeric material are compressed in so doing. The spaces between the portions enable the material to expand circumferentially as the bearing is pressed onto the mounting surface, and the inner bearing race is effectively central on the mounting surface so its axis is coincident with the rotational axis of the shaft port. Therefore, the inner bearing race is firmly retained on the mounting surface 28, but without the requirement for extremely accurate sizing of the surface 28. The surface can be turned to size prior to heat treatment, so this surface does not need a post heat treatment grinding operation.

When used in this specification and claims, the terms "comprises" and "comprising" and variations thereof mean that the specified features, steps or integers are included. The terms are not to be interpreted to exclude the presence of other features, steps or components.

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.