Pivot bearings in a vehicle trailing arm suspension are subjected in use to forces in vertical, horizontal, axial and torsional directions. It is desirable that the bearings should be able to absorb these forces, including shock and out of phase wheel loading, and have a prolonged useful life.

Conventionally, pivot bearings for vehicle trailing arm suspension systems comprise a housing containing a generally cylindrical bush on a rigid axial sleeve in which a pivot of a trailing arm is located. Whilst being essentially stiff, the bush has some resilience intended to absorb vertical, horizontal and torsional forces, particularly roll induced forces and out of phase wheel loads. Usually the bush is made of a rubber material. Bushes have been made solid and with the same level of stiffness/resilience all around the axial sleeve. This limits the effectiveness of the bush because the stiffness/resilience requirements at different angularly positioned parts of the bush around the pivot may vary appreciably in practice according to the direction in which loads are exerted on the bush in use. If the bush is heavily loaded in use it will usually have a high level of stiffness which makes it too stiff for satisfactory absorption of loads. Alternatively, if the bush is made with a compromise level of stiffness/resilience for the range of loads exerted on it in use in different directions, its performance is clearly limited.

In order to vary the stiffness of the bush for different levels of forces acting on the pivot bearing from different directions in use, bushes have been made with voids, usually arcuate, above and below the axial sleeve.

This softens the rate of the bush under general vertical loading whilst retaining greater stiffness in the generally longitudinal direction of the vehicle for compliance under roll and out of phase wheel loading.

However, the stiffness provided in the generally longitudinal direction is limited and may be insufficient to cope satisfactorily with increasing loading conditions under which some vehicles are expected to operate.

According to a first aspect of the present invention a pivot bearing is provided, comprising a housing by which the pivot bearing is attached to support means for use, a resilient generally cylindrical bush contained in the housing, and a rigid axial sleeve secured in the bush at which the pivot bearing is located for use, the bush being formed with voids in first portions thereof which when the pivot bearing is fitted for use are disposed above and below the axial sleeve, and having stiffening elements of stiffer material than that of the bush contained in second portions of the bush extending between said first portions at opposite sides of the axial sleeve.

The stiffening elements increase the stiffness of the bush in generally horizontal directions for improved vehicle dynamics and reduced vibration when the pivot bearing is in use.

The stiffening elements may be rigid. They may, for example, be of metal such as steel, or be of a suitable plastics material. Preferably the stiffening elements are securely retained, by bonding, to the bush. They may be of a plate or leaf form. The elements may extend arcuately in the second portions about the sleeve. They may take other forms. There

may be a single stiffening element at each side of the sleeve, or there may be more than one. Each stiffening element may extend through the axial length of the bush, and may project from the opposite ends of the bush.

The bush is preferably formed by moulding, the voids being formed in the bush as it is moulded. The stiffening elements may be incorporated into the bush as it is moulded; the material of the bush may then be bonded to the elements in the course of the moulding process.

The voids may extend arcuately, or generally arcuately, in the first portions of the bush about the sleeve. They may extend through the axial thickness of the bush, or partially through the thickness. Voids may extend into the bush from opposite end faces of the bush. In this latter arrangement similar, directly opposed, voids may extend towards one another from the opposite end faces but be separated by a central solid region of the bush.

Preferably as viewed from each of the opposite ends of the bush, in the position of use of the pivot bearing, there is one elongated void above and one below the sleeve, each void extending for a longer distance about the sleeve than the external diameter of the sleeve. Opposite ends of each void extend through and beyond notional parallel planes extending vertically tangentially of diametrically opposite parts of the external circumference of the sleeve. This increases the flexibility of the bush under generally vertical loading. Preferably the ends of the voids are also enlarged which assists in reducing stresses in the material of the bush at the ends of voids and facilitates compression of the bush under vertical loading. Enlargement may be provided by increasing the annular width of the end regions of the voids. In another form the ends of the voids may

be enlarged by shaping them into two or more lobes, fingers or comparable projections running from the main bodies of the voids. At least one such projection at each end of a void may extend inwardly towards the sleeve. In a preferred form the enlargements are provided by having the ends of the voids turned inwardly towards the sleeve. The ends may be turned inwardly at an angle, preferably substantially radially of the sleeve. Each end may taper generally triangularly towards the sleeve.

The bush may be an interference fit in the housing. Alternatively, it may be bonded and/or moulded into the housing.

In a preferred embodiment the bush is formed, as by moulding, separately from the housing and is then compressed into and bonded in the housing.

The bush is fixed on the sleeve before its insertion into the housing. The voids of the uncompressed bush are open so that the opposite longitudinal sides of the elongated voids extending above and below the sleeve are spaced apart. Ends of the voids are turned inwardly towards the sleeve in the manner described above and taper generally triangularly towards the sleeve. Upon insertion of the bush into the housing, and its radial compression thereby, the compression of the first portions containing the voids causes the opposite longitudinal sides of the voids to close together.

In the assembled pivot bearing, therefore, the voids are substantially closed; only the inturned ends of the voids may remain open, though to a lesser extent than in the uncompressed state of the bush. Although the voids are closed the first portions remain relatively compressible, thereby affording substantial compliance in the bush under loading in vertical, and generally vertical, directions.

By contrast, the compression of the bush at the second portions resulting from its insertion into the housing in combination with the stiffening afforded by the stiffening elements leaves the second portions substantially stiffened against further compression under horizontal, and generally horizontal, loading on the bush when it is in use.

The stiffening elements, at least in the plate or leaf form, may extend into opposite ends of the voids. When the ends of the voids are enlarged into lobes, fingers or comparable projections, as described, the stiffening elements preferably extend into the voids between adjacent projections.

In the preferred form of the voids having the inwardly turned ends the material of the bush is radiused into the ends of the voids at the stiffening elements where the elements break into the voids. These arrangements reinforce the bush where stresses are concentrated under vertical, and generally vertical, loading and help to prevent separation of the material of the bush from the stiffening elements adjacent the voids.

The bush may be bonded to the sleeve. When the bush is made as a moulding it may be bonded onto the sleeve as it is moulded. The sleeve may protrude from the opposite end faces of the bush.

The sleeve may be axially longer than the housing for compliance of the bush under axial and tilting loading. The sleeve may project symmetrically from the opposite axial ends of the housing. Preferably the bush is shaped to correspond substantially in axial length to the length of the sleeve at its internal diameter and to have its ends inclined away from the sleeve so that the axial length of the bush reduces towards its external diameter. This allows for tilting of the bush relative to the sleeve and bulging of the ends under loading.

In one embodiment, a pivot bearing is made to be used in a vehicle trailing arm and its attachment to a supporting part of the vehicle. The pivot bearing is designed to withstand horizontal, vertical, axial and torsional loading when in use. The housing of the pivot bearing is cylindrical and co-axial with the sleeve. The bush is bonded onto the rigid axial sleeve and securely retained in the housing. Both the sleeve and housing are made of metal, for example steel. The bush has a cylindrical body with frusto-conical, or convex, end faces. The sleeve is longer than the housing and projects from the end faces of the body. The body is made of a rubber, polyurethane, or comparable, flexible material.

Generally arcuately extending elongated voids are formed in first portions of the body which when the pivot bearing is fitted for use are above and below the sleeve, the voids opening through the end faces of the body.

The voids are longer arcuately than the external diameter of the sleeve and have inwardly turned end portions which taper triangularly, generally radially, towards the sleeve. Stiffening elements extend through the second portions of the body adjacent diametrically opposed sides of the sleeve. There is one stiffening element at each side of the sleeve. The stiffening elements are made of metal, for example steel, and are of a plate or leaf form arcuately curved concentrically about the sleeve. They extend through the full axial length of the body and protrude from the opposite end faces of the body but are shorter than the sleeve. Each stiffening element projects into the adjacent end portions of the voids.

The housing is fixed to the trailing arm for use of the pivot bearing such that the central longitudinal axis of the sleeve extends horizontally transversely of the arm. A pivot pin is located in the sleeve and supported by opposed limbs of a mounting which straddles the pivot bearing and is fixed to the supporting part of the vehicle. The protruding ends of the sleeve abut, or bear on thrust washers which abut, opposed

inner surfaces of the respective limbs of the mounting. In use of the suspension system generally vertical and horizontal loadings imposed on the pivot bearing by relative movement between the pivot pin and trailing arm are accommodated respectively by the voided first portions of the bush and the second portions stiffened by the stiffening elements.

The body of the bush is able to sustain axial, torsional and tilting loading on the bush.

The pivot bearing may be included as original equipment on a trailing arm of a vehicle trailing arm suspension system.

Thus, according to a second aspect of the present invention there is provided a vehicle trailing arm including a pivot bearing in accordance with the first aspect of the invention herein set forth, the housing of the pivot bearing being fixed with respect to the trailing arm.

According to a third aspect of the present invention there is provided a vehicle trailing arm suspension system including at least one trailing arm in accordance with the foregoing second aspect of the invention.

An embodiment of the invention will now be described by way of example only with reference to the accompanying drawings, in which: Figure 1 is an end view of a bush of a pivot bearing in accordance with the present invention, Figure 2 is an axial section through the bush on line 2-2 of Figure 1,

Figure 3 is an end view of the pivot bearing including the bush of Figures 1 and 2, Figures 4 and 5 are end views of the bush showing modifications, Figure 6 is a perspective view of a trailing arm suspension system including the pivot bearing of Figure 3.

The pivot bearing in this embodiment of the present invention is to be used in a vehicle trailing arm suspension system.

Referring to Figure 3, the pivot bearing comprises a housing 1, an axial sleeve 2 and a bush 3.

The housing 1 is cylindrical being made of circular section steel tube.

The sleeve 2 is also made of circular section steel tube and is longer than the housing The bush 3, as best seen in Figures 2 and 3, comprises a cylindrical body 4 of a rubber material having a substantial degree of stiffness but some resilience. The body is concentrically moulded onto, and bonded to, the sleeve 2. It is of an external diameter such that it has to be radially compressed to fit into the housing 1 and of a length to be fully received at its outer cylindrical surface into the housing. Opposite end faces 5 are shallowly frusto-conical. They merge into the external cylindrical surface 6 of the body at convexly radiused edges 7 and meet the external surface of the sleeve 2 at concave radii 8. The sleeve projects symmetrically from the opposite end faces 5 of the body 4.

Extending into the body 4 from each of the opposite end faces are two similar voids 9. The voids 9 are formed in the body as it is moulded.

They are in diametrically opposed segments of the body which when the pivot bearing is fitted for use are respectively above and below the sleeve. The voids 9 at one end face are axially directly opposite those of the other end face. The voids extend almost to, but are separated by a solid web 10 of the material of the body at, the centre of the length of the body. They taper gradually towards their closed axially inner ends.

In the free state of the body as moulded, before the bush is inserted into the housing, as shown in Figure 3, each void 9, as viewed at the end faces 5 of the body, is elongated, having an arcuate outer side wall 11 curved about, but having a radius of curvature greater than its distance from, the central longitudinal axis of the body, and an inner side wall 12 of a larger radius of curvature extending substantially as a chord of the arc of the outer side wall. The void is of substantially greater length than the external diameter of the sleeve 2. Its opposite end portions 13 are enlarged by being turned generally radially inwardly in similar manner.

Each end portion is of a substantially isosceles triangle shape elongated towards the sleeve, one side 14 extending from the inner side wall 12 of the void and the opposite side 15 extending from the outer side wall 11, and being directed generally towards the central longitudinal axis of the body. The portion of the body between each void 9 and the sleeve 2 forms a buffer 16 of the bush.

Set in the body 4 of the bush as it is moulded are two similar rigid metal stiffening elements 17. The stiffening elements are securely bonded to the material of the body. They are in two diametrically opposed segments of the body between the two segments containing the voids 9. Each stiffening element 17 is in the form of a generally rectangular leaf which

is bowed co-axially about the central longitudinal axis of the body. The two stiffening elements are similarly radially spaced from the sleeve. They extend through the full axial length of the body and protrude from the end faces 5 of the body, but do not extend as far as the ends of the sleeve. Opposite side edges 18 of the stiffening elements, at the extremities of the bows of the elements, extend through the sides 15 of the adjacent end portions 13 of the voids, substantially opposite the inner side walls 12, and project into the voids. Side walls 15 are concavely radiused to merge with the side edges 18 of the stiffening elements so as to enhance resistance to separation of the material of the bush from the extremities of the bows of the stiffening elements. The portions of the segments of the body radially inside and outside of the stiffening elements 17 form shear blocks 19 of the bush.

As stated, the body is radially compressed to fit into the housing. The compression of the body results in the outer and inner side walls 11,12 of the voids 9 being urged together so that the voids are effectively closed between those walls, as shown in Figure 1. The opposed sides 14,15 of the end portions 13 of the voids are also urged towards one another but though the end portions are narrowed they are not closed.

The stiffening elements 17 substantially increase the stiffness of the body of the bush in horizontal, and generally horizontal, directions, i. e. at the shear blocks 19, for fore and aft loading on the bush when the pivot bearing is in use. They considerably reduce the extent of the deflection of the body under such loading. It has been found that the extent of the deflection may be reduced to up to as much as half that which may be experienced in a bush without the stiffening elements but otherwise similar. The increased stiffness, which increases non-linearly with increasing loading, is particularly advantageous when the pivot bearing is

used in a trailing arm suspension for a trailer vehicle because of the improved stability it provides for the vehicle when carrying high loads with a high centre of gravity. The stiffness also reduces self-induced steering effects in the pivot bearing, reduces tyre wear in the vehicle and generally helps to enhance the durability of the vehicle's running gear in use.

On the other hand, the provision of the voids 9 in the body, though closed when the bush is compressed into the housing, affords appreciable resilience in the segments of the body in which they are formed, including the buffers 16, thereby giving the bush substantial resilience under the loading in vertical, and generally vertical, directions.

Resilience in the body allows relative axial and tilting movement between the bush and sleeve under loading in the generally axial direction of the pivot bearing.

Compliance in roll and out of phase wheel loading manoeuvres of the vehicle to which the pivot bearing is applied in use is improved by the differing degrees of deflection provided for in the bush.

Two modified forms of the voids 9 in the body of the bush are shown in Figures 4 and 5 of the drawings.

Referring to Figure 4, each void 9 is elongated, having an arcuate outer side wall 20 curved about the central longitudinal axis of the body and substantially straight inner side wall 21 extending along a chord of the arc of the outer side wall. Under generally vertical loading on the body the outer and inner side walls 20,21 will be urged towards one another and the inner side wall will assume a curvature which increases towards that

of the outer side wall with increasing loading. The void is of substantially greater length that the external diameter of the sleeve 2. Its opposite end portions 22 are enlarged in similar manner, each end portion being shaped into two divergent lobes 23,24 with one, inner, lobe 23 being directed generally toward the central longitudinal axis of the body.

A cuspidated land 25 separates the two lobes 23,24.

In this form of the voids 9 the opposite side edges 18 of the stiffening elements 17 extend through the lands 25 at the adjacent enlarged end portions 22 of the voids and project into the voids. The arrangement resists separation of the material of the bush from the extremities of the bows of the stiffening elements.

Referring now to Figure 5, in this form the voids 9 are elongated to a similar extent as before, but an inner side wall 25 of each void is arcuately curved co-axially about the sleeve 2 and a central portion 27 of an outer side wall 28 is oppositely, inwardly, curved, although with a similar radius of curvature. Thus the two side walls 26,28 are convergent at the central part of the void. At either side of the inwardly curved central portion 27 the curvature of the outer side wall 28 reverses so that the end portions 29 of the wall curve co-axially about the sleeve 2, parallel to the inner side wall. There is a smooth radiused transition between the central and end portions of the outer side wall 28. The change of curvature of the outer side wall results in opposite end portions 30 of the void being enlarged. A substantial part of the enlargement of the end portions 30 is beyond the said horizontally diametrically opposed sides of the external circumference of the sleeve.

Each end wall 31 of each void is cuspidated on the central longitudinal axis of the void.

The opposite side edges 18 of the stiffening elements 17 project into the voids 9 at the centres of their cuspidated end walls 31.

An example is shown in Figure 6 of the drawings of a trailing arm 32 of a vehicle trailing arm suspension system in which the pivot bearing described with reference to Figures 1 to 3 may be included. This system is suitable for a heavy trailer vehicle. The arm 32 is fabricated from metal plate. The pivot bearing, indicated at 33, is secured transversely in one bifurcated end 34 of the arm 32. At its opposite end the arm is provided with a seat 35 for an air spring, not shown, and at an intermediate part of its length the arm has an axle 36 attached to it by means of a wrapper 37.