A SUSPENSION FOR A MOTOR VEHICLE WHEEL

Abstract: In order to reduce the wheel offset (distance from steering axis to wheel centre) in a Macpherson strut type of suspension, an additional outboard link (66) is mounted between an outboard extension (64) of the fore and aft locating link (58) and a point (70) intermediate the ends of the shock absorber strut. The additional link (66) defines the new steering axis. This arrangement provides the benefits of reduced wheel offset and negative camber on jounce. The invention is not restricted in application to steered wheels.

Description: A SUSPENSION FOR A MOTOR VEHICLE WHEEL This invention relates to a Macpherson strut type suspension for a vehicle wheel. The invention is particularly, but not exclusively, suitable for use with a steered vehicle wheel. One problem which arises when a vehicle is in use is known as 'nibble' or 'judder'. This problem manifests itself as vibration transmitted from the wheels to the vehicle body, and arises from the application of uneven forces to the wheel itself. These forces can occur on braking, for example if the brake disks are out of line, or in general running if for example the wheels are unbalanced. These forces are transmitted back to the vehicle body through the suspension joints. In a Macpherson strut type suspension there is a certain distance (known as the wheel offset) between the steering axis and the centre of the wheel. This distance acts as a lever arm in transmitting the forces which cause judder and nibble back to the vehicle. If the wheel offset can be reduced, then it is believed that the effect of judder and nibble can also be reduced. It is therefore an object of this invention to reduce the wheel offset in a Macpherson strut type suspension. According to a first aspect of the invention, there is provided a Macpherson strut type suspension for a steered vehicle wheel, wherein the steering axis is separated from, and outboard of, the strut, and wherein the angle between the steering axis and the axis of the strut changes on jounce so that a negative camber angle is maintained or increased. According to a second aspect of the invention there is provided a suspension arrangement for a vehicle wheel comprising a telescopic strut, a lateral locating arm, a fore and aft locating link and an auxiliary link, wherein the lateral locating arm, the fore and aft locating link and the telescopic strut each have one end mounted on the vehicle bodywork and extend generally towards the wheel centre position, the outboard ends of the strut and of the fore and aft locating link are both connected to the lateral locating arm, the fore and aft locating link has an outboard extension beyond its connection to the lateral locating arm, and the auxiliary link is connected at one end to the extension and at the other end to a fitting secured to the strut and carries a knuckle for mounting the wheel. The fore and aft locating link can either be a rearwardly extending compression link or a forwardly extending tie bar. A compression link is preferred. If the suspension is provided for a steered wheel, then the wheel knuckle may have provision for attachment of a steering arm to it. With this arrangement, the steering axis of the wheel is defined by the auxiliary link which is positioned outboard of the common junction where the locating arm, locating link and strut all meet. Thus the distance between the wheel centre and the steering axis can be considerably reduced relative to prior art arrangements where the knuckle has been mounted directly at the common junction of the locating link, locating arm and strut. As the wheel moves up relative to the vehicle body work (so called 'jounce') it is important that negative camber is maintained. This is achieved by the structure as set out above with the auxiliary link being mounted at both its ends by means of joints with some degree of movement. For example the top joint could be a trunnion type joint and the bottom joint could be a compliant bush. Preferably however both top and bottom of the auxiliary link are connected to their respective components by ball joints. The joint between the fore and aft locating link and the lateral locating arm can also be of any suitable form ,such as a ball joint or a compliant bush. Preferably the telescopic strut is connected to the outboard end of the lateral locating arm by a pivot bush with an axis of rotation which is parallel to the axis by which the inboard end of the lateral locating arm is mounted, for up and down movement, on the vehicle body work. The invention also extends to a telescopic strut for use in the suspension arrangement set forth above. The invention will now be further described, by way of example, with reference to the accompanying drawings, in which: Figures 1 and 2 shown two alternative prior art constructions, both in their normal positions and in their 'full jounce' positions; Figure 3 is a schematic elevation of a suspension arrangement in accordance with the invention; Figure 4 is a plan view of the suspension arrangement of Figure 3; and Figure 5 illustrates schematically the geometric conditions which occur on jounce. In the drawings, the reference numbers 3 to 14 are used to denote certain significant points of the suspension and to identify the different positions of these points during the suspens ion travel. Addi tional reference numerals, commencing with the numeral 50 , will be used to denote the various parts of the suspension. Figure 1 i s an e leva t i on of a conven t i ona l modern Macpherson strut suspension which has small scrub radius and is used in conjunction with wide wheels. In F igure 1 , a suspension arm 50 is arranged generally horizontally and a telescopic s hock absorber s trut 52 extend s downwardly to meet the arm 50 at a point 6. The steering axis l ies on the li ne of the strut 52. The incl ination of thi s axis to the vertical ( termed the ki ng pin angle) is relatively high in F igure 1. For example , the current vers i on of the Ford S ierra which has thi s type of front suspens ion has a king pin angle of 14.3 °. This leads, on jounce, to a negative camber which is desirable to counteract the adverse ef f ects of body roll when cornering. However the high king pin angle shown is disadvantageous for two reasons. Firstly it gives rise to packaging problems in the vehicle design in that the top of the strut has to be relatively far inboard. Secondly the steering axis is relatively far from the centre of the wheel and thus there is a large wheel offset which, as explained earlier, leads to a magnification of any forces arising from imbalance of the wheels or brakes. To avoid these problems, the king pin angle can be reduced as shown in Figure 2 by arranging the strut 52 almost vertically and providing a rigid horizontal link 54 at the lower end of the strut. The end of the suspension arm 50 (point 6) is connected at the outboard end of the link 54 and this reduces wheel offset and minimizes any packaging difficulties. However it gives rise to the serious disadvantage that on jounce, as illustrated in dotted lines in Figure 2, a tendency towards positive camber is induced which gives undesirable road holding characteristics. This system also produces high bending loads on the strut 52 and a coning action occurs at point 7 whilst steering. In an attempt to avoid all these disadvantages, the system as shown in Figures 3, 4 and 5 has been developed. In these figures, the numeral 56 indicates the vehicle tyre. The wheels themselves and the knuckles on which the wheels are mounted are not shown, because to do so would reduce the clarity of the illustrations. In Figures 3 and 5, the designation F/J after some of the point numbers indicates that these points are shown in their • full jounce' position. In these figures, point 9 is the wheel centre and the steering axis is line 6-7. The arrangement of the suspension arm 50, the compression link 58 and the telescopic shock absorber strut 52 are generally conventional, and so they will not be described in great detail. The springing necessary to control the up and down movement of the wheel can be effected by a spring mounted at the top of the shock absorber strut 52, in a conventional manner. In the plan view of Figure 4 it will be seen that the strut 52 is connected to the arm 50 by means of a pivot pin 60. It will be noted that the axis of the pin 60 is parallel to the axis 51 which passes through the point 4 at which the arm 50 is mounted on the vehicle and through the point 3, and the significance of this will become apparent later on. The compression link 58 extends from a point 3 (this point lies on the pivot axis 51, passing through the point 4, of the arm 50) to the point 8A where the link 58 is connected to the arm 50 through a ball joint 62. This joint 62 could alternatively be a compliant bush. The compression link 58 also has an outboard extension 64 which can be seen most clearly in Figure 4. This extension 64 is formed rigidly with the link 58 and is preferably formed integrally with the link. At the outboard end of the extension 64 (point 6) the lower end of an auxiliary link 66 is mounted by means of a ball joint 68. The upper end of this link 66 is connected by means of another ball joint 70 (or a trunnion) to a bracket 72 welded to the outer tube of the strut 52. In Figure 3 this link 66 is shown as a simple rod, but this is for explanation purposes only. in practice the knuckle to which the wheel itself is bolted will be supported between these two ball joints 68 and 70, but the steering axis will still lie on the line 6-7. In one embodiment, the wheel offset of an arrangement as shown amounted to 46.0 mm compared to a figure of 80.0 mm for a Ford Sierra car with a conventional Macpherson strut suspension. Figure 5 shows schematically what happens on jounce. The solid lines indicate the position of the various struts and links and their design position. The dotted lines indicate the positions of the same links in the full jounce position. The auxiliary link 66 is however shown in chain-dotted lines in both conditions. The normal condition of the steering axis 6-7 is with a small negative camber. As this link moves to its full jounce position, the negative camber increases to a small, but desirable extent. On jounce, the length of the strut 52 is reduced as shown by the normal telescopic movement of the strut. However the other links 50, 58 and 64 remain the same length and because of the constraints on their movement, the result of jounce will be that the lower ball joint 68 between the auxiliary link 66 and the extension 64 moves slightly outboard. The upper ball joint 70 of the link will also move to a small degree outboard, because it has a fixed distance relationship relative to the strut 52 and the strut 52 itself is angled outboard, but this outboard movement of the upper joint 70 will be less than that of the lower joint 68. The invention thus allows a substantially reduced wheel offset to be obtained without the necessity of having to make major alterations to the vehicle body structure, as the connections of the various links to the body structure transmit similar forces and are in similar positions to those used for a conventional Macpherson strut suspension.

Claims: CLAIMS 1. A Macpherson strut type suspension for a steered vehicle wheel, wherein the steering axis is separated from, and outboard of, the strut, and wherein the angle between the steering axis and the axis of the strut changes on jounce so that a negative camber angle is maintained or increased. 2. A suspension arrangement for a vehicle wheel comprising a telescopic strut, a lateral locating arm, a fore and aft locating link and an auxiliary link, wherein the lateral locating arm, the fore and aft locating link and the telescopic strut each have one end mounted on the vehicle bodywork and extend generally towards the wheel centre position, the outboard ends of the strut and of the fore and aft locating link are both connected to the lateral locating arm, the fore and aft locating link has an outboard extension beyond its connection to the lateral locating arm, and the auxiliary link is connected at one end to the extension and at the other end to a fitting secured to the strut and carries a knuckle for mounting the wheel. 3. A suspension arrangement as claimed in Claim 2, wherein the fore and aft locating link is a rearwardly extending compression link. 4. A suspension arrangement as claimed in Claim 2, wherein the fore and aft locating link is a forwardly extending tie bar. 5. A suspension arrangement as claimed in any one of Claims 2 to 4, and for use with a steered wheel, wherein the wheel knuckle has provision for attachment of a steering arm to it. 6. A suspension arrangement as claimed in any one of Claims 2 to 5, wherein the auxiliary link is mounted at both its ends by means of ball joints and wherein the joint between the fore and aft locating link and the lateral locating arm at the common junction is also by way of a ball joint. 7. A suspension arrangement as claimed in any one of Claims 2 to 6, wherein the telescopic strut is connected to the outboard end of the lateral locating arm by a pivot bush with an axis of rotation which is parallel to the axis by which the inboard end of the lateral locating arm is mounted, for up and down movement, on the vehicle body work. 8. A telescopic strut for use in vehicle wheel suspension arrangement as claimed in any preceding claim, and having a mounting point intermediate its ends for the attachment of an auxiliary suspension link.

Inventors: STRUTT DEREK WILLIAM, STRUTT, DEREK, WILLIAM
Applicants: FORD FRANCE, FORD MOTOR CO, FORD WERKE AG, FORD FRANCE S.A., FORD MOTOR COMPANY, FORD MOTOR COMPANY LIMITED, FORD WERKE A.G.
Application year: 1987
Main classification: B60G3
IPC codes: B60G3, B60G13