GB2229976A

GB2229976A - Vehicle suspension with variable spring rate

Info

Publication number: GB2229976A
Application number: GB8907757A
Authority: GB
Inventors: John Edward Vines
Original assignee: Individual
Current assignee: Individual
Priority date: 1989-04-06
Filing date: 1989-04-06
Publication date: 1990-10-10
Anticipated expiration: 2009-04-06
Also published as: GB8907757D0; GB2229976B

Abstract

A vehicle suspension is described which comprises a wheel movably mounted relative to the vehicle body 10 and a spring 14 acting between the wheel and the vehicle body. A cam mechanism 22, responsive to the relative position of the wheel and the body 10, is interposed in a linkage 20 between the wheel and the spring 14 so that as the wheel moves the spring compression varies as a predetermined function of the wheel displacement in order to achieve a variable spring rate. Preferably the cam member 16 is pivotally mounted on the chassis 10, at 18. Member 12 is the upper arm of a double wishbone type arrangement. A single arm Macpherson strut arrangement could also be adapted. <IMAGE>

Description

VEHICLE SUSPENSION The present invention relates to a vehicle suspension and seeks to provide a suspension which enables better control of the spring rate.

According to the present invention there is provided a vehicle suspension comprising a wheel movably mounted relative to the vehicle body and a spring acting between the wheel and the vehicle body, wherein a cam mechanism, which is responsive to the relative position of the wheel and the body, is interposed in the linkage between the wheel and the spring so that as the wheel moves the spring compression varies as a predetermined function of the wheel displacement in order to achieve a variable spring rate.

Preferably, the wheel is connected by upper and lower pivotable arms to the body.

The spring may conveniently be mounted with one end fixed to the vehicle body and the other end acting on a link rod connected to the wheel.

In one embodiment of the invention, the link rod may be constituted by an extension of one of pivotable suspension arms.

The cam mechanism advantageously comprises a member pivotably mounted on the vehicle body and pivotably connected to one of the end of the spring and the link arm, a cam and follower arrangement being provided to connect the pivotable member to the other of the end of the spring and the link arm.

The cam is formed by a groove or slot in the pivotable arm and the follower may be a roller contacting both sides of the groove or slot.

The invention will now be described further, by way of example, with reference to the accompanying drawings, in which Figure 1 is a schematic representation of a first embodiment of the invention, and Figure 2 is a similar representation of second embodiment of the invention.

There are many applications in which it is desirable to provide a non-linear relationship between the collapse of the suspension of a vehicle and the return force of the suspension springs.

The road holding of a motor vehicle is affected by the stiffnes of the springs, being generally improved by stiffer springs. On the other hand ride comfort is improved by softer springs. One application of a suspension with a variable spring rate is that minor bumps through irregularity of the road surface can be absorbed without adversely affecting the road holding.

This can be advantageous in racing cars as well as cars intended for road use.

Another application for a suspension of variable spring rate is to reduce the ground clearance of a racing car at high speed by allowing limited compression of the springs through aerodynamic forces on a vehicle.

Hitherto, yariable rate springs have been proposed but calibration of such springs presents difficulty and they are expensive to manufacture.

The present invention relies on the use of cam between the body and the spring to vary the effective spring rate.

The detail of a suspension shown in Figure 1, shows an upper chassis member 10 which is connected by a top suspension link 12 to the wheel hub (not shown). In a similar manner, a lower chassis member (not shown) is connected by a second suspension link to a second point on the wheel hub. By this parallel arrangement of two suspension links, the wheel hub is free to move up and down in relation to the chassis. This suspension geometry can be applied to the front or rear wheels of a car.

Upward movement of the wheel is opposed by a spring and damper unit 14 which is coupled to the wheel indirectly.

A cam plate 16 is mounted about a pivot 18 fixed to the upper chassis member 10. The cam plate 16 is connected to the wheel hub by a rod 20 which causes the cam plate 16 to rock about the pivot 18 as the wheel moves up and down in relation to the chassis. A cam groove 22, of which the shape determines the variation of the return force on the wheel with wheel displacement, is formed in the cam plate and receives a cam follower roller 24 mounted on the upper end of the spring and damper unit 14. The suspension unit is prevented from moving laterally by a tie bar 26 which is pivotably mounted at its one end on the chassis and at its other end on the spring and damper unit 14.

As the wheel moves up and down, the rod 20 causes the cam plate 16 to rock about the pivot 18. During this pivotal motion of the cam plate, the roller 24 moves along the cam groove 22 and the spring and damper unit 14 expands and contracts in synchronism with the wheel movement but following a relationship determined by the shape of the cam groove 22. Thus by suitably designing the cam groove 22, it is possible to set any desired variation of spring rate with wheel displacement.

The shape of cam illustrated in Figure 1 is for achieving a sudden increase in stiffness after an initial wheel displacement, but a more gradual increase can also be produced as-can a decrease in stiffness, if so desired.

As mentioned earlier, the purpose of the tie bar 26 is to prevent lateral displacement of the unit 14 and alternative means may be used for achieving the same objective. For example, the end of the spring and damper unit 14 can be guided along a groove or an extension of the unit 14 can be received in a guide sleeve.

Turning now to Figure 2, which shows an alternative embodiment of the invention, a cam plate 16' mounted about a pivot 18' is pivotably connected to a pin 34 fitted to the end of the spring and damper unit 14. The end of the cam plate 16' remote from the pivot 18' is formed with a shaped cam groove 22' which receives a cam follower roller 32 fitted to an extension 12' of the top suspension link.

As the link extension 12' rocks about its pivot with up and down movement of the wheel, it acts by way of the cam plate 16' on the spring and damper unit 14. During movement, the roller 32 rolls along the cam groove 22' and alters the mechanical advantage of the lever system connecting the spring and damper unit 14 to the wheel and thereby alters the spring rate.

As can be seen from a comparison of the two illustrated embodiments, widely differing geometries may used in implementing the invention. Numerous possibilities exist for the positioning of the cam and the various levers to ensure that the spring rate varies with wheel displacement. In particular it should be mentioned that it is common in racing vehicles to place the spring and damper unit on the chassis with its axis pointing along the direction of travel in order to reduce the drag created by the unit. In this case, a three dimensional cam can be used to transmit movement of the wheel to the spring and damper unit.

Claims

1. A vehicle suspension comprising a wheel movably mounted relative to the vehicle body and a spring acting between the wheel and the vehicle body, wherein a cam mechanism, which is responsive to the relative position of the wheel and the body, is interposed in the linkage between the wheel and the spring so that as the wheel moves the spring compression varies as a predetermined function of the wheel displacement in order to achieve a variable spring rate.

2. A vehicle suspension as claimed in claim 1, wherein the wheel is connected by upper and lower pivotable arms to the body.

3. A vehicle suspension as claimed in claim 2, wherein the spring is mounted with one end fixed to the vehicle body and the other end acting on a link rod connected to the wheel.

4. A vehicle suspension as claimed in claim 3, wherein the link rod is constituted by an extension of one of pivotable suspension arms.

5. A vehicle suspension as claimed in claim 3 or 4, wherein the cam mechanism comprises a member pivotably mounted on the vehicle body and pivotably connected to one of the end of the spring and the link arm, a cam and follower arrangement being provided to connect the pivotable member to the other of the end of the spring and the link arm.

6. A vehicle suspension as claimed in claim 5, wherein the cam is formed by a groove or slot in the pivotable arm and the follower is a roller contacting both sides of the groove or slot.

7. A vehicle suspension as claimed in claim 5 or 6 wherein means are provided to prevent the end of the cam follower from moving in a direction perpendicular to the throw of the cam.

8. A vehicle suspension as claimed in any preceding claim further comprising means for remote adjustment of the spring parameters of the suspension.

9. A vehicle suspension constructed, arranged and adapted to operate substantially as herein described with reference to and as illustrated in Figure 1 or Figure 2 of the accompanying drawings.