GB2360259A

GB2360259A - Vehicle suspensions

Info

Publication number: GB2360259A
Application number: GB0006351A
Authority: GB
Inventors: Roland Schmidt
Original assignee: Bayerische Motoren Werke AG
Current assignee: Bayerische Motoren Werke AG
Priority date: 2000-03-17
Filing date: 2000-03-17
Publication date: 2001-09-19
Also published as: EP1134099A2; GB0006351D0; EP1134099A3; EP1134099B1; ES2286049T3; DE50112678D1

Abstract

A steering knuckle assembly for a steerable vehicle wheel comprises a wheel carrier 16 and a brake calliper support plate 18 which are rotatable relative to each other about the rotational axis X of the wheel. The upper mounting connecting the wheel carrier 16 to the upper suspension arm 10 includes a rotatable member 22 with the upper ball joint 27 at its upper end. A coupling link connects the member 22 to the caliper support plate so that rotation of the caliper support plate 18 under braking tends to mover the upper ball joint forwards relative to the wheel carrier 16. This counteracts the tendency for the wheel carrier 16 to rotate under braking, and thereby minimizes vertical movement of the steering arm 29 under braking.

Description

2360259 Vehicle Suspensions The present invention relates to independent

vehicle suspensions and in particular to such suspensions for steerable vehicle wheels.

It is known to provide an independent suspension for a steerable wheel in which the wheel is mounted on a steering knuckle which is pivotably mounted at two spaced apart mounting points to upper and lower suspension arms such that it can be pivoted about its steering axis, defined by the mounting points, to steer the wheel. A steering arm is rigidly connected to, or integrally formed with, the steering knuckle, and extends forwards or backwards, having a ball joint or other connection at its end for connection to a track rod. It is further known to mount the brake caliper of a disc brake on the steering knuckle.

It can be a problem with such suspensions that, under heavy braking, the torque applied to the steering knuckle through the brake caliper can cause rotation of the steering knuckle about the wheel axis, this movement being accommodated by compliance in the mountings for the suspension arms. This rotation can cause significant movement of the end of the steering arm, in a generally vertical direction, which in turn can produce undesirable steering effects. This problem is particularly significant where the suspension arms cannot provide a high level of resistance to the rotation of the steering knuckle, for example in double wishbone suspensions where the wishbones are close together.

Accordingly the present invention provides a suspension for a vehicle wheel, the suspension comprising a wheel carrier mounted at upper and lower mountings to upper and lower support means and arranged to carry a wheel, and a brake caliper supporting member for supporting a brake caliper for braking the wheel, the brake caliper supporting member being rotatable relative to the wheel carrier, wherein one of the upper and lower mountings includes a mounting member attached to the wheel carrier so as to be movable relative thereto and coupled to the caliper supporting member such that, during braking, movement of the caliper supporting member relative to the wheel carrier produced by braking torque produces movement of the mounting member relative to the wheel carrier so as to tend to produce rotation of the wheel carrier in the opposite direction to the direction of rotation of the braked wheel.

Preferred embodiments of the present invention will now be described by way of example only with reference to Figure 1 in the accompanying drawing which is a side view of a suspension according to the invention.

An independent front suspension for a steerable vehicle wheel comprises an upper suspension arm 10 and a lower suspension arm 12, arranged to be approximately horizontal and parallel to each other, and pivotably mounted at their inboard ends to the vehicle body. A steering knuckle assembly 14 is pivotably mounted between the two suspension arms 10, 12 so that it can be rotated about an approximately vertical steering axis to steer the vehicle. The steering knuckle assembly comprises a wheel carrier 16, a caliper support plate 18 with a brake caliper 20 mounted on it, and an upper mounting member 22. The wheel carrier 16 is pivotably mounted at its lower end to the lower suspension arm 12 in a conventional manner, and pivotably mounted at its upper end to the upper suspension arm 10 by means of the upper mounting member 22. This upper mounting member 22 is substantially L shaped, having one arm 24 extending vertically upwards with the ball part 26 of a ball joint 27 mounted on its upper end, and another arm 28 extending horizontally forwards. At the central angle of the mounting member 22, where the two arms 24, 28 are joined, the mounting member 22 is pivotably connected to the wheel carrier 16. The ball joint 27 joins the upper mounting member 22 to the upper suspension arm 10. The wheel carrier 16 is joined to the lower suspension arm 12 by means of a lower pivotable joint, not shown in the drawing, and the whole steering knuckle assembly 16, 18, 22 can therefore be rotated about the upper 27 and lower joints to steer the vehicle. A steering arm 29 is formed integrally with the wheel carrier 16 and extends forwards, having a joint 30 at its front end for connection to a track rod. This provides the steering input to control the steering of the wheel. The wheel carrier 16 is arranged to support the wheel, by means of bearings, such that it can rotate about an axis X.

The caliper support plate 18 is mounted on the wheel carrier so that it can rotate relative to it about the axis of rotation X of the wheel. It extends generally forwards of this axis and, at its front end, the brake caliper 20 is mounted. A spring 31 acts between the wheel carrier 16 and the caliper support plate 18 urging the caliper support plate 18 to rotate relative to the wheel carrier 16 in the anti-clockwise direction as seen in Figure 1. A stop (not shown) is provided to limit rotation in this direction and define the base relative position of these two components. From this base position, as shown in Figure 1, the caliper support plate can only move clockwise relative to the wheel carrier 16, and this movement is resisted by the spring 31.

A connecting link 32 is provided to connect the front end of the horizontal arm 28 of the upper mounting member 22 to the caliper support plate 18. This link 32 is substantially vertically arranged with its upper end pivotably connected to the upper mounting member 22 and its lower end pivotably connected to the caliper support plate 18 at a point forward of the wheel rotation axis X.

In operation, when the vehicle is travelling forwards and the brake caliper 20 is actuated to apply a braking torque to the wheel, the wheel applies a torque in the direction of the arrow A to the caliper support plate 18 and hence also to the whole steering knuckle assembly 16, 18, 22. Considering first the whole steering knuckle assembly, the torque applied to it during braking tends to rotate it in the direction of rotation of the wheel. The upper mounting 27 is therefore urged forwards, and the lower mounting is urged backwards. Compliance in the bushes connecting the suspension arms 10, 12 to the vehicle body allows this rotation to 5 occur.

Considering now the relative movement of the parts of the steering knuckle assembly 16, 18, 22, the braking torque tends to rotate the caliper support plate 18 relative to the wheel carrier 16 in the direction of rotation of the wheel, i.e. in the direction of the arrow A. This therefore pulls downwards on the connecting link 32, rotating the upper mounting member 22 in the same direction as the wheel, i.e. clockwise as seen in Figure 1. This moves the ball joint 27 forwards relative to the wheel carrier, or to put it another way, moves the top end of the wheel carrier 16 backwards relative to the ball joint 27. The wheel carrier 16 therefore rotates relative to the suspension arms 10, 12 in the opposite direction to the direction of rotation of the wheel. The amount of this movement for a given braking torque will depend on the rate of the spring 31 and the lengths of the arms 24, 28 of the upper mounting member 22. Therefore by tuning these characteristics and the level of compliance of the suspension arm mountings, it possible to arrange the system such that under braking the rotation in one direction of the whole steering knuckle assembly is compensated for by rotation in the opposite direction of the wheel carrier 16 relative to the suspension arms 10, 12. Total rotation of the wheel carrier is therefore minimized. This has benefits for ride and handling of the vehicle, and in particular minimizes vertical movement of the steering arm 29 under braking which can otherwise have undesirable effects on the steering of the vehicle.

As an alternative to the arrangement shown it would be possible to make the lower mounting of the steering knuckle assembly move rearwards under braking instead of, or as well as, the upper mounting moving forwards. However there is a further advantage of the system of Figure 1 in that, under braking, the castor of the wheel tends to increase which increases steering stability under braking. If the lower mounting were to move rearwards, this advantage would be lost.

It will be understood to the skilled man that, as well as the double wishbone suspension described above, the invention could be used in other types of suspension where rotation of the wheel carrier under braking might otherwise cause problems.

Claims

-6CIAIMS

1. A suspension for a vehicle wheel, the suspension comprising a wheel carrier mounted at upper and lower mountings to upper and lower support means and arranged to carry a wheel, and a brake caliper supporting member for supporting a brake caliper for braking the wheel, the brake caliper supporting member being rotatable relative to the wheel carrier, wherein one of the upper and lower mountings includes a mounting member attached to the wheel carrier so as to be movable relative thereto and coupled to the caliper supporting member such that, during braking, movement of the caliper supporting member relative to the wheel carrier produced by braking torque produces movement of the mounting member relative to the wheel carrier so as to tend to produce rotation of the wheel carrier in the opposite direction to the direction of rotation of the braked wheel.

2. A suspension according to claim 1 wherein the upper and lower support means comprise upper and lower suspension arms respectively, each arranged to be pivotable connected to a vehicle body.

3. A suspension according to claim 2 in which the suspension arms are arranged to be substantially parallel and horizontal.

4. A suspension according to any foregoing claim wherein the upper and lower mountings are pivotable to allow the wheel to be steered.

5. A suspension according to any foregoing claim wherein the caliper support member is rotatable relative to the wheel carrier about an axis which coincides with the axis of rotation of the wheel relative to the wheel carrier.

6. A suspension according to any foregoing claim wherein the mounting member is pivotably mounted on the wheel carrier.

7. A suspension according to claim 6 wherein the mounting member is coupled to the caliper supporting member by means of a connecting link.

8. A suspension according to claim 6 or claim 7 wherein the mounting member includes a part spherical portion forming part of a ball joint by means of which the wheel carrier is mounted to one of the upper and lower support means.

9. A suspension according to any foregoing claim wherein said one mounting is the upper mounting and the mounting member is arranged to move forwards relative to the wheel carrier under braking.

10. A suspension for a vehicle wheel substantially as hereinbefore described with reference to the accompanying drawings.