GB2187524A

GB2187524A - Vehicle having torsion suspension and load conscious brake pressure

Info

Publication number: GB2187524A
Application number: GB08704855A
Authority: GB
Inventors: Glyn Phillip Reginald Farr
Original assignee: Lucas Industries Ltd
Current assignee: ZF International UK Ltd
Priority date: 1986-03-06
Filing date: 1987-03-02
Publication date: 1987-09-09
Also published as: DE8703322U1; GB8605540D0; GB2187524B; GB8704855D0; FR2595634A1

Abstract

A vehicle is provided with a torsion suspension unit comprising a suspension arm (9) carried by a torsion bar (7) which is connected by splines (8) to a torsion tube (6) having a reaction arm (10) fixed to it for reacting the suspension load imposed by the wheel assembly (14). The torsion suspension unit is rotatably mounted on the vehicle body and the suspension load is reacted partly by the control member (17) of a brake pressure control valve (13) and partly by a spring (22) which is interposed between the body of the control valve and the reaction arm (10). <IMAGE>

Description

SPECIFICATION Vehicle having torsion suspension and load conscious brake pressure This invention relates to a vehicle having a torsion suspension for at least one of the road wheels thereof and provided with load conscious brakes.

It is well known to provide motor vehicles with one or more brake pressure control valves which are responsive to vehicle loading to vary the characteristics of the vehicle braking system. Typically, such valves will provide uninterrupted communication between front and rear brakes when the brake pressure is below a critical "cut-in pressure" and above cut-in pressure will provide a lower brake pressure to the rear brakes than that supplied to the front brakes. The load of the vehicle is sensed by some means and used to vary the cut-in pressure.

The present invention relates to a vehicle having a torsion suspension system, and in the preferred embodiment provides a particularly simple and desirable means of furnishing such a vehicle with load conscious brake pressure.

According to one aspect of the present invention there is provided a vehicle comprising: a torsion suspension unit rotatably mounted on the vehicle body and having a suspension arm connected to a wheel assembly and a reaction arm for reacting the torsion load of the suspension unit on the vehicle body; a brake pressure control valve interposed between the reaction arm and the vehicle body, the brake pressure control valve including a valve body bearing relation with one of the reaction arm and the vehicle body and a control member in load bearing relation with the other of the reaction arm and the vehicle body such that the load of the reaction arm biases the control member in one direction relative to the valve body; and a compensating spring for applying a substantially constant force to the reaction arm in the direction tending to reduce the load on the brake pressure control valve.

It will be understood that the term "torsion suspension unit" is intended to mean any suspension unit in which movement of the associated vehicle wheel relative to the vehicle body is accomodate by resilient torsional deflection of one or more elements of the suspension unit. For example, the torsion suspension unit may be a torsion bar, a torsion tube, or any combination thereof. It will also be understood that whilst the torsion suspension unit must be rotatably mounted on the vehicle body in order to permit the torsional load applied to the suspension unit to be transferred to the vehicle body via the reaction arm, the extent of rotational movement required will vary with the suspension unit design, and the position on the suspension unit at which rotation is measured.At the reaction arm the amount of rotatio < nal movement required is merely that to move the control member of the valve, and this can be very small indeed.

The invention will be better understood from the following description of a preferred embodiment thereof, given by way of example only, reference being had to the accompanying drawings wherein: Figure 1 is a schematic sectional view through the rear suspension of a motor car; Figure 2 is a perspective view corresponding to part of the arrangement shown in Fig.

1; and Figure 3 is a cross-sectional view through a portion of the arrangement of Figs. 1 and 2.

Referring to the drawings, there is shown schematically a portion of a vehicle having a body 1, parts only of which are shown in the drawings. A pair of torsion suspension units 2A, 2B are rotatably mounted on the vehicle body. The arrangement is symmetrical about the centre-line of the vehicle, and for the purposes of the following description only the left-hand portion of the vehicle (as illustrated in Fig. 1) will be described.

The torsion suspension unit 2A is rotatably mounted on the body 1 by means of bearings 3,4. The bearing 4 is carried by a locating member 5 which is itself fixed to the vehicle body and which serves to support the suspension unit 2A, 2B for rotational movement relative to the vehicle body.

The suspension unit 2A comprises a torsion tube 6 which is rotationally fast with a torsion bar 7 via a splined connection 8. A suspension arm 9 is rotationally fast with the outboard end of the tube 6 and a reaction arm 10 is rotationally fast with the out-board end of the torsion bar 7. A bearing 11 rotationally supports the torsion bar 7 within the torsion tube 6 adjacent the reaction arm 10.

In use, the free end 12 of the reaction arm 10 abuts a brake pressure control valve 13 as described in more detail hereinafter. Although the free end 12 will move a very smail amount as the valve opens and closes in use, the free end 12 may be regarded from the point of view of the suspension as being substantially fixed. Accordingly, any variation in the load on the wheel assembly 14 carried by suspension arm 9 will result in torsional deformation of the tube 6 and/or the bar 7. Since the suspension unit is rotatably mounted by means of bearings 3,4, substantially the entire torsional loading applied to the torsion tube 6 by the suspension arm 9 will be reacted by the reaction arm 10 on the valve 13. Thus, the force with which the free end 12 of the torsion arm abuts the control valve will vary directly in proportion to changes in the vehicle suspension loading.

Referring now to Fig. 3, it will be seen that the control valve 13 comprises a valve body 1 5 which is fixed in load bearing relation with the vehicle body by a bracket 16. The valve includes a control piston 17 which is in load bearing relation with the arm 10 via a rigid force transmitting cap 18. The load of the suspension system imposes on the piston 17 a force acting in the direction of the arrow A.

The valve body 15 defines a fluid inlet 19 and a fluid outlet 20 which are interconnected within the valve body via a normally open valve 21. As will be understood by those skilled in the art, the valve 21 provides free communication between the inlet 19 and the outlet 20 until the pressure within the brake system rises to a value at which the brake pressure acting over the area of the piston 17 is able to move the piston in the direction opposite to the arrow A, thereby interrupting the communication between the inlet 19 and outlet 20. Further increases in inlet brake pressure are not fully communicated to the outlet, but rather the pressure at the outlet increases more slowly than pressure at the inlet.

A compensating spring 22 reacts between the valve body 15 and the cap member 18 to impose on the reaction arm 10 a substantially constant spring force. The load imposed by the compensating spring is substantially constanct because the piston 1 7 moves very little in use, and accordingly there is substantially no deflection of the spring 22. Accordingly, the cut-in pressure of the valve will be determined by the equation: S-K=PA Wherein S is the force imposed by the reaction arm 10, K is the force of the compensating spring 22, A is the effective area of the piston 17, and P is the brake pressure. It will be appreciated that the force S increases with increased vehicle loading, thereby rendering the cut-in pressure of the valve 13 dependent upon vehicle loading.

Claims

1. A vehicle comprising: a torsion suspension unit rotatably mounted on the vehicle body and having a suspension arm connected to a wheel assembly and a reaction arm for reacting the torsion load of the suspension unit on the vehicle body; a brake pressure control valve interposed between the reaction arm and the vehicle body, the brake pressure control valve including a valve body in load bearing relation with one of the reaction arm and the vehicle body and a control member in load bearing relation with the other of the reaction arm and the vehicle body such that the load of the reaction arm biases the control member in one direction relative to the valve body; and compensating spring for applying a substantially constant force to the reaction arm in the direction tending to reduce the load on the brake pressure control valve.

2. A vehicle according to claim 1 wherein the compensating spring is interposed between the reaction arm and the valve body.

3. A vehicle according to claim 1 or claim 2 wherein the torsion suspension unit comprises first and second torsion members, the first torsion member being mounted co-axially within the second torsion member and being connected to the second torsion member in a rotationally fast manner at one end of the torsion suspension unit, and wherein the first and second torsion members carry, at the ends thereof remote from the rotationally fast connection, respective radially extending arms, one of which forms the reaction arm and the other of which forms the suspension arm.

4. A vehicle according to claim 3 wherein the second torsion member is rotatably supported on the vehicle body via a bearing located adjacent the arms, and the first torsion member is rotatably supported by the second torsion member via a bearing located adjacent the arms.

5. A vehicle according to any preceding claim wherein the vehicle has a pair of front wheels and a pair of rear wheels, and each wheel of at least one of said pairs is provided with a said torsion suspension unit and brake pressure control valve.

6. A vehicle according to claim 5 wherein the torsion suspension units of said at least one pair of wheels extend transversely of the longitudinal axis of the vehicle and are rotatably supported adjacent the longitudinal axis of the vehicle in a common locating member.

7. A vehicle substantially as herein described with reference to the accompanying drawings.