GB2347394A - Beam axle suspension system which resists roll yet accommodates pitch - Google Patents

Abstract

A beam axle suspension system in which the wheels 16 on each side of the vehicle are connected to opposite ends of a roll balance member 18, 20. A roll torsion bar 30 is connected between the mid points, so that the roll balance members 18, 20 can accommodate vehicle pitch without resistance from the torsion bar 30, and the torsion bar acts to resist vehicle roll. The mechanical connections may be replaced by hydraulics (see figs 2 and 4) for ease of packaging.

Description

VehicleSuspensions The present invention relates to vehicle suspension systems.

The present invention provides a suspension system for a vehicle having a pair of wheels on each side comprising a front wheel and a rear wheel, wherein each pair of wheels is connected to opposite ends of a respective roll balance member and a roll control spring is connected between intermediate points on the roll balance members between their ends so that the roll balance members can rock about their intermediate points to accommodate vehicle pitch without resistance from the roll control spring, and the roll control spring acts to resist movement in opposite directions of the intermediate points of the two balance members.

Preferably the system further comprising two pitch balance members each having each of its ends connected to a respective one of the roll balance members, at least one of the pitch balance members having a pitch control spring connected to its mid point such that it can rock about its mid point to accommodate vehicle roll.

At least one of the pitch balance members may comprise a beam axle of the vehicle.

Preferably at least one end of each roll balance member is remote from its respective wheel and is connected to its axle by means of an interconnection which translates vertical movement of the wheel into movement of the end of each roll balance member. This enables the size and orientation of the roll balance members to be varied, and, for example it allows each roll balance member to be substantially shorter than the distance between the respective pair of wheels.

Preferably each end of each roll balance member is remote from its respective wheel and is connected to its axle by means of an interconnection which translates vertical movement of the wheel into movement of the end of each roll balance member.

The interconnection may be a hydraulic interconnection. Alternatively it may be a mechanical interconnection.

Preferably the roll control means comprises a torsion bar operating between the intermediate points of the two roll balance members.

Preferred embodiments of the present invention will now be described by way of example only with reference to the accompanying drawings in which: Figure 1 is a schematic view of a vehicle suspension system according to a first embodiment of the invention; Figure 2 is a schematic view of a vehicle suspension system according to a second embodiment of the invention; Figure 3 is a schematic view of part of a vehicle suspension system according to a third embodiment of the invention; and Figure 4 is a schematic view of a vehicle suspension system according to a fourth embodiment of the invention.

Referring to Figure 1, a vehicle 10 has a suspension comprising front and rear beam axles 12,14 each having a wheel 16 at each end, and a body supported on the beam axles by load supporting suspension components which are not shown but which could comprise coil springs for example. Along each side of the vehicle a roll balance beam 18,20 extends longitudinally over substantially the whole length of the vehicle having one end connected by a rigid vertical link 22 to the front axle 12 close to one of the front wheels 16 and the other end connected by a similar link 24 to the rear axle 14 close to one of the rear wheels 16.

At an intermediate point on each of the roll balance beams 18,20, approximately mid-way along them, the beam is connected to the vehicle body by means of a bounce control spring 26,28, and a torsion bar 30 extends across the vehicle having each end connected to a respective one of the roll balance beams at the intermediate point. The centre of the rear axle 14 is connected to the body by a pitch control spring 32.

It will be appreciated that with the arrangement shown in Figure 1 in pure roll the axles 12,14 will rotate about their centres relative to the body, so the roll stiffness of the vehicle is dependent on the stiffness of the torsion bar and the bounce control springs 26,26 but independent of the stiffness of the pitch control spring 32. Also because the torsion bar 30 is connected to the mid points of the roll balance beams 18,20 it experiences the average of the roll of the front and rear axles. This means that the overall roll stiffness can be controlled by varying the stiffness of a single torsion bar. In pure pitch the roll balance beams 18,20 will rotate about their centres relative to the body, i. e. about the intermediate points at which the bounce control springs 26, 28 and torsion bar 30 are connected to them, so the pitch stiffness of the vehicle is dependent on the stiffness of the pitch control spring 32, but independent of the stiffness of the torsion bar 30 and the bounce control springs 26,28. It is therefore easy to design the suspension so as to give the desired suspension characteristics. A further advantage of this arrangement is that it provides substantially no resistance to cross articulation, which is a desirable feature in off-road vehicles.

Referring to Figure 2, the second embodiment of the invention operates in a similar manner to the first embodiment and parts corresponding to those in the first embodiment are indicated by the same reference numeral preceded by a 1.

The difference with this embodiment is that the balance beams 118,120 are much shorter and are located at the rear end of the vehicle. Whilst the rear ends of the balance beams are connected to the rear axle 114 by means of vertical links 124, the front end of each of the balance beams is connected to the front axle 112 by means of a hydraulic interconnection comprising a pair of pistons 134, 136, one connected to the front axle 112 and one connected to the front end of the balance beam 118,120, and each slidable in a respective cylinder 138,140, and a pipe connecting the two cylinders so that vertical movement in one direction of one of the front wheels 116 produces vertical movement in the same direction of the front end of the respective balance beam 118,120. This means that the balance beams can be made much shorter with consequent packaging and weight advantages.

Referring to Figure 3, in a third embodiment of the invention the second embodiment is modifie by rotating the balance beams through 90 so that they are transverse to the vehicle, one on either side of its longitudinal centre line, with their outboard ends connected to the rear axle 114 by a rigid vertical link 124, their inboard ends connected to respective pistons providing one end of a hydraulic link with the front axle. The centre points of the balance beams are interconnected by a torsion beam which provides roll control and connected to the vehicle body by bounce control springs 126,128. It will be appreciated that this system operates in the same manner as the second embodiment, but that it can have packaging advantages as the balance beams 118,120 are parallel with the rear axle.

Referring to Figure 4, in a fourth embodiment of the invention the hydraulic interconnection is carried a stage further so that the frame in the first embodiment formed by the beam axles and the balance beams is replicated as a balance frame 410 comprising two longitudinal roll balance beams 412,414 and two lateral pitch balance beams 416, 418 having their ends pivotably linked together so that they form the sides and ends of a rectangular frame 410. Each corner of the frame is hydraulically connected to a respective one of the wheels, by means of a hydraulic pipe 426 with a wheel-end piston 428 connected to the axle of the respective wheel and a frame-end piston 430 connected to the corner of the frame 410, so that vertical movement of each of the wheels produces corresponding vertical movement of the respective corner of the frame 410. Clearly the cross sectional areas of the pistons of the hydraulic connections can be selected so as to control the ratio of displacements of the frame corners and the wheels.

The mid points of the longitudinal roll balance beams 412,414 are interconnected by a torsion bar 420 and the mid points of the lateral pitch balance beams 416,418 are connected to the vehicle body by pitch control coil springs 422, 424.

In each of the hydraulic interconnections a hydraulic accumulator 432 comprising a piston acting against a gas spring is connected into the hydraulic pipe 426 close to the wheel-end piston 428. This allows a limited amount of hydraulic fluid to flow into and out of the wheel-end piston 428 without passing through the whole length of the pipe 426. This is so that for high frequency wheel movements the wheel movement is not unduly restricted due to the diameter of the pipe 426.

In roll the lateral pitch balance beams 416,416 will rotate simultaneously about their midpoints against the resistance of the torsion bar 420 and without movement of the pitch control springs 422,424. In pitch, the longitudinal roll balance beams 412,414 will rotate about their midpoints against the resistance of the pitch control springs 422, 424 and without movement of the torsion bar 420.

Therefore pitch and roll stiffnesses can be tuned independently of each other. In bounce the whole frame 410 will move vertically against the resistance of the pitch control springs 422,424 which therefore also define the bounce stiffness of the suspension. In cross articulation, because the longitudinal and lateral balance beams are pivotably connected together one pair of diagonally opposed corners of the frame 410 can move upwards while the other pair of diagonally opposed corners moves downwards without any resistance from the torsion bar 420 or the coil springs 422,424. Therefore the resistance of the system to cross articulation is low.

It will be appreciated that various modifications can be made to the embodiments described. For example in some circumstances it might be preferable to replace the hydraulic interconnections between the wheels and the balance beams with mechanical interconnections. This would avoid potential problems of hydraulic lock-up at high frequencies. Furthermore it will be appreciated that with the embodiment of Figure 4, because the frame 410 is remotely connected to each of the wheels, the frame can actually be placed in any position or orientation which is desirable. It will also be appreciated that the embodiment of Figure 4 could be used with an independent suspension rather than a beam axle suspension.

Claims (12)

1. CLAIMS 1. A suspension system for a vehicle having a pair of wheels on each side comprising a front wheel and a rear wheel, wherein each pair of wheels is connected to opposite ends of a respective roll balance member and a roll control spring is connected between intermediate points on the roll balance members between their ends so that the roll balance members can rock about their intermediate points to accommodate vehicle pitch without resistance from the roll control spring, and the roll control spring acts to resist movement in opposite directions of the intermediate points of the two balance members.
2. 2. A system according to claim 1 further comprising two pitch balance members each having each of its ends connected to a respective one of the roll balance members, at least one of the pitch balance members having a pitch control spring connected to its mid point such that it can rock about its mid point to accommodate vehicle roll.
3. 3. A system according to claim 2 wherein at least one of the pitch balance members comprises a beam axle of the vehicle.
4. 4. A system according to any foregoing claim wherein at least one end of each roll balance member is remote from its respective wheel and is connected to its axle by means of an interconnection which translates vertical movement of the wheel into movement of the end of each roll balance member.
5. 5. A system according to claim 1 or claim 2 wherein each end of each roll balance member is remote from its respective wheel and is connected to its axle by means of an interconnection which translates vertical movement of the wheel into movement of the end of each roll balance member.
6. 6. A system according to claim 4 or claim 5 wherein said interconnection is a hydraulic interconnection.
7. 7. A system according to claim 6 wherein at least one of the hydraulic interconnections includes a hydraulic pipe having one end connected to a first piston assembly operated by the wheel and the other end connected to a second piston assembly operated by the roll balance member, and a hydraulic accumulator connected to the first piston assembly so as to allow vertical movement of its wheel without the need for hydraulic fluid to flow through the whole length of the pipe.
8. 8. A system according to any foregoing claim wherein each roll balance member is substantially shorter than the distance between the respective pair of wheels.
9. 9. A system according to any foregoing claim wherein the roll control means comprises a torsion bar operating between the intermediate points of the two roll balance members.
10. 10. A system according to any foregoing claim wherein the balance members are arranged to extend laterally of the vehicle.
11. 11. A system according to any one of claims 2 to 4 wherein the roll balance members are arranged to extend longitudinally of the vehicle.
12. 12. A vehicle suspension system substantially as hereinbefore described with reference to the accompanying drawings.