FIELD OF THE INVENTION

The present invention relates to a suspension system suitable as a rear suspension system for a vehicle. It is particularly applicable to relatively small, load carrying vehicles such as small trucks, with large variation in rear wheel axle weight. It is also particularly applicable to such trucks when designed with a rear engine configuration, and rear wheel drive.

BACKGROUND TO THE INVENTION

The provision of adequate suspension for small trucks, having a rear engine configuration, presents some difficulties in design. Firstly, the suspension must accommodate the engine. Secondly, the rear axle weight of such trucks may vary between, for instance, 350 kg in an un-laden condition to 1,350 kg when laden. It is important to provide adequate wheel travel to accommodate this variation.

Further, it is desirable to limit vehicle roll. Roll centre for the suspension should be as high as possible in both unladen and laden configurations. Similarly, it is desirable for the un-sprung mass to be as low as possible. Finally, the suspension system should lead to desirable vehicle steer characteristics.

Currently, rear wheel suspension systems for small rear wheel driven trucks are generally of one of two types. The first common type is a leaf spring mounted on a rigid rear axle. Such systems have a relatively high un-sprung mass (in excess of 100 kg), and a roll centre which lowers with wheel travel.

The second common type of rear wheel suspension is a trailing or semi-trailing arm suspension, sprung by coil, rubber, or torsion bar springs. This suspension type has a relatively low un-sprung mass. It also has a roll centre close to the ground, resulting a large rolling moment, reducing vehicle stability during steering. Further, use of semi-trailing arm suspension results in high tyre wear rates due to variation in wheel camber. As the vehicle is rear-wheel driven, such wear is problematic.

An object of the present invention is to provide a suspension system, particularly a rear suspension system, which provides improved vehicle handling, whilst meeting the requirements outlined above.

SUMMARY OF THE INVENTION

In accordance with an aspect of the present invention there is provided a suspension system for a pair of wheels on a vehicle, the vehicle having a chassis, the suspension system having a primary supporting member, the primary supporting member being connected to the chassis at a plurality of locations, the primary supporting member having two rearward extending portions, one rearward extending portion being connected to each wheel, each rearward extending portion including a spring and a damping means.
Preferably, the supporting member is connected to the chassis at at least three locations. At the first location, the primary supporting member is directly connected to the chassis by means of a central connecting arm attached to a mounting bush. The primary supporting member is arranged to be able to pivot freely about the chassis at least the first location. Kinematically this acts like a spherical joint.

Preferably, at second and third locations, the primary supporting member is connected to the chassis by respective stabilising bars. Each stabilising bar extends from a mounting above the primary supporting member to the chassis. When viewed in the vertical plane, the primary supporting member is thus angled with respect to the supporting member. The location of the vehicle roll centre. Is a function of this angle to (which is preferably at 13.2° in the present invention).

This three-way connection of the supporting member to the chassis allows the traction and braking forces transferred from the wheel to the chassis to be distributed at three locations providing an acceptable degree of suspension.

The stabilising bars are located such that, when viewed in the horizontal plane, they splay outwardly from the primary supporting member to the chassis. The stabilising bars thus each form an angle a with respect to a longitudinal axis of the vehicle (this angle is preferably 24° in the present invention). This arrangement assists in minimising lateral movement of the wheels relative to the vehicle sprung-mass during cornering and rear wheel toe change which in turn assists understeer behaviour of vehicle.

The higher the angle OJ, the higher is the roll centre. However, as roll centre increases it Increases lateral load transfer, which beyond a limit is not desirable. At a same time in order to sustain lateral and longitudinal forces, the mounting bracket has to be thicker and heavier. Similarly, a higher angle a helps in minimising lateral movement of wheels but reduces traction and braking load carrying capability of stabilising bars; also small lateral movement of wheels results in high toe change which is not good from handling point of view and tyre life.

Thus selection of both these angles a and to is based on various factors like location of Centre of Gravity, wheel reaction, wheel base and track etc.

Each stabilising bar is connected, to its respective mounting on the primary supporting member, and to the chassis, by means of mounting bushes which permit rotation of the stabilising bar relative to the chassis and to the supporting member.

The suspension system provides adequate suspension while limiting vehicle roll and tyre wear.

BRIEF DESCRIPTION OF THE DRAWINGS

It will be convenient to further describe the suspension system of the invention with reference to the accompanying drawings which illustrate preferred embodiments of the suspension system of the present invention. Other embodiments are possible, and consequently, the particularity of the accompanying drawings is not to be understood as superseding the generality of the preceding description of the invention.

Figure 1 is a perspective of a suspension means in accordance with the present invention;

Figure 2 is a schematic perspective of the suspension means of Figure 1; Figure 3a is a schematic plan view of the suspension means of Figure 1; and Figure 3b is a schematic side view of the suspension means of Figure 1.

DESCRIPTION OF PREFERRED EMBODIMENT

Referring to the Figures, there is depicted a suspension system 10 for the rear wheels of a rear wheel drive, rear-engine configuration vehicle being a small truck. The suspension system 10 includes a primary supporting member 12 having a cross-member 14 which is substantially perpendicular to a longitudinal axis of the truck, and two rearward extending portions in the form of trailing arms 16 which extend substantially parallel to the longitudinal axis of the truck. The primary supporting member 12 is an Omega arm, being O-shaped in cross section.

Each of the trailing arms 16 is connected at a remote end thereof to a rear wheel 40 of the truck.

The primary supporting member 12 has a central connecting arm 18 connected to the chassis of the truck at three locations including a first connection location 20. The connection at the location 20 is made by a mounting bush, allowing pivoting and twist of the" central connecting arm 18 and hence the primary supporting member 12, with respect to the chassis of the truck.

The primary supporting member 12 has two mountings 22, located near the outer ends of the cross-member 14, Each of the mountings 22 is substantially vertical.

The suspension system 10 includes two stabilising bars 24. Each stabilising bar 24 extends between one of the mountings 22, above the primary supporting member 12, and the vehicle chassis to form second and third locations of connection of primary supporting member 12 to the chassis. Such three way connection of the primary supporting member 12 to the chassis allows the fraction and braking force from the wheels to the chassis to be distributed at three locations. The connection of the stabilising bars 24 to the chassis is laterally offset from the mountings 22, such that the stabilising bars 24 splay out. In the horizontal plane, the stabilising bars thus form an angle a with respect to a longitudinal axis of the truck. This angle w can be seen in Figure 3a and it is preferably 24°.

The height of the mounting 22 determines an angle cu, in the vertical plane, between the primary supporting member 12 and the stabilising bars 24. This can be seen in Figure 3b. In the embodiment of the drawings, ID is set at 13.2°.

Angle ω determines the location of the vehicle roll centre. The higher the angle w, the higher is the roll centre. However, as roll centre increases it increases lateral load transfer, which beyond a limit, equating to an angle to of 13.2", is not desirable. At a same time in order to sustain lateral and longitudinal forces, the mounting bracket has to be thicker and heavier. Similarly, a higher angle a helps in minimising lateral movement of wheels 40 but reduces traction and braking load carrying capability of stabilising bars 24; also small lateral movement of wheels results in high toe change which is not good from handling point of view and tyre life. Thus selection of both these angles α and ω is based on various factors such as location of Centre of Gravity, wheel reaction, wheel base and wheel track.

The stabilising bars 24 are each connected to the mountings 22 and the truck chassis by mounting bushings 20, allowing each the stabilising bars 24 to pivot and twist relative to both the chassis and the supporting member 12.

Each of the trailing arms 16 includes a coil spring 26 and a hydraulic damper 28 as damping means. Each of the coil springs 26 is oriented with its axis parallel to the spring load vector resulting during maximum deformation {i.e., in full bump condition). This is to minimize a buckling load on each of the coil springs 26.

Each of the dampers 28 is mounted on the vehicle frame tangential to wheel stroke path at mean position in order to minimise its angular variation during wheel stroke.

In testing of an embodiment of the invention in accordance with the drawings, it has been observed that the un-sprung mass of this assembly was only 75 kg, of which 49 kg represents the wheel assembly. The rear suspension roll centre height varied from 408mm in an un-laden condition (rear axle weight of 350 kg) to 412mm in a laden condition (rear axle weight of 1,350 kg).

During cornering, lateral deflection of the suspension system 10 was measured to show an understeer gradient of about two degrees per "g" of lateral acceleration.

Modifications and variations to the suspension system as would be apparent to a skilled addressee are deemed to be within the scope of the present invention.

WE CLAIM.-

1. A suspension system for a pair of wheels on a vehicle, the vehicle having a chassis, the suspension system having a primary supporting member, the primary supporting member being connected to the chassis at a plurality of locations, the primary supporting member having two rearward extending portions, one rearward extending portion being connected to each wheel, each rearward extending portion including a spring and a damping means.

2. A suspension system of claim 1 wherein said primary supporting member is connected to the chassis at least three locations.

3. A suspension system of claim 2 wherein, at a first location of connection, said primary supporting member is directly connected to the chassis by means of a central connecting arm attached to a mounting bush.

4. A suspension system of any one of the preceding claims wherein said primary supporting member is arranged to be able to pivot freely about the chassis.

5. A suspension system of claim 4 wherein said primary supporting member is arranged to be able to pivot freely about the chassis at at least said first location.

6. A suspension system as claimed in claim 2 or any one of claims 3 to 5 as dependent from claim 2, wherein at second and third locations, the primary supporting member is connected to the chassis by respective stabilising bars.

7. A suspension system as claimed in claim 6 wherein each stabilising bar extends from a mounting above the primary supporting member to the chassis so that, when viewed in the vertical plane, each stabilising bar is angled, at an angle w with respect to the primary supporting member, said location of vehicle roll centre being a function of angle ω.

8. A suspension system as claimed in claim 7 wherein said angle co is 13.2°.

9. A suspension system as claimed in any one of the preceding claims wherein three-way connection of the primary supporting member to the chassis allows the lateral and longitudinal forces transferred from the wheels to the chassis to be distributed at three locations.

10. A suspension system as claimed in any one of claims 6 to 9 wherein said stabilising bars are located such that, when viewed in the horizontal plane, the stabilising bars splay outwardly from the primary supporting member to the chassis, each stabilising bar each forming an angle a with respect to a longitudinal axis of the vehicle.

11. A suspension system as claimed in claim 10 wherein angle a is 24°.

12. A suspension system as claimed in any one of claims 7, 8, 10 or 11 wherein angles a and UJ are selected on the basis of at least one factor selected from the group consisting of location of Centre of Gravity, wheel reaction, wheel base and wheel track.

13. A suspension system as claimed in any one of claims 6 or claims 7 to 12, as dependent from claim 6, wherein each stabilising bar is connected to its respective mounting on the primary supporting member, and to the chassis, by mounting bushes which permit each stabilising bar to pivot and twist relative to both the chassis and to the primary supporting member.

14. A suspension system as claimed in any one of the preceding claims wherein said primary supporting member is an Omega arm, being Q-shaped in cross-section.

15. A suspension system as claimed in any one of the preceding claims being a rear suspension system for rear wheels of a vehicle.

16. A suspension system substantially as hereinbefore described with reference to the drawings.

17. A vehicle comprising the suspension system of any one of the preceding claims.