GB2245234A - A suspension system for a vehicle - Google Patents

Abstract

A suspension system which has two vehicle supports, usually road wheels 14, 16, and having provision whereby when one support rises relatively to the chassis (for instance if it rides over an obstacle) the other support is pressed down. This is achieved by two transmission levers 30, 30a, connected respectively to the two supports 14, 16 for turning when the respective support rises and a linkage 34 connecting the two transmission levers together. The linkage 34 comprises an extension and retraction mechanism which is remotely actuable. For example it may comprise a hydraulic piston/cylinder. By altering the length of the linkage, the height of the chassis is altered. <IMAGE>

Description

A SUSPENSION SYSTEM FOR A VEHICLE The invention is concerned with vehicle suspension systems, and more particularly is intended to be used on road vehicles, although it could also be used on other vehicles e.g. rail vehicles. In particular the invention is applicable to vehicles in which there are two or more wheels, or sets of wheels (or other supports e.g. tracks or skids) spaced from each other lengthwise of the vehicle, e.g. front and rear wheels.

In British Patent No. 2172253 there is described a suspension system for a vehicle comprising two vehicle supports (e.g. road wheels, tracks or skids) spaced lengthwise of the vehicle, each vehicle support being carried on a suspension lever pivoted about an axis on the chassis and trailing from that axis and a resilient suspension device active between each vehicle support and the vehicle chassis, there being a mechanism connected to the two suspension levers so as to transmit force between them in a manner such that any tendency for one vehicle support to rise relatively to the chassis applies a force tending to press the other vehicle support downwardly relatively to the chassis.

In the device described in British Patent No. 2172253 the mechanism connected between the two suspension levers comprises a respective transmission lever connected to each suspension lever and a linkage rod connected between the transmission levers. There is provision for adjusting the effective length of the linkage rod within limits, in that swivel blocks are carried on the transmission levers, to which blocks the linkage rod is secured.

In accordance with the present invention there is provided a suspension system for a vehicle comprising two vehicle supports (e.g. road wheels, tracks or skids) spaced lengthwise of the vehicle, each vehicle support being carried on a suspension lever pivoted about an axis on the chassis and trailing from that axis and a resilient suspension device active between each vehicle support and the vehicle chassis, there being a transmission lever connected to each suspension device such that the relative motion between each support and the chassis permitted by flexing of the suspension system produces turning of the transmission lever, and a linkage connecting the two transmission levers in such a manner that the turning of one transmission lever in one direction due to a reduction in the height of the chassis relatively to the support appertaining to that transmission lever tends to turn the other transmission lever in the opposite direction so as to produce an increase in height of the chassis relatively to the support appertaining to that other transmission lever, the linkage comprising an extension and retraction mechanism which is remotely actuable.

The extension and retraction mechanism may be such as to transmit force from one transmission lever to the other, and vice-versa, in only one configuration of the mechanism, the configuration it has when the vehicle is being driven. In such a case the mechanism can be extended or retracted, in order to alter the height of the chassis, at rest, for example for unloading of goods. A cylinder and piston assembly with provision for pressuring fluid on one side of the piston only is a suitable extension and retraction mechanism for this purpose.

The extension and retraction mechanism may be such as to transmit force from one transmission lever to the other, and vice-versa, in a plurality of configurations of the mechanism, so that the vehicle may be thus driven. A cylinder and piston assembly with provision for pressurising fluid on both sides, and on one side only, and on the other side only, is a suitable extension and retraction mechanism for this purpose.

By "remote actuation" is meant actuation without needing to effect direct manual adjustment of the linkage.

In one arrangement the extension and retraction mechanism comprises a hydraulic cylinder/piston so that remote actuation may be effected by operating an electric switch to power a fluid compressor or to cause pressure release.

In a completely different "remote actuation" the linkage includes a turnbuckle (rotation of which causes extension or contraction of the linkage) and in that case, the turnbuckle may be selectively rotated by means of a mechanical power drive, e.g. from a power-take- ff of the vehicle or towing vehicle engine.

The extension and retraction mechanism may also have provision for non-remote adjustment, in order to adjust for example, the maximum and minimum length of the linkage which is attainable.

As in the case of the suspension system of British Patent No. 2172253, the effect of this arrangement of the suspension system in accordance with the present invention is that whenever a vehicle support encounters an obstacle, so that that support tends to rise and the chassis tends to descend relatively to that support, a force is applied through the linkage and transmission levers tending to cause the other vehicle support to descend and the chassis tends to ascend relatively to that other vehicle support.

To put this even more simply, as one support rises, the other is pressed down. As in the earlier suspension system, both suspension devices are carried by their suspension levers trailing from their pivots so that vertical motion of each suspension device is achieved by turning of its associated lever, and if the vehicle is braked, the front end of the chassis will tend to dip.

This is preferable to the front end of the chassis tending to rise. The arrangement is very useful, in that it helps to ensure that both the supports are held in engagement with the ground even when the vehicle encounters obstacles or potholes.

However, unlike in the suspension system of British Patent No. 2172253, there is provision for extending and/or retracting the linkage by remote actuation. For example, a system may be configured in accordance with the present invention to enable the driver of a vehicle to effect, by remote actuation, changes in the chassis height, to select the chassis height at which he wishes to drive the vehicle. Alternatively, for example when the vehicle is a trailer, it may be required to lower the chassis height, not for driving at a reduced height, but only for unloading; in such an embodiment it is not necessary that the linkage transmit force from one transmission lever to the other and vice-versa, at the reduced height; only at the highest chassis position, the driving position, is this required.

It is understood that references in this specification to the vehicle chassis are intended to include the body of the vehicle in constructions where there is no chassis which is separate from the body i.e.

monocoque construction.

Preferably the transmission lever appertaining to each vehicle support is pivoted about the same axis as the suspension lever carrying that vehicle support and is connected to that suspension lever in a manner which prevents substantial angular displacement between the suspension lever and the transmission lever. It is preferred to provide a torsion rod extending between each suspension lever and its associated transmission lever, the torsion rod being journalled in a bearing or bearings to provide the pivotal mounting of the suspension lever and the elasticity of the rod in torsion providing the resilient force of the suspension device. With this arrangement, there is provision for some angular motion between the suspension lever and the transmission lever to provide the resilient effect of the suspension device, but this is relatively small. In practice, the link will transmit force between the two suspension devices and therefore the resilient force resisting raising of one vehicle support relatively to the chassis will be divided between the two torsion rods of the two suspension devices. This is because, as a torque is applied to the torsion rod appertaining to one vehicle support, due to that support attempting to rise, torque is also transmitted through the link and the other transmission lever to the other torsion rod, the turning of which is opposed by the resistance of the other vehicle support to lower (brought about by its engagement with the ground).

According to a preferred feature of the invention, there is provision for varying the distance between the suspension lever and the transmission lever to vary the effective length and therefore the compliance of the torsion rod.

Preferably the torsion rod extends transversely of the vehicle and the transmission lever is adjustable transversely of the vehicle to vary the distance between the transmission lever the and the suspension lever.

Typically, a vehicle will have one pair of vehicle supports towards one side of the vehicle and a second pair of supports towards the opposite side of the vehicle.

Preferably, each such pair of vehicle supports has its own independent suspension system in accordance with the invention.

An embodiment of the invention will now be described by way of example only, with reference to the accompanying drawings in which: Fig. 1 is a diagrammatic plan view of two road wheels forming a close-coupled pair on a vehicle; Fig. 2 is a diagrammatic side view of the arrangement shown in Fig. 1; and Figs. 3a and 3b are diagrammatic views of a linkage cylinder and piston assembly, in different positions.

In this particular example, the invention is described with reference to a vehicle - a trailer for a boat - having a chassis, of which two transverse beams 10 and 12 are illustrated. The beams are spaced longitudinally of the'vehicle. A front road wheel 14 is suspended from the front beam 10, and a rear road wheel 16 is suspended from the rear beam 12. It will be seen that the two road wheels 14 and 16 are arranged quite close to each other, in what is commonly known as a close-coupled arrangement. It will be appreciated, that the road wheel arrangement is duplicated at the other side of the vehicle. In the case of a small trailer, only the road wheels 14 and 16 and their counterparts at the other side of the vehicle will be provided adjacent to the centre of the length of the vehicle.With a larger trailer vehicle, there will be other road wheels, and these may have similar suspension arrangements to that illustrated in the drawings or alternative suspension arrangements may be employed. Moreover adjacent pairs of side-by-side road wheels may be employed, of the type shown in British Patent No. 2172253.

The road wheel 14 is mounted on an axle 18 which is carried at the distal end of a suspension lever 20. This lever broadens towards its proximal front end, where it is secured in a non-rotatable manner on a torsion rod 22.

The torsion rod extends transversely of the vehicle closely adjacent to the beam 10, and is journalled in bearings 24, 25 and 26 which are secured to the beam 10.

Bearing 26 is located at one end of the torsion rod 22 closely adjacent the outward end of the suspension lever.

Bearing 24 is located at or towards the opposite end of the torsion rod. Bearing 25 is located in an intermediate position, closely adjacent the inward end of the suspension lever 22. Hence, the suspension lever 20 is pivoted about the axis provided by the bearings 24, 25 and 26 and trails from that axis. The arrangement of the road wheel 14 on the suspension lever 20 permits movement of the road wheel relatively to the chassis of the vehicle, the axle 18 being able to turn about an arc 28 shown in Fig. 2. If the road wheel 14 encounters an obstacle, it tends to rise over that obstacle but the inertia of the chassis causes it to tend not to rise, so that there is the relative motion between the road wheel 14 and the chassis, provided by the suspension arrangement.If the torsion rod 22 merely acted as an axle freely journalled in the bearings 24, 25 and 26, the suspension would have virtually no stiffness.

A transmission lever 30 is secured on the torsion rod 22, in such a manner that it is possible to adjust the position of the transmission lever along the torsion rod, between the fixed bearings 24 and 25. As shown in Fig. 2, the transmission lever 30 projects upwardly from the axis provided by the torsion rod 22.

The suspension arrangement for the road wheel 16 is identical with that described for the road wheel 14 so that the suspension lever 20a trails from the axis provided by the bearings 24a, 25a and 26a (and similar parts have therefore been given the same reference numeral with the suffix a) but the transmission lever 30a is located on the torsion rod 22a, so that it extends downwardly from the axis provided by the torsion rod.

A linkage mechanism 34 extends between the transmission levers 30 and 30a, respective ends of the linkage mechanism being freely pivoted to transmission levers 30 and 30a by respective pivots 32 and 32a. The linkage mechanism is an assembly of a cylinder 36 and a piston 38. It will be appreciated that if the length of the linkage mechanism 34 is decreased, then the transmission lever 30 will be turned in a clockwise direction and the transmission lever 32 will be turned in anti-clockwise direction. As a result, the suspension levers 20 and 20a will press the road wheels 14 and 16 downwardly, or to be more precise, will increase the vertical distance between the chassis and the axles of the road wheels. In fact, the provision for changing the length of the linkage mechanism 34 is the means whereby the height of the chassis above the road wheel axles can be changed.

The piston 38 of the linkage mechanism comprises a piston head 40 and piston rod 41. The piston rod 41 is in two parts, which are screw-fitted together, one part 41a being a rod which carries the piston head 40 and the other part 41b being a rod pivoted to the transmission lever 30a. The assembly is a single acting cylinder/piston, that is, the movement of the piston, movement into the cylinder in this case, may be powered hydraulically by applying pressurised fluid on one side of the piston head only, in fact, to the chamber 42 rearward of the piston head 40, via the hydraulic fluid supply line 44. It is not necessary to apply pressurised fluid to the other side of the piston head because outward movement of the piston, to lengthen the linkage mechanism, occurs under gravity when the hydraulic fluid in chamber 44 is no longer pressurised.

Within the cylinder, mounted around the piston rod 41a and extending from the piston head 40, is a cylindrical stop member 46, which serves to limit the extension of the piston when the fluid is no longer pressurised. Thus, when the stop member 46 abuts the cylinder rear wall, the linkage mechanism is at its longest (Fig. 3b). Also within the cylinder, screw-fitted on the piston head 40 on the opposite side to the stop member 46, is a stop block 48 which serves to limit the retraction of the piston when the fluid is pressurised.

Thus, when the stop block 48 abuts the cylinder front wall, the linkage mechanism is at its shortest (Figs. 2 and 3a).

It will be appreciated that the linkage mechanism 34 in this embodiment has one "effective length", at which it acts in the manner of a solid bar, able to transmit force from the transmission lever 30 to transmission lever 30a and vice-versa. This is at its shortest length, shown in Fig. 3a. It is a relatively simple matter to change this "effective length", by changing the stop block 48 and/or by using a longer or shorter piston rod section 41b and/or by using a longer or shorter rod 41b in the piston assembly.

In this embodiment, it is required to be able to lengthen the linkage mechanism in order to lower the chassis and remove a boat from the trailer, and this is achieved by extending the linkage mechanism to its maximum length. However, it is not required to drive the vehicle thus, and so the linkage mechanism does not need to act as a two-way force-transmitting member in its extended configuration. The mechanism is extended by remote actuation, in that an electric switch (not shown) mounted on the trailer is operated to de-pressurise the chamber 42.

It is a relatively simple matter to change the maximum length of the linkage mechanism, again by changing the stop member 46 and/or by using a longer or shorter piston rod section 41b and/or by using a longer or shorter rod 41b in the piston assembly.

In an alternative embodiment a double acting hydraulic cylinder/piston may be employed, with provision for pressurising fluid on both sides of the piston head at the same time and for selectively releasing the pressure on either of the sides. It will be appreciated that when a double acting cylinder/piston is employed as a linkage mechanism, that the vehicle may be driven with the linkage mechanism at its maximum length, or minimum length, or any length on between, because in all such positions pressurised fluid may be arranged to act on both sides of the piston head, so that the assembly acts in the manner of a solid bar, to transmit force from the transmission lever 30 to the transmission lever 30a, and vice-versa.

In order to understand the operation of the suspension system when the vehicle is being driven, let it be considered that the transmission lever 30 is fixed to the beam 10. Then as the road wheel 14 attempts to rise, the suspension lever 20 will apply a turning movement to the torsion rod 22, and raising of the wheel will only be possible as permitted by twisting of the torsion rod 22 between its anchor position in the transmission lever 30 and the position at which it is secured in the proximal end of the suspension lever 20. In other words, the resilient load required by the suspension system to restrict upward displacement of the road wheels relatively to the chassis is provided by the elasticity in torsion of the effective length of the torsion rod 22.

Now if the position at which the transmission lever 30 is fixed to the beam 10 is adjusted, so as to vary the effective length of the torsion rod 22, it will be appreciated that the compliance of the torsion rod 22 in torsion is altered. The longer the effective length of the torsion rod (i.e. the nearer the transmission lever 30 to the fixed bearing 24) the greater will be the compliance of the torsion rod, and hence the lower the stiffness of the suspension system.

In practice the transmission lever 30 is not secured to the beam 10, but instead, its turning about the axis provided by the torsion rod is restricted by the attachment of the linkage mechanism 34 to the transmission lever 30a of the rear suspension system. When the suspension arm 20 turns due to raising of the road wheel 14, this turning motion is transmitted through the torsion rod 22 to the transmission lever 30, and then through the linkage mechanism 34 to the transmission lever 30a.

However, whereas this motion involves turning of the transmission lever 30 in an anti-clockwise direction, the lever 30a is turned in a clockwise direction - this is the result of having one transmission lever pointing upwardly and the other pointing downwardly from their respective axes. Turning of the transmission lever 30a in a clockwise direction causes the suspension lever 20a to attempt to turn in a clockwise direction and to force the road wheel 16 downwardly. In other words, the two suspension systems for the road wheels 14 and 16 are connected together by the transmission levers and the linkage mechanism 34 in such a manner that any upward motion of the road wheel 14 creates a force tending to press the road wheel 16 downwardly and vice-versa.This arrangement ensures that the two road wheels are maintained in engagement with the road surface even though one wheel may be encountering an obstacle or falling into a pothole.

By virtue of this arrangement, both torsion rods provide the resilient loading for each of the road wheels.

To put this another way, the reaction member for the front road wheel 14 is actually the rear road wheel 16, since the suspension system for the front road wheel can be considered as being: the suspension lever 20, the torsion rod 22, the transmission lever 30, the linkage mechanism 34, the transmission lever 32a, the torsion rod 22a and the suspension lever 20a. In other words, the spring loading of the suspension system is divided between the two torsion rods 22 and 22a.

It will be appreciated, that it is possible to couple together in this way more than two road wheels or road wheel sets. For instance, in addition to the transmission lever 30, an additional transmission lever 30b indicated in chain-dotted lines in Fig. 2 could be secured on the torsion rod 22, with the lever 30b projecting downwardly from that torsion rod. A linkage mechanism 34b would then be attached at its rear end to the transmission lever 30b, and at its front end (not shown) to another transmission lever pointing upwardly from a preceding road wheel or road wheel system. Similarly, a transmission lever 30c could be secured to the torsion rod .22a, with the lever 30c pointing upwardly, and a linkage mechanism 34c connected at its front end to the lever 30c and at its rear end (not shown) to another transmission lever similar to the lever 30a, appertaining to a further road wheel or road wheel sets.

It will be appreciated that similar suspension arrangements could be applied to skids or tracks rather than road or rail wheels.

Claims (5)

1. A suspension system for a vehicle comprising two vehicle supports (e.g. road wheels, tracks or skids) spaced lengthwise of the vehicle, each vehicle support being carried on a suspension lever pivoted about an axis on the chassis and trailing from that axis and a resilient suspension device active between each vehicle support and the vehicle chassis, there being a transmission lever connected to each suspension device such that the relative motion between each support and the chassis permitted by flexing of the suspension system produces turning of the transmission lever, and a linkage connecting the two transmission levers in such a manner that the turning of one transmission lever in one direction due to a reduction in the height of the chassis relatively to the support appertaining to that transmission lever tends to turn the other transmission lever in the opposite direction so as to produce an increase in height of the chassis relatively to the support appertaining to that other transmission lever, the linkage comprising an extension and retraction mechanism which is remotely actuable.

2. A suspension system as claimed in claim 1, wherein the extension and retraction mechanism is such as to transmit force from one transmission lever to the other, and vice-versa, in only one configuration of the mechanism, the configuration it has when a vehicle to which it is fitted is being driven.

3. A suspension system as claimed in claim 1, wherein the extension and retraction mechanism is such as to transmit force from one transmission lever to the other, and vice-versa, in a plurality of configurations of the mechanism, so that a vehicle to which it is fitted may be driven with its chassis at a selectable height.

4. A suspension system as claimed in any preceding claim, wherein the extension and retraction mechanism comprises a hydraulic cylinder/piston.

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