Patent Description:
The suspension may comprise leading and trailing arms or semi-leading and semi-trailing arms. In this specification the expression "leading arm" will be used to include a semi-leading arm and the expression "trailing arm" will be used to include semi-trailing arm.

Conventional vehicle suspensions, in which each wheel has a spring connecting it to the chassis, suffer from the problem that as one wheel is lifted then load is removed from or reduced at other wheels. In consequence traction for acceleration or braking is, sometimes dramatically, reduced. Zero warp stiffness suspensions do not suffer from this problem as the wheel loads are unaffected by the rise and fall of the wheels.

Common agricultural tractors are one type of zero warp stiffness suspension in which the front beam axle is pivoted, usually frictionlessly, about a central fulcrum. Warp is characterised by two diagonally opposite wheels rising while the remaining two wheels fall. In other words the contact patches between the wheels and the road do not remain all in the same plane. Zero warp stiffness is characterised by this motion happening without any resistance. Warp is important because any wheel going over any bump or hole generates a warp. It is the most common form of distortion from all the contact patches being in the same plane. Other types of wheel movements are: any two wheels together (sleeping policeman); all four wheels together (heave). These two leave the contact patches in the same plane and have to be contrived or occur naturally at random only infrequently. An undesirable feature of common agricultural tractor suspension is that nearly all the vehicle mass is attached to the rear wheels and therefore the motion of the whole vehicle responds to just two wheels thereby maximising the discomfort of the driver and disrupting the general dynamic performance of the vehicle. It will be appreciated that as the wheel reactions at the contact patches remain roughly constant then there is also minimal torsion applied to the body or chassis. It is desirable to resolve and exploit these issues whilst also saving vehicle weight and avoiding complexity.

The smoothness and comfort of a vehicle is most easily visualised by considering what causes discomfort. The bodies of vehicle occupants feel forces which are directly related to accelerations. Accelerations may be linear or angular and it is the angular accelerations that cause the greatest discomfort and are most difficult to mitigate. The present invention seeks to mitigate angular accelerations. Other desirable features include mitigating variations in wheel loads, torque stresses and deflections in the chassis/body, reducing the high load attachments points on the body/chassis to just the hinge connection of the suspension arms and reducing the number of suspension components. Addressing these matters not only reduces discomfort but also reduces the weight of the vehicle and thereby saves fuel and manufacturing cost.

Various known suspension systems include:.

This suspension system requires 'first and second balance members'. In various manifestations these are melded into one but in all cases accumulate all of the suspension forces and balance them against one or two springs which therefore have to resist the sum of all the suspension forces which would typically be two to four times the weight of the whole vehicle. Further this system has no inherent pitch stability and has to be augmented by a torsion bar for this purpose before it is an adequate suspension system.

This system is not a zero warp stiffness system but has a hydraulic balancing system. This needs other devices in order to have either roll stability or pitch stability depending on which orientation is being used. The other devices shown are torsion bars but hydraulic inputs could be used.

This system is based on connecting diagonally opposite suspension arms such that as one wheel rises the diagonally opposite wheel also rises and they are connected together without springing. This device as depicted in <FIG> is not capable of acting as a suspension system but only as an auxiliary system to some other system that suspends the vehicle. One problem with the basis of this invention is that linking two diagonally opposed wheels together without any resilience other than the small resilience in the length of the links, is that the unsprung mass of the two directly linked wheels necessarily acts as one. This means the effective unsprung mass adversely affecting the dynamic performance of each wheel is doubled. A further problem is that when one wheel rises over a bump as the result of the application of extra road reaction at that wheel then the diagonally opposite wheel also rises thereby relieving that wheel of road reaction. The increased road reaction on the first wheel times the distance to the vehicle centre of gravity gives a diagonal (combination of pitch and roll) angular acceleration and the reduction in the road reaction on the second wheel times it's distance to the vehicle centre of gravity also gives an angular acceleration in the same direction thus roughly doubling the angular acceleration and thereby maximising the discomfort.

The introduction of springs in <FIG> onwards enables the system to suspend the vehicle but does not address the fundamental flaws just described. The springs introduced necessarily have to act on two directly connected wheels simultaneously and thus collect both suspension forces. In the permutation in which there is only one spring, that spring collects two wheel suspension forces on each side which can be of the order of two to four times the weight of the vehicle. These are very large forces and demand a commensurate strong chassis adding weight to the vehicle. A worse effect of this, however, is that the effective spring rate for each wheel is that of the spring and this spring resists multiples of the weight of half the vehicle. This makes it impossible to achieve a desirable balance between heave rate and individual wheel rate because they are the same. The introduction of the balance beam in <FIG> mitigates this problem to some extent and enables zero warp stiffness but in the process the beam fulcrum accumulates all of the suspension forces equivalent to multiples of the whole weight of the vehicle.

This requires that in order for the transverse links to have a moment arm about the suspension arm hinge axis, the hinge axis has to have a significant angle relative to the <NUM> degree transverse direction. This compromises the available suspension geometry and limits the location of the links which need priority over other components of the vehicle.

Other known suspension systems are described in <CIT>, <CIT>, <CIT>, <CIT>, <CIT>, <CIT> and <CIT>.

The present invention seeks to provide a vehicle suspension which is an improvement over hitherto known vehicle suspensions of the type having zero or low warp stiffness.

In accordance with one aspect of the present invention there is provided a vehicle suspension as defined in claim <NUM>. In accordance with another aspect of the present invention there is provided a vehicle comprising a body or chassis having secured thereto a suspension of the invention.

The vehicle suspension may comprise two leading or semi-leading suspension arms for positioning respectively at opposite sides and at one end of a vehicle and two trailing or semi-trailing suspension arms for positioning respectively at opposite sides and at the other end of a vehicle. Alternatively the suspension arms may comprise sideways projecting arms or wishbones with or without auxiliary wishbones to control the camber change and/or roll centre.

The balancing hub may, by design, augment and/or provide springing for the system.

Pivotal movement of the suspension arm about the hinge axis may be arranged to apply a force which opposes approximately in magnitude and direction a force from another suspension arm on the same side and/or the same end.

An aspect of the invention is that the wheels are not connected directly in diagonally opposed pairs so that in a configuration in which there are springs between the suspension arms and the balancing hub pivot, this provides that the force paths, and hence the spring rates and masses mobilised, between any one suspension arm and each of the other three is different thereby ensuring that the dynamic movements of all wheels are out of phase and the potential for mutual mass damping is maximised. Resonance between symmetrical pairs is still possible and if necessary the weights of members and/or spring rates are adjusted anywhere in the system to negate any mass/spring symmetry.

Accordingly it is to be understood that the present invention facilitates provision of vehicle suspension arms without placing geometrical constraints on the selection of the orientation of the hinge axes of the arms. Selection of the orientation of hinge axes may be based purely on the desired geometry from the point of view of the dynamic motion of the vehicle and its components. It can include the common case with leading and trailing arm suspensions in which the hinge axes are at <NUM> degrees to the vertical longitudinal plane in the direction of vehicle travel and also the common case in which the hinge axes are parallel to said longitudinal plane.

A feature of the present invention is that by linking the suspension arms via springs and providing a slight difference in unsprung mass and spring rates (it will be difficult to avoid a difference in unsprung mass between front and rear in any case) then the wheels can act as mutual mass dampers for each other. This will mitigate and in some cases eliminate the need for conventional dampers. Thus there is an improved facility for a designer to exploit this advantage.

The arms may each be connected, at a point on the arm which has a lever arm about the hinge axis, to a balancing hub which is free to rotate about a pivot or pivots mounted on the chassis or body of the vehicle. The rotating pivot may be freely rotatable or may be varied from fully free to fully restricted in which case, with full restriction, the suspension will revert to the action and characteristics of a conventional suspension. The below described <FIG> are examples of means of achieving this. There may be provided means for controlling the rate or extent of rotation relative to the body or chassis of a vehicle by means such as friction devices or viscous dampers which may be of a type preset or variable in use of the suspension.

The connection between at least one arm and the balancing hub is via a link which may be attached by means such as rod end joints, ball joints or universal joints or by being integral with the balancing hub. The link may itself be a spring.

A link may be continuous with the balancing hub either by means of a rigid connection or by being a continuous part of the balancing hub. The hub may be a single component or an assembly of components and, within itself, may be rigid, semi-rigid or a mechanism of rigid and semi-rigid components. The hub may be a solid with a pivoted attachment to the chassis or body of a vehicle about which it rotates, the solid being rigid or resilient and having means for attachment to each of the suspension arms via a link. The hub may be a single high modulus of elasticity resilient member or an assembly of high modulus of elasticity springs and reacting components. The hub may be an assembly of high and low modulus of elasticity components arranged so as to give a desired resilience.

Instead of a single pivoted attachment of the hub to the chassis or body there may be multiple point attachments or multiple single point attachments such that the rotation is restricted but enabled by virtue of the resilience of components within the rotating member assembly.

The input forces to the balancing hub will normally be arranged so that vertical movement of one arm (due to movement of a ground engaging member such as a wheel or caterpillar type track) tends to induce opposite vertical movement in its two adjacent arms. It will be appreciated that the arms acting about their hinges and via the lever arm to their connections may pull or may push on the balancing hub. It will be appreciated that the whole system could be turned through <NUM> degrees so that the arms project sideways and forces from the arms are roughly <NUM> degrees to the longitudinal plane. In this configuration camber change and high roll centre potentially become issues and it would be advantageous to add another wishbone approximately parallel to the component that has herein been referred to as a suspension arm (but may also be in the form of a wishbone) to control the camber angle change and roll centre in a conventional manner. Bump stops may be provided by limiting the angle through which the balancing hub can rotate. The balancing hub may comprise one or more suitably proportioned and profiled solids which are connected by means of resilient materials or components such that the rotation is achieved by means of deformation of these resilient materials or components.

A or each link may extend from the balancing hub to a position of a respective suspension arm which is above or which is below a plane containing the hinge axis of that suspension arm.

The balancing hub may have the form of a solid body pivotally fixed at its centre point to a convenient part of the chassis and having its attachment points for the leading and trailing arms evenly distributed around the solid body. Alternatively attachment points may be unevenly distributed in order to achieve a particular desired effect.

The connection of the arms to the balancing hub may be via links with universal joints, ball joints or rod ends at each connection. The links may contain springs. It will normally be convenient for the links or at least one of their connections to include means for adjustment. The balancing hub may be a solid body of rigid or resilient materials and may contain sprung or resilient elements such that the input from one arm has not a direct affect on the other arms but instead a resilient affect. A link may be continuous with the balancing hub either by means of a rigid connection or by being a continuous part of the balancing hub, such as an integral part of the balancing hub. The solid body may be resilient material such as rubber or another type of elastomer. The solid body may be a resilient material stiffened or reinforced with stiffer materials and have built-in attachment points for attachment to links or arms.

The balancing hub may take the form of an assembly of resilient components such as metal springs. The attachment(s) for securing the balancing hub to a vehicle body or chassis may be free running or may offer resistance to turning and may have more than one fixing so that the rotation is achieved by the resilience of the material or springs. Thus the suspension designer is afforded the facility of maximum choice between conventional suspension action when the hub is rigid and rigidly fixed to the vehicle body or chassis and this type of zero warp stiffness suspension when the hub is fully free to rotate frictionlessly, and any combination between these two options including a facility for variation of resistance to rotation during use of the suspension. The links and balancing hub may be melded and take the form of one continuum of resilient material or springs rigidly attached to and emanating from a fulcrum block. The links may be in the same plane as the hub or may approach the hub at an angle. The arms may be configured to transmit tension or compression forces to the balancing hub.

It will be appreciated that a well balanced design in accordance with this invention will result in the forces acting on the balancing hub pivot or fulcrum tending towards zero when the vehicle is at rest. When the vehicle is not at rest the main function of the balancing hub is to maintain pitch stability and to collect and distribute transient dynamic forces from the suspension arms.

It will be further appreciated that a suspension system in accordance with this invention typically will always be part of a whole vehicle comprising other components competing for space and components necessary to achieve the necessary geometric characteristics of a modern suspension system. It is therefore likely that the links will need to be diverted to deal with space constraints and suspension geometry demands will mean that the suspension arms will have auxiliary components to achieve desired geometry. The links may therefore contain diversion means for diversion of the forces through angles, that is, along a non linear path. The suspension arms may have associated therewith auxiliary components to achieve desirable geometry for the movement of the wheels of a vehicle.

Embodiments of the invention and variations thereof will now be described, by way of example only, by reference to the accompanying drawings in which:.

As shown in <FIG> wheels I, <NUM>, <NUM> and <NUM> are mounted at the outer ends of semi-leading arms <NUM> and <NUM> and semi-trailing arms <NUM> and <NUM>. These are mounted so as to rotate about axes <NUM>, <NUM>, I I and <NUM>, which axes are orientated for optimum dynamic performance separate from the concerns of this invention. A balancing hub, in this case in the form of a plate or pair of plates <NUM> is pivotally mounted to the chassis by boss <NUM>.

Sprung links <NUM>, <NUM>, <NUM> and <NUM> connect between the balancing hub <NUM> and the upper part of upward extensions of the arms typically shown as <NUM> and <NUM> by means of rod ends typically shown as <NUM> and <NUM>. It will be appreciated that rod ends <NUM> and <NUM> could be replaced by ball joints or universal joints. Upward forces from the ground acting on the wheels I, <NUM>, <NUM> and <NUM> turn the arms <NUM>, <NUM>, <NUM> and <NUM> and via the upward extensions typically shown as <NUM> and <NUM> compress the sprung links <NUM>, <NUM>, <NUM> and <NUM> and transfer forces to the hub <NUM> where they mutually oppose and balance each other. As shown here this is a compression version of the invention wherein the arms push on the balancing hub. In <FIG> an alternative, which is not claimed, is shown using solid rods <NUM> and <NUM>.

In <FIG>, showing a tension version, which is not claimed, the arms <NUM>, <NUM>, <NUM> and <NUM> via sprung links <NUM>, <NUM>, <NUM> and <NUM> and connections, typically shown as <NUM> pull on the balancing hub which comprises a leaf spring <NUM> mounted on fulcrum block <NUM> which pivots about vertical axis <NUM>. Wheels I, <NUM>, <NUM> and <NUM> are mounted on arms <NUM>, <NUM>, <NUM> and <NUM>. These arms are different from those shown in <FIG> in that they are longer and they have upward extensions typically shown as <NUM> and <NUM> which extensions have bosses for enabling the arms to rotate about axes <NUM>, <NUM>, <NUM> and <NUM> and, as low as possible, brackets typically shown as <NUM> for attachment of the sprung links. It will be appreciated that, as in <FIG>, the sprung links <NUM>, <NUM>, <NUM> and <NUM> may be replaced by solid rods, for example rods of fixed length.

<FIG> show in plan the same balancing hub assembly in three different states of balance caused by the force inputs from links <NUM>, <NUM>, <NUM> and <NUM>. In <FIG> the hub is in a neutral state which would approximate to the normal, at rest condition where all of the inputs from the links are substantially balanced, resulting in minimal residual force on the centre pivots or swivel blocks <NUM>, <NUM>. The links are attached to hub links <NUM> and <NUM> to which are also attached the leaf springs <NUM> and <NUM> located by swivel blocks <NUM> and <NUM> to which they are attached by means of fixings typically indicated by <NUM>. Between the leaf springs <NUM> and <NUM> are adhered elastomeric shear blocks <NUM> and <NUM>. In this state the only significantly stressed elements are the links and hub links. In this state the only significantly stressed elements are the links, including the hub links.

<FIG> depicts the state when the force inputs from links <NUM> and <NUM> are greater than the force inputs from links <NUM> and <NUM> such that both the leaf springs <NUM> and <NUM> bend and the elastomeric blocks <NUM> and <NUM> deflect in a shear mode as indicated. A force balance is maintained by forces transmitted via fulcrum blocks <NUM> and <NUM> from the pivotal fixings on the body or chassis. In this state all components are significantly stressed and it is likely to be a transient state such as when passing over a sleeping policeman but a mild form of this type of deflection could also arise from an imbalance of fore and aft load distribution.

<FIG> depicts a state in which force inputs from links <NUM> and <NUM> are greater than those from links <NUM> and <NUM> the balance being restored by means of deflection of the elastomeric blocks <NUM> and <NUM> which induce tension and compression forces and some bending into the leaf springs <NUM> and <NUM> which are resisted and balanced by forces from the fulcrum blocks <NUM> and <NUM> which, it should be noted, will be substantially at right angles to the forces described for the state shown in <FIG>. This will almost always be a transient state such as when one wheel passes over a bump or hollow but could also arise if the vehicle were parked with one wheel on a bump or hollow. It will be appreciated that these states are illustrations of arbitrary and usually transient states and real conditions will be random combinations of all three. It will also be appreciated that the elastomeric blocks may be omitted, in which case the balancing hub is split into two spaced apart but linked balancing hubs that serve the same purpose as a single hub.

<FIG> shows in plan a balancing hub comprising an elastomeric block <NUM> with inserts <NUM>, <NUM>, <NUM> and <NUM> to which links from the arms are attached, the forces from the arms represented by <NUM>, <NUM>, <NUM> and <NUM>. A further insert <NUM> in the middle is the means for attachment to a pivot fixing on the body or chassis. The elastomeric block may be enhanced by a perimeter band <NUM> preferably made from a flexible high modulus of elasticity material. The action of the block closely follows the description for <FIG>, but the whole block can turn and there is no way for it to get turning resistance from the fulcrum insert <NUM> so cannot form a parallelogram as depicted in 5B.

<FIG> shows in plan a balancing hub different from <FIG> only in that the fulcrum insert <NUM> has multiple fixings to the body or chassis and so is not turnable. Turning of the hub is by shear in the elastomer around the fulcrum insert and thereby the designer has another parameter to manipulate to get a desired effect.

<FIG> shows a balancing hub comprising high modulus of elasticity spring material used as perimeter springs <NUM>, <NUM>, <NUM> and <NUM> which may be a continuous perimeter band into which are fixed attachment points <NUM>, <NUM>, <NUM> and <NUM> for links from the arms delivering forces represented by <NUM>, <NUM>, <NUM> and <NUM>. To this arrangement of springs a central fulcrum block <NUM> is fixed using fixings typically represented by <NUM>. Springs <NUM> and <NUM> resist the forces <NUM> and <NUM> and forces <NUM> and <NUM> respectively and any out of balance between combined forces <NUM> and <NUM> and combined forces <NUM> and <NUM> is resisted by springs <NUM> and <NUM> respectively. It will be appreciated that a resilient fulcrum insert such as that of item <NUM> in <FIG> could be substituted for the type depicted as item <NUM>.

<FIG> shows an example of a suspension system incorporating a balancing hub in which the hub and the links are melded together into one unit. Wheels I, <NUM>, <NUM> and <NUM> are mounted on arms <NUM>, <NUM>, <NUM> and <NUM> free to rotate around axes <NUM>, <NUM>, <NUM> and <NUM>. At a substantially vertical lever arm, either above or below the axes, are attached by suitable ball joint or universal joint not shown, but indicated typically by <NUM>, springs <NUM> and <NUM> which are rigidly fixed to fulcrum block <NUM> free to rotate about vertical axis <NUM> located on the body or chassis of the vehicle. It will be apparent that out of balance forces applied at the ends of one spring will be resisted by rotation of the fulcrum block which in turn will rotate the other spring and thereby transmit movement and/or forces to the opposing arms and hence the wheels. It will be apparent that it does not matter whether the springs are arranged to be in tension or compression. It will further be apparent that it would not matter if each spring were in two parts, each part individually fixed rigidly to the fulcrum block. It will further be apparent that the springs and fulcrum block could be one continuum of resilient material. Bump stops <NUM>, <NUM>, <NUM> and <NUM> attached to the vehicle body or chassis may be provided to limit the degree of rotation of the balancing hub and such devices may be applied to any of the examples shown.

<FIG> show a vehicle suspension, which is not claimed, which is devoid of the aforedescribed links. Instead a balancing hub <NUM>, rotatable about a vertical axis <NUM>, is connected at each of four positions <NUM> to an extension <NUM> of a respective suspension arm124, at a position of the extension which is spaced from the suspension arm hinge axis <NUM>. The connection of each extension to the hub may be by a conventional elastomeric bush of the type comprising inner and outer metal tubes having a sleeve of elastomeric material bonded therebetween. The outer tube is bonded to elastomeric material of the hub and the extension of the suspension arm extends into and is secured within the inner tube. However other forms of connection, such as ball joints may be employed.

A suspension of the type shown in <FIG> is particularly suitable for small vehicles such as wheel chairs.

In <FIG> wheels <NUM>,<NUM>,<NUM> and <NUM> are mounted on arms <NUM>,<NUM>,<NUM> and <NUM> as in <FIG>. Links <NUM>. <NUM> and <NUM> deliver forces from the suspension arms to elbow brackets <NUM>,<NUM>,<NUM> and <NUM> pivoted on the chassis about pivots at their elbows which divert the forces via continuation links <NUM>,<NUM>, <NUM> and <NUM> to central hub <NUM> mounted on the chassis (not shown) so as to rotate about central fulcrum <NUM>. In this case the hub is depicted as being of an elastomeric type. In this configuration the links are shown above suspension arm hinge axes <NUM>,<NUM>,<NUM> and <NUM> and so the forces will be in compression. It will be appreciated that if the links were positioned below the suspension arm hinges then the system would become a tension system, which is not claimed.

In <FIG> wheels <NUM>,<NUM>,<NUM> and <NUM> are mounted on suspension arms141, <NUM>, <NUM> and <NUM>, hinged approximately longitudinally. Below these hinges and attached to the arms are links in the form of cables <NUM>, <NUM>, <NUM> and <NUM> which pass over pulleys <NUM>,<NUM>, <NUM> and <NUM> mounted pivotally on the chassis, not shown. The cables <NUM> and <NUM> are fixed to leaf spring <NUM> and cables <NUM> and <NUM> are fixed to leaf spring <NUM>. The leaf springs <NUM> and <NUM> form the hub by being mounted on the fulcrum block <NUM> enabling the hub to rotate about the fulcrum <NUM>.

Claim 1:
A vehicle suspension for supporting the body or chassis of a vehicle, said suspension comprising two suspension arms (<NUM>,<NUM>) for positioning respectively at opposite sides and at one end of a vehicle and two suspension arms (<NUM>,<NUM>) for positioning respectively at opposite sides and at the other end of a vehicle, each said arm being mounted for pivotal movement about a respective hinge axis (<NUM>-<NUM>), wherein the suspension further comprises a balancing hub (<NUM>) for attachment to the vehicle body or chassis in a configuration in which at least one part of the balancing hub is free to rotate relative to the vehicle body or chassis about at least one pivotal position the rotational axis (<NUM>) of which is vertical, each suspension arm being connected to the balancing hub at a position of the suspension arm spaced from a respective hinge axis (<NUM>-<NUM>) of the suspension arm whereby pivotal movement of the suspension arm applies a force to the balancing hub and wherein, in use, said force opposes the force from another suspension arm at at least one of the same side and the same end of the vehicle suspension , wherein, in use, vertical movement of one suspension arm induces an opposite vertical movement of another suspension arm which is at the same side of the vehicle and another suspension arm which is at the same end of the vehicle, wherein each said suspension arm is connected to the balancing hub by a link (<NUM>-<NUM>) which extends from the balancing hub to a position of the suspension arm spaced from the hinge axis of the suspension arm, and characterized in that said link is a compressible link comprising a resilient member.