WO2006032858A1

WO2006032858A1 - Control system for a motor car with roll stabilization

Info

Publication number: WO2006032858A1
Application number: PCT/GB2005/003602
Authority: WO
Inventors: John Bolland Reast
Original assignee: Detroit Steel Products Co Inc
Priority date: 2004-09-20
Filing date: 2005-09-19
Publication date: 2006-03-30
Also published as: GB0420887D0

Abstract

A vehicle suspension handling stabilisation system (201) comprising: a pair a of leaf springs (210) which are mounted or mountable on respective opposed sides of an associated vehicle (208) and which extend generally longitudinally thereof, which have respective ends pin (214) jointed or pin (214) jointable to the associated vehicle (208), and which are secured or securable substantially rigidly to opposed ends of an axle (206) extending transversely of the associated vehicle (208); and anti-roll and/or anti-pitch means (220) arranged to act between the associated vehicle (208) and at least one of the leaf springs (210) to convert, during use and roll and/or pitch of the associated vehicle (208), a pin (214) jointed end of the or each leaf spring (210) to an end thereof which is fixed with respect to the associated vehicle (208), thereby increasing the rate and hence the stiffness of the or each leaf spring (210).

Description

VECHICLE SUSPENSION HANDLING STABILISATION SYSTEM

DESCRIPTION

This invention relates to a vehicle suspension handling stabilisation system which employs leaf springs, as a primary or as a secondary energy absorbing means, in conjunction with other energy absorbing means, such as air springs, coil springs, polymer springs or hydro-pneumatic devices, which operate sufficiently softly to require additional means for controlling the dynamic forces experienced by the vehicle during roll and/or pitch.

When a vehicle travels over a road surface, the major mass of the vehicle is isolated by its suspension from vibrations caused by any irregularities in that surface. The resulting loads to which the vehicle suspension is subjected, are borne and absorbed by the springs of the suspension.

The softer the vehicle springs, and/or the lower their load/deflection rates are, the better the isolation of the vehicle from the road surface. The quality of this isolation affects the ride quality of the vehicle and any damage inflicted on the road surface thereby.

However, there is a limitation on the degree on which the springs or spring systems can be softened, because the suspensions also have to control the dynamic forces exerted on them by the mass of the vehicle during roll and/or pitch motions resulting from changes of direction and/or velocity of the vehicle. This ability to control these motions is usually termed "the vehicle handling ability".

One such direction change occurs when the vehicle changes its direction of travel when being driven around, for example, a curve or bend in the road.

During this manoeuvre, the vehicle suspension has to accommodate the centrifugal forces which cause the mass of the vehicle to transfer on to the wheels on the outside of the curve or bend from the wheels on the inside of the curve or bend.

This mass transfer onto the outside wheels of the vehicle is transmitted to the suspension. The softer the suspension, the more the springs will deflect, thus causing undesirable lean or roll of the vehicle.

Owing to the practicalities associated with the design and installation of suspensions, as well as other dynamic vehicle handling characteristics, there is a limit to the amount and rate of roll which is acceptable. Such a limitation creates a compromise between the ride and handling qualities of the vehicle.

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With such a compromise, the amount and rate of roll which is acceptable, limits the softness of the suspension and the associated quality of ride which is available. To improve or resolve this compromise, additional spring means or spring modifications which are available, resist vehicle roll without increasing the vertical spring stiffness, when both wheels deflect together. Such means or modifications are usually prior art as "anti-roll" or "anti-sway" mechanisms.

As the vehicle ride is also dependent upon the vibrations to which the suspension is subjected when only one wheel of the vehicle deflects, there is often a limit as to how much the ride and handling compromise can be extended by using those available mechanisms .

For many years, anti-roll mechanisms have been based upon a separate torsion bar or tube acting transversely of vehicle between the opposed wheels of the suspensions as discussed below with reference to Figure 6 of the accompanying drawings.

A recent anti-roll development for vehicles which are suspended by leaf springs, or use leaf springs within the suspensions, on each side of the vehicle, have been mechanisms which stiffen the springs internally, only when the springs deflect in opposite directions, as they do when the vehicle rolls, as discussed below with reference to Figures 1, 2, 3, 4, 5 and 7 and as taught by WO 90/11201, WO 00/76795 and PCT/GB2004/000148. Leaf springs to which a vehicle chassis is mounted, are beams which are effectively pin jointed at their ends or end regions and are designed and act as such. Usually, the leaf springs are secured rigidly to the axles of the wheels in the region of their centres and are mounted to the vehicle chassis via bushes and/or shackles at their respective opposed ends.

Thus, with the leaf spring being pin jointed at one or both ends thereof, it is effectively freely rotatable about a pivot, such as bush or shackle.

The loads applied to the leaf springs create bending moments therein, which, in turn, cause the springs to deflect and, thus, absorb energy.

During vehicle roll, the effective mass of the vehicle is transferred at the axle, from one spring to the other, thereby changing the bending moments therein. The stiffness of the leaf springs controls the change in deflection of each spring and these now different deflections on each spring, on each side of the vehicle, create, in turn, the amount of roll in the vehicle.

In these developments of techniques in anti-roll mechanisms, a torsionally rigid member, such as an anti-roll bar or tube, connected between the leaf springs at or adjacent one end thereof, allows the leaf springs to work normally when they deflect together in the same direction, as they normally function when creating the primary ride characteristics of the vehicle.

However, and as discussed above, when the vehicle rolls, the leaf springs deflect in different directions as the vehicle mass is transferred to the outside spring from the inside spring. During such deflections, the torsionally rigid member resists the angular differences between the two opposed leaf springs, thereby creating a deflection resisting moment in the springs, which then produces a lower change in bending moment in the springs. This, in effect, changes the pin joint-ended beam nature of the springs into fixed-ended, or encastre, beams.

This lower-than-previous change in bending moments creates smaller spring deflections and thus differences to the springs during roll only.

Therefore, by adding the torsionally stiff member to the ends of the springs, an effective anti-roll mechanism is created.

In practice, this additional bending moment is applied over the length of the brackets mounting the torsionally rigid member to the ends of the opposed leaf springs on respective sides of the vehicle.

Also, this anti-roll mechanism reduces the maximum, and any change, in the bending moment and, therefore, increases the service life of the leaf springs. In practice also, this anti-roll mechanism is more effective than suggested above.

If, therefore, the torsionally rigid member is added to just one end^' of the pair of opposed leaf springs, the resultant anti-roll mechanism stiffens just one end or cantilever of the leaf springs when the vehicle rolls. This creates asymmetrical cantilever deflecting leaf springs, which means that, during vehicle roll, the axle seat area of each leaf spring which is fastened centrally to the axle, attempts to deflect in different angular directions . Such deflection is resisted by the torsional rigidity of the axle which, again, tends to stiffen-up the leaf springs. This anti-roll stiffness associated with asymmetrical springs is well known prior art in spring and suspension design practice.

Another dynamic change that limits the degree to which the vehicle suspension can be softened, can occur when a vehicle is braked or accelerated.

Normally, during these dynamic velocity changes, the mass of the vehicle has to be acted upon by forces which have to originate from the road surface. The mass of the vehicle can be considered as concentrated at its centre of gravity and this will be at a considerable vertical distance from the road surface. Therefore, a moment or couple is generated which will be resisted, or reacted, by a change in the vertical force between the road contact points at the front and rear of the vehicle.

This change in vertical forces, reacts through the vehicle suspension into the vehicle mass and will normally cause the springs within the suspension to increase or decrease their deflections, creating a change in vehicle attitude from the front to the rear thereof.

As with vehicle roll, there is a practical limit as to how much movement, and attitude change, is acceptable.

For example, the suspension travel could be used up or the vehicle could adopt unacceptable forward lean, often called "dive", or rearward lean, often called "squat".

Therefore, these practical limitations restrict the level of spring softness which can be adopted within the vehicle suspension and, again, create a ride and handling compromise. This compromise can also change between when the vehicle is fully loaded and when the vehicle is completely unloaded, except for the driver. WO 92/22438 teaches means to improve this compromise by modifying the previously discussed anti-roll means to control also the other handling abilities .

In the above-described dynamic changes of velocity and direction of the vehicle, some of the suspension loadings can be absorbed by the suspension linkages, without travelling through the springs.

This effect can further improve the ride and handling compromises but the required suspension linkage geometries have other undesirable effects during normal suspension deflection when the vehicle is travelling over the road surface.

There is, therefore, another compromise between these suspension anti-roll, anti-dive and anti-squat geometries and the ride quality.

These compromise would be less onerous if the suspension springs could be softened without the previously discussed dynamic import force limitations.

The vast majority of the currently-available anti-roll stabilisation systems require torsion bar or tubes which run transversely of the vehicle. This applies to both the separate torsion bar or tube systems, as well as the "leaf spring rate stiffening in roll" systems discussed above in detail.

Most of these torsion bar or tubes are often obstructed by other vehicle components, such as fuel tanks, engines, transmissions, spare wheels, exhaust systems, brakes and loading space, access ramps and the like, as will be discussed hereinbelow in relation to the prior art anti-roll stabilisation systems. In US-A-5098121, there is disclosed a vehicle suspension with auxiliary leaf springs which are pivotally attached at their front and rear ends to the vehicle chassis and the vehicle axle, respectively. Pivotal movement of the front ends of these auxiliary leaf springs, due to drive and/or braking torque namely, pitch, of the vehicle, is inhibited or prevented by actuators which engage the springs to convert the front ends thereof from being pin jointed to being fixed, or encastre, to the vehicle chassis, hence stiffening the suspension as a whole. These auxiliary leaf springs are provided in addition to the main leaf springs which are connected rigidly, usually at their central regions, to the vehicle axle. The degree to which this known suspension contributes to the handling ability of the associated vehicle is limited in that, firstly, the actuators can act in only one direction of bending of the leaf springs and, secondly, are not effective on a substantially continuous basis for any bending of the leaf springs. Indeed, the actuators act only as adjustable stops. Also the provision of auxiliary leaf springs adds to the cost of the suspension, as well as further obstructing other components of the vehicle.

It is an object of the present invention to provide a vehicle suspension handling stabilisation system which overcomes, or at least substantially reduces, the disadvantages associated with the prior art systems discussed above. Accordingly, the invention resides in a vehicle suspension handling stabilisation system, comprising:

a pair of leaf springs which are mounted or mountable on respective opposed sides of an associated vehicle and which extend generally longitudinally thereof, which have respective ends pin jointed or pin jointable to the associated vehicle, and which are secured or securable substantially rigidly to opposed ends of an axle extending transversely of the associated vehicle; and

anti-roll and/or anti-pitch means arranged to act between the associated vehicle and at least one of the leaf springs to convert, during use and roll and/or pitch of the associated vehicle, a pin jointed end of the or each leaf spring to an end thereof which is fixed with respect to the associated vehicle, thereby increasing the rate and hence the stiffness of the or each leaf spring.

Throughout this specification, the term "pin jointed" when used in relation to an end of a leaf spring of a vehicle suspension, means that at least one end or end region of the leaf spring, and probably both ends thereof, is pivotally attached to the associated vehicle via its chassis or frame for free pivotal movement about an axis extending generally transversely of the vehicle chassis or frame and, hence, the longitudinal axis of the leaf spring. Such pivotal attachment is usually provided by means of a bush and/or shackle connected between at least one end of the leaf spring and the vehicle chassis or frame.

Throughout this specification, also, the term "fixed", when used in relation to an end of a leaf spring of a vehicle suspension, means that at least one end or an end region of the leaf spring is held substantially rigid with respect to the chassis or frame of the vehicle and, as such, is unable to undergo any pivotal movement with respect thereto.

The anti-roll and/or anti-pitch means may be arranged to act upon at least one of the leaf springs in either direction of bending thereof.

Also, said means may be attached pivotally to at least one of the leaf springs.

Preferably, the leaf springs whose ends are pin jointed or pin jointable to the associated vehicle, are main leaf springs which are preferably secured or securable to respective ends of the associated vehicle axle at their centre or central regions.

In a vehicle suspension handling stabilisation system in accordance with the invention and as defined above, the anti-roll and/or anti-pitch means which is arranged to act between the vehicle and at least one of the opposed leaf springs, to convert an end of at least one of the leaf springs from being pin jointed to substantially encastre, namely fixed, comprises a mechanical, hydraulic, pneumatic and/or electrical arrangement, or any combination thereof. One such anti-roll arrangement of such means may connect two opposed leaf springs, via the associated vehicle chassis or frame, to apply, during roll of the associated vehicle, a resisting moment to an end of at least one of the opposed leaf springs, without having to employ a torsionally stiff, transverse anti-roll torsion bar or tube.

In one anti-roll embodiment of the invention, to be discussed in more detail hereinbelow, a mechanical arrangement comprises a bell crank linkage between the corresponding ends of the opposed leaf springs, via the vehicle frame or chassis. Such a linkage preferably comprises a pair of bell cranks associated with respective opposed leaf spring ends which are pivotally or rotatably attached to the associated vehicle chassis or frame, which are connected together by a rigid arm and which are also connected, again by respective rigid arms, to corresponding ones of the leaf spring ends for acting thereupon during roll of the associated vehicle, to change the normal ride, pin jointed attachment of the leaf spring ends to the vehicle to a substantially encastre ends fixed with request to the vehicle.

The components, such as the bell cranks, of this mechanical linkage can be positioned with respect to the vehicle frame or chassis to avoid obstructions and, if necessary, the bell cranks can be off-set, for example, with their respective pivots being in the form of a single tube or bar with the cranks as separate brackets therealong.

Thus, the linkage is designed such that, when the leaf springs deflect in the same direction during normal ride conditions, the linkage arrangement merely moves in unison therewith. However, when the leaf springs deflect in opposite directions with respect to each other during, say, a roll condition, the linkage locks solid, thereby converting the leaf spring ends from being pin jointed ends to the encastre, fixed ends discussed above.

The anti-roll means may be arranged or may comprise means arranged to transfer a force associated with a deflection of one leaf spring in a first direction to the other leaf spring, the arrangement being such that the transferred force is applied generally linearly via the vehicle frame or chassis to an end of the other leaf spring to oppose a deflection of that other leaf spring in a second direction which is opposite to the first direction.

Preferably, any force transferring means or other anti-roll means is arranged to transfer a force associated with a deflection of the other leaf spring in the second direction to an end of the one leaf spring, such that the transferred force is applied, preferably generally linearly via the vehicle frame or chassis, to the one leaf spring end to oppose a deflection of that one leaf spring in the first direction. Preferably further, any force transferring means or other anti-roll means may apply the transferred force associated with a deflection of one leaf spring directly to an end of the other leaf spring.

These anti-roll arrangements of the present invention enable a force associated with a vertical deflection of a leaf spring mounted on one side of a vehicle to be used to oppose an oppositely directed deflection of a leaf spring mounted on the other side of the vehicle during a vehicle roll condition, whereby a pin jointed attachment of the associated leaf spring end is converted to being an encastre, fixed end attachment.

An arrangement of the suspension system for providing anti-roll and/or anti-pitch handling stabilisation, comprises means arranged to create a linear force between a pin jointed end of at least one of the leaf springs and the vehicle, such as the vehicle frame or chassis, by a locked or controlled force member acting between the vehicle and the at least one leaf spring adjacent but at a finite distance from the end thereof, to create a fixed end beam effect, thereby stiffening, and hence increasing the rate of, the at least one leaf spring. This arrangement stiffens the at least one leaf spring to control handling of the vehicle during anti-roll and/or anti-pitch conditions. By arranging for the force to oppose linearly deflection (s) of the leaf spring (s) of the suspension system, the effectiveness of the force in stiffening, namely increasing the rate of the leaf spring (s) is greatly enhanced, thereby increasing its ability, to counter the roll or pitch of the vehicle when travelling around bends or during other dynamic conditions . Consequently, the leaf springs can be made softer than would otherwise be the case, thereby providing an enhanced normal ride quality.

Preferably, any force transferring means or other anti-roll means is arranged such that there is generally no transfer of a force associated with a deflection of one leaf spring to the other leaf spring when the direction of deflection of the other leaf spring is the same as that of the one leaf spring. Preferably also, the converse situation is true.

Additionally or alternatively, an anti-pitch means can be arranged such that there is no transfer of force associated with deflections in the same direction of the leaf springs, although linear forces can act between the vehicle frame or chassis and both leaf springs.

Any force transferring means or other anti-roll means may be arranged to transfer the force associated with a deflection of one leaf spring directly to the other leaf spring. Any such anti-roll means may comprise a mechanical bell crank linkage assembly connecting the first and second leaf springs.

Alternatively, the anti-roll means may comprise at least one cable attached between the first and second leaf springs.

Further, another anti-roll means may comprise a hydraulic circuit comprising a first hydraulic cylinder mounted between the vehicle chassis and one of the leaf springs, whereby movement of that one leaf spring causes movement of a piston in the first cylinder, and a second hydraulic cylinder mounted between the vehicle chassis and the other leaf spring, whereby movement of the other leaf spring causes movement of a piston in the second cylinder, wherein each of the first and second hydraulic cylinders is in fluid communication with the other and wherein movement of the leaf springs in the same direction results in a free fluid communication between at least one of the cylinders and the other, with movement of the leaf springs in opposite directions resulting in a resistive fluid communication between at least one of the two cylinders and the other.

Such first and second cylinders may be arranged in the same orientation relative to their respective leaf springs, such that an upper fluid chamber of the first cylinder is in fluid communication with a lower chamber of the second cylinder and an upper chamber of the second cylinder is in fluid communication with a lower chamber of the first cylinder.

Alternatively, the first and second cylinders may be arranged in generally opposite orientations relative to their respective leaf springs, such that the upper chambers of the cylinders are in fluid communication and/or the lower chambers of said cylinders are in fluid communication.

Otherwise, the first and second cylinders may each be in fluid communication with a reservoir and/or an accumulator for both anti-roll and anti-pitch arrangements.

With a reservoir, an open fluid circuit can be provided and with an accumulator, a closed fluid circuit can exist.

A fluid circuit connecting each cylinder to the reservoir and/or accumulator may include a valve.

The valve may include a switch for electrically actuating the valve between open and closed positions.

The valve and switch assembly may include means for metering the fluid flow in the fluid circuit.

The suspension system may include means for monitoring and/or measuring leaf spring assembly deflections, vehicle dynamic motion and combinations thereof and means for controlling the degree of metering of fluid flow in the circuit in response to measured deflections. Such means may comprise an accelerometer and/or gyroscope.

It is to be appreciated that each of the pairs of leaf springs may be incorporated or otherwise associated with respective leaf spring assemblies on opposed sides of the suspension system, which assemblies may comprise other suspension components.

The invention also provides a vehicle incorporating a suspension system as defined above or any modifications thereof, such as those discussed above and hereinbelow.

The foregoing and further features of the present invention will be more readily understood from the following description of preferred embodiments provided by way of example and with reference to the accompanying drawings in which:

Figure 1 is a diagrammatic perspective view of a first form of prior art leaf spring-based vehicle suspension system;

Figure 2 is an exploded view of the components of the prior art leaf spring-based vehicle suspension system of Figure 1;

Figures 3A and 3B are respective plan and side elevational views of the forward section of the prior art leaf spring-based vehicle suspension system of Figures 1 and 2;

Figures 4A and 4B are respective side elevational and plan views of a second form of prior art leaf spring-based vehicle suspension system;

Figure 5 is a perspective view of a third form of prior art leaf spring-based vehicle suspension system;

Figure 6 is a perspective view of a fourth form of prior art leaf spring-based vehicle suspension system;

Figure 7 is a perspective view of a fifth form of prior art leaf spring-based vehicle suspension system;

Figures 8A, 8B, 8C are respective plan, side and end elevational views of a vehicle suspension system in accordance with a first embodiment of the invention;

Figure 9 is an end elevational view of a first form of a vehicle suspension system in accordance with a second embodiment of the invention;

Figures 1OA, 1OB, 1OC are respective plan, side and end elevational views of a second form of a vehicle suspension system in accordance with a third embodiment of the invention; Figures HA and HB are respective plan and side elevational views of a vehicle suspension system in accordance with a fourth embodiment of the invention;

Figures 12A and 12B are respective plan and side elevational views of a vehicle suspension system in accordance with a fifth embodiment of the invention;

Figure 13 is a side elevational view of an alternative cylinder arrangement for the vehicle suspension system in accordance with the fifth embodiment of the invention;

Figures 14A and 14B are respective plan and side elevational views of a vehicle suspension system in accordance with a sixth embodiment of the invention; and

Figure 15 is a perspective view of a vehicle suspension system in accordance with a seventh embodiment of the invention.

Referring firstly to Figures 1, 2, 3A, and 3B, here is illustrated a prior art leaf spring-based vehicle suspension system, indicated generally at 11, comprising first and second leaf spring assemblies 12 and 14 mounted generally centrally upon an axle 16 of an associated vehicle 18 on respective opposed sides of the longitudinal axis of a chassis 20 (Figures 3A and 3B) of the vehicle 18. The axle 16 is located transversely of the chassis 20. Each of the spring assemblies 12, 14 comprises at least one leaf spring 22 mounted pivotally by an eye bush 15 at one end thereof to the chassis 20 by a generally vertical bracket 24 whose upper end is secured rigidly to the chassis 20. The other end of each leaf spring 22 is pivotally connected to the chassis 20 through a shackle 26 which, in turn, is connected to a bracket 28 whose upper end is also secured rigidly to the chassis 20. Each leaf spring 22 is secured rigidly and generally centrally to the axle 16 by a U-shaped bracket and clamp arrangement 30.

Each leaf spring assembly 12, 14 may include a conventional shock absorber 32 (Figure 2) connected via a bracket 31 between a lower leaf spring 34 which underlies the leaf spring 22 and the chassis 20.

A generally square cross-sectioned torsion bar or tube 36 is connected rigidly between the leaf springs

22, 34 at or adjacent the bushes 15 at which the one end of each of the leaf springs 22 is attached pivotally to the vehicle chassis 20.

The torsion bar or tube 36 is rigidly secured to the leaf springs 22, 34 by clamps 38 which fasten to the undersides of the lower springs 34 and clamp over the upper sides of the upper leaf springs 22. Consequently, the clamps 38 move with the leaf springs 22, 34. The anti-roll torsion bar or tube 36, which extends transversely of the longitudinal axis of the associated vehicle 18, has the effect of adding bending stiffness to the leaf springs 22, 34 during vehicle roll when the springs 22, 34 of, say, the first leaf spring assembly 12 deflect in a different direction to the springs 22, 34 of the second leaf spring assembly 14. The torsion bar or tube 36 acts to resist rotationally the angular difference in deflection of the respective leaf springs 22, 34 of the first and second leaf spring assemblies 12, 14, thereby creating a deflection resistant moment in the springs 22, 34. This has the effect of stiffening the spring rate of the leaf springs 22, 34, namely, increasing the resistance to deflection of the springs 22, 34 under vehicle roll conditions by creating a generally fix-ended spring rather than a pin joint- ended spring.

Under normal straight-line motion of the vehicle 18, the leaf springs 22, 34 are subject to loads of a similar magnitude and acting in generally the same direction. Consequently, the respective pairs of leaf springs 22, 34 of the first and second leaf spring assemblies 12, 14 tend to deflect in the same direction and generally by the same amount. In this case, the torsion bar or tube 36 simply moves with the concomitant deflections of the respective pairs of leaf springs 22, 34 and generates no deflection resistant moment in response to such normal ride deflections. Therefore, the torsion bar or tube 36 increases the stiffness of the leaf springs 22, 34 only during a roll condition of the vehicle but not during a normal straight-line motion condition. Consequently, the presence of the torsion bar or tube 36 allows the leaf spring assemblies 12, 14 to be made softer than would be the case if the bar or tube 36 were absent thus providing an enhanced ride quality for the vehicle.

In Figures 4A and 4B, there is shown another prior art leaf spring-based vehicle suspension system.

In this case, the suspension system 41 comprises a pair of air bags 42 mounted upon an axle 44 of an associated vehicle on respective opposed sides of a longitudinal axis thereof. The axle 44 is located transversely of the vehicle chassis 46 by a pair of leaf springs 48 which are located on respective opposed sides of the longitudinal axis of the vehicle and of which each has one end mounted pivotally to the vehicle chassis 46 by means of, firstly, an eye bush 47 which, in turn, is mounted to a generally vertical bracket 50 whose upper region is secured firmly to the chassis 46.

Each of the air bags 42 is mounted between the vehicle chassis 46 and the other end of the respective leaf spring 48, with the axle 44 being clamped securely to an intermediate part of each leaf spring

48 by means of a two-part clamp assembly 52A and 52B.

A generally square cross-sectioned torsion bar or tube 54 is connected rigidly between the leaf springs 48 at or adjacent the bushes 47 (pivot points) at which the one end of each of the leaf springs 48 is attached pivotally to the vehicle chassis 46. The torsion bar or tube 54 is rigidly secured to the leaf springs 48 by brackets 56.

As in the first form of prior art vehicle suspension system illustrated in Figures 1, 2, 3A and 3B, the anti-roll torsion bar or tube 54, which extends transversely of the longitudinal axis of the associated vehicle, has the effect of adding bending stiffness to the leaf springs 48 during vehicle roll when those springs 48 deflect in different directions to each other. The torsion bar or tube 54 acts to rotationally resist the angular difference in deflection of the leaf springs 48, thereby creating a deflection resistant moment in the leaf springs 48. This has the effect of stiffening the spring rate of the springs 48 by increasing the resistance to deflection of the springs, under vehicle roll conditions but not under normal straight-line motion conditions by creating a generally fixed end spring rather than a pin jointed spring end.

Referring now to Figure 5, this shows a third form of prior art leaf spring-based vehicle suspension system which is similar in construction to that depicted by Figures 1, 2, 3A and 3B and, therefore, like numerals preceded by a "1" will be utilised in the following description with respect to Figure 5 to denote like parts to those of the suspension system described with respect to Figures 1, 2, 3A and 3B. The vehicle suspension system 111 of Figure 5 differs from that depicted in Figures 1, 2, 3A and 3B in that it has an anti-roll torsion bar or tube 136 mounted in what can be considered as being a rearward position of an associated vehicle relative to an axle 116 of the associated vehicle when compared to the aforementioned prior art suspension system arrangement. The torsion bar or tube 136 is rigidly secured between lower leaf springs 134 of first and second leaf spring assemblies. Only the first assembly 112 can be seen in Figure 5.

The torsion bar or tube 136, which extends transversely of the longitudinal axis of the associated vehicle, has the effect of adding bending stiffness to the leaf springs 122,134 during vehicle roll when the leaf springs 122, 134 of the first leaf spring assembly 112 deflect in a different direction to the leaf springs of the second leaf spring assembly. The torsion bar or tube 136 acts to oppose rotationally the angular difference in deflection of the first and second leaf spring assemblies, thereby generating a deflection resistant moment in the leaf springs 122, 134. This has the effect of stiffening the leaf springs 122, 134 by increasing the resistance to deflection of the springs, under vehicle roll conditions by creating a generally fixed end spring rather than a pin jointed spring end.

In Figure 6, there is shown yet another form of prior art leaf spring-based vehicle suspension system denoted generally as 61, comprising first and second leaf spring assemblies 62, 64 mounted transversely of an axle 66 of an associated vehicle on opposed sides of the longitudinal axis of the chassis or frame 68 of the associated vehicle. Each of the leaf spring assemblies 62, 64 has at least one leaf spring 70 mounted pivotally at one end thereof to the chassis 68 by means of a bracket 72 which is itself rigidly secured to the chassis 68. At its other end, the leaf spring 70 is pivotally mounted to the chassis 68 by a shackle 74 and a bracket 76 in a known manner.

Each leaf spring 70 is mounted generally centrally with respect to the axle 66 and is secured to both the chassis 68 and the axle 66 by means of a clamp assembly 78, an upper plate 78a of which rests on an upper side of the leaf springs 70, a middle plate 78b of which rests upon an upper surface of the axle 66 and a lower plate 78c of which is located on an underside of the axle 66. U-shaped bolts which locate around the upper and lower plates 78a, 78c of the assemblies 78 to affix the leaf spring assemblies 62, 64 to both the chassis 68 and the axle 66 are not shown in this Figure for reasons of clarity.

The suspension system 61 of Figure 6 includes a generally U-shaped, anti-roll stabilising rod 80 connected transversely between the axle 66 and the chassis 68. Arms 81 of the rod 80 which extend parallel with the longitudinal axis of the chassis 68, are pivotally connected by ends 83 thereof to the axle 66. A generally horizontal portion 80b of the stabilising rod 80 which extends between the arms 81 and is arranged transversely with the longitudinal axis of the chassis 68, is secured to the chassis 68 on each opposed side of the longitudinal axis thereof 68 by shackles 82.

In this arrangement, the vehicle chassis 68 tends to move with respect to the axle 66 by a greater amount on one side of the longitudinal axis of the vehicle than the other during vehicle roll, whereas, under normal straight-line vehicle motion, the chassis 68 moves by generally the same amount on both sides with respect to the axle 66.

In use, the stabilisation rod 80 rotationally opposes the greater displacement of the chassis 68 on one side of the vehicle than the other with respect to the axle 66 under a vehicle roll condition. However, the stabilising rod 80 does not, and is not intended, to generate a deflection resistant moment in the leaf springs 70 under a vehicle roll condition and has to employ a completely separate anti-roll system to resist vehicle roll conditions. This completely separate system is generally more expensive and more heavy if the system is not to have an inferior vehicle ride quality compared to the prior art suspension systems described with reference to Figures 1 to 5.

In Figure 7, there is shown yet another prior art leaf spring-based vehicle suspension system generally denoted as 91 and, comprising first and second leaf spring assemblies, with only the first leaf spring assembly 86 being seen in the Figure. The leaf spring assemblies 86 are mounted generally transversely of an axle 88 of an associated vehicle on respective opposed sides of the longitudinal axis of the frame or chassis 90 of the vehicle, with the axle 88 being located transversely of the chassis 90.

Each of the spring assemblies 86 comprises at least one leaf spring 92 pin-mounted pivotally at one end thereof to the chassis 90 by a bush generally vertical bracket 94 whose upper end is secured rigidly to the chassis 90. The other end of each leaf spring

92 is rigidly secured to a clamping bracket assembly 95 which, in turn, is fixedly mounted to an end 99 of a stabilising bar or tube or tube 96.

The stabilising bar or tube 96 is itself rotatably mounted to the chassis 90 through brackets 97 and each leaf spring 92 is located by bolts 98 and secured rigidly intermediate its ends to the axle 88 by clamps and U-bolts (not shown) in known manner.

The stabilising bar or tube 96 comprises a generally circular cross-section torsion bar or tube

96 which extends transversely of the longitudinal axis of the associated vehicle, acts in a similar manner to the torsion bars or tubes of the prior art suspension systems described above with respect to Figures 1 to 5, wherein it has the effect of adding bending stiffness to the leaf springs 92 during vehicle roll when the leaf springs 92 of the first leaf spring assembly 86 deflect in a different direction to the leaf springs of the second leaf spring assembly.

In this arrangement, under a normal straight-line motion of the vehicle, the leaf springs 92 of the leaf spring assemblies 86 mounted on opposed sides of the vehicle chassis 90 deflect in the same direction and by generally the same amount. Consequently, the torsion bar or tube 96 rotates within its brackets 97 to accommodate the deflection of the springs 92. However, under a vehicle roll condition where the leaf springs 92 on opposed sides of the vehicle chassis 90 deflect in opposite directions, the torsion bar or tube 96 rotationally opposes the oppositely directed deflections of the springs 92, thereby generating a deflection resisting moment in the springs 92 which increases the spring rate, and hence the stiffness of the springs 92 under the roll condition, by creating a generally fixed spring end rather than a pin jointed spring end. Additionally, by mounting the torsion bar or tube 96 in the manner described with respect to Figure 7, the torsion bar or tube 96 also varies the nominal ride rate of the leaf spring assemblies 86 over different leaf spring deflections as taught in our published International Patent Application No. WO95/026887.

The various prior art anti-roll arrangements of torsion bar or tube, as described with respect to Figures 1 to 5 and 7, go some way to mitigating the limitation of the prior art stabilising bar or tube arrangement of Figure 6 but such torsion bars or tubes must be fixed rigidly to the leaf spring assemblies of the suspension system in such a manner that they are mechanically rigidly connected to the leaf springs of the spring assemblies. As such, the torsion bars or tubes must be arranged to extend between the ^' spring assemblies transversely to a longitudinal axis of the vehicle frame or chassis. This requirement can create installation design problems in that the preferred installation position is often obstructed by other major vehicle parts such as the fuel tank, engine, exhaust system, brake system etc.

In addition, the effectiveness of the torsion bar or tube in measuring the spring rates of the leaf springs during a vehicle roll condition is limited by the fact that the torsion bar or tube generates a deflection resisting moment which is applied rotationally to the leaf spring assemblies.

Prior art anti-pitch and increasing stiffness suspension systems, such as that disclosed in WO 92/22438, suffer the same problems as those discussed above in relation to anti-roll systems, at least insofar as installation is concerned.

Referring now to Figures 8A, 8B and 8C, a first embodiment of a leaf spring-based vehicle suspension system in accordance with the invention is indicated generally at 201 and comprises first and second leaf spring assemblies 202, 204 mounted generally transversely of an axle 206 of an associated vehicle on respective opposed sides of the longitudinal axis of a frame or chassis 208 of the vehicle. The axle 206 is, in turn, located transversely of the chassis 208.

Each of the spring assemblies 202, 204 comprises upper and lower leaf springs 210, 212, the lower leaf spring 212 underlying the upper arm 210. The upper leaf spring 210 is mounted pivotally by a bush 214 at one end thereof to the chassis 208 by a bracket 216 whose upper end is secured rigidly to the chassis 208. The other end (not shown) of each upper leaf spring 210 is pivotally connected to the chassis 208 in a known manner, as particularly, although not exclusively, described with respect to the prior art vehicle suspension systems depicted by Figures 1, 2, 3A and 3B. Each pair of leaf springs 210, 212 is secured rigidly intermediate its ends to the axle 206 by a U-shaped bracket and clamp arrangement 218, again in a known manner.

Each of the leaf spring assemblies 202, 204 may include conventional shock absorbers (not shown) connected between the leaf spring assemblies 202, 204 and the chassis 208, once again in a known manner.

The first and second leaf spring assemblies 202, 204 are mechanically connected by a linkage and bell crank assembly 220 which comprises a first generally vertically oriented rigid rod 222 having its lower end connected pivotally to both leaf springs 210, 212 of the first leaf spring assembly 202 by a pivot pin 209 mounted to a clamp 224. A first bell crank 226 is connected pivotally at 236 to an upper end of the first rod 222. The assembly 220 also comprises a second generally vertically oriented rigid rod 228 again having its lower end connected pivotally to both leaf springs 210, 212 of the second leaf spring assembly 204 by another pivot pin 229 mounted to another clamp 230. A second bell crank 232 is connected pivotally at 236 to an upper end of the second rod 228.

Each of the first and second bell cranks 226, 232 are linked by a rigid connecting rod 234 which extends between the cranks 226, 232 transversely to the longitudinal axis of the chassis 208. The connecting rod 234 is linked pivotally at 238 by respective ends thereof to the bell cranks 226, 232.

The points of connection of the first and second rods 222, 228 and the connecting rod 234 to the respective bell cranks 226, 232 comprise first and second spaced apart pivot points, located respectively at 236 and 238, for each of the ball cranks 226, 232.

Each crank 226, 232 has a third pivot point, located at 240, which is spaced from each of its first and second pivot points 236, 238 and about which the crank 226 or 232 can pivot.

The first and second cranks 226, 232 are arranged inversely with respect to one another, that is to say that, the first, third pivot point 240 of the first bell crank 226 is located towards a lower portion of that crank with respect to the second pivot point 238 thereof, whereas the other, third pivot point 240 of the second bell crank 232 is located in an upper portion of that crank with respect to its second pivot point 238.

In operation, when the vehicle suspension system 200 is subjected to loads resulting from a normal straight-line motion of the vehicle where the leaf spring pairs 210, 212 of the first and second leaf spring assemblies 202, 204 deflect in the same direction and by generally the same amount, the linkage and bell crank assembly 220 moves up and down in unison with the concomitant deflections of the pairs of springs 210, 212. Consequently, the assembly has no effect on the spring rates of the leaf spring assemblies 202, 204 under normal straight-line motion of the vehicle. In the particular arrangement shown in Figures 8A, 8B and 8C, the bell cranks 226, 232 are shown as extending through apertures in the chassis 208 such that they can move in unison with the concomitant deflections of the pairs of leaf springs 210, 212 without being obstructed by the chassis 208.

In contrast, when the vehicle is maneuvering around a bend, for example, undergoing a roll condition where the leaf spring pairs 210, 212 of the leaf spring assemblies 202, 204 tend to deflect in opposite directions with respect to the vehicle chassis 208, the assembly 220 linearly opposes the oppositely-directed deflections of the leaf spring pairs 210, 212 of the leaf spring assemblies 202, 204. Consider the case, for example, where the roll condition of the vehicle is such that the weight of the vehicle is bearing more heavily on that side of the vehicle corresponding to the location of the second leaf spring assembly 204 of the suspension system 201. Under this roll condition, the leaf spring pair 210, 212 of the second leaf spring assembly 204 deflects generally upwardly, whereas the leaf spring pair 210, 212 of the first leaf spring assembly 202 deflects downwardly in an opposite direction to that of the second leaf spring assembly 204.

Associated with the upward deflection of the leaf springs 210, 212 of the second leaf spring assembly 204 is a deflection bending moment which generates a force generally vertically upwardly on the rod 228 of the bell crank assembly 220, with corresponding initial pivoting between the rod 228 and leaf springs 210,212 of the second assembly 204 relative to each other about the pivot pin 229. This force is transferred to the bell crank 232 tending to rotate it in an anti-clockwise direction about the pivot 240, as viewed in Figure 8C, causing the connecting rod 234 pivotally linked to the bell crank 232 at 238, to tend to move in a direction generally parallel with its longitudinal axis towards the bell crank 226. The force is thus transferred to the bell crank 226 tending to rotate it in a clockwise direction about pivot 240, as viewed in Figure 8C, which, in turn, tends to raise the rod 222 in a generally vertical direction opposite to the direction of deflection of the leaf springs 210, 212 of the second spring assembly 204, with corresponding initial pivoting between the rod 222 and leaf springs 210,212 of the first assembly 202 relative to each other about the pivot pin 209, thus linearly opposing such deflection.

In this way, a force associated with a deflection of the first spring assembly 202 in a first direction is transferred to the second spring assembly 204 and applied linearly to the second spring assembly 204 to oppose a deflection of the second spring assembly 204 in a second direction opposite to the first direction of deflection of the first spring assembly 202. Similarly, a reverse process occurs by which a force generated by a deflection moment resulting from deflection of the second spring assembly 204 in the second direction is mechanically transferred by the bell crank assembly 220 to the first spring assembly 202 and linearly applied thereto by the first rod 222 to oppose the deflection of the first spring assembly 202 in the first direction.

In this embodiment, it can be seen that the forces associated with oppositely directed deflections of the spring assemblies 202, 204 are directly mechanically transferred to the other spring assembly

204, 202 and that the transferred force is linearly applied directly to the leaf springs 210, 212 of the spring assemblies 202, 204 by the respective first and second rods 222, 228 of the bell crank assembly 220. Thus, the ends of the leaf springs 210, 212 which are pin jointed to the chassis 208 under normal vehicle ride conditions, are converted to encastre, fixed ends under roll conditions, thereby increasing the spring rate and hence stiffness of the springs 210, 212 and thus the associated first and second spring assemblies 202, 204.

Whilst in this embodiment of the invention the mechanical connection assembly has been disclosed as comprising a linkage and bell crank assembly, it will be apparent to a skilled artisan that any rigid rod and interlinking lever member arrangement suitable for transferring a force between the spring assemblies on opposed sides of the vehicle suspension system and of applying a transferred force linearly to the respective spring assembly could be employed.

It will also be appreciated that the orientation, dimensioning and positioning of the first and second rods 222, 228, the bell cranks 226, 232 and connecting rod 234 may be altered to assist a more convenient installation of such an arrangement with respect to the positions of other vehicle components.

Referring now to Figure 9, shown herein is a second embodiment of a leaf spring-based vehicle suspension system in accordance with the invention, as indicated generally at -301 and comprising first and second leaf spring assemblies 302, 304 again mounted generally transversely of an axle (not shown) of an associated vehicle on respective opposed sides of the longitudinal axis of a frame or chassis 308 of the vehicle.

The arrangement of the first and second leaf spring assemblies 302, 304 is the same as that for the first embodiment save for the nature of the mechanical connection means between the spring assemblies 302, 304, so the general arrangement of the spring assemblies 302, 304 with respect to the chassis or frame 308 will not be described in detail here. However, like numerals to those employed in the description of the first embodiment, but with the "2" replaced by a "3", will be utilised herein to denote like components.

The first and second leaf spring assemblies 302, 304 are mechanically connected by a pair of sheathed cables 305 of the type having an inner core 305a slidably accommodated within an outer sheath 305b. Each sheath 305b has means 307 at each of its ends for fixedly securing it to the vehicle chassis or frame 308. End portions of each core 305a extend beyond respective ends of each sheath 305b, such that the core 305a remains slidably accommodated therein.

A first end 306 of each of core 305a is affixed pivotally at 363 to a clamp 324 connected to the corresponding leaf springs 310, 312 of each of the first and second spring assemblies 302, 304 at or adjacent an end thereof, in a similar manner to the first embodiment of Figures 8A to 8C, whilst the fixture means 307 of each sheath 305b adjacent its first end is fixed to a bracket 309 which, in turn, is secured to the chassis 308. The other, second end 303 of each core 305a is mounted pivotally at 364 to a clamp 330 connected to the leaf springs 310, 312 of each of the first and second spring assemblies 302, 304 in a similar manner but with the exception that each bracket 309 extends downwardly below the leaf springs 310, 312, such that the first end 306 of each core 305a extends upwardly with respect to the sheath 305b.

In operation, when the associated vehicle is under a normal straight-line motion condition, the leaf spring pairs 310, 312 of the first and second spring assemblies 302, 304 deflect in the same direction. As the spring assemblies 302, 304 deflect in the same direction, the core 305a slides within the sheath 305b to accommodate respective concomitant movement of the spring pairs 310, 312 of the spring assemblies 302, 304. The core 305a is not under tension and has no effect on the spring rates of the spring assemblies 302, 304.

Where the vehicle is in a roll condition with the leaf spring pairs 310, 312 of the spring assemblies

302, 304 deflecting in opposite directions, a downward deflection of the first spring assembly 302 and a corresponding upward deflection of the second spring assembly 304 puts one of the cable cores 305a in tension, such that a force associated with that downward deflection of the first spring assembly 302 is transferred to the second spring assembly 304 W

- 39 -

through the corresponding core 305a and is linearly applied by it directly to the leaf spring pair of the second spring assembly 304. Similarly, a force resulting from a deflection bending moment generated 5 in the second leaf spring assembly 304 on an upward deflection thereof is transferred by the cable 305 to the leaf spring pair 310, 312 of the first leaf spring assembly 302 and is applied by it linearly directly to the corresponding leaf springs 310, 312, thus opposing 10 deflection of the first leaf spring assembly 302 in the downward direction.

In this manner, the normally pin jointed ends of the leaf springs 310, 312 are converted to encastre,

15 fix-ended leaf spring ends, thus increasing the rate of the leaf spring assemblies 302, 204 and, as a result, improving handling control of the vehicle.

Referring now to Figures 1OA, 1OB and 1OC, herein

20 is shown a third embodiment of a leaf spring-based vehicle suspension system in accordance with the invention, as indicated generally at 401, comprising first and second leaf spring assemblies 402, 404 mounted generally transversely of an axle 406 of an

25 associated vehicle on respective opposed sides of the longitudinal axis of a frame or chassis 408 of the vehicle.

The arrangement of the first and second leaf

30 spring assemblies 402, 404 is the same as that for the first embodiment save for the nature of the connection means between the spring assemblies 402, 404, so the general arrangement of the spring assemblies 402, 404 with respect to the chassis 408 will not be described in detail here. However, like numerals to those employed in the description of the first embodiment but with the "2" replaced by a ^λM" will be utilised herein to denote like components.

This third embodiment differs from the first and second embodiments in that the connection means, namely the force transferring means, connecting the leaf spring assemblies 402, 404 comprises a hydraulic connection circuit, denoted generally as 450, including a first cylinder 452 with a reciprocating piston 454 connected between the chassis 408 and the leaf springs 410, 412 of the first leaf spring assembly 402 such that the piston 454 moves in unison with the leaf springs 410, 412 as they flex under load and a second cylinder 456 with a reciprocating piston 458 connected in a likewise manner between the chassis 408 and the leaf spring pair 410, 412 of the second leaf spring assembly 404. The lower end of the piston arm 422,428 of each cylinder 452,456 is attached pivotally at 409,429 to its leaf spring assembly 402,404 via a clamp 424,430.

The cylinders 452, 456 are arranged such that a volume change on each side of their respective pistons 454, 458 is the same when the piston 454, 458 moves. The cylinders 452, 456 are hydraulically connected by hydraulic lines 460, 462 which are arranged transversely of the chassis 408, such that one of the lines 460 affords fluid communication between an upper chamber 452a of the first cylinder 452 and a lower chamber 456b of the second cylinder 456. The other hydraulic line 462 allows fluid to flow between an upper chamber 456a of the second cylinder 456 and a lower chamber 452b of the first cylinder 452.

When the leaf spring pairs 410, 412 of the leaf spring assemblies 402, 404 deflect in the same direction under a normal straight-line motion condition of the associated vehicle, hydraulic fluid flows freely between the respective connected chamber pairs 452a and 456b, 452b and 456a of the cylinders 452, 456 via the lines 460, 462.

However, when the spring assemblies 402, 404 deflect in opposite directions under a vehicle roll condition, fluid attempts to flow along the lines 460, 462 between the respective connected chamber pairs 452a and 456b, 452b and 456a of the cylinders counter each other and "lock" the hydraulic circuit 450.

The hydraulic circuit 450 thereby comprises the means by which a force associated with a deflection of one of the spring assemblies 402, 404 in one direction is transferred to oppose linearly an oppositely directed deflection of the other spring assembly.

The pistons 454, 458 of the cylinders 452, 456 are coupled directly to their respective leaf spring pairs 410, 412 by brackets 424, 432. Consequently, a force transferred through the hydraulic circuit 450 to a piston 454, 458 is then applied directly and linearly by that piston 454, 458 to its respective leaf spring pair 410, 412 to oppose an oppositely directed flexure of the leaf spring pair.

Thus, the normally pin jointed ends of the leaf springs 410, 412 are stiffened by being converted to the encastre, fixed spring ends, thereby enhancing vehicle handling control.

Each of the hydraulic lines 460, 462 may include a fluid reservoir 464, 466 to maintain appropriate hydraulic fluid levels within the circuit 450 and a predetermined level of pressure within the system, whilst also providing an open fluid circuit 450.

Alternatively, the reservoirs 464, 466 may be replaced by accumulators, thus providing a closed fluid circuit 450.

The reservoirs 464, 466 or accumulators may be isolatable from their respective lines 460, 462 by separate valve means (not shown) which may enable air to be bled from the system 450 and the topping up of hydraulic fluid when the system 450 is not in use.

It will be understood that, for some vehicles, a pneumatic circuit of a similar arrangement to the hydraulic circuit as described with respect to Figures 1OA, 1OB and 1OC may be used in place of the hydraulic circuit. A hydraulic circuit as the connection means, namely the force transferring means, between the spring assemblies 402, 404 provides a more flexible connection means from a design and installation perspective.

Shown in Figures HA and HB is a fourth embodiment of a leaf spring-based vehicle suspension system in accordance with the invention. This comprises a similar arrangement to that of the third embodiment, in that it also employs a ^■ hydraulic circuit 550 as force transfer connection means between the first and second spring assemblies 502, 504.

In this fourth embodiment, the hydraulic circuit 550 comprises a first cylinder 552 with a reciprocating piston 554 connected between a frame or chassis 508 of an associated vehicle and a first leaf spring assembly 502 and a second cylinder 556 with a reciprocating piston 558 connected between the chassis 508 and a second leaf spring assembly 504. Each cylinder 552,556 is connected pivotally at 509,529a to its leaf spring assembly 502,504 via a clamp 524,530 and its piston arm 522,528.

In one arrangement of the cylinders 552, 556 as depicted in Figures HA and HB, the cylinders 552, 556, are arranged in the same general orientation with respect to the chassis 508. However, the second cylinder 556 is connected between the chassis 508 and leaf springs 510, 512 of the second spring assembly 504 at a position beyond an end 520' of the lower leaf spring 520 of the second spring assembly 504 by means of the clamp 530.

The clamp 530 is secured to the leaf springs 510, 512 of the second leaf spring assembly 504 and has a laterally extending portion 530a to which the piston rod 528 of the piston 558 of the second cylinder 556 is pivotally attached, as described above.

The arrangement is such that movement of the leaf spring pairs 510, 512 of the first and second spring assemblies 502, 504 in the same direction with respect to the chassis 508 causes the pistons 554, 558 of the cylinders 552, 556 to move in opposite directions. Consequently, it is only necessary for the cylinders 552, 556 to be hydraulically connected by a single hydraulic line 560 between fluid chambers 552a, 556a thereof.

In an alternative arrangement of the cylinders 552, 556 of this fourth embodiment, the second cylinder 556' , as shown in dotted outline in Figures HA and HB, is arranged in a reverse orientation with respect to both the chassis 508 and the orientation of the first cylinder 552, but located at a position on the other side of the chassis 508 to that of the first cylinder 552 generally aligned therewith. Again, the arrangement is such that movement of the leaf spring pairs 510, 512 of the first and second spring assemblies 502, 504 in the same direction with respect to the chassis 508 causes the pistons 554, 558 of the cylinders 552, 556 to move in opposite directions and that it is only necessary for the cylinders 552, 556 to be hydraulically connected by a single hydraulic line 560 as shown in dotted outline, between the fluid chambers 552a, 556a.

Consequently, the cylinders 552, 556 utilised in this embodiment can be of a simpler, single fluid chamber form than those employed in the third embodiment of the invention. The cylinders 552, 556 may comprise conventional brake cylinders.

Under vehicle straight-line motion where the spring assemblies 502, 504 deflect in the same direction, fluid flows freely between the chambers 552a, 556a of the cylinders 552, 556. However, when the vehicle rolls and the spring assemblies 502, 504 deflect in opposite directions, forces exerted on the pistons 554, 558 resulting from deflection moments generated in the respective spring assemblies 502, 504 are such that the pistons 554, 558 are urged to move in the same directions relative to the chassis 508 thereby "locking" fluid flow in the hydraulic circuit 550 and creating a linear force between the vehicle chassis 508 and the springs 510, 512, consequently stiffening the spring rates of the leaf springs 510, 512 through the oppositely directed forces which are transferred through the hydraulic fluid and applied linearly to the respective other spring assemblies 504, 502.

Figures 12A, 12B and 13 show a fifth embodiment of a leaf spring-based vehicle suspension system in accordance with the invention. This employs a hydraulic circuit 650 as force transfer connection means between the vehicle chassis 608 and each of the first and second spring assemblies 602, 604.

In this embodiment, hydraulic circuits 654, 658 comprise respective first and second hydraulic cylinders 652, 656 each to act between the chassis 608 of the vehicle and respective spring assemblies 602, 604. As in the case of each of the third and fourth embodiments described above, the piston arm 622 (only one shown) of each cylinder 652,656 is connected pivotally at 609,629 to its spring assembly 602,604 via a clamp 624,630.

In this fifth embodiment, the hydraulic circuits 654,658 do not hydraulically connect the first and second hydraulic cylinders 652, 656 together. Instead, each of these cylinders 652, 656 is separately hydraulically connected to a common reservoir 670 to and from which the cylinders 652, 656 pump fluid in response to deflections of their respective spring assemblies 602, 604.

As in the case of the third embodiment of Figures 1OA to 10 C, the reservoir 670 may be replaced by an accumulator.

To create hydraulically a force associated with, say, a deflection of at least one of the leaf spring assemblies 602, 604, the corresponding hydraulic circuit 654, 658 has associated therewith control means 691 which in response to the detection of a dynamic movement of vehicle, for example, a roll, pitch or yaw motion of the vehicle, by means of at least one vehicle-installed sensor, as shown diagrammatically at 690, causes total closure or restriction of one or both valves 672, 674 and/or valves 683 in the cylinders 652, 656. This creates a linear resistive force between the vehicle chassis 608 and at least one of the leaf spring assemblies 602, 604.

The control means associated with each hydraulic circuit 654, 658 may comprise an on-board computer 691 connected at 692 to the associated vehicle-installed sensor 690 which may include known means, such as an accelerometer (s) or gyroscope (s), for measuring the magnitude and/or direction of dynamic movements of the vehicle. Additionally or alternatively, a sensor could be installed on the suspension itself.

In each of a first fluid line 660 and a second fluid line 662 hydraulically connecting the first and second cylinders 652, 656 separately to the reservoir or accumulator 670 is located a first and a second valve 672, 674 which may be arranged such that they can be closed progressively dependent upon sensed dynamic movements of the vehicle and/or vehicle suspension system. Similarly, the internal valves 683 of the cylinders 652, 656 may be arranged to be closed progressively. Progressive closure or opening of the respective valves 672, 674 and 683 enables the suspension system response to vehicle handling, such as roll, pitch and/or yaw to be adjusted by converting the ends of the leaf spring assemblies from being pin jointed towards fixed ends by means of the linear force between the chassis 608 and the leaf springs 610, 612.

Figure 13 shows an alternative cylinder 680 which could be used to replace each of the hydraulic circuits 654, 658, as well as the reservoir or accumulator 670. The cylinder 680 is self-contained having a first fluid chamber 680a communicating with a second fluid chamber 680b which includes a changeable volume gas chamber 681 in a similar manner to a conventional hydraulic accumulator or gas shock absorber, and which acts as a gas-charged hydraulic accumulator.

The cylinder 680 includes also a main valve 682, which acts in a similar manner to each of the valves 672 and 674 in Figures 12A and '12B, for communication between the first and second fluid chambers 680a and 680b, as well as a secondary valve 683¹ for communicating the first fluid chamber 680a to an upper chamber 680c. That valve 683¹ acts in a similar manner to each valve 683 in Figures 12A and 12B.

This system can employ conventional hydraulic fluids and valving or is an ideal application for the use of magneto-rheological or electro-rheological fluids and magnetic field, viscosity varying, resistive valving.

The accumulator provided by the chamber 680b and gas chamber 681, may be connected to a remote hydraulic pressure source, to further enhance handling of the vehicle. In this case, the accumulator, 680b, 681 could be external of the cylinder 680.

Referring now to Figures 14A and 14B, shown herein is a sixth embodiment of a leaf spring-based vehicle suspension system in accordance with the invention. The suspension system, indicated generally at 701, comprises first and second leaf spring assemblies 702, 704 mounted generally transversely of an axle 706 of an associated vehicle on respective opposed sides of the longitudinal axis of a frame or chassis 708 of the vehicle. The axle 706 is located transversely of the chassis 708.

Each spring assembly 702, 704 comprises upper and lower leaf springs 710, 712, the lower spring 712 underlying the upper spring 710. The upper leaf spring 710 is mounted pivotally by a bush 714 at one end thereof to the chassis 708 by a generally vertical bracket 716 whose upper end is secured rigidly to the chassis 708. The other end (not shown) of each upper leaf spring 710 is pivotally connected to the chassis 708 in known manner. Each pair of leaf springs 710, 712 is secured rigidly intermediate its ends to the axle 706 by a U-shaped bracket and clamp arrangement 718, again in a known manner. On each opposed side of the chassis 708, attached to respective spring assembly clamps 724 thereof, are respective first and second brake plates 790 of which each engages with a respective braking device 794, 796. The braking devices 794, 796 are fixed to the chassis 708 and, in use, apply a braking force to their respective brake plates 790 under the control of control system (not shown) of the associated vehicle, the nature of the control system having been discussed above in relation to Figures 12A, 12B and 13. Each brake plate 790 is attached pivotally at 709 to its corresponding spring assembly 702,704 via clamp 724.

During straight-line motion of the vehicle, the braking plates 790 are generally free to move relative to their respective braking devices 794, 796 in unison with deflections of their respective spring assemblies 702, 704. However, the vehicle control system can separately and progressively engage the braking devices 794, 796 in response to sensed dynamic movements of the vehicle.

Under vehicle handling conditions, such as roll or pitch, the vehicle control system is arranged to engage the braking device 794, 796 associated with at least one of the spring assemblies 702, 704 to apply to the braking plate 790 thereof a braking force based on sensed dynamic vehicle movements.

In this way, the control system applies a linear force between the chassis 708 and at least one of the spring assemblies 702, 704. The force is applied directly to at least one of leaf springs 710, 712 of the leaf spring assembly 702, 704 through^' the brake plate 790 and clamp arrangement 724 fixed to the leaf springs 710, 712.

The vehicle control system may comprise an electronic control system and may include sensing means throughout the vehicle, such as gyroscopes and accelerometers (not shown) , for monitoring dynamic vehicle movements, such a control system having been mentioned and discussed above in relation to the embodiment of Figures 12A, 12B and 13.

In Figure 15 is shown a seventh embodiment of a leaf spring-based vehicle suspension system in accordance with the invention. The suspension system, generally indicated as 801, comprises first and second leaf spring assemblies, with only the first assembly 886 being seen in the Figure, mounted generally transversely of an axle 888 of an associated vehicle on respective opposed sides of the longitudinal axis of a frame or chassis 890 of the vehicle.

The arrangement of the first and second leaf spring assemblies 896 is the same as that for the known vehicle suspension system, as described with respect to Figure 7, so that the general arrangement of the spring assemblies 886 with respect to the chassis 890 will not be described in detail here. However, like numerals to those employed in the description of said known suspension system, but preceded by an "8", will be utilised herein to denote like parts.

Each of the spring assemblies 886 comprises at least one leaf spring 892 mounted pivotally at one end thereof to the chassis 890 by a generally vertical bracket 894 whose upper end is secured rigidly to the chassis 890. The other end of each leaf spring 892 is rigidly secured to a respective clamping bracket assembly 895 which, in turn, is fixedly mounted to a stub axle 899 and is itself rotatably mounted to the chassis 890 through brackets 897. Each leaf spring 892 is located intermediate its ends to the axle 888 by bolts 898 and clamped to the axle in a known clamping manner.

The stabilising bar or tube of the prior art vehicle suspension system of Figure 7 is replaced by a hydraulic circuit comprising a first cylinder 900 mounted and arranged to act between the chassis 890 and a crank member 902 of the stub axle 899 on a first spring assembly 886 side of the suspension system and a second cylinder 904 connected in a likewise manner to a crank member 906 of the stub axle 899 on the second spring assembly side of the suspension system. Each crank member 902, 906 rotates with its respective stub axle 899. The cylinders 900, 904 are hydraulically connected by a hydraulic line 908 extending therebetween transversely of the chassis 890. The cylinders 900, 904 are arranged such that fluid flows freely between respective chambers (not shown) thereof when the spring assemblies deflect in the same direction but resists oppositely directed deflections thereof. The cylinders 900, 904 are preferably mounted to the chassis 890 on inner sides of frame members of the chassis but it will be understood that the cylinders 900, 904 could also be mounted at any suitable locations in the suspension system where such cylinders are able to be connected for movement with their respective spring assemblies 886.

In the force transference arrangement of the present invention depicted by Figure 15, a force associated with the deflection of one spring assembly 886 in a direction opposite to a deflection of the other spring assembly 886 is transferred to the other spring assembly by means of the hydraulic circuit. In contrast with other embodiments of the invention, the transferred force is linearly applied to the other spring assembly 886 but is indirectly applied to the leaf spring 892 of the spring assembly through the respective crank member 902, 906.

This seventh embodiment can be employed in respect of not only roll control but also pitch control, if the hydraulic system is suitably modified, for example, by replacing the cylinders 900, 904 with cylinders 652, 656 and 680 from the embodiments of Figures 12A, 12B and 13 and/or employing a control system thereof. In summary, the present invention concerns leaf spring-based vehicle suspension systems which include means for converting at least one pin jointed leaf spring end to an encastre, fixed end by creating a linear force to act between the vehicle chassis or frame and the leaf spring of at least one of the leaf spring assemblies. Thus, the spring rate and stiffness of the leaf springs of the suspension are increased to control handling conditions, such as roll and pitch, of the vehicle, without jeopardizing normal ride characteristics.

The linear force creation is arranged to apply a transferred force linearly to the leaf spring of at least one of the spring assemblies and the associated means may comprise a mechanical linkage acting between the vehicle chassis and the or each leaf spring or, alternatively, a hydraulic and/or electrical control circuit.

Claims

1. A vehicle suspension handling stabilisation system (201) comprising:

a pair of leaf springs (210) which are mounted or mountable on respective opposed sides of an associated vehicle (208) and which extend generally longitudinally thereof, which have respective ends pin (214) jointed or pin (214) jointable to the associated vehicle (208), and which are secured or securable substantially rigidly to opposed ends of an axle (206) extending transversely of the associated vehicle (208); and

anti-roll and/or anti-pitch means (220) arranged to act between the associated vehicle (208) and at least one of the leaf springs (210) to convert, during use and roll and/or pitch of the associated vehicle (208), a pin (214) jointed end of the or each leaf spring (210) to an end thereof which is fixed with respect to the associated vehicle (208) , thereby increasing the rate and hence the stiffness of the or each leaf spring (210) .

2. A system according (201) to claim 1, wherein said anti-roll and/or anti-pitch means (220) is arranged to act upon at least one of the leaf springs (210) in either direction of bending thereof.

3. A system (201) according to claim 1 or 2, wherein said anti-roll and/or anti-pitch means (220) is attached pivotally to at least one of the leaf springs (210).

4. A system (201) according to claim 1, 2 or 3, wherein the leaf springs (210) whose ends are pin

(214) jointed or pin jointable to the associated vehicle (208), are main leaf springs (210) .

5. A system (201) according to any preceding claim, wherein the leaf springs (210) are secured or securable to respective ends of the associated vehicle axle (206) at their centres or central regions.

6. A system (201) according to any preceding claim, wherein said anti-roll and/or anti-pitch means (220) which is arranged to act between the vehicle (208) and at least one of the opposed leaf springs (210) , to convert an end of at least one of the leaf springs (210) from being pin (214) jointed to substantially fixed, comprises a mechanical, hydraulic, pneumatic and/or electrical arrangement, or any combination thereof.

7. A system (201) according to any preceding claim, wherein the components of the said anti-roll and/or anti-pitch means (220) is positioned or positionable with respect to the vehicle frame or chassis (208) to avoid obstructions.

8. A system (201) according to any preceding claim, wherein said anti-roll and/or anti-pitch means (220) includes a mechanical arrangement comprising a bell crank linkage (220) between corresponding ends of the opposed leaf springs (210) , via the vehicle frame or chassis (208) .

9. A system (201) according to claim 8, wherein the bell crank linkage preferably comprises a pair of bell cranks (226, 232) associated with respective opposed leaf spring ends which are pivotally attached to the associated vehicle chassis or frame (208), which are connected together by a rigid arm (234) and which are also connected, again by respective rigid arms (232, 228), to corresponding ones of the leaf spring ends for acting thereupon during roll of the associated vehicle (208), to convert the normal ride, pin (214) jointed attachment of the leaf spring ends to the vehicle (208) to a substantially encastre ends fixed with respect to the vehicle (208) .

10. A system (201) according to claim 8 or 9, wherein the bell cranks (226, 232) are or can be off-set, with their respective pivots (240) being in the form of a single tube or bar with the cranks (226, 232) as separate brackets therealong.

11. A system (201) according to any preceding claim, wherein said anti-roll means (220) is arranged to transfer a force associated with a deflection of one leaf spring (210) in a first direction to the other leaf spring (210), the arrangement being such that the transferred force is applied generally linearly via the vehicle frame or chassis (208) to an end of the other leaf spring (210) to oppose a deflection of that other leaf spring (210) in a second direction which is opposite to the first direction.

12. A system (201) according to claim 11, wherein said anti-roll means (220) is arranged to transfer a force associated with a deflection of the other leaf spring (210) in the second direction to an end of the one leaf spring (210) , such that the transferred force is applied via the vehicle frame or chassis (208) to the one leaf spring (210) end to oppose a deflection of that one leaf spring in the first direction.

13. A system (201) according to claim 12, wherein the transferred force is arranged to be applied linearly to the one leaf spring end.

14. A system (201) according to any preceding claim, wherein said anti-roll and/or anti-pitch means (220) is arranged to transfer a force associated with a deflection of one leaf spring (210) directly to an end of the other leaf spring (210) .

15. A system (201) according to any preceding claim including means arranged to create a linear force between a pin (214) jointed end of at least one of the leaf springs (210) and the vehicle (208), such as the vehicle frame or chassis (208), by a locked or controlled force member acting between the vehicle

(208) and the at least one leaf spring (210) adjacent but at a finite distance from the end thereof, to create a fixed end beam effect, thereby stiffening, and hence increasing the rate of, the at least one leaf spring (210) .

16. A system (201) according to any preceding claim, wherein anti-roll means (220) is arranged such that there is generally no transfer of a force associated with a deflection of one leaf spring (210) to the other leaf spring (210) when the direction of deflection of the other leaf spring (210) is the same as that of the one leaf spring (201) .

17. A system (201) according to any preceding claim, wherein anti-pitch means (220) is arranged such that there is no transfer of force associated with deflections in the same direction of the leaf springs (210) .

18. A system (201) according to claim 17, wherein anti-pitch means (220) is arranged such that linear forces can act between the vehicle frame or chassis (208) and both leaf springs (210) .

19. A system (301) according to any preceding claim, wherein said anti-roll and/or anti-pitch means comprises at least one cable (305) attached between the first and second leaf springs (310) .

20. A system (401) according to any preceding claim, wherein said anti-roll and/or anti-pitch means comprises a hydraulic circuit (450) comprising a first hydraulic cylinder (452) mounted between the vehicle chassis (408) and one of the leaf springs (410), whereby movement of that one leaf spring (410) causes movement of a piston (454) in the first cylinder

(452) , and a second hydraulic cylinder (456) mounted between the vehicle chassis (408) and the other leaf spring (410), whereby movement of the other leaf spring (410) causes movement of a piston (458) in the second cylinder (456) , wherein each of the first and

^■ second hydraulic cylinders (452, 456) is in fluid communication with the other (456, 452) and wherein movement of the leaf springs (410) in the same direction results in a free fluid communication between at least one of the cylinders (452, 456) and the other (456, 452), with movement of the leaf springs (410) in opposite directions resulting in a resistive fluid communication between at least one of the two cylinders (452, 456) and the other (456, 452) .

21. A system (401) according to claim 20, wherein the first and second cylinders (452, 456) are arranged in the same orientation relative to their respective leaf springs (410) , such that an upper fluid chamber (452a) of the first cylinder (452) is in fluid communication with a lower chamber (456b) of the second cylinder (456) and an upper chamber (456a) of the second cylinder (456) is in fluid communication with a lower chamber (452b) of the first cylinder (452) .

22. A system (501) according to claim 20, wherein the first and second cylinders (552, 556) are arranged in generally opposite orientations relative to their respective leaf springs (510), such that the upper chambers (552a, 556a) of the cylinders (552, 556) are in fluid communication and/or the lower chambers of said cylinders (552, 556) are in fluid communication.

23. A system (401, 501) according to claim 20, 21 or

22, wherein the first and second cylinders (452, 456; 552, 556) are each in fluid communication with a reservoir and/or accumulator (464, 446) for both anti- roll and anti-pitch arrangements.

24. A system (601) according to any of claims 20 to

23, wherein a fluid circuit (654, 658) connecting each cylinder (652, 656) to a or the reservoir and/or accumulator (670), includes a valve (672, 674) .

25. A system (601) according to claim 24, wherein the valve (672, 674) includes a sensor switch (690) for electrically actuating the valve (672, 674) between open and closed positions thereof.

26. A system (601) according to claim 25, wherein the valve (672, 674) and sensor switch (690) include means, such as computer means (601), for metering the fluid flow in the fluid circuit (654, 658) .

27. A system (601) according to claim 24, 25 or 26, wherein the fluid is a magneto-rheological or electro- rheological fluid.

28. A system (601) according to any of claims 24 to 27, wherein the valve (672, 674) comprises magnetic field, viscosity varying, resistive valving.

29. A system (201;301;401;501;601;701;801) according to any preceding claim including means arranged to monitor and/or measure leaf spring deflections, vehicle dynamic motion and combinations thereof.

30. A system (201;301;401;501; 601;701;801) according to claim 29 further comprising means for controlling the degree of metering of fluid flow in the circuit in response to measured deflections and/or accelerations.

31. A system (201;301;401;501; 601;701; 801) according to claim 30, wherein said control means comprises an accelerometer and/or gyroscope.

32. A vehicle incorporating a suspension system (201;301;401;501;601;701;801) according to any preceding claim.