BACKGROUND

Field of the Invention

The invention is in the field of suspension systems for motor vehicles. In particular it relates to enhancing passenger comfort while maintaining vehicle performance.

Description of Related Art

Suspension is the system of tires, springs, shock absorbers and linkages that connect a vehicle body to its wheels. A suspension system must support both road handling and ride quality, which are at odds with each other. The tuning of the suspension system involves finding a compromise between keeping the road wheel in contact with the road surface as much as possible and protecting the vehicle itself and cargo from damage.

A suspension system has a spring rate, defined as the ratio of change in force that a spring exerts to its change in displacement. A high spring rate results in stiff suspension, which is required for carrying heavy loads so that the suspension does not bottom out. A high spring rate is also found in the suspension systems of high performance vehicles because it allows flatter handling, better braking and lower clearance of the vehicle body from the road. A low spring rate results in soft suspension and is generally found in passenger carrying vehicles or off-road vehicles. A low spring rate requires a higher ground clearance to allow for the extra travel.

Travel is the measure of distance from the bottom to the top of the suspension stroke. Damping is the control of motion or oscillation, as seen with the use of hydraulic gates and valves in a vehicle’s shock absorber. Like spring rate, the optimal damping for comfort may be less than for control. Conventional suspension systems can be mechanical, e.g. a coil spring and damper arrangement, which is a passive system.

A typical vehicle has a chassis, as shown in Figure 1a, where two girders run in parallel from front to back of the vehicle. The vehicle body, engine and other components are fixed to the chassis. The chassis has mounting points to which the suspension assemblies are fixed. A conventional suspension assembly is shown in Figure 1b comprising a double-wishbone arrangement where there is an upper wishbone and a lower wishbone. Each wishbone is an open triangle in shape, with the ends of the triangle having bushings for rotatably mounting the wishbone to the chassis. At the apex of each wishbone is a fixing point for mounting a vertical wheel carrier. The wheel carrier spans the two wishbones and is able to rotate about a vertical axis. The wheel carrier has a horizontal wheel spindle at its mid-point to which a wheel and bearings can be mounted. This arrangement allows vertical movement of the wheel in relation to the vehicle chassis. The movement of the wheel in relation to the chassis is controlled by a spring and damper assembly, fixed at its lower end to the lower wishbone and at the upper end to the chassis. In use, when a sudden change in the surface of the road is encountered by the vehicle, the wheel moves upward relative to the vehicle chassis as the coil spring absorbs the shock. The damper prevents the system from bouncing too vigorously as equilibrium is restored to the system.

The advantage of this type of mechanical system is that it is robust and unlikely to fail, but the ride quality is not adjustable. The ride quality is adjustable in pneumatic suspension systems, which generally comprise a flexible sealed container, such as a bellow, supplied with pressurised air. Pneumatic systems are termed “active” because adjusting the quantity of air in the bellow varies the spring constant. An example of a pneumatic system may be found in Japanese patent JP2003260916A, which describes a pneumatic bellow connected in series with a coil spring; in this arrangement the spring constant of the system depends on the amount of air in the container; it is possible to adjust ride quality and ride height by adding or removing air from the bellow. However, this is a manually operated system and there is no automatic way to adjust the handling of the vehicle, for example to counteract vehicle roll while cornering. Also, such an arrangement significantly increases the overall height of the suspension strut compared to a conventional top mount solution (which is an important factor for sports cars where a low bonnet line is desired). A further element of a suspension system may include anti-roll equipment. Anti-roll equipment may be passive, as found in a conventional anti-roll bar set-up. Anti-roll bar links opposite wheels through short lever arms linked by a torsion spring, forcing the opposite wheel’s suspension to lower or rise to a similar level as the other wheel in a turn. During cornering, a vehicle tends to drop closer onto the outer wheels; the anti-roll bar tends to force the inner wheels closer to the body. As a result, the vehicle tends to hug the road closer in a fast turn. Because an anti-roll bar connects wheels on opposite sides of the vehicle, the bar transmits the force of a bump on one wheel to another, which can be jarring. Alternative active anti-roll set-ups exist which use a system of hydraulic rams and sensors to raise or lower the spring to counter the roll. These systems do not transmit bumps from one side to another but they also do not contribute to the spring properties of the suspension system because hydraulic fluid is incompressible. The present invention therefore seeks to overcome the above problems.

SUMMARY OF THE INVENTION

In an embodiment, a suspension system for a vehicle is provided, comprising i) a first suspension assembly having a resilient member and ii) a second suspension assembly having a resilient member; wherein the spring constants of the resilient members of the first and second suspension assemblies are adjustable by means of a control system, wherein the control system comprises at least one user selectable control for adjusting the ride height of the vehicle by simultaneously increasing or simultaneously decreasing the spring constant of the resilient members, and wherein the control system further includes a mechanism for detecting the roll state of the vehicle and increasing the spring constant of one of the resilient members while reducing the spring constant of the other resilient member to reduce the roll of the vehicle.

Spring constant is a measure of the ratio of the force applied to a spring to the displacement produced by that force. It represents the stiffness of a spring. The spring constant varies with many factors including the displacement itself so most springs have a non-linear spring constant representing a non-linear response to an applied force.

In this way, by decreasing the spring constant of both of the resilient members simultaneously the suspension system has a greater wheel travel and ground clearance. Increasing the spring constant of both of the resilient members simultaneously provides the suspension system with less wheel travel and less comfort. Vehicle roll can be controlled by increasing the spring constant of one resilient member while decreasing that of the other. The resilient members of the first and second suspension assemblies may be pneumatic members and furthermore the control system comprises an air compressor connected to each pneumatic member via at least one valve to regulate the amount of air supplied to it. The resilient member of the first suspension assembly may be connected in series to a second resilient member and wherein the resilient member of the second suspension assembly may be connected in series to a second resilient member. The second resilient members may be a coil spring and damper assembly.

The pneumatic elements can also be disengaged, thereby engaging only the second resilient members to provide a low ride, sports feel with hard suspension. In this way, the invention addresses the contradicting requirements of being able to provide either enhanced comfort or sports performance in the same suspension system.

In an embodiment, two suspension systems are combined in one, by providing the advantages of both the mechanical (passive) suspension and pneumatic (active) suspension. The pneumatic part can be used to i) increase ground clearance for better off-road capabilities in a 'high' setting, i.e. pneumatic members being provided with more air from the air compressor to increase the height of the air column and reduce the spring constant, or ii) a 'normal height' setting, i.e. pneumatic members being provided with less air from the air compressor and therefore a higher spring constant and regular ride quality. The resilient members can be also fully deflated, i.e. turned off, in Ό height' setting with only the mechanical second resilient members in operation. This provides lower ground clearance and stiffer suspension for sports/track mode. When active, the pneumatic members can provide vehicle levelling during cornering, i.e. a pneumatic Anti Roll Bar, while the mechanical part still provides the necessary springing.

The valve may be electronically controlled or pneumatically controlled. The pneumatic member is a pneumatic ram comprising a piston and rod assembly and having two ports; a first port providing a first inlet to a first side of the piston and a second port providing a second inlet to a second side of the piston. The air supplied to the first port of each pneumatic ram is regulated by a first valve and the air supplied to the second port of each pneumatic ram is regulated by a second valve. Each first valve is arranged to control the air supplied by the compressor for adjusting the ride height of the vehicle.

Each second valve associated with the pneumatic rams is arranged to seal each of the second ports of the pneumatic rams, for controlling the roil of the vehicle. For example, as the vehicle turns to the left, the lower part of the cylinder on the right compresses and the upper part extends. The second valve on the right cylinder seals to create a vacuum in the upper part of the cylinder which counters the roll of the vehicle.

In pneumatic-ram-only embodiment: The second valves can be partially closed to manage the compromise between limiting the roll and maintaining comfort while cornering.

The first valves associated with the pneumatic rams may be arranged to connect the first port of each pneumatic ram to a gas accumulator for controlling the roll of the vehicle. For example, if the left hand turn is extreme, the compression of the lower right cylinder can be countered by introducing more pressurised air from an accumulator.

Further valves may be arranged to connect the second port of each pneumatic ram to a gas accumulator for controlling the roll of the vehicle. For example, if the left hand turn is extreme, the compression of the upper part of the left hand cylinder can be countered by introducing more pressurised air from an accumulator.

The valves may be controlled by an ECU connected to at least one of a ride height sensor, steering wheel angle sensor, yaw rate sensor and a roll angle sensor for controlling the roll of the vehicle. One or more of the outputs from these sensors indicate when a vehicle is cornering and the severity of the corner and allow the ECU to control the valves appropriately. The second pneumatic members may be pneumatic bellows. A centrally pivoted beam may connect the resilient members and second resilient members. This arrangement reduces the overall height of the suspension system compared to a system where the two components are stacked on top of each other.

The second resilient members may be a coil spring and damper assembly.

Each suspension assembly may be a coil spring and damper assembly connected in series with a two port piston-and-rod pneumatic ram.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1a is an isometric view of a typical vehicle chassis, Figure 1b is an isometric view of a conventional suspension assembly.

Figure 2 is an isometric view of a suspension assembly with a twin port pneumatic cylinder of the type used in an embodiment of the invention.

Figure 3 is an isometric view of a coil and damper assembly of the type used in the suspension assembly of Figure 2. Figure 4 is an isometric view of a twin port pneumatic cylinder of a suspension assembly in an embodiment of the invention.

Figures 5a to 5c are side views of a suspension assembly of the type used in an embodiment of the invention.

Figure 6 is a schematic diagram of a pneumatic circuit to pneumatically control pneumatic cylinders of the type shown in Figure 4, where the control valves are set in the straight road position.

Figure 7 is a schematic diagram of a pneumatic circuit to electronically control pneumatic cylinders of the type shown in Figure 4, where the control valves are set in the straight road position. Figure 8a is an isometric view of a suspension assembly with pneumatic bellows of the type used in an embodiment of the invention.

Figure 8b is a schematic diagram of a pneumatic circuit to electronically control pneumatic bellows, where the control valves are set in the levelling after roll position. Figure 9 is an isometric view of a suspension assembly with only a twin port pneumatic cylinder of the type used in an embodiment of the invention.

Figure 10a is an isometric view of a suspension assembly with a twin port pneumatic cylinder of the type used in a further embodiment of the invention. Figure 10b is a side view of the suspension assembly of Figure 10a.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The invention replaces the conventional top-mount suspension shown in Figure 1b with an interrelated system of suspension assemblies at each wheel of the vehicle, controlled by a control system.

In an embodiment, each wheel is connected to the vehicle chassis with a suspension assembly as shown in Figure 2. An upper wishbone member 201 is formed of an open triangular member having chassis mounting points 201a, 201b at the open base ends of the triangle for fixing the member 201 to the vehicle chassis. The mounting points 201a, 201b include an axle that allows articulated movement of the member in relation to the chassis. The apex of the triangular member includes a socket 201c connected to a corresponding ball feature at the top of a vertical steering knuckle 203 that carries a horizontal wheel spindle 204. The wheel spindle 204 carries wheel bearings and a wheel (not shown). The steering knuckle 203 has a ball joint 206 on one side for connecting to a steering system if the suspension assembly is installed in the front of the vehicle or for connecting to a fixed rod if the assembly is installed in the rear of the vehicle. However, if rear wheel steering is present then the steering knuckle is also connected to a steering system. The lower end of the steering knuckle 203 has a ball feature connected to a socket joint 202c at the apex of a triangular shaped lower wishbone member 202. The lower wishbone member 202 has chassis mounting points 202a at the open base ends of the triangle for fixing the member 202 to the vehicle chassis. The mounting points 202a, 202b include an axle that allows articulated movement of the member in relation to the chassis. The upper wishbone member 201, the lower wishbone member 202 and the steering knuckle allow the wheel to move vertically in relation to the vehicle chassis. The lower wishbone member 202 has a cross member 207 that supports two spring mounting points 207a, 207b to which the lower end of a coil spring and damper assembly 205 is mounted. The joint between the spring mounting points and the coil spring and damper assembly is articulated so that rotational movement between the lower wishbone member and the coil spring and damper assembly is possible. Alternative suspension arrangements may have only a lower wishbone arrangement (for instance but not limited to a form of triangular shaped wishbone, L-shaped brace or comprising two separate links) in particular a single McPherson strut supporting the steering knuckle.

The coil spring and damper assembly 205 is shown in more detail in Figure 3. The lower end of the assembly includes a lower fixing point 301 which supports a chamber 302 filled with a suitable fluid such as oil. The upper end of the chamber 302 has an opening with an oil seal through which a rod 303 passes. An end of the rod 303 terminates inside the chamber 302 with a piston 304. The piston 304 has apertures for allowing a limited amount of oil to pass. The end of the rod terminates in an upper fixing point 305. The sealed oil-filled chamber and piston assembly together provide a damper assembly. The upper fixing point 305 and the cylinder also include spring brackets for holding a coil spring 308. The coil spring 308 is co-axial with the damper assembly. Other coil-spring and damper configurations are possible.

The upper fixing point 305 of the rod 303 of the coil spring and damper assembly 205 is fixed to a rocker arm 208 at an articulated joint 209 which allows the coil spring and damper assembly 205 to move in relation to the rocker arm 208. The rocker arm 208 has a central pivot 210 which includes a bushing and an axle. The axle is fixed to the vehicle chassis. The other end of the rocker arm 208 has an articulated mounting point 211 to which is connected a double acting pneumatic cylinder 212. The lower end of the cylinder 212 is connected to the vehicle chassis with an articulated joint 213.

The double acting pneumatic cylinder 212 is shown in more detail in Figure 4. The unit 212 comprises a rod 401 with an upper end terminating in a fixing point 402 and a lower end terminating in a piston 403. The piston 403 is free to move within a sealed chamber that has an upper end 408 and a lower end 406. The lower end 406 of the chamber 404 is sealed and terminates with a feature 407 that forms a part of the articulated joint 213 to the chassis. The interior of the lower end 406 of the chamber is fitted with a rubber bump stop 412, to prevent jarring if the piston bottoms out. The upper end of the chamber 404 has a sealing arrangement for allowing the rod 401 to move in and out without leaking air. The piston within the chamber defines two regions: i) an upper region 408 between the piston and the upper end of the chamber and ii) a lower region 406 between the piston and the lower end of the chamber. The volume of air within each region is variable in dependence on the position of the piston. Air can be introduced or released from each region of the chamber via two ports. The upper region 408 of the chamber 404 has a first port 410 while the lower region 409 has a second port 411. The complete suspension assembly shown in Figure 2 is operable between a variety of positions, as shown in Figures 5a to 5c. Figure 5a shows the system where the lower region 409 of the cylinder 212 is filled with air to its maximum capacity, while the upper region 408 is at minimum capacity and the rod 401 is at maximum extension. This forces the coil and damper assembly 205 downwards which has the effect of increasing the clearance between the wheel and the vehicle body. The large air volume under the piston 403 in the cylinder 212 is a relatively soft setting for the suspension system because the spring constant is inversely proportional to air column height, as given in this equation: where: k - air spring stiffness (N/m) S - piston surface (m ² ) n - constant dependent on thermodynamic process (-) x ₀ - initial air column height (m) x - current piston travel (from equilibrium) (m)

Po - initial (static) pressure (Pa)

A constant ride height can be maintained independently of the load that is being carried, by increasing the air pressure in the lower region of the cylinder to match the load. The ride height of the vehicle can be lowered, as shown in Figure 5b, by reducing the amount of air in the lower region 409 of the cylinder 212 to a “normal” ride height setting. While the pressure remains equal in the cylinder, the spring constant, or stiffness, of the cylinder is increased because of the reduced air column height and the suspension is therefore harder and less comfortable for the occupants of the vehicle.

A “sports mode” can be selected by allowing the piston to expel all of the air from the lower region of the cylinder and rest against the bump stop 412 so that the cylinder is inactive, as shown in Figure 5c. In this mode, the coil and damper 205 and wishbone assembly moves upwards providing the minimum clearance between the wheel and the vehicle body, and it is only the coil and damper that is providing suspension, so it will feel hard to the occupants. Under driving conditions along a straight line, the upper region port 410 is vented to atmospheric pressure so that it is only the lower region providing the suspension effect. However, when the vehicle is cornering, the weight will increase on one side of the vehicle and decrease on the other, resulting in the vehicle tending to roll to one side. For example a left hand turn will result in increased weight on the right hand side of the vehicle and decreased weight on the left hand side. Air will tend to be forced out of the lower region of the cylinder of the suspension assembly on the right side of the vehicle and drawn into the lower region of the cylinder on the left side. The space above the piston in the right hand cylinder will increase, and if this region is sealed it will create a vacuum that will resist the force to the right and prevent the right side of the vehicle from rolling to the right.

This is a pneumatic anti-roll bar. The pneumatic control circuitry required to switch the upper region of the cylinders appropriately is described in more detail below.

In an embodiment, a suspension assembly of the type shown in Figure 2 is used to mount each of the four wheels to the chassis of the vehicle: i) front left; ii) front right; iii) rear left and iv) rear right. The ports of the cylinders associated with the front left and front right suspension assemblies are connected together as shown in Figure 6. The rear left and rear right suspension assemblies must also be connected together like this so that roll can be corrected. The front left pneumatic cylinder 601 L has a lower port 601 L1 and an upper port 601 L2. The front right pneumatic cylinder 601 R has a lower port 601 R1 and an upper port 601 R2.

A compressor 600 provides pressurised air to the system by an air line 610 keeping left 611 and right 612 side accumulators topped up with a suitable pressure.

The air line 610 has branches 613, 614 to supply air to the lower port 601 L1 of the left pneumatic cylinder 601 L and to the lower port 601 R1 of the right pneumatic cylinder. The branches 613, 614 may have a height level control system (not shown) which comprises valves that are operable to introduce or release air into or from the lower regions of the pneumatic cylinders to increase or decrease the ride height. Branches 613, 614 feed into lower port feed lines 615, 616. These lines branch in two directions; one to their respective ports and the other way to lower port pneumatic control valves 617, 618. These control valves are operable between a sealed position at rest and an open position when pressure is applied to an operating port. When pressure is no longer applied to the operating port a spring urges the valve back to the sealed position. During normal riding conditions, i.e. along a straight road, the lower ports 601 L1 and 601 R1 are effectively sealed by these lower port pneumatic control valves 617, 618 so that the volume of air, and thus spring stiffness is constant.

The upper ports 601 L2 and 601 R2 of the cylinders are connected to upper port pneumatic control valves 619, 620 by lines 623, 624. These control valves are operable between an open position at rest and a sealed position when pressure is applied to an operating port. In the open position, the upper ports 601 L2 and 601 R2 are vented to air at openings 621, 622. When pressure is no longer applied to the operating port a spring urges the valve back to the open position. During normal riding conditions, i.e. along a straight road, the upper ports 601 L2 and 601 R2 are effectively open to air and have no effect on the ride quality. The operating port of each upper port pneumatic control valve 619, 620 is connected by upper port control valve control lines 627, 628 and via non-return valves to the lower ports 601 L1, 601 R1 The non- return valves are shown as a standard symbol in the Figures of a circle nested within an arrow head, the arrow head indicating the direction of non-return, i.e. the direction in which the flow is blocked. When a certain sustained pressure is reached in one of the lower ports, corresponding to the vehicle rolling to one side, the upper port pneumatic control valves 619, 620 operate to seal the upper ports.

The lines 623, 624 have restrictions 625, 626 in them which damp the system.

The upper port control valve control lines 627, 628 are cross-connected to the operating ports of secondary upper port control valves 629, 630. The secondary upper port control valves 629, 630 are operable between a first sealed position at rest and when pressure is applied to the operating port, switch to an open position to connect the upper ports 601 L2, 601 R2 to corresponding accumulators 611, 612. Thus, when a certain sustained pressure is reached in one of the lower ports, corresponding to the vehicle rolling to one side, the secondary upper port pneumatic control valves 629, 630 of the opposing side operates to introduce pressure into the upper ports to counter the roll.

The coil spring in series with the pneumatic cylinder arrangement allows a constant eigen-frequency of the suspension regardless of its load or travel; the natural frequency of the system stays closer to 1Hz (or whatever the target is, usually not more than 3Hz) even during normal wheel-over-bump operation, no tampering with valves and pressure is required.

Adding air by means of the compressor to the lower regions of each cylinder will raise the ride height of the vehicle. Letting air out of the lower regions reduces the ride height. A hydraulic damper may be added with an option of using a Pneumatic Damper Control system where the damping level is adjustable. Hydraulic damper in the embodiment is optional as most damping can be managed pneumatically via upper region openings/orifices. The hydraulic damper becomes compulsory when the embodiment consists of pneumatic bellows in place of the double acting cylinders.

In an alternative embodiment, the control valves are operated electronically, as shown in Figure 7. A compressor 700 provides pressurised air to the system via air lines 702, 703 which feed the left and right side of the system. The each line feeds an accumulator 712, 713 via electronically operated accumulator control valves 716, 717. Air lines 702, 703 branch through an electronically operated height control valve 714, 715 which is operable between three states; i) open straight through; ii) closed; iii) vent other side to air. The output of the height control valves is connected in parallel to the lower ports 701 L1 and 701 R1 of the pneumatic cylinders 701 L, 701 R and to electronically operated lower port pressure balance control valves 708, 709. The lower port pressure balance control valves 708, 709 can be switched between a resting state, where the valve is closed and therefore the lower ports 701 L1 and 701 R1 of the pneumatic cylinders 701 L, 701 R are sealed, and an open state where the lower ports are connected to their respective accumulators 712, 713 by accumulator lines 718, 719.

The upper ports 701 L2 and 701 R2 of the pneumatic cylinders 701 L, 701 R are connected via restrictions 705, 707 to electronically controlled upper port control valves 704, 706 which are operable between an open resting state where the upper ports are connected to air vents 720 and a closed state where the upper ports are sealed. The upper ports 701 L2 and 701 R2 of the pneumatic cylinders 701 L, 701 R are also connected to electronically controlled upper port secondary pressure control valves 710, 711 which are operable between a closed resting state and an open state where the upper ports are connected to their respective accumulators 712, 713. During normal operation, i.e. when the vehicle is travelling along a straight road, the lower ports are sealed and the lower region of the pneumatic cylinders, in parallel with the coil spring and damper assembly, is providing a pre-set spring stiffness, while the upper ports are vented to air and therefore not contributing to the suspension stiffness. The vehicle entering a curve is detected by inputs from the roll angle sensor, yaw rate sensor and steering wheel angle sensor input, a number of operation may occur; i) the upper port control valve 704 for that cylinder is actuated so that the upper port 701 L2 is sealed and as the piston moves downwards, a vacuum is created, which counters the roll of the vehicle during right hand turn; ii) the upper port control valve 706 seals the upper port 701 R2 so the pressure in the upper chamber starts to increase counteracting the roll.

During severe roll conditions the following may occur: iii) the lower port pressure balance control valve 708 is operated so that the pressure in the accumulator 712 counteracts the pressure induced in the lower region by the vehicle roll, thus countering the roll of the vehicle; iv) the upper port secondary pressure control valve 711 of the opposing cylinder 701 R is operated so that the pressure in the accumulator 713 counteracts the pressure induced in the upper region of the right cylinder 701 R by the rising piston, thus countering the roll of the vehicle.

Each valve is operated by a solenoid controlled by an Electronic Control Unit (ECU). The ECU 720 is connected to a series of sensors, which can include a ride height sensor 721, steering wheel angle sensor 722, yaw rate sensor 723 or roll angle sensor 724. The ECU 720 is capable of outputting control signals to the valves 704, 706 to open or close them depending on the required action. For example, if the ride height sensor indicates that a load has been added and the ride height reduced, the ECU instructs the valves 714, 715 to open until the required ride height is restored. A user interface 726 may be provided in connection with the ECU where a user can select a desired ride height, for example for travelling over rough terrain; the ECU would adjust the valves 714, 715 accordingly.

If the roll angle sensor 724 and steering wheel angle sensor 722 indicate that the vehicle is rolling to one side, for example to the right side, the ECU operates the right and left side upper port control valves 704, 706 to create a vacuum in the upper region of the right cylinder 701 R and to pressurise the upper region of the opposite cylinder 701 L2, to counter the roll. If necessary the ECU operates i) the right side lower port pressure balance control valve 709 to counter the pressure in the lower region of the right cylinder 701 R with that in the right side accumulator 713; and ii) the left side upper port secondary pressure control valve 710 to add pressurised air from the left side accumulator 712. A speed sensor 725 can be provided and if these measurements are combined with data from the yaw-rate sensor 723 and steering wheel angle sensor 722, under-steer or over-steer can be detected. If this occurs then the ECU can operate the valves to put more vertical force on the appropriate side of the vehicle for improved traction.

Furthermore, a similar control system can be used to control front pneumatic cylinders with respect to the movement of their rear counterparts and vice versa in order to control pitch/squat. In a further embodiment, the twin-port pneumatic cylinders can be replaced with air bellows, as shown in Figures 8a and 8b. Figure 8a shows a suspension assembly 800 which is similar to the assembly shown in Figure 2; it has an upper wishbone member 801 and lower wishbone member 802 carrying a steering knuckle 803. The wishbone members are flexibly joined to the chassis of the vehicle (not shown) and the lower wishbone member 802 is linked by a coil spring and damper assembly 805 to one end 809 of a rocker arm 808. In this embodiment, the other end 811 of the rocker arm is connected to an air bellow 812. The air bellow is connected to the chassis of the vehicle (not shown). The air bellow has an air inlet (also not shown).

Figure 8b shows how a pair of suspensions assemblies, each having air bellow, are connected to the air supply and control system; a compressor 801 is connected to each of a pair of air bellows 802L and 802R on the front left and right of the vehicle via air lines 804, 805 and solenoid controlled valves 806, 807. The solenoid controlled valves are under the control of ECU 820, which has inputs from a ride height sensor 821, steering wheel angle sensor 822, yaw rate sensor 823, roll angle sensor 824 or speed sensor 825. If the roll angle sensor and steering wheel angle sensor detect that the vehicle is rolling to one side, the ECU 820 sends a signal to the valves 806, 807 to open until the roll has been corrected. Valves 808-811 are provided to store excess pressurised air or provide additional air when cornering.

A user interface 826 may be provided in connection with the ECU where a user can select a desired ride height.

In a further embodiment, each suspension assembly comprises only a single controllable twin port pneumatic member, as shown in Figure 9. In this embodiment, an upper wishbone member 901 is formed of an open triangular member having chassis mounting points 901a, 901b at the open base ends of the triangle for fixing the member 901 to the vehicle chassis. The mounting points 901a, 901b include an axle that allows articulated movement of the member in relation to the chassis. The apex of the triangular member includes a socket 901c connected to a corresponding ball feature at the top of a vertical steering knuckle 903 that carries a horizontal wheel spindle 904. The lower end of the steering knuckle 903 has a ball feature connected to a socket joint 902c at the apex of a triangular shaped lower wishbone member 902. The lower wishbone member 902 has chassis mounting points 902a, 902b at the open base ends of the triangle for fixing the member 902 to the vehicle chassis. The mounting points 902a, 902b include an axle that allows articulated movement of the member in relation to the chassis. The upper wishbone member 901, the lower wishbone member 902 and the steering knuckle 903 allow the wheel to move vertically in relation to the vehicle chassis. A double acting pneumatic cylinder of the type shown in Figure 4 is supported between the lower wishbone member 902 and the chassis.

Damping can be entirely managed by the pneumatic cylinder’s upper region opening/orifice, which can be adjustable.

Figure 10a shows a suspension assembly similar to that shown in Figures 2 and 5a to 5c, but with a modified pneumatic ram. In Figures 10a and 10b an upper wishbone 1001 and lower wishbone 1003 support a wheel carrier 1002, with a resilient member (pneumatic ram 1005) and a second resilient member (coil and damper assembly 1004). The pneumatic ram 1005 has an upper port 1005a and a lower port 1005b. The operation of the assembly is the same as that shown in Figure 2.