WO2008141387A1

WO2008141387A1 - Interconnected suspension systems

Info

Publication number: WO2008141387A1
Application number: PCT/AU2008/000720
Authority: WO
Inventors: Nong Zhang
Original assignee: University Of Technology, Sydney
Priority date: 2007-05-21
Filing date: 2008-05-21
Publication date: 2008-11-27
Also published as: CN101765727B; CN101765727A

Abstract

A vehicle suspension unit (1) is disclosed. The unit (1) is configured as a hybrid suspension unit having a passive damper element (2) and an active actuator element (3). The damper element (2) extends along a longitudinal axis (4) of the suspension unit (1) between a damper upper end (2a) and a damper lower end (2b). The damper element (2) provides for damped longitudinal displacement of the damper upper end (2a) relative to the damper lower end (2)b. The suspension unit may operate in both active and passive modes.

Description

INTERCONNECTED SUSPENSION SYSTEMS

Technical Field

The present invention generally relates to vehicle suspension systems, and particularly relates to interconnected suspension systems.

Background of the Invention

Motor vehicle accidents involving the rolling of a vehicle, referred to as

"rollover accidents", account for an unacceptably high level of deaths. This problem has become more significant in recent years as urban four-wheel drive vehicles, which typically have a high centre of gravity, and thus a relatively low resistance to rollover, have increased in popularity in urban areas. It has been reported that approximately 36% of deaths in accidents involving four-wheel drive special utility vehicles (SUV's) in the US in 2004 were from rollover accidents. Rollover accidents have been reported as the second most dangerous type of accident occurring on US highways, second only in fatality numbers to frontal collisions. In Australia, rollover accidents have been reported as causing 44% of vehicle occupant fatalities in rural Western Australia and 54% in rural Northern Territory.

The susceptibility of a vehicle to roll over can be determined by way of a standard dynamic rollover propensity test, otherwise known as the "fish hook manoeuvre test", routinely performed by the US National Highway Traffic Safety Administration (NHTSA). In such a test, a motor vehicle is accelerated to a test speed and a standardised fish hook manoeuvre is then executed. Test speeds are increased until a fish hook turn limit speed is reached, at which either the two inner wheels leave the ground during the fish hook turn, or alternatively the two outer wheels have the wheel rim contact the ground. For a standard motor vehicle, a typical fish hook turn limit speed is approximately 40 mph (approximately 64km/h). It has been estimated that an increase of the fish hook turn limit speed by only 10% would reduce the death rate relating to rollover accidents by up to 30%.

In conventional passive vehicle suspension systems, rollover is resisted by way of independent passive suspension units, each comprising a hydraulic damper and spring, associated with each wheel resisting vertical displacements between the wheel and the vehicle body, typically along with transverse torsion or anti-roll bars that specifically aim to increase rolling resistance Configuring such conventional passive suspension systems to provide increased resistance to rollover, however, adversely affects the πde characteπ sties of the suspension which endeavour to insulate the vehicle body from undulations in the road

Vaπous different methodologies have been applied to attempt to address these conflicting requirements of rollover resistance and πde quality

In one previously proposed system, standard shock absorbers are replaced with four interconnected double acting hydraulic cylinders, dampers The hydraulic cylinders are interconnected by way of two separate fluid circuits, each having a high pressure hydraulic accumulator The first circuit connects the upper chambers of the two left cylinders with the lower chambers of the two right cylinders, and the second circuit connects the lower chambers of the left cylinders with the upper chambers of the right cylinders When the vehicle starts to roll, the force applied to the pistons in each cylinder resulting from the rolling motion acts to pressuπse one of the circuits and depressuπse the other, providing a passive reactive force tending to resist the rolling motion This system, however, requires very high hydraulic pressures to be maintained in the accumulators and thus the fluid circuits, which results in excessive noise and vibration being transferred to the vehicle chassis by exciting natural frequencies of the chassis As a typical vehicle chassis has many natural frequencies, this noise and vibration is very difficult to suppress This proposed system also requires very fine manufacturing tolerances and is subject to excessive valve and seal wear Being a completely passive system, it is also unable to compensate for performance degradation associated with such wear Further, this proposed system is also only able to provide resistance against rolling, and is unable to independently control other modes of instability including pitching, bouncing and articulation The system also requires significant chassis redesign, such that it is not economically feasible for after-market retrofit applications or as an optional upgrade on new vehicles

Another methodology that has been utilised to address the above problems has been to provide active suspension systems, which may be either hydraulic or mechanical in nature

Hydraulic systems typically utilise interconnected double acting hydraulic cylinders as per the above descπbed passive system, replacing standard shock absorber dampers Through typically complex control systems, fluid pressure is actively applied to the upper or the lower chambers of the hydraulic cylinders as required. These systems are typically complicated, expensive and utilise power directly from the motor vehicle engine to pressurise the system, with a resultant loss in usable power output for driving the vehicle wheels.

One proposed mechanically based active vehicle suspension system involves an active mechanical torsion bar, which uses power from the engine to apply an active torque to the torsion bar resisting any rolling tendencies. Again, such a mechanical based system is relatively expensive and has a high power requirement from the engine.

Summary of the Invention

In a first aspect, the present invention provides a vehicle suspension unit comprising: a damper element, said damper element providing damping; and an actuator element arranged in relation to said damper element.

In an embodiment, the actuator element is arranged to change damping provided by said damper element.

In an embodiment, the actuator element is arranged to enable a nominal longitudinal displacement of a damper upper end relative to a damper lower end to be altered.

In an embodiment, the actuator element is responsive to one of roll, pitch or articulation of a vehicle to vary the damping of the damping element.

In an embodiment, said actuator element is one of a plurality of interconnected suspension units forming a suspension system, the suspension system being arranged to resist one or more of roll, pitch and articulation of a vehicle.

In an embodiment, the vehicle suspension unit further comprises a vehicle body mount fixed in relation one of said damper upper end and said damper lower end. It may also comprise a wheel mount fixed in relation to one of said damper lower end and said upper end.

In an embodiment, said actuator element further comprises an actuator housing defining a longitudinally extending fluid filled actuator cavity. Said actuator housing may be fixed in relation to one of said damper upper end and said damper lower end. In an embodiment, said actuator element may further comprise an actuator piston mounted in said actuator cavity for reciprocal longitudinal displacement through said actuator cavity, said actuator piston dividing said actuator cavity into an actuator upper chamber and an actuator lower chamber.

In an embodiment, said actuator element may further comprise an actuator piston connector fixed to said actuator piston and longitudinally extending through said actuator housing. Said actuator piston connector may be fixed in relation to the other of said damper upper end and said damper lower end.

In an embodiment, said actuator element may further comprise an upper port communicating with said actuator upper chamber. Said upper port may extend through said actuator housing

In an embodiment, said actuator element may further comprise a lower port communicating with said actuator lower chamber. Said lower port may extend through said actuator housing

In an embodiment, said damper element comprises a damper housing defining a longitudinally extending liquid filled damper cavity. Said damper housing may further define one of said damper upper end and said damper lower end. Said damper element may further comprise a damper piston mounted in said damper cavity for damped longitudinal reciprocal motion through said damper cavity. Said damper piston may divide said damper cavity into a damper upper chamber and a damper lower chamber. Said damper element may further comprise a damper piston connector fixed to said damper piston and longitudinally extending through said damper housing, said damper piston connector defining the other of said damper upper end and said damper lower end.

In an embodiment, said vehicle suspension unit may further comprise a spring longitudinally extending between a spring upper end and a spring lower end, said spring upper end being fixed in relation to said damper upper end and said spring lower end being fixed in relation to said damper lower end.

In a second aspect, the present invention provides a vehicle suspension unit having a longitudinal axis and comprising: a damper element extending along said longitudinal axis between a damper upper end and a damper lower end, said damper element providing for damped longitudinal displacement of said damper upper end relative to said damper lower end; and an actuator element coaxially arranged in relation to said damper element, said actuator element comprising an actuator housing defining a longitudinally extending fluid filled actuator cavity, and said actuator element also comprising an actuator piston mounted in said actuator cavity for reciprocal longitudinal displacement through said actuator cavity, said actuator piston dividing said actuator cavity into an actuator upper chamber and an actuator lower chamber; an upper port communicating with said actuator upper chamber; and a lower port communicating with said actuator lower chamber.

In a third aspect, the present invention provides a vehicle suspension system, said suspension system comprising: a first suspension unit according to the second aspect of the invention arranged to be mounted to a front left wheel assembly; a second suspension unit according to the second aspect of the invention arranged to be mounted to a front right wheel assembly; a third suspension unit according to the second aspect of the invention arranged to be mounted to a rear left wheel assembly; and a fourth suspension unit according to the second aspect of the invention arranged to be mounted to a rear right wheel assembly, a first upper fluid line communicating with said upper port of said first suspension unit; a first lower fluid line communicating with said lower port of said first suspension unit; a second upper fluid line communicating with said upper port of said second suspension unit; a second lower fluid line communicating with said lower port of said second suspension unit; a third upper fluid line communicating with said upper port of said third suspension unit; a third lower fluid line communicating with said lower port of said third suspension unit; a fourth upper fluid line communicating with said upper port of said fourth suspension unit; a fourth lower fluid line communicating with said lower port of said fourth suspension unit; a first fluid circuit comprising two or more of said fluid lines; and a second fluid circuit comprising two or more of said fluid lines.

In an embodiment said first fluid circuit comprises said first upper fluid line, said second lower fluid line, said third upper fluid line and said fourth lower fluid line; and said second fluid circuit comprises said first lower fluid line, said second upper fluid line, said third lower fluid line, and said fourth upper fluid line.

In an embodiment said first fluid circuit comprises said first upper fluid line, said second upper fluid line, said third lower fluid line and said fourth lower fluid line; and said second fluid circuit comprises said first lower fluid line, said second lower fluid line, said third upper fluid line, and fourth upper fluid line.

In an embodiment said first fluid circuit comprises said first upper fluid line, said second upper fluid line, said third upper fluid line and said fourth upper fluid line; and said second fluid circuit comprising said first lower fluid line, said second lower fluid line, said third lower fluid line, and fourth lower fluid line.

In an embodiment said first fluid circuit comprises said first upper fluid line, said second lower fluid line, said third lower fluid line and said fourth upper fluid line; and said second fluid circuit comprising said first lower fluid line, said second upper fluid line, said third upper fluid line, and fourth lower fluid line.

In an embodiment, the passive vehicle suspension system further comprisese one or more valves to reconfigure said first and/or said second fluid circuits.

In an embodiment, at least one of the fluid circuits includes an accumulator.

In an embodiment, at least one of the fluid circuits includes a damper valve.

In a fourth aspect, the present invention provides a vehicle suspension system comprising: a first suspension unit according to the second aspect arranged to connect a first wheel to a vehicle body; a second suspension unit according to the second aspect arranged to connect a second wheel to the vehicle body; a first upper fluid line communicating with said upper port of said first suspension unit; a first lower fluid line communicating with said lower port of said first suspension unit; a second upper fluid line communicating with said upper port of said second suspension unit; a second lower fluid line communicating with said lower port of said second suspension unit.

In an embodiment, the vehicle suspension system further comprises a fluid pressure supply.

In an embodiment, the vehicle suspension system further comprises a fluid reservoir.

In an embodiment, the vehicle suspension system further comprises a valve arrangement operable in an actuator standby mode to communicate each of said first upper fluid line, said first lower fluid line, said second upper fluid line, and said second lower fluid line with said fluid reservoir, said valve arrangement further being operable in at least one actuator active mode to selectively communicate: one of said first upper fluid line and said first lower fluid line with said fluid pressure supply and the other of said first upper fluid line and said first lower fluid line with said fluid reservoir; and one of said second upper fluid line and said second lower fluid line with said fluid pressure supply and the other of said second upper fluid line and said second lower fluid line with said fluid reservoir.

In an embodiment, the vehicle suspension system further comprises a sensor system for sensing one or more vehicle parameters indicative of a condition of the vehicle. The system may comprise a control system for controlling said valve arrangement dependent upon said parameter(s) sensed by said sensor system.

In an embodiment, said vehicle body mount of said first suspension unit is mounted to the vehicle body and said wheel mount of said first suspension unit is mounted to the first wheel. Said vehicle body mount of said second suspension unit may be mounted to the vehicle body and said wheel mount of said second suspension unit may be mounted to the second wheel.

In a fifth aspect, the present invention provides a primary control valve comprising: a valve body containing an elongate cavity; a first port; a second port; a supply port; and a pair of outlet ports.

In an embodiment, a sliding spool is mounted in the valve body. The sliding spool may extend through the cavity. The sliding spool may extend through each opposing end of the valve body . Two spool pistons may be concentrically mounted on the spool. The spool 37 may be is slidingly displaced by way of a solenoid in response to control inputs. The control inputs may be from a control system.

30 may be in the form of a solenoid actuated linear spool valve, as depicted in greater detail in Figures 3, 4 and 5

In a sixth aspect, the present invention provides a vehicle suspension unit having a longitudinal axis and comprising: a damper element extending along said longitudinal axis between a damper upper end and a damper lower end, said damper element providing for damped longitudinal displacement of said damper upper end relative to said damper lower end; a vehicle body mount fixed in relation to said damper upper end; a wheel mount fixed in relation to said damper lower end; and an actuator element coaxially arranged in relation to said damper element, said actuator element including: an actuator housing defining a longitudinally extending fluid filled actuator cavity, said actuator housing being fixed in relation to one of said damper upper end and said damper lower end; an actuator piston mounted in said actuator cavity for reciprocal longitudinal displacement through said actuator cavity, said actuator piston dividing said actuator cavity into an actuator upper chamber and an actuator lower chamber; an actuator piston connector fixed to said actuator piston and longitudinally extending through said actuator housing, said actuator piston connector being fixed in relation to the other of said damper upper end and said damper lower end; an upper port extending through said actuator housing communicating with said actuator upper chamber; and a lower port extending through said actuator housing communicating with said actuator lower chamber.

In an embodiment, said damper element comprises: a damper housing defining a longitudinally extending liquid filled damper cavity, said damper housing further defining one of said damper upper end and said damper lower end; a damper piston mounted in said damper cavity for damped longitudinal reciprocal motion through said damper cavity, said damper piston dividing said damper cavity into a damper upper chamber and a damper lower chamber; a damper piston connector fixed to said damper piston and longitudinally extending through said damper housing, said damper piston connector defining the other of said damper upper end and said damper lower end.

In an embodiment, the vehicle suspension unit further comprises a spring longitudinally extending between a spring upper end and a spring lower end, said spring upper end being fixed in relation to said damper upper end and said spring lower end being fixed in relation to said damper lower end.

In an embodiment, said actuator housing extends circumferentially about said damper housing. The damper housing is typically in the form of a damper cylinder, with said damper piston being cylindrical and said damper piston connector being in the form of a piston rod. The actuator housing may have an annular cross-section, an inner wall of said actuator housing being defined by a peripheral wall of said damper housing, said actuator piston having an annular cross-section.

Alternatively, said damper housing may extend circumferentially about said actuator housing.

In a seventh aspect, the present invention provides an active vehicle suspension system comprising: a first suspension unit as defined above connecting a first wheel to a vehicle body, said vehicle body mount of said first suspension unit being mounted to the vehicle body and said wheel mount of said first suspension unit being mounted to the first wheel; a second suspension unit as defined above connecting a second wheel to the vehicle body, said vehicle body mount of said second suspension unit being mounted to the vehicle body and said wheel mount of said second suspension unit being mounted to the second wheel; a first upper fluid line communicating with said upper port of said first suspension unit; a first lower fluid line communicating with said lower port of said first suspension unit; a second upper fluid line communicating with said upper port of said second suspension unit; a second lower fluid line communicating with said lower port of said second suspension unit, a fluid pressure supply; a fluid reservoir; a valve arrangement operable in an actuator standby mode to communicate each of said first upper fluid line, said first lower fluid line, said second upper fluid line, and said second lower fluid line with said fluid reservoir, said valve arrangement further being operable in at least one actuator active mode to selectively communicate: one of said first upper fluid line and said first lower fluid line with said fluid pressure supply and the other of said first upper fluid line and said first lower fluid line with said fluid reservoir; and one of said second upper fluid line and said second lower fluid line with said fluid pressure supply and the other of said second upper fluid line and said second lower fluid line with said fluid reservoir; a sensor system for sensing one or more vehicle parameters indicative of a condition of the vehicle, and a control system for controlling said valve arrangement dependent upon said parameter(s) sensed by said sensor system.

Typically, said fluid pressure supply is pressurised by a power steering system of the vehicle. In one embodiment, said first upper fluid line is in permanent communication with said second lower fluid line, and said first lower fluid line is in permanent communication with said second upper fluid line.

For a four-wheel vehicle, the vehicle's suspension system will typically further comprise: a third suspension unit as defined above connecting a third wheel to a vehicle body, said vehicle body mount of said third suspension unit being mounted to the vehicle body and said wheel mount of said third suspension unit being mounted to the third wheel; a fourth suspension unit as defined above connecting a fourth wheel to the vehicle body, said vehicle body mount of said fourth suspension unit being mounted to the vehicle body and said wheel mount of said fourth suspension unit being mounted to the fourth wheel; a third upper fluid line communicating with said upper port of said third suspension unit; a third lower fluid line communicating with said lower port of said third suspension unit; a fourth upper fluid line communicating with said upper port of said fourth suspension unit; and a fourth lower fluid line communicating with said lower port of said fourth suspension unit; said valve arrangement being further operable in said actuator standby mode to communicate said third upper fluid line, said third lower fluid line, said fourth upper fluid line and said fourth lower fluid line with said fluid reservoir, said valve arrangement being still further operable in at least one said actuator active mode to selectively communicate; one of said third upper fluid line and said third lower fluid line with said fluid pressure supply and the other of said third upper fluid line and said third lower fluid line with said fluid reservoir; and one of said fourth upper fluid line and said fourth lower fluid line with said fluid pressure supply and the other of said fourth upper fluid line and said fourth lower fluid line with said fluid reservoir.

In one embodiment, the third upper fluid line is in permanent communication with said fourth lower fluid line and said third lower fluid line is in permanent communication with said fourth upper fluid line. Typically, the first wheel is a front left wheel, the second wheel is a front right wheel, the third wheel is a rear left wheel and the fourth wheel is a rear right wheel.

To control roll of the vehicle body, with a preferred suspension system, said sensor arrangement is configured to sense one or more parameters indicative of a roll condition of said vehicle body in which said vehicle body is inclined at a roll angle or has a potential to become inclined at a roll angle, said control system being configured to control said valve arrangement to: operate said valve arrangement in a first roll active mode when said roll condition is a first roll condition, communicating said first upper fluid line, said second lower fluid line, said third upper fluid line and said fourth lower fluid line with said fluid pressure supply and said first lower fluid line, said second upper is fluid line, said third lower fluid line and said fourth upper fluid line with said fluid reservoir; and operate said valve arrangement in a second roll active mode when said roll condition is a second roll condition, communicating said first upper fluid line, said second lower fluid line, said third upper fluid line and said fourth lower fluid line with said fluid reservoir, and said first lower fluid line, said second upper fluid line, said third lower fluid line and said fourth upper fluid line with said fluid pressure supply.

When said actuator piston connector of each said suspension unit is fixed in relation to the corresponding said damper upper end, said first roll condition is a right roll condition and said second roll condition is a left roll condition.

When said actuator piston connector of each said suspension unit is fixed in relation to the corresponding said damper lower end, said first roll condition is a left roll condition and said second roll condition is a right roll condition.

The said one or more parameters may include vehicle speed and a steering wheel angle.

Alternatively, said one or more parameters may include lateral acceleration of said vehicle.

To control bounce of the vehicle body, with a preferred suspension system, said sensor system is configured to sense one or more parameters indicative of a bounce condition of said vehicle body in which a height of the vehicle body is outside of a predetermined neutral height range, said control system being configured to control said valve arrangement to: operate said valve arrangement in a first bounce active mode when said bounce condition is a first bounce condition in which said vehicle body height is above said neutral height range, communicating said first upper fluid line, said second upper fluid line, said third upper fluid line and said fourth upper fluid line with said hydraulic pressure supply and said first lower fluid line, said second lower fluid line, said third lower fluid line, and said fourth lower fluid line with said fluid reservoir; operate said valve arrangement in a second bounce active mode when said bounce condition is a second bounce condition in which said vehicle body height is below said neutral height range, communicating said first upper fluid line, said second upper fluid line, said third upper fluid line, and said fourth upper fluid line with said fluid reservoir and said first lower fluid line, said second lower fluid line, said third lower fluid line and said fourth lower fluid line with said fluid pressure supply.

When said actuator piston connector of each said suspension unit is fixed in relation to the corresponding said damper upper end, said first bounce condition is a peak bounce condition and said second bounce condition is a trough bounce condition.

When said actuator piston connector of each said suspension unit is fixed in relation to the corresponding said damper lower end, said first bounce condition is a trough bounce condition and said second bounce condition is a peak bounce condition.

To control pitch of the vehicle body, with a preferred suspension system, said sensor system is configured to sense one or more parameters indicative of a pitch condition of said vehicle body in which said vehicle body is inclined at a pitch angle or has a potential to become inclined at a pitch angle, said control system being configured to control said valve arrangement to: operate said valve arrangement in a first pitch active mode when said pitch condition is a first pitch condition, communicating said first upper fluid line, said second upper fluid line, said third lower fluid line and said fourth lower fluid line with said fluid reservoir and said first lower fluid line, said second lower fluid line, said third upper fluid line and said fourth upper fluid line with said fluid pressure supply; and operate said valve arrangement in a second pitch active mode when said pitch condition is a second down pitch condition communicating said first upper fluid line, said second upper fluid line, said third lower fluid line, and said fourth lower fluid line with said fluid pressure supply and said first lower fluid line, said second lower fluid line, said third upper fluid line and said fourth upper fluid line with said fluid reservoir.

When said actuator piston connector of each said suspension unit is fixed in relation to the corresponding said damper upper end, said first pitch condition is a nose down pitch condition and said second pitch condition is a tail down pitch condition.

When said actuator piston connector of each said suspension unit is fixed in relation to the corresponding said damper lower end, said first pitch condition is tail down pitch condition and said second pitch condition is a nose down pitch condition.

Typically, said one or more parameters may include a brake application parameter. Said one or more parameters may also include vehicle longitudinal acceleration.

To control articulation of the vehicle, with a preferred suspension system, said sensor system is configured to sense one or more parameters indicative of an articulation condition of said vehicle, said control system being configured to control said valve arrangement to: operate said valve arrangement in a first articulation active mode when said articulation condition is a first articulation condition, communicating said first upper fluid line, said second lower fluid line, said third lower fluid line and said fourth upper fluid line with said fluid reservoir and said first lower fluid line, said second upper fluid line, said third upper fluid line and said fourth lower fluid line with said fluid pressure supply; and operate said valve arrangement in a second articulation active mode when said articulation condition is a second articulation condition communicating said first upper fluid line, said second lower fluid line, said third lower fluid line, and said fourth upper fluid line with said fluid pressure supply and said first lower fluid line, said second upper fluid line, said third upper fluid line and said fourth lower fluid line with said fluid reservoir. Typically, said valve arrangement includes a primary control valve operable to selectively communicate one of a first fluid circuit and a second fluid circuit with said fluid pressure supply pump and the other of said first fluid circuit and said second fluid circuit with said fluid reservoir; wherein said first fluid circuit comprises: one of said first upper fluid line and said first lower fluid line; one of said second upper fluid line and said second lower fluid line; one of said third upper fluid line and said third lower fluid line; and one of said fourth upper fluid line and said fourth lower fluid line; further wherein said second fluid circuit comprises: the other of said first upper fluid line and said first lower fluid line; the other of said second upper fluid line and said second lower fluid line; the other of said third upper fluid line and said third lower fluid line; and the other of said fourth upper fluid line and said fourth lower fluid line.

The valve arrangement may further comprise one or more auxiliary control valves operable to selectively configure said first fluid circuit and said second fluid circuit between at least two configurations selected from a group consisting of a roll control configuration, a pitch control configuration, a bounce control configuration and an articulation control configuration, wherein: in said roll control configuration, said first fluid circuit comprises said first upper fluid line, said second lower fluid line, said third upper fluid line and said fourth lower fluid line; in said pitch control configuration, said first fluid circuit comprises said first upper fluid line, said second upper fluid line, said third lower fluid line and said fourth lower fluid line; in said bounce control configuration, said first fluid circuit comprises said first upper fluid line, said second upper fluid line, said third upper fluid line and said fourth upper fluid line; in said articulation control configuration, said first fluid circuit comprises said first upper fluid line, said second lower fluid line, said third lower fluid line and said fourth upper fluid line.

Preferably, said one or more auxiliary control valves is operable to selectively configure said first fluid circuit and said second fluid circuit between each of said roll control configuration, said pitch control configuration, said bounce control configuration and said articulation control configuration.

In a eight aspect, the present invention provides a vehicle suspension system for a vehicle having a vehicle body and four wheels, said suspension system comprising: a first suspension unit mounted to a front left wheel; a second suspension unit mounted to a front right wheel; a third suspension unit mounted to a rear left wheel; and a fourth suspension unit mounted to a rear right wheel, each said suspension unit having: vehicle body mount mounted to the vehicle body and a wheel mount mounted to the respective wheel; a housing defining a longitudinally extending fluid filled cavity, said housing being fixed in relation to one of said vehicle body mount and said wheel mount; a piston mounted in said cavity for reciprocal longitudinal displacement through said cavity; said piston dividing said cavity into an upper chamber and a lower chamber; a piston connector fixed to said piston and longitudinally extending through said housing, said piston connector being fixed in relation to the other of said vehicle body mount and said wheel mount; an upper port extending through said housing communicating with said upper chamber; and a lower port extending through said housing communicating with said lower chamber; said suspension system further comprising: a first upper fluid line communicating with said upper port of said first suspension unit; a first lower fluid line communicating with said lower port of said first suspension unit; a second upper fluid line communicating with said upper port of said second suspension unit; a second lower fluid line communicating with said lower port of said second suspension unit; a third upper fluid line communicating with said upper port of said third suspension unit; a third lower fluid line communicating with said lower port of said third suspension unit; a fourth upper fluid line communicating with said upper port of said fourth suspension unit; a fourth lower fluid line communicating with said lower port of said fourth suspension unit; a valve arrangement operable to selectively configure a first fluid circuit and a second fluid circuit between at least two configurations selected from a group consisting of a roll control configuration, a pitch control configuration, a bounce control configuration and an articulation control configuration, wherein; in said roll control configuration, said first fluid circuit comprises said first upper fluid line, said second lower fluid line, said third upper fluid line and said fourth lower fluid line; in said pitch control configuration, said first fluid circuit comprises said first upper fluid line, said second upper fluid line, said third lower fluid line and said fourth lower fluid line; in said bounce control configuration, said first fluid circuit comprises said first upper fluid line, said second upper fluid line, said third upper fluid line and said fourth upper fluid line; in said articulation control configuration, said first fluid circuit comprises said first upper fluid line, said second lower fluid line, said third lower fluid line and said fourth upper fluid line.

Preferably, said valve arrangement is operable to selectively configure said first fluid circuit and said second fluid circuit between each of said roll control configuration, said pitch control configuration, said bounce control configuration and said articulation control configuration.

Preferably, said valve arrangement further includes a primary control valve operable to selectively communicate one of said first fluid circuit and said second fluid circuit with a fluid pressure supply pump and the other of said first fluid circuit and said second fluid circuit with a fluid reservoir.

Brief Description of the Drawings

Preferred embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings wherein:

Figure 1 is a schematic cross-sectional elevation view of a vehicle suspension unit.

Figure 2 is a schematic diagram of a two-wheel active vehicle suspension system.

Figure 3 is a cross-sectional view of a primary control valve in a first active position.

Figure 4 is a cross-sectional view of the primary control valve of Figure 3 in a second active position.

Figure 5 is a cross-sectional view of the primary control valve of Figure 3 in a passive position. Figure 6 is a schematic plan view of a four-wheel motor vehicle.

Figure 7 is a schematic diagram of a four-wheel active vehicle suspension system configured to control roll.

Figure 8 is schematic diagram of an alternate four-wheel active vehicle suspension system configured to control roll. Figure 9 is a schematic diagram of a four-wheel active vehicle suspension system configured to control pitch.

Figure 10 is a schematic diagram of a four-wheel vehicle suspension system configured to control bounce.

Figure 1 1 is a four-wheel vehicle suspension system configured to control articulation.

Figure 12 is a schematic diagram of a four-wheel vehicle suspension system configured to control roll, pitch, bounce and articulation, in a passive actuator mode.

Figure 13 is a schematic diagram of the suspension system of Figure 12 in a roll control mode. Figure 14 is a schematic diagram of the suspension system of Figure 12 in a pitch control mode.

Figure 15 is a schematic diagram of the suspension system of Figure 12 in a bounce control mode.

Figure 16 is a schematic diagram of the suspension system of Figure 12 in an articulation control mode.

Figure 17 and 18 show embodiments of tow mode suspension systems. Figure 19 shows an embodiment of a passive hydraulically interconnected suspension (PHIS) configured to resist rolling.

Figure 20 shows another embodiment of a PHIS configured to resist pitch. Figure 21 shows another embodiment of a PHIS configured to resist bounce.

Figure 22 shows another embodiment of a PHIS configured to assist articulation. Figure 23 shows a suspension unit of Figure 1 mounted to both a vehicle body and a wheel body.

Detailed Description of the Preferred Embodiments

Referring to Figure 1 , a vehicle suspension unit 1 , is configured as a hybrid suspension unit having a passive damper element 2 and an active actuator element 3. The damper element 2 extends along a longitudinal axis 4 of the suspension unit 1 between a damper upper end 2a and a damper lower end 2b. The damper element 2 provides for damped longitudinal displacement of the damper upper end 2a relative to the damper lower end 2b as per a standard shock absorber damper. In the arrangement depicted in Figure 1, the damper element 2 is in the form of a standard shock absorber. The damper element 2 has a damper housing 5, in the form of a damper cylinder, defining a longitudinally extending liquid filled damper cavity 6. The damper housing 5 also defines the damper lower end 2b, although it is envisaged that the damper element 2 may be in an inverted configuration such that the damper housing 5 defines the damper upper end 2a. A damper piston 7, here of cylindrical form to match the cylindrical damper housing 5, is mounted in the damper cavity 6 for damped longitudinal reciprocal motion through the damper cavity 6. The damper piston 7 divides the damper cavity 6 into a damper upper chamber 8 and a damper lower chamber 9. The damper piston 7 is provided with valving 10 in the usual manner to provide for the damped longitudinal reciprocal motion of the damper piston 7 through the liquid filled damper cavity 6. A damper piston connector 1 1, here in the form of a standard piston rod, is fixed to the damper piston 7 and longitudinally extends through the damper housing 5. The damper piston connector 1 1 defines the damper upper end 2a. In the inverted configuration, the damper piston connector 1 1 will define the damper lower end 2b.

The actuator element 3 is co-axially arranged in relation to the damper element 2, here with the damper element 2 located concentrically within the actuator element 3. The actuator element 3 is in the general form of a double acting cylinder and includes an actuator element housing 12 that defines a longitudinally extending fluid filled actuator cavity 13. The cylindrical actuator housing 12 is fixed in relation to the damper lower end 2b and here circumferentially extends about the damper housing 5 and is fixed thereto. In an alternate configuration, it is envisaged that the actuator housing 12 be fixed in relation to the damper upper end 2a, rather than the lower end 2b. The actuator housing 12 here has an annular cross-section, with an inner wall 14 of the actuator housing being defined by a peripheral wall of the damper housing 5. An actuator piston 15 is mounted in the actuator cavity 13 for reciprocal longitudinal displacement through the actuator cavity 13. The actuator piston 15 divides the actuator cavity into an actuator upper chamber 16 and an actuator lower chamber 17. The actuator piston 15 here has an annular cross-section to match the cross-section of the actuator cavity 13. An actuator piston connector 18 is fixed to the actuator piston 15 and longitudinally extends through the actuator housing 12. Here, given the annular form of the actuator piston 15, the actuator piston connector 18 also has an annular cross- section, extending about the damper housing 5, rather than being in the form of a solid piston rod, as per the damper piston connector 11. The actuator piston connector 18 is fixed in relation to the damper piston connector 11 , and thus fixed in relation to the damper second end 2a. In the alternate form, where the actuator element 3 is effectively inverted, the actuator piston connector 18 is fixed in relation to the damper lower end 2b.

The actuator element 3 is provided with an upper port 19 extending through the actuator housing 12 communicating with the actuator upper chamber 16 and a lower port 20 extending through the actuator housing 12 and communicating with the actuator lower sub-chamber 17. An upper fluid line 21 is connected to the upper port 19, whilst a lower fluid line 22 is connected to the lower port 20. The upper and lower fluid lines 21, 22 are utilised to supply high fluid pressure selectively to the actuator upper chamber 16 or actuator lower chamber 17 as desired to longitudinally displace the actuator piston 15 through the fluid filled actuator cavity 13 upwardly or downwardly so as to either refract or extend the suspension unit 1, as will be discussed below.

As best seen in Figure 20, a vehicle body mount 24 is bolted 2e in relation to the damper lower end 2b for mounting the suspension unit 1 to the body of a motor vehicle using a mounting plate 2d and a rubber mount isolator 2e. A wheel mount 23 is fixed in relation to the damper upper end 2a for mounting the suspension unit 1 to a vehicle wheel body W in the usual manner via a pinned joint 2c. The suspension unit 1 may thus be readily fitted to a standard motor vehicle, replacing a standard passive shock absorber, without modification. Of course, the suspension unit may be tipped through 180 degrees and suitably mounted.

The suspension unit 1 typically further comprises a spring (not depicted in Figure 1) longitudinally extending between a spring upper end and a spring lower end. The spring is typically concentrically mounted in relation to the damper element 2 and actuator element 3, with the spring upper end fixed in relation to the damper upper end and the spring lower end fixed in relation to the damper lower end in the usual manner.

In an alternate form of the vehicle suspension unit 1 , the damper element 2 and actuator element 3 are effectively interchanged, with the damper element 2 extending circumferentially about the actuator element 3.

A simple two-wheel active vehicle suspension system utilising two suspension units 1 as described above is depicted schematically in Figure 2. The two vehicle suspension units comprise a first suspension unit 101 and a second suspension unit 201. The components of each of the first and second suspension units 101 , 201 are identical to those described above, with each of the individual features being referenced with equivalent reference numerals to those described above in relation to Figure 1, with the addition of 100 for the first suspension unit 101 , and 200 for the second suspension unit 201. For clarity purposes only, the damper elements 102, 202 and springs 125, 225 have been schematically depicted adjacent the actuator elements 103, 203 rather than concentrically mounted, as would be the case in practice.

The first suspension unit 101 connects a first wheel to a vehicle body (not shown), with the vehicle body mount 123 of the first suspension unit 101 being mounted to the vehicle body and the wheel mount 124 of the first suspension unit 101 being mounted to the first wheel. The second suspension unit 201 similarly connects a second wheel to the vehicle body, with the vehicle body mount 223 of the second suspension unit 201 being mounted to the vehicle body and the wheel mount 224 of the second suspension unit 201 being mounted to the second wheel.

In the arrangement depicted, the upper fluid line 121 of the first suspension unit 101 (hereinafter referred to as the first upper fluid line 121) is joined to the second lower fluid line 222 such that they are in permanent communication. Similarly, the first lower fluid line 122 is joined to the second upper fluid line 221 such that they are also in permanent communication. The first upper fluid line 121 communicates with a first port 32 of a multi-port primary control valve 30 via a first auxiliary fluid line 46. The second upper fluid line 221 communicates with a second port 31 of the primary control valve 30 via a second auxiliary fluid line 47. The first upper fluid line 121 , second lower fluid line 222 and first auxiliary fluid line 46 define a first fluid circuit. The first lower fluid line 122, second upper fluid line 221 and second auxiliary fluid line 47 define a second fluid circuit. A fluid pressure pump 40 communicates with a supply port 33 of the primary control valve 30 by way of a supply fluid line 41 and in line supply pressure control valve 42. The fluid pressure supply pump 40 will typically be a power steering pump as otherwise used to provide power assisted steering to the motor vehicle. The suspension system will typically only require a fluid pressure supply from the fluid pressure supply pump 40 when the motor vehicle is travelling at significant speeds. At such speeds, the power steering system is generally inactive and hence the power steering pump can readily service both systems. Alternatively, the fluid pressure supply pump may be a conventional hydraulic (gear) pump.

A fluid reservoir 43 communicates with an outlet port 34 of the primary control valve 30 by way of an outlet fluid line 44 and in line outlet pressure control valve 45. The primary control valve 30, supply pressure control valve 42 and outlet pressure control valve 45 are controlled by a control system 50 based on outputs from a sensor system 51 which senses one or more vehicle parameters indicative of a condition of the vehicle. Whilst the fluid operating the actuator elements 103, 203 will typically be a hydraulic liquid, it is also envisaged that the fluid may be a gas, in which case the fluid reservoir 43 might merely be the atmosphere.

The primary control valve 30 may be in the form of a solenoid actuated linear spool valve, as depicted in greater detail in Figures 3, 4 and 5. The control valve 30 comprises a valve body 35 containing an elongate cavity 36 communicating with the exterior of the valve body 35 by way of the first port 31 , second port 32, supply port 33, and two outlet ports 34. A sliding spool 37 is mounted in the valve body 35 extending through the cavity 36 and each opposing end of the valve body 35. Two spool pistons 38, 39 are concentrically mounted on the spool 37. The spool 37 is slidingly displaced by way of a solenoid (not shown) in response to control inputs from the control system 50.

hi a first active position depicted in Figure 3, the first port 31 communicates with the left outlet port 34, such that the first fluid circuit (including the first upper fluid line 121 and second lower fluid line 222) is in fluid communication with the fluid reservoir 43 via the outlet fluid line 44. The second port 32 is in communication with the supply port 33, such that the second fluid circuit (including the first lower fluid line 122 and second upper fluid line 221) is in fluid communication with the fluid supply pump 40 via the fluid supply line 41. With this valve arrangement positioning of Figure 3, the actuator lower chamber 1 17 of the first suspension unit 101 and actuator upper chamber 216 of the second suspension unit 201 will be pressurised by the fluid pressure pump 40. The pressure supplied is regulated by the supply pressure control valve 42. The actuator upper chamber 116 of the first suspension unit 101 and the actuator lower chamber 217 of the second suspension unit 201 will communicate with the atmosphere via the fluid reservoir 43. The outlet pressure can be regulated and maintained above atmospheric pressure by the outlet pressure control valve 45 so as to provide some additional damping if desired. Accordingly, the actuator piston 1 15 of the first suspension unit 101 will tend to be driven upwards, expanding the first suspension unit 101 and the actuator piston 215 of the second suspension unit 201 will tend to be driven downwards compressing the second suspension unit 201.

If the first wheel is a left wheel, and the second wheel is a right wheel, this arrangement will tend to roll the vehicle body to the right, effectively stiffening the suspension against any tendency of the vehicle body to roll to the left during a high speed right turn. If the first wheel is a front wheel, and the second wheel is a rear wheel, then this arrangement will tend to elevate the nose of the vehicle body in relation to the tail of the vehicle body, effectively increasing the suspension stiffness against any tendency of the vehicle body to pitch nose down during, for example, heavy braking.

In an alternate embodiment where the actuator elements 103, 203 are inverted such that the actuator connectors 1 18, 218 extend downwardly and are fixed in relation to the damper lower ends 102b, 202b, the opposite effect will result. That is, the first suspension unit 101 will tend to compress and the second suspension unit 201 will tend to expand. In another alternate embodiment, the first and second upper fluid lines 121 ,

221 are in permanent communication whilst the first and second lower fluid lines 122,

222 are in permanent communication. This will be suitable for controlling bounce.

In Figure 4, the spool 37 is slidingly displaced to the left to a second active position at which the first port 31 communicates with the supply port 33 and the second port 32 communicates with the right outlet port 34. With this valve arrangement positioning of Figure 4, the actuator upper chamber 1 16 of the first suspension unit 101 and actuator lower chamber 217 of the second suspension unit 201 will be pressurised by the fluid pressure pump 40, whilst the actuator lower chamber 1 17 of the first suspension unit 101 and the actuator upper chamber 216 of the second suspension unit 201 will communicate with the fluid reservoir 43. The first suspension unit 101 will thus tend to refract and the second suspension unit 201 will tend to expand.

When the spool 37 is further slidingly displaced to the left to the passive position depicted in Figure 5, the second piston 39 blocks the supply port 33 whilst the first and second ports 31, 32 communicate with the left and right outlet ports 34. Thus, the upper and lower chambers of the first and second suspension units 101, 201 all communicate with the fluid reservoir 43 resulting in the actuator elements 103, 203 being passive and not imparting any expansion or refraction force on the suspension units 101, 201. The primary control valve 30 will remain in this passive position such that the suspension units 101 , 201 will operate as regular possible shock absorbers by way of the damper elements 102, 202 until an out of balance condition is sensed by the sensing system 51 and conveyed to the control system 50.

In alternate embodiments the primary control valve 30 may be a rotary spool valve or any of various other types of multi-port valve.

Figure 6 schematically depicts a four-wheel motor vehicle comprising a vehicle body 60, first wheel 61 (here being a front left wheel), second wheel 62 (here being a front right wheel), third wheel 63 (here being a rear left wheel) and fourth wheel 64 (here being a rear right wheel). The four wheels 61, 62, 63, 64 are connected to the vehicle body 60 by way of a first suspension unit 101 , second suspension unit 201 , third suspension unit 301 and fourth suspension unit 401 respectively. Again, the components of each of the third and fourth suspension units 301 , 401 are identical to those described above in relation to the first suspension unit 101 , with each of the individual features being referenced with equivalent reference numerals to those described above in relation to Figure 1 , with the addition of 300 for the third suspension unit 301 and 400 for the fourth suspension unit 401. Each vehicle body mount 123, 223, 323, 423 is mounted to the vehicle body 60 whilst each wheel mount 124, 224, 324, 424 is mounted to the respective wheel 61 , 62, 63, 64 in the usual manner. The first suspension unit 101 is hereinafter referred to as the front left suspension unit 101. Similarly the second suspension unit 201 is referred to as the front right suspension unit 201, the third suspension unit is referred to as the rear left suspension unit 301 and the fourth suspension unit 401 is referred to as the rear right suspension unit 401. The components of each of the suspension units are similarly prefixed with front left, front right, rear left, or rear right as the case may be.

The various vehicle body instability modes of roll, pitch, bound and articulation can also best be described by referring to Figure 6. Vehicle body roll condition exists when the vehicle body 60 rolls about the vehicle body longitudinal axis 65. A left roll condition, typically encountered in a high speed right turn, exists when the vehicle body 60 rolls to the left, tending to compress the front left and rear left suspension units 101, 301 and expand the front right and rear right suspension units 201, 401 with the risk that the front right and rear right wheels 62, 64 lift off the road surface. A right roll condition exists when the vehicle body 60 rolls about the longitudinal axis 65 in the opposing direction to the right, as would typically be encountered during a high speed left turn.

A vehicle pitch condition exists when the vehicle body 60 pitches about the transverse axis 66. A nose down pitch condition is when the motor vehicle body 60 pitches nose down, tending to compress the front left and front right suspension units 101 , 201 and expand the rear left and rear right suspension units 301 , 401 as would typically occur during heavy braking. A tail down pitch condition exists when the vehicle body 60 pitches tail down about the transverse axis 66, tending to compress the rear left and rear right suspension units 301 , 401 and expand the front left and front right suspension units 101, 201, as may occur during excessive acceleration.

A vehicle bounce condition exists when the vehicle body 60 rises in relation to the wheels above a predetermined neutral height range, or lowers in relation to the wheels below the predetermined neutral height range. In a peak bounce condition, the vehicle body 60 is in a raised position in relation to the wheels, tending to expand each of the suspension units, whilst in a trough bounce condition the vehicle body 60 is lowered in relation to the wheels, tending to compress each of the suspension units. In a vehicle articulation condition, otherwise known as a warp condition, opposing corners of the vehicle body 60 are together either raised or lowered in comparison with their respective wheels. Accordingly, in one articulation mode, the front left and rear right suspension units 101, 401 will be expanded and the front right and rear left suspension units 201 , 301 , will be compressed. In the alternate articulation mode, the opposite will apply. Articulation/warp will typically occur in four-wheel drive vehicles traversing particularly rough terrain and is associated with the front and rear axles becoming inclined in opposing directions relative to a horizontal plane.

Figure 7 schematically depicts a four-wheel active vehicle suspension system configured to control roll of the vehicle body 60. The system effectively consists of two two-wheel active vehicle suspension systems as described above in relation to Figure 2, controlling the front left and front right suspension units 101 , 201 (at the front left and front right wheels 61 , 62) separately to the rear left and rear right suspension units 301,

401 (at the rear left and rear right wheels 63, 64). Two separate primary control valves 30, 30' are provided to enable separate control of the front and rear suspension units. The primary control valves 30, 30' are coupled to a common supply fluid line 41, outlet fluid line 44 and control system 50.

For such a system configured to control roll of the vehicle body, the sensor system 51 is configured to sense one or more parameters which are indicative of a roll condition of the vehicle body. The indicated roll condition may be that the vehicle body 60 is either inclined at a roll angle or has a potential to become inclined at a roll angle. It is preferred that the parameters sensed by the sensor system 51 indicate that the vehicle body 60 has a potential to become inclined at a roll angle, so that pre-emptive action can be taken by the control system 50, rather than reactive action once the vehicle body 60 has already become inclined at an excessive roll angle. Particularly suitable parameters for the sensor system 51 to sense in this regard include the vehicle's speed and steering wheel angle, given that the vehicle body 60 will be most subject to excessive roll when a severe steering input (measured by the steering wheel angle) is made when the vehicle is travelling at high speed. Alternatively, for a more reactive configuration, the parameters sensed may include lateral acceleration of the vehicle body 60, measured by a lateral accelerometer mounted to the vehicle body 60. Parameters that may be used to indicate an actual roll angle include the relative position of the actuator pistons or damper pistons of the left suspension units within their housings as compared to the right suspension units.

When, for example, the sensor system 51 indicates a left roll condition (by, for example, initiation of a high speed right turn), the control system 50 will operate the two primary control valves 30, 30' in a left roll active mode to slidingly displace the sliding spools 37 to the first active position depicted in Figure 3. The actuator lower chambers 1 17, 317 of the front left and rear left suspension units 101 , 301 and the actuator upper chambers 216, 416 of the front right and rear right suspension units 201 , 401 will be pressurised by the fluid pressure pump 40. The actuator upper chamber 1 16, 316 of the front left and front right suspension units 101 , 301 and the actuator lower chamber 217, 417 of the front right and rear right suspension units 201, 401 will communicate with the fluid reservoir 43. The left suspension units 101, 301 will thus have an expansive force applied, stiffening against the rolling moment tending to retract the left suspension units 101 , 103 whereas the right suspension units 201 , 401 will tend to retract. The opposite will apply when a right roll condition is indicated and the primary control valves 30, 30' operate in a right roll active mode. The specific pressure applied will be controlled by the control system 50 by way of the pressure supply valve 42 and outlet pressure control valve 44 based on the severity of the indicated roll condition. The control system 50 will be programmed with control algorithms or lookup tables based upon the dynamic roll characteristics of the vehicle which will be specific to individual vehicle models and may be determined by experimentation and/or computer modelling.

In the system depicted in Figure 7, the two separate primary control valves 30, 30' have been provided to enable separate control of the front and rear suspension units as, in some scenarios, it may be desirable to activate roll control for the front suspension units prior to the rear suspension units or vice versa. Alternatively, a single primary control valve 30 may be utilised as depicted schematically in the alternate four- wheel active vehicle suspension system of Figure 8 which is again configured to control roll. The suspension system depicted in Figure 8 is effectively identical to that of Figure 7, except that a single primary control valve 30 is provided and the auxiliary fluid lines 46, 47 communicate the front and rear systems. Specifically, the front left upper fluid line 121 communicates with the rear left upper fluid line 321 by way of the first auxiliary fluid line 46. The first upper fluid line 121 , front right lower fluid line 222, rear left upper fluid line 321, and rear right lower fluid line 422 and first auxiliary fluid line 46 are thus in permanent communication and define a first fluid circuit. The front left lower fluid line 122 communicates with the rear left lower fluid line 322 by way of the second auxiliary fluid line 47. The front left lower fluid line 122, front right upper fluid line 221, rear left lower fluid line 322 and rear right upper fluid line 422 and second auxiliary fluid line 47 are thus in permanent communication and define a second fluid circuit. This suspension system works identically to that of Figure 7, except that the control system 50 controls a single primary control valve 30 only.

Figure 9 depicts a similar four-wheel active vehicle suspension system to that of Figure 8 except that the Figure 9 suspension system is configured to control pitch of the vehicle body 60.

The suspension system of Figure 9 is identical to the suspension system of

Figure 8 except that different combinations of fluid lines permanently communicate and define different first and second fluid circuits and thus communicate different combinations of actuator chambers. Specifically, the front left and the front right actuator upper chambers 1 16, 216 are in permanent communication with the rear left and rear right actuator lower chambers 317, 417 by way of a first fluid circuit defined by the front left and front right upper fluid lines 121, 221, first auxiliary line 46 and rear left and rear right lower fluid lines 322, 422. The front left and front right actuator lower chambers 117, 217 are in permanent communication with the rear left and rear right actuator upper chambers 316, 416 by way of a second fluid circuit defined by the front left lower and front right lower fluid lines 122, 222, second auxiliary fluid line 47 and rear left and rear right upper fluid lines 321, 421. The primary control valve 30 is configured to selectively communicate the first fluid circuit (by the first auxiliary line 46) or second fluid circuit (by the second auxiliary line 47) with the fluid circuits with the fluid reservoir 43, dependent upon control inputs from the control system 50.

For such a system configured to control pitch of the vehicle body 60, the sensor system 51 is configured to sense one or more parameters which are indicative of a pitch condition of the vehicle body. The indicated pitch condition may be that the vehicle body is either inclined at a pitch angle or has a potential to become inclined at a pitch angle. It is again preferred that the parameters sensed by the sensor system 51 indicate that the vehicle body 60 has a potential to become inclined at a pitch angle, so that pre- emptive action can be taken by the control system 50, rather than reactive action once the vehicle body 60 has already become inclined at an excessive pitch angle.

A particularly suitable parameter for the sensor system 51 to sense so as to indicate a potential nose down pitch angle is associated with brake application, particularly applied brake force given that excessive brake force will typically result in a nose down pitch attitude of the vehicle body 60 which may adversely affect braking performance. For a more reactive configuration, the parameters sensed may include longitudinal acceleration of the vehicle body 60, measured by a longitudinal accelerometer mounted to the vehicle body 60. Parameters that may be used to indicate an actual pitch angle include the relative position of the actuator pistons or damper pistons of the front suspension units within their housings as compared to the rear suspension units.

When, for example, the sensor system 51 indicates a nose down pitch condition (by, for example, excessive braking) the control system 50 will operate the primary control valve 30 in a nose down pitch active mode, such that the front left and front right actuator lower chambers 1 17, 217 and rear left and rear right actuator upper chambers 316, 416 communicate with the fluid pressure pump 40 via the second fluid circuit, whilst the front left and front right upper actuator chambers 116, 216 and rear left and rear right actuator lower chambers 317, 417 communicate with the fluid reservoir 43 via the first fluid circuit. The front suspension units 101 , 201 will thus have an expansive force applied, stiffening against the pitching moment tending to compress the front suspension units 101, 201 whereas the rear suspension units 301, 401 will tend to compress. The opposite will apply when a tail down condition is indicated, such as may occur due to excessive acceleration, when the primary control valve is operated in a tail down pitch active mode. The control system 50 will again control the specific pressure applied based on control algorithms or look-up tables based upon the pitch characteristics of the vehicle.

Figure 10 depicts another similar four-wheel active vehicle suspension system to that of Figure 8 except that the Figure 10 suspension system is configured to control bounce of the vehicle body 60. The suspension system of Figure 10 is again identical to that of Figures 8 and 9, except that different combinations of fluid lines permanently communicate to define different first and second fluid circuits and, thus to communicate different combinations of actuator chambers. In the bounce control suspension system of Figure 10, all of the actuator upper chambers 1 16, 216, 316, 416 are in permanent communication by way of a first fluid circuit defined by the upper fluid lines 121, 221 , 321, 421 and the first auxiliary fluid line 46. Similarly, each of the actuator lower chambers 1 17, 217, 317, 417 is in permanent fluid communication by way of a second fluid circuit defined by the various lower fluid lines 122, 222, 322, 422 and the second auxiliary fluid line 47. The four actuator pistons 1 15, 215, 315, 415 are thus all actuated with equal pressure in the same direction.

For such a system configured to control bounce of the vehicle body 60, the sensor system 51 is configured to sense one or more parameters indicative of a bounce condition of the vehicle body in which a height of the vehicle body is outside a predetermined neutral height range. A peak bounce condition is indicated if the vehicle body height is above the neutral height range whilst a trough bounce condition is indicated if the vehicle body height is below the neutral height range. Suitable parameters that may be sensed by the sensor system 51 to indicate a bounce condition are the relative positions of the actuator pistons or damper pistons within their respective housings and particularly the average actuator piston or damper piston position, averaged throughout the four suspension units 101, 201 , 301, 401.

When, for example, the sensor system 51 indicates a trough bounce condition, the control system 50 will operate the primary control valve 30 in a trough bounce active mode communicating the second fluid circuit (by the second auxiliary line 47) and thus the four actuator lower chambers 1 17, 217, 317, 417 with the pressure supply pump 40. The first fluid circuit (by the first auxiliary fluid line 46) and thus the four actuator upper chambers 1 16, 216, 316, 416 are communicated with the fluid reservoir 43. Each of the suspension units 101, 201, 301, 401 will thus have an expansive force applied tending to lift the vehicle body away from the wheels, effectively stiffening the suspension units against drawing the wheels further toward the vehicle body 60 preventing "bottoming out" of the suspension. The opposite applies when a peak bounce condition is indicated, applying a compressive force to the suspension units 101 , 201, 301, 401, thus tending to lower the vehicle body 60 and stiffening the suspension units against any possible further expansion.

Figure 11 depicts a further similar four-wheel active suspension system which is configured to control articulation or warp, which is particularly applicable for four- wheel drive vehicles travelling over uneven terrain. Again, this suspension system is identical to that of each of Figures 8 to 10 except that different combinations of fluid lines permanently communicate to define different first and second fluid circuits and thus to communicate a different combination of actuator chambers. The front left actuator upper chamber 1 16, front right actuator lower chamber 217, rear left actuator lower chamber 317 and rear right actuator upper chamber 416 are permanently communicated by way of a first fluid circuit defined by the front left upper fluid line 121, front right lower fluid line 222, rear left lower fluid line 322, rear right upper fluid line 421 and first auxiliary fluid line 46. The front left actuator lower chamber 1 17, front right actuator upper chamber 216, rear left actuator upper chamber 316 and rear left actuator lower chamber 417 are each permanently communicated by way of a second fluid circuit defined by the front left lower fluid line 122, front right upper fluid line 221 , rear left upper fluid line 321, rear right lower fluid line 422 and second auxiliary fluid line 47.

For such a system configured to control articulation/warp of the vehicle, the sensor system 51 is configured to sense one or more parameters which are indicative of an articulation/warp condition of the vehicle. Suitable parameters for the sensor system 51 to sense in this regard are the relative position of the actuator pistons or damper pistons of the front left and rear right suspension units 101 , 401 within their housings as compared to those of the front right and rear left suspension units 201 , 301.

When the sensor system 51 indicates that the front left and rear right suspension units 101, 401 are in an extended state as compared to the front right and rear left suspension units 201 , 301 indicating a first articulation mode, the control system 50 will operate the primary control valve 30 in a first articulation active mode to communicate the front left actuator upper chamber 1 16, front right actuator lower chamber 217, rear left actuator lower chamber 317 and rear right actuator upper chamber 416 with the fluid pressure pump 40 via the first fluid circuit and to communicate the front left actuator lower chamber 1 17, front right actuator upper chamber 216, left actuator upper chamber 316 and rear right actuator lower chamber 417 with the fluid reservoir 43 via the second fluid circuit. The front left and rear right suspension units 101, 401 will thus have an expansive force applied and the front right and rear left suspension units 201, 301 will have a compressive force applied so as to rebalance the vehicle body and protect it from warping. When the sensor system 51 indicates that the front left and rear right suspension units 101 , 401 are in a compressed state as compared to the front right and rear left suspension units 201 , 301 , the primary control valve 30 will operate in a second articulation active mode to communicate the opposing actuator chambers to again rebalance the vehicle body 60.

Whilst each of the four-wheel active vehicle suspension systems of Figures 7 to

1 1 are able to control only one of roll, pitch, bounce and articulation, given that various fluid lines and actuator chambers are in permanent communication, a multi-mode four- wheel active vehicle suspension system able to control each of roll, pitch, bounce and articulation independently is depicted in Figures 12 to 16.

Referring firstly to Figure 12, the multi-mode suspension system is similar to each of the mode specific suspension systems of Figures 8 to 1 1, with the addition of three additional four-way directional valves, being a front auxiliary control valve 70, centre auxiliary control valve 71, and rear auxiliary control valve 72. These three auxiliary control valves 70, 71 , 72 provide for communication between actuator chambers in configurations matching each of the mode specific suspension systems of Figures 8 to 1 1 by reconfiguring the make up of the first and second fluid circuits.

The front auxiliary control valve 70 selectively communicates the actuator chambers of the front left and front right suspension units 101, 201. Specifically, in a first position (depicted in Figure 12), the front auxiliary control valve 70 communicates the front left actuator upper chamber 1 16 with the front right actuator lower chamber 217 via the front left upper fluid line 121 and front right lower fluid line 222 whilst also communicating the front left actuator lower chamber 1 17 with the front right actuator upper chamber 216 via the front left lower fluid line 122 and front right upper fluid line 221. In a second position the front auxiliary control valve 70 communicates the front left and front right actuator upper chambers 1 16, 216 via the front left and front right upper fluid lines 121, 221 whilst also communicating the front left and front right actuator lower chambers 1 17, 217 via the front left and front right lower fluid lines 122,

222.

The rear auxiliary control valve 72 selectively communicates the actuator chambers of the rear suspension units 301,401. Specifically, in a first position (depicted in Figure 12), the rear auxiliary control valve 72 communicates the rear left actuator upper chamber 316 with the rear right actuator lower chamber 417 via the rear left upper fluid line 321 and rear right lower fluid line 422 whilst also communicating the rear left actuator lower chamber 317 with the front right actuator upper chamber 216 via the rear left lower fluid line 322 and rear right upper fluid line 421. In a second position the rear auxiliary control valve 72 communicates the rear left and rear right actuator upper chambers 316, 416 via the rear left and rear right upper fluid lines 321, 421 whilst also communicating the rear left and rear right actuator chambers 317, 417 via the rear left and rear right lower fluid lines 322, 422.

The centre auxiliary control valve 71 selectively communicates the actuator chambers of the front suspension units 101, 201 with those of the rear suspension units 301, 401. The front left upper fluid line 121 communicates with the centre control valve 71 by way of the first auxiliary fluid line 46. The first lower fluid line 122 communicates with the centre auxiliary control valve 71 by way of the second auxiliary fluid line 47. The rear left upper fluid line 321 communicates with the centre auxiliary control valve 71 by way of a third auxiliary fluid line 48. The rear left lower fluid line 322 communicates with the centre auxiliary control valve 71 by way of a fourth auxiliary fluid line 49. The centre auxiliary control valve, in a second position (depicted in Figure 12), communicates the front left actuator upper chamber 1 16 with the rear left actuator upper chamber 316 via the front left upper fluid line 121, first auxiliary fluid line 46, third auxiliary fluid line 48 and rear left upper fluid line 321 whilst also communicating the front left actuator lower chamber 1 17 with the rear left actuator lower chamber 317 via the front left lower fluid line 122, second auxiliary fluid line 47, fourth auxiliary fluid line 49 and rear left lower fluid line 322. In a first position, the centre auxiliary control valve 71 communicates the front left actuator upper chamber 1 16 with the rear left actuator lower chamber 317 via the front left upper fluid line 121, first auxiliary fluid line 46, fourth auxiliary fluid line 49 and rear left lower fluid line 322 whilst also communicating the front left actuator lower chamber 1 17 with the rear left actuator upper chamber 316 via the front left lower fluid line 122, second auxiliary fluid line 47, third auxiliary fluid line 48 and rear left upper fluid line 321. With the front auxiliary control valve 70 in the first position, rear auxiliary control valve 72 in the first position, and centre auxiliary control valve in the second position, as depicted in Figure 12, the same combination of actuator chambers are in communication as per the roll control suspension system of Figure 8. A first fluid circuit is thus defined by the front left upper fluid line 121, front right lower fluid line 222, first auxiliary fluid line 46, third auxiliary fluid line 48, rear left upper fluid line 321 and rear right lower fluid line 422. A second fluid circuit is defined by the front right upper fluid line 221 , front left lower fluid line 122, second auxiliary fluid line 47, fourth auxiliary fluid line 49, rear left lower fluid line 322 and rear right upper fluid line 421.

With the specific valve positioning schematically depicted in Figure 12, however, the primary control valve 30 is positioned in the passive position in which all actuator chambers communicate with the fluid reservoir 43 via the first and second auxiliary fluid lines 46, 47. With this valve positioning, no expansive or compressive forces apply to any of the suspension units, and the suspension units all operate in a regular passive mode by way of the individual damper elements. Some additional damping, may, however be provided by way of the outlet pressure control valve 45 if desired. Whilst the primary control valve 30 is in the passive position, it is of no importance as to whether each of the auxiliary control valves 70, 71, 72 are in their first or second positions, given that all actuator chambers will communicate with the fluid reservoir irrespective of the position of the auxiliary control valves 70, 71 , 72.

Rather than locating the auxiliary control valves 70, 71, 72 between the front suspension units 101, 201, rear suspension units 301 , 401 and between the left suspension units 101, 301 the same fluid communication solution can be readily achieved by locating the auxiliary control valves 70, 71 , 72 between the actuator chambers of any three pairs of suspension units 101 ,201 ,301. For example, any of the three auxiliary control valves 70, 71, 72 could be moved to be operatively positioned between the right suspension units 201 ,401.

Figure 13 depicts the multi-mode suspension system with the auxiliary control valves 70, 71, 72 in the same positions as depicted in Figure 12, being the roll control configuration. The primary control valve 31 is in a left roll active position, providing fluid pressure to the front left actuator lower chamber 1 17, rear left actuator lower chamber 317, front right actuator upper chamber 216 and rear right actuator upper chamber 416 via the second fluid circuit. The front left actuator upper chamber 1 16, rear left actuator upper chamber 316, front right actuator lower chamber 217 and rear right actuator lower chamber 417 all communicate with the fluid reservoir 43 via the first fluid circuit.

Figure 14 depicts the multi-mode suspension system, with the auxiliary control valves 70, 71, 72 positioned in a pitch control configuration. Each of the auxiliary control valves 70, 71 , 72 is in the alternate position to the corresponding position for the roll control configuration of Figure 13. That is, the front auxiliary control valve 70 is in the second position, communicating the front left actuator upper chamber 1 16 with the front right actuator upper chamber 216 via the front left upper fluid line 121 and front right upper fluid line 221 whilst also communicating the front left actuator lower chamber 1 17 with the front right actuator lower chamber 217 via the front left lower fluid line 122 and front right lower fluid line 222. The rear auxiliary control valve 72 is also in the second position, communicating the rear left actuator upper chamber 316 with the rear right actuator upper chamber 416 via the rear left upper fluid line 321 and rear right upper fluid line 421 whilst also communicating the rear left actuator lower chamber 317 with the rear right actuator lower chamber 417 via the rear left lower fluid line 322 and rear right lower fluid line 422.

The centre auxiliary control valve 71 is in its first position communicating the front left actuator upper chamber 1 16 with the rear left actuator lower chamber 317 via the front rear upper fluid line 121 , first and fourth auxiliary fluid lines 46, 49 and rear left lower fluid line 322 whilst also communicating the front left actuator lower chamber 1 17 with the rear left actuator upper chamber 316 via the front left lower fluid line 122, second and third auxiliary fluid lines 47, 48 and the front left rear fluid line 321. This auxiliary valve positioning provides the same actuator chamber communication as the pitch control suspension system of Figure 9. The first fluid circuit is thus defined by the front left upper fluid line 121 , front right upper fluid line 221, first auxiliary fluid line 46, fourth auxiliary fluid line 49, rear left lower fluid line 322 and rear right lower fluid line 422. The second fluid circuit is defined by the front left lower fluid line 122, front right lower fluid line 222, second auxiliary fluid line 47, third auxiliary fluid line 48, rear left upper fluid line 321 and rear right upper fluid line 421. The primary control valve 30 is depicted in a tail down pitch active position, communicating the front left actuator upper chamber 1 16, front right actuator upper chamber 216, rear left actuator lower chamber 317 and rear right actuator lower chamber 417 with the fluid pressure supply pump 40. In Figure 15, the multi-mode suspension system is depicted with the auxiliary control valves 70, 71, 72 positioned in a bounce control configuration. The front auxiliary control valve 70 and rear auxiliary control valve 72 are each in their second position, the same as depicted in the pitch control configuration of Figure 14.

The centre auxiliary control valve 71 is in its second position, communicating the front left actuator upper chamber 1 16 with the rear left actuator upper chamber 316 via the front left upper fluid line 121, first and third auxiliary fluid lines 46, 48 and rear left upper fluid line 321 whilst also communicating the front left actuator lower chamber 1 17 with the rear left actuator lower chamber 317 via the front left lower fluid line 122, second and fourth auxiliary fluid lines 47, 49 and rear left lower fluid line 322. This auxiliary valve positioning provides the same actuator chamber communication as the bounce control suspension system of Figure 10. The first fluid circuit is thus defined by the front left upper fluid line 121, the front right upper fluid line 221, first auxiliary fluid line 46, third auxiliary fluid line 48, rear left upper fluid line 321 and rear right upper fluid line 421. The second fluid circuit is defined by the front left lower fluid line 122, front right lower fluid line 222, second auxiliary fluid line 47, fourth auxiliary fluid line 49, rear left lower fluid line 322 and rear right lower fluid line 422. The primary control valve 30 is depicted in a peak bounce active position communicating each of the actuator chambers 1 16, 216, 316, 416 with the fluid pressure supply pump 40.

In Figure 16, the multi-mode suspension system is depicted with the auxiliary control valve 70, 71 , 72 positioned in an articulation control configuration. Each of the actuator control valves 70, 71, 72 is depicted in its first position, providing the same actuator chamber communication as the articulation control suspension system of Figure 1 1. The first fluid circuit is thus defined by the front left upper fluid line 121 , the front right lower fluid line 222, the first auxiliary fluid line 46, fourth auxiliary fluid line 49, rear left lower fluid line 322 and rear right upper fluid line 421. The second fluid circuit is defined by the front right upper fluid line 221 , front left lower fluid line 122, second auxiliary fluid line 47, third auxiliary fluid line 48, rear left upper fluid line 321 and rear right lower fluid line 422. The primary control valve 30 is depicted in an articulation active position, communicating the front left actuator lower chamber 1 17, front right actuator upper chamber 216, rear left actuator upper chamber 316 and rear right actuator lower chamber 417 with the fluid pressure supply pump 40. For all of the above-described suspension systems, the primary control valve 30 will operate opposite to that described above, (i.e., interchanging communication of the first and second fluid circuits with the fluid pressure supply pump 40 and the fluid reservoir 43) if the actuator piston connectors 1 18, 218, 318, 418 of the various suspension units are arranged to be connected to the damper lower end rather than the damper upper end (that is, the actuator piston connector extends downwardly rather than upwardly).

Whilst the multi-mode suspension systems of Figures 12 to 16, employing three separate control valves, 70, 71 , 72, enables independent control of roll, pitch, bounce and warp, it is envisaged that either the central auxiliary control valve 71 or both the front and rear auxiliary control valves 70, 72 could be omitted when more limited functionality is required. For example, with omission of the front and rear auxiliary control valves 70, 72, the central auxiliary control valve 71 alone can be utilised to independently control bounce and pitch only or roll and articulation only, depending upon whether the actuator upper chambers of the left suspension units are permanently communicated with the actuator upper chambers or actuator lower chambers of the right suspension units.

An example of such a two mode suspension system, which is identical to that of

Figures 12 to 16 apart from omission of the front and rear auxiliary control valves 70, 72, is depicted in Figures 17 and 18. In this two mode suspension system configured to control roll and articulation, the left actuator upper chambers 1 16, 316 are in permanent communication with the right actuator lower chambers 207, 417, whilst the left actuator lower chambers 1 17, 317 are in permanent communication with the right actuator upper chambers 216, 416. In a roll control configuration depicted in Figure 17, the centre auxiliary control valve 71 is in the second position such that the first fluid circuit is defined by the front left upper fluid line 121 , front right lower fluid line 222, first auxiliary fluid line 46, third auxiliary fluid line 48, rear left upper fluid line 321 and rear right lower fluid line 422. The second fluid circuit is defined by the front right upper fluid line 221 , the front left lower fluid line 122, second auxiliary fluid line 47, fourth auxiliary fluid line 49, rear left lower fluid line 322 and rear right upper fluid line 421. The first and second fluid circuits are thus identical to those of the multi-mode suspension system roll control configuration of Figure 13. In an articulation control configuration depicted in Figure 18, the two mode suspension system has the centre auxiliary control valve 71 in the first position such that the first and second fluid circuits are identical to those of the multi-mode suspension system in the articulation control configuration of Figure 16. This two mode suspension system, utilising only a single auxiliary control valve 71 , will be a more cost effective solution to the multi- mode suspension system of Figures 12 to 16 when active pitch and bounce control is not required.

Similarly, either bounce and roll or pitch and articulation can be controlled with omission of the central auxiliary control valve, depending upon the manner in which the actuator chambers are communicated front to rear.

Figure 19 shows one embodiment of a passive hydraulically interconnected suspension (PHIS) system for a vehicle having a vehicle body and four wheels, the suspension system being generally indicated by numeral 500. This embodiment is configured to resist vehicle roll. The suspension system 500 has a first suspension unit 502 mounted to a front left wheel, a second suspension unit 504 mounted to a front right wheel, a third suspension unit 506 mounted to a rear left wheel and a fourth suspension unit 508 mounted to a rear right wheel. Each of the suspension units 502- 508 are similar or identical to that shown in the other figures, especially Figure 1.

The passive suspension system 500 has a first upper fluid line 510 communicating with an upper port 512 of the first suspension unit 502, a first lower fluid line 514 communicating with a lower port 516 of the first suspension unit 502, a second upper fluid line 517 communicating with an upper port 518 of the second suspension unit 504, a second lower fluid line 520 communicating with a lower port 522 of the second suspension unit 504, a third upper fluid line 524 communicating with an upper port 526 of the third suspension unit 506, a third lower fluid line 528 communicating with a lower port 530 of the third suspension unit 506, a fourth upper fluid line 532 communicating with an upper port 534 of the fourth suspension unit 508 and a fourth lower fluid line 536 communicating with a lower port 538 of the fourth suspension unit 508. The passive suspension unit 500 also has two fluid circuits 540 and 542. A first fluid circuit 540 is formed by connecting the first upper fluid line 510, the second lower fluid line 520, the third upper fluid line 524 and the fourth lower fluid line 536. A second fluid circuit 542 is formed by connecting the first lower fluid line 514, the second upper fluid line 517, the third lower fluid line 528, and the fourth upper fluid line 532. Each of the fluid circuits 540 and 542 have connected to them a respective accumulator 544, 546 via a respective damper valve 548, 550.

When a vehicle turns, which has the suspension system 500 fitted, under a steering input at high speed, an anti-roll couple is generated by the fluid circuits and is applied to the vehicle chassis. For example, in a roll situation the pressurized fluid in circuit 542, may flow into the lower chambers 560 and 562 of the left hand units 502 and 506 and into the upper chambers 564 and 568 of the right hand units 504 and 506. Consequently, the roll stiffness will increase significantly.

The accumulators 544 and 546 are pre-charged with a specific pressure between 10 and 30 bars. The fluid lines 540 and 546 consists of hoses and pipes such as 570, and curve fittings such as 572. The fluid circuit configuration shown in Figure 19 may provide additional roll stiffness in response to roll motion of the chassis without changes in stiffness of other modes such as bounce, pitching and articulation. Some variations of the embodiment shown in Figure 19 break the compromise between hide comfort, road handling and vehicle handling inherent in most existing passenger cars, possibly preventing roll over.

Figures 20, 21 and 22 show alternative embodiments of passive hydraulically interconnected suspension systems for resisting pitch, bounce and assisting articulation, respectively. These are similar to the PHIS system shown in Figure 19 except the fluid circuits are configured to connect different fluid lines. In some embodiments, a PHIS installed on a vehicle is arranged for swaping between all the different configurations shown in Figs. 19-22 through the use of valves (such as those in figures 3,4 and 5) which reconfigure the fluid circuits as required. It will be appreciated that the active vehicle systems described above could be simplified to achieve this. The use of these valves The reconfiguration may be initiated on a signal from an onboard system which may sense, for example, strong braking. In this case, the system would be reconfigured to resist pitch. Similarly, a sensor associated with the vehicle's steering system may detect a sharp turn of the steering wheel, and the system may then be reconfigured to resist roll.

Passive vehicle suspension systems retain the main advantages of both passive independent and interconnected suspensions, and in many circumstances are desirable for use in passenger cars, particularly four wheel drives. The systems use no additional energy. Suspension systems work most of the time just like a conventional passive suspension system but also provide additional roll, bounce, pitch and in some circumstances articulation stiffness when the vehicle is subjected to large steering or brake inputs at high speed. The additional roll and pitching stiffness provided in response to the vehicle dynamic state may prevent the vehicle rolling over, and hence the braking performance and may also improve safety. Each suspension unit such as 502-508 operates as conventional shock absorbers when there is no demand for additional functionality.

The auxiliary drive arrangements described above will also be applicable to other suspension systems employing interconnected double acting cylinders, either arranged to operate in an active or passive manner, and not just the hybrid suspension unit described above in relation to Figure 1.

Claims

1. A vehicle suspension unit having a longitudinal axis and comprising: a damper element extending along said longitudinal axis between a damper upper end and a damper lower end, said damper element providing for damped longitudinal displacement of said damper upper end relative to said damper lower end; a vehicle body mount fixed in relation to said damper upper end; a wheel mount fixed in relation to said damper lower end; and an actuator element coaxially arranged in relation to said damper element, said actuator element including: an actuator housing defining a longitudinally extending fluid filled actuator cavity, said actuator housing being fixed in relation to one of said damper upper end and said damper lower end; an actuator piston mounted in said actuator cavity for reciprocal longitudinal displacement through said actuator cavity, said actuator piston dividing said actuator cavity into an actuator upper chamber and an actuator lower chamber; an actuator piston connector fixed to said actuator piston and longitudinally extending through said actuator housing, said actuator piston connector being fixed in relation to the other of said damper upper end and said damper lower end; an upper port extending through said actuator housing communicating with said actuator upper chamber; and a lower port extending through said actuator housing communicating with said actuator lower chamber.

2. A vehicle suspension unit defined by claim 1 wherein said damper element comprises: a damper housing defining a longitudinally extending liquid filled damper cavity, said damper housing further defining one of said damper upper end and said damper lower end; a damper piston mounted in said damper cavity for damped longitudinal reciprocal motion through said damper cavity, said damper piston dividing said damper cavity into a damper upper chamber and a damper lower chamber; and a damper piston connector fixed to said damper piston and longitudinally extending through said damper housing, said damper piston connector defining the other of said damper upper end and said damper lower end.

3. A vehicle suspension unit defined by either claim 1 or 2 further comprising a spring longitudinally extending between a spring upper end and a spring lower end, said spring upper end being fixed in relation to said damper upper end and said spring lower end being fixed in relation to said damper lower end.

4. A vehicle suspension unit defined by any one of the preceding claims wherein said actuator housing extends circumferentially about said damper housing.

5. A vehicle suspension unit defined by any one of claims 2 to 4 wherein said damper housing is in the form of a damper cylinder, with said damper piston being cylindrical and said damper piston connector being in the form of a piston rod.

6. A vehicle suspension unit defined by any one of claims 2 to 5 wherein the actuator housing typically has an annular cross-section, an inner wall of said actuator housing being defined by a peripheral wall of said damper housing, said actuator piston having an annular cross-section.

7. A vehicle suspension unit defined by any one of claims 2 to 6 wherein said damper housing extends circumferentially about said actuator housing.

8. An active vehicle suspension system comprising: a first suspension unit as defined by any one of claims 1 to 7 connecting a first wheel to a vehicle body, said vehicle body mount of said first suspension unit being mounted to the vehicle body and said wheel mount of said first suspension unit being mounted to the first wheel; a second suspension unit as defined by any one of claims 1 to 7 connecting a second wheel to the vehicle body, said vehicle body mount of said second suspension unit being mounted to the vehicle body and said wheel mount of said second suspension unit being mounted to the second wheel; a first upper fluid line communicating with said upper port of said first suspension unit; a first lower fluid line communicating with said lower port of said first suspension unit; a second upper fluid line communicating with said upper port of said second suspension unit; a second lower fluid line communicating with said lower port of said second suspension unit, a fluid pressure supply; a fluid reservoir; a valve arrangement operable in an actuator standby mode to communicate each of said first upper fluid line, said first lower fluid line, said second upper fluid line, and said second lower fluid line with said fluid reservoir, said valve arrangement further being operable in at least one actuator active mode to selectively communicate: one of said first upper fluid line and said first lower fluid line with said fluid pressure supply and the other of said first upper fluid line and said first lower fluid line with said fluid reservoir; and one of said second upper fluid line and said second lower fluid line with said fluid pressure supply and the other of said second upper fluid line and said second lower fluid line with said fluid reservoir; a sensor system for sensing one or more vehicle parameters indicative of a condition of the vehicle, and a control system for controlling said valve arrangement dependent upon said parameter(s) sensed by said sensor system.

9. An active vehicle suspension system define by claim 8 wherein said fluid pressure supply is pressurised by a power steering system of the vehicle.

10. An active vehicle suspension system define by either claim 8 or claim 9 wherein said first upper fluid line is in permanent communication with said second lower fluid line, and said first lower fluid line is in permanent communication with said second upper fluid line.

11. An active vehicle suspension system defined by any one of claims 8 to 10 further comprising: a third suspension unit as defined by any one of claims 1 to 7 connecting a third wheel to a vehicle body, said vehicle body mount of said third suspension unit being mounted to the vehicle body and said wheel mount of said third suspension unit being mounted to the third wheel; a fourth suspension unit as defined by any one of claims 1 to 7 connecting a fourth wheel to the vehicle body, said vehicle body mount of said fourth suspension unit being mounted to the vehicle body and said wheel mount of said fourth suspension unit being mounted to the fourth wheel; a third upper fluid line communicating with said upper port of said third suspension unit; a third lower fluid line communicating with said lower port of said third suspension unit; a fourth upper fluid line communicating with said upper port of said fourth suspension unit; and a fourth lower fluid line communicating with said lower port of said fourth suspension unit; said valve arrangement being further operable in said actuator standby mode to communicate said third upper fluid line, said third lower fluid line, said fourth upper fluid line and said fourth lower fluid line with said fluid reservoir, said valve arrangement being still further operable in at least one said actuator active mode to selectively communicate; one of said third upper fluid line and said third lower fluid line with said fluid pressure supply and the other of said third upper fluid line and said third lower fluid line with said fluid reservoir; and one of said fourth upper fluid line and said fourth lower fluid line with said fluid pressure supply and the other of said fourth upper fluid line and said fourth lower fluid line with said fluid reservoir.

12. An active vehicle suspension system defined by claim 1 1 wherein said third upper fluid line is in permanent communication with said fourth lower fluid line and said third lower fluid line is in permanent communication with said fourth upper fluid line.

13. An active vehicle suspension system defined by any one of claims 8 to 12 wherein said sensor arrangement is configured to sense one or more parameters indicative of a roll condition of said vehicle body in which said vehicle body is inclined at a roll angle or has a potential to become inclined at a roll angle, said control system being configured to control said valve arrangement to: operate said valve arrangement in a first roll active mode when said roll condition is a first roll condition, communicating said first upper fluid line, said second lower fluid line, said third upper fluid line and said fourth lower fluid line with said fluid pressure supply and said first lower fluid line, said second upper is fluid line, said third lower fluid line and said fourth upper fluid line with said fluid reservoir; and operate said valve arrangement in a second roll active mode when said roll condition is a second roll condition, communicating said first upper fluid line, said second lower fluid line, said third upper fluid line and said fourth lower fluid line with said fluid reservoir, and said first lower fluid line, said second upper fluid line, said third lower fluid line and said fourth upper fluid line with said fluid pressure supply.

14. An active vehicle suspension system defined by any one of claims 8 to 12 wherein said sensor system is configured to sense one or more parameters indicative of a bounce condition of said vehicle body in which a height of the vehicle body is outside of a predetermined neutral height range, said control system being configured to control said valve arrangement to: operate said valve arrangement in a first bounce active mode when said bounce condition is a first bounce condition in which said vehicle body height is above said neutral height range, communicating said first upper fluid line, said second upper fluid line, said third upper fluid line and said fourth upper fluid line with said hydraulic pressure supply and said first lower fluid line, said second lower fluid line, said third lower fluid line, and said fourth lower fluid line with said fluid reservoir; operate said valve arrangement in a second bounce active mode when said bounce condition is a second bounce condition in which said vehicle body height is below said neutral height range, communicating said first upper fluid line, said second upper fluid line, said third upper fluid line, and said fourth upper fluid line with said fluid reservoir and said first lower fluid line, said second lower fluid line, said third lower fluid line and said fourth lower fluid line with said fluid pressure supply.

15. An active vehicle suspension system defined by any one of claims 8 to 12 wherein said sensor system is configured to sense one or more parameters indicative of a pitch condition of said vehicle body in which said vehicle body is inclined at a pitch angle or has a potential to become inclined at a pitch angle, said control system being configured to control said valve arrangement to: operate said valve arrangement in a first pitch active mode when said pitch condition is a first pitch condition, communicating said first upper fluid line, said second upper fluid line, said third lower fluid line and said fourth lower fluid line with said fluid reservoir and said first lower fluid line, said second lower fluid line, said third upper fluid line and said fourth upper fluid line with said fluid pressure supply; and operate said valve arrangement in a second pitch active mode when said pitch condition is a second down pitch condition communicating said first upper fluid line, said second upper fluid line, said third lower fluid line, and said fourth lower fluid line with said fluid pressure supply and said first lower fluid line, said second lower fluid line, said third upper fluid line and said fourth upper fluid line with said fluid reservoir.

16. An active vehicle suspension system defined by any one of claims 8 to 12 wherein said sensor system is configured to sense one or more parameters indicative of an articulation condition of said vehicle, said control system being configured to control said valve arrangement to: operate said valve arrangement in a first articulation active mode when said articulation condition is a first articulation condition, communicating said first upper fluid line, said second lower fluid line, said third lower fluid line and said fourth upper fluid line with said fluid reservoir and said first lower fluid line, said second upper fluid line, said third upper fluid line and said fourth lower fluid line with said fluid pressure supply; and operate said valve arrangement in a second articulation active mode when said articulation condition is a second articulation condition communicating said first upper fluid line, said second lower fluid line, said third lower fluid line, and said fourth upper fluid line with said fluid pressure supply and said first lower fluid line, said second upper fluid line, said third upper fluid line and said fourth lower fluid line with said fluid reservoir.

17. An active vehicle suspension system defined by any one of claims 8 to 16 wherein said valve arrangement includes a primary control valve operable to selectively communicate one of a first fluid circuit and a second fluid circuit with said fluid pressure supply pump and the other of said first fluid circuit and said second fluid circuit with said fluid reservoir; wherein said first fluid circuit comprises: one of said first upper fluid line and said first lower fluid line; one of said second upper fluid line and said second lower fluid line; one of said third upper fluid line and said third lower fluid line; and one of said fourth upper fluid line and said fourth lower fluid line; further wherein said second fluid circuit comprises: the other of said first upper fluid line and said first lower fluid line; the other of said second upper fluid line and said second lower fluid line; the other of said third upper fluid line and said third lower fluid line, and the other of said fourth upper fluid line and said fourth lower fluid line

wherein the valve arrangement may further comprise one or more auxiliary control valves operable to selectively configure said first fluid circuit and said second fluid circuit between at least two configurations selected from a group consisting of a roll control configuration, a pitch control configuration, a bounce control configuration and an articulation control configuration, wherein in said roll control configuration, said first fluid circuit compπses said first upper fluid line, said second lower fluid line, said third upper fluid line and said fourth lower fluid line, in said pitch control configuration, said first fluid circuit comprises said first upper fluid line, said second upper fluid line, said third lower fluid line and said fourth lower fluid line, in said bounce control configuration, said first fluid circuit compnses said first upper fluid line, said second upper fluid line, said third upper fluid line and said fourth upper fluid line, in said articulation control configuration, said first fluid circuit comprises said first upper fluid line, said second lower fluid line, said third lower fluid line and said fourth upper fluid line

18 A vehicle suspension system for a vehicle having a vehicle body and four wheels, said suspension system comprising a first suspension unit mounted to a front left wheel, a second suspension unit mounted to a front right wheel, a third suspension unit mounted to a rear left wheel, and a fourth suspension unit mounted to a rear right wheel, each said suspension unit having vehicle body mount mounted to the vehicle body and a wheel mount mounted to the respective wheel, a housing defining a longitudinally extending fluid filled cavity, said housing being fixed in relation to one of said vehicle body mount and said wheel mount, a piston mounted in said cavity for reciprocal longitudinal displacement through said cavity, said piston dividing said cavity into an upper chamber and a lower chamber, a piston connector fixed to said piston and longitudinally extending through said housing, said piston connector being fixed in relation to the other of said vehicle body mount and said wheel mount; an upper port extending through said housing communicating with said upper chamber; and a lower port extending through said housing communicating with said lower chamber; said suspension system further comprising: a first upper fluid line communicating with said upper port of said first suspension unit; a first lower fluid line communicating with said lower port of said first suspension unit; a second upper fluid line communicating with said upper port of said second suspension unit; a second lower fluid line communicating with said lower port of said second suspension unit; a third upper fluid line communicating with said upper port of said third suspension unit; a third lower fluid line communicating with said lower port of said third suspension unit; a fourth upper fluid line communicating with said upper port of said fourth suspension unit; a fourth lower fluid line communicating with said lower port of said fourth suspension unit; a valve arrangement operable to selectively configure a first fluid circuit and a second fluid circuit between at least two configurations selected from a group consisting of a roll control configuration, a pitch control configuration, a bounce control configuration and an articulation control configuration, wherein; in said roll control configuration, said first fluid circuit comprises said first upper fluid line, said second lower fluid line, said third upper fluid line and said fourth lower fluid line; in said pitch control configuration, said first fluid circuit comprises said first upper fluid line, said second upper fluid line, said third lower fluid line and said fourth lower fluid line; in said bounce control configuration, said first fluid circuit comprises said first upper fluid line, said second upper fluid line, said third upper fluid line and said fourth upper fluid line; in said articulation control configuration, said first fluid circuit comprises said first upper fluid line, said second lower fluid line, said third lower fluid line and said fourth upper fluid line.

19. A vehicle suspension unit having a longitudinal axis and comprising: a damper element extending along said longitudinal axis between a damper upper end and a damper lower end, said damper element providing for damped longitudinal displacement of said damper upper end relative to said damper lower end; and an actuator element coaxially arranged in relation to said damper element.

20. A vehicle suspension unit having a longitudinal axis and comprising: a damper element extending along said longitudinal axis between a damper upper end and a damper lower end, said damper element providing for damped longitudinal displacement of said damper upper end relative to said damper lower end; and an actuator element coaxially arranged in relation to said damper element, said actuator element comprising an actuator housing defining a longitudinally extending fluid filled actuator cavity, and said actuator element also comprising an actuator piston mounted in said actuator cavity for reciprocal longitudinal displacement through said actuator cavity, said actuator piston dividing said actuator cavity into an actuator upper chamber and an actuator lower chamber; an upper port communicating with said actuator upper chamber; and a lower port communicating with said actuator lower chamber.

21. A vehicle suspension system, said suspension system comprising: a first suspension unit according to the second aspect of the invention arranged to be mounted to a front left wheel assembly; a second suspension unit according to the second aspect of the invention arranged to be mounted to a front right wheel assembly; a third suspension unit according to the second aspect of the invention arranged to be mounted to a rear left wheel assembly; and a fourth suspension unit according to the second aspect of the invention arranged to be mounted to a rear right wheel assembly, a first upper fluid line communicating with said upper port of said first suspension unit; a first lower fluid line communicating with said lower port of said first suspension unit; a second upper fluid line communicating with said upper port of said second suspension unit; a second lower fluid line communicating with said lower port of said second suspension unit; a third upper fluid line communicating with said upper port of said third suspension unit; a third lower fluid line communicating with said lower port of said third suspension unit; a fourth upper fluid line communicating with said upper port of said fourth suspension unit; a fourth lower fluid line communicating with said lower port of said fourth suspension unit; a first fluid circuit comprising two or more of said fluid lines; and a second fluid circuit comprising another two or more of said fluid lines.

22. A vehicle suspension system comprising: a first suspension unit according to the second aspect arranged to connect a first wheel to a vehicle body; a second suspension unit according to the second aspect arranged to connect a second wheel to the vehicle body; a first upper fluid line communicating with said upper port of said first suspension unit; a first lower fluid line communicating with said lower port of said first suspension unit; a second upper fluid line communicating with said upper port of said second suspension unit; a second lower fluid line communicating with said lower port of said second suspension unit.

23. A primary control valve comprising: a valve body containing an elongate cavity; a first port; a second port; a supply port; and a pair of outlet ports.