Vehicle suspension system

A suspension system for a pair of spaced-apart wheels on a vehicle, the system comprising:

• a spring means and a damping means associated with each wheel and working in parallel such that their forces are additive,
• a hydraulic actuator mounted in series with the spring means such that the force in the actuator equals either the spring force or the sum of the spring force and damping force,
• each hydraulic actuator connected between the wheel and a chassis of the vehicle so as to transmit a force from the wheel to the chassis,
• each hydraulic actuator having a variable volume fluid chamber, said fluid chamber being filled with a substantially incompressible hydraulic fluid,
• an hydraulic fluid transfer line communicating between the fluid chambers of both hydraulic actuators,
• a pump mounted in the hydraulic fluid transfer line, said pump having a fluid inlet and a fluid outlet,
• fluid control valve means associated with the pump mounted in the fluid transfer line,
• said control valve means being operable to isolate both hydraulic actuator fluid chambers from each other and from the pump or to selectively connect a first hydraulic actuator fluid chamber to an inlet of the pump and connect a second hydraulic actuator fluid chamber to an outlet of the pump,
• means for sensing at least one vehicle attitude parameter, the sensing means being operatively connected to a controller,
• said controller having means for regulating operation of the control valve means in response to said sensed vehicle attitude parameter or parameters to counteract one or both of lateral roll and longitudinal pitch of the vehicle.