Self-energizing, self-levelling controllable damper unit for a vehicle suspension

A self-energizing self-levelling damper unit for use in a vehicle suspension system comprising:

• a piston and cylinder arrangement for connection between two relatively movable portions of the system, said piston and cylinder arrangement containing a damping fluid and defining two piston members and three chambers of variable volume dependent upon the relative positions of the piston members within the chambers of the arrangement;
• a first gas reservoir to which an internal pressure of one of said chambers is communicated and which varies in volume to compensate for a difference in the volume of the piston and cylinder arrangement as the components of the arrangement move relative to one another;
• a second gas reservoir to which an internal pressure of another of said chambers is communicated;
• valve means for regulating a flow of the damping fluid between a first chamber and a second chamber and between a second chamber and a third chamber, said first, second and third chambers being said three chambers of variable volume;
• and
• control means connected to said valve means to permit the damping fluid to flow in a closed loop from the third chamber to the second chamber and thence to the first chamber and vice versa on relative movement of the components of the piston and cylinder arrangement until a desired position is reached, and said control means for preventing the flow of the damping fluid in said closed loop between at least said first chamber and said second chamber and for controlling the movement of fluid between said second chamber and said third chamber for continuously variable damping of said relative movement of the portions of the system.