Active suspensions for vehicles

An active suspension system for a vehicle comprising:

• (a) a main control loop including a suspension actuator, said loop including first comparator means for receiving an input signal representative of a suspension demand and a feed back signal representative of the response of said actuator to said demand, said input and feed back signals being compared in said first comparator means to provide a deficiency signal indicative of the deficiency between said demand and the response of said actuator, and a low-pass filter in said main control loop through which said deficiency signal passes, and
• (b) a second control loop providing a restraining signal for restraining operation of said actuator, said second loop comprising means for deriving said restraining signal from a suspension parameter which varies with operation of said actuator, and a high pass filter in said second control loop through which said restraining signal is passed and which is substantially complementary to said low-pass filter, and
• (c) second comparator means coupled to said main control loop and to said second control loop for comparing said deficiency signal and said restraining signal after said signals have passed through said low-pass and high-pass filters respectively, and operative in response to said comparison to provide a resultant signal for controlling said actuator.