The application of a programmable servo controller to state control of an electrohydraulic active suspension

Abstract

Fully active electrohydraulic control of a 1/4 car test rig is considered from both a modelling and experimental point of view. Both pole assignment (PA) and linear quadratic control (LQC) techniques are used to design the state feedback gains with a view to achieving an optimum body acceleration characteristic, based on a validated linearized mathematical model. Computer simulation of the complete system suggests that the LQ control design approach gives the better performance characteristic. An industrial programmable servo controller (PSC) is implemented to drive two servo valves, one used for the road input actuator and the other used for the active control actuator. Programmable features are introduced, such as gain scheduling and state gain switching to achieve improved control. It is shown that although body displacement compensation is naturally achieved for road input changes, the global optimum design for acceleration transmissibility could not be achieved, due to practical limitations caused by the predicted low transducer gain between wheel and body. A further feature of the programmable controller approach was the ability to change state feedback gains during operation. This was found necessary to move the suspension from its initial rest position to its operating position. However, an improved performance in body acceleration amplitude control was still possible compared with the optimum passive suspension theoretical predictions.