This paper describes an active suspension employing an electrohydraulic servo system in which pressure control valves are applied for the first time. The suspension is controlled by a microprocessor and acceleration sensors. This paper describes the theoretical and experimental analyses which were conducted in developing this system, including the studies of the active control system, vehicle system dynamics and transmission of vertical inputs from the road surface. This system features a skyhook damper which can reduce body vibration to less than one-half that of conventional suspensions at low frequencies. This is accomplished by applying an active damping force to the body proportional to its absolute velocity. The hydraulic system has passive damping characteristics dependent on the frequencies of road inputs. Optimization of these characteristics results in a reduction of vibration caused by high-frequency road surface inputs. An active moment control function is provided, using lateral and longitudinal sensors, which can reduce body pitching and rolling caused by braking, accelerating and lane changing. Optimization of the electrohydraulic servo system parameters has resulted in improved ride comfort and handling properties.
Abstract