Design of Active Suspension Control Systems for a Flexible Vehicle Body

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From a viewpoint of energy saving, it is required to design a lightweight vehicle body for high speed ground vehicles. But some problems will occur such as an elastic vibration of the flexible structure which leads to an uncomfortable ride quality and bad running stability. In such cases, active suspensions are required to realize a high stability and ride quality of the vehicles running on rough surface of roads and tracks.At first, an experimental apparatus has been made up so that the scale model of the vehicle body is suspended by the pneumatic spring and the actuator, the pressure of which is controlled by servo-valves. The servo-valves are driven by PWM (Pulse Width Modulation) and controlled by both the digital PID compensation of the vertical acceleration and the optimal feed back control law. These feed back control systems are realized by a 16 bit micro-computer. According to the result of this experiment, the amplitude of the vibration at resonant frequency 4.5 Hz is sufficiently suppressed up to 70 % the passive system.Next, it is proposed to design the control systems of a flexible vehicle body with front and rear suspensions, by use of multi-variable control method of centralized and decentralized controls. These control systems are aimed to suppress not only rigid body motions but also structural vibrations. According to the computer simulation, it is found the ride quality and the stability of the flexible vehicles are clearly improved by the actively controlled suspensions.