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We adopted the active hydropneumatic suspension and the dual-mode 4WS system for the 1989 Toyota CELICA. The active control suspension system detects the vehicle state with various sensors to control the oil pressure in the hydraulic cylinder with the linear pressure control valve; controlling attitude, ride comfort, stability & controllability and three-level vehicle height. The 4WS system continuously changes the steering angle ratio between the front and rear wheel according to the vehicle speed, decreasing the minimum turning radius at a low speed by 0.5 m and improving the controllability at a medium speed and the stability at a high speed. In addition, we further improved the performance of each system by integrally controlling the active control suspension system and the 4WS system. Thus, we succeeded in improving the total performance of vehicle dynamics by adding ABS to these systems to control the vertical, lateral and longitudinal accelerations.

We have developed a new semi-active suspension, called Piezo TEMS, that uses piezoelectric ceramic for suspension control with sensor and actuator. It improves remarkably driveability with the firm damping force mode and enhances the ride comfort with the soft damping force mode immediately after the road surface input exceeding the threshold level.