DRIVING DEVICE

PURPOSE:To produce a small sized driving system with excellent reliability which can be driven at high speed even in a large sized movable machinery by providing an electric power unit to apply cyclically changing electric energy to a piezoelectric unit. CONSTITUTION:A cylinder 20 is connected with an automobile seat 10, and the inlet port 42 and outlet port 41 of a piezoelectric pump 40 are connected with the cylinder 20 through a solenoid-controlled valve 30 and check valves 61, 62. The piezoelectric pump 40 and solenoid-controlled valve 30 are connected with a control unit 50. When the one side electric coil of the solenoid-controlled valve 30 is not excited, fluid can not flow between four ports 31, 32, 33, 34, and when the one side electric coil of the valve 30 is excited, the port 31 and 32 communicate with the port 33 and 34 respectively, and when both the electric coils of the valve 30 are excited, the port 31 and 32 communicate with the port 34 and 33 respectively. When high voltage is applied to the piezoelectric unit 45, its thickness dimension becomes larger by several the mum. In this case, since the application and release of the high voltage are reciprocally carried out at high speed, the position of a piston 46 can be also changed at high speed.