| 摘要 |
PURPOSE:To reduce an oil hammering and working sound, by connecting a power supply and a piezoelectric element by a variable resistance device, and by making the piezoelectric element operate at a high speed until the voltage applied to the variable resistance device reaches a predetermined voltage, and further, by making the piezoelectric element operate at a low speed on and after the voltage applied to the variable resistance device reaches the predetermined voltage. CONSTITUTION:At the time of starting changing, the resistance value between a piezo-actuator 15 and a high voltage power supply 34 is substantially only the that of the charging/discharging resistor 45. Then, when the charging proceeds to some extent, the resistance value between the piezo-actuator 15 and the high voltage power supply 34 becomes the sun of the charging/discharging resistor 45 and a charging resistor 47. Hereupon, the displacement and speed of the piezo--actuator 15 correspond to a charging voltage and current respectively. Thereby, the extending speed of the piezo-actuator 15 is made to change from a high speed to a low speed according to the change of the resistance value between the piezo-actuator 15 and the high voltage power supply 34, and the oil hammering and working sound can be reduced. |
