To release shock applied on a piezoelectric element with a simple structure, and improve reliability and durability of the piezoelectric element by controlling voltage applied on the piezoelectric element on the basis of a current value which flows the piezoelectric element, in a fuel injection device having a valve element which performed reciprocating motion in association with the distortion motion of the piezoelectric element.
At the time of start, voltage is applied from the power supply circuit 6 of a control circuit 23 on a piezoelectric element 2, the piezoelectric element 2 extends for about 0.5 seconds while compressing a spring 3. Applying voltage of the piezoelectric element is set to 0V instantly, and thereby, piezoelectric element 2 is reverted in a natural length at about 10-4 seconds. At this time, the spring constant of the spring 3 is selected suitably, and a damper 22 is weighted, and thereby, it is not followed with rapid contracting motion of the piezoelectric element 2, and acted as a fixing end of the piezoelectric element 2. A plunger 1 which is a comparative light weight is lifted up by contraction of the piezoelectric element 2, fuel is injected. After fuel is injected, the plunger 1 descends by extending motion of the piezoelectric element 2 so as to shut-out fuel injection.
TANAKA SHIGERU
SHIONO OSAMU
KANEDA JUNYA
