Patent ID: 7140353

Claim:
A method for providing preload to a piezoelectric actuator of a fuel injector during operation of the injector, comprising: providing a fuel injector including a nozzle valve element movable between an open position permitting fuel flow and a closed position blocking fuel flow, a control volume positioned to receive a pressurized supply of fuel, a drain circuit for draining fuel from said control volume to a low pressure drain, an injection control valve including a control valve member positioned along said drain circuit to control fuel flow from said control volume, a piezoelectric actuator including a stack of piezoelectric elements movable between expanded and contracted positions, and a preload chamber positioned a spaced axial distance from said control volume between said control volume and said piezoelectric actuator to receive high pressure fluid; and supplying high pressure fluid of at least approximately 200 bar to said preload chamber to generate a high fluid pressure preload force on said stack of piezoelectric elements.