Fuel Injector
Piezoelectric injectors require electrical current, high pressure fuel, low pressure fuel, and reversed electrical current to inject fuel and close the injector after injection. Piezoelectric injectors use high and low fuel pressure within the injector and piezo crystals within a stack of ceramic discs. High pressure fuel near the top of the high pressure control chamber holds the injector needle in place until it is time to inject. When the ECM sends current through the piezo stack, the piezo crystals expand. This expansion is amplified by the hydraulic pressure of the fuel in the low pressure chamber to move the control valve. High pressure fuel in the control chamber exits to the low pressure chamber when the control valve opens. This action unseats the injector needle and fuel is injected. To close the injector, current must flow in the opposite direction (reverse polarity) to retract the piezo crystals and allow fuel pressure in the injector to seat the injector needle.