Fuel Injector: Description and Operation
ENGINE CONTROL COMPONENTSFuel Injectors
The fuel injectors are connected to the high pressure fuel rail and deliver a calibrated amount of fuel directly into the combustion chamber. The piezo actuator is commanded on by the powertrain control module (PCM) during the main injection stage for approximately 0-400 microseconds. The fuel injectors on and off time is controlled by the piezo actuator device which allows extreme precision during the injection cycle. For additional information on fuel injection operation, refer to Fuel System.
O-ring and Combustion Gasket
The fuel injector has 1 replaceable O-ring on the fuel return, 1 replaceable O-ring on the fuel injector body and 1 replaceable stepped copper combustion gasket on the tip of the fuel injector.
Piezo Actuator
The piezo actuator consists of a series of small disks. When the piezo actuator is electrically energized, it causes the disks to deform which results in an expansion. The expansion generates a longitudinal motion which pushes down against the valve piston. The piezo actuator returns to its non-energized state by fuel and spring pressure during engine operation, and by the spring pressure from the fuel injector valve return spring when the engine is shut down.
Hydraulic Coupler
The hydraulic coupler transfers the longitudinal movement from the piezo actuator to the fuel injector control valve. It also acts as a seal preventing fuel from entering the piezo actuator device.
Fuel Injector Control Valve
The fuel injector control valve is a hydraulic check valve that allows the high fuel pressure to bleed off into the fuel return chamber directly above it, when the piezo actuator is energized and the valve piston pushes down on it.
Fuel Injector Valve Return Spring
The fuel injector valve return spring holds the fuel injector valve in the sealed position to prevent any fuel from leaking into the fuel return chamber when the piezo actuator is not energized.
Control Piston
The control piston uses its large surface area on top as a downward force to overcome an upward force created by the smaller surface area in the high pressure chamber. The control piston also keeps the nozzle needle in the closed position when the piezo actuator is not energized.
Nozzle Needle and Needle Control Spring
The high pressure chamber uses the high fuel pressure to lift the nozzle needle inwards whenever the piezo actuator is energized. When the nozzle needle is lifted the fuel at the high pressure nozzle is atomized and is injected directly into the combustion chamber through 8 spray holes. The needle control spring holds the nozzle needle in a closed position when the piezo actuator is not energized.