Injector(S), Fuel: Operation

Courtesy of CHRYSLER GROUP, LLC

Injector Closed 

• In the closed state, the solenoid valve is not energized. The bleed orifice is closed because the armature spring forces the ball onto its seat.
• Fuel from the rail under high pressure (up to 2000 bar) enters the injector in the fuel inlet fitting or edge filter and fill the control valve chamber. The fuel applies hydraulic forces against the top of the control valve plunger. It also fills the nozzle feed passage against the nozzle needle pressure shoulder at the tip of the injector.
• The same amount of pressure is applied to the top of the valve control plunger and the nozzle pressure shoulder. Because there is more area on the top of the control valve plunger fro the hydraulic force to work against, the nozzle needle pressure shoulder is held closed and cannot overcome the hydraulic force being applied to the plunger.
• The nozzle needle spring is only used when the engine is off and there is no pressure in the fuel injector. It holds the needle closed against the seat.

Injector Opens 

• The command the injector on, the Powertrain Control Module (PCM) energizes the injector solenoid valve using an initial pickup current of 20 amps to ensure that it opens quickly. The force exerted by the triggered solenoid exceeds that of the spring and the armature opens the bleed orifice by lifting the valve ball off its seat. Almost immediately, the high-level pickup current is reduced to the lower holding current of 14 amps required by the electromagnet.
• When the bleed orifice opens, fuel flows from the valve control chamber into the cavity above it. Fuel then returns out of the top of the injector and into the return line circuit, back to the fuel supply tank. The reduction in pressure in the valve control chamber causes the high-pressure at the nozzle needle shoulder to overcome the pressure acting on the control plunger, which allows the nozzle needle to come off its seat, injection begins.

Injector Closes 

• When the solenoid valve is deactivated, the armature spring forces the armature down and the ball closes the bleed orifice and is able to seal off the control valve chamber and hold it closed.
• Closing the bleed orifice leads to a pressure build up in the valve control chamber and causes the pressure in the control chamber to again become equal to the pressure at the nozzle needle shoulder. This equal pressure forces down the valve control plunger. The area on top of the valve control plunger is greater then the affected area at the nozzle needle pressure shoulder. Because of the difference in affected areas, the control plunger pushes down and closes the nozzle needle into its seat (stopping the fuel injection).