C. Operation The TWV (solenoid valve) controls the pressure in the chamber by opening and closing the outlet orifice passage, which in turn controls the start and end of injection. a. When not injecting When the solenoid is not energized, the outlet orifice passage is closed by the downward force of the TWV (solenoid valve) spring. From this, the control chamber pressure trying to push down the command piston and the pressure trying to push up the nozzle needle is the same. The differences in the areas receiving pressure and the force of the nozzle spring closes the nozzle needle, so there is no injection. b.
During injection When the solenoid is energized, the TMV (solenoid valve) is pulled up by the force of the solenoid, which opens the outlet orifice, discharging the fuel from the control chamber. When fuel is discharged, the pressure in the control chamber is reduced, which pulls up the command piston. This raises the nozzle needle, and injection is started. c. End of injection As the solenoid continues to be energized, the nozzle reaches its maximum lift point, creating the maximum injection rate. When the energization of the solenoid is turned OFF, the TWV (solenoid valve) lowers, closing the outlet orifice.
Because of this, fuel enters the control chamber from the inlet orifice, which increases the pressure. The makes the noz- zle needle close abruptly, stopping the injection. Solenoid Actuating current Actuating current Actuating current TWV Outlet orifice Rail Inlet orifice Control chamber pressure Control chamber pressure Control chamber pressure Command piston Nozzle Injection rate Injection rate Injection rate No Injection Injection End of Injection QD0717E -7-