(4) Operation a. The TWV (Two-Way Valve) solenoid valve opens and closes the outlet orifice to control both the pressure in the control chamber, and the start and end of injection. [No injection] • When no current is supplied to the solenoid, the spring force is stronger than the hydraulic pressure in the control chamber. Thus, the solenoid valve is pushed downward, effectively closing the outlet orifice. For this reason, the hydraulic pressure that is applied to the command piston causes the nozzle spring to compress. This closes the nozzle needle, and as a result, fuel is not injected.
[Injection] • When current is initially applied to the solenoid, the attraction force of the solenoid pulls the solenoid valve up, effectively opening the outlet orifice and allowing fuel to flow out of the control chamber. After the fuel flows out, the pressure in the control chamber decreases, pulling the command piston up. This causes the nozzle needle to rise and the injection to start. • The fuel that flows past the outlet orifice flows to the leak pipe and below the command piston. The fuel that flows below the piston lifts the piston needle upward, which helps improve the nozzle's opening and closing response.
• When current continues to be applied to the solenoid, the nozzle reaches its maximum lift, where the injection rate is also at the maximum level. When current to the solenoid is turned OFF, the solenoid valve falls, causing the nozzle needle to close immediately and the injection to stop. Leak pipe Solenoid Actuation current Actuation current Actuation current TWV Valve spring Outlet orifice Rail Inlet orifice Command piston Control chamber pressure Control chamber pressure Control chamber pressure Nozzle needle Injection rate Injection rate Injection rate No injection Injection End of injection Q000149E 19