[3] Operation The TWV portion of the injector consists of two valves, an inner valve (fixed) and an outer valve (movable). Both valves are precision-fitted on the same axis. The valves respectively form inner and outer seats, and either of the seats opens selectively depending upon whether the TWV is ON or OFF. a. No Injection When no current is applied to the solenoid, the valve spring and hydraulic pressure forces push the outer valve downward, causing the outer seat to remain closed. Because the rail high pressure is applied to the control chamber via the orifices, the nozzle remains closed without injecting fuel. b.
Begin Injection When current is applied to the TWV, the solenoid force pulls the outer valve upward, causing the outer seat to open. As a result, fuel from the control chamber flows out via the orifice, causing the needle to lift and to start fuel injection. Furthermore, the injection ratio increases gradually in accordance with the movement of the orifice. As the application of current continues to apply, the injector reaches its maximum injection ratio. c. End Injection When current to the TWV is cut off, the valve spring and hydraulic force (fuel pressure) cause the outer valve to descend and the outer seat closes.
At this time, high-pressure fuel from the rail is immediately introduced into the control chamber, causing the nozzle to close suddenly. As a result, injection ends swiftly. Inner valve Outer valve Outer seat Orifice 2 Orifice 1 Rail (constant high pressure) 18-130 MPa Command piston Control chamber Nozzle No Injection Begin Injection End Injection Q000098E 12