Operation Section
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54
5.3 Injector Operation
z The injector controls injection through the fuel pressure in the control chamber. The TWV executes leak control of the
fuel in the control chamber to control the fuel pressure within the control chamber. The TWV varies with the injector type.
Non-Injection
• When the TWV is not energized, the TWV shuts off the leak passage from the control chamber, so the fuel pressure
in the control chamber and the fuel pressure applied to the nozzle needle are both the same rail pressure. The nozzle
needle thus closes due to the difference between the pressure-bearing surface area of the command piston and the
force of the nozzle spring, and fuel is not injected. For the X1 type, the leak passage from the control chamber is shut
off by the outer valve being pressed against the seat by the force of the spring, and the fuel pressure within the outer
valve. For the X2/G2 types, the control chamber outlet orifice is closed directly by the force of the spring.
Injection
• When TWV energization starts, the TWV valve is pulled up, opening the leak passage from the control chamber.
When this leak passage opens, the fuel in the control chamber leaks out and the pressure drops. Because of the drop
in pressure within the control chamber, the pressure on the nozzle needle overcomes the force pressing down, the
nozzle needle is pushed up, and injection starts. When fuel leaks from the control chamber, the flow quantity is re-
stricted by the orifice, so the nozzle opens gradually. The injection rate rises as the nozzle opens. As current continues
to be applied to the TWV, the nozzle needle eventually reaches the maximum amount of lift, which results in the max-
imum injection rate. Excess fuel is returned to the fuel tank through the path shown.
End of Injection
• When TWV energization ends, the valve descends, closing the leak passage from the control chamber. When the
leak passage closes, the fuel pressure within the control chamber instantly returns to the rail pressure, the nozzle
closes suddenly, and injection stops.
Q000867E
Outer Valve
Injection Rate
Control
Chamber
Pressure
Control
Chamber
Pressure
Control
Chamber
Pressure
Solenoid
TWV
Outlet Orifice
Inlet Orifice
Command
Piston
Nozzle
Injection Rate
Injection Rate
Non-Injection Injection End of Injection
Rail
X1
X2 · G2
Outlet Orifice
Actuating
Current
Actuating
Current
Actuating
Current
Inner
Valve
To Fuel Tank
Leak Passage
Leak
Passage
TWV
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