1.3 Construction and Operation of the System The rail system is comprised of a supply pump, a rail, and injectors, and also includes an ECU and sensors to regulate those components. The supply pump generates the internal fuel pressure in the rail. Fuel pressure is regulated by the quantity of fuel discharged by the supply pump. In turn, the fuel discharge quantity is regu- lated by electronic signals from the ECU that turn the PCVs (pump control valves) ON and OFF. Upon receiving fuel pressurized by the supply pump, the rail distributes the fuel to the cylinders.
The pressurized fuel is detected by the rail pressure sensor (installed in the rail) and undergoes feedback control so that actual pressure will match the command pressure (designated accord- ing to the engine speed and load). Pressurized fuel in the rail passes through the injection pipes that lead to the cylinders, and applies pressure to the injector nozzles and the control chamber. The injector regulates injection quantity and timing by turning the TWV (two-way valve) ON and OFF. When the TWV is ON (current applied), the fuel circuit switches over, causing the high-pressure fuel in the control chamber to flow out via the orifice.
As a result, the force of the high-pressure fuel at the nozzle valve opening causes the needle valve to lift, thus starting the injection of fuel. When the TWV is turned OFF (current not applied), the fuel circuit switches over so that high- pressure fuel, traveling via the orifice, is introduced to the control chamber. As a result, the nee- dle valve lowers, thus ending the injection of fuel. Thus, through electronic control, the timing of the current applied to the TWV determines the injection timing, and the duration in which current is applied to the TWV determines the injection quantity.
TWV TWV control pulse · Injection quantity control · Injection timing control · Injection rate control Additional information (temperature, pressure) Rail pressure sensor Engine load Leak Rail Orifice Injection pressure control Control chamber Hydraulic piston Nozzle Supply Pump Needle Injector Q000084E 4 ECU