FUSO 4M4 – FUEL AND ENGINE CONTROL – STRUCTURE AND OPERATION – Common rail

• The common rail distributes to the injectors high-pressure fuel that has been fed from the supply pump.
• Each flow limiter prevents an abnormal outflow of fuel. It does so by blocking the fuel passage in the event of fuel leakage from the injection pipe or excessive injection of fuel from the injector.
• The common rail pressure sensor is used in feedback control. It senses the fuel pressure (actual common rail pressure) inside the common rail and feeds a corresponding signal to the engine electronic control unit.
• If the fuel pressure in the common rail exceeds a certain, set level, the valve piston in the pressure limiting valve pushes and compresses the spring such that fuel is able to escape. The pressure limiting valve thus prevents the fuel pressure from becoming higher than the set pressure.

Flow limiter
•During normal operation, the piston moves (thus pushing and compressing the spring) to the extent necessary for one injection quantity to pass through. The piston does not make contact with the seat at this time. When injection is complete, the piston is returned to its initial position by the spring.
• If the amount of fuel passing through the flow limiter becomes excessively great, the piston presses against the seat, thereby closing the fuel passage and preventing an abnormal outflow of fuel. When the piston has pressed against the seat, it does not return to its original position until the engine has been stopped and the pressure in the common rail has come down.

 

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