Fuel Supply System Description - High Pressure Fuel Pump
Outline
The high pressure fuel pump is installed in the cylinder head; it is driven mechanically by a square cam installed on the exhaust camshaft. The pump pressurizes the fuel sent from the fuel tank to high pressure, and supplies the fuel via the fuel joint pipe and the fuel rail to the injectors. The PCM controls the fuel control solenoid to obtain the optimum fuel pressure for the driving conditions, based on the signal from the fuel rail pressure sensor.
Construction
The high pressure fuel pump is composed of the pulsation damper, the suction valve, the fuel control solenoid, the suction valve spring, the piston, the pressure check valve, and the pressure relief valve.
Operation
Suction
The piston is moved down by the rotation of the square cam of the exhaust camshaft, and the fuel from the fuel tank passes through the suction valve and is drawn into the pressure chamber.
Pressure adjustment
The piston is pushed up by the cam because of the rotation of the camshaft, and the fuel drawn in is returned from the suction valve. The pulsation damper absorbs and damps the pulsations caused by the piston displacement, and performs mixing of the fuel sent under pressure from the fuel tank.
Compression
The PCM uses the signal from the fuel rail pressure sensor to control the fuel control solenoid to match the driving conditions; it also closes the suction valve as required. The piston rises further, and the pressurized fuel passes through the pressure check valve, and is then supplied as high pressure fuel to the injectors. When the camshaft rotates further and the piston starts to descend, the pressure check valve closes, the PCM switches the fuel control solenoid OFF, the suction valve opens, and fuel is drawn in again.
