High-pressure pump

High-pressure pump

The high-pressure pump comprises the following components:

• Pre-supply pump
• Fuel metering valve
• High-pressure pump unit

All parts are combined in a single housing.

Fuel system within high-pressure pump

The electric fuel pump pumps diesel fuel out of the fuel tank through the fuel filter to the pre-supply pump. The pre-pressure regulation valve controls the fuel pressure in the pre-supply pump. It opens at 5bar and returns the fuel to the intake side of the pre-supply pump. The pre-supply pump delivers the fuel to the high-pressure pump via the actuated fuel metering valve. From the high-pressure pump, the fuel passes through the fuel pressure regulating valve to the high-pressure accumulator (rail) and then via high-pressure pipes to the injectors.

Pre-supply pump

The pre-supply pump is a mechanically-operated gear wheel pump and is part of the high-pressure pump. It has the task of delivering the fuel supplied from the fuel tank to the high-pressure pump via the fuel metering valve. The fuel pressure is increased to approx. 5bar. This guarantees a constant supply of fuel to the high-pressure pump in all engine operating modes.

Effects upon failure

If the high-pressure pump unit is not supplied with fuel. You cannot start the engine.

Fuel metering valve N290

The fuel metering valve controls the fuel supply to the high-pressure pump unit and ensures that fuel is supplied to the high-pressure pump. This allows the delivery quantity of the high-pressure pump to be adjusted to the engine requirements on the low-pressure side. The advantage of this is that the high-pressure pump only has to generate the pressure which is required for the current operating situation.

Function

Valve not activated

The fuel metering valve is not powered. The spring force moves the plunger to close the passage to the high-pressure pump. The fuel supply to the highpressure pump is interrupted.

Valve activated

The fuel metering valve is powered and the solenoid generates a magnetic field. The plunger is pressed against the spring force by the valve armature. The fuel supply to the high-pressure pump is opened and fuel reaches the high-pressure pump.

Effects upon failure

The valve is closed if the voltage supply fails. Fuel is not delivered to the high-pressure pump. You can no longer start the engine.

High-pressure pump unit

The high-pressure pump unit has the task of generating the high fuel pressure of up to 1600 bar, which is required for fuel injection. It is an on-demand radial piston pump with two highpressure units arranged at 180 ° that are operated by a cam.

Delivery stroke

The cam pushes the piston upwards. The inlet valve is closed by the spring force and the pressure builds up in the compression chamber. The outlet valve opens when the pressure inside the compression chamber is greater than the fuel pressure in the high-pressure accumulator.

Suction stroke

The downwards movement of the piston creates a vacuum in the compression chamber that opens the inlet valve against the spring force. The fuel coming from the fuel metering valve is drawn in. At the same time, the outlet valve is closed due to the difference in pressure between the compression chamber and the fuel pressure in the high-pressure accumulator.