Fuel High-Pressure Pump, Basic Function - GF07.02-P-2000A
Engine All (4xWD)
Engine All (CAR)
Sample illustration of high-pressure fuel pump
Overview
This document contains information on:
- General
- Function
- Spark-ignition engine
- Diesel engine
- Low-pressure side
- High-pressure side
- Filling the piston
- Generation of high pressure
General
The high-pressure fuel pump (1) delivers the fuel for the high-pressure direct injection.
The high-pressure fuel pump (1) is mechanically driven in spark-ignition and diesel engines. The delivery rate of the high-pressure fuel pump (1) is thus RPM dependent.
The high-pressure fuel pump (1) is mechanically driven via the following devices:
- Roller tappet via intake or exhaust camshaft
- Toothed belt
- Timing chain
Sample illustration of high-pressure fuel pump design
Function
Spark-ignition engine
During the upward motion of the pump element (8), the fuel volume in the pump cylinder is pressurized. When system pressure is achieved, the high-pressure exhaust valve (11) opens and fuel is delivered via the high-pressure lines to the rails. A pressure limiting valve (5) protects the high-pressure fuel pump (1) from an excessive pressure buildup.
The fuel quantity that reaches the pump element (8) is regulated so that the high-pressure fuel pump (1) only delivers the fuel that is required by the engine. In this way, the high fuel pressure is regulated up to approx. 200 bar depending on the operating status of the engine.
The high-pressure fuel pump (1) is cooled and lubricated with fuel. Consequently, the fuel delivered is not able to mix with lubricant.
Sample illustration of diesel engine high-pressure fuel pump
Sample illustration of diesel engine high-pressure fuel circuit
Diesel engine
For the fuel pump in the diesel engine, a differentiation is made between the low-pressure side and high-pressure side.
Low-pressure side
The fuel delivered by the electric fuel pump arrives at the high-pressure fuel pump flange at which the fuel temperature sensor (12) is also located, and is routed from there to the quantity control valve (2) as well as to the fuel overpressure valve.
The quantity control valve (2) regulates the fuel volume that is fed via the annular passage to the two pump elements (8) of the high-pressure fuel pump (1) (fuel feed to high-pressure elements).
Fuel is led from the fuel feed directly into the pump drive over a cooling and lubricating throttle for cooling and lubrication of the pump drive.
The mechanical fuel overpressure valve integrated in the high-pressure fuel pump (1) regulates the fuel pressure that is applied to the quantity control valve (2) to approx. 5 bar.
The excess fuel is led back over the pump drive into the fuel tank.
Any air carried along by the fuel is routed via the fuel overpressure valve and the cooling and lubricating throttle to the return flow of the high-pressure fuel pump (1).
High-pressure side
With its cam plate, the eccentric shaft moves the piston back and forth against the piston spring.
A differentiation is made between the following functions at the high-pressure side:
- Filling the piston
- Generation of high pressure
Filling the piston
The piston is moved down as a result of the piston spring. The fuel supplied by the fuel pump flows through the annular passage and fuel feed, and pushes against the valve spring to pass through the valve into the cylinder.
A ball valve prevents the fuel from flowing back into the fuel tank from the high-pressure channel.
Generation of high pressure
The piston is moved upward by the upward movement of the eccentric shaft. This compresses the fuel. The valve closes the delivery volume against the fuel feed. If the fuel pressure in the cylinder exceeds the pressure in the high-pressure fuel circuit, the ball valve opens and the fuel is delivered into the high-pressure fuel circuit.