Page 245 - 05. Subyek Teknik Mesin - Automobile Mechanical and Electrical Systems Automotive Technology Vehicle Maintenance and Repair (Vehicle Maintenance Repr Nv2) by Tom Denton

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Engine systems 229

Figure 2.302 High-pressure pump. (Source: Bosch Media)

The low-pressure delivery components are the fuel tank, a prefi lter, presupply
(low-pressure) pump, a fuel fi lter and the low-pressure delivery pipes to the
high-pressure pump and for excess fuel return. The low-pressure pump,
depending on application, can be of the roller cell type and be fi tted either in the
fuel tank or in-line where it is mounted to the vehicle body close to the fuel tank.
Where the pump is fi tted in the fuel tank, it includes a prefi lter and has the fuel
gauge sender unit attached to the same attachment fl ange on the side or top of
the fuel tank.
The electrical supply to the fuel pump is made either directly or through a relay
Key fact
from the EDC module. An inertia switch is generally used to cut the electrical
current to the pump motor in an accident. On some vehicles, a gear-type pump An inertia switch is generally used to

may be incorporated into the high-pressure pump and be driven from a common cut the electrical current to the pump
drive shaft. It can be a separate pump attached to the engine with a geared drive motor in an accident.
from the camshaft or crankshaft. The low-pressure delivery pipes connect to
a fuel fi lter and water trap. A continuous fl ow of fuel runs through the fi lter and
primes the high-pressure pump or returns to the fuel tank.
The high-pressure pump is driven from the engine crankshaft through a
geared drive at half engine speed and can be fi tted where a conventional
distributor pump would be. It can also be fi tted on the end of the camshaft
housing and be driven by the camshaft. It is lubricated by the diesel fuel that
fl ows through it.

The pump has to produce all of the high pressure for fuel injection ( Fig. 2.302 ).
It is a triple-piston radial pump, with a central cam for operation of the pressure
direction of the pistons and return springs to maintain the piston rubbing shoes
in contact with the cam. The pump has a positive displacement with inlet and
outlet valves controlling the direction of fl ow through the pump.
The pump delivery rate is proportional to the speed of rotation of the engine
so that it meets most engine speed requirements. To meet the engine load Safety fi rst
requirements the pump has a high volume. To meet the high-pressure A CR pump can produce pressures
requirements for fi ne atomization of the fuel on injection, the pump can produce in the region of 1400 bar.
pressures in the region of 1400 bar (scary!). A pressure control valve returns
excess fuel to the fuel tank.