DAF CF65, CF75, CF85 Series . Manual — part 418

©

200416

3-1

Description of components

CE ENGINE FUEL SYSTEM

ΧΦ65/75/85 series

4

2

3. DESCRIPTION OF COMPONENTS

3.1 HIGH-PRESSURE PUMP

The high-pressure pump is driven by the
crankshaft by means of the camshaft gear. The
pump shaft rotates at a speed 1.33 times the
speed of the crankshaft. The pump shaft drives
the fuel lift pump. The fuel drawn from the suction
side by the gears is discharged through the exit
by the gears due to the reduction in volume. The
fuel lift pump has two added valves. The first
valve (1) limits the pump pressure, for example if
the fine filter is blocked. The second valve (2)
opens the by-pass over the fuel lift pump when
the primer pump is being used.

The high-pressure pump shaft (1) has an
eccentric. The eccentric drives the eccentric
ring (4). The pump plungers (3) are driven by the
eccentric ring and pushed back by the spring (2).

The fuel is supplied via the connection (5) and
then internally distributed among the three pump
elements. Before it is distributed among the pump
elements, the supplied fuel is dosed by means of
the fuel pump control solenoid valve (6).

The fuel pump control solenoid valve is controlled
by the electronic unit on the basis of the rail
pressure sensor signal. This creates a closed
control circuit. The fuel pump control solenoid
valve is "normally open" and is activated via duty
cycle control. The value when the engine is
started is fixed. When the measured pressure
deviates from the desired (programmed)
pressure, the duty cycle value will be adapted
until the measured and the desired values
correspond. If this is impossible, the electronic
unit will generate a warning and record a fault
code.

1

2

B

A

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5

4

2
3

1

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©

200416

Description of components

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ΧΦ65/75/85 series

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During the downward stroke, the fuel is supplied
by the fuel lift pump via the suction valve (9) (see
illustration on left). During the delivery stroke
(illustration on right), the suction valve closes
under the load of the spring (8) and the fuel
pressure that has built up. The fuel leaves the
pump element via the delivery valve (10). The
compressed fuel from the three pump elements is
collected in the pump housing and leaves the
pump via a joint high-pressure connection.

Leaking fuel from the pump elements is
discharged via the return connection.

The fuel lift pump has over-capacity in relation to
the high-pressure pump. If there is only limited
fuel off-take on the rail, the fuel pump control
solenoid valve will be virtually closed. The over-
supplied fuel will cause an increase in pressure at
the inlet of the fuel pump control solenoid valve.
The pressure is limited by the circulation valve
(7). If the valve is open, the excess supplied fuel
will be returned to the suction side of the fuel lift
pump. A small amount of fuel is diverted via a
restriction to the shaft and the eccentric of the
high-pressure pump for lubrication.

When bleeding with the primer pump, any air
bubbles will be carried along by the fuel through
the low-pressure circuit. Fuel is forced inwards at
the connection (5). The fuel pump control
solenoid valve is opened fully without being
energised, so that the fuel can pass. The pump
elements create a high resistance to the fuel, so
that the fuel will escape via the lubricating
restriction in the pump. In this way the fuel, along
with any air bubbles, is discharged to the return
pipe.

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8

2

9

3

10

©

200416

3-3

Description of components

CE ENGINE FUEL SYSTEM

ΧΦ65/75/85 series

4

2

3.2 FUEL PUMP CONTROL SOLENOID VALVE

The high-pressure pump has an over-capacity for
normal operating conditions. This could lead to
large quantities of fuel being forced at high
pressure to the fuel rail and then directly being
drained out to the return pipe via the pressure-
limiting valve on the fuel rail. This produces too
much unnecessary heat and loss of capacity
because large amounts of fuel are flowing at high
pressure.

The system has been designed such that only
fuel that will be used will be forced under high
pressure to the rail. For this reason, a fuel pump
control solenoid valve has been fitted at the
suction side of the high-pressure pump. This
solenoid valve is opened without being
energised, so that the high-pressure pump
elements can be filled in the normal manner.

If the fuel rail pressure becomes too high, for
example because of lower fuel off-take on the rail,
the solenoid valve will be energised by the
electronic unit with a higher duty cycle, so that the
plunger is pressed with a greater force against
the spring pressure and the valve reveals a more
constricted opening. This reduces the fuel supply
to the pump elements and the pump output will
thus fall. The fuel rail pressure will also fall as a
consequence.
If the rail pressure is too low, the reverse is true.

The current is supplied to the coil (3) via the
connector (1). The current pushes the core (2)
with the plunger (4) against the pressure of the
spring (5). This controls the fuel current from
input A to output B.

Due to this valve, under normal circumstances
very little fuel flows back from the rail. This
improves performance and reduces the
generation of heat.

B

A

B

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2

3

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©

200416

Description of components

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ΧΦ65/75/85 series

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3.3 INJECTOR

The injectors can be opened and closed
electrically. The injector is normally closed. The
load of the spring (2) and the fuel rail pressure
that controls chamber C ensure this.

The fuel is supplied from the fuel rail via A. The
return fuel can flow back to the fuel tank via B.

When the coil (7) is energised, the armature
housing (5) moves up. As a result the pressure in
chamber C drops slightly and the injector
needle (1) is forced up to chamber D by the rail
pressure. The fuel can then be injected.

7

C

E

A

B

F

D

6

5

4

3

2

1

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