DAF LF45, LF55 Series. Manual — part 289

©

200416

2-9

General

BE ENGINE FUEL SYSTEM

ΛΦ45/55 series

4

2

2.5 OVERVIEW DRAWING, FUEL SYSTEM, CYLINDER HEAD

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1

1

2

4

8

7

6

9

3

1.

Injector pipe

2.

Union

3.

Nut

4.

Fuel supply pipe

5.

Connector to injectors

6.

O-ring

7.

Return opening

8.

Injector

9.

Electrical connection

BE ENGINE FUEL SYSTEM

2-10

©

200416

General

2

ΛΦ45/55 series

4

©

200416

3-1

Description of components

BE ENGINE FUEL SYSTEM

ΛΦ45/55 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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BE ENGINE FUEL SYSTEM

3-2

©

200416

Description of components

2

ΛΦ45/55 series

4

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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2

9

3

10