DAF XF105. Manual - part 92

1

©

 200528

2-17

Description of components

DMCI ENGINE MANAGEMENT SYSTEM

XF105 series

2.11 PUMP UNIT

General

The pump unit supplies fuel to the injector. The 

pump unit consists of a metal housing (3) in 

which an electrical coil (2) opens a valve (1). In 

the rest position, the valve (1) is pushed up by a 

spring (4). The electrical connection (8) is 

screwed onto the outside of the pump unit. The 

roller tappet (6) rotates around the camshaft and 

actuates the plunger (5), which builds up the fuel 

pressure. The fuel enters the pump unit via the 

fuel gallery opening (A). This opening goes into 

the fuel supply gallery in the engine block. The 

fuel leaves the pump unit in the direction of the 

injector via a delivery valve (7). The fuel pipe is 

fitted to the injector supply connection (C). Leak-

off/lubricating fuel from the plunger is fed back to 

the return gallery in the engine block via the 

return opening (B). 

B

C

A

1
2

3

4

5

6

8

7

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A.

Fuel gallery opening

B.

Return opening

C.

Injector inlet connection

1.

Lid

2.

Coil

3.

Pump unit housing

4.

Spring

5.

Plunger

6.

Roller tappet

7.

Delivery valve

8.

Electrical connection

1

DMCI ENGINE MANAGEMENT SYSTEM

2-18

©

 200528

Description of components

XF105 series

Electrical control
The pump unit is activated with a voltage of 

approximately 50V. This voltage is the discharge 

from a capacitor in the DMCI electronic unit. The 

current increases rapidly because of this 

relatively high voltage. As a result, the valve in the 

pump unit opens quickly. This is the pick-up 

phase. If the current were not limited, it would 

become too high and damage the coil in the pump 

unit. The increase in the current is limited by 

switching to pulsating control of approximately 

24V after discharging the capacitor. This is the 

withstand phase. The current now remains high 

enough to hold the valve open. The length of the 

pick-up phase stays practically the same under 

all circumstances. The length of the withstand 

phase will vary depending on the calculations 

carried out by the electronic unit. When the pump 

unit is deactivated a negative induction peak is 

created by switching off the current through the 

pump unit coil.

Operation
The fuel is supplied to the pump unit via the 

gallery in the engine block flowing towards the 

delivery chamber above the plunger. The delivery 

chamber now fills.

U (V)

60

40

20

  0

i400845

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©

 200528

2-19

Description of components

DMCI ENGINE MANAGEMENT SYSTEM

XF105 series

The pressure does not build up immediately 

when the plunger is pushed up by the camshaft. 

The fuel can still flow back to the fuel gallery via 

the supply opening. 

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DMCI ENGINE MANAGEMENT SYSTEM

2-20

©

 200528

Description of components

XF105 series

When the coil is activated, the valve is pulled 

down and the opening to the fuel gallery closes. 

Pressure only starts to be built up by the plunger 

now. The fuel cannot flow back to the gallery and 

now has to flow towards the injector outlet via the 

delivery valve. Fuel is now supplied to the 

injector. 

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