DAF CF65, CF75, CF85 Series . Manual — part 262

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Description of components

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3.3 COOLANT FILTER

The task of the coolant filter is to filter the coolant

to prevent cavitation. The coolant filter is

necessary when the cooling system is filled with

low-quality coolant.

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3.4 VISCOUS FAN CLUTCH

The fan is connected to the engine by means of a

viscous fan clutch. If, under certain

circumstances, the heat is not sufficiently

dissipated by the air flow passing through the

radiator, the fan will have to draw in extra cooling

air through the radiator. In a viscous fan clutch,

the drive torque is transmitted by a silicone fluid.

The fan clutch is divided into two chambers. In the

working area (1) is the rotor (2), which is

connected to the drive flange (7). The supply

chamber (3) rotates freely round the drive flange

(7) and is connected to the fan. There is silicone

fluid in the supply chamber (3). The opening (4) in

the supply chamber (3) is closed by a valve (5).

The valve (5) is operated by a bimetallic strip (6).

If the opening (4) in the supply chamber (3) is

closed by the valve (5), no silicone fluid can enter

the working area (1). The silicone fluid still

present in the working area (1) will flow back to

the supply chamber (3) through the bores (8). As

only very little fluid will be left in the working area

(1), there will be a great difference in rotating

speed (slip) between the drive flange (7) and the

supply chamber (3) with the fan.

When the air temperature increases, the

bimetallic strip (6) will bend and the valve (5) will

partially release the opening (4) in the supply

chamber (3). Through this opening, a limited

amount of silicone fluid can enter the working

area (1) and flow past the rotor (2). This will cause

friction, so that the difference in rotating speed

(slip) between the drive flange (7) and the supply

chamber (3) with the fan will decrease.

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XE ENGINE COOLING SYSTEM

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As the air temperature rises, the bimetallic strip

(6) will continue to bend and the opening (4) in the

supply chamber (3) will be fully released.

The further the opening (4) in the supply chamber

(3) is released, the more silicone fluid will flow into

the working area (1) and past the rotor (2). As a

result of the increase in friction, the difference in

rotating speed (slip) between the drive flange (7)

and the supply chamber (3) will further decrease.

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3.5 ELECTRONICALLY CONTROLLED VISCOUS FAN CLUTCH

For accurate fan speed control, an electronically

controlled viscous fan clutch is used.

The electronically controlled viscous fan clutch

checks and controls the fan speed to ensure that

the flow of cooling air through the cooling system

is sufficient to keep the coolant temperature and/

or inlet air temperature within certain limits.

The fan clutch is activated by a PWM signal (duty

cycle). Activation depends on several variables:

- the coolant temperature

- the inlet air temperature

- the vehicle speed

- the engine speed

- intarder engaged/disengaged

- the heat production of the fan clutch (slip heat

protection)

In the event of failure of the control system of the

fan clutch, the fan will be fully engaged.

The speed of the fan is sensed by an inductive

sensor.

Construction
The fan clutch is divided into two parts, a primary

part (1) and a secondary part (2).

The primary part (1) consists of the rotor (3),

which is fixed to the drive shaft (4). It also

includes the supply chamber (6) for the silicone

fluid.

The secondary part (2) includes the working area

(5). The fan is fitted to the secondary part (2) and

rotates freely round the drive shaft (4).

The supply chamber (6) is enclosed by a raised

ring (7) and part of the rotor (3). The supply

chamber (6) has an opening (8) to the working

area (5), which is closed by a valve (9).

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