Component description for the electromagnetic viscous coupling

W20.40-1110-72

Location

Shown on engine 541.9 without code (ML3) High-speed fan drive with belt drive

15 Electromagnetic viscous coupling

Vehicles without code (ML3) High-speed fan drive with belt drive.

The electromagnetic viscous coupling (15) is screwed onto the front vibration damper of the crankshaft via an intermediate flange.

Vehicles with code (ML3) High-speed fan drive with belt drive.

The electromagnetic fan clutch (15) is screwed onto the fan drive belt pulley.

Task

The electromagnetic viscous coupling (15) creates the connection between the engine and the fan wheel. Stepless cut-in is dependent on the cooling requirements of the engine. This ensures a constant operating temperature of the engine under all operating conditions.

 A defective electromagnetic viscous coupling cannot be repaired if this is required.

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Design

1 Valve ring

2 Cover (storage room)

3 Oil return duct

4 Cover

5 Clutch plate

6 Seal

7 Oil feed bore

8 Housing

9 Sensor ring

10 Flange

11 Electrical line

B122 Fan clutch rpm sensor

Y170 Fan solenoid valve

The clutch shaft and the firmly attached parts with the clutch shaft such as the valve ring (1) and the clutch plate (5) are driven by the flange (10). These parts always turn at the current drive speed and are designated as the primary side of the electromagnetic viscous coupling.

The secondary side consists of a number of parts including the cover (4) and the housing (8), which is screwed onto the fan wheel. The secondary side is separated from the primary side by the main bearing. If the electromagnetic fan clutch is switched off the fan wheel is difficult to turn.

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11 Electrical line

12 Torque support

The fan clutch rpm sensor (B122) is attached to the fan solenoid valve (Y170). The fan solenoid valve (Y170) is mounted rotatable on the clutch shaft but is prevented from turning by the torque support (12).

 The fan clutch rpm sensor (B122) is connected firmly with the fan solenoid valve (Y170) and cannot be replaced in the case of repairs being needed.

The torque support (12) is screwed onto the housing of the coolant pump. The electrical line (11) is laid along the torque support (12) and connected via a multiplug with the engine control (MR) control unit (A6).

Function

Power transmission between the primary side and the secondary side takes place via the shear of silicone oil in the operating space. A shear is the displacement of silicone oil between the drive lamellae of the clutch plate (5) and the power take-off lamellae of the housing (8) or the cover (4). Flow of silicone oil from the storage room into the operating space takes place via the centrifugal force created by the rotation and the adjustable valve ring (1). The valve ring (1) is located on the clutch shaft which can be adjusted by the fan solenoid valve (Y170).

Adjustment takes place through actuation of the fan solenoid valve (Y170) by means of a pulse width modulated signal (PWM signal) whereby a large positioning signal is generated by a longer "On" pulse or a small positioning signal by a shorter "On" pulse.

In the case of request for a higher torque transmission between the primary and secondary side, which means an increased cooling requirement, the fan solenoid valve (Y170) receives a smaller positioning signal from the engine control (MR) control unit (A6).

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The magnetic field at the fan solenoid valve (Y170) is reduced and the clutch shaft with the valve ring (1) is pressed by a spring upwards. In this way the oil feed bore (7) increases in size and increases the amount of silicone oil flowing into the operating space. The transferred torque between the primary and the secondary side increases and the fan speed increases.

In the case of a request for a lower torque transmission between the primary and secondary side, which means a lower cooling requirement, the fan solenoid valve (Y170) receives a larger positioning signal from the engine control (MR) control unit (A6). The magnetic field on the fan solenoid valve (Y170) is enlarged and the clutch shaft with valve ring (1) is now pressed downwards against the spring force of the spring. In this way the oil feed bore (7) reduces in size and reduces the amount of silicone oil flowing into the operating space. The shear between the primary and secondary side reduces and the fan speed is reduced.

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Reverse current of the silicone oil into the storage room takes place through the oil return flow duct (3).