Location
1 | Coolant pump |
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The coolant pump (1) is located at the front left of the engine.
Task
The task of the coolant pump (1) is to circulate the coolant in the engine's cooling circuit. The coolant is circulated as needed, depending on the operating status. This means that the engine management (MCM) control unit (A4) regulates the delivery rate of the coolant pump continuously via an electromagnetic viscous fan clutch (1).
This reduces the delivery rate in the partial-load range in particular. Due to the reduced delivery rate, the required drive energy is decreased, and the fuel consumption is reduced accordingly.
Sectional view |
2 | Base body |
3 | Cover |
4 | Working chamber (filled with silicone oil) |
5 | Viscous disk |
6 | Intermediate disk |
7 | Armature (with valve lever) |
8 | O-ring (sealing ring) |
9 | Belt pulley |
10 | Dual ring bearing (with drive shaft) |
11 | Slide ring seal |
12 | Seal (to engine) |
13 | Pump impeller |
14 | Signal ring for coolant pump rpm sensor (B640) |
15 | Pump housing |
16 | Solenoid |
B640 | Coolant pump rpm sensor |
Y644 | Switched water pump solenoid valve |
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Function
The frictional connection between the belt pulley (9) and drive shaft is created via an electromagnetic viscous fan clutch that is driven by the engine management (MCM) control unit (A4).
The power is transmitted between the belt pulley (9) and the drive shaft by the shearing of the silicone oil in the working chamber (4). Shearing refers to the displacement of the silicone oil between the drive slats of the base body (2) and the drive slats of the viscous disk (5).
To regulate the electromagnetic viscous fan clutch, the engine management (MCM) control unit (A4) requires the clutch speed of the clutch output (pump speed of the pump impeller (13)) and the input speed of the belt pulley (9).
The input speed of the belt pulley (9) is determined via the engine speed and the diameter of the belt pulley (9).
The gear ratio via the poly-V-belt is taken into account here.
This information is stored in the engine management (MCM) control unit (A4).
The clutch speed of the clutch output is determined by the coolant pump rpm sensor (B640) and evaluated by the engine management (MCM) control unit (A4).
On the basis of this information, the engine management (MCM) control unit (A4) determines the current pump speed and thus the delivery rate of the coolant pump (1).
Due to the configuration, the coolant pump (1) always delivers the full delivery rate in the non-actuated state. This means that the belt pulley (9) and the pump impeller (13) are 95 % friction-locked. If the delivery rate of the coolant pump (1) is to be reduced, the engine management (MCM) control unit (A4) actuates the switched water pump solenoid valve (Y644) via a pulse width modulated signal.
When the switched water pump solenoid valve (Y644) is actuated, the armature (7) is closed. The centrifugal force then pumps the silicone oil out of the working chamber (4) between the cap (3) and the viscous disk (5), thereby reducing the operating energy input of the pump impeller (13).
By constantly comparing the input and output speeds, the engine management (MCM) control unit (A4) can detect the current delivery rate at all times. The engine management (MCM) control unit (A4) increases or reduces the delivery rate of the coolant pump (1) depending on the respective cooling request.
The coolant pump (1) is designed as what is known as a "fail-safe component part". This means that the working chamber (4) of the electromagnetic viscous fan clutch is filled with silicone oil in the quiescent state. If the electronic actuation of the electromagnetic viscous fan clutch is omitted due to a defect, work is always performed with 100 % of the possible cooling output. However, this also means that the functionality of the viscous fan clutch may be restricted at very low temperatures or during a cold engine start. At low engine speeds in particular, the highly viscous cold silicone oil cannot be pumped out of the working chamber (4), which results in the coolant pump (1) being fully engaged.
The coolant pump (1) is equipped with the following emergency running characteristics:
In the event of electrical faults (e.g. cable break, sensor system failure), the coolant pump (1) delivers the maximum delivery quantity automatically due to its configuration.
Mechanical defects (e. g. rpm drop due to oil loss at the viscous fan clutch or a cracked poly-V-belt) are detected by means of the coolant pump rpm sensor (B640) and result in a limitation of the engine power output.
A mechanical defect of the coolant pump (1) with a simultaneous failure of the coolant pump rpm sensor (B640) can be detected via the course of the coolant temperature and also results in an engine power output limitation.
In the event of an error, the driver is informed by a corresponding warning message in the multifunction display (A1 p1) or in the instrument cluster screen (ICS) control unit (A153).