Location
The coolant pump (1) is located at the front left of the engine.
1 | Coolant pump |
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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 (1) continuously via a magnetic clutch (viscous).
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 |
Y631 | Coolant pump solenoid valve |
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Function
The frictional connection between the belt pulley (9) and the drive shaft is created via a magnetic clutch (viscous) 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 magnetic clutch (viscous), the engine management (MCM) control unit (A4) needs the rotational speed of the clutch output (rotational speed of 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 rotational speed of the clutch output is determined via 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 rotational 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 coolant pump solenoid valve (Y631) via a pulse width modulated signal.
When the coolant pump solenoid valve (Y631) is actuated, the armature (7) is closed. As a result of the centrifugal force, the silicone oil is then pumped out of the working chamber (4) between the cap (3) and the viscous disk (5). This reduces 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 magnetic clutch (viscous) is filled with silicone oil in quiescent state. If the electronic actuation of the magnetic clutch (viscous) 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 magnetic clutch (viscous) can be limited at very low temperatures or 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 magnetic clutch (viscous) or a cracked poly-V-belt)are detected via 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 a fault, the driver is informed by a corresponding warning message (e.g. in the instrument cluster).