Drive Motor / Generator Cooling - Hybrid Drive: Description and Operation
Charge-air Cooling
One charge-air intercooler for each cylinder bank is installed in the air-charging module. Coolant flows through the coolers, which are integrated in parallel in the charge-air cooling system.
NOTE: The charge-air cooler must be installed and removed with great care. Read the instructions in the Workshop Data.
Charge-air cooling system
The charge-air cooling system is an independent high-temperature cooling system that also cools the hybrid power electronics. The system operates independently of the main cooling system, although the two systems are connected to one another and both utilize the coolant expansion tank. The temperature levels in the charge-air cooling system are lower than those in the main system.
Pump for charge-air cooling (G)
The charge-air cooling pump is an electrically powered coolant pump. The pump conveys the heated coolant from the charge-air intercoolers in the air-charging module to the low-temperature cooler. This cooler is installed in the cooling module in the vehicle engine compartment (in front of the main cooler viewed in the direction of travel). The pump is installed at the front left of the engine compartment near the oil cooler. The pump is designed based on a centrifugal pump.
A centrifugal pump is not self-aspirating and should therefore not be allowed to run dry because the pump bearings may overheat. The following assemblies are integrated in the pump module:
- Centrifugal pump
- Electric motor
- Electronic control
Function of the pump control
The pump is activated depending on the temperature from a map in the engine control module downstream of the charge-air cooler and the pressure downstream of the charge-air cooler. It always runs from 1,300 mbar or from a coolant temperature of 122° F. (50° C). The pump is controlled by the engine control unit via a PWM signal. The pump electronics use this signal to calculate the required pump speed and control the electric motor. If the pump is working correctly, the pump electronics send the current pump speed back to the engine control module. This process runs cyclically throughout pump operation.
Effects in the event of faults
If the pump electronics detect an error, the PWM signal changes. The changed signal is evaluated by the engine control unit. The actual response depends on the nature of the fault. If a fault is detected, fault entries are made in the memory of the engine control unit. In the event of a failure, no indicator lights are activated because a reduction in power is only noticeable at full throttle and the exhaust gases are not affected. No direct replacement reaction is triggered in the engine control unit in the event of pump failure. However, the charge air temperature is monitored. If this is found to be too high, the engine control unit reduces the engine power. If the signal line to the pump is interrupted or there is a short circuit to positive on the signal line, the pump switches to emergency mode, in which it delivers 100% output. The pump stops in the event of a short circuit to ground on the signal line.
Fault detection
NOTE: Please refer to the repair guidelines for more detailed information on coolant pump diagnosis.
Attempts are made to protect the pump whenever a fault is detected. Either the pump speed is reduced or the pump is switched off. The following table contains a list of possible faults and potential consequences:
Diagnosis options with the PIWIS Tester, second generation
The following diagnostic options are available:
- Read out the fault memory in the engine control unit
- Guided Fault Finding
- Read out actual values
- Drive link test
During the drive link test, the pump operates at different speeds and the engine control module evaluates the results. The drive link check must not therefore be interrupted.