(Cooling System Low-Temperature Circuit For Electric Drive, Basic Function - GF20.00-P-1009A)

Electric vehicles and hybrid vehicles 

Overview 

This document contains information on:

• General 
• Function requirements 
• Function 
  • Electric vehicle low-temperature circuit 
  • Hybrid vehicle low-temperature circuit 

General 

For example, the following component parts are cooled or heated via the electric drive low-temperature circuit:

• DC/DC converter control unit (electric vehicle)
• Power electronics control unit
• Transmission oil heat exchanger (hybrid vehicle)
• AC charger for high-voltage battery (electric vehicle)
• Front electric machine (electric vehicle, depending on vehicle)
• Front electric machine power electronics control unit (electric vehicle, depending on vehicle)
• Rear electric machine (electric vehicle, depending on vehicle)
• Rear electric machine power electronics control unit (electric vehicle, depending on vehicle)

The following applies for hybrid vehicles: The electric drive low-temperature circuit is separated from the combustion engine cooling circuit and has a separate expansion reservoir.

The following applies for hybrid vehicles with front wheel drive: The electric machine is cooled by the transmission oil.

Function requirements 

• Hybrid system operational (hybrid vehicle)
• Drivetrain operational (electric vehicle)
• Circuit 15ON

Function 

Electric vehicle low-temperature circuit 

The powertrain control unit evaluates the temperatures of the electric machine, electric machine 2 (vehicles with all-wheel drive), the DC/DC converter control unit and the AC charger for the high-voltage battery (electric vehicle). It calculates the required coolant flow volume and accordingly actuates the circulation pump of low-temperature circuit 1. To support this regulation, the low-temperature coolant circuit 1 temperature sensor is also evaluated.

The circulation pump pumps the coolant into low-temperature circuit 1. The component parts connected to the cooling circuit dissipate heat to the coolant.

The coolant then flows into the low-temperature circuit cooler, where it is cooled by the airstream or the air flow of the fan motor and flows back to the circulation pump. To regulate the cooling output at the cooler, the powertrain control unit actuates the fan motor and the radiator shutters. As the cooling output requirements increase, the radiator shutters are initially actuated to increase the air flow. The fan motor is then actuated according to the cooling requirement.

Depending on the model, there is also a self-regulating thermostat in the circuit. This separates the cooler from the circuit so long as the coolant is below a certain temperature and there is no cooling requirement.

Hybrid vehicle low-temperature circuit 

The power electronics control unit evaluates the temperature of the low-temperature circuit 1 and requests, if necessary, cooling output from the powertrain control unit.

The powertrain control unit evaluates the request for charge air, transmission, and power electronics cooling and accordingly actuates the circulation pump and, if necessary, the low-temperature circuit switchover valve. To support this regulation, the low-temperature circuit temperature sensor is also evaluated.

The circulation pump ensures coolant circulation in the low-temperature circuit 1. The component parts connected to the cooling circuit dissipate heat to the coolant.

In the low-temperature circuit cooler, the coolant is cooled by the airstream or the air flow of the fan motor and flows back into the cooling circuit. To regulate the cooling output at the cooler, the powertrain control unit actuates the fan motor and the radiator shutters. As the cooling output requirements increase, the radiator shutters are initially actuated to increase the air flow. The fan motor is then actuated according to the cooling requirement.

To prevent hot combustion engine coolant from passing into the low-temperature circuit 1, a thermal shutoff valve closes the filling hose to the common expansion reservoir from a combustion engine coolant temperature of approx. 60°C.

A min. coolant volume flow continues to flow through the components connected to the cooling circuit also at very low outside temperatures (depending on the coolant temperature).