Electric drive low-temperature circuit, basic function

Overview

This document contains information on:

 General

 Function requirements

 Electric drive low-temperature circuit (low-temperature circuit 1)

General

The following components 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)

 Electric machine (electric vehicle)

 AC charger for high-voltage battery (electric vehicle)

 Front electric machine power electronics control unit (electric vehicle)

 Electric machine 2 (electric 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.

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

Function requirements

 Hybrid system operational (hybrid vehicle)

 Drivetrain operational (electric vehicle)

 Circuit 15 ON

Electric drive low-temperature circuit (low-temperature circuit 1)

The following applies for electric vehicles:

The powertrain control unit evaluates the temperatures of the electric machine, electric machine 2 (electric vehicle), DC/DC converter control unit and AC charger for 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 control, the low-temperature coolant circuit 1 temperature sensor is also evaluated.

The circulation pump pumps the coolant into low-temperature circuit 1. The components connected to the cooling circuit output heat into 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. The powertrain control unit actuates the fan motor and radiator shutters to control the cooling output at the cooler. In the case of an increasing cooling output requirement, the radiator shutters are initially actuated to increase the air flow. The fan motor is then actuated according to the cooling requirement.

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.

The following applies for hybrid vehicles:

The power electronics control unit evaluates the temperature of the low-temperature circuit 1 and requests, if necessary, the 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 causes the circulation of the coolant in low-temperature circuit 1. The component parts that are connected to the cooling circuit output heat into 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. The powertrain control unit actuates the fan motor and radiator shutters to control the cooling output at the cooler. In the case of an increasing cooling output requirement, 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 transferring 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).