High-voltage battery low-temperature circuit basic function

Overview

This document contains information on:

 General

 Function requirements

 Low-temperature circuit of high-voltage battery (low-temperature circuit 2)

General

To optimize the charge capacity, the number of charge cycles and the life expectancy of the high-voltage battery, the operating temperature of the high-voltage battery must lie in a specific range. The performance of the high-voltage battery is also temperature-dependent and significantly decreases in the case of falling temperatures. Furthermore, the electrolyte can congeal at extremely low temperatures. To this end, the high-voltage battery temperature-controlled via a low-temperature circuit.

 The following applies for hybrid vehicles: The charge air, transmission and power electronics cooling have a common low-temperature circuit that is coupled with an expansion reservoir and a bi-metal valve. Among other things, this protects the power electronics control unit (N129/1) from damage from overheating.

Function requirements

 Hybrid drive system operational (hybrid vehicle)

 Powertrain operational (electric vehicle)

 Circuit 15 ON

Low-temperature circuit of high-voltage battery (low-temperature circuit 2)

The powertrain control unit detects the coolant temperature via low temperature coolant circuit temperature sensor 2 and actuates the switchover valves and the coolant pump as required. The pumps distribute the coolant evenly within the high-voltage battery and control the cooling output and the heat output.

The powertrain control unit also evaluates the high-voltage battery temperature (model-dependent) and the status of the battery management system.

 The temperature sensors of the high-voltage battery are integrated into the high-voltage battery module.

Depending on the ambient temperature, the waste heat of the component parts connected in the low-temperature circuit 2 is dissipated via the low-temperature circuit 2 cooler or via the heat exchanger connected to the refrigerant circuit.

The low-temperature circuit 2 cooler releases the waste heat directly to the environment. The powertrain control unit activates the fan motor and the radiator shutters in order to regulate cooling output on the cooler. As the demand for cooling output increases, the radiator shutters are activated in order to increase the air flow. The fan motor is then activated if necessary.

The heat exchanger cools the coolant via the refrigerant circuit. The cooled down coolant is then available to the low-temperature circuit 2.

If the enable signal was issued by the energy management, the powertrain control unit requests actuation of the electrical refrigerant compressor from the control for the climate control. The refrigerant flows through the evaporator or the heat exchanger. Heat is thus removed from the low-temperature circuit 2.

The cooling output is primarily dependent on the level of actuation to the electric refrigerant compressor.

The following applies for electric vehicles: At low outside temperatures, the PTC heater heats the coolant and thus the component parts connected in the low-temperature circuit 2.

The following applies for hybrid vehicles: Depending on the position of the low-temperature circuit switchover valve 2, the coolant is routed via the high-voltage battery or the AC charger.