For electric vehicles, the thermal management system consists of three parts:
- air conditioning thermal management
- motor electronic control thermal management
- battery thermal management
Since there is no engine to provide heating, air conditioning thermal management needs to use PTC/heat pump/thin film heater to provide heat source. Hydrogen fuel cell vehicles can theoretically provide heat source from the power system like fuel vehicles, but the startup time is longer.
PTC technology is mature. Due to its electric heating technical principle, the electric energy utilization efficiency is lower. More than 1 joule of power is consumed for every 1 joule of heat generated. It consumes a large amount of battery.
Especially considering that the most important usage scenario of air conditioning and heating functions is winter, and the lower the temperature, the greater the heating power required. Using PTC heating will make the already pitiful cruising range of electric vehicles in winter worse, seriously reducing the practicality.
Heat pump system for electric vehicles air conditioning
Heat pump heating moves heat from a relatively low temperature (outside the car) to a relatively high temperature (inside the car). It use low boiling point refrigerant to bring heat from the environment into the passenger compartment. The heat consumed in the passenger compartment is the sum of the electric energy and the absorbed low-level heat energy. So its heating coefficient COP [(absorbed low-level heat energy + consumed electric energy) / consumed electric energy] must be greater than 1 (usually 1.5-5). It reduces the load on the battery. After the Volkswagen ID.4 CROZZ is equipped with a CO2(R744) heat pump, its winter cruising range is increased by 30%.
Thermal management for E-motor and controller
The thermal management for E-motor and controller can be designed similar to the engine and gearbox thermal management modules of fuel vehicles. It also use air cooling,oil cooling and water cooling. Air cooling is mainly used in low-end models with smaller motor power. While water cooling is mainly used in higher-power models. During operation, the water pump is relied on to drive the coolant to circulate in the cooling pipe. Through the heat exchange process such as the radiator, the coolant takes away the heat generated by the motor and electronic control.
Battery thermal management system
Battery thermal management can be said to be the biggest increase in thermal management of electric vehicles. At the same time, because the ambient temperature has a huge impact on the working status of the battery. The quality of battery thermal management is crucial to the user experience of electric vehicles.
The efficient working temperature range of power batteries is 20-35℃. Too low temperature (<0℃) will cause battery activity to decrease, charge and discharge power performance to decrease, shorten cruising range, and destroy battery life. Too high temperature (>45℃) will destroy the battery life, and may also lead to battery thermal runaway or even serious accidents such as fire.
The internal temperature of the battery and the temperature uniformity between battery modules will also affect the battery performance and cycle life. Therefore, the battery thermal management system requires a complex and sophisticated cooling circuit to maintain the consistency of the cell temperature and to accurately measure and monitor the battery temperature. When the battery temperature is too high, it will quickly dissipate heat. When the battery temperature is too low, it will quickly heat up. Currently, battery thermal management includes air cooling, water cooling, direct cooling, phase change materials and other methods.
Liquid cooling is the best application prospect for battery thermal management solution. It could offer faster cooling speed and higher heat transfer coefficient. It can be assisted by technical assistance such as phase change materials. Since the power battery cells are relatively neatly arranged, battery liquid cooling is mainly carried out in the form of a liquid cooling version.
The traditional battery liquid cooling plate adopts a whole plate structure and is placed under the battery pack. In its just-released flagship product(the Qilin Battery showed in below), CATL adopts a new layout with a liquid-cooling plate installed between two cells. It reduces the heat conduction of two adjacent cells and improves safety. However, the amount of liquid-cooling plate used in a single vehicle It will also increase exponentially.
