From an auto mechanic’s point of view, this type of electric car is less interesting at first glance: combustion engines, which are quite exciting thanks to a large number of complex components, have had to make room for a comparatively simple electric motor. The mechanical drivetrain has also had to step aside. “What’s left to repair on an electric car?” is often the fatalistic view.
But, thankfully, it’s not quite as bad as that: other components and technologies are gaining in importance. Thermal management in particular plays an important role in electric cars and will probably become even more important in the future. Thermal management systems in e-cars are generally more complex than those in conventional vehicles. After all, pure electric cars, or battery electric vehicles (BEV), have a number of components that are particularly sensitive to hot and cold. And it’s also common knowledge that it’s a bit tricky to heat and cool the vehicle interior.
Due to their high level of efficiency, electric drives only emit a small amount of heat into their surroundings compared to conventional combustion engines. Additional heaters are required so that the interior can be heated to a reasonable level at low outside temperatures. The problem: As additional energy consumers, they draw a considerable part of the energy stored in the battery. The warmer the interior, the shorter the range. Electric auxiliary heaters integrated in the ventilation system are a simple, effective but also a very energy-intensive device. For this reason, energy-efficient heat pumps are now also used. They can then be utilised as air conditioning units for cooling in the summer as well.
So much for comfort. For an electric motor to be operated in a reasonable way and with a particularly high degree of efficiency in the first place, the temperatures of the electric motor, the power electronics and the battery must always be kept within a temperature range that allows optimum efficiency. A sophisticated and complex thermal management system is responsible for this, in which the refrigerant and cooling circuits interact perfectly. “Due to the components’ different temperature requirements, generally speaking, several cooling circuits are used in electric vehicles at different temperature levels, sometimes with different cooling media,” explains Prof. Dr. of Engineering Boris Schilder, Professor of Thermodynamics and Fluid Mechanics at Frankfurt University of Applied Sciences.
Thermal management also has a decisive influence on the performance and durability of the battery: batteries must be operated within a clearly defined temperature window. Lithium-ion batteries are particularly comfortable in a range between 15 °C and 30 °C. If the operating temperature is too high, the battery life will be reduced, meaning that the battery may fail prematurely. Even at very low temperatures, the battery cells age, resulting in them being less durable.
Something that makes things even more difficult is that it’s not just the battery’s overall temperature that has to stay in this defined window. The temperature difference between the individual cells also has to remain below a certain value. Furthermore, brief peak loads connected to high current flows, for example from recuperation and boosting, heat up the cells.
To be able to operate all components, especially the battery, in the optimum temperature ranges, automotive manufacturers and suppliers have developed intelligent battery cooling and thermal management systems. Even in the age of the electric car, these systems ensure that auto mechanics never get bored and, not least, generate revenue for automotive workshops.