Electric vehicles (EVs) experience thermal loads from heat generated by the battery pack, motor, power electronics, brakes, and the cabin heating, ventilation, and air conditioning (HVAC) system. These thermal loads must be managed to varying degrees to ensure the critical vehicle systems are kept within their optimal operating temperature range.
If battery cells, motors, or inverters overheat, it can lead to significant performance loss and damage. There are many different ways to measure and manage these thermal loads.
The types of sensors used to measure temperature include contact and non-contact sensors. Contact sensors include thermocouples, negative temperature coefficient (NTC) thermistors, resistance temperature detectors, and optical fiber temperature sensors. Non-contact sensors include electrochemical impedance spectroscopy, Johnson noise thermography, and infrared thermography.
The battery thermal management system (BTMS) has the most complex thermal management challenge. A battery pack consists of thousands of individual cells, which may be loaded differently and generate different thermal loads. The electrochemical reactions can result in significant temperature gradients across any individual cell — meaning that internal temperature sensing can provide valuable information for the battery management system (BMS). Battery cells may incorporate embedded temperature sensors within the cell.
A typical EV BTMS will mount the battery cells to a metallic plate, which acts as a heat sink for the batteries and a heat exchanger for a coolant fluid flowing over the other side of the metallic plate. The coolant fluid then dissipates heat using a radiator and fan, similar to those found on an internal combustion engine (ICE) vehicle. Such an arrangement allows coolant fluid to be circulated through the battery pack to maintain the required temperature.
A heating element can also be used so the fluid pre-heats the battery pack during cold-weather starts. Due to the greater cooling demand of an EV compared to an ICE vehicle, a smaller radiator can be used, which typically need not be located in direct airflow at the front of the vehicle. A liquid cooling system may be centralized so that the same coolant fluid and radiator dissipate heat from the battery pack, motor, and inverter.
Some EVs do away with a liquid cooling system, relying on air cooling instead. This means exposing metal fins on the underside of the metallic plate to airflow beneath the vehicle. Air cooling is cheaper, lighter, and easier to maintain. However, there are better ways to control battery temperature, as this leads to a less favorable trade-off between battery performance and lifespan.
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