The thermal management system of automobiles is an important system for regulating the cabin environment and working environment of automotive components. It comprehensively improves energy utilization efficiency through refrigeration, heating, and internal heat conduction. The thermal management system of pure electric vehicles is more complex than that of regular fuel vehicles, due to the fact that pure electric vehicles have more components that require thermal control, such as batteries, controllers, and electric motors. The thermal management system of pure electric vehicles not only includes the air conditioning system, but also adds different parts such as battery pack environment, power electronic devices, and motor heat dissipation according to the thermal management requirements.
01、 Why thermal management is needed
The self ignition accident of electric vehicles is believed to have deeply rooted in people's hearts, and the reason why self ignition accidents occur is not only due to circuit problems such as leakage or short circuits, but also the thermal management strategy and circuit design of the controller on the vehicle directly affect the safety of electric vehicles. Of course, the spontaneous combustion of electric vehicles is a rare occurrence, but through such incidents, every automotive company and supplier's automotive business unit can attach more importance to thermal management as a technical department. After all, most companies' powertrain departments still rely on battery motors and electric drives as the main force, with thermal management as a supplement. Part of the reason for spontaneous combustion is due to excessive heating and not being cooled in a timely manner, while there are also other scenarios where the environment is too cold to receive timely heating.
1.1 Heating demand:
One of the heating needs: cabin heating in winter, where the driver and passengers need warmth inside the car, which involves the heating needs of the thermal management system. A simple example is that the electric vehicles supplied by the same car company to Nordic countries may use a rated power of 5kW electric heaters, while those supplied to countries in the equatorial region may only have 2-3kW or even no heaters. In addition to latitude, altitude also has a certain impact, but there is currently no specific design for distinguishing altitude, as it is not guaranteed that car owners will drive from the basin to the plateau. The other biggest influencing factor is the people inside the car, because whether it is an electric vehicle or a fuel powered vehicle, the needs of the people inside are still the same, so the temperature demand range designed is almost identical, usually between 16 degrees Celsius and 30 degrees Celsius. That is to say, the cabin cooling does not exceed 16 degrees Celsius, and the heating does not exceed 30 degrees Celsius, covering the normal human body's environmental temperature requirements.
Heating demand 2: The most common high-voltage batteries nowadays are lithium-ion batteries, which have been used for a long time in mobile phones and laptops. They have always been seen as "born for fever", but I have never heard that they still need to be heated. This is mainly because mobile phones do not freeze alone in outdoor sub zero environments, at least they are covered by people's hands or pockets. Some users may have experienced that they cannot turn on the phone outdoors in low temperatures or the phone consumes a lot of electricity after brushing for a while. This is the beauty of lithium-ion batteries. Lithium ion batteries prefer to charge and discharge between 15 and 35 degrees Celsius, which can limit the charging and discharging current and also affect their SOH (State of Health) health.
1.2 Cooling requirements
One of the cooling requirements: High voltage battery cooling. Due to the existence of internal resistance and discharge balance circuit, the current flowing during the charging and discharging process will cause the battery to heat up. The longer the continuous driving time, the more times and intensity of acceleration and deceleration, all of which promote the heating of the battery. The current during the charging process also increases heating, especially during DC charging. The temperature rise of the battery varies depending on the vehicle and the type of battery. For example, some micro cars or small cars have low charging and discharging power, and the continuous temperature rise of the battery is not too large. Therefore, some air cooling methods or smaller water cooling cooling circuits can be used; Some electric models of SUVs and luxury cars require strong battery cooling capacity to meet the needs of high-power charging and driving.
Cooling Requirement 2: In addition to the battery, the high-voltage power electronic cooling three electric appliances also have electric motors and electronic controls. In fact, the on-board charger OBC (On Board Charger), high-voltage to low-voltage DC/DC, and high-voltage distribution box also have cooling requirements.
The demand for heating and cooling has spawned the entire industry of thermal management systems, and these demands come from multiple aspects such as safety, comfort, component life, and charging power of electric vehicles. While meeting the demand, the thermal management system consumes a large amount of battery power. Many times, customers' expectations for thermal management systems are indirect, wanting both comfortable temperature in the cabin and the safety of the power components inside the car. Most importantly, they are also very concerned about the range. This actually establishes the main theme of current thermal management system research and development: indirectly meeting customers' direct needs for various aspects of the vehicle system with as little energy as possible.
02. Pure electric vehicle thermal management system The thermal management system of pure electric vehicles assists in driving by maximizing the use of battery energy. By carefully reusing the heat energy in the vehicle to the air conditioning and batteries inside the vehicle, thermal management can save battery energy and extend the driving range of the vehicle. Its advantages are particularly significant in extreme cold and hot temperatures. The thermal management system of pure electric vehicles mainly includes high-voltage battery management system (BMS), battery cooling plate, battery cooler, high-voltage PTC electric heater, and heat pump system according to different vehicle models.
The thermal management system solution for pure electric vehicles covers the entire system range, from control strategies to intelligent components, managing two extreme temperatures by flexibly distributing the heat generated by powertrain components during operation. By allowing all components to operate at the optimal temperature, the pure electric vehicle thermal management system solution shortens charging time and extends battery life.
The High Voltage Battery Management System (BMS) is more complex than the battery management system of traditional fuel vehicles, and as a core component, it is integrated into the battery pack of pure electric vehicles. Based on the collected system data, the system can transfer thermal energy from the battery cooling circuit to the vehicle's cooling circuit to maintain the optimal battery temperature. The system has a modular structure, which mainly includes devices such as battery management controller (BMC), battery monitoring circuit (CSC), and high-voltage sensor.
The battery cooling plate can be used for direct cooling of pure electric vehicle battery packs, which can be divided into direct cooling (refrigerant cooling) and indirect cooling (water cooling). It can be designed and matched based on the battery to achieve efficient battery operation and extended lifespan. The inner chamber of the dual circuit battery cooler is composed of dual medium refrigerant and coolant, which is suitable for cooling pure electric vehicle battery packs, maintaining the battery temperature in an efficient area and ensuring optimal battery life.
Pure electric vehicles do not have a heat source, so a high voltage PTC electric heater with a standard output power of 4-5kW is required to provide fast and sufficient heat inside the vehicle. However, the residual heat of pure electric vehicles is not sufficient to fully heat the carriages, so a heat pump system is needed for heating.