Brief description of power battery thermal management system

　　Tesla has spontaneously ignited again. In Tianhe District, Guangzhou City, a Tesla Model S spontaneously ignited, causing serious damage to the vehicle. This was not the last time a Tesla Model S spontaneously ignited after a collision in the United States. to two months.

　　Tesla's spontaneous combustion incidents have occurred not once or twice, but each time it has caused a great sensation, but the result is often nothing. Tesla has not announced the cause of the car's spontaneous combustion.

　　In fact, people are not only concerned about Tesla's spontaneous combustion problem, but also about the safety of new energy vehicles. After all, Tesla is a banner presence in the new energy vehicle market. If Tesla's products do not If it can make people trust, then consumers will naturally have concerns when facing new energy vehicles.

　　The safety of new energy vehicles has always received great attention, and everyone's focus is related to batteries, including fire and explosion, leakage, water wading, radiation, etc. In fact, car companies will take these issues into consideration when developing new energy vehicles, and will solve problems or make compromises in some aspects for the sake of safety.

　　Here, we mainly understand the cooling system of power batteries. The quality of cooling performance will directly affect the efficiency of the battery, and will also affect the life and safety of the battery.

　　The power battery will generate a certain amount of heat during the charging and discharging process, which will cause the temperature to rise. The temperature rise will affect many characteristic parameters of the battery, such as internal resistance, voltage, available capacity, discharge efficiency, battery life, etc.

　　In order to extend the service life of the power battery as much as possible and obtain maximum power, the battery needs to be used within a specified temperature range, which involves the cooling system of the power battery.

　　At present, the thermal management of new energy vehicle power battery systems can be mainly divided into four categories: natural cooling, air cooling, liquid cooling and direct cooling. Natural cooling is a passive thermal management method, while air cooling, liquid cooling and direct current are active methods. , and the main difference between the three is the difference in heat exchange medium.

　　natural cooling

　　Natural cooling does not have additional devices for heat exchange. In layman's terms, it relies on natural wind. For example, BYD Qin, Tang, Denza and other models using LFP batteries all use natural cooling.

　　The advantages of natural cooling are simple structure, low cost, and small space occupation. The disadvantages are also obvious: low heat dissipation efficiency, which cannot adapt to the cooling needs of high-power charging and discharging. It is generally only used for electric vehicles with moderate operating conditions and cost-sensitive .

　　air cooling

　　Among the new energy electric vehicles sold on the market, air cooling still accounts for a large proportion, and it is currently the most widely used heat dissipation technology in the power batteries of new energy vehicles.

　　Air cooling uses air as the heat exchange medium. The principle is to use a cooling fan to draw air from inside the cabin into the power battery box to cool the power battery and the control unit of the power battery and other components. Models such as the Toyota Prius, Honda Insight, Camry Hybrid and Corolla Twin Engine all use air-cooled battery cooling systems.

　　Compared with other technologies, air cooling technology is relatively simple and convenient for safety and maintenance. It can achieve good heat dissipation performance at low cost.

　　However, the disadvantages of air cooling technology are also very obvious, especially compared with liquid cooling technology, the heat exchange coefficient between it and the battery surface is low, the cooling and heating speed is still relatively slow, and the temperature uniformity inside the battery box is not easy to control. , and the sealing design of the battery box is difficult, and the dustproof and waterproof effect is poor. It has to be said that some electric vehicle fire incidents are due to the poor thermal management performance of air-cooling technology.

　　liquid cooling

　　As the usage environment places higher and higher demands on power batteries, liquid cooling technology has gradually replaced air cooling technology and become the preferred choice of major car companies. Especially in large and medium-sized pure electric vehicles, the usage rate of liquid cooling systems is very high. , in small pure electric vehicles and even plug-in hybrid vehicles, more and more new models use liquid cooling.

　　The principle of liquid cooling technology is to use the coolant inside the battery pack to take away the heat generated by the battery during operation to achieve the effect of reducing the battery temperature.

　　To put it simply, the liquid cooling system technology passes through a water pipe in the battery pack. When the battery needs to be cooled, cold water is passed into the water pipe. The cold water takes away the heat and cools it down. When the battery needs to be heated, hot water is passed into the water pipe. .

　　The liquid cooling system has a better temperature control effect on the battery pack than the air cooling system. The liquid medium has a high heat transfer coefficient, large heat capacity, and faster cooling speed.

　　It is understood that Tesla Model S, Emgrand EV, JAC IEV6E, etc. currently all use liquid cooling technology. It is worth mentioning that the JAC IEV6E sports version is the first domestic mini pure electric vehicle to use liquid cooling technology. It is equipped with The liquid-cooled battery temperature control system can control the battery temperature between 15-35℃, and it can be used normally in an environment of -30-55℃.

　　Directly cold

　　The last thing to talk about is the direct cooling system. The structure of the direct cooling system is similar to the liquid cooling system, but direct cooling will directly inject the refrigerant from the automobile air conditioning system into the battery pack. The refrigerant can absorb a large amount of energy during the gas-liquid phase change process. Heat, take away the heat inside the battery more quickly, and have higher heat dissipation efficiency.

　　Direct cooling uses refrigerant as the heat exchange medium, and the refrigerant can absorb a large amount of heat during the process. Compared with liquid cooling, direct cooling can increase the heat exchange efficiency by more than three times and remove the heat inside the battery system more quickly. The BMW i3 uses a direct cooling solution.

　　The direct cooling system improves the heat exchange efficiency, but it also has shortcomings. It requires higher air tightness of the system and puts forward higher requirements for the production and manufacturing process. In addition, the heat dissipation uniformity of the direct cooling system is difficult to control, and the battery core temperature difference There are excessive risks.

　　In addition, the direct cooling system can only integrate the heat dissipation function and does not have the heating function. An independent heating system needs to be installed to cope with the low temperature in winter.

　　In the early days of the development of new energy vehicles, the market was dominated by A00 and A0-class models. These models did not have high performance requirements and were mostly used for commuting in cities. Moreover, due to cost constraints, they often used natural cooling or Wind chill.

　　However, with the development of new energy vehicles and further promotion of the market, the structure of the new energy vehicle market is gradually becoming mature, and the market share of A-class vehicles and above is gradually increasing. At the same time, new requirements for cruising range, energy density, battery capacity and charging speed are proposed. higher requirement.

　　As battery energy density becomes higher and higher, battery safety issues must also attract special attention, because the negative impact of thermal runaway will be relatively large, and the liquid cooling system has significant advantages in heat exchange efficiency, control of temperature rise and fall, and NVH It has performed well in other aspects, and may be more widely used.

　　The development of new energy vehicles has entered a white-hot stage. The requirements for battery technology are getting higher and higher. The thermal management system can play a great role in the safety of batteries. Its rapid development can also put new energy vehicles in a better position. in progress.

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