In electric vehicles, the cooling system is mainly divided into two parts: one is to cool the drive motor, vehicle controller, DC/DC and other components of the power system, and the other is to cool the power battery and on-board charger of the power supply system. This article discusses the power battery cooling system.

　　At present, the power battery of electric vehicles is lithium-ion battery. The performance of lithium-ion power battery is sensitive to temperature changes. The loading space on the vehicle is limited. The number of batteries required for the vehicle is large, and the batteries are closely arranged and connected. When the vehicle is running under different driving conditions such as high speed, low speed, acceleration, deceleration, etc., the battery will be discharged at different rates and generate a large amount of heat at different heat generation rates. In addition, time accumulation and spatial effects will cause uneven heat accumulation. , thus causing the battery pack operating environment temperature to be complex and changeable.

　　The cooling performance of the power battery directly affects the efficiency of the battery, and also affects the battery life and safety. Since the battery itself will generate a certain amount of heat during the charging and discharging process, the temperature will rise, and the temperature rise will affect many characteristic parameters of the battery, such as internal resistance, voltage, SOC, available capacity, charging and discharging efficiency, and battery life.

　　In order to maximize the performance and life of the battery pack, it is necessary to optimize the structure of the battery pack, conduct thermal management, add heat dissipation facilities, and control the temperature environment in which the battery operates.

　　Main cooling solutions

　　Different thermal management systems have different component types, structures, weights, system costs, and control methods, so the performance achieved by the system is also different. When selecting the type of battery pack thermal management system, the cooling performance requirements of the battery need to be taken into consideration. Combined with the performance of the vehicle and the size of the space, the stability and cost of the system are also factors to be considered.

　　Chart 1 Comparison of the advantages and disadvantages of different battery cooling solutions

　　Working diagram of different cooling systems

　　1. Air cooling

　　There are mainly the following cooling methods for electric vehicle battery packs at home and abroad: air cooling, liquid cooling, and heat pipe cooling. At present, air cooling is still the main method used. Air cooling is relatively easy to achieve, but the cooling effect is not good.

　　Chart 2 Typical air cooling system working diagram

　　2. Liquid cooling

　　Liquid cooling has a better cooling effect and can evenly distribute the temperature of the battery pack. However, liquid cooling has high requirements on the sealing performance of the battery pack. If a conductive liquid such as water is used, a water jacket is required to separate the liquid and battery cells. This not only increases the complexity of the system but also reduces the cooling effect.

　　Generally, the cooling system is installed near the battery pack module. The principle is similar to the refrigeration principle of the air conditioner. The cooling system is connected to a single battery module through a pipeline. Coolant (usually ethylene glycol) circulates in the pipeline to separate the single battery module. The heat is taken away, the cooling system cools the ethylene glycol, and the excess heat is discharged to the outside through the fan, while the ethylene glycol circulates into the battery module again and continues to absorb the heat emitted by the battery.

　　3. Heat pipe technology

　　Heat pipe technology can meet the dual working conditions of high-temperature heat dissipation and low-temperature preheating of the battery pack, with fast response and good temperature uniformity. After being proposed as a new cooling method for battery packs, it has developed to a certain extent and has become a key direction of industrial research. , but due to layout and volume restrictions, it has not yet been used in actual vehicles.

　　Chart 4 Schematic diagram of heat pipe technology working

　　Judging from the current cooling methods of electric vehicle power batteries, air cooling has always occupied a major position, especially Japanese electric vehicles, which basically use air cooling systems. As the application environment places higher and higher requirements on batteries, liquid cooling has also become a priority solution for automobile companies, such as Tesla, BMW and other brands. Mainstream electric passenger car companies in my country have also begun to turn to liquid cooling systems. Judging from the mid- to long-term trend, liquid cooling will become the mainstream.

　　Main components of battery pack cooling system

　　Different cooling systems have corresponding cooling components: the main component of the air cooling system is the fan, and the main component of the liquid cooling system is the cooling plate.

　　Air cooling system components: cooling air duct, fan, resistance wire

　　The selection of the fan directly affects the cooling effect of the battery pack air cooling system. The fan selection requirements are as follows: determine the air flow rate based on the heat generation rate of the battery; meet the temperature rise requirements of each module; select a fan that meets the requirements based on the air flow required by the system and the pressure drop curve of the system.

　　Liquid cooling system components: water cooling pipes, cooling pumps, cooling valves, cooling plates

　　The cooling plate is one of the most critical components in the battery pack liquid cooling system, and the selection of the cooling plate is crucial. The selection of the cooling plate must meet the following requirements: the pressure drop of the cooling plate must meet customer requirements; consistency requirements of cooling water flow; burst pressure requirements; mechanical requirements of the cooling plate; the cooling plate must pass vibration and impact load tests; the cooling plate Tolerance requirements as well as spatial dimensional requirements must be met.

　　There are many battery cooling system component manufacturers, and most of the main components are provided by traditional electrical companies. Currently, battery management system companies and PACK assembly companies are also involved in the production of customized products.

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