Research Of Electric Vehicle Liquid Cooling System Which Directly Contact With Battery Pack

Batteries are the key components of electric vehicles. Temperature has a great influence on the performance and life of batteries. So recently the battery thermal management technology which makes the battery work at a reasonable temperature range has become a hot area of research.And the study of heat dissipation is one of the most important content in the area. This paper presents a method of liquid cooling with direct contact and confirms its feasibility with theoretical analysis, numerical calculation and tests.Firstly,the NCM battery was tested by the charge and discharge test. Including the influence of temperature rise under different temperature and different ratio,law of battery heating,the change of internal resistance and open circuit voltage with different SOC and temperature. Established the battery thermal model based on the theory of heat generation and transformation and simulated the temperature field distribution of the battery under 1C(37A)、2C(74A)、3C(111A)、4C(148A)discharging conditions. Simulation was consistent with test and the model can accurately simulate the actual thermal behavior. Large discharge conditions caused high temperature problem. The highest temperature under 4C discharging condition was 58.3℃,heat dissipation had to be considered.Secondly,studied the heat dissipation of battery modules based on the thermal characteristics and modeling theory. The maximum temperature was over 70℃ by natural cooling,there were serious security implications. Under the same discharging condition,the maximum temperature rise and temperature difference between batteries can be 43.1℃ and 6.7℃ by the method of direct contact liquid cooling. Optimized the cooling structure and the structure of 3 in 1 out made a good cooling effect. The cooling effect was improved obviously,the maximum temperature rise and temperature difference between batteries can be controlled at 34.2℃ and 2℃.And this structure was applied to the test.Thirdly, finished the designation and processing of battery box based on the consideration of fixation and sealing. Completed parameter calculation and selection of the component such as pump, radiator and filter. Seted up the test platform and tested the effect of dissapation. Temperature uniformity was fine in the test under different discharging conditions. Transformer oil can be used as an excellent cooling medium in the area of liquid cooling.However the test value of temperature rise was higher than the simulation.Improved the boundary conditions of original model according to the actual test,then the simulation value and experiment value can fit well,the model can approximately simulate the real situation. Verified the problem of uncontrollable coolant temperature by adding small fan.Meanwhile,this method illustrates the feasibility of the active cooling methods to improve the effect of heat dissipation.