The Study On Power Battery Thermal Management System Of Hybrid Heavy Vehicle

Hybrid armored vehicles as a new generation of combat equipment have focused the country's attention.Power battery system as the main source of energy for the motor,its performance on the impact of the vehicle is essential.At present,the mainstream lithium-ion battery is more sensitive to changes in temperature,when temperature is too high,too low or even uneven will affect the battery performance,safety and consistency.The traditional parallel ventilation structure has a non-uniform wind assignment,and for the square battery only "one-dimensional cooling" takes roles on(only the front and rear surfaces of the battery can be cooled by air in parallel,other surfaces are not effective cooled).In the high-power conditions of operation,this structure is unable to effectively reduce the battery maximum temperature and temperature difference.Therefore,an effective battery thermal management system is required for the hybrid powertrain system,this paper studies from the following aspects:First,three structures were proposed,which were considered as wedge shape,trapezoidal shape and round holes baffle to achieve uniformity,and the "round holes baffle" structure has been selected to improve the cooling dimension,the effect was compared between parallel cooling and vertical cooling,by the CFD simulation analysis(the front and rear side of the battery while cooling).For the vertical cooling condition,the effects of discharge rate,ambient temperature,outlet velocity and battery gap on the heat dissipation characteristics of the battery were studied.The results showed that when the ambient temperature is 25?,the natural convection can meet its cooling demand during the small discharge rate process,but that was not the situation during the large discharge rate process.The ambient temperature directly determines the temperature of the battery surface,for example,when the ambient temperature exceeds 30?,the battery temperature is easy to exceed the appropriate temperature range.Outlet velocity reflects the mass flow rate of air,the greater of outlet velocity the greater mass flow rate,which means a heavier heat taken away.However,if the energy consumption and maintenance costs are taken into account,the increase of outlet velocity is limited.As the battery gap increases,the temperature uniformity of the cell and consistency of the module improve,but the maximum temperature of the battery pack increases.Secondly,with reference to the traditional cold start mode of heavy-duty vehicles,a power battery preheating system for vehicle fuel heater is proposed,and the "PI electric heating film" is selected as the contrast.The results show that: PI heating film can quickly warm up,but it need to consume electricity and fuel heater heating time is long,which does not affect the mileage.The two preheating methods were simulated and analyzed respectively.For fuel heating,the effect of heating time,inlet temperature,and outlet velocity on the battery temperature were analyzed,for PI heating.In order to solve the contradiction between the temperature difference and the heating time,the heating film power is changed at different times to shorten the warm-up time and reduce the temperature difference.The improved battery module structure is then applied to the power battery pack system.The temperature field of the battery heat dissipation system is optimized by changing the shape of the air inlet(round,square,diamond,waist).The flow field of the battery preheating system is optimized by changing the inlet mode of the heater.In the large discharge rate,the air-cooled has been unable to meet the cooling needs,through slotting in the surface of round hole baffle,embedded liquid flow of aluminum,this paper innovative change round hole baffle into a "round hole liquid ",without changing the size of the original structure of the case.,to achieve gas-liquid dual media co-thermal management.This change not only increase the cooling medium,and achieve the six surface of the battery "three-dimensional cooling",even at high magnification discharge,but also reduce the maximum temperature of the battery down to 45 ? and control the maximum temperature within 5?.The results show that the single cooling method has been unable to meet the battery heat dissipation requirements in high temperature environment or large discharge rate,electric heating for the battery preheating will affect the battery mileage in low temperature environment.In this paper,the use of "gas-liquid dual media" co-cooling and fuel heater auxiliary preheat for the hybrid heavy power battery thermal management system provides a design idea.