| Hilly and mountainous areas account for 64% of the total land area of China.The cultivated land and orchards in these areas are mostly small,scattered,with height difference and poor road conditions,which cause great troubles to the transportation of crops,fertilizers and other materials.With its characteristics of small unit pressure on the ground,strong adhesion,large load capacity and strong driving ability,tracked vehicle can be better applied to the short distance transportation of agricultural products,fertilizers and other materials in hilly and mountainous areas with poor road conditions.Compared with the internal combustion engine tracked vehicle,the electric tracked vehicle also has the advantages of low vibration,low cost and no exhaust gas emission.Under the increasingly severe energy problems and increasingly stringent environmental protection requirements,the electric tracked vehicle has a broader application prospect.However,the effective thermal management of the battery pack is an important condition to ensure the safety and service life of the tracked vehicle which uses the lithium battery pack as the energy source.The related studies show that the appropriate temperature range for lithium-ion batteries is 20℃～40℃,and the temperature difference within the battery pack should be less than 5℃.Excrescent working temperature will accelerate battery aging and affect battery life.For the power battery pack,if the heat accumulation is caused by ineffective heat dissipation,the internal temperature of the battery pack will be too high and the temperature difference will be too large.Especially in the hilly and mountainous areas of southern China,when climbing with full loads in the process of summer and autumn fruit harvest,the heat generation of the tracked vehicle battery pack is more serious.If the heat dissipation is not carried out in time,it will have a negative impact on the performance and service life of the battery pack.In serious cases,safety problems such as thermal runaway,fire and explosion will occur.Therefore,it is of great significance to manage the heat dissipation of the battery pack of the electric track vehicle.In this paper,we study the heat generation condition of an electric tracked vehicle by combining experiment and simulation methods under the actual working condition,which is mainly used in the southwest hilly area of China.We clear and definite the ambient temperature and working conditions for heat dissipation management,and designed and studied the liquid cooling cooling system to meet the heat dissipation requirements of the electric tracked vehicle.The main works and conclusions of this paper are as follows:(1)Based on the analysis of the heat generation mechanism of the lithium battery,the capacity and internal resistance of the lithium ion battery used in the electric track vehicle were tested.Through the discharge experiments at ambient temperature at 0℃,10℃,20℃,25℃,30℃,40℃,the capacity of the lithium-ion battery used in the electric track vehicle changed with the temperature: in the range at 0℃～25℃,the capacity of the battery had a great increase with the rise of temperature;in the range at 25℃～40℃,the capacity of the battery had a small fluctuation with the rise of temperature.Then,HPPC experiments were carried out at the above ambient temperatures to obtain the internal resistance data of the battery under different ambient temperatures and different states of charge.(2)The discharge current of lithium-ion battery pack under four typical working conditions,namely,no load on flat road,no load on ramp,heavy load on flat road and heavy load on ramp,was obtained by measuring the current of electric tracked vehicle in actual working conditions.Using the measured current data,the charging and discharging experiments of the single battery were carried out at three typical temperatures at 0℃,25℃ and 40℃,and the temperature rise data of the charging of the single battery at different ambient temperatures and the temperature rise data of the charging under different ambient temperatures and different working conditions were obtained.(3)According to the internal resistance data of lithium-ion battery at different temperatures and current data of actual working conditions,the change rule of the internal heat rate with time in the whole discharge cycle of the battery at different ambient temperatures and working conditions was calculated.CFD simulation software was used to conduct thermal simulation of the single battery,and the accuracy of the above data and simulation method was verified by comparing with the experiment.Then,the temperature field distribution of the lithium battery pack at 0℃,25℃,40℃ at the end of different discharge conditions was simulated,and the temperature of the lithium battery pack under extreme conditions was discussed.The ambient temperature and actual working conditions needed to conduct heat dissipation management were clarified,which laid a theoretical foundation for the safe use of the electric tracked vehicle.The simulation results showed that the temperature at 0 ℃,flat road racing conditions,no-load condition,flat road overload conditions,ramp slope overloading condition and environment at the environment temperature at 25 ℃,flat road racing conditions,no-load condition,flat road overload conditions ramp down at the end of the electric battery were less than the maximum temperature at 40 ℃,natural convection can meet the cooling requirements of the battery pack;Environmental temperature at 25 ℃,slope overloading condition and the environment temperature at 40 ℃,flat road racing conditions,no-load condition,flat road overload conditions,ramp slope overloading condition down the highest temperature at the end of the electric battery are: 45.377 ℃,47.425 ℃ and 48.295 ℃,49.697 ℃ and53.214 ℃,the above five kinds of the battery pack under the condition of high temperature had been beyond the optimum temperature range of lithium batteries work,natural convection can not meet the cooling needs of the battery pack.(4)According to the actual using scene and body structure of electric track vehicle,the cooling system using liquid cooling plate was designed.By using the orthogonal experimental design method,the influences of the channel direction,the channel section shape and the thickness of the liquid cooling plate on the cooling effect of the liquid cooling system were analyzed,and the optimal combination of the liquid cooling plate structure was determined.The results showed that the flow path had the greatest influence on the maximum temperature of the battery pack,followed by the thickness of the liquid cooled plate,and the flow path section has the least influence on the maximum temperature of the battery pack.When the liquid cooling system with the optimal combination was used,the maximum temperature of the battery pack was 32.511℃ and the maximum temperature difference within the battery pack was 4.992℃.Compared with the natural convection heat dissipation,the high temperature of the battery pack was reduced by 11.681℃ and the maximum temperature difference was reduced by 3.528℃,and the heat dissipation effect was obvious.(5)In order to reduce the maximum temperature difference in the battery pack,a liquid cooling structure was designed,which combined the cooling graphite sheet and the heat conduction column,and the cooling performance of the system was simulated and analyzed.The simulation results showed that the maximum temperature of the battery pack was 27.769℃ and the maximum temperature difference within the battery pack was1.633℃ after using above battery pack cooling system discharging.The heat dissipation experiment platform was built to carry out the verification experiment of the heat dissipation system,and the experimental measuring point temperature and the simulation temperature were compared to verify the accuracy of the model and the effectiveness of the heat dissipation scheme.Finally,the model was established and simulated according to the actual size of the battery box.The results showed that the maximum temperature of the battery pack was 34.252℃ after the discharge,and the maximum temperature difference within the battery pack was 2.923℃.The liquid cooling system combining graphite sheet and heat conducting column can meet the requirement of electric track rotation battery pack with good cooling effect. |
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