| As the core component of electric vehicle, the working performance of power battery and motor is closely related to temperature. Therefore, the efficient thermal management is one of the key issues that ensure the power output and the vehicle performance. Meanwhile, the thermal states of the multi-thermal systems including battery, motor and air conditioning system in the underhood are easy to interact with each other. In order to improve the vehicle thermal management performance and further enhance the vehicle power, the heat flow and interaction problems in the underhood should be focused. At present, the electric vehicle thermal management technology is gradually moving towards system integration and the electric-thermal complementation and coordination to further realize the energy saving, consumption reduction and improvement of the vehicle performance and mileage.To break through the above-mentioned problems of the electric vehicle thermal management technology, this paper designs and prepares two kinds of liquid flow heat transfer structures, namely, tube bundle soft contact type and high thermal conductivity local immersion type, and their corresponding battery modules for cylindrical and prismatic power battery under the support of National Natural Science Foundation of China(No. 51376079). At the same time, the simulation and experiment of the battery modules cooling and preheating performance are carried out. Thereinto, for cylindrical battery module, the battery and the heat exchange surface adopted the elastic soft contact, which can increase the contact area and the fitting degree. Thus, the heat transfer effect is improved. Meanwhile, the prismatic battery module adopts high thermal conductivity graphite gasket to further achieve heat transfer enhancement, and the temperature uniformity of the battery was improved. The two kinds of heat transfer forms that adopt local contact between the liquid flow and the battery have a good cooling effect and temperature uniformity, besides, the local contact liquid flow heat transfer form is more light weight than the ordinary full contact liquid flow heat transfer form.The analysis of thermal management influence factors indicates that the liquid flow temperature has an important effect on the temperature variation and temperature uniformity of the battery. A lower cooling temperature is conducive to the rapid heat transfer in the battery cooling process, but unfavorable to the temperature uniformity. To further improve the temperature uniformity of the battery module in the thermal management process, a method of variable temperature cascade cooling is proposed to realize disparted step small temperature difference progressive cooling. At the same time, the effect of different thermal control methods include temperature period control and time period control was compared and analyzed. Through the experiment and numerical computation, it can be found that the temperature fluctuation of the battery module with large temperature difference heat transfer could be reduced effectively by using the method of variable temperature cascade cooling, thus the temperature uniformity could be improved.Meanwhile, the working process of the battery and motor thermal management is closely related to the electric vehicle power. So it is usually required to design the corresponding thermal management system and further analysis the thermal management performances of different flow paths. Therefore, the model, module and correlation algorithm of the system are built on MATLAB by using theory and experiment.Then combine with the dynamic performance of the vehicle, the thermal management performance and effect of influence factors in working process can be calculated and analysed, including the speed, slope, pump, fan and working conditions. In addition, the auxiliary cooling effect of the heat pump for battery is further analysed based on the established system. The relevant performance prediction and simulation analysis are carried out, which laid the foundation for the accurate control of the thermal management process.Furthermore, the three dimensional(3D) entity model of the underhood in pure electric vehicle is established and the layout of the internal components is carried out.The heat transfer components in the underhood mainly include battery thermal management subsystem radiator, motor thermal management subsystem radiator and air conditioning system condenser. Based on one dimensional(1D) platform Matlab, a 1D battery and motor thermal management system and air conditioning system are established by using the lumped parameter, theory and experiment method. The 1D and 3D combined calculation of power system thermal management and air conditioning process is realized. Moreover, on the basis of the traditional engine cooling performance analysis method, the cooling constant K is introduced to measure the cooling effect of the electric power system.The analysis and evaluation method and evaluation index of electric vehicle power system thermal management are further proposed to analyze the battery and motor thermal management effect and the air conditioning system performance under different layout forms of heat exchangers. Among them, the thermal interaction influence between power system and air conditioning system is revealed, and the effect on the influence factors for the thermal interaction behavior is simultaneously analyzed, such as the liquid flow rate, the fan rotational speed and the heat exchanger position. The results show that the adjustment of the heat exchanger position can effectively reduce the adverse effects of the air conditioning system on the electric power system thermal management. This chapter provides the basis and method to evaluate and optimize the thermal management performance of electric vehicle underhood.Finally, the research work of the electric vehicle thermal energy reusing and storage device are developed. A whole liquid flow pattern pure electric vehicle integrated thermal management system with a heat storage device is presented. And the whole vehicle heat integration is achieved through the whole liquid circulation medium. As a result, the fine coordinated thermal control of electric power system is satisfied and the waste heat recovery and reuse of electric components is fulfilled, which can promote the integration, complementation and coordination of the whole vehicle electric power and thermal energy systems. Meanwhile, according to the requirement of rapid thermal storage and heat release for the vehicle applications, a small scale contact heat transfer PCM thermal storage device is designed, which has a fast phase change heat transfer rate. In addition, combined application of PCM thermal storage units with multiple melting points is proposed to meet the demand of multiple temperature levels power unit heat recovery. And the descending and ascending cascade combination arrangement of the melting point can enhance the phase change synchronization. It is beneficial to further enhance the heat storage and heat release rate, and achieve the promotion of heat storage and heat release efficiency. The content of this chapter is only an exploratory research on the electric vehicle thermal-electric integrated thermal management. In the future, the thermal storage device should be combined with the whole vehicle and the power system to carry out a further research on the integration of the systems. |
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