Study On Thermal-Mechanical Characteristics Of Electric Connection In Automobile Power Battery

There are a large number of electrical connectors between the cells and modules of the electric vehicle battery pack.The random vibration of the road surface will inevitably loosen the electrical connectors,which will increase the contact resistance and lead to the increase of the contact temperature.The rise of temperature will cause thermal stress inside the connecting piece,resulting in thermal expansion,affecting its reliability and safety.At present,the research on the safety of the battery system mainly focuses on battery thermal management,battery pack structure optimization,etc.,and the reliability of the electrical connection of the battery system has not been paid enough attention.It is urgent to carry out research on electrical connection in the research and development of electric vehicles.In this paper,the connector of the square lithium iron phosphate battery module is taken as the research object.Through the finite element simulation and experimental verification,the influence of different electrical connection contact conditions on the temperature of the battery module is analyzed,and the thermal and mechanical properties of the connector are studied.Firstly,the formation mechanism and calculation method of contact resistance are analyzed,and the main influencing factors are explored.The heat generation mechanism and heat transfer characteristics of the battery are analyzed,and the heat generation rate and thermophysical parameters of the battery are calculated.The thermal effect model of the battery cell is established and simulated.An experimental platform was built to test the accuracy of the battery thermal effect model.Secondly,it was extended to a battery module with three cells in series to study the temperature distribution and temperature rise of the battery module and the electrical connector under different discharge rates with different contact resistances.The connector was selected as the research object to analyze the thermal stress of the connector.The research shows that under the same discharge rate,the increase of contact resistance will make the highest temperature,the lowest temperature and their difference of the battery module have a significant upward trend,and the connector also has a large temperature gradient due to the existence of contact resistance.The overall deformation of the connecting piece is symmetrical,and the deformation mainly occurs at both ends of the connecting piece and on both sides of the middle.The areas with equivalent stress and equivalent strain are similar,which are mainly concentrated in the area where the surface of the connecting piece is in contact with the nut and the pole and its vicinity,and both show uneven characteristics.Finally,the influence of the connecting piece material and the ambient temperature on the thermal-mechanical characteristics of the connecting piece is studied.The results show that the temperature of copper and aluminum connectors is consistent with the influence of contact resistance,and the areas of deformation and stress are roughly the same.As the ambient temperature becomes higher,the maximum temperature of the connecting piece will increase,and its maximum equivalent stress and maximum overall deformation will also increase accordingly.When the ambient temperature is high,the contact resistance has a greater impact on the connecting piece than when the ambient temperature is low.When the ambient temperature is 40 °C,the connector of battery module III with large contact resistance begins to yield failure,and the failure position is located at the edge of the screw hole on the upper and lower surfaces of the connector.The battery thermal effect model established in this paper can better reflect the temperature field distribution and temperature rise of the battery.The analysis of the thermal and mechanical characteristics of the connector also reveals the thermal-mechanical characteristics of the connector.The research results can provide reference for the thermal management of electric vehicle power batteries and the optimization design of the connector.