Study On Thermal Reliability Of Controller In Tractor Drive System

With the intelligence and automation development of tractor,the integration,modularization and miniaturization of electronic equipment development,as an important electronic control system of tractor transmission system controller,power per unit volume is more and more big,produce a lot of heat and not easy to send out,leading to TCU temperature is too high,easy to failure in advance.Therefore,the thermal reliability of a tractor drive system controller based on thermal simulation analysis and accelerated life test is studied in this paper.By determining the weak position and life prediction of the controller,the paper provides a basis for the optimal design of thermal characteristics and reliability of the controller.In this paper,the temperature field and stress field simulation models of the controller are established by Flotherm and ANSYS Workbench.Then,temperature test tests were carried out under different environmental temperature conditions,it is concluded that the variation rule of component temperature approximately increased linearly with the environmental temperature.By comparing the component test data and simulation data under the same working conditions,the accuracy of the temperature field simulation model is verified.Through the simulation and study of the circuit board component temperature field under different ambient temperature conditions,it is concluded that the variation rule of the component temperature rising about 9.6? for every 10? increase of the ambient temperature.It is confirmed that under high temperature conditions,the components such as power supply chip,master control chip and driver chip will easily fail in advance due to high temperature,which provides a basis for the follow-up accelerated life test.The influence of ambient temperature on thermal stress of controller circuit board was studied.Based on the results of simulation of thermal stress and thermal deformation,it can be concluded that the thermal stress and thermal deformation are the minimum when the controller works at the ambient temperature of 20?.The effect of the fixed constraint mode on the thermal stress was studied,and the results showed that the location of the constraint holes in the four corners and the middle area of the circuit board was beneficial to reduce the maximum thermal stress.Under high temperature condition,the element with large thermal stress and thermal deformation is the main control chip.A detailed thermal stress simulation model of the main control chip was established,and the thermal stress and thermal deformation of the pin were determined to be large at high temperature.Based on the comparative study of thermal stress of three kinds of pin materials,it is concluded that the pin stress of the master chip is the least when the cutting alloy material with a small coefficient of thermal expansion is used.When conducting reliability research,TCU with high reliability and long life adopts performance degradation based on components.The temperature cycle accelerated life test method of key modules and then the whole system is adopted to conduct reliability research and life prediction for the controller.Based on the temperature cycle test data of the controller of tractor drive system in a certain enterprise,the life prediction and reliability evaluation of the controller are carried out according to the accelerated life test scheme and reliability analysis method studied in this section.Under the condition of 60% confidence,it is estimated that the average life of the main control chip and the driver chip is 12798.83 h.According to the reliability function,it can be concluded that when the chip is used at the normal stress level to 65000 h,it will completely fail.The average service life of TCU in series system is 6399.41 h.When it is used for 32500 h under normal environmental conditions,TCU fails completely.