Design And Temperature Field Analysis Of In-wheel Motor For Electric Vehicle

Under the background of environmental pollution and the crisis of fossil energy,it has become the strategic planning of the country to vigorously develop the new-energy automobile industry,and the electric vehicle has entered a new stage of rapid development.Using in-wheel motor to drive directly is the future development direction of electric vehicle.The in-wheel motor driving system is regarded as the most ideal driving mode for pure electric vehicles in the future due to its remarkable technical advantages in compact structure,high transmission efficiency,flexible control and high vehicle space utilization.In this paper,the structure design,electromagnetic field analysis,loss calculation,temperature field simulation and cooling system design of high power density in-wheel motor are studied.First,according to the parameters and performance indexes of the whole electric vehicle,the performance requirements of the in-wheel motor driving system are analyzed.Through theoretical analysis,the basic parameters of the in-wheel motor,such as torque,power and speed,are obtained.Based on the structural design of the in-wheel motor parameters and rotor parameters,the design basis of the key parameters of the motor,such as the number of pole slots and the polar arc coefficient,is given,and the structural scheme of the in-wheel motor is preliminarily determined.Secondly,Maxwell software was used to verify the rationality of the electromagnetic structure design of the motor through electromagnetic field simulation.The results show that the electromagnetic torque,no-load counter potential and load torque of the motor are all within the reasonable range.Based on the theory of electromagnetic field,the size and distribution of copper loss,iron loss and eddy current loss of permanent magnet under different working conditions are analyzed in detail.Thirdly,the three-dimensional temperature field simulation model of the motor was established through Workbench software,and the influence of natural air cooling environment on the transient temperature field distribution of the motor was analyzed under different overload conditions,and the steady-state temperature field distribution and transient temperature rise curve of the motor components under different overload conditions were obtained.The results show that the natural air cooling can only meet the cooling requirements of the motor under the rated working condition,and the motor will overheat under the overload working condition,exceeding the maximum allowable temperature specified by the national standard under the insulation level of the motor.Finally,the design and research of the water cooling system of in-wheel motor is carried out through CFD simulation,and the influence of the structural parameters of the cooling system on the flow field and temperature field is analyzed.The radial "Z" type waterway structure was selected,and the optimized water cooling system of in-wheel motor was determined after the reasonable selection of the type of waterway,coolant flow rate,number of waterways,width of waterway section and rounded corners of waterways.The steady-state temperature field of the motor under the condition of water cooling and cooling was simulated and analyzed by using Fluent software.The results show that the overall temperature of the in-wheel motor is greatly improved under the condition of liquid cooling.Compared with natural air cooling,the windings,stator,permanent magnets and other heat-generating parts have a significant temperature drop.Under rated working conditions,the maximum temperature of the motor drops from 81.20℃ to 65.57℃,a decrease of 19.2%.Under 2 times overload condition,the maximum temperature of the motor dropped from 170.50℃ to 93.53℃,a decrease of 45.1%.The maximum temperature under overload condition is lower than the performance reference temperature of the motor,which meets the insulation grade requirements under the condition of overload of the motor.