Design And Temperature Rise Calculation Of Oil-immersed Cooling In-wheel Permanent Magnet Synchronous Motor

The oil-immersed cooling in-wheel motors have high power density and strong heat dissipation capacity,eliminating oil pumps,oil pipelines and other equipments required for circulating oil cooling,improving the integration and reliability of the drive system.It has important application value in special occasions where the hub space is limited and there is no external circulation condition of oil circuit.However,the cooling oil immersed inside the in-wheel motor will generate additional oil friction loss,which reduces the output torque and efficiency of the motor,and makes it difficult to calculate the temperature rise of the motor.Therefore,this thesis takes oil-immersed cooling in-wheel motor as the research object,and carries out in-depth research on analytical calculation of oil friction loss,electromagnetic design and optimization considering oil friction loss,temperature rise calculation and other aspects.The main research contents of this thesis include:(1)Aiming at the problem that the traditional analytical calculation of oil friction loss simplifies the stator and rotor structure as a concentric cylinder,which leads to large calculation errors,an analytical model of oil friction loss is established,considering the effects of stator cogging and cup type rotor structure.Firstly,according to the structural characteristics of the rotor,the analytical derivation of the oil friction loss at the airgap considering the effect of the stator cogging and the analytical derivation of the oil friction loss at end-face considering the effect of the cup type rotor structure are carried out respectively.Secondly,a flow field simulation model based on Computational Fluid Dynamics(CFD)is established,and a cooling oil churning testing platform is built to test the oil friction loss,the accuracy of the analytical model is verified by simulation and testing results.Finally,the variation law of motor structure parameters such as slot opening,slot shoulder height,air gap length,and the physical parameters of cooling oil such as viscosity and density on oil friction loss is analyzed.(2)Aiming at the problem of complex coupling between oil friction loss and electromagnetic performance of oil-immersed cooling hub motor,which may lead to large overall loss and low efficiency in motor design,a optimization model of oil immersed cooling in-wheel motor considering oil friction loss is established to minimize the loss.Firstly,according to the design requirements,a preliminary design scheme of the motor is obtained,and the finite element model is established to analyze its electromagnetic performance.Secondly,a math model of in-wheel motor loss considering oil friction loss is established.After parameterizing the finite element model,the loss optimization design is carried out based on the response surface model and genetic algorithm.Finally,the effectiveness of the optimization scheme is verified by comparing the loss of the scheme before and after optimization under different operating conditions.(3)Aiming at the problem that there are two physical phases,cooling oil and air inside the oil-immersed cooling in-wheel motor,it is not suitable to accurately calculate its temperature rise through the conventional single-phase fluid-solid coupling model.A two-phase fluid-solid coupling model is established to calculate the temperature rise of the motor.Further,the laws of different oil levels on the temperature rise of the motor under the rated operating conditions of the motor was studied,and the oil level coefficient with the best cooling effect is determined.Based on the optimal oil level,the temperature rise of the motor under different operating conditions is evaluated.(4)The prototype was manufactured according to the design scheme,and the withstand voltage testing was carried out for the stator winding,and the dynamic balance treatment was carried out for the rotor.Finally,the no-load back EMF of the motor at different speeds was tested through the drag testing,which verified the accuracy of the design scheme.The research results of this thesis provide technical support for the accurate calculation of oil friction loss and temperature rise of oil immersed cooling in-wheel motor,and also lay a foundation for the optimization design of oil immersed cooling inwheel motor.