Design And Performance Research On Oil Cooling System Of New Energy Vehicle Drive Motor

With the development of new energy vehicles,it puts forward higher requirements for the power density of the drive motor.Higher power density leads to higher internal temperature rise of the motor,which directly affects the life and safety of the motor.Therefore,higher requirements are put forward for the motor cooling system.Aiming at the problems of long heat transfer path,large contact thermal resistance and low heat transfer efficiency of water cooling system,a combined oil cooling system is proposed in this research that composed of the casing oil circuit and the spray oil circuit at the front and rear windings.The cooling oil directly contacts the stator core and the end windings through the oil circuit,which shortens the heat transfer path in the motor and reduces the contact thermal resistance.The cooling system adopts a combined oil path structure,which composed of the casing,stator core and oil injection ring through interference fit,without welding,which simplifies the casing processing procedure.A new type of S-shaped reentrant oil channel with low flow resistance and good temperature uniformity is designed in this research.Compared with the right-angle return oil passage,the S-shaped oil passage pressure loss is reduced by half,and the heat transfer coefficient and temperature uniformity performance are improved.Through fluid simulation calculation,the number of reentrants and cross-sectional parameters of the S-shaped rereturn oil passage of the casing and the arrangement of spray oil passage nozzles are optimized.A visual verification prototype of the motor oil cooling system was made.The flow performance of the cooling oil in the oil cooling system was tested under the motor running and nonoperation.The cooling oil in the oil channel flows smoothly,the combined oil passage has good sealing performance.There is no oil leakage and oil pressure fluctuation during the motor testing process,the oil film in the end winding is uniform,and the structure of the cooling system is reasonable.A simulation model of the two-dimensional magnetic field and three-dimensional temperature field of the motor was established.The internal energy loss distribution of the motor at different speeds is calculated and applied to the relevant parts as heat source.The thermal conductivity of the winding and core and the heat dissipation coefficient of each surface of the motor are calculated equivalently.The reasonable boundary conditions are established.The cooling oil flow of the motor at different speeds is analyzed and calculated.The temperature field of the motor under different oil temperature and different speed and the temperature rise characteristics of key components are analyzed which provide guidance for the selection of motor cooling parameters.The simulation results show that the maximum temperature rise in the motor is 111.2℃,which is far lower than the design requirements of insulation grade.An oil-cooled motor engineering prototype was made,and the oil-cooled motor temperature rise experiment platform was built.According to the simulated working conditions,the winding temperature rise is tested under different working conditions and different cooling parameters.The maximum error between the experimental results and simulation results is4.5℃,indicating that the simulation analysis of temperature field is accurate.Compared with the water cooling system,the temperature rise of the motor winding in the oil cooling system decreases by 41.6 ℃ under the rated condition and the same cooling condition.It indicates that the oil cooling system designed in this paper can significantly reduce the temperature rise of motor winding and promote the development of high power density of new energy vehicle drive motor.