| The constant aggravation of energy crisis and environmental pollution has promoted the rapid development of electric vehicles, mini electric vehicle is one of the main trends of the electric vehicle research. The driving motor is one of the most impotant part of a mini vehicle. Being fixed in a limited space, it has high power density and current. Also, the low drive voltage leads to high current density of motor in mini vehicle. The increase of temperature rise results from all these factors. The overheat of a motor can damage its operational reliability and service life. Therefore, the motor’s temperature rise is considered as one of the main limiting factors for the overall motor performance. Thus, the establishment of an accurate and efficient calculating model of the temperature rise, temperature distribution and heat point location is the key factors to ensure the stable and safe operation of a motor. And, the optimal design of cooling system is significant in theoretical analysis and practical application. In this paper, based on the water-cooled induction motor used for mini electric vehicles, the calculation method for whole domain thermal fields of induction motor, the effects of cooling system on temperature rise and the optimal design of cooling structures are researched deeply.The accurate calculation of temperature distribution is vital to rational design of motor cooling system and safe operation of electric vehicle motors. In this paper, the equivalent thermal network model and the 3D steady temperature field calculation model for water-cooled induction motor used for mini electric vehicles are established to calculate temperature distribution and heat point location accurately. In addition, the calculation methods for boundary conditions, heat loss and heat transfer coefficients used in these models are given. The stator core and ceiling’s assembly gap influence on temperature distribution are researched. And the multilayer overlapping stator slot winding equivalent thermal model between the conductor and insulation layer are put forward. The temperature distribution based on improved model is close to real value. Based on the calculation of the motor temperature field, the motor temperature distribution is obtained, which can benifit the cooling system design and optimization. By comparing the calculation results of the equivalent thermal network method and the 3D finite element method, the application scope of the two methods when being used for guiding the desigh of motors is given. A motor temperature rise experimental platform was constructed to verify the results.The heat dissipation of the motor is directly affected by cooling methods, mediums and environmental factors. Considering the effects of different cooling modes, mediums and materials, the steady temperature field of induction motor is calculated by using 3D finite element method. Comparision has been made between air cooling mode and liquid cooling mode. The cooling effect of circumferential circular structure and axial Z-shaped structure has also been compared. The variation law with the speed of the convection radiating coe fficient in wind-cooled motor is calculated.Based on the above study, the temperature distribution in the different operating conditions of air-cooled motors is studied and the applicable operating conditions of the self fan-cooled induction motor are given. The distribution of motor tempreture field with different materials of rotor squirrel cage and chassis are studied, as well as with different cooling mediums which are water, transformer oil and ethylene glycol with different concentrations. The above s tudies may be useful for the optimal selection of the motor cooling mode, medium and material.The efficiency of the motor heat dissipation and cooling system is determined mainly by the flow rate of the cooling medium. In this paper, the relation between the cooling water flow rate and the motor internal temperature in cooling motor is derived by using heat transfer and hydrodynamics theories. Thus, the changing of the motor internal temperature with different water flow rates is obtained, which can provide theoretical basis for proper flow rate selection. Using the thermal network method, the motor internal temperature distribution with different cooling water flow rates, when the water-cooled induction motor is working at the rated state, is calculated. Both numerical and expetimental simulations are carried out to verify the calculation. The proposed flow rate selection method can provide a theoretical basis for optimal flow rate selection for motors with casing water-cooled structure.The cooling efficiency of the motor is affected directly by the restricted exterior size of water-cooled motor and the parameters of the structure of the cooling system. Based on coupling analysis between the fluid field and temperature field, the cooling system of the water-cooled motor is optimized considering the channel number, the water gap width of adjacent waterways, and the materials and shapes of waterways. The relation between the number of waterways, the heat dissipation area, convective heat transfer coefficient, and the flow resistance is derived for motors with circumferential circular structure and axial Z-shaped structure. The pressure loss of fluid flowing through the chassis and the motor temperature distribution of water-cooled motors with different numbers of waterways are obtained based on CFX fluid analysis software. The distribution pattern of flow resistance, flow rate and motor temperature with different casing materials, gas widths of adjacent waterways opening, and waterway shapes is studied. The cooling capacities of circumferential circular structure and axial Z-shaped structure are compared. The optimization of cooling structure for water-cooled motors is proposed. Numerical simulation has shown that after optimization, the temperature-rise has significantly decreased. The proposed optimization method is applicable to all cooling structure design for small and medium water-cooled motors with shorter axial length. |
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