Abstract
Oil-immersed cooling provides an effective cooling scheme for high-power hub motors with compact structure and serious heating problems. However, with this cooling method, some oil friction loss will be generated, making the output torque and efficiency of the motor lower, which limits its application in the motor. It is essential to get an exact calculation of the oil friction loss so that it can be reduced in the future research. Firstly, a new method was proposed to improve the accuracy of oil friction loss calculated by an existing analytical method (Kori’s method), while the influence laws of oil-soaked depth and rotation speed on it were explored. Secondly, a three-dimensional transient Computational Fluid Dynamic (CFD) model based on Volume of Fluid (VOF) was established, considering the actual complex structure and the disorderly mixing of oil and air inside the motor. Finally, the oil friction loss calculated with an improved analytical method and a VOF model was verified by a testing. It was indicated that the VOF model was more precise but more time-consuming. The proposed method has the second highest accuracy but takes less time.
Highlights
IntroductionAn in-wheel motor is the development trend of electric vehicles, towards the trend of high power, large torque, and small volume [1,2,3]
O o o selection of cooling oil and optimization design of motor structure are of great significance It could be seen that the oil friction loss is affected by some physical parameters of to reduce the loss
In order to accurately calculate the oil friction loss of Permanent Magnet Synchronous Motor (PMSM) with oil-immersed cooling, an improved analytical method and a three-dimensional transient Volume of Fluid (VOF) model were used, and the calculation was verified by a load-independent mechanical loss testing
Summary
An in-wheel motor is the development trend of electric vehicles, towards the trend of high power, large torque, and small volume [1,2,3]. The cooling effect of these studies is satisfactory and can greatly reduce the temperature rise of the motor, with nearly no oil friction loss due to rotor rotation. The oil-immersed cooling is more suitable for in-wheel motors integrated with reducers and inverters [11] In this cooling scheme, a certain amount of cooling oil is directly sealed inside the motor, exchanging heat with water used to cool the inverter beforehand. The rotor rotation improves the heat transferability, oil friction loss occurs between the rotor and the cooling oil, which cuts down the output torque and efficiency of the motor, and makes it difficult to calculate accurately the temperature increase. A relevant testing of oil friction loss is carried out in the end
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