Wei Jiang

To improve the life of the meshing pair in single screw compressor (SSC), several meshing pair profiles (MPP) were proposed for raising the lubrication properties. Therefore, it is necessary to evaluate the lubrication performance of the MPPs. In this paper, an evaluation method based on micro deflecting motion trajectory (MDMT) is proposed and the theoretical model to realize MDMT is established. The model mainly contains a geometric model, a thermodynamics model, a hydrodynamic lubrication model and corresponding algorithm. With the presented method, three kinds of MPP including single straight line type (SSLT), single column type (SCT) and multi column type (MCT) have been analyzed. Obtained results show that compared to the SSLT and SCT, the MCT generates the greatest peak value of the water film pressure. The total torque applied on the gate-rotor generated by the water films decreases with the increment of the discharge pressure and increases with the machine size. The water film stiffness firstly decreases and then increases with the micro deflecting angle increasing. The water film stiffness at trailing side is always larger than that at leading side. As the discharge pressure increases, the MDMT curves approach the leading flank, and the lubrication properties get worse. With the machine size increasing, the MDMT curves move towards the trailing side and the lubrication performance is improved. Comparing to the other two MPPs, the MCT can achieve floating mesh without contact in relatively larger machines and comparably lower discharge pressure.

The temperature gradient of high-torque-density short-time duty permanent magnet (PM) brushless DC motors (BLDCM) is large. Increasing the torque will cause the copper loss and the winding temperature to rise rapidly, which will lead to the risk of the winding insulation damage. A split ratio optimization method is proposed to raise the torque considering winding temperature limitation in this paper. The analytical relationship between the torque, the losses and the split ratio is derived. The transient temperature of the winding is calculated analytically based on the expressions of this analytical relationship. The maximum allowable temperature rise of the winding is converted to the optimization constraint. The optimal split ratio is calculated and the maximum torque within the temperature limit range is obtained. The method is verified by finite element (FE) simulation and experimental test. The FE predicted optimal split ratio value is equal to the analytically predicted value. The error between the simulated and calculated torque is less than 5.7%. The maximum error between measured and analytically predicted temperature is 7.2%. The verification results show that the proposed method can accurately calculate the optimal split ratio and maximizes the torque within the winding temperature limitation.