Study On Analytical Model And Parameter Characterstics Of Hybrid Magnetic Circuit PVT

Compared with mechanical variable transmissions, permanent variable transmissions (PVT) possess many favorable features, like non-contact flexibe transmission, clean and quiet, low starting torque, self overload protection, et al. However, the drawback of poor utilization of permanent magnets has limited their applications in large torque areas. By applying modulation principle of magnetic field into PVT, full utilization of magnet field and high torque density can be achieved, which is of great significance to the development of PVT. In this thesis, a novel hybrid magnetic circuit PVT is put into forward, and the problems of magnetic circuit structure, fundemantal equations and parameter restrictions, influence of structural parameters on torque capability and torque ripple have been studied.Analytical analysis and numerical analysis were used to research the modulation principle of PVT. A novel hybrid magnetic circuit PVT was put into forward which is suitable to be applied in large torque area. Output torque capability was compared among radial circuit, axial cuicuir and hybrid circuit. The results showed that three magnetic circuit structures have their own features. Axial and hybrid circuits which possess similar torque density while larger compared with radial cuircuit structure. Considering unbalanced force and framework supporting, hybrid magnetic circuit structure is the preferential choice.According to the magnetic features of the PVT, mathematical model was set up. The expressions of electromagnetic torque and power banlance equations were deduced with the virtual work method. Theoretical analysis and FEM were adopted to research the main parameter restricion modes and their features of the PVT. Comparisions were made among these modes for further. Results showed that there are five parameter restricion modes in which the former two modes are equal speed following mode and the latter two modes are variable speed mode. The working modes with the same pole pair number on two rotors could not realize the speed variation. Generally speaking, opposite direction subtraction match mode is the best variable speed mode due to the ability of variation speed as well as lager torque density.FEM was used to analyze the influence of magnetization length, radial length and circumferential width of modulation pole pieces, especially transmission ratio, axial length ratio of two rotors and length-radius ratio on torque capability of PVT. The results showed that circumferential width at around 0.4 of modulation pole pieces help to enhance the torque capability. The PVT gets largest torque capability with the ratio of axial length of low speed rotor and high speed rotor at around 1.5. Smaller length-radius ratio or tabular shape indicates larger torque capability for PVT. Starting process and steady working point of the PVT is analyzed; variation rule of cogging torque and its influence on torque ripple were studied, and effective methods were adopted to restrain torque ripple in PVT. Results showed that steady working point featured that axes of two rotors consistent with that of modulation pole pieces and the polarity of magnets on two rotors is opposite. There are ripple component in following torque when the PVT works in steady state due to cogging torque. The ripple ratio inclined gradually with the increase of load quantity. The effective match of pole pair number of magnets and the number of modulation pole pieces and elaborate choice of circumferential width of modulation pole pieces can restrain torque ripple effectively.