# Influence of Interference Fit and Temperature on High-Speed Permanent Magnet Motor
## 1 Introduction  
A high-speed permanent magnet motor has a sound momentum of growth [1], and its application areas involve aerospace [2, 3], new energy vehicles, high-speed turbomachinery, industrial machinery [4], intelligent agriculture [5], etc. This is due to their small size and light weight while achieving high-density power and the maximum satisfaction of working conditions [6, 7]. The development of a high-speed permanent magnet motor follows the trend of lightweight technology. The application area will be fully popular and covered in the future when the technology becomes more mature [8]. In motors, the compressive strength of permanent magnets is much greater than the tensile strength; therefore, permanent magnets and alloy steel sheath are generally assembled by interference fit [9]. In the interference fit, the interference value is one ofthe key factors that affects the rotation of the high-speed motor [10]. If the interference value is too large, the magnet will collapse. In the process of high-speed rotation, the actual interference value is less than the static value. If the interference value is too small, it will easily cause the sheath to fall off. On the one hand, the magnet cannot be protected; on the other hand, it will cause the safety problem of falling off and splashing [11]. A high-speed permanent magnet motor is the core driving component of a centrifugal air compressor. The power of the centrifugal air compressor is output by the motor. Energy conversion is transmitted to the impeller through the motor. Its safety and reliability are embodied in the stability of the rotor structure, which greatly affects the stability and working efficiency of the centrifugal air compressor. This paper focuses on the rotor system of aero-dynamic bearing in the centrifugal compressor. Through simulation, the stress of the magnet and sheath of a high-speed permanent magnet motor under the interference fit is explored, and the factors of rotor strength are analyzed [12; 13; 14]. [PERSON] et al. [15] analyzed the critical speed, unbalance response, and stability of the shaft system in detail, and they proposed an investigation scheme of the rotor strength and rotor dynamic characteristics for high-speed and high power switched reluctance machines (SRMs). On the basis of rotor strength constraint, [PERSON] et al. [16] presented the composite sheath of a high-speed permanent magnet generator to make the stress distribution reasonable and reduce eddy current loss. [PERSON] et al. [17] analyzed the influences of static interference and the thickness of sleeve and sleeve material on the rotor strength and summarized the strength design rules of an ultra-high-speed permanent magnet synchronous rotor. A lot of research mainly focuses on the influence of parameters, and research on the variation in the interference structure is insufficient. According to the simulation results of stress, we adopt a method which adds chamfer to the end covers of the magnet to reduce the maximum principal stress. This method can reduce the probability of permanent magnet collapse. The heating condition of an ordinary motor may be relatively low, but the heating condition of a high-speed motor is serious due to the higher speed and greater power. The temperature has a great impact on the stability of a high-speed motor [18; 19; 20]. It is valuable to focus on the relationship between temperature and rotor strength of a high-speed motor. It has been found that most studies focusing on the rotor strength of the interference fit and temperature only analyze the relationship between stress and temperature under one simple interference condition. [PERSON] et al. [21] simplified the rotor stress condition as a plane stress problem, and the analytical formulae for rotor strength was proposed based on the displacement method in polar coordinates to accurately predict the stress and displacement of the motor rotor with a high speed and rising temperature. [PERSON] et al.