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This paper focuses on the electromagnetic vibration and its reduction in PM brush dc motors. First, the air gap flux density distribution and the radial force density distribution are derived in detail, and compared with the results of the finite element method. Next, two types of vibration sources, called pulsating force and bending moment, are analyzed. Then, two passive improvement methods, called varied PM pole width in axial direction and copper ring, are proposed to reduce the magnetic forces and their vibration, and their principles of the vibration reduction are described in detail. For further explanation, a rotor-skewed motor is used for comparison, and the radial force on the motor is discussed and the influence of four different thicknesses of copper ring on the motor vibration is analyzed. Finally, three 2p/24s sample motors are manufactured and the experimental vibration results confirm the analysis and the proposed improvement technique. [ABSTRACT FROM AUTHOR]

The vibration mode of electric machines is an important characteristic of vibration, which is useful for finding the vibration sources with different frequencies, but has always been neglected before. In this paper, the vibration characteristics, especially the vibration mode, of permanent magnet (PM) brush DC motors are studied. First, the air gap flux density distribution and radial force density distribution are derived in detail and compared with the results of the finite-element method. Then, two types of vibration modes, called pulsating and bending modes, and their reasons as pulsating force and bending moment are analyzed and elaborated, which have not been analyzed and verified sufficiently before. In addition, the relationships between these two vibrations and pole width, pole number, and slot number are analyzed. The main modal shapes and their frequencies are acquired from the modal test. To confirm the analysis and theory, the multiprobe mode-included test method of vibration acceleration is proposed and emphasized to obtain the vibration mode information of motors, and the experimental results on a PM brush DC motor match well with the simulation results. [ABSTRACT FROM AUTHOR]