This paper aims to study the NVH and acoustic performance of a 3-phase AC induction motor in order to develop an approach to reduce the magnetic component of noise from an electric motor in an electric vehicle (EV). The final goal of this project is to reduce the magnetic component of sound from the motor by making modifications to the end bracket of the motor housing.
EVs are being considered the future of mobility mainly due to the fact that they are environment-friendly. As many companies are already investing in this technology, electric drives are set to become extremely popular in the years to come. The heart of an EV is its motor. Modern electric vehicles are quiet, furthermore with the lack of an IC engine to mask most sounds from other components, the sound from the electric motor and other auxiliary parts become more prominent. The primary source of electromagnetic noise in a motor arises from magnetic flux variations in the air gap which interfere with the resonant frequencies of the stator core. These flux variations result in a time-varying force that acts on the stator core or teeth and causes it to deform. This paper studies the radial and tangential components of this force and how these structural vibrations can be dampened by using a modified end bracket with properties that can help reduce the overall sound radiated by the motor.
The paper shows a process to analyze the sound radiated from an electric motor in three broad steps. First, an impact hammer test is performed on the stator and assembled motor to analyze its resonant frequencies. Second, the operational deflection shapes of the motor in the operating condition are extracted to visualize the housing deformation and identify resonant frequencies being excited. Finally, a sound intensity analysis is conducted to calculate sound pressure levels at different frequencies.