How to electromagnetic noise of permanent magnet DC motor for automotive cooling fan

With the continuous development of the society, our living standards are advancing with the times. At the same time, people's quality and comfort level have also improved, and the problem of noise control inside the car has become increasingly prominent.

First of all, from the sound source, the noise inside the vehicle is mainly from engine noise, chassis noise, engine cooling fan noise and so on. Especially intolerable is that when the vehicle is turned off, there is still a noise inside the vehicle for a short time. The main source of the study is the noise of the motor for the engine cooling fan, and the whistling sound occurs when the motor speed drops to a specific speed range. This will seriously affect the evaluation of the quality of the car. The permanent magnet DC motor is one of the main types of motors for automotive cooling fans. Electromagnetic excitation force and motor structure dynamic response are the two key factors determining the electromagnetic noise of permanent magnet DC motor. This paper studies the electromagnetic noise problem of the permanent magnet DC motor after the vehicle cooling fan is powered off.

Secondly, due to the large range of speed change after the motor is de-energized, this paper uses the time-step finite element method to calculate the magnetic flux harmonics and torque of each air gap generated by the stator and rotor at different speeds after the permanent magnet DC motor for the cooling fan of the automobile is powered off. The pulsating harmonics and the unbalanced magnetic pulling force are used to analyze the variation law of the amplitude of each order electromagnetic wave with the rotation speed. The design parameters of the motor that affect the amplitude, frequency and frequency of the electromagnetic force are studied. The noise reduction optimization design lays the foundation.

In the research of dynamic response of motor structure, the modal analysis and harmonic response analysis of permanent magnet DC motor are carried out by finite element method. The influence of each component on the natural mode of the motor structure is studied. The electromagnetic vibration with time and space distribution is proposed. The equivalent force application method calculates the structural dynamic response of a given electromagnetic excitation force. Combined with the finite element method and the boundary element method, the numerical calculation method of motor acoustic radiation is studied, and the variation of electromagnetic noise with the rotational speed after motor power failure is calculated.

An experimental study of the company's examples was conducted. The no-load vibration data of different rotational speeds were collected and the vibration spectrum was analyzed. The variation of the noise component caused by the electromagnetic force wave after the motor is powered off is studied by means of experimental methods. The modal mode experiment of the motor is used to test the inherent mode of the motor structure, and the accuracy of the material definition in the structural dynamic analysis is verified. .

Finally, it has been found that the whistling sound generated in the specific speed range after the permanent magnet DC motor of the automobile cooling fan is powered off is electromagnetic noise, and the main reason is frequency division resonance. Taking into account the economic and force indicators of the motor, improving the electromagnetic force wave order and suppressing the dynamic response of the motor structure is the best method for motor noise reduction optimization.