What is the electromagnetic noise of permanent magnet DC motors for automobile cooling fans

With the continuous development of society, our living standards are advancing with the times. At the same time, people have improved the quality and comfort of cars, and the problem of noise control in cars has become increasingly prominent.

 

First of all, from the point of view of the sound source, the noise in the vehicle when the vehicle is running mainly comes from engine noise, chassis noise, engine cooling fan noise and so on. In particular, it cannot be tolerated that when the vehicle is turned off, there will still be noise in the car for a short time. The main source is the noise of the motor for the engine cooling fan, and when the motor speed drops to a specific speed range, there will be howling. This will seriously affect the evaluation of car quality. Permanent magnet DC motors are one of the main types of motors for automotive cooling fans. The electromagnetic excitation force and the dynamic response of the motor structure are two key factors that determine the magnitude of the electromagnetic noise of the permanent magnet DC motor. This article starts from these two aspects to study the electromagnetic noise problem of the permanent magnet DC motor used in the automobile cooling fan after power failure.

Secondly, due to the large range of speed changes after the motor is powered off, this paper uses the time-stepping finite element method to calculate the air gap flux density harmonics and torque generated by the stator and rotor at different speeds after the power failure of the permanent magnet DC motor for automotive cooling fans. Pulsating harmonics and unbalanced magnetic tension, the law of the amplitude of each order of electromagnetic force with the speed is analyzed, and the motor design parameters that affect the amplitude, frequency and frequency of the electromagnetic force wave are studied, which is the best choice for automotive cooling fans. Lay the foundation for noise reduction optimization design.

In the study of the dynamic response of the motor structure, the modal analysis and the response analysis of the permanent magnet DC motor were carried out using the finite element method, and the influence of each component on the inherent modal of the motor structure was studied. The electromagnetic excitation with temporal and spatial distribution was proposed. The equivalent force application method calculates the dynamic response of the structure under a given electromagnetic excitation force. Combining the finite element method and the boundary element method, the numerical calculation method of the acoustic radiation of the motor is studied, and the change of the electromagnetic noise with the speed of the motor is calculated.

An experimental study was conducted on the company's case. The no-load vibration data at different speeds are collected, and the vibration frequency spectrum is analyzed. The experimental method is used to study the changes of the noise component caused by the electromagnetic force wave with the speed of the motor after the power is cut off; the hammering method modal experiment 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, after research, it is found that the whistling sound generated in a specific speed range of the permanent magnet DC motor for automobile cooling fan is electromagnetic noise after power failure, and the main reason is frequency division resonance. Taking into account the economy and performance indicators of the motor, improving the order of electromagnetic force waves and suppressing the dynamic response of the motor structure are the best methods for motor noise reduction optimization.