How to reduce the noise generated by motor operation

Electromagnetic noise suppression

Electromagnetic noise is mainly caused by the electromagnetic force in the air gap magnetic field, which triggers the vibration of the stator and rotor.

1.Optimize electromagnetic design: Choose appropriate stator and rotor slot matching (far slot matching), adopt rotor inclined groove or double inclined groove structure, which can effectively weaken tooth harmonics and radial electromagnetic force waves. Optimizing the shape or magnetization method of the magnetic steel to sinusoidate the air gap magnetic field can also reduce harmonics. ‌

2.Improve manufacturing and assembly processes: ensure the concentricity of the stator and rotor, reduce air gap unevenness, and reduce unilateral magnetic pulling force. By using magnetic slot wedges or reducing the width of the slot, electromagnetic noise caused by cogging effects can be reduced.

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Optimization of drive and control (for brushed/brushless motors): Using sine wave drive (such as FOC vector control) instead of square wave drive can significantly reduce torque ripple and electromagnetic howling. Increasing the switching carrier frequency of power devices to above the audible range of the human ear (20kHz) can eliminate switching noise.

 

 

Mechanical noise control

Mechanical noise mainly comes from bearings, rotor imbalance, and component friction.

1.Ensure rotor dynamic balance: Perform high-precision (such as G1.0 or higher) dynamic balance correction on the rotor to eliminate vibration caused by mass eccentricity. ‌‌

Selection and maintenance of bearings: Use low-noise, high-precision grade bearings (such as P5/P4 grade ball bearings). Ensure proper preloading during assembly (such as using waveform spring washers) to avoid abnormal noise caused by clearance. Regularly clean and replenish appropriate lubricating grease.

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Ensure assembly accuracy and structural rigidity: Improve component processing accuracy, ensure proper installation, and prevent the stator core from loosening inside the casing. Increase the thickness of the base or stator yoke to improve structural rigidity and avoid resonance.

Aerodynamic noise is mainly caused by the rotation of cooling fans and airflow disturbances.

Optimize fan and duct design: By reducing the fan diameter and adopting a backward tilting or non-uniform blade design while meeting the requirements of heat dissipation, wind noise can be reduced. Ensure smooth inlet and outlet ducts to avoid turbulence caused by sharp bends and edges. ‌‌

Adopting vibration isolation and sound insulation: using flexible damping materials such as rubber pads between the motor and the installation base for vibration isolation and blocking structural sound transmission. For the generated air noise, a soundproof cover can be installed. ‌‌

Daily inspection and maintenance: Regularly clean the motor dust, check and tighten the installation bolts, replace worn bearings, belts and other components. Using a regulated power supply ensures power quality and also helps reduce noise caused by power fluctuations. ‌‌

 

 

Motor Sound Insulation Tips

1, Choose appropriate sound insulation materials

The key to making sound insulation for the motor is the material. Common sound insulation materials include foam, rubber and sound insulation cotton, which can effectively absorb the vibration and noise generated when the motor is running. Foam is light and easy to install, suitable for small motors; Rubber is durable and has good sound insulation effect, suitable for industrial environments; Soundproofing cotton has better comprehensive performance and is suitable for household appliances.

2, Optimize installation method

In addition to materials, installation methods are also important. Firstly, ensure that the motor base is stable and reduce vibration transmission. Secondly, soundproof covers can be installed around the motor to further block noise. Finally, check the connection between the motor and the equipment, and use flexible connectors to reduce noise transmission.

3, Regular maintenance and upkeep

Motor noise is often related to equipment aging or insufficient lubrication. Regular inspection of motor bearings and gears, timely addition of lubricating oil, can effectively reduce friction noise. At the same time, clean the dust and debris around the motor to avoid increased noise caused by poor heat dissipation.

 

 

1, Mechanical vibration is the main cause

During the operation of the motor, internal components are inevitably subject to vibration. Bearing wear, rotor imbalance, or fan blade deformation can amplify this vibration, resulting in a significant increase in noise. Regular inspection and maintenance of these components can effectively reduce noise.

2, Electromagnetic interference cannot be ignored

When current passes through the motor winding, an electromagnetic field will be generated. If the design is unreasonable or the power supply is unstable, the electromagnetic force will cause the iron core to vibrate and produce a buzzing sound. This situation is more common in old or inferior motors.

3, Installation issues are easily overlooked

Improper installation of the motor, uneven base, or loose connecting components can amplify vibration and noise during operation. Ensure that the motor is installed on a sturdy and flat foundation, and check that all fasteners are tightened to significantly improve noise issues.

 

01

The origin and development of structural noise

The noise emitted by the motor does not come out of thin air, but is the result of the interaction between the excitation force, structure, and air.

Root causes: electromagnetic force, mechanical imbalance, airflow disturbance;

Transmission: through bearings, end caps, and machine bases;

Response: The stator core, casing, and end cap are forced to vibrate;

Radiation: The vibrating surface compresses air, creating audible sounds.

Therefore, only by simultaneously addressing the three links of "source path response" can the noise be suppressed

 

02

The three major culprits of noise

2.1 ▲ Electromagnetic factors - mid to high frequency "buzzing" sound

Uneven air gap magnetic field: sinusoidal wave doped with spatial harmonics.

Magnetic flux saturation: waveform distortion after the iron core is "stretched".

Tooth slot effect: The stator tooth slot cuts the rotating magnetic field like a "fence".

Power harmonic: Inject high-frequency noise into the PWM current of the frequency converter.

2.2 ▲ Mechanical factors - low-frequency "rumbling" and "clicking" sounds

Dynamic unbalance of rotor: The center of mass and the center of rotation are eccentric, resulting in vibration at 1 times the rotational frequency.

Bearing defects: raceway roundness error, improper assembly interference, poor lubrication.

Processing error: The end cap is not concentric with the machine base, and the iron core is loosely matched with the casing.

Structural resonance: The excitation frequency approaches the natural frequencies of the stator, end cover, and rotor.

2.3 ▲ Aerodynamic Factors - Fan and Ventilation Duct Noise

Fan eddy current: The periodic "exhaust" of the blades produces eddy current noise.

Turbulence in ventilation ducts: airflow hitting the hood, sudden changes in the cross-section of sharp turns.

 

03

System Noise Reduction Roadmap

3.1 ▲ Reduce excitation force from the source

Electromagnetic solution: skewed slots/poles, optimized pole slot matching, magnetic pole chamfering, injection of high-frequency sine current, addition of epoxy adhesive or high damping composite material between stator core and casing.

Driving strategy: FOC algorithm makes the current waveform more circular and reduces harmonic content.

Structural flexibility: An elastic coupling is added between the motor and the load, and damping materials are used to 'consume' the vibration energy.

3.2 ▲ Blocking the transmission path midway

Modal analysis: Obtain the natural frequencies and vibration modes of the stator, casing, and end caps through FEA or experimental methods.

Frequency offset: Reinforcement, variable wall thickness, integrated design, raising or lowering the natural frequency of the structure to avoid excitation peaks.

3.3 ▲ End of pipe treatment - aerodynamic noise

Fan optimization: Select low-noise airfoil blades, match the number and inclination angle of blades reasonably, and ensure uniform clearance between the fan cover.

Smooth air duct: Avoid sharp turns and sudden changes in cross-section, allowing the airflow to transition into laminar flow.

 

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