Analysis of Motor Vibration and Noise Sources

Hengli Motor provides a brief summary of the axial vibration of the end cap and the vibration caused by the electric brush. In the actual process of motor production and manufacturing, vibration and noise are a pair of problems that go hand in hand, especially mechanical noise, whose fundamental cause is vibration. That is to say, controlling motor mechanical noise should start with eliminating mechanical vibration.

Axial vibration and noise of Hengli motor end cover

The axial vibration of the motor end cover is one of the sources of mechanical noise, which is mainly excited by bearing vibration and is more important in small motors. The smaller the axial dynamic stiffness of the end cap, the easier it is to excite larger vibration velocities and noise.

Vibration and Noise of Constant Force Motor Brush Device

The vibration and noise of the electric brush device are caused by poor surface condition of the commutator, excessive gap between the electric brush and the brush holder, insufficient or improper pressure on the electric brush causing it to tilt, as well as structural and technological reasons such as insufficient rigidity of the brush holder, brush holder, and brush rod.

Practice has proven that during no-load operation, due to the low temperature of the sliding contact surface, the above-mentioned thin film is not easily formed, and the dry friction between the electric brush and the commutator increases the noise. When the no-load operation cycle of a steel rolling DC motor accounts for more than 50% of the total time, the noise under no-load conditions is 6-10dB higher than that under load. This kind of vibration is different from the vibration caused by mechanical reasons on the surface of the commutator, which can be detected when the motor is running at low speed (there is a vibration sensation when the brush is lightly touched by hand). The frequency spectrum of the brush vibration noise generated by sliding contact is generally in the range of 1000~-8000Hz, and it does not change much when the motor speed changes, which is also one of its characteristics that distinguishes it from mechanical reasons.

The vibration noise of the electric brush generated by sliding contact is also related to the polarity of the electric brush. For example, the positive brush of a DC generator vibrates less than the negative brush; Because the positive brush can separate the crystals of graphite and carbon, absorb moisture on the surface of the commutator to form a lubricating film, while the negative brush removes it. The formation of sliding contact film is also related to the grade of the electric brush. The selection of the grade should first ensure good commutation performance, but at the same time, the vibration and noise of the electric brush should also be considered.

In addition to mechanical noise, aerodynamic noise is also a major challenge in motor noise control, especially for high-speed motors.