Noise is one of the three major public nuisance environmental pollution in modern society. In order to protect people's health, the international organization for standardization (ISO)Specifies the people allow noise standard. In our country for all kinds of electrical noise also made the corresponding limit standard. Motor controller is one of the sound source of the noise, the controller in household appliances, automobiles, office appliances and health of workers and peasants and other industries widely used, and is closely related to people's lives. Therefore, as far as possible to reduce the noise from the motor controller, the production of low noise motor controller, to create a comfortable and quiet living environment is the responsibility of each designer and producer. Cause vibration and noise of brushless dc motor for many reasons, can be roughly summed up in mechanical noise and electromagnetic noise. There are primary mechanical noise and the causes of mechanical noise. 1. Bearing noise. Cooperate to be not appropriate because of the bearing and the bearing chamber size, the rotation noise with rotor motor controller. Ball is not round or internal mixed sundry, caused by the collision between them produce vibration and noise. The bearing of stress value is undeserved, cause of raceway surface micro vibration also can produce noise. 2. Due to unbalanced rotor noise. 3. Assembly eccentricity caused by noise. Reduce mechanical noise of brushless dc motor should adopt the following methods: 1. General sealed bearing should be adopted to prevent debris entering. 2. Bearing in the assembly, demagnetization cleaning, degreasing and iron filings. After cleaning the bearing cleaning before bearing noise than generally reduce 2 ~ 3 db. Grease should be clean, not contain dust and impurities. 3. With the bearing outer ring and the bearing chamber, the inner ring and shaft, usually should not be too tight. With the bearing outer ring and the bearing chamber, the radial clearance should be in the range of 3 ~ 9 microns. 4. To eliminate the axial clearance of the rotor, bearing must be appropriate pressure. Generally choose waveform spring washer or three point elastic washer, and on the shaft extension end as appropriate. 5. Use to heavy or aggravating method for rotor dynamic unbalance correction. 6. Magnetic steel with the output shaft between the cushion filling materials, absorb the tiny vibration of rotor in the process of commutation, at the same time avoid the output shaft load rigid connection with the outside world, and the external vibration is passed to the magnets, impact excitation torque generated by the mutation. Prevent rotational frequency and the load resonance noise caused by air.
