Aluminum shell motor is to use the die-casting aluminum shell to replace the traditional cast iron shell of the motor. Due to the ductility of aluminum can good, small proportion. Aluminum shell motor has a beautiful appearance, small volume, light weight, simple structure, convenient maintenance, production process is more environmental protection, high efficiency, easy to transport advantages, which is popular among users.
but because of the demand is high, one of aluminum processing technology casing, the end cover the concentricity of poor: second aluminum shell no magnetic field, the frontal relative than iron shell motor magnetic circuit saturation of the motor, the electromagnetic wave is opposite bigger, the two characteristics of aluminum shell motor noise is bigger, to the production and manufacture of high quality products on the technological difficulty
aluminum shell motor noise analysis process
according to the different ways of producing brushless motor noise, can be roughly to its noise is divided into three categories: electromagnetic noise, mechanical noise, aerodynamic noise.
1, the generation of electromagnetic noise and control
in the motor air gap magnetic field pulsating cause and the motor stator and rotor structure vibration resulting from the low frequency noise of electromagnetic noise. The point of view of the influence from magnetic field, electromagnetic noise is mainly by the magnetic field force wave and the distribution of magnetic flux caused by asymmetry.
（1), the eccentricity of the rotor, or magnetic circuit asymmetry, will cause the asymmetric distribution of magnetic flux and appear side force, side force is small, thus produce electromagnetic noise. Therefore, in the design or process, and the rotor roundness must reach the requirements, must be symmetrical, uniform magnetic circuit. Aluminum shell motor end cover die casting processing precision, stator core to the frame assembly, related to, the alignment of the rotor, the precision requirement of aluminum shell motor is very important.
（2), rotor winding of the fundamental wave magnetic potential and every harmonic magnetic potential, they interaction can produce a series of waves. Fundamental wave magnetic field with low frequency, impact was not significant; Harmonic wave magnetic field produced by the force caused by the noise and the wave amplitude of the size and number. Choose appropriate, rotor slot on craft,, and adopt the method of chute to avoid low gravity wave.
in the face of the electromagnetic noise, the following methods can be used to reduce the aluminum shell motor electromagnetic noise:
(1)Select the appropriate slot coordination, avoid low power wave, using the rotor chute, oblique a stator slot distance;
（2)Select the appropriate air gap flux density and should not be too high, but too low and affect the utilization rate of materials, set, rotor magnetic circuit to be symmetrical, uniform and overlapping pressure closely; （3)As far as possible using sine winding, reduce the harmonic component, pay attention to avoid, rotor resonance frequency. （4), rotor machining and assembly should pay attention to their roundness and alignment, as much as possible to use heat or after being connected in the car first with the stator frame craft, of the end frame can be used with the end cover of the conjoined structure, better guarantee the alignment, reducing, the rotor eccentricity; 2, and control of mechanical noise brushless motor functioning part of the friction, impact and unbalance produces mechanical noise and structural resonance. Aluminum shell motor mechanical noise is opposite bigger, usually account for about 10%15%. Mechanical noise including bearing noise, the noise due to unbalanced rotor as well as assembly eccentricity caused by noise and so on. Bearing the noise value with the ball, inside and outside the ring grooves of dimensional accuracy, surface roughness and shape tolerance, etc. Lower bearing noise can adopt the following methods: (1)Assembly should be strictly the demagnetization of cleaning process, wash the oil and scrap iron; （2)The sealed bearing, prevent sundry into; With the bearing outer ring and the bearing chamber and the matching of the inner ring and shaft shoulds not be too tight; （3)To eliminate the axial clearance of the rotor, bearing must be appropriate pressure; The rational allocation of sealed elastic washer, appropriate to add lubricant to reduce friction. （4)For special motor noise requirements, appropriate chooses low noise bearings; When the load is not too big, can use oil bearing, it is lower than with the size of the rolling bearing noise can sometimes 10 db. in addition, the dynamic balance of rotor and fan is also an important means to reduce mechanical noise. 3, and control of aerodynamic noise the aerodynamic noise of the brushless motor is due to the rotation of the rotor and the shaft rotating cooling fan with the change of air flow and produced. It increases with the increasing of fan and the rotor speed, flow changes the faster, more strong, the noise is larger. The aerodynamic noise and speed, fan and the shapes of the rotor, roughness, unbalance, the change of the air duct section, air duct shape and so on. to reduce aerodynamic noise is the main measures are: (1)Fan and shaft connection without linkage, and USES the knurling straight grain process; Fan should be uniform thickness, no distortion, uniform spacing, with the dynamic balance; （2)For heat dissipation is good or not high temperature fan motor, eliminate noise source; For outer fan, when the design should not ventilated allowance, preferred axial flow fan; （3)The rotor surface should be smooth. （4)Air duct should reduce obstacles, there are appropriate USES the special air duct flow linear duct, duct section don't suddenly change.
