Ⅰ. Introduction

Nowadays more and more people choose to use PMSM(Permanent Magnet Synchronous Motor) because of its up to 20% energy-saving effect. Today I want to introduce the effect of Magnet Geometry and Tolerances on Motor Magnet Width. I hope it will be helpful to you.

Ⅱ. Effect of the thickness of the magnetic steel

When the inner or outer magnetic circuit ring is fixed, when the thickness increases, the air gap decreases, and the effective magnetic flux increases. The obvious performance is that the no-load speed decreases under the same residual magnetism, and the no-load current decreases. Maximum efficiency increase.

However, there are also disadvantages, such as the commutation vibration of the permanent magnet motor increasing, and the efficiency curve of the permanent magnet motor becoming relatively steep. Therefore, the thickness of the permanent magnet motor magnet should be as consistent as possible to reduce vibration;

Ⅲ. Effect of the width of the magnetic steel

For brushless motor magnets with dense row distribution, the total accumulated gap cannot exceed 0.5 mm, too small will not be installed, and too large will lead to vibration and lower efficiency of permanent magnet motor, this is because the position of the Hall element to measure the position of the magnets and the actual position of the magnets do not correspond, and must ensure the consistency of the width, otherwise the efficiency of the permanent magnet motor is low and the vibration is high.

For brush motors, there is a certain gap between the magnets gap, which is reserved for the mechanical commutation transition area.

Although there is a gap left, most manufacturers have a strict magnet installation process to ensure the accuracy of the mounting position of the permanent magnet motor magnets. If the width of the magnets exceeds, it will not be installed; if the width of the magnets is too small, it will lead to misalignment of the magnets and increase vibration and decrease the efficiency of the permanent magnet motor.

Ⅳ. Effect of magnet chamfer size and non-chamfer

If not chamfered, the rate of change of the magnetic field at the edge of the permanent magnet motor is large, causing pulse vibration of the permanent magnet motor, the larger the chamfer, the smaller the vibration.
However, chamfering generally has a certain loss of flux, for some specifications chamfering to 0.8, the flux loss is 0.5~1.5%.

For the brush motor remanent magnetism is low, appropriate reduce the size of the chamfer, is conducive to compensating the remanent magnetism, but the permanent magnet motor pulse vibration increased.

Generally speaking, when the remanent magnetism is low, the tolerance in the length direction can be enlarged appropriately, which can improve the effective flux to a certain extent and make the performance of the permanent magnet motor basically unchanged.

Ⅴ. Effect of remanent magnetism

For DC motors, under the same winding parameters and test conditions, the higher the remanence, the lower the no-load speed, and the lower the no-load current; the higher the maximum torque, the higher the efficiency at the highest efficiency point. In the actual test, the remanence standard of the magnets is generally judged by the no-load speed and the maximum torque.
For the same winding parameters and electrical parameters, the higher the remanence, the lower the no-load speed and the lower the no-load current, because the motor in operation, with a relatively low speed, generates enough reverse inductive voltage to reduce the algebraic sum of the electric potential applied to the winding.

Ⅵ. Effect of coercivity

During the operation of the motor, there is always the problem of temperature and reverse degaussing of the magnetic field. From the motor design point of view, the higher the coercivity, the smaller the coercivity can be in the direction of the thickness of the magnets, while the thickness of the magnets can be in the direction of the smaller coercivity. But the magnets are useless after exceeding a certain coercivity, because the other components of the motor cannot work stably at that temperature either. If the coercivity can be achieved, then it can be recommended to meet the needs under experimental conditions and there is no need to waste resources.

Ⅶ. Effect of squareness

Squareness only affects the straightness of the motor performance test efficiency curve. Although the straightness of the motor efficiency curve is not yet an important indicator criterion, it is very important for the range of the wheel motor under natural road conditions. This is one of the reasons why some motors do not have a high maximum efficiency but have a long range. A good hub motor should not only have high maximum efficiency, but also the efficiency curve should be as horizontal as possible, and the slope of efficiency reduction is as small as possible. As the market, technology, and standards of hub motors mature, this will gradually become an important criterion.

Ⅷ. Effect of performance consistency

Inconsistent remanent magnetism: Even if there are individual ones with particularly high performance, they are not good, and vibration occurs due to the inconsistency of magnetic flux in each unidirectional magnetic field section, resulting in asymmetry of torque.
Coercive force inconsistency: Especially the coercive force of individual products is too low, which is easy to produce reverse demagnetization, resulting in inconsistent flux of each magnet to make the motor vibrate.
This effect is more significant for brushless motors, permanent magnet motor self-learning of the geometry and tolerance of the magnets on the width of the motor magnets: for the dense row distribution of brushless motor magnets, the total cumulative gap can not exceed 0.5 mm, too small will not be installed, too large will lead to motor vibration and reduced efficiency, this is because the position of the Hall element to measure the position of the magnets and the actual position of the magnets do not correspond. In addition, the consistency of the width must be ensured, otherwise, the motor will have low efficiency and high vibration.