What are effects of the shape and tolerance of permanent magnet motor magnets on motor performance?-Xinda Motor- electric motors and EV accessories supplier|INDEX--

What are effects of the shape and tolerance of permanent magnet motor magnets on motor performance?

Date：2023-12-19　　　Author：XINDA MOTOR

Why so many people choose to use permanent magnet motors now? It is precisely because of its energy saving, which can reach about 20%, but Have you ever understood some of the self-learning contents of permanent magnet motors?

1. The influence of magnetic steel thickness:

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 manifestation is that the no-load speed decreases and the no-load current decreases under the same residual magnetism. The permanent magnet motor's Maximum efficiency improvement. However, there are also disadvantages, such as the increase in commutation vibration of the permanent magnet motor and the relative steepening of the efficiency curve of the permanent magnet motor. Therefore, the thickness of the permanent magnet motor magnets should be as consistent as possible to reduce vibration;

2. The influence of magnet width:

For brushless motor magnets that are densely packed, the total cumulative gap cannot exceed 0.5 mm. If it is too small, it will not be installed. If it is too large, it will cause vibration and reduced efficiency of the permanent magnet motor. This is because of the position of the Hall element that measures the position of the magnet. It does not correspond to the actual position of the magnets, and the consistency of the width must be ensured, otherwise the permanent magnet motor will have low efficiency and large vibrations; for brush motors, there is a certain gap between the magnets, which is left for mechanical commutation transition. District.

Although there is a gap, in order to ensure the accurate installation position of the permanent magnet motor magnets, most manufacturers have strict magnet installation procedures to ensure installation accuracy. If the width of the magnet is exceeded, it will not be installed; if the width of the magnet is too small, the positioning of the magnet will be misaligned, the vibration of the permanent magnet motor will increase, and the efficiency will decrease.

3. The influence of magnetic steel chamfering size and non-chamfering:

If there is no chamfering, the magnetic field change rate at the edge of the magnetic field of the permanent magnet motor will be large, causing pulse vibration of the permanent magnet motor. The larger the chamfering, the smaller the vibration.

However, chamfering generally causes a certain loss of magnetic flux. For some specifications, when chamfering is to 0.8, the magnetic flux loss is 0.5~1.5%. When the residual magnetism of the brushed motor is low, appropriately reducing the chamfer size will help compensate for the residual magnetism, but the pulsation of the permanent magnet motor will increase. Generally speaking, when the residual magnetism is low, the tolerance in the length direction can be appropriately enlarged, which can increase the effective magnetic flux to a certain extent and keep the performance of the permanent magnet motor basically unchanged.

4. The influence of residual magnetism

For DC motors, under the same winding parameters and test conditions, the higher the residual magnetism, the lower the no-load speed and the smaller the no-load current; the greater the maximum torque, the higher the efficiency at the highest efficiency point. In actual tests, the level of no-load speed and the size of the maximum torque are generally used to judge the residual magnetism standard of magnets.

For the same winding parameters and electrical parameters, the reason why the higher the residual magnetism, the lower the no-load speed, and the smaller the no-load current is because the running motor generates sufficient reverse induction at a relatively low speed. Generates a voltage, causing the algebraic sum of the electromotive force applied to the winding to decrease.

5. The influence of coercivity

During the operation of the motor, there are always problems with temperature and reverse demagnetization. From the perspective of motor design, the higher the coercivity, the smaller the thickness direction of the magnet, the smaller the coercivity, and the larger the thickness direction of the magnet. However, magnetic steel is useless after it exceeds a certain coercivity, because other components of the motor cannot work stably at that temperature. If the coercivity can meet the requirements, it can be recommended to meet the needs under experimental conditions, and there is no need to waste resources.

6. The influence of squareness

The squareness only affects the flatness of the motor performance test efficiency curve. Although the flatness of the motor efficiency curve has not yet been listed as an important indicator standard, this is very important for the continuation distance of the wheel hub motor under natural road conditions. important. Because of different road conditions, the motor cannot always work at the maximum efficiency point. This is one of the reasons why the maximum efficiency of some motors is not high but the driving distance is long. A good hub motor should not only have a high maximum efficiency, but also the efficiency curve should be as horizontal as possible. The smaller the slope of efficiency reduction, the better. As the market, technology and standards for in-wheel motors mature, this will gradually become an important standard.

7. Impact of performance consistency

Residual magnetism inconsistency: Even some with particularly high performance are not good. Due to the inconsistency of the magnetic flux in each unidirectional magnetic field section, the torque is asymmetric and vibration occurs.

Inconsistent coercive force: Especially if the coercive force of individual products is too low, reverse demagnetization is likely to occur, causing the magnetic flux of each magnet to be inconsistent and causing the motor to vibrate.

What are effects of the shape and tolerance of permanent magnet motor magnets on motor performance?

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