1. The influence 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 increases, and the efficiency curve of the permanent magnet motor becomes relatively steep. Therefore, the thickness of the permanent magnet motor magnet should be as consistent as possible to reduce vibration;
2. the influence of the width of the magnetic steel:
For densely packed brushless motor magnets, the total cumulative gap cannot exceed 0.5 mm, too small will cause installation failure, and too large will cause permanent magnet motor vibration and reduced efficiency, which 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 magnet, and the consistency of the width must be ensured, otherwise the efficiency of the permanent magnet motor is low and the vibration is large; for the brushed motor, there is a certain gap between the magnets, which is reserved for the mechanical commutation transition District.
Although there is a gap, most manufacturers have strict magnet installation procedures to ensure the installation accuracy of the permanent magnet motor magnets in order to ensure the correct installation position. If the width of the magnetic steel is too large, it will not be able to be installed; if the width of the magnetic steel is too small, the positioning of the magnetic steel will be misaligned, the vibration of the permanent magnet motor will increase, and the efficiency will decrease.
3. The influence of the size of the magnetic steel chamfer and no chamfer:
If there is no chamfering, the rate of change of the magnetic field at the edge of the magnetic field of the permanent magnet motor is large, resulting in pulse vibration of the permanent magnet motor. The larger the chamfer, the smaller the vibration. However, chamfering generally has a certain loss of magnetic flux. For some specifications, when the chamfering reaches 0.8, the magnetic flux loss is 0.5~1.5%. When the residual magnetism of the brushed motor is low, appropriately reducing the size of the chamfer will help to compensate for the residual magnetism, but the pulse vibration 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 flux to a certain extent, so that the performance of the permanent magnet motor basically does not change.
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 of the highest efficiency point. In the actual test, the level of no-load speed and the maximum torque are generally used to judge the residual magnetism standard of the magnet.
For the same winding parameters and electrical parameters, the reason why the higher the remanence, the lower the no-load speed and the smaller the no-load current is that the motor in operation produces enough reverse inductance at a relatively low speed. The generated voltage reduces the algebraic sum of the electromotive forces applied to the windings.
5. The influence of coercive force
During the operation of the motor, there are always problems of temperature and reverse demagnetization field. From the perspective of motor design, the higher the coercive force, the smaller the thickness direction of the magnet, the smaller the coercive force, and the larger the thickness direction of the magnet. But magnetic steel is useless after exceeding a certain coercive force, because other components of the motor cannot work stably at that temperature. If the coercive force can meet the requirements, it can be recommended to meet the requirements under the experimental conditions, and there is no need to waste resources.
6. the influence of squareness
The squareness only affects the straightness of the efficiency curve of the motor performance test. Although the straightness of the motor efficiency curve has not been listed as an important indicator standard, it is very important for the continued distance of the hub motor under natural road conditions. important. Due to different road conditions, the motor cannot always work at the maximum efficiency point, which is one of the reasons why the maximum efficiency of some motors is not high and the continuation distance is longer. For a good in-wheel motor, not only should the maximum efficiency be high, but also the efficiency curve should be as horizontal as possible. The smaller the slope of the efficiency reduction, the better. As the market, technology and standards of in-wheel motors mature, this will gradually become an important standard.
7. The impact of performance consistency Inconsistent residual magnetism:
Even if there are individual ones with particularly high performance, it is not good. Due to the inconsistency of the magnetic flux in each unidirectional magnetic field section, the vibration occurs due to the asymmetry of the torque. Inconsistent coercive force: especially if the coercive force of individual products is too low, it is easy to produce reverse demagnetization, resulting in inconsistent magnetic flux of each magnet and vibrating the motor.
This effect is more significant for brushless motors. The geometric shape and tolerance of permanent magnet motor self-learning magnets affect the width of motor magnets: for densely packed brushless motor magnets, the total cumulative gap cannot exceed 0.5mm, If it is too small, it will not be installed, and if it is too large, it will cause the vibration of the motor and reduce the efficiency, because the position of the Hall element that measures the position of the magnet does not correspond to the actual position of the magnet. In addition, the consistency of the width must be ensured, otherwise the efficiency of the motor will be low and the vibration will be large.