What is a permanent magnet motor
What is a permanent magnet motor?
The permanent magnet motor uses permanent magnets to generate the motor’s magnetic field. It does not require an excitation coil or excitation current. Compared with the traditional electric excitation motor, it has significant advantages such as high efficiency and simple structure. The application range of permanent magnet motors is extremely wide, covering almost all fields of aerospace, national defense, industrial and agricultural production and daily life. With the development of high-performance permanent magnet materials and the rapid development of control technology, the application of permanent magnet motors will become More extensive. Today, yueci will take you to understand the impact of permanent magnet motors and permanent magnet material performance on motors.
Everyone knows that there are many types of motors, but the basic principles are the application of electromagnetism and electromagnetic induction to realize the mutual conversion of electric energy and kinetic energy. If you want to know more about the basic principles and structure of motors, you can click to view the basic principles and basics of motors. structure. Today we take permanent magnet DC motors and permanent magnet synchronous motors as examples to briefly introduce permanent magnet motors.
Permanent magnet DC motor
Permanent magnet DC motors can be divided into permanent magnet brushless DC motors and permanent magnet brush DC motors according to whether there are brushes. Permanent magnet DC motor is a type of DC motor that uses permanent magnets to build a magnetic field.
Permanent magnet brushless DC motor
The permanent magnet brushless DC motor is a DC motor whose magnetic field is established by one or more permanent magnets. Its performance is similar to that of a separately excited DC motor with a constant excitation current. The speed can be easily adjusted by changing the armature voltage. Compared with separately-excited DC motors, it has the advantages of small size, high efficiency, simple structure, and less copper consumption. It is the main type of low-power DC motors.
The permanent magnet brushless DC motor is composed of a motor body and a driver, and is a typical mechatronic product.
1. The stator windings of motors are mostly made into three-phase symmetrical star connection, which is very similar to three-phase asynchronous motors. Magnetized permanent magnets are glued to the rotor of the motor. In order to detect the polarity of the motor rotor, a position sensor is installed in the motor. The driver is composed of power electronic devices and integrated circuits. Its function is to receive the start, stop, and brake signals of the motor to control the start, stop and brake of the motor; receive position sensor signals and forward and reverse signals to control the reverse The on and off of each power tube of the variable bridge produces continuous torque; accepts speed commands and speed feedback signals to control and adjust the speed; provide protection and display, etc.
The main circuit is a typical voltage type AC-DC-AC circuit. The inverter provides a symmetrical alternating rectangular wave with a constant amplitude and equal frequency 5-26KHZ modulation wave.
The permanent magnet NS is alternately exchanged to make the position sensor generate U, V, W square waves with a phase difference of 120°, and combine the forward/reverse signal to generate an effective six-state encoding signal: 101, 100, 110, 010, 011, 001, through Logic component processing produces T1-T4 conduction, T1-T6 conduction, T3-T6 conduction, T3-T2 conduction, T5-T2 conduction, and T5-T4 conduction, which means that the DC bus voltage is sequentially applied to A+B-, A+C-, B+C-, B+A-, C+A-, C+B- up, so that every time the rotor rotates a pair of NS poles, the T1-T6 power tubes are combined according to the fixed combination Turn on sequentially in six states. In each state, only two-phase windings are energized, and one state is changed in turn. The magnetic field axis generated by the stator winding rotates in space by 60° electrical angle, and the rotor follows the stator magnetic field to rotate equivalent to 60° electrical angle in space. The rotor is in the new position Above, make the position sensor U, V, W generate a set of new codes according to the agreement. The new codes change the conduction combination of the power tube, and make the magnetic field axis generated by the stator winding move forward by 60° electric angle. The DC motor will generate continuous torque and drag the load for continuous rotation. Because the commutation of the permanent magnet DC motor is generated by itself, rather than forced by the inverter, it is also called a self-controlled synchronous motor.
2. The position sensor code of the permanent magnet brushless DC motor makes the energized two-phase winding composite magnetic field axis position ahead of the rotor magnetic field axis position, so no matter where the starting position of the rotor is, the motor will generate enough power at the moment of starting. Starting torque, so no additional starting winding is required on the rotor.
Since the axis of the stator magnetic field can be regarded as perpendicular to the axis of the rotor, when the iron core is not saturated, the average electromagnetic torque produced is proportional to the winding current, which is the same as the current-torque characteristic of a separately excited DC motor.
The motor torque is proportional to the average winding current:
- Tm=KtIav (N·m)
The difference of the back EMF between the two phase windings of the motor is proportional to the angular velocity of the motor:
- ELL=Keω (V)
So the average current in the motor winding is:
- Iav=(Vm-ELL)/2Ra (A)
Among them, Vm=δ·VDC is the average value of the voltage applied between the motor wires, VDC is the DC bus voltage, δ is the duty cycle of the modulation wave, and Ra is the winding resistance of each phase. From this, the electromagnetic torque of the DC motor can be obtained:
Kt and Ke are the structural constants of the motor, and ω is the angular speed of the motor (rad/s). Therefore, at a certain ω, changing the duty cycle δ can linearly change the electromagnetic torque of the motor, and obtain the externally excited DC current The motor armature voltage control has the same control characteristics and mechanical characteristics.
The speed setting of the permanent magnet brushless DC motor depends on the level of the speed command Vc. If the maximum speed command is +5V, the highest speed: Vc(max)ón max, then any level below +5V corresponds to the equivalent The speed n, which realizes the variable speed setting.
When Vc is set, regardless of load change, power supply voltage change, or environmental temperature change, when the speed is lower than the command speed, the feedback voltage Vfb becomes smaller, the duty ratio δ of the modulation wave becomes larger, and the armature current changes Large, the electromagnetic torque produced by the motor increases and acceleration is generated until the actual speed of the motor is equal to the command speed; on the contrary, if the actual speed of the motor is higher than the command speed, δ decreases, Tm decreases, and deceleration occurs. Until the actual speed is equal to the command speed. It can be said that the permanent magnet DC motor is within the allowable grid fluctuation range and below the allowable overload capacity, its steady-state speed differs from the commanded speed by about 1%, and can achieve constant torque operation within the speed range.
Because the excitation of permanent magnet brushless DC motor comes from permanent magnets, it does not need to draw excitation current from the grid like asynchronous motors; because there is no alternating magnetic flux in the rotor, there is neither copper loss nor iron loss on the rotor, so the efficiency It is about 10% higher than the same capacity asynchronous motor. Generally speaking, the force index (ηcosθ) of the permanent magnet DC motor is 12%-20% higher than the same capacity three-phase asynchronous motor.
3. Since the permanent magnet brushless DC motor operates in a self-controlled manner, it will not add a start winding to the rotor like a synchronous motor started under heavy load under variable frequency speed regulation, nor will it cause oscillation and loss when the load changes suddenly. step.
The permanent magnets of small and medium capacity permanent magnet brushless DC motors are mostly made of rare earth neodymium iron boron (Nd-Fe-B) materials with high magnetic energy product. Therefore, the volume of the rare earth permanent magnet brushless motor is one size smaller than the three-phase asynchronous motor of the same capacity.
In the past 30 years, the research on the variable frequency speed regulation of asynchronous motors is ultimately looking for a method to control the torque of the asynchronous motor, and the current of the permanent magnet DC motor or the terminal voltage of the armature is the physical quantity that directly controls the torque of the motor. In the past, due to factors such as the relatively high price of rare earth permanent magnets, the application field of rare earth permanent magnet permanent magnet DC motors was limited. However, with the continuous innovation of technology, the price has dropped rapidly. For example, there is a BS series permanent magnet DC motor on sale. The price is almost the same as the sum of the selling price of asynchronous motors and ordinary frequency converters. Rare-earth permanent magnet permanent magnet DC motors are bound to show advantages in the field of speed regulation due to their wide speed regulation, small size, high efficiency and small steady-state speed error.
According to the different permanent magnet materials used, permanent magnet brushless DC motors are divided into alnico permanent magnet DC motors, ferrite permanent magnet DC motors and rare earth permanent magnet DC motors. Alnico permanent magnet brushless DC motors need to consume a lot of precious metals and are relatively expensive, but they have good adaptability to high temperatures and are used in occasions where the ambient temperature is high or the temperature stability of the motor is high. Ferrite permanent magnet brushless DC motors are known for their low cost and good performance. They are widely used in household appliances, automobiles, toys, power tools and other fields. The rare earth permanent magnet brushless DC motor, which uses rare earth permanent magnet materials as magnetic poles, is small in size and better in performance, but expensive. It is mainly used in aerospace, computers, and downhole instruments. However, in recent years, a new generation of rare earth permanent magnet DC motors-neodymium iron boron permanent magnet brushless DC motors has emerged. Since my country has more than 80% of the world’s reserves of neodymium resources, it has a unique advantage in price. The price-performance ratio of iron-boron permanent magnet materials has been greatly improved, so that the high-quality and cheap neodymium-iron-boron permanent magnet DC motors have been widely used in industrial production, and it also promotes the rapid development of the performance and structure of permanent magnet brushless DC motors.
(1) Choice of type
Ferrite permanent magnet DC motors with high efficiency, low price and low temperature rise should be preferred. Only when the performance requirements are strict, the volume is small, and the ambient temperature is high, should AlNiCo permanent magnet DC motors or rare earth permanent magnet DC motors be considered.
(2) Reasonably choose the power of the motor
The maximum output power of the motor is limited. If the power of the motor is selected too small, and the load exceeds the rated output power of the motor, the motor will be overloaded. When overloaded, the motor will generate heat, vibration, decrease in speed, and abnormal sound. When overloaded, the motor will be burned. If the power is too large, it will cause economic waste. Therefore, it is very important to choose the power of the motor reasonably.
(3) Specification selection
Often because the actual product specifications are not many, it is difficult to select products. When selecting product specifications, consider: In the case where the power supply voltage is adjustable, you can select the specifications whose torque and speed are close to the corresponding rated value of the product according to actual needs, and obtain the required speed by changing the voltage; in the case where the power supply voltage is fixed, If there is no product with proper specifications to choose from, the proper specifications can be selected according to the torque first, and the voltage and speed of the product can be adjusted appropriately.
Pay attention to the application of permanent magnet brushless DC motor:
- (1) If the product has no special instructions, under normal circumstances (such as Al-Ni-Co permanent magnet DC motors or ferrite permanent magnet DC motors) permanent magnet DC motors are not allowed to run under the rated voltage with reverse braking, otherwise it will cause The permanent magnet is demagnetized; if it is really necessary to operate in this way, a current-limiting resistor should be added to limit the excessive current.
- (2) Perform a preliminary inspection of the quality of the motor according to the following steps:
- First check the appearance of the motor: there should be no scratches, bruises, and peeling off the coating; then rotate the shaft, it should be able to rotate flexibly without obvious jamming. Check whether the wiring of the motor is firm and energized to run. There should be no friction during the rotation of the motor, the most prominent of which is bearing friction. After the bearing is worn, it will make an abnormal sound and cause local overheating and temperature rise.
- (3) Pay attention to the permanent magnet demagnetization caused by excessive current, temperature changes and open magnetic circuit during disassembly and assembly. Especially for Alnico permanent magnet motors, the permanent magnet magnetic circuit must be protected against magnetic short-circuit during disassembly and assembly, otherwise magnetize separately after demagnetization.
Permanent magnet brushed DC motor
The stator of the brush motor is equipped with fixed main magnetic poles and brushes, and the rotor is equipped with an armature winding and a commutator. The electric energy of the DC power supply enters the armature winding through the brush and the commutator to generate armature current. The magnetic field generated by the armature current interacts with the main magnetic field to generate electromagnetic torque, which makes the motor rotate to drive the load. Due to the existence of brushes and commutators, the brushed motor has a complex structure, poor reliability, many failures, large maintenance workload, short life, and commutation sparks are prone to electromagnetic interference.
The working principle diagram of a brushed DC motor is shown in Figure 2-1. There are magnets in the fixed part of the brushed DC motor, here called the main pole; the fixed part also has brushes. The rotating part has an annular iron core and a winding wound on the annular iron core.
The fixed part (stator) of the two-pole brushed DC motor shown in Figure 2-1 is equipped with a pair of DC-excited stationary main magnetic poles N and S, and an armature core is installed on the rotating part (rotor). There is an air gap between the stator and the rotor. An armature coil composed of two conductors A and X is placed on the armature core. The head and end of the coil are respectively connected to two arc-shaped copper plates, which are called commutating plates. The commutator segments are insulated from each other, and the whole composed of commutator segments is called a commutator. The commutator is fixed on the rotating shaft, and the commutator segments and the rotating shaft are insulated from each other. A pair of fixed brushes B1 and B2 are placed on the commutator segment. When the armature rotates, the armature coil is connected to the external circuit through the commutator segment and the brushes.
- ① Motor with brushed disk winding. The brushed disk winding motor is bonded with rare earth materials on a cylinder body, and the disk winding made of enameled copper wire is placed in the cylinder body to form a rotor. The phase of the motor is adjusted by a mechanical inverter. The mechanical inverter adjusts the voltage phase by friction between a fixed carbon brush and a rotating copper commutation surface. The brushes of this kind of motor have been worn out during use, and the service life of the motor is difficult to exceed 2000h. At the same time, due to the high speed of the motor, it is necessary to adopt a two-stage gear reduction, which brings two problems. One is that the noise is large, and the other is the efficiency loss. The rated efficiency of the motor after deceleration can only reach 68%. ~72%. The capacity of the battery used in electric bicycles is limited, generally 36V/12Ah. If the motor efficiency is not high, it will increase the power consumption and affect the continued mileage.
- ② Motor with brush printed winding. The brush printed winding motor uses printed copper foil as the winding, so the weight of the motor is reduced. Since this motor is all produced on an automatic production line, the process is reliably guaranteed, so that the life of the motor is increased to 3000h, the noise is greatly reduced, and the efficiency is increased to 72% to 76%. However, this kind of motor has “humming” high-frequency noise, and the efficiency is still not ideal after the gear is reduced. The use of the brushed commutator makes the life of the motor unable to be improved.
- ③ Brushed winding motor. This kind of motor presses the wound copper wire into a new type of winding, and its efficiency can be increased to 74% to 78%. This kind of motor is still used by many electric bicycle manufacturers, but its efficiency, noise, and life defects are still problems that must be improved.
The hub-type gear-driven brushed DC motor is composed of a disk-shaped armature brushed motor and a gear reduction and transmission system. The disk armature is a high-speed rotor. The structure of a geared brushed DC motor is shown in Figure 2-2. The torque of the motor is transmitted to the first-stage gear through the shaft, and the hub shell is driven to rotate through the gear reduction.
The disc-shaped armature of the brushed geared hub motor is thin, small in size, light in weight and easy to install. After the winding is prepared, it is formed by hot pressing with resin and glass fiber. Due to the friction between the brush and the commutator and the gear meshing and decelerating during operation, the running sound of the brush motor is louder than the brushless motor. .
Due to the improvement in the design of the brush motor, there is no need for gear reduction, which can achieve low noise and low cost. Many low-priced electric bicycles widely use this motor. However, this kind of motor has small torque, small load, poor climbing ability, and consumes a lot of power during use. Mechanical brush inverters are still used. The motor life problem has not been solved, so medium and high-end electric bicycles are not used. This kind of motor.
Uses of permanent magnet DC motors
In terms of stage lighting, permanent magnet DC motors, especially small permanent magnet DC gear motors, are used very much. In the computer industry, a large number of permanent magnet DC motors are used in printers, scanners, hard disk drives, optical disc drives, recorders, cooling fans, etc.
Various permanent magnet DC motors are used in various fans, wipers, water spray pumps, flame extinguishers, mirrors, and air pumps in the automotive industry. The hotel’s automatic doors, automatic door locks, automatic curtains, automatic water supply systems, soft towel machines, etc. all use permanent magnet DC motors. In weapon equipment, permanent magnet DC motors are widely used in missiles, artillery, satellites, and spacecraft. , Ships, airplanes, tanks, rockets, radars, tanks, etc.
In industry and agriculture, permanent magnet DC motors are also widely used in electrical and automation control and instrumentation. In medical applications, permanent magnet DC motors are even more useful, such as various medical instruments, surgical tools, such as electric bone saws in brain surgery, and in particular, various instruments in field surgery are basically permanent Magnetic DC motor. In terms of supplies for the disabled, such as manipulators and disabled vehicles, permanent magnet DC motors are used. In terms of life, it is more useful. Even toothbrushes are made of electric toothbrushes with permanent magnet DC motors. The application of permanent magnet DC motor is really endless, it can be said that it is everywhere.
With the development of the times, there will be more applications of permanent magnet DC motors, and many occasions where AC motors were originally used are replaced by permanent magnet DC motors. Especially after the emergence of permanent magnet brushless motors, the production volume of permanent magnet DC motors is constantly increasing. my country produces more than billions of various permanent magnet DC motors every year, and there are countless manufacturers of permanent magnet DC motors.
Permanent magnet synchronous motor
The permanent magnet synchronous motor uses permanent magnets to provide excitation, which makes the motor structure simpler, reduces the processing and assembly costs, and saves the slip ring and brush that are prone to problems, which improves the reliability of the motor operation; and because there is no need for excitation Electric current, no excitation loss, improve the efficiency and power density of the motor.
The permanent magnet synchronous motor is composed of stator, rotor and end cover. The stator is basically the same as an ordinary induction motor, and uses a laminated structure to reduce the iron loss when the motor is running. The rotor can be made solid or laminated. The armature winding can adopt concentrated full-pitch winding, distributed short-pitch winding and unconventional winding.
Classification of permanent magnet synchronous motors
Classified by excitation current supply method
A permanent magnet synchronous motor is a synchronous motor that uses permanent magnets to establish an excitation magnetic field. Its stator generates a rotating magnetic field and the rotor is made of permanent magnet materials. Synchronous motors need a DC magnetic field to achieve energy conversion, and the DC current that generates this magnetic field is called the excitation current of the motor.
- Separately excited motor: a motor that obtains excitation current from other power sources.
- Self-excited motor: A motor that obtains the excitation current from the motor itself.
Classified by power supply frequency
Permanent magnet brushless motors include permanent magnet brushless DC motors and permanent magnet brushless AC motors, both of which require variable frequency power supply when operating as motors. The former requires only a square wave inverter for power supply, and the latter requires a sine wave inverter for power supply.
Classified by air gap magnetic field distribution
Sine wave permanent magnet synchronous motor: The magnetic poles are made of permanent magnet materials. When a three-phase sine wave current is input, the air gap magnetic field is distributed according to the sine law, referred to as permanent magnet synchronous motor.
Trapezoidal wave permanent magnet synchronous motor: The magnetic poles are still permanent magnet materials, but the square wave current is input, the air gap magnetic field is distributed in a trapezoidal wave, and the performance is closer to that of a DC motor. A self-control variable frequency synchronous motor composed of a trapezoidal wave permanent magnet synchronous motor is also called a brushless DC motor.
Advantages of permanent magnet synchronous motors
The permanent magnet synchronous motor can be integrally installed on the axle to form an integral direct drive system, that is, one axle is a drive unit, eliminating the need for a gear box. The advantages of permanent magnet synchronous motors are as follows:
- The permanent magnet synchronous motor itself has high power efficiency and high power factor;
- The permanent magnet synchronous motor generates little heat, so the motor cooling system has a simple structure, small size and low noise;
- The system adopts a fully enclosed structure, no transmission gear wear, no transmission gear noise, no lubricating oil, no maintenance;
- The allowable overload current of the permanent magnet synchronous motor is large, and the reliability is significantly improved;
- The entire transmission system is light in weight, and the unsprung weight is lighter than that of the traditional axle drive, and the power per unit weight is greater;
- Since there is no gear box, the bogie system can be designed at will: such as flexible bogies and single-axle bogies, greatly improving the power performance of the train.
- Due to the use of permanent magnetic material poles, especially the use of rare earth metal permanent magnets (such as neodymium iron boron, etc.), its magnetic energy product is high, and a higher air gap flux density can be obtained. Therefore, the size of the motor is small under the same capacity , Light weight.
- The rotor has no copper loss and iron loss, and there is no friction loss of the collector ring and brush, and the operation efficiency is high.
- The moment of inertia is small, the allowable impulse torque is large, high acceleration can be obtained, the dynamic performance is good, the structure is compact, and the operation is reliable.
The development of permanent magnet motors is closely related to the development of permanent magnet materials
The first motor in the world that appeared in the 1820s was a permanent magnet motor whose excitation magnetic field was generated by permanent magnets. However, the permanent magnet material used at that time was natural magnetite (Fe3O4), which had a very low magnetic energy density. The motor made from it was bulky and was soon replaced by an electric excitation motor.
With the rapid development of various motors and the invention of current magnetizers, people have conducted in-depth research on the mechanism, composition and manufacturing technology of permanent magnet materials, and have successively discovered a variety of permanent magnet materials such as carbon steel, tungsten steel, and cobalt steel. . In particular, the AlNiCo permanent magnets that appeared in the 1930s and the ferrite permanent magnets that appeared in the 1950s have greatly improved their magnetic performance, and various micro and small motors have used permanent magnets for excitation. However, the coercivity of AlNiCo permanent magnets is low, and the remanence density of ferrite permanent magnets is not high, which limits their application range in motors. Until the 1960s and 1980s, samarium-cobalt permanent magnets and neodymium-iron-boron permanent magnet materials came out one after another. Their high remanence, high coercivity, high energy product and excellent magnetic properties of linear demagnetization curve are particularly suitable for Manufacturing motors, so that the development of permanent magnet motors has entered a new historical period.
The relationship between magnetic steel performance and motor performance
The influence of remanence
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 greater the maximum torque, the higher the efficiency at the highest efficiency point. In the actual test, the level of the no-load speed and the maximum torque are generally used to judge the remanence 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 lower the no-load current, is that the running motor produces sufficient reversal at a relatively low speed. The voltage is generated so that the algebraic sum of the electromotive force applied to the winding is reduced.
The influence of coercivity
In the process of motor operation, there is always the influence of temperature and reverse demagnetization. From the perspective of motor design, the higher the coercive force, the smaller the thickness direction of the magnet can be, and the smaller the coercive force, the greater the thickness direction of the magnet. But after the magnetic steel exceeds a certain coercive force, it is useless, because other components of the motor cannot work stably at that temperature. If the coercivity meets the demand, the standard is to meet the demand under the recommended experimental conditions, and there is no need to waste resources.
The influence of squareness
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 index standard, this is very important for the continuous travel distance of the in-wheel motor under natural road conditions. important. Because of the 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 continuous travel distance is long. A good in-wheel motor should not only have a high maximum efficiency, but also the efficiency curve should be as level as possible. The lower the slope of efficiency reduction, the better. As the market, technology and standards of in-wheel motors mature, this will gradually become an important standard.
To understand what the directionality of a magnetic material is, please click on an article to understand the hysteresis curve (magnetization curve, demagnetization curve, intrinsic curve, magnetic energy product curve)
The impact of performance consistency
Inconsistent remanence: even some of the ones with particularly high performance are not good. Due to the inconsistency of the magnetic flux of each unidirectional magnetic field section, the torque is asymmetry and vibration occurs.
Inconsistent coercivity: In particular, if the coercivity of individual products is too low, it is prone to reverse demagnetization, which leads to inconsistent magnetic fluxes of the magnets and vibration of the motor. This effect is more significant for brushless motors.
The influence of the shape and tolerance of the magnet on the performance of the motor
The influence of magnet 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 performance is that the no-load speed decreases under the same remanence, the no-load current decreases, and the maximum efficiency of the motor improve. However, there are also disadvantages. For example, the motor’s commutation vibration increases and the motor’s efficiency curve becomes relatively steep. Therefore, the thickness of the motor magnet should be as consistent as possible to reduce vibration.
The influence of magnetic steel width
For close-packed brushless motor magnets, the total cumulative gap cannot exceed 0.5 mm. If it is too small, it will not be installed. If it is too small, it will cause the motor to vibrate and reduce the efficiency. This is due to the position and magnetic The actual position of the steel does not correspond, and the width must be consistent, otherwise the efficiency of the motor will be low and the vibration will be large.
For brushed motors, there is a certain gap between the magnets, which is left to the transition zone of mechanical commutation. Although there is a gap, most manufacturers have strict magnet installation procedures to ensure the accuracy of installation in order to ensure the accurate installation position of the motor magnet. If the width of the magnet is exceeded, it will not be able to be installed; if the width of the magnet is too small, it will cause the magnet to be misaligned, increase the vibration of the motor and reduce the efficiency.
The influence of magnetic steel chamfer size and non-chamfer
If the corner is not chamfered, the rate of change of the magnetic field at the edge of the magnetic field of the motor will be large, causing the pulse of the motor. The larger the chamfer, the smaller the vibration. However, chamfering generally has a certain loss of magnetic flux. For some specifications, the magnetic flux loss is 0.5~1.5% when the chamfer is 0.8. When the residual magnetism of the brush motor is low, appropriately reducing the chamfer size is beneficial to compensate the residual magnetism, but the pulse vibration of the motor increases. Generally speaking, when the remanence is low, the tolerance in the length direction can be appropriately enlarged, so that the effective magnetic flux can be improved to a certain extent, so that the performance of the motor is basically unchanged.
Source: China Permanent Magnet Manufacturer – www.rizinia.com