Outer rotor brushless motor suitable for environmental electric appliance and pole slot matching method thereof

Abstract

The invention relates to the technical field of motors, in particular to an outer rotor brushless motor suitable for an environmental electric appliance and a pole slot matching method of the outer rotor brushless motor. Comprising a rotor assembly and a stator assembly. The rotor assembly comprises a rotor casing and rotor magnetic steel fixed on the inner wall of the rotor casing, and N poles and S poles of the rotor magnetic steel are uniformly distributed in a staggered manner; the stator assembly comprises a stator iron core and an armature winding wound on the stator iron core; the number of pole pairs of the rotor magnetic steel is P, and P is an even number greater than 7; the number of pole teeth of the stator core is Z, and Z is an integer greater than 12 and can be exactly divided by 3; according to the structure and the method, the number Z of pole teeth of a stator core is matched with the number P of pole pairs of rotor magnetic steel to suppress electromagnetic vibration caused by armature current harmonic waves and reduce cogging torque, so that the outer rotor brushless motor can suppress the electromagnetic vibration caused by the armature current harmonic waves and reduce the cogging torque; the mute performance of the motor is improved, the operation noise is reduced, and the motor can be better suitable for environmental electric appliances.

Description

Technical Field

[0001] This invention relates to the technical field of electric motors, and more particularly to an external rotor brushless motor suitable for environmental electrical appliances and its pole slot matching method. Background Technology

[0002] In current technology, environmental appliances such as fans, air purifiers, and humidifiers are developing towards energy saving, quiet operation, and high power. These devices typically use external rotor brushless motors as their power source, with operating speeds generally below 2000 rpm. Traditional designs often employ 12-slot 10-pole or 12-slot 14-pole configurations, corresponding to 5 and 7 pole pairs respectively. With this configuration, the electrical speed range is between 10,000 and 14,000 rpm, making it difficult to achieve high power density and efficiency. Theoretically, increasing the number of pole pairs improves power density, but it also increases iron losses, requiring a reasonable balance between iron and copper losses.

[0003] In terms of drive technology, the industry currently widely adopts FOC (Field-Oriented Control) technology to achieve three-phase sinusoidal current drive. However, in practical applications, factors such as differences in motor manufacturing processes, resistance changes caused by coil temperature rise, dead-zone effects of power switches, and response delays in control algorithms can lead to current waveform distortion, generating significant 5th and 7th harmonic components. When these harmonics interact with traditional 5-pole or 7-pole rotor structures, they can easily generate 5th and 7th harmonic electromagnetic vibrations, severely affecting the overall machine's quiet operation.

[0004] In addition, cogging torque is another important factor affecting motor noise. When the motor windings are not energized, the change in magnetic reluctance between the rotor magnets and the stator pole teeth will generate periodic torque fluctuations. Especially in the region corresponding to the magnet edge and the stator tooth slots, the drastic change in magnetic reluctance will lead to obvious cogging torque peaks. This torque fluctuation not only generates vibration noise, but also affects the motor's starting performance and low-speed running smoothness. Summary of the Invention

[0005] The purpose of this invention is to address the deficiencies in the existing technology by providing a structure and method for an external rotor brushless motor suitable for environmental appliances to reduce electromagnetic vibration caused by armature current harmonics and decrease cogging torque. This achieves the effect of suppressing electromagnetic vibration caused by armature current harmonics and reducing cogging torque, improving the motor's quietness performance, reducing operating noise, and making it more suitable for environmental appliances.

[0006] To achieve the above objectives, the technical solution adopted by the present invention includes a rotor assembly and a stator assembly. The rotor assembly includes a rotor housing and rotor magnets fixed to its inner wall, wherein the N poles and S poles of the rotor magnets are evenly distributed in an alternating manner. The stator assembly includes a stator core and an armature winding wound thereon; The rotor magnet has P pole pairs, where P is an even number greater than 7; The number of pole teeth of the stator core is Z, where Z is an integer greater than 12 and divisible by 3; The number of pole teeth Z of the stator core is matched with the number of pole pairs P of the rotor magnet to suppress electromagnetic vibrations caused by armature current harmonics and reduce cogging torque.

[0007] Furthermore, the number of pole teeth Z in the stator core is odd.

[0008] Furthermore, the number of pole teeth Z of the stator core is 15.

[0009] Furthermore, the pole-slot configuration is either 16 poles and 15 slots or 20 poles and 15 slots.

[0010] Furthermore, the number of pole teeth Z of the stator core is 18.

[0011] Furthermore, the pole-slot configuration is either 16 poles and 18 slots or 20 poles and 18 slots.

[0012] Furthermore, the rotor magnets are configured as a ring structure made of permanent magnet material and are attached to the inner wall of the rotor housing.

[0013] Furthermore, the rotor magnet is made of rectangular magnetic strips rolled up and attached to the inner wall of the rotor housing.

[0014] Furthermore, environmental appliances include fans, air purifiers, humidifiers, dehumidifiers, bathroom heaters, or fresh air systems.

[0015] A pole slot mating method for an external rotor brushless motor suitable for environmental electrical appliances includes the following steps: Provide a stator core, wherein the number of slots Z of the stator core is set to an integer greater than 12; A rotor magnet assembly is provided, wherein the number of poles 2P of the rotor magnet is set to 16 or 20 poles; The stator core and rotor magnet assembly are assembled into a motor to form a specific pole slot fit. The pole-slot fit is selected with an odd number of slots, such as 16 poles and 15 slots or 20 poles and 15 slots, to reduce cogging torque; By matching the poles and slots, the spatial harmonic order of the motor's magnetic field is mismatched with the main low-order harmonic order in the armature current time harmonic generated by the drive circuit, thus avoiding the generation of strong electromagnetic excitation force at the same frequency and suppressing electromagnetic vibration. By increasing the number of stator slots in the pole slot configuration and utilizing their combination with the number of rotor poles, the peak value of the motor's cogging torque can be reduced.

[0016] The external rotor brushless motor comprises a rotor assembly and a stator assembly. The rotor assembly includes a rotor housing and rotor magnets fixed to its inner wall, with the N and S poles of the rotor magnets evenly distributed alternately. The stator assembly includes a stator core and an armature winding wound thereon. The rotor magnets have a pole pair number of P, where P is an even number greater than 7. The stator core has a tooth number of Z, where Z is an integer greater than 12. The number of pole teeth Z of the stator core and the number of pole pairs P of the rotor magnets work together to suppress electromagnetic vibrations caused by armature current harmonics and reduce cogging torque. This structure and method achieve the effect of suppressing electromagnetic vibrations caused by armature current harmonics and reducing cogging torque, improving motor quietness, reducing operating noise, and making it more suitable for environmental electrical applications. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 This is a schematic diagram of the 15-slot, 16-pole electromagnetic scheme of the present invention; Figure 2 This is a schematic diagram of the 15-slot, 20-pole electromagnetic scheme of the present invention; Figure 3 This is a schematic diagram of the 18-slot, 16-pole electromagnetic scheme of the present invention; Figure 4 This is a schematic diagram of the 18-slot 20-pole electromagnetic scheme of the present invention; Figure 5 This is a schematic diagram illustrating the reduction of cogging torque due to odd-numbered slots.

[0019] Figure label: 1. Rotor housing; 2. Rotor magnet; 3. Stator core; 8. Armature winding. Detailed Implementation

[0020] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0021] In the description of this invention, it should be noted that the orientations or positional relationships indicated by terms such as "center", "up", "down", "left", "right", "vertical", "horizontal", "inner", and "outer" are based on the orientations or positional relationships shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0022] An external rotor brushless motor suitable for environmental electrical appliances, such as Figures 1-5 As shown, it includes a rotor assembly and a stator assembly; the rotor assembly includes a rotor housing 1 and rotor magnets 2 fixed to its inner wall, the N poles and S poles of the rotor magnets 2 being evenly distributed in an alternating pattern; the stator assembly includes a stator core 3 and an armature winding 8 wound on it; the number of pole pairs of the rotor magnets 2 is P, where P is an even number greater than 7; the number of pole teeth of the stator core 3 is Z, where Z is an integer greater than 12 and divisible by 3; the number of pole teeth Z of the stator core 3 and the number of pole pairs P of the rotor magnets 2 work together to suppress electromagnetic vibrations caused by armature current harmonics and reduce cogging torque.

[0023] Specifically, by employing a rotor magnet 2 with an even number of poles P greater than 7 and a stator core 3 with an integer number of pole teeth Z greater than 12, the electromagnetic energy conversion method is altered, significantly improving the motor's power density and torque output capability. This allows for higher electrical frequencies and efficiency at lower mechanical speeds (below 2000 rpm). Through electromagnetic optimization, electromagnetic force waves generated by the interaction between the 5th and 7th harmonics in the armature winding 8 current and the rotor magnetic field are effectively suppressed, thereby significantly reducing electromagnetic vibration and noise during operation and solving the key problem of overall noise caused by harmonic torque under FOC drive. Simultaneously, the special pole-slot combination makes the magnetic reluctance change between the rotor magnet 2 poles and the stator core 3 slots smoother, significantly reducing the peak value of cogging torque and improving the motor's starting performance and low-speed running stability. Through the innovative combination of rotor magnet 2 and stator core 3, high power density, low electromagnetic vibration and weak cogging torque are simultaneously optimized within the structure of rotor housing 1, perfectly meeting the stringent requirements of environmental electrical appliances for quiet operation, high efficiency and high reliability.

[0024] As a preferred embodiment of the above, such as Figures 1-5 As shown, the number of pole teeth Z of stator core 3 is odd.

[0025] Specifically, by setting the number of pole teeth Z of the stator core 3 to an odd number, the noise reduction effect is further improved on the basis of the original high-pole-slot combination. The asymmetry causes the relative positional relationship between each magnetic pole of the rotor magnet 2 and each slot of the stator core 3 to be different, thereby dispersing the peak point of the cogging torque on the circumference. The direct effect is to significantly smooth the overall waveform of the cogging torque and significantly reduce its amplitude, fundamentally improving the starting performance and low-speed stability of the motor. At the same time, this odd-numbered tooth structure also effectively changes the harmonic components of the magnetic circuit reluctance, which can further suppress specific orders (such as the 5th and 7th orders) of electromagnetic excitation force, making it difficult for them to resonate with the rotor housing 1 and other structural components. Thus, a superimposed optimization effect is achieved in reducing electromagnetic vibration and noise, enabling the motor to achieve a higher power density while achieving a better level of quietness.

[0026] As a preferred embodiment of the above, such as Figures 1-5 As shown, the number of pole teeth Z of stator core 3 is 15.

[0027] Specifically, by setting the number of pole teeth Z of the stator core 3 to 15, an optimized matching scheme is provided for even-numbered pole pairs P (such as 8 or 10 poles) greater than 7. When using 15 pole teeth, the 15-slot 8-pole structure formed when it matches the common 8-pole rotor magnet 2 can significantly increase the number of cycles of cogging torque, thereby significantly reducing the amplitude of cogging torque and making the motor start-up and low-speed operation smoother. At the same time, this pole-slot matching can effectively avoid the generation of major low-order (such as 5th and 7th) electromagnetic force waves, preventing them from resonating with structural components such as the rotor housing 1, thus reducing electromagnetic vibration and noise at the source. The specific 15-tooth design allows the magnetic field interaction between the stator core 3 and the rotor magnet 2 to reach a better balance, further minimizing vibration and noise while ensuring high power density, ultimately enabling the motor's overall performance to meet the stringent requirements of environmental electrical appliances for quietness levels.

[0028] As a preferred embodiment of the above, such as Figures 1-5 As shown, the pole-slot configuration is either 16 poles and 15 slots or 20 poles and 15 slots.

[0029] Specifically, by defining the pole-slot configuration as 16 poles and 15 slots or 20 poles and 15 slots, and using 16-pole or 20-pole rotor magnets 2 paired with a 15-pole stator core 3, the number of pole pairs is increased. This allows the motor to generate a stronger magnetic field and greater torque output within the same rotor housing 1, significantly improving power density. The coprime relationship between the number of poles and slots in these two configurations greatly smooths torque fluctuations and effectively improves the motor's starting and low-speed operation stability. Simultaneously, this high pole-slot configuration effectively avoids the electromagnetic excitation force generated by the interaction of low-order harmonics such as the 5th and 7th harmonics in the drive current with the rotor magnetic field, suppressing electromagnetic vibration noise at its source. The 20-pole, 15-slot configuration increases the number of pole pairs to 10, resulting in a higher electrical frequency at the same speed, further optimizing power density and making it more suitable for environmental applications, thus achieving high efficiency, energy saving, and ultra-quiet operation.

[0030] As a preferred embodiment of the above, such as Figures 1-5 As shown, the number of pole teeth Z of stator core 3 is 18.

[0031] As a preferred embodiment of the above, such as Figures 1-5 As shown, the pole-slot configuration is either 16 poles and 18 slots or 20 poles and 18 slots.

[0032] Specifically, by setting the number of pole teeth Z of the stator core 3 to 18, the 18-slot structure provides greater flexibility in winding arrangement, helps shorten the coil end length, reduces copper losses, and improves efficiency. When combined with a 16-pole rotor magnet 2, a 16-pole 18-slot structure is formed. The greatest common divisor of this combination is 2, which effectively reduces the amplitude of cogging torque. The 20-pole 18-slot structure formed by combining with a 20-pole rotor magnet 2 further increases the number of pole pairs, generating a stronger magnetic field within the same volume of the rotor housing 1, significantly improving the motor's power density and torque output capability. These two combinations, by increasing the number of pole pairs and slots, optimize the sinusoidal nature of the air gap magnetic field, effectively suppressing the electromagnetic excitation force generated by the interaction of the 5th and 7th harmonics of the armature current with the rotor magnetic field, thus reducing electromagnetic vibration and noise at the source. Simultaneously, the larger number of pole teeth makes the magnetic flux change more gradual, reducing harmonic components in iron losses and improving the motor's efficiency characteristics. The electromagnetic performance was comprehensively improved within the limited space of the rotor housing 1, which not only met the requirements of environmental electrical appliances for high power density, but also achieved the effect of ultra-quiet operation.

[0033] As a preferred embodiment of the above, such as Figures 1-5 As shown, the rotor magnet 2 is configured as a ring structure made of permanent magnet material and is attached to the inner wall of the rotor housing 1.

[0034] Specifically, by designing the rotor magnet 2 with a ring structure, the manufacturability and production efficiency are significantly improved while ensuring electromagnetic performance. The ring structure rotor magnet 2, made of permanent magnet material, is directly attached to the inner wall of the rotor housing 1, ensuring the shortest path of the magnetic circuit, reducing magnetic flux leakage, and improving magnetic field utilization efficiency.

[0035] As a preferred embodiment of the above, such as Figures 1-5 As shown, the rotor magnet 2 is made of rectangular magnetic strips rolled up and attached to the inner wall of the rotor housing 1.

[0036] Specifically, the manufacturing process of rotor magnets 2, which are made by rolling rectangular magnetic strips, makes it easier to achieve directional magnetization of high-performance rare-earth permanent magnet materials compared to integral annular magnetic rings, resulting in higher remanence and coercivity. Simultaneously, this segmented structure effectively reduces eddy current losses and iron loss heating during motor operation. In terms of assembly, the rectangular magnetic strips can be pre-magnetized before rolling and installation, avoiding the magnetization effect on the rotor housing 1 that occurs when magnetizing integral annular magnets, thus simplifying the production process. This innovative structure ensures a tight fit between the rotor magnets 2 and the rotor housing 1, and by optimizing magnetic material utilization and manufacturing processes, it reduces costs while improving the overall performance and reliability of the motor.

[0037] As a preferred embodiment of the above, such as Figures 1-5 As shown, environmental appliances include fans, air purifiers, humidifiers, dehumidifiers, bathroom heaters, or fresh air systems.

[0038] Specifically, by clearly defining the application scope to environmental appliances such as fans, air purifiers, humidifiers, dehumidifiers, bathroom heaters, and fresh air systems, the special electrode slot design effectively suppresses electromagnetic vibration and cogging torque, significantly reducing motor operating noise and making it more suitable for environments requiring quiet, such as bedroom fans and air purifiers. Furthermore, the optimized electromagnetic design and low-loss characteristics ensure the motor's high efficiency and reliability in long-term continuous operation scenarios (such as dehumidifiers and fresh air systems).

[0039] A pole slot mating method for an external rotor brushless motor suitable for environmental electrical appliances includes the following steps: Provide a stator core, wherein the number of slots Z of the stator core is set to an integer greater than 12; A rotor magnet assembly is provided, wherein the number of poles 2P of the rotor magnet is set to 16 or 20 poles; The stator core and rotor magnet assembly are assembled into a motor to form a specific pole slot fit. The pole-slot fit is selected with an odd number of slots, such as 16 poles and 15 slots or 20 poles and 15 slots, to reduce cogging torque; By matching the poles and slots, the spatial harmonic order of the motor's magnetic field is mismatched with the main low-order harmonic order in the armature current time harmonic generated by the drive circuit, thus avoiding the generation of strong electromagnetic excitation force at the same frequency and suppressing electromagnetic vibration. By increasing the number of stator slots in the pole slot configuration and utilizing their combination with the number of rotor poles, the peak value of the motor's cogging torque can be reduced.

[0040] Specifically, a systematic pole-slot matching design process resolves the contradiction between high power density and low noise vibration in motors for environmental electrical applications. By setting the number of slots Z of the stator core 3 to an integer greater than 12, and determining the number of poles of the rotor magnet 2 to be 16 or 20, the parameter selection lays the foundation for increasing power density. By prioritizing odd-numbered slot combinations such as 16 poles and 15 slots or 20 poles and 15 slots, and utilizing their coprime characteristics, the number of cogging torque cycles is effectively increased, ensuring a significant reduction in the peak value of cogging torque. Furthermore, the design principle of "mismatch" between the spatial harmonics of the magnetic field and the time harmonics of the armature current through pole-slot matching actively avoids the generation of strong electromagnetic excitation forces at the same frequency by major low-order harmonics (such as the 5th and 7th harmonics), thus suppressing electromagnetic vibration at its source. This method optimizes the matching relationship between the stator core 3 and the rotor magnet 2, elevating electromagnetic design from traditional empirical selection to a predictable and controllable system approach. Ultimately, within the limited space of the rotor housing 1, it simultaneously achieves the comprehensive optimization goals of high power density, low electromagnetic vibration, and weak cogging torque.

[0041] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of the present invention is defined by the appended claims and their equivalents.

Claims

1. An outer rotor brushless motor suitable for environmental electrical appliances, characterized in that: it comprises a rotor assembly and a stator assembly; the rotor assembly comprises a rotor housing (1) and rotor magnets (2) fixed to the inner wall thereof, the N and S poles of the rotor magnets (2) being evenly distributed in an alternating manner; the stator assembly comprises a stator core (3) and an armature winding (8) wound thereon; the rotor magnets (2) have a pole pair number P, P being an even number greater than 7; the stator core (3) has a pole tooth number Z, Z being an integer greater than 12 and divisible by 3; the pole tooth number Z of the stator core (3) and the pole pair number P of the rotor magnets (2) cooperate to suppress electromagnetic vibration caused by armature current harmonics and reduce cogging torque.

2. An external rotor brushless motor suitable for environmental appliances as claimed in claim 1, wherein, The pole tooth number Z of the stator core (3) is an odd number.

3. An external rotor brushless motor suitable for environmental appliances according to claim 2, characterized in that, The pole tooth number Z of the stator core (3) is 15.

4. An external rotor brushless motor suitable for use in environmental appliances according to claim 3, characterized in that, The pole-slot combination is 16-pole 15-slot or 20-pole 15-slot.

5. An external rotor brushless motor suitable for environmental appliances as claimed in claim 1, wherein, The pole tooth number Z of the stator core (3) is 18.

6. An external rotor brushless motor suitable for use in environmental appliances according to claim 5, characterized in that, The pole-slot combination is 16-pole 18-slot or 20-pole 18-slot.

7. An external rotor brushless motor suitable for environmental appliances as claimed in claim 1, wherein, The rotor magnets (2) are arranged in an annular structure of permanent magnetic material and are attached to the inner wall of the rotor housing (1).

8. An external rotor brushless motor suitable for environmental appliances as claimed in claim 1, wherein, The rotor magnets (2) are made of rectangular magnetic strips and are attached to the inner wall of the rotor housing (1).

9. An external rotor brushless motor suitable for environmental appliances as claimed in claim 1, wherein, The environmental electrical appliances include fans, air purifiers, humidifiers, dehumidifiers, bathroom heaters, or fresh air machines.

10. A pole-slot matching method for an outer rotor brushless motor for environmental appliances according to claim 1, characterized in that, The method is achieved by optimizing the electromagnetic structure scheme of the motor, comprising the following steps: providing a stator core, the slot number Z of the stator core being set to an integer greater than 12 and divisible by 3; providing a rotor magnet assembly, the pole number P of the rotor magnet being set to 16-pole or 20-pole; assembling the stator core and the rotor magnet assembly into a motor to form a specific pole-slot combination; the pole-slot combination selects an odd-slot combination of 16-pole 15-slot or 20-pole 15-slot to weaken the cogging torque; through the pole-slot combination, the spatial harmonic number of the motor magnetic field and the main low-order harmonic number of the armature current time harmonics generated by the drive circuit are mismatched, avoiding the generation of strong same-frequency electromagnetic excitation force, suppressing electromagnetic vibration; through the pole-slot combination, the stator slot number is increased and the cogging torque peak value of the motor is reduced by utilizing the cooperation of the rotor pole number.

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