BRUSHLESS MOTOR

Abstract

The present invention relates to a motor capable of minimizing the total harmonic distortion of the counter-electromotive force at no load and reducing torque ripple and cogging torque. According to the present invention, it is possible to reduce motor vibrations and noise by minimizing the total harmonic distortion of the motor's counter-electromotive force at no load by providing various combinations of pole and slot numbers and thus offering optimal parameters, and by reducing torque ripple and cogging torque through an optimal design of the permanent magnets.

Description

[Technical field]

[0001] The present invention relates to a brushless motor, and more particularly to a motor capable of minimizing the total harmonic distortion of the counter electromotive force at no-load and reducing the torque ripple and cogging torque. [State of the art]

[0002] Due to concerns about fossil fuel depletion and environmental pollution, policies emphasizing low emissions and fuel efficiency have spurred the development and growing popularity of hybrid vehicles, which use both fossil fuels and electricity as energy sources, as well as electric vehicles.

[0003] Hybrid and electric vehicles are powered by electric motors. In contrast to conventional vehicle air conditioning systems, which largely used mechanical compressors, there has recently been a shift toward electric compressors.

[0004] Electric compressors consist of an electric motor that converts electrical energy into mechanical energy and an inverter that controls the rotation of the electric motor. The electric motor of such an electric compressor typically consists of a cylindrical rotor and a stator, around whose outer circumference coils are wound. Depending on the winding type, these coils can be divided into distributed and concentrated windings.

[0005] In this type of electric compressor, the rotor of the electric motor rotates when current supplied by the inverter flows through the coils, and this rotational power is transferred to the rotating shaft. The mechanical means, which receive mechanical energy from the rotating shaft, perform a reciprocating motion to compress the refrigerant.

[0006] Electric compressors have the disadvantage of lower refrigerant compression capacity compared to conventional mechanical compressors, due to the weaker driving force of the electric motor compared to the torque of motor-driven mechanical compressors, as well as strong vibrations and the lower control performance of inverters. Furthermore, the low efficiency of electric motors leads to wasted electricity supplied to the vehicle.

[0007] One of the main causes of vibration and reduced precision in such electric motors is the cogging torque and torque ripple caused by the interaction between permanent magnets and slots, which are unavoidable in motors with slots.

[0008] Cogging torque is a non-uniform torque that occurs due to the interaction between permanent magnets and slots, causing a radial force toward the position where the magnetic energy of the motor system is minimized, that is, toward the equilibrium state, regardless of the load current, and significantly affects motor control and precision.

[0009] A known method for reducing cogging torque is to structurally combine the number of magnetic poles of the permanent magnets and the number of slots. However, in the field of electric motors used for compressors in hybrid vehicles, there is still a lack of specific research results on the optimal ratio of magnetic poles to slots or on designs and structures that can reduce cogging torque and torque ripple.

[0010] The Fig. 1 shows a conventional electric compressor motor, wherein the conventional electric compressor motor 3 is constructed with an inner rotor 4 rotating in a stator 5 configured with 6 poles and 27 slots, using a distributed winding method with coils widely distributed over several teeth.

[0011] Due to the relatively low speed (approximately 10,000 rpm) and high motor load in conventional electric compressors, the weight and size of the motor must be reduced. To reduce the weight and size of the motor, a design with a higher number of poles is required. This means increasing the number of poles and reducing the stacking of the motor, but as mentioned above, there are no concrete research results in this area yet. Prior Art Documents (Patent Document) Korean Patent Publication No. 10-2018-0113296 (Published on October 16, 2018) [Disclosure] [Technical Problem]

[0012] The present invention has been developed to solve the above-mentioned problems, and it is an object of the present invention to provide optimized pole-slot combinations and design parameters of motor components to minimize the total harmonic distortion of the back electromotive force of the motor at idle and to reduce the torque ripple and cogging torque. [Technical solution]

[0013] A brushless motor of the present invention may include a stator having a body hollowed out in the axial direction and a plurality of winding slots formed along the inner circumference of the body, a rotor installed axially inside the stator and having a plurality of insertion grooves formed circumferentially along its circumference, and a plurality of permanent magnets respectively inserted into the plurality of insertion grooves of the rotor, wherein the number of poles corresponding to the plurality of permanent magnets and the number of slots corresponding to the plurality of winding slots can be variously combined to reduce cogging torque and torque ripple.

[0014] According to an embodiment of the present invention, the motor may have a 10-pole 24-slot structure, wherein the plurality of permanent magnets are configured with 10 permanent magnets and the plurality of winding slots are configured with 24 winding slots.

[0015] The stators and the rotors may have a rotor radius to stator radius ratio that satisfies 0.594 ≤ Rr / Rs ≤ 0.646, where Rs is the stator radius, Rr is the rotor radius, and Rr / Rs is the rotor radius to stator radius ratio.

[0016] The stators can have an arc angle of 28° ≤ α ≤ 32°, where α is the arc angle formed by the center of the rotor and the ends of one of the permanent magnets.

[0017] The rotor may have a ratio between the shortest distance from the center of the rotor to one of the plurality of permanent magnets and the rotor radius Rr that satisfies 0.847 ≤ Rm / Rr ≤ 0.898, where Rm denotes the shortest distance to the permanent magnet.

[0018] The rotor may include a plurality of hollow holes axially penetrating the rotor, and the plurality of hollow holes may be configured with 10 holes corresponding to the plurality of permanent magnets.

[0019] The rotor may have a plurality of rivet holes axially penetrating the rotor and inserted through the rivets, and the plurality of rivet holes may be configured with 10 holes formed between the adjacent hollow holes.

[0020] According to another embodiment of the present invention, the motor may have a 10-pole 12-slot structure, wherein the plurality of permanent magnets are configured with 10 permanent magnets and the plurality of winding slots are configured with 12 winding slots.

[0021] The stator may comprise a plurality of stator teeth forming a plurality of winding slots, each tooth having a pole piece at its end, the pole piece having the opposite surface with a predetermined curvature facing the outer surface of the rotor, the curvature varying from the radial center of the opposite surface to the radial end.

[0022] The opposite surface of the pole piece may have a radius of curvature satisfying 30 mm ≤ Rs_in ≤ 120 mm, where Rs_in denotes the radius of curvature of the opposite surface of the pole piece.

[0023] The pole piece must have a minimum thickness of 0.8 mm or more.

[0024] The radius of curvature of the radial center of the opposite surface of the pole piece may be 30 mm, and the radius of curvature of the radial end of the opposite surface of the pole piece may be 120 mm, with the radius of curvature gradually increasing from the center to the end.

[0025] The thickness of the pole piece at the radical end of the opposite surface can be 0.8 mm.

[0026] The pole piece may have a mirror-symmetric shape with respect to the radical center of the pole piece.

[0027] According to another embodiment of the present invention, the motor has a 10-pole 27-slot structure with the plurality of permanent magnets configured with 10 permanent magnets and the plurality of winding slots configured with 27 winding slots.

[0028] The stators and the rotors may have a rotor radius to stator radius ratio that satisfies 0.520 ≤ Rr / Rs ≤ 0.646, where Rs is the stator radius, Rr is the rotor radius, and Rr / Rs is the rotor radius to stator radius ratio.

[0029] The stators can have an arc angle of 29° ≤ α ≤ 32°, where α is the arc angle formed by the center of the rotor and the ends of one of the permanent magnets.

[0030] The two adjacent insertion grooves of the plurality of insertion grooves may have a web thickness corresponding to 1.6 mm ≤ WD ≤ 2.2 mm, where WD denotes the web thickness corresponding to the distance between the two adjacent insertion grooves. [Beneficial Effects]

[0031] According to the present invention, it is advantageous to reduce motor vibration and noise by minimizing the total harmonic distortion of the motor's back electromotive force at idle by providing various combinations of pole and slot numbers and offering optimal parameters accordingly, and by reducing torque ripple and cogging torque by optimally designing the permanent magnets. [Description of the characters] The Fig. 1 is a diagram showing a conventional electric compressor motor; the Fig. 2 is a cross-sectional view of an engine according to the first embodiment of the present invention; the Fig. 3 is a cross-sectional view of a stator and a rotor; the Fig. Figure 4 is a diagram illustrating the web thickness and the bridge thickness; the Fig. Figure 5 is a graph showing the efficiency of the motor as a function of the web thickness; the Fig. Figure 6 is a graph showing the efficiency of the motor as a function of the bridge thickness; the Fig. Figure 7 is a diagram illustrating the design parameters of the engine; the Fig. 8 is a graph showing the torque ripple characteristic as a function of the ratio of the rotor radius to the stator radius; the Fig. Figure 9 is a graph showing the efficiency and distortion characteristics of the counter electromotive force of the motor as a function of the magnitude of the arc angle; the Fig. 10 is a diagram showing the torque ripple characteristic based on the relationship between the rotor radius and the shortest distance to the permanent magnet; the Fig. 11 and Fig. 12 are cross-sectional views of an engine according to the second embodiment of the present invention; the Fig. 13 is a diagram comparing a conventional motor and a motor of the present invention; the Fig. 14 is a diagram showing a pole piece according to an embodiment of the present invention; the Fig. 15 is a graph comparing cogging torque between a conventional motor and a motor of the present invention; the Fig. 16 is a graph comparing load torque between a conventional motor and a motor of the present invention; the Fig. 17 is a cross-sectional view of a motor according to the third embodiment of the present invention; the Fig. 18 is a diagram for comparing a conventional motor and a motor of the present invention; the Fig. Figure 19 is a diagram illustrating the design parameters of the engine; the Fig. 20 is a graph showing the torque ripple characteristic as a function of the ratio of the rotor radius to the stator radius; the Fig. Figure 21 is a graph showing the efficiency and distortion characteristics of the counter electromotive force of the motor as a function of the magnitude of the arc angle. [Embodiments of the invention]

[0032] The present invention will now be described with reference to the accompanying figures.

[0033] First, the motor of the present invention may be a brushless motor used in an electric compressor for vehicles. An electric compressor for vehicles typically includes a compression unit in which the refrigerant is compressed by the reciprocating motion of mechanical components, an electric motor that transmits mechanical power to the compression unit, and an inverter that supplies electrical power to the electric motor. The motor of the present invention may be the same as the electric motor used in such a typical electric compressor for vehicles. Below, the motor of the present invention will be described in detail through various embodiments. < First embodiment >

[0034] The first embodiment of the present invention will be described. The Fig. 2 to 10 are diagrams illustrating the engine according to the first embodiment of the present invention.

[0035] The Fig. 2 is a cross-sectional view of the engine according to the first embodiment of the present invention, and the Fig. 3 is a cross-sectional view of the stator and the rotor; as shown, the motor 10 of the present invention includes a stator 100, a rotor 200, and a plurality of permanent magnets M inserted into the rotor 200.

[0036] The stator 100 includes a substantially cylindrical body 110 hollowed out in the axial direction, and a plurality of winding slots 120 are formed circumferentially along the inner periphery of the hollow body 110, and a coil C is wound in each winding slot 120. Each winding slot 120 penetrates the body in the axial direction and is spaced apart from each other so that the coils C can be wound in a distributed winding process extending across a plurality of winding slots 120.

[0037] The rotor 200 is a cylindrical member installed axially within the stator 100, that is, within the hollow body 110. A plurality of permanent magnets can be combined so that the rotor 200 rotates by absorbing an electromagnetic force generated when current flows through the coil C wound on the stator 100. For this purpose, a plurality of insertion grooves 210 can be formed such that each of a plurality of permanent magnets is inserted into the outer peripheral side of the cylindrical member. Each insertion groove 210 penetrates axially and is circumferentially spaced from each other.

[0038] Meanwhile, the rotor 200 may have a plurality of hollow holes 230 penetrating the rotor in the axial direction in correspondence with the permanent magnets M, and rivet holes 240 may be formed between adjacent hollow holes 230. The rivet holes 240, like the hollow holes 230, may penetrate the interior of the rotor 200 in the axial direction, and rivets may be inserted into the rivet holes 240 to permanently connect the plurality of steel plates constituting the rotor. As described below, the hollow holes 230 may be formed in a number of 10, corresponding to the number of permanent magnets M, and the rivet holes 240 may be formed between the hollow holes, also in a number of 10.This can help improve the flux characteristics due to the permanent magnets and the manufacturability of the rotor while reducing the weight compared to conventional electric compressor motors.

[0039] The plurality of permanent magnets M are each axially inserted into the respective insertion grooves 210, with adjacent insertion grooves 210 accommodating permanent magnets M with different polarities. That is, the motor 10 of the present invention is configured such that the permanent magnets M are embedded in the surface of the rotor rather than being fixed to the surface, which enables the utilization of both magnetic torque (torque generated by the orientation and strength of the magnetic field) and reluctance torque (torque generated by changes in magnetic resistance), thereby achieving the same torque with less current and improving motor efficiency.

[0040] In this configuration, the motor 10 of the present invention includes 24 winding slots 120 and 10 permanent magnets M, forming a 10-pole 24-slot structure. That is, the stator 100 includes 24 winding slots 120 arranged at regular intervals, with each winding slot forming an angle of approximately 13 degrees with the adjacent winding slot 120. The rotor 200 has ten insertion grooves 210, each arranged at a uniform interval and forming an angle of approximately 36 degrees with the adjacent insertion grooves. A plurality of permanent magnets M are inserted into these insertion grooves 210, respectively, to conform to the structure of the insertion grooves.

[0041] It is important to minimize the total harmonic distortion (THD) of the motor's back electromotive force at no load, as a THD closer to a sine wave reduces cogging torque and torque ripple during operation, thereby reducing motor vibration and noise. The motor 10 of the present invention has a 10-pole, 24-slot structure. This 10-pole, 24-slot structure is an advantageous design for minimizing the total harmonic distortion of the back electromotive force at no load and significantly reduces cogging torque, which generates noise during operation.

[0042] Specifically, the motor efficiency increases with increasing bridge thickness, while an increase in bridge thickness decreases the motor efficiency. Considering these factors, along with the minimum thickness achievable for motor production, the 10-permanent magnet (M) motor configuration can maximize both efficiency and manufacturability. Fig. 4 is a diagram illustrating the web thickness and the bridge thickness, the Fig. Figure 5 is a graph showing the motor efficiency characteristics based on the web thickness, and the Fig. Figure 6 is a graph illustrating the motor efficiency characteristics based on the bridge thickness; considering these data together with the motor size and thickness, the present invention configures the motor with 10 permanent magnets M. Furthermore, the invention optimizes the number of poles considering the switching frequency of the inverter by configuring 24 winding slots 120 corresponding to 10 permanent magnets M, thereby minimizing the total harmonic distortion of the back electromotive force at no load.

[0043] That is, the motor of the present invention minimizes the total harmonic distortion of the counter electromotive force at no-load and significantly reduces the cogging torque and torque ripple by adopting a 10-pole 24-slot structure, thereby reducing motor vibration and noise while ensuring manufacturability.

[0044] To maintain high motor efficiency while minimizing cogging torque and configuring the total harmonic distortion of the back electromotive force at idle as a sine wave, it is necessary to optimize design parameters such as the magnetic angle of the permanent magnets embedded in the rotor. The following describes the optimized motor design that meets these requirements.

[0045] The Fig. 7 is a diagram illustrating the design parameters of the motor, including the rotor center O, the arc angle α, the stator radius Rs, the rotor radius Rr, and the shortest distance to the permanent magnets Rm. The arc α represents the angle formed by the center of the rotor O and the two ends of one of the permanent magnets M, that is, the angle that each permanent magnet M makes with the center of the rotor O. The stator radius Rs represents the distance from the center of the rotor O to the outer surface of the stator 100. The rotor radius Rr represents the distance from the center of the rotor O to the outer surface of the rotor 200. The shortest distance to the permanent magnets Rm is the shortest distance from the center of the rotor O to one of the plurality of permanent magnets M, that is, the shortest distance between each permanent magnet M and the center of the rotor O.

[0046] The Fig. Figure 8 is a graph illustrating the torque ripple characteristic based on the rotor radius to stator radius ratio. As shown, the rotor to stator radius ratio (Rr / Rs) in the range of 0.594 to 0.646 results in a torque ripple of approximately 7.6% or less at rated load, effectively minimizing motor vibration and noise. Table 1 Rr / Rs 0.56 0.58 0.60 0.62 0.64 0.66 Drehmomentwelligkeit [%] 7.8 8.0 6.7 4.2 4.3 7.8

[0047] Table 1 presents data corresponding to the diagram in the Fig. 8 and show that the torque ripple decreases sharply at a rotor-to-stator radius ratio (Rr / Rs) of 0.594, increases again at 0.63, and rises sharply again at 0.646. In the range of Rr / Rs from 0.594 to 0.646, the torque ripple falls within a range of about 7.6% to 3.6% or more, as indicated by ①, and in the range from 0.618 to 0.646, the torque ripple falls within a range of about 4.9% to 3.6% or more, as indicated by ②. That is, based on the analysis of these data, the present invention proposes a motor configured such that the ratio of the rotor radius length Rr to the stator radius length Rs (Rr / Rs) satisfies the condition 0.594 ≤ Rr / Rs ≤ 0.646, and preferably 0.618 ≤ Rr / Rs ≤ 0.646.

[0048] The Fig. Figure 9 is a graph illustrating the efficiency and distortion characteristics of the motor's back electromotive force as a function of the arc angle. As shown, maintaining an arc angle α in the range of 28° to 32° effectively reduces the total harmonic distortion (THD) of the back electromotive force while maintaining efficiency above 95.23%. Table 2 a [°] 28 29 30 31 32 33 Eff[%] 95.23 95.28 95.33 95.36 95.43 95.48 THD[%] 0.62 0.70 0.74 0.73 0.72 0.82

[0049] Table 2 contains data corresponding to the diagram in the Fig. 9 and show that the efficiency of the motor increases linearly with increasing arc angle α from 95.24% to 95.43% (1), while the THD remains relatively low between 0.62% and 0.75% (2) in the arc angle α range from 28° to 32° and even decreases from 0.75% to 0.72% (3) in the arc angle α range from 30° to 32°. Therefore, based on the analysis of these data, the present invention proposes a motor configured to satisfy the condition 28° ≤ α ≤ 32° for the arc angle α, and preferably 30° ≤ α ≤ 32°.

[0050] The Fig. Figure 10 is a graph illustrating the torque ripple characteristic based on the ratio of the rotor's radial length to the shortest distance to the permanent magnet. As shown, in the radius ratio (Rm / Rr) range of 0.847 to 0.898, there is a cogging torque of approximately 7% or less and a torque ripple of approximately 6% or less, effectively minimizing torque ripple to reduce motor vibration and noise. Table 3 Rm / Rr 0.84 0.85 0.86 0.87 0.88 0.89 0.90 Drehmomentwelligkeit [%] 8.0 4.7 3.6 3.5 4.1 4.4 4.8 Rastmoment 1.3 2.8 4.0 5.1 6.8 7.3 7.9

[0051] Table 3 presents data corresponding to the diagram in the Fig. 10, showing that with an increase in the radius ratio (Rm / Rs) from 0.847, the torque ripple decreases sharply, increases again around 0.865, and then gradually increases to 0.898. In the radius ratio (Rm / Rs) range from 0.847 to 0.898, the torque ripple is in a range of about 5.5% to 3.6% or more, as indicated by ①, indicating low torque ripple. In the radius ratio (Rm / Rs) range from 0.85 to 0.88, the torque ripple falls in a range of about 0.44% to 3.6%, as indicated by ②, thus providing improved torque ripple characteristics.

[0052] Furthermore, the cogging torque increases linearly with increasing radius ratio (Rm / Rs), especially in the range of radius ratio (Rm / Rs) from 0.847 to 0.898, the cogging torque is in the range of approximately 0.007 Nm to 0.026 Nm, as indicated by 3, indicating low cogging torque. When the radius ratio (Rm / Rs) falls into the range of 0.85 to 0.88, the cogging torque is in the range of approximately 0.008 Nm to 0.022 Nm, as indicated by 4, indicating improved cogging torque characteristics.

[0053] That is, based on the analysis of these data, the present invention proposes a motor configured such that the ratio between the length of the rotor radius Rr and the shortest distance to the permanent magnets Rm (Rm / Rr) satisfies the condition 0.847 ≤ Rm / Rr ≤ 0.898 and preferably 0.85 ≤ Rm / Rr ≤ 0.88 for optimum performance.

[0054] The various design parameters described above are interrelated by the sizes, shapes, and arrangements of the components that comprise the motor. By considering the relationships between these design parameters, they can be implemented in a single motor by overlapping the ranges of each parameter to meet the respective conditions, thus maximizing the motor's efficiency, torque ripple, and cogging torque. <Zweite Ausführungsform>

[0055] Next, the second embodiment of the present invention will be described. Fig. 11 to 16 are diagrams illustrating the motor according to the second embodiment of the present invention. To avoid redundancy, repetition of the above description is omitted.

[0056] The Fig. 11 and Fig. 12 are cross-sectional views of the motor 10 according to this embodiment, which has 10 permanent magnets and 12 winding slots, resulting in a 10-pole, 12-slot structure. Because the motor has a 10-pole, 12-slot structure, the cogging torque frequency is composed of 60 harmonics, which offers advantages in reducing vibration and noise compared to conventional motors.

[0057] In this embodiment, the pole piece is designed to differ from the shape of conventional motors. The stator is provided with a plurality of stator teeth 130 that form a plurality of winding slots, and a pole piece 140 extends radially outward at the end of each stator tooth 130.

[0058] The mating surface of the pole piece 140 facing the outer circumference of the rotor 200 is referred to as the mating surface 140A of the pole piece, and in contrast to conventional motors in which the mating surface 140A typically has the same curvature as the outer circumference of the rotor 200, the present invention has a pole piece mating surface 140A with a predetermined curvature, wherein the curvature in the radial center c of the pole piece mating surface 140A is not identical to the curvature at the radial end e, but deviates therefrom.

[0059] The Fig. Figure 13 is a graph comparing a conventional motor with the motor of the present invention. It shows that in the conventional motor, the pole piece mating surface has a constant curvature, resulting in a cogging torque of 126 mNm and a torque ripple of 465 mNm with a deviation of 6.68%. In contrast, the present invention has a pole piece mating surface 140A with different curvatures in the middle and at the end, resulting in a cogging torque of 44 mNm and a torque ripple of 214 mNm with a deviation of 3.19%, which significantly reduces the cogging torque and torque ripple compared to the conventional motor.

[0060] In detail, when the radius of curvature at a point on the pole piece mating surface 140A is Rs_in, the present invention configures the radius of curvature Rs_in of the pole piece mating surface to satisfy 30 mm ≤ Rs_in ≤ 120 mm, thereby increasing the efficiency of the motor. Furthermore, it is desirable for the pole piece to have a minimum thickness, and the present invention configures the pole piece 140 to have a minimum thickness of at least 0.8 mm.

[0061] More specific examples that meet these conditions are as follows. Fig. 14 is a diagram showing a pole piece according to an embodiment of the present invention, wherein the radius of curvature of the radial center c of the pole piece mating surface 140A is 30 mm and the radius of curvature of the radial end e of the pole piece mating surface 140A is 120 mm, wherein the radius of curvature increases smoothly from the center c to the end e.

[0062] Furthermore, as the curvature of the pole piece mating surface 140A decreases, the radius of curvature Rs_in increases. To achieve the above-described minimum thickness of the pole piece 140, the thickness at the radial end e of the mating surface 140A with the maximum radius of curvature Rs_in can be set to 0.8 mm. Furthermore, as shown in the figure, the pole piece 140 of the present invention can have a mirror-symmetrical shape relative to the radial center c of the pole piece.

[0063] The Fig. 15 is a graph comparing the cogging torque between a conventional motor and a motor of the present invention, showing that the conventional motor has a significant cogging torque in the range of -0.06 to 0.06, while the present invention shows a reduced cogging torque in the range of -0.02 to 0.02.

[0064] The Fig. 16 is a graph comparing the load torque between a conventional motor and a motor of the present invention, showing that the conventional motor has a significant load torque in the range of 6.45 to 6.92, while the present invention shows a reduced load torque in the range of 6.58 to 6.8.

[0065] As mentioned above, the motor in this embodiment is configured in a 10-pole 12-slot structure, with the radius of curvature of the pole piece mating surface ranging from 30 to 120 mm and gradually increasing towards the end from the axial center, thereby minimizing the torque ripple during operation, resulting in improved vibration and noise reduction, while reducing the overall weight compared to conventional motors. <Dritte Ausführungsform>

[0066] Next, the third embodiment of the present invention will be described. Fig. Figures 17 to 21 are diagrams illustrating the motor according to the third embodiment of the present invention. To avoid redundancy, repetition of the above description is omitted.

[0067] The Fig. 17 is a cross-sectional view of a motor according to the third embodiment of the present invention, wherein the motor 10 includes 10 permanent magnets M and 27 winding slots 120, resulting in a 10-pole 27-slot structure. The effect of area changes on weight based on motor cross-section is relatively greater for electrical laminations compared to permanent magnets, necessitating shape optimization to minimize the area of ​​electrical laminations to reduce cogging torque, improve performance, and reduce weight in the motor. To achieve this, the present invention adopts a 10-pole 27-slot structure.

[0068] To achieve high efficiency and weight reduction in the motor, it is also necessary to optimize the length of the permanent magnets embedded in the rotor and the design of the rotor core. For this purpose, the motor can be configured with 10 hollow holes and rivet holes in the rotor, each corresponding to the permanent magnets.

[0069] The Fig. 18 is a graph comparing a conventional motor and a motor of the present invention, showing the conventional motor with an efficiency of 94.6%, a cogging torque of 0.027 Nm, and a rotor mass of 532 g, and the motor of the present invention with an efficiency of 94.7%, a cogging torque of 0.019 Nm, and a rotor mass of 374 g, confirming an increase in motor efficiency and a significant reduction in both cogging torque and rotor mass compared to the conventional motor.

[0070] The specific numbers of the design parameters for this embodiment are as follows. Fig. 19 is a diagram illustrating the design parameters of the motor. The motor of this embodiment satisfies the conditions of 0.520 ≤ Rr / Rs ≤ 0.646 for the ratio of rotor radius Rr to stator radius Rs, 29° ≤ α ≤ 32° for the arc angle α, and 1.6 mm ≤ WD ≤ 2.2 mm for the web thickness WD. The web thickness WD may correspond to the distance between two adjacent lead-in grooves 210. When the individual parameters of the motor of this embodiment are configured to satisfy these conditions, the motor efficiency can be improved, and the cogging torque and rotor weight can be reduced.

[0071] The Fig. Figure 20 is a graph illustrating the torque ripple characteristic based on the ratio of rotor radius to stator radius, showing that for this motor, the ratio of rotor radius Rr to stator radius Rs (Rr / Rs) is in the range of 0.520 to 0.646, preferably 0.54 to 0.6, within which the torque ripple is proven to be only about 10.8%.

[0072] The Fig. Figure 21 is a graph illustrating the efficiency and distortion characteristics of the motor's back electromotive force as a function of the arc angle. It shows that for this motor, the arc angle α is between 29° and 32°, within which the motor efficiency is significantly high, at approximately 95.1% or more, while the total harmonic distortion (THD) of the back electromotive force at no load is only approximately 1.2%.

[0073] As described above, the motor in this embodiment is designed with a 10-pole 27-slot structure, and by using the ratio of rotor radius to stator radius, arc angle, and web thickness as design parameters and limiting each parameter to a suitable range, vibration and noise can be minimized by reducing torque ripple, while achieving high motor efficiency and effectively reducing the THD of the back electromotive force.

[0074] Although the present invention has been described with reference to the accompanying figures and preferred embodiments, it should be understood by those skilled in the art that various modifications and changes may be made without departing from the spirit and scope of the present invention. Therefore, it should be understood that the above-described embodiments are illustrative and not restrictive in any respect. DESCRIPTION OF THE NEXT SYMBOLS 10 Engine 100 stators 110 bodies 120 winding groove 130 stator teeth 140 Pole shoe 200 rotor 210 insertion groove 230 hollow hole 240 rivet hole C coil M permanent magnet

Claims

[1] A brushless motor comprising: a stator having a body hollowed out in the axial direction and a plurality of winding slots formed along the inner circumference of the body; a rotor installed axially inside the stator and having a plurality of insertion grooves formed circumferentially along its circumference; and several permanent magnets, each inserted into the several insertion grooves of the rotor, wherein the number of poles corresponding to the plurality of permanent magnets and the number of slots corresponding to the plurality of winding slots are differently combined to reduce the cogging torque and torque ripple. [2] The brushless motor according to claim 1, wherein the plurality of permanent magnets are configured with 10 permanent magnets and the plurality of winding slots are configured with 24 winding slots, resulting in a 10-pole 24-slot structure. [3] The brushless motor according to claim 2, wherein the stators and the rotors have a ratio of a rotor radius to a stator radius satisfying 0.594 ≤ Rr / Rs ≤ 0.646, where Rs denotes the stator radius, Rr denotes the radius of the rotor, and Rr / Rs denotes the ratio of the rotor radius to the stator radius. [4] The brushless motor according to claim 3, wherein the stators have an arc angle satisfying 28° ≤ α ≤ 32°, where α denotes the arc angle formed by the center of the rotor and the ends of one of the permanent magnets. [5] The brushless motor according to claim 4, wherein the rotor has a ratio of the shortest distance from the center of the rotor to one of the plurality of permanent magnets to the rotor radius Rr that satisfies 0.847 ≤ Rm / Rr ≤ 0.898, where Rm denotes the shortest distance to the permanent magnet. [6] The brushless motor according to claim 5, wherein the rotor has a plurality of hollow holes axially penetrating the rotor, and the plurality of hollow holes is configured with 10 holes corresponding to the plurality of permanent magnets. [7] The brushless motor according to claim 6, wherein the rotor has a plurality of rivet holes axially penetrating the rotor and inserted through the rivets, and the plurality of rivet holes are configured with 10 holes formed between the adjacent hollow holes. [8] The brushless motor according to claim 1, wherein the plurality of permanent magnets are configured with 10 permanent magnets and the plurality of winding slots are configured with 12 winding slots, resulting in a 10-pole 12-slot structure. [9] The brushless motor according to claim 8, wherein the stator comprises a plurality of stator teeth forming a plurality of winding slots, each tooth having a pole piece at its end, the pole piece having the mating surface with a predetermined curvature facing the outer surface of the rotor, the curvature of the pole piece varying from the radial center of the mating surface to the radial end. [10] The brushless motor according to claim 9, wherein the mating surface of the pole piece has a radius of curvature satisfying 30 mm ≤ Rs_in ≤ 120 mm, where Rs_in denotes the radius of curvature of the mating surface of the pole piece. [11] The brushless motor according to claim 10, wherein the pole piece has a minimum thickness of 0.8 mm or more. [12] The brushless motor according to claim 11, wherein the radius of curvature of the radial center of the mating surface of the pole piece is 30 mm and the radius of curvature of the radial end of the mating surface of the pole piece is 120 mm, the radius of curvature gradually increasing from the center to the end. [13] The brushless motor according to claim 12, wherein the thickness of the pole piece at the radical end of the mating surface is 0.8 mm. [14] The brushless motor according to claim 13, wherein the pole piece has a mirror-symmetrical shape with respect to the radial center of the pole piece. [15] The brushless motor according to claim 1, wherein the plurality of permanent magnets are configured with 10 permanent magnets and the plurality of winding slots are configured with 27 winding slots, resulting in a 10-pole 27-slot structure. [16] The brushless motor according to claim 15, wherein the stators and the rotors have a ratio of a rotor radius to a stator radius that satisfies 0.520 ≤ Rr / Rs ≤ 0.646, where Rs denotes the stator radius, Rr denotes the radius of the rotor, and Rr / Rs denotes the ratio of the rotor radius to the stator radius. [17] The brushless motor according to claim 16, wherein the stators have an arc angle satisfying 29° ≤ α ≤ 32°, where α denotes the arc angle formed by the center of the rotor and the ends of one of the permanent magnets. [18] The brushless motor according to claim 17, wherein the two adjacent insertion grooves among the plurality of insertion grooves have a land thickness satisfying 1.6 mm ≤ WD ≤ 2.2 mm, where WD denotes the land thickness corresponding to the distance between the two adjacent insertion grooves.

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