Motor

Abstract

Provided is an outer rotor type motor, said motor comprising a rotor (11) and a stator (13) in which teeth (18) and grooves (19) are formed, wherein: the number of permanent magnets (12) is 32; the number of grooves (19) is 24; the cross-sectional shape of the permanent magnets (12) has chamfering (21) and protrudes toward the stator (13) side; when half the width of the permanent magnets (12) is defined as a magnet width Mw (mm), half the width of the teeth (18) is defined as a tooth width Tw (mm), the angle formed by an inclined surface (22) at either end of a permanent magnet (12) and a vertical surface continuous with that inclined surface (22) on the inside of the cross-sectional shape of that permanent magnet (12) is defined as a magnet angle θ (rad), and the height of a wedge-shaped protrusion (20) when there is a wedge-shaped protrusion (20) is defined as a wedge height H (mm), the expression 30.8≤(Mw1.4×θ0.5×Tw0.45) / H0.08≤33.1 is satisfied; and when there is no wedge-shaped protrusion (20), the expression 30.7≤Mw1.4×θ0.5×Tw0.45≤33.9 is satisfied.

Description

motor

[0001] This invention relates to an outer rotor type motor used, for example, in drones, robotic arms, and in-wheel motor vehicles.

[0002] The challenges in motor development include increasing torque, efficiency, and rotational speed. However, a common requirement across all these is quiet operation. Generally, a motor rotates due to the repeated attractive and repulsive forces between magnets on the rotor and the teeth of the stator, which are wound around the rotor. This rotation generates torque pulsation. Torque pulsation becomes vibration and ultimately noise, thus hindering quiet operation. In the no-load state (when no current is applied), this torque pulsation is called cogging torque and is a unique value determined by the stator shape, the number and shape of the magnets, and the number and shape of the stator teeth. In other words, once the specifications are set, it is impossible to reduce cogging torque. Therefore, minimizing cogging torque has been a crucial aspect of motor magnetic field design and analysis.

[0003] In this regard, Patent Document 1 discloses a motor for in-wheel motor vehicles whose primary purpose is to reduce cogging torque. In-wheel motor vehicles are, for example, electric vehicles. The motor described in Patent Document 1 has a structure that can achieve both a reduction in cogging torque and suppression of heat generation without impairing the formability of the windings. In addition, it has a structure that allows for easy control by keeping the inverter frequency low, and that ensures sufficient groove margin, and is not disadvantageous in terms of coil manufacturing or the effects of heat generation. In other words, this motor has a structure that is advantageous in reducing cogging torque within a range that is not disadvantageous in manufacturing or practical use, and is suitable for outer rotor type in-wheel motors for driving the wheels of in-wheel motor vehicles.

[0004] Japanese Patent Publication No. 2018-164366

[0005] In recent years, motors have been increasingly used not only in electric vehicles but also in drones and even in robotic arms that previously relied on hydraulic systems. Among electric vehicles, in-wheel motor vehicles and drones, in particular, are equipped with multiple motors, requiring a higher level of quietness compared to single-motor systems. Similarly, in robotic arms, high vibration can affect precise movements, so low vibration and quietness are also required. On the other hand, while it is important to suppress vibration and pursue quietness by reducing cogging torque, it is crucial to ensure that the output torque does not decrease accordingly when determining the motor specifications.

[0006] In view of the above-mentioned background, the present invention aims to provide an outer rotor type motor that is advantageous in reducing cogging torque while ensuring a predetermined output torque.

[0007] To achieve the above objective, the motor of the present invention is an outer rotor type motor comprising a surface magnet type rotor on which a plurality of permanent magnets are fixed along the inner circumferential surface, and a stator disposed inside the rotor and having teeth and grooves alternately formed on its outer circumference, wherein the number of permanent magnets is 32 and the number of grooves is 24, the cross-sectional shape of the permanent magnets in the direction perpendicular to the rotation axis of the rotor has chamfers on both ends to avoid concentration of magnetic flux, the stator side is convex, the half width of the permanent magnet is the magnet width Mw (mm), the half width of the teeth is the tooth width Tw (mm), the angle between the inclined surfaces formed on both ends of the permanent magnet and the vertical surface continuous with the inclined surfaces in the cross-sectional shape of the permanent magnet in the direction perpendicular to the rotation axis of the rotor is the magnet angle θ (rad), and when there is a wedge-shaped projection for fixing the permanent magnet to the rotor, the height of the wedge-shaped projection is the wedge height H (mm), then the following equation is satisfied: 30.8 ≤ (Mw 1.4 ×θ 0.5 ×Tw 0.45 ) / H 0.08 ≤33.1 When the wedge-shaped projection is absent, the magnet width Mw, the tooth width Tw, and the magnet angle θ satisfy the following equation: 30.7 ≤ Mw 1.4 ×θ 0.5 ×Tw 0.45≤33.9

[0008] According to the present invention, by adopting a fractional groove structure with a ratio of 32:24 permanent magnets to grooves, it is possible to reduce cogging torque and suppress heat generation without compromising winding formability. This allows for easy control by keeping the inverter frequency low, and sufficient groove margins can be secured. This does not disadvantage the coil manufacturing process or the effects of heat generation. In addition to being advantageous in reducing cogging torque within a range that does not disadvantage manufacturing or practical use, by satisfying predetermined conditions, it is advantageous in reducing cogging torque while securing a predetermined output torque.

[0009] A perspective view of a drone equipped with a motor according to one embodiment of the present invention. A cross-sectional view of the motor and its vicinity according to one embodiment of the present invention. A plan view showing the main part of the motor structure according to one embodiment of the present invention. An enlarged view of part A in Figure 3. An enlarged view of part B in Figure 4. An enlarged view of the specification in Figure 5 with the wedge-shaped projection omitted. A diagram showing two examples of magnet angle θ. A diagram showing the verification results for samples numbered 1-1 to 1-4 in Table 1. A diagram showing the verification results for samples numbered 2-1 to 2-4 in Table 1. A partial enlarged view of the stator to explain the groove margin. A diagram explaining cogging torque. A diagram showing the changes in cogging torque T and D1 when the tooth width Tw is changed for each case where the wedge height H is a predetermined value in a motor structure with a wedge-shaped projection. A diagram in Figure 12 in which a line showing the change in output torque is added to the line showing the change in cogging torque T. A diagram showing the changes in cogging torque T and D1 when the tooth width Tw is changed for each case where the magnet width Mw is a predetermined value in a motor structure with a wedge-shaped projection. Figure 14 shows a line added to the line showing the change in cogging torque T, with a line showing the change in output torque added. Figure 16 shows a line added to the line showing the change in cogging torque T, with a line added to the line showing the change in output torque, for each case where the magnet angle θ is a predetermined value, in a motor structure with a wedge-shaped projection. Figure 18 shows a line added to the line showing the change in cogging torque T, with a line added to the line showing the change in output torque, for each case where the magnet width Mw is a predetermined value, in a motor structure without a wedge-shaped projection. Figure 20 shows a line added to the line showing the change in cogging torque T, with a line added to the line showing the change in output torque. Perspective view of a robot arm equipped with a motor according to one embodiment of the present invention. Perspective view of a part of an in-wheel motor vehicle equipped with a motor according to one embodiment of the present invention.

[0010] Hereinafter, one embodiment of the present invention will be described with reference to the drawings. This embodiment relates to an outer rotor type motor used, for example, in drones, robot arms, and in-wheel motor vehicles. Hereinafter, the motor according to this embodiment will be described as a motor for drones, but this description is also applicable to motors used in robot arms, in-wheel motor vehicles, etc.

[0011] Figure 1 shows a perspective view of a drone 1 equipped with a motor 10 according to one embodiment of the present invention. A pair of T-shaped arms 3 are attached to the aircraft body 2, and two motors 10 are fixed to each arm 3. The motors 10 rotate the propeller 4.

[0012] Figure 2 shows a cross-sectional view of the motor 10 and its vicinity as shown in Figure 1. The motor 10 comprises a case 15 to which a rotor 11 is fixed to the inner circumferential surface, and the motor structure is built inside the case 15. Permanent magnets 12 are fixed to the inner circumferential surface of the rotor 11. The stator (iron core) 13 is fixed to a support 13a, and the support 13a is fixed to the rotating shaft 17 via a bearing 16. A coil 14 is wound around the stator 13.

[0013] The motor 10 is an outer rotor type, where the stator 13 does not rotate, but the rotor 11, which is the outer rotor, rotates. The case 15 rotates together with the rotor, and the rotating shaft 17 fixed to the case 15 rotates. As a result, the rotating shaft 17a attached to the rotating shaft 17 rotates, and the propeller 4 fixed to the rotating shaft 17a rotates.

[0014] Figure 3 is a plan view showing the main parts of the motor structure of the motor 10. Figure 4 is an enlarged view of part A in Figure 3, and Figure 5 is an enlarged view of part B in Figure 4. The shape of the permanent magnet 12 in Figure 5 is also the cross-sectional shape in the direction perpendicular to the rotation axis of the rotor 11 (Figure 3) (the same applies to Figure 6). In Figure 3, the rotor 11 is a surface magnet type, and a plurality of permanent magnets 12 are fixed along the inner circumferential surface of the rotor 11. More specifically, as shown in Figures 4 and 5, the permanent magnets 12 are fixed to the rotor 11 by wedge-shaped projections 20 that are integrated with the rotor 11. In Figure 3, a stator 13 is arranged inside the rotor 11, and teeth 18 and grooves 19 are alternately formed on the outer circumference of the stator 13.

[0015] In Figure 4, the permanent magnet 12 shows its cross-sectional shape in a direction perpendicular to the rotation axis 17 of the rotor 11 (see Figure 2). The permanent magnet 12 has a convex shape on the stator 13 side, and chamfers 21 are formed on both ends to avoid concentration of magnetic flux. As shown in Figure 5, the permanent magnet 12 engages with a wedge-shaped projection 20 on an inclined surface 22 on the end side of the chamfer 21. The inclined surface 22 is flat in Figure 5, but it may also be a curved surface.

[0016] Figure 6 shows an enlarged view of the vicinity of the end of the permanent magnet 12 in a specification where the wedge-shaped projection 20 is omitted, as in Figure 5. Even in the specification without the wedge-shaped projection 20, the permanent magnet 12 can be fixed to the inner surface of the rotor 11 by adhesive or by engagement between the permanent magnet 12 and the inner surface of the rotor 11. In Figures 5 and 6, the magnet angle θ is the angle between the inclined surfaces 22 formed at both ends of the permanent magnet 12 and the vertical surface 23 continuous with the inclined surfaces 22, within the cross-sectional shape of the permanent magnet 12. The definition of the magnet angle θ will be explained more specifically below with reference to Figure 7.

[0017] Figure 7 shows two examples of the magnet angle θ. In Figure 7(a), the inclined surface 22 is a flat surface, and the magnet angle θ in this case is the angle between the inclined surface 22 and the vertical surface 23 inside the permanent magnet 12. In Figure 7(b), the inclined surface 22 is a curved surface. In this case, the magnet angle θ is, according to the definition above, the angle between the inclined surface 22 and the vertical surface 23 inside the permanent magnet 12, but this angle is not uniquely determined. Therefore, in this embodiment, the angle between the curved inclined surface 22 and the vertical surface 23 is defined as the angle between the straight line 26 connecting the point 25a where the vertical surface 23 switches to a curved surface and the point 25b where the curved surface of the inclined surface 22 switches to the curved surface of the chamfer 21, and the vertical surface 23.

[0018] When the inclined surface 22 is a curved surface, the magnet angle θ was set to the magnet angle when the curved surface is considered as a straight line as described above. However, it was verified that this approach has almost no effect on the analysis results, as shown below. The verification was performed on samples numbered 1-1 to 2-4 in Table 1. Samples numbered 1-1 to 1-4 have wedge-shaped protrusions 20, and include samples where the inclined surface 22 is flat and samples where the inclined surface 22 is curved (with three different radii of curvature R). Samples numbered 2-1 to 2-4 do not have wedge-shaped protrusions 20, and include samples where the inclined surface 22 is flat and samples where the inclined surface 22 is curved (with three different radii of curvature R).

[0019]

[0020] Figure 8 shows the verification results for samples with wedge-shaped protrusions 20 (wedge height 1.6 mm) numbered 1-1 to 1-4 in Table 1. Figure 8 shows the changes in output torque T (Nm) and cogging torque T (Nm) when the tooth width Tw (mm) is changed while the magnet width Mw is fixed at 6.0 mm and the magnet angle θ is 2.71 rad. The method for calculating the magnet angle θ is as explained above using Figure 7 (the same applies to Figure 9). The output torque T (Nm) is the average value (integral average) (the same applies hereafter), and the cogging torque T (Nm) is the total amplitude, as will be explained later with reference to Figure 11 (the same applies hereafter).

[0021] Figure 9 shows the verification results for samples without the wedge-shaped protrusions 20, numbered 2-1 to 2-4 in Table 1. Figure 9 shows the changes in output torque T (Nm) and cogging torque T (Nm) when the tooth width Tw (mm) is changed while the magnet width Mw is fixed at 6.0 mm and the magnet angle θ is fixed at 2.71 rad.

[0022] As shown in Figure 8, the output torque T (Nm) and cogging torque T (Nm) values ​​for samples numbered 1-1 to 1-4 are almost the same. Similarly, as shown in Figure 9, the output torque T (Nm) and cogging torque T (Nm) values ​​for samples numbered 2-1 to 2-4 are almost the same. In other words, when the inclined surface 22 is a curved surface, treating the inclined surface 22 as a plane, as explained using Figure 7, has almost no effect on the analysis results.

[0023] The above describes the general configuration of the motor 10 and the magnet angle θ. In this embodiment, in order to reduce cogging torque, a structure with 32 permanent magnets 12 and 24 grooves 19 is adopted. The reason for this is explained below. The combination of the number of permanent magnets and the number of grooves is sometimes called a slot combination, but in this embodiment, it is simply called a structure. For example, the combination of 32 permanent magnets 12 and 24 grooves 36 is called a structure with permanent magnet count:groove count = 32:24. Also, when referring to the ratio rather than the number of permanent magnets and grooves, it is clearly stated that it is a ratio.

[0024] Structures with a ratio of 2:3 between the number of permanent magnets and the number of grooves are called integer grooves, while all others are called fractional grooves. Cogging torque tends to decrease as the least common multiple of the number of permanent magnets and the number of grooves increases. For example, in an integer groove structure with a ratio of 16:24 permanent magnets to grooves, the least common multiple is 48, whereas in a fractional groove structure with a ratio of 20:24 permanent magnets to grooves, it is 120, resulting in a smaller cogging torque in the fractional groove structure compared to the integer groove structure.

[0025] On the other hand, the fractional groove structure has disadvantages: it becomes more complex because the winding direction is not uniform, and it limits the number of parallel winding circuits. In other words, the current flowing through the coil is obtained by dividing the total current flowing through the motor by the number of parallel circuits, so if the number of parallel circuits cannot be increased, the current flowing through the coil becomes large, and the heat generated by the resistance increases. To suppress the heat generation, one can increase the coil diameter to increase the cross-sectional area of ​​the coil, or wind two or three coils with thin wire diameters simultaneously, but both methods have the problem of being difficult to form the windings.

[0026] The number of parallel circuits is determined by the greatest common divisor of the number of permanent magnets and the number of grooves; the larger the greatest common divisor, the more parallel circuits can be made. The greatest common divisor of the number of permanent magnets and the number of grooves is 8 for a structure with a ratio of 16:24 permanent magnets to grooves, while it is 4 for a structure with a ratio of 20:24 permanent magnets to grooves. The structure with a ratio of 20:24 permanent magnets to grooves is advantageous in reducing cogging torque compared to the structure with a ratio of 16:24 permanent magnets to grooves, but it is disadvantageous in suppressing heat generation without compromising the formability of the winding. In other words, none of the above structures could achieve both a reduction in cogging torque and suppression of heat generation without compromising the formability of the winding.

[0027] On the other hand, the fractional groove structure with a ratio of 4:3 between the number of permanent magnets and the number of grooves is a structure that satisfies both the need to increase the least common multiple of the number of permanent magnets and the number of grooves, and the need to increase the greatest common divisor of the number of permanent magnets and the number of grooves. This structure can reduce cogging torque and suppress heat generation by increasing the number of parallel circuits, that is, it can suppress heat generation without impairing the formability of the windings. This structure will be explained in detail below.

[0028] It is known that increasing the number of permanent magnets to create a multi-pole system reduces the pole pitch, thereby reducing cogging torque. On the other hand, the inverter frequency f (Hz) is expressed by the following equation 1, where N (rpm) is the motor rotation speed and P is the number of permanent magnets. Equation 1: f = (N / 60) × (P / 2) According to equation 1, increasing the number of permanent magnets increases the inverter frequency, making motor control difficult, so increasing the number of poles is undesirable. However, in this embodiment, if the motor 10 is an outer rotor type motor and there is no reduction gear, and the motor 10 directly rotates the propeller 4 in a direct drive system, the gear ratio becomes 1. Therefore, the motor rotation speed required to bring the propeller 4 to the target rotation speed is significantly lower compared to a configuration with a reduction gear, and consequently the inverter frequency also decreases. Therefore, in the case of a direct drive system as in this embodiment, there is room to increase the number of permanent magnets.

[0029] On the other hand, in motor design, consideration must be given to the groove margins. Groove margins refer to the area of ​​the groove other than the coils. Figure 10 shows a partially enlarged view of the stator 30. Coils 31 are wound around the teeth 33 of the stator 30, and the space between adjacent coils 31 is the groove margin 32. In contrast, the space utilization ratio is the ratio of the groove area to the area occupied by the coils 31.

[0030] In Figure 10, increasing the number of turns of the coil 31 to increase the output torque or increasing the wire diameter of the coil 31 can suppress heat generation from the coil 31 when current flows through it; therefore, a higher packing ratio is desirable in this respect. However, increasing the packing ratio increases the area of ​​the coil 31, which reduces the remaining space 32 in the groove.

[0031] In the manufacture of the coil 31, a winding machine is used to wind the coil 31 discharged from the tip of a needle provided in the winding machine around the teeth 33 of the stator 30. If the margin 32 of the groove is small, interference between the coil and the needle is likely to occur, making it difficult to insert the needle into the groove. Also, when inserting the previously wound coil 31 into the teeth 33, it becomes difficult to insert the coil 31 into the groove. Further, when the margin 32 of the groove is small, the heat generated by the coil 31 when an electric current flows will affect the other coils 31.

[0032] Therefore, having a small margin 32 of the groove is disadvantageous in terms of manufacturing the coil 31 (especially the automation of winding), and is also disadvantageous in terms of the influence of heat generation between the coils 31. Thus, it is desirable to have a larger margin 32 of the groove. In this regard, under the same conditions of motor size, the ratio of teeth to grooves (pitch), and the space factor, the margin 32 of the groove becomes smaller in proportion to the number of grooves. For this reason, if the number of grooves is increased too much, the margin 32 of the groove will become too small, so it is desirable to appropriately limit the number of grooves.

[0033] Based on the above, it can be said that the fractional-slot structure with a ratio of the number of permanent magnets to the number of grooves of 4:3 is a structure that can achieve both heat generation suppression without impairing cogging torque reduction and winding formability. Hereinafter, it will be described more specifically while referring to Table 2.

[0034] Table 2 shows the least common multiple, greatest common divisor, inverter frequency, and groove margin for five types of structures with different combinations of the number of permanent magnets and the number of grooves. The groove margin is shown as a ratio when the groove margin in Structure No. 1 is set to 1. The inverter frequency is represented by the above formula 1, and the inverter frequency in Table 2 is the value when the motor rotation speed N in formula 1 is 2500 (rpm).

[0035]

[0036] According to Table 2, No. 1 has a small least common multiple, which is disadvantageous for reducing cogging torque. No. 2 has a small greatest common divisor, which is disadvantageous for suppressing heat generation without impairing the formability of the winding. In contrast, for No. 3 to No. 5, the ratio of the number of permanent magnets to the number of grooves is 4:3 in all cases. Both the least common multiple and the greatest common divisor are large, and it can be understood that they can achieve both reduction of cogging torque and suppression of heat generation without impairing the formability of the winding. Also, for No. 3 to No. 5, the inverter frequency is within a sufficiently small value.

[0037] More specifically, for No. 3 to No. 5, the number of permanent magnets increases in this order. The more the number of permanent magnets, the larger both the least common multiple and the greatest common divisor become. Therefore, regarding the ability to achieve both reduction of cogging torque and suppression of heat generation without impairing the formability of the winding, No. 5 is the most suitable.

[0038] However, No. 5 has a large number of grooves and the ratio of the groove margin is 1, which is disadvantageous in terms of coil manufacturing and the influence of heat generation between coils. On the other hand, No. 4 has fewer grooves than No. 5 and maintains a ratio of 1 for the margin, eliminating the disadvantages of No. 5. That is, it can be understood that No. 4 has a structure that is advantageous for reducing cogging torque within a range that does not cause disadvantages in manufacturing and practical use.

[0039] Based on the above, the fractional groove structure with the number of permanent magnets: the number of grooves = 32:24 can achieve both reduction of cogging torque and suppression of heat generation without impairing the formability of the winding. In addition, it can keep the inverter frequency low, making control easy, and can ensure sufficient groove margin, and is also a structure that is not disadvantageous in terms of coil manufacturing and the influence of heat generation between coils. That is, it can be seen that the fractional groove structure with the number of permanent magnets: the number of grooves = 32:24 is a structure that is advantageous for reducing cogging torque within a range that does not cause disadvantages in manufacturing and practical use.

[0040] Based on the premise of adopting a structure with 32 permanent magnets 12 and 24 grooves 19 for the reasons mentioned above, the inventors of this application returned to the motor principle and examined how to reduce cogging torque. In this regard, as shown in Figure 3, torque pulsation occurs in the motor due to the attraction and repulsion between the rotor 11 and the stator 13, and this phenomenon occurs precisely because of the exchange of magnetic force. In other words, to reduce cogging torque, it is extremely important how to smoothly change the magnetic force and how to form the magnetic path for that exchange.

[0041] Regarding the exchange of magnetic force, in Figure 3, on the stator 13 side, the tooth width portion of the teeth 18 around which the coil (not shown in Figure 3) is wound is the only magnetic path, and it is the opposing part that communicates with the rotor 11. On the other hand, on the rotor 11 side, the permanent magnets 12, which are the source of the magnetic force, play the role of exchanging magnetic force. Specifically, the magnet width of the permanent magnets 12 and the opposing shape with respect to the stator 13 are factors that determine whether the magnetic force changes smoothly or not. In addition, the inclination angle of the ends of the permanent magnets 12 affects the change in magnetic force between adjacent permanent magnets 12 with opposing magnetic poles.

[0042] Furthermore, as shown in Figure 5, when the permanent magnet 12 is fixed to the rotor 11 by a wedge-shaped projection 20 integrated with it, the wedge-shaped projection 20 becomes a magnetic path that determines the degree of short-circuiting between adjacent permanent magnets 12 having opposing magnetic poles. In addition, regarding the exchange of magnetic force between the stator 13 and the rotor 11, the wedge-shaped projection 20 also plays a bridging role in transmitting magnetic force to the adjacent permanent magnet 12.

[0043] From the above perspective, the inventors of this invention focused on the fact that, in a motor structure, tooth width, magnet width, magnet angle, presence or absence of wedge-shaped protrusions, and the height of wedge-shaped protrusions are highly related to the reduction of cogging torque. On the other hand, while it is important to suppress vibration and pursue quietness by reducing cogging torque, it is also important to ensure that the output torque does not decrease accordingly when determining the specifications of the motor. Based on these considerations, the inventors of this invention conducted extensive analysis and found that, if certain conditions are met, it is possible to reduce the cogging torque to below a predetermined standard value while ensuring a predetermined output torque.

[0044] Specifically, in FIG. 4 having the wedge-shaped protrusion 20, when the magnet width (half-width) of the permanent magnet 12 is Mw (mm) and the tooth width (half-width) of the tooth 18 is Tw (mm), and in FIG. 5, when the magnet angle of the permanent magnet 12 is the magnet angle θ (rad) and the height of the wedge-shaped protrusion 20 is the wedge height H (mm), by satisfying the following formula 2, it has been found that while ensuring a predetermined output torque, the cogging torque can be reduced to a value below a predetermined reference value. Formula 2: 30.8 ≤ (Mw 1.4 × θ 0.5 × Tw 0.45 ) / H 0.08 ≤ 33.1

[0045] Further, in FIG. 6 without the wedge-shaped protrusion 20, the present inventors have found that by satisfying the following formula 3 for the magnet width Mw, the tooth width Tw, and the magnet angle θ, while ensuring a predetermined output torque, the cogging torque can be reduced to a value below a predetermined reference value. Formula 3: 30.7 ≤ Mw 1.4 × θ 0.5 × Tw 0.45 ≤ 33.9

[0046] For the sake of convenience of explanation, the mathematical formula in formula 2 is designated as D1 as shown in the following formula 4, and the mathematical formula in formula 3 is designated as D2 as shown in the following formula 5. Formula 4: D1 = (Mw 1.4 × θ 0.5 × Tw 0.45 ) / H 0.08 Formula 5: D2 = Mw 1.4 × θ 0.5 × Tw 0.45

[0047] FIG. 11 shows a diagram for explaining the cogging torque. As shown in this figure, the cogging torque is represented by a waveform that changes periodically, and the total amplitude T of this waveform is the value of the cogging torque. For example, when referring to a cogging torque of 1.5 (Nm), the total amplitude T is 1.5 (Nm).

[0048] The analysis results for a motor structure with wedge-shaped protrusions 20 will be explained below with reference to Figures 12 to 17. Figure 12 shows the changes in cogging torque T (Nm) and D1 (Equation 4) when the tooth width Tw (mm) is changed for each of the following wedge heights H (mm): 1.3 mm, 1.4 mm, 1.6 mm, and 1.8 mm, with the magnet width Mw fixed at 6.0 mm and the magnet angle θ at 2.71 rad. The motor used as the subject of the analysis results in Figure 12 has the motor structure shown in Figures 2 to 5, and has a fractional groove structure with a ratio of permanent magnets to grooves of 32:24. This is the same in Figures 13 to 17.

[0049] In Figure 12, line 101 shows the change in cogging torque T (Nm) when the tooth width Tw is changed while the wedge height H is 1.3 mm, and line 201 shows the change in D1 when the wedge height H remains the same at 1.3 mm. Similarly, lines 102 and 202 show the changes in cogging torque T (Nm) and D1 when the wedge height H is 1.4 mm, respectively, lines 103 and 203 show the changes in cogging torque T (Nm) and D1 when the wedge height H is 1.6 mm, respectively, and lines 104 and 204 show the changes in cogging torque T (Nm) and D1 when the wedge height H is 1.8 mm, respectively. Line 100a indicates that the value of D1 on line 100a is 31.94 (the same applies in Figures 14 and 16).

[0050] On line 101, the cogging torque T is at its minimum value at point A1, and the value of D1 at this point is the same as the value at point B1 on line 201. Similarly, on line 102, the cogging torque T is at its minimum value at point A2, and the value of D1 at this point is the same as the value at point B2 on line 202. On line 103, the cogging torque T is at its minimum value at point A3, and the value of D1 at this point is the same as the value at point B3 on line 203. On line 104, the cogging torque T is at its minimum value at point A4, and the value of D1 at this point is the same as the value at point B4 on line 204. Points B1, B2, B3, and B4 are all on or near line 100a, and the value of D1 at each point is 31.94 or a value close to it.

[0051] In the line 101 to line 104, at points A1 to A4 where the cogging torque T is at its minimum value, this minimum value is well below 1.0 (Nm), which is a sufficiently small value for cogging torque, and the value of D1 in this setting is 31.94 or a value close to it. Furthermore, in the line 101 to line 104, even within a range of a predetermined value above or below the minimum value, the cogging torque T is still well below 1.0 (Nm).

[0052] Figure 13 is a diagram in which lines 301 to 304, which show the change in output torque, are added to lines 101 to 104, which show the change in cogging torque T in Figure 12. Line 301 shows the change in output torque (Nm) when the tooth width Tw is changed when the wedge height H is 1.3 mm, line 302 shows the change in output torque (Nm) when the tooth width Tw is changed when the wedge height H is 1.4 mm, line 303 shows the change in output torque (Nm) when the tooth width Tw is changed when the wedge height H is 1.6 mm, and line 304 shows the change in output torque (Nm) when the tooth width Tw is changed when the wedge height H is 1.8 mm.

[0053] In Figure 13, points A1 to A4 indicate the points where the cogging torque T is at its minimum value, similar to Figure 12. Line 401 is a vertical line passing through point A1, and line 402 is a vertical line passing through point A4. Points A1 to A4 lie between lines 401 and 402, and it can be seen that the output torque values ​​corresponding to each point are all large values ​​exceeding 100 Nm. Furthermore, in lines 101 to 104, even within the range slightly above and below the minimum value, the output torque still exceeds 100 Nm.

[0054] Figure 14 shows the changes in cogging torque T (Nm) and D1 (Equation 4) when the tooth width Tw (mm) is varied, with the wedge height H fixed at 1.6 mm and the magnet angle θ at 2.71 rad, and the magnet width Mw at 5.9 mm, 6.0 mm, and 6.1 mm, respectively.

[0055] Line 105 shows the change in cogging torque T (Nm) when the tooth width Tw is changed while the magnet width Mw is 5.9 mm, and line 205 shows the change in D1 when the magnet width Mw remains the same at 5.9 mm. Similarly, lines 106 and 206 show the change in cogging torque T (Nm) and D1 when the magnet width Mw is 6.0 mm, respectively, and lines 107 and 207 show the change in cogging torque T (Nm) and D1 when the magnet width Mw is 6.1 mm, respectively.

[0056] On line 105, the cogging torque T is at its minimum value at point A5, and the value of D1 at this point is the same as the value at point B5 on line 205. Similarly, on line 106, the cogging torque T is at its minimum value at point A6, and the value of D1 at this point is the same as the value at point B6 on line 206. On line 107, the cogging torque T is at its minimum value at point A7, and the value of D1 at this point is the same as the value at point B7 on line 207. Points B5, B6, and B7 are all on or near line 100a, and the value of D1 at each point is 31.94 or a value close to it.

[0057] In the line 105 to line 107, at points A5 to A7 where the cogging torque T is at its minimum value, this minimum value is well below 1.0 (Nm), which is a sufficiently small value for cogging torque, and the value of D1 in this setting is 31.94 or a value close to it. Furthermore, in the line 105 to line 107, even within a range of a predetermined value above or below the minimum value, the cogging torque T is still well below 1.0 (Nm).

[0058] Figure 15 is a diagram in which lines 305 to 307, which show the change in output torque, are added to lines 105 to 107, which show the change in cogging torque T in Figure 14. Line 305 shows the change in output torque (Nm) when the tooth width Tw is changed when the magnet width Mw is 5.9 mm, line 306 shows the change in output torque (Nm) when the tooth width Tw is changed when the magnet width Mw is 6.0 mm, and line 307 shows the change in output torque (Nm) when the tooth width Tw is changed when the magnet width Mw is 6.1 mm.

[0059] In Figure 15, points A5 to A7 indicate the points where the cogging torque T is at its minimum value, similar to Figure 14. Line 403 is a vertical line passing through point A5, and line 404 is a vertical line passing through point A7. Points A5 to A7 lie between lines 403 and 404, and it can be seen that the output torque values ​​corresponding to each point are all large values ​​exceeding 100 Nm. Furthermore, in the range around the minimum value, from line 105 to line 107, the output torque still exceeds 100 Nm.

[0060] Figure 16 shows the changes in cogging torque T (Nm) and D1 (Equation 4) when the tooth width Tw (mm) is changed, for each of the following magnet angles θ: 2.62 rad, 2.71 rad, and 2.79 rad, with the magnet width Mw fixed at 6.0 mm and the wedge height H at 1.6 mm.

[0061] Line 108 shows the change in cogging torque T (Nm) when the tooth width Tw is changed while the magnet angle θ is 2.62 rad, and line 208 shows the change in D1 when the magnet angle θ is the same 2.71 rad. Similarly, lines 109 and 209 show the change in cogging torque T (Nm) and D1, respectively, when the magnet angle θ is 2.71 rad, and lines 110 and 210 show the change in cogging torque T (Nm) and D1, respectively, when the magnet angle θ is 2.79 rad.

[0062] On line 108, the cogging torque T is at its minimum value at point A8, and the value of D1 at this point is the same as the value at point B8 on line 208. Similarly, on line 109, the cogging torque T is at its minimum value at point A9, and the value of D1 at this point is the same as the value at point B9 on line 209. On line 110, the cogging torque T is at its minimum value at point A10, and the value of D1 at this point is the same as the value at point B10 on line 210. Points B8, B9, and B10 are all on or near line 100a, and the value of D1 at each point is 31.94 or a value close to it.

[0063] In the range from line 108 to line 110, at points A8 to A10 where the cogging torque T is at its minimum value, this minimum value is well below 1.0 (Nm), which is a sufficiently small value for cogging torque, and the value of D1 in this setting is 31.94 or a value close to it. Furthermore, in the range from line 108 to line 110, even within a predetermined range around the minimum value, the cogging torque T is still well below 1.0 (Nm).

[0064] Figure 17 is a diagram in which lines 308 to 310, which show the change in output torque, are added to lines 108 to 110, which show the change in cogging torque T in Figure 16. Line 308 represents the change in output torque (Nm) when the tooth width Tw is changed when the magnet angle θ is 2.62 rad, line 309 represents the change in output torque (Nm) when the tooth width Tw is changed when the magnet angle θ is 2.71 rad, and line 310 represents the change in output torque (Nm) when the tooth width Tw is changed when the magnet angle θ is 2.79 rad.

[0065] In Figure 17, points A8 to A10 indicate the points where the cogging torque T is at its minimum value, similar to Figure 16. Line 405 is a vertical line passing through point A8, and line 406 is a vertical line passing through point A10. Points A8 to A10 lie between lines 405 and 406, and it can be seen that the output torque values ​​corresponding to each point are all large values ​​exceeding 100 Nm. Furthermore, in the range around the minimum value, from line 108 to line 110, the output torque still exceeds 100 Nm.

[0066] As explained above with reference to Figures 12 to 17, the analysis results for the motor structure with wedge-shaped protrusions 20 are as follows: In the setting where the cogging torque T is at its minimum value, this minimum value is well below 1.0 (Nm), and the value of D1 in this setting is 31.94 or a close value thereto. Also, in the setting where the cogging torque T is at its minimum value, the output torque values ​​are all large values ​​exceeding 100 Nm. Therefore, in Equation 4, if Mw, θ, Tw, and H are set so that the value of D1 is 31.94 or a close value thereto, an outer rotor type in-wheel motor can be obtained in which the cogging torque T is well below 1.0 (Nm) and the output torque exceeds 100 Nm.

[0067] Furthermore, as described above, in the line representing the cogging torque T in Figures 12 to 17, even within a range where the cogging torque T is within a predetermined range from the minimum value, the cogging torque T remains below 1.0 (Nm). According to the analysis results in Figures 12, 14, and 16, if the value of D1 is between 30.8 and 33.1, the cogging torque T is below 1.0 (Nm). Moreover, within the range where the value of D1 is between 30.8 and 33.1, the output torque still exceeds 100 Nm. In other words, by setting Mw, θ, Tw, and H to satisfy Equation 2, an outer rotor type in-wheel motor can be obtained in which the cogging torque T is below 1.0 (Nm) and the output torque exceeds 100 Nm.

[0068] The analysis results for a motor structure without wedge-shaped protrusions 20 will be explained below with reference to Figures 18 to 21. Figure 18 shows the changes in cogging torque T (Nm) and D2 (Equation 5) when the tooth width Tw (mm) is changed for each of the following cases, with the magnet angle θ fixed at 2.71 rad and the magnet width Mw being 5.9 mm, 6.0 mm, and 6.1 mm. The motor used as the subject of the analysis results in Figure 18 has the motor structure shown in Figures 2, 4 (however, without wedge-shaped protrusions 20) and 6, and has a fractional groove structure with a ratio of permanent magnets to grooves of 32:24. This is the same in Figures 19 to 21.

[0069] In Figure 18, line 111 shows the change in cogging torque T (Nm) when the tooth width Tw is changed while the magnet width Mw is 5.9 mm, and line 211 shows the change in D2 when the magnet width Mw remains the same at 5.9 mm. Similarly, lines 112 and 212 show the change in cogging torque T (Nm) and D2, respectively, when the magnet width Mw is 6.0 mm, and lines 113 and 213 show the change in cogging torque T (Nm) and D2, respectively, when the magnet width Mw is 6.1 mm. Line 100b indicates that the value of D2 on line 100b is 32.35 (the same applies in Figure 20).

[0070] In Figure 18, on line 111, the cogging torque T is at its minimum value at point A11, and the value of D2 at this point is the same as the value at point B11 on line 211. Similarly, on line 112, the cogging torque T is at its minimum value at point A12, and the value of D2 at this point is the same as the value at point B12 on line 212. On line 113, the cogging torque T is at its minimum value at point A13, and the value of D2 at this point is the same as the value at point B13 on line 213. Points B11, B12, and B13 are all on or near line 100b, and the value of D2 at each point is 32.35 or a value close to it.

[0071] In the line 111 to line 113, at points A11 to A13 where the cogging torque T is at its minimum value, this minimum value is well below 1.0 (Nm), which is a sufficiently small value for cogging torque, and the value of D2 in this setting is 32.35 or a value close to it. Furthermore, in the line 111 to line 113, even within a range of a predetermined value above or below the minimum value, the cogging torque T is still well below 1.0 (Nm).

[0072] Figure 19 is a diagram in which lines 311 to 313, which show the change in output torque, are added to lines 111 to 113, which show the change in cogging torque T in Figure 18. Line 311 shows the change in output torque (Nm) when the tooth width Tw is changed when the magnet width Mw is 5.9 mm, line 312 shows the change in output torque (Nm) when the tooth width Tw is changed when the magnet width Mw is 6.0 mm, and line 313 shows the change in output torque (Nm) when the tooth width Tw is changed when the magnet width Mw is 6.1 mm.

[0073] In Figure 19, points A11 to A13 indicate the points where the cogging torque T is at its minimum value, similar to Figure 18. Line 407 is a vertical line passing through point A11, and line 408 is a vertical line passing through point A13. Points A11 to A13 lie between lines 407 and 408, and it can be seen that the output torque values ​​corresponding to each point are all large values ​​exceeding 100 Nm. Furthermore, in the range around the minimum value, from line 111 to line 113, the output torque still exceeds 100 Nm.

[0074] Figure 20 shows the changes in cogging torque T (Nm) and D2 (Equation 5) when the tooth width Tw (mm) is varied, with the magnet width Mw fixed at 6.0 mm and the magnet angle θ at 2.62 rad, 2.71 rad, and 2.79 rad, respectively.

[0075] Line 114 shows the change in cogging torque T (Nm) when the tooth width Tw is changed while the magnet angle θ is 2.62 rad, and line 214 shows the change in D2 when the magnet angle θ remains the same at 2.62 rad. Similarly, lines 115 and 215 show the change in cogging torque T (Nm) and D2, respectively, when the magnet angle θ is 2.71 rad, and lines 116 and 216 show the change in cogging torque T (Nm) and D2, respectively, when the magnet angle θ is 2.79 rad.

[0076] On line 114, the cogging torque T is at its minimum value at point A14, and the value of D2 at this point is the same as the value at point B14 on line 214. Similarly, on line 115, the cogging torque T is at its minimum value at point A15, and the value of D2 at this point is the same as the value at point B15 on line 215. On line 116, the cogging torque T is at its minimum value at point A16, and the value of D2 at this point is the same as the value at point B16 on line 216. Points B14, B15, and B16 are all on or near line 100b, and the value of D2 at each point is 32.35 or a value close to it.

[0077] In the line 114 to line 116, at points A14 to A16 where the cogging torque T is at its minimum value, this minimum value is well below 1.0 (Nm), which is a sufficiently small value for cogging torque, and the value of D2 in this setting is 32.35 or a value close to it. Furthermore, in the line 114 to line 116, even within a range of a predetermined value before or after the minimum value, the cogging torque T is still well below 1.0 (Nm).

[0078] Figure 21 is a diagram in which lines 314 to 316, which show the change in output torque, are added to lines 114 to 116, which show the change in cogging torque T in Figure 20. Line 314 represents the change in output torque (Nm) when the tooth width Tw is changed when the magnet angle θ is 2.62 rad, line 315 represents the change in output torque (Nm) when the tooth width Tw is changed when the magnet angle θ is 2.71 rad, and line 316 represents the change in output torque (Nm) when the tooth width Tw is changed when the magnet angle θ is 2.79 rad.

[0079] In Figure 21, points A14 to A16 indicate the points where the cogging torque T is at its minimum value, similar to Figure 20. Line 409 is a vertical line passing through point A14, and line 410 is a vertical line passing through point A16. Points A14 to A16 lie between lines 409 and 410, and it can be seen that the output torque values ​​corresponding to each point are all large values ​​exceeding 100 Nm. Furthermore, in the range around the minimum value, from line 114 to line 116, the output torque still exceeds 100 Nm.

[0080] The analysis results for a motor structure without the wedge-shaped protrusion 20 have been explained above with reference to Figures 18 to 21. In the setting where the cogging torque T is at its minimum value, this minimum value is well below 1.0 (Nm), and the value of D2 in this setting is 32.35 or a close value thereto. Also, in the setting where the cogging torque T is at its minimum value, the output torque values ​​are all large values ​​exceeding 100 Nm. Therefore, in Equation 5, if Mw, θ, and Tw are set so that the value of D2 is 32.35 or a close value thereto, an outer rotor type in-wheel motor can be obtained in which the cogging torque T is well below 1.0 (Nm) and the output torque exceeds 100 Nm.

[0081] Furthermore, as described above, in Figures 18 to 21, even within a range where the cogging torque T is within a predetermined range of approximately 1.0 (Nm) relative to the minimum value, the cogging torque T remains below 1.0 (Nm). According to the analysis results in Figures 18 and 20, if the value of D2 is between 30.7 and 33.9, the cogging torque T remains below 1.0 (Nm). Moreover, within the range where the value of D2 is between 30.7 and 33.9, the output torque still exceeds 100 Nm. In other words, by setting Mw, θ, and Tw to satisfy Equation 3, an outer rotor type in-wheel motor can be obtained in which the cogging torque T is below 1.0 (Nm) and the output torque exceeds 100 Nm.

[0082] Furthermore, although Figure 1 shows the motor 10 according to the present invention being used as a motor for a drone 1, as mentioned above, there are no limitations on its use, and it can also be used as an outer rotor type motor for, for example, a robot arm or an in-wheel motor vehicle.

[0083] Figure 22 shows a perspective view of a robot arm 40 equipped with a motor 10a according to the present invention. The robot arm 40 is equipped with multiple motors 10a, enabling rotation of the entire robot arm 40, as well as rotation of the upper arm 41, lower arm 42, and wrist 43.

[0084] Figure 23 shows a perspective view of the vicinity of the vehicle suspension system 50 of an in-wheel motor vehicle when the motor according to the present invention is used as an in-wheel motor 10b. For convenience of illustration, the wheel 51 is shown in cross-sectional view, and the tire attached to the wheel 51 is not shown. The case 51 rotates together with the rotor built into the in-wheel motor 10b, and the wheel 52 rotates together with the rotor.

[0085] Although one embodiment of the present invention has been described above, the present invention is not limited thereto and may include any modified configurations. For example, the motor 10 in the above embodiment is just one example and may be modified as appropriate without changing the outer rotor structure.

[0086] 1 Drone 10, 10a, 10b Motor 11 Rotor 12 Permanent magnet 13 Stator 14 Coil 18 Teeth 19 Grooves 20 Wedge-shaped projections 21 Chamfer

Claims

1. An outer rotor type motor comprising a surface magnet type rotor in which a plurality of permanent magnets are fixed along the inner circumferential surface, and a stator disposed inside the rotor and having teeth and grooves alternately formed on its outer circumference, wherein the number of permanent magnets is 32 and the number of grooves is 24, the cross-sectional shape of the permanent magnets in the direction perpendicular to the rotation axis of the rotor has chamfers on both ends to avoid concentration of magnetic flux, and the stator side is convex, the half width of the permanent magnet is the magnet width Mw (mm), the half width of the teeth is the tooth width Tw (mm), the angle between the inclined surfaces formed on both ends of the permanent magnet and the vertical surface continuous with the inclined surfaces in the cross-sectional shape of the permanent magnet in the direction perpendicular to the rotation axis of the rotor is the magnet angle θ (rad), and when there is a wedge-shaped projection for fixing the permanent magnet to the rotor, the height of the wedge-shaped projection is the wedge height H (mm), then the following equation is satisfied: 30.8 ≤ (Mw 1.4 ×θ 0.5 ×Tw 0.45 ) / H 0.08 ≤33.1 A motor characterized in that, when the wedge-shaped projection is absent, the magnet width Mw, the tooth width Tw, and the magnet angle θ satisfy the following formula: 30.7 ≤ Mw 1.4 ×θ 0.5 ×Tw 0.45 ≤33.9

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