electric motor

Abstract

To provide an electric motor capable of enhancing an arrangement degree-of-freedom of a magnetic sensor for detecting a rotational position of an outer rotor.SOLUTION: An outer rotor 4 comprises: a cylinder rotor yoke part 25 that is opposite to an outer peripheral surface 17a of a stator core 17 to a radial direction; a plurality of leg parts 26 that is projected toward a shaft direction outer side from an end part 25b side of the rotor yoke part 25; a bottom part 27 that is bonded to an end opposite to the rotor yoke part 25 in the plurality of leg parts 26, and is opposite to a shaft direction with an end surface 17b of the stator core 17; and a plurality of magnets 24 that is fixed to an inner peripheral surface 25a of the rotor yoke part 25. In each of the plurality of magnets 24, an end part 24a on at least bottom part 27 side is projected from the end part 25b of the rotor yoke part 25, and is interposed between the adjacent leg parts 26 in a peripheral direction.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an electric motor. [Background technology]

[0002] A brushless motor, which is an electric motor, includes a stator around which a coil is wound and a rotor that is rotatable relative to the stator. Some brushless motors have a so-called outer rotor, in which the rotor is formed in a cylindrical shape with a bottom so as to surround the periphery of the stator. A magnet is provided on the inner peripheral surface of the cylindrical rotor yoke (yoke) of the rotor. With this configuration, when current is applied to the coil, a magnetic flux linkage is generated in the stator. Magnetic attractive and repulsive forces are generated between this magnetic flux linkage and the magnet, causing the rotor to rotate continuously.

[0003] In brushless motors, the rotational position of the rotor may be detected by detecting changes in magnetic flux in the rotor magnet to control the timing of energization of the coil. In this case, a magnetic sensor such as a Hall IC is provided on the opening side of the outer rotor. With this configuration, the axial end of the magnet faces the magnetic sensor in the axial direction, and the magnetic flux of the magnet is detected by the magnetic sensor. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2004-222464 Summary of the Invention [Problem to be solved by the invention]

[0005] When detecting the rotational position of the outer rotor as in the above-described conventional technology, there is a problem in that the location where the magnetic sensor can be placed is limited.

[0006] Therefore, the present invention provides an electric motor that allows for greater freedom in the placement of a magnetic sensor for detecting the rotational position of the outer rotor. [Means for solving the problem]

[0007] In order to solve the above problems, in a first aspect of the present invention, an electric motor comprises a stator having a coil wound thereon and an outer rotor covering the stator, the outer rotor comprising a cylindrical rotor yoke portion radially facing the outer peripheral surface of the stator, a plurality of legs protruding axially outward from one axial end of the rotor yoke portion, a bottom portion joined to the ends of the legs opposite the rotor yoke portion and axially facing the axial end face of the stator, and a plurality of magnets fixed to the inner peripheral surface of the rotor yoke portion, at least the bottom side end of each of the plurality of magnets protruding from one axial end of the rotor yoke portion and interposed between adjacent legs in the circumferential direction.

[0008] This configuration allows the axial end of the magnet to protrude from the bottom side of the outer rotor. This allows the magnet and magnetic sensor to be arranged axially opposite each other not only on the opening side of the outer rotor (the side opposite the bottom), but also on the bottom side of the outer rotor. This makes it possible to provide an electric motor that allows for greater freedom in the placement of the magnetic sensor.

[0009] In a second aspect of the present invention, in the electric motor of the first aspect, the plurality of legs protrude from an inner peripheral surface of the rotor yoke portion.

[0010] With this configuration, the position of the legs can be offset radially inward compared to when the legs protrude from one axial end of the rotor yoke. As a result, it is easier to make the one axial end of the magnet protrude further than the legs. This allows the magnetic sensor to be positioned closer to the one axial end of the magnet. This improves the accuracy of the magnetic sensor's detection of the magnetic flux of the magnet.

[0011] In the third aspect of the present invention, in the electric motor according to the first aspect or the second aspect, when the distance between the inner peripheral surface of the magnet and the outer peripheral surface of the stator is A, and the distance between the circumferential side surface of the magnet and the circumferential side surface of the leg portion as viewed in the axial direction is B, the distances A and B satisfy A < B.

[0012] By configuring in this way, it is possible to suppress the leakage of magnetic flux from the axial end portion of the magnet to the leg portion, and to contribute the magnetic flux of the magnet to the rotational torque of the outer rotor as much as possible. Therefore, even when the magnet protrudes to the bottom side of the outer rotor, it is possible to prevent the motor characteristics of the electric motor from deteriorating.

[0013] In the fourth aspect of the present invention, in the electric motor according to any one of the first aspect to the third aspect, when the distance between the inner peripheral surface of the magnet and the outer peripheral edge of the bottom portion as viewed in the axial direction is C, and the shortest distance between the end portion on the bottom side of the magnet and the axial end portion on the bottom side of the stator is D, the distances C and D satisfy D < C.

[0014] By configuring in this way, it is possible to suppress the leakage of magnetic flux from the axial end portion of the magnet to the bottom portion, and to contribute the magnetic flux of the magnet to the rotational torque of the outer rotor as much as possible. Therefore, even when the magnet protrudes to the bottom side of the outer rotor, it is possible to prevent the motor characteristics of the electric motor from deteriorating.

[0015] In the fifth aspect of the present invention, in the electric motor according to any one of the first aspect to the fourth aspect, a magnetic sensor for detecting the magnetic flux of the magnet is provided, and the magnetic sensor is disposed axially outside the bottom portion of the outer rotor and is disposed opposite to the axial end portion of the magnet in the axial direction.

[0016] In this way, even when the magnetic sensor is provided axially outside the bottom portion of the outer rotor, the magnetic flux of the magnet can be detected by the magnetic sensor, and the rotational position of the outer rotor can be detected. [Effects of the Invention]

[0017] According to the present invention, it is possible to provide an electric motor that allows for increased freedom in the placement of magnetic sensors. [Brief explanation of the drawings]

[0018] [Figure 1] 1 is a cross-sectional view taken along the direction of a rotation axis of an electric motor according to an embodiment of the present invention. [Figure 2] 1 is an exploded perspective view of an electric motor according to an embodiment of the present invention. [Figure 3] FIG. 2 is a plan view of the stator and the outer rotor in the embodiment of the present invention, as viewed from the cover side in the axial direction. [Figure 4] FIG. 2 is a perspective view of a rotor core and a magnet according to the embodiment of the present invention. [Figure 5] 10 is a graph comparing the amounts of effective magnetic flux of magnets according to embodiments of the present invention. [Figure 6] 10 is a graph showing a change in effective magnetic flux of a magnet depending on a distance B in an embodiment of the present invention. [Figure 7] 10 is a graph showing a change in effective magnetic flux of a magnet depending on a distance D in an embodiment of the present invention. [Figure 8] FIG. 10 is a perspective view of an outer rotor according to a modified example of the embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0019] Next, an embodiment of the present invention will be described with reference to the drawings.

[0020] <Electric motor> 1 is a cross-sectional view of the electric motor 1 taken along the direction of the rotation axis C. FIG. As shown in Figures 1 and 2, the electric motor 1 is a so-called outer rotor type brushless motor. The electric motor 1 includes a motor case 2, a stator 3, an outer rotor 4, and a rotational position detection device 5, all of which are housed in the motor case 2. The rotation axis C refers to the rotation axis of the outer rotor 4. In the following description, the direction of the rotation axis C will be simply referred to as the axial direction. The rotation direction of the outer rotor 4 will be simply referred to as the circumferential direction. The radial direction of the outer rotor 4, which is perpendicular to the axial and circumferential directions, will be simply referred to as the radial direction.

[0021] <Motor case> The motor case 2 includes a cylindrical case body 6 with a bottom, and a cover 7 that closes an opening 6a of the case body 6. A stator seat 8 that protrudes toward the opening 6a is integrally formed in the radial center of the bottom 6b of the case body 6. The stator 3 is placed on the stator seat 8. A first shaft insertion hole 9 that penetrates the axial direction is formed in the radial center of the stator seat 8. A first bearing housing recess 10 is formed on the opening 6a side of the first shaft insertion hole 9. A first bearing 11 for rotatably supporting the outer rotor 4 is provided in the first bearing housing recess 10. A ball bearing, for example, is used as the first bearing 11.

[0022] The cover 7 is formed by integrally molding a disk-shaped cover body 12 and a cylindrical fitting portion 13 extending from the outer peripheral edge of the cover body 12 toward the case body 6. The fitting portion 13 is fitted into the opening 6a of the case body 6. This causes the cover 7 to close the opening 6a of the case body 6. A second shaft insertion hole 14 is formed in the radial center of the cover body 12, penetrating in the axial direction.

[0023] The second shaft insertion hole 14 is arranged coaxially with the first shaft insertion hole 9. A second bearing accommodating recess 15 is formed on the case body 6 side of the second shaft insertion hole 14. A second bearing 16 for rotatably supporting the outer rotor 4 is provided in the second bearing accommodating recess 15. Like the first bearing 11, the second bearing 16 is also formed of, for example, a ball bearing.

[0024] <Stator> The stator 3 includes a stator core 17 and a coil 18 wound around the stator core 17. The stator core 17 is formed by laminating a plurality of magnetic steel plates. The stator core 17 includes an annular core body 19 and a plurality of (for example, 12 in this embodiment) teeth 20 formed radially outward from the outer circumferential surface of the core body 19. The core body 19 is placed on a stator seat 8 of the case body 6.

[0025] A plurality of (for example, three in this embodiment) bolt insertion holes 21 are formed in the core body 19 at equal intervals in the circumferential direction. Bolts 30 are inserted into these bolt insertion holes 21 from the opening 6a side of the case body 6. By fastening these bolts 30 to the stator seat 8, the stator core 17 is fixed inside the case body 6.

[0026] The teeth 20 are formed in a T-shape when viewed axially, with their radially outer ends extending circumferentially. Radially outer end faces 20a of the teeth 20 form the outer peripheral surface 17a of the stator core 17 (stator 3). A coil 18 is wound around each tooth 20. The terminals of the coils 18 are electrically connected to a control unit (not shown). The control unit is connected to an external power source (not shown). The control unit controls the supply of electricity to each coil 18.

[0027] <Outer rotor> Fig. 3 is a plan view of the stator 3 and the outer rotor 4 as viewed in the axial direction from the cover 7 side. Fig. 4 is a perspective view of the rotor core 23 and the magnet 24. As shown in Figures 1 to 4, the outer rotor 4 comprises a rotor shaft 22 rotatably supported on the motor case 2 via a first bearing 11 and a second bearing 16, a rotor core 23 housed within the motor case 2 and fixed to the rotor shaft 22, and a plurality of magnets 24 (for example, 10 in this embodiment) fixed to the rotor core 23.

[0028] A rotor shaft 22 is rotatably supported by the bearings 11 and 16. The rotor shaft 22 is inserted through the shaft insertion holes 9 and 14 of the motor case 2 via the bearings 11 and 16. Both axial ends of the rotor shaft 22 protrude axially outward through the shaft insertion holes 9 and 14.

[0029] Rotor core 23 is formed in a cylindrical shape with a bottom. Rotor core 23 includes a cylindrical rotor yoke portion 25 that radially covers outer peripheral surface 17a of stator core 17, a plurality of (e.g., ten in this embodiment) leg portions 26 that protrude from the cover 7 side end of inner peripheral surface 25a of rotor yoke portion 25 toward cover body 12 of cover 7, and a disk-shaped bottom portion 27 joined to the end of each leg portion 26 opposite to rotor yoke portion 25.

[0030] An inner peripheral surface 25a of rotor yoke portion 25 faces radially an outer peripheral surface 17a of stator core 17. The axial length of rotor yoke portion 25 is the same as the axial length of stator core 17. Leg portions 26 extend in an arc shape radially inward from inner circumferential surface 25a of rotor yoke portion 25 toward cover body 12 of cover 7. Leg portions 26 are arranged at equal intervals in the circumferential direction. Because legs 26 protrude from inner circumferential surface 25a of rotor yoke portion 25, end portion 25b of rotor yoke portion 25 facing cover 7 is not partially covered by legs 26 and is exposed over the entire circumference.

[0031] An outer peripheral edge 27a of the bottom portion 27 is joined to the end of the leg portion 26 opposite the rotor yoke portion 25. The end of the leg portion 26 on the bottom portion 27 side is formed so that its circumferential width gradually increases toward the bottom portion 27. As a result, an arc portion 26a is formed at the joint between the leg portion 26 and the bottom portion 27 so that the leg portion 26 and the bottom portion 27 are smoothly connected. The arc portion 26a makes it possible to prevent stress from acting locally at the joint between the leg portion 26 and the bottom portion 27.

[0032] Bottom portion 27 faces axially end face 17b of stator core 17 on the cover 7 side. By connecting rotor yoke portion 25 and bottom portion 27 with leg portions 26, openings 23a are formed between rotor yoke portion 25 and bottom portion 27 between adjacent leg portions 26 in the circumferential direction.

[0033] A through hole 27b is formed in the radial center of the bottom portion 27. The rotor shaft 22 is press-fitted or inserted into the through hole 27b. When the rotor shaft 22 is inserted into the through hole 27b, the bottom portion 27 and the rotor shaft 22 are joined by welding or the like, for example. This integrates the rotor shaft 22 and the rotor core 23. With the rotor core 23 fixed to the rotor shaft 22, the end 25b of the rotor yoke portion 25 facing the cover 7 and the end face 17b of the stator core 17 facing the cover 7 are positioned on the same plane.

[0034] Magnet 24 is fixed to inner peripheral surface 25a of rotor yoke portion 25 by, for example, adhesive, etc. This allows rotor yoke portion 25 to function as a magnetic path for magnet 24. Magnet 24 faces outer peripheral surface 17a of stator core 17 in the radial direction via a small gap. The magnets 24 are arranged at equal intervals in the circumferential direction. More specifically, the magnets 24 are arranged at the circumferential center between the leg portions 26 adjacent to each other in the circumferential direction when viewed from the axial direction.

[0035] Both axial ends 24a, 24b of the magnet 24 protrude from both axial ends 25b, 25c of the rotor yoke portion 25. Since the number of magnets 24 and the number of leg portions 26 are the same, a magnet 24 is present in each opening 23a. With this configuration, the end 24a of the magnet 24 on the cover 7 side (the bottom 27 side of the rotor core 23) is inserted into the corresponding opening 23a of the rotor core 23. In other words, the end 24a of the magnet 24 on the cover 7 side (the bottom 27 side of the rotor core 23) is interposed between adjacent leg portions 26 in the circumferential direction.

[0036] Here, when the distance between end 24a of magnet 24 on the cover 7 side (bottom 27 side of rotor core 23) and end 25b of rotor yoke portion 25 on the cover 7 side is defined as E, and the distance between end 24b of magnet 24 on the case main body 6 side and end 25c of rotor yoke portion 25 on the bottom 6b side of case main body 6 is defined as F, distances E and F are expressed as follows: E>F (1) Meet the following.

[0037] When the distance between the inner peripheral surface 24c of the magnet 24 and the outer peripheral surface 17a of the stator core 17 is A, and the distance between the circumferential side surface 24d of the magnet 24 as viewed from the axial direction and the circumferential side surface 26b of the leg portion 26 is B, the distance A and the distance B are expressed as follows: A Meet the following.

[0038] When viewed from the axial direction, the distance between the inner peripheral surface 24c of the magnet 24 and the outer peripheral edge 27a of the bottom portion 27 is defined as C, and the shortest distance between the end portion 24a of the magnet 24 on the cover 7 side and the end face 17b of the stator core 17 on the cover 7 side is defined as D, the distances C and D are expressed as follows: D <C ···(3) Meet the following.

[0039] <Rotational position detection device> 1 and 2, the rotational position detection device 5 is provided on the inner surface 12a of the cover body 12, and faces the rotor core 23 in the axial direction. The rotational position detection device 5 includes a sensor board 31 formed of epoxy resin or the like, and a magnetic sensor 32 mounted on the sensor board 31.

[0040] A sensor board 31 is provided on the inner surface 12a of the cover body 12. The sensor board 31 is formed in an arc shape so as to follow the rotor yoke portion 25 when viewed in the axial direction. The sensor board 31 is disposed at a position overlapping with the end portion 24a of the magnet 24 when viewed in the axial direction. The sensor board 31 is electrically connected to a control unit (not shown). ​A magnetic sensor 32 is mounted on the surface of the sensor board 31 facing the magnet 24. The magnetic sensor 32 faces the end 24a of the magnet 24 in the axial direction. The magnetic sensor 32 is configured with, for example, a Hall IC or the like, and detects changes in the magnetic flux of the magnet 24.

[0041] <Electric motor operation> Next, the operation of the electric motor 1 will be described. When power from an external power source (neither of which is shown) is supplied to the coil 18 via the control unit, a magnetic flux linkage is generated in each tooth 20 of the stator 3. A magnetic attractive force or a repulsive force is generated between this magnetic flux linkage and the magnet 24 of the outer rotor 4, causing the outer rotor 4 to rotate. As the outer rotor 4 rotates, a change in the magnetic flux of the magnet 24 is detected by the magnetic sensor 32. This detection result is output as a signal to a control unit (not shown). The control unit calculates the rotational position of the outer rotor 4 based on the output signal from the rotational position detection device 5. In this way, by controlling the timing of energizing the coil 18, the outer rotor 4 is allowed to rotate continuously.

[0042] In this way, rotor core 23 is configured with rotor yoke portion 25, multiple legs 26, and bottom portion 27, thereby forming opening 23a in rotor core 23. End 24a of magnet 24 is inserted into opening 23a, thereby making it possible to arrange rotational position detection device 5 on the cover 7 side (bottom 27 side of rotor core 23).

[0043] Here, both axial ends 24a, 24b of the magnet 24 protrude from both axial ends 25b, 25c of the rotor yoke portion 25. In other words, both axial ends 24a, 24b of the magnet 24 protrude axially outward from both axial ends of the teeth 20 of the stator 3. This increases the amount of effective magnetic flux in the outer rotor 4. As a result, the interlinkage magnetic flux formed in the stator 3 can efficiently contribute to the rotational force of the outer rotor 4, and the electric motor 1 can produce high torque.

[0044] As mentioned above, rotor yoke portion 25 functions as a magnetic path for magnet 24. Therefore, it is ideal that the axial length of rotor yoke portion 25 is equal to the axial length of magnet 24.

[0045] Figure 5 is a graph comparing the amount of effective magnetic flux [μWb] of magnet 24 when the entire outer surface of magnet 24 is covered by rotor yoke portion 25 (hereinafter referred to as with a back yoke) and when, as in this embodiment, both axial ends 24a, 24b of magnet 24 protrude from both axial ends 25b, 25c of rotor yoke portion 25 (hereinafter referred to as without a back yoke). As shown in FIG. 5, it can be seen that the amount of effective magnetic flux of the magnet 24 is greater when there is a back yoke than when there is no back yoke.

[0046] However, in this embodiment, the back yoke is intentionally omitted, and the rotational position detector 5 is arranged on the bottom portion 27 side of the rotor core 23 . When the rotational position detector 5 is disposed on the bottom 27 side of the rotor core 23, the distance E between the end 24a of the magnet 24 facing the cover 7 and the end 25b of the rotor yoke 25 facing the cover 7, and the distance F between the end 24b of the magnet 24 facing the case body 6 and the end 25c of the rotor yoke 25 facing the bottom 6b of the case body 6 are set to satisfy the above formula (1). This allows the end 24a of the magnet 24 to be as close as possible to the magnetic sensor 32. This improves the accuracy of the detection results obtained by the rotational position detector 5.

[0047] To address the reduction in the amount of effective magnetic flux of the magnet 24 due to the absence of a back yoke, the distance A between the inner peripheral surface 24c of the magnet 24 and the outer peripheral surface 17a of the stator core 17, and the distance B between the circumferential side surface 24d of the magnet 24 and the circumferential side surface 26b of the leg portion 26 as viewed in the axial direction, satisfy the above formula (2). Therefore, even when the end portion 24a of the magnet 24 is inserted into the opening portion 23a of the rotor core 23, leakage of the magnetic flux of the magnet 24 to the leg portion 26 is suppressed. In other words, by satisfying the above formula (2), the magnetic flux of the magnet 24 actively flows toward the teeth 20. This increases the amount of effective magnetic flux of the magnet 24.

[0048] FIG. 6 is a graph showing the change in the effective magnetic flux of the magnet 24, with the vertical axis representing the amount of effective magnetic flux [μWb] of the magnet 24 and the horizontal axis representing the distance B. As shown in Figure 6, it is desirable to set distance B to around 0.6 mm. This is because it is possible to ensure a sufficient amount of effective magnetic flux of magnet 24 while also ensuring the rigidity of leg 26. If distance B is 1.4 mm or more, it becomes almost impossible to detect any change in the effective magnetic flux of magnet 24. For this reason, setting distance B to 1.4 mm or more is undesirable from the perspective of the effective magnetic flux of magnet 24 and the rigidity of rotor core 23.

[0049] Furthermore, the distance C between the inner peripheral surface 24c of the magnet 24 and the outer peripheral edge 27a of the bottom portion 27 as viewed in the axial direction, and the shortest distance D between the end portion 24a of the magnet 24 on the cover 7 side and the end face 17b of the stator core 17 on the cover 7 side, satisfy the above formula (3). Therefore, even when the end portion 24a of the magnet 24 is inserted into the opening portion 23a of the rotor core 23, leakage of the magnetic flux of the magnet 24 to the bottom portion 27 is suppressed. In other words, by satisfying the above formula (3), the magnetic flux of the magnet 24 actively flows toward the teeth 20. This increases the amount of effective magnetic flux of the magnet 24.

[0050] FIG. 7 is a graph showing the change in the effective magnetic flux of the magnet 24, with the vertical axis representing the amount of effective magnetic flux [μWb] of the magnet 24 and the horizontal axis representing the distance D. As shown in Fig. 7, it is desirable to set the distance D to around 4 mm. This is because this allows the rigidity of the legs 26 to be secured while ensuring a sufficient amount of effective magnetic flux of the magnet 24. If the distance D is 5 mm or more, it becomes almost impossible to detect any change in the effective magnetic flux of the magnet 24. For this reason, setting the distance D to 5 mm or more is undesirable from the perspective of the effective magnetic flux of the magnet 24 and the rigidity of the rotor core 23.

[0051] As described above, in the embodiment described above, the end 24a of the magnet 24 on the cover 7 side protrudes from the end 25b of the rotor yoke portion 25 on the cover 7 side. The end 24a of the magnet 24 is inserted into the opening 23a of the rotor core 23. In other words, the end 24a of the magnet 24 is interposed between the leg portions 26 adjacent to each other in the circumferential direction. Therefore, the end 24a of the magnet 24 can protrude toward the bottom portion 27 of the rotor core 23.

[0052] As a result, the magnet 24 and the magnetic sensor 32 can be arranged to face each other in the axial direction not only on the opening 23a side of the rotor core 23, but also on the bottom 27 side of the rotor core 23. Therefore, it is possible to provide an electric motor 1 that allows for greater freedom in the placement of the magnetic sensor 32.

[0053] Furthermore, the legs 26 of the rotor core 23 protrude from the inner peripheral surface 25a of the rotor yoke portion 25. Therefore, the position of the legs 26 can be offset radially inward compared to when the legs 26 protrude from the end 25b of the rotor yoke portion 25. As a result, it is easier to make the end 24a of the magnet 24 protrude more than the legs 26. This allows the magnetic sensor 32 to be disposed closer to the end 24a of the magnet 24. Therefore, the accuracy with which the magnetic sensor 32 detects the magnetic flux of the magnet 24 can be improved.

[0054] Furthermore, leg portion 26 extends in an arc shape radially inward from inner circumferential surface 25a of rotor yoke portion 25 toward cover body 12 of cover 7. Because leg portion 26 is arc-shaped, end portion 24a of magnet 24 can be made to protrude further than leg portion 26.

[0055] The distance A between the inner peripheral surface 24c of the magnet 24 and the outer peripheral surface 17a of the stator core 17, and the distance B between the circumferential side surface 24d of the magnet 24 and the circumferential side surface 26b of the leg portion 26 as viewed in the axial direction, satisfy the above formula (2). Therefore, even when the end portion 24a of the magnet 24 is inserted into the opening portion 23a of the rotor core 23, leakage of the magnetic flux of the magnet 24 to the leg portion 26 can be suppressed.

[0056] As a result, the amount of effective magnetic flux of the magnet 24 is increased, and the magnetic flux of the magnet 24 can be made to contribute as much as possible to the rotational torque of the outer rotor 4. Therefore, even if the end 24a of the magnet 24 protrudes toward the bottom 27 of the rotor core 23, it is possible to prevent the motor characteristics of the electric motor 1 from being reduced.

[0057] Distance C between inner peripheral surface 24c of magnet 24 and outer peripheral edge 27a of bottom portion 27 as viewed in the axial direction, and minimum distance D between end portion 24a of magnet 24 on the cover 7 side and end face 17b of stator core 17 on the cover 7 side, satisfy formula (3) above. Therefore, leakage of magnetic flux from magnet 24 to bottom portion 27 can be suppressed while end portion 24a of magnet 24 is inserted into opening 23a of rotor core 23.

[0058] As a result, the amount of effective magnetic flux of the magnet 24 is increased, and the magnetic flux of the magnet 24 can be made to contribute as much as possible to the rotational torque of the outer rotor 4. Therefore, even if the end 24a of the magnet 24 protrudes toward the bottom 27 of the rotor core 23, it is possible to further prevent the motor characteristics of the electric motor 1 from being reduced.

[0059] In the electric motor 1 described above, the magnetic sensor 32 is disposed axially outward of the bottom 27 of the rotor core 23. Even in this configuration, the magnet 24 and the magnetic sensor 32 can be disposed axially opposite each other to detect the rotational position of the outer rotor 4.

[0060] Since it is possible to increase the degree of freedom in the placement of the rotational position detection device 5 of the electric motor 1, it will be possible to contribute to Goal 7 of the Sustainable Development Goals (SDGs) led by the United Nations, which is to "Ensure access to affordable, reliable, sustainable and modern energy for all," and Goal 9, which is to "Build resilient infrastructure, promote inclusive and sustainable industrialization and foster innovation."

[0061] [Variations] The present invention is not limited to the above-described embodiment, and includes various modifications to the above-described embodiment without departing from the spirit of the present invention. For example, in the above embodiment, the motor case 2 is described as including a cylindrical case body 6 with a bottom and a cover 7 that closes the opening 6a of the case body 6. However, this is not limited to this, and the motor case 2 may have any shape as long as it can accommodate the stator 3, outer rotor 4, and rotational position detection device 5.

[0062] In the above embodiment, the case where end 24b of magnet 24 on the case body 6 side protrudes from end 25c of rotor yoke portion 25 on the bottom 6b side of case body 6 has been described. However, this is not limited to this, and end 24b of magnet 24 does not have to protrude from end 25c of rotor yoke portion 25. It is sufficient that at least end 24a of magnet 24 on the cover 7 side protrudes from end 25b of rotor yoke portion 25 on the cover 7 side.

[0063] In the above embodiment, the case where the number of magnets 24 and the number of legs 26 are the same has been described. The case where a magnet 24 is provided for each opening 23a has been described. The case where the end 24a of the magnet 24 on the cover 7 side (the bottom 27 side of the rotor core 23) is inserted into the corresponding opening 23a of the rotor core 23 has been described. However, this is not limited to this, and the number of magnets 24 and legs 26 does not have to be the same. It is sufficient that the end 24a of the magnet 24 on the cover 7 side (the bottom 27 side of the rotor core 23) is interposed between adjacent legs 26 in the circumferential direction.

[0064] FIG. 8 is a perspective view of the outer rotor 4 in a modified example of the embodiment. In the above embodiment, the distance A between the inner peripheral surface 24c of the magnet 24 and the outer peripheral surface 17a of the stator core 17, and the distance B between the circumferential side surface 24d of the magnet 24 and the circumferential side surface 26b of the leg portion 26 as viewed in the axial direction, have been described as satisfying the above formula (2). The distance C between the inner peripheral surface 24c of the magnet 24 and the outer peripheral edge 27a of the bottom portion 27 as viewed in the axial direction, and the shortest distance D between the end portion 24a of the magnet 24 on the cover 7 side and the end face 17b of the stator core 17 on the cover 7 side have been described as satisfying the above formula (3). In other words, the case has been described where a gap is formed between the opening 23a formed in the rotor core 23 and the magnet 24.

[0065] However, the present invention is not limited to this, and the shape of the opening 23a of the rotor core 23 may be formed to correspond to the shape of the magnet 24, as shown in Fig. 8. The magnet 24 may then be inserted into the opening 23a without any gaps. Even in this configuration, the electric motor 1 can detect the rotational position of the outer rotor 4 by arranging the magnet 24 and the magnetic sensor 32 axially opposite each other on the bottom 27 side of the rotor core 23. [Explanation of symbols]

[0066] 1...electric motor, 2...motor case, 3...stator, 4...outer rotor, 5...rotational position detection device, 6...case body, 6a...opening, 6b...bottom, 7...cover, 8...stator base, 9...first shaft insertion hole, 10...first bearing accommodating recess, 11...first bearing, 12...cover body, 12a...inner surface, 13...fitting portion, 14...second shaft insertion hole, 15...second bearing accommodating recess, 16...second bearing, 17...stator core, 17a...outer peripheral surface, 17b...end face (axial end face of stator), 18...coil, 19...core A main body, 20... teeth, 20a... end face, 21... bolt insertion hole, 22... rotor shaft, 23... rotor core, 23a... opening, 24... magnet, 24a... end, 24b... end, 24c... inner circumferential surface, 24d... circumferential side surface, 25... rotor yoke portion, 25a... inner circumferential surface, 25b... end (one axial end of rotor yoke portion), 25c... end, 26... leg portion, 26a... arc portion, 26b... circumferential side surface, 27... bottom, 27a... outer circumferential edge, 27b... through hole, 30... bolt, 31... sensor board, 32... magnetic sensor

Claims

1. a stator wound with a coil; an outer rotor covering the stator; a cylindrical case body having a bottom to which the stator is fixed; a cover that closes the opening of the case body; a sensor substrate provided on the inner surface of the cover; Equipped with The outer rotor is a cylindrical rotor yoke portion that faces the outer peripheral surface of the stator in the radial direction; a plurality of legs protruding axially outward from one axial end of the rotor yoke; a bottom portion joined to an end of each of the plurality of legs opposite to the rotor yoke portion and facing an axial end surface of the stator in the axial direction; a plurality of magnets fixed to the inner peripheral surface of the rotor yoke; Equipped with the sensor substrate includes a magnetic sensor that detects the magnetic flux of the magnet; the magnetic sensor is disposed axially outward of the bottom portion of the outer rotor and axially opposed to an end portion of the magnet on the cover side, Each of the plurality of magnets protrudes from both axial ends of the rotor yoke portion and is interposed between the leg portions adjacent to each other in the circumferential direction. An electric motor characterized by:

2. The plurality of legs protrude from the inner peripheral surface of the rotor yoke.

2. The electric motor according to claim 1.

3. When the distance between the inner peripheral surface of the magnet and the outer peripheral surface of the stator is A, and the distance between the circumferential side surface of the magnet and the circumferential side surface of the leg portion as viewed from the axial direction is B, the distance A and the distance B are expressed as follows: A < B fulfill 3. The electric motor according to claim 1 or 2.

4. When the distance between the inner peripheral surface of the magnet and the outer peripheral edge of the bottom as viewed in the axial direction is defined as C, and the shortest distance between the end of the magnet on the bottom side and the axial end of the stator on the bottom side is defined as D, the distances C and D are expressed as follows: D<C fulfill 3. The electric motor according to claim 1 or 2.

5. When the distance between the cover-side end of the magnet and the cover-side end of the rotor yoke is E, and the distance between the case body-side end of the magnet and the bottom-side end of the rotor yoke of the case body is F, the distances E and F are E>F fulfill 3. The electric motor according to claim 1 or 2.

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