Brushless motor

Abstract

A rotor (40) has a rotor core (41) and a plurality of rotor magnets (48) which constitute a plurality of magnetic poles having polarities alternated in the circumferential direction of the rotor core (41). The rotor (40) rotates about a shaft (14) by means of a rotating magnetic field generated through energization to a coil (26). One or more magnetic sensors (31, 32) are provided to a substrate (33) fixed to a stator (20) at a position away from the end surface of the rotor core (41) in the axial direction of the rotor (40), and detect the rotation angle of the rotor (40) on the basis of a change in magnetism of the rotor magnets (48). Magnetic induction members (501-508) each have a bottom part (52) that abuts against the end surface of the rotor core (41), and an axial extension part (55p, 55c) erected from the bottom part (52) toward the magnetic sensor (31). The magnetic induction members (55p, 55c) induce the magnetism of the rotor magnet (48) to the magnetic sensors (31, 32).

Description

Brushless motor CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application is based on Japanese Application No. 2023-208784 filed on December 11, 2023, the contents of which are incorporated herein by reference.

[0002] The present disclosure relates to brushless motors.

[0003] Conventionally, brushless motors have been known that use a magnetic sensor to detect magnetic changes in a rotor magnet that occur as the motor rotates, thereby detecting the rotation angle. For example, the brushless motor disclosed in Patent Document 1 includes a rod-shaped magnetic induction member that extends from the rotor magnet side to the magnetic sensor side and induces magnetism generated by the rotor magnet to the magnetic sensor mounted on a circuit board.

[0004] Japanese Patent Application Laid-Open No. 2017-143727

[0005] In the brushless motor of Patent Document 1, a rod-shaped magnetic induction member is arranged so as to overlap the stator coil in the radial direction of the rotor. As a result, the induced magnetism is affected by the magnetic field generated when the coil is energized, resulting in a problem of reduced rotation angle detection accuracy. In addition, a separate member is required to support the magnetic induction member, increasing the number of parts and costs.

[0006] An object of the present disclosure is to provide a brushless motor in which the accuracy of rotation angle detection by a magnetic sensor is improved and a member for supporting a magnetic induction member is not required.

[0007] A brushless motor according to the present disclosure includes a stator, a rotor, one or more magnetic sensors, and a magnetic induction member. The stator has a plurality of circumferentially arranged teeth on which coils are wound, and slots are formed between adjacent teeth.

[0008] The rotor includes a rotor core and a plurality of rotor magnets that form a plurality of magnetic poles with alternating polarities in the circumferential direction of the rotor core. The rotor rotates around the shaft due to a rotating magnetic field generated by energizing a coil.

[0009] The magnetic sensor is mounted on a substrate fixed to the stator at a position axially spaced from the end face of the rotor core, and detects the rotation angle of the rotor based on changes in the magnetism of the rotor magnet.

[0010] The magnetic induction member has a bottom portion that abuts against the end face of the rotor core and an axial extension portion that stands from the bottom portion toward the magnetic sensor. The magnetic induction member induces the magnetism of the rotor magnet to the magnetic sensor.

[0011] In this disclosure, the axial extension of the magnetic induction member is positioned away from the stator in the radial direction of the rotor, making it less susceptible to the magnetic field generated when the coil is energized. This improves the accuracy of rotation angle detection by the magnetic sensor. Furthermore, because the bottom of the magnetic induction member is fixed in contact with the end face of the rotor core, a separate member for supporting the magnetic induction member is not required, reducing the number of parts and costs.

[0012] The above and other objects, features, and advantages of the present disclosure will become more apparent from the following detailed description taken in conjunction with the accompanying drawings, in which Fig. 1 is an overall axial cross-sectional view of a brushless motor according to a first embodiment, Fig. 2 is a schematic plan view taken along line II-II of Fig. 1 (within a mechanical angle range of 360°), Fig. 3 is a schematic plan view enlarging section III of Fig. 2 (within a mechanical angle range of 90°), Fig. 4 is a circumferential development view as viewed from the direction of IV of Fig. 3, Fig. 5 is a diagram showing a magnetic sensor in Fig. 3, Fig. 6 is a schematic axial cross-sectional view taken along line VI-VI of Fig. 5, Fig. 7 is a schematic axial cross-sectional view of a brushless motor according to a comparative example, Fig. 8 is a schematic plan view of a brushless motor according to a second embodiment, and Fig. 9 is a schematic plan view of a brushless motor according to a third embodiment. FIG. 10 is a schematic plan view of a brushless motor of a fourth embodiment, showing a magnetic sensor; FIG. 11 is a schematic axial cross-sectional view taken along line XI-XI in FIG. 10; FIG. 12 is a schematic plan view of a brushless motor of a fifth embodiment; FIG. 13 is a circumferential development as viewed from line XIII in FIG. 12; FIG. 14 is a schematic axial cross-sectional view of a brushless motor of a sixth embodiment; FIG. 15 is a schematic axial cross-sectional view of another embodiment (1); and FIG. 16 is a schematic axial cross-sectional view of another embodiment (2).

[0013] Several embodiments of a brushless motor will be described with reference to the drawings. The following first to sixth embodiments will be collectively referred to as "the present embodiments." The brushless motor of the present embodiments is applied to vehicle accessories, etc., and the rotation angle is detected by a magnetic sensor.

[0014] First Embodiment The configuration and effects of a brushless motor 101 according to a first embodiment will be described with reference to FIGS. 1 to 6. First, the overall configuration of the brushless motor 101 will be described with reference to FIGS. 1 and 2. FIG. 1 shows an axial cross section of the brushless motor 101. With the upper side of the paper in FIG. 1 being the top, only the upper part of the axial cross section is shown in FIG. 1, and the lower part is omitted. FIG. 2 corresponds to the cross section of FIG. 1, but in this specification, the following figures similar to FIGS. 2 and 3 will be considered to be plan views of the end faces of the rotor 40 as seen from above, and will be referred to as "schematic plan views."

[0015] Brushless motor 101 is an inner rotor motor that includes a stator 20 and a rotor 40 that rotates around a shaft 14 radially inside stator 20. The outer shell of brushless motor 101 is composed of an upper plate 11 and a cylindrical case 12. A bearing 13 fixed to upper plate 11 rotatably supports an upper portion of shaft 14. The lower portion of shaft 14 is rotatably supported by another bearing (not shown).

[0016] The stator 20 and the rotor 40 are arranged coaxially with respect to the rotation axis O of the shaft 14. The outer wall of the stator 20 is fixed to the inner wall of the case 12. The rotor 40 is fixed to the shaft 14 and rotates integrally with the shaft 14. A substrate 33 on which elements for controlling the drive of the brushless motor 101 are mounted is fixed to, for example, the lower surface of the upper plate 11. Therefore, the substrate 33 is indirectly fixed to the stator 20.

[0017] The stator core 21 of the stator 20 has an annular back yoke 23 and a plurality of teeth 24 arranged circumferentially and protruding radially inward from the back yoke 23. The stator core 21 is formed, for example, by laminating thin magnetic steel plates. The stator 20 is formed by winding coils 26 around the plurality of teeth 24. Slots 25 are formed between adjacent teeth 24.

[0018] The stator 20 of this embodiment has 12 teeth 24, with 12 slots 25 formed between each tooth. Three-phase current is passed through the coils 26 of the stator 20. That is, four sets of three teeth 24, each with a three-phase winding of U-phase, V-phase, and W-phase wound therearound, are provided circumferentially.

[0019] The rotor 40 includes a rotor core 41 and a plurality of rotor magnets 48 that form a plurality of magnetic poles with alternating polarities in the circumferential direction of the rotor core 41. The rotor core 41 is formed, for example, by laminating thin magnetic steel plates. An air gap δ is provided between the outer wall of the rotor core 41 and the inner walls of the tips of the teeth 24. The rotor 40 rotates around the shaft 14 due to a rotating magnetic field generated by energizing the coils 26.

[0020] More specifically, the rotor 40 has an IPM structure in which rectangular parallelepiped rotor magnets 48 are embedded in rectangular holes in the rotor core 41. Salient pole portions 44 are formed between adjacent rotor magnets 48 in the circumferential direction. The rotor 40 of this embodiment has eight rotor magnets 48. In other words, the brushless motor 101 exemplified in this embodiment is an "8-pole (4-pole pairs) 12-slot" IPM motor.

[0021] Brushless motor 101 also includes one or more magnetic sensors 31 provided on substrate 33. Fig. 1 shows a first magnetic sensor 31. However, as will be described later with reference to Fig. 5, this embodiment basically includes two magnetic sensors 31 and 32. Substrate 33 is fixed to stator 20 at a position spaced apart from the end face of rotor core 41 in the axial direction of rotor 40. Magnetic sensors 31 and 32 detect the rotation angle of rotor 40 based on changes in magnetism of rotor magnet 48.

[0022] More specifically, each of the magnetic sensors 31, 32 outputs a sensor signal, for each pair of magnetic poles, having a fundamental wave of one cycle of a sine wave, to a signal processing device such as a microcomputer. The signal processing device calculates the rotation angle of the rotor 40 based on the sensor signals from the magnetic sensors 31, 32. However, if the magnetic sensors 31, 32 cannot adequately detect the magnetism of the rotor magnet 48, the accuracy of rotation angle detection will decrease. Therefore, the brushless motor 101 includes a magnetic induction member 501 that induces the magnetism of the rotor magnet 48 to the magnetic sensors 31, 32.

[0023] However, in the conventional configuration in which a rod-shaped magnetic induction member is arranged radially around the rotor and overlaps the stator coil, there are problems such as the induced magnetism being affected by the magnetic field generated when the coil is energized, reducing the accuracy of rotation angle detection, and the need for a separate member to support the magnetic induction member, which increases the number of parts and costs.

[0024] Therefore, in this embodiment, the rotation angle detection accuracy is improved by configuring the magnetic sensors 31, 32 so that they are less susceptible to the influence of the magnetic field generated when the coil 26 is energized. Also, the number of parts and costs are reduced by eliminating the need for a member to support the magnetic induction member 501. To achieve this, the magnetic induction member 501 has a bottom portion 52 and an axial extension portion 55p.

[0025] Next, the detailed configuration and effects of the magnetic induction member 501 will be described with reference to Figures 3 to 6. Figure 3 shows a schematic plan view of a range of 90° mechanical angle, corresponding to part III in Figure 2. The format of Figure 3 is used in the second to sixth embodiments. Figure 4 shows a circumferential development view as viewed from part IV in Figure 3.

[0026] The magnetic induction member 501 has a bottom 52 that abuts against the end face 42 of the rotor core 41, and an axial extension 55p that stands from the bottom 52 toward the magnetic sensors 31, 32. A portion of the magnetic field of the rotor magnet 48 propagates directly through the air toward the magnetic sensors 31, 32, and another portion is guided by the axial extension 55p and propagates from the tip of the axial extension 55p to the magnetic sensors 31, 32.

[0027] The bottom portion 52 and the axial extension portion 55p are formed integrally by, for example, press working using a material such as magnetic steel plate. A hole having an inner diameter that fits tightly to the outer diameter of the shaft 14 is formed in the center of the bottom portion 52. The shaft 14 is press-fitted into the center hole of the bottom portion 52, thereby fixing the magnetic induction member 501 to the rotor core 41. Note that in other embodiments, the magnetic induction member 501 may be fixed to the rotor core 41 not only by press-fitting into the shaft 14, but also by caulking the end face 42 of the rotor core 41.

[0028] In this embodiment, the axial extension 55p of the magnetic induction member 501 is positioned away from the stator 20 in the radial direction of the rotor 40, and is therefore less susceptible to the magnetic field generated when current is applied to the coil 26. This improves the accuracy of rotation angle detection by the magnetic sensors 31, 32. Furthermore, because the bottom 52 of the magnetic induction member 501 is fixed in contact with the end face 42 of the rotor core 41, a separate member for supporting the magnetic induction member is not required, thereby reducing the number of parts and costs.

[0029] The axial extension portion 55p of the magnetic induction member 501 is formed in the shape of a polygonal prism having the same number of side surfaces as the rotor magnets 48. The polygonal prism-shaped axial extension portion 55p is easy to manufacture by press working or the like. In the rotor 40 of this embodiment, which has eight rotor magnets 48, the axial extension portion 55p is formed in the shape of an octagonal prism. The axial extension portion 55p is essentially formed in the shape of a regular octagonal prism with equal side lengths and a central angle of 45°. The flat plate portion forming one side surface of the octagonal prism of the axial extension portion 55p is referred to as the "unit plate of the axial extension portion 55p." Each unit plate of the axial extension portion 55p is arranged along the long side of the end face of the rotor magnet 48.

[0030] In the bottom portion 52, a plurality of inter-pole slits 54 are formed between circumferentially adjacent rotor magnets 48. In addition, in the axial extension portion 55p, a plurality of inter-pole slits 56 are formed between circumferentially adjacent rotor magnets 48. By forming the inter-pole slits 56 from the upper end to the lower end of the axial extension portion 55p, the unit plates are arranged separated from each other. The inter-pole slits 54, 56 are formed along radial lines centered on the rotation axis O. This reduces leakage magnetic flux between circumferentially adjacent magnetic poles of opposite polarity, allowing more magnetism to be guided to the magnetic sensors 31, 32. This improves the accuracy of rotation angle detection.

[0031] In other embodiments, it is sufficient to form at least one of the inter-pole slits 54 in the bottom portion 52 and the inter-pole slits 56 in the axial extension portion 55p. By reducing the leakage magnetic flux between the magnetic poles in at least one of the bottom portion 52 and the axial extension portion 55p, more or less magnetism can be guided to the magnetic sensors 31, 32.

[0032] Furthermore, in the first embodiment, the inter-pole slits 54 of the bottom portion 52 have a constant width radially inward from the bending point F, and form widened portions 54w radially outward from the bending point F, the width of which increases with increasing distance from the rotation axis O. The minimum width of the inter-pole slits 54 is greater than the air gap δ between the rotor core 41 and the teeth 24. The inner wall of the widened portions 54w is parallel to the short sides of the rotor magnet 48. In an eight-pole configuration, the widened portions 54w widen at an angle of 22.5° on one side and 45° on both sides with respect to the center line M.

[0033] The circumferential width W1 of the unit plate of the axially extending portion 55p is equal to the length a of the long side of the rotor magnet 48 plus a margin d×2 at both ends (W1=a+d×2). Because the circumferential width of the unit plate of the axially extending portion 55p is shorter than in the second embodiment described below, the radial position of the axially extending portion 55p can be brought closer to the outer diameter of the rotor core 41, increasing the degree of freedom in design.

[0034] Additionally, a plurality of magnet slits 53 are formed in the bottom 52 in a portion that overlaps the end face of the rotor magnet 48. The end face of the rotor magnet 48 is exposed through the magnet slits 53. This reduces leakage magnetic flux in the magnetic induction member 501, allowing more magnetism to be induced to the magnetic sensors 31 and 32. This improves the accuracy of rotation angle detection.

[0035] For convenience of illustration, the dashed lines representing the outline (hidden lines) of the rotor magnet 48 and the solid lines representing the outline of the magnet slits 53 are drawn slightly offset from each other. In practice, it is preferable that the outline of the magnet slits 53 be formed in the same shape as the outline of the rotor magnet 48 so that it matches the outline of the rotor magnet 48. However, the magnet slits 53 may be formed not necessarily over the entire portion overlapping the end face of the rotor magnet 48, but over at least a portion of the portion overlapping the end face of the rotor magnet 48. The dashed lines drawn at both ends of the rotor magnet 48 in the longitudinal direction represent gaps that provide relief for the rectangular holes.

[0036] Next, the arrangement of the magnetic sensors 31 and 32 mounted on the substrate 33 will be described with reference to Figures 5 and 6. In Figure 5, the first magnetic sensor 31 and the second magnetic sensor 32 are shown schematically as circles, but do not represent their actual shapes. Using the first magnetic sensor 31 as a reference, the second magnetic sensor 32 is arranged either at the position indicated by the solid line or at the position indicated by the dashed line.

[0037] Here, an imaginary plane including the center of the slot 25 in the circumferential direction of the stator 20 is defined as a slot center plane Ssc. Furthermore, an imaginary plane passing through the center of the rotor magnet 48 in the circumferential direction of the rotor 40 (hereinafter referred to as the "rotor circumferential direction") is defined as a rotor magnet center plane Smc. In an 8-pole, 12-slot configuration, slot center planes Ssc appear every 30° of mechanical angle, and rotor magnet center planes Smc appear every 45° of mechanical angle. In the rotor rotation position shown in FIG. 5, some of the slot center planes Ssc and some of the rotor magnet center planes Smc coincide with each other.

[0038] The first magnetic sensor 31 and the second magnetic sensor 32 are disposed on both sides of the slot center plane Ssc in the circumferential direction of the stator 20. Preferably, the circumferential centers of the magnetic sensors 31 and 32 are disposed on the slot center plane Ssc. This increases the circumferential distance between the magnetic sensors 31 and 32 and the coil 26, thereby reducing the distortion of the magnetic field induced in the magnetic sensors 31 and 32 and improving the accuracy of rotation angle detection.

[0039] Regarding the relative arrangement of the magnetic sensors 31 and 32, the second magnetic sensor 32 is arranged at a position of 120° electrical angle relative to the first magnetic sensor 31. When the number of magnetic poles is 8, i.e., the number of pole pairs is 4, a mechanical angle of 90° (= 360° / 4) corresponds to an electrical angle of 360°, and an electrical angle of 120° corresponds to a mechanical angle of 30°. The positive and negative directions of the electrical angle are defined arbitrarily, and the second magnetic sensor 32 may be arranged on either the clockwise or counterclockwise side of the first magnetic sensor 31. The second magnetic sensor 32 may also be arranged at a position of 240° electrical angle, i.e., 60° mechanical angle, relative to the first magnetic sensor 31.

[0040] In a brushless motor in which a three-phase current flows through the coil 26, a 3n-th harmonic component (n is an integer) is superimposed on the fundamental wave of the sensor signals from the magnetic sensors 31 and 32. Therefore, the 3n-th harmonic component can be canceled by taking the difference between the sensor signals from the two magnetic sensors 31 and 32, which are shifted in phase by an electrical angle of 120° or 240°. Furthermore, even if noise is introduced into the signal line from the magnetic sensors 31 and 32 to the signal processing device, line noise can be reduced by taking the difference between the two sensor signals.

[0041] 6 shows a schematic axial cross section at the rotor magnet center plane Smc. The following schematic axial cross section shows the first magnetic sensor 31, which will be referred to as the "magnetic sensor 31" in the description of the specification. However, because the magnetic sensors 31 and 32 are arranged on the same circumference centered on the rotation axis O, the same applies to the second magnetic sensor 32.

[0042] At the rotor magnet center plane Smc, the axial extension 55p is closest to the rotation axis O. At this position, the center Cs of the magnetic sensor 31 is disposed on the "opposite side from the stator 20" in the radial direction of the rotor 40 (hereinafter referred to as the "rotor radial direction") with respect to the position Ex of the axial extension 55p of the magnetic induction member 501. In an inner rotor motor, the center Cs of the magnetic sensor 31 is disposed radially inward with respect to the position Ex of the axial extension 55p.

[0043] By positioning the magnetic sensor 31 away from the coil 26, the magnetic sensor 31 is less susceptible to the influence of the magnetic field generated when the coil 26 is energized. This reduces the distortion of the magnetic field induced in the magnetic sensor 31, improving the accuracy of rotation angle detection. Note that if the magnetic sensor 31 is positioned too far inward in the radial direction, it will be unable to detect the magnetic field from the axial extension portion 55p. Therefore, it is preferable to position the magnetic sensor 31 in an optimal position where it can detect the magnetic field with as little influence as possible from the coil 26.

[0044] As described above, the brushless motor 101 of the first embodiment is provided with a magnetic induction member 501 that induces the magnetic field of the rotor magnet 48 to the magnetic sensors 31 and 32, thereby reducing the influence of magnetic distortion caused by the magnetic field of the coil 26 and improving the accuracy of rotation angle detection.

[0045] Furthermore, since the magnetic induction member 501 has the axial extension 55p, the degree of freedom in the axial position of the magnetic sensors 31, 32 is improved, making it possible to use a surface-mounted magnetic sensor. Figure 7 shows a magnetic sensor mounting structure for a brushless motor 109 of a comparative example that does not use a magnetic induction member. In this comparative example, the magnetic sensor 39 is inserted and mounted on the substrate 33 via a holder 38, which is a support member. This increases the number of parts in the holder 38, increases assembly labor, and causes variation in the mounting position of the magnetic sensor 39.

[0046] In contrast to the comparative example, the first embodiment uses a surface-mounted magnetic sensor, which reduces the number of components and costs, facilitates mounting on the substrate 33, and reduces variations in the mounting positions of the magnetic sensors 31 and 32. Therefore, the first embodiment is superior in terms of rotation angle detection accuracy and cost.

[0047] Next, several embodiments that differ from the first embodiment in terms of the shape of the magnetic induction member, the arrangement of the magnetic sensor, etc. will be described, focusing mainly on the differences from the first embodiment. The reference numerals for the brushless motors of each embodiment are assigned the third digit following "10," and the reference numerals for the magnetic induction members are assigned the third digit following "50," indicating the embodiment number. In several embodiments, components that are substantially the same as those in the first embodiment are assigned the same reference numerals, and descriptions thereof will be omitted.

[0048] Second Embodiment Figure 8 shows a schematic plan view of a brushless motor 102 according to a second embodiment. Unlike the first embodiment, a magnetic induction member 502 according to the second embodiment has a bottom 52 with an inter-pole slit 54 that does not have a widened portion 54w, and the inter-pole slit 54 is formed in a straight shape with a constant width. Therefore, the circumferential width W2 of the unit plate of the axially extending portion 55p according to the second embodiment is greater than the circumferential width W1 of the unit plate of the axially extending portion 55p according to the first embodiment (W2 > W1). In the second embodiment, the machining of the inter-pole slit 54 is simpler than in the first embodiment.

[0049] 9 shows a schematic plan view of a brushless motor 103 according to a third embodiment. Unlike the first embodiment, a magnetic induction member 503 according to the third embodiment does not have magnet slits 53 formed in the bottom 52. The rotor magnet 48 hidden below the bottom 52 is indicated by a dashed line. The magnetic field of the rotor magnet 48 is transmitted to the bottom 52, which is made of a magnetic material, and is induced from the bottom 52 to the magnetic sensors 31, 32 through the air or the axial extension 55p. For example, this configuration may be used when the thickness of the bottom 52 is thin and leakage magnetic flux at the bottom 52 is slight.

[0050] Fourth Embodiment FIGS. 10 and 11 show a schematic plan view and a schematic axial cross-sectional view of a brushless motor 104 according to a fourth embodiment. A magnetic induction member 504 according to the fourth embodiment includes a bottom portion 52 and a cylindrical axial extension portion 55c. Similar to FIG. 6, FIG. 11 shows a cross-section at the rotor magnet center plane Smc in the rotor circumferential direction. However, because the axial extension portion 55c is cylindrical, the position Ex of the axial extension portion 55c remains constant regardless of the rotor circumferential position. The center Cs of the magnetic sensor 31 is located on the "opposite side of the stator 20" in the rotor radial direction relative to the position Ex of the axial extension portion 55c of the magnetic induction member 504. Therefore, as with the first embodiment, the influence of the magnetic field of the coil 26 on the magnetic sensor 31 can be reduced, improving the accuracy of rotation angle detection.

[0051] 10, the magnet slit 53 is formed in the bottom 52, but the inter-pole slit 54 in the bottom 52 and the inter-pole slit 56 in the axial extension 55c are not formed. In addition to this example, variations can be set by providing or not providing the magnet slit 53 or the inter-pole slits 54, 56 in the magnetic induction member having the cylindrical axial extension 55c.

[0052] 12 and 13 show a schematic plan view and a circumferentially developed view of a brushless motor 105 according to a fifth embodiment. In contrast to the fourth embodiment, in the fifth embodiment, an inter-pole slit 54 is formed in the bottom 52 of a magnetic induction member 505, and an inter-pole slit 56 is formed in an axial extension 55 c. The inter-pole slit 56 in the axial extension 55 c is not open at its upper end, and the upper portion is connected by a connecting portion 565.

[0053] In the fifth embodiment, similarly to the first to third embodiments, the inter-pole slits 54, 56 reduce leakage magnetic flux between adjacent rotor magnets 48, allowing more magnetism to be guided to the magnetic sensors 31, 32. Furthermore, by connecting the upper portions of the inter-pole slits 56, although the effect of reducing leakage magnetic flux is somewhat sacrificed, deformation of the axial extension portions 55c during press working and assembly is suppressed, improving workability.

[0054] Sixth Embodiment Fig. 14 shows a schematic axial cross-sectional view of a brushless motor 106 according to a sixth embodiment. In contrast to the first embodiment shown in Fig. 6, in the sixth embodiment, the center Cs of the magnetic sensor 31 is located on the stator 20 side in the rotor radial direction relative to the position Ex of the axial extension 55p of the magnetic induction member 506 in the rotor magnet center plane Smc. In an inner rotor motor, the center Cs of the magnetic sensor 31 is located radially outward relative to the position Ex of the axial extension 55p. This configuration may be used, for example, when the axial distance between the coil 26 and the magnetic sensor 31 is relatively large and the magnetic sensor 31 is less susceptible to the magnetic influence of the coil 26.

[0055] (Other Embodiments) (a) Figures 15 and 16 show other embodiments of the shape of the magnetic induction member. Figures 15 and 16 show an example of a cylindrical axial extension portion 55c. Furthermore, the magnetic induction member is not limited to the illustrated form, and may be formed of a single part or may be configured by combining multiple parts.

[0056] 15 , in brushless motor 107 of another embodiment (1), magnetic induction member 507 is fixed to rotor core 41 by crimping protrusions 52c provided on bottom portion 52 into recesses 41p formed on the surface of rotor core 41. Therefore, the inner edge of bottom portion 52 does not need to abut against the outer periphery of shaft 14. Magnetic induction member 507 also has radial extensions 57 that extend radially from the upper ends of axial extensions 55c toward magnetic sensor 31.

[0057] (b) In a brushless motor 108 according to another embodiment (2) shown in Figure 16, a magnetic induction member 508 has a second axial extension 58 in addition to the axial extension 55c. The second axial extension 58 stands upright from the bottom 52 radially inside the rotor magnet 48. The magnetism of the rotor magnet 48 is induced to the magnetic sensor 31 via the two axial extensions 55c, 58. The magnetic induction member 508 is formed, for example, by welding two types of press parts each having an L-shaped axial cross section.

[0058] (c) The axial extensions 55p, 55c do not necessarily have to be arranged parallel to the shaft 14, i.e., standing vertically from the bottom 52, as shown in each axial cross-sectional view, but may be arranged at an angle to the shaft 14.

[0059] (d) In addition to the 8 poles and 12 slots illustrated in the above embodiment, the brushless motor may have any number of magnetic poles and slots. The present invention may also be applied to multi-phase motors other than three-phase motors. When it is desired to cancel k-th harmonic components other than the third harmonic superimposed on the detection signals of the magnetic sensors 31 and 32, it is preferable that the two magnetic sensors 31 and 32 be positioned at positions that are multiples of an electrical angle of (360 / k)°.

[0060] (e) In cases where superposition of 3n-th harmonic components is permitted, a configuration may be provided with only one magnetic sensor 31. Furthermore, to increase reliability against magnetic sensor failure, three or more magnetic sensors may be provided redundantly.

[0061] (f) The brushless motor of the present disclosure is not limited to inner rotor motors, but can also be applied to outer rotor motors. Regarding the positional relationship in the rotor radial direction between the center Cs of the magnetic sensor in the rotor magnet center plane Smc and the axial extensions 55p, 55c (see Figures 6, 14, etc.), in an outer rotor motor, the radially inner side corresponds to the stator side, and the radially outer side corresponds to the "opposite side from the stator."

[0062] As described above, the present disclosure is not limited to the above-described embodiments, and can be embodied in various forms without departing from the spirit of the present disclosure.

[0063] (Disclosure of Technical Ideas) This specification discloses multiple technical ideas described in the following multiple clauses. Some clauses may be described in a multiple dependent form, with the subsequent clause alternatively referring to the preceding clause. Furthermore, some clauses may be described in a multiple dependent form, with the subsequent clause referring to another multiple dependent clause. These multiple dependent clauses define multiple technical ideas.

[0064] (Technical Idea 1) A brushless motor comprising: a stator (20) in which a coil (26) is wound around a plurality of teeth (24) arranged in the circumferential direction, with slots (25) formed between adjacent teeth; a rotor (40) having a rotor core (41) and a plurality of rotor magnets (48) constituting a plurality of magnetic poles whose polarity alternates in the circumferential direction of the rotor core, the rotor (40) rotating around a shaft (14) by a rotating magnetic field generated by energizing the coils; one or more magnetic sensors (31, 32) provided on a substrate (33) fixed to the stator at a position spaced from an end face of the rotor core in the axial direction of the rotor, the magnetic sensors detecting a rotation angle of the rotor based on a change in magnetism of the rotor magnet; and magnetic induction members (501-508) having a bottom (52) abutting the end face of the rotor core and axial extensions (55p, 55c) erected from the bottom toward the magnetic sensors, the magnetic induction members inducing the magnetism of the rotor magnet to the magnetic sensors. (Technical Idea 2) The brushless motor according to Technical Idea 1, wherein the magnetic induction member has the bottom and the axial extension formed integrally. (Technical Idea 3) The brushless motor according to Technical Idea 1 or 2, wherein the magnetic induction member has a plurality of inter-pole slits (54, 56) formed between circumferentially adjacent rotor magnets in at least one of the bottom or the axial extension. (Technical Idea 4) The brushless motor according to any one of Technical Ideas 1 to 3, wherein the magnetic induction member has a plurality of magnet slits (53) formed in at least a part of the portion of the bottom that overlaps with the end face of the rotor magnet. (Technical Idea 5) The brushless motor according to any one of Technical Ideas 1 to 4, wherein the axial extension of the magnetic induction member is formed in the shape of a polygonal pillar having a number of side surfaces equal to the number of the rotor magnets.(Technical Idea 6) Defining the circumferential direction of the rotor as the rotor circumferential direction and the radial direction of the rotor as the rotor radial direction, the brushless motor according to any one of Technical Ideas 1 to 5, wherein in an imaginary plane (Smc) passing through the center of the rotor magnet in the rotor circumferential direction, the center (Cs) of the magnetic sensor is disposed on the opposite side of the axial extension of the magnetic induction member from the stator in the rotor radial direction. (Technical Idea 7) The brushless motor according to any one of Technical Ideas 1 to 6, wherein at least one of the magnetic sensors is disposed across both sides of an imaginary plane (Ssc) including the center of the slot in the circumferential direction of the stator. (Technical Idea 8) The brushless motor according to any one of Technical Ideas 1 to 7, in which a three-phase current is passed through the coils of the stator, wherein a plurality of the magnetic sensors are provided, and a second magnetic sensor (32) is disposed at an electrical angle of 120° or 240° relative to the first magnetic sensor (31).

[0065] The present disclosure has been described based on the embodiments. However, the present disclosure is not limited to the embodiments and structures. The present disclosure also encompasses various modifications and variations within the scope of equivalents. Furthermore, various combinations and forms, including only one element, more than one element, or less than one element, are also within the scope and spirit of the present disclosure.

Claims

1. A brushless motor comprising: a stator (20) in which a coil (26) is wound around a number of teeth (24) arranged in the circumferential direction, with slots (25) formed between adjacent teeth; a rotor (40) having a rotor core (41) and a number of rotor magnets (48) constituting a number of magnetic poles whose polarity alternates in the circumferential direction of the rotor core, the rotor (40) rotating about a shaft (14) by a rotating magnetic field generated by passing current through the coils; one or more magnetic sensors (31, 32) provided on a substrate (33) fixed to the stator at a position spaced from an end face of the rotor core in the axial direction of the rotor, the magnetic sensors detecting the rotation angle of the rotor based on changes in the magnetism of the rotor magnet; and a magnetic induction member (501-508) having a bottom (52) abutting the end face of the rotor core and an axial extension (55p, 55c) erected from the bottom toward the magnetic sensor, the magnetic induction member inducing the magnetism of the rotor magnet to the magnetic sensor.

2. The brushless motor according to claim 1, wherein said magnetic induction member has said bottom portion and said axial extension portion integrally formed therewith.

3. A brushless motor as described in claim 1, wherein the magnetic induction member has a plurality of interpole slits (54, 56) formed between circumferentially adjacent rotor magnets at at least one of the bottom portion or the axial extension portion.

4. A brushless motor according to claim 1, wherein said magnetic induction member has a plurality of magnet slits (53) formed in at least a portion of the bottom portion which overlaps with the end face of said rotor magnet.

5. A brushless motor according to claim 1, wherein said axial extension of said magnetic induction member is formed in the shape of a polygonal column having a number of sides equal to the number of said rotor magnets.

6. A brushless motor as claimed in any one of claims 1 to 5, wherein, when the circumferential direction of the rotor is defined as the rotor circumferential direction and the radial direction of the rotor is defined as the rotor radial direction, in an imaginary plane (Smc) passing through the center of the rotor magnet in the rotor circumferential direction, the center (Cs) of the magnetic sensor is positioned on the opposite side of the stator in the rotor radial direction with respect to the axial extension of the magnetic induction member.

7. A brushless motor according to any one of claims 1 to 5, wherein at least one of the magnetic sensors is arranged astride both sides of an imaginary plane (Ssc) including the center of the slot in the circumferential direction of the stator.

8. A brushless motor as described in any one of claims 1 to 5, in which a three-phase current is passed through the coil of the stator, a plurality of the magnetic sensors are provided, and the second magnetic sensor (32) is positioned at an electrical angle of 120° or 240° relative to the first magnetic sensor (31).

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