Rotor magnet and brushless motor

Abstract

The disclosed rotor magnet (2) is rotatably provided to a substrate (8) to which a stator (5) or a rotation angle sensor (9) is fixed, is disposed facing the stator (5) or the rotation angle sensor (9), and is formed by injection molding a mixed material of a magnetic body and a resin via a pinpoint gate (42). The rotor magnet (2) is provided with: a cylindrical part (21) which is formed in a cylindrical shape and in which a plurality of magnetic poles are arranged; and a rib (22) which is formed in a shape protruding in the radial direction at an axial end part of the cylindrical part (21). The thickness (T1) of the cylindrical portion (21) has a dimension less than the inner diameter (D0) of the tip portion of the pinpoint gate (42), and the thickness (T2) of the rib (22) has a dimension greater than or equal to the inner diameter (D0) of the tip portion of the pinpoint gate (42).

Description

[Technical Field]

[0001] The present invention relates to a rotor magnet and a brushless motor including the same. [Background technology]

[0002] Conventionally, rotors used in motors and rotary encoders have been known in which the rotor magnet is manufactured by injection molding. For example, a rotor in which a ring-shaped rotor magnet (resin-bonded magnet) is formed by injection molding a mixed material of magnetic powder and thermoplastic resin, and this is then inserted and bonded inside a cylindrical rotor yoke is known. Patent Document 1 also describes a rotor in which the rotor magnet is integrally molded inside the rotor yoke. This configuration makes it easy to reduce the weight and thickness of the rotor magnet. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2005-198447 Summary of the Invention [Problem to be solved by the invention]

[0004] On the other hand, when attempting to form a rotor magnet that is thinner than the inner diameter of the tip of the pinpoint gate through which the mixed material is injected during injection molding, the injection pressure of the mixed material (the pressure of the mixed material inside the mold) becomes high, reducing the number of rotor magnets that can be produced in one filling process. This makes it difficult to improve productivity and raises the issue of increased manufacturing costs.

[0005] One of the objects of the present invention was invented in light of the above-mentioned problems, and is to provide a rotor magnet and a brushless motor that can improve productivity and cost. However, in addition to this object, another object of the present invention is to achieve effects derived from the various configurations shown in the "Mode for Carrying Out the Invention" below, which are effects that cannot be obtained with conventional technology. [Means for solving the problem]

[0006] The disclosed rotor magnet can be realized as the following aspect 1 (application example), which solves at least part of the above-mentioned problems. The disclosed brushless motor can be realized as the following aspect 7, which solves at least part of the above-mentioned problems. Each of aspects 2 to 6 is an aspect that can be selected additionally as appropriate, and each is an aspect that can be omitted. None of aspects 2 to 6 discloses an aspect or configuration that is essential to the present invention.

[0007] Aspect 1: The disclosed rotor magnet is rotatably mounted on a substrate on which a stator or a rotation angle sensor is fixed, and is disposed opposite the stator or the rotation angle sensor, and is formed by injection molding a mixed material of a magnetic substance and a resin through a pinpoint gate. This rotor magnet has a cylindrical portion formed in a cylindrical shape and having a plurality of magnetic poles arranged thereon, and an axial end portion of the cylindrical portion. One end of In only and a rib formed to protrude in the radial direction. The thickness of the cylindrical portion is smaller than the inner diameter of the tip of the pinpoint gate, and the thickness of the rib is equal to or greater than the inner diameter of the tip of the pinpoint gate.

[0008] Aspect 2. Regarding the above aspect 1, it is preferable that the rib end face, which is the axial end face of the rib, has a trace portion that is a substantially circular bulge corresponding to the inner diameter of the tip of the pinpoint gate as a trace of injection molding of the rotor magnet. It is also preferable that the thickness of the cylindrical portion is less than the outer diameter of the trace portion, and the thickness of the rib is equal to or greater than the outer diameter of the trace portion. Aspect 3. With regard to the above aspect 2, it is preferable that the cylindrical portion end face, which is the axial end face of the cylindrical portion, has a shape that protrudes more toward the substrate in the axial direction than the rib end face, and that the step dimension between the rib end face and the cylindrical portion end face is equal to or greater than the height dimension of the trace portion.

[0009] Aspect 4. In relation to the aspect including Aspect 1 above, it is preferable that the ribs are arranged so as to avoid the boundaries between the plurality of magnetic poles when viewed in the axial direction of the rotor magnet. Aspect 5. With regard to the aspect 4, it is preferable that the rib is disposed in the center of one of the magnetic poles when viewed in the axial direction of the rotor magnet. Aspect 6. Regarding the above aspect 5, it is preferable that the rotor magnet is a polar anisotropic ring magnet.

[0010] Aspect 7: The disclosed brushless motor comprises a stator, a rotor magnet arranged radially opposite the stator, and a rotor housing that holds the rotor magnet, the rotor magnet being formed by injection molding a mixed material of a magnetic substance and a resin through a pinpoint gate. The rotor magnet has a cylindrical portion formed in a cylindrical shape and having a plurality of magnetic poles arranged thereon, and a rib formed at the axial end of the cylindrical portion in a shape that protrudes radially and engages with the rotor housing. The thickness of the cylindrical portion is a dimension that is less than the inner diameter of the tip of the pinpoint gate, and the thickness of the rib is a dimension that is equal to or greater than the inner diameter of the tip of the pinpoint gate. The outer peripheral surface of the cylindrical portion is fitted to the inner peripheral surface of the rotor housing. do. [Effects of the Invention]

[0011] According to the disclosed rotor magnet and brushless motor, in a rotor magnet having a cylindrical portion with a thickness less than the inner diameter of the tip of the pinpoint gate, by forming a rib with a thickness equal to or greater than the inner diameter of the tip of the pinpoint gate, it is possible to reduce the injection pressure of the mixed material during molding. This makes it easy to increase the number of rotor magnets that can be manufactured in a single filling process, improving productivity and costs. It also prevents molding defects caused by increased injection pressure, improving product quality. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 1 is an exploded perspective view illustrating a brushless motor according to an embodiment of the present invention. [Figure 2] 2 is a perspective view showing the lower surface side of the rotor magnet shown in FIG. 1. [Figure 3] FIG. 2 is a bottom view of the rotor magnet shown in FIG. [Figure 4] FIG. 2 is a cross-sectional view of the rotor magnet shown in FIG. [Figure 5] FIG. 2 is a cross-sectional view of the rotor housing shown in FIG. [Figure 6] 2 is a perspective view illustrating an example of an injection-molded state of the rotor magnet shown in FIG. 1. FIG. [Figure 7] FIG. 10 is a perspective view illustrating an injection-molded state of a rotor magnet according to the prior art. DETAILED DESCRIPTION OF THE INVENTION

[0013] [1. Configuration] Below, a rotor magnet 2 and a brushless motor 10 will be described as embodiments with reference to the drawings. The rotor magnet 2 in this example is a component included in a rotor (rotor) used in a motor (e.g., a brushless motor, a brushed motor, etc.) or a rotary encoder. Regarding the definitions of directions in the embodiments, the direction in which the central axis of rotation of the rotor extends is referred to as the "axial direction," and the direction perpendicular to this central axis of rotation is referred to as the "radial direction." Furthermore, in a plane perpendicular to the central axis of rotation of the rotor, the direction along the circumference of a circle centered on the central axis of rotation is referred to as the "circumferential direction." Note that the radial side closer to the central axis of rotation is referred to as the "radial inner side," and the radial side farther from the central axis of rotation is referred to as the "radial outer side."

[0014] FIG. 1 is an exploded perspective view of a brushless motor 10 including a rotor magnet 2 according to an embodiment. The case (casing) that forms the exterior of the brushless motor 10 is not shown here. FIGS. 2 to 6 are diagrams for explaining the configuration of the rotor magnet 2. FIG. 7 is a perspective view illustrating an injection-molded rotor magnet according to the prior art, with the molding die omitted for ease of explanation. Note that while the motor shown in FIG. 1 is an outer rotor brushless DC motor, the rotor magnet 2 of the present invention can also be applied to an inner rotor brushless DC motor. Furthermore, while the motor shown in FIG. 1 is an 8-pole, 6-slot motor, the number of poles and the number of slots of the motor to which the rotor magnet 2 of the present invention can be applied are not limited to these.

[0015] (A) Motor As shown in Fig. 1, the brushless motor 10 of this invention includes a rotor 1, a stator 5, and a substrate 8. The rotor 1 is rotatably mounted on the substrate 8, and the stator 5 is fixed to the substrate 8. For example, a permanent magnet is mounted on the rotor 1, and for example, a coil is mounted on the stator 5. When current is applied to the stator 5, a magnetic field is generated, and the rotor 1 rotates under the influence of this magnetic field.

[0016] Furthermore, a control circuit (not shown) for controlling the state of current supply to the stator 5 is provided on the substrate 8, and a magnetic sensor 9 (rotation angle sensor, Hall IC) for detecting the rotation angle of the rotor 1 is attached to the substrate 8. The desired angular velocity is achieved by controlling the state of current supply to the stator 5 in accordance with the rotation angle of the rotor 1. The magnetic sensor 9 is positioned, for example, to face the end face (the end face closest to the substrate 8) of the rotor magnet 2, which will be described later. The number of magnetic sensors 9 is set, for example, depending on the number of poles and slots of the brushless motor 10.

[0017] The rotor 1 is provided with a rotor magnet 2, a rotor housing 3, and an output shaft 4. The rotor magnet 2 is a hollow, cylindrical plastic magnet formed from a compound (mixture) of a magnetic material (e.g., magnetic powder) and a resin (e.g., thermoplastic resin). The rotor magnet 2 is manufactured by injection molding the mixed material of the magnetic material and the resin through a pinpoint gate 42 in an injection molding die 41 (described later). The pinpoint gate 42 refers to a hollow portion drilled inside a bushing, which is a component constituting the injection port of the injection molding die 41, to serve as a flow path for the injected material. The pinpoint gate 42 is typically formed in a tapered shape, but is not limited to this shape. The rotor magnet 2 is disposed radially opposite the stator 5. In the brushless motor 10 shown in FIG. 1, the rotor magnet 2 is disposed radially opposite the stator 5 on the outside.

[0018] The rotor housing 3 is a hollow cylindrical part that holds the rotor magnet 2. The rotor magnet 2 is fitted and fixed inside the rotor housing 3 shown in FIG. 1. An output shaft 4, which serves as the center of rotation of the rotor 1, is also fixed to the rotor housing 3. The output shaft 4 is rotatably supported via bearings 14 with respect to a stator holder 12 that is fixed to a substrate 8. Gears, reduction mechanisms, and the like (not shown) may be connected to the output shaft 4.

[0019] Stator holder 12 is a member that is attached, for example, to the back side of substrate 8 (the bottom surface in FIG. 1 ), and that supports output shaft 4 and fixes stator 5. Stator holder 12 is provided with a cylindrical stator fixing portion 13 to which stator 5 is fixed, and a bearing 14 is attached to the tip end of the stator fixing portion 13. Stator fixing portion 13 is provided vertically from the plate surface of stator holder 12, is inserted into opening 11 drilled in substrate 8 from the back side of substrate 8, and is provided so as to protrude from the front side of substrate 8 (the top surface in FIG. 1 ). Stator 5 is fixed to substrate 8 by being fitted into stator fixing portion 13 of stator holder 12.

[0020] The stator 5 is provided with a laminated core 6 and windings 7. The laminated core 6 is a component formed by laminating multiple steel plates of the same shape. The lamination direction of the steel plates is the same as the axial direction of the rotor 1 (the extension direction of the output shaft 4). The laminated core 6 is provided with a hollow cylindrical shaft portion fitted onto the outer peripheral surface of the stator fixing portion 13, and multiple teeth portions protruding radially outward from the shaft portion. The multiple teeth portions are arranged at equal intervals around the circumferential direction of the shaft portion in a cross section perpendicular to the axial direction of the rotor 1. Furthermore, each tooth portion is formed in a shape that extends radially outward in the axial direction from the shaft portion and in a shape that extends in an arc from its outer end in the circumferential direction in the cross section perpendicular to the axial direction of the rotor 1. Electric wires wound around each tooth portion form windings 7 (coils).

[0021] (B) Rotor magnet FIG. 2 is a perspective view showing the underside of rotor magnet 2 (the side closest to substrate 8), and FIG. 3 is a bottom view of the same. FIG. 4 is a cross-sectional view of rotor magnet 2 (cross-sectional view taken along line AA in FIG. 3), and FIG. 5 is a cross-sectional view of rotor housing 3 cut along the same plane. Rotor magnet 2 is provided with cylindrical portion 21, ribs 22, and trace portion 23. The trace portion 23 is generated because an injection molding die 41 (not shown) has a pinpoint gate 42 in the upper die and a rotor magnet 2 in the lower die. Pinpoint gate 42 has a tapered structure, for example, with a diameter that narrows toward the tip toward rotor magnet 2 (see FIG. 4). As a result, when the upper and lower dies are opened in the molding process, the mixed material solidified within pinpoint gate 42 and the rotor magnet 2 solidified within the lower die are separated into upper and lower parts near the tip of pinpoint gate 42 (pinpoint gate tip), leaving a trace. For this reason, although the trace 23 is depicted as a cylinder in FIGS. 2 and 4 for convenience and as if it has a constant height, in reality it is not necessarily cylindrical, and the height is not necessarily constant.

[0022] The cylindrical portion 21 is a cylindrically shaped portion on which multiple magnetic poles are arranged. The outer diameter of the cylindrical portion 21 is dimensioned to correspond to the inner diameter of the rotor housing 3. As a result, the outer peripheral surface of the cylindrical portion 21 fits into the inner peripheral surface of the rotor housing 3. The magnetic poles are oriented so that, when the cylindrical portion 21 is divided equally in the circumferential direction, each portion generates a magnetic field toward the adjacent portion, as shown in FIG. 3 . A ring magnet in which the magnetic flux direction is biased toward the circumferential direction rather than the radial direction is generally called a polar anisotropic ring magnet. The rotor magnet 2 shown in FIG. 3 has eight magnetic poles, but the specific number of magnetic poles, magnetic field direction, density, etc. can be arbitrarily set in relation to the stator. Note that in this embodiment, the magnetic pole layout is such that the magnetic field is denser on the radial inner side of the rotor magnet 2 than on the radial outer side.

[0023] The rib 22 is a portion formed in a shape that protrudes radially at the axial end of the cylindrical portion 21. The rib 22 shown in FIGS. 2 to 4 is formed at the end on the lower surface side (the side close to the substrate 8) of the axial end of the cylindrical portion 21 among the axial ends of the cylindrical portion 21. The ribs 22 are arranged at a plurality of positions on the outer peripheral surface of the cylindrical portion 21 at intervals in the circumferential direction. These ribs 22 are preferably arranged at equal intervals. The number of ribs 22 shown in FIGS. 2 to 4 is four, but the number of ribs 22 can be arbitrarily changed.

[0024] At least two functions are imparted to the rib 22. The first function is to engage the rotor magnet 2 and the rotor housing 3. The rib 22 of the rotor magnet 2 is engaged with a notch portion 33 of the rotor housing 3, which will be described later. The second function is to ensure a sufficient size of the inflow port of the compound supplied from the pinpoint gate 42 of the injection mold 41 when manufacturing the rotor magnet 2. The size of the rib 22 is formed larger than the size of the tip of the pinpoint gate 42.

[0025] As shown in FIG. 4, let the thickness (radial dimension) of the cylindrical portion 21 be T1 and the thickness (radial dimension) of the rib 22 be T2. Also, let the inner diameter of the tip of the pinpoint gate 42 of the injection mold 41 be D0. The dimensions of the rotor magnet 2 of the present case are set such that at least T1 < D0 ≤ T2 is satisfied. That is, the thickness T1 of the cylindrical portion 21 is set to a dimension less than the inner diameter D0 of the tip of the pinpoint gate 42. On the other hand, the thickness T2 of the rib 22 is set to a dimension greater than or equal to the inner diameter D0 of the tip of the pinpoint gate 42. In FIG. 4, the overall shape of the injection mold 41 is omitted to make the explanation of the injection molding structure easier to understand.

[0026] As shown in FIG. 2, a trace portion 23 is provided on a rib end face 24 which is an axial end face of the rib 22 (the end face close to the substrate 8). The trace portion 23 is a portion remaining as a trace of the injection molding of the rotor magnet 2, and is a portion bulged in a substantially circular shape having a size corresponding to the inner diameter D0 of the tip of the pin point gate 42. As shown in FIG. 4, let the outer diameter of the trace portion 23 be D1. The outer diameter D1 is substantially the same dimension as the inner diameter D0. The dimensions of the rotor magnet 2 of the present case are set such that T1 < D1 ≤ T2 holds.

[0027] That is, the thickness T1 of the cylindrical portion 21 is set to be less than the outer diameter D1 of the trace portion 23. On the other hand, the thickness T2 of the rib 22 is set to be greater than or equal to the outer diameter D1 of the trace portion 23. Note that the shape of the trace portion 23 is not necessarily a perfect circular shape. For example, it may be cylindrical or may be a substantially cylindrical shape with a partial notch. In any case, the shape of the trace portion 23 corresponds to the shape of the tip of the pin point gate 42, and the outer diameter D1 of the trace portion 23 can be regarded as substantially the same as the inner diameter D0 of the tip of the pin point gate 42.

[0028] As shown in FIG. 2, a cylindrical portion end face 25 which is an axial end face of the cylindrical portion 21 (the end face close to the substrate 8) is formed in a shape protruding toward the substrate 8 side in the axial direction from the rib end face 24. In other words, the rib end face 24 is formed in a concave shape compared to the cylindrical portion end face 25. Also, as shown in FIG. 4, let the height dimension of the most axially protruding portion of the trace portion 23 with respect to the rib end face 24 be H1, and let the step dimension between the rib end face 24 and the cylindrical portion end face 25 be H2. The dimensions of the rotor magnet 2 of the present case are set such that H1 ≤ H2 holds. That is, the step dimension H2 between the rib end face 24 and the cylindrical portion end face 25 is set to be greater than or equal to the height dimension H1 of the trace portion 23.

[0029] As shown in FIG. 3, the layout of the ribs 22 in the axial view of the rotor magnet 2 is such that they are arranged to avoid the boundaries between multiple magnetic poles when the rotor magnet 2 is viewed axially from the end face side closest to the substrate 8. The boundaries of the magnetic poles are indicated by dashed lines in FIG. 3. The circumferential positions of the ribs 22 are set so as not to overlap with at least the boundaries of the magnetic poles indicated by the dashed lines. Preferably, the positions of the ribs 22 are set so that they are farthest from the boundaries of the magnetic poles when moved circumferentially. In other words, the ribs 22 are arranged in the center of one of the magnetic poles when the rotor magnet 2 is viewed axially.

[0030] (C) Rotor housing As shown in Fig. 5, the rotor housing 3 is provided with a side surface portion 31, an end surface portion 32, a notch portion 33, and a hole portion 34. The side surface portion 31 is a cylindrical portion attached so as to surround the outside of the rotor magnet 2, and is formed with a size such that its inner peripheral surface fits into the outer peripheral surface of the cylindrical portion 21. The axial dimension of the side surface portion 31 (the vertical dimension in Fig. 5) is set to a size such that the rotor magnet 2 fits completely inside it, for example.

[0031] The end surface portion 32 is a disk-shaped portion that forms the axial end surface of the side surface portion 31 (the end surface that is remote from the substrate 8). This end surface portion 32 is the upper surface of the rotor housing 3 shown in FIG. 1. The cutout portions 33 are cut out in shapes that correspond to the ribs 22 of the rotor magnet 2 and fit into the ribs 22. The cutout portions 33 are arranged at multiple locations on the side surface portion 31 at equal intervals in the circumferential direction, the same number as the number of ribs 22. The hole portion 34 is a circular opening that is drilled in the center of the end surface portion 32. The output shaft 4 of the rotor 1 is inserted and fixed in the hole portion 34.

[0032] [2. Actions and Effects] FIG. 7 is a perspective view illustrating the injection molding of a rotor magnet 2' according to the prior art. For ease of explanation, the overall shape of the injection molding die 41 is omitted. In this rotor magnet 2', the thickness T1 of the cylindrical portion 21 is small relative to the inner diameter D0 of the tip of the pinpoint gate 42, and no ribs 22 are formed. This results in high injection pressure (the pressure of the mixed material flowing inside the mold), which can easily damage the mold and cause burrs at the mold joints. This necessitates an increase in the number of pinpoint gates 42 (number of gates) that inject the mixed material into each rotor magnet 2', thereby reducing the number of rotor magnets 2' that can be manufactured in one filling process. In the example shown in FIG. 7, there are six gates for each rotor magnet 2', and one rotor magnet 2' is manufactured using one injection molding die 41.

[0033] In contrast, FIG. 6 is a perspective view illustrating the injection molding of a rotor magnet 2 according to this embodiment. For ease of explanation, the overall shape of the injection molding die 41 is omitted. A mixed material of magnetic material and resin flows through the upper die of the injection molding die 41, passing through a spool 43, a runner 44, and a pinpoint gate 42, in that order, and is injected into the rotor magnet 2 in the lower die. This rotor magnet 2 is formed with a rib 22 having a thickness T2 equal to or greater than the inner diameter D0 of the tip of the pinpoint gate 42. This reduces the injection pressure and reduces the number of gates per rotor magnet 2. This increases the number of rotor magnets 2 that can be manufactured in one filling process, facilitating so-called multi-cavity molding. In the example shown in FIG. 6, there are four gates per rotor magnet 2, and four rotor magnets 2 are manufactured using one injection molding die 41.

[0034] (1) The rotor magnet 2 is rotatably provided with respect to the substrate 8 to which the stator 5 is fixed, is disposed opposite the stator 5, and is formed by injection molding a mixed material of a magnetic substance and a resin through a pinpoint gate 42. The rotor magnet 2 includes a cylindrical portion 21 formed in a cylindrical shape and having a plurality of magnetic poles arranged thereon, and a rib 22 formed in a shape that protrudes radially from the axial end of the cylindrical portion 21. As shown in FIG. 4, the thickness T1 of the cylindrical portion 21 is a dimension that is less than the inner diameter D0 of the tip of the pinpoint gate 42, and the thickness T2 of the rib 22 is a dimension that is equal to or greater than the inner diameter D0 of the tip of the pinpoint gate 42.

[0035] With this configuration, the injection pressure of the mixed material during molding can be reduced compared to when the rib 22 is not present. This allows for an increase in the number of rotor magnets 2 that can be manufactured in one filling process, improving productivity and costs. It also prevents molding defects caused by increased injection pressure, improving product quality. Furthermore, there is no need to upgrade the injection molding mold 41 or replace it with the latest model in order to increase the production volume of the rotor magnet 2, so the productivity of the rotor magnet 2 can be improved while effectively utilizing existing production facilities. Note that this effect can be obtained regardless of the size of the inner diameter D0 of the tip of the pinpoint gate 42, but a particularly significant effect is obtained when the inner diameter D0 is 1.5 mm or less.

[0036] (2) The rotor magnet 2 has a trace portion 23, which is a generally circular bulge corresponding to the inner diameter D0 of the tip of the pinpoint gate 42, on a rib end surface 24, which is the axial end surface of the rib 22, as a trace of injection molding of the rotor magnet 2. As shown in Fig. 4, the thickness T1 of the cylindrical portion 21 is less than the outer diameter D1 of the trace portion 23, and the thickness T2 of the rib 22 is equal to or greater than the outer diameter D1 of the trace portion 23.

[0037] In this way, by referring to the dimensions of the trace 23 corresponding to the tip of the pinpoint gate 42, it is possible to more reliably determine that the injection pressure of the mixed material during molding has decreased compared to when the rib 22 is not present, thereby improving productivity and costs and enhancing product quality. Also, by omitting post-processing (deburring) after injection molding (i.e., leaving the trace 23), the productivity of the rotor magnet 2 can be improved. Furthermore, deformation or damage to the rotor magnet 2 due to post-processing after injection molding can be prevented, further improving product quality.

[0038] (3) In the rotor magnet 2 described above, as shown in FIGS. 2 to 4, the rib end faces 24, which are the axial end faces of the ribs 22, are formed in a shape that is recessed relative to the cylindrical portion end faces 25, which are the axial end faces of the cylindrical portion 21. In other words, the cylindrical portion end faces 25 have a shape that protrudes more toward the substrate 8 in the axial direction than the rib end faces 24. In addition, the step dimension H2 between the rib end faces 24 and the cylindrical portion end faces 25 is equal to or greater than the height dimension H1 of the trace portions 23.

[0039] In this way, by making the cylindrical portion end face 25 protrude axially toward the substrate 8 beyond the rib end face 24, the trace portion 23 can be accommodated inside the step between the rib end face 24 and the cylindrical portion end face 25. This reliably prevents interference between the magnetic sensor 9 and various electronic components arranged closer to the substrate 8 than the rotor 1 and the trace portion 23, as well as deformation and damage due to contact, and improves product quality.

[0040] (4) The ribs 22 are positioned to avoid boundaries between multiple magnetic poles when viewed in the axial direction of the rotor magnet 2. This improves the accuracy with which the magnetic sensor 9 detects the rotation angle of the rotor 1. Because the magnetic sensor 9 detects the boundaries of the magnetic force of the rotor magnet 2, for example, if the ribs 22 are formed so as to straddle the boundaries between magnetic poles, the distance between the magnetic sensor 9 and the rib end faces 24 increases, reducing the output of the magnetic sensor 9 and the accuracy with which the rotation angle is detected. Furthermore, the axial height of the traces 23 on the rib end faces 24 varies depending on the location, making detection accuracy more unstable. However, by positioning the ribs 22 in positions that avoid the boundaries between magnetic poles, this degradation in accuracy can be avoided. This improves the controllability of the brushless motor 10. Even when the rotor magnet 2 is applied to motors other than the brushless motor 10 or to rotary encoders, the degradation in detection accuracy of the boundaries between magnetic poles due to the ribs 22 can be suppressed.

[0041] (5) The rib 22 may be located at the center of one of the magnetic poles when viewed in the axial direction of the rotor magnet 2. In this case, the distance between the rib 22 and the boundary between the magnetic poles when viewed in the axial direction of the rotor magnet 2 can be maximized, and the decrease in accuracy (decrease in detection accuracy by the magnetic sensor 9) caused by the rib 22 can be minimized. This further improves the controllability of the brushless motor 10.

[0042] (6) The rotor magnet 2 is a polar-anisotropic ring magnet, as shown in Figure 3. Compared to radially anisotropic ring magnets, polar-anisotropic ring magnets tend to be more susceptible to the influence of the ribs 22 on the magnetic sensor 9 (the influence that changes in the distance between the rotor magnet 2 and the magnetic sensor 9 have on the detection accuracy of the magnetic sensor 9). Therefore, by positioning the ribs 22 in the polar-anisotropic ring magnet at the center of the magnetic poles, it is possible to effectively prevent the ribs 22 from reducing the detection accuracy of the boundaries of the magnetic poles, thereby improving the controllability of the brushless motor 10.

[0043] (7) The brushless motor 10 described above includes a stator 5, a rotor magnet 2 disposed radially opposite the stator 5, and a rotor housing 3 that holds the rotor magnet 2. The rotor magnet 2 is formed by injection molding a mixed material of a magnetic substance and a resin through a pinpoint gate 42. The rotor magnet 2 has a cylindrical portion 21 formed in a cylindrical shape and having a plurality of magnetic poles arranged thereon, and a rib 22 formed at an axial end of the cylindrical portion 21 in a shape that protrudes radially and engages with the rotor housing 3. As shown in FIG. 4 , the thickness T1 of the cylindrical portion 21 is a dimension that is less than the inner diameter D0 of the tip of the pinpoint gate 42, and the thickness T2 of the rib 22 is a dimension that is equal to or greater than the inner diameter D0 of the tip of the pinpoint gate 42.

[0044] With this configuration, compared to a rotor magnet 2' without ribs 22, the productivity and cost of the rotor magnet 2 can be improved, and product quality can be enhanced. Therefore, the productivity of the brushless motor 10 can be improved. Also, no adhesive is required to bond the rotor magnet 2 to the rotor housing 3, simplifying the device configuration. Therefore, the productivity and cost of the brushless motor 10 can be further improved. Furthermore, by engaging the ribs 22 of the rotor magnet 2 with the cutout portions 33 of the rotor housing 3, circumferential positional deviation of the rotor magnet 2 that occurs as the rotor 1 rotates can be suppressed. Therefore, the controllability of the brushless motor 10 can be further improved.

[0045] [3. Other] The above-described embodiments are merely illustrative and are not intended to exclude various modifications or applications of techniques not explicitly described in the present embodiments. Each configuration of the present embodiments can be modified in various ways without departing from the spirit of the present embodiments. Furthermore, each configuration of the present embodiments can be selected as needed, or can be appropriately combined with various configurations included in known techniques.

[0046] Although the above embodiment illustrates an outer rotor brushless motor, a similar configuration can also be applied to an inner rotor brushless motor. For example, in an inner rotor brushless motor in which the stator is arranged in an annular shape, a cylindrical portion and ribs may be formed on a rotor magnet arranged facing the radially inner side of the stator. The ribs are formed, for example, at the axial end of the cylindrical portion so as to protrude radially inward. In such a rotor magnet, the thickness of the cylindrical portion can be made smaller than the inner diameter of the pinpoint gate, and the thickness of the ribs can be made equal to or larger than the inner diameter of the pinpoint gate, thereby achieving the same effects as those of the above embodiment.

[0047] The rotor magnet of this invention can be applied not only to brushless motors but also to brushed motors and rotary encoders. The rotor magnet applied to a rotary encoder is provided rotatably with respect to a substrate 8 on which a rotation angle sensor (e.g., a magnetic sensor, an optical sensor, an electrostatic sensor, etc.) is fixed, and is positioned opposite the rotation angle sensor, and is formed by injection molding a mixture of a magnetic substance and a resin through a pinpoint gate. In such a rotor magnet, the thickness of the cylindrical portion is set to a dimension less than the inner diameter of the pinpoint gate, and the thickness of the rib is set to a dimension equal to or greater than the inner diameter of the pinpoint gate, thereby achieving the same effects as those of the above-described embodiment. [Industrial Applicability]

[0048] The present invention is applicable to the manufacturing industry of rotor magnets used in motors and rotary encoders, as well as to the manufacturing industry of brushless motors. [Explanation of symbols]

[0049] 1 rotor 2 rotor magnet 3 Rotor housing 4 output shaft 5 Stator 6 Laminated Core 7 windings 8 PCB 9 Magnetic sensor (rotation angle sensor) 10 Brushless motor 11 Opening 12 Stator holder 13 Stator fixing part 14 Bearings 21 Cylindrical part 22 Ribs 23 Trace part 24 Rib end face 25 Cylindrical end face 31 Side part 32 End section 33 Cutout 34 Hole 41 Injection mold 42 Pinpoint Gate 43 spool 44 Runner D0 Inner diameter of pinpoint gate tip D1 Outer diameter of trace T1 Thickness of cylindrical part T2 rib thickness H1 Height of trace H2 Step between the end face of the cylindrical part and the end face of the rib

Claims

1. A rotor magnet is provided rotatably with respect to a substrate on which a stator or a rotation angle sensor is fixed, is disposed opposite the stator or the rotation angle sensor, and is formed by injection molding a mixed material of a magnetic substance and a resin through a pinpoint gate, a cylindrical portion formed in a cylindrical shape and having a plurality of magnetic poles arranged therein; a rib formed in a radially protruding shape only at one end of the axial end of the cylindrical portion, The thickness of the cylindrical portion is smaller than the inner diameter of the tip of the pinpoint gate, The thickness of the rib is equal to or greater than the inner diameter of the tip of the pinpoint gate. A rotor magnet characterized by:

2. a rib end surface, which is an axial end surface of the rib, having a trace portion expanded in a substantially circular shape as a trace of injection molding of the rotor magnet, the trace portion having a size corresponding to an inner diameter of the tip end portion of the pinpoint gate; The thickness of the cylindrical portion is less than the outer diameter of the trace portion, The thickness of the rib is equal to or greater than the outer diameter of the trace portion.

2. The rotor magnet according to claim 1, wherein:

3. a cylindrical portion end surface, which is an axial end surface of the cylindrical portion, has a shape that protrudes toward the substrate in the axial direction more than the rib end surface; The step dimension between the rib end surface and the cylindrical portion end surface is equal to or greater than the height dimension of the trace portion.

3. The rotor magnet according to claim 2, wherein:

4. The ribs are arranged to avoid boundaries between the plurality of magnetic poles when viewed in the axial direction of the rotor magnet.

2. The rotor magnet according to claim 1, wherein:

5. The rib is disposed at the center of one of the magnetic poles when viewed in the axial direction of the rotor magnet.

5. The rotor magnet according to claim 4, wherein:

6. The rotor magnet is a polar anisotropic ring magnet.

6. The rotor magnet according to claim 5, wherein:

7. A brushless motor comprising: a stator; a rotor magnet disposed radially opposite the stator; and a rotor housing that holds the rotor magnet, wherein the rotor magnet is formed by injection molding a mixed material of a magnetic substance and a resin through a pinpoint gate; the rotor magnet has a cylindrical portion formed in a cylindrical shape and having a plurality of magnetic poles arranged thereon, and a rib formed at an axial end of the cylindrical portion in a shape that protrudes in the radial direction and engages with the rotor housing, The thickness of the cylindrical portion is smaller than the inner diameter of the tip of the pinpoint gate, The thickness of the rib is equal to or greater than the inner diameter of the tip of the pinpoint gate, The outer peripheral surface of the cylindrical portion is fitted to the inner peripheral surface of the rotor housing. A brushless motor characterized by:

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