Rotor magnet and brushless motor
By incorporating a thickness difference between the cylindrical section and the rib section in the rotor magnet design, and by adding a trace section to the rib section, the high pressure problem during injection molding was solved, which improved productivity, reduced costs, and improved product quality.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- MABUCHI MOTOR CO LTD
- Filing Date
- 2023-05-15
- Publication Date
- 2026-07-31
AI Technical Summary
When forming a rotor magnet with a thin inner diameter during injection molding, the injection pressure of the mixed materials is high, resulting in low productivity and increased costs, making it difficult to improve.
The thickness of the cylindrical part of the rotor magnet is less than the inner diameter of the front end of the pin gate, while the thickness of the rib part is greater than or equal to the inner diameter of the front end of the pin gate. A mark part is set on the rib part to adapt to the shape of the pin gate, forming a rib-rotor housing engagement structure.
The injection pressure was reduced, increasing the number of rotor magnets that can be manufactured in a single filling process, improving productivity and cost, while preventing poor molding and improving product quality.
Smart Images
Figure CN120077552B_ABST
Abstract
Description
Technical Field
[0001] The present invention relates to a rotor magnet and a brushless motor including the rotor magnet. Background Technology
[0002] Conventionally, rotors used in motors and rotary encoders have been known to have rotors whose rotor magnets are manufactured by injection molding. For example, rotors are known to have a ring-shaped rotor magnet (resin-bonded magnet) formed by injection molding a mixture of magnetic powder and thermoplastic resin, which is then inserted into and bonded to the inside of a cylindrical rotor yoke. Alternatively, Patent Document 1 describes a rotor formed by integrally molding the rotor magnet into the inside of the rotor yoke. With this structure, it becomes easier to reduce the weight and thin the wall of the rotor magnet.
[0003] Prior art literature
[0004] Patent documents
[0005] Patent Document 1: Japanese Patent Application Publication No. 2005-198447 Summary of the Invention
[0006] The problem that the invention aims to solve
[0007] On the other hand, when forming rotor magnets with thinner inner walls than the front end of the pin-point gate during injection molding, the injection pressure of the mixed material (the pressure of the mixed material inside the mold frame) becomes higher, and the number of rotor magnets that can be manufactured in a single filling process decreases. This results in the following problems: difficulty in improving productivity and increased manufacturing costs.
[0008] One of the objectives of this invention is to address the aforementioned issues by providing a rotor magnet and brushless motor that can improve productivity and reduce costs. It should be noted that this invention is not limited to this objective; other objectives may also include achieving effects derived from the structures shown in the "Specific Embodiments" described below that are unattainable in conventional technologies.
[0009] Solution for solving the problem
[0010] The disclosed rotor magnet can be implemented as Solution 1 (applicable example) below, solving at least a portion of the aforementioned problems. Furthermore, the disclosed brushless motor can be implemented as Solution 7 below, solving at least a portion of the aforementioned problems. Solutions 2 through 6 are all optional and can be omitted. None of the disclosed solutions 2 through 6 are essential or indispensable for this application.
[0011] Option 1. The disclosed rotor magnet is configured to rotate relative to a substrate on which a stator or rotation angle sensor is fixed, and is disposed opposite to the stator or rotation angle sensor. The rotor magnet is formed by injection molding a mixture of magnetic material and resin via a pin-point gating system. The rotor magnet comprises: a cylindrical portion formed in a cylindrical shape and having a plurality of magnetic poles arranged thereon; and ribs formed at the axial ends of the cylindrical portion in a radially protruding shape. Furthermore, the thickness of the cylindrical portion is smaller than the inner diameter of the front end of the pin-point gating system, and the thickness of the ribs is greater than or equal to the inner diameter of the front end of the pin-point gating system.
[0012] Option 2. Based on Option 1 above, preferably, the rotor magnet has a trace portion that protrudes from the axial end face of the rib, i.e., the rib end face, as a trace from the injection molding of the rotor magnet, and is configured to be approximately circular in shape, corresponding to the inner diameter of the front end of the pin-point gate. Furthermore, preferably, the thickness of the cylindrical portion is smaller than the outer diameter of the trace portion, and the thickness of the rib is greater than or equal to the outer diameter of the trace portion.
[0013] Option 3. Based on Option 2 above, preferably, the axial end face of the cylindrical portion, i.e., the end face of the cylindrical portion, has a shape that protrudes from the rib end face towards the axial substrate side, and the step size between the rib end face and the end face of the cylindrical portion is greater than or equal to the height of the trace portion.
[0014] Option 4. Based on the options including Option 1 above, it is preferred that the ribs are arranged to avoid the boundaries of the plurality of magnetic poles when viewed axially from the rotor magnet.
[0015] Option 5. Based on Option 4 above, preferably, the rib is positioned at the center of any of the magnetic poles when viewed axially from the rotor magnet.
[0016] Option 6. Based on Option 5 above, preferably, the rotor magnet is an anisotropic toroidal magnet.
[0017] Option 7. The disclosed brushless motor is a brushless motor comprising a stator, a rotor magnet arranged radially opposite to the stator, and a rotor housing holding the rotor magnet, wherein the rotor magnet is formed by injection molding a mixture of magnetic material and resin through a pin-point gate. The rotor magnet has: a cylindrical portion formed in a cylindrical shape and having a plurality of magnetic poles arranged thereon; and ribs formed in a radially protruding shape at the axial end of the cylindrical portion and engaging with the rotor housing. Furthermore, the thickness of the cylindrical portion is less than the inner diameter of the front end of the pin-point gate, and the thickness of the ribs is greater than or equal to the inner diameter of the front end of the pin-point gate.
[0018] Invention Effects
[0019] According to the disclosed rotor magnet and brushless motor, in a rotor magnet having a cylindrical portion with a thickness greater than the inner diameter of the pin-point gate tip, ribs are formed within this rotor magnet, thereby reducing the injection pressure of the mixed materials during molding. This allows for an increase in the number of rotor magnets that can be manufactured in a single filling process, improving productivity and cost. Furthermore, it prevents molding defects caused by increased injection pressure, thus improving product quality. Attached Figure Description
[0020] Figure 1 This is an exploded perspective view used to illustrate the brushless motor as an example.
[0021] Figure 2 It means Figure 1 A perspective view of the lower surface of the rotor magnet shown.
[0022] Figure 3 yes Figure 1 The image shows a bottom view of the rotor magnet.
[0023] Figure 4 yes Figure 1 The cross-sectional view of the rotor magnet shown.
[0024] Figure 5 yes Figure 1 The cross-sectional view of the rotor housing shown.
[0025] Figure 6 This is an example Figure 1 A three-dimensional view of the injection-molded rotor magnet shown.
[0026] Figure 7 This is a perspective view illustrating the injection molding state of a rotor magnet as described in conventional technology. Detailed Implementation
[0027] [1. Structure]
[0028] The rotor magnet 2 and brushless motor 10, as embodiments, will be described below using the accompanying drawings. The rotor magnet 2 in this embodiment is a component included in the rotor (rotor) used in motors (e.g., brushless motors, brushed motors, etc.) and rotary encoders. Regarding the definition of directions in the embodiments, the direction extending from the rotation center axis of the rotor is called the "axial direction," and the direction perpendicular to the rotation center axis is called the "radial direction." Furthermore, in a plane perpendicular to the rotation center axis of the rotor, the direction along the circumference of a circle centered on the rotation center axis is called the "circumferential direction." It should be noted that the side closer to the rotation center axis in the radial direction is called the "radial inner side," and the side farther from the rotation center axis in the radial direction is called the "radial outer side."
[0029] Figure 1 This is an exploded perspective view of a brushless motor 10, including the rotor magnet 2, as an embodiment. The housing (outer shell) forming the brushless motor 10 is omitted from the view here. Figures 2-6 This is a diagram used to illustrate the structure of rotor magnet 2. Figure 7 This is a perspective view illustrating the injection molding state of a rotor magnet as described in conventional techniques, without omitting the molding die, for illustrative purposes. It should be noted that... Figure 1 The motor shown is an external rotor type brushless DC motor, but the rotor magnet 2 in this case can also be used in an internal rotor type brushless DC motor. Furthermore, Figure 1 The motor shown is an 8-pole, 6-slot motor, but the number of poles and slots of the motor to which the rotor magnet 2 of this case is applicable are not limited to this.
[0030] (A) Motor
[0031] like Figure 1 As shown, the brushless motor 10 of this case includes a rotor 1, a stator 5, and a base plate 8. The rotor 1 is configured to rotate relative to the base plate 8, and the stator 5 is fixed relative to the base plate 8. For example, a permanent magnet is provided in the rotor 1, and a coil is provided in the stator 5. A magnetic field is generated by energizing the stator 5, and the rotor 1 rotates under the influence of the magnetic field.
[0032] Additionally, a control circuit (not shown) for controlling the energizing state of 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 mounted on it. The desired angular velocity is achieved by controlling the energizing state of the stator 5 based on the rotation angle of the rotor 1. The position of the magnetic sensor 9 is, for example, set opposite to the end face of the rotor magnet 2 (the end face close to the substrate 8) described later. The number of magnetic sensors 9 is, for example, set according to the number of poles and slots of the brushless motor 10.
[0033] 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 component made of a plastic magnet formed from a composite (mixed material) of a magnetic material (e.g., magnetic powder) and a resin (e.g., a thermoplastic resin material). This rotor magnet 2 is manufactured by injection molding the mixture of magnetic material and resin through a pin-point gate 42 within an injection molding mold 41, described later. The pin-point gate 42 refers to a cavity portion that is perforated inside the bushing, which constitutes the injection port of the injection molding mold 41, to form a flow path for the injected material. The shape of the pin-point gate 42 is typically a tapered shape tapering at the front end, but it is not limited to this shape. Furthermore, the rotor magnet 2 and the stator 5 are arranged opposite each other in the radial direction of the rotor 1. Figure 1In the brushless motor 10 shown, the rotor magnet 2 is arranged radially outward relative to the stator 5.
[0034] The rotor housing 3 is a hollow cylindrical component that holds the rotor magnet 2. Figure 1 The rotor magnet 2 is fixedly mounted inside the rotor housing 3 shown. Additionally, an output shaft 4, which serves as the rotation center of the rotor 1, is fixed to the rotor housing 3. The output shaft 4 is rotatably supported by a stator retainer 12 fixed to the base plate 8 via a bearing 14. The output shaft 4 can be connected to gears, reduction gears, etc. (not shown).
[0035] Stator retainer 12 is a component that, for example, is mounted on the back side of substrate 8 (in... Figure 1 The lower surface of the stator 5 is supported by the output shaft 4 and the stator 5 is fixed. A cylindrical stator fixing part 13 for fixing the stator 5 is provided on the stator retainer 12, and a bearing 14 is mounted on the front end side of the stator fixing part 13. The stator fixing part 13 is configured to stand vertically from the plate surface of the stator retainer 12, be inserted into an opening 11 formed by a through hole in the substrate 8 from the back side of the substrate 8, and extend towards the surface side of the substrate 8 (on the lower surface of the stator 5). Figure 1 The upper surface protrudes. The stator 5 is fixed to the substrate 8 by the stator fixing part 13 embedded in the stator retainer 12.
[0036] The stator 5 is provided with a laminated iron core 6 and a winding 7. The laminated iron core 6 is a component formed by stacking multiple steel plates of the same shape. The stacking 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 iron core 6 is provided with: a hollow cylindrical shaft portion that is fitted into the outer peripheral surface of the stator fixing part 13; and multiple teeth portion that protrude radially outward from the shaft portion. The multiple teeth portion are evenly spaced along the circumferential direction of the shaft portion in a section perpendicular to the axial direction of the rotor 1. In addition, each tooth portion is formed to extend radially outward from the shaft portion in a section perpendicular to the axial direction of the rotor 1, and is formed to extend in an arc shape circumferentially from its outer end. The wire wound around each tooth portion forms the winding 7 (coil).
[0037] (B) Rotor magnet
[0038] Figure 2 This is a perspective view showing the lower surface of the rotor magnet 2 (the side closest to the substrate 8). Figure 3 This is a bottom view of rotor magnet 2. Additionally, Figure 4 This is a cross-sectional view of rotor magnet 2. Figure 3 (AA section view) Figure 5This is a cross-sectional view when the rotor housing 3 is cut along the same cutting plane. The rotor magnet 2 has a cylindrical portion 21, ribs 22, and a trace portion 23. As a principle for generating the trace portion 23, in the injection molding mold 41 (details omitted), a pin-point gate 42 exists in the upper mold, and the rotor magnet 2 exists in the lower mold. The pin-point gate 42, for example, has a tapered structure whose diameter tapers towards the front end in the direction of the rotor magnet 2 (see reference). Figure 4 Therefore, when the upper and lower molds are opened based on the molding process, the mixed material solidified in the pin-point gate 42 and the rotor magnet 2 solidified in the lower mold separate near the front end of the pin-point gate 42 (the front end of the pin-point gate), and this separation becomes a mark and remains. Therefore, in Figure 2 , Figure 4 The trace part 23 is expediently represented as a cylinder with a constant height, but in reality it may not be cylindrical and its height may not be constant.
[0039] The cylindrical portion 21 is a portion formed into a cylindrical shape and having multiple magnetic poles arranged thereon. The outer diameter of the cylindrical portion 21 is formed to correspond to the inner diameter of the rotor housing 3. Thus, the outer peripheral surface of the cylindrical portion 21 fits into the inner peripheral surface of the rotor housing 3. The orientation of the magnetic poles is as follows... Figure 3 As shown, the cylindrical portion 21 is divided into equal parts along the circumference, and each part generates a magnetic field by oriented towards the adjacent part. In this way, a toroidal magnet in which the direction of magnetic flux is oriented in the circumferential direction rather than the radial direction is generally called an anisotropic toroidal magnet. Figure 3 The rotor magnet 2 shown has 8 poles, but the specific number of poles, the orientation of the magnetic field, and the density can be arbitrarily set according to the relationship with the stator. It should be noted that in this embodiment, the magnetic poles are arranged in a position where the magnetic field is densely formed at a position closer to the radial inner side than the radial outer side of the rotor magnet 2.
[0040] Rib 22 is a part formed in a radially protruding shape at the axial end of cylindrical part 21. Figures 2-4 The ribs 22 shown are formed at the axial end of the cylindrical portion 21 on the lower surface side of the rotor magnet 2 (the side close to the substrate 8). The ribs 22 are arranged at multiple locations on the outer peripheral surface of the cylindrical portion 21 at circumferential intervals. These ribs 22 are preferably arranged at equal intervals. Figures 2-4 The number of ribs 22 shown is four, but the number of ribs 22 can be changed arbitrarily.
[0041] The rib 22 is given at least two functions. The first function is to engage the rotor magnet 2 with the rotor housing 3. The rib 22 of the rotor magnet 2 engages with the notch 33 of the rotor housing 3, which will be described later. The second function is to ensure, during the manufacturing of the rotor magnet 2, the size of the inlet of the composite material supplied from the pin-point gate 42 of the injection mold 41 is sufficiently large. The rib 22 is sized to be larger than the size of the front end of the pin-point gate 42.
[0042] like Figure 4 As shown, the thickness (radial dimension) of the cylindrical portion 21 is set to T1, and the thickness (radial dimension) of the rib 22 is set to T2. Furthermore, the inner diameter of the front end of the injection mold 41's pin-point gate 42 is set to D0. In this case, the rotor magnet 2 has each dimension set such that T1 < D0 ≤ T2. That is, the thickness T1 of the cylindrical portion 21 is set to be smaller than the inner diameter D0 of the front end of the pin-point gate 42. On the other hand, the thickness T2 of the rib 22 is set to be greater than or equal to the inner diameter D0 of the front end of the pin-point gate 42. It should be noted that in Figure 4 In order to make the explanation of the injection molding structure easier to understand, the overall shape of the injection molding mold 41 has been omitted.
[0043] like Figure 2 As shown, a trace portion 23 is provided on the axial end face of rib 22 (the end face close to the substrate 8), i.e., the rib end face 24. The trace portion 23 is a bulge, approximately circular in shape, formed from the injection molding trace of the rotor magnet 2, and corresponding to the inner diameter D0 of the front end of the pin-point gate 42. Figure 4 As shown, the outer diameter of the trace portion 23 is set to D1. The outer diameter D1 is approximately the same size as the inner diameter D0. In this case, the rotor magnet 2 is sized such that T1 < D1 ≤ T2.
[0044] That is, the thickness T1 of the cylindrical portion 21 is set to be smaller 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 larger than the outer diameter D1 of the trace portion 23. It should be noted that the shape of the trace portion 23 is not necessarily a perfect circle; for example, it may sometimes be cylindrical, or sometimes it may be a roughly cylindrical shape with partial defects. In any case, the shape of the trace portion 23 corresponds to the shape of the front end of the pin-point gate 42, and the outer diameter D1 of the trace portion 23 can be regarded as being actually the same as the inner diameter D0 of the front end of the pin-point gate 42.
[0045] like Figure 2 As shown, the axial end face (the end face close to the substrate 8) of the cylindrical portion 21, namely the cylindrical portion end face 25, is formed to protrude axially toward the substrate 8 side compared to the rib end face 24. In other words, the rib end face 24 is formed to be recessed compared to the cylindrical portion end face 25. Furthermore, as... Figure 4As shown, the height of the most protruding part of the trace portion 23 along the axial direction, with the rib end face 24 as the reference, is set as H1, and the step size between the rib end face 24 and the cylindrical end face 25 is set as H2. In this case, the rotor magnet 2 sets each dimension in such a way that H1 ≤ H2. That is, the step size H2 between the rib end face 24 and the cylindrical end face 25 is a dimension greater than or equal to the height size H1 of the trace portion 23.
[0046] The layout of ribs 22 when viewed axially as follows Figure 3 As shown, when viewed axially from the end face side close to the substrate 8, the ribs 22 are arranged to avoid the boundaries of the multiple magnetic poles. Here, in Figure 3 The boundaries of the magnetic poles are shown by dashed lines. The circumferential position of the rib 22 is set such that it does not overlap with the boundaries of the magnetic poles shown by the dashed lines. Preferably, the position of the rib 22 is set as far away from the boundaries of the magnetic poles as the rib 22 can be moved along the circumferential direction. In other words, when viewed axially from the rotor magnet 2, the rib 22 is positioned at the center of any magnetic pole.
[0047] (C) Rotor housing
[0048] like Figure 5 As shown, the rotor housing 3 is provided with a side portion 31, an end portion 32, a notch portion 33, and a hole portion 34. The side portion 31 is a cylindrical part that is mounted to surround the outer side of the rotor magnet 2, and its inner circumferential surface is formed to fit into the outer circumferential surface of the cylindrical portion 21. The axial dimension of the side portion 31 (in Figure 5 (The dimension in the vertical direction) is set to, for example, the dimension that completely accommodates the rotor magnet 2 inside.
[0049] The end face 32 is a disk-shaped portion that forms the axial end face (the end face separated from the substrate 8) of the side face 31. This end face 32... Figure 1 The upper surface is shown in the rotor housing 3. The notch 33 is a portion cut into a shape corresponding to the rib 22 of the rotor magnet 2 and fitted into the rib 22. The notches 33 are arranged at equal intervals along the circumference of the side surface 31, the same number as the ribs 22. The hole 34 is a circular opening obtained by perforating the center portion of the end face 32. The output shaft 4 of the rotor 1 is fixed through the hole 34.
[0050] [2. Function, effect]
[0051] Figure 7This is a perspective view illustrating the injection molding state of a rotor magnet 2' as described in conventional technology. The overall shape of the injection mold 41 is omitted for illustrative purposes. In this rotor magnet 2', the thickness T1 of the cylindrical portion 21 is small relative to the inner diameter D0 of the front end of the pin-point gate 42, and no ribs 22 are formed. Therefore, the injection pressure (the pressure of the mixed material flowing inside the mold frame) becomes high, easily leading to mold frame breakage and flash at the mold joint. Therefore, the number of pin-point gates 42 (gate number) injecting the mixed material into one rotor magnet 2' must be increased, reducing the number of rotor magnets 2' that can be manufactured in a single filling process. Figure 7 In the example shown, there are 6 gates for a single rotor magnet 2′, and the number of rotor magnets 2′ manufactured by a single injection molding die 41 is one.
[0052] In contrast, Figure 6 This is a perspective view illustrating the injection molding state of the rotor magnet 2 according to this embodiment. The overall shape of the injection molding mold 41 is omitted for illustrative purposes. In the upper mold of the injection molding mold 41, a mixture of magnetic material and resin flows sequentially through the sprue 43, runner 44, and pin gate 42, and is injected into the lower mold of the rotor magnet 2. The rotor magnet 2 has a rib 22 with an inner diameter D0 or greater and a thickness T2 at the front end of the pin gate 42. This reduces the injection pressure and the number of gates for a single rotor magnet 2. Therefore, the number of rotor magnets 2 that can be manufactured in a single filling process increases, making it easier to achieve multiple processing steps at once. Figure 6 In the example shown, there are 4 gates for a rotor magnet 2, and four rotor magnets 2 are manufactured by one injection molding die 41.
[0053] (1) The rotor magnet 2 described above is configured to rotate relative to the base plate 8 of the fixed stator 5 and is disposed opposite to the stator 5. The rotor magnet 2 is formed by injection molding a mixture of magnetic material and resin through a pin-point gate 42. The rotor magnet 2 includes: a cylindrical portion 21, which is formed in a cylindrical shape and has a plurality of magnetic poles arranged thereon; and ribs 22, which are formed in a radially protruding shape at the axial end of the cylindrical portion 21. Figure 4 As shown, the thickness T1 of the cylindrical part 21 is smaller than the inner diameter D0 of the front end of the pin gate 42, and the thickness T2 of the rib 22 is larger than the inner diameter D0 of the front end of the pin gate 42.
[0054] Based on this structure, the injection pressure of the mixed materials during molding can be reduced compared to the case without ribs 22. This allows for an increase in the number of rotor magnets 2 that can be manufactured in a single filling process, improving productivity and cost. Furthermore, it prevents molding defects caused by increased injection pressure, improving product quality. Moreover, it eliminates the need for upgrading the injection molding die 41 or replacing it with the latest model to increase the production volume of rotor magnets 2, effectively utilizing existing production equipment while improving the productivity of rotor magnets 2. It should be noted that the effects of this design are independent of the inner diameter D0 of the front end of the pin-point gate 42, and are particularly significant when the inner diameter D0 is 1.5 mm or less.
[0055] (2) The rotor magnet 2 described above has a trace portion 23, which protrudes from the axial end face 24 of the rib 22 as a trace of the injection molding of the rotor magnet 2 and is approximately circular in shape, corresponding to the inner diameter D0 of the front end of the pin-point gate 42. Additionally, as... Figure 4 As shown, the thickness T1 of the cylindrical portion 21 is smaller than the outer diameter D1 of the trace portion 23, and the thickness T2 of the rib 22 is greater than or equal to the outer diameter D1 of the trace portion 23.
[0056] In this way, by referring to the dimensions of the trace portion 23 corresponding to the front end of the injection gate 42, the injection pressure of the mixed material during molding can be more reliably controlled compared to the case without ribs 22, thus reducing the risk of defects, improving productivity and cost, and enhancing product quality. Furthermore, by omitting post-processing (deburring) (i.e., residual trace portion 23) in injection molding, the productivity of the rotor magnet 2 can be improved. Moreover, deformation and damage of the rotor magnet 2 caused by post-processing in injection molding can be prevented, further improving product quality.
[0057] (3) In the rotor magnet 2 described above, as Figures 2-4 As shown, the axial end face of rib 22, i.e., rib end face 24, is formed to be concave than the axial end face of cylindrical portion 21, i.e., cylindrical portion end face 25. In other words, cylindrical portion end face 25 has a shape that protrudes axially toward the substrate 8 side compared to rib end face 24. Furthermore, the step dimension H2 between rib end face 24 and cylindrical portion end face 25 is equal to or greater than the height dimension H1 of the trace portion 23.
[0058] In this way, by making the cylindrical end face 25 protrude axially toward the substrate 8 side from the rib end face 24, the trace portion 23 can be accommodated inside the step between the rib end face 24 and the cylindrical end face 25. As a result, for example, it is possible to reliably prevent deformation and damage caused by interference or contact between the magnetic sensor 9, which is disposed on the side of the rotor 1 closer to the substrate 8, and the trace portion 23, thereby improving product quality.
[0059] (4) The rib 22 described above is positioned to avoid the boundaries of multiple magnetic poles when viewed axially from the rotor magnet 2. This improves the detection accuracy of the rotation angle of the rotor 1 by the magnetic sensor 9. The magnetic sensor 9 senses the boundaries of the magnetic force of the rotor magnet 2. Therefore, if the rib 22 is formed across the boundaries of the magnetic poles, for example, the distance between the magnetic sensor 9 and the rib end face 24 increases, thereby reducing the output of the magnetic sensor 9 and decreasing the detection accuracy of the rotation angle. Furthermore, the axial height of the trace portion 23 on the rib end face 24 varies depending on the location, making the detection accuracy even more unstable. On the other hand, by positioning the rib 22 to avoid the boundaries of the magnetic poles, such a decrease in accuracy can be avoided. Therefore, the controllability of the brushless motor 10 can be improved. It should be noted that even when the rotor magnet 2 described above is used in motors other than the brushless motor 10, such as rotary encoders, the decrease in detection accuracy of the magnetic pole boundaries caused by the rib 22 can be suppressed.
[0060] (5) The rib 22 described above can also be positioned at the center of any magnetic pole when viewed axially from the rotor magnet 2. In this case, the distance between the rib 22 and the boundary of the magnetic pole when viewed axially from the rotor magnet 2 can be maximized, and the reduction in accuracy caused by the rib 22 (the reduction in detection accuracy caused by the magnetic sensor 9) can be minimized. Therefore, the controllability of the brushless motor 10 can be further improved.
[0061] (6) The rotor magnet 2 described above is as follows Figure 3 The image shows an anisotropic toroidal magnet. Compared to radially anisotropic toroidal magnets, anisotropic toroidal magnets tend to have a greater influence on the ribs 22 generated by the magnetic sensor 9 (the effect of changes in the distance between the rotor magnet 2 and the magnetic sensor 9 on the detection accuracy of the magnetic sensor 9). Therefore, by setting the position of the ribs 22 in the anisotropic toroidal magnet at the center of the magnetic poles, the reduction in detection accuracy at the magnetic pole boundaries caused by the ribs 22 can be effectively suppressed, and even the controllability of the brushless motor 10 can be improved.
[0062] (7) The brushless motor 10 described above is a brushless motor 10 that includes a stator 5, a rotor magnet 2 arranged radially opposite to the stator 5, and a rotor housing 3 holding the rotor magnet 2. The rotor magnet 2 is formed by injection molding a mixture of magnetic material and resin through a pin-point gate 42. The rotor magnet 2 has: a cylindrical portion 21, which is formed in a cylindrical shape and has a plurality of magnetic poles arranged thereon; and ribs 22, which are formed in a radially protruding shape at the axial end of the cylindrical portion 21 and engage with the rotor housing 3. In addition, as Figure 4As shown, the thickness T1 of the cylindrical part 21 is smaller than the inner diameter D0 of the front end of the pin gate 42, and the thickness T2 of the rib 22 is larger than the inner diameter D0 of the front end of the pin gate 42.
[0063] According to this structure, compared with the case where the rotor magnet 2' has no ribs 22, the productivity and cost of the rotor magnet 2 can be improved, and the product quality can be enhanced. Therefore, the productivity of the brushless motor 10 can be improved. In addition, the adhesive material used to bond the rotor magnet 2 to the rotor housing 3 is not required, which simplifies the device structure. Therefore, the productivity and cost of the brushless motor 10 can be further improved. Moreover, by engaging the ribs 22 of the rotor magnet 2 with the notch 33 of the rotor housing 3, the circumferential positional displacement of the rotor magnet 2 caused by the rotation of the rotor 1 can be suppressed. Therefore, the controllability of the brushless motor 10 can be further improved.
[0064] [3. Other]
[0065] The above embodiments are merely illustrative and are not intended to exclude the applicability of various modifications and techniques not explicitly shown in these embodiments. The structures of these embodiments can be implemented with various modifications without departing from their spirit. Furthermore, the structures of these embodiments can be selected and omitted as needed, or appropriately combined with various structures included in known technologies.
[0066] In the above embodiments, an external rotor type brushless motor was illustrated, but the same structure can also be applied to an internal rotor type brushless motor. For example, in an internal rotor type brushless motor with a stator arranged in a ring shape, a cylindrical portion and ribs can be formed in the rotor magnet arranged radially inward opposite to the stator. The ribs, for example, are formed in a shape that protrudes radially inward at the axial end of the cylindrical portion. In such a rotor magnet, by making the thickness of the cylindrical portion smaller than the inner diameter of the pin sprue and the thickness of the ribs larger than the inner diameter of the pin sprue, the same effect as in the above embodiments can be achieved.
[0067] It should be noted that the rotor magnet of this invention is applicable not only to brushless motors but also to brushed motors and rotary encoders. The rotor magnet for rotary encoders is configured to rotate relative to a substrate 8 on which a rotation angle sensor (e.g., a magnetic sensor, optical sensor, electrostatic sensor, etc.) is fixed, and is positioned opposite the rotation angle sensor. This rotor magnet is formed by injection molding a mixture of magnetic material and resin through a pin-point gating system. In such a rotor magnet, the thickness of the cylindrical portion is smaller than the inner diameter of the pin-point gating system, and the thickness of the ribs is greater than or equal to the inner diameter of the pin-point gating system, thereby achieving the same effect as in the embodiments described above.
[0068] Industrial availability
[0069] This technology can be applied to the manufacturing industry of rotor magnets for motors and rotary encoders, and also to the manufacturing industry of brushless motors.
[0070] Explanation of reference numerals in the attached figures:
[0071] 1. Rotor
[0072] 2. Rotor magnet
[0073] 3 Rotor housing
[0074] 4 Output shaft
[0075] 5 stators
[0076] 6-layer iron core
[0077] 7 windings
[0078] 8 substrate
[0079] 9. Magnetic sensor (rotation angle sensor)
[0080] 10 brushless motors
[0081] 11. Opening
[0082] 12 Stator retainers
[0083] 13 Stator fixing part
[0084] 14 bearings
[0085] 21. Cylindrical section
[0086] 22 ribs
[0087] 23. Trace Section
[0088] 24 Rib end face
[0089] 25. End face of cylindrical section
[0090] 31 Side profile
[0091] 32 End face
[0092] 33. Notch
[0093] 34 Holes
[0094] 41 Injection molding die
[0095] 42 Needle point gate
[0096] 43 notes
[0097] 44 branch channels
[0098] D0 Inner diameter of the tip of the pinpoint gate
[0099] D1 Outer diameter of the trace
[0100] T1 Thickness of the cylindrical section
[0101] Thickness of T2 rib
[0102] H1 Height dimension of the trace area
[0103] H2 is the step size between the end face of the cylindrical section and the end face of the rib.
Claims
1. A rotor magnet, configured to be rotatable relative to a substrate on which a stator or a rotation angle sensor is fixed, and disposed opposite to said stator or said rotation angle sensor, wherein the rotor magnet is formed by injection molding a mixture of a magnetic material and a resin via a pin-point gating system, characterized in that, The rotor magnet has the following features: The cylindrical section is formed in a cylindrical shape and has multiple magnetic poles arranged thereon; Ribs, which are formed in a radially protruding shape only at one end of the axial end of the cylindrical portion; as well as The trace portion, which protrudes from the axial end face of the rib, i.e. the rib end face, as a trace of the injection molding of the rotor magnet, is set to an approximately circular shape corresponding to the inner diameter of the front end of the pin-point gate. The thickness of the cylindrical portion is smaller than the inner diameter of the front end of the pin-point gate and smaller than the outer diameter of the mark portion. The thickness of the rib is greater than or equal to the inner diameter of the front end of the needle point gate and greater than or equal to the outer diameter of the mark portion.
2. The rotor magnet according to claim 1, characterized in that, The axial end face of the cylindrical portion, i.e. the end face of the cylindrical portion, has a shape that protrudes from the axial side of the substrate compared to the rib end face. Furthermore, the step size between the rib end face and the cylindrical end face is greater than or equal to the height of the trace portion.
3. The rotor magnet according to claim 1, characterized in that, The ribs are configured to avoid the boundaries of the plurality of magnetic poles when viewed axially from the rotor magnet.
4. The rotor magnet according to claim 3, characterized in that, The rib is positioned at the center of any of the magnetic poles when viewed axially from the rotor magnet.
5. The rotor magnet according to claim 4, characterized in that, The rotor magnet is an anisotropic toroidal magnet.
6. A brushless motor comprising a stator, a rotor magnet disposed radially opposite to the stator, and a rotor housing holding the rotor magnet, the rotor magnet being formed by injection molding a mixture of a magnetic material and a resin through a pin-point gating system, characterized in that... The rotor magnet has: a cylindrical portion formed in a cylindrical shape and having a plurality of magnetic poles arranged thereon; a rib formed in a radially protruding shape at the axial end of the cylindrical portion and engaging with the rotor housing; and a trace portion, which protrudes from the axial end face of the rib, i.e., the rib end face, as a trace of the injection molding of the rotor magnet, and is set to a roughly circular shape corresponding to the inner diameter of the front end of the pin-point gate. The thickness of the cylindrical portion is smaller than the inner diameter of the front end of the pin-point gate and smaller than the outer diameter of the mark portion. The thickness of the rib is greater than or equal to the inner diameter of the front end of the pin-point gate and greater than or equal to the outer diameter of the mark portion. The outer circumferential surface of the cylindrical portion fits into the inner circumferential surface of the rotor housing.