Ring-shaped magnet, method for manufacturing a ring-shaped magnet, and mold used therefor.

Abstract

When fitting a magnet into the magnet holder, it is possible to set the direction in which the magnet is fitted in one direction, and in order to reduce the difference in magnetic flux density values ​​between multiple valleys or peaks of magnetic flux density that appear when the angle is changed along the circumferential direction to obtain the magnetic flux density, the first groove or protrusion is magnetized in the radial direction of the ring shape and is arranged along the axial direction of the ring shape magnet, and is arranged along the axial direction of the ring shape magnet A ring-shaped magnet is provided with a second groove or protrusion on its outer surface, the second groove or protrusion having a different shape from the first groove or protrusion, the cross-sectional area of ​​the second groove or protrusion being 1.0 to 2.8 times the cross-sectional area of ​​the first groove or protrusion, and the position where the second groove or protrusion is provided is 110° to 180° or -110° to -180°, with the first groove or protrusion as the reference 0°, and a method for manufacturing the same and a mold used for manufacturing are provided.

Description

【Technical Field】 【0001】 The present invention relates to a ring-shaped magnet, a method for manufacturing the ring-shaped magnet, and a mold used therefor. 【Background Art】 【0002】 Magnetic rotary angle detectors are used for the purpose of detecting the angle of any component in various devices. For example, Patent Document 1 describes a magnet holding unit having a substantially cylindrical magnet in which S poles and N poles are alternately arranged in the circumferential direction, and a holding member into which the magnet is fitted. The magnetic holding unit is attached to the tip of a rotary drive shaft. The rotation angle of the magnet is detected by a magnetic detection device. 【Prior Art Documents】 【Patent Documents】 【0003】 【Patent Document 1】 Japanese Unexamined Patent Application Publication No. 2015-135295 【Summary of the Invention】 【Problems to be Solved by the Invention】 【0004】 In the magnet holding unit of Patent Document 1, a first ridge portion and a second ridge portion are provided on the magnet, a first insertion portion and a second insertion portion are provided on the holding member, and the first ridge portion and the second ridge portion of the magnet are respectively engaged with the first insertion portion and the second insertion portion of the holding member to fit the magnet into the holding member. 【0005】 In the magnet holding unit of Patent Document 1, since the first ridge portion and the second ridge portion have the same shape, there is a problem that the direction of the magnet is not unidirectionally determined when the magnet is fitted into the magnet holding unit. For example, when the S pole and the N pole are arranged in a direction perpendicular to the straight line connecting the first ridge portion and the second ridge portion of the magnet, it can be fitted so that the S pole is located on the upper side of the magnet holding unit, or it can be fitted so that the N pole is located on the lower side of the magnet holding unit. 【0006】 When the direction in which the magnet is fitted into the magnet holding unit is limited to one direction, it was found that if the shape of the first and second protrusions is changed without limitation, differences in magnetic flux density values ​​appear between multiple troughs or peaks of magnetic flux density that appear when the magnetic flux density is obtained by changing the angle along the circumferential direction of the ring-shaped magnet. 【0007】 On the other hand, in a sensor that detects rotation angle using magnetism, when the angle is changed along the circumferential direction and the magnetic flux density is obtained, the accuracy of the sensor can be ensured if there is no difference in the magnetic flux density value between multiple troughs of magnetic flux density, or between multiple peaks of magnetic flux density, or if the difference is as small as possible. 【0008】 The present invention is a magnet holding part Material When inserting a magnet into the object, it is possible to set the direction in which the magnet is inserted to one direction, and when the magnetic flux density is obtained by changing the angle along the circumferential direction, the magnetic flux density value appears between multiple valleys of magnetic flux density. difference To reduce the value of the magnetic flux density between multiple peaks of magnetic flux density difference The objective is to provide a ring-shaped magnet that can be made smaller, a method for manufacturing the same, and a mold used for manufacturing the same. [Means for solving the problem] 【0009】 The ring-shaped magnet is magnetized in the radial direction of the ring shape, and has a first groove or protrusion arranged along the axial direction of the ring-shaped magnet and a second groove or protrusion arranged along the axial direction of the ring-shaped magnet on its outer surface, the first groove or protrusion and the second groove or protrusion have different shapes, the cross-sectional area of ​​the second groove or protrusion is 1.0 to 2.8 times the cross-sectional area of ​​the first groove or protrusion, and the second groove or protrusion is The above problem is solved by using a ring-shaped magnet positioned at 110° to 180° or -110° to -180°, with the first groove or protrusion being the reference 0°. 【0010】 This is a mold for manufacturing a ring-shaped magnet, the mold having a ring-shaped cavity, a sleeve made of a non-magnetic material provided on the inner circular side of the cavity, and a cylindrical magnet disposed inside the sleeve, the cylindrical magnet being magnetized in the radial direction of the cylinder, the inner wall of the mold having a first groove or protrusion arranged along the axial direction and a second groove or protrusion arranged along the axial direction, the first groove or protrusion and the second groove or protrusion having different shapes, the cross-sectional area of ​​the second groove or protrusion being 1.0 to 2.8 times the cross-sectional area of ​​the first groove or protrusion, and the position where the second groove or protrusion is provided is the same as the first groove or The above problem is solved by using a mold for a ring-shaped magnet, where the ridge is set as the reference 0°, and the angle is between 110° and 180° or between -110° and -180°. 【0011】 A method for manufacturing a ring-shaped magnet, wherein the mold has a ring-shaped cavity, a sleeve made of a non-magnetic material provided on the inner circular side of the cavity, and a cylindrical magnet disposed inside the sleeve, the inner wall of the mold is provided with a first groove or protrusion arranged along the axial direction and a second groove or protrusion arranged along the axial direction, the first groove or protrusion and the second groove or protrusion have different shapes, the cross-sectional area of ​​the second groove or protrusion is 1.0 to 2.8 times the cross-sectional area of ​​the first groove or protrusion, and the second groove or protrusion is provided. The above problem is solved by a method for manufacturing a ring-shaped magnet, which includes a step of filling the cavity with a mixture containing magnetic powder and a binder, where the position is 110° to 180° or -110° to -180°, with the first groove or protrusion as the reference 0°. [Effects of the Invention] 【0012】 According to the present invention, the magnet holding part Material When inserting a magnet into the object, it is possible to set the direction in which the magnet is inserted to one direction, and when the magnetic flux density is obtained by changing the angle along the circumferential direction, the magnetic flux density value appears between multiple valleys of magnetic flux density. differenceReduce it, or reduce the value of the magnetic flux density between the peaks of multiple magnetic flux densities difference It is possible to provide a ring-shaped magnet capable of reducing difference , a method for manufacturing the same, and a mold used for the manufacturing. 【Brief Description of Drawings】 【0013】 [Figure 1] It is a perspective view showing an example of a ring-shaped magnet and a mold for manufacturing the ring-shaped magnet. [Figure 2] It is a plan view of the ring-shaped magnet and the mold in FIG. 1. [Figure 3] In a sleeve disposed on the inner circle side of a ring-shaped magnet and a cylindrical magnet disposed on the inner circle side of the sleeve, it is a diagram showing the magnetic flux lines of the cylindrical magnet. [Figure 4] It is a diagram showing the magnetization direction in the ring-shaped magnet of FIG. 3. [Figure 5] It is a plan view showing another example of a ring-shaped magnet and a mold for manufacturing the ring-shaped magnet. [Figure 6] It is a plan view showing another example of a ring-shaped magnet and a mold for manufacturing the ring-shaped magnet. [Figure 7] It is a plan view showing another example of a ring-shaped magnet and a mold for manufacturing the ring-shaped magnet. [Figure 8] It is a plan view showing another example of a ring-shaped magnet and a mold for manufacturing the ring-shaped magnet. [Figure 9] It is a plan view showing another example of a ring-shaped magnet and a mold for manufacturing the ring-shaped magnet. [Figure 10] It is a plan view showing another example of a ring-shaped magnet and a mold for manufacturing the ring-shaped magnet. [Figure 11] It is a plan view showing another example of a ring-shaped magnet and a mold for manufacturing the ring-shaped magnet. [Figure 12] It is a plan view showing another example of a ring-shaped magnet and a mold for manufacturing the ring-shaped magnet. [Figure 13]It is a plan view showing another example of a ring-shaped magnet and a mold for manufacturing the ring-shaped magnet. [Figure 14] In the ring-shaped magnet, it is an explanatory diagram of the angle in the analysis of Table 2 for changing the angle at which the second concave groove is provided with respect to the first concave groove, and is a diagram showing an example where the angle θ is 330° based on the case where the right side orthogonal to the magnetization direction is 0°. [Figure 15] In the ring-shaped magnet, it is an explanatory diagram of the angle in the analysis of Table 2 for changing the angle at which the second concave groove is provided with respect to the first concave groove, and is a diagram showing an example where the angle θ is 45° based on the case where the right side orthogonal to the magnetization direction is 0°. [Figure 16] In the ring-shaped magnet, it is an explanatory diagram of the angle in the analysis of Table 2 for changing the angle at which the second concave groove is provided with respect to the first concave groove, and is a diagram showing an example where the angle difference of the second concave groove with respect to the first concave groove is -165°. [Figure 17] It is an explanatory diagram of the cross-sectional area of the concave groove. [Figure 18] It is an explanatory diagram of the cross-sectional area of the concave groove. [Figure 19] It is an explanatory diagram of the cross-sectional area of the protrusion. [Figure 20] It is an explanatory diagram of the cross-sectional area of the protrusion. [Figure 21] It is a graph showing the analysis result of the change in magnetic flux density from 0 to 360° in the ring-shaped magnet according to FIG. 6 (Manufacturing Example 3). [Figure 22] It is a graph showing the analysis result of the change in magnetic flux density from 0 to 360° in the ring-shaped magnet according to FIG. 2 (Manufacturing Example 1). [Figure 23] It is a graph showing the analysis result of the change in magnetic flux density from 0 to 360° in the ring-shaped magnet related to the angle 45° of the other groove in Table 2. [Figure 24] The position of the first concave groove is 135°, and it is a graph of the analysis result of the magnetic flux density from 0 to 360° of each ring-shaped magnet when the positions of the second concave grooves are 270°, 285°, 300°, 315°, 330°, and 345°. [Figure 25] It is a plan view showing a state where the ring-shaped magnet is fitted inside the magnet holding member. [Figure 26] This is a plan view showing a ring-shaped magnet fitted inside a magnet holding member. [Figure 27] This is a plan view showing a ring-shaped magnet fitted inside a magnet holding member. [Figure 28] This is a plan view showing a ring-shaped magnet fitted inside a magnet holding member. [Modes for carrying out the invention] 【0014】 An embodiment of the ring-shaped magnet of the present invention will be described below. The embodiment shown below is merely a limited example of the embodiments of the present invention, and the technical scope of the present invention is not limited to the embodiment shown. 【0015】 Figures 1 to 20 show examples of molds 11 used in manufacturing ring-shaped magnets and ring-shaped magnets 12 manufactured by the molds 11. The molds and ring-shaped magnets in Figures 1 to 20 differ in the shape of the grooves or protrusions, or the position where the grooves or protrusions are provided, as shown in each figure, but for the sake of explanation, the same reference numerals are used. 【0016】 The mold 11 comprises a ring-shaped cavity 13, a sleeve 14 made of a non-magnetic material provided on the inner circular side of the cavity 13, and a cylindrical magnet 15 positioned inside the sleeve 14. The cavity 13 of the mold 11 is cylindrical, and the central axis of the sleeve 14 is positioned to extend along the central axis of the cylinder. 【0017】 The sleeve 14 is cylindrical in shape. A cylindrical magnet 15 is positioned so as to be in contact with the inner wall. As its name suggests, the cylindrical magnet 15 is cylindrical and consists of a single permanent magnet. 【0018】 As shown in Figure 1, the cavity 13 is located at the center of the cylindrical mold 11, with the flat side of the mold 11 being an opening and the bottom side of the mold 11 being closed. The sleeve 14 is placed on the inner circular side of the cavity 13, and the cylindrical magnet 15 is placed on the inner circular side of the sleeve 14. 【0019】 The mold 11 is provided with a ring-shaped cavity 13. A ring-shaped magnet can be manufactured by filling the cavity 13 with bonded magnet whose fluidity has been increased by heating and then solidifying it. The bonded magnet mainly consists of a mixture of magnet powder and a binder. The magnet powder is, for example, Nd-Fe-B rare earth magnet, Sm-Fe-N rare earth magnet, S Any of the following types of magnets may be used: m-Co rare earth magnets, Sr ferrite magnets, Ba ferrite magnets, Sr-La-Co ferrite magnets, Ca-La-Co ferrite magnets, etc., and the magnet powders may be anisotropic or isotropic. Two or more types of these magnets may also be used in combination. 【0020】 The binder acts as an adhesive between the magnetic powders and is not particularly limited, but a resin binder is suitable. Thermoplastic resins are especially suitable for injection molding of bonded magnets. Examples of thermoplastic resins include nylon 6, nylon 12, and PPS. Commercially available injection molding materials for bonded magnets may also be used. For example, Mate Corporation's injection molding materials for bonded magnets include the HM series, RNI series, RSI series, or HNI series. For example, Sumitomo Metal Mining Co., Ltd.'s injection molding materials for bonded magnets include Wellmax-S3, S4, or S5. 【0021】 A cylindrical magnet 15, positioned inside the sleeve 14 and magnetized in the radial direction of its cylindrical shape, exerts a magnetic field on the circumferential side of the cylindrical magnet 15 within the cavity 13. In Figures 3 and 4, the white arrow placed to the right of the cylindrical magnet 15 or the white arrow placed on top of the cylindrical magnet indicates the magnetization direction of the cylindrical magnet 15. When the molten bond magnet material is filled into the cavity 13, it is oriented and magnetized by the magnetic field and simultaneously molded. If the bond magnet material contains anisotropic magnetic powder, the magnetic powder is oriented and magnetized and molded. If the bond magnet material contains only isotropic magnetic powder, it is only magnetized and molded. 【0022】 The sleeve 14 in the mold 11 is thought to be unnecessary because it reduces the intensity of the magnetic flux density in the cavity 13. However, it is necessary because not installing the sleeve 14 would lead to wear on the cylindrical magnet 15 and poor dimensional accuracy of the ring-shaped magnet being molded. Furthermore, if it is desired to improve the uniformity of the magnetic flux density in the space on the inner side of the ring-shaped magnet 12 being molded, or to increase the intensity of the magnetic flux density, a thinner sleeve is preferable. For example, the thickness of the sleeve can be 0.5 to 4 mm. If the material of the sleeve 14 is a magnetic material, the magnetic flux lines generated from the cylindrical magnet 15 will concentrate in the sleeve 14, reducing the magnetic flux density in the cavity 13, and furthermore, changing the pattern of the magnetic flux lines, so a non-magnetic material is desirable. Examples of non-magnetic materials include non-magnetic steel, ceramics, or non-magnetic cemented carbide. The permeability (μ) of the non-magnetic material can be, for example, 1.02 H / m or less. 【0023】 Furthermore, the material used for the mold 11 (outer frame 111) is a non-magnetic material, taking into consideration applications where leakage of magnetic flux lines to the outside of the ring-shaped magnet should be avoided. If the outer frame 5 is made of a soft magnetic material, magnetic flux lines will leak from the cavity 13 to the outer frame 111, causing magnetic flux to leak into the space 17 (Figure 17) on the outer side of the molded ring-shaped magnet 12. This will worsen the uniformity of the magnetic flux density in the space 17 on the inner side of the ring-shaped magnet 12. For example, the same material as the sleeve 14 can be used for the outer frame 111. 【0024】 The manufacturing method for ring-shaped magnets is not limited to the injection molding described above; for example, they may be manufactured using methods such as compression molding or extrusion molding, but manufacturing by injection molding is the simplest method. 【0025】 According to the mold 11 shown in Figures 1 and 9, the magnet is ring-shaped, and the magnet is magnetized in the radial direction of the ring shape, and the outer surface of the ring-shaped magnet is provided with a first groove 121a or protrusion 121b arranged along the axial direction of the ring-shaped magnet, and a second groove 122a or protrusion 122b arranged along the axial direction of the ring-shaped magnet, and the first groove 121a or protrusion 121b and the second groove 122a or protrusion 122b The two shapes are different, and the cross-sectional area of ​​the second groove 122a or protrusion 122b is 1.0 to 2.8 times the cross-sectional area of ​​the first groove 121a or protrusion 121b. The position where the second groove 122a or protrusion 122b is provided is 110° to 180° or -110° to -180°, with the first groove 121a or protrusion 121b as the reference 0°. Ring-shaped magnets (hereinafter sometimes simply referred to as magnets) can be manufactured using these methods. Similar ring-shaped magnets can also be manufactured using the molds shown in Figures 5 to 11 and Figures 12 and 13. 【0026】 According to the magnet, the magnet holding part Material When inserting a magnet into a magnet holder, it is possible to specify a single direction for inserting the magnet. For example, as shown in Figures 25 and 28, when attempting to insert a ring-shaped magnet 12 into a ring-shaped magnet holder 16, the first groove 121a or protrusion 121b and the second groove 122a or protrusion 122b have different shapes. As shown in Figures 25 and 28, for example, if the north pole is placed in a position where there is no groove 123a or projection 123b in the magnet holder 16, and the south pole is placed in a position where there is no groove 124a or projection 124b in the magnet holder 16, then the direction in which the magnet is inserted is always fixed to a single direction. 【0027】 As will be described later using Figures 21 to 23, when the magnetic flux density is measured over 360° along the circumference of the ring-shaped magnet at a radius of 0.25 mm from the center point of the ring-shaped magnet, two peaks and two valleys appear in the magnetic flux density value. By setting the position where the second groove 122a or protrusion 122b is provided to 110° to 180° or -110° to -180°, with the first groove 121a or protrusion 121b as the reference 0°, the difference in magnetic flux density values ​​between the two peaks and the difference in magnetic flux density values ​​between the two valleys can be reduced. The position in which the second groove 122a or protrusion 122b is provided is more preferably 120 to 180° and -120° and -180°, with the first groove 121a or protrusion 121b as the reference 0°, more preferably 130 to 180° and -160° and -180°, and more preferably 170° to 180° and -170° to -180°. By reducing the difference in magnetic flux density between the peaks and valleys, the reliability of detecting the direction of rotation is improved and the detection of the direction of rotation becomes easier when the ring-shaped magnet is used as a magnetic rotation angle detector or the like. Furthermore, with the first groove 121a or protrusion 121b set as the reference 0°, the clockwise movement of the second groove 122a or protrusion 122b is represented by a negative value, and the counterclockwise movement of the second groove 122a or protrusion 122b is represented by a positive value. 【0028】 On the other hand, in the ring-shaped magnets shown in Figures 12, 26, and 27, the first groove 121a and the second groove 122a have the same shape, therefore the magnet holding part Material When inserting a magnet into a magnet holder, it is not possible to determine the direction in which the magnet is inserted. When inserting a ring-shaped magnet 12 into a ring-shaped magnet holder 16, for example, the magnet can be inserted so that the north pole is positioned at a 90° angle to the magnet holder, or the south pole can be inserted so that the south pole is positioned at a 90° angle to the magnet holder. For this reason, the magnet magnet The direction in which the magnet is fitted into the retaining member is not uniformly determined. Although not shown in the illustration, the same applies when the first protrusion 121b and the second protrusion 122b have the same shape. MaterialWhen inserting a magnet into it, it is not possible to specify a single direction for inserting the magnet. 【0029】 In this specification, "a different shape for the first groove or protrusion and the second groove or protrusion" includes cases where, for example, the groove or protrusion is a combination of a triangle and a semicircle, a combination of a square and a semicircle, or a combination of a square and a triangle, so that when the ring-shaped magnet is observed in plan view, the contour of one groove or protrusion is different from the contour of the other groove or protrusion. Furthermore, "a different shape for the first groove or protrusion and the second groove or protrusion" also includes cases where, for example, the groove or protrusion is a semicircle, but the cross-sectional area of ​​one groove or protrusion is different from the cross-sectional area of ​​the other groove or protrusion, and as a result, the ring-shaped magnet and the magnet holding member can only be fitted in one direction. 【0030】 As shown in Figures 1 to 16, if a groove is provided in the ring-shaped magnet 12, a protrusion shaped to follow the groove is provided on the inner wall surface of the cavity 13 of the mold 11. If a protrusion is provided in the ring-shaped magnet 12, a groove shaped to follow the protrusion is provided on the inner wall surface of the cavity 13 of the mold 11. This makes it possible to form a groove or protrusion of a desired shape in the ring-shaped magnet. 【0031】 The cross-sectional area of ​​the groove or protrusion provided on the ring-shaped magnet is determined as follows. That is, as shown in Figures 17 to 20, a straight line (imaginary line) is assumed to connect the circumference forming the outline of the ring-shaped magnet and the two points of contact of the edge forming the groove or protrusion. The area of ​​the figure enclosed by the straight line and the edge forming the groove or protrusion is taken as the cross-sectional area of ​​the groove or protrusion. In Figures 17 to 20, the cross-sectional area of ​​the groove or protrusion is shown by hatching. The cross-sectional area of ​​the second groove 122a or protrusion 122b is more preferably 1.0 to 1.8 times the cross-sectional area of ​​the first groove 121a or protrusion 121b, and more preferably 1.0 to 1.2 times. 【0032】 Furthermore, the cross-sectional area of ​​the protrusions provided on the inner wall surface of the cavity 13 of the mold 11 can be considered to be the cross-sectional area of ​​the grooves 121a and 122a shown in Figures 17 and 18. The cross-sectional area of ​​the groove provided on the inner wall surface of cavity 13 can be considered to be the same as the cross-sectional area of ​​the protrusions 121b and 122b shown in Figures 19 and 20. 【0033】 The magnet holding member 16 can be any shape, but it shall have a receiving portion that follows the protrusion or groove of the ring-shaped magnet 12, that is, a shape that includes a groove or protrusion. The magnet holding member can be made of any material such as plastic. As shown in Figures 25 to 28, the receiving portion may have a first groove 123a or protrusion 123b, a second groove 124a or This can be composed of a protrusion 124b. When the ring-shaped magnet 12 is provided with protrusions 121b and 122b, the grooves 123a and 124a are shaped to follow the protrusions, and when the ring-shaped magnet 12 is provided with grooves 121a and 122a, the protrusions 123b and 124b are shaped to follow the grooves. 【0034】 The ring-shaped magnet of the present invention can be used as a magnetic rotation angle sensor. In particular, it can be suitably used as a rotation angle sensor for control components in automobiles, home appliances, office automation equipment, and residential equipment. 【0035】 The dimensions of the ring-shaped magnet can be determined as appropriate depending on the application. For example, the outer diameter of the ring-shaped magnet can be 15 to 95 mm. Also, for example, the inner diameter of the ring-shaped magnet can be 1 to 71 mm. 【0036】 The grooves or protrusions provided on the ring-shaped magnet can have a width of 5 to 21% of the diameter (outer diameter) of the ring-shaped magnet. The depth (height) can be 0.5 to 8.5% of the diameter of the ring-shaped magnet. The width and depth are based on the aforementioned straight line (dummy line). The depth (height), as shown in Figures 17 and 20, refers to the length of a straight line perpendicular to the aforementioned straight line (dummy line) at the position where the depth of the groove or the height of the protrusion is maximum. The width refers to the length of the aforementioned straight line (dummy line). [Examples] 【0037】 The present invention will be described in detail below with reference to examples. The examples shown below are merely limited examples of embodiments of the present invention, and the technical scope of the present invention is not limited to the examples shown. 【0038】 [Manufacturing Example 1] As shown in Figure 2, a ring-shaped magnet 12 having a first groove 121a at the 0° position and a second groove 122a at the 180° position was manufactured using a mold 11 having a ring-shaped cavity 13, a sleeve 14 made of a non-magnetic material provided on the inner circular side of the cavity 13, and a cylindrical magnet 15 arranged on the inner circular side of the sleeve 14, as shown in Figure 4. 【0039】 The dimensions of cavity 13 are as follows: the outer diameter of the outer frame is 28 mm, the inner diameter of the outer frame is 22 mm, the outer diameter of the sleeve is 16 mm, and the axial length (height) of the ring-shaped magnet is 14 mm. This allows for the manufacture of a ring-shaped magnet with an outer diameter of 22 mm, an inner diameter of 16 mm, and an axial length (height) of 14 mm. 【0040】 The material of the cylindrical magnet 15 is a neodymium magnet (N46MH manufactured by Shin-Etsu Chemical Co., Ltd.). The cylindrical magnet has an outer diameter of 14 mm and an axial length of 17 mm, and is magnetized radially as shown in Figures 3 and 4. The position where the north pole is located is defined as 90°, the position where the south pole is located as 270°, the position to the right of the line perpendicular to the line connecting the north and south poles is defined as 0°, and the line perpendicular to the line connecting the north and south poles left The side position is set to 180°. 【0041】 The thickness of sleeve 14 is 1 mm, and the material of sleeve 14 is HPM75 (manufactured by Tatei Metal Co., Ltd.). The outer frame 5 has an inner diameter of 22 mm as described above, an outer diameter of 28 mm, and an axial length of 15 mm. 【0042】 The material of the mold 11 (outer frame) is non-magnetic steel (HPM75 manufactured by Hitachi Metals, Ltd.). In addition, the top surface of the mold is also made of non-magnetic steel (HPM75 manufactured by Hitachi Metals, Ltd.) and serves as a cover for the opening of the cavity 13. 【0043】 A mixture of anisotropic ferrite magnetic powder and PPS resin (HM-1616, HM series, injection molding material for bonded magnets, manufactured by Mate Co., Ltd.) was used as the main component of the ring-shaped magnet 12. 【0044】 The injection molding conditions were a cylinder temperature of 280-320°C and a mold temperature of 100°C. 【0045】 In manufacturing example 1, a rectangular groove and a triangular groove were formed on the inner wall of the mold cavity at the 0° and 180° positions in a plan view, as shown in Figure 2. The dimensions and cross-sectional area of ​​each groove are as shown in Table 1. The grooves extend along the axial direction of the ring-shaped magnet, and their length is the same as the height of the ring-shaped magnet. That is, the cross-sectional shape of the grooves shown in Figure 2 is continuous in the axial direction. The ring-shaped magnet in this manufacturing example is based on Figure 2, and is the magnet with the mold removed as shown in Figure 2. The shapes of the following manufacturing examples also correspond to the respective reference diagrams shown in Table 1. 【0046】 [Manufacturing Examples 2 to 10] In Manufacturing Example 1, the combination of groove shapes and cross-sectional areas provided at the 0° and 180° positions was changed as shown in Table 1 to produce ring-shaped magnets according to Manufacturing Examples 2 to 10. Plan views of the ring-shaped magnets according to Manufacturing Examples 2 to 8 are shown in the respective reference figures in Table 1. Note that the "ridge" in Table 1 refers to a ridge of the shape described in Table 1, provided along the axial direction of the ring-shaped magnet, instead of a groove. This ridge extends along the axial direction of the ring-shaped magnet, and its length is the same as the height of the ring-shaped magnet. That is, the cross-sectional shape of the ridge shown in Figure 9 is continuous in the axial direction. Furthermore, the ring-shaped magnet according to Manufacturing Example 7 was manufactured in the same manner as in Example 1, except that the manufacturing conditions, including the dimensions of the mold cavity, were changed so that the outer diameter was 44 mm, the inner diameter was 32 mm, and the thickness of the ring-shaped magnet was 14 mm. The sleeve thickness remained unchanged at 1 mm, while the outer diameter of the sleeve and the outer diameter of the cylindrical magnet were changed to match the size of the ring-shaped magnet in Manufacturing Example 7. The outer diameter of the cylindrical magnet was made to be large enough to fit snugly against the sleeve, similar to Manufacturing Example 1. 【0047】 [Analysis 1] For the ring-shaped magnets in manufacturing examples 1 to 10 described above, the point where the N pole and S pole switch was defined as 0°, as shown in Figure 4. The 0° position is perpendicular to the magnetization direction and is located on the right side. The cross-section of the ring-shaped magnet was set at the center position in the height direction of the ring-shaped magnet, i.e., at a position of 7 mm. The magnetic flux density from 0° to 360° was analyzed at a position 0.25 mm from the center of the ring-shaped magnet in this cross-section. Three-dimensional analysis was performed using JMAG-Designer from JSOL. The analysis conditions were the same as those for each of the manufacturing examples described above. 【0048】 Figure 21 shows the analysis results for manufacturing example 3. Figure 22 shows the analysis results for manufacturing example 1. As shown in Figures 21 and 22, the bottom of the magnetic flux density valley appears near 0° and 180° where the grooves or protrusions are provided. The peaks of the magnetic flux density valley appear near 90° and 270°. 【0049】 The "difference in magnetic flux density (mT)" was calculated by subtracting the magnetic flux density value at the bottom of the magnetic flux density trough near 0° from the magnetic flux density value at the bottom of the magnetic flux density trough near 180°, and summarized in Table 1. The absolute value of the "difference in magnetic flux density (mT)" is also shown in Table 1. 【0050】 [Table 1] 【0051】 In Table 1, "Type" indicates whether a groove or a protrusion is provided on the ring-shaped magnet. "Groove" indicates that a pair of grooves are provided on the ring-shaped magnet. "Protrusion" indicates that a pair of protrusions are provided on the ring-shaped magnet. In Table 1, "Magnification" indicates the ratio of the cross-sectional area of ​​the groove or protrusion at the 0° position to the cross-sectional area of ​​the groove or protrusion at the 180° position. Note that R1 in Manufacturing Example 2 refers to the radius of the circle. 【0052】 In magnetic rotation angle detectors, accuracy can be ensured if the difference between the magnetic flux density values ​​at the troughs of one magnetic flux density and those at the troughs of the other magnetic flux density is small. Similarly, accuracy can be ensured if the difference between the magnetic flux density values ​​at the peaks of one magnetic flux density and those at the peaks of the other magnetic flux density is small. 【0053】 In Table 1, a magnetic flux density difference of less than 0.0002 mT was classified as "Excellent," a difference of 0.0002 mT or more and less than 0.001 mT was classified as "Good," a difference of 0.001 mT or more and less than 0.0075 mT was classified as "Acceptable," and a difference of 0.0075 mT or more was classified as "Unacceptable." In Table 1, in all manufacturing examples, the bottom of the magnetic flux density trough appeared around 0° and 180°, and the bottom of the magnetic flux density trough appeared around 90° and 270°. 【0054】 The above manufacturing example The ring-shaped magnets in example 8 showed a small difference in magnetic flux density. However, the ring-shaped magnets in example 8 had a problem in that when fitting the magnets into the magnet holding member, the direction in which the magnets were fitted was not fixed to one direction, which complicated the manufacturing process of the magnetic rotation angle detector. 【0055】 [Analysis 2] As shown in Figures 14 and 15, a ring-shaped magnet was manufactured in which the position of the first groove was fixed at 135° relative to the 0° position, and the position of the second groove was changed in increments of 15° from the 0° position. The first groove was triangular in shape, and the second groove was square in shape. The areas of the first groove and the second groove were the same, and the details were the same as in Manufacturing Example 1. Details such as the thickness and diameter of the ring-shaped magnet were also the same as in Manufacturing Example 1. 【0056】 For each manufactured ring-shaped magnet, the center position in the height direction of the ring-shaped magnet was set, i.e., at a position of 7 mm. The magnetic flux density from 0° to 360° was analyzed at a position 0.25 mm from the center of the ring-shaped magnet in the said cross-section. Three-dimensional analysis was performed using JMAG-Designer from JSOL. The analysis conditions for the mold, sleeve, cylindrical magnet, etc., were the same as those specified in Manufacturing Example 1 in Table 1 above. 【0057】 Figure 23 shows an example of the results of an analysis of the relationship between the angle and magnetic flux density of a ring-shaped magnet having the shape shown in Figure 15. In Figure 23, the position of the first groove is 135°, and the position of the second groove is 45°. Compared to the case where the second groove is located symmetrically to the first groove, the difference in magnetic flux density obtained by subtracting the magnetic flux density of the first valley from the magnetic flux density of the second valley was larger. Also, the difference in magnetic flux density obtained by subtracting the magnetic flux density of the first peak from the magnetic flux density of the second peak was larger. 【0058】 Figure 24 shows graphs of the analysis results of the magnetic flux density from 0 to 360° for each ring-shaped magnet, when the position of the first groove is fixed at 135° and the position of the second groove is changed to 270°, 285°, 300°, 315°, 330°, and 345°. Compared with the example in Figure 23, it can be seen that the difference in magnetic flux density is smaller both between peaks and valleys. 【0059】 Table 2 summarizes the results of analyzing the difference in magnetic flux density, calculated by subtracting the magnetic flux density of the first valley from the magnetic flux density of the second valley, and the difference in magnetic flux density, calculated by subtracting the magnetic flux density of the first peak from the magnetic flux density of the second peak, for each manufacturing example in which the angle of the second groove was changed. As shown in Figure 16, Table 2 also shows the angle of the second groove, with the angle of the first groove, 135°, set as 0° (reference). When measuring the angle, the line connecting the center point in the width direction of the groove and the center point of the ring-shaped magnet was used as the reference. The absolute value of the difference in magnetic flux density is also shown in Table 2. 【0060】 [Table 2] 【0061】 In Table 2, for both the difference in magnetic flux density between peaks and between valleys, an absolute value of less than 0.0010 mT of the difference in magnetic flux density was classified as "Excellent," an absolute value of 0.0010 mT or more but less than 0.005 mT was classified as "Good," an absolute value of 0.005 mT or more but less than 0.0075 mT was classified as "Acceptable," and a difference of 0.0075 mT or more was classified as "Unacceptable." The "Overall Judgment" in Table 2 indicates the worse of the evaluations based on the magnetic flux density between peaks and valleys. 【0062】 As is clear from Table 2, the difference in magnetic flux density between the peaks and valleys decreases when the angle difference between the two grooves is 110-180°, -110-180°, 120-180°, and -120-180°, relative to the angle of one groove. 【0063】 [Manufacturing examples 9 to 12] As shown in Table 3 below, ring-shaped magnets according to Manufacturing Examples 9 to 12 were manufactured in the same manner as in Example 1, except that the outer and inner diameters of the ring-shaped magnets, the type of groove or protrusion on the ring-shaped magnets, and the dimensions of the groove or protrusion were changed. The thickness of the sleeve remained unchanged at 1 mm, and the outer diameter of the sleeve and the outer diameter of the cylindrical magnets were changed to match the size of the ring-shaped magnets in Manufacturing Examples 9 to 12. The outer diameter of the cylindrical magnets was made to be large enough to fit snugly against the sleeve, as in Manufacturing Example 1. In Table 3, if "Type" is groove, it indicates that grooves are provided at both the 0° and 180° positions. If "Type" is protrusion, it indicates that protrusions are provided at both the 0° and 180° positions. In addition, "Magnification" in Table 3 indicates the magnification of the outer and inner diameters of the ring-shaped magnets relative to Manufacturing Example 1. Manufacturing Examples 1 and 7 are the same as described above. 【0064】 [Table 3] 【0065】 [Analysis 3] For each manufactured ring-shaped magnet, the center position in the height direction of the ring-shaped magnet was set, i.e., at a position of 7 mm. The magnetic flux density from 0° to 360° was analyzed at a position 0.25 mm from the center of the ring-shaped magnet in the said cross-section. Three-dimensional analysis was performed using JMAG-Designer from JSOL. The analysis conditions for the mold, sleeve, cylindrical magnet, etc., were the same as those for each manufacturing example shown in Table 3 above. 【0066】 As is clear from the results in Table 3, even when the outer or inner diameter, groove, or protrusion dimensions of the ring-shaped magnet change, the difference between the magnetic flux density value at the 0° position and the magnetic flux density value at the 180° position remains small. The evaluation criteria in Table 3 are the same as those in Table 1 above. Note that, as in Table 1, the difference in magnetic flux density indicates the difference in magnetic flux density in the valleys. 【0067】 When the magnetic flux density of the ring-shaped magnets used in the analyses described in Tables 1 to 3 above was measured, the results were consistent with the analysis results. The ring-shaped magnets that received a rating of "Excellent," "Good," or "Acceptable" in the above analyses had a fixed orientation when fitted into the magnet holder and were able to accurately detect the rotation angle when used as a magnetic rotation angle detector. [Explanation of Symbols] 【0068】 12 Ring-shaped magnets 121a Groove 121b Projection 122a Groove 122b Projection 11 molds 13 Cavity 14 sleeves 15 cylindrical magnets

Claims

[Claim 1] It is a ring-shaped magnet that fits inside the magnet holding member. The aforementioned magnet is magnetized such that the south pole and north pole are arranged in the radial direction of the ring shape. The outer surface of the ring-shaped magnet is provided with a first groove or protrusion arranged along the axial direction of the ring-shaped magnet and a second groove or protrusion arranged along the axial direction of the ring-shaped magnet. The first groove or protrusion and the second groove or protrusion have different shapes. The cross-sectional area of ​​the second groove or protrusion is 1.0 to 2.8 times the cross-sectional area of ​​the first groove or protrusion. The first groove or protrusion is located on the outer surface of the ring-shaped magnet at a position perpendicular to the straight line connecting the north pole and the south pole, or on the outer surface of the ring-shaped magnet excluding the position perpendicular to the straight line connecting the north pole and the south pole. The position where the second groove or protrusion is provided is 170° to 180° or -170° to -180°, with the first groove or protrusion being the reference 0°. A ring-shaped magnet that allows you to determine the direction in which the ring-shaped magnet is fitted into the magnet holding member. [Claim 2] This is a mold for manufacturing a ring-shaped magnet that fits inside a magnet holding member. The mold comprises an outer frame made of a non-magnetic material, a ring-shaped cavity, a sleeve made of a non-magnetic material provided on the inner circular side of the cavity, and a cylindrical magnet disposed inside the sleeve. The cylindrical magnet is magnetized such that the south pole and north pole are arranged in the radial direction of the cylinder, and the direction in which the ring-shaped magnet is fitted into the magnet holding member can be determined. On the inner wall of the mold, It comprises a first groove or protrusion arranged along the axial direction, and a second groove or protrusion arranged along the axial direction, The first groove or protrusion and the second groove or protrusion have different shapes. The cross-sectional area of ​​the second groove or protrusion is 1.0 to 2.8 times the cross-sectional area of ​​the first groove or protrusion. The first groove or protrusion is located on the inner wall of the mold at a position perpendicular to the straight line connecting the north pole and the south pole, or on the inner wall of the mold excluding the position perpendicular to the straight line connecting the north pole and the south pole. A mold for a ring-shaped magnet, wherein the position where the second groove or protrusion is provided is 170° to 180° or -170° to -180°, with the first groove or protrusion being the reference 0°. [Claim 3] This is a method for manufacturing a ring-shaped magnet that fits inside a magnet holding member. The mold comprises an outer frame made of a non-magnetic material, a ring-shaped cavity, a sleeve made of a non-magnetic material provided on the inner circular side of the cavity, and a cylindrical magnet positioned inside the sleeve. On the inner wall of the mold, It comprises a first groove or protrusion arranged along the axial direction, and a second groove or protrusion arranged along the axial direction, The first groove or protrusion and the second groove or protrusion have different shapes. The cross-sectional area of ​​the second groove or protrusion is 1.0 to 2.8 times the cross-sectional area of ​​the first groove or protrusion. The first groove or protrusion is located on the inner wall of the mold at a position perpendicular to the straight line connecting the north pole and the south pole, or on the inner wall of the mold excluding the position perpendicular to the straight line connecting the north pole and the south pole. The position where the second groove or protrusion is provided is 170° to 180° or -170° to -180°, with the first groove or protrusion being the reference 0°. The process includes the steps of filling the cavity with a mixture containing magnetic powder and a binder, and magnetizing the mixture in the cavity of the mold so that the south pole and north pole are arranged in the radial direction of the cylinder, and forming it into a ring shape. A method for manufacturing a ring-shaped magnet, wherein the direction in which the ring-shaped magnet is fitted into the magnet holding member can be determined.

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