JP2019158408A - Magnet structure, rotation angle detector, and electric power steering device - Google Patents

Abstract

To provide a magnet structure, a rotation angle detector and an electric power steering device with which it is possible to improve sensor accuracy.SOLUTION: In a magnet structure, a first end 35 of a support 34 is terminated in a second portion 33b of a bonded magnet molding 32 and is short of a first portion 33a. For this reason, the first portion 33a having a disk shape is composed only of a magnet material and can be considered to be a single entity of magnet of the same dimension and having a disk shape. In this case, the magnetic flux distribution of the first portion 33a is substantially the same as the magnetic flux distribution of the single entity of magnet having the disk shape and it is possible to obtain an ideal magnetic flux distribution or a magnetic flux distribution close to it. Using a magnet structure having an ideal magnetic flux distribution, it is possible to realize high sensor accuracy in a rotation sensor when a rotation sensor is oppositely arranged on the first end 35 side of the support 34 of the magnet structure.SELECTED DRAWING: Figure 4

Description

  The present invention relates to a magnet structure, a rotation angle detector, and an electric power steering apparatus.

  In recent years, development of technology for detecting the rotation angle of an electric motor of an electric power steering device using a magnetic sensor has been advanced. For example, in Patent Document 1 below, a rotation sensor that detects the direction of the magnetic field of a sensor magnet is disposed close to and opposed to a sensor magnet of a sensor magnet assembly attached to a rotation shaft of the electric motor. A technique for detecting the rotation angle of the rotating shaft is disclosed.

International Publication No. 2015/140961

  As a result of diligent research, the inventors have found that the sensor accuracy of the magnetic sensor is improved when the magnetic flux distribution of the sensor magnet is close to an ideal magnetic flux distribution without any disturbance. However, in the prior art described above, sufficient consideration has not been given to the magnetic flux distribution of the sensor magnet.

  It is an object of the present invention to provide a magnet structure, a rotation angle detector, and an electric power steering device that can improve sensor accuracy.

  A magnet structure according to an aspect of the present invention is a bonded magnet molded body having a first portion having a plate shape with a uniform thickness and a second portion adjacent to the first portion in the thickness direction of the first portion. And a support body that extends along the thickness direction of the first portion of the bonded magnet molded body and that has a coated end portion covered with the bonded magnet molded body, and the support body has a thickness direction of the first portion. Is located on the second part side of the bonded magnet molding, and the coated end portion terminates in the second part.

  In the magnet structure, the coated end portion terminates at the second portion of the bonded magnet molding and does not reach the first portion. Therefore, about the 1st part of a bonded magnet molding, it comprises only magnet material and can be regarded as a magnet simple substance. In this case, the magnetic flux distribution of the first part of the bonded magnet molding is substantially the same as the magnetic flux distribution of the magnet alone, and an ideal magnetic flux distribution or a magnetic flux distribution close to it is obtained. Therefore, when a magnetic sensor is disposed opposite to the coated end portion side of the magnet structure (that is, the first part side of the bonded magnet molded body), high sensor accuracy can be realized in the magnetic sensor.

  In the magnet structure according to another embodiment, the shape of the first portion is symmetric with respect to the axis of the support when viewed from the axial direction of the support. In this case, the magnetic flux distribution around the axis of the support body approaches the ideal magnetic flux distribution, and the sensor accuracy can be further improved.

  In the magnet structure according to another embodiment, the shape of the first portion is a disc shape having the axis of the support as the central axis. In this case, since a uniform magnetic field is formed around the axis of the support, the sensor accuracy can be further improved.

  In the magnet structure according to another embodiment, the shape of the second part is a disk shape having the axis of the support as the central axis, and the diameter of the second part is smaller than the diameter of the first part.

  In the magnet structure according to another embodiment, the support is made of a nonmagnetic material. When the support is made of a magnetic material, the influence of the support on the magnetic flux distribution of the bonded magnet molding is large. However, when the support is made of a non-magnetic material, the influence is relatively small. .

  The rotation angle detector which concerns on one form of this invention is provided with the said magnet structure and the magnetic sensor arrange | positioned facing the magnet structure in the coating | coated end part side. An electric power steering apparatus according to an aspect of the present invention includes the rotation angle detector.

  According to the present invention, a magnet structure, a rotation angle detector, and an electric power steering device that can improve sensor accuracy are provided.

FIG. 1 is a schematic cross-sectional view illustrating a motor assembly including a rotation angle detector according to the embodiment. FIG. 2 is a block diagram showing an electric power steering apparatus in which the motor assembly shown in FIG. 1 is used. FIG. 3 is a schematic perspective view showing the rotation angle detector shown in FIG. 4A is a side view and FIG. 4B is an end view showing the form of the bonded magnet molded body shown in FIG. 3.

  Hereinafter, embodiments for carrying out the present invention will be described in detail with reference to the accompanying drawings. In addition, the same code | symbol is attached | subjected about the same or equivalent element, and the description is abbreviate | omitted when description overlaps.

  FIG. 1 is a schematic cross-sectional view showing a motor assembly 10 including a rotation angle detector according to the embodiment. The motor assembly 10 has a configuration in which a rotation angle detector 15 and an electric motor 20 are accommodated in a housing 12.

  The electric motor 20 includes a rotating shaft 22 having a torque side end 22a and a sensor side end 22b. The torque side end 22a of the rotary shaft 22 is rotatably held by a ball bearing 14A provided on the housing 12, and the sensor side end 22b is rotated by a ball bearing 14B provided on the housing 12. It is held freely.

  A magnet structure 30 to be described later is attached to the sensor side end 22b. In addition, a rotation sensor (magnetic sensor) 40 is disposed in the housing 12 at a position facing and close to the magnet structure 30. In the present embodiment, the rotation angle detector 15 is configured by the magnet structure 30 and the rotation sensor 40. The rotation sensor 40 detects a magnetic field generated from the magnet structure 30. The rotation sensor 40 includes a detection circuit configured by, for example, a Wheatstone bridge circuit, and includes a magnetoresistive effect element (MR element: Magnetoresistance Effect element) as a magnetic detection element of the Wheatstone bridge circuit. As MR elements, anisotropic magnetoresistance effect elements (AMR elements: Anisotropic Magnetoresistance Effect elements), giant resistance effect elements (GMR elements: Giant Magnetoresistance Effect elements), tunnel magnetoresistance effect elements (TMR elements: Tunnel Magnetoresistance Effect elements) Etc. can be used. The rate of change in resistance of the MR element is represented by a magnetoresistance ratio (MR ratio). The MR ratio is the difference between the resistance values in the two magnetization states divided by the resistance value in the equilibrium state. That is, the MR ratio indicates how large the resistance value when the magnetization direction of the MR element is opposite to the resistance value when the magnetization direction is the same direction, and the higher the MR ratio, the higher the sensitivity. It can be said that this is an MR element. The MR ratio of the AMR element and the GMR element is about 3% and 12%, respectively, whereas the MR ratio of the TMR element is 90% or more. By using a high-sensitivity MR element as the rotation sensor of the rotation angle detector 15, a large output can be obtained from the rotation angle detector 15. The output when the TMR element is used as the rotation sensor is about 20 times the output when the AMR element is used and about 6 times the output when the GMR element is used. For this reason, in order to obtain the output of the rotation angle detector 15, it is preferable to use a TMR element, thereby improving the detection accuracy of the rotation angle. Hereinafter, a case where the rotation sensor 40 of the rotation angle detector 15 is a TMR element will be described. Further, by using a TMR element as the rotation sensor 40, the rotation angle detector 15 can be reduced in size. The rotation sensor 40 can be a biaxial type having two MR elements, and detects the direction of a magnetic field in a plane orthogonal to the central axis of the magnet structure 30.

  Here, an electric power steering apparatus 50 in which the motor assembly 10 is used will be described with reference to FIG.

  In addition to the motor assembly 10 described above, the electric power steering device 50 includes a control unit 52 generally called an ECU (Electronic Control Unit) and a torque sensor 56 that detects the steering force of the steering wheel 54. . The control unit 52 receives a vehicle speed signal from the vehicle, information regarding the rotation angle of the rotating shaft 22 detected by the rotation angle detector 15 of the motor assembly 10, and a torque signal of the torque sensor 56 regarding the steering force of the steering wheel 54. It is configured to be able to. Further, the control unit 52 is configured to be able to adjust a current for driving the electric motor 20. When the control unit 52 receives the vehicle speed signal and the torque signal, the control unit 52 drives the electric motor 20 by sending a current corresponding to them to the electric motor 20 for power assist, and assists the steering force by the torque of the rotating shaft 22. Do it. At this time, the control unit 52 performs feedback control of the current of the electric motor 20 according to the rotation angle of the rotary shaft 22 received from the rotation sensor 40, and adjusts the amount of power assist.

  Hereinafter, the configuration of the magnet structure 30 and the rotation sensor 40 of the rotation angle detector 15 will be described with reference to FIGS.

  As shown in FIGS. 3 and 4, the magnet structure 30 includes a bonded magnet molded body 32 and a support 34.

  As shown in FIG. 4, the bonded magnet molded body 32 includes a first portion 33a and a second portion 33b that are integrally formed. The first portion 33a has a complete disc shape having a diameter D1 and a thickness T1. The first portion 33a is not provided with a convex portion or a concave portion, and is designed so that its thickness T1 is uniform. The diameter D1 of the 1st part 33a can be 5-25 mm, for example, and can also be 10-20 mm. The second portion 33b is adjacent to the first portion 33a in the thickness direction of the first portion 33a, and has a disk shape with a diameter D2 and a thickness T2. The diameter D2 of the second portion 33b is smaller than the diameter D1 of the first portion 33a. The diameter D2 of the second portion 33b can be set to 4 to 10 mm, for example. The ratio (D2 / D1) of the diameter D2 of the second portion 33b to the diameter D1 of the first portion 33a can be 1.2 to 5. The second portion 33b is designed so that its thickness T2 is uniform. The total thickness (T1 + T2, the length in the central axis direction) of the bonded magnet molded body 32 can be set to 1 to 12 mm, for example, and can also be set to 3 to 10 mm. The first portion 33a and the second portion 33b are aligned (coaxially arranged) so that their central axes coincide.

  The bonded magnet molded body 32 is disposed such that the end surface 32a on the first portion 33a side faces the rotation sensor 40. That is, the bonded magnet molded body 32 is arranged such that the first portion 33a is closer to the rotation sensor 40 than the second portion 33b. As shown in FIG. 3, both the N pole and the S pole appear on the end face 32a.

  The bonded magnet molded body 32 may be an isotropic bonded magnet molded body or an anisotropic bonded magnet molded body. As the bonded magnet molded body 32, an isotropic bonded magnet molded body can be adopted from the viewpoint of productivity and cost reduction.

  The bonded magnet molded body 32 contains resin and magnet powder. Although the said resin is not specifically limited, It can be a thermosetting resin or a thermoplastic resin. Examples of the thermosetting resin include an epoxy resin and a phenol resin. Examples of the thermoplastic resin include elastomers, ionomers, ethylene propylene copolymers (EPM), and ethylene-ethyl acrylate copolymers. Specific examples of the elastomer include styrene, olefin, urethane, polyester, and polyamide. The resin is selected according to a molding method, moldability, heat resistance, mechanical properties, and the like. When the bonded magnet molded body 32 is manufactured by injection molding, the resin can be a thermoplastic resin. In addition to these resins, a coupling agent and other additives may be used for manufacturing the bonded magnet molded body 32. The melting point of the thermoplastic resin can be set to, for example, 100 to 350 ° C., or 120 to 330 ° C. from the viewpoints of moldability and durability. The bonded magnet molded body 32 may contain one type of resin alone, or may contain two or more types of resins.

  Examples of the magnet powder include rare earth magnet powder and ferrite magnet powder. From the viewpoint of obtaining high magnetic properties, the magnet powder is preferably a rare earth magnet powder. Examples of rare earth magnets include R—Fe—B, R—Co, and R—Fe—N. R refers to a rare earth element. Note that in this specification, the rare earth element means scandium (Sc), yttrium (Y), and a lanthanoid element belonging to Group 3 of the long-period periodic table. Examples of lanthanoid elements include lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy). ), Holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), lutetium (Lu), and the like. The rare earth elements can be classified into light rare earth elements and heavy rare earth elements. In the present specification, “heavy rare earth element” indicates Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu, and “light rare earth element” indicates Sc, Y, La, Ce, Pr, Nd, Sm and Eu. Show.

  The magnet powder is more preferably an R—Fe—B magnet powder. The R—Fe—B magnet powder is preferably an R (Nd, Pr) —Fe—B magnet powder containing at least one of Nd and Pr as R (rare earth element). In addition to R, Fe, and B, R-Fe-B magnet powder may be Co, Ni, Mn, Al, Cu, Nb, Zr, Ti, W, Mo, V, Ga, Zn, Si, etc. Other elements or inevitable impurities may be included.

  When the bonded magnet molded body 32 is an isotropic bonded magnet molded body, the shape of the magnet powder is not particularly limited, and may be any of a spherical shape, a crushed shape, a needle shape, a plate shape, and the like. On the other hand, when the bonded magnet molded body 32 is an anisotropic bonded magnet molded body, the shape of the magnet powder is preferably needle-shaped or plate-shaped. The average particle size of the magnet powder is preferably 30 to 250 μm, and more preferably 50 to 200 μm. The bonded magnet molded body 32 may contain one type of magnet powder alone, or may contain two or more types of magnet powder. The definition of the average particle diameter is d50 of the volume-based particle size distribution in the laser diffraction particle size measurement method.

  Moreover, content of resin can be 40-90 volume% with respect to the total volume of the bonded magnet molded object 32 from a viewpoint of obtaining a desired magnetic characteristic and moldability, and shall be 50-80 volume%. You can also. Moreover, content of magnet powder can be 10-60 volume% with respect to the whole volume of the bonded magnet molding 32 from the same viewpoint, and can also be 20-50 volume%.

  The support body 34 is a long member extending along the thickness direction of the bonded magnet molded body 32 and has a substantially cylindrical outer diameter. The length of the support body 34 can be 3-20 mm, for example, and can also be 5-15 mm.

  The material constituting the support 34 can be selected from non-magnetic materials. Examples of the nonmagnetic material constituting the support 34 include aluminum, copper, brass, and stainless steel. The support 34 is made of brass in this embodiment.

  The support 34 has a first end 35 (covered end) to which the bonded magnet molded body 32 is attached and a second end 36 attached to the rotary shaft 22 of the electric motor 20. The second end portion 36 is provided with a hole 36 a extending along the axis 34 a of the support body 34. When the rotary shaft 22 arranged coaxially with respect to the support 34 is attached to the support 34 at the second end 36, the sensor side end of the rotary shaft 22 of the electric motor 20 is inserted into the hole 36 a of the second end 36. 22b is press-fitted.

  The first end portion 35 of the support 34 is covered with the bonded magnet molded body 32 so as to be embedded in the bonded magnet molded body 32. The first end 35 of the support 34 is located on the second portion 33 b side of the bonded magnet molded body 32. Moreover, the 1st edge part 35 of the support body 34 is terminated in the 2nd part 33b of the bonded magnet molding 32, and does not reach the 1st part 33a, as shown to Fig.4 (a). In other words, the separation length L between the end surface 32a of the bonded magnet molded body 32 and the end surface 35a of the first end portion 35 of the support 34 is longer than the thickness T1 of the first portion 33a. The first end portion 35 of the support body 34 is aligned (coaxially arranged) so that its axis (that is, the axis of the support body 34) coincides with the central axis of the bonded magnet molded body 32.

  Here, the bonded magnet molded body 32 is attached to the first end 35 of the support 34 by injection molding. When injection molding is performed, first, the support 34 is fixed in the lower mold so that the second end 36 faces upward. The lower mold has a recess that accommodates the support 34 and a space that forms the lower part of the bonded magnet molding. Next, the upper mold is attached to the lower mold, the mold is closed, and a cavity capable of manufacturing the bonded magnet molded body 32 is formed in the mold. Subsequently, the raw material composition containing the resin and the magnet powder is fluidized by heating or the like, injected into the cavity in the mold, and solidified by cooling or the like, whereby the bonded magnet is formed on the first end 35 of the support 34. A molded body 32 is formed. When the bonded magnet molded body 32 is an isotropic bonded magnet molded body, the injection molding is performed without a magnetic field. On the other hand, when the bonded magnet molding 32 is an anisotropic bonded magnet molding, the injection molding is performed in a magnetic field. The bonded magnet molded body 32 may be formed by so-called transfer molding using a thermosetting resin.

  Returning to FIG. 3, in the magnet structure 30, the north pole and south pole of the bonded magnet molded body 32 are spaced apart in a direction perpendicular to the axis 34 a of the support 34. As a result, a static magnetic field such as M shown in the figure is generated around the magnet structure 30, and a magnetic field in a direction perpendicular to the axis 34 a is generated on the axis 34 a of the support 34. Since the direction of the magnetic field on the shaft 34a changes according to the rotational position in the rotational direction R of the magnet structure 30, the rotation sensor 40 disposed opposite to the magnet structure 30 on the first end 35 side is subjected to the magnetic field. By detecting the direction, the rotation angle of the magnet structure 30 can be detected.

  In the rotation angle detector 15, the rotation shaft 22 of the electric motor 20 is attached to the second end 36 of the support 34. Then, the magnet structure 30 rotates in the direction R around the axis 34 a of the support 34 in conjunction with the rotation of the rotary shaft 22. Therefore, the rotation angle of the rotation shaft 22 of the electric motor 20 can be detected by detecting the rotation angle of the magnet structure 30.

  As described above, in the magnet structure 30, the first end portion 35 of the support 34 terminates at the second portion 33 b of the bonded magnet molded body 32 and does not reach the first portion 33 a. Therefore, the 1st part 33a which has a disk shape is comprised only with the magnet material, and can be regarded as the magnet of the same dimension which has a disk shape. In this case, the magnetic flux distribution of the first portion 33a is substantially the same as the magnetic flux distribution of the disk-shaped magnet alone, and an ideal magnetic flux distribution or a magnetic flux distribution close thereto is obtained. Here, the ideal magnetic flux distribution is a magnetic flux distribution in which a region showing parallel magnetic flux vectors in a wide range is wide.

  The inventors have obtained knowledge that the sensor accuracy of the rotation sensor 40 is improved by bringing the magnetic flux distribution of the bonded magnet molded body 32 close to the ideal magnetic flux distribution. Therefore, by using the magnet structure 30 having an ideal magnetic flux distribution, the first end portion 35 side of the support 34 of the magnet structure 30 (that is, the bonded magnet molded body 32) as in the above-described embodiment. When the rotation sensor 40 is disposed opposite to the first portion 33a side), high sensor accuracy can be realized in the rotation sensor 40.

  On the other hand, when the 1st part 33a is the shape in which the convex part and the recessed part were provided, or the shape in which the through-hole was provided, it will move away from ideal magnetic flux distribution, and it is thought that the sensor accuracy in the rotation sensor 40 falls. In particular, when the first portion 33a has a through hole extending in the thickness direction, the robustness of the sensor constituted by the magnet structure 30 and the rotation sensor 40 is further reduced, and the sensor characteristics are deteriorated. It is done.

  Further, as in the above-described embodiment, the shape of the first portion 33a is a perfect disc shape with the axis 34a of the support 34 as the central axis, so that a uniform magnetic field around the axis 34a of the support 34 is obtained. Is formed. Thereby, the further improvement of the sensor accuracy of the rotation sensor 40 arrange | positioned on the extension line | wire of the axis | shaft 34a is achieved.

  Further, in the magnet structure 30, the shape of the second portion 33 b is also a disk shape having the axis 34 a of the support 34 as the central axis, like the first portion 33 a, and the diameter D 2 of the second portion 33 b is the first value. It is smaller than the diameter D1 of the 1 part 33a. The ratio (D2 / D1) of the diameter D2 of the second portion 33b to the diameter D1 of the first portion 33a is preferably in the range of 1.2-5. In this case, an ideal magnetic flux distribution can be obtained while the support 34 holds the bonded magnet molded body 32 with sufficient strength.

  In addition, like embodiment mentioned above, the support body 34 is comprised with a nonmagnetic material, and the magnetic flux distribution of the bonded magnet molding 32 is brought close to ideal magnetic flux distribution. When the support is made of a magnetic material, the support has a great influence on the magnetic field of the bonded magnet molded body 32. However, the support 34 is made of a nonmagnetic material, so that the bond magnet of the support 34 is made. The influence of the molded body 32 on the magnetic field can be made relatively small.

  The present invention is not limited to the above embodiment, and various modifications can be made.

  For example, the shape of the first portion 33a of the bonded magnet molded body 32 is not limited to a disk shape, but may be any other plate shape (for example, a quadrangular plate shape, a hexagonal plate shape, etc.) (Polygonal plate shape). In this case, by making the shape of the first portion 33a symmetrical with the axis 34a of the support 34, the magnetic flux distribution around the axis 34a of the support 34 approaches the ideal magnetic flux distribution, and the axis The sensor accuracy of the rotation sensor 40 disposed on the extension line 34a can be further improved.

  Further, the shape of the second portion 33b of the bonded magnet molded body 32 is not limited to a disk shape, but may be other plate shapes (for example, a polygonal plate shape such as a quadrangular plate shape or a hexagonal plate shape). Good. The second portion 33b may be a plate having a uniform thickness, and is not limited to a plate having a uniform thickness. For example, the second portion 33b may have a shape (tapered shape) that decreases in diameter with increasing distance from the first portion 33a in the thickness direction of the first portion 33a.

  In the above embodiment, a support body having a cylindrical outer shape is used, but a support body having a prismatic outer shape or an elliptic columnar outer shape may be used. Furthermore, in the said embodiment, although the aspect which arrange | positions a support body and a magnet molding body coaxially was shown, the position which shifted | deviated from the axis | shaft of the magnet molding body, and the axis | shaft of a support body and the axis | shaft of a magnet molding body shifted | deviated It is also possible to adopt a mode in which a support is attached to the.

  Moreover, in the said embodiment, as the structure where the support body 34 of the magnet structure 30 and the rotating shaft 22 of the electric motor 20 are connected by press-fitting, in the hole 36a provided in the 2nd end part 36 side of the support body 34, it is. Although the aspect which inserts the rotating shaft 22 was shown, it can also be set as the aspect which provides the hole in the rotating shaft 22 side and inserts the 2nd end part 36 of the support body 34 in the hole.

  Furthermore, an engagement portion having predetermined irregularities can be provided on the outer peripheral surface of the first end portion 35 of the support 34. When the first end 35 of the support 34 is embedded in the bonded magnet molded body 32 by injection molding or the like, the first end 35 of the support 34 and the bonded magnet molded body 32 at the engaging portion are Thus, the relative positional deviation of the bonded magnet molded body 32 relative to the support 34 and the detachment of the bonded magnet molded body 32 from the support 34 can be suppressed.

  DESCRIPTION OF SYMBOLS 10 ... Motor assembly, 15 ... Rotation angle detector, 20 ... Electric motor, 22 ... Rotation shaft, 30 ... Magnet structure, 32 ... Bond magnet molding, 33a ... 1st part, 33b ... 2nd part, 34 ... Support body, 35 ... first end, 36 ... second end, 40 ... rotation sensor.

Claims (7)

A bonded magnet molded body having a first portion having a plate shape with a uniform thickness and a second portion adjacent to the first portion in the thickness direction of the first portion;
And extending along the thickness direction of the first portion of the bonded magnet molded body, and comprising a support having a coated end portion coated with the bonded magnet molded body,
The magnet structure, wherein the support is positioned on the second part side of the bonded magnet molded body with respect to the thickness direction of the first part, and the covered end portion is terminated at the second part.   The magnet structure according to claim 1, wherein the shape of the first portion has symmetry with respect to the axis of the support when viewed from the axial direction of the support.   2. The magnet structure according to claim 1, wherein the shape of the first portion is a disk shape having the axis of the support as a central axis.   4. The magnet structure according to claim 3, wherein a shape of the second portion is a disk shape having an axis of the support as a central axis, and a diameter of the second portion is smaller than a diameter of the first portion.   The magnet structure as described in any one of Claims 1-4 with which the said support body is comprised with the nonmagnetic material.   A rotation angle detector comprising the magnet structure according to any one of claims 1 to 5 and a magnetic sensor arranged to face the magnet structure on the covered end portion side.   An electric power steering apparatus comprising the rotation angle detector according to claim 6.

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