JP6954187B2 - Magnet structure, rotation angle detector and electric power steering device - Google Patents

Description

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

In recent years, the development of a technique for detecting the rotation angle of an electric motor of an electric power steering device using a magnetic sensor has been progressing. For example, in Patent Document 1 below, a rotation sensor for detecting the direction of the magnetic field of the sensor magnet is arranged close to the sensor magnet of the sensor magnet assembly attached to the rotation shaft of the electric motor, and the rotation sensor for detecting the direction of the magnetic field of the sensor magnet is arranged so as to face each other. A technique for detecting the rotation angle of a rotating shaft is disclosed.

International Publication No. 2015/140961

After diligent research, the inventors have found that the sensor accuracy of the magnetic sensor improves when the magnetic flux distribution of the sensor magnet is close to the ideal magnetic flux distribution without disturbance. However, in the above-mentioned prior art, the magnetic flux distribution of the sensor magnet has not been sufficiently considered.

An object of the present invention is to provide a magnet structure, a rotation angle detector, and an electric power steering device capable of improving sensor accuracy.

The magnet structure according to one embodiment of the present invention is a bonded magnet molded body having a first portion having a plate shape having a uniform thickness and a second portion adjacent to the first portion in the thickness direction of the first portion. And a support extending along the thickness direction of the first portion of the bonded magnet molded body and having a coated end portion coated on the bonded magnet molded body, and the support is provided in the thickness direction of the first portion. Is located on the second portion side of the bonded magnet molded body, and the coated end portion is terminated at the second portion.

In the magnet structure, the coated end portion is terminated at the second portion of the bonded magnet molded body and does not reach the first portion. Therefore, the first part of the bonded magnet molded body is made of only the magnet material, and can be regarded as a single magnet. In this case, the magnetic flux distribution of the first portion of the bonded magnet molded body 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 can be obtained. Therefore, when the magnetic sensor is arranged to face the coated end portion side of the magnet structure (that is, the first portion side of the bonded magnet molded body), high sensor accuracy can be realized in the magnetic sensor.

In the magnet structure according to the other form, 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. In this case, the magnetic flux distribution around the axis of the support approaches the ideal magnetic flux distribution, and the sensor accuracy can be further improved.

In the magnet structure according to the other form, the shape of the first portion is a disk shape with 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 the other form, the shape of the second portion is a disk shape with the axis of the support as the central axis, and the diameter of the second portion is smaller than the diameter of the first portion.

In the magnet structure according to another form, the support is made of a non-magnetic material. When the support is made of a magnetic material, the influence of the support on the magnetic flux distribution of the bonded magnet molded body is large, but when the support is made of a non-magnetic material, the influence is relatively small. ..

The rotation angle detector according to one embodiment of the present invention includes the magnet structure and a magnetic sensor arranged so as to face the magnet structure on the coated end side. Further, the electric power steering device according to one embodiment of the present invention includes the above-mentioned rotation angle detector.

According to the present invention, a magnet structure, a rotation angle detector, and an electric power steering device capable of improving sensor accuracy are provided.

FIG. 1 is a schematic cross-sectional view showing a motor assembly including the rotation angle detector according to the embodiment. FIG. 2 is a block configuration diagram showing an electric power steering device 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. FIG. 4 is a side view (a) and an end view (b) showing the form of the bonded magnet molded body shown in FIG.

Hereinafter, embodiments for carrying out the present invention will be described in detail with reference to the accompanying drawings. The same or equivalent elements are designated by the same reference numerals, and the description thereof will be omitted if the description is duplicated.

FIG. 1 is a schematic cross-sectional view showing a motor assembly 10 including a rotation angle detector according to an embodiment. The motor assembly 10 has a configuration in which the rotation angle detector 15 and the electric motor 20 are housed in the 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 rotating shaft 22 is rotatably held by a ball bearing 14A provided in the housing 12, and the sensor side end 22b is rotated by a ball bearing 14B provided in the housing 12. It is held freely.

A magnet structure 30, which will be described later, is attached to the sensor side end portion 22b. Further, inside the housing 12, a rotation sensor (magnetic sensor) 40 is arranged at a position close to and facing the magnet structure 30. In the present embodiment, the rotation angle detector 15 is composed of the magnet structure 30 and the rotation sensor 40. The rotation sensor 40 detects the magnetic field generated from the magnet structure 30. The rotation sensor 40 has a detection circuit composed of, for example, a Wheatstone bridge circuit, and has a magnetoresistance effect element (MR element: Magnetoresistance Effect element) as a magnetic detection element of the Wheatstone bridge circuit. MR elements include anisotropic magnetoresistive element (AMR element: Anisotropic Magnetoresistance Effect element), giant resistance effect element (GMR element: Giant Magnetoresistance Effect element), and tunnel magnetoresistive element (TMR element: Tunnel Magnetoresistance Effect element). Etc. can be used. The rate of change in the resistance of the MR element is represented by the magnetoresistance ratio (MR ratio). The MR ratio is the difference between the resistance values in the two magnetization states divided by the resistance values in the equilibrium state. That is, the MR ratio indicates how much the resistance value when the magnetization directions of the MR elements are opposite to each other is larger than the resistance value when the magnetization directions are the same, and the higher the MR ratio, the higher the sensitivity. It can be said that it is an MR element. The MR ratios of the AMR element and the GMR element are about 3% and 12%, respectively, while the MR ratio of the TMR element is 90% or more. By using a highly sensitive MR element as a 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. Therefore, in order to obtain the output of the rotation angle detector 15, it is preferable to use a TMR element, which can improve 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 the TMR element as the rotation sensor 40, the rotation angle detector 15 can be miniaturized. The rotation sensor 40 can be a biaxial type having two MR elements, and detects the direction of the magnetic field in a plane orthogonal to the central axis of the magnet structure 30.

Here, the electric power steering device 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 on the rotation angle of the rotation 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 so that the current for driving the electric motor 20 can be adjusted. When the control unit 52 receives the vehicle speed signal and the torque signal, it sends a current corresponding to them to the electric motor 20 for power assist to drive the electric motor 20, and assists the steering force by the torque of the rotating shaft 22. Do it. At this time, the control unit 52 feedback-controls the current of the electric motor 20 according to the rotation angle of the rotation shaft 22 received from the rotation sensor 40, and adjusts the amount of power assist.

Hereinafter, the configurations of the magnet structure 30 of the rotation angle detector 15 and the rotation sensor 40 will be described with reference to FIGS. 3 and 4.

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 bond magnet molded body 32 is composed of a first portion 33a and a second portion 33b that are integrally formed. The first portion 33a has a perfect disc shape with 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 first portion 33a can be, for example, 5 to 25 mm, or 10 to 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 having 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, for example, 4 to 10 mm. Proportion to the diameter D2 of the second portion 33b of the diameter D1 of the first portion 33a (D 1 / D 2) may be a 1.2-5. Further, the second portion 33b is designed so that its thickness T2 is uniform. The total thickness (T1 + T2, length in the central axial direction) of the bonded magnet molded body 32 can be, for example, 1 to 12 mm, or 3 to 10 mm. The first portion 33a and the second portion 33b are aligned (coaxially arranged) so that their central axes coincide with each other.

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

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

The bond magnet molded body 32 contains a resin and a magnet powder. The resin is not particularly limited, but may be a thermosetting resin or a thermoplastic resin. Examples of the thermosetting resin include epoxy resin and phenol resin. Examples of the thermoplastic resin include elastomers, ionomers, ethylene-propylene copolymers (EPM), ethylene-ethylacrylate copolymers, and the like. Specific examples of the elastomer include styrene-based, olefin-based, urethane-based, polyester-based, and polyamide-based elastomers. The resin is selected according to the molding method, moldability, heat resistance, mechanical properties, and the like. When the bond magnet molded body 32 is manufactured by injection molding, the resin can be a thermoplastic resin. In addition to these resins, a coupling agent, other additives, and the like may be used in the production of the bonded magnet molded body 32. The melting point of the thermoplastic resin can be, for example, 100 to 350 ° C. or 120 to 330 ° C. from the viewpoint of moldability, durability and the like. The bond magnet molded body 32 may contain one kind of resin alone, or may contain two or more kinds 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 type, R-Co type, R-Fe-N type and the like. R refers to a rare earth element. In the present specification, the rare earth element means scandium (Sc), yttrium (Y) and lanthanoid element belonging to Group 3 of the long periodic table. Examples of lanthanoid elements include lanthanum (La), cerium (Ce), placeodium (Pr), neodymium (Nd), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), and dysprosium (Dy). ), Holmium (Ho), Elbium (Er), Thulium (Tm), Ytterbium (Yb), Lutetium (Lu) and the like. Rare earth elements can be classified into light rare earth elements and heavy rare earth elements. In the present specification, "heavy rare earth element" means Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu, and "light rare earth element" means Sc, Y, La, Ce, Pr, Nd, Sm and Eu. show.

The magnet powder is more preferably R-Fe-B based 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, the R-Fe-B magnet powder includes Co, Ni, Mn, Al, Cu, Nb, Zr, Ti, W, Mo, V, Ga, Zn, Si and the like, if necessary. It may contain other elements or unavoidable impurities.

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 spherical, crushed, needle-shaped, plate-shaped or the like. On the other hand, when the bond magnet molded body 32 is an anisotropic bond magnet molded body, the shape of the magnet powder is preferably needle-shaped, plate-shaped, or the like. The average particle size of the magnet powder is preferably 30 to 250 μm, 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 size is d50 of the volume-based particle size distribution in the laser diffraction type particle size measurement method.

Further, the content of the resin can be 40 to 90% by volume and 50 to 80% by volume with respect to the total volume of the bonded magnet molded body 32 from the viewpoint of obtaining desired magnetic properties and moldability. You can also do it. Further, from the same viewpoint, the content of the magnet powder can be 10 to 60% by volume and 20 to 50% by volume with respect to the total volume of the bonded magnet molded body 32.

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

The material constituting the support 34 can be selected from non-magnetic materials. Examples of the non-magnetic 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 rotating shaft 22 of the electric motor 20. The second end 36 is provided with a hole 36a extending along the shaft 34a of the support 34. When the rotary shaft 22 coaxially arranged 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 36a of the second end 36. 22b is press-fitted.

The first end 35 of the support 34 is covered with the bond magnet molded body 32 so as to be embedded in the bond magnet molded body 32. The first end 35 of the support 34 is located on the second portion 33b side of the bonded magnet molded body 32. Further, as shown in FIG. 4A, the first end portion 35 of the support body 34 is terminated at the second portion 33b of the bond magnet molded body 32, and does not reach the first portion 33a. 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 35 of the support 34 is aligned (coaxially arranged) so that its axis (that is, the axis of the support 34) coincides with the central axis of the bond magnet molded body 32.

Here, the bond magnet molded body 32 is attached to the first end portion 35 of the support 34 by injection molding. When performing injection molding, first, the support 34 is fixed in the lower mold so that the second end portion 36 faces upward. The lower mold has a recess for accommodating the support 34 and a space for forming the lower portion of the bonded magnet molded body. Next, the upper mold is attached to the lower mold, the mold is closed, and a cavity capable of manufacturing the bond 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 bond magnet is attached to the first end portion 35 of the support 34. The molded body 32 is formed. When the bond magnet molded body 32 is an isotropic bond magnet molded body, injection molding is performed in a magnetic field. On the other hand, when the bond magnet molded body 32 is an anisotropic bond magnet molded body, injection molding is performed in a magnetic field. The bond 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 and south poles of the bonded magnet molded body 32 are arranged apart from each other in the direction perpendicular to the axis 34a of the support 34. As a result, a static magnetic field as shown in M is generated around the magnet structure 30, and a magnetic field in a direction perpendicular to the shaft 34a is generated on the shaft 34a of the support 34. Since the direction of the magnetic field on the shaft 34a changes according to the rotation position of the magnet structure 30 in the rotation direction R, the rotation sensor 40 arranged to face the magnet structure 30 on the first end 35 side is 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 with the second end portion 36 of the support 34. Then, the magnet structure 30 rotates in the direction R about the shaft 34a of the support 34 in conjunction with the rotation of the rotating shaft 22. Therefore, by detecting the rotation angle of the magnet structure 30, the rotation angle of the rotation shaft 22 of the electric motor 20 can be detected.

As described above, in the magnet structure 30, the first end 35 of the support 34 is terminated by the second portion 33b of the bonded magnet molded body 32 and does not reach the first portion 33a. Therefore, the first portion 33a having a disk shape is made of only a magnet material, and can be regarded as a single magnet having a disk shape and having the same dimensions. In this case, the magnetic flux distribution of the first portion 33a is substantially the same as the magnetic flux distribution of a single magnet having a disk shape, and an ideal magnetic flux distribution or a magnetic flux distribution close to it can be obtained. Here, the ideal magnetic flux distribution is a magnetic flux distribution having a wide region showing parallel magnetic flux vectors in a wide range.

The inventors have found that the sensor accuracy of the rotation sensor 40 is improved by bringing the magnetic flux distribution of the bonded magnet molded body 32 closer to the ideal magnetic flux distribution. Therefore, by using the magnet structure 30 having an ideal magnetic flux distribution, as in the above-described embodiment, the first end 35 side (that is, the bond magnet molded body 32) of the support 34 of the magnet structure 30 is used. When the rotation sensor 40 is arranged to face each other on the first portion 33a side of the above, high sensor accuracy can be realized in the rotation sensor 40.

On the other hand, when the first portion 33a has a shape in which a convex portion or a concave portion is provided or a shape in which a through hole is provided, it is considered that the magnetic flux distribution is deviated from the ideal and the sensor accuracy of the rotation sensor 40 is lowered. In particular, when the first portion 33a has a through hole extending in the thickness direction thereof, it is considered that the robustness of the sensor composed of the magnet structure 30 and the rotation sensor 40 is further lowered, and the sensor characteristics are deteriorated. Be done.

Further, as in the above-described embodiment, the shape of the first portion 33a is a perfect disk shape centered on the shaft 34a of the support 34, so that a uniform magnetic field is formed around the shaft 34a of the support 34. Is formed. As a result, the sensor accuracy of the rotation sensor 40 arranged on the extension line of the shaft 34a is further improved.

Further, in the magnet structure 30, the shape of the second portion 33b is also a disk shape centered on the shaft 34a of the support 34 as in the case of the first portion 33a, and the diameter D2 of the second portion 33b is the second. It is smaller than the diameter D1 of one portion 33a. Proportion to the diameter D2 of the second portion 33b of the diameter D1 of the first portion 33a (D 1 / D 2) is preferably in the range of 1.2 to 5. In this case, the support 34 holds the bonded magnet molded body 32 with sufficient strength, and an ideal magnetic flux distribution can be obtained.

By making the support 34 made of a non-magnetic material as in the above-described embodiment, the magnetic flux distribution of the bonded magnet molded body 32 is brought closer to the ideal magnetic flux distribution. When the support is made of a magnetic material, the influence of the support on the magnetic field of the bonded magnet molded body 32 is large, but by making the support 34 made of a non-magnetic material, the bond magnet of the support 34 is formed. 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 can take various modifications.

For example, the shape of the first portion 33a of the bonded magnet molded body 32 is not limited to the disk shape, but if it is a plate shape having a uniform thickness, it may be another plate shape (for example, a quadrangular plate shape, a hexagonal plate shape, or the like). It may be in the shape of a polygonal plate). In this case, by making the shape of the first portion 33a symmetrical with respect to the shaft 34a of the support 34, the magnetic flux distribution around the shaft 34a of the support 34 approaches the ideal magnetic flux distribution, and the shaft It is possible to further improve the sensor accuracy of the rotation sensor 40 arranged on the extension line of 34a.

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

In the above embodiment, a support having a cylindrical outer shape is used, but a support having a prismatic outer shape or an elliptical columnar outer shape may be used. Further, in the above embodiment, the embodiment in which the support and the magnet molded body are coaxially arranged is shown, but the axis of the support and the axis of the magnet molded body are displaced from each other to a position deviated from the central axis of the magnet molded body. It is also possible to have a support attached to the magnet.

Further, in the above embodiment, the support 34 of the magnet structure 30 and the rotary shaft 22 of the electric motor 20 are connected by press-fitting into the hole 36a provided on the second end 36 side of the support 34. Although the embodiment in which the rotary shaft 22 is inserted is shown, it is also possible to provide a hole on the rotary shaft 22 side and insert the second end portion 36 of the support 34 into the hole.

Further, an engaging portion having a predetermined unevenness can be provided on the outer peripheral surface of the first end portion 35 of the support body 34. When the first end 35 of the support 34 is embedded in the bond magnet molded body 32 by injection molding or the like, the first end 35 of the support 34 and the bond magnet molded body 32 are engaged in the engaging portion. The engaging force between them is strengthened, and the relative positional deviation of the bond magnet molded body 32 with respect to the support 34 and the detachment of the bond magnet molded body 32 from the support 34 can be suppressed.

10 ... Motor assembly, 15 ... Rotation angle detector, 20 ... Electric motor, 22 ... Rotating shaft, 30 ... Magnet structure, 32 ... Bond magnet molded body, 33a ... First part, 33b ... Second part, 34 ... Support, 35 ... 1st end, 36 ... 2nd end, 40 ... Rotation sensor.

Claims (5)

A bonded magnet molded body having a first portion having a plate shape of a uniform thickness and a second portion adjacent to the first portion in the thickness direction of the first portion.
It is provided with a support extending along the thickness direction of the first portion of the bonded magnet molded body and having a coated end portion coated on the bonded magnet molded body.
The support is located on the second portion side of the bonded magnet molded body with respect to the thickness direction of the first portion, and the covering end portion is terminated at the second portion .
The shape of the first portion is a disk shape with the axis of the support as the central axis.
A magnet structure in which the shape of the second portion is a disk shape with the axis of the support as a central axis, and the diameter of the second portion is smaller than the diameter of the first portion. 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. The magnet structure according to claim 1 or 2 , wherein the support is made of a non-magnetic material. A rotation angle detector comprising the magnet structure according to any one of claims 1 to 3 and a magnetic sensor arranged so as to face the magnet structure on the coated end side. An electric power steering device including the rotation angle detector according to claim 4.

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