Rotation angle detection device and electric power steering device

Abstract

To provide a rotation angle detection device and an electric power steering device that are able to reduce the size of a magnet member.SOLUTION: In a rotation angle detection device (a magnetic rotation angle sensor 7) and an electric power steering device PS according to the present invention, a magnet member 73 is fixed to a shaft member 71 via an intermediate member 72 having strength higher than the magnet member 73. Therefore, in comparison with a case where the magnet member 73 is directly fixed to the shaft member 71, torque per unit area capable of maintaining a fixed state relative to the shaft member 71 can be improved. Accordingly, the axial length of a fixing portion of the intermediate member 72 relative to the shaft member 71 can be shortened, making it possible to reduce the axial size of the magnet member 73.SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] The present invention relates to a rotation angle detection device and an electric power steering device.

Background Art

[0002] As a conventional rotation angle detection device, for example, the one described in Patent Document 1 below is known.

[0003] Briefly explained, this rotation angle detection device has a magnet member that fits on the outer peripheral surface of the rotation shaft of the motor and is provided so as to be rotatable integrally with the rotation shaft, and a magnetic sensor that detects the magnetic field of the magnet member, and detects the rotation angle of the rotation shaft based on the detection output of the magnetic sensor.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, in the conventional rotation angle detection device, the magnet member is fixed to the outer peripheral surface of the rotation shaft. For this reason, when enhancing the resistance to the inertial moment accompanying the sudden acceleration or sudden stop of the motor (rotation shaft), vibration during vehicle travel, and external input from the road surface, it is necessary to increase the contact area of the magnet member with respect to the rotation shaft, and there still remains room for improvement in that the magnet member becomes large in the axial direction.

[0006] The present invention has been devised in view of such technical problems, and provides a rotation angle detection device and an electric power steering device capable of miniaturizing the magnet member.

Means for Solving the Problems

[0007] In one aspect of the present invention, the magnet member is fixed to the shaft member via an intermediate member having a higher strength than the magnet member.

Advantages of the Invention

[0008] According to the present invention, the magnet member can be miniaturized.

Brief Description of the Drawings

[0009]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Embodiments for Carrying Out the Invention

[0010] Hereinafter, embodiments of a rotation angle detection device and an electric power steering device according to the present invention will be described in detail with reference to the drawings.

[0011] (Configuration of Electric Power Steering Device) FIG. 1 shows a schematic diagram of an electric power steering device PS according to the present embodiment.

[0012] For example, as shown in FIG. 1, there are provided an input shaft 1 connected to a steering wheel SW, an output shaft 2 rotatably connected to the input shaft 1 via a torsion bar (not shown), and a motor unit 3 that applies a steering assist torque corresponding to a driver's steering torque to the output shaft 2. Further, on the outer peripheral side of the input shaft 1, a torque sensor TS is provided for detecting the steering torque input from the steering wheel SW based on the relative rotational displacement amount between the input shaft 1 and the output shaft 2. The torque sensor TS is electrically connected to the motor unit 3 (a control unit 32 described later). The motor unit 3 generates a steering assist torque corresponding to the steering torque of the driver detected by the torque sensor TS.

[0013] The output shaft 2 is linked to left and right steered wheels WL and WR via a well-known rack and pinion mechanism RP. The rack and pinion mechanism RP is configured by the engagement of a pinion tooth 20 formed on the outer peripheral side of one axial end of the output shaft 2 and a rack tooth 40 formed in a predetermined axial range of a rack shaft 4 disposed substantially orthogonally to the output shaft 2. Further, both axial ends of the rack shaft 4 are linked to the steered wheels WR and WL via tie rods 5, 5 and knuckle arms 6, 6, respectively.

[0014] Thus, in the electric power steering apparatus PS, the output shaft 2 rotates by inputting the driver's steering torque input via the input shaft 1 and the steering assist torque applied via the motor unit 3. Then, the rotational motion of the output shaft 2 is converted into the axial movement of the rack shaft 4, and the rack shaft 4 moves axially according to the rotational direction of the output shaft 2. As a result, the tie rods 5, 5 and the knuckle arms 6, 6 connected to the rack shaft 4 are pulled, thereby changing the directions of the steered wheels WR and WL.

[0015] (Configuration of the rotation angle detection device) FIGS. 2 and 3 show a first embodiment of the rotation angle detection device according to the present invention.

[0016] 〔First Embodiment〕 FIG. 2 is an enlarged view of the motor unit 3 shown in FIG. 1, and shows a longitudinal sectional view of a magnetic rotary angle sensor 7, which is a rotary angle detection device attached to the electric motor 31, cut along the rotation axis Z of the electric motor 31. In the description of this figure, the direction parallel to the rotation axis Z of the electric motor 31 is referred to as the "axial direction", the direction orthogonal to the rotation axis Z of the electric motor 31 is referred to as the "radial direction", and the direction around the rotation axis Z of the electric motor 31 is referred to as the "circumferential direction" for explanation.

[0017] For example, as shown in FIG. 2, the motor unit 3 includes an electric motor 31 that generates a steering assist torque, and a control unit 32 that is an ECU for driving and controlling the electric motor 31. The electric motor 31 and the control unit 32 are integrally configured as a so-called mechatronic unit. That is, in the present embodiment, the electric motor 31 and the control unit 32 are arranged in series in the axial direction, and the control unit 32 is attached to the first end portion 31a in the axial direction of the electric motor 31.

[0018] The electric motor 31 includes a motor housing 311, a motor element (not shown) (for example, a stator that is a fixed iron core and a rotor that is a movable iron core) housed inside the motor housing 311, and a motor output shaft 312 that rotates integrally with a rotating body (for example, the rotor) of the motor element (not shown). The motor output shaft 312 has a first end portion 312a in the axial direction that is exposed at the second end portion 31b on the opposite side in the axial direction from the control unit 32, and the first end portion 312a is linked to the output shaft 2 via a speed reducer 33 (see FIG. 1) such as a worm gear. Specifically, for example, as shown in FIG. 1, a worm shaft 331 is connected to the first end portion 312a of the motor output shaft 312, and a worm wheel 332 that meshes with the worm shaft 331 is attached to the outer peripheral side of the output shaft 2. That is, when the worm shaft 331 meshes with the worm wheel 332, the rotational speed of the electric motor 31 is reduced and transmitted to the output shaft 2.

[0019] As shown in FIG. 2 for example, the control unit 32 includes an ECU housing 321 whose first end portion 321a is attached to the first end portion 311a of the motor housing 311 in the axial direction, a control board 322 housed inside the ECU housing 321, and a connector portion 323 that is electrically connected to the control board 322 and is provided so as to be exposed to the outside at the second end portion 321b on the side opposite to the electric motor 31 of the ECU housing 321 in the axial direction.

[0020] The ECU housing 321 is generally formed in a cylindrical shape from a metal material with relatively high heat dissipation properties, such as aluminum for example. The first end portion 321a of the ECU housing 321 is attached to the first end portion 311a of the motor housing 311 by fitting. The connector portion 323 is fixed to the second end portion 321b of the ECU housing 321, for example, by adhesion, in a state where it is liquid-tightly sealed with the ECU housing 321.

[0021] The control board 322 is formed from a resin material such as glass epoxy resin for example. Also, various electronic components such as a microcomputer are mounted on the control board 322. Then, on the control board 322, the necessary steering assist torque is calculated based on detection signals from the torque sensor TS and a vehicle speed sensor (not shown), and the electric motor 31 is driven and controlled according to the calculated steering assist torque.

[0022] The connector portion 323 is integrally formed from a resin material for example, and is connected to an external device (not shown) such as a torque sensor TS, a vehicle speed sensor (not shown), and a battery (not shown) via a harness member (not shown). The connector portion 323 is electrically connected to the control board 322 via a wiring 323b connected to the connector terminal 323a inside the ECU housing 321, and is used for supplying power from a battery (not shown) to the control board 322 and inputting detection signals from the torque sensor TS and a vehicle speed sensor (not shown).

[0023] Further, inside the ECU housing 321, a magnetic rotary angle sensor 7 is provided as a rotary angle detection device capable of detecting the rotation angle of the electric motor 31 between the motor output shaft 312 of the electric motor 31 and the control board 322. The magnetic rotary angle sensor 7 includes a magnetic rotary angle sensor detected part 70a provided on the motor output shaft 312 of the electric motor 31 and a magnetic rotary angle sensor detection part 70b provided on the control board 322.

[0024] The magnetic rotary angle sensor detected part 70a includes a shaft member 71 fixed to the motor output shaft 312 corresponding to the rotating body of the electric motor 31, an intermediate member 72 fixed to the shaft member 71, and a magnet member 73 fixed to the intermediate member 72. The magnetic rotary angle sensor detection part 70b is constituted by a magnetic sensor element 74 mounted on the control board 322. The magnetic sensor element 74 is a well-known MR element (magnetoresistive element) or Hall element, and is arranged to face the magnet member 73 in the axial direction, and detects the rotation angle of the motor output shaft 312 by detecting a change in the magnitude or direction of the magnetic field of the magnet member 73 accompanying the rotation of the motor output shaft 312.

[0025] FIG. 3 shows an enlarged cross-sectional view of the magnetic rotary angle sensor detected part 70a of the magnetic rotary angle sensor 7 shown in FIG. 2, with the magnetic rotary angle sensor detected part 70a enlarged and displayed.

[0026] The magnetic rotary angle sensor detected part 70a includes a shaft member 71 provided coaxially with the motor output shaft 312 of the electric motor 31 and connected to be integrally rotatable with respect to the motor output shaft 312, an intermediate member 72 fitted to the shaft member 71 and fixed to be integrally rotatable with respect to the shaft member 71, and a magnet member 73 formed integrally with the intermediate member 72 and coupled to be integrally rotatable with respect to the intermediate member 72.

[0027] The shaft member 71 is made of a non-magnetic material, such as a stainless steel material, and is formed to have substantially the same diameter throughout the axial direction. Specifically, the shaft member 71 has a first end portion 711 with a smooth surface (outer peripheral surface) and a second end portion 712 with a concavo-convex surface (outer peripheral surface). The first end portion 711 has an outer diameter slightly larger than the inner diameter of the shaft insertion hole 312c (see FIG. 2) formed in a concave shape along the axial direction at the central portion of the second end portion 312b of the motor output shaft 312 of the electric motor 31, and is fixed to the inner surface of the shaft insertion hole 312c by press-fitting. The second end portion 712 has a knurled portion 713 formed by performing a well-known knurling process in which the surface (outer peripheral surface) is concavo-convex in all or part of the axial region where the intermediate member 72 is fitted. In the present embodiment, the knurled portion 713 is provided in a part of the axial region of the second end portion 712 where the intermediate member 72 is fitted.

[0028] The intermediate member 72 integrally has a substantially cylindrical base portion 721 fitted to the outer peripheral surface of the shaft member 71 and a plate-shaped diameter-expanded portion 722 provided at a first end portion 721a which is an axial end portion of the base portion 721 on the side of the first end portion 711 of the shaft member 71 closer to the electric motor 31 and extending in the radial direction of the shaft member 71. At this time, the intermediate member 72 is formed of a resin material having a higher strength than the magnet member 73, such as a glass fiber resin or ceramics. In the present embodiment, the diameter-expanded portion 722 is formed in a disc shape.

[0029] The base portion 721 has a tapered surface 721c formed on the outer peripheral side so that the outer diameter gradually decreases from the second end portion 721b side opposite to the first end portion 721a toward the first end portion 721a side. In other words, the tapered surface 721c has the largest outer diameter at the first end portion 721a which is the axial end portion closest to the diameter-expanded portion 722, and the smallest outer diameter at the second end portion 721b which is the axial end portion farthest from the diameter-expanded portion 722. Further, the base portion 721 is fixed to the shaft member 71 in such a manner that the tip 721d of the second end portion 721b is offset slightly inward (toward the first end portion 711 side) in the axial direction from the tip 712a of the second end portion 712 of the shaft member 71.

[0030] The diameter-expanded portion 722 is formed in such a manner that it expands in diameter with a substantially constant thickness width T from the first end portion 721a of the base portion 721 toward the radially outer side. In the present embodiment, as shown in FIG. 3, the diameter-expanded portion 722 extends to a radial position substantially the same diameter as the magnet member 73. Note that, as shown in FIG. 4, the diameter-expanded portion 722 may be set to an outer diameter Rx smaller than the outer diameter Rm of the magnet member 73. In other words, the diameter-expanded portion 722 may be formed so as to face a partial radial region of the magnet member 73 in the axial direction. Thus, in the aspect where the diameter-expanded portion 722 faces a partial radial region of the magnet member 73, the outer peripheral surface 722c of the diameter-expanded portion 722 is surrounded by the magnet member 73, and the second end surface 732 (described later) of the magnet member 73 and the outer side surface 722b of the diameter-expanded portion 722 are formed to be substantially flush.

[0031] The magnet member 73 is formed of a mixed material obtained by mixing a magnetic material such as neodymium and a resin material such as polyphenylene sulfide (PPS), and is integrally formed with the intermediate member 72 by injection molding on the outer peripheral side of the intermediate member 72. Then, the magnet member 73 is magnetized by a predetermined magnetization means, and in the rotational direction of the motor output shaft 312, N poles and S poles (not shown) are alternately arranged. Further, the magnet member 73 is formed such that the first end surface 731, which is the axial end surface on the side opposite to the electric motor 31, protrudes from the tip 721d of the second end portion 721b of the base portion 721 of the intermediate member 72 and is substantially flush with the tip 712a of the second end portion 712 of the shaft member 71. On the other hand, the magnet member 73 is formed such that the second end surface 732, which is the axial end surface on the electric motor 31 side, is connected to the inner side surface 722a of the diameter-expanded portion 722 of the intermediate member 72. Further, the magnet member 73 has an outer diameter Rm equal to the outer diameter Rx of the diameter-expanded portion 722 of the intermediate member 72, and the outer peripheral surface 733 of the magnet member 73 is formed to be substantially flush with the outer peripheral surface 722c of the diameter-expanded portion 722 of the intermediate member 72.

[0032] (Operational effects of the present embodiment) As described above, in the conventional rotation angle detection device and the electric power steering device, the magnet member 73 is fixed to the outer peripheral surface of the shaft member 71. Therefore, when enhancing the resistance to the inertial moment associated with the rapid acceleration or rapid stop of the motor output shaft 312 of the electric motor 31, or the vibration during vehicle travel or external input from the road surface, it was necessary to increase the contact area of the magnet member 73 with respect to the motor output shaft 312. As a result, there still remained room for improvement in that the magnet member 73 became large in the axial direction.

[0033] On the other hand, in the rotation angle detection device (magnetic rotation angle sensor 7) and the electric power steering device PS according to the present embodiment, the following effects are achieved, thereby solving the problems of the conventional rotation angle detection device and the electric power steering device.

[0034] The rotation angle detection device and the electric power steering device PS according to the present embodiment include a shaft member 71 that rotates integrally with a rotating body (in this embodiment, the motor output shaft 312) of the electric motor 31, an intermediate member 72 fixed to the shaft member 71, and a magnet member 73 provided on the outer peripheral side of the intermediate member 72, and the intermediate member 72 has a higher strength than the magnet member 73.

[0035] Thus, in the present embodiment, the magnet member 73 is fixed to the shaft member 71 via an intermediate member 72 having a higher strength than the magnet member 73. Therefore, compared with the case where the magnet member 73 is directly fixed to the shaft member 71, the torque per unit area capable of maintaining the fixed state with the shaft member 71 can be increased. As a result, it becomes possible to shorten the axial length of the fixed portion of the intermediate member 72 with respect to the shaft member 71, and the axial size of the magnet member 73 can be reduced.

[0036] Further, in the present embodiment, the intermediate member 72 is formed of a resin material (for example, glass fiber resin or ceramics). Thereby, while ensuring the necessary strength of the intermediate member 72, the weight of the intermediate member 72 can be reduced.

[0037] Also, in the present embodiment, in the intermediate member 72, the end portion on the side closer to the electric motor 31 in the axial direction is formed in a plate shape facing the magnet member 73 in the axial direction. In other words, a diameter-expanded portion 722 that expands in the radial direction is provided at the axial end portion of the intermediate member 72 on the side closer to the electric motor 31. Therefore, the diameter-expanded portion 722 that expands the intermediate member 72 in the radial direction enables an increase in the fixed area between the intermediate member 72 and the magnet member 73. As a result, the fixing strength of the magnet member 73 with respect to the intermediate member 72 is enhanced, and the torque resistance of the magnet member 73 with respect to the intermediate member 72 can be further improved.

[0038] In addition, in the present embodiment, although an aspect in which the intermediate member 72 is formed of the resin material is exemplified, the intermediate member 72 may be made of a material having a higher strength than the magnet member 73 and is not limited to the resin material. In other words, in addition to the resin material, the intermediate member 72 may be formed of a magnetic member that does not generate magnetism, such as iron or magnetic stainless steel. Thus, when the intermediate member 72 is formed of a magnetic member that does not generate magnetism, the intermediate member 72 can absorb and shield the magnetism acting from the electric motor 31 side. Thereby, the detection accuracy of the rotation angle of the electric motor 31 can be improved.

[0039] 〔Second Embodiment〕 FIG. 5 shows a second embodiment of the rotation angle detection device and the electric power steering device according to the present invention, in which the configuration of the magnet type rotation angle sensor detected portion 70a according to the present invention is changed. Since the basic configuration other than the changed points is the same as that of the first embodiment, the same components as those of the first embodiment are denoted by the same reference numerals and the description thereof is omitted.

[0040] (Configuration of Rotation Angle Detection Device) FIG. 5 shows an enlarged cross-sectional view of the magnet type rotation angle sensor detected portion 70a, which is an enlarged view of the magnet type rotation angle sensor detected portion 70a of the magnet type rotation angle sensor 7 according to the present embodiment.

[0041] For example, as shown in FIG. 5, in this embodiment, the enlarged diameter portion 722 of the intermediate member 72 is omitted. That is, in this embodiment, the intermediate member 72 is composed of only the base portion 721 formed in a substantially cylindrical shape, and a magnet member 73 is provided on the outer peripheral side of the base portion 721 constituting the intermediate member 72.

[0042] (Operational effects of this embodiment) Thus, since the intermediate member 72 is composed of only the base portion 721, the axial dimension of the magnetic rotation angle sensor detection portion 70a can be reduced by the amount corresponding to the omission of the enlarged diameter portion 722 according to the first embodiment.

[0043] In addition, since the intermediate member 72 is composed of only the base portion 721, the structure of the intermediate member 72 is simplified, and it becomes possible to manufacture the intermediate member 72 easily and inexpensively. This can contribute to reducing the manufacturing cost of the magnetic rotation angle sensor 7 as a rotation angle detection device and the electric power steering device PS.

[0044] 〔Third Embodiment〕 FIG. 6 shows a third embodiment of the rotation angle detection device and the electric power steering device according to the present invention, in which the configuration of the magnetic rotation angle sensor detection portion 70a of the magnetic rotation angle sensor 7 according to the present invention is changed. Since the basic configuration other than the changed points is the same as that of the first embodiment, the same components as those in the first embodiment are denoted by the same reference numerals and the description thereof is omitted.

[0045] (Configuration of the rotation angle detection device) FIG. 6 shows an enlarged cross-sectional view of the magnetic rotation angle sensor detection portion 70a, which is an enlarged view of the magnetic rotation angle sensor detection portion 70a of the magnetic rotation angle sensor 7 according to the present embodiment.

[0046] For example, as shown in FIG. 6, in the present embodiment, in the magnet-type rotation angle sensor detection unit 70a of the magnet-type rotation angle sensor 7, the outer surface 722b of the enlarged diameter portion 722 of the intermediate member 72, the outer peripheral surface 722c of the enlarged diameter portion 722 of the intermediate member 72, and the outer peripheral surface 733 of the magnet member 73 are covered by, for example, a metal cover member 75. The cover member 75 is formed in a bottomed cylindrical shape with one end side in the axial direction open and the other end side closed. Specifically, the cover member 75 includes a substantially plate-shaped end wall portion 751 that covers the outer surface 722b of the enlarged diameter portion 722 provided at the axial end of the intermediate member 72 on the side closer to the electric motor 31, and extends axially from the outer peripheral edge portion of the end wall portion 751 to an axial position substantially flush with the first end surface 731 of the magnet member 73, and a substantially cylindrical tubular portion 752 that surrounds the outer peripheral surface 722c of the enlarged diameter portion 722 of the intermediate member 72 and the outer peripheral surface 733 of the magnet member 73. At this time, the end wall portion 751 and the tubular portion 752 are connected by a rounded portion 753 having a smooth arc-shaped longitudinal section.

[0047] (Operational effects of the present embodiment) As described above, according to the present embodiment, there is a cover member including an end wall portion 751 that covers the end surface (outer surface 722b of the enlarged diameter portion 722) on the side closer to the electric motor 31 in the axial direction of either the magnet member 73 or the intermediate member 72, and a tubular portion that surrounds the outer peripheral surface 733 of the magnet member 73.

[0048] Thus, in the present embodiment, in the magnet-type rotation angle sensor detection unit 70a that constitutes the rotation angle detection device (rotation angle detection unit), a cover member 75 that covers the magnet member 73 is provided. Therefore, even when cracks or the like occur in the magnet member 73, it is possible to restrict the scattering of the magnet member 73 by the cover member 75. Thereby, the durability of the magnet member 73, and thus the durability of the magnet-type rotation angle sensor 7 which is the rotation angle detection device (rotation angle detection unit), can be improved.

[0049] In addition, in the present embodiment, a mode in which the cover member 75 is combined with the first embodiment has been exemplified. However, the cover member 75 according to the present embodiment can also be applied to a mode in which the enlarged diameter portion 722 of the intermediate member 72 is omitted as in the second embodiment. Also in this case, the advantageous effects of the present embodiment such as preventing scattering due to cracking or the like of the magnet member 73 can be enjoyed.

[0050] The present invention is not limited to the configurations of the above-described embodiments, and can be freely changed according to the specifications of the electric motor 31 and the electric power steering device PS to which the present invention is applied, as long as it can exhibit the effects of the present invention.

[0051] For example, the means for fixing the shaft member 71 to the motor output shaft 312 of the electric motor 31 is not limited to the press-fitting exemplified in the above-described embodiments, and any mode that can be fixed using the first end portion 711, such as fastening, may be used. Further, the shaft member 71 is not limited to the mode configured separately from the motor output shaft 312 of the electric motor 31 exemplified in the above-described embodiments. Although specific illustrations are omitted, it may be integrated with the motor output shaft 312 of the electric motor 31.

Explanation of Reference Numerals

[0052] 31... Electric motor, 32... Control board (control unit), 312... Motor output shaft (rotating body), 7... Magnetic rotary angle sensor (rotary angle detection device or rotary angle detection unit), 71... Shaft member, 72... Intermediate member, 73... Magnet member, 74... Magnetic sensor, 75... Cover member, 751... End wall portion, 752... Cylindrical portion, PS... Electric power steering device, Z... Axis of rotation

Claims

1. An electric power steering apparatus having a control unit that generates a steering assist torque by driving and controlling an electric motor, and a rotation angle detection unit that detects the rotation angle of the electric motor, wherein the rotation angle detection unit includes a shaft member that rotates integrally with a rotating body of the electric motor, an intermediate member fixed to the shaft member, and a magnet member provided on an outer peripheral side of the intermediate member, and the intermediate member has a higher strength than the magnet member, characterized in that it is an electric power steering apparatus.

2. In the electric power steering apparatus according to Claim 1, the intermediate member is formed of a resin material, characterized in that it is an electric power steering apparatus.

3. In the electric power steering apparatus according to Claim 1, the intermediate member is formed in a plate shape in which an end portion on a side closer to the electric motor in the axial direction of the shaft member faces the magnet member in the axial direction, characterized in that it is an electric power steering apparatus.

4. In the electric power steering apparatus according to Claim 3, the intermediate member is formed of a magnetic member that does not emit magnetism, characterized in that it is an electric power steering apparatus.

5. In the electric power steering apparatus according to Claim 1, it has a cover member including an end wall portion that covers an end face on a side closer to the electric motor in the axial direction of either the magnet member or the intermediate member, and a cylindrical portion that surrounds the outer peripheral side of the magnet member, characterized in that it is an electric power steering apparatus.

6. A rotation angle detection device for detecting the rotation angle of an electric motor, including a shaft member that rotates integrally with a rotating body of the electric motor, an intermediate member fixed to the shaft member, and a magnet member provided on an outer peripheral side of the intermediate member, and the intermediate member has a higher strength than the magnet member, characterized in that it is a rotation angle detection device.

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