JP2015014614A - Torque sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a torque sensor which reduces output variation to be generated by a magnetic flux which directly reaches a magnetic sensing unit from a multipolar magnet when the multipolar magnet and a yoke are rotated integrally.SOLUTION: A torque sensor 201 includes: a torsion bar 13; a multipolar magnet 14; a pair of yokes 31, 32 forming a magnetic circuit radially outside the multipolar magnet 14; and a magnetic sensor 41 having a magnetic sensing unit (410) for detecting magnetic flux density generated in the magnetic circuit. The torque sensor 201 also includes a magnetic shield member 71. The magnetic shield member 71 is formed of a soft magnetic material, and is arranged between the pair of yokes 31, 32 axially, on the radially outside of the multipolar magnet 14 and on the inside of the magnetic sensing unit, to shield the magnetic flux which directly reaches the magnetic sensing unit of the magnetic sensor 41 from the multipolar magnet 14. The magnetic flux can be prevented from directly reaching the magnetic sensor 41 from the multipolar magnet 14 through the space without passing through the yokes 31, 32, thereby reducing output variation.

Description

  The present invention relates to a torque sensor that detects an axial torque applied to a rotating shaft as a change in magnetic flux density (magnetic field strength).

  Conventionally, a torque sensor for detecting shaft torque in an electric power steering device or the like is known. For example, in the torque sensor described in Patent Document 1, when a torsion bar that connects an input shaft and an output shaft is twisted, a magnetic flux generated by a change in relative position in the circumferential direction between the multipolar magnet and the yoke is generated. The shaft torque is detected by detecting the fixed magnetic sensor. Here, in the multipolar magnet, the N pole and the S pole are alternately magnetized at a constant magnetization angle in the circumferential direction. For example, the torque sensor of Patent Document 1 is provided with 24 poles in total, 12 poles each for N poles and S poles.

JP 2003-149062 A

  Since the torque sensor detects the relative position in the circumferential direction between the multipolar magnet and the yoke, when the multipolar magnet and the yoke rotate integrally with respect to the magnetic sensor, that is, the multipolar magnet and the yoke When the relative position in the circumferential direction does not change, the output of the magnetic sensor is preferably constant.

  However, in reality, when the multipolar magnet and the yoke are rotated together with the torque sensor described in Patent Document 1, the output varies according to the rotation angle. For example, when the N pole and the S pole of the multipolar magnet are each 12 poles, output fluctuation of 12 cycles occurs per rotation. This output fluctuation causes a decrease in the detection accuracy of the rotation angle.

The present inventor has clarified that this output fluctuation is caused by magnetic flux that directly reaches the magnetic sensor from the multipolar magnet through the space without passing through the yoke.
The present invention has been made in view of the above-described problems, and its purpose is to produce output fluctuations caused by magnetic flux that directly reaches the magnetic sensing portion from the multipolar magnet when the multipolar magnet and the yoke are rotated together. It is an object of the present invention to provide a torque sensor that reduces the noise.

A torque sensor according to the present invention includes a torsion bar, a multipolar magnet, a pair of yokes that form a magnetic circuit outside the diameter of the multipolar magnet, and a magnetism sensor that detects a magnetic flux density generated in the magnetic circuit. The torque sensor including the sensor further includes a magnetic shield member. The magnetic shield member is made of a soft magnetic material, and is provided between the pair of yokes in the axial direction and outside the multipolar magnet and inside the magnetic sensing portion in the radial direction. The magnetic flux that directly reaches the magnetically sensitive part of the screen is shielded.
Thereby, it is possible to prevent magnetic flux from reaching the magnetic sensor directly from the multipolar magnet through the space without passing through the yoke, and to reduce output fluctuation.

1 is an exploded perspective view of a torque sensor according to a first embodiment of the present invention. 1 is a schematic configuration diagram of an electric power steering apparatus to which a torque sensor according to a first embodiment of the present invention is applied. It is (a): sectional drawing of the torque sensor by 1st Embodiment of this invention, (b): The b direction arrow line view of (a). It is a front view (IV direction arrow view of FIG. 3) which shows the neutral state of the torque sensor by 1st Embodiment of this invention. In the torque sensor by a 1st embodiment of the present invention, it is a front view showing the state where a multipolar magnet rotated to the left (a): the state rotated to the right (b). It is a disassembled perspective view of the torque sensor by 11th Embodiment of this invention. It is (a): sectional drawing of the torque sensor by 11th Embodiment of this invention, (b) The b direction arrow directional view of the magnetism collection part. It is a front view which shows the neutral state of the torque sensor by 11th Embodiment of this invention. It is a front view which shows the state which the multipolar magnet rotated in the left direction (a) the state rotated to the left direction, (b) the state rotated in the right direction in the torque sensor by 11th Embodiment of this invention. It is a schematic diagram explaining the effect | action of the magnetic shielding member by 11th Embodiment of this invention. It is an output characteristic view of a torque sensor according to an eleventh embodiment of the present invention. It is sectional drawing of the torque sensor by 12th Embodiment of this invention. It is sectional drawing of the torque sensor by 13th Embodiment of this invention. It is a front view (XIV direction arrow line view of FIG. 13) which shows the neutral state of the torque sensor by 13th Embodiment of this invention. It is sectional drawing of the torque sensor by 14th Embodiment of this invention.

Hereinafter, torque sensors according to a plurality of embodiments of the present invention will be described with reference to the drawings. In a plurality of embodiments, substantially the same configuration is denoted by the same reference numeral, and description thereof is omitted.
Note that the first embodiment is a reference form for explaining a common configuration. The second to tenth embodiments are omitted.
[Overall configuration of torque sensor applied to electric power steering device]
First, a configuration common to the torque sensors of the embodiments of the present invention will be described. Note that the torque sensor 101 of the first embodiment is used as a representative for the reference numeral of the torque sensor.
As shown in FIG. 2, the torque sensor 101 according to the embodiment of the present invention is applied to an electric power steering apparatus for assisting a steering operation of a vehicle.

  FIG. 2 shows an overall configuration of a steering system including the electric power steering device 90. A steering shaft 94 connected to the handle 93 is provided with a torque sensor 101 for detecting steering torque. A pinion gear 96 is provided at the tip of the steering shaft 94, and the pinion gear 96 meshes with the rack shaft 97. A pair of wheels 98 are rotatably connected to both ends of the rack shaft 97 via tie rods or the like. The rotational motion of the steering shaft 94 is converted into a linear motion of the rack shaft 97 by the pinion gear 96, and the pair of wheels 98 are steered.

  The torque sensor 101 is provided between the input shaft 11 and the output shaft 12 constituting the steering shaft 94, detects the steering torque applied to the steering shaft 94, and outputs it to the ECU 91. The ECU 91 controls the output of the motor 92 according to the detected steering torque. The steering assist torque generated by the motor 92 is decelerated via the reduction gear 95 and transmitted to the steering shaft 94.

Next, a configuration common to the torque sensors of the embodiments will be described with reference to FIGS. 1 and 3 to 5 of the first embodiment.
As shown in FIG. 1, the torque sensor (101) includes a torsion bar 13, a multipolar magnet 14, a set of yokes 31, 32, a set of magnetism collecting rings (502), a magnetic sensor 41, and the like. . Since the reference numerals of the torque sensor and the pair of magnetism collecting rings are different for each embodiment, the reference numerals are shown here in parentheses.

One end side of the torsion bar 13 is fixed to the input shaft 11 as a “first axis”, and the other end side is fixed to an output shaft 12 as a “second axis” by a fixing pin 15. 12 are connected on the same axis as the rotation axis O. The torsion bar 13 is a rod-like elastic member, and converts the steering torque applied to the steering shaft 94 into a torsional displacement.
The cylindrical multipolar magnet 14 is fixed to the input shaft 11 and N and S poles are alternately magnetized in the circumferential direction. For example, in this embodiment, the number of N poles and S poles is 12 pole pairs, for a total of 24 poles.

  The pair of yokes 31 and 32 are annular bodies made of a soft magnetic material, and are fixed to the output shaft 12 on the outer side of the multipolar magnet 14. In the yokes 31 and 32, the same number (12 in this embodiment) of claws 315 and 325 as the north and south poles of the multipolar magnet 14 are provided at equal intervals along the inner edge of the ring. The claws 315 of one yoke 31 and the claws 325 of the other yoke 32 are alternately arranged with a shift in the circumferential direction. Thus, one yoke 31 and the other yoke 32 are opposed to each other via the air gap in the axial direction. The pair of yokes 31 and 32 form a magnetic circuit in the magnetic field generated by the multipolar magnet 14.

  Here, when the multipolar magnet 14 and the pair of yokes 31 and 32 are not twisted and displaced in the torsion bar 13, that is, when steering torque is not applied between the input shaft 11 and the output shaft 12. The centers of the claws 315 and 325 of the yokes 31 and 32 and the boundary between the north and south poles of the multipolar magnet 14 are arranged so as to coincide with each other.

  The pair of magnetic flux collecting rings (502) is formed of a soft magnetic material and includes a main body portion (56), a connecting portion (57), and magnetic flux collecting portions (521, 522). The pair of magnetic flux collecting rings (502) are provided so as to face each other in the axial direction of the torsion bar 13 which is the vertical direction in FIG. 1, and the magnetic flux collecting portions (521, 522).

At least one magnetic sensor 41 is provided between the magnetic flux collectors (521, 522). The magnetic sensor 41 converts the magnetic flux density passing through the magnetic sensing unit 410 into a voltage signal and outputs it to the lead wire 49. Specifically, a Hall element, a magnetoresistive element, or the like can be used as the magnetic sensor 41.
Hereinafter, for each of the embodiments, a specific configuration of a set of magnetism collecting rings, a magnetic sensor, and the like, and operational effects derived from the configuration will be described.

[Embodiment for Reducing Output Fluctuation Using Magnetic Shield Member]
Next, the 11th-14th embodiment of this invention which reduces an output fluctuation | variation using a magnetic shielding member is described with reference to FIGS.

(Eleventh embodiment)
A configuration unique to the eleventh embodiment will be described with reference to FIGS. A set of magnetism collecting rings 501 of the torque sensor 201 of the eleventh embodiment includes a semicircular main body portion 56, a magnetism collecting portion 51 projecting radially outward of the main body portion 56, and the main body portion 56 and the magnetism collecting portion. 51, and the magnetic flux of the yokes 31 and 32 is collected in the magnetic flux collector 51. The set of magnetism collecting rings 501 corresponds to a “set of magnetism collectors” recited in the claims.
As shown in FIGS. 8 and 9, the main body portion 56 of the pair of magnetism collecting rings 501 is provided between the pair of yokes 31 and 32 in the axial direction. Here, since the main-body part 56 is formed in the semicircle shape, it can be assembled | attached from the radial direction of the yokes 31 and 32. As shown in FIG.
Further, as shown in FIG. 7, the main body 56 is provided so that the outer edge of the semicircle coincides with the outer periphery of the yokes 31 and 32, and overlaps with the yokes 31 and 32 when projected in the axial direction. .

When distinguishing the upper magnetic flux collector of FIG. 6 and the lower magnetic flux collector of the magnetic flux collector 51 of a set of magnetic flux collectors 501, add “1” to the end of the reference numeral of the upper magnet flux collector. Then, “2” is added to the end of the code of the lower magnetic flux collector. The same applies to the following twelfth to fourteenth embodiments.
As shown in FIGS. 6, 8, and 9, a magnetic sensor 41 is provided between the magnetic flux collector 511 and the magnetic flux collector 512. The magnetic sensor 41 is configured in the form of a flat plate IC package in which the magnetic sensing part 410 is molded with resin, and specifically, is an IC package of a Hall element or a magnetoresistive element.

The torque sensor 201 includes a ring-shaped magnetic shield member 71. The magnetic shield member 71 is made of a soft magnetic material such as iron or permalloy, and is between the pair of yokes 31 and 32 in the axial direction and outside the magnetized circumferential surface of the multipolar magnet 14 in the radial direction. In addition, it is provided inside the magnetic sensing part 410 of the magnetic sensor 41.
In the present embodiment, the magnetic shield member 71 is provided outside the claws 315 and 325 of the yokes 31 and 32 and inside the inner edge of the main body 56 of the magnetism collecting ring 501 in the radial direction. In other words, the magnetic shield member 71 is provided at a position shifted from the main body portion 56 of the pair of magnetism collecting rings 501 in the radial direction.
Furthermore, in this embodiment, the magnetic shield member 71 is installed on the side that can rotate together with the multipolar magnet 14 or the yokes 31 and 32.

Here, the operation of the torque sensor 201 will be described with reference to FIGS.
FIG. 8 shows a neutral state in which no steering torque is applied between the input shaft 11 and the output shaft 12 and no torsional displacement occurs in the torsion bar 13. At this time, the south pole is visible in the center of the front of the multipolar magnet 14 in the figure. Further, the centers of the claws 315 and 325 of the yokes 31 and 32 coincide with the boundary between the N pole and the S pole of the multipolar magnet 14.

  In this state, the same number of lines of magnetic force enter and exit the claws 315 and 325 of the magnetic yokes 31 and 32 from the north and south poles of the multipolar magnet 14. Each magnetic field line forms a closed loop. Therefore, magnetic flux does not leak into the gap between the magnetic yoke 31 and the magnetic yoke 32, and the magnetic flux density detected by the magnetic sensor 41 is zero.

  When a steering torque is applied between the input shaft 11 and the output shaft 12 and the torsion bar 13 is twisted and displaced, a set of magnets fixed to the input shaft 11 and the output shaft 12 are fixed. The relative position with respect to the yokes 31 and 32 changes in the circumferential direction. 9A and 9B show a state in which the multipolar magnet 14 is rotated relative to the yokes 31 and 32 from the neutral state. FIG. 9A shows a state in which the multipolar magnet 14 is rotated by 7.5 ° in the left direction when viewed from the front, and FIG. A state rotated by 5 ° is shown.

In the state of FIG. 9A, the claw 315 of the yoke 31 faces the N pole, and the claw 325 of the yoke 32 faces the S pole. In the state of FIG. 9B, the claw 315 of the yoke 31 faces the south pole, and the claw 325 of the yoke 32 faces the north pole. Therefore, the magnetic yoke 31 and the magnetic yoke 32 have increased lines of magnetic force having opposite polarities.
As a result, the density of the magnetic flux passing through the magnetic sensor 41 is substantially proportional to the amount of torsional displacement of the torsion bar 13 and the polarity is reversed according to the torsional direction of the torsion bar 13. The magnetic sensor 41 detects this magnetic flux density and outputs it as a voltage signal, so that the torque sensor 201 detects the steering torque between the input shaft 11 and the output shaft 12.

  Referring to FIG. 10, the magnetic flux ΦD detected by the magnetic sensor 41 reaches the magnetic sensor 41 from the north pole of the multipolar magnet 14 via the yoke 31 and the magnetic flux collecting portion 511 of the magnetic flux collecting ring 501. Then, it passes through the magnetic sensor 41 and further passes through the magnetism collecting portion 512 of the magnetism collecting ring 501 and the yoke 32 toward the S pole having a cross section different from the illustrated cross section of the multipolar magnet 14.

  By the way, in the torque sensor 201 having the above-described configuration, it is desirable that the output of the magnetic sensor 41 is constant when the multipolar magnet 14 and the yokes 31 and 32 rotate together. However, if the magnetic shield member 71 is not provided, the magnetic flux ΦR indicated by the broken line in FIG. 10 passes directly through the space from the multipolar magnet 14 without passing through the yokes 31 and 32, and the magnetic sensing part 410 of the magnetic sensor 41. To reach. The output fluctuation occurs due to the influence of the magnetic flux ΦR.

Therefore, in the present embodiment, by providing the magnetic shield member 71, the magnetic flux ΦR directed from the multipolar magnet 14 directly to the magnetic sensor 41 is shielded. When this is represented by an image, the magnetic flux ΦR ′ radiated from the multipolar magnet 14 into the air hits the magnetic shield member 71 and is bounced back, so that it does not reach the magnetic sensor 41.
Referring to FIG. 10, it is possible to estimate an optimal position where the magnetic shield member 71 is provided. In the axial direction, it is obvious that the magnetic shield member 71 needs to be provided between the yokes 31 and 32. In particular, it is preferable that the magnetic shield member 71 includes the magnetic sensor 41 in the axial range. .

  In the radial direction, it is obvious that the magnetic shield member 71 needs to be provided closer to the magnetic sensor 41 than the claws 315 and 325 of the yokes 31 and 32, that is, outside the claws 315 and 325. Also, if the magnetic shield member 71 and the main body portion 56 of the pair of magnetic flux collecting rings 501 overlap in the radial direction, the other main body portion passes through the magnetic shield member 71 from one main body portion 56 of the magnetic flux collecting ring 501. A magnetic path towards 56 is constructed. Then, a part of the magnetic flux collected on the magnetic flux collecting ring 501 escapes to this path, so that the magnetic flux transmitted to the magnetic sensor 41 is reduced. In order to prevent this, the magnetic shield member 71 is preferably provided at a position shifted from the main body portion 56 of the pair of magnetism collecting rings 501 in the radial direction.

  With the above configuration, the torque sensor 201 of the present embodiment can shield the magnetic flux directly directed from the multipolar magnet 14 toward the magnetic sensor 41 by providing the magnetic shield member 71. Therefore, as shown in FIG. 11, output fluctuation when the magnet 14 and the yokes 31 and 32 are rotated together can be reduced.

  Here, in this embodiment, since the magnetic shield member 71 is installed on the side that can rotate together with the multipolar magnet 14 or the yokes 31 and 32, the part that faces the magnetic sensor 41 and exhibits the shield function is accompanied by the rotation. Changes in the circumferential direction. Therefore, the magnetic shield member 71 needs to be formed in a ring shape over the entire circumference.

Further, in the present embodiment, by providing a set of magnetic flux collecting rings 501, the magnetic fluxes of the yokes 31 and 32 can be efficiently collected in the magnetic flux collecting portion 51. The body 56 of the pair of magnetic flux collecting rings 501 is formed in a semicircular shape, and can be assembled from the radially outward direction of the yokes 31 and 32. Therefore, the assemblability is improved as compared with the annular magnetic flux collecting rings.
The main body 56 of the pair of magnetic flux collecting rings 501 is provided between the yokes 31 and 32 in the axial direction and overlaps with the yokes 31 and 32 when projected in the axial direction. The amount can be increased.

  Subsequently, twelfth to fourteenth embodiments will be described with reference to FIGS. In these embodiments, the arrangement of the magnetic shield members in the axial direction is the same as that of the eleventh embodiment, and the arrangement and shape of the magnetic shield members in the radial direction are different from those of the eleventh embodiment.

(Twelfth embodiment)
As shown in FIG. 12, the torque sensor 202 of the twelfth embodiment is provided with an annular magnetic shield member 72 as in the eleventh embodiment. The magnetic shield member 72 is installed on the side that can rotate together with the multipolar magnet 14 or the yokes 31 and 32.
Further, the magnetic shield member 72 is provided on the outer side of the outer edge of the main body 56 of the magnetism collecting ring 501 and on the inner side of the magnetic sensing part 410 of the magnetic sensor 41 in the radial direction. In this case, although the magnetic shield member 72 partially overlaps the connecting portion 57 of the magnetic flux collecting ring 501 in the radial direction, most of the magnetic shield member 72 is provided at a position shifted from the main body portion 56 of the magnetic flux collecting ring 501.
With this configuration, the same operational effects as those of the eleventh embodiment can be obtained.

(13th and 14th embodiments)
As shown in FIGS. 13 and 14, the torque sensor 203 of the thirteenth embodiment is provided with a “C-shaped” magnetic shield member 73 having a ring cut in half. Unlike the eleventh and twelfth embodiments, the magnetic shield member 73 is installed not on the rotating side but on the side fixed together with the magnetic sensor 41. In the case of being installed on the fixed side, it is only necessary to have a portion exhibiting a shielding function only on the circumferential side of the magnetic sensor 41, and therefore, it is formed in such a C shape.

  In short, when the magnetic shield member is installed on the fixed side, the minimum magnetic shield member 74 is at least within the range of the magnetic sensor 41 in the circumferential direction, like the torque sensor 204 of the fourteenth embodiment shown in FIG. As long as it is provided in a range corresponding to. That is, the circumferential width Ws of the magnetic shield member 74 may be equal to or greater than the circumferential width Wd of the magnetic sensor 41. By forming the magnetic shield member 74 to a minimum, the component cost can be reduced.

(Modification of Embodiment Using Magnetic Shielding Member)
In the torque sensor that shields the magnetic flux directly directed from the multipolar magnet 14 toward the magnetic sensor 41 by the magnetic shield member, it is not necessary to include a set of magnetism collecting rings as a “set of magnetism collectors”. When a set of magnetism collecting rings is not provided, it is not necessary to consider that the magnetic shield member and the magnetism collecting rings overlap in the radial direction as in the eleventh and twelfth embodiments.

[Other Embodiments of Torque Sensor for Reducing Output Fluctuation According to the Present Invention]
(A) The number of magnetic poles of a multipolar magnet is not limited to 12 pole pairs and 24 poles. In addition, the number of claws 315 and 325 of the yokes 31 and 32 corresponding to this is not limited to twelve.
(A) The N pole and the S pole in the above description may be reversed.

  (C) In the above embodiment, “a magnet and a set of magnet end yokes” are fixed to the input shaft 11 side of the torsion bar 13, and “a set of intermediate yokes” are fixed to the output shaft 12 of the torsion bar 13. . Conversely, the “magnet and the set of magnet end yokes” may be fixed to the output shaft 12, and the “set of intermediate yokes” may be fixed to the input shaft 11.

  As mentioned above, this invention is not limited to such embodiment, In the range which does not deviate from the meaning of invention, it can implement with a various form. For example, the present invention can be applied not only to an electric power steering device but also to various devices that detect shaft torque.

201-204 ... torque sensor,
11 ... input shaft (first axis), 12 ... output shaft (second axis),
13 ... Torsion bar, 14 ... Multipole magnet,
31, 32 ... a set of yokes,
41 ... Magnetic sensor,
410 ... magnetic sensitive part,
501 ... a set of magnetism collecting rings (a set of magnetism collectors),
71, 72, 73, 74 ... Magnetic shield members.

Claims (4)

A torsion bar (13) which connects the first shaft (11) and the second shaft (12) coaxially and converts torque applied between the first shaft and the second shaft into a torsional displacement. )When,
A multi-pole magnet (14) fixed to one end of the first shaft or the torsion bar and having N and S poles alternately magnetized in the circumferential direction;
A magnetic circuit is formed in the magnetic field generated by the multipolar magnet, fixed to the second shaft or the other end of the torsion bar outside the diameter of the multipolar magnet, and opposed in the axial direction through a gap. A set of yokes (31, 32)
A magnetic sensor (41) provided on the radially outer side of the set of yokes and having a magnetic sensing part (410) for detecting a magnetic flux density generated in the magnetic circuit;
It is formed of a soft magnetic material, and is provided between the pair of yokes in the axial direction and outside the multipolar magnet and inside the magnetic sensing portion in the radial direction, from the multipolar magnet to the magnetic sensor. A magnetic shield member (71, 72, 73, 74) that shields the magnetic flux that directly reaches the magnetic sensing part;
A torque sensor (201, 202, 203, 204) comprising:   The torque sensor according to claim 1, wherein the magnetic shield member (71, 72) is provided in an annular shape and is rotatable with respect to the magnetic sensor together with the multi-pole magnet or the set of yokes. (201, 202). A set of magnetic collectors (501) for collecting magnetic flux from the set of yokes to the magnetic sensor;
The torque sensor according to claim 2, wherein the magnetic shield member is provided at a position shifted from the set of magnetic current collectors in a radial direction.   The torque according to claim 1, wherein the magnetic shield member (73, 74) is fixed to the magnetic sensor and is provided in a range corresponding to at least the range of the magnetic sensor in the circumferential direction. Sensor (203, 204).

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