JP2010122104A - Torque detector - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a torque detector capable of preventing the degradation of accuracy and reliability. <P>SOLUTION: Torque detector includes: an annular permanent magnet fixed to a second shaft co-coaxially connected to a first shaft via a connection shaft and multi-pole magnetized along the circumferential direction; first and second sensor yokes fixed to the first shaft; first and second magnetic flux collection yokes each arranged so as to surround the corresponding first or second sensor yoke from outside in the radial direction; a magnetic flux collection yoke holder integrally holding the first and second magnetic flux collection yokes; and a magnetic flux detector detecting the magnetic flux induced by the first and second magnetic flux collection yokes and the like. The first and second magnetic flux collection yokes are formed in a shape so that a part overhangs outward in the radial direction with respect to the outer circumferential shape of the first and second sensor yokes. The magnetic flux collection yoke holder holds the first and second magnetic flux collection yokes from the inner circumferential side at least in the part overhanging outward in the radial direction with respect to the outer circumferential shape of the first and second sensor yokes. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a torque detector, which is suitable for application to, for example, an electric power steering system (EPS).

  2. Description of the Related Art Conventionally, various configurations of torque detectors (torque sensors) for electric power steering devices mounted on automobiles and the like have been proposed.

As one of such torque detectors, a pair of sensor yokes (a multipole yoke and a magnetic yoke) are opposed to the outer peripheral surface of an annular permanent magnet magnetized in the circumferential direction through a gap. And a pair of magnetic flux collecting yokes (magnetic flux collecting rings) so as to face the sensor yokes with a gap between them, and based on the amount of magnetic flux detected by the magnetic flux sensor disposed between the magnetic flux collecting rings. Thus, a torque detector that detects torque generated on the permanent magnet side or the sensor member side has been proposed (see, for example, Patent Document 1 and Patent Document 2).
JP 2003-329523 A Japanese Patent Laid-Open No. 2005-265587

  By the way, Patent Document 1 discloses that the magnetic collecting yoke and the magnetic flux sensor are integrally covered with a molding resin. In this case, in the embodiment of Patent Document 1, the inner peripheral surface facing the sensor yoke in the magnetism collecting ring is exposed, and the portion of the magnetism collecting ring covered by the molding resin is the outer circumference. There is a problem in that it is difficult to reliably hold the magnetic collecting yoke with the molding resin by using only the surface and the upper and lower end surfaces.

  Further, in Patent Document 2, when a magnetism collecting yoke and a magnetic flux detector are integrally molded with a molding resin, the molding resin is molded with a molding resin in order to reduce a stress generated in the magnetism collecting yoke due to a volume change when the molding resin is cured. It is disclosed that the mold body to be formed has a perforated shape, and further, a method of assembling the magnetic flux collecting yoke to the holder using the elasticity of the magnetic flux collecting yoke is also disclosed. However, when the mold body has a perforated shape as described above, there is a problem that the contact surface of the mold body with the magnetic flux collecting yoke is reduced, and the holding of the magnetic flux collecting yoke by the mold body becomes unstable.

  When the holding state of the magnetism collecting yoke by the molding resin (mold body) changes, even if the same torque is given to the torque detector by changing the positional relationship with the sensor yoke, the magnetic flux sensor The accuracy and reliability of the torque detector will decrease due to changes in the amount of magnetic flux detected.

  The present invention has been made in consideration of the above points, and intends to propose a torque detector capable of preventing deterioration in accuracy and reliability.

  In order to solve such a problem, in the present invention, in the torque detector, the first and second shafts that are coaxially connected via the connecting shaft, and are fixed to the second shaft, and are arranged along the circumferential direction. Annular first magnet and second sensor which are fixed to the first shaft and are provided so that the claw portions facing each surface of the permanent magnet are sequentially positioned alternately. The first and second sensor yokes are disposed so as to surround the corresponding first or second sensor yoke from the outside in the radial direction, and form a magnetic circuit together with the permanent magnet and the first and second sensor yokes. Two magnetic flux collecting yokes, a magnetic flux collecting yoke holder that integrally holds the first and second magnetic flux collecting yokes, the first and second sensor yokes, and the first and second magnetic flux collecting yokes. Magnetic flux detection The first and second magnetism collecting yokes are formed in a shape that protrudes at least partially outward in the radial direction with respect to the outer peripheral shape of the first and second sensor yokes, and The magnetic yoke holder holds the first and second magnetic flux collecting yokes from the inner peripheral side at a portion projecting outward in the radial direction with respect to the outer peripheral shape of the corresponding first or second sensor yoke. It is characterized by that.

  As a result, in the torque detector according to the present invention, the first and second magnetic flux collecting yokes can be reliably held by the magnetic flux collecting yoke holder.

  According to the present invention, since the first and second magnetic flux collecting yokes can be reliably held by the magnetic flux collecting yoke holder, the state of the first and second magnetic flux collecting yokes held by the magnetic flux collecting yoke holder is changed. Not likely to occur. Accordingly, it is possible to realize a torque detector that hardly changes in the positional relationship between the sensor yoke and the first and second magnetic flux collecting yokes and thus can prevent deterioration in accuracy and reliability.

  Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings.

(1) Configuration of Electric Power Steering Device FIG. 1 shows an electric power steering device according to this embodiment. As shown in FIG. 1, the electric power steering apparatus according to the present embodiment detects a steering torque generated in the steering shaft 2 in response to the operation of the steering wheel 1 with a torque detector 3, and based on the detection result, The control unit 13 controls the electric motor 12 to generate necessary auxiliary steering torque in the electric motor 12 to assist the steering force of the steering wheel 1.

  A steering shaft 2 connected to the steering wheel 1 includes an input shaft 2A and an output shaft 2B to which a driver's steering force is applied, and a torque detector 3 and a reduction gear are provided between the input shaft 2A and the output shaft 2B. A box 11 is provided. The steering force transmitted to the output shaft 2B of the steering shaft 2 is transmitted to the steering mechanism. Specifically, the steering force is transmitted to the lower shaft 5 through the universal joint 4 and further transmitted to the pinion shaft 7 through the universal joint 6. Further, the steering force transmitted to the pinion shaft 7 is transmitted to the tie rod 9 via the steering gear 8 to steer a steered wheel (not shown). The steering gear 8 is configured as a rack-and-pinion type having a pinion 8A connected to the pinion shaft 7 and a rack 8B meshing with the pinion 8A, and the rotational motion transmitted to the pinion 8A is converted into a linear motion by the rack 8B. Is done.

  An auxiliary steering mechanism 10 that transmits auxiliary steering torque to the output shaft 2B is connected to the output shaft 2B of the steering shaft 2. The auxiliary steering mechanism 10 includes a reduction gear box 11 connected to the output shaft 2B, and an electric motor 12 connected to the reduction gear box 11 and generating auxiliary steering torque. The steering shaft 2, the torque detector 3, and the reduction gear box 11 constitute a column, and the electric motor 12 applies auxiliary steering torque to the output shaft 2B of the column. That is, the electric power steering apparatus in this embodiment is a column assist type.

  The torque detector 3 detects the steering force transmitted to the input shaft 2A via the steering wheel 1 as a steering torque. Details of the torque detector 3 will be described later. The control unit 13 that controls the driving of the electric motor 12 is supplied with electric power from the battery 15 with the ignition switch 14 turned on. The control unit 13 calculates an assist steering command value of the assist command based on the steering torque T detected by the torque detector 3 and the traveling speed V detected by the vehicle speed sensor 16, and the calculated assist steering command value is calculated. Based on this, the supply current value to the electric motor 12 is controlled.

(2) Configuration of Torque Detector According to this Embodiment Next, the configuration of the torque detector 3 mounted on the electric power steering apparatus will be described with reference to FIGS.

  As shown in FIG. 2, the torque detector 3 forms a magnetic circuit with a torsion bar 2C that connects the input shaft 2A and the output shaft 2B, and a permanent magnet assembly 31 that includes a permanent magnet 31A (see FIG. 4). The sensor yoke assembly 32 and the magnetic flux collecting yoke assembly 33, and the detector assembly 34 for detecting the magnetic flux amount of the magnetic flux from the permanent magnet assembly 31 induced by the sensor yoke assembly 32 and the magnetic flux collecting yoke assembly 33 are configured. .

  The torsion bar 2C is a connecting shaft that connects one axial end of the input shaft 2A and one axial end of the output shaft 2B. As shown in FIGS. 2 and 3, the input shaft 2A is covered with a hollow shaft 2D. The gear cover 2E connected to the hollow shaft 2D is attached to the reduction gear box 11, so that the structure (the reduction gear and the torque detector 3) in the reduction gear box 11 is protected. The output shaft 2B is rotatably supported in the reduction gear box 11 by a bearing 30, and a steered wheel (not shown) is connected to the other end in the axial direction via a universal joint 4 (FIG. 1). It is attached.

  As shown in FIGS. 3 and 4A, the permanent magnet assembly 31 includes a permanent magnet 31A formed as a flat annular body surrounding the output shaft 2C, and a metal back yoke that houses the permanent magnet 31A. 31B. The permanent magnet 31A is configured by alternately magnetizing different magnetic poles (N pole and S pole) in the circumferential direction, and is fixed to the back yoke 31B by bonding.

  The back yoke 31B has an inner peripheral side wall surface 31C as shown in FIG. 4B, and as shown in FIG. 3, the back yoke 31B is press-fitted and fixed to the output shaft 2B so that the inner peripheral side wall surface 31C contacts. ing. It is preferable to employ a ferromagnetic material as the material of the back yoke 31B because the magnetic force of the permanent magnet 31A can be used efficiently.

  In addition, as a magnet material which comprises 31 A of permanent magnets, a ferrite magnet, rare earth magnets (Nd-Fe-B system magnet, Sm-Co system magnet, etc.), a metal magnet, a sintered magnet, etc. are employable. Moreover, you may employ | adopt as a permanent magnet the bond magnet (rubber magnet or plastic magnet) integrally molded with the back yoke 31B.

  The sensor yoke assembly 32 is an annular magnetic body including the first and second sensor yokes 32A and 32B shown in FIG. 5, and is arranged in the magnetic field of the permanent magnet 31A to form a magnetic circuit together with the permanent magnet 31A. As shown in FIG. 5, the first sensor yoke 32A includes a plurality of flat plate-like claw portions 32AA and a side wall portion 32AB formed by bending the outer periphery of the first sensor yoke 32A perpendicularly to the steering wheel side. Is provided. The second sensor yoke 32B includes a plurality of flat plate trapezoidal claw portions 32BA and a side wall portion 32BB formed by bending the outer peripheral portion of the second sensor yoke 32B perpendicularly to the steered wheel side.

  As shown in FIGS. 3, 6, and 7, the first and second sensor yokes 32A and 32B surround the input shaft 2A while the claw portions 32AA and 32BA face each other on one side in the axial direction of the permanent magnet 31A. The molding resin 32C (FIG. 3) is positioned so that the claw portions 32AA of the first sensor yoke 32A and the claw portions 32AA of the second sensor yoke 32B are alternately positioned in the circumferential direction. Are integrated.

  The side wall portion 32BB of the second sensor yoke 32B is disposed on the radially outer side of the permanent magnet assembly 31. In other words, the permanent magnet assembly 31 is housed in a cylindrical space composed of the side wall portion 32BB and the claw portion 32BA of the second sensor yoke 32B. For this reason, the axial dimension of the structure which consists of the permanent magnet assembly 31 and the sensor yoke assembly 32 can be shortened, and by extension, the axial dimension of the torque detector 3 can be shortened.

  As shown in FIGS. 3, 8, and 9, the magnetic flux collecting yoke assembly 33 has an annular magnetic collecting yoke holder 33B coaxially fixed to one surface side of the annular bearing holder 33A and covers the magnetic collecting yoke holder 33B. In addition, the cover 33D is fixed to the bearing holder 33A so that the upper end surface of the magnetism collecting yoke holder 33B and the inner surface of the upper surface through the O-ring 33C are in contact with each other.

  The magnetic flux collecting yoke holder 33B holds the first and second magnetic flux collecting yokes 33E and 33F (FIG. 6) on the inner peripheral surface side thereof, and is formed into a substantially cylindrical shape using a nonmagnetic material such as a resin material. It is formed. The first and second magnetic flux collecting yokes 33E and 33F are annular auxiliary magnetic bodies provided in correspondence with the first or second sensor yokes 32A and 32B, respectively, as is apparent from FIGS. As shown in FIG. 7, the corresponding first or second sensor yoke 32A, 32B is surrounded from the outside in the radial direction of the first or second sensor yoke 32A, 32B (more specifically, Are held by the magnetic flux collecting yoke holder 33B so that the side walls 32AB and 32BB of the first or second sensor yoke 32A and 32B face each other from the outside in the radial direction of the first or second sensor yoke 32A and 32B. The

  As is apparent from FIG. 6, the first and second magnetic flux collecting yokes 33E and 33F are partially stretched radially outward with respect to the outer peripheral shapes of the first and second sensor yokes 32A and 32B, respectively. Three projecting portions 33EA and 33FA that are projected (parts of the ring shape projecting radially outward from the arc) are provided at intervals of 90 degrees in the circumferential direction, as shown in FIG. In the overhang portions 33EA and 33FA, the magnetic flux collecting yoke holder 33B can be held from the inner peripheral side of the magnetic flux collecting yokes 33E and 33F.

  Further, as shown in FIGS. 6 and 9, the first and second magnetism collecting yokes 33 </ b> E and 33 </ b> F are provided with convex portions 33 </ b> EB and 33 </ b> FB projecting radially outward in a state of facing each other. The parts 33EB and 33FB function as magnetic flux concentrating parts. Since the distance between the convex portions 33EB and 33FB in the axial direction is narrower than the distance between the first magnetism collecting yoke 33E and the second magnetism collecting yoke 33F in the axial direction, the magnetic flux generated from the permanent magnet 31A is reduced. It can be collected intensively.

  As shown in FIGS. 3, 8 and 9, the detector assembly 34 is fitted into a detector mounting portion 33 </ b> BA (FIG. 8) that is formed to protrude from the outer peripheral surface of the magnetic flux collecting yoke holder 33 </ b> B of the magnetic flux collecting yoke assembly 33. The magnetic flux detector 34A (FIG. 9) is inserted into the gap in the axial direction of the convex portions 33EB and 33FB as magnetic flux concentrating portions provided in the first and second magnetic flux collecting yokes 33E and 33F. have. The magnetic flux detector 34A has a function of detecting the amount of magnetic flux that passes through the gap in the axial direction of the magnetic flux concentrating portions (convex portions 33EB and 33FB), and includes a Hall element, MR element, MI element, and the like.

  The magnetic characteristics (output hysteresis) are improved by adopting an alloy containing nickel as the material of the first and second sensor yokes 32A and 32B and the first and second magnetic flux collecting yokes 33E and 33F. As a result, it is possible to obtain good performance as the torque detector 3. If hysteresis is not a problem, the first and second sensor yokes 32A, other magnetic metals (for example, a rolled steel plate such as a silicon steel plate or SPCC generally used as a material for a motor or the like) are used. 32B and the first and second magnetic flux collecting yokes 33E and 33F can be configured. Further, any one of the first and second sensor yokes 32A and 32B and the first and second magnetic flux collecting yokes 33E and 33F may be configured using an alloy containing nickel.

  Next, the principle of torque detection of the torque detector 3 according to this embodiment will be described with reference to FIG. FIG. 11 shows the positional relationship between the permanent magnet 31A constituting the torque detector 3 and the first sensor yoke 32A. In FIG. 11, the second sensor yoke 32B and the like are omitted in order to clarify the positional relationship between the claw portion 32AA of the first sensor yoke 32A and the permanent magnet 31A. As described above, the claw portion 32BA of the second sensor yoke 32B is disposed between the claw portions 32AA of the sensor yoke 32A.

  When no torque is input to the torque detector 3, each of the claw portions 32AA of the first sensor yoke 32A is positioned on the boundary between the magnetic poles (N pole and S pole) constituting the permanent magnet 31A. Since the permeance (reciprocal of the magnetic resistance) with respect to the N pole and the S pole of the permanent magnet 31A viewed from the claw portion 32AA is equal, the magnetic flux flows as shown in FIG. Specifically, the magnetic flux generated from the N pole of the permanent magnet 31A enters the claw portion 32AA of the first sensor yoke 32A and enters the S pole of the permanent magnet 31A as it is. Therefore, the magnetic flux does not flow through the magnetic flux detector 34A.

  When the driver rotates the steering wheel 1 from this state and torque is applied to the input shaft 2A, the input side of the torsion bar 2C rotates in the same manner as the steering wheel 1 and the torsion bar 2C itself responds to the input torque. Twist occurs. This twist causes relative angular displacement between the input side and the output side of the torsion bar 2C. The relative angular displacement generated between the input side and the output side of the torsion bar 2C appears as a relative angular displacement between the permanent magnet 31A of the torque detector 3 and the first sensor yoke 32A.

  When a relative angular displacement occurs between the permanent magnet 31A and the first sensor yoke 32A, the balance of permeance as shown in FIG. 11 is lost, and the magnetic circuit including the magnetic flux detector 34A (that is, from the N pole of the permanent magnet 31A). The generated magnetic flux flows into the claw portion 32AA of the first sensor yoke 32A, passes through the magnetic flux detector 34A from the first sensor yoke 32A via the convex portion 33EB of the first magnetism collecting yoke 33AA, and the second The magnetic flux flows through the claw portion 32BA of the magnetism collecting yoke 33B to the magnetic circuit returning to the south pole of the permanent magnet 31A. By detecting the magnetic flux generated in the magnetic circuit including the magnetic flux detector 34A by the magnetic flux detector 34A, the relative angular displacement can be measured, and the torque applied to the torsion bar 2C can be detected.

(3) Effects of the present embodiment As described above, in the torque detector 3 according to the present embodiment, a part of the ring shape with respect to the first and second magnetism collecting yokes 33E and 33F has a diameter from above the arc. Since the projecting portions 33EA and 33FA projecting to the outer peripheral side in the direction are provided, the magnetism collecting yoke holder 33B is located on the inner peripheral side of the first and second magnetism collecting yokes 33E and 33F in these projecting portions 33EA and 33FA. The first and second magnetism collecting yokes 33E and 33F can be reliably held by the magnetism collecting yoke holder 33B. As a result, the positional relationship between the first and second sensor yokes 32A and 32B and the first and second magnetism collecting yokes 33E and 33F hardly changes, thus reducing the accuracy and reliability of the torque detector 3. This can be prevented in advance and effectively.

  Further, by adopting such a holding method of the first and second magnetic flux collecting yokes 33E and 33F, the magnetic flux collecting yoke holder 33B covers the entire outer periphery of the first and second magnetic flux collecting yokes 33E and 33F. Since there is no need to hold the magnetic flux collecting yoke holder 33B, the magnetic flux collecting yoke holder 33B has a shape including only a portion for holding the first and second magnetic flux collecting yokes 33E and 33F and a skeleton connecting them while ensuring the necessary rigidity. It is also possible. As a result, it is possible to obtain the effects of reducing the material cost and weight of the magnetism collecting yoke holder 33B and reducing the influence of thermal expansion during molding and operation of the magnetism collecting yoke holder 33B.

(4) Other Embodiments In the above-described embodiment, the outer peripheral shapes of the first and second sensor yokes 32A and 32B are respectively provided on the first and second magnetism collecting yokes 33E and 33F of the torque detector 3. However, the present invention is not limited to this, and the present invention is not limited to this, but the overhang portions 33EA and 33FA, which are partially extended outward in the radial direction, are provided at three positions at intervals of 90 degrees, for example. , 33FA may be provided at intervals other than 90 degrees. In this case, the number of the overhang portions 33EA and 33FA may be less than three or four or more.

  However, when the first and second magnetic flux collecting yokes 33E and 33F are assembled and fixed to the magnetic flux collecting yoke holder 33B, the overhang portions 33EA and 33FA are equally arranged at intervals of 120 degrees (three-point support) from the viewpoint of assembly accuracy. The fixed position and shape are determined by the balance between the sensor performance and the assembly property. Regarding the sensor performance, the fixed portion of the magnetic flux collecting yoke holder 33B is arranged so that the positions of the first and second sensor yokes 32A and 32B with respect to the claw portions 32AA and 32BA are shifted, so that the convex portions 33EB and 33FB Magnetic flux fluctuations can be kept to a minimum.

  Further, for example, the convex portions 33EB and 33FB of the first and second magnetic flux collecting yokes 33E and 33F may be projected in the outer circumferential direction of the first or second magnetic flux collecting yokes 33E and 33F, respectively. By doing in this way, since distance with the 1st or 2nd sensor yoke 32A and 32B which counters can be separated, the reduction effect of leakage magnetic flux can be acquired.

  Further, the first and second magnetism collecting yokes 33E and 33F are not provided with the overhanging portions 33EA and 33FA, and the first and second magnetism collecting yokes 33E and 33F themselves have an elliptical shape as shown in FIG. It is good also as a shape which changes periodically according to a shape and the number of magnetic poles of 34 A of permanent magnets. Further, as shown in FIG. 12B, the first and second magnetic flux collecting yokes 33E and 33F are formed in an annular shape, and a part of the first and second magnetic flux collecting yokes 33E and 33F is projected from the arc as a whole to the radially outer peripheral side. The first and second magnetism collecting yokes 33E and 33F may be formed in a shape in which a part of the annular shape is cut out or a semicircular shape as shown in FIG.

  The present invention can be widely applied to torque detectors for various uses in addition to torque detectors used in electric power steering devices.

It is a basic diagram which shows the whole structure of the electric power steering device to which the torque detector by this Embodiment is applied. It is a disassembled perspective view which shows the structure of the torque detector by this Embodiment. It is sectional drawing which shows the structure of the torque detector by this Embodiment. (A) is a perspective view which shows the structure of a permanent magnet assembly, (B) is an exploded perspective view which shows the structure of a permanent magnet assembly. It is a perspective view which shows the structure of the 1st and 2nd sensor yoke. It is a perspective view which shows the structure of the 1st and 2nd sensor yoke and the 1st and 2nd magnetism collection yoke. It is a basic diagram with which it uses for description of the positional relationship of the 1st and 2nd sensor yoke and the 1st and 2nd magnetism collection yoke. (A) is an exploded perspective view showing a configuration of the magnetic flux collecting yoke assembly, and (B) is a perspective view showing a configuration of the magnetic flux collecting yoke assembly. It is sectional drawing which shows the structure of a magnetism collection yoke assembly. It is a perspective view with which it uses for description of the 1st and 2nd magnetism collection yoke. It is a conceptual diagram with which it uses for operation | movement description of the torque detector by this Embodiment. It is a perspective view with which it uses for description of other embodiment.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Electric power steering device, 2 ... Steering shaft, 2A ... Input shaft, 2B ... Output shaft, 2C ... Torsion bar, 3 ... Torque detector, 12 ... Electric motor, 31 ... Permanent magnet Assembly, 31A ... Permanent magnet, 31B ... Back yoke, 32 ... Sensor yoke assembly, 32A, 32B ... Sensor yoke, 32AA, 32BA ... Claw part, 32AB, 32BB ... Side wall part, 32C ... Molding resin , 33... Magnetic collecting yoke assembly, 33 B... Magnetic collecting yoke holder, 33 E, 33 F... Magnetic collecting yoke, 33 EA, 33 FA .. Overhang portion, 33 EB, 33 FB. ... magnetic flux detector.

Claims (4)

First and second shafts connected coaxially via a connecting shaft;
An annular permanent magnet fixed to the second shaft and multipolarly magnetized along the circumferential direction;
Annular first and second sensor yokes fixed to the first shaft and provided so that claw portions facing each of the permanent magnets are alternately positioned sequentially;
The first and second sensor yokes are arranged so as to face the corresponding first or second sensor yoke from the outside in the radial direction, and form a magnetic circuit together with the permanent magnet and the first and second sensor yokes. A magnetic collecting yoke,
A magnetic flux collecting yoke holder that holds the first and second magnetic flux collecting yokes together;
A magnetic flux detector for detecting magnetic flux induced by the first and second sensor yokes and the first and second magnetic flux collecting yokes,
The first and second magnetic collecting yokes are
At least a part of the outer circumferential shape of the first and second sensor yokes is formed in a shape protruding outward in the radial direction,
The magnetism collecting yoke holder is
The first and second magnetism collecting yokes are held from the inner peripheral side at least in a portion protruding outward in the radial direction with respect to the outer peripheral shape of the first or second sensor yoke. Detector. 2. The torque detector according to claim 1, wherein each of the first and second magnetism collecting yokes is formed in an annular shape, and includes a projecting portion projecting radially outward in a part of the annular shape. 3. The torque detector according to claim 2, wherein the projecting portions are provided at three positions at intervals of 120 degrees. The torque detector according to claim 1, wherein the first and second magnetism collecting yokes are formed in an elliptical shape.

Images