JP5091630B2 - Magnetostrictive torque sensor and electric power steering apparatus - Google Patents

Description

  The present invention relates to a magnetostrictive torque sensor and an electric power steering apparatus, and more particularly to a magnetostrictive torque sensor that detects a torque applied to a steering shaft or the like using a magnetic change based on a magnetostrictive action in a magnetostrictive film, and the magnetostrictive torque. The present invention relates to an electric power steering apparatus that uses a sensor as a steering torque detector.

  For example, in an electric power steering apparatus equipped as a steering system for an automobile, a steering torque applied to a steering shaft from a steering wheel by a driver's steering operation is generally detected by a steering torque detector. In recent years, a steering torque detector that uses a magnetostrictive torque sensor is known. The steering shaft is a rotating shaft that rotates in response to the rotational force generated by the driver's steering, and functions as the rotating shaft in the steering torque detector. The electric power steering device drives and controls a motor for assisting the steering force in accordance with the torque signal detected from the steering torque detector, thereby reducing the driver's steering force and providing a comfortable steering feeling.

  The principle of torque detection of a magnetostrictive torque sensor that functions as a steering torque detector will be described with reference to the drawings. The magnetostrictive torque sensor is actually configured as a sensor device, and includes a sensor portion that is sensitive to an inherent torque and a detection electric circuit portion that processes a sensor output signal.

  In the magnetostrictive torque sensor, as shown in FIG. 6, magnetic anisotropies that are opposite to each other at the surface of the steering shaft (rotating shaft) 101 over the entire circumference in the circumferential direction and along the axial center, for example. Magnetostrictive films 102A and 102B are formed so as to have 103 and 104, respectively. The magnetostrictive film 102A has a characteristic of increasing the axial permeability and the magnetostrictive film 102B has a characteristic of decreasing the axial permeability when positive torque is applied in the operation range of the magnetostrictive torque sensor. Yes. The magnetostrictive torque sensor 100 detects changes in the magnetostrictive characteristics of the magnetostrictive films 102A and 102B according to the twist generated in the steering shaft 101 when input torque is applied to the steering shaft 101 from the steering wheel as indicated by an arrow 105. It has a sensor configuration for non-contact detection by 106A and 106B. The detection coil 106A is disposed around the magnetostrictive film 102A so as to surround it. The detection coil 106B is disposed around the magnetostrictive film 102B so as to surround it.

  In the magnetostrictive torque sensor, the detection coils 106A and 106B detect changes in the magnetostriction characteristics of the corresponding magnetostrictive films 102A and 102B. Excited. A sinusoidal alternating current for excitation is applied to each of the detection coils 106A and 106B, thereby applying an alternating magnetic field to the corresponding magnetostrictive films 102A and 102B. In addition, although the example which uses a detection coil as an exciting coil was demonstrated here, the structure which uses an exciting coil separately from a detecting coil may be sufficient. In any case, an exciting coil for applying an alternating magnetic field to the magnetostrictive film is required.

  FIG. 7 shows the detection principle of the input torque based on the configuration of the sensor device using the magnetostrictive torque sensor 100. A characteristic VT1 is an input torque output characteristic created based on the output signal from the detection coil 106A, and a characteristic VT2 is an input torque output characteristic created based on the output signal from the detection coil 106B. Since the directions of the magnetic anisotropy 103 and 104 in the magnetostrictive films 102A and 102B are reversed, the slopes of the characteristics VT1 and VT2 are reversed. The characteristic VT3 is an input torque output characteristic created by taking the difference between the characteristic VT1 and the characteristic VT2. An artificial input torque applied to the steering shaft is obtained based on the characteristic VT3. In practice, the point B of the characteristic VT3 is set as the origin, and the right area is treated as a positive area and the left part is treated as a negative area. Information about the rotation direction and magnitude of the input torque applied to the steering shaft is obtained based on the characteristic VT3.

  In a conventional magnetostrictive torque sensor, as a method of giving magnetic anisotropy of the magnetostrictive film, a portion that becomes a magnetostrictive film is formed by plating on the rotary shaft that becomes a steering shaft, and then a torsion torque is applied to the rotary shaft. A stress was applied to the circumferential surface of the material, and heat treatment was performed in a thermostatic bath while applying the torsional torque. Specifically, according to Patent Document 1, after a magnetostrictive film is plated on the rotating shaft to a thickness of 40 μm, a stress is applied by applying a torsional torque of 2 kgm, and heat treatment is performed at 150 to 550 ° C. for 10 minutes to 20 hours. What to do has been proposed.

As other related prior art, there are techniques described in Patent Document 2 and Patent Document 3. The torque sensors described in these documents have a structure in which an intermediate layer is sandwiched. The purpose is to improve adhesion or release stress.
Japanese Patent Laid-Open No. 2002-82000 Japanese Patent No. 3114455 Japanese Patent No. 3377519

  With regard to the structure of a conventional magnetostrictive torque sensor, a structural steel material that requires strength is selected as a base material for a rotating shaft in order to process a pinion gear. This steel material has a high magnetic permeability (approximately 500), and the magnetostrictive film formed directly on the circumferential surface of the rotating shaft by electrolytic plating is easily affected by the magnetic material of the rotating shaft base material. It was a cause of variations in detection characteristics. Furthermore, the magnetic permeability of the base material of the rotating shaft itself hardly changes due to the application of torque, but the magnetic permeability of the magnetostrictive film changes greatly, and the change becomes sensor sensitivity. However, the magnetic influence from the base material with high magnetic permeability has suppressed the change in the magnetic permeability of the magnetostrictive film, causing a problem that the structural steel material forming the rotating shaft reduces the detection sensitivity. For this reason, in manufacturing a magnetostrictive torque sensor, it is necessary to adjust the detection sensitivity on the detection side when the detection circuit is assembled.

  In view of the above problems, the object of the present invention is to reduce the magnetic interaction between the base material of the rotating shaft and the magnetostrictive film, to increase the permeability change of the magnetostrictive film, and to improve the detection sensitivity. Another object of the present invention is to provide a magnetostrictive torque sensor that can reduce the influence of variations in magnetism of a base material and can reduce variations in impedance characteristics, and an electric power steering device that is configured using the magnetostrictive torque sensor.

  The magnetostrictive torque sensor and the electric power steering apparatus according to the present invention are configured as follows in order to achieve the above object.

A first magnetostrictive torque sensor (corresponding to claim 1) is used to rotate according to an input torque and is provided with a rotating shaft provided with a magnetostrictive film, an exciting coil for applying an alternating magnetic field to the magnetostrictive film, and a detecting coil for detecting a change in magnetic properties of the magnetostrictive film, further, substantially smaller than approximately 500 permeability of a material forming the rotating shaft between the circumferential surface and the magnetostrictive film of the rotating shaft A base film having a magnetic permeability of 100 is provided.

  In the above magnetostrictive torque sensor, in order to reduce the magnetic interaction between the base material of the rotating shaft and the magnetostrictive film, a material having a lower permeability than the base material is used between the base material and the magnetostrictive film. As a film formation. As a result, the magnetic interaction with the base material, which is the cause of suppressing the change in the magnetic permeability of the magnetostrictive film due to the application of torque, is reduced. For this reason, the magnetic permeability of the magnetostrictive film is likely to change, and the sensitivity can be improved. In addition, the influence of the magnetic variation of the base material, which has caused the variation of orientation in the magnetostrictive material plating part, is reduced by increasing the distance between the magnetic film and the base material. Reduced.

In the first magnetostrictive torque sensor (corresponding to claim 1 ), in the above configuration, the rotating shaft is made of structural steel, and the main component of the magnetostrictive film is Ni-Fe having a permeability of approximately 2000. , and the used is Ni-Fe or Ni of low compositional ratio magnetic permeability than the magnetostrictive film on the underlying film, and wherein the Rukoto nearly 100 of the magnetic permeability of the base film is formed.

The electric power steering device according to the present invention (corresponding to claim 2 ) detects the steering torque applied to the steering shaft of the steering device by the steering torque detector, and assists according to the steering torque detected by the steering torque detector. Yes out electric power steering apparatus comprises control means for driving and controlling the motor to provide torque to the steering shaft, using a first magnetostrictive torque sensor of the steering torque detecting unit, and a steering shaft of the magnetostrictive torque sensor rotation axis It is characterized by becoming.

  According to the present invention, since the base film having a lower magnetic permeability than the base material is formed between the base material of the rotating shaft and the magnetostrictive film, the magnetic interaction between the base material and the magnetostrictive film is achieved. Further, it is easy to change the magnetic permeability of the magnetostrictive film, and the detection sensitivity of the magnetostrictive torque sensor can be improved. Furthermore, the influence of the magnetic variation in the base material of the rotating shaft, which caused the variation in the plating orientation, increases the distance between the magnetostrictive film and the base material and is separated by the magnetic action relationship. Variations can be reduced.

  DESCRIPTION OF EMBODIMENTS Preferred embodiments (examples) of the present invention will be described below with reference to the accompanying drawings.

  The basic configuration of the magnetostrictive torque sensor will be described with reference to FIGS. 1 to 3 show one structural example of a magnetostrictive torque sensor. FIG. 1 is a partially sectional side view showing a basic structure of a magnetostrictive torque sensor, and FIG. 2 is a side view conceptually showing a basic configuration (including an electric circuit portion) of the magnetostrictive torque sensor. 3 shows a cross-sectional view of the main part of the portion where the magnetostrictive film is formed on the rotating shaft.

  As shown in FIGS. 1 and 2, the magnetostrictive torque sensor 10 includes a rotation shaft 11, one excitation coil 12 and two detection coils 13 </ b> A and 13 </ b> B arranged around the rotation shaft 11. . In FIG. 1 and FIG. 2, the rotating shaft 11 is shown with its upper and lower parts cut away and omitted for convenience of explanation.

  The rotating shaft 11 is a part of a steering shaft of a steering system, for example. The rotating shaft 11 receives a rotational force (torque) of clockwise rotation (clockwise) or counterclockwise rotation (counterclockwise) as indicated by an arrow A around the axis 11a. The rotating shaft 11 is provided with magnetostrictive films 14A and 14B at two locations in the upper and lower directions in FIG. 1 along the axis (axial center) direction. Each of the magnetostrictive films 14 </ b> A and 14 </ b> B has a constant width (axial width) in the axial direction of the rotating shaft 11 and is formed over the entire circumference of the rotating shaft 11 in the circumferential direction. The width dimension in the axial direction of each of the magnetostrictive films 14A and 14B and the distance between the two magnetostrictive films 14A and 14B are arbitrarily set according to conditions. The magnetostrictive films 14A and 14B are actually formed as magnetostrictive material plating portions on the surface of the rotating shaft 11 by electrolytic plating processing or the like. The magnetostrictive films 14A and 14B having magnetic anisotropy are formed by applying magnetic anisotropy processing to the magnetostrictive material plated portion. In FIG. 1 and the like, the film thicknesses of the magnetostrictive films 14A and 14B are slightly exaggerated.

  The rotating shaft 11 is a metal rod, and a structural steel material (base material) such as a chrome molybdenum steel material (SCM material) is used as the material.

  An alloy material of Fe (iron) -Ni (nickel) is used for the magnetostrictive material of the two magnetostrictive films 14A and 14B. Magnetostrictive films 14 </ b> A and 14 </ b> B are formed in the circumferential direction on the surface of the rotating shaft 11 based on electrolytic plating. The magnetostrictive films 14A and 14B may be magnetic films that exhibit magnetostriction, and are not limited to permalloy but may be films such as supermalloy. The completed two magnetostrictive films 14A and 14B have their magnetic anisotropy axisymmetric and in opposite directions, and one magnetostriction with respect to positive torque application in the operating range of the magnetostrictive torque sensor. The film has a characteristic that the magnetic permeability in the axial direction increases, and the other magnetostrictive film has a characteristic that the magnetic permeability in the axial direction decreases. In the following description, the upper magnetostrictive film 14A has a characteristic that the magnetic permeability in the axial direction increases with respect to positive torque application in the operation range of the magnetostrictive torque sensor. It is assumed that the magnetic permeability is reduced.

  Further, as shown in FIG. 3, a base film 61 is formed as an intermediate layer between the base material of the rotating shaft 11 and the magnetostrictive film 14A (14B). The base film 61 is made of a material having a lower magnetic permeability than that of the rotating shaft base material. Examples of the material of the base film 61 include Ni (nickel) and Co (cobalt), and an Fe—Ni alloy material having a low magnetic permeability and composition ratio can also be used. If it is Ni or Fe—Ni having a low magnetic permeability, the adhesion to the magnetostrictive films 14A and 14B will be good. With this structure, the magnetic interaction between the base material of the rotating shaft 11 and the magnetostrictive films 14A and 14B can be weakened by the base film 61, and the magnetic influence from the rotating shaft base material to the magnetostrictive film is reduced. it can. The thicker the base film 61, the less the magnetic influence from the rotating shaft base material to the magnetostrictive film.

  In the above, for example, typically, the permeability of the base material of the rotating shaft 11 is approximately 500, the permeability of Fe—Ni forming the magnetostrictive films 14A and 14B is approximately 2000, and the permeability of the base film 61 is Nearly 100. The value of magnetic permeability is not limited to these.

  The excitation coil 12 and the detection coils 13A and 13B are provided in correspondence with the two magnetostrictive films 14A and 14B formed on the surface of the rotating shaft 11, as shown in FIG. That is, as shown in FIG. 1, the detection coil 13A is disposed around the magnetostrictive film 14A with a gap interposed therebetween. The ring-shaped detection coil 13A surrounds the entire circumference of the magnetostrictive film 14A, and the axial width dimension of the detection coil 13A is substantially equal to the axial width dimension of the magnetostrictive film 14A. A detection coil 13B is disposed around the magnetostrictive film 14B with a gap interposed therebetween. Similarly, the ring-shaped detection coil 13B surrounds the entire circumference of the magnetostrictive film 14B, and the axial width dimension of the detection coil 13B is substantially equal to the axial width dimension of the magnetostrictive film 14B. Further, a ring-shaped excitation coil 12 is disposed around each of the two detection coils 13A and 13B. In FIG. 1, the exciting coils 12 are individually provided corresponding to the magnetostrictive films 14 </ b> A and 14 </ b> B, respectively, but actually, two portions of one exciting coil 12 are shown separately. is there. The detection coils 13A and 13B and the excitation coil 12 are provided in a space around the magnetostrictive films 14A and 14B using ring-shaped support frame bodies 15A and 15B provided around the rotation shaft 11 so as to surround the rotation shaft 11. It is wound.

In FIG. 2, the excitation coil 12 and the detection coils 13A and 13B arranged with respect to the magnetostrictive films 14A and 14B of the rotating shaft 11 are conceptually shown as electrical relationships. An AC power supply 16 that constantly supplies an AC current for excitation (AC sine wave current) is connected to the excitation coil 12 that is arranged in common to the magnetostrictive films 14A and 14B. In the electric circuit configuration for supplying the exciting current of the exciting coil 12 according to the present embodiment, in addition to the AC power source 16 that outputs an AC sine wave current, a bias power source 17 that supplies a bias current (I ₀ ) that is a DC current. Is provided. Inductive voltages V _A and V _B corresponding to the torque to be detected are output from the output terminals of the detection coils 13A and 13B arranged corresponding to the magnetostrictive films 14A and 14B, respectively.

  The magnetostrictive films 14A and 14B formed on the surface of the rotating shaft 11 are magnetostrictive films having different magnetic anisotropies made by electrolytic plating processing by Ni-Fe plating. Each of the two magnetostrictive films 14A and 14B is made to have magnetic anisotropies in opposite directions. When torque due to rotational force is applied to the rotating shaft 11, reverse magnetostrictive characteristics generated in the magnetostrictive films 14A and 14B are detected by using the detection coils 13A and 13B arranged around the magnetostrictive films 14A and 14B. To detect.

The manufacturing method of the magnetostrictive torque sensor 10 according to the present embodiment is as follows.
Regarding the manufacturing method of the magnetostrictive torque sensor 10, in particular, the manufacturing process of the rotating shaft 11 of the magnetostrictive torque sensor 10 is roughly divided into a magnetostrictive film forming process, a magnetic anisotropy adding process, a characteristic stabilizing process, and an inspection. It consists of processes. In order to complete the magnetostrictive torque sensor 10, a detector attaching step for attaching detectors such as an excitation coil 12 and detection coils 13 </ b> A and 13 </ b> B to the rotating shaft 11 is provided after the inspection step.
Conventionally, in the magnetostrictive film forming step that is usually performed first, a magnetostrictive material plating portion is formed as a base portion of the magnetostrictive film at a predetermined location on the surface of the rotating shaft 11 by electrolytic plating.
In the magnetostrictive torque sensor 10 according to the present embodiment, the base film forming step is executed before the magnetostrictive film forming step. In the base film forming step, the base film 61 is formed by various film forming methods.

  By providing the base film 61 as an intermediate layer between the rotating shaft base material and the magnetostrictive film as described above, the magnetic interaction between the base film 61 and the magnetostrictive film is small. Is easy to rotate, and has a characteristic that a permeability change occurs with a small input torque. As a result, sensor sensitivity is improved. As an improvement in sensor sensitivity, for example, an improvement effect of about 23% was obtained experimentally.

  Further, by providing the base film 61, the distance between the base material of the rotating shaft 11 and the magnetostrictive films 14A and 14B can be increased. Therefore, the influence of the base material magnetism when the magnetostrictive film is formed. As a result, the influence of variations in the base material magnetism of the rotating shaft 11 can be reduced, and as a result, the impedance (Z) characteristics of the magnetostrictive films 14A and 14B can be reduced. As a reduction in the variation, for example, a reduction of 45% was achieved experimentally.

  In addition to the magnetic materials Ni and Co, nonmagnetic materials such as Cu, Al, Au, Sn, Pd, Bi, In, Zn, Ti, and Pt are used as the material for the base film as the intermediate layer. It can also be used.

  The magnetostrictive torque sensor 10 is incorporated as a steering torque detection unit in a steering shaft of an electric power steering apparatus, for example, as shown in FIG. 4, elements that are substantially the same as those described in FIGS. 1 and 2 are denoted by the same reference numerals. FIG. 4 shows the structure of the steering torque detector 20, the support structure of the steering shaft 21 (corresponding to the rotating shaft 11), the rack and pinion mechanism 34, the power transmission mechanism 35, and the steering force assisting motor 42.

  In FIG. 4, the upper part of the steering shaft 21 is coupled to a steering wheel (not shown) of the vehicle. A lower portion of the steering shaft 21 is configured to transmit a steering force to an axle provided with a rack shaft via a rack and pinion mechanism 34. The steering torque detector 20 attached to the upper part of the steering shaft 21 is configured using the magnetostrictive torque sensor 10 described above. The steering torque detector 20 corresponds to the magnetostrictive torque sensor 10, and the portion of the steering shaft 21 on which the magnetostrictive films 14 </ b> A and 14 </ b> B are formed corresponds to the rotating shaft 11.

  In the housing 31 a forming the gear box 31, the steering shaft 21 is supported by two bearing portions 32 and 33 so as to be rotatable. A rack and pinion mechanism 34 and a power transmission mechanism 35 are accommodated in the housing 31a.

  A steering torque detector 20 (magnetostrictive torque sensor 10) is attached to the steering shaft 21. The above-described magnetostrictive films 14A and 14B are formed on the steering shaft 21, and the excitation coil 12 and the detection coils 13A and 13B correspond to the magnetostrictive films 14A and 14B, and the support frame portions 15A and 15B and the yoke portions 36A and 36B. Supported and provided.

  The upper opening of the housing 31 a is closed with a lid 37. A pinion 38 provided at the lower end portion of the steering shaft 21 is located between the bearing portions 32 and 33. The rack shaft 39 is guided by a rack guide 40 and is urged by a compressed spring 41 to be pressed against the pinion 38 side. The power transmission mechanism 35 is formed by a worm gear 44 fixed to a transmission shaft 43 coupled to an output shaft of the steering force assisting motor 42 and a worm wheel 45 fixed to the steering shaft 21. The steering torque detector 20 is attached to the inside of the cylindrical portion 37 a of the lid 37.

The steering torque detector 20 detects a steering torque that acts on the steering shaft 21. The detected value is input to a control device (not shown) and used as a reference signal for causing the motor 42 to generate an appropriate auxiliary steering torque. When the steering torque from the steering wheel acts on the steering shaft 21, the steering torque detector 20 detects changes in the magnetic characteristics of the magnetostrictive films 14 </ b> A and 14 </ b> B according to the twist generated in the steering shaft 21. Are detected as changes in induced voltages V _A and V _B from the respective output terminals.

When steering torque is applied to the steering shaft 21, the steering shaft 21 is twisted, resulting in a magnetostrictive effect in the magnetostrictive films 14A and 14B. In the steering torque detector 20, since the exciting current is always supplied from the AC power source 16 to the exciting coil 12, the change in the magnetic field caused by the magnetostrictive effect in the magnetostrictive films 14A and 14B is induced by the detecting coils 13A and 13B. _a, is detected as a change in _{V B.} According to the steering torque sensor 20, the induced voltage _V A, based on the change in _{V B,} and outputs two induction voltages _V A, the difference _{V B} as a detected voltage value. Therefore, the direction and magnitude of the steering torque applied to the steering shaft 21 can be detected based on the output voltage value (V _A −V _B ) of the steering torque detector 20.

  FIG. 5 is a diagram showing the magnetostrictive characteristic curves 51A and 51B of the two magnetostrictive films 14A and 14B, respectively. In FIG. 5, the horizontal axis represents the steering torque applied to the steering shaft 21, and the positive side (+) corresponds to the right rotation and the negative side (−) corresponds to the left rotation. The vertical axis in FIG. 5 means the voltage axis.

The magnetostrictive characteristic curves 51A and 51B for the magnetostrictive films 14A and 14B simultaneously represent the detection output characteristics of the detection coils 13A and 13B. That is, an exciting alternating current is supplied to the magnetostrictive films 14A and 14B having the magnetostrictive characteristic curves 51A and 51B by the common exciting coil 12, and the detecting coils 13A and 13B generate an induced voltage in response to the exciting alternating current. Since the voltage is output, the change characteristic of the induced voltage of the detection coils 13A and 13B corresponds to the magnetostriction characteristic curves 51A and 51B of the magnetostrictive films 14A and 14B. In other words, the magnetostrictive characteristic curve 51A shows the changing characteristics of the induced voltage V _A output from the sensor coil 13A, the magnetostrictive characteristic curve 51B shows the changing characteristics of the induced voltage V _B output from the detection coil 13B Yes.

According to the magnetostrictive characteristic curve 51A, the value of the induced voltage _VA output from the detection coil 13A is substantially linear as the steering torque value changes from the negative region to the positive region and further reaches the positive value T1 of the steering torque. It has a characteristic that it increases in the characteristic, reaches a peak value when the steering torque becomes a positive value T1, and gradually decreases when the steering torque further increases from T1. On the other hand, according to the magnetostrictive characteristic curve 51B, the value of the induced voltage V _B output from the detection coil 13B gradually increases until the steering torque reaches a negative value −T1, and the steering torque is negative. When the value is -T1, the peak value is obtained, and when the steering torque further increases from -T1 and changes from the negative region to the positive region, it has a characteristic of decreasing in a substantially linear characteristic.

  As shown in FIG. 5, the magnetostrictive characteristic curve 51A related to the detection coil 13A and the magnetostrictive characteristic curve 51B related to the detection coil 13B have magnetic anisotropies that are opposite to each other in the magnetostrictive films 14A and 14B. As a result, the relationship between the vertical axis and the vertical axis including the point where both magnetostrictive characteristic curves intersect is substantially symmetrical.

A line 52 shown in FIG. 5 indicates a detection coil based on each value of the magnetostrictive characteristic curve 51A obtained as an output voltage of the detection coil 13A in a common area of the magnetostrictive characteristic curves 51A and 51B and having a substantially linear characteristic. The graph produced based on the value which subtracted each corresponding value of the magnetostriction characteristic curve 51B obtained as an output voltage of 13B is shown. When the steering torque is zero, the induced voltages output from the detection coils 13A and 13B are equal, so the difference value is zero. The steering torque detector 20 uses the region regarded as a substantially constant gradient near the neutral point (zero point) of the steering torque in the magnetostrictive characteristic curves 51A and 51B, so that the line 52 has a substantially linear characteristic. It is formed as. Regarding the characteristic graph of the line 52, the vertical axis in FIG. 5 means the axis indicating the value of the differential voltage. A straight line 52 which is a characteristic graph is a straight line passing through the origin (0, 0), and exists on the positive and negative sides of the vertical axis and the horizontal axis. Since the detection output value of the steering torque detection unit 20 is obtained as the difference (V _A −V _B ) between the induction voltages output from the detection coils 13A and 13B as described above, based on the use of the straight line 52, The direction and magnitude of the steering torque applied to the steering shaft 21 can be detected.

  As described above, based on the output value of the steering torque detector 20, a detection signal corresponding to the rotational direction and magnitude of the steering torque input to the steering shaft 21 (rotating shaft 11) can be extracted. That is, the rotation direction and magnitude of the steering torque that has acted on the steering shaft 21 can be known from the detection value output from the steering torque detector 20.

  The configurations, shapes, sizes, materials, and arrangement relationships described in the above embodiments are merely schematically shown to the extent that the present invention can be understood and implemented. Therefore, the present invention is not limited to the described embodiments, and can be variously modified without departing from the scope of the technical idea shown in the claims.

  The present invention is used to improve the sensitivity performance of a magnetostrictive torque sensor used as a steering torque detector of an electric power steering apparatus and to simplify the manufacturing process.

1 is a partial cross-sectional side view showing a basic structure of a magnetostrictive torque sensor according to the present invention. It is a side view which shows notionally the electric circuit for detection of a magnetostriction type torque sensor. It is principal part sectional drawing of the part of the rotating shaft in which the magnetostrictive film was formed. It is a principal part longitudinal cross-sectional view of the concrete structure which incorporated the magnetostrictive torque sensor in the steering shaft of the electric power steering apparatus as a steering torque detection part. It is a graph which shows the magnetostriction characteristic curve and sensor detection characteristic regarding each detection coil in a magnetostriction type torque sensor. It is a side view which shows the principal part structure of the conventional general magnetostrictive torque sensor. It is a graph which shows the input torque and the output characteristic for demonstrating the principle of the input torque detection in the sensor structure of a magnetostriction type torque sensor.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Magnetostrictive torque sensor 11 Rotating shaft 12 Excitation coil 13A, 13B Detection coil 14A, 14B Magnetostrictive film 20 Steering torque detection part 21 Steering shaft 51A, 51B Magnetostrictive characteristic curve (impedance characteristic curve)
61 Underlayer

Claims (2)

A rotating shaft that is used to rotate according to an input torque and provided with a magnetostrictive film, an excitation coil that applies an alternating magnetic field to the magnetostrictive film, and a detection coil that detects a change in magnetic characteristics of the magnetostrictive film In a magnetostrictive torque sensor having
A base film having a permeability of about 100, which is smaller than the permeability of about 500 of the material forming the rotation axis, is provided between the circumferential surface of the rotation axis and the magnetostrictive film ,
The material of the rotating shaft is a structural steel material,
The main component of the magnetostrictive film is Ni—Fe having a permeability of approximately 2000,
Wherein the base film Ni-Fe or Ni of low compositional ratio permeability is used than the magnetostrictive film, the magnetostrictive torque sensor according to claim Rukoto permeability of the nearly 100 are formed. Electric power provided with a control means for detecting and controlling a steering torque applied to the steering shaft of the steering device, and for driving and controlling a motor for applying an auxiliary torque to the steering shaft in accordance with the steering torque detected by the steering torque detecting unit. In the power steering device,
Wherein the steering torque detecting unit using a magnetostrictive torque sensor according to claim 1, wherein the electric power steering device steering shaft, characterized in that the said rotation shaft of the magnetostrictive torque sensor.

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