JP2008224678A - Anisotropy imparting method of magnetostrictive torque sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To impart magnetic anisotropy on a magnetostrictive film provided on a surface of a shaft. <P>SOLUTION: The method includes a step for forming the magnetostrictive films 24, 25 on an outer surface of the shaft 23, a step for applying torque to the shaft 23 in one direction, a step for heating one part 24 of the magnetostrictive films, a step for releasing the torque applied in the one direction after cooling, a step for applying torque in other direction to the shaft 23, a step for heating another part 25 of the magnetostrictive films, and a step for releasing the torque applied in the other direction after cooling. Different magnetic anisotropy is imparted respectively to the one part 24 and another part 25 of the magnetostrictive films. <P>COPYRIGHT: (C)2008,JPO&amp;INPIT

Description

  The present invention is an anisotropy of an optimal magnetostrictive torque sensor that is mounted on an electric power steering device such as an automobile and is used for a detection device for magnetically detecting a steering torque applied to the shaft via a steering shaft. It relates to the grant method.

  In general, an electric power steering apparatus installed in an automobile or the like detects torque applied from a steering shaft to a shaft by a steering operation of a driver using a torque sensor. Then, in accordance with the detection signal from the torque sensor, the motor for assisting the driver in the steering operation (applying an auxiliary steering force) is driven and controlled, and the driver's steering force is reduced, so that a comfortable steering fee is achieved. Try to give a ring.

  A magnetostrictive torque sensor is known as such a conventional torque sensor (see, for example, Patent Document 1). In this magnetostrictive torque sensor, a magnetostrictive film (for example, a Ni—Fe alloy film) having magnetic anisotropy is deposited on the surface of a shaft. When a torque is applied to the shaft from the outside, a change in the magnetic characteristics (permeability) of the magnetostrictive film according to the twist generated in the shaft is detected magnetically in contact.

  Therefore, an example in which this type of conventional magnetostrictive torque sensor is used in an electric power steering apparatus for an automobile will be described as an example with reference to FIGS. FIG. 7 is a schematic view showing an electric power steering apparatus according to the prior art, and FIG. 8 is an explanatory view showing the relationship between the steering torque and the pinion torque according to the prior art. 9 is an enlarged longitudinal sectional view showing a conventional magnetostrictive torque sensor, FIG. 10 is a characteristic diagram showing the relationship between steering torque and impedance according to the prior art, and FIG. 11 shows a conventional magnetostrictive torque sensor. It is a circuit diagram.

  As shown in FIG. 7, the electric power steering apparatus 101 includes a magnetostrictive torque sensor 103 that detects a steering torque from the handle 102, a motor 104 that applies an auxiliary steering force to the operation of the handle 102, and the motor 104. A reduction device 105 that increases the rotational torque of the motor, an ECU (Electrical Control Unit) 107 that drives and controls the motor 104 in accordance with detection signals from the magnetostrictive torque sensor 103, the vehicle speed sensor 106, and the like, and the rotation of the motor 104 by the tire 108 , 108 to change the direction of the tire 108, and a rack shaft 109 and a pinion 110 are roughly configured. Further, as shown in FIG. 8, the speed reducer 105 includes a worm 105A and a worm wheel 105B.

  In this prior art, the steering torque when the driver performs a steering operation is detected using the magnetostrictive torque sensor 103, and the ECU 107 detects a detection signal (torque signal) from the magnetostrictive torque sensor 103 and a detection from the vehicle speed sensor 106. The motor 104 is driven and controlled in accordance with a signal (vehicle speed signal) or the like, and the torque of the motor 104 at this time is increased by the speed reducer 105 and transmitted to the tires 108 and 108 via the rack shaft 109 and the pinion 110.

  In such an electric power steering apparatus 101, as shown in FIG. 8, the steering torque of the driver is TH, the torque transmitted to the pinion 110 is TP, and a constant related to the magnitude of the auxiliary torque by the motor 104 is KA. Then, the relationship TH = TP / (1 + KA) is established, and the driver's steering force can be reduced by the auxiliary torque of the motor 104.

  Next, the magnetostrictive torque sensor 103 will be described. As shown in FIG. 9, the magnetostrictive torque sensor 103 is housed in a sensor housing case 111 including an upper case portion 111A and a lower case portion 111B. The magnetostrictive torque sensor 103 is connected to the steering shaft 102A (see FIG. 7) of the handle 102, and is supported by the sensor housing case 111 rotatably via bearings 112, 113, etc., and the upper case. Coils 115, 115 which are detection means provided on the inner peripheral side of the portion 111A and spaced apart from each other, and provided on the outer peripheral surface (outer surface) of the shaft 114 so as to face the coil 115 and are anisotropically opposite to each other. The first and second magnetostrictive films 116 and 117 having characteristics are generally constituted.

  Here, the magnetostrictive films 116 and 117 are formed using a magnetostrictive material made of, for example, a Ni—Fe alloy film or the like, and are plated on the outer peripheral surface of the shaft 114. For example, as shown in FIG. 11, the magnetostrictive torque sensor 103 includes a primary coil 119 connected to an AC power source 118 and a secondary coil provided to face the primary coil 119 with the magnetostrictive films 116 and 117 interposed therebetween. 120, 120.

When torque from the handle 102 is applied to the shaft 114, changes in the magnetic characteristics of the magnetostrictive films 116 and 117 in response to the twist generated in the shaft 114 are electrically detected on the secondary coils 120 and 120 side, respectively. As a result, for example, two substantially convex magnetostrictive characteristic curves as indicated by solid lines A and B in FIG. 10 are obtained, and the steering torque applied to the shaft 114 is calculated by calculating the difference between the two magnetostrictive characteristic curves. The direction and size of the are detected.
Japanese Patent Laid-Open No. 2002-257648 (paragraph numbers 0002 and 0003, FIG. 6) JP 2002-250662 A (2nd to 6th lines from the upper left column on page 5 and 23rd to 26th lines from the upper right column on page 6)

  Incidentally, Patent Document 1 describes a torque sensor in which a magnetostrictive film is provided on the surface of a shaft (rotating shaft), but does not disclose a method for imparting magnetic anisotropy.

  Accordingly, an object of the present invention is to provide a method for imparting anisotropy of a magnetostrictive torque sensor that imparts magnetic anisotropy to a magnetostrictive film provided on the surface of a shaft.

  In order to solve the above-described problems, according to the anisotropy imparting method of the magnetostrictive torque sensor of the present invention, a step of providing a magnetostrictive film on the outer surface of the shaft, a step of applying torque in one direction to the shaft, Heating a part of the magnetostrictive film; releasing a torque applied in the one direction after cooling; applying a torque in the other direction to the shaft; and heating the other part of the magnetostrictive film. And a step of releasing the torque applied in the other direction after cooling, and imparting different magnetic anisotropy to each of the part of the magnetostrictive film and the other part.

  According to this, for example, it is not necessary to quench the shaft after imparting anisotropy to the magnetostrictive film, and it is possible to stably impart anisotropy to the magnetostrictive film, and to detect torque with high linearity. Performance (see magnetostrictive characteristic curves A and B in FIG. 10) can be obtained.

  The shaft before the magnetostrictive film is provided preferably has a Rockwell hardness of HRC 40-60. Thereby, even if an excessive torque (for example, about 30 kgf · m (294 N · m)) is applied to the shaft, the plastic deformation of the shaft can be suppressed. Therefore, the shaft can be elastically deformed, the magnetostrictive film can be prevented from peeling off from the shaft, and the detection accuracy by the magnetostrictive torque sensor can be increased.

  Moreover, it is preferable that the pinion is provided in the lower end of the shaft. For example, after performing a case hardening process by carburizing and quenching the chromium molybdenum steel material that is the material of the shaft in advance, the pinion, the bearing, etc., together with the shaft, are attached in the same process by depositing a magnetostrictive film on the surface of the shaft. Can be heat-treated. That is, it is not necessary to heat-treat the bearing and pinion in different processes, and the process can be shortened.

  The shaft is preferably used for a steering shaft of an electric power steering apparatus. Thereby, the detection accuracy of the steering torque can be increased by the magnetostrictive film provided on the shaft, and the performance, reliability, etc. of the electric power steering device can be improved.

  In addition, it is set as the structure which provides the elastic member which relieve | moderates the impact force when both collide between the edge part of the rack axis | shaft which comprises an electric power steering apparatus, and the edge part of the rack storage case which accommodates the said rack axis | shaft. Thus, when the electric power steering apparatus is operated, the elastic member can absorb the impact force when the end of the rack shaft and the end of the rack housing case collide with each other.

  According to the present invention, magnetic anisotropy can be imparted to the magnetostrictive film provided on the surface of the shaft.

(First embodiment)
The case where the magnetostrictive torque sensor according to the first embodiment of the present invention is applied to an electric power steering apparatus (see FIG. 7) will be described as an example, and will be described in detail with reference to FIGS.

FIG. 1 is an enlarged longitudinal sectional view showing a magnetostrictive torque sensor according to this embodiment, and FIG. 2 is a characteristic diagram showing a relationship between a torsion angle and a steering torque according to this embodiment.
FIG. 3 is a characteristic diagram showing the relationship between the hardness and hysteresis of the shaft according to the present embodiment.

  As shown in FIG. 1, the magnetostrictive torque sensor 1 according to the present embodiment is provided with bearings 3, 4, 5, etc. in a sensor housing case 2 composed of an upper case portion 2A and a lower case portion 2B, as in the prior art. , A shaft 6 rotatably supported via the coil, coils 7 and 7 which are detection means provided on the inner peripheral side of the upper case portion 2A and spaced apart from each other, and a shaft facing the coils 7 and 7 6 has first and second magnetostrictive films 8 and 9 which are attached to the outer peripheral surface (outer surface) of FIG. The magnetostrictive films 8 and 9 are formed using a magnetostrictive material made of, for example, a Ni—Fe alloy film. The lower case portion 2B of the sensor housing case 2 is provided with a motor 10, a reduction gear 11, a rack shaft 12, a pinion 13, and the like. The reduction gear 11 includes a worm 11A, a worm wheel 11B, and the like.

  When torque from the handle is applied to the shaft 6, a change in the magnetic characteristics of the magnetostrictive films 8 and 9 corresponding to the twist generated in the shaft 6 is electrically detected using the coil 7 or the like. As a result, for example, two substantially convex magnetostrictive characteristic curves as indicated by solid lines A and B in FIG. 10 are obtained, and the steering torque applied to the shaft 6 is calculated by calculating the difference between the two magnetostrictive characteristic curves. It is configured to detect the direction and size.

Here, the shaft 6 according to the present embodiment is formed using a chromium molybdenum steel material (for example, SCM822) or the like. The shaft 6 is subjected to a heat treatment such as quenching on the chromium molybdenum steel material in advance, and then the magnetostrictive films 8 and 9 are coated using a PVD method such as sputtering or ion plating, a plating method, a plasma spraying method, or the like. By wearing, the Rockwell hardness is set within the range of HRC 40-65. Further, the shaft 6 may be formed by subjecting the surface of the chromium molybdenum steel material to a case hardening process by carburizing and quenching. The reason why the Rockwell hardness of the shaft 6 is set to HRC65 or less is that if the Rockwell hardness is set larger than the HRC65, the shaft 6 becomes brittle and breaks. On the other hand, the reason why the Rockwell hardness of the shaft 6 is set to HRC40 or more is that the shaft 6 is elastically deformed even when an excessive torque acts on the shaft 6 as described later.

  In the present embodiment configured as described above, the steering torque when operated by the driver is detected using the magnetostrictive torque sensor 1, and the detection signal from the magnetostrictive torque sensor by the ECU and the vehicle speed sensor (both are both). The motor 10 is driven and controlled in accordance with the detection signal from the control signal (see FIG. 7), and the torque of the motor 10 at this time is increased by the speed reducer 11 and the tire (not shown) is provided via the rack shaft 12 and the pinion 13. To tell.

  By the way, when the magnetostrictive torque sensor 1 according to the present embodiment is rotated clockwise or counterclockwise until the handle is locked, as described in the prior art, the end of the rack shaft 12 is attached to the rack housing case. There is a possibility that a large impact torque at this time is transmitted to the shaft 6 and the shaft 6 is plastically deformed by colliding with an end (not shown). When the amount of plastic deformation increases, the magnetostrictive films 8 and 9 on the surface of the shaft 6 are peeled off, and this peeling causes hysteresis in the sensor output.

  However, as a result of trial and error by experiment, by setting the Rockwell hardness of the shaft 6 to HRC 40 to 65 as in this embodiment, 30 kgf · m (294 N · m) with respect to the shaft 6 as shown in FIG. ) Even when an excessive steering torque is applied, the plastic deformation amount a of the shaft 6 according to the present embodiment can be suppressed to be significantly smaller (a <b) than the plastic deformation amount b in the prior art. It was found that the magnetostrictive films 8 and 9 do not peel off.

  Accordingly, since the Rockwell hardness of the shaft 6 is set to HRC 40 to 65, even if a large steering torque of, for example, 30 kgf · m (294 N · m) or more is applied to the shaft 6 during the steering operation, FIG. As shown, it was found that the hysteresis due to plastic deformation of the shaft 6 at this time can be remarkably reduced to an allowable value of 5% or less.

  Thereby, it is possible to prevent the magnetostrictive films 8 and 9 from being peeled off from the surface of the shaft 6, and even when an excessive steering torque acts on the shaft, the detection accuracy by the magnetostrictive torque sensor 1 can be kept good. It is possible to reduce the occurrence of hysteresis due to the peeling of the magnetostrictive films 8 and 9, and to improve the steering feeling.

  In addition, when the shaft 6 is manufactured, the magnetostrictive films 8 and 9 are attached to the surface of the shaft 6 after the case-hardening treatment by carburizing quenching is performed on the chromium molybdenum steel material which is the material of the shaft 6 in advance. The bearings 3, 4, 5, the pinion 13, and the like can be subjected to heat treatment with the shaft 6 in the same process, for example, Rockwell hardness HRC58 or higher. Accordingly, it is not necessary to heat-treat the bearings 3, 4, 5 and the pinion 13 in different processes, the process can be shortened, and these members can be easily manufactured. Moreover, when heat-treating the bearings 3, 4, 5, the shaft 6, the pinion 13, etc., the process can be managed in consideration of the influence of distortion of these members, and the quality can be stabilized. .

  Further, in the present embodiment, since the magnetostrictive films 8 and 9 are attached to the shaft 6, the detection sensitivity of the magnetostrictive torque 1 is 10 as compared with the case where the entire shaft 6 is formed using a magnetostrictive material. It can be increased up to about 100 times.

  In addition, since the magnetostrictive torque sensor 1 is applied to an electric power steering device that applies an auxiliary steering force to the steering mechanism of the automobile, the magnetostrictive torque sensor 1 can improve the detection accuracy of the steering torque. The performance, reliability, etc. of the electric power steering device can be improved.

(Second Embodiment)
Next, FIG. 4 shows a second embodiment of the present invention. The feature of this embodiment is that the shaft is subjected to heat treatment so that the hardness becomes HRC 40 to 65, and then the magnetostrictive film is applied to the shaft. Next, the structure is such that anisotropy is imparted to the magnetostrictive film.

  FIG. 4A is a perspective view showing a state in which a counterclockwise torque is applied to the shaft on which the magnetostrictive film according to the present embodiment is attached, and FIG. 4B shows the magnetostrictive film according to the present embodiment. It is a perspective view which shows the state which provided clockwise torque to the attached shaft.

  As shown in FIG. 4, the magnetostrictive torque sensor 21 includes a shaft 23 having a pinion 22 formed on the lower end side and an outer peripheral surface of the shaft 23 spaced apart from each other in the vertical direction, almost as in the first embodiment. The first and second magnetostrictive films 24 and 25 are generally constituted.

Next, a method for manufacturing the magnetostrictive torque sensor 21 will be described.
First, the shaft 23 is subjected to heat treatment with a Rockwell hardness of HRC 40 to 65, and then the magnetostrictive films 24 and 25 are attached to the outer peripheral surface of the shaft 23 so as to be spaced apart from each other. Next, by twisting the shaft 23 in the directions indicated by arrows P and S in FIG. 4A, a counterclockwise torque T (for example, 10 kgf) with respect to the first magnetostrictive film 24 (part of the magnetostrictive film). In this state, the magnetostrictive film 24 is vibrated at a high frequency by using the coil 26, so that the magnetostrictive film 24 is heated at about 300 ° C. for several seconds and then cooled counterclockwise. When the torque T is removed, anisotropy is imparted to the magnetostrictive film 24.

  Next, by twisting the shaft 23 in the direction indicated by the arrows P and S in FIG. 4B, the torque T (for example, 10 kgf · clockwise) with respect to the second magnetostrictive film 25 (the other part of the magnetostrictive film) is twisted. In this state, the magnetostrictive film 25 is vibrated at a high frequency similarly to the magnetostrictive film 24 by using the coil 27 to heat the magnetostrictive film 25 at about 300 ° C. As a result, the magnetostrictive film 25 is given anisotropy in the direction opposite to that of the magnetostrictive film 24.

  In this embodiment configured as described above, the magnetostrictive films 24 and 25 are integrally provided on the shaft 23 whose Rockwell hardness is set to HRC 40 to 65, and thereafter, the magnetostrictive films 24 and 25 are anisotropically provided. Since the shaft 23 is not plastically deformed in the step of applying the torque T to the shaft 23 to impart anisotropy to the magnetostrictive films 24, 25, the magnetostrictive films 24, 25 Anisotropy can be stably imparted. Further, since the shaft 23 is not plastically deformed in this way, highly linear torque detection performance (see the magnetostriction characteristic curves A and B in FIG. 10) can be obtained.

(Third embodiment)
Next, FIG. 5 and FIG. 6 show a third embodiment of the present invention, and the feature of this embodiment is that a rack housing case that houses the end of the rack shaft and the rack shaft constituting the electric power steering device. An elastic member that relaxes the impact force when the two collide with each other is provided.

  In the present embodiment, the same components as those in the first embodiment are denoted by the same reference numerals, and the description thereof is omitted. 5 is an external view showing the rack shaft, the rack housing case, etc. in a partially broken state, and FIG. 6 is an enlarged cross-sectional view showing a portion a in FIG.

  5 and 6, the rack shaft 31 has stepped end portions 31A and 31A on both the left and right sides thereof. A rack housing case 32 that houses the rack shaft 31 extends in the left-right direction, and is fitted to the long cylindrical portion 32A into which the rack shaft 31 is inserted on the inner peripheral side, and the left and right sides of the long cylindrical portion 32A. Further, a stepped end portion 32C to which a buffer member 34 described later is attached is formed on the inner peripheral side of the short tube portion 32B.

  As shown in FIG. 6, the elastic member 33 is formed in an annular shape using an elastic material such as rubber, and the buffer member 34 fixed to the end portion 32C of the rack housing case 32 and an annular shape using a steel material. And a steel member 35 fixed to the inner peripheral side of the buffer member 34. Further, the buffer member 34 is provided with a flange portion 34A protruding radially outward.

  In the present embodiment configured as described above, when the handle is rotated clockwise or counterclockwise until either the handle is locked, one of the end portions 31A and 31A of the rack shaft 31 becomes the end portion of the rack housing case 32. It can collide with the flange 34A of the elastic member 33 (buffer member 34) provided on the 32C side, and the impact force at this time can be buffered by the buffer member 34. Accordingly, the elastic member 33 can suppress a significant increase in steering torque when the steering wheel is locked, etc., can prevent the magnetostrictive film from peeling off the shaft, and the hysteresis and durability of the magnetostrictive torque sensor 1 (21). Etc., and the steering feeling can be enhanced.

  In each of the above embodiments, the case where the magnetostrictive torque sensor is applied to the electric power steering apparatus has been described as an example. However, the present invention is not limited to this, and can be applied to other various apparatuses.

  In the third embodiment, the elastic member 33 is described as an example in which the elastic member 33 is configured by the buffer member 34 and the steel member 35 made of a rubber material or the like. However, the present invention is not limited thereto, For example, the elastic member may be formed of a member having elasticity such as a spring.

  Furthermore, in the third embodiment, the case where the elastic member 33 is provided on the rack housing case 32 side of the rack shaft 31 and the rack housing case 32 has been described as an example. However, the present invention is not limited to this. For example, an elastic member may be provided on the rack shaft 31 or may be provided on both the rack shaft 31 and the rack housing case 32. Further, the present invention may be applied to a pinion assist electric power steering device or a rack assist electric power steering device.

1 is an enlarged longitudinal sectional view showing a magnetostrictive torque sensor according to a first embodiment of the present invention. It is a characteristic diagram which shows the relationship between the twist angle and steering torque which concern on 1st Embodiment. It is a characteristic diagram which shows the relationship between the hardness of the shaft which concerns on 1st Embodiment, and hysteresis. (A) is a perspective view which shows the state which gave the counterclockwise torque to the shaft which concerns on the 2nd Embodiment of this invention, (b) is clockwise rotation to the shaft which concerns on 2nd Embodiment. It is a perspective view which shows the state which provided the torque. It is an external view shown in the state where a rack axis, a rack storage case, etc. concerning a 3rd embodiment of the present invention were partially broken. It is a principal part expanded sectional view which expands and shows the a part in FIG. It is a schematic diagram which shows the electric power steering apparatus which concerns on a prior art. It is explanatory drawing which shows the relationship between the steering torque and pinion torque which concern on a prior art. It is a longitudinal cross-sectional view which expands and shows the magnetostrictive torque sensor which concerns on a prior art. It is a characteristic diagram which shows the relationship between the steering torque and impedance which concerns on a prior art. It is a circuit diagram which shows the magnetostrictive torque sensor which concerns on a prior art. It is a characteristic diagram which shows the relationship between the steering torque which concerns on a prior art, and the detected value of a magnetostrictive torque sensor.

Explanation of symbols

1,21 Magnetostrictive torque sensor 3, 4,5 Bearing 6,23 Shaft 7 Coil (detection means)
8, 24 First magnetostrictive film (part of magnetostrictive film)
9, 25 Second magnetostrictive film (other part of magnetostrictive film)
DESCRIPTION OF SYMBOLS 10 Motor 11 Deceleration device 12, 31 Rack shaft 31A, 32C End part 32 Rack accommodation case 33 Elastic member 101 Electric power steering apparatus

Claims (4)

Providing a magnetostrictive film on the outer surface of the shaft;
Applying torque in one direction to the shaft;
Heating a portion of the magnetostrictive film;
Releasing the applied torque in one direction after cooling;
Applying torque in the other direction to the shaft;
Heating the other part of the magnetostrictive film;
Releasing the torque applied in the other direction after cooling;
Anisotropy imparting method for a magnetostrictive torque sensor, characterized by imparting different magnetic anisotropy to each of a part of the magnetostrictive film and the other part.   2. The method of applying anisotropy for a magnetostrictive torque sensor according to claim 1, wherein the shaft before the magnetostrictive film is provided with a Rockwell hardness of HRC 40-60.   3. The method of applying anisotropy for a magnetostrictive torque sensor according to claim 1, wherein a pinion is provided at a lower end of the shaft.   The method of claim 3, wherein the shaft is used as a steering shaft of an electric power steering apparatus.

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