JP4827167B2 - Method for producing composite magnetic material - Google Patents

Description

  The present invention relates to an apparatus for detecting the axial torque of a rotating shaft in a non-contact manner using magnetostrictive characteristics, and is particularly applicable to the automobile field, industrial machine field, and the like.

  For the power steering mechanism, engine control mechanism, power transmission mechanism, and the like of automobiles, a means for accurately detecting shaft torque has long been desired. Various techniques have been proposed so far because precise control and efficiency can be improved by increasing detection accuracy. In particular, the non-contact method of detecting shaft torque using the magnetostriction characteristics of the rotating shaft is excellent in responsiveness, is relatively easy to increase sensitivity, and has a large overload capability. Therefore, it is attracting attention as an alternative to the conventional method for detecting torque.

  For example, Patent Document 1 proposes a method in which a magnetic film 115 having an inclination angle is fixed to a rotating shaft and excitation and detection are performed by a solenoid coil on the outer periphery of the rotating shaft, as shown in FIG. However, since this method requires additional processing on the rotating shaft, there is a risk that reliability such as peeling of the magnetic film may be impaired. Furthermore, since it is essential to specialize the shaft and increase the diameter, it is considered that the wearability is poor.

  Further, in Patent Document 2, as shown in FIG. 6B, a method is proposed in which torque is detected in the same manner as Patent Document 1 by disposing the rotating shaft unprocessed and arranging the loop coil while maintaining a constant inclination angle. Has been. Although this method does not require any additional work on the shaft, it is necessary to detect a wide area in the longitudinal direction of the shaft in order to increase sensitivity, and there is a concern that the size of the apparatus will increase.

  Furthermore, in Patent Document 3, as shown in FIG. 6 (c), a structure that greatly reduces the coil portion is proposed to overcome the problem of Patent Document 2, but since the coil structure is complicated, a large number of windings are required. It is difficult to achieve high sensitivity depending on the number of turns of the coil.

  In addition, the above three types of structures all have a high risk of disconnection of the coil due to the influence of rotational runout of the shaft and contamination of foreign matter because the coil is adjacent to the rotation shaft. In order to ensure reliability, it may be necessary to take measures such as covering and reinforcing the coil part with resin or the like, or enlarging the gap between the shaft and the coil to sacrifice sensitivity.

  Patent Document 4 describes a structure in which a U-shaped iron core is provided on the outer periphery of a rotating shaft, as shown in FIG. However, if a plurality of U-shaped iron cores are arranged on the outer periphery of the rotating shaft, the structure becomes complicated and it becomes difficult to downsize, the productivity is poor, and it is difficult to increase the working area of the magnetic poles. It appears to be.

JP-A-1-94230 JP-A-6-273247 JP-A-6-194239 Japanese Patent No. 2905561

  The object of the present invention is to solve the problems related to the mountability, reliability, downsizing, high sensitivity, and productivity associated with the conventional magnetostriction detection type torque detection device.

  In order to solve the above problems, in the present invention, the structure of the excitation / detection coil is eliminated by providing a structural feature to the soft magnetic magnetic head portion that forms the magnetic circuit of the sensor, thereby eliminating the need for processing on the rotating shaft. Thus, a highly sensitive torque detecting device can be realized without complicating the above.

The present first invention, a soft magnetic portion mainly containing a binder and a soft magnetic powder, a nonmagnetic portion which mainly binder and nonmagnetic powder, alternately arranged spirally in the circumferential direction compression A composite magnetic body characterized by being molded and integrated.

  The spiral inclination angle with respect to the central axis is preferably 35 to 55 degrees.

  A second invention of the present application is a composite magnetic head formed by winding a coil around the composite magnetic body.

  The composite magnetic body of the present invention may have a structure divided in the circumferential direction.

The present third invention, the main binder and a material made of a soft magnetic powder under pressure to form a soft magnetic portion is temporarily formed into a spiral shape, material consisting primarily binder and nonmagnetic powder A composite characterized in that a non-magnetic portion is formed by pressurizing and temporarily forming a non-magnetic portion, and the soft magnetic portion and the non-magnetic portion are combined and finally formed and integrated at a pressure higher than the temporary forming pressure. It is a manufacturing method of a magnetic body.

  The features of the present invention will be described below while explaining the principle of the magnetostrictive detection type rotating shaft torque detection device. When a current is passed through the exciting coil provided in the sensor, a magnetic flux 201 as shown in FIG. 7A is generated around the coil. The magnetic flux 201 generated by the coil forms a closed loop according to the right-handed screw rule in a plane orthogonal to the coil. In many cases, a plurality of closed magnetic paths are formed by devising a magnetic circuit such as a coil winding method. Even if the relative position of the sensor changes due to the rotation of the shaft, the magnetic permeability does not change unless a rotational torque is applied to the shaft to cause distortion, so that the coil inductance does not change.

  When rotational torque is applied to the shaft as shown in FIG. 7B from the no-load state in FIG. 7A, tensile stress (−σ in the directions inclined by + 45 ° and −45 ° with respect to the longitudinal direction of the shaft. ) And compressive stress (+ σ) are simultaneously generated while being orthogonal to each other. Here, it can be used that the magnetic permeability increases when a tensile stress is applied to the soft magnetic material, whereas the magnetic permeability decreases when a compressive stress is applied.

  In other words, the magnetic flux generated by the exciting coil is easy to flow in the direction in which tensile stress is applied, and on the other hand, it is difficult to flow in the direction in which compressive stress is applied. The amount can be estimated. For example, as shown in FIG. 7, it is assumed that there is a spiral exciting coil in a direction inclined by + 45 ° with respect to the axis. Since the magnetic flux generated in the coil forms a closed magnetic circuit according to the right-handed screw law, the magnetic flux is greatly affected by the permeability change in the −45 ° direction perpendicular to the coil. Here, assuming that a tensile stress is applied in the −45 ° direction, the magnetic flux flows more easily than when there is no load, so the coil inductance increases compared to when there is no load. Conversely, when compressive stress is applied, the inductance decreases.

  As described above, when rotational torque is applied to the shaft, stresses having different directions are generated simultaneously in both directions of + 45 ° and −45 °. Therefore, in the method of estimating the torque from the amount of change in inductance with respect to no load, + 45 ° Or a change in magnetic permeability in one direction of −45 ° may be detected. Further, by detecting both the + 45 ° and −45 ° directions at the same time and detecting the difference amount, it is possible to estimate the torque with higher accuracy. As means for detecting both + 45 ° and -45 ° directions simultaneously, as shown in FIG. 3 (b), there are those having a tilt angle clockwise with respect to the rotating shaft 2 and those having a tilt angle counterclockwise. It becomes realizable by combining and using by one pair.

  In any case, in the magnetostrictive rotating shaft torque detection device, it is important to read the change in permeability in the direction of inclination of + 45 ° and −45 ° with respect to the shaft. Instead of winding in the form of a solenoid without an inclination angle, a magnetic film is provided in a direction inclined by ± 45 ° with respect to the rotation axis so that the magnetic flux flows only in the inclination direction. Moreover, in patent document 2 and patent document 3, axial torque can be detected by giving the coil an inclination angle.

  Although the structure of Patent Document 1 has a great feature that a coil is a simple solenoid and can be easily wound in a large number and is easy to achieve high sensitivity, the need for machining on the shaft deteriorates reliability and mountability. It was.

  Therefore, in this method, the rotating shaft is not processed, and a plurality of magnetic pole portions are formed in which the soft magnetic portions and the nonmagnetic portions are alternately arranged in the circumferential direction through gaps with respect to the rotating shaft, and the soft magnetic portions rotate. The main structural features are that the coil has an inclination angle with respect to the shaft and the coil for exciting the magnetic pole portion is a simple solenoid.

  By eliminating the need for complicated machining on the shaft, it is possible to greatly improve the mounting and reliability. Even if the rotating shaft does not have magnetostriction characteristics such as non-magnetic SUS, it is only necessary to cover the outer peripheral portion of the shaft with a ring having magnetostriction characteristics. There is nothing. Further, since the coil can be formed in a solenoid shape, high sensitivity depending on the number of turns is facilitated. Furthermore, since the coil can be arranged also on the outer peripheral surface of the magnetic head, it is possible to avoid the risk of the coil being disconnected. Furthermore, it becomes easy to achieve high sensitivity by greatly reducing the gap between the rotating shaft and the magnetic head.

  As the structure of the magnetic head, the soft magnetic part has an inclination angle of 35 to 55 °, and the width of the nonmagnetic part in the circumferential direction is 0.7 to 1 of the length of the soft magnetic part in the inclination angle direction. If the number is five times, magnetic interference between a plurality of closed magnetic paths that is generated in the same number as the number of soft magnetic portions is difficult to occur, so that a change in permeability in a direction inclined by 45 ° with respect to the axis is efficiently detected. be able to.

  As a means of obtaining a composite magnetic head in which soft magnetic parts and non-magnetic parts are alternately arranged in the circumferential direction, for example, in the prior art, after each part is individually manufactured by cutting, forging, casting, etc., bonding and screwing A method of assembling by, for example, is conceivable. However, this method is difficult to assemble because of the increased number of parts, and there are concerns that the bonding strength may vary and the structural reliability may be lowered. As another method, a method in which only a soft magnetic part is manufactured and then a plurality of soft magnetic pieces are arranged in a ring shape at equal intervals and insert-molded with a resin or the like, or a method of casting by aluminum die casting can be considered. However, in this method, since the mechanical strength of a nonmagnetic part such as resin or aluminum must be strong as a structure that wraps the soft magnetic part, it seems difficult to achieve both joint strength and compactness.

  Therefore, in the present invention, each of the soft magnetic part and the non-magnetic part is formed of a compression molded body made of various fine powders including a resin binder (binder), and each compression molded body is molded at the initial stage of manufacture. Temporary molding is performed at a low pressure so that the fine powder on the surface is bonded weakly enough to be removed. Thereafter, the obtained soft magnetic part and the non-magnetic part are combined according to the shape of the finally obtained composite magnetic body and subjected to main molding at high pressure. The composite magnetic body produced in this way has the feature that fine powder on the joint surface can be well bitten and the binding force of the resin binder after thermosetting can be generated stably even at the interface. .

  As the soft magnetic powder, it is preferable to use pure Fe powder having an average particle size of 200 μm or less, Fe—Al—Si based sendust powder, fine met powder of Fe-based nanocrystalline material, and the like. For the non-magnetic powder, it is preferable to use a mixed powder such as Cu—Zn type or Al—Si type having an average particle diameter of 200 μm or less. Moreover, it is preferable to use a thermoplastic resin having an average particle size of 100 μm or less in consideration of dispersibility in each raw material powder and the like.

  The present invention eliminates the need for complicated additional work on the rotating shaft that detects torque. In addition, the structural reliability of the magnetic head portion is improved, and compactness is facilitated. Further, since the winding process of the excitation / detection coil is easy, the productivity of the entire apparatus is improved.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. Here, the soft magnetic part mainly composed of the binder and the soft magnetic powder, and the nonmagnetic part mainly composed of the binder and the nonmagnetic powder are alternately arranged in the circumferential direction in a helical manner, and are integrally formed by compression molding. A manufacturing method for obtaining a ring-shaped composite magnetic material is shown in FIG.

  As shown in FIG. 1, the soft magnetic part 10 and the nonmagnetic part 11 are temporarily formed at a low pressure in individual compression molding apparatuses 30 and 31. In addition, even if it is a complicated spiral shape, since it is not necessary to increase the density of the molded body more than necessary, the mold structure should be simplified or a configuration in which a large number of molded bodies can be obtained by one molding. Is also possible. As a standard of the temporary molding pressure, about 300 MPa, which allows easy handling of the product, is preferable. Next, spiral soft magnetic pieces and non-magnetic pieces are alternately arranged in the circumferential direction, put into a cylindrical compression molding cavity of the compression molding apparatus 32, and subjected to main molding at a high pressure of about 1000 MPa. In addition, since the total length of each of the helical soft magnetic piece and the non-magnetic piece is uniformly shortened during the main forming, it is necessary to change the angle of the temporary formed body in advance so as to obtain a desired angle. There is.

  As shown in FIG. 2, a guide 13 is fitted to both ends of the composite magnetic ring 12 in which soft magnetic portions and nonmagnetic portions are alternately arranged in a spiral shape, which is obtained by the above compression molding method. The composite magnetic head 1 used in the torque detection device is obtained by winding the excitation / detection coil 14 and inserting the rotating shaft 2 as the test object on the inner peripheral side.

(overall structure)
2 (a) to 2 (c) show an embodiment of the magnetostrictive torque detector of the present invention. FIGS. 2A and 2B are perspective views of the composite magnetic ring 12 and the guide 13. The portion that becomes the iron core of the magnetic circuit is composed of four soft magnetic bodies 10 having an inclination angle of 45 degrees, four nonmagnetic portions 11 arranged between them, and guides 13 at both ends of the outer periphery. . As the soft magnetic part, a pure Fe powder having an average particle diameter of about 50 μm and 1% by mass of a thermoplastic resin was used. As the nonmagnetic part, a Cu—Zn powder having an average particle diameter of about 80 μm and 3% by mass of a thermoplastic resin was used. The temporary molding pressure was 300 MPa, and the main molding pressure was 1000 MPa. After this molding, a thermosetting treatment was performed at 200 ° C. for 2 hours. FIG. 2 (c) shows a case where an excitation / detection coil is wound around the outer periphery of the composite magnetic ring, a rotating shaft as a test object is inserted on the inner periphery, and an alternating current is applied to both ends of the coil. It is the perspective view which showed a mode that it is. The rotating shaft used was nickel-molybdenum steel that was carburized.

  The outer diameter of the rotating shaft was Φ20 mm, the inner diameter of the composite magnetic ring was Φ20.6 mm, and the outer diameter was Φ25 mm. The excitation / detection coil used was an enamel wire with a diameter of 0.5 mm, wound 120 turns around the outer periphery of the composite magnetic head, and the frequency of the alternating current was 100 kHz.

  FIG. 8 shows an actual measurement of the change in inductance of the coil when a torque of −200 to +200 Nm is applied to the rotating shaft. It can be seen from FIG. 8 that good linearity is shown in the inductance change when torque is applied. Therefore, if circuit processing is added to the configuration of the present invention, an output signal with extremely good linearity can be obtained.

  Further, as shown in FIG. 5, by dividing the composite magnetic ring 12 into two in the circumferential direction, it can be mounted so as to sandwich the shaft, and the mounting property to the shaft can be improved.

  As a winding method of the excitation / detection coil, in addition to a method of winding the magnets around each of the soft magnetic pieces as described in Patent Document 4 of FIG. 6D, FIGS. 4A to 4C are used. As described, it can be wound so as to surround the entire magnetic head.

It is a schematic diagram which shows the manufacturing method of the composite magnetic ring concerning one Example of this invention. It is a schematic diagram which shows the apparatus attachment method concerning one Example of this invention. It is a schematic diagram which shows the other apparatus attachment method in connection with one Example of this invention. It is a schematic diagram which shows the coil winding method concerning one Example of this invention. It is a schematic diagram which shows the other structure in connection with one Example of this invention. It is a schematic diagram which shows another Example. It is a schematic diagram which shows the principle of the torque detection in connection with one Example of this invention. It is a graph which shows the experimental result regarding one Example of this invention.

Explanation of symbols

1: Composite magnetic head 2: Rotating shaft
10: Soft magnetic part
11: Non-magnetic part
12: Composite magnetic ring
13: Guide
14: Excitation / detection coil
102: Rotation axis
110: Soft magnetic yoke
113: Excitation / detection coil
115: Magnetic film
201: Magnetic flux

Claims (1)

Mainly material composed of soft magnetic powder and binder pressurized by preliminarily molded spirally to form a soft magnetic portion mainly material composed of a non-magnetic powder and binding material is pressurized in a spiral A method for producing a composite magnetic body, comprising: forming a non-magnetic portion by temporary molding, combining the soft magnetic portion and the non-magnetic portion, and forming and integrating them at a pressure higher than a temporary molding pressure.

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