JP2008096220A - Manufacturing method of rotating shaft for magnetostrictive torque sensor, and twisting device of rotating shaft for magnetostrictive torque sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a twisting device of a rotating shaft for a magnetostrictive torque sensor capable of suppressing torque fluctuation even when heat is applied to the rotating shaft. <P>SOLUTION: In this twisting device 10 of the rotating shaft for the magnetostrictive torque sensor for twisting the rotating shaft 11 on which a magnetostrictive film 17 is formed with a prescribed torque by a torque generation means 16, a torsion bar 14 is interposed between the rotating shaft 11 and the torque generation means 16. A rotation angle of the torque generation means becomes a total of an angle of torsion of the rotating shaft and an angle of torsion of the torsion bar by interposing the torsion bar. If the rotation angle is large, an influence of an angle change caused by irregularities becomes small, and resultantly the torque fluctuation is mitigated and the torque fluctuation can be suppressed. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an improvement in manufacturing technology of a magnetostrictive torque sensor.

  In general, in an electric power steering apparatus installed in an automobile or the like, torque applied from a steering shaft to a rotating shaft by a steering operation of a driver is detected by a torque sensor. And according to the detection signal from this torque sensor, a motor is drive-controlled and power is added, a driver's steering force is reduced and a comfortable steering feeling is given.

Various types of torque sensors are known, one of which is a magnetostrictive torque sensor.
A magnetostrictive torque sensor has a basic configuration in which a magnetostrictive film having magnetic anisotropy is deposited on the surface of a rotating shaft. When torque is applied to the rotation shaft from the outside, the magnetic characteristics of the magnetostrictive film change according to the twist of the rotation shaft. The basic principle is to output the applied torque by detecting this change in magnetic characteristics and converting it to torque.

In order to impart magnetic anisotropy, a technique has been proposed in which heat treatment is performed in a state where stress is generated by applying torque to the rotating shaft (see, for example, Patent Document 1).
Japanese Patent Laid-Open No. 2002-82000 (FIG. 3)

Patent document 1 is demonstrated based on the following figure.
FIG. 4 is a configuration diagram of the main part of a conventional magnetostrictive torque sensor, in which a magnetostrictive film 106 is formed on the rotating shaft 101. And the predetermined | prescribed torque is applied to the rotating shaft 101 by fixing the X mark location of one end and twisting the other end. Heat treatment is performed in this state. Through the above process, magnetic anisotropy is added to the magnetostrictive film 106.

In order to implement Patent Document 1, the present inventors produced an apparatus shown in the following figure.
FIG. 5 is a principle diagram of a conventional rotating shaft twisting device. A rotating shaft twisting device 100 is a device for twisting a rotating shaft 101 arranged in a steering system of a vehicle with a predetermined torque. A support portion 103 provided on the apparatus frame 102 and supporting one end (upper end) of the rotating shaft 101, a torque meter 104 connected to the other end (lower end) of the rotating shaft 101 supported by the supporting portion 103, and the torque A servo motor 105 connected to the meter 104 and fixed to the device frame 102, an induction heating coil 107 for heating the magnetostrictive film 106 provided on the device frame 102 and formed on the rotating shaft 101, and a torque meter 104 A control unit that controls the motor driver 109 so that the difference between the detected torque signal and the target value stored in advance by the input device 108 becomes zero. Consisting of 10.

  When the magnetostrictive film 106 is heated to several hundred degrees Celsius, the rotating shaft 101 inevitably undergoes thermal expansion. The rotating shaft 101 extends downward from the drawing starting from the support portion 103.

The operation of FIG. 5 will be described in detail with reference to the next figure.
FIG. 6 is an explanatory diagram of the operation of FIG. 5, in which the rotating shaft is twisted with the predetermined curve shown in FIG. 5A and the torque is stabilized, and the heating and cooling are performed with the curve shown in FIG. The torsion device 100 was operated. However, the torque measured with the torque meter (Fig. 5, reference numeral 104) was as shown in (c). That is, the torque fluctuated greatly in the heat treatment range.

Such fluctuations vary and adversely affect the quality of the magnetostrictive film (FIG. 5, reference numeral 106). Therefore, the present inventors estimated the torque fluctuation mechanism as follows as part of the work to eliminate the torque fluctuation.
FIG. 7 is a cross-sectional view taken along the line 7-7 in FIG. 5, and the angular shaft 112 on the rotating shaft side is fitted into a square hole 114 provided on the boss 113 on the torque meter side.
FIG. 8 is a cross-sectional view showing the relationship between the square hole and the square axis. The bottom of the square hole 114 is sufficiently deep so that the square axis 112 may be lowered by thermal expansion.

FIG. 9 is an enlarged view of part 9 in FIG. 8 (an extremely enlarged view for promoting understanding).
(A) shows the relationship between the angular axis 112 before thermal expansion and the boss 113, for example, and it is assumed that a point (mark) P1 is attached to the angular axis 112 and a point P2 is attached to the boss 113.
The surface of the square axis 112 inevitably generates extremely fine irregularities due to the influence of machining or the like. Similarly, extremely fine irregularities are inevitably generated on the surface of the boss 113.
Assume that the horizontal distance between the point P1 and the point P2 is L1.

  (B) shows the state in the middle of thermal expansion, for example, and the square axis 112 has moved downward relative to the boss 113. By this movement, the convex on the angular axis 112 side is fitted into the concave on the boss 113 side. As a result, the horizontal distance L2 between the point P1 and the point P2 is smaller than L1.

  (C) shows a state after thermal expansion, for example, and the angular axis 112 has moved further downward with respect to the boss 113. By this movement, the convex on the angular axis 112 side is opposed to the convex on the boss 113 side. As a result, the horizontal distance L3 between the point P1 and the point P2 is larger than L2 and L1.

FIG. 10 is a diagram for explaining the influence of unevenness, and the angular axis 112 indicated by an imaginary line rotates like the angular axis 112 indicated by a solid line by the change in the horizontal distance (L1 → L2 or L1 → L3). It is possible. Although the figure is exaggerated, the angle θ is about 0.04 °.

Incidentally, the torque fluctuation shown in FIG. 6C is unacceptable because it may adversely affect the quality of the magnetostrictive film.
Therefore, a technique capable of suppressing torque fluctuations is desired based on the inferences shown in FIGS.

  It is an object of the present invention to provide a method for manufacturing a rotating shaft for a magnetostrictive torque sensor and a twisting device for the rotating shaft for a magnetostrictive torque sensor that can suppress fluctuations in torque.

  The invention according to claim 1 is a film forming step of forming a magnetostrictive film on the rotating shaft, a step of applying a predetermined torque to the rotating shaft, and a state in which the predetermined torque is applied to the rotating shaft. In a method of manufacturing a rotary shaft for a magnetostrictive torque sensor comprising a heat treatment step for performing heat treatment and a step for eliminating the torque, in the step of applying a predetermined torque to the rotary shaft, the torque generating means and the rotary shaft are torsioned. It is characterized in that it is connected by a bar and the rotating shaft is twisted by torque generating means through this torsion bar.

According to a second aspect of the present invention, there is provided a twisting device for a rotational shaft for a magnetostrictive torque sensor in which a rotational shaft on which a magnetostrictive film is formed is twisted with a predetermined torque by a torque generating means.
A torsion bar is interposed between the rotating shaft and the torque generating means.

In the invention according to claim 1, the rotating shaft is twisted by the torque generating means via the torsion bar. There is a mechanical connection between the rotating shaft and the torque generating means. This connecting portion has inevitable irregularities due to machining or the like. When the rotation shaft is thermally expanded, the position of the unevenness in the connecting portion is relatively moved, and the influence thereof appears in the rotation angle in the torque generating means.
When the torsion bar is interposed, the rotation angle of the torque generating means is the sum of the twist angle of the rotating shaft and the twist angle of the torsion bar. When the rotation angle of the torque generating means is large, the influence of the angle change due to the unevenness is reduced, and as a result, the torque fluctuation is mitigated and the torque fluctuation can be suppressed.

  In the invention according to claim 2, when the torsion bar is interposed, the rotation angle of the torque generating means is the sum of the torsion angle of the rotating shaft and the torsion angle of the torsion bar. When the rotation angle of the torque generating means is large, the influence of the angle change due to the unevenness is reduced, and as a result, the torque fluctuation is mitigated and the torque fluctuation can be suppressed.

  In addition, by adding a torsion bar to a conventional twisting device, the device can be improved. In other words, by remodeling an inexpensive torsion device at an inexpensive remodeling cost, the torsion device of the present invention can be obtained, so that fluctuations in torque can be suppressed while maintaining productivity. It is possible to promote the popularization of a twisting device for a rotating shaft for a magnetostrictive torque sensor that can add the magnetic anisotropy.

The best mode for carrying out the present invention will be described below with reference to the accompanying drawings. The drawings are viewed in the direction of the reference numerals.
FIG. 1 is a diagram for explaining a method of manufacturing a rotating shaft for a magnetostrictive torque sensor according to the present invention, wherein (a) shows a process, (b) shows a timing for applying torque, and (c) shows a process. The time for heat treatment is shown.

The step (a) will be described in detail.
As shown in (a-1), the shaft member 11 is subjected to a pretreatment that includes roughening the surface using an acid etching method or the like. This is because the rough surface can increase the adhesive strength of the magnetostrictive film. As shown in (a-2), a magnetostrictive film 13 is formed on the shaft member 12 that has been subjected to this pretreatment by electroplating.

As shown in (a-3), the shaft member 14 with the magnetostrictive film 13 is twisted with a predetermined torque.
As shown in (a-4), in a state where torque is applied, it is rapidly heated to several hundred degrees Celsius and then slowly cooled. This heat treatment and cooling treatment are collectively called heat treatment. Magnetic anisotropy can be imparted by performing heat treatment while twisting. Next, torque addition is canceled (a-5).
Preferably, an annealing treatment is performed as shown in (a-6).

Among the steps described above, a rotating shaft twisting apparatus suitable for the steps (a-3) (torque applying step) to (a-4) (step of performing heat treatment while twisting) will be described below. .
FIG. 2 is a principle diagram of a rotating shaft twisting device according to the present invention. The rotating shaft twisting device 10 is a device for twisting a rotating shaft 11 arranged in a steering system of a vehicle with a predetermined torque. A support member 13 that is provided on the apparatus frame 12 and supports one end (upper end) of the rotary shaft 11, and a torsion bar 14 connected to the other end (lower end) of the rotary shaft 11 supported by the support member 13. A torque meter 15 connected to the other end (lower end) of the torsion bar 14, a servo motor 16 connected to the torque meter 15 and fixed to the device frame 12, as torque generating means, and provided on the device frame 12 The induction heating coil 18 for heating the magnetostrictive film 17 formed on the rotary shaft 11, the torque signal detected by the torque meter 15, and the eyes stored in advance by the input device 19 And a control unit 22 for the difference between the value controls the motor driver 21 to be zero.

With the apparatus 10, a torque of 100 Nm was applied to the rotating shaft 11. As a result, the rotating shaft 11 was twisted by 0.40 °. The torsion bar 14 was twisted 2.30 °.
The upper end of the torsion bar 14 is called P11, and the lower end is called P12. And the twist angle in P11 and P12 was measured. For comparison, measurement was also performed with a conventional apparatus under the same conditions. The measurement results are shown in the following table.

In the comparative example, the twisting device shown in FIG. 5 was used, and a torque of 100 Nm was applied to the rotating shaft with a servo motor. The twist angle of the rotating shaft was 0.40 °, and the rotation angle of the servo motor was 0.40 °. As described with reference to FIG. 10, the angle change at P1 was 0.04 °.
When the influence of the change is defined as (angle change / rotation angle of the servo motor), it is 10% by the calculation of 0.04 / 0.40 = 0.10.

In the embodiment, the twisting device shown in FIG. 2 was used, and a torque of 100 Nm was applied to the rotating shaft by a servo motor. The twist angle of the rotating shaft was 0.40 °, and the twist angle of the torsion bar was 2.30 °. The rotation angle of the servo motor was the sum of the twist angle of the rotating shaft and the twist angle of the torsion bar, and was 2.70 °. The angle change at P1 (see FIG. 2) was 0.04 °, and the angle change at P2 was 0.04 °.
When the influence of the change is defined as (angle change / rotation angle of the servo motor), it is 3% by calculation of (0.04 + 0.04) /2.70=0.03.
In the example, the influence of the change was 1/3 or less compared to the comparative example.

  FIG. 3 is a graph showing a torque curve according to the present invention. Although the torque once decreases at the point P3, it returns immediately, and as a result, the large fluctuation in torque as shown in FIG. 6C is greatly improved. I was able to.

  Note that the twisting device 10 of the rotating shaft only shows the basic structure, and the configuration can be changed as appropriate. In particular, the position of the torque meter 15 is arbitrary, and can be provided between the support member 13 and the rotating shaft 11. If the servo motor 16 has a built-in torque meter function, the torque meter 15 can be omitted apparently.

  The present invention is suitable for a twisting device for a rotating shaft for a magnetostrictive torque sensor used in a vehicle steering system.

It is a figure explaining the manufacturing method of the rotating shaft for magnetostrictive torque sensors concerning the present invention. It is a principle figure of the twist apparatus of the rotating shaft which concerns on this invention. It is a graph which shows the torque curve in this invention. It is a block diagram of the principal part of the conventional magnetostrictive torque sensor. It is a principle diagram of a conventional rotating shaft twisting device. FIG. 6 is an operation explanatory diagram of FIG. 5. FIG. 7 is a cross-sectional view taken along line 7-7 in FIG. 5. It is sectional drawing which shows the relationship between a square hole and a square axis. FIG. 9 is an enlarged view of part 9 of FIG. 8 (an extremely enlarged view for promoting understanding). It is a figure explaining the influence of unevenness.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... Twist apparatus of a rotating shaft, 11 ... Rotating shaft, 14 ... Torsion bar, 16 ... Torque generation means (servo motor).

Claims (2)

  A film forming step of forming a magnetostrictive film on a rotating shaft, a step of applying a predetermined torque to the rotating shaft, a heat treatment step of applying a heat treatment to the magnetostrictive film in a state where a predetermined torque is applied to the rotating shaft, In the method of manufacturing a rotating shaft for a magnetostrictive torque sensor comprising the step of eliminating torque, in the step of applying a predetermined torque to the rotating shaft, the torque generating means and the rotating shaft are connected by a torsion bar. A method of manufacturing a rotating shaft for a magnetostrictive torque sensor, wherein the rotating shaft is twisted by a torque generating means via In a twisting device for a rotational shaft for a magnetostrictive torque sensor in which a rotational shaft on which a magnetostrictive film is formed is twisted with a predetermined torque by torque generating means
A torsion device for a rotating shaft for a magnetostrictive torque sensor, wherein a torsion bar is interposed between the rotating shaft and the torque generating means.

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