JP2512554B2 - Magnetostrictive torque sensor shaft manufacturing method - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a magnetostrictive torque sensor shaft, in which transmission torque is sensed as a change in magnetic permeability due to a change in stress generated by the transmission torque.

2. Description of the Related Art In this type of magnetostrictive torque sensor shaft, a magnetic anisotropy in a spiral direction is given to a part of its surface in order to make it possible to detect a change in magnetic permeability. As a method for imparting such magnetic anisotropy, there is a method disclosed in JP-A-63-252487. This is to impart a magnetic anisotropy based on this residual stress by applying an excessive torsional strain to the shaft to generate a residual stress area. Specifically, for example, in the case of a thermosetting shaft, an excessive torsional strain is applied to the shaft made of maraging steel before the thermosetting,
Age-hardened in a short time.

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention However, in the case of generating a residual stress area by adding with such an excessive torsional strain, the required torsional torque becomes too large when the shaft has a large diameter, which is not practical. There is a point. Further, there is a problem that the direction of anisotropy is limited to the direction of the principal stress of torsion, that is, the direction of ± 45 degrees with respect to the axis, and cannot be selected. Further, since tensile residual stress is generated when twisted, there is a problem that fatigue strength and other mechanical strength are reduced. Especially for materials such as Ni iron alloy, which has a high probability of being used as materials for torque sensor shafts,
Since the notch sensitivity is high and the crack growth resistance is small, there is a problem that the fatigue strength is significantly disadvantageous.

Therefore, an object of the present invention is to solve these problems in the prior art and to reduce the hysteresis of the sensor characteristics and improve the sensitivity by setting the easy axis of magnetization of the torque sensor axis in the plane perpendicular direction.

Means for Solving the Problems In order to achieve the above object, the method of the present invention comprises forming a stress concentration portion on the surface of a shaft body, applying a mechanical load to the shaft body, and compressing the stress concentration portion. A compressive strain is generated based on the stress, and then, under the condition that the mechanical load is applied to the shaft body, the strain at the time of tensile yielding of the material of the shaft body is uniformly distributed on the surface of the shaft body. A larger tensile strain is generated by shot peening, and thereafter, the mechanical load and the cause of the tensile strain are removed, and a compressive residual stress based on the tensile strain is generated on the surface of the shaft body. .

The method of the present invention can be carried out under temperature conditions in which the tensile yield stress becomes smaller than that at room temperature.

According to the method of the present invention, it is possible to form a plurality of grooves and peaks as stress concentration portions alternately on the surface of the shaft body in the circumferential direction and in a spiral shape.

According to the method of the present invention, it is possible to form a pair of stress concentration portions that are inclined in opposite directions with respect to the axis.

According to the method of the present invention, in a state in which a mechanical load is applied to the shaft so that a compressive strain is generated in one stress concentrated portion, a tensile strain is generated only in this one stress concentrated portion, and thereafter,
In the state where a mechanical load in the opposite direction is applied to the shaft body so that compressive strain is generated in the other stress concentrated portion, tensile strain is generated only in the other stress concentrated portion.

Action According to the present invention, first, a stress concentration portion is formed on the surface of the shaft body, and a mechanical load such as a torsion torque is applied to the shaft body to generate compressive strain −ε _c in the stress concentration portion. In this state, a tensile strain + ε _s, which is larger than the strain at the time of tensile yielding, is then uniformly generated in the shaft body by shot peening.

Then, in the stress concentration part, the difference ε between the tensile strain and the compressive strain is
Strain (elongation) corresponding to _{s −} ε _c occurs, and tensile strain ε _s occurs in other parts.

Next, when the mechanical load and the cause of the tensile strain were removed, the tensile strain was larger than the strain at tensile yielding, so the surface of the shaft body was compressed corresponding to the tensile strain. Residual stress occurs. At this time, in the direction of the compressive strain in the stress concentrated portion, the tensile strain is relaxed by an amount corresponding to the magnitude of the compressive strain −ε _c , so that the compressive residual stress is smaller than that in other portions of the shaft body. It becomes a value. As a result, anisotropy of residual stress, that is, magnetic anisotropy based on residual stress is imparted to the shaft body.

Since the yield stress of ordinary materials decreases as the temperature rises compared to normal temperature, it is advantageous to perform a process that imparts magnetic anisotropy under such temperature conditions that yield stress becomes small, that is, at high temperatures. Is.

The stress concentrating portion can be formed in a shape desired to obtain magnetic anisotropy on the surface of the shaft body. The stress concentration portion has a plurality of groove portions and mountain portions, which are alternately arranged in the circumferential direction on the surface of the shaft body.
Advantageously, it is formed in a spiral shape. In such a case, when the above-mentioned compressive strain −ε _c is generated in the direction of the easy axis of magnetization, that is, the direction of the crest portion by the torsion torque, in the direction orthogonal to this compressive strain −ε _c , that is, the direction crossing the groove portion, At the same time, tensile strain + ε _T due to torsional torque is generated. Therefore, a total tensile strain ε _s + ε _{T of the} tensile strain + ε _s is generated in the direction traversing the groove portion, and the compressive residual stress becomes a large value accordingly. As a result, the magnetic anisotropy generated in the stress concentration portion becomes remarkable due to the synergistic effect of the compressive strain −ε _c and the tensile strain + ε _T.

It is particularly advantageous to form a pair of spiral stress concentrating portions on the surface of the shaft body and to incline both of them in opposite directions with respect to the axis.

First, in a state in which a mechanical load such as a torsion torque is applied to the shaft so that a compressive strain is generated in one of the pair of stress concentrating portions that are inclined in opposite directions, only one of the stress concentrating portions is applied. Causes tensile strain. Then, in the state where a mechanical load in the opposite direction of the shaft is applied so that compressive strain is generated in the other stress concentrated portion, tensile strain is generated only in the other stress concentrated portion. By doing so, chevron-like magnetic anisotropy inclined in opposite directions is imparted.

Embodiment 1 In FIG. 1, reference numeral 1 denotes a shaft body for manufacturing a torque sensor shaft, which is made of a soft magnetic material.

First, in the shaft body 1 of FIG. 1, the stress concentrating portion 2 is formed in a shape desired to obtain magnetic anisotropy. This stress concentration part 2
As shown in FIG. 2, the plurality of groove portions 3 and the mountain portions 4 are
The shaft 1 is formed in a spiral shape alternately in the circumferential direction on the surface thereof. The groove portion 3 and the mountain portion 4 can be formed by, for example, knurling the surface of the shaft body 1. The groove portion 3 can be formed in a V shape as shown in FIGS. 2 and 3, or can be formed in a rectangular shape as shown in FIG. 4, and other suitable stress concentration can be generated. It can also be in the shape of.

Next, as shown in FIG. 5, a torsion torque T as a mechanical load is applied to the shaft body 1. The torsion torque T is applied in a direction in which a compressive stress acts on the stress concentrating portion 2 in the lengthwise direction of the groove portion 3 and the crest portion 4. Then, as shown in FIG. 6, a compressive strain −ε _{c in} the direction of the crest 4 is generated at the crest of the crest 4 of the stress concentrating portion 2 (since it is compressive strain, it is negative). This compressive strain-ε _c is α times as large as when the stress concentration portion 2 is not provided, where α is the stress concentration coefficient of the stress concentration portion 2. At the groove bottom of the groove portion 3, a tensile stress is generated in the direction traversing the groove portion 3 due to the torsional torque T, a tensile strain + ε _T is generated due to the tensile stress, and stress concentration also occurs in this direction.

As shown in FIG. 7, the tensile strain (elongation strain) uniformly distributed on the surface of the shaft body 1 in the state where the torsion torque T is still applied so that a large compressive strain −ε _c is generated. + Ε _s
Cause This tensile strain + ε _s is generated by subjecting the surface of the shaft body 1 to shot peening 5, and is set to a value larger than the strain at the time of tensile yield of the material of the shaft body 1.

Next, the torsion torque T is removed and the shot peening 5 is stopped. Then, the shaft body 1 is plastically worked on the tensile side by the amount that the tensile strain generated on the surface exceeds the strain at the tensile yielding. Then, a tensile residual strain is generated based on this plastic working, and a compressive residual stress corresponding to this tensile residual strain is generated on the surface of the shaft body 1.

However, in the direction of the peak portion 4 of the stress concentrating portion 2, a larger compressive strain −ε _c is generated due to the torsional torque T than in other portions, so that the tensile strain based on the shot peening 5 is ε _s −ε _c. Stays in and smaller than the other parts. Therefore, in the direction of the peak portion 4 of the stress concentration portion 2, the tensile residual strain and the compressive residual stress based on the tensile residual strain are also
Smaller than other parts. On the other hand, in the direction transverse to the grooves 3 in the stress concentration portion 2, resulting tensile strain corresponding to the sum ε _s + ε _T and tensile strain + epsilon _s by tensile strain + epsilon _T and shot peening 5 by twisting torque T, compared to other Large compressive residual stress occurs.

Eventually, the shaft body 1 as a whole produces a compressive residual stress 6 having a distribution as shown in FIG. This compressive residual stress 6 is
As shown in the figure, the distribution has anisotropy such that the stress concentration portion 2 has a minimum in the direction of the groove portion 3 and the peak portion 4 and has a maximum in the direction perpendicular thereto. Also tensile strain + ε _T
Occurs in a direction that promotes tensile strain + ε _s , so the above anisotropy becomes particularly remarkable.

FIG. 9 is a stress-strain diagram when the shot peening 5 is performed, and shows that the residual stress in the peak portion is smaller in the stress concentrated portion 2 than in the valley bottom portion.

Thus, the tensile strain + ε _s is given by the shot peening 5 after the torsion torque T is loaded in advance, and the strain ε _s −ε _c is obtained by subtracting the compressive strain −ε _c due to the torsion torque T from the tensile strain + ε _s. Since the residual stress anisotropy is imparted to the residual stress, it is not necessary to apply an excessive torque as in the conventional case, and the torsion torque T may be within the elastic limit. Further, as a method of imparting anisotropy of residual stress, conversely to the above, it is conceivable to apply torque after performing shot peening in advance, but as described above, shot peening is performed with the torque applied. This has the advantage that the torque load is small.

FIG. 10 shows a specific example of a magnetostrictive torque sensor shaft manufactured by the method of the present invention. Here, a pair of stress concentrating portions 2A, 2B inclined in opposite directions with respect to the axis of the shaft body 1 are provided.
Are formed at a distance from each other in the axial direction.

In such a structure, when imparting magnetic anisotropy to the shaft body 1, first, a torsion torque T1 is applied so that a compressive strain is generated in the stress concentrating portion 2A, and in that state, the stress concentrating portion 2B is masked to concentrate the stress. Shot peening is applied only to part 2A. In the figure, 7 indicates a boundary for masking. Next, the torsion torque T2 in the opposite direction is applied to generate compressive strain in the stress concentrating portion 2B, and in that state, the stress concentrating portion 2A is masked and shot peening is applied only to the stress concentrating portion 2B. Then, as shown in the figure, in the stress concentrating portions 2A and 2B, a distribution of chevron-shaped compressive residual stresses 6A and 6B inclined in mutually opposite directions is obtained.

The work of imparting the magnetic anisotropy due to the compressive residual stress in this manner can of course be carried out at room temperature. However, since the tensile yield stress of ordinary materials decreases as the temperature rises, it should be made to work under such temperature conditions that the tensile yield stress becomes small, that is, when anisotropy treatment is performed at high temperature. The stress can be small.

Further, according to the present invention, since magnetic anisotropy is imparted based on the difference in the magnitude of the compressive residual stress, unlike the conventional technique in which anisotropy is imparted by tensile stress, the easy axis of magnetization is The shaft 1 is oriented in the direction perpendicular to the surface of the shaft 1. That is, it is known that the magnetization process of the shaft body 1 as a magnetic body includes a rotation magnetization process and a domain wall movement process, and the domain wall movement process increases the hysteresis of the sensor characteristic and lowers the sensitivity. However, as in the present invention, if the easy axis of magnetization is oriented in the direction perpendicular to the surface of the axis, only the rotating magnetization process can be used without passing through the domain wall movement process, so that a sensor characteristic of low hysteresis and high sensitivity can be obtained. You can

A material containing Ni, which is often used as a magnetic material for a magnetostrictive torque sensor shaft, has high notch sensitivity and has characteristics that cracks grow rapidly in a portion where tensile residual stress is distributed. However, by distributing the compressive residual stress as in the present invention, the mechanical strength, especially the fatigue strength can be increased.

Further, according to the present invention, by providing the stress concentrating portions 2, 2A, 2B, anisotropy can be imparted in a desired direction, and other portions of the shaft body 1 are not subjected to an excessive load. There is. Further, when forming the pair of stress concentrating portions 2A and 2B that are inclined in opposite directions as described above, even if a torsion torque is applied to the entire shaft body 1, only the stress concentrating portions in the direction of the compressive stress are different. And the other stress concentration part is
It is not affected by this torsion torque.

Further, according to the present invention, by distributing the compressive residual stress, the torque until reaching the magnetic saturation point on the tensile stress side is increased, and the linearity is improved. That is, FIG. 11 exemplifies the characteristics when the torque is detected by using the magnetostrictive torque sensor shaft, in which the horizontal axis indicates the torque acting on the sensor shaft and the vertical axis indicates the detection voltage or the like. Show the output. The horizontal axis is positive when torque in the tensile direction acts on the magnetically anisotropic portion, and negative when torque in the compression direction acts on the magnetically anisotropic portion. In the figure, the solid line shows the characteristics of the torque sensor manufactured by the conventional method. Here, on the compression side, the linearity of the detection characteristic is good even if the torque increases,
It is shown that the tensile side reaches the magnetic saturation point with a relatively small torque, and the linearity is likely to be impaired. However,
According to the present invention, since the compressive residual stress is applied,
The same effect as when the origin O of the coordinate axis in FIG. 11 is shifted to the compression side as shown by the alternate long and short dash line in the figure can be obtained. Therefore, according to the present invention, the torque required to reach the magnetic saturation point on the tension side is increased, and the linearity on the tension side is improved.

FIG. 12 is a diagram showing sensor characteristics when a torque sensor shaft according to the present invention is used, and FIG. 13 is a diagram showing sensor characteristics when a torque sensor shaft manufactured by a conventional method is used. In both figures, the horizontal axis is the torque detected by the sensor, and the vertical axis is the detection output by voltage. ± 60 kgf ・ m
Looking at the detection voltage when the torque is applied, the conventional voltage shown in FIG. 13 is 58.017 mV, whereas the voltage detected by the present invention shown in FIG. 12 is 78.091 mV, and the sensitivity is correspondingly high. Has improved.

Further, the maximum value of the deviation from the straight line for the characteristic curve is 4.897 mV in the conventional one of FIG. 13, whereas
In the case of the present invention shown in FIG. 12, it is 1.684 mV, and the linearity is improved accordingly.

EFFECTS OF THE INVENTION As described above, according to the present invention, the compressive strain generated in the stress-concentrated portion due to the torsional torque and the shot peening generate uniform distribution on the surface of the shaft body and the tensile yield of the material of the shaft body. The stress residual stress in the direction of the stress concentration part is released by causing a tensile strain larger than the strain at the time to the surface of the shaft body, thereby giving the shaft body magnetic anisotropy due to the compressive residual stress. Therefore, the torque sensor shaft having high mechanical strength, particularly fatigue strength can be obtained. Moreover, since the easy axis of magnetization is oriented in the direction perpendicular to the surface of the axis, only rotational magnetization can be used, and the hysteresis of the sensor can be reduced and its sensitivity can be increased.
In addition, by forming the stress concentration part, anisotropy can be given in the desired direction, and also anisotropy can be given without adding too much torsional torque, and no excessive load is applied to other parts. Complete. Further, by distributing the compressive residual stress, the torque required to reach the magnetic saturation point on the tensile stress side increases, and the linearity of the sensor can be improved.

The stress to be applied can be further reduced by carrying out the work of applying anisotropy under a high temperature condition where the tensile yield stress becomes small.

As the stress concentration portion, a plurality of groove portions and mountain portions are alternately formed in the circumferential direction on the surface of the shaft body in a spiral shape, and a pair of spiral shapes inclined in opposite directions with respect to the axis are formed. By forming the stress concentration portion, a sensor shaft particularly suitable for torque detection can be manufactured.

In this way, if a pair of spiral stress concentration parts are formed on the surface of the shaft body, first a torsion torque in the direction in which compressive strain is generated is applied to one stress concentration part, and this one stress concentration part is applied to this one stress concentration part. Only causes tensile strain. Next, by applying a torsional torque in the opposite direction to generate compressive strain in the other stress concentrating portion, a tensile strain is applied only to this other stress concentrating portion, so that It is possible to impart anisotropy according to the above. Moreover, when a torsional torque is applied to generate a compressive strain in one stress concentration part, this torsional torque has an advantage that it does not adversely affect the other stress concentration part.

[Brief description of drawings]

FIG. 1 is a front view of a shaft body for manufacturing a magnetostrictive torque sensor shaft according to the present invention, FIG. 2 is an enlarged perspective view of a stress concentration portion in the shaft body of FIG. 1, and FIGS. FIG. 1 is a view showing an example of the shape of a stress concentrating portion in the shaft body, FIGS. 5 to 8 are explanatory views of a method for manufacturing a magnetostrictive torque sensor shaft according to the present invention, and FIG. 9 is a compression residue based on the present invention. A stress-strain diagram showing a stress generation state, FIG. 10 is a perspective view of a specific example of a magnetostrictive torque sensor shaft according to the present invention, and FIG. 11 is an example of a torque detection characteristic based on the conventional and the present invention. FIG. 12 is a diagram showing details of the torque detection characteristic based on the present invention, and FIG. 13 is a diagram showing details of the torque detection characteristic based on the conventional example. 1 ... shaft, 2, 2A, 2B ... stress concentration, T, T1, T2 ... twisting torque (mechanical load), - epsilon _c ... compressive strain, + epsilon _s ... tensile strain, 5 ...
Shot peening, 6 ... compressive residual stress.

Claims (5)

(57) [Claims] 1. A stress-concentrated portion is formed on the surface of a shaft body, and a mechanical load is applied to the shaft body to generate a compressive strain based on a compressive stress in the stress-concentrated portion. With the mechanical load applied to
On the surface of this shaft body, a tensile strain larger than the strain at the time of tensile yielding of the material of the shaft body is generated by shot peening, and then the mechanical load and the cause of the tensile strain are generated. A method of manufacturing a magnetostrictive torque sensor shaft, characterized in that a compressive residual stress based on the tensile strain is generated on the surface of the shaft body. 2. The method for manufacturing a magnetostrictive torque sensor shaft according to claim 1, wherein the method is carried out under a temperature condition in which the tensile yield stress is smaller than that at room temperature. 3. The magnetostrictive type according to claim 1 or 2, wherein a plurality of grooves and peaks are alternately formed in the circumferential direction on the surface of the shaft body in a spiral shape as the stress concentration portion. Method for manufacturing torque sensor shaft. 4. A method of manufacturing a magnetostrictive torque sensor shaft according to claim 3, wherein a pair of spiral stress concentration portions that are inclined in opposite directions with respect to the shaft center are formed. 5. A tensile strain is generated only in one stress concentrating portion in a state where a mechanical load is applied to the shaft so that a compressive strain is generated in one stress concentrating portion, and then the other stress concentration is concentrated. 5. The magnetostrictive torque according to claim 4, wherein a tensile strain is generated only in the other stress concentrating portion while a mechanical load in the opposite direction is applied to the shaft body so that a compressive strain is generated in the portion. Manufacturing method of sensor shaft.