JP2512553B2 - 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 helical magnetic anisotropy is imparted to a part of the surface of the shaft so that the change in magnetic permeability can be sensed. 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 heat-hardened shaft, an excessive torsional strain is applied to the shaft made of maraging steel before heat-hardening to age-harden the shaft in a short time.

SUMMARY OF THE INVENTION However, simply applying excessive torsional strain to give residual stress is not advantageous in terms of mechanical strength because tensile stress remains when twisted. In particular, a material such as a Ni iron alloy, which has a high probability of being used as a material for a torque sensor shaft, has a defect that fatigue strength is impaired because the notch sensitivity is high and the crack growth resistance is small. For example, Japanese Patent Laid-Open No. 252487/1988 describes that "on a shaft after thermosetting, the shaft is always damaged when excessive torsional strain is applied."
There is a problem.

Therefore, the present invention solves such a problem and provides a method for manufacturing a magnetostrictive torque sensor shaft having excellent mechanical strength, particularly fatigue strength, and a sensor in which the easy axis of magnetization of the torque sensor shaft is perpendicular to the surface. The purpose is to reduce the hysteresis of the characteristics and improve the sensitivity.

Means for Solving the Problems In order to achieve the above object, the method of the present invention is to detect a change in the magnetic permeability of a shaft body based on a transmission torque. Performing a treatment to be distributed almost uniformly, then applying a torsion torque to the portion, set so that the sum of the compression main stress based on the torsion torque and the compression residual stress is larger than the compression yield stress, Then, the torsional torque is removed, and the residual compressive stress in the direction of the compressive principal stress whose total is larger than the compressive yield stress is released to give the shaft a magnetic anisotropy of residual stress. is there.

The method of the present invention can be carried out under temperature conditions in which the compressive yield stress becomes small.

Action That is, according to the present invention, as the first step, a compressive residual stress exhibiting a uniform distribution without directivity is applied to the main portion of the shaft body through which the exciting magnetic flux passes. At the second stage, a torsion torque is applied to both ends of the portion to which the compressive residual stress is applied. Then, shear stress is generated based on the torsion, and a compressive principal stress is generated in the direction of 45 degrees with the axis.

At this time, even if a torsional torque is applied so that the total of the compressive principal stress and the compressive residual stress becomes larger than the compressive yield stress of the shaft material, in reality, the stress above the compressive yield stress acts on the shaft body. do not do. On the other hand, this torsional torque is applied so that the sum of both stresses becomes equal to or less than the compressive yield stress in the directions other than the direction of the compressive principal stress.

Therefore, when the torsional torque is released, the part where the total is less than the compressive yield stress returns to the original uniform distribution of compressive residual stress, but the part where the total exceeds the compressive yield stress is compressed residual stress. Is released. As a result, after the torque is removed, the compressive residual stress in the direction of the compressive principal stress becomes a value smaller than the compressive residual stress in the other directions, and the anisotropy of the residual stress, that is, the magnetic anisotropy based on the residual stress is reduced. Will be granted.

Since the compressive yield stress of ordinary materials decreases as the temperature rises compared to normal temperature, magnetic anisotropy treatment is performed under temperature conditions that reduce such compressive yield stress, that is, high temperature conditions. Is advantageous.

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, when a torque sensor shaft is configured by the shaft body 1 and a transmission torque is applied, compression residual is caused in a main portion through which an exciting magnetic flux passes in order to detect a change in permeability. Apply stress −σ _R. This compressive residual stress −σ _R (negative because it is compressive stress) is
It is given so as to have a uniform distribution having no directionality.
In FIG. 1, the compressive residual stress −σ _R is indicated by a circle to represent this uniform distribution. This compressive residual stress −σ _R is
It can be applied by carburizing and quenching, nitriding, heat treatment such as shot peening, mechanical treatment and the like.

Next, as shown in FIG. 2, a torsion torque T is applied to the portion of the shaft body 1 corresponding to the main portion. Then, a shear stress is generated based on the torsion torque T, and the shear stress causes a compressive stress having a distribution as shown in FIG. Here, a compressive principal stress-[sigma] _T is generated in the direction of -45 degrees with the axis 2 of the shaft body 1. Note that the compressive residual stress −σ _R is not shown in FIG. 2 for the sake of simplicity. Further, when the torsional torque T is applied, a tensile stress is generated in addition to the compressive stress, and a direction orthogonal to the compressive principal stress −σ _T (axis
A tensile principal stress σ _T occurs in the direction of 45 degrees), but this is not shown for simplicity.

When the compressive residual stress −σ _R is applied and then the compressive stress due to the torsion torque T is applied, the resultant force is applied to the shaft body 1. FIG. 3 shows the distribution of the resultant force. In FIG. 3, the compressive yield stress −σ _Cy of the shaft body 1 is shown by a circle.

In FIG. 3, the total of the compressive stress in the −45 degree direction in the shaft body 1 is the sum of the compressive residual stress −σ _R and the compressive main stress due to the torsion torque T −σ _T − (σ _R + σ _T ). However, if a large torsional torque T is applied to such an extent that the total exceeds the compressive yield stress −σ _Cy , a compressive stress larger than the compressive yield stress −δ _Cy does not actually act on the shaft body 1 and the compression due to the torsional torque T occurs. Only the strain increases.

When the torsional torque T is removed and the total − (σ _R + σ _T ) exceeds the compressive yield stress −σ _Cy (σ _R + σ _T > σ
_Cy ) releases the compressive residual stress. On the other hand, when the total is less than or equal to the compressive yield stress −σ _Cy as shown in FIG. 3 in a direction other than the direction of compressive principal stress −σ _T (σ _R + σ _T ≦ σ _Cy ).
Removes the twisting torque T and returns to the original uniform distribution of compressive residual stress −σ _R +.

As a result, the distribution of the compressive residual stress after releasing the torsion torque T becomes as shown in FIG. 4, and the anisotropy of the residual stress occurs. As a result, magnetic anisotropy based on the residual stress is given to the shaft body 1.

As described above, when the torsional torque T is applied, a tensile stress is generated in addition to the compressive stress, but this tensile stress is canceled by the compressive residual stress −σ _R given in advance. Therefore, regarding the tensile stress, a large stress that exceeds the yield stress does not occur, and this does not cause anisotropy of the residual stress.

In this way, the compressive residual stress −σ _R is applied in advance and then the compressive force based on the torsion torque T is applied, and the sum of the compressive principal stress −σ _T and the compressive residual stress −σ _{R at} that time − (σ _R Since + σ _T ) is set to be larger than the compressive yield stress −σ _Cy , anisotropy of residual stress can be easily imparted by adding a relatively small torsion torque T.

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 compressive yield stress of ordinary materials decreases as the temperature rises, the twisting that should be applied should be carried out under such temperature conditions that the compressive yield stress becomes small, that is, at the high temperature. There is an advantage that the torque can be made 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 performance with small 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.

FIG. 5 shows a specific example of the magnetostrictive torque sensor shaft manufactured by the method of the present invention. In FIG. 5, a shaft body 11 constituting a sensor shaft includes a central portion 12, a pair of small diameter portions 13 and 14 formed on both sides of the central portion 12, and the small diameter portions 13, 14.
14 has shaft portions 15 and 16 which are continuous with each other.

In such a shaft body 11, after compressive residual stress is distributed almost uniformly in the small diameter portions 13 and 14, the central portion 12 is fixed and both small diameter portions 13 and 14 are twisted in opposite directions. Then, as shown in the figure, the small-diameter portions 13 and 14 provide the chevron-shaped residual stress magnetic anisotropic portions 17 and 18 that are inclined in opposite directions.

As described above, according to the present invention, the sum of the compressive residual stress and the compressive principal stress due to the torsion torque is made larger than the compressive yield stress of the shaft material, and the direction of the compressive principal stress at the time of releasing the torsion torque is determined. By releasing the residual compressive stress of
Since the shaft is given magnetic anisotropy due to residual compressive stress, a torque sensor shaft with high mechanical strength, especially fatigue strength can be obtained, and the easy axis of magnetization is perpendicular to the shaft surface. Therefore, only rotational magnetization can be used, and the hysteresis of the sensor can be reduced and the sensitivity can be increased. Also, since the total of the compressive residual stress and the compressive principal stress due to the torsion torque is used,
It becomes possible to easily exceed the compressive yield stress with a small torsional torque.

If the work of applying anisotropy is carried out under a high temperature condition where the compressive yield stress becomes small, the torsion torque to be applied can be further reduced.

[Brief description of drawings]

1 to 4 are explanatory views of a method for manufacturing a magnetostrictive torque sensor shaft according to the present invention, and FIG. 5 is a perspective view of a specific example of the magnetostrictive torque sensor shaft according to the present invention. 1,11 ... Shaft,-? _R ... Compressive residual stress,-? _T ... Compressive principal stress,-? _Cy ... Compressive yield stress.

Claims (2)

(57) [Claims] 1. In order to detect a change in the magnetic permeability of a shaft body due to a transmission torque, a main portion of the shaft body through which an exciting magnetic flux passes is subjected to a treatment so that the compressive residual stress is substantially evenly distributed. Is set so that the sum of the compressive principal stress based on the twist torque and the compressive residual stress is larger than the compressive yield stress, then the torsion torque is removed, and the sum is the compressive yield stress. A method of manufacturing a magnetostrictive torque sensor shaft, characterized in that the residual compressive stress in the direction of the compressive principal stress that has become larger than that is released, and the magnetic anisotropy of the residual stress is imparted to 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 compressive yield stress is smaller than that at room temperature.