JPH0452633B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <<Industrial Application Field>> The present invention relates to a magnetostrictive torque detection device, and particularly to a torque detection device with high detection accuracy and good durability.

<<Background of the Invention>> When a torque is applied to a shaft to be measured, such as a rotating shaft or a fixed shaft, for example, when a torque T is applied in a clockwise direction toward the cross section of the shaft, a torque is applied around the shaft as shown in Fig. 1. Tensile stress +σ occurs in the right direction at an angle of 45° with respect to the axial direction, and compressive stress -σ occurs in the left direction at an angle of 45°.

On the other hand, magnetic materials have so-called magnetostrictive properties in which their magnetic permeability changes when stress is applied, and this can be used to magnetically measure the stress in magnetic materials.

That is, in a magnetic material having positive magnetostriction, the magnetic permeability increases in the direction of tensile stress, and conversely, in a magnetic material having negative magnetostriction, the magnetic permeability decreases in the direction of tensile stress.

To use this property to detect the torque applied to a rotating or fixed shaft, magnetic flux emitted from an excitation coil is passed through the shaft to be measured, and changes in magnetic permeability due to magnetostriction are induced in the detection coil. This is done by extracting it as electricity.

By the way, in order to obtain high detection sensitivity, there is a method in which the shaft to be measured itself is made of magnetostrictive material such as nickel or permalloy, but in this case the mechanical strength is insufficient and it is difficult to transmit power beyond a certain level. In such a region, large distortion occurs on the shaft surface of the shaft to be measured, and hysteresis as shown in FIG. 2 appears.

In other words, there is a difference in the detection output when the torque increases and when the torque decreases, and although this hysteresis phenomenon is not a problem when detecting large torque changes,
In order to detect torque changes with higher accuracy, this is a problem that requires some kind of countermeasure.

On the other hand, if the shaft to be measured is made of high-strength material, such as high carbon steel, the magnetic permeability of the entire shaft is low, so the magnetic flux emitted from the excitation coil does not penetrate into the shaft to be measured, as shown in Figure 3. The detection sensitivity becomes extremely low, making it impossible to put it into practical use.

It has also been proposed to form a coating layer of magnetostrictive material by plating or the like on the shaft surface of the shaft to be measured made of high-strength material (Japanese Patent Publication No. 14985/1983).

However, in the torque detection method configured in this way, coatings made of different materials are laminated around the outer periphery of the shaft to be measured, and this is difficult to do when there are large temperature changes in the environment in which the detector is used. However, if the measured shaft itself is used for a long time under conditions where the temperature changes are large, the coating tends to peel off or fall off from the outer surface of the measured shaft due to the difference in the coefficient of thermal expansion of the coating. be.

Under these circumstances, especially when detecting the driving torque of an automobile, temperature changes and torque fluctuations are extremely large, and when using the above-mentioned device, stable high detection sensitivity and detection accuracy over a long period of time can be ensured. It was extremely difficult to do so.

<<Object of the Invention>> An object of the present invention is to provide a torque detection device that has high torque detection sensitivity, low hysteresis, high accuracy, and excellent durability.

<<Structure of the Invention>> In order to achieve the above object, the present invention provides: a shaft to be measured whose main component is a magnetic substance; an excitation coil forming a magnetic circuit in which the shaft to be measured is part of a magnetic path; A torque detection device comprising: a detector for detecting a magnetostrictive component passing through the shaft to be measured; the shaft to be measured is made of a high magnetic permeability material based on iron; This is characterized in that the composition ratio is changed between the shaft surface portion and the inside of the shaft by subjecting the shaft portion to carbon penetration heat treatment, thereby forming a hardened structure on the shaft surface portion.

<<Description of Embodiment>> Hereinafter, one embodiment of the present invention will be described in detail using the accompanying drawings.

FIG. 4 is a front view A and a side view B showing an embodiment of the torque detection device of the present invention.

In the same figure, the outer periphery of the shaft to be measured 1 is made of blunt iron with high magnetic permeability and large magnetostriction, and iron containing carbon on the surface of the shaft. A yoke 4 is arranged close to and spaced from the axis to be measured 1, and an excitation coil 2 and a detection coil 3 are arranged on this yoke 4 as shown in the figure. Therefore, the magnetic flux emitted from the excitation coil 2 forms a magnetic circuit using the shaft 1 to be measured and the yoke 4 as a magnetic path.

The shaft surface of shaft 1 to be measured is 0.4 to 0.8 mm from the surface.
After infiltrating carbon into the deep part at high temperature, a hardened structure is formed by rapid cooling from the high temperature. Since pure iron is a gas under this hardened structure, the magnetic permeability is high and the magnetostriction is also large.

When an iron-carbon alloy heated to an austenitic state at high temperature is rapidly cooled, this hardened structure is formed at a constant temperature determined by the alloy composition, that is, Ms
Below this point, tissue is formed due to abnormal expansion. Since this structural change due to rapid cooling is a phenomenon accompanied by volume expansion, large internal stress is generated as the structural change progresses.

That is, unlike the stress that remains on the shaft due to machining, it has a relatively uniform stress that is related to the distance from the surface of the shaft.

The torque detection device configured in this way has a uniform internal stress acting on the shaft surface of the shaft 1 to be measured, so it is possible to prevent residual uneven strain when torque is applied and when torque is released. The detection output is stable when torque is applied and when torque is released, hysteresis can be eliminated, and torque detection can be performed with extremely high precision.

Further, the carbon-penetrated and hardened structure portion of the shaft 1 to be measured is formed by the diffusion of carbon from the surface of the shaft to be measured toward the inside, and the change in carbon concentration is gradual.

That is, since the above-mentioned hardened structure is formed integrally with the shaft 1 to be measured, there is no risk of peeling due to environmental changes such as temperature changes and torque fluctuations.
It has excellent durability and can provide stable output.

Next, an example of a preferred method for eliminating hysteresis by infiltrating the shaft surface of the shaft 1 to be measured in this embodiment with carbon to form a hardened structure and applying uniform internal stress will be described.

That is, the shaft 1 to be measured made of pure iron is heated at about 900° C. in PX gas in which propane (C ₃ H ₈ ) is modified using a nickel catalyst. Then, as shown in the following equation, the reaction 2C ₃ H ₈ + 30 ₂ + 11.28N ₂ = 6CO + 8H ₂ + 11.28N ₂ occurs, and a mixed gas of CO, H ₂ and N ₂ is obtained, and Fe + CO + H as shown in the following equation The reaction ₂ = (C) γ + H ₂ O causes carbon to penetrate into the iron.

Here, (C) γ in the above formula represents carbon that has penetrated into iron.

The amount of carbon permeation is determined by a function of the material, the diffusion constant determined by the permeation time and temperature, and the surface carbon concentration.

The measured shaft 1 impregnated with carbon as described above is rapidly cooled in oil from about 900°C. This treatment aims at refining the austenite crystal grains of the high-temperature structure and destroys the carbides (Fe ₃ C) formed in the carbon permeation portion.

Next, it is heated to about 800°C and quenched in water. This process increases the height of the surface of the shaft 1 to be measured.

Furthermore, by heating this to approximately 150°C and cooling it in air, it is possible to remove the local rapid cooling distortion and create a shaft 1 to be measured with almost uniform internal stress.
is obtained.

The shaft to be measured 1 thus obtained is made of pure iron inside, has high magnetic permeability, and has large magnetostriction.
The magnetic flux emitted by the excitation coil 2 passes through the pure iron part, and the stress caused by the application of torque causes a large change in magnetic permeability, and the magnetic energy effectively appears as a magnetostriction output, resulting in a large detection output.

Furthermore, since the shaft surface of the shaft 1 to be measured has a hardened structure due to carbon penetration, the homogeneous internal stress existing in this portion can prevent distortion from remaining when torque is applied and when torque is removed.

Therefore, hysteresis is eliminated and highly accurate torque detection becomes possible.

According to the inventor's experiments, when a high frequency current of 10 KHz and 300 mA was applied to the excitation coil 2 and changes in left and right rotational torque output were investigated, the results from the detection coil 3 as shown in FIG. 5 were obtained.

On the other hand, when we conducted a similar experiment using a torque detection device similar to the configuration shown in FIG. 4 without subjecting the measured shaft 1 to the carbon penetration hardening heat treatment according to the present invention, we found that A magnetostrictive output as shown in Figure 2 was obtained.

According to the above experimental results, it can be seen that when the shaft 1 to be measured is subjected to carbon penetration hardening heat treatment, the hysteresis is smaller and the effect of improving the detection accuracy is remarkable.

In addition, in the above-mentioned embodiment, as the axis to be measured 1,
Although an example of using pure iron with good magnetic permeability has been shown, the present invention is not limited to this. The object of the present invention can be achieved by infiltrating the shaft surface with carbon to obtain a hardened structure.

Furthermore, for the detection coil 3, conventionally known means for detecting magnetic flux, such as a Hall element, can be used, and the excitation coil and the detection coil can be arranged coaxially with the shaft 1 to be measured. Needless to say, the present invention can also be applied to a torque detection device made of

<<Effects of the Invention>> As explained above, the torque detection device of the present invention forms a hardened structure in which carbon is infiltrated in the shaft surface of the shaft to be measured, thereby creating a state with homogeneous internal stress. , it suppresses the hysteresis that appears when torque is applied and when torque is removed, improving the accuracy of torque detection, and unlike joining different materials, there is no bonding surface, so there is no coating caused by temperature changes or large torque fluctuations. Since there is no peeling or falling off, it has excellent durability and can ensure stable operation under various conditions.

As described above, the present invention has various advantages, and is therefore extremely useful particularly in detecting driving torque of automobiles.

[Brief explanation of the drawing]

Figure 1 is an explanatory diagram showing the relationship between shaft torque and stress.
2 and 3 are diagrams respectively showing conventional torque detection output characteristics, FIG. 4 is a front view and side view showing an embodiment of the torque detection device of the present invention, and FIG. 5 is a diagram showing torque detection of the present invention. FIG. 3 is a detection output characteristic diagram of the device. 1... Axis to be measured, 2... Excitation coil, 3... Detection coil, 4... Yoke.

Claims (1)

[Claims] 1. A shaft to be measured whose main component is a magnetic substance; An excitation coil forming a magnetic circuit in which the shaft to be measured is part of a magnetic path; Detecting a magnetostrictive component passing through the shaft to be measured. In a torque detection device comprising a detector that A torque detection device characterized in that a composition ratio is changed between a shaft surface portion and a shaft interior, and a hardened structure is formed on the shaft surface portion.