JPH0416727A - Torque detector - Google Patents

Abstract

PURPOSE:To make hysteresis of torque-output characteristic approximately zero and increase sensitivity with little irreversible change in the sensitivity at high and allow temperatures by making an amount of austenite in the surface part of a shaft to be measured a predetermined value or lower. CONSTITUTION:A torque detector 1 is provided with a plurality of recessed parts 3a, 3b and protruding parts 4a, 4b which are tilted toward left and right with an interval along an axial line on a surface of a shaft 2 to be measured along a circumference to provide a shape magnetic anisotropic part, coils 5a, 5b are placed oppositely to the above part on an outer periphery of the shaft 2 to be measured via a slit 6, and a yoke 7 is provided outside the coils. By making an austenite amount at a surface part of the shaft to be measured of the detector 25% or lower, hysteresis of torque-output characteristics is close to approximately zero so that irreversible change in sensitivity will occur both at high and low temperatures and a high accurate torque detector can be obtained.

Description

[Detailed description of the invention] [Purpose of the invention]

(Industrial Application Field) The present invention relates to a torque detection device used to detect torque applied to a shaft to be measured. (Prior art) As a conventional torque detection device of this type, for example, a fourth
There is one shown in Japanese Patent Application Laid-Open No. 117230/1983 as shown in the figure. The torque detection device 101 shown in FIG.
Concave portions 1 inclined left and right at intervals in the axial direction on the surface of the
03a, 103b and a plurality of convex portions 104a, 104b are formed in the circumferential direction to provide a shape magnetic anisotropy section, and coils 105a, 105b are placed on the outer periphery of the shaft 102 to be measured, facing the shape magnetic anisotropy section. are arranged through the gap 106,
It has a structure in which a yoke 107 is provided on the outside of the coils 105a and 105b. In the torque detection device 101 having such a structure, the coils 105a and 105b are combined with one resistor 111 and 112 to form a bridge circuit as illustrated in FIG. 113
At the same time, an excitation oscillator 114 is connected between the connection points A and C of the bridge circuit, and a differential amplifier 115 is connected between the connection points B and B', and the output terminals 116 and 117 are connected as shown in FIG. It is possible to take out the detection output of the torque-output characteristic as illustrated. In such a conventional torque detecting device 101, the shaft to be measured 102 is mainly made of steel, and is subjected to heat treatment such as carburizing and quenching or tempering as necessary, or the recessed portions 103a and 103b are A magnetic thin film with a correspondingly shaped cutout is attached to it. (Problem to be Solved by the Invention) However, such a conventional torque detection device 101
In this case, when the shaft to be measured 102 is to be subjected to heat treatment such as carburizing and quenching, tempering, etc., the shaft to be measured 102
Due to the difference in the heat treatment loft of 02, the resulting torque-output characteristic of the torque detection device 101 may have a large variation in hysteresis (h) as shown in FIG. However, there was a problem in that there was an irreversible change in sensitivity at higher or lower temperatures than at room temperature, making it impossible to accurately detect torque. (Purpose of the Invention) This invention was made in view of such conventional problems, and it is possible to stably reduce the hysteresis of the torque-output characteristic to approximately 0, and also to make it possible to reduce the hysteresis in the torque-output characteristic to almost zero. It is an object of the present invention to provide a torque detection device that can prevent irreversible changes in sensitivity when the torque is changed.

[Structure of the invention]

(Means for Solving the Problems) The present invention includes a shaft to be measured, excitation means for forming a magnetic circuit in which the shaft to be measured is a part of a magnetic path, and a detector for detecting a magnetostrictive component of the shaft to be measured. The torque detecting device is characterized in that the shaft to be measured is made of a steel shaft having an austenite content of at least 25% in its surface layer, and the structure of such a torque detecting device is characterized in that: is used as a means to solve the conventional problems mentioned above. FIG. 1 shows an embodiment of the torque detection device according to the present invention, and this f! The torque detection device 1 shown in FIG.
A plurality of coils 4b are formed in the circumferential direction to provide a shape magnetic anisotropy section, and a coil 5a is disposed on the outer periphery of the shaft 2 to be measured, facing the shape magnetic anisotropy section. 5b is arranged through a gap 6, and the coil 5a. It has a structure in which a yoke 7 is provided on the outside of the yoke 5b. In such a torque detection device 1 shown in FIG. 1, the shaft to be measured 2 is made of a steel shaft whose austenite content is 25% or less at least in its surface layer, but the steel material used here is , Steel materials for machine structures established in JIS, such as carbon steel materials for machine structures (S
C material) and alloy steel materials for machine structures (SCr material, SM material, S
MnC material, SCM material, SNC material, SNCM material, etc.) are used, and in addition, Co is used to improve various properties. Cu, AM, N, B, etc., W, V, Ti, Nb. Ta, Zr, Hf, REM, etc., Pb, Bi. One or two selected from S, P, Te, Se, Ca, etc.
A steel shaft made of such a steel material and having an austenite content of at least 25% or less in the surface layer is used as the shaft 2 to be measured. In the torque detection device M1 shown in FIG. 1, the measured shaft 2 includes C: 0.2% by weight, Cr2: 2.0% by weight, Ni:
0.1% by weight, Mo: 0, 16% by weight as the main alloy component.
mm, depth: 1 mm, and then carburized and quenched in several types of carburizing furnaces to produce various shafts 2 to be measured. As a result of analyzing the relationship between the torque-output characteristics and the metallographic structure when using each of these measured shafts 2, the following powerful findings were obtained. In other words, Ii! As shown in Figure 2, there is a correlation between the amount of retained austenite present in the carburized layer, which is the surface layer of the shaft 2 to be measured, and the hysteresis in the torque-output characteristics, and the amount of retained austenite in the surface layer is 25% or less. It was observed that the hysteresis was approximately 0 when the amount of retained austenite in the surface layer exceeded 25%, and the hysteresis increased accordingly. This influence on hysteresis is thought to be due to the following reasons. That is, in the magnetostrictive torque detection device 1 of the present invention, when steel is used as the material of the shaft 2 to be measured and the steel material is carburized and quenched, all non-magnetic austenite crystals are formed during the carburizing heat treatment process. The shaft material to be measured, which is in this state, is transformed into martensitic crystals, most of which have magnetism, through quenching. Here, austenite that remains without being transformed into martensite is residual austenite. This retained austenite is softer than martensite and is relatively easily deformed by stress due to torque application. Martensite coexisting with the retained austenite is also deformed by being dragged by the retained austenite due to the stress caused by the torque application. At this time, if there is a large amount of austenite, the residual austenite tends to cause microscopic plastic deformation, and the magnetic martensite crystals are also affected by this, causing an irreversible change in magnetization. By the way, when the residual austenite is 25% or less, hard and dense martensite accounts for approximately 75% or more, so martensite crystals form a network over almost the entire surface layer of the shaft 2 to be measured, and the torque is reduced. Microplastic deformation can be prevented from easily occurring due to applied stress. Therefore, it has been found that by setting the amount of austenite in at least the surface layer of the shaft 2 to be measured to be 25% or less, the hysteresis of the torque-output characteristic can be made to be 1% or less, which is approximately O. In this case, the means to actually reduce the amount of austenite in at least the surface layer of the shaft 2 to be measured to 25% or less is to prevent the amount of carbon during carburization from becoming too large, and more preferably the carbon content in the surface layer. The amount is preferably 1.0% by weight or less. It has also been found that the temperature during quenching following carburization must not be too high, and is more preferably 900° C. or lower. In this way, for example, if the amount of austenite in at least the surface layer of the shaft 2 to be measured is reduced to 25% or less by controlling the heat treatment conditions, the hysteresis can be reduced to approximately 0.
It has become clear that a highly accurate torque detection device M1 can be obtained. (Operation of the Invention) The torque detection device according to the present invention has a structure in which the shaft to be measured is made of a steel shaft in which the amount of austenite is 25% or less in at least the surface layer thereof, so that the hysteresis of the torque-output characteristic is stable. This brings about the effect that irreversible changes in sensitivity are difficult to occur even when exposed to high or low temperatures. (Example) Next, an example of the torque detection device according to the present invention will be described. In this example, in the torque detection device 1 having the structure shown in FIG. 1, the materials of the shaft 2 to be measured are C: 0.2% by weight, Cr: 2.0% by weight, and Ni: 0.1% by weight. , Mo:
The concave portions 3a, 3 forming the shape magnetic anisotropy portion are made of alloy steel having a composition of 0.16% by weight as the main alloy component.
A shaft 2 to be measured was used, in which the width of the groove b was 2 mm, the depth was 1 mm, and the amount of austenite in the surface layer portion after carburizing and quenching was 15%. As shown in FIG. 3, the torque-output characteristic of the torque detection device M1 in this embodiment has a hysteresis of almost 0.
The sensitivity of the torque-output characteristic is 6mV.
/kgf@m. This sensitivity is stable; for example, when we tested it at temperatures above 50°C or below freezing and then tested it again at room temperature, we found that there was almost no change in sensitivity; Moreover, the sensitivity changed reversibly at low temperatures and had excellent reproducibility. (Comparative example) In the torque detection device 101 having the structure shown in FIG.
The shaft to be measured 102 was made of the same material as in the previous example, the shape magnetic anisotropy part was formed in the same way, and the amount of austenite in the surface layer after carburizing and quenching was 40%. there was. As shown in FIG. 6, the torque-output characteristics of the torque detection device 101 in this comparative example had a hysteresis of about 5%, and a sensitivity of 6 m/kgf11 m. In such a torque detection device 101, the sensitivity is stable when used at a room temperature of about ±20°C, and there is no problem. When the test was carried out again at room temperature using this method, the sensitivity changed (increased) by about 15 to 30%. This was thought to be a phenomenon caused by some unstable residual austenite being transformed into martensite by being exposed to the high or low temperatures. Therefore, in order to make it more stable over a wide temperature range, it is better to perform a so-called sub-zero treatment by immersing it in liquid nitrogen, etc., and this reduces the retained austenite from, for example, 40% to 13%. It has been found that by doing so, irreversible changes in sensitivity upon exposure to sub-zero temperatures and high temperatures can be prevented, and stable characteristics can be obtained from low to high temperatures.

【Effect of the invention】

The torque detection device according to the present invention includes a shaft to be measured, excitation means for forming a magnetic circuit in which the shaft to be measured is part of a magnetic path, and a detection means for detecting a magnetostrictive component of the shaft to be measured. In this torque detection device, the shaft to be measured is made of a steel shaft in which the amount of austenite in at least its surface layer is 25% or less, so that the hysteresis of the torque-output characteristic can be stably reduced to almost 0. At the same time, it is possible to prevent irreversible changes in sensitivity when exposed to high or low temperatures, and furthermore, by reducing austenite, which is non-magnetic and is not included in the magnetostrictive component, to 25% or less, Since martensite, which is a magnetostrictive component, increases, the sensitivity itself increases by 20 to 30%, which is a remarkable effect.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram illustrating the configuration of a torque detection device according to the present invention, FIG. 2 is an explanatory diagram illustrating the relationship between the amount of austenite and hysteresis in the surface layer of the shaft to be measured,
Fig. 3 is a graph illustrating the torque-output characteristics of the torque detection device according to the present invention, Fig. 4 is an explanatory diagram illustrating the configuration of a conventional torque detection device, and Fig. 5 is a graph illustrating torque detection using this type of magnetostrictive method. An explanatory diagram illustrating a torque detection circuit of the device,
FIG. 6 is a graph illustrating the torque-output characteristics of a conventional torque detection device. DESCRIPTION OF SYMBOLS 1... Torque detection device, 2... Axis to be measured, 5a, 5b... Coil (excitation means and detection means). Patent applicant Nissan Motor Co., Ltd.

Claims (1)

[Claims] (1) In a torque detection device comprising a shaft to be measured, an excitation means forming a magnetic circuit in which the shaft to be measured is part of a magnetic path, and a detection means to detect a magnetostrictive component of the shaft to be measured. . A torque detection device, wherein the shaft to be measured is made of a steel shaft having an austenite content of 25% or less at least in a surface layer thereof.