JP2010230636A - Method of manufacturing magnetostrictive torque sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of easily manufacturing a magnetostrictive torque sensor having a magnetostrictive film in a rotary shaft where residual austenite is reduced locally. <P>SOLUTION: Fig.(a) illustrates a heat treating process in first and second magnetostrictive film sections as local parts; and a carburizing quenching treating process, a cooling process by oil cooling, a tempering process by low temperature, and a cooling process by air cooling are applied to the whole steel material as the rotary shaft. Then, a local heating process of heating only the local parts of the rotary shaft is performed. Fig.(b) illustrates a heat treating process in a part other than the local parts; and the carburizing quenching treating process, the cooling process by oil cooling, the tempering process by low temperature, and the cooling process by air cooling are applied to the rotary shaft. The magnetostrictive torque sensor having the magnetostrictive films in the rotary shaft where the residual austenite is reduced locally can be easily manufactured. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a method for manufacturing a magnetostrictive torque sensor in which a magnetostrictive film is locally provided on a rotating shaft.

  For example, a torque sensor in which magnetic anisotropy is imparted to a part of the rotating shaft is known as a torque sensor that detects torque applied to the rotating shaft. (For example, refer to Patent Document 1 (FIG. 1).)

The technique of this patent document 1 is demonstrated below based on drawing.
As shown in FIG. 8, the rotating shaft 101 includes joint portions 102 and 103, sensor portions 104 and 105, and bearing mounting portions 106 and 107. Torque applied to the rotating shaft 101 is detected by a change in magnetic permeability in the sensor units 104 and 105 to which magnetic anisotropy is imparted.

  Generally, such a rotating shaft is subjected to carburizing and quenching in order to improve mechanical strength. Residual austenite may be generated during the carburization. This retained austenite is a very unstable phase, and gradually changes to martensite when repeatedly stressed or subjected to a temperature change. Since martensite affects magnetism, the magnetic characteristics of the rotating shaft 101 change with time.

  In order to prevent these problems, in the prior art, first, as shown in (a), the carburizing prevention quenching tempering process is performed on the sensor parts 104, 105, and the carburizing quenching tempering process is performed on the parts other than the sensor parts 104, 105. Apply. Further, as shown in (b), shot peening is performed on at least the sensor units 104 and 105.

  However, in the prior art, the carburizing prevention processing and shot peening are required for the sensor units 104 and 105, and the processing becomes complicated. Moreover, by performing shot peening, the surface of the rotating shaft 101 becomes rough and is not suitable for a magnetostrictive film formed thereafter. Although it is necessary to give magnetic anisotropy to the base material itself of the rotating shaft 101, the magnetostrictive characteristic becomes weaker than that of a type that gives magnetic anisotropy to the magnetostrictive film, so that it is necessary to amplify the signal. That is, there is a demand for a method for easily manufacturing a magnetostrictive torque sensor in which a magnetostrictive film is provided on a rotating shaft in which residual austenite is locally reduced.

JP-A-4-246123

  An object of the present invention is to provide a method for easily manufacturing a magnetostrictive torque sensor in which a magnetostrictive film is provided on a rotating shaft in which residual austenite is locally reduced.

  According to a first aspect of the present invention, there is provided a magnetostrictive torque sensor manufacturing method in which a magnetostrictive film is locally provided on a rotating shaft, and an overall carburizing and quenching treatment step of carburizing the entire steel material as the rotating shaft, A cooling process for cooling the entire hardened rotating shaft, an entire tempering process for tempering the entire cooled rotating shaft at a low temperature, a local heating process for heating a local part of the tempered rotating shaft, and this heating A magnetostrictive film forming step for forming a magnetostrictive film on a local portion of the rotating shaft, a magnetic anisotropy providing step for imparting magnetic anisotropy to the formed magnetostrictive film, and the magnetic anisotropy are provided. And a detection coil arranging step of arranging a detection coil for detecting a change in magnetostriction characteristics around the magnetostrictive film.

  The invention according to claim 2 is characterized in that the local heating step is performed by high-frequency heating.

  According to the first aspect of the present invention, after performing the carburizing and quenching treatment process and the tempering process on the entire rotating shaft, the local heating step of heating the local portion of the rotating shaft is performed. By locally heating, the retained austenite only in the magnetostrictive film forming part of the rotating shaft can be reduced. Since the rotating shaft part other than the magnetostrictive film forming part is not subjected to the local heat treatment, the mechanical strength can be maintained. As a result, it is possible to easily manufacture a magnetostrictive torque sensor in which a magnetostrictive film is provided on a rotating shaft in which residual austenite is locally reduced.

  In the invention which concerns on Claim 2, a local heating process is implemented by high frequency heating. Since it is only heated by a coil, a magnetostrictive torque sensor can be manufactured in a short time.

It is a figure explaining the usage example of the magnetostrictive torque sensor which concerns on this invention. It is sectional drawing of the electric power steering which concerns on embodiment of this invention. 1 is a cross-sectional view of a magnetostrictive torque sensor according to the present invention. It is a figure explaining the effect | action of the magnetostrictive torque sensor which concerns on this invention. It is a graph which shows the magnetostriction characteristic curve and sensor detection characteristic regarding each detection coil in the magnetostriction type torque sensor which concerns on this invention. It is a figure explaining each heat treatment process of the magnetostriction type torque sensor concerning the present invention. It is a figure explaining the local heating process which concerns on this invention. It is a figure explaining the basic principle of the prior art.

  Embodiments of the present invention will be described below with reference to the accompanying drawings. The drawings are viewed in the direction of the reference numerals.

First, an embodiment of the present invention will be described with reference to the drawings.
As shown in FIG. 1, when the steering handle 11 is turned in the vehicle 10, this rotational force is transmitted to the electric power steering mechanism 13 (detailed structure will be described later) via the steering shaft 12. Torque corresponding to the rotational force is applied by the electric power steering mechanism 13. The rack shaft 14 is moved horizontally with the increased torque, and the wheels 15 are steered.

  As shown in FIG. 2, the electric power steering mechanism 13 includes a rotary shaft 16, a magnetostrictive torque sensor 20 that detects torque of the rotary shaft 16, an auxiliary power transmission mechanism 21 that transmits auxiliary power, and a rotary shaft. It consists of a pinion rack mechanism 22 that converts 16 rotational movements into reciprocating movement, and a housing 23 and a lid 24 that surround the pinion rack mechanism 22. The rotary shaft 16 is rotatably supported by the housing 23 using bearings 25 and 26.

  The magnetostrictive torque sensor 20 is provided on the lid 24 so as to face the first and second magnetostrictive films 27 and 28 provided on the rotating shaft 16 and the first and second magnetostrictive films 27 and 28. The first detection coil 31 and the second detection coil 32 are provided.

  The auxiliary power transmission mechanism 21 includes an auxiliary motor 34 that is provided in the housing 23 and generates auxiliary power, a transmission shaft 35 that is provided in the auxiliary motor 34 and transmits rotational force, and a worm gear 36 that is provided on the transmission shaft 35. And a worm wheel 37 that is provided on the rotary shaft 16 so as to mesh with the worm gear 36 and transmits auxiliary power.

  The pinion rack mechanism 22 includes a pinion 40 provided on the rotary shaft 16, a rack 41 provided so as to mesh with the pinion 40, and a housing 41 slidably provided toward the rack 41. And a compression spring 44 which is provided on the housing 23 via a cap 43 and urges the rack guide 42 to be pressed against the pinion 40.

  As shown in FIG. 3, the magnetostrictive torque sensor 20 includes a rotating shaft 16, a first magnetostrictive film 27 covered with the rotating shaft 16 and provided with magnetic anisotropy, and covered with the rotating shaft 16. A second magnetostrictive film 28 having a magnetic anisotropy applied in a direction opposite to that of the first magnetostrictive film 27, and a magnetic property change in the first magnetostrictive film 27 that is disposed facing the first magnetostrictive film 27 is detected. A first detection coil 31, a second detection coil 32 that is arranged facing the second magnetostrictive film 28 and detects a change in magnetic characteristics in the second magnetostrictive film 28, and one piece arranged around the rotation shaft 16. An exciting coil 47. The direction of magnetic anisotropy is indicated by A and B. Reference numerals 48 and 48 denote yokes provided in the first and second detection coils 31 and 23.

The operation of the magnetostrictive torque sensor described above will be described next.
As shown in FIG. 4, the excitation coil 47 disposed with respect to the first and second magnetostrictive films 27 and 28 and the first and second detection coils 31 and 32 are conceptually shown as an electrical relationship. ing. An AC power supply 51 that always supplies an AC current for excitation is connected to the excitation coil 47 that is disposed in common with the first and second magnetostrictive films 27 and 28. When torque is applied to the rotating shaft 16, induced voltages V _A and V _B corresponding to the torque are output from the output terminals of the first and second detection coils 31 and 32.

The induced voltages V _A and V _B output from the output terminals of the first and second detection coils 31 and 32 are input to the torque calculation unit 52. The torque calculation unit 52 calculates the torque applied to the rotating shaft 16 based on the induced voltages V _A and V _B.
The torque calculation unit 52 is configured by calculation means such as a microcomputer or a calculation electric circuit.

  As shown in FIG. 5, the magnetostrictive characteristic curve 53 relating to the first detection coil (FIG. 3, reference numeral 31) and the magnetostriction characteristic curve 54 relating to the second detection coil (FIG. 3, reference numeral 32) are the first and second. Reflecting that each of the magnetostrictive films (FIG. 3, reference numerals 27 and 28) has magnetic anisotropies that are opposite to each other, the relationship is substantially line-symmetric with respect to the vertical axis including the point where the two magnetostrictive characteristic curves intersect. .

A line 55 shown in FIG. 5 is a region common to the magnetostrictive characteristic curves 53 and 54 and has a substantially linear characteristic, and from the respective values of the magnetostrictive characteristic curve 53 obtained as the output voltage of the detection coil 31, the detection coil 32. The graph produced based on the value which deducted each corresponding value of the magnetostriction characteristic curve 54 obtained as an output voltage is shown. When the torque is zero, the induced voltages output from the detection coils 31 and 32 are equal, so the difference value is zero. In the magnetostrictive torque sensor (FIG. 3, reference numeral 20), by using a region regarded as a constant gradient near the neutral point (zero point) of the torque in the magnetostrictive characteristic curves 53 and 54, the substantially linear characteristic of the line 55 is obtained. It is formed as having. A line 55 is a straight line passing through the origin, and exists on the positive side and the negative side of the vertical axis and the horizontal axis. Since the detection output value of the magnetostrictive torque sensor 20 is obtained as a difference between induced voltages output from the first and second detection coils 31 and 32 (V _A −V _B ), the line 55 is used. Thus, the direction and magnitude of the torque applied to the rotating shaft (FIG. 3, reference numeral 16) can be detected.

  Based on the output value of the magnetostrictive torque sensor 20, a detection signal corresponding to the rotational direction and magnitude of the torque input to the rotating shaft 16 can be extracted. That is, the detection value of the magnetostrictive torque sensor 20 is output as any point on the line 55 according to the torque. When the detected value is positioned on the positive side on the horizontal axis, the torque is determined to rotate right, and when the detected value is positioned on the negative side on the horizontal axis, the torque is determined to rotate left. Further, the absolute value of the detected value on the vertical axis is the magnitude of the steering torque.

A method for manufacturing the magnetostrictive torque sensor described above will be described next.
In FIG. 6, (a) is a figure explaining the heat processing process in the 1st, 2nd magnetostrictive film part as a local part.
First, a carburizing and quenching process, a cooling process by oil cooling, a tempering process by low temperature, and a cooling process by air cooling are performed on the entire steel material (FIG. 2, reference numeral 16) as a rotating shaft.
And the local heating process which heats only the local part (FIG. 2, code | symbol 27, 28) of the rotating shaft 16 is implemented.

(B) is a figure explaining the heat processing process in parts other than a local part.
A carburizing and quenching process, a cooling process by oil cooling, a tempering process by low temperature, and a cooling process by air cooling are performed on the rotating shaft (FIG. 2, reference numeral 16).

The mechanical strength of the pinion 40 can be maintained by performing the tempering process at a low temperature on the pinion (FIG. 2, reference numeral 40).
By performing the local heating process on the local portions 27 and 28, the retained austenite of the local portions 27 and 28 can be reduced. As a result, in the local portions 27 and 28, it is possible to prevent the secular change in which the retained austenite is changed to ferromagnetic martensite.

As shown in FIG. 7, the local heating step is performed by high-frequency heating with the heating coils 56 and 56 facing the first and second magnetostrictive films 27 and 28 as local portions.
Since the high-frequency heating by the heating coil is about 10 seconds at the longest, the man-hour of the local heating process can be shortened. In addition, local fatigue strength and surface hardness can be improved.

A magnetostrictive film forming step is performed in which a magnetostrictive film is formed on the local part of the rotating shaft (reference numeral 16 in FIG. 2) subjected to the heat treatment. The first and second magnetostrictive films (FIG. 2, reference numerals 27 and 28) are sprayed or plated with a Ni—Fe alloy having a composition ratio showing magnetostrictive characteristics.
A magnetic anisotropy imparting step for imparting magnetic anisotropy to the formed magnetostrictive film is performed. Magnetic anisotropy can be applied, for example, by heating the first magnetostrictive film 27 with high frequency while applying torque to the rotating shaft 16 to release the torque. Further, in the second magnetostrictive film 28 portion, the first magnetostrictive film 28 is heated at a high frequency in the second magnetostrictive film 28 portion in a state where a torque in the direction opposite to that of the first magnetostrictive film 27 portion is applied, and the torque is released. Magnetic anisotropy opposite to that of the film 27 can be applied.
The first and second magnetostrictive film portions 27 and 28 are not limited to Ni—Fe alloy materials, and other materials may be used as long as the materials exhibit magnetostrictive characteristics.

  Further, a first detection coil (reference numeral 31 in FIG. 2) that detects a change in magnetostriction characteristics is arranged around the first magnetostrictive film 27, and a first detection coil that detects a change in magnetostriction characteristics around the second magnetostrictive film 28 ( By arranging FIG. 2, reference numeral 32), the detection coil arranging step is performed to complete the magnetostrictive torque sensor (FIG. 2, reference numeral 20).

  The magnetostrictive torque sensor according to the present invention is applied to the steering shaft of an automobile in the embodiment. However, the magnetostrictive torque sensor can also be applied to a rudder of a ship and can be used as long as it can detect torque of a rotating shaft. It can be applied to parts.

  The magnetostrictive torque sensor of the present invention is suitable for a steering shaft of an automobile.

  DESCRIPTION OF SYMBOLS 16 ... Rotary shaft (steel material), 20 ... Magnetostrictive torque sensor, 27 ... Local part (1st magnetostrictive film), 28 ... Local part (2nd magnetostrictive film), 31 ... 1st detection coil, 32 ... 2nd detection coil, 56 ... heating coil, A, B ... magnetic anisotropy.

Claims (2)

In a manufacturing method of a magnetostrictive torque sensor in which a magnetostrictive film is locally provided on a rotating shaft,
An overall carburizing and quenching process for carburizing the entire steel material as the rotating shaft;
A cooling process for cooling the entire hardened rotating shaft;
An overall tempering step of tempering the entire cooled rotating shaft at a low temperature;
A local heating step of heating the local part of the tempered rotating shaft;
A magnetostrictive film forming step of forming a magnetostrictive film on a portion of the heated rotating shaft;
A magnetic anisotropy imparting step for imparting magnetic anisotropy to the formed magnetostrictive film;
A method of manufacturing a magnetostrictive torque sensor, comprising: a detecting coil arranging step of arranging a detecting coil for detecting a change in magnetostrictive characteristics around the magnetostrictive film provided with the magnetic anisotropy.   2. The method of manufacturing a magnetostrictive torque sensor according to claim 1, wherein the local heating step is performed by high frequency heating.

Images