JP2008170450A - Torque sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce changes in output due to axial displacement errors. <P>SOLUTION: A torque sensor includes an input shaft 1 (rotary shaft) to which prescribed residual stress or plastic strain is added, a pinion gear 1a provided for an end part of the rotary shaft 1 for transmitting power to a rack shaft 6, a coil 11 for detecting changes in magnetic permeability to rotation torque input to the rotary shaft 1, and a plurality of bearings 3-5 for rotation-freely supporting the rotary shaft 1 to a casing 2. Only the bearing 4 is a bearing which restricts axial displacements of the rotary shaft 1. <P>COPYRIGHT: (C)2008,JPO&amp;INPIT

Description

  The present invention relates to a torque detection device that detects rotational torque, and more particularly, to a torque detection device that electrically detects a magnetostriction effect generated in a rotation shaft with a detection coil.

A magnetostrictive torque sensor is a sensor that electrically detects a magnetostrictive effect generated in a rotating shaft according to the torque when the torque acts on the rotating shaft by a detection coil.
As such a magnetostrictive torque sensor, for example, a torque sensor disclosed in JP-A-6-221940 is known.
As shown in FIG. 9A, the magnetostrictive torque sensor 100 is composed of two excitation coils 102 and 103, and one of the excitation coils 102 is used for AC magnetizing an axis using an AC power source 104. The other coil is the detection coil 103 for detecting the magnetic flux corresponding to the magnetic permeability difference in the direction of ± 45 degrees at the shaft surface portion caused by the torque as an induced voltage.
In addition, the magnetostrictive torque sensor 100 has a substantially 8-shaped detection coil 103 provided on an approximately 8-shaped excitation coil 102 so as to face the peripheral surface of a torque transmission shaft (rotating shaft) 101 having magnetostrictive characteristics. It is provided by concentrically overlapping with the phase changed by 90 degrees.
When the torque T in the direction as shown in FIG. 9A acts on the torque transmission shaft (rotation shaft) 101, the magnetostriction effect generated in the torque transmission shaft (rotation shaft) 101 according to this torque is detected by the detection coil 103. It is detected electrically (for example, as a voltage value V).
JP-A-6-221940

However, in the conventional magnetostrictive torque sensor 100, (1) the values detected by the excitation coil 102 and the detection coil 103 are different depending on the rotation angle of the torque transmission shaft (rotating shaft) 101, the torque detection values are different, and the axial displacement There was a problem that the output changed due to an error.
(2) Further, when applied to a torque sensor that detects the steering torque of the electric power steering apparatus, the steering feeling is uncomfortable. For example, because the torque detection value differs depending on the rotation angle, the steering wheel center shifts, the steering wheel fluctuates, the steering wheel fluctuates, and the steering wheel fluctuates due to fluctuations in the load from the road surface, such as tire kickback and split road surfaces. There were problems that occurred or hindered the return of the handle.

  The present invention has been made to solve the above-described problem, and an object of the present invention is to provide a torque detection device in which an output hardly changes due to an axial displacement error or the like.

  A torque detection device according to claim 1 of the present invention, which has been made to solve the above-mentioned problems, is provided at a rotating shaft provided with a predetermined residual stress or plastic strain, and at an end of the rotating shaft, and is provided on a rack shaft. A pinion gear that transmits power; a coil that detects a change in magnetic permeability with respect to rotational torque input to the rotating shaft; and a plurality of bearings that rotatably support the rotating shaft with respect to a casing, Only one of the bearings is a bearing that restricts the axial displacement of the rotating shaft. As a result, the output is less likely to change due to an axial displacement error or the like.

  According to a second aspect of the present invention, there is provided a torque detecting device including a magnetostrictive film having a permeability that changes in accordance with a rotational torque input to the rotating shaft, around the rotating shaft. 2. The torque detecting device according to claim 1, wherein the torque detecting device is provided with a width, and a predetermined residual stress or plastic strain is applied to the magnetostrictive film.

This
(1) It is possible to increase the change in inductance of the multiple winding coil fitted to the rotating shaft and improve the detection sensitivity without being affected by the shaft material. As a result, when used in an electric power steering device, the gain of the system can be reduced, and torque control can be stabilized and a high steering feeling that is not affected by noise can be obtained.
(2) By applying a predetermined residual stress or plastic strain to the magnetostrictive film, it is possible to stably provide a change in inductance of the multi-turn coil fitted to the rotating shaft and further improve the detection sensitivity. Can do.

  According to a third aspect of the present invention, the torque detecting device divides the magnetostrictive film into two parts in the axial direction, applies a first predetermined residual stress or plastic strain to one, and the first predetermined predetermined to the other. A pair of cylindrical multi-winding coils that attach a second residual stress or plastic strain different from the residual stress or plastic strain and detect a change in permeability with respect to the rotational torque are opposed to each magnetostrictive film. And As a result, it is possible to provide a system capable of improving the temperature characteristics and achieving a high steering feeling and increasing the detection probability when a failure occurs.

  The torque detector according to claim 4 of the present invention applies a predetermined torque to one side with the axial center of the magnetostrictive film as a support point, and applies a predetermined torque in the opposite direction to the other. It is characterized by that.

  A torque detector according to a fifth aspect of the present invention is used in an electric power steering apparatus including an electric motor that applies assist torque corresponding to the rotational torque to the rotating shaft via a worm wheel. .

A rotating shaft to which a predetermined residual stress or plastic strain is applied; and a cylindrical multiple winding coil that surrounds the rotating shaft and detects a change in magnetic permeability with respect to the rotating torque input to the rotating shaft. By detecting the rotational torque input to the rotating shaft based on the detection value of the multiple winding coil,
(1) Since the rotating shaft is provided so as to surround the shaft, the change in the magnetic permeability for each rotation angle due to the influence of the distortion during the processing of the shaft material, the heat treatment, the variation in the external dimensions, and the like can be averaged.
(2) Further, by averaging the change in permeability for each rotation angle with respect to an axial displacement error, a large local change in permeability can be reduced.
As a result, it is possible to reduce the detection value from fluctuating with the rotation of the rotating shaft and from fluctuating with respect to the axial displacement error.
(3) Since an approximately 8-shaped exciting coil is not disposed in the housing, the strength of the housing is not reduced, and the detection accuracy during torque load can be increased.

Further, by using the torque detection device according to claim 1 for a steering torque detection device of an electric power steering device,
(1) Since fluctuations in the detected torque value with respect to the rotation angle can be reduced, fluctuations in the assist amount of the motor can also be reduced. As a result, it is possible to obtain a smooth steering feeling with good return characteristics, with no shift of the steering wheel center, little fluctuation in rotation, and good return characteristics.
(2) Noise associated with rotational fluctuation can be reduced. Further, since there is no need to perform special machining on the rotating shaft, neither the strength is reduced nor the processing cost is increased. This makes it possible to directly detect the steering shaft.
(3) Furthermore, since an approximately 8-shaped exciting coil is not disposed in the housing, the strength of the housing is not reduced, the steering rigidity can be increased, and the torque control of the electric motor can be stabilized. .

  Further, the magnetostrictive film is divided into two in the axial direction, and the predetermined residual stress or plastic strain having a positive sign is applied to one side, and the predetermined residual stress or plastic strain having a negative sign is applied to the other side. By attaching a pair of the multi-turn coils to each magnetostrictive film, the temperature characteristics can be improved and a high steering feeling can be achieved, and the detection probability at the time of failure can be increased. Can be provided.

  The magnetostrictive film is divided into two in the axial direction, and a change in permeability with respect to the rotational torque is detected by making a change in permeability of one magnetostrictive film different from a change in permeability of the other magnetostrictive film. By attaching a pair of coiled multi-turn coils to each magnetostrictive film, it is possible to improve the temperature characteristics and further increase the detection feeling when a failure occurs with a high steering feeling.

A step of forming a rotating shaft to which a predetermined stress or strain is applied, a step of forming a magnetostrictive film by plating the rotating shaft with a magnetic material in a state where the predetermined stress or strain is applied, and the rotating shaft. A step of applying a predetermined residual stress or plastic strain to the magnetostrictive film by releasing the predetermined stress or strain, and a cylinder for detecting a change in permeability with respect to a rotational torque of the rotating shaft on which the magnetostrictive film is formed Including a step of arranging a multi-turn coil in a shape so as to face the magnetostrictive film,
(1) It is possible to manufacture a torque detection device in which the detected value does not fluctuate with the rotation of the rotating shaft or fluctuates with respect to an axial displacement error.
(2) Since an approximately 8-shaped exciting coil is not disposed in the housing, a torque detecting device with high detection accuracy at torque load can be manufactured without reducing the strength of the housing.
(3) A rotating shaft having high torsional strength can be used.

  According to the present invention, the output hardly changes due to an axial displacement error or the like.

A first embodiment of a torque detection device according to the present invention will be described with reference to FIG.
As shown in FIG. 1, the torque detection device of the first embodiment includes an input shaft 1 that is a rotating shaft to which torque (torsional stress) is transmitted, and the input shaft 1 via bearings 3, 4, and 5. A casing 2 that is rotatably supported.
A worm wheel 7 integrally provided below the central portion of the input shaft 1 (inside the upper portion in the case portion 2b) and meshing with a worm gear 9 connected to a drive shaft of an electric motor 8 fixed to the upper outer peripheral side of the case portion 2b. When,
A helical pinion gear 1a provided below the input shaft 1 and meshing with the rack teeth 6a of the rack shaft 6;
A torque sensor 10 provided so as to surround a substantially central portion of the input shaft 1 and detecting a change in magnetic permeability with respect to a rotational torque input to the input shaft 1;
A control device 18 for controlling the electric motor 8 based on a detection value detected by the torque sensor 10;
The main part consists of

The input shaft 1 which is a rotating shaft is made of a magnetic material having a substantially cylindrical shape. A ferromagnetic material, which is an iron material, is used as the magnetic material. As other magnetic materials, for example, Ni material, SCM material (chromium-molybdenum steel) or the like can be used. As the magnetic material, a material containing a rare earth element may be used.
The input shaft 1 is preliminarily applied with residual stress or plastic strain. The reason for this will be described later.
The input shaft 1 is rotatably supported by three bearings 3, 4, and 5 inside the casing 2.
The bearing 4 is a four-point contact type ball bearing, and is a bearing that regulates axial displacement. The other bearings 3 and 5 are two-point contact ball bearings.
The upper part of the input shaft 1 protrudes from the upper end surface of the casing 2 to the outside.
A worm wheel 7 is provided integrally with the input shaft 1 below the central portion of the input shaft 1 (upper part in the case portion 2b). The worm wheel 7 transmits auxiliary power from the electric motor 8 to the input shaft 1 via a worm gear 9 provided on the drive shaft of the electric motor 8.
A helical pinion gear 1 a is provided at the lower part of the input shaft 1, and meshes with the rack teeth 6 a of the rack shaft 6.

  The casing 2 is formed of a housing 2a (upper part) and a case part 2b (lower part), and is a cover that supports the input shaft 1 rotatably in the axial direction via bearings 3, 4, and 5.

  The housing 2a is provided on the case portion 2b, and the upper end surface of the case portion 2b and the flange FL on the lower surface of the housing 2a are fixed. The housing 2a accommodates a detection circuit 17 formed of a torque sensor 10 and an output circuit that rectifies, smoothes, and amplifies the output obtained from the torque sensor 10 and then inputs the output circuit to the control device 18. . The room in which the output circuit is accommodated is a room that is separately partitioned outside the room in which the multiple winding coil 11 is fixed.

  The case portion 2b meshes with a worm gear 9 connected to the drive shaft of the electric motor 8, a worm wheel 7 meshed with the worm gear 9, and a helical pinion gear 1a provided below the input shaft 1. The rack teeth 6a of the rack shaft 6 are accommodated. An electric motor 8 is fixed on the outer peripheral side of the upper portion of the case portion 2b.

The torque sensor 10 is provided so as to surround the shaft at a substantially central portion of the input shaft 1.
The torque sensor 10 constitutes a part of a detection circuit 17 including the torque sensor 10 and an output circuit as shown in FIG. 3A, and when the torque is applied to the AC power supply 13 and the input shaft 1. A main part is formed from a cylindrical multiple winding coil 11 whose inductance changes in accordance with a change in magnetic permeability, a resistor 12 coupled in series with the multiple winding coil 11, and a connection wiring connecting them. .
As shown in FIG. 1, the multi-turn coil 11 is fitted in a magnetic circuit which is a space defined by combining a groove-type bobbin 11a and a back yoke 11b.
On the other hand, the output obtained by the multiple winding coil 11 of the torque sensor 10 is taken out from the wiring between the multiple winding coil 11 and the resistor 12 as shown in FIG. Is output as a DC voltage output V 0 proportional to the torque via an output circuit consisting of a smoothing circuit 15 and an amplifier circuit 16.

  The control device 18 is composed of, for example, a computer. When the DC voltage output V0 detected by the multiple winding coil 11 of the torque sensor 10 is input from the detection circuit 17, the residual stress or plastic strain previously applied to the input shaft 1 is provided. The torque acting on the actual rotating shaft is obtained based on the magnetic permeability corresponding to (reference value) and the output value (detected value) detected by the multi-turn coil 11, and the drive signal corresponding to this torque is sent to the electric motor 8. To reduce the torque of the rotating shaft.

  The worm wheel 7 is a gear that is provided integrally with the input shaft 1 between the bearing 3 and the bearing 4 and meshes with a worm gear 9 that is connected to a drive shaft of an electric motor 8 that is fixed to the upper outer periphery of the case portion 2b. It is. With this configuration, the rotational torque of the electric motor 8 can be boosted according to the reduction ratio and transmitted to the input shaft 1.

  The helical pinion gear 1 a is provided below the input shaft 1 and meshes with the rack teeth 6 a of the rack shaft 6.

Next, the operation of the torque detection device of the first embodiment configured as described above will be described with reference to FIGS. 1 and 3.
For example, a constant alternating voltage is applied from an AC power source 13 to a circuit in which a resistor 12 as shown in FIG. When a magnetic field is applied to the input shaft 1, the magnetic permeability of the input shaft 1 changes when torque is input to the input shaft 1, so that the self-inductance of the multiple winding coil 11 changes. As a result, an output current in which the amplitude of the sine wave of the alternating current is changed can be obtained. The output current is output as a DC voltage output V 0 via a rectifier circuit (diode) 14, a smoothing circuit 15, and an amplifier circuit 16. The DC voltage output V 0 is further input to the control device 18, and the control device 18 outputs a corresponding drive signal to the drive circuit of the electric motor 8. After determining the optimum assist torque from the data input to the drive circuit of the electric motor 8, the worm wheel meshes with the worm gear 9 attached to the drive shaft of the electric motor 8 and is provided integrally with the input shaft 1. 7 is rotated to reduce the torque required to rotate the input shaft 1.

As described above, when the torque detection device according to the present invention is used, the invention uses the ferromagnetic material that is an iron material for the input shaft that is the rotating shaft and pays attention to the magnetostriction characteristics (permeability) due to the inverse effect of the magnetostriction. Therefore, when tensile stress or compressive stress in the main stress direction is applied so that the input shaft, which is a ferromagnetic material, is torsionally deformed, the magnetization changes, but a predetermined residual stress or plastic strain is applied in advance. Thus, it can be taken out as a change in the magnetic field direction orthogonal to the multiple winding coil 11. As a result, the ratio of the influence on the detected values such as the distortion at the initial stage of the shaft material, the heat treatment, and the variation in the external dimensions is reduced.
In addition, even if the magnetic permeability changes depending on the rotation angle of the rotary shaft, the change in the magnetic permeability for each rotation angle can be averaged, and the change in the magnetic permeability for each rotation angle can also be averaged against an axial displacement error. This can reduce a large local change in the magnetic permeability.
Therefore, it is possible to reduce the fluctuation of the detection value with the rotation of the rotary shaft and the fluctuation of the detection value with respect to the axial displacement error.
Furthermore, since an approximately 8-shaped exciting coil is not disposed in the housing, the strength of the housing is not reduced. Therefore, the detection accuracy at the time of torque load can be increased.
Further, since it is not necessary to perform special machining on the input shaft, the strength of the shaft material is not lowered and the processing cost is not increased.
Further, since an approximately 8-shaped exciting coil is not disposed in the housing, the strength of the housing is not reduced.

Next, a specific example in which the torque detection device of the first embodiment is applied to a torque detection device for steering torque of an electric power steering device for a vehicle will be described.
The configuration in this case is different from the configuration of the first embodiment only in the following points.
1. The input shaft 1 is connected to a handle (not shown).
2. Tie rods (not shown) are provided at both ends of the rack shaft 6 that meshes with a helical pinion gear 1a provided at the lower part of the input shaft 1, and tires (not shown) are connected to the ends of the tie rods.
By doing so, the steering operation can be performed by changing the direction of the tire relative to the vehicle via the rack teeth 6a meshing with the helical pinion gear 1a of the input shaft 1 when the steering wheel of the vehicle is rotated.
The steering torque of the electric power steering device is detected by the torque detection device of the first embodiment, and the power of the steering device of the electric power steering device is assisted based on the electric output signal detected by the torque detection device. The motor is configured to drive and control, and the multiple winding coil is fixed to the housing of the casing that rotatably supports the rotating shaft, so that there is little fluctuation in rotation and good return characteristics when operating the handle. A smooth steering feeling can be obtained. In addition, noise accompanying rotational fluctuation can be reduced. In addition, since it is not necessary to perform special machining on the input shaft, the strength is not reduced and the machining cost is not increased. In addition, since an approximately 8-shaped exciting coil is not disposed in the housing, the strength of the housing is not reduced, the steering rigidity can be increased, and the torque control of the electric motor can be stabilized.

Here, a method for analyzing the output of the torque detection device according to the present invention will be described with reference to FIGS.
[How to create an analysis map]
Usually, the relationship between the magnetic permeability and torque of the magnetic material is axially symmetric as shown in FIG. 2A, and therefore it is possible to determine whether the torque is right torque or left torque from the absolute value of the magnetic permeability. Can not.
Therefore, as a result of intensive studies, the present inventor has found that when the residual stress or plastic strain is applied to the magnetic material, the relationship between the magnetic permeability and the torque is not axially symmetric, and the origin as shown in FIG. It has been found that it exhibits the characteristics of translation.
If the curve of the relationship between the magnetic permeability and the torque shown in FIG. 2 (b) is partially enlarged and used as shown in FIG. 2 (c), the direction of the torque is determined from the absolute value of the magnetic permeability. And understand the size. That is, in FIG. 2C, a value with a large magnetic permeability is a left torque, and a value with a small permeability is a right torque.

[Torque detection method]
A detection circuit that outputs the torque of the input shaft 1 as an electrical signal will be described with reference to FIGS. 3 (a) and 3 (b).
A. Detection Circuit Utilizing Change of Self-Inductance The detection circuit 17 shown in FIG. 3A includes a torque sensor 10 (see FIG. 1) and an output circuit. When a constant AC voltage is applied from an AC power source 13 to a circuit in which a multi-turn coil 11 and a resistor (constant) 12 are coupled in series, the permeability of the input shaft 1 is generated by the torque input to the input shaft 1 that is a magnetic material. The change in self-inductance (change in current amplitude) in the multi-turn coil 11 that occurs at this time is half-wave rectified or full-wave rectified by a rectifier circuit (diode) 14, and is further smoothed by a resistor and a capacitor. After the circuit 15 makes a direct current, it is amplified by an amplifier circuit and output as a direct current voltage output V0.
By configuring the detection circuit in this manner, the direction of torque and the value of torque can be detected from the voltage output value.
B. Detection Circuit Utilizing Mutual Inductance Detection Circuit 17 'in FIG. 3 (b) is provided with excitation coil L1 and detection coil L2 across input shaft 1 to determine the mutual inductance of excitation coil L1 and detection coil L2. The change (change in current amplitude) is detected by the detection coil L2, and the torque value is converted to the DC voltage value V0 through the rectifier circuit 14 ', smoothing circuit 15', and amplifier circuit 16 ', respectively, as in FIG. Output as ′. Note that the detection circuit 17 ′ in FIG. 3B can easily increase the output simply by increasing the number of turns of the detection coil L 2 as compared with the detection circuit 17 in FIG.
Either of the detection circuits may be used as required, but only the detection circuit using the change of the self-inductance will be described in the following description.

Next, a torque detection device according to a second embodiment will be described with reference to FIG.
The configuration of the torque detection device of the second embodiment is different from the configuration of the torque detection device of the first embodiment only in that the magnetostrictive film 19 is provided on the surface of the input shaft 1 that is the rotating shaft. To do.
The magnetostrictive film 19 is formed by, for example, plating a Ni—Fe alloy film on a part of the input shaft 1 that is a rotating shaft facing the multi-turn coil 11 over the entire circumference by a vapor phase plating method. The magnetostrictive film 19 is plated with a predetermined torque applied to the input shaft 1.
Accordingly, the magnetostrictive film 19 is given a torque from a stable rotating shaft and is given a residual stress and a plastic strain, so that a change in inductance of the multi-turn coil 11 fitted to the input shaft 1 is increased. The detection sensitivity can be stably improved without being affected by the shaft material.
When the torque detection device of the second embodiment is applied to the torque detection device of the steering torque of the electric power steering device of the vehicle, the gain of the electric power steering device can be reduced for the reasons described above, and torque control can be stabilized and noise can be reduced. The influence can be reduced and a high steering feeling can be obtained. In addition, since the shaft member can be used with a high strength that does not decrease (small) strength during processing, and the shaft portion of the steering can be directly detected, the size and weight can be reduced.

Next, a torque detection device according to a third embodiment will be described with reference to FIGS.
The configuration of the torque detection device of the third embodiment is different from the configuration of the torque detection device of the second embodiment in that the magnetostrictive film is divided into two and different predetermined residual stresses or plastic strains are applied to the magnetostrictive films 20a and 20b. Only the magnetostrictive film 20 will be described.
The magnetostrictive film 20 is formed by plating a magnetostrictive film, for example, a Ni-Fe alloy film, over the entire circumference on a part of the input shaft 1 which is a rotating shaft facing each of the multiple winding coils 21 and 22 by vapor phase plating. Is. The magnetostrictive film 20 has a first portion 20a plated with a predetermined torque applied to the input shaft 1 with a point A as a support point, and a predetermined torque applied in the opposite direction with the point A as a support point. And a second portion 20b plated in a state (or a portion plated without applying torque). By arranging in this way, the impedance of the first coil 21 is (1) (predetermined torque is loaded), and the impedance of the second coil 22 is (2) ′ (predetermined torque is loaded in the reverse direction). In such a case, characteristics as shown in FIG. On the other hand, when the impedance of the first coil 21 is (1) (a predetermined torque is loaded) and the impedance of the second coil 22 is (2) (no torque is loaded), as shown in FIG. Characteristics can be obtained. Each characteristic (1) and (2) or (2) ′ changes in the same way corresponding to the temperature change of the external environment (for example, when the temperature rises, it changes like a broken line). When the output is taken out by the dynamic amplification circuit, the difference value hardly changes. Further, when the output shows the impedance characteristics of (1) and (2) ′, an output of about twice is obtained. Since a large output can be obtained, controllability is improved.
Furthermore, failure diagnosis can be performed by comparing the two characteristics. For example, in FIG. 6A, the value of ((1) + (2) ′) / 2 is constant. Therefore, when a value different from this value is obtained, it can be determined that the torque sensor has failed. .
When the torque detection device of the third embodiment is applied to the torque detection device of the steering torque of the electric power steering device of the vehicle, the torque detection device is mounted in the engine room, and thus is exposed to an environment where the temperature change is large. For the above reasons, it is possible to obtain a smooth and stable steering feeling with little fluctuation in steering torque. In the unlikely event that a failure occurs, failure diagnosis can be performed, so that the system can be stopped reliably.

Next, a torque detection device according to a fourth embodiment will be described with reference to FIGS.
The configuration of the torque detection device of the fourth embodiment divides the magnetostrictive film into two sections from the configuration of the torque detection device of the third embodiment, and inputs two magnetostrictive films 23a, 23b having different permeability changes (different compositions). Only the magnetostrictive films 23a and 23b will be described because only the points plated on the shaft 1 with a predetermined torque applied thereto are different.
The magnetostrictive film 23 covers a part of the input shaft 1 facing each of the multiple coils 21 and 22 with a predetermined torque applied to the input shaft 1 over the entire circumference. It is plated by the phase plating method. At this time, the magnetostrictive film 23 includes, for example, a first portion 23a plated with 50% nickel and a second portion 23b plated with 60% nickel. By arranging in this way, it is possible to obtain characteristics when the impedance of the first coil 21 is (1) and the impedance of the second coil 22 is (2) as shown in FIG. When the output is taken out by the differential amplifier circuit, the respective characteristics (1) and (2) change similarly (for example, change as indicated by a broken line when the temperature rises) corresponding to the temperature change of the external environment. The difference value hardly changes. Also, failure diagnosis can be performed by comparing the two characteristics.
When the torque detection device of the fourth embodiment is applied to the torque detection device of the steering torque of the electric power steering device of the vehicle, the torque detection device is mounted in the engine room, so that it is exposed to an environment where the temperature change is large. For the reasons described above, it is possible to obtain a smooth and stable steering feeling with little fluctuation in steering torque. In the unlikely event that a failure occurs, failure diagnosis can be performed, so that the system can be stopped reliably.

Finally, a torque detection device and a manufacturing method thereof according to the present invention will be described.
The manufacturing method of the torque detector according to the second to fourth embodiments of the present invention is a manufacturing method including the following steps.
1. In the first step, a predetermined torque is applied to an input shaft (magnetic material) that is a rotating shaft to apply a predetermined stress or strain. The predetermined torque to be loaded is a value within elastic deformation with respect to the input shaft.
2. In the second step, the magnetostrictive film is formed by plating the input shaft with a magnetic material in a state where the predetermined stress or strain is applied.
3. In the third step, a predetermined residual stress or plastic strain is applied to the magnetostrictive film by releasing a predetermined stress or strain of the rotating shaft.
4). In the fourth step, a cylindrical multiple winding coil that detects a change in magnetic permeability with respect to the rotational torque of the input shaft on which the magnetostrictive film is formed is disposed so as to face the magnetostrictive film.
By including such a process, it is possible to manufacture a torque detection device in which the detected value does not fluctuate with the rotation of the input shaft or fluctuates with respect to an axial displacement error.
In addition, since an approximately 8-shaped exciting coil is not disposed in the housing, the strength of the housing is not reduced, and a torque detection device with high detection accuracy at torque load can be manufactured. In addition, a rotating shaft having a high torsional strength can be used.
The torque detection device manufacturing method according to the first embodiment of the present invention includes the first step and the fourth step. However, the predetermined torque in the first step is a torque that gives plastic strain to the input shaft. That is, the change in the magnetic permeability with respect to the rotational torque of the input shaft to which the plastic strain is applied without detecting the magnetostrictive film is detected by the multiple winding coil.

1 is a longitudinal sectional view showing a first embodiment of a torque detection device according to the present invention. It is a figure for demonstrating the creation method of the map for analysis used with the torque detection apparatus which concerns on this invention. (A) It is a figure which shows the structure of the detection circuit of the torque detection apparatus based on this invention. (B) It is a figure which shows the structure of the other detection circuit of the torque detection apparatus based on this invention. It is a longitudinal cross-sectional view which shows 2nd Embodiment of the torque detection apparatus which concerns on this invention. It is a longitudinal cross-sectional view which shows 3rd Embodiment of the torque detection apparatus which concerns on this invention. (A) It is a figure which shows the impedance characteristic obtained by 3rd Embodiment of the torque detection apparatus based on this invention. (B) It is a figure which shows the impedance characteristic obtained by other embodiment of 3rd Embodiment of the torque detection apparatus based on this invention. It is a longitudinal cross-sectional view which shows 4th Embodiment of the torque detection apparatus which concerns on this invention. It is a figure which shows the impedance characteristic obtained by 4th Embodiment of the torque detection apparatus which concerns on this invention. (A) It is a figure which shows the state which attached the conventional torque detection apparatus to the torque transmission shaft. (B) It is a figure which shows the exciting coil used with the conventional torque detection apparatus.

Explanation of symbols

1 Input shaft (rotary shaft)
2 Casing 2a Housing 2b Case part 3, 4, 5 Bearing 6 Rack shaft 6a Rack tooth 7 Worm wheel 8 Electric motor 9 Worm gear 10 Torque sensor 11, 21, 22 Multiple winding coil 11a Bobbin 11b Back yoke 12 Resistance 13 AC power supply 14 Rectification Circuit 15 Smoothing circuit 16 Amplifying circuit 17 Detection circuit 19, 20, 23 Magnetostrictive film

Claims (5)

A rotating shaft provided with a predetermined residual stress or plastic strain;
A pinion gear provided at an end of the rotating shaft and transmitting power to the rack shaft;
A coil for detecting a change in magnetic permeability with respect to rotational torque input to the rotational shaft;
A plurality of bearings that rotatably support the rotating shaft with respect to the casing;
Only one of the bearings is a bearing that restricts the axial displacement of the rotating shaft.   A magnetostrictive film having a predetermined width is provided around the rotating shaft in accordance with the rotational torque input to the rotating shaft, and a predetermined residual stress or plastic strain is applied to the magnetostrictive film. The torque detection device according to claim 1.   The magnetostrictive film is divided into two in the axial direction, and a first predetermined residual stress or plastic strain is applied to one, and a second residual having a direction different from that of the first predetermined residual stress or plastic strain is applied to the other. The torque detection according to claim 2, wherein a pair of cylindrical multi-turn coils that apply stress or plastic strain and detect a change in magnetic permeability with respect to the rotational torque are attached to each magnetostrictive film facing each other. apparatus.   4. The torque according to claim 3, wherein a predetermined torque is applied to one of the magnetostrictive films with the axial center as a supporting point, and a predetermined torque opposite to the one is applied to the other. Detection device. 5. The electric power steering apparatus according to claim 1, wherein the electric power steering apparatus includes an electric motor that applies an assist torque corresponding to the rotational torque to the rotating shaft via a worm wheel. The described torque detector.

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