JPH11326080A - Torque sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To maintain a signal quality at a practicable level by determining the maximum surface roughness of an inner and outer surface of a cylindrical portion such that a specific expression is realized. SOLUTION: A magnetic circuit is formed by a magnetic flux induction case 9 and a cylindrical portion 21 and a magnetic flux S detecting a variation by an action of a torsion torque applied to an input portion 22 and an output portion 23 becomes a signal of a sensitive coil 13. However, since a transmittance of the cylindrical potion 21 is higher than that of an air forming a space between the magnetic flux induction case 9 and the cylindrical portion 21, a magnetic flux N passes on a surface of an inner surface of the cylindrical portion 21. Therefore, the surface state of the inner surface of the cylindrical portion 21 influences to the signal of the torsion torque. Here, if a conductivity of detecting portions (x), (y) is defined as (s), an alternating current excitation frequency is defined as (f) at the time of measuring a rotation torque, a relative magnetic permeability of the detecting portions (x), (y) at the frequency (f) is defined as (u) and a skin depth is defined as ξs , an expression I is realized. At this time, the maximum surface roughness of the inner and outer surface of the cylindrical portion 21 is determined when a thickness of the detecting portions (x), (y) is defined as T such that an expression II is realized. Thereby, a practicable level of a signal quality can be maintained without influenced by a material of the detecting portions and the surface roughness.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a torque sensor for detecting a torque acting on a rotating body by utilizing a change in magnetic permeability of a magnetic anisotropic portion formed on the rotating body such as an output shaft. It is about.

[0002]

2. Description of the Related Art Japanese Patent Laid-Open No.
What is described in -1136983 is known conventionally. FIG. 3 shows this conventional torque sensor. In this torque sensor, a rotating shaft 4 made of a ferromagnetic magnetostrictive material is rotatable by bearings 2 and 3 provided in a casing 1 made of aluminum or the like. Supported.

A pair of anisotropic parts x and y are formed on the rotating shaft 4, and these anisotropic parts x and y form a pair of annular convex parts 5 and 6 on the rotating shaft 4. In addition, a number of spiral slits 7 and 8 are formed in these annular convex portions 5 and 6. The slits 7 and 8 are approximately 4 with respect to the axis.
While maintaining the angle of 5 degrees, with the slits 7 and 8,
Their angles are opposite to each other.

Accordingly, when a torque acts on the rotating shaft 4, a compressive stress acts on one anisotropic portion x or y and a tensile stress acts on the other anisotropic portion y or x in accordance with the direction of rotation. Works. At this time, the magnetic permeability of one anisotropic part increases and the magnetic permeability of the other anisotropic part decreases according to the stress.

A magnetic flux guide case 9 made of a material having high magnetic permeability is provided between the casing 1 and the rotating shaft 4.
In the magnetic flux guide case 9, the exciting coils 10 and 11 are provided inside and the sensing coils 12 and 13 are provided outside. The exciting coil 10 and the sensing coil 12 correspond to one anisotropic part x, and the exciting coil 11 and the sensing coil 13 correspond to the other anisotropic part y.

When the torque is not acting on the rotating shaft 4, the stress in the anisotropic portions x and y is symmetric and equal, so that the magnetic permeability of the anisotropic portions x and y becomes equal. Therefore, when an AC voltage is applied to the exciting coils 10 and 11, the voltages induced in the sensing coils 12 and 13 are equal in magnitude. Therefore, no difference occurs between the induced voltages.

Further, when a torque acts on the rotating shaft 4, for example, the magnetic permeability of one anisotropic portion x increases and the magnetic permeability of the other anisotropic portion y decreases according to the direction of rotation. . Therefore, when an AC voltage is applied to the exciting coils 10 and 11, the voltage induced in the sensing coil 12 corresponding to one anisotropic part x is induced in the sensing coil 13 corresponding to the other anisotropic part y. Voltage. If the difference between the voltages induced in the sensing coils 12 and 13 is determined as described above, the direction and magnitude of the torque can be detected.

The voltage induced in the sensing coils 12 and 13 is proportional to the torsion angle of the rotating shaft 4. The torsion angle is proportional to the torsion torque, but the inclination of the straight line varies depending on the diameter of the rotating shaft 4 as shown in FIG. That is, if the rotating shaft 4 is thin, the torsion angle increases even with a slight torsion torque. Conversely, rotating shaft 4
Is large, the torsion angle does not become so large even if a large torsion torque acts.

As described above, since the voltage induced in the sensing coils 12 and 13 is proportional to the torsion angle, when the rotating shaft 4 needs to be thickened, the accuracy of detecting the torque deteriorates. In order to prevent the elastic change of the rotating shaft 4 from occurring even when a particularly large torque is generated,
The shaft diameter must be increased. However, as the thickness is increased, the accuracy of torque detection becomes worse. On the other hand, if the rotating shaft is made thinner in order to increase the accuracy of torque detection, the strength cannot be maintained.

As described above, in the conventional torque sensor, the strength of the rotating shaft must be sacrificed in order to increase the torque detection accuracy. On the other hand, there is a trade-off problem in that the detection accuracy must be sacrificed to maintain the strength of the rotating shaft. Therefore,
The present applicant has proposed a torque sensor having a configuration as described in Japanese Patent Application Laid-Open No. 9-21708.

4 to 6, the rotating body A functioning as the conventional rotating shaft 4 is constituted by separate members such as a cylindrical portion 21, an input portion 22, an output portion 23 and a stopper shaft 24. doing. The cylindrical portion 21 is provided with a pair of anisotropic portions x and y as in the conventional case. The input portion 22 is press-fitted into one end of the cylindrical portion 21 as described above, and the output portion 23 is press-fitted into multiple ends. Therefore, by rotating the input unit 22, the cylindrical unit 21 and the output unit 2 are rotated.
3 also rotates integrally, but in the process of transmitting the rotational force from the input section 22 to the output section 23, the cylindrical section 21 is twisted.

The input unit 22 has a stopper shaft 24
Is press-fitted so that the stopper shaft 24 rotates integrally with the input section 22.

A hole 25 in the diametrical direction (which may be oval) is formed in the end face of the output section 23 which is press-fitted into the cylindrical section 21.
Is formed. An insertion portion 26 is formed on the stopper shaft 24 on the side opposite to the side pressed into the input portion 22, and the cross-sectional shape of the insertion portion 26 is as shown in FIG.

That is, the central portion of the side surface of the insertion portion 26 is projected in a mountain shape, and both sides of the mountain-shaped ridges 26a, 26b are tapered portions 26c, 26d, 26e, 26f. The thickness between the ridges 26a and 26b exactly matches the width of the hole 25, and when the stopper shaft 24 is in the neutral position, each tapered portion 2
6c to 26f all have a space 27 between the wall and the hole 25.
To ensure that. In addition, the space 27 constitutes a clearance of the present invention.

The input unit 22 and the output unit 23 are
It is rotatably supported by bearings 2 and 3 provided on the conventional casing 1. The casing 1 and its internal structure are the same as in the above-mentioned Japanese Patent Application Laid-Open No. Hei 7-113983, so that the details thereof will be omitted.

Next, the operation of this structure will be described. When a rotational torque acts on the input portion 22, the cylindrical portion 21
And the stopper shaft 24 rotates. At this time, the input unit 22
The torsion torque acts on the cylindrical portion 21 in accordance with the torque input to the cylinder and the load on the output portion 23 side. The magnitude of the voltage induced in the sensing coils 12 and 13 is determined according to the torsional torque applied to the cylindrical portion 21.

When the rotation torque acts on the input section 22 as described above, the stopper shaft 24 also rotates. However, as long as the rotation angle does not exceed the space 27, no torsional torque acts on the stopper shaft 24. However, after one of the tapered portions formed on the insertion portion 26 of the stopper shaft 24 hits the wall surface of the hole 25, torsional torque also acts on the stopper shaft 24.

For example, when the steering torque is detected by a power steering device of an automobile or the like, the cylinder 2
It is sufficient to set the torque detection range only while the torsional torque is acting on only one. This is because there is a limit to the maximum assisting force of the power steering device, and it is sufficient to maximize the assisting force for a detected torque equal to or greater than a certain value.

In such a configuration, within the range in which the required torque is detected, the torsion torque acts only on the cylindrical portion 21 to increase the rate of change of the torsion angle with respect to the torsion torque. The greater the rate of change of the torsion angle, the greater the rate of change of the induced voltage generated in proportion thereto, so that the torque detection accuracy is improved. As an example, in a power steering device of an automobile, the rigidity of the torque detection range is required for the rotating body A. However, in this configuration, the stiffness greater than the torque detection range is a combination of the stiffness of the cylindrical portion 21 and the stopper shaft 24, so that the strength is sufficiently maintained.

In other words, the rotating body A of the present invention can cope with accurate torque detection while maintaining sufficient strength, and can be said to solve the conventional trade-off problem at the same time.

[0021]

However, according to the above-described structure, the conventional inconsistent problems can be solved, but the torque measurement results are affected by the influence of the material and surface roughness of the detecting portion. There was a problem that noise increased. SUMMARY OF THE INVENTION An object of the present invention is to provide a torque sensor having a signal quality that can be put to practical use.

[0022]

According to a first aspect of the present invention, there is provided a sensor comprising: a casing; a rotating body rotatably supported by the casing; and a magnetically anisotropic or shape anisotropic member formed on the rotating body and having plane symmetry. A pair of detection units having a characteristic, an excitation coil and a sensing coil provided around the detection unit, and when a rotational torque is applied to the rotating body, the magnetic permeability of the detection unit changes and responds to the change. A torque sensor that detects a mutual inductance change with the sensing coil, wherein the rotating body includes a detection unit provided with a detection unit, an input unit provided at one end of the cylinder unit, and an output unit provided at the other end. A rotation shaft is provided in one of the stopper shaft and the input portion, or the stopper shaft and the output, and the stopper shaft and the input portion are provided within the range of the rotation clearance portion. Or the output section In the torque sensor configured to rotate, the conductivity of the detection unit is ρ, the AC excitation frequency of the coil at the time of measuring the rotation torque is f, the relative permeability of the detection unit at the AC excitation frequency f is μ, and the skin depth is μ. and it is referred to as δ _S is,

[0023]

(Equation 5)

If the thickness of the detecting portion is T and the maximum surface roughness of the outer and inner surfaces of the cylindrical portion is R, the maximum surface roughness R is

[0025]

(Equation 6)

[0026]

A torque sensor according to a second aspect of the present invention has a casing, a rotating body rotatably supported by the casing, and a plane-symmetric magnetic anisotropy or shape anisotropy formed on the rotating body. A pair of detection units and a coil provided around the detection unit are provided, and when a rotational torque is applied to the rotating body, the magnetic permeability of the detection unit changes, and a change in self-inductance according to the change is detected by the coil. A torque sensor, wherein the rotating body is provided with a detection section, an input section provided at one end of the cylinder section, an output section provided at the other end,
A rotation shaft is provided in one of the stopper shaft and the input portion, or the stopper shaft and the output, and a rotation clearance portion is provided within a range of the rotation clearance portion.
In a torque sensor in which a stopper shaft and an input unit or an output unit are relatively rotated, the conductivity of the detection unit is ρ, the AC excitation frequency of the coil at the time of measuring the rotation torque is f, and the AC excitation frequency is f. the relative magnetic permeability of the detecting portion mu, when the skin depth and [delta] _S,

[0028]

(Equation 7)

If the thickness of the detecting portion is T and the maximum surface roughness of the outer and inner surfaces of the cylindrical portion is R, the maximum surface roughness R is

[0030]

(Equation 8)

[0031]

[0032]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, an embodiment in which the present invention is embodied in a torque sensor of a power steering device of an automobile will be described.

In a torque sensor of the type according to the invention,
The reverse magnetostriction phenomenon is used, which is (stress distortion)-(magnetic property change) phenomenon.However, regarding the method of detecting the stress of the magnetostrictive material detecting section, magnetic flux is efficiently applied to the surface of the base material. In order to flush, a "skin effect" is often used.

The "skin effect" means that if the medium is a perfect conductor, the magnetic flux cannot penetrate into the inside, but the closer the medium is from the perfect conductor to the non-conductor, the more the magnetic flux penetrates inside from the surface of the medium. Means more. Assuming that the magnetic flux density on the surface of the medium is B ₀ and the skin depth is δ _S , (the total amount of magnetic flux up to the depth of semi-infinity of the medium) = δ _S · B ₀ (1) depth [delta] _S is shown as follows.

[0035]

(Equation 9)
・ ・ ・ ・ ・ (2)

Here, f indicates the excitation frequency (Hz), μ indicates the magnetic permeability of the medium, and ρ indicates the conductivity of the medium.

It is known that the magnetic flux density B _Y decreases exponentially with the depth t from the surface of the medium, and B _Y = B ₀ · exp (−t / δ _S )・ ・ (3)

FIG. 1 is a diagram showing the flow of magnetic flux in a typical embodiment of the present invention. In the drawing, S and N show the flow of the magnetic flux, and now the excitation coil 11 and the sensing coil 13 on one side are shown. Only, and other parts are the same as those in FIG. 3 shown in the conventional example, so that illustration and description are omitted. A magnetic circuit is formed by the magnetic flux induction case 9 and the cylindrical portion 21, and a magnetic flux S for detecting the change is generated by the action of the torsional torque applied to the input portion 22 and the output portion 23, and the sensing coil 13.
Signal. However, since the magnetic permeability of the cylindrical portion 21 is higher than the air that forms the gap between the magnetic flux guide case 9 and the cylindrical portion 21 and the magnetic flux easily flows on the medium surface as described above, the inner surface of the cylindrical portion 21 is removed. A passing magnetic flux N exists.
Therefore, the surface condition of the inner surface of the cylindrical portion 21 also affects the signal quality of the torsional torque. If the thickness of the cylindrical portion 21 is T, because to penetrate flux T / 2, the magnetic flux amount (.mu.H) _S is
From equation (3)

[0039]

[Equation 10]
... (4)

When the maximum surface roughness of the outer surface and the inner surface of the cylindrical portion 21 is R, the amount of magnetic flux (μ
H) _N is

[0041]

[Equation 11]
... (5)

The amount of magnetic flux in equation (4) is considered to be the contribution of the torque sensor signal, the amount of magnetic flux wrapping around the inner surface of the cylindrical portion 21 is considered to be about 1/2 of the outer surface, and the formula (5) is considered in consideration of noise. and, its SN ratio S _N,

[0043]

[Equation 12]
... (6)

It is considered practical when S _N ≥40 [dB].

[0045]

[Equation 13]
... (7)

This is organized

[0047]

[Equation 14]
... (8)

As an example, permalloy (N
When T = 4 [mm], μ = 5000 (where μ ₀ = 4π × 10 ⁻⁷ [H / m] ρ = 0.958 [Ω · m] f = 50 [KH _Z ] Δ _S = 2.424 [mm] = 2.424 × 10
^-3 [m] At this time, assuming that R = 0.0274 [mm] and the maximum surface roughness R _MAX ≦ 27.4 [μm] from the equation (8), S _N
≧ 40 [dB], indicating that the signal quality of the torque sensor of this embodiment is improved. The only difference is.

[0049]

According to the first and second aspects of the present invention, the signal quality of the torque sensor can be maintained at a practical level.

FIG. 2 shows a second embodiment using the coils 10 'and 11' having both excitation and sensing. In this case, the only difference is that the self-inductance change is used for signal detection.

[0051]

[Brief description of the drawings]

FIG. 1 is a partial sectional view of a rotating body of the present invention.

FIG. 2 is a sectional view of a torque sensor.

FIG. 3 is a sectional view of a conventional torque sensor.

FIG. 4 is a sectional view of a rotating body having a conventional structure.

FIG. 5 is a sectional view taken along line BB of FIG. 4;

FIG. 6 is a graph showing a relationship between a torsion angle and a torsion torque of a rotating body.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Casing A Rotating body X, Y detection part 10 Exciting coil 12 Sensing coil 21 Tube part 22 Input part 23 Output part 24 Stopper shaft 27 Rotation clearance part

Claims (2)

[Claims] A casing, a rotating body rotatably supported by the casing, and a pair of detecting units formed on the rotating body and having plane-symmetric magnetic anisotropy or shape anisotropy;
An exciting coil and a sensing coil provided around the detecting unit are provided, and when a rotating torque is applied to the rotating body, the magnetic permeability of the detecting unit changes, and a mutual inductance change corresponding to the change is detected by the sensing coil. A torque sensor, wherein the rotating body includes a cylinder provided with a detection unit, an input unit provided at one end of the cylinder, an output unit provided at the other end, and a stopper shaft located in the cylinder. A rotation clearance portion is provided on one of the stopper shaft and the input portion or between the stopper shaft and the output portion so that the stopper shaft and the input portion or the output portion rotate relative to each other within the range of the rotation clearance portion. In the torque sensor, the conductivity of the detection unit is ρ, the AC excitation frequency of the coil at the time of measuring the rotational torque is f, the relative permeability of the detection unit at the AC excitation frequency f is μ, and the skin depth is δ. and _S And that, [number 1] When the thickness of the detection unit is T and the maximum surface roughness of the outer surface and the inner surface of the cylindrical portion is R, the maximum surface roughness R is given by: A torque sensor characterized by the following. 2. A casing, a rotating body rotatably supported by the casing, and a pair of detecting units formed on the rotating body and having plane-symmetric magnetic anisotropy or shape anisotropy;
A coil provided around the detection unit is provided, and when a rotation torque is applied to the rotating body, the magnetic permeability of the detection unit changes,
A torque sensor for detecting a change in self-inductance according to the change with the coil, wherein the rotating body has a cylinder provided with a detection section, an input section provided at one end of the cylinder section, and an output section provided at the other end. And a stopper shaft located in the cylindrical portion. A rotational clearance is provided in one of the stopper shaft and the input portion, or one of the stopper shaft and the output. , The input unit or the output unit is configured to rotate relative to each other, wherein the conductivity of the detection unit is ρ, the AC excitation frequency of the coil at the time of measuring the rotational torque is f, and the detection unit at the AC excitation frequency f Let μ be the relative magnetic permeability and δ _{S be the} skin depth of Where T is the thickness of the detection portion and R is the maximum surface roughness of the outer and inner surfaces of the cylindrical portion, the maximum surface roughness R is given by: A torque sensor characterized by the following.