JP2002098599A - Torque sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve the problem where, with the magnetic material constituting a magnetic circuit part comprising a soft magnetic material such as ferrite stainless sintered material, the variation in characteristics of the soft magnetic material degrades variation in an output torque at handle neutral, which prevents improving in reliability of a torque sensor. SOLUTION: There are provided a magnetic circuit part 27 where an inductance changes according to the change of a torque acting on an object, and a torque detection coil 26 which electrically detects the change of the inductance. The magnetic circuit part 27 comprises a soft magnetic material whose porosity is 3% or less while average crystal grain size is 80 μm or more.

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 an object, which acts between an input shaft connected to a steering wheel of a vehicle and an output shaft connected to a steering wheel. The present invention relates to a torque sensor suitable for detecting torque.

[0002]

2. Description of the Related Art As this type of torque sensor, for example, a torque sensor described in Japanese Patent Publication No. 21433/1995 is known.
The one described in this publication provides a first cylinder and a second cylinder made of a magnetic material on an input shaft and an output shaft connected via a torsion bar, respectively, and straddles these first and second cylinders. A cylinder made of a magnetic material having an inner flange around which a detection coil is wound is provided on the outer periphery, and the first and second cylinders and the cylinder constitute a magnetic circuit. And
The torque is detected based on a change in the facing area of the teeth due to the relative rotation between the input shaft and the output shaft.

[0003]

In many cases, the magnetic material constituting the magnetic circuit portion is made of a soft magnetic material. However, due to variations in the characteristics of the soft magnetic material, the torque sensor is not operated when the steering wheel is neutral. The output torque varies greatly, which hinders the improvement of the reliability of the torque sensor. Further, in order to solve the above-mentioned problem, it is necessary to perform an adjustment for suppressing the characteristic variation between individuals by means such as structurally changing the magnetic path length of the magnetic circuit unit. As described above, the conventional torque sensor is
It is necessary to adjust the output characteristics, which hinders improvement in reliability and reduction in manufacturing cost.

Accordingly, the present invention is to provide a torque sensor capable of eliminating the step of adjusting the output characteristics by reducing the variation in the magnetic characteristics of the soft magnetic material, thereby improving the reliability and reducing the manufacturing cost. With the goal.

[0005]

According to the present invention, in order to achieve the above object, according to the first aspect of the present invention, there is provided a magnetic circuit section in which an inductance changes in response to a change in torque acting on an object. A torque sensor comprising a coil for electrically detecting a change and detecting the torque based on an inductance obtained from an output of the coil, wherein a constituent material of the magnetic circuit portion is a soft magnetic material having a porosity of 3% or less. It was done.

In the invention according to claim 2, the soft magnetic material has an average crystal grain size of 80 μm or more.

[0007]

According to the first aspect of the present invention, since the porosity is reduced, the density variation due to the processing conditions of each part during processing of the magnetic circuit part is minimized, and the density change (the porosity of the Change) and magnetic annealing before and after processing hardly causes a difference in the compared magnetic properties.

According to the second aspect of the present invention, the size of the crystal grains is increased, so that the spin becomes easy to move. In addition to the reduction in the magnetic characteristic variation of the soft magnetic material according to the first aspect, Has the effect of improving the magnetic properties and reducing the porosity.

[0009]

As described above, according to the first aspect of the present invention, by reducing the porosity, the change in density (change in porosity) due to processing conditions is reduced, and the magnetic properties before and after processing are reduced. Since there is almost no difference in the magnetic properties compared after annealing, the variation in the magnetic properties of each soft magnetic material is suppressed, and the reliability of the torque sensor can be improved.

According to the second aspect of the present invention, the increase in the size of the crystal grains makes the spin easier to move, improves the magnetic characteristics, and reduces the porosity, thereby reducing the variation in the magnetic characteristics. In addition, the reliability of the torque sensor can be further improved.

[0011]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a sectional view of a power steering apparatus provided with a torque sensor 10, and FIG. 2 is a half sectional view of the torque sensor 10.

In FIGS. 1 and 2, a hollow input shaft 13 connected to a steering wheel (not shown) of a vehicle and an output shaft 15 having a pinion 14 are formed in the housing 11 of the power steering device. Each is rotatably supported on an axis. A rack 16 is attached to the pinion 14 on the output shaft 15.
And the rack 16 is connected to unillustrated steered wheels via a predetermined steering link mechanism. The rack 16 is provided with an axial thrust by a motor shown in the drawing to assist the steering force.

The torsion bar 1 is provided inside the input shaft 13.
7, one end of the torsion bar 17 is connected to the input shaft 13 by a pin 18, and the other end is
The output shaft 15 is spline-engaged. This allows
When torque is applied to the input shaft 13 by operating the handle, the torsion bar 17 is twisted, and relative rotation between the input shaft 13 and the output shaft 15 occurs.

A first sensor ring 21 made of a magnetic material is fixed concentrically to the output shaft 15 at the shaft end of the output shaft 15 on the input shaft 13 side. On the outer periphery of the input shaft 13, a second sensor ring 22 made of a magnetic material is opposed to the first sensor ring 21 with a slight gap in the axial direction via a sleeve 23 made of a non-magnetic material. The second sensor ring 22 is fitted and fixed integrally to the input shaft 13. First and second sensor ring 2
On the opposing surfaces of the first and second gears, tooth portions 21A and 22A having projections and notches formed alternately in the circumferential direction are formed, respectively, and the first rotation is performed by the relative rotation of the input shaft 13 and the output shaft 15.
When the second sensor rings 21 and 22 rotate relative to each other, the wrap amount of the protrusions of the tooth portions 21A and 22A changes.

In the housing 11, first and second
A third sensor ring 25 made of a magnetic material is attached so as to surround the sensor rings 21 and 22. Third
The sensor ring 25 includes a cylindrical portion 25A parallel to the first and second sensor rings 21 and 22, and a cylindrical portion 25A.
A on both sides of A, flange portions 25 extending in the radial direction so as to approach the outer circumferences of the first and second sensor rings 21 and 22.
B, 25C.

The outer circumferences of the first and second sensor rings 21 and 22 and the cylindrical portion 25 forming the third sensor ring 25
A torque detection coil 26 is housed in an annular space surrounded by the inner periphery of A and the flange portions 25B and 25C, and the torque detection coil 26 is fixed to the third sensor ring 25. Accordingly, a magnetic path is formed by the first and second sensor rings 21 and 22 and the third sensor ring 25 surrounding the torque detection coil 26.

Therefore, when relative rotation occurs between the input shaft 13 and the output shaft 15, the inductance changes due to the change in the amount of overlap between the tooth portions 21A and 22A, and the inductance changes according to the torque applied to the steering wheel. Signal is obtained.
The first and second sensor rings 21 and 22 and the third sensor ring 25 constitute a magnetic circuit unit 27.

The sensor rings 21, 22 and the third
Is made of a sintered ferritic stainless steel material (soft magnetic material) having a porosity of 0.5% and an average crystal grain size of 200 μm, and the variation of the inductance output from the torque detection coil 26 is 1. 5%.

It has been experimentally confirmed that the porosity of the ferritic stainless sintered material is effective in the range of 0 to 3% as shown in FIG. 4, and the variation range is 5% or less. It is. Further, as shown in FIG. 5, it has been experimentally confirmed that the average crystal grain size of the ferrite-based stainless sintered material has an effect on the variation in magnetic properties in a region of 80 μm or more as shown in FIG.

The torque detecting coil 26 is connected to an interface circuit (hereinafter, I / F) provided in the housing 11.
Circuit 30) and an I / F circuit 30
Is connected to a microcomputer (not shown) provided in the vehicle.

Next, the operation of the I / F circuit 30 will be described with reference to FIG.
This will be described with reference to FIG. The DC current supplied from the DC power supply 31 is filtered by a filter circuit 32 to remove excess harmonic components.
The DC current output from the input is input to generate a reference voltage. Subsequently, the oscillation circuit 34 generates a sine wave signal based on the reference voltage generated from the regulator circuit 33, and the sine wave signal is applied to the torque detection coil 26.
Then, a sine wave voltage proportional to the inductance of the torque detection coil 26 is generated at both ends of the torque detection coil 26. Subsequently, the AC component of the sine wave voltage is extracted by the DC cut circuit 35, and the detection circuit 36 extracts the amplitude of the extracted AC component and converts it into a signal having a DC voltage proportional to the extracted amplitude. I do.
The converted signal is input to the adding circuit 37.

The sine wave voltage generated at both ends of the torque detecting coil 26 is input to a temperature compensating circuit 38, and is converted into a temperature drift signal indicating the amount by which the inductance of the torque detecting coil 26 drifts under the influence of temperature. And
This temperature drift signal is input to the adding circuit 37.
Then, the addition circuit 37 extracts the difference between the signal output from the detection circuit 36 and the temperature drift signal output from the temperature compensation circuit 38, and converts the torque component signal of only the torque component in which the temperature drift component is canceled out into a scaling circuit. Output to 39.

Subsequently, the scaling circuit 39 converts the gain of the torque component signal, and the gain-converted torque component signal is amplified by the output amplifier circuit 40. Subsequently, the torque component signal amplified by the output amplifier circuit 40 is converted into a torque signal by the A / D conversion circuit 4.
1 and converted into a digital signal, and this digital signal is output to a microcomputer provided in the vehicle. Then, the microcomputer calculates an assist amount of the power steering device based on the magnitude of the input digital signal, outputs a drive signal corresponding to the calculated assist amount to a motor, and performs steering by rotating the motor. Assists the steering wheel torque applied to the steering wheel.

According to the above-described embodiment, the porosity of the sintered ferritic stainless steel constituting the magnetic circuit portion 27 is set to 0 to 3%, and the average crystal grain size is set to 80 μm or more. There is an effect that the variation is reduced and the reliability of the torque sensor 10 can be increased.

In the above embodiment, 1
Although the torque sensor 10 including one coil has been described, it is needless to say that the present invention is not particularly limited to such a configuration.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a power steering device including a torque sensor according to an embodiment of the present invention.

FIG. 2 is a half sectional view of a torque sensor in which a main part of FIG. 1 is enlarged.

FIG. 3 is an explanatory diagram showing an electric configuration of a torque sensor by blocks.

FIG. 4 is a diagram showing the relationship between the porosity of a soft magnetic material and the variation in magnetic properties.

FIG. 5 is a diagram showing a relationship between an average crystal grain size of a soft magnetic material and magnetic properties.

[Explanation of symbols]

 Reference Signs List 10 Torque sensor 11 Housing 13 Input shaft 15 Output shaft 17 Torsion bar 21, 22, 25 Sensor ring 26 Torque detection coil 27 Magnetic circuit

Claims (2)

[Claims] 1. A magnetic circuit part whose inductance changes in response to a change in torque acting on an object, and a torque detection coil for electrically detecting the change in inductance, and an inductance obtained from an output of the torque detection coil. Wherein the constituent material of the magnetic circuit portion is a soft magnetic material having a porosity of 3% or less. 2. The soft magnetic material has an average crystal grain size of 80 μm.
The torque sensor according to claim 1, wherein the torque sensor is at least m.