JPH08114518A - Torque sensor - Google Patents

Abstract

PURPOSE: To measure highly accurate torque with simple constitution. CONSTITUTION: Thin two cylinder members 4 and 5 composed of a conductive and nonmagnetic material are coaxially arranged in a condition of being relatively rotatably fitted together so as to surround a large diameter part 1A formed on an input shaft 1 composed of a magnetic material, and the cylinder member 4 is integrally formed in the rotational direction with the input shaft 1, and the cylinder member 5 is integrally formed in the rotational direction with an output shaft 2. Windows 4a, 4b, 5a and 5b are formed in the cylinder members 4 and 5 so that a superposed condition changes according to a relative rotation position of these, and a part in which the windows 4a and 5a of the cylinder members 4 and 5 are formed, is surrounded with a coil 10, and a part in which the windows 4b and 5b are formed, is surrounded with a coil 11, and self-induction electromotive force of these coils 10 and 11 is measured, and torque is found on the basis of its result.

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 generated on a rotary shaft, and more particularly to a torque sensor having a simple structure to enhance detection sensitivity.

[0002]

2. Description of the Related Art A conventional torque sensor is disclosed, for example, in FIG. 11 of Japanese Patent Application Laid-Open No. 57-190240. This conventional torque sensor has an input coaxially rotatably arranged. The overlapped portion of the shaft and the output shaft is surrounded by a relatively short cylindrical member made of aluminum, and the cylindrical member is advanced and retracted in the axial direction according to the relative displacement between the input shaft and the output shaft. A coil is arranged around the cylindrical member, and the self-induced electromotive force induced in the coil is measured, and the relative rotational displacement (torque) between the input shaft and the output shaft is detected based on the result. I was trying to do it. That is, when the cylindrical member moves back and forth in the axial direction, the self-inductance of the coil changes, so that the torque generated in the input shaft and the output shaft can be detected based on the self-induced electromotive force of the coil.

[0003]

However, the above-mentioned conventional torque sensor requires a mechanism for converting the relative rotational displacement between the first and second rotary shafts into the axial displacement of the cylindrical member. Therefore, there is a problem that the structure is complicated and reliability is reduced accordingly. Moreover, the self-inductance of the coil cannot be changed sharply only by displacing the aluminum cylindrical member.
Therefore, in order to increase the sensor sensitivity, for example, it is necessary to increase the number of windings of the coil, but this has a drawback that the size of the device is increased.

The present invention has been made by paying attention to the unsolved problems of the prior art as described above, and an object thereof is to provide a torque sensor having a simple structure and capable of enhancing the detection sensitivity. I am trying.

[0005]

To achieve the above object, in a torque sensor according to the present invention, first and second cylindrical members made of a conductive and non-magnetic material are coaxially rotatably arranged. The first that is fitted and is coaxially arranged
And a second rotary shaft are connected via a torsion bar, the first and second cylindrical members and the first and second rotary shafts are arranged coaxially, and the first cylindrical member and the A first rotating shaft is integrally formed in the rotating direction, the second cylindrical member and the second rotating shaft are integrally formed in the rotating direction, and the first and second cylindrical members are respectively rotated relative to each other. A window is formed so that the degree of overlap changes depending on the position, and a member made of a magnetic material is arranged in a space inside the portion of the first and second cylindrical members in which the window is formed, and A coil is arranged so as to surround the portion of the first and second cylindrical members in which the window is formed, and an electromotive force measuring means for inducing an electromotive force in the coil to measure the electromotive force is provided. Generated on the first and second rotating shafts based on the measurement result of the power measuring means. It was to detect the torque that.

[0006]

For example, if the first rotary shaft is used as the input shaft and the second rotary shaft is used as the output shaft, torque is transmitted from the first rotary shaft to the second rotary shaft through the torsion bar. Relative rotation occurs between the first rotating shaft and the second rotating shaft with the torsion of the torsion bar. Then, since relative rotation also occurs between the first and second cylindrical members, the degree of overlap of the windows formed in those cylindrical members changes.

If the overlapping areas of the windows of the first and second cylindrical members are small, the outer peripheral surfaces of the members made of magnetic material disposed in the space inside the first and second cylindrical members are compared. It is equivalent to covering a large part with a material made of a conductive and non-magnetic material. On the contrary, if the overlapping area of the windows is large, it is equivalent to covering a relatively small portion of the outer peripheral surface of the member made of the magnetic material with the material made of the conductive and non-magnetic material.

Here, the non-magnetic material in the present invention means a paramagnetic material and a part of diamagnetic material, and the magnetic material means a ferromagnetic material. The magnetic permeability of the non-magnetic material is about the same as that of air, which is smaller than the magnetic permeability of the magnetic body. Also, when magnetic flux is linked to a conductor, an "eddy current" occurs so as to prevent the magnetic flux from changing, and this causes a magnetic field, so that the magnetic flux does not evenly pass through the substance and concentrates on the skin. The skin effect appears. Therefore,
The region made of a conductive and non-magnetic material has a property that it is harder for magnetic flux to pass therethrough than air.

Therefore, as described above, when the area covered with the conductive and non-magnetic material on the outer peripheral surface of the member made of a magnetic material changes due to the change in the overlapping degree of the windows, the self-inductance of the coil, The mutual inductance has a large difference in easiness of passing magnetic flux between the magnetic material and the conductive and non-magnetic material, so that the mutual inductance sharply changes in accordance with relative rotation between the first and second cylindrical members. To do.

Then, the induced electromotive force of the coil is measured by the electromotive force measuring means. Since the self-inductance and the mutual inductance of the coil change according to the relative rotation between the first and second cylindrical members, Based on the measurement result, the torque generated on the first and second rotating shafts is detected.

[0011]

Embodiments of the present invention will be described below with reference to the drawings. 1 to 6 are views showing a first embodiment of the present invention, in which the torque sensor according to the present invention is applied to an electric power steering device for a vehicle. First, the structure will be described. As shown in FIG. 1, which is a sectional view of a part of a steering system of a vehicle, a torsion bar 3 is provided between an input shaft 1 and an output shaft 2 which are coaxially and rotatably arranged. It is connected. The input shaft 1 and the output shaft 2 are made of a magnetic material such as iron.

A steering wheel is integrally mounted in the rotational direction on the right end side of the input shaft 1 (not shown) in FIG. 1, and a known rack and pinion is mounted on the left end side of the output shaft 2 (not shown) in FIG. The pinion shaft which comprises a steering system is connected. Therefore, the steering force generated by the operator steering the steering wheel is transmitted through the input shaft 1, the torsion bar 3, the output shaft 2 and the rack and pinion type steering device.
It is transmitted to the steered wheels (not shown).

On the end surface of the output shaft 2 on the input shaft 1 side, a groove 2 extending further in the radial direction from the insertion portion of the torsion bar 3 is formed.
a is formed, and the convex portion 1a formed on the end surface of the input shaft 1 on the output shaft 2 side is inserted into the groove 2a. However, the width (circumferential dimension) of the groove 2a is slightly larger than the width of the convex portion 1a, and as a result, the width of the groove 2a is not less than a predetermined range (for example, about ± 5 degrees) between the input shaft 1 and the output shaft 2. Relative rotation is prevented.

The rotating force of an electric motor (not shown) is transmitted to the output shaft 2 via, for example, a worm gear. That is, by appropriately controlling the direction and magnitude of the drive current to the electric motor, the steering assist torque of any direction and magnitude is applied to the output shaft 2. On the other hand, a large diameter portion 1A coaxial with the input shaft 1 is formed on the outer peripheral surface of the input shaft 1 in the vicinity of the output shaft 2 and surrounds the outer peripheral surface of the large diameter portion 1A. Therefore, two thin cylindrical members 4 and 5 are arranged.

That is, the cylindrical members 4 and 5 are made of a conductive and non-magnetic material (for example, aluminum), and the cylindrical member 5 is inserted into the cylindrical member 4 so as to be coaxially rotatable relative to each other. It is fitted. A small diameter portion 4A is formed on the inner surface of the right end of the cylindrical member 4 in FIG. 1, and the small diameter portion 4A is fitted onto the input shaft 1. Thereby, the cylindrical member 4 is integrated with the input shaft 1 in the rotation direction. A small-diameter portion 5A is formed on the inner surface of the left end of the cylindrical member 5 in FIG. 1, and the small-diameter portion 5A is fitted onto the output shaft 2. Thereby, the cylindrical member 5 is integrated with the output shaft 2 in the rotational direction.

Further, among the thin portions surrounding the large diameter portion 1A of the cylindrical member 4, on the side close to the small diameter portion 4A, a plurality of rectangular shapes (six in this embodiment) are equally spaced in the circumferential direction. , 4a are formed, and a plurality of rectangles (same shape as the window 4a) are equally spaced in the circumferential direction on the side close to the small diameter portion 5A so that the phases of the windows 4a ,. (In this embodiment, six windows) 4b, ..., 4b are formed.

More specifically, the windows 4a, ..., 4a are formed by dividing the circumferential surface of the cylindrical member 4 into 12 equal parts in the circumferential direction, and opening the regions corresponding to the 12 equal parts in a rectangular shape. The windows 4b, ..., 4b are formed by opening portions corresponding to the unopened portions between the windows 4a ,. On the other hand, in the thin portion surrounding the large diameter portion 1A of the cylindrical member 5, inside the portion where the windows 4a, ..., 4a are formed, a rectangle (same shape as the window 4a) is equally spaced in the circumferential direction. , 5a are formed, and windows 4b, ..., 4b are formed (six in this embodiment).
, 5a, and a plurality of rectangular windows (same shape as the window 5a) (six in this embodiment) 5b, ... , 5b are formed.

However, when relative rotation does not occur between the input shaft 1 and the output shaft 2 (when the steering torque is zero), it is a sectional view of the cylindrical members 4 and 5 taken along the line AA of FIG. As shown in FIG. 2, the cylindrical members 4 and 5 are aligned and fixed to the input shaft 1 or the output shaft 2 so that the windows 4a and 5a overlap each other by half. Therefore, FIG.
As shown in FIG. 3, which is a cross-sectional view of the cylindrical members 4 and 5 taken along the line BB, when the steering torque is zero, the windows 4b and 5b also overlap each other by half, but between the windows 4a and 4b. Are 180 degrees out of phase, so windows 4a and 5a
2 and FIG. 3 and the front view of the input shaft 1 and the output shaft 2 with the cylindrical members 4 and 5 fixed as shown in FIG. 4 and the overlapping state of the windows 4b and 5b. And, it is reversed in the circumferential direction.

The cylindrical members 4 and 5 are surrounded by a bobbin 9 around which coils 10 and 11 of the same standard are wound. That is, the coils 10 and 11 are arranged coaxially with the cylindrical members 4 and 5, and the coil 10 has the windows 4a,
, 4a is wound around the bobbin 9 so as to surround the portion where the windows 4b are formed, and the coil 11 is wound around the bobbin 9 so as to surround the portion where the windows 4b ,.

The coils 10 and 11 are connected to a motor control circuit housed in a sensor case (not shown).
The motor control circuit includes, for example, as shown in FIG. 5, an oscillating unit 21 that supplies an alternating current having a predetermined frequency to the coils 10 and 11.
A rectifying / smoothing circuit 22 for rectifying and smoothing the self-induced electromotive force of the coil 10 and outputting the rectified / smoothing circuit 23 for rectifying and smoothing the self-induced electromotive force of the coil 11 and outputting
And differential amplifiers 24A and 24B for amplifying and outputting the difference between the output of the rectifying / smoothing circuit 22 and the output of the rectifying / smoothing circuit 23.
A noise removal filter 25A for removing an external noise component included in the output of the differential amplifier 24A, a noise removal filter 25B for removing an external noise component included in the output of the differential amplifier 24B, and those noises. Steering generated in the steering system by calculating the direction and magnitude of the relative rotational displacement of the cylindrical members 4 and 5 based on, for example, the average value of the outputs of the removal filters 25A and 25B and multiplying the result by, for example, a predetermined proportional constant. Torque calculation unit 26 for obtaining torque
And a drive current I such that a steering assist torque for reducing the steering torque is generated based on the calculation result of the torque calculation unit 26.
Is provided to the electric motor.

Next, the operation of this embodiment will be described. Now, assuming that the steering system is in a straight traveling state and the steering torque is zero, relative rotation does not occur between the input shaft 1 and the output shaft 2. Therefore, the cylindrical member 4 rotating integrally with the input shaft 1,
No relative rotation occurs between the output shaft 2 and the cylindrical member 5 that rotates integrally.

On the other hand, when the steering wheel is steered to generate a rotational force on the input shaft 1, the rotational force is transmitted to the output shaft 2 via the torsion bar 3. At this time, the output shaft 2 is provided with a frictional force between the steered wheels and the road surface and a resistance force corresponding to the frictional force such as the meshing of gears of the rack-and-pinion steering device configured on the left end side (not shown) of the output shaft 2. Therefore, the torsion bar 3 is twisted between the input shaft 1 and the output shaft 2 so that relative rotation occurs in which the output shaft 2 is delayed, and relative rotation also occurs between the cylindrical members 4 and 5.

Here, for example, when the right steering torque (steering torque generated during steering in the right rotation direction) is generated, the overlapping area of the windows 4a and 5a becomes larger than that when the steering torque is zero, and the windows 4b and 5b are larger. The overlapping area becomes smaller. On the contrary, when the left and right steering torque (steering torque generated in the steering in the left rotation direction) is generated, the overlapping area of the windows 4a and 5a is smaller than that when the steering torque is zero, whereas the overlapping of the windows 4b and 5b is smaller. The area is large.

Then, windows 4a and 5a, windows 4b and 5b
The overlapped portion exposes the surface of the large-diameter portion 1A made of a magnetic material and disposed inside thereof. In other words, the portion of the outer peripheral surface of the large-diameter portion 1A covered with the cylindrical members 4 and 5 made of a conductive and non-magnetic material changes according to the steering torque. When the right steering torque is generated, the exposed region of the outer peripheral surface of the large diameter portion 1A increases inside the coil 10 and the exposed region of the outer peripheral surface inside the coil 11 decreases as the steering torque in that direction increases. Conversely, when the left steering torque is generated,
As the steering torque in that direction increases, the coil 1
On the inside of 0, the exposed area of the outer peripheral surface of the large diameter portion 1A decreases,
Inside the coil 11, the exposed area of its outer peripheral surface increases.

Then, since the large-diameter portion 1A has a property of allowing magnetic flux to pass through more easily than the cylindrical members 4 and 5, the self-inductance of the coil 10 increases and the self-inductance of the coil 11 increases when the right steering torque is generated. Decrease,
The self-induced electromotive force of the coil 10 becomes large, and the coil 11
Self-induced electromotive force becomes smaller. On the contrary, when the left steering torque is generated, the self-inductance of the coil 10 decreases and the self-inductance of the coil 11 increases, so that the self-induced electromotive force of the coil 10 decreases and the self-induced electromotive force of the coil 11 increases.

Therefore, the outputs of the differential amplifiers 24A and 24B for obtaining the difference between the self-induced electromotive forces of the coils 10 and 11 change linearly according to the direction and magnitude of the steering torque, as shown in FIG. . Further, since the difference between the rectifying / smoothing circuits 22 and 23 is obtained in the differential amplifiers 24A and 24B, the change in the self-inductance due to the temperature or the like is canceled.

Then, the torque calculation unit 26 calculates the average value of the outputs of the differential amplifiers 24A, 24B supplied through the noise removal filters 25A, 25B, and multiplies the average value by a predetermined proportional constant, for steering. The torque is obtained and the result is supplied to the motor drive unit 27. The motor drive unit 27 is
A drive current I according to the direction and magnitude of the steering torque is supplied to the electric motor.

Then, a rotating force is generated in the electric motor according to the direction and magnitude of the steering torque generated in the steering system, and the rotating force is transmitted to the output shaft 2 via the worm gear or the like. Since the steering assist torque is applied to the output shaft 2, the steering torque is reduced and the burden on the operator is reduced. When the cylindrical members 4 and 5 made of a conductive and non-magnetic material interlink with the alternating magnetic field, an eddy current is generated to make it difficult for magnetic flux to pass therethrough. It has the property. On the other hand, the large-diameter portion 1A close to the inner peripheral surfaces of the cylindrical members 4 and 5 is more likely to pass magnetic flux (easier to pass than air). Therefore, since the change of the exposed area of the outer peripheral surface of the large diameter portion 1A causes the self-inductance of the coils 10 and 11 to change abruptly, the outputs of the differential amplifiers 24A and 24B can be made abrupt and the sensor sensitivity can be increased. it can. On the contrary, if the sensor sensitivity is the same as the conventional one, the number of turns of the coils 10 and 11 may be reduced and the coil 1
0, 11 can be miniaturized.

The magnetic flux passing through the cylindrical members 4 and 5 is coiled by the skin effect of the eddy current.
It will be concentrated on the skin portion close to 1. By the way, if the frequency of the alternating current supplied to the coils 10 and 11 is f, the magnetic permeability of the material forming the cylindrical members 4 and 5 is μ, and its electrical conductivity is σ, the skin thickness δ at which the magnetic flux concentrates is , As in the following equation (1).

Δ = 2 / (2πf · σ · μ) ^1/2 (1) In other words, the thickness of the cylindrical members 4 and 5 may be equal to or greater than the thickness δ calculated by the above formula (1). The outer diameter of the sensor portion including the cylindrical members 4 and 5 can be reduced. From the above,
The configuration of the present embodiment has an advantage that the portion where the torque sensor is arranged can be made smaller (thinner) than the conventional one, and is applied to a vehicle having a small space margin as in the present embodiment. It is especially beneficial for the device.

Furthermore, since there is no need for a mechanism for converting the relative rotational displacement between the input shaft 1 and the output shaft 2 into the linear motion of another member, the structure is simple and the conversion mechanism is unnecessary.
There is an advantage that accuracy is improved. Here, in this embodiment, the input shaft 1 corresponds to the first rotation shaft and the output shaft 2 corresponds to the second rotation shaft.
The cylindrical member 4 corresponds to the first cylindrical member, the cylindrical member 5 corresponds to the second cylindrical member, and the large diameter portion 1A
Corresponds to a member made of a magnetic material, and has an oscillating part 21, a rectifying /
The smoothing circuits 22 and 23 and the differential amplifiers 24A and 24B constitute electromotive force measuring means.

FIG. 7 is a view showing a second embodiment of the present invention. As in FIG. 4 of the first embodiment, the front surface of the input shaft 1 and the output shaft 2 with the cylindrical members 4 and 5 fixed. It is a figure. The same members and parts as those in the first embodiment are designated by the same reference numerals, and their duplicated description will be omitted. That is, the first
In the embodiment, two rows of windows 5 are axially separated from each other in the cylindrical member 5.
, 5a and windows 5b, ..., 5b are formed. In this embodiment, the cylindrical member 5 has windows 5c ,.
By forming c, the two rows of windows 5a, ..., 5
a, windows 5b, ..., 5b are shared. This has the advantage that the manufacturing cost can be reduced. Other functions and effects are similar to those of the first embodiment.

In the above embodiment, two systems of differential amplifiers 24A and 24B and noise removal filters 25A and 25B are provided in order to improve the reliability, but this is not always necessary, and it is not necessary for each circuit. If the reliability is sufficient, one system may be provided, or conversely, three or more systems may be provided. Further, in the above embodiment, the case where the torque sensor according to the present invention is applied to the electric power steering device for a vehicle has been described, but the application target of the present invention is not limited to this.

In the above embodiment, the coils 10, 1
Although the self-induced electromotive force of No. 1 is measured, the mutual induced electromotive force may be measured by providing an oscillation coil. Alternatively, the torque may be obtained based on the self-induced electromotive force and the mutual induced electromotive force of one coil without taking the differential.

[0035]

As described above, according to the present invention,
The first and second cylindrical members made of a conductive and non-magnetic material are coaxially fitted to each other so as to be relatively rotatable, and the first and second rotating shafts coaxially arranged are connected via a torsion bar. Then, the first and second cylindrical members and the first and second rotating shafts are coaxially arranged, and the first cylindrical member and the first rotating shaft are integrated in a rotating direction, The second cylindrical member and the second rotating shaft are integrated in the rotating direction, and the first and second cylindrical members are each provided with a window so that the degree of overlap changes according to the relative rotational position between them. And forming a member made of a magnetic material in a space inside the portion of the first and second cylindrical members in which the window is formed, and the windows of the first and second cylindrical members are A coil is placed so as to surround the formed part, and an electromotive force is applied to the coil. Since the electromotive force measuring means for inducing and measuring this is provided and the torque generated in the first and second rotating shafts is detected based on the measurement result of the electromotive force measuring means, a simple structure is provided. The torque can be detected with high accuracy, and the size of the device can be reduced.

[Brief description of drawings]

FIG. 1 is a front sectional view showing a configuration of a first embodiment of the present invention.

FIG. 2 is a cross-sectional view of the cylindrical member taken along the line AA of FIG.

3 is a cross-sectional view of the cylindrical member taken along the line BB in FIG.

FIG. 4 is a front view showing a state where a cylindrical member is fixed.

FIG. 5 is a circuit diagram showing an example of a motor control circuit.

FIG. 6 is a graph showing the relationship between steering torque and the output of a differential amplifier.

FIG. 7 is a front view of the second embodiment of the present invention with a cylindrical member fixed.

[Explanation of symbols]

 1 Input Shaft (First Rotation Shaft) 2 Output Shaft (Second Rotation Shaft) 3 Torsion Bar 4 Cylindrical Member (First Cylindrical Member) 4a, 4b Window 5 Cylindrical Member (Second Cylindrical Member) 5a, 5b Window 10, 11 Coil 21 Oscillator 22,23 Rectification / smoothing circuit 24A, 24B Differential amplifier 25A, 25B Noise removal filter 26 Torque calculator 27 Motor drive circuit

Claims (1)

[Claims] 1. A first member made of a conductive and non-magnetic material.
And the second cylindrical member are coaxially fitted to each other so as to be rotatable relative to each other, and the coaxially arranged first and second rotating shafts are connected to each other via a torsion bar, and the first and second cylindrical members are connected. The first and second rotating shafts are arranged coaxially,
The first cylindrical member and the first rotating shaft are integrally formed in the rotating direction, the second cylindrical member and the second rotating shaft are integrally formed in the rotating direction, and the first and second cylindrical members are integrally formed. A window is formed so that the degree of overlap changes depending on the relative rotational position between them, and a magnetic material is formed in the space inside the portion of the first and second cylindrical members in which the window is formed. A member is disposed, and a coil is disposed so as to surround the portion of the first and second cylindrical members where the window is formed, and an electromotive force is induced in the coil to measure the electromotive force. A torque sensor characterized in that an electric power measuring means is provided and the torque generated in the first and second rotating shafts is detected based on the measurement result of the electromotive force measuring means.