JP3346102B2 - Torque sensor - Google Patents

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 rotating shaft, and more particularly to a sensor having a simple structure and having high 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. 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 moved in the axial direction according to the relative displacement between the input shaft and the output shaft. A coil is provided around the cylindrical member, and a self-induced electromotive force induced in the coil is measured, and a 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 advances and retreats in the axial direction, the self-inductance of the coil changes. Therefore, the torque generated on 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 rotating shafts into the axial displacement of the cylindrical member. Because of this, the device is likely to be large,
In addition, there is a problem that the reliability is lowered due to the complicated structure.

SUMMARY OF THE INVENTION The present invention has been made in view of such unresolved problems of the prior art, and has as its object to provide a torque sensor which has a simple structure and can increase detection sensitivity. And

[0005]

To achieve the above object, a torque sensor according to the present invention comprises a first cylindrical member made of a non-conductive and ferromagnetic material, and a first cylindrical member made of a non-conductive and non-magnetic material. A second cylindrical member made of a material is coaxially fitted so as to be relatively rotatable with the first cylindrical member inside, and the first and second rotating shafts arranged coaxially are connected via a torsion bar. Connecting the first and second cylindrical members and the first and second rotation axes coaxially,
The cylindrical member and the first rotary shaft are integrated in the rotational direction, the second cylindrical member and the second rotary shaft are integrated in the rotational direction, and the cylindrical member and the first rotary shaft are respectively integrated into the first and second cylindrical members. A window is formed so that the degree of overlap varies according to the relative rotational position between the first and second cylindrical members, and a coil is disposed so as to surround the portion of the first and second cylindrical members where the window is formed. An electromotive force measuring means for inducing an electromotive force in the coil to measure the electromotive force, and detecting a torque generated in the first and second rotating shafts based on a measurement result of the electromotive force measuring means. I made it.

[0006]

For example, if the first rotating shaft is an input shaft and the second rotating shaft is an output shaft, torque is transmitted from the first rotating shaft to the second rotating shaft via a torsion bar. A relative rotation occurs between the first rotation axis and the second rotation axis with the torsion bar being twisted. 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.

In this case, if the overlapping area between the windows of the first and second cylindrical members is small, a relatively large portion of the surface of the first cylindrical member located inside will be exposed. Conversely, if the overlapping area between the windows is large, a relatively large portion of the surface of the first cylindrical member is made of the second cylindrical member made of a conductive and non-magnetic material that is less permeable to magnetic flux than air. You will be hiding inside. Here, the non-magnetic material in the present invention refers to a paramagnetic material and some diamagnetic materials.

[0008] Since the non-conductive and ferromagnetic material forming the first cylindrical member has a property of transmitting magnetic flux more easily than air, the first window member is changed by the change of the overlapping state of the windows as described above. When the rate at which the surface of the cylindrical member is exposed to the outside changes, the self-inductance and mutual inductance of the coil change sharply according to the relative rotation between the first and second cylindrical members.

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, the induced electromotive force is measured. Based on the measurement result, the torque generated on the first and second rotating shafts is detected.

[0010]

Embodiments of the present invention will be described below with reference to the drawings. 1 to 6 show a first embodiment of the present invention, in which a torque sensor according to the present invention is applied to an electric power steering device for a vehicle. First, the configuration will be described. As shown in FIG. 1 which is a cross-sectional view of a part of a steering system of a vehicle, a portion between an input shaft 1 and an output shaft 2 which are coaxially and rotatably disposed via a torsion bar 3. Are linked.

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

A groove 2 extending in the radial direction from the insertion portion of the torsion bar 3 is formed in the end face of the output shaft 2 on the input shaft 1 side.
a is formed, and a 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 (dimension in the circumferential direction) of the groove 2a is slightly larger than the width of the convex portion 1a, whereby the width between the input shaft 1 and the output shaft 2 is not less than a predetermined range (for example, about ± 5 degrees). Prevents relative rotation.

The rotational 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, a steering assist torque of any direction and magnitude is applied to the output shaft 2. On the other hand, two thin cylindrical members 4 and 5 are arranged so as to surround the outer peripheral surface of a portion of the input shaft 1 close to the output shaft 2 with a certain gap 1A.

That is, the cylindrical member 4 is formed of a non-conductive (low-conductivity) and ferromagnetic material (eg, ferrite), and the cylindrical member 5 is formed of a conductive and non-magnetic material (eg, aluminum). The cylindrical member 4 is inserted into the cylindrical member 5 and is coaxially fitted so as to be relatively rotatable. A small diameter portion 4A is formed on the inner surface of the right end portion of FIG.
Are externally fitted to the input shaft 1. Thus, the cylindrical member 4 is integrated with the input shaft 1 in the rotation direction. A small-diameter portion 5 </ b> A is formed on the inner surface of the left end of FIG. 1 of the cylindrical member 5, and the small-diameter portion 5 </ b> A is fitted on the output shaft 2. Thus, the cylindrical member 5 is integrated with the output shaft 2 in the rotation direction.

Further, of the portion of the cylindrical member 4 that is fitted with the cylindrical member 5, a plurality of rectangular (e.g.,
, 4a are formed, and a rectangle (same shape as the window 4a) is equally spaced in the circumferential direction so as to be 180 degrees out of phase with the windows 4a,. ) Are formed (six in this embodiment).

More specifically, the windows 4a,..., 4a are formed by dividing the circumferential surface of the cylindrical member 4 into twelve equal parts in the circumferential direction, and opening the rectangular area every other twelve equal parts. The windows 4b,..., 4b are formed by opening portions corresponding to the portions of the windows 4a,. On the other hand, among the portions of the cylindrical member 5 fitted with the cylindrical member 4, the windows 4a,.
Outside the portion where a is formed, a plurality of rectangles (having the same shape as the window 4a) which are equally spaced in the circumferential direction (in this embodiment,
6a) are formed, and windows 4b,.
Outside the portion where b is formed, a rectangle (same shape as the window 4a) is equally spaced circumferentially in the same window as the windows 5a,.
, 5b are formed (six in this embodiment).

However, when no relative rotation occurs 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 in 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, respectively, so that the windows 4a and 5a overlap 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 by half, but the distance between the windows 4a and 4b Are shifted by 180 degrees, the windows 4a and 5a
2 and FIG. 3 as well as FIG. 4 which is a front view of the input shaft 1 and the output shaft 2 in a state where the cylindrical members 4 and 5 are fixed. In addition, 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 is
, 4a are wound around the bobbin 9 so as to surround the portion where the window 4b is 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 an oscillating unit 21 that supplies an alternating current having a predetermined frequency to the coils 10 and 11, as shown in FIG.
And a rectifying / smoothing circuit 22 for rectifying and smoothing the self-induced electromotive force of the coil 10 and outputting the same, and a rectifying / smoothing circuit 23 for rectifying and smoothing and outputting the self-induced electromotive force of the coil 11.
Amplifiers 24A and 24B that amplify and output 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 high-frequency noise components from the output of the differential amplifier 24A;
A noise removal filter 25B for removing high frequency noise components from the output of
A torque for calculating the direction and magnitude of the relative rotational displacement of the cylindrical members 4 and 5 based on, for example, an average value of the output of B and multiplying the result by, for example, a predetermined proportionality constant to obtain a steering torque generated in the steering system. The motor control unit 26 includes a calculation unit 26 and a motor drive unit 27 that supplies a drive current I to the electric motor to generate a steering assist torque for reducing the steering torque based on the calculation result of the torque calculation unit 26.

Next, the operation of this embodiment will be described. Now, assuming that the steering system is in a straight running state and the steering torque is zero, no relative rotation occurs between the input shaft 1 and the output shaft 2. Therefore, the cylindrical member 4 that rotates 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 torque on the input shaft 1, the torque is transmitted to the output shaft 2 via the torsion bar 3. At this time, a resistance force corresponding to a frictional force between the steered wheels and the road surface and a frictional force such as meshing of gears of a rack-and-pinion type steering device formed on the left end side (not shown) of the output shaft 2 are applied to the output shaft 2. Therefore, the relative rotation of the output shaft 2 is delayed between the input shaft 1 and the output shaft 2 due to the twisting of the torsion bar 3, and the relative rotation also occurs between the cylindrical members 4 and 5.

Here, for example, when the right steering torque (steering torque generated at the time of steering in the right rotation direction) is generated, the overlapping area of the windows 4a and 5a is smaller than that when the steering torque is zero, and the windows 4b and 5b are not overlapped. The overlapping area increases. Conversely, when the left steering torque (steering torque generated at the time of steering in the left rotation direction) is generated, the overlapping area of the windows 4a and 5a is larger than the case where the steering torque is zero, but the overlapping of the windows 4b and 5b. Area becomes smaller.

The windows 4a and 5a and the windows 4b and 5b
Are exposed in the gap 1A between the cylindrical member 4 and the input shaft 1. That is, the surface area of the cylindrical member 4 exposed through the windows 5a and 5b changes according to the steering torque. Specifically, when the right steering torque is generated, as the steering torque in that direction increases, the cylindrical shape increases. The exposed area of the surface area of the member 4 increases, and the exposed area of the surface area decreases inside the coil 11. Conversely, when the left steering torque is generated, as the steering torque in that direction increases, the cylindrical member 4
The exposed area of the surface area decreases, and the exposed area of the surface area increases inside the coil 11.

Then, since the cylindrical member 4 made of a non-conductive and ferromagnetic material has a property of transmitting magnetic flux more easily than the gap 1A, the self-inductance of the coil 10 increases when the right steering torque is generated. Since the self-inductance of the coil 11 decreases, the self-induced electromotive force of the coil 10 increases, and the self-induced electromotive force of the coil 11 decreases. Conversely, 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.

Accordingly, 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, a change in self-inductance due to temperature or the like is canceled.

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

Then, a torque is generated in the electric motor according to the direction and magnitude of the steering torque generated in the steering system, and the torque is transmitted to the output shaft 2 via a worm gear or the like. This means that the steering assist torque has been applied to the output shaft 2, so that the steering torque is reduced and the burden on the driver is reduced. As described above, according to the configuration of the present embodiment, the torque between the input shaft 1 and the output shaft 2 can be reduced without converting the relative rotational displacement between the input shaft 1 and the output shaft 2 into a linear motion of another member. Since the detection can be performed, the structure is simple and there is an advantage that the portion where the torque sensor is disposed can be made smaller (thinner) than that of the related art, and there is a space margin as in the present embodiment. This is particularly useful for a device applied to a small vehicle, and has the advantage that accuracy is improved because the conversion mechanism is not required.

Further, if the cylindrical member 4 is formed of a non-conductive and ferromagnetic material such as ferrite, rust prevention is not required for such a member. As a result, since the processing cost during mass production can be reduced, there is also an advantage that the cost of parts can be reduced. Here, in this embodiment, the input shaft 1 corresponds to the first rotating shaft, and the output shaft 2
Corresponds to the second rotating shaft, the cylindrical member 4 corresponds to the first cylindrical member, the cylindrical member 5 corresponds to the second cylindrical member, the oscillating section 21, the rectifying / smoothing circuits 22, 23 and the differential section. Amplifier 24
A and 24B constitute an electromotive force measuring means.

FIG. 7 is a view showing a second embodiment of the present invention. As shown in FIG. 4 of the first embodiment, the front surfaces of the input shaft 1 and the output shaft 2 with the cylindrical members 4 and 5 fixed thereto. FIG. The same members and portions as those in the first embodiment are denoted by the same reference numerals, and the description thereof will not be repeated. That is, the first
In the embodiment, two rows of windows 4 are axially separated from each other in the cylindrical member 4.
, 4a and windows 4b,..., 4b are formed. In the present embodiment, windows 4c,.
c, the two rows of windows 4a,.
a, windows 4b,..., 4b are shared. Thereby, there is an advantage that manufacturing cost can be reduced. Other functions and effects are the same as those of the first embodiment.

In the above embodiment, two systems of the differential amplifiers 24A and 24B and the noise elimination filters 25A and 25B are provided in order to improve the reliability. However, this is not always necessary. If the reliability is sufficient, one system may be provided, or 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 configuration of measuring the self-induced electromotive force of Example 1 is adopted, the configuration of measuring the mutual induced electromotive force by providing an oscillation coil may be adopted. 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.

[0032]

As described above, according to the present invention,
A first cylindrical member made of a non-conductive and ferromagnetic material and a second cylindrical member made of a conductive and non-magnetic material are coaxially rotatable with the first cylindrical member inside. And the first and second rotating shafts arranged coaxially are connected via a torsion bar,
And a second cylindrical member and the first and second rotating shafts are disposed coaxially, and the first cylindrical member and the first rotating shaft are integrated in a rotational direction, and the second cylindrical member is provided. And the second rotation axis is integrally formed in the rotation direction, and a window is formed on each of the first and second cylindrical members so that the degree of overlap changes according to a relative rotation position between them. A coil is provided so as to surround a portion of the first and second cylindrical members where 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. Since the torque generated in the first and second rotating shafts is detected based on the measurement result of the power measuring means, the structure is simple, and the portion where the torque sensor is disposed is correspondingly reduced in comparison with the related art. It has the advantage that it can be made smaller (thinner), and the conversion mechanism Needed for minute, there is an effect that the accuracy is improved.

[Brief description of the drawings]

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

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

FIG. 3 is a sectional view of the cylindrical member taken along the line BB of FIG. 1;

FIG. 4 is a front view of a state in which the cylindrical member is fixed.

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

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

FIG. 7 is a front view showing a state where a cylindrical member according to a second embodiment of the present invention is fixed.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Input shaft (1st rotating shaft) 2 Output shaft (2nd rotating shaft) 3 Torsion bar 4 Cylindrical member (1st cylindrical member) 4a, 4b Window 5 Cylindrical member (2nd cylindrical member) 5a, 5b Windows 10, 11 Coil 21 Oscillator 22, 23 Rectifier / smoothing circuit 24A, 24B Differential amplifier 25A, 25B Noise removal filter 26 Torque calculator 27 Motor drive circuit

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-8-114518 (JP, A) JP-A-8-240492 (JP, A) JP-A-8-240491 (JP, A) JP-A-8-114 240490 (JP, A) JP-A-4-22039 (JP, A) JP-A-57-190240 (JP, A) JP-B 5-58128 (JP, B2) JP-B 63-45528 (JP, B2) (58) Field surveyed (Int. Cl. ⁷ , DB name) G01L 3/10 B62D 5/04 G01L 5/22

Claims (1)

(57) [Claims] 1. A first cylindrical member made of a non-conductive and ferromagnetic material and a second cylindrical member made of a conductive and non-magnetic material, with the first cylindrical member inside. The first and second rotating shafts are coaxially fitted with each other via a torsion bar, and are coaxially fitted with each other so as to be rotatable relative to each other. A rotation axis is disposed coaxially, the first cylindrical member and the first rotation axis are integrated in the rotation direction, the second cylindrical member and the second rotation axis are integrated in the rotation direction, A window is formed in each of the first and second cylindrical members such that the degree of overlap changes according to a relative rotational position therebetween, and the windows of the first and second cylindrical members are formed. A coil is arranged so as to surround the part where the And an electromotive force measuring means for measuring this, based on the measurement result of the electromotive force measuring means,
A torque sensor for detecting torque generated in the first and second rotating shafts.