JP3346152B2 - 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 torque sensor having a coil whose impedance changes according to the generated torque. Is increased so that the sensor sensitivity is improved.

[0002]

2. Description of the Related Art A conventional torque sensor is disclosed, for example, in Japanese Patent Publication No. 63-55528.
That is, in this conventional torque sensor, two cylindrical bodies are fitted coaxially so as to rotate relatively in accordance with the torque generated on the shaft, and the outer circumferential surface of the inner cylindrical body is A long groove and teeth are formed alternately, and a cutout is formed in the outer cylinder so that the degree of overlap with the groove changes according to the relative rotation between the cylinders. A coil is arranged to surround.
When the relative rotational position of the two cylinders changes and the degree of overlap with the notch in the groove changes, the impedance of the coil changes, so measuring the impedance of the coil reduces the torque generated on the shaft. It could be detected.

[0003]

Although the conventional torque sensor described above can detect the torque generated in the shaft based on the change in the impedance of the coil, the change in the impedance is so steep. However, there was an insufficient point that the sensor sensitivity was not so high.

[0004] 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 capable of further improving sensor sensitivity.

[0005]

In order to achieve the above object, a torque sensor according to the present invention connects a first and a second rotating shaft arranged coaxially through a torsion bar, and further comprises a conductive member. A cylindrical member made of a non-magnetic material and a non-magnetic material, so as to surround the outer peripheral surface of the first rotating shaft, and integrally with the second rotating shaft in a rotating direction; An enclosing portion surrounded by a cylindrical member is formed of a magnetic material, and the enclosing portion is formed with a groove extending in an axial direction and having a side surface rising along a radial direction of the first rotation axis; A window is formed so that the degree of overlap with the groove changes according to the relative rotation position with respect to the first rotation shaft, and a portion surrounding the window of the cylindrical member is formed. A coil is provided, and the impedance of the coil is And to detect the torque generated in the first and second rotary shafts based on Nsu change.

Here, the non-magnetic material in the present invention refers to a paramagnetic material and some diamagnetic materials, and the magnetic material refers to a ferromagnetic material. The magnetic permeability of the non-magnetic material is substantially equal to that of air, and is smaller than the magnetic permeability of the magnetic material.

[0007]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a cross-sectional view showing the overall configuration of an embodiment of the present invention, which is an example in which a torque sensor according to the present invention is applied to an electric power steering device for a vehicle.

First, the structure will be described. In the housing 1, an input shaft 2 and an output shaft 3 connected via a torsion bar 4 are rotatably supported by bearings 5a and 5b. The input shaft 2, the output shaft 3 and the torsion bar 4 are coaxially arranged. The input shaft 2 and the torsion bar 4 are connected to each other via a sleeve 2A whose ends are spline-coupled. The other end of 4 is spline-coupled to a position in the output shaft 3 that goes deeply. The input shaft 2 and the output shaft 3 are made of a magnetic material such as iron.

A steering wheel is integrally mounted on the input shaft 2 at the right end (not shown) of FIG. 1 in the rotational direction, and at the left end of the output shaft 3 (not shown) of FIG. A pinion shaft constituting the AND pinion type steering device is connected. Therefore, the steering force generated by the steering of the steering wheel by the driver is applied to the input shaft 2, the torsion bar 4,
The power is transmitted to steered wheels (not shown) via the output shaft 3 and the rack-and-pinion type steering device.

A sleeve 2A fixed to the end of the input shaft 2
Has a length that surrounds the outer peripheral surface of the end of the output shaft 3. A plurality of projections 2 long in the axial direction are provided on the inner peripheral surface of the portion surrounding the outer peripheral surface of the end portion of the output shaft 3 of the sleeve 2A.
are formed on the outer peripheral surface of the output shaft 3 opposed to these convex portions 2a.
Are formed, and the projections 2a and the grooves 3a are fitted with a margin in the circumferential direction, whereby relative rotation between the input shaft 2 and the output shaft 3 over a predetermined range (for example, about ± 5 degrees) or more is achieved. Preventing.

A worm wheel 6 which coaxially and integrally rotates with the output shaft 3 is externally fitted to the output shaft 3. A resin meshing portion 6 a of the worm wheel 6 and an outer peripheral surface of the output shaft 7 a of the electric motor 7 are provided. The formed worm 7b is engaged. Accordingly, the torque of the electric motor 7 is transmitted to the output shaft 3 via the output shaft 7a, the worm 7b and the worm wheel 6, and the electric motor 7
By appropriately switching the rotation direction, a steering assist torque in an arbitrary direction is applied to the output shaft 3.

Further, a thin cylindrical member 8 is integrally fixed in the rotational direction to the sleeve 2A integrated with the input shaft 2 so as to approach and surround the outer peripheral surface of the output shaft 3. I have. That is, the cylindrical member 8 is formed of a conductive and non-magnetic material (for example, aluminum), and as shown in FIG. Of the part surrounding shaft 3,
On the side close to the sleeve 2A, a plurality of (nine in this embodiment) rectangular windows 8a,.
a is formed, and windows 8a, 8a,
, 8a are formed (in this embodiment, nine) of windows 8b,..., 8b which are equally spaced in the circumferential direction so as to be 180 ° out of phase with each other.

On the outer peripheral surface of a portion of the output shaft 3 surrounded by the cylindrical member 8, a plurality of grooves (same in number as the windows 8a and 8b, that is, nine in this example) having a substantially rectangular cross section extending in the axial direction. 3A is formed. More specifically, FIG.
FIG. 3 is a sectional view of the cylindrical member 8 and the output shaft 3 taken along a line.
As shown in FIG. 4 which is a cross-sectional view of the cylindrical member 8 and the output shaft 3 along the line BB in FIG. 1, the circumferential surface of the cylindrical member 8 is equally divided into N (in this example, N = 9) in the circumferential direction. Angle obtained as one cycle angle θ (= 360 / N, θ = 40 degrees in this example)
In the portion of the cylindrical member 8 on the side closer to the sleeve 2A, a portion a degrees from one end of the one-cycle angle θ is the window 8a,.
a, and the remaining (θ-a) degree portion is closed,
Also, at a portion of the cylindrical member 8 farther from the sleeve 2A, a portion at a degree from the other end of the one-period angle θ is such that the phase with the windows 8a,. 8
.., 8b, and the remaining (θ−a) degree portion is closed. .., 3A, the circumferential width of the convex portion 3B having a transverse cross section is b degrees, and the relative rotatable range between the cylindrical member 8 and the output shaft 3 (between the input shaft 2 and the output shaft 3). Is c degrees.

However, when the torsion bar 4 is not twisted (when the steering torque is zero), as shown in FIG. 3, the center of the circumferential width of the window 8a and one of the circumferential direction of the groove 3A are provided. The end part (one edge part of the convex part 3B) overlaps,
As shown in FIG. 4, the center of the window 8 b in the circumferential width direction and the groove 3 A
And the other end in the circumferential direction (the other edge of the projection 3B). Therefore, the overlapping state of the window 8a and the groove 3A and the overlapping state of the window 8b and the groove 3A are opposite in the circumferential direction, and the center of the circumferential width of the windows 8a and 8b and the center of the circumferential width of the groove 3A. Are shifted from each other by θ / 4. In the present embodiment, the relationship between the angles is as follows: a = (θ−a) = b = (θ−b) = θ / 2 (1)

Further, in the present embodiment, the side surface 3C of each groove 3A rises along the radial direction of the output shaft 3, as shown in FIG. 3 and FIG. . Specifically, each side surface 3C rises radially outward along a line extending radially around the axis of the output shaft 3 (same as the axis of the torsion bar 4) in the cross-sectional view. ing.

The cylindrical member 8 is surrounded by a yoke 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 member 8, and the coil 10 is wound around the yoke 9 so as to surround the portion where the windows 8a,.
The coil 11 is wound around the yoke 9 so as to surround the portion where the windows 8b,..., 8b are formed, and the yoke 9 is fixed to the housing 1. The space in the housing 1 where the worm wheel 6 is disposed and the yoke 9
Is separated by an oil seal 12 so that lubricating oil supplied to the meshing portion of the worm wheel 6 and the worm 7 does not enter the yoke 9 side. .

The coils 10 and 11 are connected to a motor control circuit formed on a control board 14 in the sensor case 13. For example, as shown in FIG. 5, the motor control circuit supplies an alternating current of a predetermined frequency to the constant current unit 20.
, A rectifying / smoothing circuit 22 for rectifying and smoothing the self-induced electromotive force of the coil 10 for output, and rectifying and smoothing the self-induced electromotive force of the coil 11. A rectifying / smoothing circuit 23 for outputting, a differential amplifier 24A, 24B for amplifying and outputting a difference between an output of the rectifying / smoothing circuit 22 and an output of the rectifying / smoothing circuit 23, and a high frequency noise component from an output of the differential amplifier 24A. A noise removal filter 25A for removing high-frequency noise components from the output of the differential amplifier 24B;
B and the direction and magnitude of the relative rotational displacement of the input shaft 2 and the cylindrical member 8 based on, for example, the average value of the outputs of the noise removal filters 25A and 25B, and multiplies the result by, for example, a predetermined proportional constant to perform steering. A torque calculating unit 26 for obtaining a steering torque generated in the system, and a motor for supplying a drive current I to the electric motor 7 such that a steering assist torque for reducing the steering torque is generated based on the calculation result of the torque calculating unit 26. And a drive unit 27.

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 2 and the output shaft 3. Therefore, no relative rotation occurs between the output shaft 3 and the cylindrical member 8. On the other hand, when the steering wheel is steered to generate a torque on the input shaft 2, the torque is transmitted to the output shaft 3 via the torsion bar 4. 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 3 are applied to the output shaft 3. Therefore, the torsion bar 4 is twisted between the input shaft 2 and the output shaft 3 so that the output shaft 3
Occurs, and relative rotation also occurs between the output shaft 3 and the cylindrical member 8.

When there is no window in the cylindrical member 8, the cylindrical member 8 is made of a conductive and non-magnetic material. An eddy current is generated on the outer peripheral surface in a direction opposite to the coil current. When the magnetic field due to the eddy current and the magnetic field due to the coil are overlapped, the magnetic field inside the cylindrical member 8 is canceled.

When windows 8a and 8b are provided in the cylindrical member 8,
Since the eddy current generated on the outer peripheral surface of the cylindrical member 8 cannot go around the outer peripheral surface by the windows 8a and 8b, the eddy current wraps around the inner peripheral surface side of the cylindrical member 8 along the end surfaces of the windows 8a and 8b, and the inner peripheral surface is coiled. The current flows in the same direction as the current and returns to the outer peripheral surface along the end surfaces of the adjacent windows 8a and 8b to form a loop. That is,
Inside the coil, a loop of eddy currents is periodically arranged in the circumferential direction (θ = 360 / N).

The magnetic field generated by the coil current and the eddy current are superimposed, and a magnetic field having a periodic magnetic field strength in the circumferential direction and a magnetic field having a gradient that becomes smaller toward the center are formed inside and outside the cylindrical member 8. . The strength of the circumferential magnetic field is strong at the center of the windows 8a and 8b, which are strongly affected by adjacent eddy currents.
A half cycle (θ / 2) deviates therefrom. A shaft 3 made of a magnetic material is coaxially disposed inside the cylindrical member 8, and the shaft 3 has a projection 3A and a recess 3B on the windows 8a and 8b.
It is formed with the same period as b.

A magnetic substance placed in a magnetic field is magnetized and emits spontaneous magnetization (magnetic flux), but the amount increases according to the strength of the magnetic field until saturation is reached. For this reason, the spontaneous magnetization of the shaft 3 is increased or decreased by the relative phase with the cylindrical member 8 by the magnetic field having the periodic periodic strength and the radial gradient generated by the cylindrical member 8.

The phase at which the spontaneous magnetization becomes maximum is determined by the windows 8a, 8
This is a state in which the center of b and the center of the convex portion match. As the spontaneous magnetization increases or decreases, the inductance of the coil also increases or decreases. The change is substantially sinusoidal. When no torque is applied, the phase is shifted by １ ／ period (θ / 4) from the phase at which the spontaneous magnetization (inductance) is maximized. The phase with the window row is a phase difference of 1/2 cycle (θ / 2) as described above.

For this reason, the cylindrical member 8 and the shaft 3
When the phase difference occurs, the inductance of the two coils 10, 11 increases on one side and decreases on the other side at the same rate.
Here, for example, when the right steering torque is generated, the cylindrical member 8 rotates counterclockwise in FIGS. 3 and 4, and as shown in FIG. according to the torque increases, the inductance L ₁₀ of the coil 10 is increased, the inductance L ₁₁ of the coil 11 is reduced. Conversely, according to the left steering torque is increased, the inductance L ₁₀ of the coil 10 is decreased, the coil 1
1 of the inductance L ₁₁ is to increase. FIG. 6 shows the relative rotation angle between the cylindrical member 8 and the output shaft 3, and
The relationship with the steering torque is also shown, and according to this, the range in which the relative angle changes by an angle (θ / 4) from the position where the steering torque is 0 to the direction in which the right steering torque or the left steering torque increases. so although the inductance L ₁₀ and the inductance L ₁₁ is increased or decreased monotonously, beyond which, comes to change in opposite directions. Therefore, as described above, the relative rotation range is limited to the range of ± c degrees.

[0025] Then, if the change inductance L ₁₀ and L ₁₁ is as shown in FIG. 6, under the condition that the frequency ω is constant current supplied by the oscillator 21, the coil 10 and 11 impedance of FIG. 6 change sushi in the same tendency as the inductance L ₁₀ and L _11, self-induced electromotive force of the coils 10 and 11 vary in a similar trend. Therefore, the outputs of the differential amplifiers 24A and 24B that determine 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. Further, the rectifying / smoothing circuits 22, 24 in the differential amplifiers 24A and 24B,
23, the 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 according to the direction and magnitude of the steering torque is supplied to the electric motor 7.

Then, a rotational force corresponding to the direction and magnitude of the steering torque generated in the steering system is generated in the electric motor 7, and the rotational force is transmitted to the output shaft 3 via a worm gear or the like.
, The steering assist torque is applied to the output shaft 3, the steering torque decreases, and the burden on the driver is reduced. Here, in a case where the circumferential widths of the windows 8a and 8b, the groove 3A, and the protrusion 3B are all equal in the relationship of the angles as shown in FIGS. 3 and 4, a = (θ−a) = b = (θ−b) = θ / 2, and N = 9, so that θ / 2 = 20 degrees.

Then, while fixing b = (θ−b) = 20 degrees, the impedance was measured by appropriately changing the angle a, which is the circumferential width of the windows 8 a and 8 b, within the range of 20 to 8 degrees. As a result, the result shown in FIG. 7 was obtained. In FIG. 7, the horizontal axis represents the angle a, and the vertical axis represents the sensitivity ratio (impedance change ratio) of the torque sensor.
As shown in FIG. 8, the two broken lines in FIG.
Measurement results when C is raised along the radial direction of the rotating shaft 3 (that is, in the present embodiment), and when the groove 3A is formed into a square-shaped key groove shape as shown in FIG. And the measurement results of the conventional example described in the above-mentioned publication. However, in the configuration of FIG. 9, the angle of the upper end width of the groove 3A is set to 20 degrees.

According to the measurement results, the case where the side face 3C is raised along the radial direction of the rotating shaft 3 as in the present embodiment is the same as the conventional keyway shape having a square cross section. It can be seen that the sensitivity ratio is higher than that of the conventional method (the sensitivity is about 10% higher than that of the related art). That is, according to the present embodiment, since the side surface 3C is raised along the radial direction of the rotating shaft 3, the impedance change ratio is increased while the materials and dimensions of the other members are unchanged, and the sensitivity of the sensor is increased. Can be increased.

If the detection sensitivity of the sensor can be increased without changing the number of windings or the like, on the contrary, if the sensitivity can be the same as the conventional one, the number of windings of the coils 10 and 11 can be reduced accordingly to reduce the size of the device, or By lowering the gain of the amplifier, the temperature characteristic of the electronic component can be reduced, and an electronic circuit that is strong against disturbance noise can be provided. In particular, the advantage that the size of the device can be reduced is particularly advantageous for a device applied to a vehicle having a small space margin as in the present embodiment.

FIG. 7 also shows that the sensitivity ratio can be further improved by appropriately adjusting the widths of the windows 8a and 8b. Incidentally, the optimum value of the width dimension of the windows 8a and 8b is 12
It can be seen that the degree (that is, a = 12 degrees, (θ-a) = 28 degrees). However, this optimum value may slightly change depending on the material and dimensions of the other members constituting the torque sensor, but can be easily measured. The actual production of the torque sensor may be performed accordingly.

Also, as in the present embodiment, the groove 3A is
If the side surface 3C is formed so as to rise along the radial direction of the rotating shaft 3, the groove 3A can be processed easily because the cross-sectional shape of the groove 3A is narrow on the bottom side. That is, FIG.
In the conventional groove shape shown in FIG. 8, the groove 3A had to be machined by cutting. However, in the case of the shape shown in FIG. It becomes easier and leads to cost reduction due to the increase in manufacturing method options. For example, according to the configuration of the present embodiment, since the side surface of the groove 3a functioning as a stopper in the rotation direction also rises in the radial direction of the rotation shaft 3, both the groove 3A and the groove 3a are used. It can be formed at the time of forging (cold forging) or casting of the rotating shaft 3, and the cost is reduced as the cutting of the groove 3 </ b> A becomes unnecessary.

Here, in the present embodiment, the input shaft 2 corresponds to the second rotating shaft, the output shaft 3 corresponds to the first rotating shaft, the projection 3B corresponds to a portion that is not a groove, and The portion of the shaft 3 surrounded by the cylindrical member 8 corresponds to the surrounded portion.

[0034]

As described above, according to the present invention,
A window is formed in a cylindrical member made of a conductive and non-magnetic material that rotates integrally with the first rotating shaft, and an enclosed portion surrounded by at least the cylindrical member of the second rotating shaft is formed of a magnetic material. Then, a groove extending in the axial direction and having a side surface rising in the radial direction of the first rotating shaft is formed in the surrounding portion, and a change in the degree of overlap between the window and the groove is determined based on the electromotive force of the coil. And the torque generated in the first and second rotating shafts is detected based on the measurement result. Therefore, there is an effect that the impedance change ratio of the coil is increased and the sensor sensitivity can be improved.

[Brief description of the drawings]

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

FIG. 2 is a perspective view of a main part of the embodiment.

FIG. 3 is a cross-sectional view of a cylindrical member and an output shaft taken along line AA of FIG.

FIG. 4 is a sectional view of the cylindrical member and the output shaft taken along line BB of FIG.

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 a coil inductance.

FIG. 7 is a graph showing a comparison between the sensitivity ratio of the present embodiment and the sensitivity ratio of a conventional example.

FIG. 8 is a diagram showing a shape of a groove of the present embodiment used for measurement.

FIG. 9 is a view showing the shape of a conventional groove used for measurement.

[Explanation of symbols]

 Reference Signs List 2 input shaft (second rotating shaft) 3 output shaft (first rotating shaft) 3A groove 3B convex portion 3C side surface 4 torsion bar 8 cylindrical member 8a, 8b window 10, 11 coil 20 constant current unit 21 oscillation unit 22, 23 Rectifier / smoothing circuit 24A, 24B Differential amplifier 25A, 25B Noise removal filter 26 Torque calculator 27 Motor drive circuit

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-57-190240 (JP, A) JP-A-9-189625 (JP, A) JP-A-9-101212 (JP, A) JP-A-9-190 JP-A-9-61264 (JP, A) JP-A-9-61263 (JP, A) JP-A-8-240491 (JP, A) JP-B-63-45528 (JP, B1) (58) Field surveyed (Int. Cl. ⁷ , DB name) G01L 3/10 B62D 5/04

Claims (1)

(57) [Claims] 1. A coaxially disposed first and second rotation shafts are connected via a torsion bar, and a cylindrical member made of a conductive and non-magnetic material is connected to the first rotation shaft. The second rotating shaft is integrally formed with the second rotating shaft in a rotating direction so as to surround an outer peripheral surface, and at least the surrounded portion of the first rotating shaft surrounded by the cylindrical member is formed of a magnetic material; A groove extending in the axial direction and having a side surface rising along the radial direction of the first rotation shaft is formed, and the cylindrical member is formed with the groove in accordance with a relative rotation position with respect to the first rotation shaft. Form a window so that the degree of overlap changes,
And disposing a coil so as to surround a portion of the cylindrical member where the window is formed, and detecting a torque generated in the first and second rotating shafts based on a change in impedance of the coil. Characteristic torque sensor.