JP3346151B2 - 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; The surrounding part surrounded by the cylindrical member is formed of a magnetic material, a groove extending in the axial direction is formed in the surrounding part, and the circumferential width of the groove is equal to the circumferential direction of the non-groove part of the surrounding part. Wider than the width, a window is formed in the cylindrical member so that the degree of overlap with the groove changes according to the relative rotation position with respect to the first rotation axis, and the window of the cylindrical member is A coil is arranged so as to surround the formed portion, and And to detect the torque generated in the first and second axis of rotation on the basis of the impedance change Le.

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 b (= θ−a) degree portion is closed, and the phase with the windows 8a,.
2) In the portion of the cylindrical member 8 farther from the sleeve 2A, the portion at a degree from the other end of the one-cycle angle θ becomes windows 8b,. Part is closed. .., 3A between the grooves 3A,..., 3A.
Is d 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 e degrees.

However, when the torsion bar 4 is not twisted (when the steering torque is zero), for example, c =
In the case of 20 degrees, as shown in FIG. 3, the center in the circumferential width of the window 8a and one end of the groove 3A in the circumferential direction (one edge of the convex portion 3B) overlap, as shown in FIG. Thus, the center in the circumferential direction of the window 8b and the other end in the circumferential direction of the groove 3A (the other edge of the projection 3B) overlap each other. Therefore, the overlapping state of the window 8a and the groove 3A and the window 8b
The overlapping state of the groove 3A and the groove 3A is reversed in the circumferential direction, and the center of the windows 8a and 8b in the circumferential direction and the center of the groove 3A in the circumferential direction are shifted from each other by θ / 4.

In the present embodiment, the relationship between the angles is as follows: b> a (1) d> c (2) e <θ / 4 (3) The conditions in the expressions (1) and (2) are for steeply changing the impedance of the coil described later. The condition of the expression (3) is for making the impedance change of the coil monotonically increase or decrease.

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 ± e 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 according to the direction and magnitude of the steering torque. Also, the differential amplifier 2
Since the difference between the rectifying / smoothing circuits 22 and 23 is obtained in 4A 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 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 the relationship of the angles as shown in FIG. 3 and FIG. 4, the case where the windows 8a, 8b, the closed portions between the windows 8a, 8b, the grooves 3A, and the circumferential widths of the protrusions 3B are all equal. Considering this, a = b = c = d = θ / 2, and since N = 9, θ / 2 = 20 degrees.

Then, the impedance was measured by appropriately adjusting the angles a to d on the basis of a = b = c = d = 20 degrees. The results shown in FIG. 7 were obtained. In FIG. 7, the horizontal axis represents the angle d, and the vertical axis represents the sensitivity ratio (impedance change ratio) of the torque sensor. In each broken line in FIG. 7, the angle a is appropriately changed in the range of 20 to 8 degrees. Each measurement result in each case is shown.

According to this measurement result, by setting the angle d, which is the circumferential width of the groove 3A, larger than 20 degrees,
It can be seen that the sensitivity ratio increases (that is, by making the angle d larger than the angle c that is the circumferential width of the projection 3B). At the same time, the angle a which is the circumferential width of the windows 8a and 8b
Is smaller than 20 degrees (that is, the angle a
Is smaller than the angle b), the sensitivity ratio is increased.

In this embodiment, since the above expressions (1) and (2) are satisfied, the impedance change ratio is increased while the materials and dimensions of the other members are unchanged. The sensitivity 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 is 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 the amplifier. By lowering the gain, the temperature characteristics of the electronic component can be relaxed, or 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. 8 shows that the angles a = 8, 10, 12 (de
For each case g), the results are shown for the case where the sensitivity ratio was measured while changing the angle d in a wider range. According to this, it is understood that the optimum value of the width dimension of the groove 3A is 28 degrees (that is, d = 28 degrees and c = 12 degrees). Also, from the measurement results of FIGS. 7 and 8, the windows 8a, 8b
Is 12 degrees (that is, a = 12 degrees, b =
28 degrees). The sensitivity ratio when these optimum values are adopted is about 50% higher than the sensitivity ratio when the angle d and the angle c are equal (d = c = 20 degrees).

It should be noted that these optimum values may slightly vary depending on the material and dimensions of the other members constituting the torque sensor, but can be easily measured. An actual torque sensor may be manufactured according to the result. In the above embodiment,
Although both of the above equations (1) and (2) are satisfied, as can be seen from the measurement results of FIGS. 7 and 8, only one of them satisfies the sensor sensitivity as compared with the related art. Can be improved.

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 is formed in the surrounding portion, the circumferential width of the groove is larger than the circumferential width of the non-groove portion, and the change in the degree of overlap between the window and the groove is determined by the coil. Since the measurement is performed based on the electromotive force and the torque generated in the first and second rotating shafts is detected based on the measurement result, the effect that the impedance change ratio of the coil can be increased and the sensor sensitivity can be improved. There is.

[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 the relationship between the size of each part and the sensitivity ratio.

FIG. 8 is a graph showing the relationship between the dimensions of each part and the sensitivity ratio in a wider range than FIG.

[Explanation of symbols]

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

Continuation of front page (56) References JP-A-9-189626 (JP, A) JP-A-9-101212 (JP, A) JP-A-9-61265 (JP, A) JP-A-9-61264 (JP) , A) JP-A-9-61263 (JP, A) JP-B-63-45528 (JP, B1) (58) Fields investigated (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 is formed, the circumferential width of the groove is larger than the circumferential width of the non-groove portion of the enclosed portion, and the cylindrical member has a relative width with respect to the first rotation shaft. A window is formed so that the degree of overlap with the groove changes according to the rotational position, and a coil is disposed so as to surround a portion of the cylindrical member where the window is formed, and the impedance of the coil changes. Based on the torque generated in the first and second rotating shafts. A torque sensor that detects torque.