JPH04160331A - torque sensor - Google Patents

Abstract

PURPOSE:To simplify a processing circuit and to improve the accuracy of measurement by a method wherein the result of computation of a difference between electromotive forces induced by first and second coils is subjected to phase conversion in accordance with the polarity of the electromotive force of the first coil. CONSTITUTION:When a torque is transmitted to an input shaft 2 and an output shaft 3 being coaxial, a relative rotation corresponding to the direction and magnitude of the torque occurs, with a torsion, in a coaxial elastic member (torsion bar) 4 provided between them. Thereby the inductions of coils 16 and 17 increase and decrease in the reverse direction to each other, the induced electromotive forces accompanying them are increased and decreased, and a difference between these forces is determined by a difference value computing means. The result of this computation is turned into the same phase or a reverse phase by a phase changeover means in accordance with the positive or negative state of the polarity of the electromotive force induced in the coil 16, and outputted. Based on the output, the torque transmitted to the input and output shafts 2 and 3 is computed by a torque computing means.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a torque sensor that detects torque transmitted to a rotating shaft.

[Conventional technology]

When torque is transmitted to two rotating shafts connected via an elastic member such as a torsion bar, relative rotation occurs between the two rotating shafts due to twisting of the torsion bar. Since the direction and amount of the relative rotation are determined by the direction and magnitude of the torque transmitted to the rotating shaft, the torque can be detected by measuring the relative rotation.

In addition, the inductance of the two coils is increased or decreased in opposite directions according to the relative rotation between the two rotating shafts, and the difference in electromotive force is determined when the electromotive force is induced in the coils. By determining the relative rotation between two rotating shafts, that is, the torque transmitted to the rotating shafts, from the difference in power, the relative rotation can be measured without contact, reducing the risk of failure due to wear, etc. In addition, since the torque measurement is based on the differential between two coils, it is possible to obtain detection results with twice the slope compared to when measuring with a single coil, making it possible to measure minute torques with high precision. It becomes possible.

[Invention or problem to be solved]

However, in the above torque sensor,
Since the electromotive force induced in the two coils is alternating current, a function to rectify the measured electromotive force is required, which has the disadvantage of low measurement accuracy. This is because when measuring the electromotive force of two coils using a bridge circuit, etc., the bridge circuit output is generally a low voltage (usually lV or less).
Therefore, if rectification is performed using a silicon diode, etc., the forward voltage drop cannot be ignored, and to compensate for this, a current □ boost is required to drive the subsequent smoothing circuit. This is because it becomes complicated.

The present invention has been made by focusing on the unresolved problems of the conventional technology, and aims to provide a torque sensor in which the processing circuit is simplified and the measurement accuracy is improved. .

[Means to solve the problem]

In order to achieve the above object, the present invention provides first and second rotating shafts disposed coaxially, an elastic member connecting these first and second rotating shafts, and an elastic member connecting the first and second rotating shafts. first and second coils whose inductance increases and decreases in opposite directions according to relative rotation between the rotation axes of the first and second coils; an electromotive force inducing means for inducing an electromotive force in the first and second coils; and the difference to determine the difference in the electromotive force induced in the second coil.

a value calculation means and a calculation result of the difference value calculation means;
a phase switching means for outputting the electromotive force induced in the coil in the same phase when the polarity is one of positive and negative, and outputting the electromotive force in opposite phase when the polarity is the other of positive and negative; and an output of the phase switching means. torque calculating means for calculating the torque transmitted to the first and second rotating shafts based on the above.

[Effect]

When torque is transmitted to the first and second rotating shafts, relative rotation occurs between the first and second rotating shafts depending on the direction and magnitude of the torque, accompanied by twisting of the elastic member. arise.

Then, the inductance of the first and second coils increases and decreases in opposite directions, and the first and second coils have
The electromotive force inducing means induces an electromotive force according to the inductance.

Then, the difference value calculation means calculates the difference between those electromotive forces,
Depending on the polarity of the electromotive force induced in the phase switching means or the first coil, the calculation result of the difference value calculation means is output as in-phase or anti-phase.

As a result, even if the calculation result of the difference value calculation means fluctuates between positive and negative, the output of the phase switching means will always be a positive value when torque in the negative rotation direction is generated, and when torque in other rotation directions is generated, the output of the phase switching means will always be a positive value. When the torque is generated, the value is always negative, and the torque calculation means selects the first torque based on the output of the phase switching means.
and calculate the torque transmitted to the second rotating shaft.

〔Example〕

Embodiments of the present invention will be described below based on the drawings.

First, to explain the configuration, FIG. 1 is a sectional view of a vehicle power steering device to which a torque sensor according to the present invention is applied. An input shaft 2 made of a magnetic material as a first rotating shaft, an output shaft 3 as a second rotating shaft, or a bearing 5a.

It is rotatably supported by 5b and 5C.

However, input shaft 2. The output shaft 3 and torsion bar 4 are
are arranged coaxially.

The opening of the housing 1 on the input shaft 2 side is sealed by a seal ring 6, and the opening on the output shaft 3 side is sealed with a cap 7.

A steering wheel is integrally attached to the right end side of the input shaft 2 in the rotation direction in FIG. A shaft 3a is integrally formed, and the pinion shaft 3a is connected to a rack shaft 8 of a rack and pinion steering device within the housing 1.
It meshes with the

Therefore, the steering force generated by the operator steering the steering wheel is applied to the input shaft 2° torsion bar 4. Output shaft 3. The signal is transmitted to steered wheels (not shown) via the pinion shaft 3a and the rack shaft 8.

On the other hand, as shown in FIG. 1 and FIG. 2, which is a cross-sectional view taken along the line A-A in the same figure, the left end of the input shaft 2 is formed with protrusions 2a, 2a that are continuous in the axial direction. Projections 2a, 2a
is formed on the right end portion of the output shaft 3, and is formed on the protruding portions 2a, 2a.
The input shaft 2 and the output shaft 3 are inserted into vertical grooves 3b, 3b that are slightly wider than the input shaft 2, thereby preventing relative rotation between the input shaft 2 and the output shaft 3 beyond a predetermined range (approximately ±5 degrees).

Incidentally, FIG. 1 is a sectional view taken along the line BB in FIG. 2.

In addition, the input shaft 2 includes a flange portion 9 formed by molding to a larger diameter than other portions, and this flange portion 9.
A flange portion 10 made of a ring-shaped magnetic material is provided which is spaced apart from the input shaft 2 in the axial direction and is integrally fitted onto the input shaft 2 in the axial and rotational directions.
A cylindrical member 11 made of a non-magnetic material and rotatable relative to the input shaft 2 is disposed between the input shaft 2 and the input shaft 2 .

The outer peripheral surfaces of the flange parts 9 and 10 are provided with a plurality of protrusions 9a and 10a scattered at equal intervals in the circumferential direction,
These protrusions 9a and 10a are of the same size, or as shown in FIG.
The protrusions 10a are placed opposite to each other between the protrusions a, and the protrusions 9a are placed opposite to each other between the protrusions 10a and 10a.

Note that the gap between the input shaft 2 and the cylindrical member 11 and the gap between the cylindrical member 11 and the flange portion 9.10 are relatively narrow, and are adjusted to about 20 μm to 30 μm.

A cylindrical shaft 12 is attached to the cylindrical member 11 and is inserted loosely into the square groove 3C of the output shaft 3, passing through the flange portion 9 with a sufficient gap so that one end side does not come into contact with the cylindrical member 11, and parallel to the input shaft 2. is press-fitted.

Here, the shaft 12 and the square groove 3c are either integral in the rotational direction of the output shaft 3 or loosely inserted in the axial direction of the shaft 12, so that relative displacement can be achieved with a relatively small force. It becomes.

Further, a ring 1 made of a magnetic material is provided on the outer peripheral surface of the cylindrical member 11.
3 are integrally fitted externally in the rotational and axial directions.

The ring 13 has a plurality of protrusions 13a on the end face facing the flange 9 side, and a plurality of protrusions 13b on the end face facing the flange 10 side, which are scattered at equal intervals in the circumferential direction.
As shown in FIG. 3, these protrusions 1'3a and 13b have the same size and pitch, and when there is no relative rotation between the input shaft 2 and the output shaft 3, the protrusions 9a and 1'
The arrangement is such that the amount of overlap S1 between the protrusion 10a and the protrusion 13b is 50%, and the amount S2 of overlap between the protrusion 10a and the protrusion 13b is 50%.

Note that the gap G1 between the protrusion 9a and the protrusion 13a and the protrusion 10
The gap G2 between a and the protrusion 13b is the same distance,
It is relatively wide and is adjusted to about 0.3M to 0.6E.

Further, the inner circumferential surface of the housing 1 and the flange portion 9.
A cylindrical holder 15 made of a magnetic material is embedded in a portion surrounding IO and the cylindrical member 11, and this holder 15 has an opening on the input shaft 2 side and has gaps G+ and G2.
Two circumferential grooves 15a and 15b are formed surrounding the circumferential grooves 15a and 15b, and coils 16 and 17 of the same standard are housed in each of the circumferential grooves 15a and 15b.

The coils 16 and 17 calculate the difference between the electromotive forces induced in these coils 16 and 17, calculate the torque transmitted to the input shaft 2 and the output shaft 3 based on the calculation result, and calculate the torque transmitted to the input shaft 2 and the output shaft 3. For example, the rack axis 8
The steering wheel is connected to a controller that outputs a control signal to a steering assist force applying device comprising an electric motor or the like connected to the steering wheel.

FIG. 4 is a diagram showing an example of a circuit that is configured in the controller and calculates torque based on the difference between the electromotive forces induced in the coils 16 and 17. A bridge circuit 20 whose one end is connected and whose other end is connected via two resistors R1 and R2 having the same resistance value, an oscillator 21 that supplies an alternating current of a predetermined frequency to this bridge circuit 20, and a coil. 1
6 and resistance 8. A differential amplifier 22 is connected between the coil 16 and the resistor R1 to the non-inverting input terminal, and the coil 17 and the resistor R2 is connected to the non-inverting input terminal, and the ground is the inverting input terminal. a comparator 23 connected to the differential amplifier 23; The comparator 2 is interposed between the output terminal of the dynamic amplifier 22 and the inverting input terminal of the differential amplifier 24.
The analog switch 26 is turned on or off depending on the value obtained by inverting the output of the differential amplifier 24 by the inverter 27, and the smoothing circuit 28 smoothes the output of the differential amplifier 24.

Next, the operation of this embodiment will be explained.

Now, assuming that the steering system is moving straight and the steering torque is zero, there is no relative rotation between the input shaft 2 and the output shaft 3. 9.10, and a cylindrical member 11 to which the rotational force of the output shaft 3 is transmitted via the shaft 12. No relative rotation occurs with the ring 13 either. Therefore, the protrusion 9a and the protrusion 13a
Since the overlap amount S1 between the projection 10a and the projection 13b and the overlap amount S2 between the projection 10a and the projection 13b each maintain a state of 50%,
The self-inductance L1 of the coil 16 and the self-inductance L2 of the coil 17 are equal.

On the other hand, when a rotational force is generated on the input shaft 2 by steering the steering wheel, the rotational force is transmitted to the output shaft 3 via the torsion bar 4.

At this time, a resistance force is generated on the output shaft 3 according to the frictional force between the steered wheels and the road surface, the frictional force of the rack and pinion type steering device, etc., so between the input shaft 2 and the output shaft 3,
When the torsion bar 4 is twisted, a delayed relative rotation occurs on the output shaft 3 side.

Then, the flange portion 9.10 that rotates together with the input shaft 2
During this period, the cylindrical member 11 to which the rotational force of the output shaft 3 is transmitted via the shaft 12 is displaced in the rotational direction, so the ring 13 is also displaced in the rotational direction, and the wrap amounts S1 and S2 change.

At this time, as shown in FIG. 3, since the protrusions 9a and 10a are arranged half a pitch apart, when the ring 13 is displaced in the rotational direction between them, the overlap amounts S1 and S2
One increases and the other decreases, and in accordance with this increase and decrease, the self-inductances L1 and R2 of the coils 16 and 17 increase and decrease in opposite directions.

Here, for example, when torque in the clockwise rotation direction is generated, the wrap amount Sl increases and the wrap amount S2 decreases, and when torque in the counterclockwise rotation direction is generated, the wrap amount Sl decreases and the wrap amount Assuming that S2 is configured to increase, the self-inductance and R2 are
As shown in FIG. 5, the characteristics are exactly opposite and intersect when the torque is zero.

Figures 7 to 9 are graphs showing the internal and output waveforms of the circuit shown in Figure 4. Figure 7 is a waveform diagram when steering torque is generated in the left rotation direction, and Figure 8 is a waveform diagram when a steering torque is generated in the left rotation direction. FIG. 9 is a waveform diagram when the torque is zero, and FIG. 9 is a waveform diagram when a steering torque in the clockwise rotation direction is generated.

Here, assuming that the steering torque is zero, as described above, the self-inductance L1 of the coils 16 and 17
and R2 are equal, even if the output voltage V of the oscillator 21 is supplied to the bridge circuit 20, the electromotive force induced in the coils 16 and 17 is equal, and therefore, as shown in FIG. The voltage VA between them and the voltage V between the resistor R1 and the coil 16 are equal.

Therefore, the output voltage v6 of the differential amplifier 22 is zero, and it is determined that the output voltage v1 of the smoothing circuit 28 is zero and the steering torque is zero, regardless of the effects of other circuits.

As a result, the controller does not operate the steering assist force applying device that applies steering assist torque to the rack shaft 8.
No steering assist torque is generated, and the steering system maintains a straight-ahead state.

On the other hand, assuming that a steering torque in the left rotation direction is generated in the steering system, as described above, the self-inductance L1 of the coil 16 decreases according to the characteristics shown in FIG. 5, and the self-inductance L2 of the coil 17 decreases. As shown in FIG. 7, when the output voltage V of the oscillator 21 is supplied to the bridge circuit 20, the electromotive force induced in the coil 17 increases, and the electromotive force induced in the coil 16 increases. The power becomes smaller, so that the amplitude of voltage VA increases and the amplitude of voltage v8 becomes smaller.

Also, the output voltage V of the comparator 23. is a rectangular wave that is in phase with the voltage VB, and the output voltage V of the inverter 27 is a rectangular wave that is in opposite phase to the voltage vll, so the analog switch 25 is turned on only when the polarity of the voltage VIl is positive. , analog switch 26 is turned on only when the polarity of voltage VB is negative.

That is, when the polarity of the voltage V is positive, the output voltage V of the differential amplifier 22. is supplied to the non-inverting input terminal of the differential amplifier 24, so the output voltage V of the differential amplifier 24. is in phase with the voltage V8, and when the polarity of the voltage V is negative, the output voltage V6 of the differential amplifier 22 is in phase with the differential amplifier 24.
Since the output voltage (v)I of the differential amplifier 24 is supplied to the inverting input terminal of the differential amplifier 24, the output voltage (v)I of the differential amplifier 24 has an opposite phase to the voltage V.

Therefore, when a steering torque in the counterclockwise direction is generated, the signal appearing on the negative side of the voltage V is inverted in the differential amplifier 24, so that the output voltage of the differential amplifier 24 as shown in FIG. v8 appears only on the positive side.

Therefore, the output of the differential amplifier 24 is directly transmitted to the smoothing circuit 28.
When smoothed by , the output voltage V1 becomes a positive value as shown in FIG.

Furthermore, when a steering torque in the clockwise direction is generated in the steering system, the self-inductance L1 of the coil 16 increases and the self-inductance L2 of the coil 17 decreases according to the characteristics shown in FIG. As shown in FIG. 9, the amplitude of voltage VA is small and the amplitude of voltage Vs is large.

Even in this case, the output voltage V of the comparator 23.

is a rectangular wave that is in phase with the voltage v8, and the output voltage V of the inverter 27 is a rectangular wave that is in opposite phase to the voltage v8.
The analog switch 25 is turned on only when the polarity of the voltage VB is positive, and the analog switch 26 is turned on only when the polarity of the voltage VB is positive.
is turned on only when the polarity of is negative, but in this case the output voltage vl of the differential amplifier 22 is the voltage vA and V,
Since the amplitudes of V have the above-mentioned relationship, the voltage V (see FIG. 7) has a value opposite in phase to the voltage V when torque in the counterclockwise direction is generated (see FIG. 7).

Therefore, if the signal appearing on the positive side of the voltage V, the differential amplifier 24
9, the output voltage of the differential amplifier 24 appears only on the negative side, as shown in FIG.

Therefore, the output of the differential amplifier 24 is directly transmitted to the smoothing circuit 28.
When smoothed by , the output voltage V1 becomes a negative value as shown in FIG.

Then, the controller outputs the output voltage V1 of the smoothing circuit 28.
If it is not zero, the value is proportional to the steering torque, and therefore a control signal is output to the steering assist force applying device so that the steering torque is reduced based on that value.

Then, since a steering assist torque corresponding to the steering torque is applied to the steering system, the steering torque decreases.
The burden on the operator is reduced.

And the self-inductance L1 of the coils 16 and 17
As shown in FIG. 6, the difference between L2 and L2 is due to the self-inductance of the coil 16 or 17, and the slope is twice the slope of L2 (see FIG. 5), so as in this embodiment, Voltages vA and V determined by the electromotive force induced in the coils 16 and 17.

By calculating the torque based on the output of the differential amplifier 22, which calculates the difference between the two, minute changes in torque can be determined with high precision.

As a result, measurement accuracy can be improved without making the torsion bar 4 easy to twist, that is, without increasing the size of the device or deteriorating the torque transmission characteristics between the input shaft 2 and the output shaft 3. In other words, the same accuracy as the conventional device can be achieved with a small device with a short torsion bar 4.

Furthermore, since the difference between the self-inductances L1 and L2 is calculated, for example, the temperature around the coils 16 and 17 may fluctuate, or various noises may occur, resulting in changes in the self-inductances L1 and L2 that are unrelated to the torque. Even if fluctuations occur, they appear in the same direction in the self-inductances L1 and L2, so when their difference is determined, they are canceled out and removed from the final measurement. In other words,
In addition to temperature compensation, the device is also resistant to noise.

Furthermore, since the axial coupling force between the shaft 12 and the square groove 3c is eliminated or reduced, and the cylindrical member 1.1 is fitted onto the input shaft 2 with a small gap, for example, Even if a directional force is applied, the force is absorbed by the shaft 12 moving back and forth within the square groove 3C, so the influence of the axial force is not transmitted to the cylindrical member 11, and the cylindrical member 11 , maintaining proper axial position between the flanges 9 and 10.

In other words, with the configuration of this embodiment, even if an axial force is applied and the relative axial position between the input shaft 2 and the output shaft 3 changes, the measurement results are not affected, and only the torque is applied. You can get output according to the

Furthermore, unless the cylindrical member 11 is displaced in the axial direction, the frictional resistance between the cylindrical member 11 and the flange portion 9.10 will not change from its initial state, so high heat may be generated due to increased frictional force. There is no problem that the load applied to the shaft 12 increases and its durability deteriorates.

In this embodiment, as shown in FIG.
Because the torque is determined based on the signal that makes the output of the differential amplifier 22 in-phase or out-of-phase depending on the phase of the Torque measurement becomes possible.

Here, in this embodiment, the coil 16 corresponds to the first coil, the coil 17 corresponds to the second coil, and the resistor R1l
The R21 bridge circuit 20 and the oscillator 21 constitute an electromotive force induction means, the differential amplifier 22 corresponds to a difference value calculation means, and the comparators 23 . Differential amplifier 24. The analog switches 25 and 26 and the inverter 27 constitute phase switching means, and the smoothing circuit 28 corresponds to torque calculation means.

In addition, in the above embodiment, the torque sensor according to the present invention is
Although the case where the present invention is applied to a power steering device for a vehicle has been described, the present invention is not limited to this.

Furthermore, in the above embodiment, the present invention is applied to a torque sensor of a type that increases or decreases the self-inductance of the coils 16 and 17 according to the relative rotation between the input shaft 2 and the output shaft 3, or is limited to this. The input shaft 2 is equipped with an excitation coil and two detection coils.
The torque sensor may be of a type that increases or decreases the mutual inductance between the excitation coil and the detection coil in accordance with the relative rotation between the output shaft 3 and the output shaft 3.

〔Effect of the invention〕

As explained above, in the present invention, the first and second
In addition to calculating the difference in the electromotive force induced in the coil,
The calculation result is set to be in phase or out of phase depending on the polarity of the electromotive force induced in the first coil, and the torque is determined based on the phase-converted signal, which simplifies the circuit configuration and enables measurement. This has the effect of improving accuracy.

[Brief explanation of drawings]

Fig. 1 is a cross-sectional view showing the configuration of an embodiment of the present invention, Fig. 2 is a cross-sectional view taken along the line A-A in Fig. 1, Fig. 3 is a developed view of the part that changes the inductance of the coil, and Fig. 4 is a circuit diagram showing an example of a circuit for measuring the electromotive force induced in a coil, Fig. 5 is a graph showing the relationship between torque and self-inductance of the coil, and Fig. 6 is a graph showing the relationship between torque and the difference in self-inductance. Figure 7 is a waveform diagram when torque is generated in the counterclockwise rotation direction, Figure 8 is a waveform diagram when torque is zero, and Figure 9 is a waveform diagram when torque is generated in the clockwise rotation direction. FIG. 2... Input shaft (first rotating shaft), 3... Output shaft (second rotating shaft), 4... Torsion bar (elastic member),
16... Coil (first coil), 17... Coil (second coil), 20... Bridge circuit, 21...
- Oscillator, 22... Differential amplifier (difference value calculation means), 2
3... Comparator, 24... Differential amplifier, 25,
26...analog switch, 27...inverter,
28...Smoothing circuit

Claims (1)

[Claims] (1) First and second rotating shafts disposed coaxially, an elastic member connecting these first and second rotating shafts, and an elastic member that responds to the relative rotation between the first and second rotating shafts. first and second coils whose inductance increases and decreases in opposite directions;
an electromotive force inducing means for inducing an electromotive force in the first and second coils; a difference value calculation means for calculating the difference between the electromotive forces induced in the first and second coils; a phase switching means that outputs the calculation result in the same phase when the polarity of the electromotive force induced in the first coil is one of positive and negative, and outputs the calculation result in the opposite phase when the polarity of the electromotive force induced in the first coil is the other; A torque sensor comprising: torque calculation means for calculating torques transmitted to the first and second rotating shafts based on the output of the phase switching means.