JP2001336995A - Torque detector - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a safe and inexpensive torque detector having temperature compensating function and failure detecting function by a pair of coils of one series. SOLUTION: A pair of coils 17 and 18 is serially connected to a load resistor RL, an AC driving voltage V1 is applied to the serial circuit. A differential amplifier circuit 31 outputs a differential voltage V3 between the voltage value V1 of the serial circuit and the voltage value V2 of the connection point of the coils, a first synchronous wave detecting circuit 107 performs a wave detection synchronously to the driving voltage V1, and a torque output circuit 23 outputs a torque signal based on the difference or ratio of impedance of the coils. A second synchronous wave detecting circuit 108 performs a wave detection synchronously to a control signal having a phase different from the driving voltage V1 by 90 deg., and a failure detecting circuit 109 performs a failure judgment on the basis of the sum of the impedances of the coils.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a torque detecting device for detecting a torque when an external force is applied to a rotating shaft in a non-contact manner, such as a power steering mechanism of an automobile, and more particularly to a failure detection of the torque detecting device. It is.

[0002]

2. Description of the Related Art (1) Description of Configuration of Prior Art In a power steering mechanism of an automobile, it is necessary to detect a torque applied to a steered wheel in order to determine an amount of power assist. If this mechanism malfunctions, it is extremely dangerous because a steering operation contrary to the intention of the operator can occur. Therefore, there is a torque detection device having a failure detection function. As such a torque detecting device, for example, there is a torque detecting device disclosed in Japanese Utility Model Laid-Open Publication No. 1-180737. The structure of this device will be described with reference to FIG.

In FIG. 1, an input shaft 100 has a first shaft 11a to which a steering wheel (not shown) is attached and a second shaft 11 to which a pinion gear (not shown) of a steering mechanism is attached.
and c are coaxially connected via a torsion bar 11b. The first shaft 11a is rotatably supported via a bearing 13 in, for example, a cylindrical case 12 fixed to the vehicle body. The second shaft 11c is provided with a recess 11d, and the inner diameter of the second shaft 11c is set at the position of the recess 11d.
A first sleeve 14a made of a non-magnetic material having a diameter larger than the outer diameter of c is provided. The pin 15 engaged with the first sleeve 14a penetrates in the radial direction of the second shaft 11c and engages with the small diameter portion of the first shaft 11a. A plurality of pins 15 are provided in the circumferential direction of the first sleeve 14a,
In addition, a portion of the second shaft 11c through which the pins penetrate is provided with a pin hole 11e having an appropriate length in the circumferential direction so that the rotation of the second shaft 11c is not hindered. Thus, the first sleeve 14a is interlocked with the first shaft 11a. Further, a first cylinder 61 made of a magnetic material and having a plurality of teeth 61a provided around one shaft end face is fixed to the first sleeve 14a.

A second sleeve 14b made of a non-magnetic material is fixed to the large diameter portion of the first shaft 11a. The second sleeve 14b has a plurality of teeth having the same pitch as the teeth 61a on one shaft end face. A second cylinder 62 made of a magnetic material and surrounding the portion 62a is fixed. First shaft 11 of second shaft 11c
A third sleeve 14c made of a non-magnetic material is fixed to the a-side end, and the third sleeve 14c is
A third cylinder 63 made of a magnetic material having a plurality of teeth 63a provided at the same pitch as 1a and a fourth cylinder 64 made of a magnetic material provided with a plurality of teeth 64a are fixed.
Then, the tooth portion 61a of the first cylinder 61 and the third cylinder 63
And the tooth portion 62a of the second cylinder 62 and the tooth portion 64a of the fourth cylinder 64 are opposed to each other at equal intervals. Also, the tooth portions 61a and 63a and the tooth portion 62
a and 64a have the same facing state.

In the case 12, a bobbin 16 having four circumferential grooves 16a, 16b, 16c and 16d arranged in the axial direction on the inner circumferential surface is fixed. The center of the circumferential groove 16a in the axial direction is at a position facing the tooth portions 61a and 63a, and the circumferential grooves 16b and 16c are at positions facing the other shaft end surfaces 63b and 64b of the third and fourth cylinders 63 and 64. Close to the peripheral groove 16d
Are arranged to be located at positions facing the tooth portions 62a and 64a, respectively. And the peripheral groove 16
The first torque detecting coil 17 is disposed in a, and the second torque detecting coil 18 is disposed in the circumferential groove 16d. A first temperature compensation coil 19 is provided in the peripheral groove 16b, and the peripheral groove 16c
Is provided with a second temperature compensation coil 20.

FIG. 4 is a circuit diagram showing a main part of an electric circuit of the torque detecting device. In the figure, one ends of a first torque detecting coil 17 and a first temperature compensating coil 19 are connected to input terminals + and-of a first differential amplifier 21, and one ends of a second torque detecting coil 18 and a first temperature compensating coil 20 are connected. Are connected to the input terminals + and-of the second differential amplifier 22. The outputs of the first and second differential amplifiers 21 and 22 are output from a torque output circuit 23,
24 and the input terminal 2 of the multiplexer 25
5a and 25b. The output signal TS selected by the multiplexer 25 is supplied to a control circuit (not shown) of the power steering motor, and a selection control section (not shown) supplies a selection command signal SS to the multiplexer 25.

(2) Description of Operation and Operation of Conventional Technique Next, the operation of the above-described conventional torque detecting device will be described. When an external torque is applied between the first shaft 11a and the second shaft 11c, the torsion bar 11b is twisted, and the first and second magnetic elements 61, 62 and the third, fourth A relative angular displacement occurs between the magnetic elements 63 and 64. Thereby, the tooth portions 61a and 63a and the tooth portions 62a and 6
The opposing area 4a changes, and the impedance of the first and second torque detecting coils 17, 18 changes. here,
By applying an AC drive current to these four coils by a drive circuit (not shown) and detecting the generated voltage,
The impedance of each of these coils is determined. Since the amount of change in the impedance of the torque detection coil is proportional to the torque, the torque can be obtained by detecting this. However, the impedance of the torque detecting coils 17 and 18 varies not only with the torque but also with the temperature. , Temperature compensation is performed. Outputs of the differential amplifier circuits 21 and 22 are amplified by torque output circuits 23 and 24 to output signals indicating torque, respectively.

[0008] A control circuit of a power steering mechanism (not shown) supplies a selection command signal SS to the multiplexer, selects an output signal of one of the torque output circuits, and obtains a torque output TS. If there is a discrepancy between the output signals of the two torque output circuits, the control circuit determines that a failure has occurred in the torque sensor and stops the assist operation, or the control circuit determines which of the torque output circuits can be determined to be normal. Continue the assist operation using the output.

[0009]

Since the conventional torque detecting device is configured as described above, if a failure detecting function is provided in addition to the temperature compensating function, two pairs of coil pairs are required. there were. Therefore, there is a problem that the cost of the torque detecting device is increased.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-described problems, and provides a safe and low-cost torque detection device having a temperature compensation function and a failure detection function with a single coil pair. It is intended to be.

[0011]

According to a first aspect of the present invention, there is provided a torque detecting device provided between a first shaft and a second shaft and acting between the first shaft and the second shaft. Depending on the torque,
An elastic member that causes a torsional displacement between the first and second axes, a magnetic element that is relatively displaced by the torsional displacement between the first axis and the second axis, and a magnetic element that is wound around the magnetic element A pair of coils whose impedance changes in the opposite direction due to the relative displacement of the pair, a torque output circuit that outputs a torque signal based on the difference or ratio of the impedance of the pair of coils, and a And a failure detection circuit for performing a failure determination.

According to a second aspect of the present invention, in the first aspect of the invention, a pair of coils are connected in series, and a load resistor connected in series to these coils and an AC drive voltage V1 is applied to the coils. A drive circuit and a voltage value V1 of the series circuit.
And a differential amplifier circuit for inputting a voltage value V2 at a connection point between the pair of coils and outputting a differential output voltage V3;
, And a first synchronous detection circuit for performing detection in synchronization with the drive voltage V1, and a differential output voltage V3 to receive the drive voltage V3.
A second synchronous detection circuit that performs detection in synchronization with a control signal having a phase difference of 1 and 90 degrees.

[0013] The invention of claim 3 is claim 1 or claim 2.
In the invention, a yoke is provided to surround a pair of coils and guides a magnetic flux generated by passing an AC drive current to these coils to the magnetic element. The thickness is not more than twice the thickness D.

According to a fourth aspect of the present invention, there is provided the first to third aspects.
In the invention, the magnetic element or the yoke is made of a soft magnetic amorphous metal.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiment 1 FIG. 1 is a partial front sectional view showing the structure of a torque detecting device according to Embodiment 1 of the present invention. In the drawing, the same or equivalent members and portions as those in FIG. 3 are denoted by the same reference numerals.

In FIG. 1, an input shaft 100 has a first shaft 11a to which a steering wheel (not shown) is attached and a second shaft 11 to which a pinion gear (not shown) of a steering mechanism is attached.
c, and these two shafts 11a and 11b are elastically connected by a torsion bar 11b provided on the central axis. The first shaft 11a is rotatably supported via a bearing 13 in, for example, a cylindrical case 12 fixed to the vehicle body. The second shaft 11c is provided with a concave portion 11d.
Made of a non-magnetic material larger than the outer diameter of the shaft 11c.
A sleeve 14a is provided. This first sleeve 14
The pin 15 engaged with the first shaft 11a penetrates in the radial direction of the second shaft 11c and is engaged with the small diameter portion of the first shaft 11a. A plurality of pins 15 are provided in the circumferential direction of the first sleeve 14a, and the second shaft 11 through which these pins pass is provided.
The portion c is provided with a pin hole 11e having an appropriate length in the circumferential direction so that the rotation of the second shaft 11c is not hindered. Thus, the first sleeve 14a is interlocked with the first shaft 11a. In addition, the first sleeve 14a has a magnetic body (in particular,
A cylindrical first magnetic element 61 made of a soft magnetic amorphous metal foil) is fixed.

A second sleeve 14b made of a non-magnetic material is fixed to a large diameter portion of the first shaft 11a, and a plurality of teeth having the same pitch as the teeth 61a are formed on one shaft end face of the second sleeve 14b. Cylindrical second magnetic element 6 made of a magnetic material (particularly, soft magnetic amorphous metal foil) surrounding the portion 62a
2 is fixed. A third sleeve 14c made of a non-magnetic material is fixed to an end of the second shaft 11c on the side of the first shaft 11a.
A cylindrical third magnetic element 63 made of a magnetic material having a plurality of teeth 63a provided at the same pitch and a plurality of teeth 6
A cylindrical fourth magnetic element 64 made of a magnetic material around 4a is fixed.

The teeth 61a of the first magnetic element 61
And the teeth 63a of the third magnetic element 63, and the teeth 62a of the second magnetic element 62 and the teeth 6a of the fourth magnetic element 64.
4a are opposed to each other at equal intervals. The opposing states of the teeth 61a and 63a and the teeth 62a and 64a are the same.

In the case 12, a yoke 16 having two peripheral grooves 16a and 16d arranged in the axial direction on the inner peripheral surface is fixed. The center of the circumferential groove 16a in the axial direction is located at a position facing the teeth 61a and 63a, and the center of the peripheral groove 16d is located at a position facing the teeth 62a and 64a. Then, the first groove is provided in the peripheral groove 16a.
A torque detection coil 17 is provided, and a second torque detection coil 18 is provided in the circumferential groove 16d. Further, the yoke 16 is formed of a resin material, and a magnetic material, particularly a soft magnetic amorphous metal foil 50, serving as an effective portion is provided only at the portions indicated by the thick lines around the coil wires 16 and 17 to be wound. I have.

FIG. 2 is a circuit block diagram of the torque detector according to the first embodiment. The oscillation circuit 101 has a frequency of several kHz
Oscillates a frequency signal of several tens of kHz and generates a timing circuit 1
Numeral 02 divides the frequency of the oscillation circuit 101 by 、, thereby generating a rectangular wave whose duty is exactly １ ／. The timing circuit 103 is also the oscillation circuit 1
In addition to dividing the frequency of 01 by １ ／, a rectangular wave whose phase is delayed by 90 degrees from the timing circuit 102 is generated. RL 105 is a load resistor connected in series with the torque detection coils 17 and 18, and the drive circuit 104 applies an AC drive voltage V 1 in the same phase as the timing circuit 102 to these series circuits. The differential amplifier circuit 21 receives the voltage value V1 of the series circuit and the voltage value V2 at the connection point of the torque detection coils 17 and 18, and outputs a differential output voltage V3 ｛V3 =
A (V1-2 × V2), A outputs a constant｝. The synchronous detection circuit 107 receives the output voltage V3 of the differential amplifier circuit 21 and performs synchronous detection synchronized with the timing circuit 102.
The synchronous detection circuit 108 outputs the output voltage V3 of the differential amplification circuit 21.
And performs synchronous detection synchronized with the timing circuit 103. The torque output circuit 23 receives a DC output proportional to the change in inductance of the synchronous detection circuit 107 and generates a torque output signal. The failure detection circuit 109 detects whether the output value of the synchronous detection circuit 107 is within a certain range, and outputs a signal indicating a failure to the torque output circuit 23 if the output value is outside the certain range.

Next, the operation of the torque detecting device according to the first embodiment will be described.

Z1 = R1 + jX1 (1) Z2 = R2 + jX2 (2) X1 = ωL1 (3) X2 = ωL2 (4) Z1, Z2: First and second detection coils Impedance R1, R2: Resistance of first and second detection coils X1, X2: Reactance of first and second detection coils j: Imaginary unit L1, L2: Inductance of first and second detection coils ω: Drive Voltage angular frequency

Then, the resistances R1 and R2 represent the loss of the coil. In conventional ordinary applications, the magnetic element and the yoke are often made of an iron-based metal material, so that the resistance of the coil is as large as the reactance due to the eddy current or the magnetic hysteresis of the magnetic material. Often have. However, in this embodiment, as proposed by the present inventor in Japanese Patent Application No. 11-308931, the magnetic element and the yoke have a very small magnetic hysteresis and a plate thickness represented by the following equation (5). Since the soft magnetic amorphous metal foil having a thickness smaller than twice the skin thickness D is used, it is hardly affected by eddy current. Therefore, the resistance can be made sufficiently smaller than the reactance.

D = root (2ρ / (ωμsμ0)) ‥‥‥‥ (5) ρ: specific resistance of magnetic material μs: relative magnetic permeability of magnetic material μ0: magnetic permeability of vacuum

When an external torque is applied between the first shaft 11a and the second shaft 11c, the torsion bar 11b
Is twisted, and a relative angular displacement occurs between the first and second magnetic elements 61 and 62 connected to the first axis 11a and the third and fourth magnetic elements 63 and 64 connected to the second axis 11c. appear. As a result, the facing areas of the teeth 61a of the first magnetic element 61 and the teeth 63a of the third magnetic element 63, and the facing areas of the teeth 62a of the second magnetic element 62 and the fourth magnetic element 64a change. , First and second torque detecting coils 17, 18
Changes in the opposite direction. The amount of change due to this torque is δL, and the inductance at the time of neutrality is L0 for both torque detection coils. Since the resistance is small and ignored, the impedance becomes as follows.

Z1 = jω (L0 + δL) (6) Z2 = jω (L0-δL) (7)

Therefore, the impedance ZS obtained by adding the load resistance 105 to the sum of the impedances of the series circuit of the two torque detecting coils is

ZS = RL + Z1 + Z2 = RL + 2jωL0 (8)

And does not change with torque. Further, as described in detail in Japanese Patent Application No. 11-308931 proposed by the present inventors, the magnetic elements 61 to 64 and the yoke 1
6, the temperature change of L0 is small by using a soft magnetic amorphous metal foil having extremely excellent magnetic properties.
ZS changes little with temperature.

Here, when the drive circuit 104 applies an AC voltage V1 having a constant amplitude at an angular frequency ω to the series circuit, an AC current I flows. Since the change in ZS is small, the amplitude of the alternating current I does not change much depending on the torque and the temperature.

Assuming that the voltage at the connection point between the torque detection coils 17 and 18 is V2, the output voltage V3 of the differential amplifier 21 is
Is set to be as follows.

V3 = A (V1-2 × V2) (9) A: constant

From equations (6) to (9),

V3 = A {(V1−V2) − (V2−0)} = A · I {jω (L0 + δL) + RL) −jω (L0−δL)} (10)

Since the load resistance RL is set sufficiently smaller than Z1 and Z2, the equation (8) is simplified by using this.

ZS = 2jωL0 (11) ∴I = V1 / ZS = V1 / (2jωL0) (12)

By substituting equation (12) into equation (10),

V3 = A · V1 · δL / L0 + A · I · RL (13)

As can be seen from the equation (12), the phase of the current I and the voltage V1 are different from each other by 90 degrees.
Is the product of the drive voltage V1, that is, the AC voltage component having the same phase as that of the timing circuit 102 and having an amplitude proportional to the amount of change δL of the inductance, the current I delayed by 90 degrees from that, and the load resistance RL. It can be seen that an AC voltage in which an AC voltage component proportional to is superimposed appears.

The synchronous detection circuit 107 extracts only a component having the same phase as that of the output signal of the timing circuit 102 and generates a DC output proportional to the amplitude, so that a DC output proportional to only the inductance change amount δL can be obtained. . This is amplified by a torque output circuit 23 and output as a torque output.

On the other hand, the synchronous detection circuit 108 extracts only a component having the same phase as that of the output signal of the timing circuit 103 and generates a DC output proportional to the amplitude thereof, so that a DC output proportional to only the amplitude of the current I is obtained. Can be

A torque detection coil, an oscillation circuit, a drive circuit,
If there is no failure in the timing circuit, the amplitude of the current I should not deviate much from a constant value because the sum of the impedances of the torque detection coil only slightly changes due to the temperature change. Conversely, when a disconnection or a rare short occurs in the torque detection coil and the sum of the impedance of the torque detection coil changes, the amplitude of the current I changes and the output of the synchronous detection circuit 108 deviates from a constant value. When this deviation increases, it can be determined that a failure has occurred in the torque detection coil, any of the above circuits, or the differential amplifier circuit. The failure detection circuit 109 includes a synchronous detection circuit 108
Is out of the predetermined range, a signal indicating a failure is sent to the torque output circuit 23, and the operation of setting the output of the torque output circuit 23 to outside the normal output range is performed. As a result, the control circuit of the power steering mechanism determines that a failure has occurred in the torque detection device and stops the assist operation. Therefore, the power steering mechanism does not operate abnormally and is safe.

In the above embodiment, the resistance and the load resistance of the torque detecting coil are set to be sufficiently smaller than the reactance of the torque detecting coil in order to simplify the calculation formula. If the size is equal to or less than, the operation is practically almost the same for a certain size. Therefore, the failure detection circuit can be applied to a torque detection device using an iron-based magnetic element or yoke.

In the above embodiment, the independent load resistor RL is provided.
The load resistance RL may be substituted for the load resistance RL using the resistance of the coil wire itself by making the coil longer or thinner than the coil wire of the other detection coil.

[0045]

As described above, according to the first to fourth aspects of the present invention, a torque signal based on the difference or ratio of the impedance of a pair of coils is detected, and based on the sum of the impedances of the pair of coils. As a result, the temperature compensation function and the failure detection function can be provided by one coil pair, and there is an effect that a safe and low-cost torque detection device can be obtained.

According to the third or fourth aspect of the present invention, the magnetic element and the yoke are made of a magnetic material having a very small magnetic hysteresis and a plate thickness smaller than twice the skin thickness D, especially a soft magnetic material. Since the amorphous metal foil is used, it is hardly affected by the eddy current, the resistance of the coil can be made sufficiently smaller than the reactance, and the detection accuracy of torque and failure can be increased.

[Brief description of the drawings]

FIG. 1 is a partial front sectional view showing a torque detecting device according to Embodiment 1 of the present invention.

FIG. 2 is a circuit block diagram showing a torque detector according to Embodiment 1 of the present invention.

FIG. 3 is a partial front sectional view showing a conventional torque detecting device.

FIG. 4 is a circuit block diagram of a conventional torque detection device.

[Explanation of symbols]

11a first shaft, 11b second shaft, 11c torsion bar, 14a-c sleeve, 16 yoke, 61-
64 magnetic element, 17, 18 torque detecting coil, 21
Differential amplifier circuit, 23 torque output circuit, 101 oscillation circuit, 102, 103 timing circuit, 107, 10
8 Synchronous detection circuit, 109 failure detection circuit, RL load resistance.

Claims (4)

[Claims] A first shaft provided between the first shaft and the second shaft;
An elastic member that causes a torsional displacement between the first and second shafts in response to a torque acting between the first and second shafts; and a torsion between the first and second shafts. A pair of coils wound around the magnetic element and whose impedance changes in the opposite direction due to the relative displacement of the magnetic element, based on a difference or ratio of the impedance of the pair of coils; A torque output circuit for outputting a detected torque signal; and a failure detection circuit for performing failure determination based on a sum of impedances of the pair of coils. 2. A pair of coils connected in series, a load resistor connected in series with these coils, a drive circuit for applying an AC drive voltage V1 to the coils, and a voltage value V1 of the series circuit. And a differential amplifier circuit for inputting a voltage value V2 at a connection point of a pair of coils and outputting a differential output voltage V3, and a first amplifier for inputting the differential output voltage V3 and performing detection in synchronization with the drive voltage V1. 2. A synchronous detection circuit comprising: a synchronous detection circuit; and a second synchronous detection circuit that receives the differential output voltage V3 and performs detection in synchronization with a control signal having a phase different from the drive voltage V1 by 90 degrees. 3. The torque detecting device according to 1. 3. The thickness of a yoke provided surrounding the pair of coils and guiding a magnetic flux generated by flowing an AC drive current to these coils to the magnetic element, and the thickness of an effective portion of the magnetic element is as follows. 2 of skin thickness D calculated by equation (5)
3. The torque detecting device according to claim 1, wherein the torque is not more than twice. D = root (2ρ / (ωμsμ0)) ‥‥‥‥ (5) ρ: specific resistance of magnetic material ω: angular frequency of drive voltage μs: relative magnetic permeability of magnetic material μ0: magnetic permeability of vacuum 4. The torque detecting device according to claim 1, wherein the magnetic element or the yoke is made of a soft magnetic amorphous metal.