JP3161867B2 - Magnetostrictive 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 magnetostrictive torque sensor suitable for detecting, for example, an output shaft torque of an automobile engine.

[0002]

2. Description of the Related Art For an automatic vehicle or the like having an automatic transmission, it has been proposed to attach a magnetostrictive torque sensor to an output shaft or the like for the purpose of optimizing the shift timing of the automatic transmission.

A conventional magnetostrictive torque sensor of this type will be described with reference to FIGS. 3 and 4. FIG.

In FIG. 1, reference numeral 1 denotes a casing constituting a torque sensor main body. The casing 1 is formed of a nonmagnetic material in a stepped cylindrical shape, and is fixed to a case (not shown) of an automatic transmission. It has become.

[0005] Reference numeral 2 denotes a magnetostrictive shaft rotatably disposed in a casing 1 via bearings 3 and 3. The magnetostrictive shaft 2 is formed of a stainless steel or the like in a rod shape, and both ends 2A and 2B of the casing 1 are formed of a casing. 1 to form a magnetostrictive shaft. An axially intermediate portion of the magnetostrictive shaft 2 is a slit forming portion 2 </ b> C located in the casing 1.
, 5, 5,... Are formed on the outer peripheral surface of the slit forming portion 2C at an angle of 45 ° obliquely downward and 45 ° obliquely upward.

Reference numerals 6 and 7 denote magnetically anisotropic portions. The magnetic anisotropic portions 6 and 7 are slit forming portions 2C of the magnetostrictive shaft 2.
Is coated with a magnetic material of Fe (83%) and Al (13%) and heat-treated. Then, a first magnetic anisotropic portion 6 is formed in a portion between the slit grooves 4, and a second magnetic anisotropic portion 7 is formed in a portion between the slit grooves 5. A magnetic path is formed in the isotropic portions 6 and 7 by a surface magnetic field.

Reference numeral 8 denotes a core member fixed to the inner peripheral surface of the casing 1 and surrounding the slit forming portion 2C of the magnetostrictive shaft 2 from the outside in the radial direction. The core member 8 is a stepped cylinder made of a magnetic material such as iron. Exciting and detecting coils 9 and 10 to be described later are arranged on the inner peripheral side.

Reference numerals 9 and 10 denote excitation and detection coils as a pair of detection coils which are located on the outer peripheral side of the magnetostrictive shaft 2 and face the magnetic anisotropic parts 6 and 7, respectively. Are provided on the inner peripheral side of the core member 8 via coil bobbins (not shown), respectively. An AC voltage V having a frequency f is applied by an oscillator 12 described later to perform an exciting action and a detecting action. The exciting and detecting coils 9, 10 have self-inductances L1, L2 as shown in FIG.
, R2.

Since the AC voltage V is applied to the excitation and detection coils 9 and 10 from the oscillator 12, the impedances Z1 and Z1 of the excitation and detection coils 9 and 10 are controlled.
2 becomes like Equation 1.

[0010]

(Equation 1)

Here, L1 and L2 in Equation 1 are self-inductances set by Equation 2.

[0012]

(Equation 2)

FIG. 4 shows a detection circuit of a magnetostrictive torque sensor according to the prior art. This detection circuit includes a bridge circuit 11, an oscillator 12 as an AC voltage applying means, a differential amplifier 13, and a phase detection circuit 14. And so on. Here, the bridge circuit 11 is composed of the excitation and detection coils 9 and 10 and the adjustment resistors R and R, and constitutes a full bridge in which the resistance values (impedances) of the corresponding sides are equal. A connection point a between the excitation and detection coils 9 and 10 and a connection point b between the adjustment resistors R and R are connected to an oscillator 12 of an AC voltage V having a frequency f of, for example, about 30 kHz.

Further, in the bridge circuit 11, L1 and r1 of one of the excitation and detection coils 9 are adjusted resistances R1 and R1.
Since the other excitation and detection coils L2 and r2 are connected in series to the adjustment resistor R, the currents i1 and i2 flowing through the excitation and detection coils 9 and 10 are:

[0015]

(Equation 3) And the detection voltages V1 and V2 at the connection points c and d
Is

[0016]

(Equation 4) Here, α1, α2 are calculated by the phase angles.

The excitation and detection coils 9 and 10
The connection points c and d between the differential amplifier 13 and the adjustment resistors R and R are connected to both ends of the differential amplifier 13, and output the respective detection voltages V 1 and V 2 from the excitation and detection coils 9 and 10 to the differential amplifier 13. I do. The output terminal 13A of the differential amplifier 13 is connected to the input side of the phase detector 14 together with the oscillator 12, and the phase detector 14 converts the output voltage V3 from the differential amplifier 13 to the AC voltage V from the oscillator 12. The rectifier synchronizes and rectifies the output to output an output voltage V4.

In the conventional magnetostrictive torque sensor having the above-described configuration, when an AC voltage V from the oscillator 12 is applied to the excitation and detection coils 9 and 10, the magnetostrictive shaft 2
In the slit forming portion 2C, a magnetic path is formed by the surface magnetic field along the magnetic anisotropic portions 6, 7 between the slit grooves 4, 5. In this case, the adjustment resistor R shown in FIG. 4 is connected to the differential amplifier 13 when the torque acting on the magnetostrictive shaft 2 is zero.
Is adjusted so that the output voltage V3 from the terminal becomes zero.

In this prior art, when a torque is applied to the magnetostrictive shaft 2 in the direction of arrow T as shown in FIG. 3, the magnetically anisotropic material between the slit grooves 4 is formed in the slit forming portion 2C of the magnetostrictive shaft 2. Tensile stress + σ along the active part 6
Acts, and a compressive stress −σ acts along the magnetic anisotropic portion 7 between each slit groove 5. Thereby, the magnetic anisotropic part 6
In this case, the magnetic permeability μ increases due to the tensile stress + σ, and the magnetic permeability μ decreases in the magnetic anisotropic portion 7 due to the compressive stress −σ.

On the other hand, the self-inductance L1 of the excitation and detection coil 9 disposed opposite to the magnetic anisotropic part 6 of the magnetostrictive shaft 2 increases due to the increase of the magnetic permeability μ, and the current flowing through the excitation and detection coil 9 i1 decreases. Also,
The excitation and detection coil 10 disposed opposite to the magnetic anisotropic part 7 has a self-inductance L2 based on the decrease in the magnetic permeability μ.
And the current i2 flowing through the excitation and detection coil 10
Increase.

As a result, the detection voltage V1 from the excitation and detection coil 9 decreases and the detection voltage V2 from the excitation and detection coil 10 increases.

[0022]

V3 = K × (V1−V2) where K is an amplification factor, and an AC output voltage V3 is output from the output terminal 13A of the differential amplifier 13 to the phase detection circuit 14. Then, the phase detection circuit 14 can synchronously detect and rectify the output voltage V3 with the AC voltage V from the oscillator 12, rectify the output voltage V3, and output the output voltage V4 as an output signal corresponding to the torque acting on the magnetostrictive shaft 2. .

[0023]

The detection circuit of the magnetostrictive torque sensor according to the prior art described above forms a bridge circuit 11 by excitation and detection coils 9 and 10, and the bridge circuit 11 loses its balance. Since the torque is detected, fine adjustment of each adjustment resistor R is required in the preparation stage of setting the bridge circuit 11, and there is a problem that the adjustment work is time-consuming.

Further, when the magnetostrictive torque sensor is mounted on, for example, an output shaft of a vehicle, the temperature greatly changes. Therefore, heat is applied to the magnetostrictive shaft 2, the excitation and detection coils 9, 10 and the core member 8 and the like. As a result, there is a problem that accurate and reproducible torque detection cannot be performed.

In order to solve this problem of the prior art, the present applicant has previously disclosed in Japanese Patent Application No. 5-32678 (hereinafter referred to as "prior art") a half bridge circuit as a detection circuit of a magnetostrictive torque sensor. We applied for what was.

This prior art magnetostrictive torque sensor comprises a magnetostrictive shaft having a pair of magnetically anisotropic portions on the outer periphery which are spaced apart in the axial direction, and a magnetically anisotropic shaft which is located on the outer periphery of the magnetostrictive shaft. A pair of detection coils provided to face each other, a half-bridge circuit formed by connecting the respective detection coils in series, and a triangular wave having a 180 ° phase difference at both ends of the half-bridge circuit. And a half-wave rectified waveform obtained by dividing a signal from a middle point of each detection coil of the half-bridge circuit into a positive part and a negative part based on a fundamental wave from the triangular wave generator. And a processing circuit for processing a signal from the phase detection circuit as an output signal.

In the prior art, the operation of adjusting the equilibrium state of the bridge circuit 11 of the prior art can be omitted, and erroneous detection of torque due to external heat can be prevented.

However, in this prior art, although the problem in the prior art can be solved as described above, a triangular wave having a phase difference of 180 ° is generated from the triangular wave generator, but noise is included in each waveform. Or, if there is a distortion, there is an unsolved problem that the signal is processed as it is as an output signal and the detection accuracy of the torque is reduced.

The present invention has been made in view of the above-mentioned unsolved problems of the prior art, and an object of the present invention is to provide a magnetostrictive torque sensor capable of performing high-accuracy torque detection with a simple circuit configuration. And

[0030]

In order to solve the above-mentioned problems, a magnetostrictive torque sensor employed in the present invention is provided with a magnetostrictive shaft having a pair of magnetically anisotropic portions on an outer peripheral side which are spaced apart in an axial direction. A pair of detection coils provided on the outer peripheral side of the magnetostrictive shaft so as to face the respective magnetic anisotropic parts, and a half bridge circuit formed by connecting the respective detection coils in series; An oscillator for inputting input waveforms having a phase difference of 180 ° to both ends of the half-bridge circuit, and an input for removing noise and distortion from the oscillator included in the detection signal output from the midpoint of the half-bridge circuit A signal correction circuit, a phase detection circuit that outputs a signal output from the input signal correction circuit as a rectified waveform based on a reference wave from the oscillation device, and a rectified wave from the phase detection circuit. And a processing circuit for processing the input signal as an output signal, wherein the input signal correction circuit adds two input waveforms input from the oscillation device and extracts noise and distortion of the oscillation circuit as an output signal. An adder circuit, and a second adder circuit for canceling noise and distortion by adding an output signal from the first adder circuit and a detection signal from a midpoint of the half bridge circuit. .

[0031]

The first adder adds input waveforms output from the oscillating device having phases different from each other by 180 °, so that only noise and distortion are detected.
By adding to the detection signal from the half-bridge circuit by the addition circuit, only the noise and distortion from the oscillation device included in the detection signal are canceled, and the noise and the noise included in the signal output from the input signal correction circuit to the phase detection circuit are eliminated. Eliminates distortion.

[0032]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS. In the embodiments, the same components as those of the above-described conventional technology are denoted by the same reference numerals, and description thereof will be omitted. Further, in the excitation and detection coils 9 and 10 shown in the drawings, the DC resistance components r1 and r2 are omitted, and only the coil symbols are shown.

In the figure, reference numeral 21 denotes a half bridge circuit,
The half bridge circuit 21 includes an exciting and detecting coil 9,
10 are connected in series, and a triangular wave generator 22 described later is connected to terminals A and B on both sides. The midpoint connection point C is connected to the phase detection circuit 24 via the input signal correction circuit 23.

Reference numeral 22 denotes a triangular wave generator as an oscillating device. The triangular wave generator 22 outputs two triangular waves having a frequency of 30 kHz and a phase difference of 180 ° as input waveforms input to the half bridge circuit 21. Are input to terminals A and B on both sides of the half bridge circuit 21, respectively. The input side of the triangular wave generator 22 is connected to a reference voltage VS, and each input waveform is a waveform on which the reference voltage VS is superimposed. The triangular wave generator 22 outputs a detection voltage VK corresponding to the input waveform to the phase detection circuit 24.

Reference numeral 23 denotes an input signal correction circuit. The input signal correction circuit 23 comprises an average value circuit 26 and an adder circuit 31 which will be described later, and the input signal correction circuit 23 is connected to the detection coils 9 and 10 of the half bridge circuit 21. , And amplifies the detection signal from the connection point C, which is the middle point, and outputs it to the phase detection circuit 24.

Reference numeral 24 denotes a phase detection circuit. An input signal correction circuit 23 and a triangular wave generator 22 are connected to the input side of the phase detection circuit 24, and a processing circuit 25 described later is connected to the output side. The phase detection circuit 24 performs a detection process on the signal from the input signal correction circuit 23 based on the detection voltage VK from the triangular wave generator 22 and outputs a rectified waveform divided into a positive portion and a negative portion.

Reference numeral 25 denotes a processing circuit, which obtains an output voltage by DA-converting the rectified waveform from the phase detection circuit 24. For example, an LPF (low-pass filter circuit), a differential amplifier circuit And so on.

Next, the configuration of the input signal correction circuit 23 will be specifically described with reference to FIG.

In FIG. 2, reference numeral 26 denotes an average value circuit as a first adder circuit.
And input resistors 28, 2 connected to the inverting input terminal of the operational amplifier 27 and having resistance values R1, R2 (R1 = R2).
9 and a non-feedback resistor 30 having a resistance value R3 (2R3 = R1 = R2) connected between the inverting input terminal and the output terminal of the operational amplifier 27. The input resistor 28 is connected to one output side of the triangular wave generator 22 via a terminal A of the half bridge circuit 21, and the input resistor 29 is connected to the triangular wave generator 22 via a connection point B of the half bridge circuit 21. The other output side is connected, and the non-inverting input terminal of the operational amplifier 27 is connected to the reference voltage VS. The averaging circuit 26 constitutes an inverting and adding circuit having an amplification factor of 1/2.

Reference numeral 31 denotes an addition circuit as a second addition circuit. The addition circuit 31 is connected to an operational amplifier 32 and an inverting input terminal of the operational amplifier 32, and has resistance values R4 and R5.
Input resistors 33 and 34 having (R4 = R5), and a non-feedback resistor 3 having a resistance value R6 (R6> R4 = R5) connected between the inverting input terminal and the output terminal of the operational amplifier 32.
And 5. The input resistor 33 is connected to the output terminal of the operational amplifier 27 of the average circuit 26, the input resistor 34 is connected to the terminal C of the half bridge circuit 21, and the non-inverting input terminal of the operational amplifier 32 is connected to the reference voltage VS. Have been. The addition circuit 31 constitutes an inversion addition amplification circuit having an amplification factor K0 (K0 = R6 / R4). Then, the output terminal 36 of the input signal correction circuit 23
Are connected to the phase detection circuit 24.

However, in this embodiment, in the detection circuit of the magnetostrictive torque sensor, a triangular wave is input from the triangular wave generator 22 to the half bridge circuit 21 in which the excitation and detection coils 9 and 10 are connected in series, and the excitation and detection coils are detected. 9,1
By adopting a configuration in which the change of 0 is processed by the phase detection circuit 24 and the processing circuit 25, unlike the full bridge circuit 11 of the related art, it can be configured by a simple circuit, and the number of parts can be reduced. The adjustment work for setting the equilibrium state of the circuit can be omitted.

Further, even in the half-bridge circuit 21 in which the full-bridge circuit is simplified, triangular waves having a phase difference of 180 ° are supplied to the terminals A,
By inputting to B, torque detection processing equal to or more than that of the full bridge circuit can be performed.

Next, the input signal correction circuit 23 will be described. First, assuming that the input forms 1 and 2 of two triangular waves generated from the triangular wave generator 22 are:

[0044]

(Equation 6) Becomes

In the mean value circuit 26, the resistance values of the input resistors 28 and 29 are R1 = R2, and the resistance ratio between the input resistors 28 and 29 and the non-feedback resistor 30 is 2R3 = R1.
Since R = R2, the waveform 3 from the output terminal of the operational amplifier 27 has an amplification factor of-の, and becomes as shown in the following Expression 7.

[0046]

(Equation 7)

On the other hand, when the torque is zero, the output waveform 0 as a detection signal output from the connection point C of the half bridge circuit 21 is as follows:

[0048]

(Equation 8) Becomes

Further, regarding the addition circuit 31, since the resistance values R4 = R5 of the input resistors 33 and 34, the waveform 4 on the inverting input terminal side of the operational amplifier 32 is

[0050]

(Equation 9) Becomes

Thus, looking at the inverting input terminal side of the operational amplifier 32, the noise (distortion) from the triangular wave generator 22
ΔV1 and ΔV2 can be eliminated.

The noise (distortion) .DELTA.V1 and .DELTA.V2 contained in the waveform output from the triangular wave generator 22 are extracted by the average value circuit 26 as Expression 7, and the output from the average value circuit 26 is expressed as Expression 8. By adding the detected signal from the half bridge circuit 21 to the added signal by the adder circuit 31, the noise (distortion) ΔV1 and ΔV2 can be canceled as shown in Expression 9.

On the other hand, even when a torque is applied, the output waveform 0 from the connection point C of the half bridge circuit 21 changes only the amplitude of the input waveforms 1 and 2 and generates noise (distortion) Δ
Since the DC components of V1, ΔV2 and the reference voltage VS do not change, the addition of the waveform 3 from the average value circuit 26 and the output wave 0 from the half bridge circuit 21 by the addition circuit 31 as shown in Expression 9 gives Noise (distortion) ΔV1,
ΔV2 can be offset.

Then, the noises (distortion components) ΔV 1 and ΔV 2 from the triangular wave generator 22 included in the detection signal from the half bridge circuit 21 are removed, and the subsequent phase detection circuit 2
4. Processing is performed as an output signal by the processing circuit 25, and accurate torque detection can be performed.

In the above-described embodiment, the magnetostrictive shaft 2 is described as being formed of only the pair of magnetic anisotropic portions 6 and 7 made of a magnetic material. 2 may be formed entirely of a magnetic material.

In the above embodiment, the input waveform is set to 180 °.
Triangular wave generator 2 for generating two triangular waves having different phases
Although 2 is used, the present invention is not limited to this, and a sine wave generator that generates two sine waves having a phase difference of 180 ° may be used.

[0057]

As described in detail above, according to the present invention, a pair of detection coils for detecting the torque applied to the magnetostrictive shaft are connected in series to form a half-bridge circuit, and 180 ° is applied to both ends of the half-bridge circuit. Waveforms having different phases are respectively input from the oscillator, and an input signal correction circuit, a phase detection circuit, and a processing circuit are connected to the subsequent stage of the half bridge circuit, and the input signal correction circuit is connected to two input waveforms from the oscillator. And a second addition circuit for adding the output from the first addition circuit and the detection signal from the midpoint of the half-bridge circuit. The first adder circuit extracts noise and distortion included in the input waveform of the second adder, and the second adder adds the output from the first adder circuit and the output from the half-bridge circuit. Only volume to offset noise and distortion. Then, by preventing noise and distortion from the oscillation device from being added to the detection signal input to the phase detection circuit, torque detection accuracy can be improved.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a torque detection circuit according to an embodiment of the present invention.

FIG. 2 is a circuit diagram specifically showing an input signal correction circuit in FIG. 1;

FIG. 3 is a configuration diagram of a conventional magnetostrictive torque sensor.

FIG. 4 is a circuit diagram showing a conventional torque detection circuit.

[Explanation of symbols]

 2 Magnetostrictive shaft 6, 7 Magnetic anisotropic part 9, 10 Excitation and detection coil (detection coil) 21 Half bridge circuit 22 Triangular wave generator (oscillator) 23 Input signal correction circuit 24 Phase detection circuit 25 Processing circuit 26 Average value circuit (First Addition Circuit) 31 Addition Circuit (Second Addition Circuit)

Continuation of front page (58) Field surveyed (Int.Cl. ⁷ , DB name) G01L 3/10

Claims (1)

(57) [Claims] 1. A magnetostrictive shaft having a pair of magnetically anisotropic parts on an outer peripheral side separated from each other in an axial direction, and provided on the outer peripheral side of the magnetostrictive shaft so as to face each magnetically anisotropic part. A pair of detection coils, a half-bridge circuit formed by connecting the respective detection coils in series, an oscillating device for inputting input waveforms having a phase difference of 180 ° to both ends of the half-bridge circuit, An input signal correction circuit for removing noise and distortion from the oscillation device included in the detection signal output from the midpoint of the bridge circuit, and an output signal from the input signal correction circuit based on a reference wave from the oscillation device. And a processing circuit for processing the rectified waveform from the phase detection circuit as an output signal, wherein the input signal correction circuit is A first adder circuit for adding two input waveforms to be input and extracting noise and distortion of the oscillation circuit as an output signal; and an output signal from the first adder circuit and a midpoint of the half bridge circuit. And a second addition circuit for canceling noise and distortion by adding the detection signal of the magnetostrictive torque sensor.