JPH072943U - Magnetostrictive torque sensor - Google Patents

Abstract

(57) [Abstract] [Purpose] A torque sensor can detect torque applied to a magnetostrictive shaft with high accuracy. [Structure] Since one bias voltage VS0 different from the other bias voltage VS is applied to the bridge circuit 9, the differential amplifier circuit 31, and the oscillation circuit 21 in the detection circuit, the amplitude V00 of the oscillation circuit 21 is increased. be able to. As a result, the detection voltages V1 'and V2' from the bridge circuit 9 are obtained.
And the detection voltage V3 'from the differential amplifier circuit 31 can be increased accordingly. Then, the torque applied to the magnetostrictive shaft can be detected with high accuracy.

Description

[Detailed description of the device]

[0001]

[Industrial applications]

 The present invention relates to a magnetostrictive torque sensor suitable for use in detecting a torque generated in an output shaft of an automobile engine, for example.

[0002]

[Prior art]

 In an automatic vehicle or the like equipped with an automatic transmission, it has been proposed to attach a torque sensor to a propeller shaft or the like, for example, in order to optimize the shift timing by an automatic transmission mechanism.

Therefore, FIGS. 5 to 7 show a two-coil type magnetostrictive torque sensor as an example of a torque sensor according to this type of conventional technology.

In the figure, reference numeral 1 denotes a magnetostrictive shaft made of a magnetostrictive material such as chrome molybdenum steel, and the magnetostrictive shaft 1 is provided, for example, in the middle of a propeller shaft. It becomes the output side mounting portion 1B, and the slit groove forming portion 1C is formed in the middle thereof. The slit groove forming portions 1C are provided with slit grooves 2 and 3 engraved at 45 ° downward and 45 ° upward, respectively. They are provided so as to face each other.

Reference numeral 4 denotes a coil fixing member that is provided so as to be rotatable relative to the magnetostrictive shaft 1 via a pair of bearings 5 and 5 so as to surround the outer periphery of the slit groove forming portion 1C. Reference numeral 4 is fixedly attached to the vehicle body (not shown). Reference numeral 6 denotes a ring-shaped core member fixed to the inner peripheral side of the coil fixing member 4. The core member 6 is provided with exciting and detecting coils 7 and 8 at positions facing the slit grooves 2 and 3, respectively. Therefore, the self-inductances of the exciting and detecting coils 7 and 8 are L1 and L2.

Next, the circuit configuration of the detection circuit of the two-coil type magnetostrictive torque sensor will be shown and described with reference to FIG.

In FIG. 6, reference numeral 9 denotes a bridge circuit, and the bridge circuit 9 includes exciting and detecting coils 7 and 8, iron losses r1 and r2 of the exciting and detecting coils 7 and 8, and the exciting and detecting coil 7. , 8 which are connected so as to oppose each other, and will be described later between the connection point a of the excitation and detection coils 7, 8 and the connection point b of the adjustment resistors R, R. The oscillation circuit 10 is connected, and the connection point c (one output end) between the excitation / detection coil 7 and the adjustment resistor R and the connection point d (other output end) between the excitation / detection coil 8 and the adjustment resistor R are , Which serve as output terminals for deriving output voltages V1 and V2 from the excitation and detection coils 7 and 8, respectively, and the connection points c and d are respectively connected to input terminals of a differential amplifier circuit 11 which will be described later. The connection point b of the bridge circuit 9 is connected to the DC bias voltage VS.

Reference numeral 10 denotes an oscillating circuit, which oscillates an AC voltage V having a peak value (amplitude) V 0 and a frequency f (for example, 30 kHz) by a DC power source such as a battery (not shown). The output side is connected to the connection point a of the bridge circuit 9 and the phase adjusting circuit 13. A direct current bias voltage VS (VS≉V0) of, for example, 2.7 V is connected to the ground side of the oscillator circuit 10, whereby the negative side amplitude (-V0) as shown in FIG. It is regulated so that it will not be lower than (GND).

Reference numeral 11 denotes a differential amplifier circuit. The differential amplifier circuit 11 is composed of an operational amplifier or the like. By connecting the connection points c and d of the bridge circuit 9 to each input terminal, the output voltage V1 , V2 are input, and the detection processing circuit 14 is connected to the output terminal 12 via an AC coupling circuit 17, which will be described later, so that the detection voltage V3 is output to the detection processing circuit 14.

Reference numeral 13 denotes a phase adjusting circuit connected to the output side of the oscillator circuit 10. The phase adjusting circuit 13 is synchronized with the phase angle of the output voltage V1 (V2) when torque is not applied to the magnetostrictive shaft 1. The phase adjustment voltage VP is output to the detection processing circuit 14.

Reference numeral 14 denotes a detection processing circuit. The input side of the detection processing circuit 14 is connected to the output terminal 12 of the differential amplification circuit 11 and the output side of the phase adjustment circuit 13 via the AC coupling circuit 17, and detection is performed. The voltage V3 and the phase adjustment voltage VP are input. Then, the detection processing circuit 14 outputs a portion obtained by synchronizing the detection voltage V 3 with the phase adjustment voltage VP from the phase adjustment circuit 13 to the LPF 15 described later.

Reference numeral 15 denotes a low-pass filter (hereinafter referred to as “LPF15”) as a DC conversion circuit. The LPF15 integrates a portion obtained by synchronizing the detection voltage V3 by the phase adjustment voltage VP and outputs a DC output. The voltage V4 is output to the amplifier circuit 16. Then, in the amplifier circuit 16, the DC output voltage V4 input from the LPF 15 is amplified and output to a control unit (not shown).

Reference numeral 17 denotes an AC coupling circuit. The AC coupling circuit 17 includes a capacitor 17A connected between the output terminal 12 of the differential amplifier circuit 11 and the detection processing circuit 14, and an output side of the capacitor 17A. And a resistor 17B connected between the bias voltage VS and the bias voltage VS, which constitutes a so-called high-pass filter circuit. The AC coupling circuit 17 removes the DC component of the detection voltage V3 from the differential amplifier circuit 11, passes the AC component (especially, frequency f or more), and outputs it to the detection processing circuit 14. is there.

Since the bias voltage VS is applied to the ground side of the oscillator circuit 10, the differential amplifier circuit 11, the detection processing circuit 14, the LPF 15, and the amplifier circuit 16, each signal is a signal. Is in a state in which the bias voltage VS is applied.

Next, the principle of torque detection will be described.

First, since the AC voltage V is applied to the exciting and detecting coils 7 and 8 from the oscillation circuit 10, the impedances Z1 and Z2 of the exciting and detecting coils 7 and 8 are given by the following equation (1).

[0017]

[Equation 1]

However, L1 and L2 in the equation 1 are self-inductances set by the equation 2.

[0019]

[Equation 2] However, μ: permeability N: number of coil windings S: magnetic path cross-sectional area

Further, in the bridge circuit 9, L1 and r1 of one exciting and detecting coil 7 are connected in series to the adjusting resistor R, and L2 and r2 of the other exciting and detecting coil 8 are connected to the adjusting resistor R in series. Therefore, the currents i 1 and i 2 flowing through the excitation and detection coils 7 and 8 are

[0021]

[Equation 3] The output voltages V1 and V2 at the connection points c and d are calculated by

[0022]

[Equation 4] However, it is calculated by α1, α2: phase angle.

Further, the connection points c and d between the exciting and detecting coils 7 and 8 and the adjusting resistors R and R are connected to both side terminals of the differential amplifier circuit 11, respectively, and are connected from the exciting and detecting coils 7 and 8, respectively. The output voltages V1 and V2 of the above are output to the differential amplifier circuit 11. The output terminal 12 of the differential amplifier circuit 11 is connected to the input side of the detection processing circuit 14 together with the phase adjustment circuit 13, and the detection processing circuit 14 applies the detection voltage V 3 from the differential amplification circuit 11 to the phase adjustment circuit. It is synchronized based on the phase adjustment voltage VP from 13 and is integrated by the LPF 15 to output a DC output voltage V 4 to the amplifier circuit 16.

In the two-coil type magnetostrictive torque sensor configured as described above, when the AC voltage V of the oscillation circuit 10 is applied to the excitation and detection coils 7 and 8, a magnetic path is formed on the surface of the magnetostrictive shaft 1. Although formed, the slit grooves 2 and 3 are provided on the surface of the slit groove forming portion 1C, so that the magnetic path due to the surface magnetic field is formed along the slit grooves 2 and 3.

On the other hand, when torque T (hereinafter referred to as “positive torque”) in the direction of the arrow (clockwise) as shown in FIG. 5 is applied to the input side mounting portion 1 A of the magnetostrictive shaft 1, the slit groove 2 has A compressive stress −σ is generated, and a tensile stress + σ is generated in the slit groove 3. When a positive magnetostrictive material is used for the magnetostrictive shaft 1, it is known that the tensile stress + σ increases the magnetic permeability μ and the compressive stress −σ decreases the magnetic permeability μ.

As a result, the output voltage V1 from the excitation / detection coil 7 decreases and the output voltage V2 from the excitation / detection coil 8 increases, so that in the differential amplifier circuit 11,

[0027]

## EQU00005 ## V3 = A.times. (V1 -V2) where A: Amplification with an amplification factor is performed, and the AC detection voltage V3 is output from the output terminal 12 of the differential amplifier circuit 11 to the detection processing circuit 14. . The detection processing circuit 14 synchronously detects the detection voltage V3 by the phase adjustment voltage VP from the phase adjustment circuit 13 and outputs a DC output voltage V4 as an output signal corresponding to the torque acting on the magnetostrictive shaft 1. be able to.

For example, in the prior art, as shown in FIG. 7, when torque is applied to the magnetostrictive shaft 1, the detection voltage V3 output from the differential amplifier circuit 11 is a two-dot chain line centered on the bias voltage VS. The DC output voltage V4 output from the LPF 15 via the detection processing circuit 14 becomes a characteristic line 19 and is output to the amplifier circuit 16. As described above, in the prior art, since the bias voltage VS is applied to the ground side of the oscillator circuit 10, the differential amplifier circuit 11, the detection processing circuit 14, the LPF 15, and the amplifier circuit 16, the oscillator circuit 10 is also applicable. The sine wave has an amplitude V0 centered on the bias voltage VS, and the output is also output as a change with respect to the bias voltage VS in each of the other circuits.

The bias voltage VS is a DC voltage value for correcting the detection signal of the torque sensor output from the amplifier circuit 16 to the control unit to the input value of the control unit, and is set to 2.7 V, for example. Has been done.

[0030]

[Problems to be solved by the device]

 By the way, in the above-mentioned conventional technique, the bias voltage VS is set according to the situation on the detection circuit side, for example, the DC output voltage V4 when the torque is zero is set as the bias voltage VS, and the torque sensor to the control unit is set. The detection signal from was corrected.

Further, as shown in FIG. 7, the AC voltage V of the oscillation circuit 10 is a sine wave with an amplitude V 0 centered on the bias voltage VS, so that there are a battery voltage VCC as a DC power source and a sine wave of the AC voltage V. The difference (VCC-2.times.V0) is wasted. That is, if the amplitude V0 of the AC voltage applied between the connecting points a and b of the bridge circuit 9 is small, the currents i1 and i2 applied to the excitation and detection coils 7 and 8 in the bridge circuit 9 are also small, and the magnetostrictive shaft The amount of change in the excitation and detection coils 7 and 8 when torque is applied to 1 becomes small. Therefore, in the prior art, the detection is performed while the torque detection sensitivity is lowered.

Further, in order to increase the detection signal output from the torque sensor to the control unit, the amplification factor of the amplification circuit 16 at the final stage may be increased, but noise output from the LPF 15 is included. Even if the DC output voltage V4 is amplified, noise is also amplified and the torque cannot be accurately detected.

The present invention has been made in view of the above-mentioned problems of the prior art, and an object of the present invention is to provide a magnetostrictive torque sensor capable of highly accurate torque detection.

[0034]

[Means for Solving the Problems]

 In order to solve the above-mentioned problems, the feature of the configuration adopted by the present invention is that one bias applied to the bridge circuit, the oscillation circuit, and the differential amplification circuit in the detection circuit that detects the torque applied to the magnetostrictive shaft. This is because the voltage was set to a voltage value different from other bias voltages applied to the DC conversion circuit and the amplification circuit.

[0035]

[Action]

 With the above configuration, the AC voltage of the oscillation circuit applied to the bridge circuit can be generated as a sine wave having a large amplitude with respect to one bias voltage, and the amplitude of the AC voltage applied to the bridge circuit can be increased. Then, the current flowing through each detection coil can be increased.

[0036]

【Example】

 An embodiment of the present invention will be described below with reference to FIGS. In addition, in the embodiment, the same components as those of the above-described conventional technique are designated by the same reference numerals, and the description thereof will be omitted.

First, FIG. 1 shows a detection circuit of a two-coil type magnetostrictive torque sensor according to the present embodiment. Although each circuit is configured almost the same as the circuit of the prior art, according to the present embodiment. The characteristic of the detection circuit is that the oscillator circuit 21, the differential amplifier circuit 31, and the bridge circuit 9, which will be described later, have a bias voltage VS0 (hereinafter referred to as "other bias voltage VS") higher than the bias voltage VS (hereinafter referred to as "other bias voltage VS") of the prior art. , "One bias voltage VS0") is applied. The detection signal from the torque sensor to the control unit is corrected by applying the other bias voltage VS to the detection processing circuit 14, the LPF 15 and the amplification circuit 16 as in the prior art.

First, in the bridge circuit 9, the oscillation circuit 21 is connected between the connection point a of the excitation and detection coils 7 and 8 and the connection point b of the adjustment resistors R and R, and the excitation and detection coils are connected. The connection point c (one output end) between 7 and the adjustment resistor R and the connection point d (other output end) between the excitation and detection coil 8 and the adjustment resistor R are the changes in the excitation and detection coils 7 and 8, respectively. Becomes an output terminal for deriving output voltages V1 'and V2', and the connection points c and d are connected to the input terminals of the differential amplifier circuit 31, respectively. In this embodiment, since the connection point b of the bridge circuit 9 is connected to one bias voltage VS0 (VS0> VS), the output voltages V1 'and V2' are centered around the one bias voltage VS0. Outputs a sine wave (frequency f ′) that

Next, a specific example of the oscillation circuit 21 will be described with reference to FIG.

In FIG. 2, reference numeral 21 denotes an oscillating circuit, which is composed of a Wien bridge type oscillating circuit 22 and a bootstrap circuit 23 for eliminating noise transmission.

Here, the Wien bridge type oscillation circuit 22 includes an operational amplifier 24, a variable negative feedback resistor 25 having a resistance value R 1 connected between an inverting input terminal and an output terminal of the operational amplifier 24, and an inverting circuit. A negative feedback resistor 26 having a resistance value R2 connected between the input terminal and one bias voltage VS0, and a resistor connected in series in the positive feedback loop between the non-inverting input terminal and the output terminal. 27 (resistance value R0) and capacitor 28 (electrostatic capacitance C0), and a resistor 29 (resistance value R0 connected in parallel in the middle of the positive feedback loop between the non-inverting input terminal and one bias voltage VS0. ) And a capacitor 30 (electrostatic capacitance C0).

The oscillation frequency f ′ of the AC voltage V ′ of the Wien bridge type oscillation circuit 22 configured as described above is as shown in the following equation 6.

[0043]

[Equation 6]

Further, the amplitude V00 of the AC voltage V'can be adjusted by changing the resistance value R1 of the variable negative feedback resistor 25.

The voltage difference between the battery voltage VCC of the DC power supply and the ground is input to the drive voltage supply terminal (not shown) of the operational amplifier 24, while the ground side of the operational amplifier 24 has one bias voltage. It is connected to VS0. As a result, the waveform of the AC voltage V'oscillated from the oscillation circuit 21 becomes as shown in FIG. 4, and a sine wave of amplitude V00 centered on one bias voltage VS0 can be generated.

The amplitude V00 of the AC voltage V'is set by adjusting the negative feedback resistor 25 so that the amplitude V00 is extended around one bias voltage VS0 and approaches the ground. As a result, when the AC voltage V'is applied to the connection points a and b of the bridge circuit 9, the currents i1 and i2 flowing through each side can be increased, which is clear from the equations 3 and 4 shown in the prior art. As described above, the detection sensitivity of the torque applied to the magnetostrictive shaft 1 can be improved.

Further, as a specific example of the differential amplifier circuit 31 based on FIG. 3, in the differential amplifier circuit 31 of the present embodiment, an arbitrary amplification factor is obtained without being affected by the CMRR (common mode voltage rejection ratio) of the operational amplifier. A so-called instrumentation amplifier using three operational amplifiers in order to set is explained.

That is, in the differential amplifier circuit 31 shown in FIG. 3, reference numerals 32 and 32 denote operational amplifiers that respectively configure the input side amplifier circuit, and each operational amplifier 32 has a negative feedback resistor 33 having a resistance value R11. It is connected between the inverting input terminal and the output terminal, the connection points c and d of the bridge circuit 9 are connected to the non-inverting input terminal of each operational amplifier 32, and the output voltage V1 ′ is connected to each non-inverting input terminal. , V2 'are input. A resistor 34 having a resistance value R12 is connected between the inverting input terminals of each operational amplifier 32.

Reference numeral 35 denotes a differential amplifier, which has an operational amplifier 36 and a resistance value R00 connected midway between each input terminal of the operational amplifier 36 and the output terminal of the operational amplifier 32. Input resistors 37, 37, a negative feedback resistor 38 having a resistance value R00 connected between the inverting input terminal and the output terminal, and a resistor R00 connected between the non-inverting terminal and one bias voltage V S0. And a resistor 39 having In the differential amplifier 35, the resistors 37 to 39 have the same resistance value R00, so that the common mode gain is set to 1 even in the high gain differential circuit, and the influence of the CMRR by the operational amplifier 36. Is reduced.

The detection voltage V3 ′ output from the differential amplifier circuit 31 configured as described above is as shown in the following Expression 7.

[0051]

[Equation 7]

In addition, the differential amplifier circuit 31 can be configured as an amplifier circuit that is less affected by the CMRR of each operational amplifier 32 and 36, and the detection voltage V3 ′ to which one bias voltage VS0 is added is detected in the subsequent stage. It can be output to the circuit 14.

In the detection circuit of the present embodiment configured as described above, one bias voltage VS0 is applied to the bridge circuit 9, the oscillation circuit 21 and the differential amplification circuit 31, and the oscillation circuit 21 generates the bias voltage VS0. Since the amplitude V00 of the alternating voltage V'to be set close to the voltage difference between one bias voltage VS0 and the ground, the amplitude V00 of the alternating voltage V'input to the connection points a and b of the bridge circuit 9 is set. Can be increased, the currents i1 and i2 flowing through the excitation and detection coils 7 and 8 can be increased, and changes in magnetic permeability μ can be detected with high sensitivity as changes in self-inductance.

Therefore, as shown in FIG. 4, when torque is applied to the magnetostrictive shaft 1, the detection voltage V3 'from the differential amplifier circuit 31 is shown by a two-dot chain line centered on one bias voltage VS0. The characteristic line 40 is output. Further, the DC output voltage V4 'output from the LPF 15 via the detection processing circuit 14 becomes a characteristic line 41 and is output to the amplifier circuit 16. As a result, compared with the characteristic lines 18 and 19 shown in FIG. 7 of the conventional technique, the amplitude of the characteristic line 40 of the detection voltage V3 ′ output from the differential amplifier circuit 31 is smaller than that of the characteristic line 18 of the conventional technique. Can be made large, and highly accurate torque detection can be performed. Also, the DC output voltage V4 (characteristic line 41) from the LPF 15 can be made larger than the characteristic line 19 of the prior art.

As described above, in the present embodiment, the oscillation circuit 21 outputs the AC voltage V ′ having the amplitude V00 centered on the one bias voltage VS0, and the torque applied to the magnetostrictive shaft 1 is detected with high sensitivity. At the same time, the detection voltage V3 'from the differential amplifier circuit 31 can be output as a change larger than the output (amplitude) of the prior art, and the detection sensitivity of the torque applied to the magnetostrictive shaft 1 can be significantly improved.

Further, in the embodiment, the relation between one bias voltage VS0 and the battery voltage VCC (≈12V) is VS0≈1 / 2VCC (≈6V), and the amplitude V00, of the AC voltage V ′ from the oscillation circuit 21 is Since the relationship between one bias voltage VS0 and the battery voltage VCC is set to V00 = VS0 = 1 / 2VCC, even if a minute torque is applied to the magnetostrictive shaft 1, the output voltage V1 ′ from the bridge circuit 9, V2 'can be detected as a large output. Further, the detection voltage V3 'from the differential amplifier circuit 31 and the DC output voltage V4' from the LPF 15 can be made large, and the minute torque applied to the magnetostrictive shaft 1 can be detected.

By using the peak value VP-P of the AC voltage V in the full range of the battery voltage VCC, it is possible to configure a detection circuit of a magnetostrictive torque sensor with a small error and a high S / N ratio.

Although the two-coil torque sensor has been described in the above embodiment, the present invention is not limited to this and may be used for a four-coil torque sensor.

[0059]

[Effect of device]

 As described in detail above, according to the present invention, one bias voltage applied to the bridge circuit, the oscillator circuit, and the differential amplifier circuit, which are configured to include a pair of detection coils among the detection circuits, is converted into a DC conversion circuit. By setting a voltage value that is different from the other bias voltage applied to the amplifier circuit, the amplitude of the alternating voltage from the oscillator circuit applied to the bridge circuit can be increased, and the differential amplifier circuit The output signal can be a large signal. Then, it is possible to perform highly accurate torque detection with less noise.

[Brief description of drawings]

FIG. 1 is a circuit configuration diagram showing a detection circuit of a magnetostrictive torque sensor according to an embodiment.

FIG. 2 is a circuit diagram showing a specific configuration of the oscillator circuit in FIG.

FIG. 3 is a circuit diagram showing a specific configuration of the differential amplifier circuit in FIG.

FIG. 4 is a waveform diagram showing voltage waveforms of an oscillator circuit, a differential amplifier circuit, and an LPF when torque is zero according to an embodiment.

FIG. 5 is a configuration diagram of a magnetostrictive torque sensor according to a conventional technique.

FIG. 6 is a circuit configuration diagram showing a detection circuit of a magnetostrictive torque sensor according to a conventional technique.

FIG. 7 is a waveform diagram showing voltage waveforms of an oscillator circuit, a differential amplifier circuit, and an LPF when torque is zero according to a conventional technique.

[Explanation of symbols]

 1 Magnetostrictive shaft 7, 8 Excitation and detection coil 9 Bridge circuit 14 Detection processing circuit 15 LPF (DC conversion circuit) 21 Oscillation circuit 31 Differential amplifier circuit VS0 One bias voltage VS Other bias voltage

Claims (1)

[Scope of utility model registration request] 1. A magnetostrictive shaft, at least a pair of detection coils provided on the outer peripheral side of the magnetostrictive shaft, and a detection circuit for detecting a torque applied to the magnetostrictive shaft by a change in inductance from each detection coil. , The detection circuit includes a bridge circuit including the detection coils, an oscillation circuit that generates an AC voltage applied to the bridge circuit, and differentially amplifies detection signals of the detection coils from the bridge circuit. In a magnetostrictive torque sensor including a differential amplifier circuit, a DC conversion circuit that processes an output signal from the differential amplifier circuit as a DC signal, and an amplifier circuit that amplifies the signal from the DC conversion circuit, Of the detection circuits, one bias voltage applied to the bridge circuit, the oscillation circuit and the differential amplifier circuit is applied to the DC conversion circuit and the amplifier circuit. A magnetostrictive torque sensor characterized by being set to a voltage value different from other bias voltages used.