JP4657807B2 - PHYSICAL QUANTITY DETECTION DEVICE HAVING BRIDGE CIRCUIT AND ZERO POINT ADJUSTMENT METHOD - Google Patents

Description

  The present invention relates to a physical quantity detection device including a bridge circuit, and more particularly, to a detection device including a pair of sensor elements whose impedance changes according to a physical quantity to be measured. The “physical quantity” in this specification is a physical quantity that can be measured by the sensor element to be used, and widely includes force (various forces including torque load), current, voltage, light quantity, temperature, and the like.

  Conventionally, a magnetostrictive load detecting device including a magnetostrictive sensor element has been developed. The magnetostrictive sensor element is an element that uses a magnetostrictive material whose initial permeability changes according to a load, and detects a change in the initial permeability of the magnetostrictive material as a change in impedance (inductance and resistance value) of a detection coil or the like. As the magnetostrictive material, for example, iron-based, iron-chromium-based, iron-nickel-based, iron-cobalt-based, pure iron, iron-silicon-based, iron-aluminum-based, permalloy-based magnetic materials, soft magnetic materials, or supermagnetic materials are suitable. Used for.

  FIG. 1A is an equivalent circuit diagram showing a typical detection circuit in a conventional magnetostrictive load detection device. The bridge circuit shown in this figure includes first and second input points N1 and N2 to which an alternating voltage (alternating current) is input, and first and second outputs connected to a differential amplifier circuit (not shown). The AC voltage having points S1 and S2 is supplied from the AC voltage generation circuit unit 10 to the first and second input points N1 and N2.

  In the bridge circuit of FIG. 1A, magnetostrictive sensor elements SE1 and SE2 are connected in parallel. Such a bridge circuit is referred to as a “parallel bridge circuit”. For example, Patent Literatures 1 to 4 describe load detection devices including a parallel bridge circuit.

  In a parallel bridge circuit, if there is a variation in initial permeability between a pair of magnetostrictive sensor elements, the equilibrium point at no load and the output sensitivity at load will not be stable, so the accuracy and reliability of the detection value will be reduced. There's a problem. For this reason, it is necessary to reduce the influence of variations in the initial permeability existing between the magnetostrictive sensor elements.

The most effective method for reducing the influence of such variations in initial permeability is to increase the alternating current (excitation current) flowing through the bridge circuit.
Japanese Patent Laid-Open No. 5-60627 JP-A-10-261128 Japanese Utility Model Publication No. 5-45537 JP 2001-356059 A

  However, when the conventional parallel bridge circuit is employed, it is extremely difficult to further increase the excitation current for the purpose of reducing the characteristic variation of the magnetostrictive sensor element for the following reason.

  In the parallel bridge circuit shown in FIG. 1A, in order to expand the measurable load range (detection range), the magnitude of the fixed resistance in the bridge circuit is set to the resistance value of the magnetostrictive sensor elements SE1 and SE2. It is necessary to set to approximately the same value as (impedance). Since the impedance of a normal magnetostrictive sensor element is about 100Ω or less, the magnitude of the bridge resistance is also set to about 100Ω. For this reason, it is difficult to further increase the impedance of the bridge circuit.

  On the other hand, when the influence of the impedance change generated in the parallel bridge circuit reaches the oscillation circuit (not shown) of the AC voltage generation circuit unit 10, the oscillation waveform of the AC signal output from the oscillation circuit changes. . In order to prevent such a problem from occurring, it is necessary to insert an operational amplifier or the like between the oscillation circuit and the parallel bridge so as to function as a buffer amplifier. When such a circuit configuration is adopted, since the AC voltage output from the oscillation circuit is input to the parallel bridge circuit via the operational amplifier, the impedance change in the parallel bridge circuit does not affect the oscillation circuit. However, the magnitude of the excitation current that can be supplied to the parallel bridge circuit is at most about several tens of mA (milliamperes) due to operational performance limitations. In addition, since current flows symmetrically in the parallel bridge circuit, the magnitude of the excitation current flowing through each of the magnetostrictive sensor elements SE1 and SE2 is reduced to half of the excitation current supplied to the input points N1 and N2. .

  For the above reasons, it is extremely difficult to significantly reduce the influence caused by variations in sensor element characteristics by increasing the magnitude of the excitation current flowing through each of the magnetostrictive sensor elements SE1 and SE2.

  Further, when the impedance of the magnetostrictive sensor element is extremely low, it is necessary to insert a resistor between the bridge circuit and the operational amplifier to limit the current so that the operational amplifier does not cause output saturation. As a result, there is a problem that the voltage applied to the bridge circuit is further reduced and the load detection range is narrowed.

  On the other hand, when a bridge circuit is configured using a magnetostrictive sensor element, a zero point adjustment is required to compensate for the initial permeability variation of the magnetostrictive sensor element, but this is disclosed in Japanese Utility Model Application Publication No. 7-2943. In the parallel bridge circuit, the zero point adjustment is performed by adjusting the resistance value of the variable resistor connected in series to each magnetostrictive sensor. However, as will be described below, such a zero point adjustment cannot achieve a perfect equilibrium state.

  Since the magnetostrictive sensor element is excited by an alternating current, impedance imbalance in both the real part and the imaginary part needs to be zero in order to achieve complete balance adjustment. However, in the conventional zero point adjustment method, only one of the real part and the imaginary part can be removed from the impedance imbalance. Therefore, even if the zero point adjustment is performed so that the output voltage under no load is as small as possible, a residual voltage is always generated. When the residual voltage is generated, a difference occurs between the output characteristics of the two magnetostrictive sensor elements. In addition, since the output voltage at no load is not zero, the dynamic range of the output voltage is reduced. As described above, the conventional bridge circuit cannot achieve perfect balance adjustment, so that the measurement accuracy is insufficient.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to reduce the influence of variations in output characteristics of a pair of sensor elements in a physical quantity detection device including an AC bridge circuit.

  Another object of the present invention is to provide a physical quantity detection device that realizes complete balance adjustment in a bridge circuit and further suppresses a change with time of the complete balance point.

  A physical quantity detection device according to the present invention includes a bridge circuit having first and second input points to which an AC voltage is supplied and first and second output points connected to a differential amplifier circuit. The bridge circuit includes a first bridge arm that electrically connects the first input point and the first output point, and the first output point and the second input point. A second bridge arm that is electrically connected, a third bridge arm that is electrically connected to the first input point and the second output point, and a second output point and the second input point The first bridge arm includes a first sensor element whose impedance changes in accordance with a physical quantity to be measured, and the second bridge arm Impedance depending on the physical quantity There includes a second sensor element which changes the impedance of the total with the first and second bridge arms is set to be smaller than the sum of the impedance of the third and fourth bridge arm has.

  In a preferred embodiment, each of the first and second sensor elements is a magnetostrictive sensor element whose impedance changes in accordance with a load, and a physical quantity to be measured is a value of the first and second sensor elements. It is the load applied to either one.

  In a preferred embodiment, the first sensor element is a first magnetostrictive sensor element having a first magnetostrictive member formed of a magnetostrictive material and a first coil surrounding the first magnetostrictive member, and the first coil. Electrically connects the first input point and the first output point, and the second sensor element includes a second magnetostrictive member formed of a magnetostrictive material, and the second magnetostrictive member. The second magnetostrictive sensor element has a second coil surrounding the first coil, and the second coil electrically connects the first output point and the second input point.

  In a preferred embodiment, the total impedance of the first and second bridge arms is 90% or less of the total impedance of the third and fourth bridge arms.

  In a preferred embodiment, at least one of the first and second bridge arms includes a balance adjusting variable resistor.

  In a preferred embodiment, the bridge circuit includes a balancing variable resistance element connected in series between the first sensor element and the second sensor element, and the first output The point is connected to the balance adjusting variable resistance element.

  In a preferred embodiment, the bridge circuit includes a second variable resistance element for balance adjustment connected in series between the third bridge arm and the fourth bridge arm sensor element. The second output point is connected to the second variable resistance element for balance adjustment.

  In a preferred embodiment, during the measurement operation, current is substantially between the first output point and the differential amplifier circuit and between the second output point and the differential amplifier circuit. Not flowing.

  In a preferred embodiment, an AC voltage generation circuit that generates an AC voltage applied to the first and second input points in the bridge circuit, and the differential amplifier circuit connected to the first and second output points Are mounted on the same electronic circuit board.

  In a preferred embodiment, the AC voltage generation circuit includes an oscillation circuit and an amplitude limiting circuit that limits the amplitude of a signal output from the oscillation circuit.

  In a preferred embodiment, a detection circuit unit including the differential amplifier circuit is provided, and the detection circuit unit is measured by the value of the physical quantity measured by the first sensor element and the second sensor element. Even when the value of the physical quantity is equal, it is possible to determine whether or not the wiring that propagates the output signal of the detection circuit unit is disconnected by outputting a signal indicating a non-zero value. .

  The vehicle of the present invention includes any one of the physical quantity detection devices described above and an engine whose operation is controlled according to the physical quantity detected by the physical quantity detection device.

  In a preferred embodiment, the physical quantity detected by the physical quantity detection device is an amount dependent on the force applied to the vehicle handle by the operator.

  The zero point adjustment method of the present invention is a zero point adjustment method for a bridge circuit in the physical quantity detection device described above, wherein the balance adjustment is performed with the physical quantity to be detected by the first and second sensor elements set to zero. A first adjustment step of minimizing the amplitude of the differential voltage between the first and second output points by adjusting one of the variable resistors for use, and the first and second sensor elements A second adjustment step of minimizing the amplitude of the differential voltage between the first and second output points by adjusting the other of the balance adjustment variable resistors in a state in which the physical quantity applied to is zero. including.

  In a preferred embodiment, the differential voltage is minimized by repeating the first adjustment step and the second adjustment step.

  According to the present invention, the sensor elements are arranged in series in one of the two current paths in the bridge circuit, and the excitation current flowing through the sensor elements is increased, thereby reducing the influence of characteristic variations of the sensor elements. can do. Further, according to the present invention, zero point perfect balance adjustment can be realized, so that the difference in output characteristics that can occur between two sensor elements is markedly greater than the conventional example employing a parallel bridge circuit. It can also be reduced.

  The physical quantity detection device of the present invention includes a bridge circuit in which sensor elements for physical quantity detection are connected in series. As shown in FIG. 1B, the bridge circuit includes first and second input points N1 and N2 to which an AC voltage is supplied, and first and second output points connected to a differential amplifier circuit. The AC voltage supplied to the first and second input points N1 and N2 is supplied from the AC voltage generation circuit unit 10. An output of a differential amplifier circuit (not shown in FIG. 1) connected to the first and second output points S1 and S2 is output as a signal voltage from a detection circuit unit (not shown).

  The bridge circuit shown in FIG. 1B includes a first bridge arm that electrically connects the first input point N1 and the first output point S1, and the first output point S1 and the second input point N2. A second bridge arm that electrically connects the first input point N1 and the second output point S2, and a second bridge arm that electrically connects the second output point S2 and the second input. A fourth bridge arm that electrically connects the point N2 is provided.

  The first bridge arm includes a first sensor element SE1 whose impedance changes according to the physical quantity to be measured, and the second bridge arm includes a second sensor element SE2 whose impedance changes according to the physical quantity. Including. As described above, in the bridge circuit shown in FIG. 1B, the two sensor elements SE1 and SE2 are connected in series. Therefore, such a bridge circuit is compared with the conventional “parallel bridge circuit”. It can be referred to as a “series bridge circuit”.

  In the present invention, the total impedance of the first and second bridge arms to which the sensor elements SE1 and SE2 are connected in series is greater than the total impedance (fixed resistance value) of the third and fourth bridge arms. It is set small. For this reason, when an alternating current flows between the first and second input points N1 and N2, the current flowing through the first and second bridge arms becomes larger than the current flowing through the third and fourth bridge arms. . As a result, the current flowing through the two sensor elements SE1 and SE2 connected in series can be remarkably increased as compared with the parallel type, so that the influence due to the characteristic variation of the sensor elements SE1 and SE2 can be reduced. More specifically, when the total impedance of the first and second bridge arms is set to 1/9 of the total impedance of the third and fourth bridge arms, the AC voltage generation circuit unit 10 to the bridge circuit unit 90% of the alternating current supplied to 20 flows through the first and second bridge arms.

  The total impedance of the first and second bridge arms is preferably 90% or less, more preferably 50% or less, and more preferably 20% or less of the total impedance of the third and fourth bridge arms. Most preferably.

[Embodiment 1]
Hereinafter, a magnetostrictive load detection device will be described as a preferred embodiment of the physical quantity detection device of the present invention.

  FIG. 2 shows a circuit configuration of a main part in the load detection device of the present embodiment. The load detection device includes an AC voltage generation circuit unit 10, a bridge circuit unit 20, and a detection circuit unit 30.

  The AC voltage generation circuit unit 10 includes a reference DC power supply circuit 16, a sine wave oscillation circuit 17 that generates a sine wave around the reference voltage, a buffer amplifier 18 having a high input impedance, and a magnitude of a current flowing through the bridge circuit unit 20. And a current limiting fixed resistor 19 for adjusting the thickness.

  The bridge circuit unit 20 includes a magnetostrictive sensor element 21 and 22 connected in series with a balance adjusting variable resistor 23 in between, and a bridge fixing connected in series with a balance adjusting variable resistor 26 in between. Resistors 24 and 25 are provided. The bridge circuit unit 20 has basically the same configuration as the bridge circuit shown in FIG.

  The detection circuit unit 30 includes an AC differential amplifier circuit 31 that amplifies the differential voltage of the bridge circuit unit 20, a DC blocking capacitor 32 that cuts a DC component in the output signal, and an AC signal that has passed through the capacitor 32. A full-wave rectifier circuit 33, a low-pass filter 34 that smoothes the output voltage from the full-wave rectifier circuit 33, a DC amplifier circuit 35 that includes a variable resistor for gain adjustment, and a signal voltage output terminal 36. And.

  Next, the configuration of the bridge circuit unit 20 will be described in detail with reference to FIG.

  In the bridge circuit unit 20 in the present embodiment, as shown in FIG. 3, the first bridge arm BA <b> 1 includes a magnetostrictive sensor element 21, and the second bridge arm BA <b> 2 includes a magnetostrictive sensor element 22.

  Each of the magnetostrictive sensor elements 21 and 22 has a magnetostrictive member formed of a magnetostrictive material and a coil surrounding the magnetostrictive member. The coil of the magnetostrictive sensor element 21 electrically connects the first input point N1 and the first output point S1, and the coil of the magnetostrictive sensor element 22 has the first output point S1 and the second input point N2. And are electrically connected.

  A connection node (first output point S1) between the first bridge arm BA1 and the second bridge arm BA2 exists in the balance adjusting variable resistor 23. The balance adjusting variable resistor 23 used in the present embodiment has a configuration as shown in FIG. 4, and the resistance value R of the resistor 40 existing between the terminal A and the terminal B is a fixed value. However, by moving the connection point (contact position) between the contact 42 connected to the terminal C and the resistor 40, the resistance value between the terminal A and the terminal C can be made variable. When the resistance value between the terminal A and the terminal C is increased, the resistance value between the terminal B and the terminal C is decreased. Depending on the position of the connection point between the contact 42 and the resistor 40, the resistor 40 can be divided into two resistance portions connected in series. If the resistance values of these two resistance portions are R1 and R2, respectively, the relationship R = R1 + R2 is established.

  Refer to FIG. 3 again.

  The impedance of the first bridge arm BA1 is represented by the sum of the impedance of the magnetostrictive sensor element 21 and the resistance component R1 in the balance adjusting variable resistor 23 (wiring resistance is ignored; the same applies hereinafter). On the other hand, the impedance of the second bridge arm BA2 is represented by the sum of the impedance of the magnetostrictive sensor element 7 and the resistance component R2 of the balance adjusting variable resistor 23. Therefore, the total impedance of the first and second bridge arms BA1 and BA2 is represented by the sum of the total impedance of the magnetostrictive sensor elements 21 and 22 and the resistance value R in the balance adjusting variable resistor 23. The resistance value R only needs to be as large as the difference between the impedance of the magnetostrictive sensor element 21 and the impedance of the magnetostrictive sensor element 22, and is set to a value sufficiently smaller than the impedance of the magnetostrictive sensor elements 21 and 22. Is possible. The impedance of the magnetostrictive sensor elements 21 and 22 used in the present embodiment is in the range of 50 to 100Ω, but the difference in impedance between the two magnetostrictive sensor elements 21 and 22 is about 5 to 10Ω. For example, a resistance value R having a size in the range of 5 to 10Ω can be used.

  On the other hand, the third bridge arm BA3 in the bridge circuit unit 20 includes a fixed resistor 24, and the fourth bridge arm BA4 includes a fixed resistor 25. A connection node (second output point S2) between the third bridge arm BA3 and the fourth bridge arm BA4 exists in the balance adjusting variable resistor 26. The structure of the balance adjustment variable resistor 26 is the same as the structure of the balance adjustment variable resistor 23.

  In the present embodiment, as described above, the terminal C (see FIG. 4) in the balance adjustment variable resistors 23 and 26 is connected to the detection circuit unit 30 shown in FIG. For this reason, when the input impedance of the AC differential amplifier circuit 31 is set high, a configuration in which no current flows between the output point of the bridge circuit unit 20 and the signal input unit of the detection circuit unit 30 can be realized. The effect of this will be described later.

(Magnetostrictive sensor element)
Next, an arrangement example of the magnetostrictive sensor elements 21 and 22 used in the load detection device of the present embodiment will be described with reference to FIGS. 5 and 6. The load detection device according to the present embodiment can be used for various devices that require load measurement. Here, an example in which the load detection device is attached to a steering shaft of a vehicle and used to detect torque will be described.

  FIG. 5 is a perspective view showing the load sensor unit 5 attached to the steering shaft, and FIG. 6 is a view showing a cross section of the load sensor unit 5 across the steering shaft. The load sensor unit 5 shown in FIG. 5 is provided at a portion connecting the upper steering shaft 3a and the lower steering shaft 3b. The lower steering shaft 3b has a sensor housing portion 51 at a connection portion with the upper steering shaft 3a located at the upper end portion thereof, and in the sensor housing portion 51, there is an outer peripheral portion of the lower end portion of the upper steering shaft 3a. A pressing portion 3c protruding from the portion has entered.

  The pressing portion 3c protrudes into the sensor housing portion 51 from the outer peripheral portion of the upper steering shaft 3a. The sensor accommodating part 51 is divided into two parts on the right and left sides with the pressing part 3c as a boundary, the magnetostrictive sensor element 21 is accommodated in the right part, and the magnetostrictive sensor element 22 is accommodated in the left part. .

  The magnetostrictive sensor element 21 is pressed in the direction toward the pressing portion 3c by the spring 53A provided between the bottom of the magnetostrictive sensor element 21 and one side wall of the sensor housing portion 51. A pressed portion 55A provided so as to protrude on the opposite side to the bottom portion is in contact with and presses the pressing portion 3c.

  Similarly, the magnetostrictive sensor element 22 is pressed in the direction toward the pressing portion 3c by the spring 53B provided between the bottom of the magnetostrictive sensor element 22 and the other wall of the sensor housing 51. As a result, the pressed portion 55B provided so as to protrude to the opposite side of the bottom portion of the magnetostrictive sensor element 22 comes into contact with and presses the pressing portion 3c.

  The magnetostrictive sensor elements 21 and 21 have a magnetic coil for detecting a magnetic change, and constitute a magnetostrictive sensor using the inverse magnetostrictive effect together with the pressed portions 55A and 55B corresponding to the magnetostrictive sensors. When the pressed parts 55A and 55B are pressed and distorted by the pressing part 3c, the magnetic change of the pressed parts 55A and 55B generated according to the distortion, specifically, the change in the magnetic permeability or the magnetization characteristic is detected. , 22 can be detected as a change in impedance of the magnetic coil.

  When detecting the torque of the steering shaft using the load sensor unit 5, when the handle is operated, for example, in the left direction, the upper steering shaft 3a connected to the handle rotates as indicated by an arrow 301. When the upper steering shaft 3a rotates in this way, the pressing portion 3c rotates with the upper steering shaft 3a as indicated by an arrow 302, and the pressed portion 55A and the magnetostrictive sensor element are in accordance with the rotational force of the upper steering shaft 3a. 21 is pressed against the spring 53A as indicated by an arrow 303.

  As described above, when the pressed portion 55A is pressed via the pressing portion 3c by the rotational force of the upper steering shaft 3a, the pressed portion 55A is distorted according to the rotational force of the upper steering shaft 3a. Accordingly, a magnetic change occurs in the pressed portion 55A. This magnetic change is detected by the magnetic coil constituting the magnetostrictive sensor element 21 as the rotational torque of the upper steering shaft 3a.

  When the handle is operated in the opposite right direction, the magnetostrictive sensor element 22, the pressed portion 55B, and the spring 53B perform the same actions instead of the magnetostrictive sensor element 21, the pressed portion 55A, and the spring 53A. Since only the rotation direction and the pressing direction are different, the description thereof is omitted.

  If a constant load, for example, F Newton (N) is applied to the spring 53A in advance, when the pressed portion 55A and the magnetostrictive sensor element 21 are pressed by the pressing portion 3c, the pressing load is F. As long as it does not exceed Newton, the pressed portion 55A and the magnetostrictive sensor element 21 do not move. However, if it exceeds F Newton, the pressed portion 55A and the magnetostrictive sensor element 21 move in the right direction. The magnetostrictive sensor element 21 realizes an overload prevention function in which a pressing load of F Newton or more is not applied.

  The load application method for the magnetostrictive sensor element in the load detection device is not limited to the above-described example, and can be applied to various application methods. However, in a preferred embodiment of the present invention, a load is applied to only one of the pair of magnetostrictive sensor elements, and the other magnetostrictive sensor element to which no load is applied is used as a measurement reference. For this reason, in the case of the load detection device of the present embodiment, it is necessary to apply the load to be measured to one of the magnetostrictive sensor elements. This is true for all cases where a predetermined physical quantity is measured by the physical quantity measuring device of the present invention.

  5 and 6, an electronic circuit board on which circuit elements such as an amplifier and a resistor are integrated is not shown, but the electronic circuit board may be arranged in the vicinity of the magnetostrictive sensor element. Further, it may be integrated with another control circuit unit at a position away from the magnetostrictive sensor element.

(Load detection operation)
Hereinafter, the details of the measurement operation in the load detection device of the present embodiment will be described with reference to FIG.

  First, the reference DC power supply circuit 16 outputs a reference DC voltage of 2.5 V based on a power supply voltage (not shown) of 5 V (volts). This reference DC voltage is input to the sine wave oscillation circuit 17. The sine wave oscillation circuit 17 outputs a sine wave oscillation signal that oscillates around the reference DC voltage. The frequency of the sine wave oscillation signal is set to 1 kHz, for example, and the amplitude Vpp (peak to peak) is adjusted to 2 V, for example.

  This oscillation signal is supplied to the bridge circuit unit 20 via the high impedance buffer amplifier 18 and the current limiting fixed resistor 19.

  When a load is applied to one of the magnetostrictive sensor elements 21 and 22, the initial permeability of the magnetostrictive material in the magnetostrictive sensor element 21 or the magnetostrictive sensor element 22 to which the load is applied changes due to the magnetostrictive effect. As a result, since the impedance of the magnetostrictive sensor element 21 or 22 changes from the initial value, the impedance balance is lost between the first bridge arm and the second bridge arm.

  When the impedance balance is lost as described above, a differential voltage is generated between the first output point S1 and the second output point S2 of the bridge circuit unit 20. This differential voltage is amplified by the AC differential amplifier circuit 31 in the detection circuit unit 30. The AC component of the signal output from the AC differential amplifier circuit 31 passes through the DC blocking capacitor 32 and is input to the full-wave rectifier circuit 33.

  The full-wave rectifier circuit 33 is composed of a rectifier diode or the like, and cannot perform a rectification operation below a forward voltage, resulting in a dead zone. In order to avoid such a situation and cause the full-wave rectifier circuit 33 to perform an appropriate rectification operation, it is preferable to set the gain of the AC differential amplifier circuit 31 as high as possible. In the present embodiment, the gain of the AC differential amplifier circuit 31 is adjusted to the maximum level at which the output of the AC differential amplifier circuit 31 is not saturated even when an absolute maximum rated load is applied to one of the magnetostrictive sensor elements 21 and 22. is doing.

  In the present embodiment, in order to improve the detection sensitivity in the full-wave rectifier circuit 33, the signal amplitude is doubled after full-wave rectification. In order to sufficiently remove an AC component having a frequency equal to the excitation current frequency (oscillation frequency) input to the low-pass filter 34 from the amplified signal, the cutoff frequency of the low-pass filter 34 is set to the oscillation frequency. 1/10 or less.

  The output of the low-pass filter 34 is amplified by the DC amplification circuit 35 and then output from the signal voltage output terminal 36. The signal voltage on the signal voltage output terminal 36 has a magnitude corresponding to the load applied to one of the magnetostrictive sensor element 21 and the magnetostrictive sensor element 22.

(Initial adjustment)
In order to measure the load with high accuracy, it is necessary to perform initial adjustment. In this embodiment, two types of initial adjustments are performed. The first initial adjustment is “zero point adjustment” in which the signal voltage output from the signal voltage output terminal 36 is set to zero in a state where no load is applied to the magnetostrictive sensor elements 21 and 22. The second initial adjustment is “sensitivity adjustment” in which the signal voltage output from the signal voltage output terminal 36 is set to a predetermined required value in a state where the maximum load is applied to one of the magnetostrictive sensor elements 21 and 22.

  In the present embodiment, while measuring the AC output output from the AC differential amplifier circuit 31, the balance adjusting variable resistors 23 and 26 are adjusted so that the amplitude value of the AC output is minimized (zero point adjustment). ). Next, a load of 400 Newton is applied to the magnetostrictive sensor element 21 or the magnetostrictive sensor element 22 while measuring the DC output of the DC amplifier circuit 35. The gain of the DC amplification circuit 35 is adjusted (sensitivity adjustment) so that the DC voltage output from the DC amplification circuit 35 becomes equal to, for example, 3.5 V in a state where this load is applied.

  Note that the output current of the operational amplifier 13 functioning as a buffer amplifier is about 10 mA. In the present embodiment, instead of using a parallel bridge circuit, a series bridge circuit is employed, so that the current flowing through the first and second bridge arms provided with the magnetostrictive sensor elements 21 and 22 is The current flowing through the third and fourth bridge arms can be made larger. For this reason, even if there are variations in initial characteristics due to differences in initial permeability between the two magnetostrictive sensor elements 21 and 22, a sufficiently large current can be passed through the magnetostrictive sensor elements 21 and 22. It is possible to prevent the difference in output characteristics of the magnetostrictive sensor elements 21 and 22 from deteriorating the detection accuracy.

  In order to improve the detection sensitivity of the AC differential amplifier circuit 31, it is important to widen the differential amplitude range of the signal input to the AC differential amplifier circuit 31. In order to maximize the amplitude of the differential output voltage at the maximum load, it is necessary to set the impedance of the first bridge arm in the bridge circuit to be approximately equal to the impedance of the second bridge arm. If the impedance is set approximately equal between the first bridge arm and the second bridge arm, the center of the differential amplitude range can be set near the reference voltage, so that the gain of the AC differential amplifier circuit 31 is improved. be able to.

  Since the impedances of the magnetostrictive sensor elements 21 and 22 used in the present embodiment are substantially equal to each other, the impedance of the first bridge arm is set to be substantially equal to the impedance of the second bridge arm as compared with the conventional example employing a parallel bridge circuit. Easy to do. This is one of the advantages of connecting the magnetostrictive sensor elements 21 and 22 in series.

  Further, when the impedance of the magnetostrictive sensor element 21 and the impedance of the magnetostrictive sensor element 22 are substantially equal, the range of resistance change required for the balance adjusting variable resistor 23 is markedly greater than the impedance of the magnetostrictive sensor elements 21 and 22. Can be made smaller. This contributes to reducing the overall impedance of the first and second bridge arms and also helps to reduce the influence of the temperature characteristics of the balancing variable resistor 23. Normally, the resistance of the balance adjusting variable resistor 23 has a relatively large temperature dependency. Therefore, when the temperature of the balance adjusting variable resistor 23 fluctuates after the zero point adjustment, the impedance is changed accordingly. It becomes easy to lose balance. However, according to the present embodiment, the resistance value of the balance adjusting variable resistor 23 can be set to a sufficiently small value as compared with the sensor impedance, so that the influence due to the temperature characteristic of the resistance is hardly exerted.

(Balance adjustment)
Hereinafter, the balance adjustment method in the present embodiment will be described. The “balance adjustment” means a differential voltage (output points S1, S2) output from the bridge circuit unit 20 in a state where no load is applied to any of the magnetostrictive sensor elements 21, 22 (no load state). Is zero).

  First, one of the balance adjusting variable resistors 23 and 26 is adjusted in a no-load state to minimize the output amplitude of the AC differential amplifier circuit 31. Next, the other of the balance adjusting variable resistors 23 and 26 is adjusted in a no-load state to minimize the output amplitude of the AC differential amplifier circuit 31. Such an adjustment operation is alternately performed for the two variable resistors 23 and 26 for balance adjustment, so that the residual voltage is reduced to zero in principle when the output amplitude is minimized. Equilibrium) is possible.

  If the residual voltage is not adjusted to zero because the zero point adjustment is incomplete, when a load is applied to one of the magnetostrictive sensor elements 21 and 22, the output signal temporarily decreases. As a result, an output characteristic difference occurs between the two magnetostrictive sensor elements. However, in this embodiment, such a phenomenon can be prevented.

  FIG. 7 is a graph showing output characteristics of two magnetostrictive sensor elements when balance adjustment is performed using a conventional parallel bridge circuit, and FIG. 8 is a bridge circuit according to the present embodiment in which complete balance adjustment is performed. 6 is a graph showing output characteristics of two magnetostrictive sensor elements obtained from As can be seen from FIG. 7, if the balance adjustment is incomplete, the output difference between the two magnetostrictive sensor elements is large. On the other hand, in this embodiment in which perfect balance adjustment is performed, as can be seen from FIG. 8, there is almost no output difference between the two magnetostrictive sensor elements.

  According to the circuit configuration shown in FIG. 2, perfect balance adjustment is realized, and the residual voltage can be made zero. When the residual voltage becomes zero, it means that the output voltage level under no load becomes zero.

  7 and 8, the output of the minute load region is not 0 (zero) but shows a value of about 0.5V. This is for “disconnection detection”. Hereinafter, this “disconnection detection” will be described.

  In the load detection device of the present embodiment, when the residual voltage is made zero by complete balance adjustment, when the load applied to the magnetostrictive sensor element is zero, the signal voltage at the input portion of the DC amplification circuit 35 is zero volts (0 V). Become.

  When the load detection device is used in a system such as a vehicle, the output signal of the signal voltage output terminal 36 is supplied to an engine control unit or the like via a harness. When a disconnection occurs in a part of the wiring such as the harness, a voltage of 0 V is supplied to the engine control unit or the like regardless of whether or not a load is applied to the load detection device. For this reason, it becomes difficult to identify whether a load is not applied or a disconnected state.

  Therefore, in this embodiment, even if the input voltage of the DC amplifier circuit 35 is 0V, the DC amplifier circuit 35 is designed so that the output voltage of the DC amplifier circuit 35 becomes a value shifted from 0V (about 0.5V). is doing. In other words, the load detection device according to the present embodiment always displays a “non-zero value (distinguishable from that at the time of stepping) even when a load is applied to the magnetostrictive sensor element or when no load is applied. A signal indicating “possible value)” is output. For this reason, for example, when the engine control unit receives an output voltage lower than a reference value (for example, 0.5 V) from the load detection device, it can be determined that a disconnection has occurred, and thus disconnection detection is realized.

  It was examined how much the difference in the balance adjustment circuit affects the residual voltage. In the case of the imperfect balance adjustment circuit, the residual voltage level and the variation are large, but from the data of the complete balance adjustment circuit, it has been found that the measurement dynamic range is effective.

  As described above, the stability of the zero point has a great influence on the left-right variation of the sensor and the detection accuracy of a minute load. Therefore, it is necessary to stabilize this zero point as much as possible.

  Circuit components such as wiring, resistors, amplifiers, and capacitors constituting the circuit shown in FIG. 2 are preferably mounted on one electronic circuit board. The electronic circuit board is preferably sealed by resin casting after adjustment. By thus covering the surface of the electronic circuit board with the resin, the movable parts of the balance adjusting variable resistors 23 and 26 do not move. However, since the contact 42 (FIG. 4) of the balance adjusting variable resistors 23 and 26 is not completely fixed, the resistance value of the contact portion between the resistor 40 and the contact 42 shown in FIG. The contact resistance value) is unstable and easily changes over time.

  In an example in which a variable resistor is used in a conventional parallel bridge circuit, a configuration is adopted in which a current flows through a contact. In such a circuit, the change in the contact resistance value changes the resistance value between the terminals A and B shown in FIG. 4B, which causes a change in the equilibrium point of the bridge circuit.

  However, in the bridge circuit unit 20 of the present embodiment, since the input impedance of the AC differential amplifier circuit 31 is set high, almost no current flows through the contacts of the balance adjusting variable resistors 23 and 26. Therefore, even if the contact resistance value existing in the contacts of the balance adjusting variable resistors 23 and 26 changes due to a change over time, the detection voltage is not affected, and the measurement reliability is improved. improves.

  In the series bridge circuit used in the present invention, balance adjustment is possible even if a variable resistor is inserted into at least one (preferably both) of the bridge arms. However, in this case, since a current flows through the contacts in each variable resistor, stability can be degraded due to fluctuations in contact resistance. However, even in such a case, if a variable resistor having sufficiently improved contact resistance stability is used, it is possible to avoid a decrease in zero point stability.

[Embodiment 2]
Hereinafter, an embodiment of a water vehicle including the load detection device of the first embodiment will be described. Here, a water jet propulsion boat will be described as this embodiment of a water vehicle. The water jet propulsion watercraft can be propelled by its reaction by jetting water pressurized by a jet propulsion device driven by an engine from a nozzle. When a physical quantity detection device such as a load detection device is used for such a vehicle, since it is used in a harsh environment such as the sea, durability and long-term reliability are required. Therefore, the physical quantity detection device of the present invention is advantageous. Can be effective.

  FIG. 9 shows a schematic configuration of the water jet propulsion boat 100 of the present embodiment. A water jet propulsion boat body 100 includes a lower hull member 101 and an upper deck member 102, and a straddle-type seat 103 is provided on the deck member 102. A steering handle 104 is provided in front of the seat 103.

  An engine 1 as a driving source is disposed in the boat body, and an impeller 107 of a jet propulsion device 106 is connected to an output shaft 105 of the engine 1. Accordingly, when the impeller 107 of the jet propulsion device 106 is rotationally driven by the engine 1, water is sucked from the water suction port 108 on the bottom of the boat, and the water pressurized and accelerated in the jet propulsion device 106 is rearward from the nozzle 109. The boat moves forward by the reaction. Further, when the steering wheel 104 is steered, a steering device called a deflector behind the nozzle 109 swings and the boat can turn left and right. That is, when the steering wheel 104 is steered, the direction of the water to be sprayed changes, so that the boat can be turned. It is possible to reverse the own boat by operating the reverse lever 120 to raise and lower the reverse gate 121 behind the nozzle 109 and to change the direction of water sprayed from the nozzle 109 to the front of the own boat. Become. Reference numeral 112 in the drawing is a reverse switch that detects that the boat is moving backward by operating the reverse lever 120.

  FIG. 10 shows the configuration of the handle 104. The handle 104 is rotatable around the steering shaft 113, and the handle 104 can be steered left and right. In the vicinity of the right grip of the handle 104, a throttle lever 110 that is operated in accordance with the boat operator's intention to accelerate or decelerate is provided. The throttle lever 110 is separated from the grip when released, and when accelerating, the boat operator holds the throttle lever 110 close to the grip side. Returning the throttle lever 110 means releasing the throttle lever 110.

  The steering shaft 113 is provided with a steering torque sensor 111 for detecting a steering force to the handle 104, specifically, a steering torque. The steering torque sensor 111 has the same configuration as that of the magnetostrictive load detection device according to the first embodiment. When the handle 104 can reach a predetermined angle, the handle shaft is restricted and cannot move. The steering torque sensor 111 functions as a load cell that detects the steering torque related to the handle 104 in a state where a steering force is further applied to the handle 104. The configuration of the steering torque sensor 111 is not limited to the specific configuration of the load sensor unit shown in FIGS. 5 and 6, and the arrangement and mechanical connection relationship of the magnetostrictive sensor elements can be realized in various modes. it can. The throttle lever 110 is provided with a throttle opening sensor 114 that detects an operation amount of the throttle lever 110 by the boat operator, that is, a throttle opening.

  FIG. 11 schematically shows the engine of the water jet propulsion watercraft 100 and its control device. The engine 201 of this embodiment is a stroke engine 201 having a relatively small displacement, and includes a cylinder body 202, a crankshaft 203, a piston 204, a combustion chamber 205, an intake pipe 206, an intake valve 207, an exhaust pipe 208, and an exhaust valve 209. The ignition plug 210 and the ignition coil 211 are provided. In addition, a throttle valve 212 that is opened and closed according to the opening degree of the throttle lever 110 is provided in the intake pipe 206, and an injector 213 as a fuel injection device is provided in the intake pipe 206 on the downstream side of the throttle valve 212. It has been. The injector 213 is connected to a filter 218, a fuel pump 217, and a pressure control valve 216 disposed in the fuel tank 219.

  A bypass passage 206a that bypasses the throttle valve 212 is provided in the vicinity of the throttle valve 212 of the intake pipe 206, and a bypass valve 214 (deceleration engine output control means) that adjusts the opening of the bypass passage is provided in the bypass passage 206a. Is provided. The bypass valve 214, like an idle valve, controls the engine output, in this case, the engine torque, by adjusting the intake flow rate to the engine 201 separately from the opening of the throttle valve 212. The opening degree of the bypass path 206a, that is, the engine torque can be controlled by controlling the current value or the duty ratio to the actuator 223 for driving the bypass valve 214, such as an electromagnetic duty valve.

  The operating state of the engine 201 and the driving state of the actuator 223 of the bypass valve 214 are controlled by the engine control unit 215, and the engine control unit 215 includes an arithmetic processing unit such as a microcomputer. As a means for detecting the control input of the engine control unit 215, that is, the operating state of the engine 201, the crank angle for detecting the rotation angle, that is, the phase of the crankshaft 203, or detecting the rotation speed of the crankshaft 203 itself. The sensor 220, the temperature of the cylinder body 202 or the coolant temperature, that is, the coolant temperature sensor 221 that detects the temperature of the engine body, the exhaust air / fuel ratio sensor 222 that detects the air / fuel ratio in the exhaust pipe 208, and the intake pressure in the intake pipe 206 An intake pressure sensor 224 for detecting the intake air temperature and an intake air temperature sensor 225 for detecting the temperature in the intake pipe 206, that is, the intake air temperature, are provided.

  Normally, the output signal of the throttle opening sensor 114 (throttle opening sensor) provided on the throttle lever 110 is used for engine torque control, but at the time of off-throttle, the steering torque sensor provided on the steering handle 104 ( The output signal of the magnetostrictive load sensor) 111 can also be used for engine torque control. The engine control unit 215 inputs detection signals from these sensors and outputs control signals to the fuel pump 217, the pressure control valve 216, the injector 213, the ignition coil 211, and the actuator 223.

  According to the present embodiment, since the steering torque is detected using the load detection device that has been completely balanced, the measurement accuracy is high and the reliability is improved even in a small load region. In the present embodiment, the embodiment of the water jet propulsion boat is described as a vehicle, but the scope of application of the present invention is not limited to such a case.

  The sensor element used in the above embodiment is a magnetostrictive sensor element. However, the sensor element in the present invention is not limited to this, for example, a change in capacitance instead of a magnetic change. In addition, a sensor element using a change in piezoelectric effect or electrical resistance may be used. In the case of a sensor that uses a change in capacitance, the pressed portion is constituted by a capacitance electrode, and the predetermined capacitance change detection means is caused by the electrode being pressed by the rotational force of the steering shaft. A change in capacitance is detected as a change in the pressed portion. Further, in the case of a sensor using the piezoelectric effect, the pressed portion is composed of a piezoelectric element, and the predetermined piezoelectric change detecting means is electrically connected to the piezoelectric element due to the pressing of the piezoelectric element by the rotational force of the steering shaft. The change is detected as a change of the pressed part. Further, in the case of a sensor that uses a change in electrical resistance, the pressed portion is configured by a resistance means, and the predetermined resistance change detection means is a resistance means that is caused by the resistance means being pressed by the rotational force of the steering shaft. A change in electrical resistance is detected as a change in the pressed portion.

  Of the various sensor elements, the present invention can exert a particularly remarkable effect when the magnetostrictive sensor element is used. This is because when a magnetostrictive sensor element is used, for the reason described above, flowing a large current to the sensor element helps to eliminate the influence of characteristic variation, but in reality, a large current cannot flow. Because there is. Therefore, the present invention can exert a remarkable effect in performing accurate load measurement using the magnetostrictive sensor element having such a problem.

  Since the physical quantity detection device of the present invention is suitably used for load detection in various vehicles used on land or at sea, the industrial applicability is high.

(A) is a diagram showing a bridge circuit (conventional example) in which a pair of sensor elements are connected in parallel, and (b) is a bridge circuit in which a pair of sensor elements are connected in series (the present invention). (C) is a diagram showing a bridge circuit (preferred embodiment of the present invention) in which a pair of sensor elements are connected in series and variable resistors are provided at two output points. It is a circuit diagram which shows the circuit structure in Embodiment 1 of the physical quantity detection apparatus of this invention. 2 is a circuit diagram illustrating in detail a configuration of a bridge circuit unit 20 according to the first embodiment. FIG. (A) shows a variable resistor, (b) is a figure which shows the specific structural example of a variable resistor. It is a perspective view which shows the load sensor apparatus (load sensor unit) attached to the steering shaft. It is sectional drawing which shows the structure of the load sensor unit of FIG. It is a graph which shows the relationship (comparative example) of the load in a load detection apparatus in which perfect balance adjustment of a bridge circuit part is not achieved, and two sensor outputs. It is a graph which shows the relationship (Example) of the load in a load detection apparatus with which perfect balance adjustment of the bridge circuit part was achieved, and two sensor outputs. It is a figure showing the schematic structure of water jet propulsion boat 100 which is an embodiment of vehicles provided with the physical quantity detection device of the present invention. It is a figure which shows the structure of the handle | steering-wheel 104. FIG. It is a figure which shows the outline of the engine of the water jet propulsion boat 100, and its control apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 AC voltage generation circuit part 20 Bridge circuit part 30 Detection circuit part 16 Reference | standard DC power supply circuit 17 Sinusoidal oscillation circuit 18 Buffer amplifier 19 Current limiting fixed resistors 21 and 22 Magnetostrictive sensor element 23 Balance adjustment variable resistors 24 and 25 Bridge Fixed resistor 26 Variable resistor 31 for balance adjustment AC differential amplifier circuit 32 DC blocking capacitor 33 Full wave rectifier circuit 34 Low pass filter 35 DC amplifier circuit 36 Signal voltage output terminal BA1 First bridge arm BA2 Second bridge arm BA3 3rd bridge arm BA4 4th bridge arm N1 1st input point N2 2nd input point S1 1st output point S2 2nd output point 100 water jet propulsion boat 101 hull member 102 deck member 103 straddle-type seat 104 Steering handle 105 Output shaft 106 of engine 1 Jet propulsion unit 1 7 Impeller 108 Water suction port 109 Nozzle 110 Throttle lever 111 Steering torque sensor 112 Reverse switch 113 Steering shaft 114 Throttle opening sensor 120 Reverse lever 121 Reverse gate 201 Engine 202 Cylinder body 203 Crankshaft 204 Piston 205 Combustion chamber 206 Intake pipe 206a Bypass Passage 207 intake valve 208 exhaust pipe 209 exhaust valve 210 ignition plug 211 ignition coil 212 throttle valve 213 injector 214 bypass valve 215 engine control unit 216 pressure control valve 217 fuel pump 218 filter 219 fuel tank 220 crank angle sensor 221 cooling water temperature sensor 222 Exhaust air / fuel ratio sensor 223 Actuator 224 Intake pressure sensor 225 Intake air temperature sensor

Claims (14)

A physical quantity detection device comprising a bridge circuit having first and second input points to which an alternating voltage is supplied and first and second output points connected to a differential amplifier circuit,
The bridge circuit is
A first bridge arm that electrically connects the first input point and the first output point; a second bridge arm that electrically connects the first output point and the second input point; A third bridge arm that electrically connects the first input point and the second output point, and a fourth bridge that electrically connects the second output point and the second input point Has an arm,
The first bridge arm includes a first sensor element whose impedance changes in accordance with a physical quantity to be measured, and the second bridge arm has a second sensor element whose impedance changes in accordance with the physical quantity. Including
The total impedance of the first and second bridge arms is set smaller than the total impedance of the third and fourth bridge arms ,
The first and second sensor elements are both magnetostrictive sensor elements whose impedance changes according to the load,
The physical quantity detection device is a physical quantity to be measured , which is a load applied to any one of the first and second sensor elements . The first sensor element is a first magnetostrictive sensor element having a first magnetostrictive member formed of a magnetostrictive material and a first coil surrounding the first magnetostrictive member, and the first coil is the first magnetostrictive sensor element. Are electrically connected to the first output point,
The second sensor element is a second magnetostrictive sensor element having a second magnetostrictive member formed of a magnetostrictive material and a second coil surrounding the second magnetostrictive member, and the second coil is the first magnetostrictive element. The physical quantity detection device according to claim 1 , wherein the output point and the second input point are electrically connected. The first and the sum of the impedances second bridge arm has, the third and the physical quantity detecting device according to claim 1 or 2, the fourth bridge arm is less than 90% of the total impedance is having. Wherein at least one of the first and second bridge arm, a physical quantity detecting device according to claim 1 comprising a balancing adjustment variable resistor 3. The bridge circuit includes a variable resistance element for balance adjustment connected in series between the first sensor element and the second sensor element.
The first output point, the equilibrium adjustment is connected to the variable resistance element, a physical quantity detecting device according to any one of claims 1 to 3. The bridge circuit includes a second variable resistance element for balance adjustment connected in series between the third bridge arm and the fourth bridge arm sensor element.
The physical quantity detection device according to claim 5 , wherein the second output point is connected to the second balance adjustment variable resistance element. The current substantially does not flow between the first output point and the differential amplifier circuit and between the second output point and the differential amplifier circuit during a measurement operation. 6. The physical quantity detection device according to 6 . An AC voltage generation circuit that generates an AC voltage applied to the first and second input points in the bridge circuit and the differential amplifier circuit connected to the first and second output points are the same electronic circuit. are mounted on the substrate, the physical quantity detecting device according to any one of claims 1 to 7. The physical quantity detection device according to claim 8 , wherein the AC voltage generation circuit includes an oscillation circuit and an amplitude limiting circuit that limits an amplitude of a signal output from the oscillation circuit. A detection circuit unit including the differential amplifier circuit;
The detection circuit unit has a non-zero value even when the physical quantity value measured by the first sensor element is equal to the physical quantity value measured by the second sensor element. by outputting a signal indicating the wiring for propagating the output signal of the detection circuit section is possible determination of whether or not broken, the physical quantity detecting device according to any one of claims 1 to 9. The physical quantity detection device according to any one of claims 1 to 10 ,
An engine whose operation is controlled according to a physical quantity detected by the physical quantity detection device;
With a vehicle. The vehicle according to claim 11 , wherein the physical quantity detected by the physical quantity detection device is an amount depending on a force applied to a handle of the vehicle by an operator. A zero point adjustment method for a bridge circuit in the physical quantity detection device according to claim 6 ,
By adjusting one of the variable resistors for balance adjustment in a state where the physical quantity to be detected by the first and second sensor elements is set to zero, between the first and second output points A first adjustment step for minimizing the amplitude of the differential voltage;
The amplitude of the differential voltage between the first and second output points is adjusted by adjusting the other of the balance adjusting variable resistors in a state where the physical quantity applied to the first and second sensor elements is zero. A second adjustment step that minimizes
Method for adjusting zero point of bridge circuit including The zero adjustment method according to claim 13 , wherein the differential voltage is minimized by repeating the first adjustment step and the second adjustment step.

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