JP2009128155A - Magnetostrictive torque sensor device and measurement value midpoint deviation compensation method therefor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To compensate measurement value midpoint deviation of a forward/backward torque, in an accurate and easy manner, without requiring volume resistance, additional circuits for midpoint output voltage adjustment, increase in troublesome adjustment man-hours, or operator's skills. <P>SOLUTION: This device has a bias component setting part 28 for variably setting a bias component for generating a bias magnetic field by feeding coils 33-36 of a sensor part 30A and compensates for the measured value midpoint deviation of the forward/backward torque, by setting a direct current component by the bias component setting part 28. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a magnetostrictive torque sensor and a method for compensating a midpoint deviation of a measured value thereof, and in particular, a magnetostrictive method that is used in an electric steering device of an automobile and measures a forward / reverse torque acting on a steering shaft or the like by a magnetostrictive effect. The present invention relates to a technique for compensating for a midpoint shift in a measured value of a torque sensor device.

  As a magnetostrictive torque sensor device used for an electric steering device of an automobile, etc., there are two magnetostrictive films (magnetostrictive portions) having opposite magnetic anisotropies in two axial directions on the surface of a shaft to be measured for torque. The magnetostrictive film is subjected to alternating current excitation by flowing an alternating current excitation current of a predetermined frequency through at least two coils arranged in close proximity to the film, and the change in permeability of the magnetostrictive film due to the twist of the shaft caused by the torque acting on the shaft is coiled. There is known a technique that quantitatively measures forward and reverse torque acting on a shaft based on a change in impedance of the coil, based on a change in impedance characteristics of the coil (for example, Patent Documents 1 and 2).

  In the magnetostrictive torque sensor device as described above, there is an individual difference in the impedance of the coil for each product, and the measured value (output voltage) of the forward / reverse torque at the midpoint (zero point) where the torque does not act on the shaft, Variations occur between products. For this reason, the magnetostrictive torque sensor corrects the measured value of the forward / reverse torque at the midpoint to the normal value, so that the measured value of the forward / reverse torque is shifted from the midpoint, that is, the measured value of the forward / reverse torque at the midpoint. It is necessary to compensate for the deviation from the normal value of each product.

In contrast to this, a sensor unit that adjusts the offset voltage of the amplifier output with a volume resistor or generates an output voltage with a constant sensor characteristic with respect to the pulse width modulation output for excitation output from the microcomputer is provided. In the torque sensor device, it has been proposed to sequentially and repeatedly change the sensor characteristics until the sensor unit outputs a predetermined midpoint output voltage with respect to a predetermined pulse width modulation output (for example, Patent Document 3).
Japanese Patent No. 3990683 JP 2007-285862 A JP 2003-83832 A

  However, with the volume resistor, a volume resistor connected to the coil must be provided separately, and also includes problems such as an increase in troublesome adjustment man-hours and unstable adjustment accuracy depending on the skill level of the operator. It is out.

  In the case of using pulse width modulation, the midpoint output voltage is adjusted by adding a correction voltage to the output voltage of the sensor unit. Therefore, it is necessary to add a circuit for adjusting the midpoint output voltage. growing.

  The problem to be solved by the present invention is that an additional circuit for adjusting a volume resistance and a midpoint output voltage, an increase in troublesome adjustment man-hours, and measurement of forward / reverse torque accurately and easily without requiring skill of an operator. This is to compensate for the midpoint deviation.

  A magnetostrictive torque sensor device according to the present invention includes a magnetostrictive portion provided on a torque measurement target shaft, and converts a change in magnetic characteristics of the magnetostrictive portion into an electrical value change of at least two coils arranged opposite to the magnetostrictive portion. A magnetostrictive torque sensor measurement value midpoint deviation compensation device that detects forward and reverse torque acting on the shaft from the change in electrical value, and generates a bias magnetic field by supplying power to the coil Bias component setting means for variably setting the bias component is provided, and the measured value midpoint deviation of the forward / reverse torque is compensated by setting the bias component by the bias component setting means.

  In the magnetostrictive torque sensor device according to the present invention, a magnetostrictive portion is provided on a shaft to be measured for torque, at least two coils are disposed opposite to the magnetostrictive portion, an excitation current is applied to the coil, and a magnetism of the magnetostrictive portion is provided. It is a magnetostrictive torque sensor measurement value midpoint deviation compensation device that detects a characteristic change by converting it to an electrical value change of the coil, and measures forward and reverse torque acting on the shaft from the electrical value change, Bias component setting means for variably setting the bias component to be applied to the excitation current is provided, and the measured value midpoint deviation of the forward / reverse torque is compensated by setting the bias component by the bias component setting means.

  In the magnetostrictive torque sensor device according to the present invention, preferably, the exciting current is a pulse wave having a predetermined frequency, and the bias component setting means variably sets the duty ratio of the exciting current.

  In the magnetostrictive torque sensor device according to the present invention, preferably, the at least two coils have a magnetic imbalance with each other due to magnetic influences from the coils themselves or others.

  According to the magnetostrictive torque sensor device according to the present invention, the measured value midpoint deviation compensation method includes a magnetostrictive portion provided on a torque measurement target shaft, wherein at least two coils are disposed opposite to the magnetostrictive portion, and an excitation current is applied to the coil. Among the measured values of a magnetostrictive torque sensor that detects a change in the magnetic characteristic of the magnetostrictive portion by converting it into an electrical value change of the coil, and measures forward and reverse torque acting on the shaft from the electrical value change. In the point deviation compensation method, a bias component to be applied to the excitation current is set according to a midpoint deviation of the measured value of the forward / reverse torque, and the midpoint deviation of the measured value of the forward / reverse torque is set by the setting of the bias component. To compensate.

  According to the magnetostrictive torque sensor device and the measured value midpoint deviation compensation method of the present invention, the measured value midpoint deviation of the forward / reverse torque is compensated by setting a bias component that generates a bias magnetic field in the coil. The midpoint deviation of the measured value can be compensated only by adjusting the current, for example, the duty ratio control of the exciting current.

  As a result, according to the present invention, an additional circuit for adjusting the volume resistance and the midpoint output voltage, an increase in troublesome adjustment man-hours, and a measured value of the forward / reverse torque accurately and easily without requiring skill of the operator. Midpoint deviation can be compensated.

  In the following, an embodiment of a magnetostrictive torque sensor device and a method of compensating for a measured value midpoint deviation according to the present invention will be described with reference to FIGS.

  First, as one embodiment of a magnetostrictive torque sensor device according to the present invention, an electronically controlled electric steering device for an automobile incorporating a magnetostrictive torque sensor device with compensation for measured value midpoint deviation will be described with reference to FIG. explain.

  The steering wheel 1 has a wheel shaft 2, and the wheel shaft 2 is drivingly connected to the upper end portion of the steering shaft 4 by a universal joint 3. A pinion 5 is formed at the lower end of the steering shaft 4.

  The left and right wheels 6 and 7 are connected to the left and right ends of the rack shaft 10 by tie rods 8 and 9 or the like. The rack shaft 10 has a rack tooth portion 11, and the pinion 5 meshes with the rack tooth portion 11. Thereby, the rotation of the steering wheel 1 is transmitted to the rack shaft 10, and the steering is performed in which the directions of the left and right wheels 6 and 7 are changed.

  A worm wheel 12 is attached to the vicinity of the lower end of the steering shaft 4. The worm wheel 12 meshes with a worm 15 attached to an output shaft 14 of an electric motor 13 that generates a steering assist force. Thereby, a steering assist force generated by the electric motor 13 is applied to the steering shaft 4.

  The electric motor 13 is controlled by an electronic control unit (ECU) 20 including a microcomputer. The ECU 20 provides information on the torque generated in the steering shaft 4 from the magnetostrictive torque sensor device 30 provided with the sensor unit 30A in the vicinity of the upper end of the steering shaft 4, and information on the vehicle speed from a vehicle speed sensor (not shown) (vehicle speed sensor signal). Is input, an appropriate steering assist force is calculated according to the information, and the output of the electric motor 13 is controlled.

  Next, details of the sensor unit 30A of the magnetostrictive torque sensor device 30 according to the present embodiment will be described with reference to FIG. The sensor unit 30A includes magnetostrictive films 31 and 32 formed as magnetostrictive portions at two locations in the axial direction on the surface of the steering shaft 4 that is a shaft to be measured for torque, and a coil disposed in close proximity to one of the magnetostrictive films 31. 33 and 34, and coils 35 and 36 that are disposed opposite to each other in the vicinity of the other magnetostrictive film 32.

  The magnetostrictive films 31 and 32 are Ni—Fe-based alloy films formed by plating or the like, and as shown by arrows A and B in the figure, the magnetic anisotropy is in the direction of 90 ° inclination different from each other. Have Thereby, the magnetic anisotropy of the magnetostrictive film 31 and the magnetic anisotropy of the magnetostrictive film 32 are out of phase with each other in the direction of 90 degrees.

  The coils 33 and 34 are wound around a bobbin 37, and the coils 35 and 36 are wound around another bobbin 38, respectively, a cylindrical yoke 39 made of magnetic material arranged at the outer periphery, and an annular plate-like yoke made of magnetic material arranged at the end. 40, a spacer 41, an end cap 42, and the like are incorporated in a housing 43 fixedly arranged on the vehicle body side.

  Since the annular plate-shaped yoke 40 is installed only at the upper end portion of the bobbin 37, the coil 33 close to the yoke 40 is different from the other coils 34, 35, and 36 not close to the yoke 40. Show properties. This means that the coil 33 and the coils 34, 35, and 36 have a magnetic imbalance.

  The magnetic imbalance may be applied by either a magnetic material or a non-magnetic material. When the housing 43 is made of a non-magnetic material such as aluminum, the housing is configured as shown in FIG. Due to the magnetic loss due to the eddy current 43, the coil 33 and the coils 34, 35, and 36 have a magnetic imbalance.

  As shown in FIG. 4, the coils 33 and 35 and the coils 34 and 36 are individually connected in series. These two series circuits are connected in parallel to each other, and an exciting current (alternating current) Imag having a predetermined frequency is applied to each of the series circuit of the coils 33 and 35 and the series circuit of the coils 34 and 36. An excitation current Imag having a predetermined frequency flows through the coils 33 to 36, an excitation voltage is applied to the coils 33 to 36, and the coils 33 to 36 are AC-excited. The magnetostrictive films 31 and 32 are AC magnetized by the AC magnetic field of the coils 33 to 36.

  When torque is generated in the steering shaft 4, a compressive force acts on one of the magnetostrictive films 31 and 32 and a tensile force acts on the other against the magnetic anisotropy of the magnetostrictive films 31 and 32. As a result, the magnetic permeability of one of the magnetostrictive films 31 and 32 in the alternating magnetic field increases, and the magnetic permeability of the other decreases. Due to this change in magnetic permeability, the impedance of the coils 33 and 34 increases, and an electrical value change occurs in which the impedance of the coils 35 and 36 decreases. That is, changes in the magnetic characteristics of the magnetostrictive films 31 and 32 are detected by converting them into electrical value changes called impedance changes of the coils 33 to 36.

  The impedance change of the coils 33 and 35 is the change of the voltage (first output voltage) VS1 at the midpoint 51 of both coils, and the impedance change of the coils 34 and 36 is the voltage of the midpoint 52 of both coils (second output voltage). ) Each is output as a change in VS2.

  As shown in FIG. 5, the first output voltage (AC) VS1 is rectified by the rectifier circuit 22 of the rectifier / amplifier 21 and amplified by the amplifier circuit 23 to become the DC first output voltage VT1. Is input. The second output voltage (AC) VS2 is rectified by the rectifier circuit 24 of the rectifier / amplifier 21, is amplified by the amplifier circuit 25, and is input to the ECU 20 as the DC second output voltage VT2.

  The ECU 20 includes a difference calculation unit 26 as a sensor signal processing unit belonging to the magnetostrictive torque sensor device 30. The difference calculation unit 26 receives the first output voltage VT1 and the second output voltage VT2, and calculates a differential voltage VT3 indicating the forward / reverse torque acting on the steering shaft 4 according to the following equation (1).

VT3 = k (VT1-VT2) +2.5 (1)
However, k is a gain.

  The forward / reverse torque is a designation when the torque in the clockwise direction of the steering shaft 4 is a positive torque and the opposite counterclockwise torque is a negative torque.

  If the initial impedances of the coils 33 to 36 are all the same, (VT1−VT2) = 0 in the state where the forward / reverse torque is not acting on the steering shaft 4 at all, and the differential voltage VT3, that is, the forward / reverse torque is measured. The value will be 2.5V. 2.5V corresponds to 1/2 of the rated voltage 5V of the ECU 20, which is called a normal midpoint voltage. The measured value VT3 of the forward / reverse torque increases from the midpoint voltage 2.5V to 5V in proportion to the increase in the forward torque, and decreases from the midpoint voltage 2.5V to 0V in proportion to the increase in the reverse torque.

  On the other hand, if the initial impedances of the coils 33 to 36 are not uniform, the forward / reverse torque is not applied to the steering shaft 4 and (VT1-VT2) = 0, and the measured value of the forward / reverse torque. The (midpoint voltage) is shifted from the normal midpoint voltage of 2.5V, such as 2.6V. This is the midpoint deviation between the measured values of forward and reverse torque.

  The ECU 20 includes an exciting current setting unit 27 as an electric circuit that operates the sensor unit 30 </ b> A of the magnetostrictive torque sensor device 30. The exciting current setting unit 27 sets the exciting current Imag of the coils 33 to 36, in other words, the exciting voltage applied to the coils 33 to 36. The excitation current Imag is based on a pulse wave having a predetermined frequency. When the duty ratio is 0.5, only the AC component is applied. When there is an increment from the duty ratio of 0.5, the direct current corresponding to the increment is applied. Component voltage application will be added. This DC component voltage corresponds to a bias voltage, and the bias voltage generates a bias magnetic field in the coils 33 to 36. The bias magnetic field depends on the amount of bias magnetization corresponding to the DC component voltage.

  The ECU 20 includes a bias component setting unit 28 as a measured value midpoint deviation compensation unit of the magnetostrictive torque sensor device 30. The bias component setting unit 28 variably sets the duty ratio of the excitation current Imag, and instructs the excitation current setting unit 27 to apply a bias component to the excitation current Imag by increasing the duty ratio.

  As shown in FIG. 6, the impedance of the coils 33 to 36 decreases in proportion to the increase of the bias voltage. Thus, the impedance characteristics of the coils 33 to 36 can be changed by adjusting the bias voltage, that is, by setting the duty ratio increment by the bias component setting unit 23, and by the bias component setting by the bias component setting unit 28, It is possible to compensate for the deviation in the measured value midpoint between the forward and reverse torques.

  The bias component setting unit 28 receives the first output voltage VS1 and the second output voltage VS2 or the differential voltage VT3 so that the differential voltage VT3 becomes 2.5V, that is, in the measured value of the forward / reverse torque. A command for incrementally setting the duty ratio of the excitation current Imag is output to the excitation current setting unit 27 so that the point deviation becomes zero.

  Since the coil 33 and the coils 34, 35, and 36 have a magnetic imbalance with each other, even if a current having a duty ratio including the same increment, that is, the same bias voltage is applied to the coils 33 to 36, the coil 33 Produces a different impedance change from the other coils 34, 35, 36.

  As a result, the first output voltage VS1 and the second output voltage VS2 change from each other. For example, as shown in FIG. 7, the bias voltage is set to 1V from the default value of 2V by duty ratio control of the excitation current. The measured value (midpoint voltage) of the forward / reverse torque is compensated from 2.6V to 2.5V simply by lowering to. This measured value midpoint deviation compensation may be performed for each product at the time of product shipment or the like.

  As described above, since the deviation of the measured value midpoint between the forward and reverse torques is compensated by setting the bias component for generating the bias magnetic field in the coils 33 to 36, adjustment of the excitation current applied to the coils 33 to 36, for example, the excitation current The midpoint deviation of the measured value can be compensated only by duty ratio control, additional circuit for adjusting the volume resistance and midpoint output voltage, cumbersome adjustment man-hours, no need for operator skill, and by adding the circuit The deviation of the midpoint of the measured value of the forward / reverse torque can be compensated accurately and simply without causing an increase in the size of the circuit board and a decrease in the on-vehicle performance.

  The bias magnetic field is not limited to a DC magnetic field, and may be an AC magnetic field. The mutual magnetic imbalance between the coil 33 and the coils 34, 35, and 36 has a magnetic unbalance with each other due to a deviation in the magnetic characteristics of the coil itself, in addition to the above-described magnetic influence from others. May be.

1 is a diagram showing an electronically controlled electric steering device for an automobile incorporating a magnetostrictive torque sensor device with compensation for measured value midpoint deviation as one embodiment of a magnetostrictive torque sensor device according to the present invention. FIG. It is sectional drawing which shows one Embodiment of the sensor part of the magnetostrictive torque sensor apparatus by this invention. It is sectional drawing which shows other embodiment of the sensor part of the magnetostrictive torque sensor apparatus by this invention. It is a coil connection figure of the sensor part of the magnetostriction type torque sensor device by this embodiment. 1 is a block diagram showing an embodiment of a magnetostrictive torque sensor device with a measured value midpoint deviation compensation according to the present invention. FIG. It is a graph which shows the relationship between the impedance of the coil of the sensor part of a magnetostriction type torque sensor apparatus, and bias voltage. It is a graph which shows the relationship between the midpoint voltage of a magnetostrictive torque sensor apparatus, and a bias voltage.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Steering wheel 4 Steering shaft 5 Pinion 6, 7 Wheel 10 Rack shaft 20 Electronic control unit (ECU)
26 Difference Calculation Unit 27 Excitation Current Setting Unit 28 Bias Component Setting Unit 30 Magnetostrictive Torque Sensor Device 30A Sensor Unit 31, 30 Magnetostrictive Film 33, 34, 35, 36 Coil

Claims (5)

A magnetostrictive portion is provided on a torque measurement target shaft, and a change in the magnetic characteristics of the magnetostrictive portion is detected by converting it into an electrical value change of at least two coils arranged opposite to the magnetostrictive portion. A magnetostrictive torque sensor device for measuring forward and reverse torque acting on the shaft,
Bias component setting means for variably setting a bias component that feeds the coil and generates a bias magnetic field;
A magnetostrictive torque sensor device that compensates for a deviation in the measured value midpoint between the forward and reverse torques by setting a bias component by the bias component setting means. A shaft for torque measurement is provided with a magnetostrictive portion, and at least two coils are disposed opposite to the magnetostrictive portion, an excitation current is applied to the coil, and a change in magnetic characteristics of the magnetostrictive portion is changed to an electric value change of the coil. A magnetostrictive torque sensor device that converts and detects and measures forward and reverse torque acting on the shaft from the change in electrical value,
Bias component setting means for variably setting a bias component to be applied to the excitation current;
A magnetostrictive torque sensor device that compensates for a deviation in the measured value midpoint between the forward and reverse torques by setting a bias component by the bias component setting means.   3. The magnetostrictive torque sensor device according to claim 2, wherein the exciting current is based on a pulse wave having a predetermined frequency, and the bias component setting means variably sets the duty ratio of the exciting current.   The magnetostrictive torque sensor device according to any one of claims 1 to 3, wherein the at least two coils have a magnetic imbalance with each other due to a magnetic influence from the coil itself or others. A shaft for torque measurement is provided with a magnetostrictive portion, and at least two coils are disposed opposite to the magnetostrictive portion, an excitation current is applied to the coil, and a change in magnetic characteristics of the magnetostrictive portion is changed to an electric value change of the coil. It is a method of compensating for the midpoint deviation of the measured value of the magnetostrictive torque sensor device that detects the converted and detected and measures the forward / reverse torque acting on the shaft from the change in electrical value,
A magnetostrictive torque sensor device that sets a bias component to be applied to the excitation current according to a measured value midpoint deviation of the forward / reverse torque and compensates for the measured value midpoint deviation of the forward / reverse torque by setting the bias component. Compensation method for measured value midpoint deviation.

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