JP2722296B2 - Magnetostrictive torque sensor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetostrictive torque sensor suitable for detecting, for example, an output shaft torque of an automobile engine.

[0002]

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

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

In FIG. 1, reference numeral 1 denotes a casing constituting a torque sensor main body. The casing 1 is formed of a nonmagnetic material in a stepped cylindrical shape, and is fixed to a case (not shown) of an automatic transmission. It has become. Reference numeral 2 denotes a magnetostrictive shaft rotatably disposed in the casing 1 via bearings 3 and 3. The magnetostrictive shaft 2 is formed in a rod shape from a positive magnetostrictive material such as chromium molybdenum steel, and has both ends 2A and 2A.
B projects out of the casing 1 and constitutes an output shaft. The axially intermediate portion of the magnetostrictive shaft 2 is located in the casing 1 to be a slit forming portion 2C, and the outer peripheral surface of the slit forming portion 2C is inclined obliquely downward.
The slit grooves 4, 4,..., 5, 5,.

The slit grooves 4, 5 are spaced at a predetermined interval in the axial direction of the magnetostrictive shaft 2 and are formed at equal intervals on the entire outer peripheral surface of the slit forming portion 2C. Then, the slit forming portion 2C of the magnetostrictive shaft 2
A first magnetic anisotropic portion 6 is formed between each slit groove 4 and a second magnetic anisotropic portion 7 is formed between each slit 5. 7, a magnetic path is formed by the surface magnetic field.

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

Reference numerals 9 and 10 denote excitation and detection coils as a pair of coils radially opposed to the magnetically anisotropic portions 6 and 7 of the magnetostrictive shaft 2, respectively. The excitation and detection coils 9 and 10 are core members. 8 are provided on the inner peripheral side via coil bobbins (not shown), respectively.
, An AC voltage V having a frequency f is applied to perform an exciting action and a detecting action. Each of the exciting and detecting coils 9, 10 has a self inductance L1,
L2, and its iron loss and DC resistance are r1 and r2.

Here, each excitation and detection coil 9, 10
Is supplied with the AC voltage V from the oscillator 12,
Impedance Z1 of each excitation and detection coil 9,10
, Z2 are as shown in Equation 1.

[0009]

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

[0010]

(Equation 2)

FIG. 4 shows a detection processing circuit of a magnetostrictive torque sensor according to the prior art. This detection processing circuit comprises a bridge circuit 11, an oscillator 12 as an AC voltage applying means, a differential amplifier 13, a synchronous detection circuit. It is composed of a processing circuit 14 and the like. Here, the bridge circuit 11 is composed of the excitation and detection coils 9 and 10 and the adjustment resistors R and R. A connection point a between the excitation and detection coils 9 and 10 and a connection point b between the adjustment resistors R and R are , For example, 30k
It is connected to an oscillator 12 of an AC voltage V having a frequency f on the order of Hz.

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

[0013]

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

[0014]

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

Further, each of the excitation and detection coils 9, 1
0 and the connection points c and d between the adjustment resistors R and R are connected to the differential amplifier 13.
And outputs the respective detection voltages V 1 and V 2 from the respective excitation and detection coils 9 and 10 to the differential amplifier 13. The output terminal 13A of the differential amplifier 13 is connected to the synchronous detection processing circuit 14 together with the oscillator 12.
The synchronous detection processing circuit 14 rectifies the output voltage E0 from the differential amplifier 13 in synchronization with the AC voltage V from the oscillator 12, and outputs a DC output voltage E.

In the conventional magnetostrictive torque sensor having the above-described configuration, when an AC voltage V from the oscillator 12 is applied to the excitation and detection coils 9 and 10, the slit forming portion 2C of the magnetostrictive shaft 2 has the slit A magnetic path is formed by the surface magnetic field along the magnetic anisotropic portions 6 and 7 between the grooves 4 and 5, respectively. In this case, the adjustment resistor R shown in FIG. 4 is connected to the differential amplifier 1 when the torque acting on the magnetostrictive shaft 2 is zero.
3 is adjusted so that the output voltage E0 is zero.

In this prior art, since a positive magnetostrictive material is used for the magnetostrictive shaft 2, when a torque is applied to the magnetostrictive shaft 2 in the direction of arrow T in FIG. In the portion 2C, a tensile stress + σ acts along the magnetic anisotropic portion 6 between the slit grooves 4, and a compressive stress −σ along the magnetic anisotropic portion 7 between the slit grooves 5.
Works. Thereby, the magnetic permeability μ increases in the magnetic anisotropic part 6 due to the tensile stress + σ, and decreases in the magnetic anisotropic part 7 due to the compressive stress −σ.

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

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

[0020]

E0 = A × (V1−V2) where A is the amplification factor, and the AC output voltage E0 is output from the output terminal 13A of the differential amplifier 13 to the synchronous detection processing circuit 14. . The synchronous detection processing circuit 14 is connected to the oscillator 12
The output voltage E0 is synchronously detected and rectified by the AC voltage V from the DC power supply, and the DC output voltage E is output as an output signal corresponding to the torque acting on the magnetostrictive shaft 2.

[0021]

In the prior art described above, since the magnetostrictive shaft 2 is made of a positive magnetic material, the magnetic anisotropic portions 6, 6 formed between the slit grooves 4, 5 are formed. The impedances Z1 and Z2 of the excitation and detection coils 9 and 10 provided at positions corresponding to 7 are as shown in FIGS.

That is, when a torque is applied to the magnetostrictive shaft 2 in the positive direction (the direction indicated by the arrow T in FIG. 3), the slit grooves 4
Accordingly, a tensile stress + σ acts on the exciting and detecting coil 9 side of the magnetostrictive shaft 2, and a compressive stress −σ acts on the exciting and detecting coil 10 side by the slit groove 5. When a torque is applied to the magnetostrictive shaft 2 in the opposite direction (the opposite direction of the arrow T in FIG. 3), a compressive stress −σ acts on the excitation of the magnetostrictive shaft 2 and the detection coil 9 side, and the excitation is performed. Further, a tensile stress + σ acts on the detection coil 10 side.

For this reason, the magnetostrictive shaft 2 is formed of a positive magnetic material, and the impedance Z1 when the positive direction torque is applied to the exciting and detecting coil 9 side by the respective slit grooves 4 and 5 as described above. Equation 1 and Equation 2
, But the impedance Z1 when a torque in the reverse direction is applied is a value having unknown variation that cannot be calculated by the equations (1) and (2).

On the excitation and detection coil 10 side, the impedance Z when a reverse torque is applied
Although 2 is a value that can be calculated from Equations 1 and 2,
The impedance Z2 when a positive torque is applied is a value having unknown variation that cannot be calculated by the equations (1) and (2).

In the prior art, the exciting and detecting coils 9 and 10 are connected to a bridge circuit 11, and the difference between the impedances Z 1 and Z 2 of the exciting and detecting coils 9 and 10 is detected by a differential amplifier 13. Therefore, as described above, when a positive torque is applied to the magnetostrictive shaft 2, an accurate value corresponding to the torque of the excitation and detection coil 9 and a value with variation in the excitation and detection coil 10 are obtained. Is detected. When a torque in the opposite direction is applied to the magnetostrictive shaft 2, the value of the excitation and detection coil 9 having a variation and the value of the excitation and detection coil 10
The difference from the accurate value corresponding to the torque of is detected.

For this reason, in the detection processing circuit according to the prior art, one of each of the excitation and detection coils 9 and 10 detects a value corresponding to the torque according to the direction of the torque applied to the magnetostrictive shaft 2, but the other one. Has a problem in that accurate detection of torque cannot be performed because a difference value is detected by the differential amplifier 13.

Also, in the case where the detection processing circuit is configured such that the excitation and detection coils 9 and 10 are connected in series and a voltage is detected from the connection point, one of the excitation and detection coils 9 and 10 is similarly connected. Since 10 has a variation, accurate torque detection cannot be performed.

The present invention has been made in view of the above-mentioned problems of the prior art, and the present invention selects a detection signal from a coil corresponding to a torque and rejects a detection signal from a coil having a variation, thereby achieving high efficiency. It is an object of the present invention to provide a magnetostrictive torque sensor capable of performing accurate torque detection.

[0029]

In order to solve the above-mentioned problems, a magnetostrictive torque sensor employed in the first invention is:
A magnetostrictive shaft formed of a magnetic material and having a pair of magnetically anisotropic portions on an outer peripheral side spaced apart in the axial direction, and a pair of magnetically anisotropic portions provided on the magnetostrictive shaft and provided in a radially opposed manner. When the respective magnetic anisotropic parts are formed of a positive magnetic material, the coil and the detection processing circuit for detecting only the detection signal on the coil side which is the tensile stress side.

The magnetostrictive torque sensor adopted in the second invention is a magnetostrictive shaft formed of a magnetic material and having a pair of magnetically anisotropic parts on an outer peripheral side spaced apart in an axial direction.
A pair of coils provided radially opposite to each magnetic anisotropic part of the magnetostrictive shaft, and when each of the magnetic anisotropic parts is formed of a negative magnetic material, it is on the compressive stress side. And a detection processing circuit for detecting only the detection signal on the coil side.

Further, the detection processing circuit compares a pair of signal detection means for detecting the impedance of each of the coils as a detection signal with each detection signal from each of the signal detection means, and outputs a larger detection signal. It is preferable that it is composed of a comparing and selecting means for selecting.

Further, each of the comparison and detection means is provided with a correction means for setting a detection signal from each of the coils detected by each of the signal detection means to a predetermined value when no torque is applied to the magnetostrictive shaft. Is preferred.

[0033]

According to the above construction, the detection signal from each coil selected by the comparison and selection means is the detection signal from the coil on the tensile stress side when the magnetic anisotropic portion is formed of a positive magnetic material. When the selected magnetic anisotropic portion is formed of a negative magnetic material, a detection signal from the coil on the compressive stress side can be selected, and a detection signal corresponding to the torque applied to the magnetostrictive shaft can be output. .

[0034]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS. In the embodiments, the same components as those of the above-described conventional technology are denoted by the same reference numerals, and description thereof will be omitted.

FIG. 1 shows a detection processing circuit according to the present embodiment. The detection processing circuit comprises an oscillator 12, excitation and detection coils 9, 10 connected in parallel to the output side of the oscillator 12, and Impedance detection circuits 21 and 22 for detecting the respective impedances Z1 and Z2 of the excitation and detection coils 9 and 10, and a comparison circuit 23 for comparing the detection signals VZ1 and VZ2 from the impedance detection circuits 21 and 22; And a correction circuit 25 for correcting the detection signals VZ1 and VZ2 from the impedance detection circuits 21 and 22, respectively. The excitation and detection coils 9 and 10 are provided at positions facing the magnetically anisotropic parts 7 and 8 of the magnetostrictive shaft 2 as in the prior art.

In the figure, reference numerals 21 and 22 denote impedance detecting circuits as a pair of signal detecting means, respectively, and excitation and detecting coils 9 and 10 are connected to the input sides of the impedance detecting circuits 21 and 22, respectively. ing.

Each of the impedance detection circuits 2
In Steps 1 and 22, the impedances Z1 and Z2 of the excitation and detection coils 9 and 10 are detected as shown in Equation 1, and the input side of the comparison circuit 23 and the changeover switch 24 is set as a voltage corresponding to the impedances Z1 and Z2. Detection signal VZ
1, VZ2 is output. One end of each of the excitation and detection coils 9 and 10 is connected to the output side of the oscillator 12, and the other end is connected to the ground.

Reference numeral 23 denotes a comparison circuit. The comparison circuit 23 compares the detection signals VZ1 and VZ2 from the impedance detection circuits 21 and 22, and sends a switching signal to the changeover switch 24 so as to select the larger one. Is output via the signal line 23A.

Reference numeral 24 denotes a changeover switch. The input side of the changeover switch 24 is connected to each of the impedance detection circuits 21 and
The output side is connected to the synchronous detection processing circuit 14 described in the related art.

Here, the comparison circuit 23 and the changeover switch 24 constitute comparison selection means according to the present embodiment.

Reference numeral 25 denotes a correction circuit as correction means.
The correction circuit 25 includes the impedance detection circuits 21,
22, each of the impedance detection circuits 21 and
The correction of the detection signals VZ1 and VZ2 output from the control unit 2 is performed.

Here, the correction circuit 25 indicates the torque on the horizontal axis,
As shown in a characteristic diagram of FIG. 2 in which the impedances Z1 and Z2 of the excitation and detection coils 9 and 10 are plotted on the vertical axis, when the torque is zero, the characteristic lines 26 and 2 indicated by dotted lines are shown.
Correction is made when the intersection with 7 does not fall on the impedances Z1 and Z2 on the vertical axis.

That is, in this case, the point Z10 of the characteristic line 26 at which the torque is zero is shifted downward so as to become the predetermined value Z00 to obtain the correction characteristic line 26 ', and the point Z20 of the characteristic line 27 where the torque is zero.
Is shifted upward to a predetermined value Z00 to make a correction characteristic line 27 '. When the torque is zero, the correction characteristic lines 26' and 27 'are crossed at the predetermined value Z00.

In the detection processing circuit according to the present embodiment configured as described above, when the magnetic anisotropic portions 6 and 7 of the magnetostrictive shaft 2 are formed of a positive magnetic material as described in the related art, When a positive torque is applied to the magnetostrictive shaft 2 by the comparison circuit 23 and the changeover switch 24 according to the present embodiment, the correction characteristic line 2 in the first quadrant becomes a thick line.
When 6 'is selected and a torque in the reverse direction is applied, the correction characteristic line 27' in the second quadrant, which is a thick line, is selected.

Thus, no matter which direction the torque is applied to the magnetostrictive shaft 2, the comparison circuit 23 and the changeover switch 24 correspond to the magnetic anisotropic parts 6 and 7 on the side where the tensile stress (+ σ) is generated. The detection signals VZ1 and VZ2 from one of the excitation and detection coils 9 and 10 provided are selected and output. And a stable output can always be obtained. On the other hand, the other excitation and detection coils 9 or 10 on the side where the compression stress (-σ) is applied do not output the detection signals VZ1 and VZ2.

Furthermore, the correction signals 25 and VZ1 and VZ2 can be reliably corrected by the excitation and detection coils 9 and 10 by the correction circuit 25, and accurate detection signals VZ1 and VZ2 can be output.

Therefore, the variation in the torque sensitivity output from the torque sensor can be greatly reduced, and the torque can be detected with high accuracy.

Next, in the above-described embodiment, the case where the magnetically anisotropic portions 6 and 7 of the magnetostrictive shaft 2 are formed of a positive magnetic material has been described. However, the present invention is not limited to this. It can be used when 6 and 7 are formed of a negative magnetic material. In this case, high-accuracy torque detection is performed by selecting the excitation signal on the side where the compression stress (-σ) is to be generated and the detection signal VZ1 or VZ2 of the detection coil 9 or 10.

That is, when the magnetic anisotropic parts 6 and 7 are formed of a negative magnetic material, the detection signal detected by the excitation and detection coil 9 in FIG.
A detection signal detected by the excitation and detection coil 10 becomes a characteristic line 26. As a result, in the detection processing circuit, the excitation and detection coil 9 or 1 on the compressive stress (-σ) side
Select the 0 detection signal.

In the above embodiment, the comparison and selection means according to the present invention is constituted by the comparison circuit 24 and the changeover switch 24. However, the present invention is not limited to this, and may be constituted by a single circuit.

Further, in the above-described embodiment, the magnetostrictive shaft 2 is described as being formed entirely of a magnetic material. However, the present invention is not limited to this.
In this case, the magnetically anisotropic portions 6 and 7 can be formed by heat treatment, selection of a material composition, or the like.

[0052]

As described above in detail, according to the present invention, when each of the magnetically anisotropic portions formed on the magnetostrictive shaft is formed of a positive magnetic material, the portion on the coil side which is on the tensile stress side is formed. Because the detection processing circuit is configured to detect only the detection signal and detect only the detection signal on the coil side that becomes a compressive stress when each magnetic anisotropic portion is formed of a negative magnetic material. Even when torque in any direction is applied to the magnetostrictive shaft, highly accurate torque detection can be performed.

The detection processing circuit compares a pair of signal detection means for detecting the impedance of each of the coils as a detection signal with each detection signal from each of the signal detection means, and outputs a larger detection signal. And a comparing / selecting means for selecting, and a correction means for setting a detected signal from each of the detected coils to a predetermined value is added to each of the signal detecting means, so that more accurate torque detection can be performed. Can be.

[Brief description of the drawings]

FIG. 1 is a circuit configuration diagram showing a detection processing circuit according to an embodiment of the present invention.

FIG. 2 is a characteristic diagram illustrating a change in impedance with respect to torque detected by a pair of excitation and detection coils when a magnetic anisotropic portion according to the present embodiment is formed of a positive magnetic material.

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

FIG. 4 is a circuit diagram showing a detection processing circuit according to the related art.

FIG. 5 is a characteristic diagram showing a change in impedance with respect to torque detected by one of the excitation and detection coils when a magnetic anisotropic portion according to the related art is formed of a positive magnetic material.

FIG. 6 is a characteristic diagram showing a change in impedance with respect to torque detected by the other excitation and detection coils when the magnetic anisotropic portion according to the related art is formed of a positive magnetic material.

[Explanation of symbols]

 2 Magnetostrictive shaft 6,7 Magnetic anisotropic part 9,10 Excitation and detection coil 12 Oscillator 21,22 Impedance detection circuit (Signal detection means) 23 Comparison circuit (Comparison / selection means) 24 Changeover switch (Comparison / selection means) 25 Correction circuit (Correction means)

Claims (4)

(57) [Claims] 1. A magnetostrictive shaft formed of a magnetic material and having a pair of magnetically anisotropic parts on an outer peripheral side spaced apart in an axial direction, and radially opposed to each magnetically anisotropic part of the magnetostrictive shaft. A pair of coils provided, and a detection processing circuit that detects and processes only a detection signal on a coil side that is a tensile stress side when each of the magnetic anisotropic parts is formed of a positive magnetic material. Magnetostrictive torque sensor. 2. A magnetostrictive shaft formed of a magnetic material and having a pair of magnetically anisotropic parts on an outer peripheral side spaced apart in an axial direction, and radially opposed to each magnetically anisotropic part of the magnetostrictive shaft. A pair of coils provided, and a detection processing circuit that detects and processes only a detection signal on a coil side that is a compressive stress side when each of the magnetic anisotropic parts is formed of a negative magnetic material. Magnetostrictive torque sensor. 3. The detection processing circuit compares a pair of signal detection means for detecting the impedance of each of the coils as a detection signal with each detection signal from each of the signal detection means, and outputs a larger detection signal. 3. A magnetostrictive torque sensor according to claim 1, wherein said magnetostrictive torque sensor comprises a comparison selecting means. 4. Each of the comparison and detection means is provided with a correction means for setting a detection signal from each of the coils detected by each of the signal detection means to a predetermined value when no torque is applied to the magnetostrictive shaft. The magnetostrictive torque sensor according to claim 3.