JPS618639A - Magnetostriction type torque detector - Google Patents

Abstract

PURPOSE:To detect accurately torque without receiving the influence of a gap for an object to be measured in the stage of measuring the torque by connecting a capacitor to a coil for excitation and a coil for detection respectively to constitute a resonance circuit and adjusting the resonance characteristic. CONSTITUTION:The coils 3, 4 are wound to the leg parts 1a, 1b of a magnetic core 1 for excitation made into a U-shape and the coils 5, 6 are wound on the leg parts 2a, 2b of the magnetic core 2 for detection. The core 1 and the core 2 are intersected orthogonally with each other to constitute a magnetostriction type torque detector. The leg parts 1a, 1b, 2a, 2b are brought into contact with the magnetostriction material 7 of the material to be measured. The capacitor 20 is connected in series to the coils 3, 4 and the capacitor 21 is connected in parallel to the coils 5, 6 to constitute both into the resonance circuit. An oscillator 22 for excitation is provided to an excitation circuit and the values of the capacitors 20, 21 are so selected that the resonance circuit tunes to the frequency of an AC power source for excitation. The resonance characteristics of the resonance circuits on the excitation side and detection side are adjusted and therefore the torque to output voltage is detected without receiving influence of the spacing with the material to be measured.

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Technical Field The present invention relates to a magnetostrictive torque detection device that is capable of correcting variations in output characteristics due to variations in distance between objects to be measured during torque measurement using a simple circuit configuration.

(b) Prior art Conventionally, the torque applied to the steering shaft or transmission shaft of an automobile is detected, and the hydraulic pump of the power steering mechanism is operated, or the clutch is connected smoothly to stabilize the running of the automobile. It is known to keep. One method of detecting the torque applied to a shaft is to utilize the inverse magnetostrictive effect generated in the shaft. Figure 1 shows an example of the magnetostrictive torque detection device proposed in Japanese Patent Publication No. 31-942. It is shown attached to a shaft, which is the object to be measured. In the figure, 1 is a U-shaped excitation magnetic core having a pair of legs 1a and 1b, and 2 is a detection core having a pair of legs 2a + 2b arranged orthogonally to the excitation magnetic core l. These magnetic cores 1 and 2 are made of a magnetic material such as ferrite or permalloy.

3.4 is an excitation coil arranged on the legs 1a and 1b; 5
, 6Iri are detection coils disposed on the legs 2a and 2b, and 7 is a shaft made of a magnetostrictive material that serves as an object to be measured. The shaft-side end surface of the magnetic core 1.2 is arranged so as not to contact the shaft.

In order to detect the torque applied to the shaft 7 using the torque detection device, an AC excitation voltage of a constant amplitude is applied to the excitation coil 3.4 to form a magnetic bridge circuit P on the surface of the shaft 7.

Now, when torque is applied to the shaft 7, the balance of the magnetic bridge circuit is lost due to the inverse magnetostrictive effect of the shaft 7, and an unbalanced magnetic flux corresponding to the magnitude of the torque is generated in the detection coils 5 and 6. Since an induced electromotive force is generated at 6, the magnitude of the torque can be measured by detecting the unbalanced magnetic flux at that time.

By the way, when installing the above-mentioned torque detection device, the distance between the shaft and the magnetic core may change if the mounting positions of the excitation magnetic core and the detection magnetic core vary, or if the shaft becomes eccentric or deflects during rotation. As a result, the actual magnetic flux attributed to detection changes, so the characteristics of the output voltage with respect to torque are not always constant, and specifically, the distance between the shaft and the magnetic core increases. There is a problem in that the output voltage decreases as the output voltage increases.

Therefore, in order to solve this problem, for example,
In No. 1-60580, as shown in Fig. 2, in addition to the magnetic core 1.2 and coils 3 to 6 for torque measurement, a magnetic core 8.9 and coils 10' and 11 for detecting magnetic flux changes are also used. Arranged so as not to contact the shaft 7,
These magnetic cores 8 and 9 and the coil 10.11 detect the magnetic flux change due to the change in the distance t between the shaft 7 and the magnetic core 1.2, and based on this magnetic flux change, the torque vs. output is calculated. The voltage characteristics are corrected.

However, in this torque detection device, the processing circuit for correcting the torque vs. output voltage characteristics becomes complicated, and the detection device becomes large due to the magnetic core and coil for magnetic flux detection. In addition to the fluctuation factor due to the variation in the mounting position of the magnetic core, the fluctuation factor due to the variation in the mounting position of the magnetic core placed for detecting magnetic flux changes is added, making accurate detection impossible, making it difficult to put it into practical use.

(c) Object and structure of the invention The present invention has been made with attention to the above points, and includes: (1) excitation coil means for flowing an alternating magnetic flux through an object to be measured whose surface is at least magnetic; In a torque detection device that includes a detection fill means for detecting a change in flowing alternating magnetic flux and detects a torque acting on the object to be measured based on a change in the magnetic flux, there is a change in the distance between the object to be measured and the object to be measured during torque measurement. The second purpose is to be able to correct variations in output characteristics caused by The coil means and the detection coil means are arranged at predetermined intervals with respect to the object to be measured so that a resonant circuit constituted by the excitation coil and the capacitor and the detection coil and the capacitor, respectively, is tuned to the frequency of the excitation AC power source. The configuration is such that the value of each capacitor is selected.

) Example The present invention will be explained below based on the drawings.

FIG. 3 shows an embodiment of the magnetostrictive torque detection device according to the present invention attached to a shaft as an object to be measured, and the same reference numerals as in FIG. 1 indicate the same components. In this embodiment, a capacitor 20 is connected in series to the excitation coil 3.4, and these coils 3, 4 and the capacitor 20 constitute a series resonant circuit, and a capacitor 20 is connected to the excitation coil 5.6. 21 are connected in parallel, and these coils 5, 6 and capacitor 21 form a series resonant circuit. In the figure, 22 is the excitation coil 3
, 4 is an oscillator for applying excitation voltage, and 23 is a voltmeter, and the equivalent circuit of FIG. 3 is shown in FIG.

In the equivalent circuit shown in Fig. 4, the impedance of both the excitation side and the detection side is at its minimum when tuned to the resonance frequency IN, so on the excitation side, the maximum excitation current is applied to the excitation coil 3 at a constant excitation voltage. 4, and on the detection side, since the charge 13 flow to capacitor C2 is maximum, the maximum voltage is generated across capacitor C2, that is, the maximum sensitivity is obtained. The resonant frequencies of the excitation-side and detection-side resonant circuits are determined by the following equations.

However, fl: excitation side resonance frequency f2: detection side resonance frequency Ls: inductance C1 of excitation coil 3.4: capacitance L2 of excitation side capacitor 20: inductance C2 of detection coil 5.6:
Capacity of Detection Side Capacitor 21 Next, a description will be given of correction for variations in the torque vs. output voltage characteristics due to changes in the distance between the magnetic core and the shaft of the torque detection device.

First, considering the case where the distance between the magnetic core 1.2 and the shaft 7 on the excitation side and the detection side increases, in this case, the distance in the closed magnetic path formed by the magnetic core 1 or 2 and the shaft 7 Because the reactance of the part increases,
The inductances Lx and L21'' of the excitation coil 3.4 and the detection coil 5.6 are reduced. Therefore, the resonant frequencies fl and f2 of the excitation side and detection side resonance circuits determined by the above equation are shifted to the high frequency side. For example, from the mounting accuracy of the torque detection device, the shaft 7
and the magnetic core of the detection device.

If we consider that the distance between 2 and 2 varies in the range of 0.5 to 1.5, the change in the resonant frequency with respect to the change in the distance can be expressed as the relationship between frequency and impedance.
The result will be as shown in the figure. A in the figure is when the distance is 0.5-,
When B has a distance of 1.0111111, C has a distance of 1.0111111.
5.Characteristics when foggy.

Now, capacitors C1 and C2 are set so that the inductance L1 of the excitation coil 3.4 and the inductance L2 of the detection coil 5.6 are tuned to the excitation frequency fo when the maximum interval is 1.5. By doing so, the maximum excitation current can be obtained on the excitation side and the maximum sensitivity can be obtained on the detection side at this time. In this way, when the interval becomes i, o WIn, the inductances L, , L2 increase on the excitation side and the detection side, resulting in an out-of-tuned state at the excitation frequency fo, and the impedance on the excitation side increases. The excitation current decreases by the increased amount, resulting in a decrease in sensitivity on the detection side. Further, when the interval is 0.54, the inductance Ll + L4 further increases, so that the excitation current decreases and the sensitivity decreases compared to when the interval is 1-Owm. Therefore, when an excitation voltage of a constant amplitude is applied to the excitation coil, when the distance between the shaft 7 and the magnetic cores 1 and 2 of the detection device is large, the excitation side is As the excitation current increases, the sensitivity on the detection side increases; on the other hand, when the above-mentioned interval is small, the excitation current on the excitation side decreases and the sensitivity on the detection side decreases so as to cancel out the change in the actance at the interval. Therefore, stable output characteristics can be obtained regardless of the change in the interval. That is, the resonance characteristics (particularly Q) of each resonance circuit on the excitation side and the detection side are adjusted.

As a result, stable output characteristics can be obtained by adjusting the degree of change in the excitation current on the excitation side and the degree of change in sensitivity on the detection side to optimal values with respect to changes in the distance between the shaft and the detection device. Specific adjustment methods include, for example, changing the wire diameter or number of turns of the coil, or connecting a resistor in series with the coil.

In this way, capacitors are connected to the coils on the excitation side and detection side to form resonance circuits on the excitation side and detection side, respectively, and the excitation is performed so as to cancel out the change in actance in the space between the shaft and the detection device. By adjusting the current and detection sensitivity together, it is possible to obtain the torque-output voltage characteristic as shown in FIG. 6(c). In the figure, the broken line indicates the distance between the shaft and the detection device is 0.5m, and the solid line indicates the distance between the shaft and the detection device is 1m.
．． At zero, the chain line shows the output characteristics when the interval is 1.5 mm. Therefore, in the case of this example, the same figure (a)
It can be seen that, compared to the conventional torque-output voltage characteristic shown in FIG. Note that Figure (B) shows the torque-output voltage characteristics when a resonant circuit is configured only on the excitation side, and in this case, the change in output characteristics is reduced to 1/2 compared to the case of Figure (A). It can be suppressed.

With this configuration, there is no need for a magnetic flux change detection section for detecting changes in magnetic flux due to changes in the distance between the shaft and the torque detection device as in the past, so the overall size of the detection device can be reduced. A processing circuit for correcting output characteristics is not required.

(E) Detailed Description of the Invention As described above, the present invention includes an excitation coil means for causing an alternating magnetic flux to flow through an object to be measured whose surface is magnetic at least, and detecting changes in the alternating magnetic flux flowing through the object to be measured. a detection coil means for detecting a torque acting on the object to be measured based on a change in the magnetic flux, wherein a capacitor is connected to each of the excitation coil means and the detection coil means; At a predetermined interval between the excitation coil means and the detection coil means with respect to the object to be measured, a resonant circuit composed of the excitation coil means and a capacitor, and the detection coil means and a capacitor, respectively, is connected to the frequency of the excitation AC power supply. Since the values of each of the capacitors are selected so as to be synchronized, stable torque vs. output voltage characteristics can be obtained without being affected by changes in the distance to the object to be measured during torque measurement. A processing circuit for correcting output characteristics is not required.

[Brief explanation of drawings]

FIGS. 1 and 2 are perspective views showing different conventional torque detection devices attached to a shaft as an object to be measured, and FIG. 3 is a perspective view showing a torque detection device according to the present invention attached to a shaft as an object to be measured. A perspective view of the installed state;
Fig. 4 is an equivalent circuit of the resonant circuit of the torque detection device shown in Fig. 3, and Fig. 5 is a diagram showing the relationship between frequency and impedance, showing changes in the resonance frequency with respect to changes in the distance between the shaft and the torque detection device. , Fig. 6 is a torque vs. output voltage characteristic diagram, where (a) is a conventional characteristic diagram, (b) is a characteristic diagram when a resonant circuit is configured only on the excitation side, and (c) is a diagram of the present example. FIG. 1...Magnetic core for excitation, 2...Magnetic core for detection, 3.4...
・Excitation coil, 5.6...Detection coil, 7...
Shaft (object to be measured), 20.21... Capacitor,
22... Oscillator patent applicant Nissan Motor Co., Ltd. agent Patent attorney Hiroshi Suzuki Figure 1JI2

Claims (1)

[Claims] It has an excitation coil means for causing an alternating current magnetic flux to flow through an object to be measured whose surface is magnetic at least, and a detection coil means for detecting a change in the alternating current magnetic flux flowing through the object to be measured, based on the change in the magnetic flux. In the torque detection device, a capacitor is connected to each of the excitation coil means and the detection coil means, and the excitation coil means and the detection coil means are set at a predetermined level with respect to the measured object. The magnetostrictive type is characterized in that the value of each of the capacitors is selected so that a resonant circuit composed of the excitation coil and the capacitor and the detection coil and the capacitor, respectively, is tuned to the frequency of the excitation AC power supply at intervals. Torque detection device.