JPS5943323A - Torque detecting apparatus - Google Patents

Abstract

PURPOSE:To enhance torque detecting preciseness, by using a trifurcated magnetic coil wherein an exciting coil is mounted to one magnetic pole and detection coils to other two magnetic coils. CONSTITUTION:A trifurcated magnetic core 2 has three mutually parallel magnetic poles 2a-2c directed to the outer peripheral surface of a shaft 1 and the end surfaces of these magnetic poles are opposed to the outer peripheral surface of the shaft 1 so as to provide definite gaps therebetween. In addition, an exciting coil 3 is mounted to one magnetic pole 2a by winding while detection coils 4, 5 are respectively mounted to the residual two magnetic poles 2b, 2c. Subsequently, the exciting coil 3 is connected to an AC power source 6 to be excited and voltages induced in the detection coils 4, 5 are inputted to a predetermined electric circuit to enable the torque detection of the shaft (a torque transmitting object) 1. By this method, even if the gap between each magnetic pole end surface and the shaft 1 is changed, the error due to this change is removed and, therefore, the preciseness of torque detection can be enhanced.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a torque detection device used as a steering torque detector for power steering, an output torque detector for an engine, or an output torque detector for other transmissions.

Various types of torque detection devices have been known in the past, such as those disclosed in Japanese Patent Publication No. 31-942 and Japanese Patent Application Laid-Open No. 1987-51.
There are types described in Japanese Patent Application Laid-open No. 60580 and Japanese Patent Application Laid-Open No. 129276/1983. The torque detection devices described in these publications all include a criss-cross magnetic core constructed by integrating a pair of U-shaped magnetic cores, and an excitation coil is connected to one U-shaped magnetic core, and an excitation coil is connected to the other U-shaped magnetic core. A detection coil is installed in each core, and the magnetic flux from the excitation coil to the detection coil via the shaft surface is unbalanced on the shaft surface due to the twist of the shaft according to the transmitted torque, and this is used to detect the disrupted magnetic flux. The shaft torque is detected by exciting an induced starting force in the coil.

However, in such conventional torque detection devices, if the gap between each magnetic pole surface of the U-shaped magnetic core and the shaft outer peripheral surface changes due to manufacturing errors of the shaft or unavoidable deflection of the shaft during torque transmission, the above-mentioned gap The density of the magnetic flux flowing through the shaft to the shaft surface also changes, and the output of the detection coil differs even for the same torque, resulting in a torque detection error.

For this reason, the correction means as shown in Japanese Patent Application Laid-open No. 51-60580 and Japanese Patent Application Laid-open No. 51-129276, that is, means for detecting the above-mentioned gap and correcting the output of the detection coil based on the change, is required. This is necessary for a torque detection device, which is expensive, and even with this, it is difficult to ensure sufficient accuracy because the mounting accuracy of the gap detection means is related to the torque detection accuracy.

On the other hand, it has a magnetic core with five legs, one in the center and four surrounding it, with an excitation coil wound around the center leg and a detection coil wound around each of the other four legs. A torque detecting device equipped with a torque sensor has also been proposed. However, when such magnetic cores are manufactured in one piece by casting, annealing is essential to equalize thermal strain after casting, which makes them extremely expensive, making it difficult to use. The only way to do this was to first press-form a magnetic core body with the legs of a book, and then attach the center legs to the center of the core by welding. However, with magnetic cores made using the latter method, it is unavoidable that the joint of the center leg creates an unbalance in magnetic properties with respect to the pair of legs, and this leads to a decrease in torque detection accuracy. It was undeniable.

The present invention provides a three-pronged magnetic core in which the three-pronged magnetic core is provided so that each of its three pole end faces faces the outer surface of a torque transmitting object with a certain gap, and one magnetic pole of the magnetic core is provided with a three-pronged magnetic core. It is configured to detect torque by winding an excitation coil and a detection coil around each of the remaining two magnetic poles, and providing an electric circuit that receives the outputs of these detection coils and detects the torque applied to the object. This idea was developed from the viewpoint that even if the gap between the torque transmitting object and each magnetic pole end surface changes, the torque detection accuracy will not be affected by this and can be kept high, thus solving the above problem. The present invention aims to provide a torque detection device that embodies the following.

Hereinafter, the present invention will be explained in detail with reference to illustrated embodiments.

FIG. 1 shows an embodiment of the torque detection device of the present invention. In the figure, 1 indicates a shaft as a torque transmission object.
The configuration is used to detect the transmitted torque of.

In the present invention, the trident-shaped magnetic core 2 is provided, and is formed into a laminated structure of magnetic thin plates such as silicon steel plates or an integral structure formed by press molding of soft ferrite. The magnetic core 2 has three mutually parallel magnetic poles 2a, 2b, 2 facing the outer peripheral surface of the shaft 1.
The end face of each of these magnetic poles is opposed to the outer circumferential surface of the shaft 1 with a certain gap therebetween. Then, the excitation coil 3 is wound around one magnetic pole 2a, and the remaining two magnetic poles 2b,
Detection coils 4 and 5 are respectively wound around 2c, the excitation coil 3 is connected to an AC power source 6, and the detection coils 4 and 5 are connected to lead wires 7 and 8, respectively.

In addition, the end faces of each of the magnetic poles 2a, 2b, and 2c facing the outer circumferential surface of the shaft 1 are curved into a cylindrical shape along the outer circumferential surface of the shaft 1, so that the end face of each magnetic pole extends over the entire surface of the shaft 1. with the above gap. The distances from the end face of the magnetic pole 2a around which the excitation coil 3 is wound to the end faces of the magnetic poles 2b and 2c around which the detection coils 4 and 5 are wound are the same, and the end faces of the magnetic poles 2b and 2c are connected from the end face of the magnetic pole 2a to the end faces of the magnetic poles 2b and 2c. The trident-shaped magnetic core 2 is constructed and arranged so that a perpendicular line drawn on the line extends in the axial direction of the shaft 1 (torque axis direction). In addition, the magnetic poles 2b, 2c
The distance between the end faces can be arbitrarily determined depending on the magnitude of the magnetostrictive effect of the material of the shaft 1.

In the illustrated example, the magnetic poles 2a, 2b, and 2c have a rectangular cross-sectional shape, but this shape can be a circular cross-sectional shape, a triangular cross-sectional shape, or another polygonal cross-sectional shape, etc. The overall shape of can also be changed arbitrarily as long as the above conditions are satisfied.

In the above configuration, the excitation coil 3 receives power from the AC power supply 6 and generates an AC magnetic flux, and this AC magnetic flux is transmitted to the magnetic pole 2.
A closed magnetic path from a to the outer circumferential surface of the shaft 1, the magnetic pole 2b, and the closed magnetic path that returns to the magnetic pole 2a via the outer circumferential surface of the shaft 1, and a closed magnetic path that returns from the magnetic pole 2a to the magnetic pole 2a via the outer circumferential surface of the shaft 1, the magnetic pole 2c, and the outer circumferential surface of the shaft 1. and generates induced electromotive force in the detection coils 4 and 5 on the magnetic poles 2b and 2c, respectively.

By the way, when the shaft 1 is not transmitting torque, the magnetic flux densities φ1 and φ2 between the magnetic pole 2a and the magnetic poles 2b and 2c are equal, respectively, as shown in FIG. 2(a), and the induction of the detection coils 4 and 5 is The electromotive force is at the same level. However, axis 1
is transmitting torque, tensile stress and compressive stress act on the outer circumferential surface of shaft 1 in directions of ±45° with respect to the axial direction, and shaft 1 arrow a
When torque is transmitted in the direction shown in FIG. 1, the outer peripheral surface of the shaft 1 receives a tensile stress indicated by +σ and a compressive stress indicated by −σ in the figure. Therefore, the outer circumferential surface of the shaft 1 between the magnetic poles 2a and 2b receives tensile stress +σ and its magnetic permeability is increased by the inverse magnetostriction effect, and the outer circumferential surface of the shaft 1 between the magnetic poles 2a and 2c receives compressive stress −σ and its permeability increases. Magnetic property is reduced. Therefore, during the torque transmission of the shaft 1, the magnetic resistance of the closed magnetic path formed between the magnetic poles 2a and 2b decreases, and as shown in FIG. 2(b), the magnetic flux density increases to φ1 in FIG. 2(a). The induced electromotive force of the detection coil 4 is increased from φ1' to φ1' according to the torque. At the same time, the magnetic resistance of the closed magnetic path formed between the magnetic poles 2a and 2c increases, and as shown in FIG. 2(b), the magnetic flux density changes from φ2 in FIG. 2(a) to φ2' according to the torque. This decreases the induced electromotive force of the detection coil 5.

Here, the difference in induced electromotive force between both detection coils 4 and 5 corresponds to the transmitted torque of shaft 1, and the sum of both is the total magnetic flux density φ1
+φ2=φ1'+φ2', so if we calculate the ratio of the sum value and the difference value, this corresponds to each magnetic pole 2a, 2b, 2c.
This represents a detected torque value from which errors due to fluctuations in magnetic flux density due to fluctuations caused by vibrations during torque transmission in the gap between the shaft 1 and the shaft 1 are removed.

In order to perform calculation processing of the induced electromotive force, the present invention uses, for example, an electric circuit shown in FIG. 3. In this electric circuit, the induced electromotive force taken out from the detection coils 4 and 5 via lead wires 7 and 8 is first changed into an analog voltage (current) value by rectifiers 9 and 10, and then these analog signals are converted into an analog voltage (current) value by a subtracter 11. The adder 12 calculates the difference value by subtracting the two, and the adder 12 adds the two to calculate the sum value.The divider 13 calculates the ratio of the sum value and the difference value, and then the filter circuit 14 This is to remove noise and output a signal Vout related to the above ratio.

This output Vout is, for example, the fourth
The direction of torque transmission (right or left) can be determined by whether it is higher or lower than the reference voltage Vs when the torque is zero, and the difference in the output Vout (voltage) with respect to the reference voltage Vs is the detected torque. Based on the correspondence, read this difference and set axis 1.
transmission torque can be detected.

Thus, as described above, the torque detecting device of the present invention includes a trident-shaped magnetic core 2 provided such that the end faces of its three magnetic poles 2a, 2b, and 2c face the outer surface of the torque transmitting object 1 with a certain gap therebetween. An excitation coil 3 connected to an AC power source 6 is wound around one magnetic pole 2a of the core 2, and the remaining two magnetic poles 2b
, 2c are respectively wound with detection coils 4 and 5, and electric circuits 11 to 13 are provided for inputting the outputs of these detection coils and detecting the torque of the object 1. Therefore, the three-pronged magnetic core 2 can be integrated and inexpensive. In addition, even if the gap between each magnetic pole end face and the object 1 changes and the magnetic flux density between the corresponding magnetic poles 2a and 2b and between 2a and 2c changes, the error caused by this can be removed and torque can be detected. , accurate torque detection is possible without adding any means for correcting this error, and torque detection accuracy can be improved with an inexpensive configuration.

[Brief explanation of the drawing]

FIG. 1 is a perspective view of the pickup of the torque detection device of the present invention, and FIG. 2 is an explanatory diagram of its operation, where (a) shows a torque non-transmission state, and (b) shows a torque transmission state. FIG. 3 is a block diagram showing the electric circuit of the device of the present invention, and FIG. 4 is an output signal characteristic diagram of the device of the present invention. 1... Axis (torque transmission object) 2... Three-pronged magnetic core 2a
, 2b, 2c...Magnetic pole 3...Exciting coil 4, 5...
・Detection coil 6...AC power supply 7, 8...Lead wire 9
, 10... Rectifier 11... Subtractor 12... Adder 13... Divider 14... Filter. 2nd t'<+ th: S1 woman 1 1st-'' t1

Claims (1)

[Scope of Claims] 1. A three-pronged magnetic core is provided so that each of its three magnetic pole end faces faces the outer surface of a torque transmitting object with a certain gap, and an alternating current is applied to one magnetic pole of the three-pronged magnetic core. In addition to winding an excitation coil connected to a power source, a detection coil is wound around each of the remaining two magnetic poles, and an electric circuit is provided to input the outputs of these detection coils and detect the torque applied to the object. A torque detection device featuring: 2. The distance from the end face of the one magnetic pole to the end faces of the remaining two magnetic poles is the same, and the distance is on a line connecting the end face of the one magnetic pole to the end faces of the remaining two magnetic poles. 2. The torque detection device according to claim 1, wherein said trident-shaped magnetic core is constructed and arranged so that a perpendicular line extends in the torque axis direction.