JPH0442016A - Displacement sensor - Google Patents

Abstract

PURPOSE:To improve detecting capability with a simple constitution without the large increase of the cost by arranging a nonmagnetic member which is a conductor and a magnetic conductor in the advancing and backing directions, and constituting a core. CONSTITUTION:A cylindrical sleeve 7 whose relative displacement in the axial direction and the turning direction is free is coupled to an input shaft 2. The sleeve 7 has a flange part (core) 7c which is continued in the circumferential direction. Both surfaces of the core 7c which face the advancing and backing directions of the sleeve 7 of a nonmagnetic ring 10 that is a conductor are held by magnetic rings 11a and 12. The permeability of the nonmagnetic body is similar to that of air and smaller that the permeability of the magnetic body. Meanwhile, when the magnetic flux is intersected with the conductor, an eddy current flows so as to hinder the change in magnetic flux. Therefore, the nonmagnetic ring that is the conductor has the property which is hard to pass the magnetic flux more than the degree of the air. In this way, the changing width of the outputs of receiving coils L2 and L3 with the advance and backing of the core 7c becomes larger in comparison with the case wherein the core 7 is formed of only one magnetic body.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a displacement sensor that measures relative displacement between members, and in particular, a displacement sensor that measures a core inside an oscillating coil and a receiving coil in accordance with relative displacement between members. This is a displacement sensor that measures the relative displacement between members based on the output of a receiving coil when moving back and forth, with improved detection ability.

[Conventional technology]

As a conventional displacement sensor, there is one shown in FIG. 10, for example.

This is a so-called differential transformer type displacement sensor, in which one oscillating coil (primary coil) L+ is coaxially arranged so as to be sandwiched between two receiving coils (secondary coils) Lz and Ls. A core C made of a magnetic material such as iron is placed inside the oscillating coil LI and the receiving coils Lz, L, so that it can move forward and backward, and the core C is coiled and ~L.
The core C is a separate member (not shown) in which relative displacement occurs.
Fixed to.

When an alternating current of a predetermined frequency is supplied to the oscillating coil L1, an electromotive force is generated in the receiving coils Lx and Lx according to their mutual inductance, but if the receiving coils L2 and L3 are of the same standard, Their mutual inductance is the degree of electromagnetic coupling with the oscillation coil L+, that is,
It is determined by the advancing and retreating position of core C.

In other words, if the core C is in the neutral position as shown in FIG. L3
There is no difference in the electromotive force generated.

However, when the core C moves from the state shown in FIG. 10 to the right in the figure, for example, since air has a lower magnetic permeability than magnetic materials such as iron, the mutual inductance between the oscillating coil LI and the receiving coil L2 decreases. Since the mutual inductance between the oscillating coil L+ and the receiving coil 3 increases, the receiving coil L
There is a difference in the electromotive force generated between the two and the two, and the difference in the electromotive force is determined depending on the direction and amount of displacement of the core C.

Therefore, based on the difference between the outputs of the receiving coils L2 and L3, the direction and amount of displacement of the core C, i.e., coils 1 to L,
The relative displacement between the member to which C is fixed and the member to which core C is fixed is determined.

[Problem to be solved by the invention] However, the member supporting the core C is often made of a magnetic material such as iron, and if it is not a magnetic material, air is used. Conventional displacement sensors have a problem in that the change in mutual inductance with respect to the displacement of the core C is small, and therefore the detection ability of the displacement sensor is low (measurable range is narrow, output accuracy is low, etc.).

This invention has been made by focusing on the unresolved problems of the conventional technology, and aims to provide a displacement sensor with a simple configuration and improved detection ability without causing a significant increase in cost. The purpose is to

[Means to solve the problem]

In order to achieve the above object, the present invention provides a member for supporting the oscillating coil and the receiving coil based on the output of the receiving coil; In a displacement sensor that measures relative displacement between a core and a member supporting the core, the core is constructed by arranging a conductive non-magnetic member and a magnetic member in the forward and backward direction.

[Effect]

The magnetic permeability of non-magnetic materials is comparable to that of air, and is smaller than that of magnetic materials.

On the other hand, when magnetic flux interlinks with a conductor, eddy current flows to prevent changes in the magnetic flux.

Therefore, a conductive and non-magnetic member has properties that allow magnetic flux to pass through it more easily than air.

Therefore, when a core is constructed by arranging conductive and non-magnetic members and magnetic members in the advancing and retreating direction as in the present invention, the mutual inductance of the oscillating coil and the receiving coil changes as the core advances and retreats, i.e. The range of change in the output of the receiving coil as the core moves back and forth is larger than when the core is made of only magnetic material.

〔Example〕

Embodiments of the present invention will be described below based on the drawings.

1 to 9 are diagrams showing one embodiment of the present invention, and this is an example in which a displacement sensor according to the present invention is applied to an electric power steering device for a vehicle.

First, to explain the configuration, in FIG. 1, in a housing l, an input shaft 2 and an output shaft 3 connected via a torsion bar 4 are rotatably supported by bearings 5a, 5b, and 5c. There is.

However, input shaft 2. The output shaft 3 and the torsion bar 4 are coaxially arranged.

A steering wheel is integrally attached to the right end side of the human power shaft 2 in the rotation direction in FIG. 1 (not shown), and a steering wheel is integrally attached to the left end side of the output shaft 3 in FIG. The pinion shafts that constitute the are connected.

Therefore, the steering force generated by the operator steering the steering wheel is transmitted to the steered wheels (not shown) via the input shaft 2°, the output 111B3, and the rank and pinion type steering device.

Further, an axially continuous protrusion 2a is formed on the outer peripheral surface of the left end of the input shaft 2, and the protrusion 2a is formed on the right end of the output shaft 3 and is longer than the protrusion 2a. Wide vertical groove 3a
is inserted into the input shaft 2 and output shaft 3.
Relative rotation beyond a predetermined range (approximately ±5 degrees) between the two is prevented.

A gear 6 that rotates coaxially and integrally with the output shaft 3 is externally fitted onto the output shaft 3. Not connected to the output shaft of the electric motor.

Furthermore, a cylindrical sleeve 7 that is movable relative to the input shaft 2 in the axial and rotational directions is fitted onto the input shaft 2, and a vertical sleeve 7 formed at the left end of the sleeve 7 is fitted on the input shaft 2. Groove 7
The outer end of a pin 3b that is press-fitted into the right end of the output shaft 3 and protrudes radially outward is inserted into a.

Therefore, the output shaft 3 and the sleeve 7 are integral in the rotational direction, but can be relatively displaced in the axial direction within the length range of the vertical groove 7a.

The sleeve 7 is always biased to the right in FIG. It is accommodated in a spiral groove 2b having a V-shaped cross section formed on the outer circumferential surface of.

The sleeve 7 has a flange portion 7c that is continuous in the circumferential direction.
The flange portion 7c has both sides of the ring 10, which is made of a conductive and non-magnetic material (e.g. aluminum), facing the advancing and retracting direction of the sleeve 7, and is made of a magnetic material (e.g., aluminum).
It is sandwiched between rings 11 and 12 made of iron).

One oscillating coil L1 and two receiving coils Lt, Lx are provided coaxially with the sleeve 7 on the inner circumferential surface of the housing 1 so as to surround the outer circumferential surface of the flange portion 7c. L is sandwiched between the receiving coils Lx and R.

Further, a sensor main body 15 is fixed to the housing l, and includes an electronic circuit for measuring the axial position of the sleeve 7 and supplying the measurement results to a controller (not shown).

The controller to which the measurement results of the sensor body 15 are supplied calculates the steering torque of the steering system based on the measurement results, and drives and controls the electric motor (not shown) described above according to the calculated steering torque. , generates steering assist torque on the output shaft 3 via the gear 6.

FIG. 2 is a circuit diagram showing an example of an electronic circuit configured within the sensor main body 15.

That is, an oscillator 16 that oscillates a rectangular wave of a predetermined frequency, a voltage applied to both ends of the oscillation coil L1 is changed in synchronization with the output of the oscillator 16, and an alternating current of a predetermined frequency is supplied to the oscillator 16. Driver 17 and receiving coil L2
and L3, an absolute value circuit 19 that calculates the absolute value of the output of this differential amplifier 18, and an integrating circuit 20 that integrates the output of this absolute value circuit 19. and an offset/gain adjustment circuit 21 that amplifies the output of the integration circuit 20 and supplies it to an output terminal 22.

Here, the thickness of the ring 10 is the oscillation coil L.

and the receiving coils L, , L, and the positional relationship between the flange portion 7c of the sleeve 7 and the coils 1 to L, so that the sleeve 7 is moved closest to the output shaft 3 side. When this happens, the axial center of the oscillating coil L faces the axial center of the ring 10 (see FIG. 3(a)), and when the sleeve 7 is at the midpoint of the range in which it can move forward and backward, the receiving coil L2 When the axial center of the oscillating coil L1 and the receiving coil Lx face the boundary between the rings 10 and 11 (see FIG. 3(b)), and when the sleeve 7 moves furthest toward the bearing 5a, the boundary between the oscillating coil L1 and the receiving coil Lx faces the boundary between the rings 10 and 11 (see FIG. 3(b)). Facing the border of 11 (3rd
(see figure (C)).

Next, the operation of the above embodiment will be explained.

Now, assuming that the steering system is in a straight-line state and the steering torque is zero, there is no relative rotation between the input shaft 2 and the output shaft 3, so the sleeve 7 rotates integrally with the output shaft 3.
No relative rotation occurs between the input shaft 2 and the input shaft 2, either. Therefore, since the ball 9 remains in a predetermined position within the spiral groove 2b, no advancing or retreating force is generated in the sleeve 7.

On the other hand, when a rotational force is generated on the input shaft 2 by steering the steering wheel, the rotational force is transmitted to the output shaft 3 via the torsion bar 4.

At this time, a resistance force is generated on the output shaft 3 according to the frictional force between the steered wheels and the road surface, the frictional force of the rack and pinion type steering device configured on the left end side (not shown) of the output shaft 3, and so on. 2 and the output shaft 3, a relative rotation occurs between the output shaft 3 and the output shaft 3 due to the torsion bar 4 being twisted.

Then, the sleeve 7 that is integrated with the output shaft 3 in the rotation direction
Also, relative rotation with respect to the input shaft 2 occurs, but the sleeve 7
Since the ball 9 accommodated in the hole 7b on the inner surface of the input shaft 2 is accommodated in the helical groove 2b on the outer peripheral surface of the input shaft 2, the sleeve 7 moves forward and backward in the axial direction according to the inclination angle of the helical groove 2b.

Note that it is necessary to provide a slight gap between the ball 9, the spiral groove 2b, and the inner surface of the hole 7b so that the ball 9 can move, but the spring 8 biases the sleeve 7 in one direction. Therefore, the sleeve 7 is prevented from wobbling due to the gap.

Here, for example, when the steering torque generated during left rotation direction steering is maximum, the sleeve 7 is displaced most toward the output shaft 3 side as shown in FIG. Figure 3 (C
), when the sleeve 7 is displaced most toward the bearing 5a and the steering torque is zero, as shown in FIG. 3(b).
The sleeve 7 is moved to the neutral position as shown in FIG.

Then, when the oscillator 16 and the driver 17 supply the oscillating coil L1 with an alternating current as shown in FIG. However, if the receiving coils L2 and L3 are of the same standard, their mutual inductance will be determined by the surrounding situation, that is, the axial position of the flange portion 7c.

That is, in the state shown in FIG. 3(a), the mutual inductance between the oscillating coil L and the receiving coil L2, and the oscillating coil L1
Since the mutual inductance of the receiving coil Lt and the receiving coil Lt are equal, the output waveform of the receiving coil Lt shown in FIG. 5(a) and the receiving coil Lt shown in FIG. 6(a).

Therefore, the output of the differential amplifier 18 is zero as shown in FIG. 7(a).

Therefore, the output of the absolute value circuit 19 shown in FIG. 8(a) is also zero, and the output appearing at the output terminal 22 is also zero as shown in FIG. 9(a).

In addition, in the state shown in Part 3), the ring 11 made of a magnetic material with high magnetic permeability enters inside the receiving coil L2, and the right end of the ring 11 made of a non-magnetic material with low magnetic permeability becomes the receiving coil. , since it protrudes from the opening side of , the oscillating coil and the receiving coil Lt! The degree of magnetic coupling increases and their mutual inductance increases, and the degree of electromagnetic coupling between the oscillating coil L1 and the receiving coil decreases and their mutual inductance decreases.

Then, the output waveform of the receiving coil L2 becomes large as shown in Fig. 5 (c), and the output waveform of the receiving coil L2 becomes small as shown in Fig. 7 (b), and as shown in Fig. 7 Φ). There is a difference in their output waveforms.

Therefore, the absolute value of the difference between the output waveforms is determined by the absolute value circuit 19, and after being integrated by the integrating circuit 20, it is amplified by the offset/gain adjustment circuit 21. ), a moderate output appears.

In the state shown in FIG. 3(C), the oscillation coil L,
The mutual inductance of the oscillating coil and the receiving coil increases further.

Since the mutual inductance of
) and the receiving coil as shown! The output waveform of receiver coil 3 is even larger, as shown in Figure 6 (C), and the output waveform of receiver coil 3 is even smaller, and the difference between these output waveforms is as shown in Figure 7 (C).
), it becomes even larger.

Therefore, a large output appears at the output terminal 22, as shown in FIG. 9(C).

Then, if the output appearing at the output terminal 22 is of medium magnitude as shown in FIG. 9(b), the controller determines that no steering torque is generated and puts the electric motor into a non-driving state. Therefore, no steering assist torque is generated in the steering system, and the steering system maintains the straight-line traveling state.If the output is smaller or larger than the intermediate level, the electric motor is rotated accordingly, so the output shaft 3 Since steering assist torque is applied to the vehicle, the steering torque is reduced and the burden on the driver is reduced.

Furthermore, the magnetic permeability of non-magnetic materials is comparable to that of air, which is lower than that of magnetic materials, and when magnetic flux interlinks with a conductor, eddy currents flow to prevent changes in the magnetic flux. The ring 10, which is made of a conductive and non-magnetic material, is even more difficult for magnetic flux to pass through than air. Therefore, the change in mutual inductance of the coils L+-Ls as the flange portion 7C moves forward and backward is caused by the change in mutual inductance of the coil L+-Ls due to the movement of the flange portion 7C. It is larger than when it is formed from the same material.

Therefore, since the output appearing at the output terminal 22 shows a steep change with respect to the displacement of the sleeve 7, even minute displacements of the sleeve 7 can be measured with high accuracy, and therefore fine-grained steering assist torque control is possible. Since there is no need to significantly amplify the output, it is less susceptible to noise.

Here, in this embodiment, the flange portion 7C corresponds to the core.

In the above embodiments, a case has been described in which the displacement sensor of the present invention is applied to an electric power steering device for a vehicle, but the scope of application of the present invention is not limited to this.

Further, in the above embodiment, the present invention is applied to a displacement sensor that measures displacement in a linear direction, but the present invention is not limited to this, and if a ring-shaped core is used, displacement in a rotational direction can be measured. It is also possible to use a displacement sensor for measurement.

〔Effect of the invention〕

As explained above, according to the present invention, the core that moves back and forth inside the oscillation coil and the reception coil is configured by arranging a conductive non-magnetic member and a magnetic member in the direction in which the core moves back and forth. Therefore, since the change in mutual inductance due to relative displacement can be increased, an output that changes sharply with respect to relative displacement can be obtained, which has the effect of improving measurement accuracy.

[Brief explanation of drawings]

Fig. 1 is a sectional view showing the overall configuration of an embodiment of the present invention, Fig. 2 is a circuit diagram showing an example of the circuit configured in the sensor body, and Figs. 3 (a) to (C) are oscillation coils and An explanatory diagram showing the relative positional relationship between the receiving coil and the flange part, Figure 4 is a waveform diagram of the alternating current supplied to the oscillation coil, and Figure 5 (a)
(C) are output waveform diagrams of one of the receiving coils, Fig. 6 (
a) to (C) are output waveform diagrams of the other receiving coil, No. 7
Figures (a) to (C) are output waveform diagrams of the differential amplifier, Figures 8 (a) to (C) are output waveform diagrams of the absolute value circuit, and Figure 9 (
a) to (C) are output waveform diagrams of output terminals, and FIG. 10 is a configuration diagram showing an example of a conventional displacement sensor.

Claims (1)

[Claims] (1) A core is arranged inside the oscillation coil and the reception coil so as to be able to move forward and backward, and based on the output of the reception coil, the relationship between the member supporting the oscillation coil and the reception coil and the member supporting the core is determined. A displacement sensor for measuring relative displacement, characterized in that the core is constructed by arranging an electrically conductive, non-magnetic member and a magnetic member in the advancing/retreating direction.