JP2001336906A - Electromagnetic induction type displacement detecting device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To attain high sensitivity, high precision and miniaturization displacement detection for in the detection of displacement. SOLUTION: This electromagnetic induction type displacement detecting device consists of an excitation coil 40 for alternating current excitation, a core 20 provided so as to be freely displaced in an axial direction of the excitation coil with displacement of an object to be measured for the displacement and penetrated by magnetic flux from the excitation coil, and a detection coil 41 penetrated by magnetic flux from the excitation coil. The core is made of non-magnetic material. Both the excitation coil and the detection coil are wound around a bobbin and the excitation coil is provided outside. For the detection coil and the excitation coil, the outside of the detection coil is covered with a shield membrane.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a highly sensitive displacement detecting device. In particular, the present invention relates to an electromagnetic induction type displacement detection device capable of detecting a small displacement without being affected by an external magnetic field and external noise. The displacement detecting device of the present invention can be applied to a device for directly detecting the displacement of a valve in a valve device driven by electromagnetic driving of an engine with high sensitivity.

[0002]

2. Description of the Related Art Conventionally, as a device for detecting the actual opening / closing timing of an engine valve, a device disclosed in Japanese Patent Application Laid-Open No. 7-332044 is known. In this device, a piezoelectric element is disposed at a position corresponding to the open position and the closed position of the valve, respectively, and a signal output from the piezoelectric element when a moving body interlocking with the valve comes into contact with these piezoelectric elements. Is used to detect the opening / closing timing of the valve.

The operating state detecting device for a valve device described in Japanese Patent Application Laid-Open No. Hei 9-217859 has a magnetic detection sensor disposed inside a spring that biases the valve.
That is, in this device, the displacement of the valve is detected by detecting the magnitude of the internal magnetic field by utilizing the fact that the expansion and contraction state of the spring linked to the displacement of the valve affects the magnitude of the internal magnetic field. I have to.

An electronic lever mechanism described in Japanese Patent Application Laid-Open No. H11-217029 has a primary coil and a secondary coil wound concentrically and a movable piston is disposed inside the primary coil and the secondary coil. . In this device, the displacement of the piston is detected based on the output signal of the secondary coil, utilizing the fact that the coupling coefficient between the primary coil and the secondary coil changes depending on the position of the piston.

Japanese Patent Application Laid-Open No. 57-204413 discloses a displacement sensor using a differential transformer using a core having a low magnetic permeability.

[0006]

SUMMARY OF THE INVENTION Japanese Patent Application Laid-Open No. 7-33204
The detection device described in Japanese Patent Application Laid-Open No. 4 (2004) detects two positions and is not a device that continuously detects displacement. JP-A-9-
The detecting devices described in Japanese Patent No. 217859, Japanese Patent Application Laid-Open No. H11-217029, and Japanese Patent Application Laid-Open No. 57-204413 are devices for continuously detecting displacement. However, the device disclosed in Japanese Patent Application Laid-Open No. 9-217859 has a problem in that the sensitivity is poor because the change in the magnetic field is performed by the expansion and contraction of the spring. In addition, this device is not an independent device as a detection device, and the displacement of the object to be measured needs to be reflected in the expansion and contraction state of the spring. The device disclosed in Japanese Patent Application Laid-Open No. H11-217029 is an electromagnetic induction type displacement detection device. However, since the core is made of a magnetic material, the core easily guides the external magnetic field. And that it is susceptible to external noise. For this reason, there is a problem that the detection accuracy and the detection sensitivity need to be further improved, and the detection accuracy is poor when used near an electromagnetic actuator such as a valve driving device of an internal combustion engine. Furthermore, the sensor disclosed in Japanese Patent Application Laid-Open No. 57-204413 is of a differential type, and therefore has good linearity near the zero point, but has a problem that the length of the sensor becomes larger than the detectable displacement range.
Further, this sensor also has a problem that the elimination of external high-frequency noise is not perfect and is weak against noise.

SUMMARY OF THE INVENTION Accordingly, the present invention has been made to solve the above-mentioned problems, and the present invention improves the detection accuracy, the detection sensitivity, and the apparatus dimensional ratio with respect to the displacement detection range by eliminating the influence of external noise. It is an object to achieve any one or more of the reductions in These objects are objects achieved by each invention disclosed in the present application individually, and it should not be understood that the present invention achieves all of these objects.

[0008]

Means for Solving the Problems and Effects of the Invention The invention according to claim 1 is an excitation coil for AC excitation, and is disposed so as to be displaceable in the axial direction of the excitation coil in accordance with the displacement of a displacement measurement object. In an electromagnetic induction type displacement detecting device including a core through which a magnetic flux from a coil penetrates and a detection coil through which a magnetic flux from an exciting coil penetrates, the core is made of a non-magnetic material. Since the core is made of a non-magnetic material, the distribution of the magnetic flux generated by the exciting coil is not disturbed by the position of the core, so that the detection accuracy is improved. Further, even when detecting displacement in an environment where an external magnetic field exists, the core does not guide the external magnetic flux, so that the influence of the external magnetic field can be eliminated. Therefore, the detection accuracy is improved. On the other hand, the exciting magnetic flux penetrates the core, and the penetration amount of the magnetic flux changes according to the position of the core. Eddy current loss increases in proportion to the amount of penetration of the magnetic flux. As a result, the exciting magnetic flux is canceled by the eddy current, and the induced electromotive force of the detection coil is reduced accordingly. The detection device of the present invention detects the displacement of the core that changes with the displacement of the displacement measurement target based on such a principle. Note that the number of detection coils is one, and it is not a differential type. For this reason, it is possible to set the substantially entire length of the detection coil as the displacement detection range.
The non-magnetic material used as the core has a smaller electric resistance,
This is desirable because eddy current loss increases. That is, the detection sensitivity is improved.

According to a second aspect of the present invention, the core is made of aluminum or copper. By using an aluminum or copper core as a nonmagnetic material, even if the core is displaced, the magnetic field distribution inside the excitation coil and the detection coil is not disturbed. Also, no magnetic flux is induced by the external magnetic field. As a result, detection accuracy is improved. In addition, since aluminum or copper has a small resistivity, eddy current loss increases and detection sensitivity can be improved.

According to a third aspect of the present invention, the exciting coil and the detecting coil are wound in a two-layered structure with the displacement direction of the core as an axis, inside and outside or outside and inside around the axis. It is characterized by the following. Since the coils are laminated in the inner and outer two-layer structure, the ratio of the coil length to the displacement detection range can be reduced. That is, it is possible to provide a small displacement detection device with respect to the size of the displacement detection range. It is to be noted that the arrangement of the coils on the inner side and the outer side is arbitrary. However, the arrangement of the excitation coil on the outer side and the detection coil on the inner side is superior in detection accuracy and detection sensitivity.

According to a fourth aspect of the present invention, the exciting coil and the detecting coil are configured such that the parallel conducting wires are
It is characterized by being wound. With this configuration also, for the same reason as the third aspect of the invention, a displacement detection device that is smaller than the size of the displacement detection range can be provided.

According to a fifth aspect of the present invention, the exciting coil and the detecting coil are wound around a bobbin, and the core is disposed so as to be axially displaceable inside the bibon. . With this configuration, it is easy to move the core in the axial direction and to wind the exciting coil and the detection coil.

According to a sixth aspect of the present invention, the bobbin is provided on a circuit board. With this configuration, AC power supply to the excitation coil, a detection signal output from the detection coil, and the like can be realized by the circuit board.
The size of the displacement detection device can be reduced.

According to a seventh aspect of the present invention, the bobbin has a flat bobbin substrate in a direction perpendicular to the axis at one end opposite to the insertion opening of the core. With this configuration, the exciting coil and the detection coil can be easily wound,
In addition, it becomes easy to input and output signals to and from the excitation coil and the detection coil.

According to an eighth aspect of the present invention, the circuit board is connected to the bobbin board in parallel, and the exciting coil and the detection coil are electrically connected to the circuit board via the bobbin board. Features. With this configuration, a circuit board on which a power supply circuit, a signal output circuit, and the like are arranged, an excitation coil,
Electrical connection with the detection coil is facilitated, and the size of the displacement detection device can be reduced.

According to a ninth aspect of the present invention, the outermost coil of the excitation coil and the detection coil, which is located on the outermost side, is covered with a shield film. With this configuration, it is possible to eliminate the influence of external high-frequency noise. The displacement detection device is susceptible to high frequency noise because it is based on the principle of generating an AC magnetic flux with an AC voltage and detecting the AC magnetic flux. Therefore, by wrapping the outer periphery of the outermost coil with a shield film such as an aluminum foil, it is possible to prevent an external AC electromagnetic field from being applied to the detection coil. Therefore, it is possible to improve the displacement detection accuracy.

According to a tenth aspect of the present invention, the shield film is made of iron, aluminum, or copper. This makes it possible to effectively shield external high-frequency noise.

[0018] The invention according to an eleventh aspect is characterized in that a rod connected to the core penetrates and further includes a metal housing for housing the excitation coil, the detection coil, the bobbin, and the circuit board. Since the entire detection device is covered with the metal housing, the influence of external noise can be further eliminated. Further, if the metal housing is made of a material having a high magnetic permeability, it is possible to shield the external magnetic field and eliminate the influence of the external magnetic field, thereby improving the detection accuracy.

[0019]
According to a twelfth aspect of the present invention, an oscillation circuit for supplying alternating current to the excitation coil and a detection circuit for detecting the amplitude of a detection signal output from the detection coil are arranged on the circuit board. With this configuration, a signal proportional to the displacement can be output, and the displacement detection device can be provided as an independent device, and the device can be downsized.

The invention according to claim 13 is characterized in that the electromagnetic induction type displacement detecting device is a device for detecting a displacement of a valve of an internal combustion engine. The displacement detecting device of the present invention has a structure capable of minimizing the influence of an external DC magnetic field, AC electromagnetic field, and electromagnetic wave. Internal combustion engine valves are
It is driven at high speed using electromagnets. At this time, a DC magnetic field, an AC electromagnetic field, and an electromagnetic wave are generated. By using the present displacement detecting device, it is possible to accurately detect a displacement driven at a high speed by such an electromagnet.

According to a fourteenth aspect of the present invention, the movable range of the core corresponding to the displacement detection range is such that at least one of the two ends of the core is one end of the axial length of the coil from both ends of the excitation coil or the detection coil. It is a range having both ends at the position of / 4. When the core is moved in this range, the linearity of the displacement detection is improved, and the detection accuracy is improved.

According to a fifteenth aspect of the present invention, the length of the core is not less than ／ of the axial length of the exciting coil or the detecting coil and not more than the axial length. According to this configuration, it is possible to detect the displacement with high linearity in the movable range of the fourteenth aspect.

The invention according to claim 16 is characterized in that the entire length of the core is located inside the metal housing. With this configuration, it is possible to eliminate the influence of the external magnetic field of the core, and it is possible to further improve the detection accuracy.

[0024]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below based on embodiments. FIG. 1 is a configuration diagram of a displacement detection device showing a specific embodiment of the present invention. Reference numeral 1 denotes a cylindrical metal housing. An opening 10 into which the core 20 is inserted is formed at one end. A bobbin 30 is provided inside the metal housing 1. The center hole 31 of the bobbin 30 is formed concentric with the opening 10 of the housing 1. The core 20 is provided in the center hole 31 of the bobbin 30 so as to be movable in the axial direction (x-axis). Note that the core 20 can move in a non-contact manner with respect to the center hole 31.

The bobbin 30 is provided with a detection coil 41 inside and an excitation coil 40 outside. Then, as shown in FIG. 2, a shield film 42 made of an acuminium foil is wound around the outermost excitation coil 40. The bobbin 30 is provided with a circular bobbin substrate 33 extending perpendicular to the axis on the opposite side of the opening 32. The bobbin board 33 is provided with fixed feet 34 extending in the axial direction, and the bobbin 30 is connected to the circuit board 50 using the fixed feet 34.
It is erected in. Further, a lid 2 is joined to the bottom surface of the housing 1. Four pins connected to the excitation coil 40 and the detection coil 41 pass through the bobbin board 33 and are electrically connected to the circuit board 50. In FIG. 1, only one pin 35 is shown.

A circuit having the structure shown in FIG. 3 is mounted on the circuit board 50. The oscillation circuit 60 supplies an alternating current to the exciting coil 40. The detection coil 41 detects a magnetic field in which the magnetic field generated by the excitation coil 40 is demagnetized by the eddy current flowing through the core 20. That is, although an eddy current flows through the core 20 due to the magnetic field generated by the exciting coil 40, a voltage lower than the exciting voltage by a voltage corresponding to the eddy current loss is detected by the detection coil 41. The output signal from the detection coil 41 is smoothed by the half-wave rectifier circuit 42, and the amplitude of the signal output from the detection coil 41 is detected. Next, the smoothed signal is input to the inverting input terminal of the differential amplifier 61. On the other hand, a signal obtained by smoothing the AC signal of the oscillation circuit 60 by half-wave rectification is input to the non-inverting input terminal of the differential amplifier 61 as a reference signal. The signal of this difference corresponds to the voltage drop due to the eddy current loss by the core 20. The output signal of the differential amplifier 61 is amplified by the amplifier 62 at the next stage, and is smoothed by the low-pass filter 63 connected to the output of the amplifier 62 to obtain a displacement detection signal.

In the above-described circuit, a half-wave rectifier circuit (charging circuit) including a diode 641 and a capacitor 642 is used to generate a reference signal. Then, the reference DC voltage is divided by a resistance and supplied as a reference signal to be supplied to the non-inverting input terminal of the differential amplifier 61. As a result, the response speed of the displacement detection device has been improved.

The displacement detecting device of the present invention has such a configuration. External noise is blocked by the shield film 42 and no noise is detected by the detection coil 41, so that the detection accuracy is improved. Further, since the external DC magnetic field, AC electromagnetic field, and electromagnetic wave are shielded by the metal casing 1 and the metal lid 2, these external components do not affect the detection signal.

Next, an example in which the displacement detecting device is applied to a device for detecting a displacement of a valve by electromagnetic driving of an internal combustion engine will be described. The core 20 of the displacement detection device is welded to a rod 81 connected to the valve 80. The plate 81 and the coil spring 83 connected to the rod 81
Are urged in the + X axis direction, and the rod 81 is urged in the −X axis direction by the action of the plate 84 and the coil spring 85. FIG. 4 shows a state where the springs are balanced by the urging forces of the coil springs 82 and 85.
Next, by energizing the coil 86 constituting the electromagnet, the plate 87 is attracted in the −X axis direction and
Moves in the −X axis direction. Conversely, when the coil 88 constituting the electromagnet is energized, the plate 87 is attracted in the + X axis direction and the rod 81 is displaced in the + X axis direction.

The displacement detecting device 3 shown in FIG. 1 is provided inside the support housing 4 shown in FIG. By detecting the displacement of the core 20 by the displacement detection device 3, it is possible to detect not only the binary state of the opening and closing of the valve 80 but also the continuous displacement of the opening and closing process. External DC magnetic fields, AC electromagnetic fields,
According to the displacement detection device of the present invention, even when radio waves are present, the displacement can be detected with high sensitivity and high accuracy without being affected by the displacement.

In FIG. 4, the core 20 and the rod 81 are
The same material may be used, or different materials may be used. That is, the rod 81 may be made of aluminum or copper. When the core 20 and the rod 81 are made of different materials, the rod 81 can be made of titanium or a non-magnetic material other than aluminum or copper, for example, ceramics or the like. Further, the core 20 may be a solid body or a hollow pipe. The rod 81 can likewise be a solid or hollow pipe, the solid and hollow core 20 and the rod 8
One solid / hollow combination is optional.

Also, in the displacement detecting device shown in FIGS.
A region of 1/4 to 3/4 in the length direction (x-axis direction) of the excitation coil 40 and the detection coil 41 shown in FIG. 5, that is, from a position 1/4 of the axial length from both ends of the coil shown in FIG. The best linearity is detected when the core 20 is displaced within the range of the region L2 inside. Therefore, it is preferable that the area L2 is set as the displacement detection range.

However, the length of the core 20 needs to be longer than the length of the coils 40 and 41 in order to set the detectable range over the entire length of the coils 40 and 41. If the length of the core 20 is shorter than the lengths of the coils 40 and 41, there is a region where the output does not fluctuate even if the core 20 is displaced. However, when the region L2 having good linearity is set as the detectable range, the amount of coupling between the core 20 and the coils 40 and 41 needs to change in proportion to the displacement. , Coil 40,
What is necessary is just to be longer than 3/4 of the axial length of 41.

When the area L2 is set as the displacement detection range,
As shown in FIG. 5, the movable range of the core 20 may be determined so that the tip W of the core 20 exists in the range of the region L2.
The point where the tip W of the core 20 exists on the boundary between the region L3 and the region L2 is the end point of the detectable range. In this state, the coupling length of the core 20 and the coils 40 and 41 is
It becomes ／ of the axial length of 0 and 41. Therefore, the shortest length of the core 20 is ／ of the axial length of the coils 40 and 41. In the case of such usage, the rod 81
The material is not particularly limited, and may be a magnetic material in addition to a non-magnetic material such as aluminum, copper, and titanium. That is, the rod 81 is not coupled to the coils 40 and 41 during the movement in the region L2 which is the displacement detection range.

On the other hand, as shown in FIG. 6, the connection point A between the core 20 and the rod 81 can be located in the range of the region L2. When used in this way,
The core 20 and the rod 81 need to be made of different materials. In particular, the material of the rod 81 needs to have a smaller eddy current loss than the core 20. When the rod 81 is made of a material having a small eddy current loss, the output of the detection coil 41 can be changed when the connection point A changes in the range of the region L2. Further, since the rod 81 enters the inside of the coils 40 and 41, the excitation coil 40 and the detection coil 41
In order to reduce the mutual inductance between them, it is desirable that the rod 81 is a non-magnetic material. In this case,
The rod 81 is optimally made of titanium. Since the eddy current loss can be reduced and is made of a non-magnetic material, it does not affect the displacement detection of the displacement detecting device. In addition to titanium, ceramics can also be employed.

When the connection point A between the core 20 and the rod 81 is located in the region L2, the tip W of the core 20 projects from the coils 40 and 41 when it moves within the displacement detection range. The protruding portion is inside the housing 1, and the core 20 is entirely inside the housing 1. Therefore, the influence of the external magnetic field on the core 20 is suppressed. When used in this manner, the core 20 can be made of a magnetic material instead of a non-magnetic material. Core 2
When 0 is a magnetic material, the excitation coil 4
The displacement is measured based on the principle that the mutual inductance between 0 and the detection coil 41 changes.

By increasing the oscillation frequency of the oscillation circuit 60, the response speed of displacement detection can be improved. The oscillation frequency is desirably in the range of 5 Hz to 100 kHz. In addition, by improving the cutoff frequency of the low-pass filter 63 of the output of the amplifier 62, the response speed of displacement detection can be improved. Further, by using the temperature compensating components as the components of the oscillation circuit 60 and other detection circuits, a displacement detection device that is not affected by temperature fluctuations can be provided.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing a displacement detection device according to a specific embodiment of the present invention.

FIG. 2 is a perspective view showing a configuration of a bobbin and a shield film.

FIG. 3 is a circuit diagram showing a configuration of an electric circuit provided on a circuit board.

FIG. 4 is a configuration diagram showing a valve displacement detection device in which the displacement detection device of the present invention is applied to detect the opening and closing displacement of a valve of an internal combustion engine.

FIG. 5 is a configuration diagram showing another example of the displacement detection device.

FIG. 6 is a configuration diagram showing another example of the displacement detection device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Metal casing 2 ... Lid 3 ... Displacement detection device 10 ... Opening 20 ... Core 30 ... Bobbin 31 ... Inner hole 33 ... Bobbin board 34 ... Foot 35 ... Pin 50 ... Circuit board 40 ... Excitation coil 41 ... Detection coil 80 ... Valve 81 ... Rod 82,84,87 ... Plate 86,88 ... Electromagnetic coil 83,85 ... Coil spring

 ────────────────────────────────────────────────── ─── Continuing from the front page (72) Inventor Remitsu Amano 68th Kamioshita, Narumi-cho, Midori-ku, Nagoya-shi, Aichi F-term (reference) 2F063 AA02 BA06 CA08 DA05 GA04 GA08 GA29 KA01 2F077 AA21 CC02 FF02 FF12 FF31 FF39 VV02 VV11

Claims (16)

[Claims] An exciting coil for AC excitation, a core disposed so as to be displaceable in the axial direction of the exciting coil with a displacement of a displacement measurement target, and through which a magnetic flux from the exciting coil passes.
An electromagnetic induction type displacement detection device comprising: a detection coil through which a magnetic flux from the exciting coil passes; wherein the core is made of a non-magnetic material. 2. The electromagnetic induction type displacement detecting device according to claim 1, wherein said core is made of aluminum or copper. 3. The apparatus according to claim 3, wherein the exciting coil and the detecting coil are wound in a two-layer structure of an inner side and an outer side or an outer side and an inner side around the axis with the displacement direction of the core as an axis. The electromagnetic induction type displacement detecting device according to claim 1 or 2, wherein: 4. The apparatus according to claim 1, wherein the exciting coil and the detecting coil are formed by winding respective parallel conducting wires in common. 2. The electromagnetic induction type displacement detection device according to claim 1. 5. The device according to claim 1, wherein the exciting coil and the detecting coil are wound around a bobbin, and the core is disposed so as to be axially displaceable inside the bibon. The electromagnetic induction type displacement detection device according to any one of claims 4 to 4. 6. The electromagnetic induction type displacement detecting device according to claim 5, wherein said bobbin is provided on a circuit board. 7. The bobbin according to claim 5, wherein the bobbin has a flat bobbin substrate in a direction perpendicular to the axis at one end opposite to the insertion opening of the core. Electromagnetic induction type displacement detector. 8. A circuit board is connected to the bobbin board in parallel, and the excitation coil and the detection coil are electrically connected to the circuit board via the bobbin board. The electromagnetic induction type displacement detection device according to claim 7. 9. The apparatus according to claim 1, wherein the outermost coil of the excitation coil and the detection coil is surrounded by a shield film. Electromagnetic induction type displacement detector. 10. The electromagnetic induction type displacement detecting device according to claim 9, wherein said shield film is made of iron, aluminum or copper. 11. A rod connected to the core penetrates,
The electromagnetic induction type displacement detection according to any one of claims 5 to 10, further comprising a metal housing that houses the excitation coil, the detection coil, the bobbin, and the circuit board. apparatus. 12. The circuit board according to claim 1, further comprising: an oscillating circuit for supplying an alternating current to said exciting coil; and a detecting circuit for detecting an amplitude of a detecting signal output from said detecting coil. An electromagnetic induction type displacement detection device according to claim 11. 13. The electromagnetic induction type displacement detecting device according to claim 1, wherein the electromagnetic induction type displacement detecting device is a device for detecting a displacement of a valve of an internal combustion engine. 14. A movable range of the core corresponding to a displacement detection range is such that at least one end of both ends of the core is a quarter of an axial length of the coil from both ends of the excitation coil or the detection coil. The electromagnetic induction type displacement detecting device according to any one of claims 1 to 13, characterized in that the range has both ends. 15. The electromagnetic induction type displacement detecting device according to claim 14, wherein the length of the core is not less than ／ of the axial length of the exciting coil or the detecting coil and not more than the axial length. 16. The electromagnetic induction type displacement detection device according to claim 11, wherein the entire length of the core is located inside the metal housing.