Current sensor

A current sensor for detecting a magnitude of a current flowing through a measuring object has a magnetic core having a first magnetic core and a second magnetic core that is arranged magnetically in parallel to the first magnetic core, wherein the first magnetic core has a magnetic permeability that is higher than that of the second magnetic core in a first frequency band, and the first magnetic core has a magnetic permeability that is lower than that of the second magnetic core in a second frequency band, the second frequency band being higher than the first frequency band, and the current sensor detects the magnitude of the current in a frequency band that is constituted by combining the first frequency band and the second frequency band.

CROSS-REFERENCE TO RELATED APPLICATION

The present application claims priority 35 U.S.C. § 119 to Japanese Patent Application 2020-039014 (filed Mar. 6, 2020) and Japanese Patent Application 2021-001731 (filed on Jan. 7, 2021), which are hereby incorporated by reference in their entirety.

TECHNICAL FIELD

The present invention relates to a current sensor.

BACKGROUND ART

JP5313024B discloses a through-type current sensor for detecting a magnitude of a current flowing through a measuring object. The through-type current sensor includes a fluxgate sensor element having an annular shape, a small diameter permalloy case formed to have a U-shaped cross-section and accommodating the fluxgate sensor element, and a large diameter permalloy case formed to have a U-shaped cross-section and covering an opening of the small diameter permalloy case.

SUMMARY OF INVENTION

The current sensor is required to have a measurement accuracy such that the current sensor outputs the same measurement values, when a measuring object locates at any positions in the inner circumference of a magnetic core. Because the current sensor disclosed in JP5313024B has the permalloy case, the accuracy for measuring the current is high when the frequency of the current is relatively low, however the accuracy for measuring the current is not high, when the frequency of the current is relatively high. As described above, it is difficult to improve the accuracy for measuring the current in a wide frequency band.

The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to improve the accuracy for measuring a current in a wide frequency band by a current sensor.

According to an aspect of the present invention disclosure, a current sensor for detecting a magnitude of a current flowing through a measuring object has a magnetic core having a first magnetic core and a second magnetic core that is arranged magnetically in parallel to the first magnetic core, wherein the first magnetic core has a magnetic permeability that is higher than that of the second magnetic core in a first frequency band, and the first magnetic core has a magnetic permeability that is lower than that of the second magnetic core in a second frequency band, the second frequency band being higher than the first frequency band, and the current sensor detects the magnitude of the current in a frequency band that is constituted by combining the first frequency band and the second frequency band.

In this aspect, the magnetic core has the first magnetic core and the second magnetic core which are arranged magnetically in parallel. In the first frequency band where the frequency of the current flowing through the measuring object is relatively low, the magnetic permeability of the first magnetic core is higher than that of the second magnetic core. In the second frequency band higher than the first frequency band, the magnetic permeability of the second magnetic core is higher than that of the first magnetic core. Therefore, the accuracy for measuring the current can be improved by the first magnetic core in the first frequency band, and the accuracy for measuring the current can be improved by the second magnetic core in the second frequency band. Therefore, it is possible to improve the accuracy for measuring the current in a wide frequency band by the current sensor.

DESCRIPTION OF EMBODIMENTS

First Embodiment

Hereinafter, a current sensor100according to a first embodiment of the present invention will be described with reference to the accompanying drawings.

First, the entire configuration of current sensor100will be described by referring toFIG.1toFIG.4.FIG.1is a perspective view of a current sensor.FIG.2is a II-II cross-sectional view inFIG.1.FIG.3Ais a cross-sectional view of a magnetic core according to a modification.FIG.3Bis a cross-sectional view of a magnetic core according to another modification.FIG.4is a diagram for explaining a relation between a frequency and a magnetic permeability in the magnetic core. InFIG.4, a horizontal axis represents a frequency of a current flowing in a measuring object9, and a vertical axis represents a magnetic permeability.

As shown inFIG.1andFIG.2, the current sensor100includes a magnetic core1, a cover5containing the magnetic core1, a fluxgate sensor6as a magnetic detection element, and a winding7. The current sensor100is a through-type current sensor for measuring a magnitude of a current flowing in a measuring object9in a state where the current sensor100surrounds the measuring object9(seeFIG.1). The current sensor100detects a magnitude of the current in a frequency band in which a first frequency band, a second frequency band that is higher than the first frequency band, and a third frequency band that is higher than the second frequency band are combined, as described below.

As shown inFIG.1, the magnetic core1is formed in a ring shape, a torus shape in this embodiment. At the time of measuring the current, the measuring object9is inserted through an inner periphery of the magnetic core1. As shown inFIG.2, the magnetic core1includes a first magnetic core10, a second magnetic core20, and a third magnetic core30. The first magnetic core10, the second magnetic core20, and the third magnetic core30are arranged magnetically in parallel.

The first magnetic core10is made of permalloy, which is an iron nickel soft magnetic material. The first magnetic core10is formed in the torus shape. The first magnetic core10has a small diameter case11and a large diameter case12.

The small diameter case11is formed to have a U-shaped cross-section. The small diameter case11has an opening11ahaving a torus shape that opens to allow the fluxgate sensor6to be inserted. The small diameter case11accommodates a pair of a fluxgate sensor6.

The large diameter case12is formed to have a U-shaped cross-section that is larger than small diameter case11. The large diameter case12has an opening12ahaving a torus shape that opens to allow the small diameter case11to be inserted. The large diameter case12is assembled with the small diameter case11by moving the opening12afrom an opposite position to the opening11aof the small diameter case11along a central axial direction of magnetic core1. The large diameter case12closes the opening11aof the small diameter case11in a state that the large diameter case12is assembled with the small diameter case11. With the configuration described above, the fluxgate sensor6is accommodated in the first magnetic core10.

The second magnetic core20is formed by ferrite. The second magnetic core20is formed in a torus shape. The second magnetic core20is formed in a thin plate shape in a central axial direction of the magnetic core1. The second magnetic cores20are provided in pairs. The pair of the second magnetic cores20are respectively arranged outside of the first magnetic core10in a central axial direction.

Surfaces of the second magnetic core20other than a surface facing the first magnetic core10are exposed from the first magnetic core10. As described above, the second magnetic core20can be assembled with the first magnetic core10from the outside, so that the second magnetic core20is partially exposed from the first magnetic core10. With the configuration described above, the structure of the magnetic core1can be simplified, so that a production cost of the magnetic core1can be reduced, as compared with a case where the second magnetic core20is not exposed completely from the first magnetic core10.

Alternatively, for example, as shown in theFIG.3A, a groove20amay also be formed in the second magnetic core20, such that the first magnetic core10is fitted in the groove. Further, as shown in theFIG.3B, a gap10amay be formed in the first magnetic core10, such that the second magnetic core20is fitted in the grooves. Therefore, one of the first magnetic core10and the second magnetic core20may be capable of being attached to another from the outside, such that the one is partially exposed from the another.

The third magnetic core30is formed by a dust core material, which is manufactured by compacting powder of a magnetic core material. The third magnetic core30is formed in the torus shape. The third magnetic core30is formed in a thin plate shape located in the central axial direction of the magnetic core1. The third magnetic core30is provided in pairs. The pair of third magnetic cores are respectively stacked on the outsides of the second magnetic core20in the center axial direction.

As shown inFIG.4, the frequency of the current flowing through the measuring object9is relatively low in the first frequency band. The first magnetic core10has a higher magnetic permeability than the second magnetic core20and the third magnetic core30in the first frequency band.

The second magnetic core20has a higher magnetic permeability than the first magnetic core10and the third magnetic core30in the second frequency band, which is higher than the first frequency band. Therefore, the first magnetic core10has a lower magnetic permeability than the second magnetic core20in the second frequency band. The third magnetic core30has a higher magnetic permeability than the first magnetic core10and the second magnetic core20in the third frequency band, which is higher than the second frequency band.

As shown inFIG.1andFIG.2, the cover5is formed in a torus shape so as to cover the entire circumference of the magnetic core1. The cover5has a first cover5aand a second cover5bwhich are divided in the central axial direction of the magnetic core1. The first cover5aand the second cover5bare formed to have a U-shaped cross-section that is larger the magnetic core1. The first cover5aand the second cover5bare formed in the same shape, and are attached to the magnetic core1with facing each other. A winding7is wound around the outer periphery of the cover5. The cover5is made of a resinous material, for example, so as to insulate between the magnetic core1and the winding7.

A pair of fluxgate sensors6is provided. The pair of fluxgate sensors6are stacked in the central axial direction of the magnetic core1, while the fluxgate sensors6are accommodated in the first magnetic core10. A detectable frequency band (a detectable band), where the fluxgate sensor6can detect the magnetic flux, is closest to the first frequency band. Providing the fluxgate sensor6makes it possible to detect not only the magnitude of A/C current but also that of D/C current. Leads6aof the fluxgate sensor6are pulled out from the magnetic core1, as shown inFIG.1.

The first magnetic core10is arranged in a sensing area of the fluxgate sensor6. In other words, the magnetic core having the highest magnetic permeability among the first magnetic core10, the second magnetic core20, and the third magnetic core30in the detectable band of the fluxgate sensor6is arranged in the sensing area of the fluxgate sensor6. With the configuration described above, it is possible to more accurately detect the magnitude of D/C current by the fluxgate sensor6, as compared with a case in which the magnetic core having a lower magnetic permeability in the detectable band of the fluxgate sensor6is arranged in the sensing area of the fluxgate sensor6.

The outer periphery of the fluxgate sensor6is surrounded by the first magnetic core10. In other words, the outer periphery of the fluxgate sensor6is surrounded by the magnetic core having the highest magnetic permeability among the first magnetic core10, the second magnetic core20, and the third magnetic core30in the detectable band of the fluxgate sensor6. With the configuration described above, the magnetic core having the higher magnetic permeability among the first magnetic core10and the second magnetic core functions as a magnetic shield. Therefore, it is possible to prevent the fluxgate sensor6from detecting the magnetic flux from other than measuring object9. As described above, the fluxgate sensor6can detect the magnitude of D/C current with high accuracy.

The winding7is wound in a poloidal direction along a toroidal direction with respect to the magnetic core1. It is possible to improve the accuracy for mearing the current by providing the winding7, as compared with a current sensor in which the negative feedback operation is not performed, which example is a current sensor using a Hall element. InFIG.1, only a part of the winding7is shown in order to make it easy to understand the configuration of the current sensor100. In actual configuration, the winding7is provided around the entire circumference of the magnetic core1in the toroidal direction.

During a current is being measured, a current flowing in the winding7generates a magnetic flux, which cancels a magnetic flux generated by the current flowing in the measuring object9. The current sensor100has a shunt resistor (not shown) in which the current flowing through winding7flows. The current sensor100detects the magnitude of the current flowing through the measuring object9, based on the magnitude of the voltage generated between the both ends of the shunt resistor.

The operation of the current sensor100will be described by referring toFIG.4mainly.

As shown inFIG.4, in the first frequency band, where the frequency of the current flowing through the measuring object9is relatively low, the magnetic permeability of the first magnetic core10is higher than that of the second magnetic core20and the third magnetic core30. Therefore, it is possible to accurately measure the magnitude of the current flowing through the measuring object9in the first frequency band, because the magnetic flux flows in the first magnetic core10.

Furthermore, in the second frequency band with a higher frequency than the first frequency band, the magnetic permeability of the second magnetic core20is higher than that of the first magnetic core10and the third magnetic core30. Therefore, it is possible to accurately measure the magnitude of the current flowing through the measuring object9in the second frequency band, because the magnetic flux flows in the second magnetic core20.

In the third frequency band with a higher frequency than the second frequency band, the magnetic permeability of the third magnetic core30is higher than that of the first magnetic core10and the second magnetic core20. Therefore, it is possible to accurately measure the magnitude of the current flowing through the measuring object9in the third frequency band, because the magnetic flux flows in the third magnetic core30.

The current sensor100is required to have a measurement accuracy for outputting the same measurement values regardless of the position of the measuring object9located anywhere in the inner circumference of the magnetic core1. However, when the magnetic permeability of the magnetic core1is low, a change of a characteristic for gain (phase)—frequency depending on a location of the measuring object9becomes large, and a hysteresis loss and an eddy current loss are increased.

Because the magnetic flux flows more while the magnetic permeability of the magnetic core1is higher, it is possible to measure the magnitude of the current with high accuracy. However, there is no magnetic material having a high magnetic permeability in a wide frequency band. Generally, a magnetic material having higher magnetic permeability in a relatively low frequency band has a lower magnetic permeability at a relatively high frequency band. A magnetic material having higher magnetic permeability in a relatively high frequency band has a lower magnetic permeability at a relatively low frequency band.

Therefore, when the magnetic core1is composed of only the first magnetic core10, the values that is measured in the second frequency band and the third frequency band vary depending on the location of the measuring object9in the inner circumference of the magnetic core1, such that the measuring accuracy is deteriorated. Similarly, when the magnetic core1is composed of only the second magnetic core20, the values that is measured in the first frequency band and the third frequency band vary depending on the location of the measuring object9in the inner circumference of the magnetic core1, such that the measuring accuracy is deteriorated.

On the other hand, the magnetic core1having the first magnetic core10, the second magnetic core20, and the third magnetic core30is employed in the current sensor100. With the configuration described above, it is possible to secure the measurement accuracy for outputting the same measurement value, regardless of the position of the measuring object9in the inner circumference of the magnetic core, in a wide frequency band from the first frequency band to the third frequency band.

As described above, the magnetic core1has the first magnetic core10and the second magnetic core20, which are arranged magnetically in parallel. In the first frequency band, where the frequency of the current flowing through the measuring object9is relatively low, the magnetic permeability of the first magnetic core10is higher than that of the second magnetic core20. In the second frequency band higher than the first frequency band, the magnetic permeability of the second magnetic core20is higher than that of the first magnetic core10. Therefore, the accuracy for measuring the current can be improved by the first magnetic core10in the first frequency band, and the accuracy for measuring the current can be improved by the second magnetic core20in the second frequency band. Therefore, it is possible to improve the accuracy for measuring the current in a wide frequency band by the current sensor100.

The number of magnetic cores may be three or more. In other words, the magnetic core1includes the first magnetic core10to a “N”th magnetic core, while each magnetic core is arranged magnetically in parallel. “N” represents a natural number of 3 or more. In the first frequency band, the magnetic permeability of the first magnetic core10is higher than that of those from the second magnetic core20to the “N”th magnetic core. In the “n”th frequency band, while “n” represents a natural number from “2” to “N−1”, the magnetic permeability of the “n”th magnetic core is higher than the magnetic permeability of those from the first magnetic core10to the “n−1”th magnetic core, and is higher than the magnetic permeability of those from the “n+1”th magnetic core to the “N”th magnetic core. In a “N”th frequency band, the magnetic permeability of the “N”th magnetic core is higher than the magnetic permeability of those from the first magnetic core10to the “N−1”th magnetic core. The current sensor100detects the magnitude of the current in a frequency band, in which the first frequency band to the “N”th frequency band are combined.

According to the configuration described above, the measurement accuracy of the current can be improved by the first magnetic core10in the first frequency band, and the measurement accuracy of the current can be improved by the “n”th magnetic core in the “n”th frequency band. “n” represents a natural number from “2” to “N”. Therefore, it is possible to improve the measuring accuracy of the current in a wider frequency band by increasing the number of the magnetic cores provided magnetically in parallel.

Next, the current sensor100according to the first to fourth modifications will be described by referring toFIG.5toFIG.9. In each of the modification described below, differences from the above-described embodiment are mainly described, and components having similar functions are denoted by the same reference numerals and descriptions thereof are omitted.

First, a current sensor100according to a first modification will be described by referring toFIG.5.FIG.5is a cross-sectional view of the current sensor100according to the first modification.

In the first modification, the current sensor100differs from that in the above embodiment in a form and an arrangement of the third magnetic core30.

As shown inFIG.5, the third magnetic core30is formed in a thin plate shape in a radial direction of the magnetic core1. The third magnetic cores30are provided in pairs. The pair of the third magnetic cores30are arranged in inner and outer peripheries of the first magnetic core10, respectively.

With the configuration of the current sensor100according to the first modification described above, because the first magnetic core10, the second magnetic core20, and the third magnetic core30are magnetically arranger in parallel in the inner circumference of the winding7, the same operation and effects as those of the above embodiment are obtained.

Next, referring toFIG.6, current sensor100according to the second modification will be described.FIG.6is a cross-sectional view of a current sensor100according to a second modification.

The current sensor100according to the second modification differs from the above embodiment in the shape and arrangement of the second magnetic core20and the third magnetic core30.

As shown inFIG.6, the second magnetic core20is formed in a thin plate shape in a radial direction of the magnetic core1. The second magnetic cores20are provided in pairs. The pair of the second magnetic cores20are arranged in inner and outer peripheries of the first magnetic core10, respectively.

The third magnetic core30is formed in a thin plate shape in a radial direction of the magnetic core1. The third magnetic cores30are provided in pairs. The pair of the third magnetic cores30are respectively stacked on the inner circumference of the inner side of the pair of the second magnetic cores20and on the outer circumference of the outer side of the pair of the second magnetic cores20.

In the current sensor100according to the second modification described above, because the first magnetic core10, the second magnetic core20, and the third magnetic core30are arranged magnetically in parallel in the inner circumference of the winding7, the same operation and effects as those of the above embodiment are obtained.

Next, a current sensor100according to a third modification will be described by referring toFIG.7.FIG.7is a cross-sectional view of the current sensor100according to the third modification.

The current sensor100according to the third modification differs from the above embodiment in the shapes and arrangements of the second magnetic core20and the third magnetic core30.

As shown inFIG.7, the second magnetic core20has a small diameter case21and a large diameter case22, similarly to the first magnetic core10.

The small diameter case21is formed to have a U-shaped cross section larger than that of the first magnetic core10. The small diameter case21has an opening21ahaving a torus shape that opens to allow the first magnetic core10to be inserted. The small diameter case21accommodates the first magnetic core10.

The large diameter case22is formed to have a U-shaped cross section larger than that of the small diameter case21. The large diameter case22has an opening22ahaving a torus shape that opens to allow the small diameter case21to be inserted. The large diameter case22is assembled with the small diameter case21by moving the opening22afrom a position facing the opening21aof the small diameter case21along the center axial direction of the magnetic core1. The large diameter case22closes the opening21aof the small diameter case21in a state that the large diameter case22is assembled with the small diameter case21. Therefore, the first magnetic core10is accommodated in the second magnetic core20.

The second magnetic core20is provided on the outer periphery of the first magnetic core10. Alternatively, the first magnetic core10provided on the outer periphery of the second magnetic core20is applicable. In other words, one of the first magnetic core10and the second magnetic core20is provided outside so as to surround the outer periphery of the other. With the configuration described above, a magnetic symmetry for the magnetic core1, which covers the outer periphery, can be provided as viewed from the outer periphery. Therefore, it is possible to measure the magnitude of the D/C current by the fluxgate sensor6with high accuracy.

The third magnetic core30has a small diameter case31and a large diameter case32, similarly to the first magnetic core10and the second magnetic core20.

The small diameter case31is formed to have a U-shaped cross section larger than that of the second magnetic core20. The small diameter case31has an opening31ahaving a torus shape that opens to allow the second magnetic core20to be inserted. The small diameter case31accommodates the second magnetic core20.

The large diameter case32is formed to have a U-shaped cross section larger than that of the small diameter case31. The large diameter case32has an opening32ahaving a torus shape that opens to allow the small diameter case31to be inserted. The large diameter case32is assembled with the small diameter case31by moving the opening32afrom a position facing the opening31aof the small diameter case31along the center axial direction of the magnetic core1. The large diameter case32closes the opening31aof the small diameter case31in a state that the large diameter case32is assembled with the small diameter case31. With the configuration described above, the second magnetic core20is accommodated in the third magnetic core30.

In the current sensor100according to the third modification described above, because the first magnetic core10, the second magnetic core20, and the third magnetic core30are arranged magnetically in parallel in the inner circumference of the winding7, the same operation and effects as those of the above embodiment are obtained.

In addition, the first magnetic core10and the second magnetic core20can be arranged symmetrical as viewed from the outer periphery of the third magnetic core30covering the outer periphery. Therefore, it is possible to measure the magnitude of D/C current by the fluxgate sensor6with high accuracy.

Next, a current sensor100according to a fourth modification will be described by referring toFIG.8andFIG.9.FIG.8is a perspective view of a magnetic core1in current sensor100according to the fourth modification.FIG.9is a IX-IX cross-sectional view inFIG.8.

The current sensor100according to the fourth modification is different from the above embodiment in that the current sensor100does not have the fluxgate sensor6and is a current sensor capable of measuring only the size of A/C current by CT (Current Transformer) type.

As shown inFIG.9, the first magnetic core10is formed in a torus shape. The first magnetic core10is formed thicker than the second magnetic core20and the third magnetic core30, in the central axial direction of the magnetic core1.

The second magnetic core20is formed in a plate shape having thinness in the central axial direction of the magnetic core1. The second magnetic cores20are provided in pairs and are disposed outward of the first magnetic core10in the center axial direction.

The third magnetic core30is formed in a plate shape having thinness in the central axial direction of the magnetic core1. The third magnetic cores30are provided in pairs and stacked on the outer sides of the second magnetic core20in the center axial direction.

In the current sensor100according to the fourth modification described above, the first magnetic core10, the second magnetic core20, and the third magnetic core30are arranged magnetically in parallel on the inner circumference of the winding7. Therefore, the same operation and effects as those of the above embodiment are obtained.

According to the above embodiment, the following effects are obtained.

A current sensor100for detecting the magnitude of the current flowing through the measuring object9includes the magnetic core1. The magnetic core1includes the first magnetic core10and the second magnetic core20, which is arranged magnetically in parallel with the first magnetic core10.

The first magnetic core10has a higher magnetic permeability than the second magnetic core20in the first frequency band. The second frequency band higher than the first frequency band has a lower magnetic permeability than the second magnetic core20. The magnitude of the current in the frequency band, in which the first frequency band and the second frequency band are combined, is detected.

With the configuration described above, the magnetic core1has the first magnetic core10and the second magnetic core20which are arranged magnetically in parallel. In the first frequency band, where a frequency of the current flowing through the measuring object9is relatively low, the magnetic permeability of the first magnetic core10is higher than that of the second magnetic core20. In the second frequency band higher than first frequency band, the magnetic permeability of the second magnetic core20is higher than that of the first magnetic core10. Therefore, in the first frequency band, it is possible to improve the measuring accuracy of the current by the first magnetic core10. In the second frequency band, it is possible to improve the measuring accuracy of the current by the second magnetic core20. Therefore, it is possible to improve the accuracy of measuring the current in a wide frequency band by the current sensor100.

The first magnetic core10and the second magnetic core20are formed as magnetic cores in a ring shape through which the measuring object9is inserted.

With the configuration described above, the magnetic core1having the first magnetic core10and the second magnetic core20is formed in a ring shape. Therefore, it is possible to secure the measurement accuracy for outputting the same measurement values, regardless of the position of the measuring object9in the inner circumference of the magnetic core1.

The current sensor100further includes the winding7wound in the poloidal direction along the toroidal direction with respect to magnetic core1.

According to this configuration, it is possible to improve the measurement accuracy of the current by providing winding7, as compared with a current sensor, an example of which is a current sensor using a Hall element, not performing a negative feedback operation by the winding.

In addition, one of the first magnetic core10and the second magnetic core20can be assembled to the other from the outside, so that the one is partially exposed from the other.

According to this configuration, because the structure of the magnetic core1can be simplified, it is possible to reduce the manufacturing cost of the magnetic core1.

One of the first magnetic core10and the second magnetic core20is provided outside of the another so as to surround the outer periphery of the another.

With the configuration described above, symmetry for the first magnetic core10and the second magnetic core20can be provided as viewed from the outer periphery. Therefore, it is possible to measure the magnitude of D/C current by the fluxgate sensor6with high accuracy.

In addition, the current sensor100further includes the fluxgate sensor6as a magnetic detection element. One of the first magnetic core10and the second magnetic core20having higher magnetic permeability than another in a detecting band by the fluxgate sensor6is arranged in a sensing area by the fluxgate sensor6.

With the configuration described above, it is possible to measure the magnitude of D/C current by the fluxgate sensor6with high accuracy.

In addition, one of the first magnetic core10and second magnetic core20having the higher magnetic permeability in the detecting band by the fluxgate sensor6surrounds the outer periphery of the fluxgate sensor6.

With the configuration described above, one of the first magnetic core10and the second magnetic core20having higher magnetic permeability functions as the magnetic shield. Therefore, it is possible to prevent the fluxgate sensor6from measuring the magnetic flux acting from other than the measuring object9.

As described above, the fluxgate sensor6can detect the magnitude of D/C current with high accuracy.

Second Embodiment

A current sensor300according to the second embodiment will be described by referring toFIG.10. In the second embodiment, only elements different from those of the first embodiment will be described, and the same reference numerals are given to the same or equivalent elements as those in the first embodiment, and description thereof will be omitted. The current sensor300according to the second embodiment differs from the current sensor100of the first embodiment in that the current sensor300is covered with an electric conductive layer. Specifically, the current sensor300differs from the current sensor100in that the current sensor300is covered with a shield200. The electric conductive layer corresponds to something forming a layer having electrical conductivity. Examples of the electric conductive layer are a conductive film, a thin plate, a tape, a film, and conductive layer containing rubber and resin.

FIG.10is a diagram showing the current sensor300according to the second embodiment of the present invention.FIG.10shows the diagram corresponding to the II-II cross section inFIG.1. The current sensor300includes a cover5and a shield200which covers the winding7wound around the cover5.

The shield200is composed of the electric conductive layer.

The electric conductive layer can be formed by extending a thin metal, by vapor deposition, or by plating. The metallic foil tapes can also be applied to form the electric conductive layer in the current sensor300. In this embodiment, a metallic foil tapes are applied to form the shield200composed of the electric conductive layer.

Examples of metals used for the metallic foil tape are aluminum, stainless steel, copper, and the like. In the present embodiment, a copper foil tape202in a belt shaped, which has a copper-made foil, is applied.

The copper foil tape202is composed of a metallic layer204made of a copper foil to form the electric conductive layer, and an adhesion layer206laminated on a back surface of the metallic layer204. The adhesion layer206is made of an insulator. The thickness dimension of the metallic layer204in the copper foil tape202is generally equal to or larger than 30 μm and equal to or smaller than 100 μm. In the present embodiment, the copper foil tape202having a thickness of 100 μm is applied, as an example of the thickness dimension of the metallic layer204.

The shield200covering the current sensor300can be formed of the single copper foil tape202or a plurality of copper foil tapes202in strip-shapes.

In a case that the shield200is formed of the plurality of copper foil tapes202in the strip-shapes, each copper foil tape202is wound in the poloidal direction and attached while being shifted in the toroidal direction with respect to magnetic core1, so that the adhesion layer206in the copper foil tape202is brought into close contact with the outer periphery of the wound winding7. The copper foil tape202is wound in toroidal direction, so that one end portion210and another end portion212of the copper foil tape202overlap on an outer peripheral surface214of the cover5, which is formed in the torus shape.

An insulated layer220is formed by the adhesion layer206, which is composed of an insulator of the adhesion layer206, between the metallic layer204in the one end portion210of the copper foil tape202and the metallic layer204in the another end portion212. Therefore, in the copper foil tape202, the one end portion210and the another end portion212are electrically insulated. With the configuration described above, it is possible to prevent the copper foil tape202from forming single-turn coil, so as to suppress an induced current generated by the magnetic flux from the measuring object9.

The overlap margin, in which the one end portion210of the copper foil tape202and the another end portion212pile up, can be arbitrarily provided. The dimension of the insulated layer220between the metallic layer204of the one end portion210and the metallic layer204of the another end portion212can also be arbitrarily provided.

The longer the overlap margin, it is possible to suppress the change in the measured values, which is caused by the positions where the measuring object9is inserted into the current sensor300. Furthermore, as the dimension of the insulated layer220is narrower, it is possible to suppress the change in the measured values, which is caused by the positions where the measuring object9is inserted into the current sensor300.

The copper foil tape202is arranged with adjoining in the toroidal direction such that the side edges overlap, and therefore, it is possible to eliminate gaps that are provided in the toroidal direction. With the configuration described above, in the current sensor300, the magnetic core1in the cover5and the winding7wound around the cover5are surrounded by the electric conductive layer, which is constituted by the metallic layer204of the copper foil tape202.

On the other hand, when the shield200is formed by the single copper foil tape202, the copper foil tape202is attached in a spiral shape, while the copper foil tape202is wound in the poloidal direction so as to be along the toroidal direction with respect to the magnetic core1. The copper foil tape202is wound with overlapping the side edges thereof, and therefore, it is possible to eliminate gaps that are provided in the toroidal direction. With the configuration described above, in the current sensor300, the cover5and the winding7wound around the cover5are surrounded by the electric conductive layer, which is constituted by the metallic layer204of the copper foil tape202.

One end and the other end of the copper foil tape202in the length direction are not electrically connected. Therefore, it is possible to prevent the copper foil tape202from forming single-turn coil, so as to suppress an induced current generated by the magnetic flux from the measuring object9.

According to the above embodiment, the following effects are obtained.

According to the present embodiment, the current sensor300detects the magnitude of the current flowing through the measuring object9using the magnetic core formed in a ring shape, while the measuring object9is inserted through the magnetic core. The current sensor300comprises a magnetic core1including the first magnetic core10and the second magnetic core20, which is arranged magnetically in parallel with the first magnetic core10. The First magnetic core10has a higher magnetic permeability than the second magnetic core20in the first frequency band, and has a lower magnetic permeability than the second magnetic core20in the second frequency band, which is higher than the first frequency band. The current sensor300detects the magnitude of the current in the frequency band, in which the first frequency band and the second frequency band are combined. The current sensor300is covered with the electric conductive layer.

With the configuration of the current sensor300according to this configuration, the same operation and effects can be obtained for the same portions as those of the first embodiment.

As described above, with the configuration of the current sensor300which detects the magnitude of the current flowing through the measuring object9using the magnetic core1formed in the ring shape, through which the measuring object9is inserted, it is possible to secure the measurement accuracy for outputting the same measurement value, regardless of the position of the measuring object9in the inner circumference of the magnetic core1. However, it is known that, in a higher frequency of the current flowing through measuring object9, the measuring accuracy deteriorates when the position of the measuring object9deviates from the center of the inner circumference of the magnetic core1. Therefore, generally on an empirical basis, in order to prevent the deterioration of the measuring accuracy, the magnetic core1is covered entirely with the thicker metallic shields.

The inventors of the present application have experimentally found the following points. Firstly, the measuring accuracy deteriorates, when the magnetic flux other than the magnetic flux in the ring shape, which is generated in the ring shape around the outer periphery of the measuring object9, intrudes into the magnetic core1. Second, the shield200makes the effect to prevent the intrusion of the magnetic flux other the ring shaped, and the lower limit of the frequency, where the effort to prevent the intrusion is obtained, becomes higher, as the shield200is thinner in the thickness dimension. Third, in the frequency band where the magnetic core1has the magnetic permeability higher than air, even if the shield200is not provided, the effect by the intrusion of the magnetic flux other than the ring shaped is suppressed, because of the effect led by a collection of the magnetic flux by the magnetic core1.

In the current sensor300according to the present embodiment based on the points above, the magnetic core1is covered with the shield200. The shield200has a thinness such that the effect, which is to prevent the intrusion of the magnetic flux other than the ring shaped, becomes equal to or less than the threshold value, in the frequency equal to or less than the first frequency band. In the first frequency band, the magnetic permeability of the first magnetic core10is higher than that of the second magnetic core20.

In the configuration described above, the magnetic core1is covered with the shield200having a thinness such that the effect, which prevents the intrusion of the magnetic flux other than the ring shaped, becomes equal to or less than the criterial effect in a frequency which is equal to or less than the first frequency band. In the first frequency band, the magnetic permeability of the first magnetic core10is higher than that of the second magnetic core20. As a result, the shield200can be made thinner as compared with a shield200formed such that the effect, which prevents the intrusion of the magnetic flux other than the ring shaped, is larger than the criterial effect even in a frequency which is equal to or less than the first frequency band. Therefore, the current sensor300can be reduced in size and weight, and the current sensor300can be provided in an inexpensive price.

The effect, which prevents the intrusion of the magnetic flux other than the ring shaped, referred to herein (hereinafter, simply referred to as an intrusion prevention effect) may be one of the first order effect and the second order effect of the intrusion prevention effect. The intrusion prevention effect may be the second order effect caused by the intrusion prevention effect. An example of the second order effect is an effect to suppress a deterioration of the measuring accuracy, when the position of the measuring object9deviates from the center of the inner circumference of magnetic core1.

A criterion for the intrusion prevention effect can be defined by a performance of the electric conductive layer (e.g., conductivity) in a frequency where one state, in which a target for the intrusion prevention effect is obtained, to another state, in which the target for the intrusion prevention effect is not obtained. For example, the criterion for the intrusion prevention effect can be defined by a specification for the measured value corresponding to the deviation of the position of the measuring object9from the center of magnetic core1(e.g., an allowable error for the current), a simulated result of the magnetic core1, an experimental measured value (e.g., current value) obtained by gradually changing the thickness of the shield200of the current sensor.

In addition, with the configuration described above, it is possible to obtain the effect, even if a surface of the magnetic core1is covered by the shield200, while the surface is positioned toward the insertion direction, such that the shield200covers only a part of the measuring object9.

In the configuration of the present embodiment, the surface of the magnetic core1positioned toward the insertion direction of the measuring object9is covered by the conductive layer, which has the thinness such that the intrusion prevention effect of the magnetic flux other than the ring shaped is equal to or less than the criterion in a frequency which is equal to or less than the first frequency band. In the first frequency band, the magnetic permeability of the first magnetic core10is higher than that of the second magnetic permeability. However, when a plurality of the magnetic core arranged magnetically in parallel are combined, a frequency band, which has a magnetic permeability higher than that of air, can be expanded. As a result, the shield200can be formed thinner such that the intrusion prevention effect of the magnetic flux other than the ring shaped becomes equal to or less than the criterion in a frequency equal to or less than the frequency band. Therefore, the current sensor300can be further reduced in size, weight, and cost.

Furthermore, because the shield200can be made thinner, the shield200can be formed of a material having flexibility.

In the current sensor300according to the present embodiment, the electric conductive layer constituted by the copper foil tape202is formed in a belt shape, and is wound around the magnetic core1. The insulated layer220made of the adhesion layer206is formed between the electric conductive layer overlapping with each other while being wound.

According to this configuration, in the copper foil tape202constituting the electric conductive layer, the one end portion210and the another end portion212are electrically separated from each other by the insulated layer220. Therefore, it is possible to prevent the electric conductive layer, which is constituted by the copper foil tape202, to prevent forming single-turn coil. With the configuration described above, in the copper foil tape202constituting the electric conductive layer, it is possible to suppress the generation of the induced current by the magnetic flux from the measuring object9. Therefore, it is possible to improve the accuracy for measuring the current, as compared with when the induced current flows in the electric conductive layer constituted by the copper foil tape202.

In the second embodiment, although the one end portion210and the another end portion212of the copper foil tape202are overlapped on the outer peripheral surface214of the cover5, which is formed in the torus shape. However, the configuration in the present invention is not limited thereto. For example, a modification of the second embodiment described below may be applicable.

FIG.11is a cross-sectional view of a current sensor300according to a modification of the second embodiment, which corresponds to the II-II cross-section view inFIG.1.

In the current sensor300according to the modification of the second embodiment, the one end portion210and the another end portion212of the copper foil tape202are overlapped on the inner peripheral surface240of the cover5, which is formed in a torus shape.

With the configuration described above, the same operation and effect as those of the second embodiment can be obtained.

Third Embodiment

Next, a current sensor400according to a third embodiment will be described by referring toFIG.12. In the third embodiment, only elements different from the second embodiment will be described, and the same reference numerals are given to the same or equivalent elements as those in the second embodiment, and description thereof will be omitted.

In the current sensor400according to the third embodiment differs from the current sensor300in the second embodiment in that a part of the current sensor400is covered with the electric conductive layer formed of the shield200.

FIG.12is a view showing the current sensor400according to the third embodiment of the present invention, which corresponds to the II-II cross section inFIG.1. The current sensor400includes the cover5, which covers the magnetic core1, and a shield200, which covers the winding7wound around the cover5.

The shield200is formed so as to cover a one end surface230and another end face232of the magnetic core1, which are located in an insertion direction SH of the measuring object9(seeFIG.1). The insertion direction SH of the measuring object9can be referred to as the center axial direction of the magnetic core1formed in the ring shape.

The shield200is composed of the copper foil tape202described above as one of the examples, and the copper foil tape202is affixed to the cover5, which covers the magnetic core1, and the winding7, which is wound around the cover5. With the configuration described above, the magnetic core1and the winding7are partially covered by the electric conductive layer formed by the copper foil tape202.

Furthermore, the one end surface230and the another end surface232, which are surfaces of the magnetic core1located in the insertion direction SH of the measuring object9, are covered with the electric conductive layer.

According to the above embodiment, the following effects are obtained.

According to the present embodiment, the current sensor400detects the magnitude of the current flowing through the measuring object9. The current sensor400has the magnetic core1including the first magnetic core10and the second magnetic core20, which is arranged magnetically in parallel with the first magnetic core10. The magnetic permeability of the first magnetic core10is higher than that of the second magnetic core20in the first frequency band, and is lower than that of the second magnetic core20in the second frequency band, which is higher than the first frequency band. The current sensor400detects the magnitude of the current in the frequency band, in which the first frequency band and the second frequency band are combined.

The first magnetic core10and the second magnetic core20are formed to be the magnetic core1in the ring shape, through which the measuring object9is inserted. The surfaces230,232of the magnetic core1, which are located in the insertion direction of the measuring object9, are covered with the electric conductive layer.

According to the present embodiment, the current sensor400further includes the winding7which is wound in the poloidal direction along the toroidal direction with respect to the magnetic core1. The electric conductive layer covers a part of the magnetic core1and the winding7.

With the current sensor400having such the configuration, the same operation and effects can be obtained for the same portions as those of the first embodiment and the second embodiment.

As shown in the current sensor400of the present embodiment, the surfaces230,232of the magnetic core1, which are located in the insertion directions of the measuring object9, are covered with the electric conductive layer (204), which is made of the metallic layer204.

The inventors of the present application have found the point as follows. When the electric conductive layer located in the insertion directions of the measuring object9is provided, the effect by the electric conductive layer becomes larger, compared with when the electric conductive layer is provided in the directions other than the insertion directions.

As a result of providing the electric conductive layer described above, it is possible to suppress the magnetic flux entering to the magnetic core1from the one end surface230and the another end surface232of the magnetic core1, among the magnetic flux formed by the current flowing through the measuring object9. Therefore, the effect made by the magnetic flux entering the magnetic core1is suppressed on the measuring accuracy.

Even when the measuring object9is arranged with deviating from the center of magnetic core1formed in the torus shape, and when the measuring object9is close to a specific point in the magnetic core1, it is possible to suppress the effect on the measuring accuracy, and to improve the measuring accuracy of the current.

In the third embodiment, the case where the one end surface230and the other end surface232of the magnetic core1, which are located in the insertion directions SH of the measuring object9, are covered with the electric conductive layer (204) is exemplified, but is not limited thereto. For example, it may be configured as in the fourth embodiment described below.

Fourth Embodiment

Next, a current sensor500according to the fourth embodiment will be described by referring toFIG.13. In the fourth embodiment, only elements different from those of the second embodiment will be described, and the same reference numerals are given to the same or equivalent elements as those in the second embodiment, and description thereof will be omitted.

The current sensor500according to the fourth embodiment differs from the current sensor300in the second embodiment in that a part of current sensor500is covered with the electric conductive layer (204), which is formed by the shield200.

FIG.13is a view showing the current sensor500according to the fourth embodiment of the present invention, and the view corresponds to the II-II cross section inFIG.1. The current sensor500includes the cover5, which covers the magnetic core1, and a shield200, which covers the winding7wound around the cover5.

The shield200is provided so as to cover the inner peripheral surface240of the magnetic core1. As a result of this configuration, the inner peripheral surface240of the magnetic core1formed in the ring shape is covered with the electric conductive layer (204).

The shield200is composed of the copper foil tape202described above, and the copper foil tape202is affixed to the winding7, which is wound around the cover5covering the magnetic core1, for example. Therefore, the magnetic core1and the winding7are partially covered by the metallic film formed by the copper foil tape202.

According to the above embodiment, the following effects are obtained.

According to the present embodiment, the current sensor500detects the magnitude of the current flowing through the measuring object9. The current sensor500has the magnetic core1including the first magnetic core10and the second magnetic core20, which is arranged magnetically in parallel with the first magnetic core10. The magnetic permeability of the first magnetic core10is higher than that of the second magnetic core20in the first frequency band, and lower than that of the second magnetic core20in the second frequency band, which is higher than the first frequency band. The current sensor500detects the magnitude of the current in the combined frequency band of the first frequency band and the second frequency band.

The first magnetic core10and the second magnetic core20are formed as the magnetic core1in the ring shape through which the measuring object9is inserted. The inner peripheral surface240of the magnetic core1in the ring shape is covered with the electric conductive layer.

The current sensor500in the present embodiment further includes the winding7, which is wound in the poloidal direction along the toroidal direction with respect to the magnetic core1. The electric conductive layer covers the magnetic core1and the winding7.

The inventors of the present application have found that, when the electric conductive layer is provided on the inner peripheral surface of the measuring object, the electric conductive layer brings the effect, which is secondly effective after when the electric conductive layer is provided in the insertion direction of the measuring object.

Therefore, by the current sensor500even where the inner peripheral surface240of the magnetic core1in the ring shape is covered with the electric conductive layer, the same operation and effect can be achieved for the same parts as those of the configurations described in the first to the third embodiments.

In the second to the fourth embodiments, the structures of the shield200described above are applied to the current sensor100in the first embodiment, but is not limited thereto. The structures of the shield200in the second to the fourth embodiments may be applied to the current sensor100of the modification of the first embodiment, for example.

While the embodiments of the present invention have been described above, the above embodiment is only a part of the application example of the present invention, and the technical scope of the present invention is not intended to limit the technical scope of the present invention to the specific configuration of the above embodiment.

In the above embodiment, the magnetic core1includes the first magnetic core10, the second magnetic core20, and the third magnetic core30, but is not limited thereto. The magnetic core1, which includes a plurality of magnetic cores having different frequency characteristics, may be applicable.

For example, the magnetic core1may have only the first magnetic core10and the second magnetic core20. The magnetic core1may have only the first magnetic core10and the third magnetic core30. The magnetic core1may have only the second magnetic core20and the third magnetic core30.

In addition, the magnetic core1may further include the fourth magnetic core (not shown) having different frequency characteristic, in addition to the first magnetic core10, the second magnetic core20, and the third magnetic core30.

The current sensor100includes the winding7in the configuration above, however, the current sensor100, which does not include the winding7, may be applicable. Such current sensor100may have a magnetic core in an arc-shaped, in which a part of a torus shape is cut, and have a Hall element in the cut part, such that the current sensor measures the magnitude of the current flowing through the measuring object9.

Further, the current sensor100is a through-type current sensor, but may be a divided type (clamping type) current sensor or the like instead of the through-type one.

The thickness of the shield200is not limited to 100 μm or less, and may be thicker than 100 μm.

In addition, the shield200is not limited to those which are attached or wound by a metallic foil. The shield200may be formed by evaporation or plating by the conductive material on a housing.

Further, the following effect can be obtained. The shield200formed by a metallic can be thinner than a shield formed of other materials having the same performance for the electromagnetic shield as the shield200. The shield200formed by the metallic has a higher performance in shielding electromagnetic, because the shield200has a higher conductivity than other materials such that a damping loss is increased. Therefore, the shield200, which is formed by the metallic, can be made thinner as compared with the shield which is formed of the other materials. Furthermore, the shield may be formed by copper or aluminum, which are examples of metallics having relatively higher conductivity among the other metallic. Such shield can be made thinner, and therefore an effect can be obtained.

In a frequency band where the magnetic core1has a magnetic permeability higher than that of air, even if no shield200is provided, an influence by the intrusion of the magnetic flux other than the ring shaped is reduced. The reduction of the influence is caused by the magnetism collecting effect by the magnetic core1. However, the higher the magnetic permeability of magnetic core1, the lower the influence caused by the intrusion of the magnetic fluxes other than the ring shape.

This application claims priority based on Japanese Patent Application No. 2020-039014 filed with the Japan Patent Office on Mar. 6, 2020 and Japanese Patent Application No. 2021-001731 filed with the Japan Patent Office on Jan. 7, 2021, the entire contents of which are incorporated into this specification by reference.

Description for Reference Numerals