JP2015135288A - Electric current sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electric current sensor restrained in wrong detection of measurable magnetic fluxes.SOLUTION: An electric current sensor comprises a magneto-electric converter (10) that converts measurable magnetic fluxes into electric signals, a magneto-electric converter that surrounds each of the magnetic shields (30) and a bus bar (110) in which the measurable electric current flows. The magnetic shield, formed in a cylindrical shape, has a first magnetic shield (31) in whose wall parts (33 to 35) surrounding the bus bar have apertures (31a) and a second magnetic shield (32) that clogs the apertures. The second magnetic shield is formed of a soft magnetic material higher in magnetic permeability and lower in saturated magnetic flux density and coercive force than the first magnetic shield. To absorb residual magnetic fluxes generated in the first magnetic shield after the first magnetic shield and the second magnetic shield are magnetically saturated, the second magnetic shield is made easier to be magnetically saturated and cleared of residual magnetic fluxes than the first magnetic shield.

Description

  The present invention relates to a current sensor that detects a current to be measured based on a magnetic flux to be measured generated by the flow of the current to be measured.

  Conventionally, for example, as shown in Patent Document 1, a bus bar, a magnetic detection element fixedly arranged with respect to the bus bar so that a magnetic field generated by a current flowing through the bus bar is applied to the magnetic sensitive surface, and a magnetic detection element A current sensor including a magnetic shield body for magnetic shielding has been proposed. The above-described magnetic shield body has an annular enclosure that encloses each of the bus bar and the magnetic detection element, and the annular enclosure includes an upper magnetic shield member and a lower magnetic shield member. As these magnetic shield members, a U-shaped silicon steel plate, permalloy, or ferrite is used.

JP 2010-2277 A

  As described above, in the current sensor disclosed in Patent Document 1, the two magnetic shield members are formed of a U-shaped silicon steel plate, permalloy, or ferrite. Accordingly, the magnetic permeability, the saturation magnetic flux density, and the coercive force are the same in both cases. Thus, for example, when each of the two magnetic shield members is magnetically saturated by a magnetic field (measured magnetic flux) generated by a current flowing through the bus bar (current to be measured), residual magnetic flux is generated in each of the two magnetic shield members. The rate at which the residual magnetic field disappears is the same for both. For this reason, even if the magnetic flux to be measured (current to be measured) becomes zero, the magnetic detection element detects the residual magnetic flux described above. As a result, there is a possibility of erroneous detection that the current to be measured is flowing even though the current to be measured is zero.

  In view of the above problems, an object of the present invention is to provide a current sensor in which erroneous detection of a magnetic flux to be measured is suppressed.

  In order to achieve the above-described object, the present invention provides a current sensor for detecting a current to be measured based on a magnetic flux to be measured generated by the flow of the current to be measured, and a magnetoelectric conversion unit that converts the magnetic flux to be measured into an electric signal. (10), and a magnetic shield part (30) surrounding each of the magnetoelectric conversion part and the bus bar (110) through which the current to be measured flows, and the magnetic shield part has a cylindrical shape and surrounds the bus bar. A first magnetic shield part (31) in which an opening part (31a) is formed in a wall part (33 to 35) that surrounds the second magnetic shield part (32) that closes the opening part. The magnetic shield part is made of a soft magnetic material having a higher magnetic permeability than the first magnetic shield part and having a low saturation magnetic flux density and a low coercive force. After the first magnetic shield part and the second magnetic shield part are magnetically saturated, First magnetic shield part To suck the residual magnetic flux generated, the second magnetic shield portions, characterized in that it is easily liable to magnetic saturation, missing residual magnetic flux than the first magnetic shield unit.

  According to this, after the first magnetic shield part (31) and the second magnetic shield part (32) are magnetically saturated by the magnetic flux to be measured, when the magnetic flux to be measured (current to be measured) becomes zero, the second magnetic The shield part (32) releases the magnetic flux earlier than the first magnetic shield part (31). Therefore, even if a residual magnetic flux is generated in the first magnetic shield part (31) due to magnetic saturation, it can be sucked by the second magnetic shield part (32). As a result, it is possible to suppress the residual magnetic flux from being detected by the magnetoelectric converter (10), and it is possible to suppress erroneous detection that the current to be measured is flowing even though the current to be measured is zero.

  The first magnetic shield part (31) has a cylindrical wall part (33-35) and an opening part (31a) formed in the wall part (33-35). (31a) is closed by the second magnetic shield part (32). Since the main part of the magnetoelectric conversion part (10) is surrounded by the cylindrical first magnetic shield part (31) in this way, even if the second magnetic shield part (32) is magnetically saturated by the external magnetic flux, External magnetic flux can be shielded by the magnetic shield part (31).

  In addition, since the wall part (33-35) of a 1st magnetic shield part (31) comprises a cylinder shape, although it has two openings on the structure, the opening formed in the above-mentioned wall part (33-35) The part (31a) is an opening different from these two openings. The opening (31a) opens in a direction perpendicular to the flow direction of the current to be measured, and the two openings of the cylindrical wall portions (33 to 35) open in the flow direction of the current to be measured. ing.

  The second magnetic shield part has a smaller volume than the first magnetic shield part. Usually, a soft magnetic material having a high magnetic permeability and a low saturation magnetic flux density and a low coercive force has a higher material cost than a soft magnetic material different from the soft magnetic material. On the other hand, as described above, the second magnetic shield part (32) has a smaller volume than the first magnetic shield part (31). Therefore, it is suppressed that cost is bulky. Moreover, compared with the structure with the same volume, the second magnetic shield part (32) is more likely to be magnetically saturated and the residual magnetic flux is likely to escape. Therefore, the residual magnetic flux of the first magnetic shield part (31) can be sucked more quickly by the second magnetic shield part (32).

  The second magnetic shield part and the first magnetic shield part are arranged to face each other at a predetermined interval and are in a non-contact state. According to this, unlike the configuration in which the second magnetic shield portion and the first magnetic shield portion are in contact with each other, the magnetic connection between the two is weakened. Therefore, the independence of the magnetic properties of the first magnetic shield part and the second magnetic shield part is increased, and the reduction of both functions is suppressed. That is, the reduction of the function of the first magnetic shield part for shielding the external magnetic flux and the function of the second magnetic shield part for sucking the residual magnetic flux are suppressed.

  In addition, although the elements described in the claims and the means for solving the problems are attached with parentheses, the parentheses are attached to each component described in the embodiment. This is to simply show the correspondence with the elements, and does not necessarily indicate the elements themselves described in the embodiments. The description of the reference numerals with parentheses does not unnecessarily narrow the scope of the claims.

It is sectional drawing which shows schematic structure of the current sensor which concerns on 1st Embodiment. It is a distribution map which shows magnetic flux density distribution when a weak electric current flows. It is a distribution map which shows magnetic flux density distribution of the area | region enclosed with the broken line shown in FIG. It is a graph which shows the relationship between a detection magnetic flux and a to-be-measured electric current. It is a distribution map which shows magnetic flux density distribution when a strong current flows. FIG. 6 is a distribution diagram showing a magnetic flux density distribution in a region surrounded by a broken line shown in FIG. 5. It is a graph which shows the relationship between a detection magnetic flux and a to-be-measured electric current. It is sectional drawing which shows the modification of a current sensor.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
(First embodiment)
The current sensor according to the present embodiment will be described with reference to FIGS. In FIG. 1, the boundaries between the plate portions 33 and 34 and the connecting portion 35 are indicated by broken lines.

  Hereinafter, the three directions orthogonal to each other are referred to as an x direction, a y direction, and a z direction. A plane defined by the x direction and the y direction is an xy plane, a plane defined by the y direction and the z direction is a yz plane, and a plane defined by the z direction and the x direction is a zx plane. It shows. The y direction corresponds to the flow direction described in the claims. The zx plane corresponds to the specified plane described in the claims. Hereinafter, the zx plane is simply referred to as a prescribed plane.

  The current sensor 100 detects the measured current based on the measured magnetic flux generated by the flow of the measured current of the bus bar 110. As shown in FIG. 1, the current sensor 100 includes a magnetoelectric conversion unit 10 and a magnetic shield unit 30. The magnetoelectric conversion unit 10 converts the magnetic flux to be measured into an electrical signal, and the magnetic shield unit 30 surrounds the magnetoelectric conversion unit 10 and the bus bar 110. Each of the bus bar 110 and the magnetic shield part 30 has a shape extending in the y direction, and the shape of the prescribed plane orthogonal to the y direction is constant.

  The current to be measured flows in the direction in which the bus bar 110 extends, that is, in the y direction. Therefore, the flow of the current to be measured in the y direction generates a magnetic flux to be measured according to the right-handed screw law in a defined plane orthogonal to the y direction. The magnetoelectric conversion unit 10 converts the magnetic flux to be measured into an electric signal. By doing so, the current sensor 100 detects the current to be measured.

  The magnetoelectric conversion unit 10 is formed by forming a magnetoelectric conversion element on a semiconductor substrate. As the magnetoelectric conversion element, a magnetoresistive effect element whose resistance value varies by transmission of magnetic flux, or a Hall element whose Hall voltage varies by transmission of magnetic flux can be adopted. The magnetoelectric conversion element is formed on the surface layer of one surface of the semiconductor substrate, and detects a magnetic flux along the one surface. One surface is opposed to the inner surface of the first plate portion 33 described later, and is along the xy plane. The magnetoelectric transducer detects a magnetic flux along the xy plane. Since the magnetic flux to be measured is along the specified plane (z-x plane) as described above, the magnetoelectric transducer detects a component along the x direction in the magnetic flux to be measured.

  The magnetic shield part 30 includes a first magnetic shield part 31 and a second magnetic shield part 32. The first magnetic shield part 31 has a cylindrical shape having two openings (not shown) in the defined plane. Further, the first magnetic shield part 31 has an opening 31a different from the two openings described above. As shown in FIG. 1, in the present embodiment, the first magnetic shield part 31 has one opening 31a that opens in the x direction, and the cross-sectional shape of the first magnetic shield part 31 in the defined plane is an annular shape having a gap. It is made. The opening 31a is closed by the second magnetic shield part 32, and the periphery of the magnetoelectric conversion part 10 and the bus bar 110 is surrounded by the magnetic shield parts 31 and 32, respectively. With this configuration, each of the magnetoelectric conversion unit 10 and the bus bar 110 is shielded from the external magnetic field. In addition, the 2nd magnetic shield part 32 and the 1st magnetic shield part 31 are opposingly arranged at predetermined intervals, and are in a non-contact state. Although not shown, each of the magnetoelectric conversion unit 10, the magnetic shield unit 30, and the bus bar 110 is integrally fixed with a nonmagnetic material.

  The first magnetic shield part 31 includes a first plate part 33 and a second plate part 34 that face each other in the z direction, and a connecting part 35 that connects the two plate parts 33 and 34. Each of the plate portions 33 and 34 has a rectangular cross-sectional shape in a prescribed plane, the principal surface having the largest area is orthogonal to the z direction, and the end surface having the smallest area is orthogonal to the x direction. On the other hand, the connecting portion 35 also has a rectangular cross-sectional shape on the prescribed plane, but the main surface with the largest area is orthogonal to the x direction, and the end surface with the smallest area is orthogonal to the z direction. . Each of the plate portions 33 and 34 has two end surfaces, one of which (the end surface located on the left side of the drawing) is connected to the main surface of the connecting portion 35, and the other (the end surface located on the right side of the drawing) is the second. It faces the magnetic shield part 32 with a predetermined interval. With this configuration, the cross-sectional shape of the first magnetic shield portion 31 on the defined plane is C-shaped, and the opening portion 31a described above is configured by the end portion including the other end surface of each of the plate portions 33 and 34. The components 33 to 35 of the first magnetic shield part 31 described above correspond to the wall part described in the claims.

  The 2nd magnetic shield part 32 has comprised the shape which obstruct | occludes the opening part 31a, and has comprised the flat plate shape in this embodiment. The second magnetic shield portion 32 includes a facing portion 36 that faces the opening 31 a, a first extending portion 37 that extends to the first plate portion 33 side with respect to the facing portion 36, and a second portion that is more than the facing portion 36. And a second extending portion 38 extending toward the plate portion 34 side. Each of the extending portions 37 and 38 is bent so as to form an L-shape on the specified plane. Accordingly, a part of the first extending portion 37 faces the other end surface of the first plate portion 33, and the rest of the first extending portion 37 is the back surface of the surface of the first plate portion 33 facing the second plate portion 34. Is facing. A part of the second extending portion 38 faces the other end surface of the second plate portion 34, and the rest of the second extending portion 38 is the back surface of the second plate portion 34 facing the first plate portion 33. Is facing. In addition, the bending part (part along the x direction) in the extending portions 37 and 38 is extremely smaller than the main part (part along the z direction) in the second magnetic shield part 32. Therefore, the second magnetic shield part 32 has a linear shape in a defined plane.

  Next, the magnetic properties of the magnetic shield portions 31 and 32 will be described. The second magnetic shield part 32 is made of a soft magnetic material having a higher magnetic permeability than the first magnetic shield part 31 and a low saturation magnetic flux density and a low coercive force. For example, as the material of the second magnetic shield part 32, PC permalloy, amorphous magnetic material or the like is employed. On the other hand, as the material of the first magnetic shield part 31, pure iron, electromagnetic steel plate or the like is adopted.

  The second magnetic shield part 32 is thinner than the first magnetic shield part 31 and has a smaller volume. As a result, the second magnetic shield part 32 is more easily magnetically saturated than the first magnetic shield part 31, and the residual magnetic flux is easily released. Therefore, even if a residual magnetic flux is generated in the first magnetic shield part 31, the residual magnetic flux can be sucked by the second magnetic shield part 32.

Next, the relationship between the magnetic saturation and the measured current flowing through the bus bar 110 and the magnetic flux detected by the magnetoelectric conversion unit 10 (hereinafter referred to as detected magnetic flux) will be described with reference to FIGS. 2 and 3 show the magnetic flux density distribution when a current to be measured (weak current) that does not cause magnetic saturation of the second magnetic shield portion 32 is caused to flow through the bus bar 110. As shown in FIG. 3, the magnetic flux density transmitted through the second magnetic shield part 32 is slightly higher than that of the first magnetic shield part 31. However, in this state, the second magnetic shield part 32 is not magnetically saturated, and most of the magnetic flux to be measured does not leak to the outside of the magnetic shield part 30. In this case, as shown in FIG. 4, the detected magnetic flux changes linearly with respect to the current to be measured. However, when the current value of the current to be measured reaches the value I ₀ indicated by the alternate long and short dash line in FIG. 3, the slope changes. This is because the second magnetic shield part 32 is magnetically saturated, but its linearity is kept almost constant.

  5 and 6 show the magnetic flux density distribution when a current to be measured (strong current) that causes the second magnetic shield portion 32 to be magnetically saturated flows through the bus bar 110. As shown in FIG. 6, the magnetic flux density transmitted through the second magnetic shield part 32 is higher than that of the first magnetic shield part 31 and is magnetically saturated. In this case, since the second magnetic shield part 32 cannot absorb the magnetic flux, it has substantially the same properties as the nonmagnetic material. However, even in this case, as shown in FIG. 7, the detected magnetic flux changes linearly with respect to the current to be measured. 7 includes FIG. 4. As can be seen from FIG. 7, the change in inclination shown in FIG. 4 is extremely small.

  As described above, as shown in FIGS. 2 to 7, in the case of the current sensor 100 according to the present embodiment, the detected magnetic flux has a linear property with respect to the current to be measured, regardless of the magnetic saturation of the second magnetic shield part 32. . Although the values of the graphs shown in FIGS. 2 to 7 are arbitrary units, the magnetic flux density distribution and the graphs are obtained by simulation.

  Next, the function and effect of the current sensor 100 according to this embodiment will be described. As described above, the second magnetic shield part 32 is made of a soft magnetic material having a higher magnetic permeability than the first magnetic shield part 31 and a low saturation magnetic flux density and a low coercive force. The second magnetic shield part 32 is more easily magnetically saturated than the first magnetic shield part 31, and the residual magnetic flux is easily released. According to this, when the magnetic flux to be measured (current to be measured) becomes zero after the first magnetic shield portion 31 and the second magnetic shield portion 32 are magnetically saturated by the magnetic flux to be measured, the second magnetic shield portion 32 is Magnetic flux escapes faster than the first magnetic shield part 31. Therefore, even if a residual magnetic flux is generated in the first magnetic shield part 31 due to magnetic saturation, it can be sucked by the second magnetic shield part 32. As a result, it is possible to suppress the residual magnetic flux from being detected by the magnetoelectric conversion unit 10, and it is possible to suppress erroneous detection that the current to be measured is flowing even though the current to be measured is zero.

  Further, the opening 31 a of the first magnetic shield part 31 is closed by the second magnetic shield part 32, and the periphery of the magnetoelectric conversion part 10 and the bus bar 110 is surrounded by the magnetic shield parts 31 and 32, respectively. Since the main part of the magnetoelectric converter 10 is surrounded by the cylindrical first magnetic shield part 31 as described above, even if the second magnetic shield part 32 is magnetically saturated by the external magnetic flux, the first magnetic shield part 31 externally Magnetic flux can be shielded.

  The second magnetic shield part 32 has a smaller volume than the first magnetic shield part 31. Usually, a soft magnetic material having a high magnetic permeability and a low saturation magnetic flux density and a low coercive force has a higher material cost than a soft magnetic material different from the soft magnetic material. On the other hand, the volume of the second magnetic shield part 32 is smaller than that of the first magnetic shield part 31 as described above. Therefore, it is suppressed that cost is bulky. Moreover, compared with the structure with the same volume, the 2nd magnetic shield part 32 is more magnetically saturated, and a residual magnetic flux is easy to escape. Therefore, the residual magnetic flux of the first magnetic shield part 31 can be sucked more quickly by the second magnetic shield part 32.

  The second magnetic shield part 32 and the first magnetic shield part 31 are arranged to face each other at a predetermined interval and are in a non-contact state. According to this, unlike the configuration in which the second magnetic shield part 32 and the first magnetic shield part 31 are in contact with each other, the magnetic connection between them is weakened. Therefore, the independence of the magnetic properties of the first magnetic shield part 31 and the second magnetic shield part 32 is increased, and the reduction of the functions of both is suppressed. That is, the reduction of the function of the first magnetic shield part 31 for shielding the external magnetic flux and the function of the second magnetic shield part 32 for sucking the residual magnetic flux are suppressed.

  The preferred embodiments of the present invention have been described above. However, the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the spirit of the present invention.

  In this embodiment, the example which the magnetic-electric conversion element which the magneto-electric conversion part 10 has detects the magnetic flux in alignment with xy plane was shown. However, the detection direction of the magnetoelectric transducer is not limited to the above example as long as it can avoid the transmission direction of the external magnetic flux that is difficult to be magnetically shielded by the magnetic shield unit 30 while detecting the magnetic flux to be measured.

  In this embodiment, the 1st magnetic shield part 31 has the one opening part 31a opened to ax direction, and the example which has the board parts 33 and 34 and the connection part 35 was shown. However, the number of openings 31a included in the first magnetic shield part 31 is not limited to the above example. For example, as shown in FIG. 8, the first magnetic shield part 31 may have two openings 31a. In this case, the magnetic shield part 30 has two second magnetic shield parts 32 in order to close each of the two openings 31a. The number of the second magnetic shield portions 32 is not limited to the above example as long as the openings 31a can be closed by the second magnetic shield portions 32. That is, the number of second magnetic shield portions 32 does not depend on the number of openings 31a.

  In the present embodiment, an example in which the second magnetic shield part 32 and the first magnetic shield part 31 are in a non-contact state is shown. However, the magnetic shield portions 31 and 32 may be in contact with each other.

  In the present embodiment, an example is shown in which the cross-sectional shape of the first magnetic shield portion 31 on the defined plane is C-shaped. However, as long as the external magnetic flux can be shielded while suppressing leakage of the magnetic flux to be measured, the shape of the first magnetic shield portion 31 is not limited to the above example.

  In the present embodiment, the example in which the second magnetic shield portion 32 has a linear shape in a prescribed plane is shown. However, as long as the residual magnetic flux of the first magnetic shield part 31 can be sucked, the shape of the second magnetic shield part 32 is not limited to the above example.

DESCRIPTION OF SYMBOLS 10 ... Magnetoelectric conversion part 30 ... Magnetic shield part 31 ... 1st magnetic shield part 31a ... Opening part 32 ... 2nd magnetic shield part 33 ... 1st board part 34 ... Second plate part 35... Connecting part 100... Current sensor

Claims (7)

A current sensor for detecting the measured current based on a measured magnetic flux generated by the flow of the measured current;
A magnetoelectric converter (10) for converting the measured magnetic flux into an electrical signal;
A magnetic shield part (30) surrounding each of the magnetoelectric conversion part and the bus bar (110) through which the current to be measured flows;
The magnetic shield part has a cylindrical shape, and a first magnetic shield part (31) in which an opening part (31a) is formed in a wall part (33 to 35) surrounding the periphery of the bus bar, and the opening part is closed. A second magnetic shield part (32)
The second magnetic shield part is made of a soft magnetic material having a higher magnetic permeability than the first magnetic shield part and having a low saturation magnetic flux density and a low coercive force.
After the first magnetic shield part and the second magnetic shield part are magnetically saturated, the second magnetic shield part is more magnetic than the first magnetic shield part so as to suck in residual magnetic flux generated in the first magnetic shield part. A current sensor characterized in that it is easily saturated and residual magnetic flux is easily removed.   The current sensor according to claim 1, wherein the second magnetic shield part has a smaller volume than the first magnetic shield part.   3. The current sensor according to claim 1, wherein the second magnetic shield part and the first magnetic shield part are arranged to face each other at a predetermined interval and are in a non-contact state.   The current sensor according to claim 1, wherein the first magnetic shield part has one opening, and the second magnetic shield part has a plate shape.   The said 1st magnetic shield part comprises C shape in the prescription | regulation plane orthogonal to the flow direction of the said to-be-measured electric current, The said 2nd magnetic shield part comprises linear form, The said 5th aspect is characterized by the above-mentioned. Current sensor. The first magnetic shield portion includes a first plate portion (33) and a second plate portion (34) facing each other, and two end portions where the first plate portion and the second plate portion are opposed to each other. A connecting portion (35) for connecting one of the two, and has a C-shape in the prescribed plane,
The second magnetic shield portion has a flat plate shape so as to close the opening formed by the other of the two end portions of the first plate portion and the second plate portion facing each other. The current sensor according to claim 5, wherein: The second magnetic shield part includes a facing part (36) facing the opening, a first extending part (37) extending to the first plate part side from the facing part, and the facing part A second extending portion (38) extending to the second plate portion side than the second plate portion,
Each of the first extending portion and the second extending portion is bent so as to form an L shape in the prescribed plane,
A part of the first extension part faces the end surface of the other end of the first plate part, and the rest of the first extension part faces the second plate part of the first plate part. Facing the back of the
A part of the second extending portion is opposed to an end surface of the other end portion of the second plate portion, and the rest of the second extending portion is a surface of the second plate portion facing the first plate portion. The current sensor according to claim 6, wherein the current sensor faces the back surface of the current sensor.

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