JP2019007935A - Current sensor - Google Patents

Abstract

To provide a current sensor with which it is possible to reduce hysteresis and detect a current with high accuracy.SOLUTION: The current sensor comprises a busbar 2 in which a current to be measured flows, a first shield plate 41 and a second shield plate 42 arranged so as to sandwich the busbar 2 in the thickness direction of the busbar 2, and a magnetism detection element 3 for detecting the strength of a magnetic field generated by the current flowing in the busbar 2, the distances of the first shield plate 41 and second shield plate 42 from the busbar 2 being equal, the magnetism detection element 3 being arranged so that its magnetism sensing position is shifted to the first shield plate 41 side from the center position in the thickness direction of the busbar 2, the second shield plate 42 consisting of a single magnetic layer 42a or a laminate in which a plurality of magnetic layers are laminated via an insulator, the first shield plate 41 consisting of a laminate in which a plurality of magnetic layers 41a, 41c are laminated via an insulator 41b, with the number of layers of the laminate larger than the second shield plate 42.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a current sensor.

  2. Description of the Related Art Conventionally, a current sensor is known that includes a magnetic detection element that detects the intensity of a magnetic field generated by a current to be measured (see, for example, Patent Document 1). By detecting the strength of the magnetic field by the magnetic detection element, the current can be obtained by calculation based on the strength of the magnetic field.

  Patent Document 1 discloses a current sensor in which a shield plate is arranged so as to sandwich a bus bar through which a current to be measured flows in order to shield a magnetic field that becomes noise.

Japanese Patent Laid-Open No. 2016-200436

  When the shield plate is arranged as in Patent Document 1, the shield plate is magnetized due to the current to be measured, and due to the influence of the magnetization, the current and the magnetic flux density detected by the magnetic detection element are Hysteresis may occur in the relationship.

  Accordingly, an object of the present invention is to provide a current sensor that can detect a current with high accuracy by reducing hysteresis.

  In order to solve the above problems, the present invention provides a bus bar through which a current to be measured flows, and a first shield plate and a second shield plate arranged so as to sandwich the bus bar in the thickness direction of the bus bar. And a magnetic detection element for detecting the strength of the magnetic field generated by the current flowing through the bus bar, wherein the first shield plate and the second shield plate are arranged so that the distance from the bus bar is equal. The magnetic sensing element is arranged such that its magnetic sensing position is shifted to the first shield plate side from the center position in the thickness direction of the bus bar, and the second shield plate is a single layer magnetic A body layer or a laminate in which a plurality of magnetic layers are laminated via an insulator, and the first shield plate is a laminate in which a plurality of magnetic layers are laminated via an insulator, and Number of layers of the laminate is greater than the second shield plate, to provide a current sensor.

  According to the present invention, it is possible to provide a current sensor that can detect a current with high accuracy by reducing hysteresis.

It is a figure which shows the current sensor which concerns on one embodiment of this invention, (a) is a perspective view, (b) is the sectional view on the AA line. In the current sensor of FIG. 1, it is a graph which shows the relationship between an electric current and the magnetic flux density detected with a magnetic detection element. (A) is sectional drawing of the current sensor of a prior art example, (b) is a graph which shows the relationship between the electric current and the magnetic flux density detected with a magnetic detection element. (A) is sectional drawing of the current sensor of a comparative example, (b) is a graph which shows the relationship between the electric current and the magnetic flux density detected with a magnetic detection element. It is sectional drawing of the current sensor which concerns on one modification of this invention.

[Embodiment]
Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.

(Overall configuration of current sensor)
1A and 1B are diagrams showing a current sensor according to the present embodiment, in which FIG. 1A is a perspective view, and FIG.

  As shown in FIGS. 1A and 1B, the current sensor 1 includes a bus bar 2 through which a current to be measured flows, and a first shield disposed so as to sandwich the bus bar 2 in the thickness direction of the bus bar 2. The plate 41 and the second shield plate 42, and the magnetic detection element 3 for detecting the strength of the magnetic field generated by the current flowing through the bus bar 2 are provided.

  The bus bar 2 is a plate-like conductor made of a good electrical conductor such as copper or aluminum, and serves as a current path through which a current flows. The bus bar 2 is used as a power line between a motor and an inverter in an electric vehicle or a hybrid vehicle, for example. In the present embodiment, a case will be described in which three bus bars 2a to 2c corresponding to the U-phase, V-phase, and W-phase of three-phase alternating current are used. A U-phase current flows through the bus bar 2a, a V-phase current flows through the bus bar 2b, and a W-phase current flows through the bus bar 2c. Here, bus bars 2a to 2c having a thickness of 3 mm were used.

  A through-hole 5 that penetrates each bus bar 2a to 2c in the thickness direction is formed at the center in the width direction of each bus bar 2a to 2c. Here, although the case where the rectangular through-hole 5 is formed is shown, the shape of the through-hole 5 is not particularly limited. By forming the through hole 5, current paths 6 are formed on both sides of the through hole 5. In the through hole 5, the magnetic fields generated in both current paths 6 cancel each other, so that the strength of the magnetic field in the through hole 5 and in the vicinity of the through hole 5 can be reduced. As a result, even in applications that detect large currents, it is possible to reduce the strength of the magnetic field detected by the magnetic detection element 3 and use the highly sensitive magnetic detection element 3, which contributes to improved current detection accuracy. To do.

  Hereinafter, the vertical direction in FIG. 1A is referred to as the thickness direction, the left rear to the right front direction is referred to as the length direction, and the left front to the right rear direction is referred to as the width direction. The bus bars 2a to 2c are arranged at equal intervals so as to be arranged in the width direction, and are arranged in parallel to each other.

  The magnetic detection element 3 is configured to output an output signal having a voltage corresponding to the intensity (magnetic flux density) of the magnetic field in the direction along the detection axis D. As the magnetic detection element 3, for example, a Hall element, a GMR (Giant Magneto Resistive effect) element, an AMR (Anisotropic Magneto Resistive) element, a TMR (Tunneling Magneto Resistive) element, or the like can be used. In the present embodiment, a GMR element having high sensitivity is used as the magnetic detection element 3.

  In the current sensor 1, a total of three magnetic detection elements 3a to 3c are provided so as to correspond to the respective bus bars 2a to 2c. Each magnetic detection element 3a-3c is arrange | positioned in the position which overlaps with the through-hole 5 by planar view seen from the thickness direction. Each of the magnetic detection elements 3 a to 3 c is mounted on a substrate (not shown), and is disposed at a predetermined position by inserting the substrate between the first shield plate 41 and the bus bar 2.

  In the present embodiment, each of the magnetic detection elements 3 a to 3 c has a magnetic sensing position (a detection position of the magnetic field strength) shifted from the center position O in the thickness direction of the bus bar 2 toward the first shield plate 41. Has been placed. That is, the magnetic detection elements 3 a to 3 c are arranged so as to be closer to the first shield plate 41 than the second shield plate 42.

  The first shield plate 41 and the second shield plate 42 are for shielding an external magnetic field so that the external magnetic field does not affect the detection result of the magnetic detection element 3. The first shield plate 41 and the second shield plate 42 are formed in a rectangular plate shape having two sides facing each other in the width direction and two sides facing each other in the length direction.

  The first shield plate 41 and the second shield plate 42 are spaced apart from the bus bar 2 so as to sandwich the bus bar 2 from the thickness direction. Further, the first shield plate 41 and the second shield plate 42 are parallel to the surface of the bus bar 2 (the thickness direction of the first shield plate 41 and the second shield plate 42 and the bus bar 2 It is arranged so that the thickness direction matches.

  In this current sensor 1, the distances (distances along the thickness direction) a and b of the first shield plate 41 and the second shield plate 42 from the bus bar 2 are equal. That is, in the current sensor 1, the intermediate position between the first shield plate 41 and the second shield plate 42 (position where the distance between the first shield plate 41 and the second shield plate 42 is equal) and the thickness direction of the bus bar 2. The center position O in FIG.

  Although not shown in the drawing, a mold resin is filled between the shield plates 41, 42, and the shield plates 41, 42, the magnetic detection element 3, and the bus bar 2 are integrally formed of the mold resin. The mold resin serves to keep the positional relationship among the magnetic detection element 3, the bus bar 2, and both the shield plates 41 and 42 constant and suppress detection errors due to vibration and the like, and because foreign matter enters between the shield plates 41 and 42. It also serves to suppress detection errors.

(Structure to reduce hysteresis)
When the shield plates 41 and 42 are exposed to a magnetic field generated by a current flowing through the bus bar 2, the shield plates 41 and 42 are magnetized according to their magnetic characteristics. When the shield plates 41 and 42 are magnetized, even when the current flowing through the bus bar 2 becomes zero, the magnetic detection element detects the magnetic flux according to the amount of magnetization. When the current flowing through the bus bar 2 is alternating current, the magnetization direction (polarity) of the shield plates 41 and 42 is reversed when the current increases and when the current decreases. Even in such a case, the magnetic flux density detected when the current increases and when the current decreases decreases in polarity. Thereby, it is considered that hysteresis occurs.

  In the current sensor 1, the magnetization directions of the shield plates 41 and 42 due to the current flowing through the bus bar 2 are opposite directions. For example, when the shield plates 41 and 42 have exactly the same configuration, the shield plates 41 , 42 at the same center position O, the influence of magnetization on both shield plates 41, 42 is canceled (cancelled). Therefore, if the magnetic detection element 3 is arranged so that the magnetic sensing position is at the center position O, the hysteresis can be reduced.

  However, since the bus bar 2 is arranged at the center position O, it is difficult to arrange the magnetic detection element 3 at the center position O. If the magnetic detection element 3 is disposed at a position deviated from the center position O, it is considered that the influence of magnetization from the shield plates 41 and 42 received by the magnetic detection element 3 cannot be canceled and the hysteresis becomes large. . When the magnetic detection element 3 is arranged closer to the first shield plate 41 than the center position O as in the current sensor 1, the magnetic detection element 3 is more affected by the magnetization of the first shield plate 41. It will end up.

  Therefore, in the present embodiment, by suppressing the influence of magnetization on the first shield plate 41 closer to the magnetic detection element 3, the magnetization of both the shield plates 41 and 42 at the magnetic sensing position of the magnetic detection element 3 is suppressed. The influence is canceled, thereby reducing the hysteresis.

  Specifically, in the current sensor 1 according to the present embodiment, the second shield plate 42 is a single-layer magnetic layer 42a, and the first shield plate 41 is a plurality of magnetic bodies via an insulator 41b. It is a laminated body in which the layers 41a and 41c are laminated. In the present embodiment, each magnetic layer 41a, 41c, 42a is made of a conductive magnetic material such as silicon steel. The plate thickness of each magnetic layer 41a, 41c, 42a was 1 mm. The insulator 41b is, for example, a film-like resin.

  When the frequency of the current flowing through the bus bar 2 is as high as 10 kHz or more, for example, the induced current (eddy current) flowing through the shield plates 41 and 42 due to the magnetic field generated by the current is concentrated near the surface of the conductor due to the skin effect. Since the second shield plate 42 is a single layer, the induced current is concentrated on the surface thereof. On the other hand, since the first shield plate 41 is made of a laminated body, the induced current is dispersed on the surfaces of the magnetic layers 41a and 41c. Therefore, the induced current flowing on the surface of the first shield plate 41 closest to the magnetic detection element 3 on the magnetic detection element 3 side is smaller than the induced current flowing on the surface of the second shield plate 42 on the magnetic detection element 3 side. As a result, the influence of magnetization on the first shield plate 41 received by the magnetic detection element 3 is suppressed, and the hysteresis can be reduced. The influence of magnetization on the first shield plate 41 includes the number of magnetic layers 41a and 41c of the first shield plate 41, the material and thickness of the magnetic layers 41a and 41c, and the magnetic layers 41a and 41c. It can be appropriately adjusted depending on the interval (thickness of the insulator 41b) and the like.

  FIG. 2 is a graph showing the result of simulating the relationship between the current flowing through the bus bar 2 and the magnetic flux density detected by the magnetic detection elements 3a and 3b in the current sensor 1 of FIG. In FIG. 2, the magnetic flux density due to the U-phase current detected by the magnetic detection element 3a is indicated by a solid line, and the magnetic flux density due to the V-phase current detected by the magnetic detection element 3b is indicated by a broken line. Note that the magnetic flux density due to the W-phase current detected by the magnetic detection element 3c is substantially the same as the magnetic flux density due to the U-phase current indicated by the solid line, and is omitted. In the simulation, the maximum value of the current flowing through the bus bar 2 was 50 A, the frequency was 20 kHz, and the residual magnetic flux density Br of the magnetic layers 41a, 41c, and 42a was 0.5T.

  As shown in FIG. 2, in the current sensor 1, hysteresis remains in the U phase (and W phase), but in the V phase, the relationship between the current and the magnetic flux density is substantially linear, reducing hysteresis. You can see that it is made.

  For comparison with the current sensor 1 according to the present embodiment, as shown in FIG. 3A, the insulator 41b and the magnetic layer 41c are omitted from the current sensor 1, and the first shield plate 41 is a single layer. A simulation was performed in the same manner for the current sensor 10 of the conventional example which is the magnetic layer 41a. In the current sensor 10 of the conventional example, both the shield plates 41 and 42 have the same thickness and the same number of layers. The simulation result is shown in FIG.

  As shown in FIG. 3B, in the current sensor 10 of the conventional example, since both the shield plates 41 and 42 have the same configuration, the magnetism detection element 3 receives the magnetization received from both the shield plates 41 and 42. The effect is unbalanced and the hysteresis is large. As can be seen from a comparison between FIG. 2 and FIG. 3B, the current sensor 1 according to the present embodiment can reduce the hysteresis as compared with the current sensor 10 of the conventional example.

  Furthermore, for comparison with the current sensor 1 of the present embodiment, as shown in FIG. 4A, the current of the comparative example in which the first shield plate 41 is a magnetic layer 41d having a thickness of 2 mm in the current sensor 10. The sensor 11 was similarly simulated. In the current sensor 11 of this comparative example, the number of layers of both shield plates 41 and 42 is the same, but the thicknesses are different. That is, the first shield plate 41 is thicker than the second shield plate 42. Further, the total thickness of the dielectric layers in the first shield plate 41 of the current sensor 11 of the comparative example is the same as that of the current sensor 1 of FIG. The simulation result is shown in FIG.

  As shown in FIG. 4B, when the frequency of the current flowing through the bus bar 2 is high, the induced current concentrates on the surfaces of the shield plates 41 and 42. Therefore, even if the first shield plate 41 is thickened, hysteresis is maintained. The effect of reducing cannot be obtained sufficiently. However, as a result of investigations by the present inventors, when the frequency of the current flowing through the bus bar 2 is as low as less than 1 kHz, for example, the skin effect is suppressed, so that the hysteresis is reduced by increasing the thickness of the first shield plate 41. I was able to confirm that it was possible.

  Therefore, the total thickness of the magnetic layers 41a and 41c of the first shield plate 41 is set to the magnetic layer 42a of the second shield plate 42 so that the hysteresis can be sufficiently reduced even when the frequency of the current flowing through the bus bar 2 is low. It is desirable to be thicker than.

(Modification)
In the present embodiment, the second shield plate 42 is a single layer, but the second shield plate 42 may be formed of a laminated body in which a plurality of magnetic layers are laminated via an insulator. In this case, by increasing the number of magnetic layers of the first shield plate 41 as compared with the second shield plate 42, the first shield plate 41 can suppress the influence of magnetization and reduce the hysteresis. Become. However, since it takes time and effort to manufacture both the shield plates 41 and 42 as a laminate, from the viewpoint of facilitating manufacture and improving mass productivity, the second shield plate 42 is a single layer, and the first shield plate 41 It can be said that a laminated body is more desirable. The number of magnetic layers 41a and 41c of the first shield plate 41 is not limited to two, and may be three or more.

  In the present embodiment, the magnetic layers 41a, 41c and 42a of the shield plates 41 and 42 have the same thickness, but the thicknesses of the magnetic layers 41a, 41c and 42a may be different. . For example, the resin film is attached to the insulator 41b by applying a metal tape provided with a metal foil made of copper or the like on one surface of the resin film to the same magnetic layer 41a as the magnetic layer 42a of the second shield plate 42. The first shield plate 41 may be formed using the metal foil as the magnetic layer 41c.

  As shown in FIG. 2, in the current sensor 1, the magnetic detection elements 3 a and 3 c that detect magnetic fields due to currents (U-phase and W-phase currents) flowing through the bus bars 2 a and 2 c arranged on both sides in the width direction. However, the hysteresis tends to be relatively large. Therefore, in order to reduce the hysteresis in the magnetic detection elements 3a and 3c, a metal tape is applied to the outer surface of the magnetic layer 41c at a portion facing the bus bars 2a and 2c, as in the current sensor 1a shown in FIG. And you may add the insulator 41e and the magnetic body layer 41f in the part facing the bus bars 2a and 2c, respectively. That is, the number of magnetic layers of the first shield plate 41 in the portion facing the bus bars 2a, 2c arranged in the width direction (the arrangement direction of the bus bars 2) in the thickness direction is arranged in the center in the width direction. The number of magnetic layers of the first shield plate 41 in the portion facing the bus bar 2b in the thickness direction may be increased. As a result, it is possible to adjust the hysteresis characteristics of all three phases to be substantially the same, and to reduce variation in current detection accuracy in each phase.

  Furthermore, in the present embodiment, the case where the magnetic layers 41a, 41c, and 42a are made of a conductive magnetic material has been described. However, the magnetic layers 41a, 41c, and 42a are non-conductive magnetic materials such as ferrite. May be.

(Operation and effect of the embodiment)
As described above, in the present embodiment, the distances a and b of the shield plates 41 and 42 from the bus bar 2 are equal, and the magnetic sensing element 3 has a magnetic sensing position at the center position in the thickness direction of the bus bar 2. In the current sensor 1 arranged so as to be shifted to the first shield plate 41 side, the second shield plate 42 is a single-layer magnetic layer 42a or a laminate in which a plurality of magnetic layers are laminated via an insulator. The first shield plate 41 is a laminate in which a plurality of magnetic layers 41a and 41c are laminated via an insulator 41b, and the number of layers of the laminate is larger than that of the second shield plate 42. .

  Thereby, especially when the frequency of the current flowing through the bus bar 2 is relatively high, the influence of magnetization by the first shield plate 41 close to the magnetic detection element 3 is reduced, and the influence of magnetization by both shield plates 41 and 42 is reduced. Thus, the hysteresis due to the magnetization of the shield plates 41 and 42 can be reduced, and the current sensor 1 capable of accurately detecting the current can be realized.

  Further, by making the total thickness of the magnetic layers 41a and 41c of the first shield plate 41 larger than the total thickness of the magnetic layers 42a of the second shield plate 42, the frequency of the current flowing through the bus bar 2 is relatively low. Even in a low case, hysteresis can be reduced and current detection accuracy can be improved.

(Summary of embodiment)
Next, the technical idea grasped from the embodiment described above will be described with reference to the reference numerals in the embodiment. However, the reference numerals and the like in the following description are not intended to limit the constituent elements in the claims to the members and the like specifically shown in the embodiments.

[1] A bus bar (2) through which a current to be measured flows, and a first shield plate (41) and a second shield arranged so as to sandwich the bus bar (2) in the thickness direction of the bus bar (2). A plate (42) and a magnetic detection element (3) for detecting the strength of the magnetic field generated by the current flowing through the bus bar (2), the first shield plate (41) and the second shield plate (42). ) Are arranged so that the distance from the bus bar (2) is equal, and the magnetic sensing element (3) has a magnetic sensing position that is more than the center position in the thickness direction of the bus bar (2). The second shield plate (42) is formed by laminating a plurality of magnetic layers through a single magnetic layer (42a) or an insulator. The first shield (41) comprises a laminate in which a plurality of magnetic layers (41a, 41c) are laminated via an insulator (41b), and the number of layers of the laminate is greater than that of the second shield plate (42). Many current sensors (1).

[2] The total thickness of the magnetic layers (41a, 41c) of the first shield plate (41) is thicker than the total thickness of the magnetic layers (42a) of the second shield plate (42). ] Current sensor (1).

[3] The second shield plate (42) includes a single magnetic layer (42a), and the first shield plate (41) includes a plurality of magnetic layers (41a) via an insulator (41b). , 41c), the current sensor (1) according to [1] or [2].

  While the embodiments of the present invention have been described above, the embodiments described above do not limit the invention according to the claims. In addition, it should be noted that not all the combinations of features described in the embodiments are essential to the means for solving the problems of the invention.

  The present invention can be appropriately modified and implemented without departing from the spirit of the present invention.

DESCRIPTION OF SYMBOLS 1 ... Current sensor 2 ... Bus bar 3 ... Magnetic detection element 41 ... 1st shield board 41a, 41c ... Magnetic body layer 41b ... Insulator 42 ... 2nd shield board 42a ... Magnetic body layer

Claims (3)

A bus bar in which the current to be measured flows,
A first shield plate and a second shield plate arranged to sandwich the bus bar in the thickness direction of the bus bar;
A magnetic detection element for detecting the intensity of a magnetic field generated by a current flowing through the bus bar,
The first shield plate and the second shield plate are arranged so that the distance from the bus bar is equal,
The magnetic detection element is arranged such that its magnetic sensitive position is shifted to the first shield plate side from the center position in the thickness direction of the bus bar,
The second shield plate is a single magnetic layer or a laminate in which a plurality of magnetic layers are laminated via an insulator,
The first shield plate is composed of a laminate in which a plurality of magnetic layers are laminated via an insulator, and the number of layers of the laminate is larger than that of the second shield plate.
Current sensor. The total thickness of the magnetic layers of the first shield plate is thicker than the total thickness of the magnetic layers of the second shield plate;
The current sensor according to claim 1. The second shield plate is composed of a single magnetic layer,
The first shield plate is composed of a laminate in which a plurality of magnetic layers are laminated via an insulator.
The current sensor according to claim 1 or 2.

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