Current detection device

A current detection device includes a plurality of current detection units arranged in the current detection device. Each of the current detection units includes a bus bar that enables a current to be measured to flow therethrough, a magnetic sensor disposed at a position facing the bus bar, and a pair of shields disposed so as to sandwich the bus bar and the magnetic sensor in a facing direction in which the bus bar and the magnetic sensor face each other. The bus bars of the plurality of current detection units extend so as to be aligned to one another and, as viewed in the facing direction, the positions of the shield and the magnetic sensor of each of the current detection units in an extension direction of the bus bars differ from the positions of the shield and the magnetic sensor of the adjacent current detection unit.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a current detection device that measures a current to be measured on the basis of the magnetic field generated by the current to be measured flowing in a bus bar.

2. Description of the Related Art

A current sensor described in Japanese Unexamined Patent Application Publication No. 2017-102023 includes a conductor through which a current to be measured flows, a magnetic sensor that measures the induced magnetic field generated by the current to be measured, a case with an accommodation space that accommodates the conductor and the magnetic sensor and an accommodation space opening that leads to the accommodation space, a lid that covers the accommodation space opening, and a lid magnetic shield fixed to the lid by integral molding. The lid has a shield-exposed opening that exposes an edge portion of the lid magnetic shield. This makes it easy to visually confirm whether the lid magnetic shield is fixed at the proper position in the lid by viewing the shield-exposed opening.

SUMMARY OF THE INVENTION

However, in the current sensor described in Japanese Unexamined Patent Application Publication No. 2017-102022, when the distance between conductors is reduced in accordance with the demand of recent years for downsizing current sensors and, thus, the configuration is changed to reduce the size of the current sensor in the extension direction of the conductors, a sufficient shielding effect cannot be obtained. For this reason, it is difficult to diminish the influence of induced magnetic fields generated by the current to be measured flowing through adjacent conductors. More specifically, when the configuration in which adjacent conductors are staggered in an extension direction of the conductors is changed to the configuration in which the adjacent conductors are aligned to each other in order to reduce the size of the current sensor in the extension direction, the effect of the induced magnetic field generated by the current to be measured flowing through the adjacent conductors increases. Furthermore, if the distance between adjacent conductors is reduced in such an aligned configuration, the influence of the magnetic field generated by the current to be measured flowing through the adjacent conductor increases more, making it difficult to perform accurate current measurement.

Accordingly, the present invention provides a current detection device capable of reducing the size of the configuration as viewed in the direction in which the bus bars and magnetic sensors face each other while diminishing the influence of a magnetic field generated by the current to be measured flowing through an adjacent bus bar (current path).

According to an aspect of the present invention, a current detection device according to the present invention includes a plurality of current detection units arranged in the current detection device. Each of the current detection units includes a bus bar that enables a current to be measured to flow therethrough, a magnetic sensor disposed at a position facing the bus bar, and a pair of shields disposed so as to sandwich the bus bar and the magnetic sensor in a facing direction in which the bus bar and the magnetic sensor face each other. The bus bars of the plurality of current detection units extend so as to be aligned to one another and, as viewed in the facing direction, the positions of the shield and the magnetic sensor of each of the current detection units in an extension direction of the bus bars differ from the positions of the shield and the magnetic sensor of the adjacent current detection unit. This configuration can reduce the influence of the magnetic field generated by the current to be measured flowing in the adjacent bus bar and, as viewed in the direction in which the bus bar and the magnetic sensor face each other, the size of the configuration can be reduced.

In the current detection device according to the present invention, it is desirable that as viewed in the extension direction of the bus bars, the shields of the adjacent current detection units partially overlap in a direction in which the bus bars are aligned. This configuration can reduce the influence of the magnetic field generated by the current to be measured flowing through the adjacent bus bar. In addition, as viewed in the direction in which the bus bar and the magnetic sensor face each other, the size of the configuration in the direction in which the bus bars are aligned can be reduced.

In the current detection device according to the present invention, it is desirable that the positions of the shields of the adjacent current detection units in the facing direction be the same, and the positions of the magnetic sensors of the adjacent current detection units in the facing direction be the same. This configuration can reduce the size of the current detection device in the facing direction.

In the current detection device according to the present invention, it is desirable that as viewed in the facing direction, at least part of one of the shields in the pair extend to a position at which the part overlaps the bus bar of the adjacent current detection unit. This allows the magnetic field generated by a current to be measured flowing through the bus bar of the adjacent current detection unit to easily pass through the shield of the current detection unit. As a result, an influence error caused by the magnetic field generated by the adjacent current detection unit (the adjacent influence error) can be reduced.

In the current detection device according to the present invention, it is desirable that as viewed in the facing direction, the shield have a notch in a portion of the outer edge of the shield, and the notch be interlocked with a portion of an outer edge of the adjacent shield. This allows the adjacent shields to be arranged more efficiently as viewed in the above-described facing direction and, thus, the overall size of the current detection device can be reduced.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

A current detection device according to an embodiment of the present invention is described in detail below with reference to the accompanying drawings. In each of figures, the X-Y-Z coordinates are illustrated as reference coordinates. In the following description, the Z1-Z2direction is referred to as the up-down direction, the X1-X2direction is referred to as the front-rear direction, and the Y1-Y2direction is referred to as the left-right direction. The X1-X2direction and the Y1-Y2direction are mutually perpendicular. The X-Y plane including these directions is perpendicular to the Z1-Z2direction. In addition, the view from the top (the Z1side) to the bottom (the Z2side) is also referred to as a plan view.

First Embodiment

As illustrated inFIG.1, a current detection device10according to the first embodiment includes a case member11and three bus bars21,22, and23disposed so as to pass through the case member11in the front-rear direction (the X1-X2direction). The bus bars21,22, and23serve as current paths. The three bus bars21,22, and23have the same elongated plate shape and are aligned to one another and extend in the front-rear direction.

As illustrated inFIGS.2B and2C, three magnetic sensors61,62, and63are provided in the case member11at positions above the three bus bars21,22, and23so as to face the three bus bars21,22, and23, respectively. The magnetic sensors61,62, and63can detect the magnetic fields generated by currents to be measured flowing through the bus bars21,22, and23, respectively.

As illustrated inFIG.2C, the first bus bar21and the first magnetic sensor61on the left face each other in the up-down direction (the Z1-Z2direction) and are sandwiched from above and below by a pair of shields31and41. That is, in the direction in which the first bus bar21and the first magnetic sensor61face each other, the pair of shields31and41are arranged so as to sandwich the first bus bar21and the first magnetic sensor61. As a result, the first upper shield31, the first magnetic sensor61, the first bus bar21, and the first lower shield41are arranged in order from the top to the bottom. In this manner, a first current detection unit10ais formed in which the members lined up above and below face each other.

Like the first current detection unit10a, a second current detection unit10bis formed in which the second bus bar22and the second magnetic sensor62in the middle face each other and are sandwiched from above and below by another pair of shields32and42, the second upper shield32, the second magnetic sensor62, the second bus bar22, and the second lower shield42are arranged in order from the top to the bottom, and the members lined up above and below face each other.

In addition, a third current detection unit10cis formed in which the third bus bar23and the third magnetic sensor63on the right face each other and are sandwiched from above and below by another pair of shields33and43, the third upper shield33, the third magnetic sensor63, the third bus bar23, and the third lower shield43are arranged in order from the top to the bottom, and the members lined up above and below face each other.

As illustrated by the first magnetic sensor61inFIG.2Aas an example, the three magnetic sensors61,62, and63are disposed on the lower surface of a substrate50, which is accommodated in the case member11. The three magnetic sensors61,62, and63are identical elements, and a magneto-resistive element or a Hall element, for example, is used as the magnetic sensor in accordance with the specifications or other conditions of the current detection device.

As illustrated inFIG.2C, the three upper shields31,32, and33are disposed at the same position in the up-down direction. In addition, the three magnetic sensors61,62, and63are disposed at the same position in the up-down direction, the three bus bars21,22, and23are also disposed at the same position in the up-down direction, and the three lower shields41,42, and43are disposed at the same position in the up-down direction.

The three upper shields31,32, and33and the three lower shields41,42, and43have the same configuration. More specifically, each of the shields has a configuration in which five plate members each having a rectangular shape in plan view and made of the same magnetic material are stacked.

As illustrated inFIG.2B, the first upper shield31, the first magnetic sensor61, and the first lower shield41below the magnetic sensor61on the left are disposed at the same positions in the front-rear direction as the third upper shield33, the third magnetic sensor63, and the third lower shield43below the third magnetic sensor63on the right, respectively. In contrast, the second upper shield32, the second magnetic sensor62, and the second lower shield42in the middle are disposed ahead of the above-described shields and sensors so as not to overlap the above-described shields and sensors. That is, when the current detection units adjacent to each other in the left-right direction are viewed in the up-down direction (the direction in which the first bus bar21and the first magnetic sensor61face each other), the shield and the magnetic sensor of one current detection unit are disposed at different positions from those of the other. In addition, the three current detection units are arranged so as to be staggered in the front-rear direction.

In addition, as illustrated inFIGS.2B and2C, the shields of the current detection units adjacent to each other in the left-right direction are arranged so as to partially overlap in the front-rear direction, that is, the direction in which bus bars21,22, and23are aligned (the Y1-Y2direction). Note that the term “adjacent in the left-right direction” means a situation in which, as illustrated inFIG.2C, the bus bars21,22, and23are arranged side by side in the left-right direction when viewed in the extension direction of the bus bars21,22, and23. This term includes the case where any of the bus bars21,22, and23is shifted in the front-rear direction.

FIG.1andFIGS.2A,2B, and2Cillustrate the case of three current detection units. However, the number of current detection units can be two or four or more. Even in the case where the number of the current detection units is other than three, the current detection units are arranged side by side in the left-right direction, and the shields and magnetic sensors of the current detection units are arranged so as to be staggered in the front-rear direction (the X1-X2direction) as viewed in the up-down direction and are partially overlap each other in the left-right direction.

According to the above-described configuration, bus bars21,22, and23can be aligned, and the distance between the current detection units can be decreased in the direction in which bus bars21,22, and23are aligned (in the Y1-Y2direction). For this reason, the size in the front-rear direction (the X1-X2direction) can be reduced by aligning the bus bars in the left-right direction without shifting the bus bars in the front-rear direction, and the staggered arrangement of the shields can reduce the size in the left-right direction (the Y1-Y2direction). Furthermore, since this arrangement decreases the distance between adjacent two of the bus bars21,22, and23without reducing the size of the shield, sufficient shielding performance is ensured.

When the current detection device10includes three or more current detection units, it is desirable that among three current detection units lined up side by side, the two current detection units located at both ends be disposed at the same position in the front-rear direction (the bus bar extension direction), as indicated by the positional relationship between the first current detection unit10aand the third current detection unit10cillustrated inFIGS.2A,2B, and2C. This arrangement can minimize the size of the current detection device10in the front-rear direction.

Modifications are described below. The above-described three upper shields31,32, and33and three lower shields41,42, and43have a structure of five flat plates of magnetic material stacked on top of one another. However, the number of layers can be set to any value other than five, or the layer can be a single layer.

According to the above embodiment, the planar shape of each of the three upper shields31,32, and33and three lower shields41,42, and43is rectangular. However, as illustrated inFIGS.3A,3B, and3C, the planar shape can be a rectangular shape having an inward notch at each of the four corners. Such a shape enables an arrangement in which in plan view, the notches of adjacent shields are engaged with each other. Thus, the three upper shields31,32, and33and three lower shields41,42, and43may be arranged in a staggered manner within a smaller range in the extension direction of the bus bars21,22, and23(the X1-X2direction) and, therefore, the overall size can be reduced. In addition, by arranging the shields so that the notches are engaged with each other, the distance between the current detection units in the left-right direction (the Y1-Y2direction) can be reduced without the shield not hanging over the bus bar of the adjacent current detection unit.

Examples of the notch are illustrated inFIGS.3A,3B, and3C. According to modification1illustrated inFIG.3A, four corners of each of three upper shields131,132, and133are notched in a rectangular shape, so that the upper shields131,132, and133have notches131c, notches132c, and notches133c, respectively. By arranging the current detection units so that vertical sides (the sides extending in the front-rear direction) of the notches of adjacent current detection units face each other in the left-right direction, the three current detection units can be compactly arranged in the left-right and front-rear directions.

According to modification2illustrated inFIG.3B, four corners of each of three upper shields231,232, and233are notched in a triangular shape, so that the upper shields231,232, and233have notches231c,232c, and233c, respectively. By arranging the current detection units so that hypotenuses of the notches of adjacent current detection units face each other, the three current detection units can be compactly arranged in the left-right and front-rear directions.

According to modification3illustrated inFIG.3C, four corners of each of three upper shields331,332, and333are notched in a triangular shape that is larger than that of modification2, so that the upper shields331,332, and333have notches331c,332c, and333c, respectively. By arranging the current detection units so that hypotenuses of the notches of adjacent current detection units face each other, the three current detection units can be more compactly arranged in the left-right and front-rear directions than the three current detection units of modification2.

Second Embodiment

Unlike the first embodiment, according to the second embodiment, a portion of the shield, that is, an end portion in the left-right direction is extended to a position where the end portion overlaps the bus bar of the adjacent current detection unit. The other configuration is similar to that of the first embodiment, and members similar to those of the first embodiment are identified by the same reference numerals, and detailed descriptions of the members are omitted.

As illustrated inFIG.4A, according to the second embodiment, three upper shields431,432, and433having the same configuration are provided. Although not illustrated, like the first embodiment, under the upper shields431,432, and433, three lower shields are provided that have the same configuration as the upper shields431,432, and433and face the upper shields431,432, and433via the three magnetic sensors61,62, and63and three bus bars21,22, and23, respectively.

Like the first embodiment, the first upper shield431on the left and the third upper shield433on the right are disposed at the same position in the front-rear direction. In contract, the second upper shield432in the middle is disposed ahead of these shields and does not overlap these shields.

In addition, in the left-right direction, the right end portion of the first upper shield431is extended to the position where the right end portion overlaps the second bus bar22in the middle. The left end portion of the second upper shield432is extended to the position where the left end portion overlaps the first bus bar21on the left, and the right end portion of the second upper shield432is extended to the position where the right end portion overlaps the third bus bar23on the right. Furthermore, the left end portion of the third upper shield433is extended to the position where the left end portion overlaps the second bus bar22in the middle.

The end portion of each of the upper shields431,432, and433in the left-right direction overlaps the adjacent bus bar by the same width L (the width in the left-right direction, the overhang). By extending the end portion of the shield in the left-right direction to a position where the end portion overlaps the bus bar of the adjacent current detection unit in this manner, the magnetic field generated by the current to be measured flowing through the bus bar of the adjacent current detection unit can easily pass through the shield of the current detection unit. For this reason, the influence error (the adjacent influence error) caused by the magnetic field generated by the adjacent current detection unit can be minimized.

FIG.5is a graph illustrating the result of simulation of a change in the adjacent influence error (unit: %) with respect to the overhang of a shield over a bus bar (unit: mm) (an overlap width L in the left-right direction) in Examples 1 and 2 of the second embodiment and Comparative Examples 1 and 2. As used herein, the term “adjacent influence error” refers to the ratio based on the value obtained by dividing the difference in measured value of the magnetic field between when the current to be measured is passed through and is not passed through an adjacent bus bar by the measured value when the current to be measured is not passed through the adjacent bus bar.

In Examples 1 and 2, the following values are set in the configuration illustrated inFIG.4A:

(1) Overlap width L of the end portion of shield with the bus bar (overhang)Example 1: −6 mm to 6 mm; Example 2: −4 mm to 4 mm

It should be noted that when the overlap width L is zero or negative, the shield and the bus bar do not overlap, and when the overlap width L is zero, the positions of the end faces of the shield and bus bar are the same in the left-right direction and, when the overlap width L is negative, the end faces are separated from each other by the value.

(2) Width W of the bus bars21,22, and2310 mm in Examples 1 and 2

Comparative Examples 1 and 2 have the configuration illustrated inFIG.4B. More specifically, like the second embodiment, three bus bars21,22, and23are aligned in the left-right direction. Three magnetic sensors (not illustrated) are disposed for the bus bars21,22, and23in the up-down direction in a one-to-one manner. In addition, three upper shields531,532, and533and three lower shields (not illustrated) are disposed so as to sandwich, from above and below, the three bus bars and three magnetic sensors that face each other, respectively. In this way, three current detection units are arranged so as to be aligned in the left-right direction. Here, the three upper shields531,532, and533and the lower shields (not illustrated) each facing one of the upper shields531,532, and533are disposed at the same position in the front-rear direction so as to extend in the left-right direction, and each of the left and right end portions of each of the shields is separated from an end portion of the adjacent shield.

In Comparative Examples 1 and 2, the following values are set in the configuration illustrated inFIG.4B:(1) Distance between an end portion of the shield and a bus bar (in the left-right direction):

This distance is the distance between an end portion of a shield and the end portion of a bus bar facing the shield in the up-down direction. For example, the distance is the distance between the left end portion of the bus bar21and the left end portion of the shield531.Comparative Example 1: 2 mm; Comparative Example 2: 1 mm(2) Width W of the bus bars21,22, and23:10 mm in both Comparative Examples 1 and 2(3) Distance P between adjacent two of bus bars21,22, and23(pitch)Comparative Example 1: 16 mm; Comparative Example 2: 14 mm.

Therefore, the distances P between adjacent two of the bus bars in Comparative Example 1 and Example 1 are the same. In addition, the distances P in Comparative Example 2 and Example 2 are the same.

InFIG.5, as can be seen from comparison of Comparative example 1 and Example 1 in which the distances P between adjacent bus bars are the same, the adjacent influence error in Comparative Example 1 is about 0.75%, whereas the adjacent influence error in Example 1 decreases with increasing overhang greater than −4 mm. When the overhang reaches 2 mm or greater, the adjacent influence error reaches as low as 0.6% or lower. This result indicates that the adjacent influence error can be decreased by setting the overhang.

In addition, as can be seen from comparison of Comparative Example 2 and Example 2, the adjacent influence error in Comparative Example 2 is about 1.35%, whereas the adjacent influence error in Example 2 decreases with increasing overhang greater than about −1.5 mm. When the overhang reaches 2 mm or greater, the adjacent influence error reaches as low as 1.23% or lower. This result indicates that the adjacent influence error can be decreased by setting the overhang. Furthermore, the results of Example 1 and Example 2 indicate that for bus bars having a variety of widths, the adjacent influence error can be controlled by using the overhang that is set in accordance with the width of the bus bar. Other operations, effects, and modifications are the same as in the first embodiment.

Third Embodiment

According to the third embodiment, as illustrated inFIGS.6A and6B, unlike the first embodiment, three pairs of bus bars (upper shields631,632, and633and lower shields641,642, and643, respectively) of three adjacent current detection units are arranged so as to be staggered in the up-down direction and are disposed at the same position in the front-rear direction. Other configurations are the same as those in the first embodiment, and detailed description of a member that is the same as in the first embodiment is omitted.

As illustrated inFIG.6B, like the first and second embodiments, three bus bars621,622, and623are aligned in the left-right (the Y1-Y2direction), and each of the bus bars621,622, and623is extended in the front-rear direction. Three magnetic sensors661,662, and663are disposed above the three bus bars621,622, and623so as to face the bus bars621,622, and623, respectively.

Furthermore, as illustrated inFIG.6A, the first upper shield631and the first lower shield641are arranged so as to face each other from above and below and sandwich, from above and below, the first bus bar621and the first magnetic sensor661that face each other. These members constitute a first current detection unit60a. Similarly, the second upper shield632and the second lower shield642are arranged so as to face each other from above and below and sandwich, from above and below, the second bus bar622and the second magnetic sensor662that face each other. These members constitute a second current detection unit60b. Furthermore, the third upper shield633and the third lower shield643are arranged so as to face each other from above and below and sandwich, from above and below, the third bus bar623and the third magnetic sensor663that face each other. These members constitute a third current detection unit60c.

As illustrated inFIG.6A, in the up-down direction, the second current detection unit60bis disposed below the first current detection unit60aand the third current detection unit60cthat are disposed at the same position. Furthermore, as illustrated inFIGS.6A and6B, the left and right end portions of the second upper shield632and the second lower shield642of the second current detection unit60benter the first current detection unit60aor the third current detection unit60csuch that the left and right end portions do not come into contact with the magnetic sensor and bus bar in the first current detection unit60aor the third current detection unit60c.

According to the configuration described above, the three bus bars can be aligned in the left-right direction without shifting the bus bars in the front-rear direction, thus preventing an increase in the size in the bus bar extension direction (the X1-X2direction). In addition, since adjacent shields in the left-right direction are overlapped, an increase in the size in the left-right direction can be prevented. While the present invention has been described with reference to the above embodiments, the present invention is not limited to the above embodiments. Various improvements and changes can be made within the purpose of improvement or within the spirit and scope of the present invention.

As described above, the current detection device according to the present invention is useful in that it can reduce the size of the configuration as viewed in the direction in which the bus bar and the magnetic sensor face each other while reducing the influence of the magnetic field generated by a current to be measured flowing through an adjacent bus bar.