Current sensor

Abstract

A current sensor 2 according to the present invention includes: a plate-like bus bar 10 extending in an X direction; and a magnetic sensor 20 capable of detecting an induction magnetic field generated when a to-be-measured current flows in the bus bar 10. The current sensor 2 includes a magnetic field control unit 30 for controlling a magnetic field detected by the magnetic sensor 20. The bus bar 10 has a first end surface 10E of which a Z direction is a direction of a normal line L10E, and a first plate surface 10S of which a Y direction is a direction of a normal line L10E. The magnetic sensor 20 is disposed to face the first end surface 10E, has a magnetic sensing direction as the Z direction, and can output the difference between a first output having an induction magnetic component towards one side of the Z direction as a plus component and a second output having an induction magnetic component towards the other side of the Z direction as a plus component. Therefore, when the current sensor 2 measures to-be-measured currents flowing in a plurality of bus bars, an adjacent influence error due to magnetic noise from a bus bar adjacent to a to-be-measured bus bar is suppressed, the measurement accuracy is good, and the size can be reduced.

Description

Current Sensor

[0001] The present invention relates to a current sensor that measures a current to be measured that flows through a bus bar.

[0002] In recent years, power semiconductors (power modules) have been used as a means for controlling power supply systems of vehicles equipped with various devices, etc. Power semiconductors are equipped with current sensors used to measure the current flowing through the devices, and various current sensors have been proposed.

[0003] In a current sensor used in a stacked, double-sided cooled power semiconductor, the magnetic sensor, which is a detection device, must be positioned so that the plate-shaped bus bar through which the current to be measured flows faces the narrow side, not the main plate surface, in accordance with the pitch of the power semiconductor. In this case, if the spacing between the bus bars becomes narrow, the error (hereinafter also referred to as adjacent influence error) generated in the magnetic sensor increases due to the influence of the adjacent bus bar adjacent to the bus bar that detects the induced magnetic field, resulting in a problem of reduced measurement accuracy of the current sensor.

[0004] Patent document 1 describes a current sensor equipped with a magnetic field shaping member that shapes the magnetic field detected by the magnetic sensor, with the aim of miniaturizing the sensor while suppressing the effects of phase shifts and detecting magnetic fields with high accuracy.

[0005] Patent document 2 describes a current sensor that can reduce noise from external magnetic disturbances, can measure large currents to be measured, and is designed to be compact and thin, and has a differential section that performs differential calculations on the output signals from a first magnetic sensor and a second magnetic sensor to cancel out noise caused by external magnetic disturbances.

[0006] Patent document 3 describes a current detection device that aims to be compact while suppressing the effects of nearby current paths and surrounding magnetic fields.The current to be measured flowing in an electric circuit is divided into two current paths by a through slit and flows in the same direction, and the device has a circuit section that performs differential calculations on detection signals obtained from a pair of magnetic detection elements arranged within the projection plane of the through slit.

[0007] Patent document 4 describes a current measuring device that aims to miniaturize the current measuring device, in which, when the substrate is viewed in plan, a conductive member is positioned within the space between a pair of side shielding portions, and the magnetic sensing surface of a magnetoelectric conversion element is contained within the thickness of the shielding member.

[0008] Patent document 5 describes a current detection device in which each bus bar has a narrow portion cut out from the side, the narrow portion is positioned so as not to face an adjacent narrow portion, and a magnetoelectric conversion element is positioned between the narrow portion and a shield, with the aim of suppressing the influence of magnetic flux from bus bars of other phases and performing highly accurate current detection.

[0009] International Publication No. 2018 / 012032 International Publication No. 2012 / 029438 JP 2022-158768 A JP 2018-36111 A JP 2018-169188 A

[0010] The current sensor described in Patent Document 1 aims to reduce the influence of phase shift while achieving miniaturization, but does not consider adjacent influence errors caused by adjacent bus bars adjacent to the bus bar being detected. The current sensors and current detection devices described in Patent Documents 2 and 3 reduce magnetic noise by differential calculation, but have difficulty suppressing adjacent influence errors when the distance between adjacent bus bars is reduced. The current measurement device described in Patent Document 4 also has difficulty suppressing adjacent influence errors when the distance between adjacent bus bars is reduced. The current detection device described in Patent Document 5 reduces magnetic noise by staggering the positions of magnetoelectric conversion elements, but has difficulty being miniaturized. The present invention aims to provide a current sensor that is miniaturized and has good measurement accuracy when measuring currents flowing through multiple bus bars, by suppressing adjacent influence errors caused by magnetic noise from bus bars adjacent to the bus bar being measured.

[0011] To achieve the above object, the present invention provides a current sensor comprising: a plate-shaped bus bar extending in a first direction; a magnetic sensor capable of detecting an induced magnetic field generated when a current to be measured flows through the bus bar; and a magnetic field control unit that controls the magnetic field detected by the magnetic sensor, wherein the bus bar has a first end portion in a second direction orthogonal to the first direction and a first flat plate surface having a normal direction in a third direction orthogonal to the first and second directions, the magnetic sensor being disposed opposite the first end portion, having a magnetic sensing direction in the second direction, and capable of outputting a difference between a first output having a component of the induced magnetic field oriented in one of the second directions as a positive component and a second output having a component of the induced magnetic field oriented in the other of the second directions as a positive component.

[0012] The magnetic field control unit may be provided on an opposite side of the bus bar from the first end in the second direction with respect to the magnetic sensor.

[0013] With the above configuration, the magnetic field control unit controls the strength and direction of the induced magnetic field generated when the current to be measured flows through the bus bar, thereby increasing the component in the second direction, which is the magnetic sensing direction of the magnetic sensor. This improves the S / N ratio of the magnetic sensor, which is disposed opposite the first end of the bus bar and whose magnetic sensing direction is the second direction, thereby improving the detection accuracy of the magnetic sensor.

[0014] The current sensor may include a plurality of detection units each including the magnetic field control unit, the bus bar, and the magnetic sensor, and the plurality of detection units may be arranged so that the first flat surfaces of adjacent bus bars face each other.

[0015] The magnetic field control unit can control magnetic noise from a bus bar adjacent to the bus bar to be detected (hereinafter referred to as an adjacent bus bar) in addition to the induced magnetic field generated by the current to be measured flowing through the bus bar to be detected that constitutes the magnetic sensor and the detection unit (hereinafter referred to as a detection bus bar, as appropriate).The magnetic field control unit controls the magnetic noise from the adjacent bus bar to the magnetic sensor so that the component in the second direction, which is the magnetic sensing direction of the magnetic sensor, becomes larger, and the magnetic sensor outputs the difference between the first output and the second output, thereby canceling the component in the second direction and suppressing the magnetic noise.

[0016] The magnetic field control unit may be a plate-like body having a second flat surface that is a plate surface normal to the second direction, the second flat surface of the magnetic field control unit facing the first end of the bus bar, and the magnetic sensor may be provided between the second flat surface and the first end in the second direction. By arranging the magnetic field control unit, which is a plate-like body, so that the second flat surface faces the first end of the bus bar and arranging the magnetic sensor therebetween, the magnetic field control unit functions as a magnetic shield, thereby improving the detection accuracy of the magnetic sensor.

[0017] The magnetic sensor may have a first sensor element that produces the first output and a second sensor element that produces the second output, and the first sensor element and the second sensor element may be arranged along the third direction. The first sensor element and the second sensor element may be arranged at positions that are line-symmetrical with respect to a center line of the bus bar in the third direction. The first sensor element and the second sensor element may be Hall elements.

[0018] By taking the difference between the outputs of the first sensor element and the second sensor element, the sensitivity to the induced magnetic field from the bus bar to be detected is increased and the second direction component of the magnetic noise from the adjacent bus bar adjacent to the bus bar to be detected can be canceled, thereby improving the detection accuracy of the magnetic sensor.

[0019] The first sensor element and the second sensor element may be housed within a single magnetic sensor. By housing the first sensor element and the second sensor element within a single magnetic sensor, they can be manufactured using the same manufacturing process. Therefore, variations between the first sensor element and the second sensor element due to errors in the manufacturing process are reduced, thereby improving the detection accuracy of the magnetic sensor.

[0020] The detection unit may be configured such that the magnetic field control unit is a plate-shaped body, a second flat surface that is the plate surface of the magnetic field control unit faces the first end of the bus bar, the magnetic sensor has a first sensor element that provides the first output and a second sensor element that provides the second output, which are arranged along the third direction, the first sensor element and the second sensor element being arranged between the second flat surface of the magnetic field control unit and the first end of the bus bar in the second direction, the center line of the bus bar and the center line of the magnetic sensor being coincident in the third direction, and the center line of the magnetic field control unit being shifted to either side of the third direction with respect to the center lines of the bus bar and the magnetic sensor.

[0021] By arranging the center line of the magnetic field control unit in the third direction to be shifted to one side of the third direction with respect to the center lines of the bus bar and the magnetic sensor, magnetic noise from the bus bar of an adjacent detection unit to the magnetic sensor can be suppressed, thereby improving the detection accuracy of the magnetic sensor.

[0022] The plurality of detection units may be disposed at equal intervals in the third direction, the distance between adjacent bus bars in the third direction may be 18 to 27 mm, the center lines of the bus bars and the magnetic sensor may coincide, and the distance between the center lines of the bus bars and the magnetic sensor and the center line of the magnetic field control unit that controls the magnetic field detected by the magnetic sensor may be 0.5 to 2.5 mm. When the distance between adjacent bus bars is within the above range, by setting the distance by which the magnetic field control unit is shifted in the third direction to be within the above range, magnetic noise from adjacent bus bars can be suppressed compared to when the magnetic field control unit is not shifted in the third direction, thereby improving the detection accuracy of the magnetic sensor.

[0023] The magnetic field control unit may be arranged at a position where, when viewed in the second direction, a distance in the third direction between one of the second ends on both sides in the third direction and the first flat plate surface of the bus bar closer to the one second end is 1 mm or less, and the other second end does not overlap with the bus bar. The magnetic field control unit may be arranged at a position where, when viewed in the second direction, one of the second ends on both sides in the third direction overlaps with the bus bar, and the other second end does not overlap with the bus bar.

[0024] When the magnetic field control unit is viewed in the second direction, one second end is positioned near the first flat surface of the bus bar and the other second end is positioned so as not to overlap with the bus bar, so that the magnetic field control unit controls noise from the adjacent bus bar and also functions as a magnetic shield. Therefore, by shielding external magnetic noise with the magnetic field control unit, the detection accuracy of the magnetic sensor is improved.

[0025] The current sensor may have a board on which the magnetic sensor is mounted, a case that holds the bus bar integrally and has a storage section in which the board can be stored, and a cover that holds the magnetic field control unit integrally, and the board may be fixed within the storage section and the cover may be arranged to cover the storage section.

[0026] The current sensor may have a substrate having a first insertion hole through which a screw can be inserted and on which the magnetic sensor is mounted, a case that holds the bus bar integrally and has a storage section in which the magnetic sensor can be housed, and a cover that holds the magnetic field control section integrally, wherein the substrate is sandwiched between the case and the cover with the magnetic sensor arranged in the storage section, the cover has a second insertion hole through which the screw can be inserted, and the case has a screw hole that can be screwed into the screw, and the case, the substrate and the cover are fixed by the screw that is inserted into the first insertion hole and the second insertion hole and screwed into the screw hole.

[0027] The current sensor may include a substrate having the magnetic sensor mounted on one surface and the magnetic field control unit fixed on the other surface, and a case that integrally holds the bus bar, and the substrate may be fixed to the case so that the one surface of the substrate faces the case. The substrate may be fixed to the case by screws or caulking.

[0028] The current sensor of the present invention can improve the signal-to-noise ratio of the magnetic field sensor by increasing the strength of the magnetic field that the magnetic sensor is intended to detect and suppressing magnetic noise using the magnetic field control unit. Furthermore, if the current sensor includes multiple bus bars, the magnetic field control unit controls the magnetic noise from adjacent bus bars adjacent to the detection bus bar so that the magnetically sensitive component is increased, and the differential output cancels the magnetically sensitive component, thereby suppressing the influence of the magnetic noise from the adjacent bus bars. Therefore, a current sensor can be provided that is compact and has good measurement accuracy.

[0029] 5 is a perspective view schematically showing a main part of a current sensor according to an embodiment of the present invention; FIG. 6 is a cross-sectional view of the current sensor of FIG. 1 taken along line AA; FIG. 7 is a plan view of the current sensor of FIG. 1 viewed in the Z2-Z1 direction; FIG. 8 is a graph showing the influence of a magnetic field control unit on the magnetic flux density detected by a magnetic sensor; FIG. 9 is a perspective view schematically showing a main part of a current sensor according to an embodiment of the present invention, which includes a plurality of detection units; FIG. 10 is a cross-sectional view of the current sensor of FIG. 5 taken along line AA; FIG. 11 is a plan view of the current sensor of FIG. 5 viewed in the Z2-Z1 direction; FIG. 12 is a schematic view showing magnetic noise from an adjacent bus bar in a conventional current sensor; FIG. 13 is a schematic view showing magnetic noise from an adjacent bus bar in the current sensor of the present embodiment; FIG. 14 is a diagram showing a simulation result of magnetic noise from an adjacent bus bar in a conventional current sensor; FIG. 15 is a diagram showing a simulation result of magnetic noise from an adjacent bus bar in a current sensor of an example having a magnetic field control unit on the Z2 side of the magnetic sensor; FIG. 16 is a diagram showing a simulation result of magnetic noise from an adjacent bus bar in a current sensor of a comparative example having a magnetic shield between the bus bars; FIG. 17 is a graph showing a simulation result of magnetic noise from an adjacent bus bar; FIG. 18 is a cross-sectional view of a current sensor in which the magnetic field control unit is shifted in the Y1 direction. 15 is a graph of a simulation result showing the relationship between the distance by which the magnetic field control unit is shifted in the Y direction and the adjacent influence error. FIG. 16 is a cross-sectional view showing an enlarged view of a part of the detection unit in the current sensor of FIG. 14. FIG. 17 is a cross-sectional view showing an example of a more specific aspect of the current sensor. FIG. 18 is a cross-sectional view showing a modified example (part 1) of a more specific aspect of the current sensor. FIG. 19 is a cross-sectional view showing a modified example (part 2) of a more specific aspect of the current sensor. FIG. 20 is a cross-sectional view showing a modified example (part 3) of a more specific aspect of the current sensor.

[0030] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. The same components in each drawing are designated by the same reference numerals, and descriptions thereof will be omitted where appropriate. Reference coordinates are indicated in each drawing as appropriate to indicate the positional relationship of each component. In the reference coordinates, the extension direction of the bus bar is defined as the X direction, the width direction of the bus bar perpendicular to the X direction is defined as the Y direction, and the stacking direction of the bus bar and the magnetic detection unit perpendicular to the X and Y directions is defined as the Z direction.

[0031] Fig. 1 is a perspective view schematically showing a main portion of a current sensor 1 according to this embodiment. Fig. 2 is a cross-sectional view of the current sensor 1 taken along line AA in Fig. 1. Fig. 3 is a plan view of the current sensor 1 in Fig. 1 as viewed in the Z2-Z1 direction. As shown in these figures, the current sensor 1 includes a bus bar 10, a magnetic sensor 20 capable of detecting an induced magnetic field generated when a current to be measured flows through the bus bar 10, and a magnetic field control unit 30. The bus bar 10, the magnetic sensor 20, and the magnetic field control unit 30 constitute a detection unit 40.

[0032] The busbar 10 is a plate-shaped body made of a conductor such as copper, brass, or aluminum, through which a current to be measured flows. The busbar 10 extends in a first direction (X direction) and has a first end face (first end) 10E and a first flat plate surface 10S in a second direction (Z direction) perpendicular to the first direction. A normal line L10E to the first end face 10E is parallel to the Z direction, and a normal line L10S to the first flat plate surface 10S is parallel to the Y direction. While FIGS. 1 to 3 illustrate an example in which both ends of the busbar 10 in the Z direction (second direction) are flat, both ends or one end in the Z direction (second direction) may have a shape other than a flat shape. For example, the end of the busbar 10 in the Z direction may have a bent portion or a notched portion, taking into account factors such as connection to an external member.

[0033] The magnetic sensor 20 is disposed opposite the first end surface 10E of the busbar 10, has a magnetic sensing direction in the Z direction (second direction), and includes a first sensor element 21 and a second sensor element 22. The first sensor element 21 outputs a first output having a positive component of an induced magnetic field oriented in the Z1 direction, which is one of the Z directions, and the second sensor element 22 outputs a second output having a positive component of an induced magnetic field oriented in the Z2 direction, which is the other of the Z directions. The magnetic sensor 20 outputs the difference between the first output detecting a magnetism oriented in the Z1 direction and the second output detecting a magnetism oriented in the Z2 direction.

[0034] The first sensor element 21 and the second sensor element 22 can be, for example, a Hall element or a magnetoresistive element such as a giant magnetoresistive element (GMR element) or a tunnel magnetoresistive element (TMR element). The configuration shown in Fig. 2 is an example in which Hall elements are used as the first sensor element 21 and the second sensor element 22, but when other magnetic detection elements are used, the orientation of the detection surface and other factors can be changed as appropriate.

[0035] 2, the first sensor element 21 and the second sensor element 22 are arranged along the Y direction (third direction). When the busbar 10 is viewed from the X direction, the first sensor element 21 and the second sensor element 22 are arranged at positions that are symmetrical with respect to a center line L10C that is parallel to the Z direction and bisects the busbar 10. Furthermore, as shown in FIG. 3, the first sensor element 21 and the second sensor element 22 are arranged at the same position in the X direction.

[0036] With the above configuration, the direction of the induced magnetic field M1 generated by the current to be measured flowing through the bus bar 10, which is the detection target of the magnetic sensor 20, is opposite between the first sensor element 21 and the second sensor element 22, as shown by the black arrows in Fig. 2. Therefore, by taking the difference between the output of the first sensor element 21 and the output of the second sensor element 22, the sensitivity to the induced magnetic field from the bus bar 10 is improved.

[0037] In contrast, the direction and strength (magnitude) of the magnetic field of magnetic noise, such as geomagnetism, present around the magnetic sensor 20 are generally uniform. Therefore, the direction and strength of the magnetic field of the magnetic noise are the same in the first sensor element 21 and the second sensor element 22. Therefore, by taking the difference between the first output of the magnetic field oriented in the Z1 direction and the second output of the magnetic field oriented in the Z2 direction, the Z-direction component of the magnetic noise can be canceled. Therefore, the S / N ratio (signal / noise ratio) of the magnetic sensor 20 is increased, and the detection accuracy of the magnetic sensor 20 is improved.

[0038] The first sensor element 21 and the second sensor element 22 are housed within one magnetic sensor 20. This allows the first sensor element 21 and the second sensor element 22 to be manufactured using the same manufacturing process. This reduces errors due to variations between the first sensor element 21 and the second sensor element 22 caused by errors in the manufacturing process, thereby improving the detection accuracy of the magnetic sensor 20.

[0039] The magnetic field control unit 30 is made of a magnetic material and controls the magnetic field detected by the magnetic sensor 20. It is located on the Z2 side, which is opposite the Z1 side of the busbar 10 where the first end face 10E is located, in the Z direction, based on the magnetic sensor 20.

[0040] 4 is a graph showing the effect of the presence or absence of the magnetic field control unit 30 on the magnetic flux density detected by the magnetic sensor 20. A simulation of the effect of the magnetic field control unit 30 shown in the figure was performed under the following conditions (see FIG. 2): Shape of the YZ cross section of the busbar 10: Rectangular with a width of 2 mm in the Y direction and a width of 12 mm in the Z direction Shape of the YZ cross section of the magnetic field control unit 30: Rectangular with a width of 5 mm in the Y direction and a width of 0.5 mm in the Z direction Distance D1 in the Z direction between the first end surface 10E of the busbar 10 and the magnetic sensor 20 (center point in the Z direction): 2 mm Distance D2 in the Z direction between the magnetic sensor 20 and the magnetic field control unit 30 (center point in the Z direction): 3 mm

[0041] The figure shows the results of a simulation of the magnetic flux density detected by the magnetic sensor 20 when a current to be measured flows through the busbar 10 of the current sensor 1 equipped with the magnetic field control unit 30. In a conventional current sensor that differs from the current sensor 1 only in that it does not have the magnetic field control unit 30, the magnetic flux density of the magnetic field detected by the magnetic sensor 20 is set to 1.0, and the figure shows the magnetic flux density ratio of the magnetic field detected by the current sensor 1 equipped with the magnetic field control unit 30 under the same conditions. As shown in the figure, it was found that the provision of the magnetic field control unit 30 increased the magnetic flux density of the magnetic field detected by the magnetic sensor 20 by approximately 20%.

[0042] That is, by using the magnetic field control unit 30 to control the strength and / or direction of the induced magnetic field M1 generated when a current to be measured flows through the busbar 10, it is possible to increase the component in the Z direction (second direction), which is the magnetic sensing direction of the magnetic sensor 20. Therefore, by improving the S / N ratio of the magnetic sensor 20, which is disposed opposite the first end face 10E of the busbar 10 and has a magnetic sensing direction in the Z direction, it is possible to improve the detection accuracy of the current sensor 1.

[0043] Note that controlling the strength and / or direction of the induced magnetic field M1 by the magnetic field control unit 30 means the following: By disposing the magnetic field control unit 30 made of a magnetic material on the opposite side of the busbar 10 with the magnetic sensor 20 in between, the induced magnetic field M1 generated in the busbar 10 is pulled toward the magnetic field control unit 30 and changes its direction. Therefore, in the region between the busbar 10 and the magnetic field control unit 30, the direction of the induced magnetic field M1 is corrected toward the Z direction compared to when the magnetic field control unit 30 is not present. Therefore, the induced magnetic field M1 passing through the magnetic sensor 20 disposed between the busbar 10 and the magnetic field control unit 30 has a larger component in the Z direction (second direction) than when the magnetic field control unit 30 is not present.

[0044] The magnetic field control unit 30 is a plate-like body such as a metal plate, and has a second flat plate surface 30S of which the normal line L30S is oriented in the Z direction (second direction), and a second end surface (second end portion) 30E of which the normal line L30E is oriented in the Y direction (third direction). Note that, although an example in which the second end portions on both sides in the Y direction (third direction) are flat is shown in Figures 1 to 3, one or both of the second end portions may be configured in a shape other than flat.

[0045] The second flat surface 30S of the magnetic field control unit 30 faces the first end surface 10E of the busbar 10. The magnetic sensor 20 is provided between the second flat surface 30S and the first end surface 10E in the Z direction (second direction).

[0046] By making the magnetic field control unit 30 a plate-shaped body and positioning its second flat surface 30S facing the first end surface 10E of the busbar 10, and placing the magnetic sensor 20 between them, the magnetic field control unit 30 also functions as a magnetic shield against external magnetic noise, thereby improving the detection accuracy of the magnetic sensor 20.

[0047] FIG. 5 is a perspective view schematically illustrating a main portion of a current sensor 2 including multiple detection units 40 according to an embodiment of the present invention. FIG. 6 is a cross-sectional view of the current sensor 2 taken along line AA in FIG. 5 . FIG. 7 is a plan view of the current sensor 2 in FIG. 5 as viewed from the Z2-Z1 direction. As shown in these figures, the current sensor 2 includes multiple detection units 40, each including a bus bar 10, a magnetic sensor 20, and a magnetic field control unit 30. The multiple detection units 40 are arranged so that the first flat plate surfaces 10S of adjacent bus bars 10 face each other. Below, a current sensor 2 including three detection units 40 will be described, but the number of detection units 40 is not limited to three. It is also preferable to provide an individual magnetic field control unit 30 for each detection unit 40, rather than using a single magnetic field control unit 30 for all detection units 40.

[0048] In the following description, when specifying the relative positions of multiple components, the component numbers will be appropriately assigned a to c, and the components will be referred to as bus bars 10a to 10c, first end faces 10aE to 10cE, first flat surface 10aS to 10cS, magnetic sensors 20a to 20c, first sensor elements 21a to 21c, second sensor elements 22a to 22c, magnetic field control units 30a to 30c, second flat surface 30aS to 30cS, second end faces (second ends) 30aE1 to 30cE1, second end faces (second ends) 30aE2 to 30cE2, detection units 40a to 40c, center lines L10aC to L10cC, L20aC to L20cC, and L30aC to L30cC. When describing matters that are common to all components regardless of their relative positions among multiple components, the lowercase letters a to c will not be used and the component will be referred to as, for example, bus bar 10.

[0049] Each of the magnetic sensors 20 is disposed between the first end surface 10E of the bus bar 10 and the second flat surface 30S of the magnetic field control unit 30.

[0050] When the bus bar 10 is viewed from the X direction, the first sensor element 21 and the second sensor element 22 in each magnetic sensor 20 are arranged in positions that are line-symmetrical with respect to the center line L10C that bisects the bus bar 10. Therefore, each magnetic sensor 20a to 20c detects the induced magnetic field of the bus bar 10a to 10c as a difference, thereby improving detection accuracy (see FIG. 2).

[0051] The second flat surface 30S of the magnetic field control unit 30 faces the first end surface 10E of the busbar 10, and the second end surface 30E1 on the Y1 side and the second end surface 30E2 on the Y2 side are arranged in line symmetry with respect to the center line L10C of the busbar 10. The magnetic field control unit 30 also functions as a magnetic shield against external magnetic noise. It is preferable to provide an individual magnetic field control unit 30 for each detection unit 40, rather than connecting the magnetic field control units 30 of each detection unit 40 to form a single magnetic field control unit 30.

[0052] 8 is a schematic diagram showing the influence of magnetic noise Ma from the busbar 10a adjacent to the busbar 10b on the first sensor element 21b and the second sensor element 22b in the magnetic sensor 20b that detects the busbar 10b in the conventional current sensor 3 that does not include the magnetic field control unit 30. In the figure, the magnetic noise from the busbar 10a in the rectangular area N is enlarged and shown in the upper right corner.

[0053] As shown in the figure, the first sensor element 21b and the second sensor element 22b are positioned differently relative to the busbar 10a. Therefore, the magnetic noise Ma1 from the busbar 10a to the first sensor element 21b and the magnetic noise Ma2 from the busbar 10a to the second sensor element 22b have different directions and magnitudes (intensities). That is, as shown in the figure, because the first sensor element 21b is positioned closer to the busbar 10a than the second sensor element 22b, the magnetic noise Ma1 detected by the first sensor element 21b has a smaller angle with the Z axis and a greater intensity than the magnetic noise Ma2 detected by the second sensor element 22b. Therefore, a difference occurs between the Z-direction component (Ma1z) of the magnetic noise Ma1 detected by the first sensor element 21b and the Z-direction component (Ma2z) of the magnetic noise Ma2 detected by the second sensor element 22b.

[0054] As described above, the magnetic noise Ma1 and the magnetic noise Ma2 have different angles and intensities, and therefore have different Z-direction components Ma1z and Ma2z. Therefore, although the influence of the magnetic noise Ma of the busbar 10a can be reduced by using the magnetic sensor 20b to calculate the difference between the output of the first sensor element 21b and the output of the second sensor element 22b, it is not possible to cancel it entirely. In other words, the magnetic sensor 20b outputs the difference Ma1z-Ma2z between the Z-direction components of the magnetic noise due to the difference in position between the first sensor element 21b and the second sensor element 22b relative to the busbar 10a, which reduces detection accuracy.

[0055] 9 is a schematic diagram showing the influence of magnetic noise Ma from the bus bar 10a adjacent to the bus bar 10b on the first sensor element 21b and the second sensor element 22b in the magnetic sensor 20b that detects the bus bar 10b in the current sensor 2 of this embodiment that includes the magnetic field control unit 30. In the figure, the magnetic noise in the rectangular area N is enlarged and shown in the upper right corner.

[0056] The current sensor 2 includes a magnetic field control unit 30b on the Z2 side of the magnetic sensor 20b. This magnetic field control unit 30b can control magnetic noise Ma1 from the busbar 10a to the first sensor element 21b and magnetic noise Ma2 from the busbar 10a to the second sensor element 22b. When the distance P in the Y direction between the busbar 10a and the busbar 10b is within a predetermined range, the magnetic field control unit 30b controls the magnetic noise Ma1 and the magnetic noise Ma2 to make the directions and magnitudes of these magnetic fields approximately the same. Therefore, by calculating the difference between the output of the first sensor element 21b and the second sensor element 22b, it is possible to cancel the influence of the magnetic noise Ma from the busbar 10a on the magnetic sensor 20b and remove the influence of the magnetic noise Ma from the output of the magnetic sensor 20b.

[0057] Fig. 10 is a schematic diagram showing the results of a magnetic noise simulation performed on a conventional current sensor 3 that does not include a magnetic field control unit. Fig. 11 is a schematic diagram showing the results of a magnetic noise simulation performed on a current sensor 2 of this embodiment that includes a magnetic field control unit 30 on the Z2 side of the magnetic sensor 20. Fig. 12 is a schematic diagram showing the results of a magnetic noise simulation performed on a current sensor 4 that includes a magnetic shield S between busbars 10 as a comparative example.

[0058] 10 to 12 show the results of a simulation of the induced magnetic field generated by a current flowing through the busbar 10a, with the same conditions except for the presence or absence of the magnetic field control unit 30 and the magnetic shield S. An isosceles triangle is shown in FIGS. 10 to 12. The isosceles triangle indicates a magnetic field directed from the side opposite the apex angle toward the apex angle. Note that the thin-line rectangles on the Z2 side of the magnetic sensor 20 and the Z1 side of the busbar 10 in FIG. 10 and on the Z1 side of the busbar 10 in FIG. 11 do not represent components, but rather represent spaces where no components are provided.

[0059] 10 to 12 were performed under the following conditions: Shape of the YZ cross section of the busbar 10: Rectangle with a width of 2 mm in the Y direction and a width of 12 mm in the Z direction Shape of the YZ cross section of the magnetic field control unit 30: Rectangle with a width of 5 mm in the Y direction and a width of 0.5 mm in the Z direction Distance D1 in the Z direction between the first end surface 10E of the busbar 10 (see FIG. 6) and the magnetic sensor 20 (center point in the Z direction): 2 mm Distance D2 in the Z direction between the magnetic sensor 20 and the magnetic field control unit 30 (center point in the Z direction): 3 mm

[0060] The effect of the magnetic field control unit 30 provided in the Z2 direction of the magnetic sensor 20 can be seen by comparing the magnetic fields on the Z2 side of the magnetic sensor 20b in Figures 10 and 11. In Figure 10, the magnetic field on the Z2 side of the magnetic sensor 20b is dominated by a magnetic field oriented diagonally downward to the right of the figure, whereas in Figure 11, the magnetic field on the Z2 side of the magnetic sensor 20b is dominated by a magnetic field with a large component oriented in the Z direction. It is presumed that the arrangement of the magnetic field control unit 30 causes the magnetic field to be attracted to the magnetic field control unit 30, increasing the Z direction component, and that the magnetic field reaching the magnetic sensor 20b also has a large Z direction component. This effect is more pronounced near the magnetic sensor 20c, where there is originally a large magnetic field with a large component oriented in the Z direction.

[0061] Next, the effect of the magnetic shield S will be similarly considered by comparing Fig. 10 with Fig. 12. Comparing the magnetic field on the Z2 side of the magnetic sensor 20b in Fig. 10 and Fig. 12, there is a large amount of magnetic field directed diagonally downward to the right in both figures, and no significant difference is observed. Therefore, even if the magnetic shield S is provided between the bus bars 10 as in Fig. 12, the same effect as that of the magnetic field control unit 30 provided in the Z2 direction of the magnetic sensor 20 can not be obtained.

[0062] Figure 13 shows the adjacent influence error that occurs in magnetic sensor 20b, which detects the induced magnetic field from bus bar 10b, due to the influence of magnetic noise from adjacent bus bar 10a when the pitch (distance P, spacing) between adjacent bus bars 10 is changed for current sensor 2, which is an embodiment of the present invention, and current sensors 3 and 4, which are comparison examples of the present invention.

[0063] According to the results shown in the figure, when the distance P (shown in FIGS. 10 to 12), which is the pitch between adjacent bus bars 10, is in the range of 10 to 30 mm, providing a magnetic shield S between bus bars 10 does not suppress adjacent-influence errors, but providing a magnetic field control unit 30 in the Z2 direction of magnetic sensor 20 can suppress adjacent-influence errors that occur in magnetic sensor 20b due to magnetic noise from bus bar 10a. Also, in current sensors 3 and 4, the adjacent-influence errors increase as the pitch between adjacent bus bars becomes smaller, whereas in current sensor 2, there is no significant fluctuation in adjacent-influence errors.

[0064] The distance D1 in the Z direction between the busbar 10 and the magnetic sensor 20 (shown in FIGS. 10 to 12) can be, for example, about 1 to 3 mm, and the distance D2 in the Z direction between the magnetic sensor 20 and the magnetic field control unit 30 can be, for example, about 2 to 4 mm. The distance D2 is preferably greater than the distance D1 and not more than twice the distance D1, i.e., D1<D2≦2D1, and more preferably, not less than 1.2 times the distance D1 and not more than 1.8 times the distance D1, i.e., 1.2D1≦D2≦1.8D1.

[0065] Fig. 14 is a cross-sectional view of a current sensor in which the magnetic field control unit 30 is shifted in the Y1 direction relative to the current sensor 2 shown in Fig. 6. Note that although the current sensor shown in Fig. 14 has a different configuration from the current sensor 2 shown in Fig. 6, for convenience of explanation it is referred to as the current sensor 2. Furthermore, the relative distances in Fig. 14 do not correspond to the actual distances in the simulation.

[0066] The magnetic field control unit 30 of the current sensor 2 is a plate-like body, and a second flat surface 30S, which is the plate surface of the magnetic field control unit 30, faces the first end surface 10E of the busbar 10. The magnetic sensor 20 has a first sensor element 21 that produces a first output and a second sensor element 22 that produces a second output, which are arranged along the Y direction (third direction), and the first sensor element 21 and the second sensor element 22 are provided between the second flat surface 30S of the magnetic field control unit 30 and the first end surface 10E of the busbar 10 in the Z direction.

[0067] In the Y direction, the center line L10C of the bus bar 10 and the center line L20C of the magnetic sensor 20, which are parallel to the Z direction, coincide with each other, and the center line L30C of the magnetic field control unit 30 is shifted toward the Y1 side with respect to the center line L10C of the bus bar 10 and the center line L20C of the magnetic sensor 20. Note that, although an example in which the center line L30C is shifted toward the Y1 side with respect to the center lines L10C and L20C is shown in FIG. 14 , the same effect can be obtained even if the center line L30C is shifted toward the Y2 side. Note that it is desirable that all of the magnetic field control units 30 are shifted toward the same side.

[0068] 15 is a graph showing the results of a simulation of the relationship between the distance D3 (positional deviation) by which the magnetic field control unit 30 is shifted in the Y direction and the adjacent influence error. The graph shows the results of a simulation performed under the same conditions as in FIG. 11, except that the distance D3 was changed. In the graph, for a current sensor 2 in which multiple detection units 40 (40a-40c) are arranged at equal intervals in the Y direction, the pitch between the busbars 10 (10a-10c), i.e., the distance P between the center lines L10C of the busbars 10, is set to 18 mm or 27 mm. When D3 = 0 mm, the current sensor 2 has the configuration shown in FIG. 6.

[0069] In this simulation, the case where the center line L30C is shifted in the Y2 direction is defined as a shift in the positive direction, and the case where the center line L30C is shifted in the Y1 direction is defined as a shift in the negative direction. Note that the value of the adjacent influence error in the simulation result of Fig. 15 differs from the value in the simulation result of Fig. 13 because the simulation was performed on magnetic sensors 20 with different designs.

[0070] As shown in Figure 15, it was found that the adjacent influence error can be reduced by arranging the center line L30C of the magnetic field control unit 30 in the Y direction so that it is shifted to either the Y2 direction or the Y1 direction relative to the center line L10C and center line L20C of the bus bar 10 and magnetic sensor 20.

[0071] When the distance P between adjacent bus bars 10 is 18 to 27 mm, setting the distance D3 between the center line L30C of the magnetic field control unit 30 and the center lines L10C and L20C of the bus bars 10 and magnetic sensor 20 to approximately 0.5 to 2.5 mm reduces magnetic noise from the bus bars 10 of the adjacent detection unit 40 to the magnetic sensor 20 compared to when the center lines L30C and L10C and L20C are aligned (D3 = 0 mm). Furthermore, by comparing the cases where the distance P between adjacent bus bars 10 is 18 mm and 27 mm, it was found that the smaller the distance P, the easier it is to obtain the effect of the configuration shown in FIG. 14 . This is presumably because the closer the distance P, the more likely adjacent bus bars 10 are to affect each other.

[0072] 16 is an enlarged cross-sectional view of a portion of the detection unit 40 in the current sensor 2 of FIG. 14. As shown in the figure, when viewed in the Z direction (second direction), the magnetic field control unit 30 has second end faces (second ends) 30E1, 30E2 on both sides in the Y direction (third direction). The second end face 30E2 on the Y2 side (one side) is located near the first flat plate surface 10S2 on the Y2 side of the busbar 10, and the other second end face 30E1 is located at a position that does not overlap with the busbar 10. Therefore, when viewed in the Z direction (second direction), the distance G1 in the Y direction between the second end face 30E1 and the first flat plate surface 10S1 on the Y1 side is greater than the distance G2 in the Y direction between the second end face 30E2 and the first flat plate surface 10S2 on the Y2 side.

[0073] In the figure, a solid line indicates an overlapping state between the second end surface 30E2 of the magnetic field control unit 30 and the first flat surface 10S2 on the Y2 side of the busbar 10. Alternatively, as indicated by a two-dot chain line, the magnetic field control unit 30 may be disposed at a position where the second end surface 30E2 does not overlap with the first flat surface 10S2 on the Y2 side closer to the second end surface 30E2 of the busbar 10. In this case, from the viewpoint of allowing the magnetic field control unit 30 to function as a magnetic shield against external magnetic noise, it is preferable that the distance G2 in the Y direction between the second end surface 30E2 and the first flat surface 10S2 on the Y2 side be 1 mm or less.

[0074] For example, when the widths in the Y direction of the busbar 10 and the magnetic field control unit are 2 mm and 5 mm, respectively, the magnetic field control unit 30 is disposed in a position where, when viewed in the Z direction, the second end face 30E2 overlaps with the busbar 10 and the second end face 30E1 does not overlap with the busbar 10 when the second end face 30E2 and the first flat plate surface 10S2 overlap, and when the second end face 30E2 is shifted toward the Y1 side and the distance G is 1 mm or less. When the second end face 30E2 is shifted toward the Y2 side and the distance G is 1 mm or less, the magnetic field control unit 30 is disposed in a position where the second end face 30E2 and the second end face 30E1 do not overlap with the busbar 10.

[0075] When the Y-direction width of the busbar 10 is approximately 1 to 3 mm and the Y-direction width of the magnetic field control unit 30 is approximately 4 to 6 mm, it is preferable that the distance G1 between the second end face 30E1 and the first flat surface 10S1 is at least twice the distance G2 between the second end face 30E2 and the first flat surface 10S2, i.e., 2G2≦G1, and it is more preferable that it is at least four times the distance G2, i.e., 4G2≦G1.

[0076] 17 is a cross-sectional view showing an example of a more specific embodiment of the current sensor 2. The figure shows an embodiment in which the detection unit 40 is formed integrally with the case 50, the cover 35, etc. The current sensor 2 has a substrate 25 on which the magnetic sensor 20 is mounted, a case 50 that integrally holds the bus bar 10 and has a storage section 51 capable of storing the substrate 25, and a cover 35 that integrally holds the magnetic field control section 30. The substrate 25 is fixed in the storage section 51 by crimping fixing bosses 54 provided in the storage section 51, and the cover 35 is disposed so as to cover the storage section 51 and is fixed to the case 50 by screws 52.

[0077] In the embodiment shown in the figure, the substrate 25 on which the magnetic sensor 20 is mounted is placed in the storage section 51 of the case 50, so that the magnetic sensor 20 is positioned opposite the busbar 10. Furthermore, the cover 35 that integrally holds the magnetic field control section 30 is placed on the case 50 so as to cover the storage section 51 of the case 50, so that the magnetic field control section 30 is positioned opposite the busbar 10. By placing the case 50, the substrate 25, and the cover 35 in this manner, the magnetic field control section 30 is placed on the opposite side of the busbar 10 with respect to the magnetic sensor 20, and a detection unit 40 for three phases is configured.

[0078] 18 is a cross-sectional view showing a modified example (part 1) of a more specific aspect of the current sensor 2. The substrate 25 of the current sensor 2 shown in the figure has a first insertion hole 26 through which a screw 52 can be inserted, and is sandwiched between a case 50 and a cover 35 with the magnetic sensor 20 disposed in a storage section 51. The cover 35 also has a second insertion hole 36 through which the screw 52 can be inserted, and the case 50 has a screw hole 53 that can be threaded with the screw 52.

[0079] The board 25 and the cover 35 are fixed together by inserting screws 52 into the first insertion holes 26 and the second insertion holes 36, and the screws 52 are threaded into threaded holes 53 of the case 50. Note that a thread that can be threaded onto the screw 52 may be provided on the inner surface of one or both of the first insertion holes 26 and the second insertion holes 36.

[0080] 19 is a cross-sectional view showing a second modified example of a more specific aspect of the current sensor 2. In the current sensor 2 shown in the figure, the magnetic sensor 20 is mounted on one surface 25S1 on the Z1 side of the substrate 25, and the magnetic field control unit 30 is fixed to the other surface 25S2 on the Z2 side. The substrate 25 is fixed to the case 50 such that one surface 25S1 faces the case 50, which integrally holds the busbar 10. There are no particular limitations on the method for fixing the substrate 25 to the case 50, but the figure shows a mode in which the substrate 25 is fixed by crimping a boss 55.

[0081] Figure 20 is a cross-sectional view showing a more specific modified example (part 3) of current sensor 2. The modified example shown in this figure differs from the modified example shown in Figure 19 in that screws 52 are used instead of bosses 55 as a means for fixing substrate 25 to case 50. As in the modified examples shown in Figures 19 and 20, by providing magnetic field control unit 30 on the other surface 25S2 of substrate 25, the size of current sensor 2 as a whole in the Z direction can be reduced, which is advantageous for miniaturization.

[0082] The embodiments disclosed in this specification are illustrative in all respects and are not limited to these embodiments. The scope of the present invention is defined by the claims rather than by the description of the above-described embodiments alone, and is intended to include all modifications within the meaning and scope of the claims.

[0083] The present invention is useful as a current sensor for measuring a current to be measured flowing through equipment, for example, in order to control a power supply system of a vehicle or the like equipped with various equipment.

[0084] 1: Current sensor 2: Current sensor 3: Current sensor 4: Current sensor 10, 10a to 10c: Bus bar 10E, 10aE to 10cE: First end face (first end) 10S, 10S1, 10S2, 10aS to 10cS: First flat plate surface 20, 20a to 20c: Magnetic sensor 21, 21a to 21c: First sensor element 22, 22a to 22c: Second sensor element 25: Substrate 25S1: Surface 25S2: Surface 26: First insertion hole 30, 30a to 30c: Magnetic field control unit 30E, 30E1, 30aE1 to 30cE1: Second end face (second end) 30E2, 30aE2 to 30cE2: Second end face (second end) 30S, 30aS to 30cS: Second flat surface 35: Cover 36: Second insertion hole 40, 40a to 40c: Detection unit 50: Case 51: Storage section 52: Screw 53: Screw hole 54: Boss 55: Boss D1: Distance D2: Distance D3: Distance G1: Distance G2: Distance P: Distance L10C, L10aC to L10cC, L20aC to L20cC, L30aC to L30cC: Center line L10E: Normal line L10S: Normal line L20C: Center line L30C: Center line L30E: Normal line L30S: Normal line M1: Induction magnetic field Ma: Magnetic noise Ma1: Magnetic noise Ma1z: Z-direction component Ma2: Magnetic noise Ma2z: Z-direction component N: Area S: Magnetic shield

Claims

1. A current sensor comprising: a plate-shaped bus bar extending in a first direction; a magnetic sensor capable of detecting an induced magnetic field generated when a current to be measured flows through the bus bar; and a magnetic field control unit that controls the magnetic field detected by the magnetic sensor, wherein the bus bar has: a first end in a second direction perpendicular to the first direction; and a first flat surface that is a plate surface and has a third direction perpendicular to the first and second directions as its normal direction; the magnetic sensor is disposed opposite the first end, has a magnetic sensitivity direction in the second direction, and is capable of outputting the difference between a first output in which the component of the induced magnetic field facing in one of the second directions is the positive component, and a second output in which the component of the induced magnetic field facing in the other of the second directions is the positive component.

2. The current sensor according to claim 1, wherein the magnetic field control unit is provided on the opposite side of the magnetic sensor from the first end of the bus bar in the second direction.

3. A current sensor as described in claim 1, comprising a plurality of detection units each including the magnetic field control unit, the bus bar, and the magnetic sensor, and the plurality of detection units are arranged so that the first flat surface of adjacent bus bars faces each other.

4. A current sensor as described in claim 1, wherein the magnetic field control unit is a plate-like body and has a second flat surface that is a plate surface normal to the second direction, the second flat surface of the magnetic field control unit faces the first end of the bus bar, and the magnetic sensor is provided between the second flat surface and the first end in the second direction.

5. A current sensor as described in claim 1, wherein the magnetic sensor has a first sensor element that produces the first output and a second sensor element that produces the second output, and the first sensor element and the second sensor element are arranged along the third direction.

6. The current sensor according to claim 5, wherein the first sensor element and the second sensor element are arranged at positions that are line-symmetrical with respect to the center line of the bus bar in the third direction.

7. The current sensor according to claim 5, wherein the first sensor element and the second sensor element are Hall elements.

8. The current sensor according to claim 5, wherein the first sensor element and the second sensor element are housed within one magnetic sensor.

9. The current sensor of claim 3, wherein the detection unit has the magnetic field control unit as a plate-like body, a second flat surface that is the plate surface of the magnetic field control unit facing the first end of the bus bar, the magnetic sensor having a first sensor element that provides the first output and a second sensor element that provides the second output, which are arranged along the third direction, the first sensor element and the second sensor element being arranged between the second flat surface of the magnetic field control unit and the first end of the bus bar in the second direction, the center line of the bus bar and the center line of the magnetic sensor coinciding in the third direction, and the center line of the magnetic field control unit being shifted to either side of the third direction with respect to the center lines of the bus bar and the magnetic sensor.

10. A current sensor as described in claim 9, wherein a plurality of the detection units are arranged at equal intervals in the third direction, the distance between adjacent bus bars in the third direction is 18 to 27 mm, the center lines of the bus bars and the magnetic sensor coincide, and the distance between the center lines of the bus bars and the magnetic sensor and the center line of the magnetic field control unit that controls the magnetic field detected by the magnetic sensor is 0.5 to 2.5 mm.

11. The current sensor according to claim 10, wherein the magnetic field control unit is arranged at a position such that, when viewed in the second direction, the distance in the third direction between one of the second ends on both sides in the third direction and the first flat surface of the bus bar closer to the one second end is 1 mm or less, and the other second end does not overlap the bus bar.

12. A current sensor as described in claim 10, wherein the magnetic field control unit is arranged at a position such that, when viewed in the second direction, one of the second ends on both sides in the third direction overlaps with the bus bar, and the other second end does not overlap with the bus bar.

13. A current sensor as described in claim 1, comprising: a substrate on which the magnetic sensor is mounted; a case that holds the bus bar integrally and has a storage section that can store the substrate; and a cover that holds the magnetic field control section integrally, wherein the substrate is fixed within the storage section and the cover is positioned to cover the storage section.

14. A current sensor as described in claim 1, comprising: a substrate having a first insertion hole through which a screw can be inserted and on which the magnetic sensor is mounted; a case that holds the bus bar integrally and has a storage section in which the magnetic sensor can be housed; and a cover that holds the magnetic field control section integrally, wherein the substrate is sandwiched between the case and the cover with the magnetic sensor disposed in the storage section, the cover having a second insertion hole through which the screw can be inserted, and the case having a screw hole that can be threaded with the screw, and the case, substrate, and cover are fixed by the screw that is inserted into the first insertion hole and the second insertion hole and threaded into the screw hole.

15. A current sensor as claimed in claim 1, comprising: a substrate having the magnetic sensor mounted on one surface and the magnetic field control unit fixed to the other surface; and a case that integrally holds the bus bar, wherein the substrate is fixed to the case so that the one surface of the substrate faces the case.

16. The current sensor according to claim 14, wherein the substrate is fixed to the case by screws or caulking.

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