JP2014006181A - Current sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a small-sized current sensor with excellent detection accuracy, capable of coping with heavy-current.SOLUTION: A current sensor 100 includes: a core 20 made of a magnetic substance having a groove part 21 surrounding a bus bar 10 in which measurement target current flows; and a detection element 30 arranged closer to an opening 26 than the bus bar 10 in the groove part 21 with a detection direction thereof aligned with an interval direction of the opening 26, and configured to detect the intensity of a magnetic field. The groove part 21 is configured to make a width of the opening gradually wider from a depth side of the opening at least up to an end on a side of the opening 26 of the bus bar 10, and a width of the opening at a location where the detection element 30 is installed is wider than a width of the opening at the end thereof.

Description

  The present invention relates to a current sensor that measures a current flowing through a conductor.

  Despite the fact that the current for driving the motors of hybrid vehicles and electric vehicles, and the current flowing through the motors of machine tools, etc. are very large, current sensors that detect such large currents must be downsized and simplified. It has been. If the current sensor is miniaturized to satisfy such a requirement, various sensor performances are deteriorated. For this reason, it is necessary to take measures against the cause.

  As this type of current sensor, a sensor using a magnetic core is used. In such a current sensor, when a large current is passed, the magnetic flux density inside the magnetic material approaches the saturation magnetic flux density, so that the linearity of the magnetic properties of the magnetic material with respect to the current to be measured is lost. As a result, when the current increases, the detection accuracy of the current sensor deteriorates. In addition, the detection accuracy of such a current sensor also deteriorates due to the disturbance magnetic field picked up by the detection element and the hysteresis of the magnetic material due to the residual magnetism after flowing the current to be measured.

  If the cross-sectional area of the magnetic material is reduced by downsizing the current sensor, magnetic saturation is likely to occur, and hysteresis characteristics are also deteriorated. Further, in a three-phase motor or the like, since the distance between adjacent bus bars of other phases becomes closer due to the miniaturization, the influence of the magnetic field due to the other-phase current is increased. Therefore, measures as described below have been studied (for example, Patent Documents 1-3).

  The current measuring device described in Patent Document 1 includes a magnetic core, first and second magnetic sensors, and a current detection circuit. The magnetic core is disposed so as to surround a current path through which a current flows, and includes a plurality of gaps. The first and second magnetic sensors are disposed in different gaps. When detecting the current flowing through the current path, the current detection circuit corrects the residual magnetic flux density of the magnetic core from the output of the first magnetic sensor and the output of the second magnetic sensor, and removes the error due to hysteresis.

  The current sensor described in Patent Document 2 includes a magnetic flux collecting core, a magnetic detection element, and a shield core. The magnetic flux collecting core is formed by a core pair provided so as to sandwich the detected current path in the central space. The magnetic detection element is provided in the gap of the core pair and detects the magnetism collected by the magnetic collecting core. The shield core is provided closer to the core pair than the gap distance between the core pairs and penetrating the detected current path.

  A current sensor described in Patent Document 3 includes a conductor through which a current to be measured flows, an annular magnetic shield plate that surrounds the conductor and has a gap, and a magnetoelectric element that is disposed inside the annular magnetic shield plate. And a conversion element. The magnetoelectric transducer detects the magnetic flux density of the magnetic field due to the current. The magnetoelectric conversion element is disposed between the gap of the annular magnetic shield plate and the conductor in the vicinity of a position where the magnetic flux density of the magnetic field generated according to the current flowing through the conductor is minimized.

JP 2006-71457 A JP 2007-114112 A JP 2008-151743 A

  In the technique described in Patent Document 1, the magnetic core forms two gaps by facing two substantially U-shaped magnetic bodies to each other. In the case of such a configuration, for example, when an external magnetic field in the direction from one of the facing magnetic bodies to the other is received, the external magnetic field collected by the magnetic body reaches the first and second magnetic sensors, and the original measurement is performed. It will have an effect on it. Moreover, in order to ensure the insulation distance of two magnetic sensors and a to-be-measured electric current path, it enlarges compared with the case where one magnetic sensor is used.

  In the technique described in Patent Document 2, since the shielding core passes through the detected current path, the cross-sectional area of the detected current path at the penetration portion is reduced. For this reason, since it is necessary to enlarge the cross-sectional area of the to-be-detected electric current path of the said penetration location according to the flowing electric current, the magnetism collecting core surrounding the circumference will also become large. Further, when the magnetic detection elements are respectively provided in the two gaps of the core pair, it is necessary to separate them by a predetermined distance in order to ensure the insulation between the two magnetic detection elements and the detected current path. Therefore, the size is further increased.

  In the technique described in Patent Document 3, a magnetoelectric conversion element is disposed outside the gap of the magnetic shield plate to reduce the influence of magnetic saturation of the magnetic shield plate. In order to reduce the influence of magnetic saturation so that it can be ignored, the magnetic shield plate needs to be largely separated from the magnetoelectric conversion element, so that the size is increased.

  In view of the above problems, an object of the present invention is to provide a small-sized current sensor with high detection accuracy that can handle a large current.

In order to achieve the above object, the characteristic configuration of the current sensor according to the present invention is as follows:
A magnetic core having a groove surrounding the bus bar through which the current to be measured flows;
A detection element that is disposed closer to the opening than the bus bar in the groove so that the detection direction is along the interval direction of the opening, and detects the strength of the magnetic field,
The groove is configured such that the opening width gradually increases from the opening back side to the position of the end of the bus bar on the opening side, and the opening width at the position where the detection element is disposed is It is in the point which is comprised so that it may become the opening width in the position of an edge part.

  With such a characteristic configuration, it is possible to reduce the influence of magnetic saturation and hysteresis of the core as will be described below, so that it is possible to suppress deterioration in detection accuracy of the current sensor.

  Since the inner wall surface of the groove portion of the core can be formed in an inclined shape, the magnetic path length of the magnetic circuit formed by the detection element and the core can be shortened while widening the opening width near the detection element, The permeance coefficient of the core is reduced (that is, the demagnetizing field is increased), and the hysteresis can be reduced.

  Further, since the opening width of the core is large, the magnetic flux density gradient near the detection element can be made gentle. For this reason, it is possible to prevent deterioration in accuracy due to position fluctuations of the detection element, and it is possible to configure a small-sized current sensor with high detection accuracy even when the assembly accuracy is low.

  In addition, it is preferable that the groove has a narrow portion that narrows the opening width on the side of the opening from the detection element.

  Thus, by narrowing the opening width of the opening by the narrow portion, it is possible to prevent the disturbance magnetic field from reaching the detection element.

  Further, it is preferable that the narrow width portion has a narrower opening width toward the opening.

  With such a configuration, since the cross-sectional area perpendicular to the interval direction of the openings in the narrow portion decreases as the opening width becomes narrow, the magnetoresistance of the narrow portion can be increased. For this reason, it becomes possible to measure a larger current while preventing the influence of the disturbance magnetic field.

  In addition, it is preferable that a pair of surfaces facing the detection element along the interval direction among the inner wall surfaces of the groove portion are configured in parallel to each other.

  With such a configuration, the magnetic flux density gradient in the interval direction in the vicinity of the detection element can be made gentle. Therefore, it is possible to suppress deterioration in accuracy due to the position variation of the detection element.

  Further, it is preferable that the core is configured such that outer wall surfaces on the outer side in the interval direction in the groove portion are configured in parallel to each other.

  For example, when a plurality of bus bars are close to each other, the size that the core can take is limited by the adjacent bus bar and the core. According to this configuration, since the size of the core can be reduced, the cross-sectional area of the core can be ensured even when the space for disposing the core is limited.

It is the perspective view which showed typically the current sensor which concerns on 1st Embodiment. It is the front view which showed typically the current sensor which concerns on 1st Embodiment. It is the front view which showed typically the current sensor which concerns on 2nd Embodiment. It is the front view which showed typically the current sensor which concerns on 3rd Embodiment. It is the front view which showed typically the current sensor which concerns on 4th Embodiment. It is the front view which showed typically the current sensor which concerns on other embodiment. It is the front view which showed typically the current sensor which concerns on other embodiment.

1. First Embodiment Hereinafter, embodiments of the present invention will be described in detail. The current sensor 100 according to the present invention is configured to be able to measure a current to be measured flowing through a conductor. Here, when a current flows through a conductor, a magnetic field is generated with the conductor as an axis according to the magnitude of the current (Amper's right-hand rule). The current sensor 100 detects the strength of such a magnetic field, and measures the current (current value) flowing through the conductor based on the detected strength of the magnetic field.

  FIG. 1 is a perspective view of a current sensor 100 according to the present embodiment. FIG. 1 shows a bus bar 10 made of a flat conductor. The direction in which the bus bar 10 extends is defined as an extending direction A, the thickness direction of the bus bar 10 is defined as B, and the width direction of the bus bar 10 is defined as C. To do. FIG. 2 schematically shows the current sensor 100 as viewed in the extending direction A of the bus bar 10. However, the lead wires included in the detection element 30 are omitted. Hereinafter, description will be made with reference to FIGS. 1 and 2.

  The current sensor 100 includes a bus bar 10, a core 20, and a detection element 30. The bus bar 10 is composed of a flat conductor as described above. For example, the bus bar 10 is used to connect a three-phase motor (not shown) and an inverter that energizes the three-phase motor. A current to be measured flows through the bus bar 10 along the direction A and is measured by the current sensor 100.

  The core 20 according to the present embodiment is formed by laminating flat plates made of a metal magnetic body having a V-shaped groove 21. The metal magnetic body is a soft magnetic metal and corresponds to an electromagnetic steel plate (silicon steel plate), permalloy, permendur, and the like. The laminated surface of the core 20 is a surface parallel to the BC plane in FIGS. 1 and 2.

  The core 20 is configured such that the groove portion 21 forms a V shape when viewed in the direction A in FIGS. 1 and 2. The V-shape is not limited to those in which the groove bottom portion 22 is formed at an acute angle. As shown in FIGS. 1 and 2, the groove bottom portion 22 has an arc shape or a linear portion on a part of the arc shape. What is formed in the shape which has is also included. In such a core 20, the surface of the bus bar 10 parallel to the AC surface on the groove bottom portion 22 side coincides with the depth direction (C direction) of the groove portion 21, and the stacking direction (A direction) of the cores 20. The current to be measured is inserted in the same flow direction. In this way, the bus bar 10 is surrounded by the groove 21. The bus bar 10 inserted through the core 20 is configured to have at least an inner wall surface 24 of the core 20 and a gap. Thereby, the core 20 and the bus bar 10 can be insulated.

  The detection element 30 is disposed closer to the opening 26 than the bus bar 10 in the groove 21 so that the detection direction is along the interval direction (B direction) of the opening 26. The opening 26 is an opening end of the groove 21. For this reason, the detection element 30 is disposed closer to the opening end of the groove 21 than the bus bar 10. Further, a gap is formed between the detection element 30 disposed in the groove portion 21 of the core 20 and the bus bar 10. As a result, the detection element 30 and the bus bar 10 can be insulated. Here, the magnetic field generated according to the current flowing through the bus bar 10 is collected in the core 20. The collected magnetic field becomes a magnetic field in the interval direction (B direction) of the opening 26 of the core 20 in the vicinity where the detection element 30 is disposed.

  The detection element 30 is arranged with the detection direction coinciding with the B direction. Therefore, it is possible to effectively detect the strength of the magnetic field formed by the current to be measured flowing through the bus bar 10.

  The core 20 is configured such that the opening width of the groove portion 21 gradually increases from the depth of the opening to the position of at least the end portion on the opening portion 26 side of the bus bar 10. The rear side of the opening is the groove bottom 22 side when the groove 21 is viewed from the opening 26 side. The end of the bus bar 10 on the opening 26 side is a part closest to the opening 26 among the constituent parts of the bus bar 10. In the present embodiment, the upper end surface 11 of the bus bar 10 indicated by the symbol U in FIG. The opening width corresponds to the width in the B direction in which the groove 21 is open. In FIG. 2, the opening width in the upper end surface 11 is indicated by the reference symbol U1. As described above, the core 20 is configured such that the width of the groove portion 21 gradually increases from the groove bottom portion 22 side to at least the position of the upper end surface 11 of the bus bar 10 (the position of U). As described above, the opening width is increased from the back side of the opening of the core 20 toward the opening 26, thereby increasing the magnetic resistance in the opening 26 and reducing the generated magnetic flux. Therefore, the magnetic flux density inside the core can be reduced without increasing the core.

  Furthermore, the core 20 according to the present embodiment is configured such that outer wall surfaces 23 on the outer side in the interval direction in the groove portion 21 are parallel to each other. The outer side in the interval direction is the outer side of the core 20 in the direction orthogonal to the B direction. Thereby, for example, even when a plurality of cores 20 are arranged, the interval between two adjacent cores 20 can be minimized. Therefore, the current sensor 100 can be reduced in size.

  As a result, in the constituent parts of the core 20, the side wall 41 is located near the back of the opening (groove bottom 22) rather than the cross-sectional area when the side wall 41 near the opening 26 is cut perpendicular to the C direction. The cross-sectional area when cut perpendicular to the direction can be made wider. Here, in the magnetic body having such a shape, the magnetic flux in the core increases as the position is closer to the groove bottom 22. Further, the larger the cross-sectional area when the side wall 41 is cut perpendicular to the C direction on the opening 26 side, the higher the magnetic flux density of the cross section obtained by cutting the side wall 41 perpendicular to the C direction on the groove bottom 22 side. Therefore, it is possible to reduce the size by reducing the cross-sectional area of the side wall 41 on the opening 26 side, and to keep the magnetic flux density in the cross section of the side wall 41 on the groove bottom 22 side low, thereby suppressing magnetic saturation.

  Further, the bottom part 42 is configured so that the cross-sectional area when the bottom part 42 is cut perpendicular to the B direction is larger than the cross-sectional area when the side wall part 41 is cut perpendicular to the C direction in the vicinity of the groove bottom part 22. The magnetic flux density of the cross section of 42 can be kept low and magnetic saturation can be suppressed.

  Further, as shown in FIG. 2, the groove 21 has an opening width V1 at a position where the detection element 30 is disposed at an opening width U1 or more at the position of the end portion (upper end surface 11) on the opening portion 26 side of the bus bar 10. It is comprised so that it may become. The position where the detection element 30 is disposed corresponds to the position denoted by the reference symbol V. Moreover, the position of the edge part by the side of the opening part 26 of the bus-bar 10 is a position of U as mentioned above. Therefore, the groove 21 is configured such that the opening width V1 at the position V is equal to or larger than the opening width U1 at the position U. Of course, it is naturally possible to configure the opening width V1 equal to the opening width U1.

2. Second Embodiment Next, a second embodiment according to the present invention will be described. In the first embodiment, it has been described that the groove portion 21 is configured so that the opening width gradually increases from the groove bottom portion 22 to the opening portion 26. The groove portion 21 according to the present embodiment is different from the first embodiment in that the opening width is not gradually increased from the groove bottom portion 22 to the opening portion 26. Since the other points are the same as those in the first embodiment, different points will be mainly described below.

  FIG. 3 shows a front view of the current sensor 100 according to the present embodiment. As in the first embodiment, the detection element 30 according to the present embodiment is disposed on the opening portion 26 side of the bus bar 10 in the groove portion 21 of the core 20. Moreover, the groove part 21 is comprised so that opening width may become large gradually from the opening back side to the position of the edge part at the side of the opening part 26 of the bus-bar 10 similarly to 1st Embodiment. Here, in this embodiment, a pair of surface 25 which opposes the detection element 30 along the space | interval direction among the inner wall surfaces 24 of the groove part 21 is comprised in parallel with each other.

  The inner wall surface 24 of the groove portion 21 is all surfaces constituting the groove portion 21. That is, all the surfaces from the groove bottom 22 to the opening 26 correspond. To face the detection element 30 along the interval direction means to face the direction B. Therefore, the pair of surfaces 25 corresponds to the inner wall surface 24 of the groove portion 21 that sandwiches the detection element 30 along the B direction. A pair of surfaces 25 which are a part of such an inner wall surface 24 are provided in parallel so as to be orthogonal to the B direction. Therefore, the opening width by the pair of surfaces 25 is a constant value.

  In the present embodiment, the groove portion 21 is configured such that the inner wall surfaces 24 closer to the opening 26 than the detection element 30 are parallel to each other. Of course, only the pair of surfaces 25 may be configured to be parallel to each other, and the opening width on the opening 26 side of the detection element 30 may be configured to be wider than the opening width of the pair of surfaces 25. is there.

3. Third Embodiment Next, a third embodiment according to the present invention will be described. In the first embodiment, it has been described that the groove portion 21 is configured so that the opening width gradually increases from the groove bottom portion 22 to the opening portion 26. The groove portion 21 according to the present embodiment is different from the first embodiment in that the opening width configured to gradually widen from the groove bottom portion 22 is configured to gradually narrow on the opening portion 26 side. Since the other points are the same as those in the first embodiment, different points will be mainly described below.

  FIG. 4 shows a front view of the current sensor 100 according to the present embodiment. As in the first embodiment, the detection element 30 according to the present embodiment is disposed on the opening portion 26 side of the bus bar 10 in the groove portion 21 of the core 20. Further, the groove portion 21 is formed with a narrow portion 44 that narrows the opening width on the side of the opening portion 26 with respect to the detection element 30. In the present embodiment, the narrow portion 44 is configured to narrow the opening width toward the opening 26 side. That is, the cross-sectional area perpendicular to the interval direction of the openings 26 in the narrow portion 44 is configured to decrease as the opening width becomes narrower.

  As shown in FIG. 4, the narrow portion 44 is provided so as to protrude in the B direction at the opening 26. In the present embodiment, the narrow portion 44 is attached to the inner wall surface 24 as a triangular convex portion. As shown in FIG. 4, the inflection portion 29 with the opening width gradually narrowing on the inner wall surface 24 is configured to be positioned closer to the opening portion 26 than the detection element 30.

4). Fourth Embodiment Next, a fourth embodiment according to the present invention will be described. In the third embodiment, it has been described that the groove portion 21 is configured so that the opening width gradually increases from the groove bottom portion 22 to the inflection portion 29. The groove portion 21 according to the present embodiment is different from the third embodiment in that a pair of surfaces 25 facing the detection element 30 are formed. Since the other points are the same as those of the third embodiment, the following description will focus on different points.

  FIG. 5 shows a front view of the current sensor 100 according to the present embodiment. As in the third embodiment, the detection element 30 according to the present embodiment is disposed on the opening portion 26 side of the bus bar 10 in the groove portion 21 of the core 20. Moreover, the groove part 21 is comprised so that opening width may become large gradually from the opening back side to the position of the edge part at the side of the opening part 26 of the bus-bar 10 similarly to 1st Embodiment. In the groove portion 21, a pair of surfaces 25 facing the detection element 30 along the interval direction (B direction) of the inner wall surface 24 of the groove portion 21 are configured in parallel to each other. Since the pair of surfaces 25 are the same as those in the second embodiment, description thereof is omitted.

5. As described above, according to the current sensor 100, the magnetic flux density in the vicinity of the groove bottom portion 22 is reduced by increasing the cross-sectional area of the core 20 from the vicinity of the opening portion 26 of the core 20 toward the back of the opening. be able to. In addition, since the opening width increases toward the opening 26 of the core 20, the magnetic resistance of the opening 26 increases and the generated magnetic flux decreases. Therefore, the magnetic flux density inside the core 20 can be reduced without increasing the size of the core 20, and even if a large current is passed, it can be detected accurately.

  Further, since the inner wall surface 24 of the groove portion 21 of the core 20 can be formed in an inclined shape, the magnetic path of the magnetic circuit formed by the detection element 30 and the core 20 while widening the opening width in the vicinity of the detection element 30. The length can be shortened, the permeance coefficient of the core 20 is reduced (that is, the demagnetizing field is increased), the hysteresis can be reduced, and the accuracy of the current sensor 100 can be improved.

  Furthermore, since the opening width of the core 20 is large, the magnetic flux density gradient in the vicinity of the detection element 30 can be made gentle. For this reason, it is possible to prevent the accuracy from being deteriorated due to the position variation of the detection element 30, and it is possible to configure the current sensor 100 with high detection accuracy.

6). Other Embodiments In the above embodiment, the core 20 has been described on the assumption that the outer wall surfaces 23 on the outer side in the interval direction in the groove portion 21 are configured in parallel to each other. However, the scope of application of the present invention is not limited to this. As shown in FIG. 6, it is naturally possible to configure the angle θ formed by the outer wall surface 23 of the core 20 and the bottom surface 43 of the bottom portion 42 as viewed in the A direction to be an acute angle. Alternatively, as shown in FIG. 7, if the angle θ formed by the outer wall surface 23 of the core 20 and the bottom surface 43 of the bottom portion 42 in the A direction view is smaller than the angle η formed by the inner wall surface 24 and the bottom surface 43, It is also possible to configure the core 20 so that the angle θ is an obtuse angle. Even in such a case, the cross-sectional area of the side wall 41 of the core 20 can be configured so as to increase as the cross-sectional area approaches the bottom 42 from the opening 26. Similar effects can be achieved.

  In the said embodiment, the narrow part 44 demonstrated as having comprised the triangular shape which protrudes in a space | interval direction. However, the scope of application of the present invention is not limited to this. Of course, the narrow portion 44 may be formed of an arcuate portion.

  In the embodiment described above, the groove portion 21 has been described as being formed in a V shape when viewed in the A direction. However, the scope of application of the present invention is not limited to this. The opening width of the groove portion 21 may be formed in an arc shape that gradually spreads from the groove bottom portion 22 in the A direction view. In addition, if the opening width gradually increases, the inner wall surface 24 can naturally be configured in a corrugated shape.

  In the said embodiment, it illustrated in figure so that the narrow part 44 was provided in both the side wall parts 41 which mutually oppose. However, the scope of application of the present invention is not limited to this. Of course, the narrow portion 44 may be provided only on one of the side wall portions 41 facing each other.

  The present invention can be used for a current sensor for measuring a current flowing through a conductor.

DESCRIPTION OF SYMBOLS 10: Bus bar 20: Core 21: Groove part 23: Outer wall surface 24: Inner wall surface 25: A pair of surface 26: Opening part 30: Detection element 44: Narrow part 100: Current sensor

Claims (5)

A magnetic core having a groove surrounding the bus bar through which the current to be measured flows;
A detection element that is disposed closer to the opening than the bus bar in the groove so that the detection direction is along the interval direction of the opening, and detects the strength of the magnetic field,
The groove is configured such that the opening width gradually increases from the opening back side to the position of the end of the bus bar on the opening side, and the opening width at the position where the detection element is disposed is A current sensor configured to be equal to or larger than the opening width at the end position.   2. The current sensor according to claim 1, wherein the groove portion is formed with a narrow portion that narrows an opening width closer to the opening portion than the detection element.   The current sensor according to claim 2, wherein the narrow portion narrows the opening width toward a side of the opening.   4. The current sensor according to claim 1, wherein, of the inner wall surfaces of the groove portion, a pair of surfaces facing the detection element along the interval direction are configured in parallel with each other.   The current sensor according to any one of claims 1 to 4, wherein the core is configured such that outer wall surfaces on the outer side in the interval direction in the groove portion are parallel to each other.

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