Electric current sensor

Abstract

This electric current sensor 10 which includes a bus-bar that is effective for cost reduction and weight reduction, comprises a bus-bar 1 through which electric current to be measured flows, and a magnetism detection unit 2 that is disposed opposing the bus-bar 1 to detect the magnetic field generated from the bus-bar 1. The bus-bar 1 is made of a laminated material in which a first metallic material 3 and a second metallic material 4, which are metallic materials of different kinds, are layered. The first metallic material 3 has a higher density than the second metallic material 4, and has a smaller electric resistance than the second metallic material 4. The magnetism detection unit 2 is disposed opposing a surface 3S of the bus-bar 1, which surface is made of the first metallic material 3.

Description

Current Sensor

[0001] The present invention relates to a current sensor that detects a magnetic field generated by a current to be measured flowing through a bus bar and measures the current value of the current to be measured from the detected magnetic field.

[0002] In recent years, current sensors have been used to control and monitor various devices by attaching them to measure the current flowing through them. One known current sensor of this type uses a magnetoelectric transducer that detects the magnetic field generated by the current flowing through a bus bar, which serves as a current path. Furthermore, with the increase in electric vehicles and hybrid vehicles that use motors as their power source, the demands for current sensors, such as weight reduction and cost reduction to improve power efficiency, are becoming more sophisticated and sophisticated.

[0003] Patent document 1 describes a current sensor that is equipped with a bus bar, a shield plate, a magnetic detection element, and a conductive plate, with the aim of improving pulse response, and that uses a plate-shaped electrically conductive material such as copper or aluminum as the bus bar.

[0004] Japanese Patent Application Laid-Open No. 2019-109126

[0005] However, the current sensor described in Patent Document 1 uses a bus bar processed from a single electrically good conductor, and does not describe a bus bar configuration for reducing the weight and cost of the current sensor. Therefore, an object of the present invention is to provide a current sensor including a bus bar that is effective for reducing the weight and cost.

[0006] The present invention provides a current sensor that solves the above-described problems and includes a bus bar through which a current to be measured flows and a magnetic detection unit that is disposed opposite the bus bar and detects a magnetic field generated in the bus bar, the bus bar being made of a laminated material in which a first metallic material and a second metallic material that are different metallic materials are laminated, the first metallic material having a density greater than that of the second metallic material and a lower electrical resistivity than that of the second metallic material, and the magnetic detection unit being disposed opposite a surface of the bus bar made of the first metallic material.

[0007] By stacking two types of metallic materials, the proportion of metallic materials with different densities and electrical resistivities can be adjusted to strike a balance between reducing the amount of heat generated by the bus bar when the current to be measured flows and making the bus bar lighter.

[0008] In the bus bar, a dimension of the second metallic material may be larger than a dimension of the first metallic material in the stacking direction. In the bus bar, a dimension of the second metallic material may be 80% or more of a dimension of the laminated materials in the stacking direction. When the magnetic detection unit is disposed facing a surface of the bus bar made of the first metallic material, the above configuration can achieve heat suppression when a current to be measured flows due to the first metallic material and weight reduction due to the second metallic material while maintaining high frequency characteristics of the bus bar.

[0009] A current sensor includes a bus bar through which a current to be measured flows and a magnetic detection unit disposed opposite the bus bar and configured to detect a magnetic field generated in the bus bar, the bus bar being made of a laminated material obtained by laminating a first metallic material and a second metallic material, the first metallic material having a density greater than that of the second metallic material and a lower electrical resistivity than that of the second metallic material, and the magnetic detection unit being disposed opposite a surface of the bus bar made of the second metallic material. The laminated configuration of two types of metallic materials allows for a balance between reducing the amount of heat generated by the bus bar when the current to be measured flows and reducing the bus bar's weight.

[0010] In the bus bar, a dimension of the second metallic material may be larger than a dimension of the first metallic material in the stacking direction. In the bus bar, a dimension of the second metallic material may be 60% or more of a dimension of the laminated materials in the stacking direction. When the magnetic detection unit is disposed facing a surface of the bus bar made of the second metallic material, the above configuration can achieve heat suppression when a current to be measured flows due to the first metallic material and weight reduction due to the second metallic material while maintaining high frequency characteristics of the bus bar.

[0011] a first measurement phase in which the magnetic detection unit is arranged to face the surface of the bus bar made of the first metal-based material, and a second measurement phase in which the magnetic detection unit is arranged to face the surface of the bus bar made of the second metal-based material, the first measurement phase being made of a laminate material in which a first metal-based material and a second metal-based material are laminated together, the first metal-based material having a density greater than that of the second metal-based material and a lower electrical resistivity than that of the second metal-based material;

[0012] Because the first metallic material has a lower electrical resistivity than the second metallic material, a larger current to be measured flows through the first metallic material. Therefore, by arranging the magnetic detection unit so that it faces the surface made of the first metallic material, the magnetic field density detected by the magnetic detection unit is increased, and the detection accuracy of the first measurement phase is better than that of the second measurement phase. Therefore, by designating the measurement phase that requires high detection accuracy as the first measurement phase, it is possible to arrange multiple measurement phases according to the required detection accuracy.

[0013] The second measurement phase may be disposed on both sides of the first measurement phase. When three or more measurement phases are provided, the measurement error of the measurement phase increases due to the influence of the adjacent measurement phases on both sides. Therefore, when measurement phases are provided on both sides, the adjacent measurement phases are designated as second measurement phases and the middle measurement phase is designated as the first measurement phase, thereby suppressing a decrease in detection accuracy of the first measurement phase and reducing the difference in measurement accuracy among the multiple measurement phases.

[0014] In the bus bar, a dimension of the second metallic material may be larger than a dimension of the first metallic material in a stacking direction. With this configuration, it is possible to maintain high frequency characteristics achieved by stacking the first metallic material on the second metallic material, while achieving a balance between weight reduction achieved by the second metallic material and heat suppression achieved by the first metallic material.

[0015] In at least one of the measurement phases, the bus bar may have a bent portion, and the magnetic detection unit may be disposed at a position where it can detect an induced magnetic field from two portions of the bus bar that are positioned on either side of the bent portion. With this configuration, the magnetic detection unit can detect an induced magnetic field from the two portions that are positioned on either side of the bent portion, thereby improving the detection accuracy of the current sensor.

[0016] The bus bar may be provided with a layer of the first metallic material on a side where the bent portion bends, and the magnetic detection unit may face the layer of the first metallic material of the bus bar. By providing the layer of the first metallic material on the side where the bent portion bends, the magnetic flux density of the induced magnetic field detected by the magnetic detection unit increases, thereby improving the detection accuracy of the current sensor.

[0017] The first metal-based material may be a copper-based material, and the second metal-based material may be an aluminum-based material. By laminating a copper-based material having low electrical resistivity and an aluminum-based material having low density, a lightweight bus bar with excellent frequency characteristics and reduced heat generation is obtained.

[0018] According to the present invention, by using a laminated material in which different metal materials are laminated, the properties of the busbar can be adjusted, making it possible to provide a current sensor that is suitable for miniaturization and thinning.

[0019] 1A is a plan view of a current sensor according to a first embodiment; FIG. 1B is a cross-sectional view of the current sensor taken along line AA in FIG. 1A; FIG. 1C is a graph showing simulation results of busbar phase characteristics and a ratio of an Al thickness T4 to a total thickness T1 when the busbar in FIG. 1B is made of Cu and Al; FIG. 1D is a cross-sectional view of the current sensor in FIG. 1B provided with a magnetic shield; FIG. 1E is a cross-sectional view of a current sensor according to a second embodiment; FIG. 1F is a graph showing simulation results of busbar phase characteristics and a ratio of an Al thickness T4 to a total thickness T1 when the busbar in FIG. 4 is made of Cu and Al; FIG. 1G is a cross-sectional view of the current sensor in FIG. 4 provided with a magnetic shield; FIG. 1H is a graph showing differences in magnetic flux density depending on the lamination order and Al ratio in a busbar made of laminated Al and Cu; FIG. 1I is a graph showing differences in the influence on adjacent busbars depending on the lamination order and Al ratio in a busbar made of laminated Al and Cu; FIG. 1J is a cross-sectional view of a multi-phase type current sensor according to a third embodiment; FIG. 1J is a perspective view of a multi-phase type current sensor according to a modified example; FIG. 1J is a perspective view of a multi-phase type current sensor according to another modified example; FIG. 1I is a plan view of a current sensor according to a reference example; 11A ; FIG. 11B is a cross-sectional view of the current sensor taken along line BB in FIG. 11A ; FIG. 11C is a graph showing the relationship between the frequency and phase angle of the current flowing in the bus bar of the reference example of FIG. 11A ; FIG. 11D is a graph showing the relationship between the frequency and gain of the current flowing in the bus bar of the reference example of FIG. 11A ; FIG. 11E is a graph showing the temperature change over time when a current to be measured is passed through a conventional bus bar having an Al fastening portion and an Al main body portion; FIG. 11F is a graph showing the temperature change over time when a current to be measured is passed through a conventional bus bar having a Cu fastening portion and a Cu main body portion; FIG. 11G is a graph showing the temperature change over time when a current to be measured is passed through a bus bar of the reference example having a Cu fastening portion and an Al main body portion; FIG. 11H is a plan view of a current sensor according to another reference example; FIG. 14A is a cross-sectional view of the current sensor taken along line BB in FIG. 14A ; FIG. 15A is a plan view of a conventional current sensor; FIG. 15A is a cross-sectional view of the current sensor taken along line AA in FIG. 15A ; FIG. 15A is a cross-sectional view of the current sensor taken along line BB in FIG. 15A .

[0020] Hereinafter, an embodiment 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 their description will be omitted. Reference coordinates are shown in each drawing as appropriate to indicate the positional relationship of each component. The reference coordinates are defined as follows: the direction in which the bus bar extends is the X direction; the direction perpendicular to the X direction on the surface of the bus bar facing the magnetic detection unit is the Y direction; and the direction perpendicular to the X and Y directions is the Z direction. The Y direction is the direction of the sensitivity axis of the magnetic detection unit, and the X and Z directions are perpendicular to the sensitivity axis.

[0021] [First Embodiment] Fig. 15A is a plan view of a conventional current sensor 60, and Fig. 15B is a cross-sectional view of the current sensor 60 taken along line AA in Fig. 15A . As shown in these figures, the conventional current sensor 60 includes a bus bar 61 and a magnetic detection unit 62. A plate-shaped conductor is used as the bus bar 61 through which the current to be measured flows. Examples of conductor materials include copper and aluminum. Copper, which has good conductivity, is often used alone. However, if the bus bar 61 is made solely of copper, it can be difficult to meet the increasingly sophisticated and sophisticated requirements for current sensors, such as low cost and weight reduction. Therefore, the present invention uses a bus bar made of a laminated material in which different metal materials are laminated together, in order to achieve low cost and weight reduction in the current sensor.

[0022] 1A and 1B are a plan view and a cross-sectional view of the current sensor 10 taken along line AA in Fig. 1A according to the present embodiment, respectively. As shown in these figures, the current sensor 10 includes a busbar 1 through which a current to be measured flows, and a magnetic detection unit 2 that is disposed opposite the busbar 1 and detects a magnetic field generated in the busbar 1.

[0023] The busbar 1 is made of a laminated material in which dissimilar metallic materials, a first metallic material 3 and a second metallic material 4, are laminated together. In the busbar 1 of this embodiment, the first metallic material 3 and the second metallic material 4 are both configured as layers with uniform thicknesses in the Z direction. The first metallic material 3 has a higher density than the second metallic material 4 (in other words, the first metallic material 3 is heavier than the second metallic material 4), and a lower electrical resistivity (hereinafter referred to as "resistivity") than the second metallic material 4. The magnetic detection unit 2 of the current sensor 10 is disposed opposite a surface 3S of the busbar 1 made of the first metallic material 3.

[0024] For example, a copper-based material can be used as the first metal-based material 3, and an aluminum-based material can be used as the second metal-based material 4. The copper-based material refers to pure copper, copper alloys, and conductive materials containing these, while the aluminum-based material refers to pure aluminum, aluminum alloys, and conductive materials containing these.

[0025] The following description will be given by taking an example in which Cu (pure copper) is used as the copper-based material and Al (pure aluminum) as the aluminum-based material. Because Al has a lower specific gravity and density than Cu and is less expensive, bus bars made of Al are more advantageous than bus bars made of Cu in terms of weight and cost.

[0026] However, the resistivity of Al is 2.65×10 -8 [Ω m], and the resistivity of Cu is 1.68 × 10 -8 Therefore, if the bus bar is made of Al, the resistivity of the bus bar will be high because the bus bar generates heat when the current to be measured flows. If the temperature of the magnetic detection unit 2 rises and exceeds its heat resistance temperature, the detection accuracy of the current sensor 10 may be reduced.

[0027] 2 is a graph showing the results of a simulation performed on the busbar 1 made of the laminate material shown in FIG. 1B by varying the thickness T3 of Cu and the thickness T4 of Al in the Z direction when Cu is used as the first metallic material 3 and Al is used as the second metallic material 4. The horizontal axis in the figure represents the ratio T4 / T1×100(%) of the thickness T4 of Al to the total thickness T1 of Cu and Al, T1=T3+T4.

[0028] The busbar 1 used in the simulation of Figure 2 has the layered structure shown in Figure 1B, in which a layer of Cu as the first metal-based material 3 is arranged on the Z2 side, which is the magnetic detection unit 2 side, and a layer of Al as the second metal-based material 4 is arranged on the Z1 side, which is the opposite side of the magnetic detection unit 2.

[0029] The graph in Figure 2 shows that when the phase characteristic on the vertical axis is 0.0°, there is no delay in the output voltage of the current sensor 10 relative to the current being measured, which is an ideal state, and that the delay in the output voltage increases as you move downward on the vertical axis (towards -1.0°). If this delay is large, the time delay of the output voltage of the current sensor 10 relative to the current being measured in the high frequency band increases, so it is preferable that the phase characteristic on the vertical axis is closer to 0.0°. This graph shows that the delay in the output voltage of the current sensor 10 is smallest when a busbar 1 with an Al ratio of 100% is included, and that there is an inflection point in the phase characteristic when the Al ratio is between 60% and 80%.

[0030] 2, from the viewpoint of suppressing deterioration of the frequency characteristics of the busbar 1 related to the delay in the output voltage of the current sensor 10 and achieving weight reduction, it can be said that it is preferable that the thickness T4, which is the dimension of the second metallic material 4 in the Z direction, which is the stacking direction, is larger than the thickness T3, which is the dimension of the first metallic material 3. Furthermore, when the thickness T1 (= T3 + T4), which is the dimension of the busbar 1 made of the stacking materials in the stacking direction, is taken as 100%, it is even more preferable that the thickness T4 of the second metallic material 4 is 80% or more.

[0031] 3 is a cross-sectional view of the current sensor 10 provided with magnetic shields 5A and 5B. As shown in the figure, the current sensor 10 may be provided with magnetic shields 5A and 5B on both sides in the Z direction, sandwiching the bus bar 1 and the magnetic detection unit 2. The magnetic shields 5A and 5B can suppress magnetic noise from the outside to the magnetic detection unit 2, thereby improving the measurement accuracy of the current sensor 10. Note that a configuration in which a magnetic shield is provided only on the Z1 side of the bus bar 1 or only on the Z2 side of the magnetic detection unit 2 (a configuration in which only one of the magnetic shields 5A and 5B is provided) may also be used.

[0032] The magnetic shields 5A and 5B are formed, for example, by stacking multiple metal plates of the same shape. Note that in the drawings used for explanation, the magnetic shields 5A and 5B are illustrated as a single plate to simplify the stack of multiple plates.

[0033] 3, a U-shaped magnetic shield having a U-shaped cross section taken along line AA in Fig. 1A may be used. More specifically, the busbar 1 may be shaped like a U on both sides in the Y direction and on the Z1 direction side of the busbar 1, and a U-shaped magnetic shield may be used that surrounds the magnetic detection unit 2.

[0034] 4 is a cross-sectional view of a current sensor 11 according to this embodiment. The current sensor 11 of this embodiment is the same as the current sensor 10 in that the laminate material constituting the busbar 1 is formed by laminating a first metallic material 3 and a second metallic material 4. However, the current sensor 11 differs from the current sensor 10 in that the magnetic detection unit 2 is disposed opposite a surface 4S of the busbar 1 made of the second metallic material 4, in that the magnetic detection unit 2 is disposed opposite a surface 3S of the busbar 1 made of the first metallic material 3.

[0035] Fig. 5 is a graph showing the results of a simulation in which the thickness T3 of Cu and the thickness T4 of Al in the Z direction are changed when a laminate material in which the first metallic material 3 is Cu and the second metallic material 4 is Al is used for the busbar 1 shown in Fig. 4. The horizontal axis in the figure represents the ratio of the thickness T4 of Al to the thickness T1 of the busbar 1.

[0036] The busbar 1 for which the simulation results are shown in Figure 5 has the laminated structure shown in Figure 4, in which a layer of Al as the second metal-based material 4 is arranged on the magnetic detection unit 2 side, and a layer of Cu as the first metal-based material 3 is arranged on the opposite side of the magnetic detection unit 2, sandwiching the layer of the second metal-based material 4.

[0037] The vertical and horizontal axes in the graph of Fig. 5 show the same content as in the graph of Fig. 2. This graph shows that the delay in the output voltage of the current sensor 10 is smallest when the busbar 1 has an Al ratio of 100%, and that there is an inflection point in the phase characteristics when the Al ratio is between 40% and 60%.

[0038] 5, when the magnetic detection unit 2 is disposed so as to face the surface 4S of the layer of Al as the second metallic material 4, it is preferable that the thickness T4, which is the dimension of the second metallic material 4 in the Z direction, which is the lamination direction, is larger than the thickness T3, which is the dimension of the first metallic material 3, from the viewpoint of suppressing deterioration of the frequency characteristics of the busbar 1 related to the delay in the output voltage of the current sensor 10 and achieving weight reduction. Furthermore, when the thickness T1, which is the dimension of the busbar 1 made of the laminated material in the lamination direction, is taken as 100%, the thickness T4 of the second metallic material 4 is more preferably 60% or more.

[0039] 6 is a cross-sectional view of the current sensor 11 provided with magnetic shields 5A and 5B. As shown in the figure, the current sensor 11 may be provided with magnetic shields 5A and 5B on both sides in the Z direction to sandwich the bus bar 1 and the magnetic detection unit 2. The magnetic shields can suppress magnetic noise from the outside to the magnetic detection unit 2, thereby improving the measurement accuracy of the current sensor 10.

[0040] The current sensors of the first and second embodiments described above include a bus bar formed by laminating two types of metallic materials. Therefore, by adjusting the ratio of the metallic materials with different densities and electrical resistivities, it is possible to reduce the amount of heat generated by the bus bar when a current to be measured flows and to reduce the weight of the bus bar.

[0041] [Third Embodiment] In this embodiment, an embodiment of the present invention will be described as a multiphase current sensor. Fig. 7A is a graph of simulation results showing the difference in magnetic flux density near the busbar 1 depending on the stacking order and Al ratio of Al and Cu when Cu is used as the first metallic material 3 and Al as the second metallic material 4 in a multiphase current sensor having multiple measurement phases. The Al ratio in the figure shows the same content as in the simulations of the frequency characteristics in the first and second embodiments.

[0042] The results shown as Cu / Al are simulation results for a current sensor 10 (see FIG. 1 ) in which the magnetic detection unit 2 is provided on the Cu-side surface 3S, which is used as the first metal-based material 3. The results shown as Al / Cu are simulation results for a current sensor 11 (see FIG. 4 ) in which the magnetic detection unit 2 is provided on the Al-side surface 4S, which is used as the second metal-based material 4. The Cu / Al and Al / Cu simulations were performed under identical conditions except for the stacking order. As shown in FIG. 7A , it was found that the magnetic flux density near the busbar 1 differs depending on whether the magnetic detection unit 2 is provided on the Cu-side surface 3S or the Al-side surface 4S. This result is thought to be due to the fact that when a current to be measured flows through a busbar 1 made of a laminated material of dissimilar metals, more current flows through the Cu side, which has lower electrical resistivity, than through the Al side, which has higher electrical resistivity.

[0043] Furthermore, from the results shown for Cu / Al, it was found that the magnetic flux density was higher when the busbar 1 was made of a laminated material than when it was made of only Cu (Al ratio 0%) or only Al (Al ratio 100%). Thus, by making the busbar 1 out of a laminated material, the magnetic flux density detected by the magnetic detection unit 2 was increased, improving the measurement accuracy of the current sensor.

[0044] Figure 7B is a graph showing the difference in the influence of the Al / Cu layering order and Al ratio on adjacent bus bars in a multiphase current sensor with multiple measurement phases. The results shown in the figure indicate the magnitude of error that occurs in the middle current sensor when three current sensors with bus bars made of the same layering material are lined up and measurements are performed under the same conditions. Furthermore, Cu / Al and Al / Cu represent the difference in the layering order of the bus bars described in Figure 7A.

[0045] 7B, it was found that in the case of a multiphase current sensor, when the busbar is made of a laminated material, it is more strongly affected by adjacent busbars than when the busbar is made of only Cu (0% Al ratio) or only Al (100% Al ratio). This is thought to be because the use of a laminated material made of different metallic materials for the busbar results in a larger difference in magnetic flux density in the Z direction in the induced magnetic field generated when the current to be measured flows than when the busbar is made of a single metallic material.

[0046] 7B , it was found that the Cu / Al busbar, in which the magnetic detection unit 2 is provided on the Cu-side surface 3S, is less affected by the adjacent busbar than the Al / Cu busbar, in which the magnetic detection unit 2 is provided on the Al-side surface 4S. This is thought to be because, in the busbar 1, the current density of the current to be measured flowing on the first metallic material 3 side, which has a low electrical resistivity, is higher than that on the second metallic material 4 side, which has a high electrical resistivity, resulting in a higher magnetic flux density measured by the magnetic detection unit 2.

[0047] 8 is a cross-sectional view showing a multi-phase current sensor 30 according to this embodiment. As shown in the figure, the current sensor 30 includes a plurality of measurement phases 20, each of which includes a bus bar 1 through which a current to be measured flows and a magnetic detection unit 2 disposed opposite the bus bar 1 and detecting a magnetic field generated in the bus bar 1.

[0048] The current sensor 30 has a first measurement phase 20A in which a magnetic detection unit 2 is arranged to face a surface 3S made of a first metal-based material 3 of the busbar 1, and a second measurement phase 20B in which a magnetic detection unit 2 is arranged to face a surface 4S made of a second metal-based material 4 of the busbar 1.

[0049] Because the first metallic material 3 has a lower electrical resistivity than the second metallic material 4, more of the current to be measured flows toward the first metallic material 3. Therefore, by arranging the magnetic detection unit 2 so that it faces the surface 3S made of the first metallic material 3, the magnetic field density of the induced magnetic field of the current to be measured detected by the magnetic detection unit 2 becomes larger. As a result, the first measurement phase 20A has better detection accuracy than the second measurement phase 20B. For example, in a current sensor 30 having multiple measurement phases 20, if the required detection accuracy for each measurement phase 20 differs, the first measurement phase 20A or the second measurement phase 20B can be selected and arranged depending on the required detection accuracy.

[0050] 8 , three measurement phases 20 are arranged in parallel in the Y direction. The measurement phase 20 arranged in the middle of the three measurement phases 20 is affected by the measurement phases 20 adjacent to it on both sides in the Y direction, resulting in a large error. Therefore, by designating the middle measurement phase 20 as the first measurement phase 20A and the measurement phases 20 on both sides as second measurement phases 20B, it is possible to suppress a decrease in detection accuracy of the middle measurement phase 20 and reduce the difference in measurement accuracy among the multiple measurement phases 20.

[0051] In addition, in the current sensor 30, the magnetic detection units 2 are provided on the same side of the busbar 1 (the Z2 side in FIG. 8 ) for all of the multiple measurement phases 20. In this case, because the second measurement phases 20B are arranged on both sides of the first measurement phase 20A, the distance between the magnetic detection units 2 in the first measurement phase 20A and the first metallic material 3 of the busbar 1 in the second measurement phases 20B on both sides is large. Furthermore, because the current to be measured flowing through the busbar 1 flows more toward the first metallic material 3, the distance between the source of the induced magnetic field in the second measurement phases 20B arranged on both sides of the first measurement phase 20A and the magnetic detection unit 2 of the first measurement phase 20A arranged in the middle is large. Therefore, the influence of the magnetic field from the busbar 1 of the adjacent second measurement phase 20B on the first measurement phase 20A can be reduced. Therefore, it is preferable that the busbars 1 of the measurement phases 20 arranged on both sides of the first measurement phase 20A have the first metal-based material 3 laminated on the Z1 side, which is farther away from the magnetic detection unit 2 of the first measurement phase 20A.

[0052] In the current sensor 30 having the multiple measurement phases 20 shown in FIG. 8 , from the viewpoint of improving frequency characteristics, the thickness T4 of the second metallic material 4 is preferably greater than the thickness T3 of the first metallic material 3 (see FIGS. 1B and 4 ) in the Z direction, which is the stacking direction of the first metallic material 3 and the second metallic material 4. As described in the first and second embodiments, when the magnetic detection unit 2 faces the surface 3S made of the first metallic material 3, the thickness T4 of the second metallic material 4 is preferably greater than 50%, more preferably 80% or greater, of the thickness of the busbar 1 in the stacking direction. Furthermore, when the magnetic detection unit 2 faces the surface 4S made of the second metallic material 4, the thickness T4 of the second metallic material 4 is preferably greater than 50%, more preferably 60% or greater, of the thickness of the busbar 1 in the stacking direction.

[0053] As described above, in the middle measurement phase 20, which is susceptible to the influence of the induced magnetic field of the adjacent measurement phases 20 among the three adjacent measurement phases 20, the first metallic material 3 is arranged on the magnetic detection unit 2 side of the busbar 1, and the second metallic material 4 is arranged on the magnetic detection unit 2 side of the busbars 1 on both sides. With this configuration, it is possible to reduce the influence of the adjacent busbars 1 on the magnetic detection unit 2 facing the middle busbar 1.

[0054] In addition, in the case of a current sensor consisting of two adjacent measurement phases 20, the measurement phase 20 requiring relatively high accuracy can be designated as the first measurement phase 20A, and the measurement phase 20 requiring less accuracy can be designated as the second measurement phase 20B, thereby making it possible to create a configuration that corresponds to the required accuracy.

[0055] [Modification] Figure 9 is a perspective view showing a multi-phase current sensor 31 according to a modification. In the current sensor 31, of three adjacent measurement phases 20, the center one is designated as a first measurement phase 20A, and the other two are designated as second measurement phases 20B. The busbar 1 includes a first portion 1X1 and a first portion 1X2 extending in the X direction, and a second portion 1Z extending in the Z direction. The first portion 1X1 and the second portion 1Z are connected by a bent portion 1B1, and the first portion 1X2 and the second portion 1Z are connected by a bent portion 1B2. When viewed from the Y direction, the busbar 1 has a crank shape in which the bent portion 1B1 and the bent portion 1B2 are bent 90 degrees in opposite directions.

[0056] The busbar 1 of the first measurement phase 20A has a Z2-direction bent portion 1B2 consisting of a second portion 1Z and a first portion 1X2 extending from its Z2-direction end toward the X2 side, and a Z1-direction bent portion 1B1 consisting of the second portion 1Z and the first portion 1X1 extending from its Z1-direction end toward the X1 side. In the Z2-direction bent portion 1B2, the second metallic material 4 is on the inside of the bent portion 1B2, and in the Z1-direction bent portion 1B1, the first metallic material 3 is on the inside of the bent portion 1B1.

[0057] 9 illustrates a busbar 1 having two first portions 1X1 and 1X2, and a second portion 1Z, with bent portions 1B1 and 1B2 at both ends of the second portion 1Z in the Z direction. However, a configuration including the first portion 1X1, the second portion 1Z, and the bent portion 1B1, or a configuration including the first portion 1X2, the second portion 1Z, and the bent portion 1B2, may also be used. Also, while the embodiment illustrates an embodiment in which all three measurement phases 20 include the bent portion 1B1 and the bent portion 1B2, a configuration in which one or two of the three measurement phases 20 include at least one of the bent portion 1B1 and the bent portion 1B2 may also be used. In the case of a busbar 1 having only the bent portion 1B1 or the bent portion 1B2, the magnetic detection unit 2 is disposed on the bent side, i.e., the inner side, of the bent portion 1B1 or the bent portion 1B2.

[0058] The magnetic detection unit 2 is disposed at a position where it can detect an induced magnetic field Mx from the first portion 1X1 that contacts the bent portion 1B1 and an induced magnetic field Mz from the second portion 1Z. The two portions of the busbar 1 that are positioned on either side of the bent portion 1B1 are the first portion 1X1 that contacts the bent portion 1B1 and the second portion 1Z.

[0059] In this modification, the induced magnetic fields Mx and Mz are each magnetic fields containing a Y-direction component, and the magnetic detection unit 2 is disposed so that the detection direction of the magnetic detection unit 2 is parallel to the Y-direction. In other words, the magnetic detection unit 2 detects a composite component of the Y-direction component of the induced magnetic field Mx and the Y-direction component of the induced magnetic field Mz.

[0060] The magnetic detection unit 2 is preferably positioned at a position where the aforementioned induced magnetic fields Mx and Mz can be detected, and the magnitude of the composite component of the Y-direction component of the induced magnetic field Mx and the Y-direction component of the induced magnetic field Mz is desirably large enough to be easily detected by the magnetic detection unit 2. This configuration allows the magnetic detection unit 2 to efficiently detect the induced magnetic field generated when a current to be measured flows through the busbar 1. Furthermore, the magnetic detection unit 2 of the central first measurement phase 20A is positioned opposite the surface 3S of the layer of the first metallic material 3 of the busbar 1, so that the magnetic flux density of the magnetic field generated when a current to be measured flows is high. This improves the magnetic detection accuracy of the magnetic detection unit 2.

[0061] When the magnetic detection units 2 are provided on the same side of the busbar 1 in the Z direction, the configuration in which the second measurement phase 20B are arranged on both sides of the first measurement phase 20A increases the distance between the magnetic detection unit 2 of the first measurement phase 20A and the first metallic material 3 of the busbar 1 of the second measurement phase 20B. This reduces the influence of the magnetic field from the second measurement phase 20B on the central first measurement phase 20A. This effect is obtained in the first portion 1X1 and the second portion 1Z, improving the detection accuracy of the current sensor 31.

[0062] Fig. 10 is a perspective view showing another modified example of a multiphase type current sensor 32. The current sensor 32 shown in Fig. 10 differs from the current sensor 31 shown in Fig. 9 in that the magnetic detection units 2 are arranged inside the bent portions 1B2 in the measurement phases 20 on both sides.

[0063] In the current sensor 32, the bus bars of the three aligned measurement phases 20 are arranged in the same manner as in the modified example shown in FIG. 9 . Regarding the arrangement of the magnetic detection units 2, the magnetic detection unit 2 of the middle measurement phase 20 is arranged facing the surface 3S of the layer of the first metal material 3 of the first portion 1X1 and the second portion 1Z on the Z1 side, as in the modified example shown in FIG. 9 . In contrast, the magnetic detection units 2 of the measurement phases 20 on both sides are arranged facing the surface 3S of the layer of the first metal material 3 of the first portion 1X2 and the second portion 1Z on the Z2 side of the busbar 1. In other words, the magnetic detection units 2 are arranged so that all three aligned measurement phases 20 are the first measurement phase 20A. By arranging the magnetic detection units 2 of the measurement phases 20 on both sides so that they face the surface 3S of the first metal material 3 of the busbar 1, the magnetic flux density detected by the magnetic detection units 2 increases, improving the detection accuracy of the measurement phases 20.

[0064] [Reference Example] Fig. 11A is a plan view of a current sensor 50 according to a reference example. Fig. 11B is a cross-sectional view of the current sensor 50 taken along line BB in Fig. 11A. As shown in these figures, the current sensor 50 has a magnetic detection unit 52 disposed opposite a busbar 51. The busbar 1 of the current sensor 50 has a fastening portion 51A and a main body portion 51B including a constricted portion facing the magnetic detection unit 52, each made of a different type of metallic material.

[0065] For example, fastening portion 51A may be made of Cu as first metallic material 53, and main body portion 51B may be made of Al as second metallic material 54. This reduces the contact resistance of fastening portion 51A and suppresses heat generation due to the current to be measured, compared to when fastening portion 61A and main body portion 61B of bus bar 61 of conventional current sensor 60 shown in Fig. 15C are made of Al. Furthermore, suppressing the skin effect in bus bar 51 improves the frequency characteristics of the magnetic flux density detected by magnetic detection portion 52.

[0066] The following table shows the frequency characteristics (phase characteristics) of Cu and Al. The skin depth in Table 2 is the distance at which an electromagnetic field incident on a material is attenuated to 1 / e (≒ 1 / 2.718 ≒ -8.7 db). When a high-frequency current is passed through a conductor, most of the current is concentrated in a very narrow region near the surface of the conductor. This means that the resistance of the conductor actually increases at high frequencies, and while thickening the conductor can be expected to reduce resistance at low frequencies, this is no longer effective at high frequencies. For this reason, from the perspective of frequency characteristics, Al, which has a large skin depth, is preferable to Cu.

[0067] Figure 12A is a graph showing the simulation results of the relationship between the frequency and phase angle of the current to be measured for a reference example current sensor 50 having a bus bar 51 whose fastening portion 51A is made of Cu and whose main body portion 51B is made of Al, and a conventional current sensor 60 having a bus bar 61 whose fastening portion 61A and main body portion 61B are made of Cu.

[0068] 12A, a larger value (phase angle) on the vertical axis (closer to 0) indicates a state in which the detected voltage does not lag behind the current being measured, i.e., a good state. This graph shows that current sensor 50 has a larger phase angle than current sensor 60, even when the frequency of the current being measured becomes higher, and the detected voltage does not lag behind the current being measured.

[0069] FIG. 12B is a graph showing the simulation results of the relationship between the frequency of the current to be measured and the gain for the current sensor 50 of the reference example shown in FIGS. 11A and 11B and the conventional current sensor 60 shown in FIGS. 15A to 15C.

[0070] 12B, the larger the value (gain) on the vertical axis (closer to 1), the better the state in which a detected voltage corresponding to the current being measured can be output. This graph shows that current sensor 50 has a larger value on the vertical axis than current sensor 60, even when the frequency of the current being measured becomes higher, and is therefore able to output a detected voltage corresponding to the current being measured.

[0071] From the results of these graphs shown in Figures 12A and 12B, it can be seen that by changing the main body 61B of the conventional bus bar 61 from Cu to Al, the delay in the detected voltage relative to the current being measured is reduced and the gain is improved.

[0072] 13A is a graph showing the temperature change over time at the constricted portions of the fastening portion 61A and the main body portion 61B of a conventional current sensor 60 including a busbar 61 whose fastening portion 61A and main body portion 61B are made of Al. FIG. 13B is a graph showing the temperature change over time at the constricted portions of the fastening portion 61A and the main body portion 61B of a conventional current sensor 60 including a busbar 61 whose fastening portion 61A and main body portion 61B are made of Cu. FIG. 13C is a graph showing the temperature change over time at the constricted portions of the fastening portion 51A and the main body portion 51B of a reference current sensor 50 including a busbar 51 whose fastening portion 51A is made of Cu and whose main body portion 51B is made of Al, when the current is passed under the same conditions.

[0073] 13A to 13C show that the bus bar 61 made only of Al is more likely to increase in temperature when a current to be measured is passed through it than the bus bar 61 made only of Cu. However, the bus bar 51 made of fastening portion 51A made of Cu and the main body portion 51B made of Al suppressed temperature increases caused by the current to be measured in both the fastening portion 51A and the constricted portion of main body portion 51B, just like the bus bar 61 made only of Cu.

[0074] A comparison of the graphs in Figures 13A to 13C reveals the difference in temperature change in each part when the current to be measured is continuously passed through it, depending on the materials used to make the fastening section and main body. The bus bar 61 made entirely of Al shown in Figure 13A generates significantly more heat than the bus bar 61 made entirely of Cu shown in Figure 13B. By simply changing the main body to Al and the fastening section to Cu, the heat generation of the bus bar 51 was significantly reduced, as shown in the graph in Figure 13C. Note that the final drop in temperature around 60 minutes in each graph is due to the current to be measured being stopped.

[0075] From these results, it can be said that a configuration in which the fastening portion 51A is made of Cu and the main body portion 51B is made of Al is effective in reducing the delay in the detected voltage relative to the current to be measured, improving the gain, and suppressing the temperature rise when the current to be measured flows.

[0076] Fig. 14A is a plan view of a current sensor 50 according to another reference example. Fig. 14B is a cross-sectional view of the current sensor 50 taken along line BB in Fig. 14A. As shown in these figures, even if the Z-axis direction surface of the Al fastening portion 51A of the busbar 51 in the current sensor 50 is covered with Cu, it is possible to reduce the temperature rise when the current to be measured flows.

[0077] 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.

[0078] The present invention is useful as a current sensor that is attached to various devices to measure a current to be measured in order to control or monitor the devices.

[0079] 1: Busbar 1B1: Bending portion 1B2: Bending portion 1X1: First portion 1X2: First portion 1Z: Second portion 2: Magnetic detection portion 3: First metallic material 3S: Surface 4: Second metallic material 4S: Surface 5A: Magnetic shield 5B: Magnetic shield 10: Current sensor 11: Current sensor 20: Measurement phase 20A: First measurement phase 20B: Second measurement phase 30: Current sensor 31: Current sensor 32: Current sensor 50: Current sensor 51: Busbar 51A: Fastening portion 51B: Main body 52: Magnetic detection portion 53: First metallic material 54: Second metallic material 60: Current sensor 61: Busbar 61A: Fastening portion 61B: Main body 62: Magnetic detection unit Mx: Induction magnetic field Mz: Induction magnetic field T1: Thickness T3: Thickness T4: Thickness

Claims

1. In a current sensor comprising a bus bar through which a current to be measured flows and a magnetic detection unit that is disposed to face the bus bar and detects a magnetic field generated in the bus bar, the bus bar is made of a laminated material in which a first metal-based material and a second metal-based material, which are different metal-based materials, are laminated, the first metal-based material has a density greater than that of the second metal-based material and an electrical resistivity smaller than that of the second metal-based material, the magnetic detection unit is disposed to face a surface of the bus bar made of the first metal-based material, and in the lamination direction, the dimension of the second metal-based material is larger than the dimension of the first metal-based material. A current sensor characterized by this.

2. The current sensor according to claim 1, wherein in the lamination direction, the dimension of the second metal-based material is 80% or more of the dimension of the laminated material.

3. In a current sensor comprising a bus bar through which a current to be measured flows and a magnetic detection unit that is disposed to face the bus bar and detects a magnetic field generated in the bus bar, the bus bar is made of a laminated material in which a first metal-based material and a second metal-based material, which are different metal-based materials, are laminated, the first metal-based material has a density greater than that of the second metal-based material and an electrical resistivity smaller than that of the second metal-based material, the magnetic detection unit is disposed to face a surface of the bus bar made of the second metal-based material, and in the lamination direction, the dimension of the second metal-based material is larger than the dimension of the first metal-based material. A current sensor characterized by this.

4. The current sensor according to claim 3, wherein in the lamination direction, the dimension of the second metal-based material is 60% or more of the dimension of the laminated material.

5. In a current sensor including a plurality of measurement phases each comprising a bus bar through which a current to be measured flows and a magnetic detection unit that is disposed to face the bus bar and detects a magnetic field generated in the bus bar, the bus bar is made of a laminated material in which a first metal-based material and a second metal-based material, which are different metal-based materials, are laminated, the first metal-based material has a density greater than that of the second metal-based material and an electrical resistivity smaller than that of the second metal-based material, the current sensor includes a first measurement phase in which the magnetic detection unit is disposed so as to face a surface of the bus bar made of the first metal-based material, and a second measurement phase in which the magnetic detection unit is disposed so as to face a surface of the bus bar made of the second metal-based material, and is characterized by satisfying at least one of the following matters I and II. Item I: In the stacking direction, the dimension of the second metal-based material is larger than the dimension of the first metal-based material Item II: In at least one of the measurement phases, the bus bar has a bent portion, and the magnetic detection unit is disposed at a position where it can detect the induced magnetic fields from two portions of the bus bar that sandwich the bent portion

6. The current sensor according to claim 5, wherein the second measurement phase is disposed on both sides adjacent to the first measurement phase

7. Satisfying Item II, a layer of the first metal-based material is provided on the side where the bent portion of the bus bar bends, the magnetic detection unit faces the layer of the first metal-based material of the bus bar, the current sensor according to claim 5

8. the first metal-based material is a copper-based material, the second metal-based material is an aluminum-based material, the current sensor according to claim 1, claim 3 or claim 5