Electric current sensor

Abstract

An electric current sensor 10 according to the present invention suppresses a decrease in detection accuracy due to heating of an electronic component, such as a magnetic detection unit, to a high temperature as a result of heat generation from a bus bar, and is suitable for measuring large electric currents. The electric current sensor 10 comprises: a bus bar 11 through which electric current being measured flows; a magnetic detection unit 13 capable of detecting magnetism generated by the bus bar 11; and a case 12 formed integrally with the bus bar 11 and having an accommodation space 14 that accommodates the magnetic detection unit 13. The magnetic detection unit 13 is disposed in a position spaced apart from the bus bar 11 and opposite to the bus bar 11. The bus bar 11 is provided on a first face 14a of the accommodation space 14, the first face 14a defining the accommodation space 14 and facing the magnetic detection unit 13 along the Z-axis direction. Air, which serves as a low thermal conductivity material having a lower thermal conductivity than a resin-based material forming the case 12, is provided between the bus bar 11 and the magnetic detection unit 13, and is in contact with an opposing face 11a of the bus bar 11, the opposing face 11a facing the magnetic detection unit 13.

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, with the increasing demand for decarbonization, there has been a shift from engines to motors to reduce CO2 emissions during vehicle operation, i.e., a shift away from gasoline-powered vehicles and toward electrification (EV shift). Current sensors are used as current measurement devices to measure the current supplied to three-phase motors (see, for example, Patent Document 1). As the shift to EVs spreads to large commercial vehicles such as trucks and buses, the motor capacity in hybrid vehicles and electric vehicles has also increased, resulting in larger measured currents for current sensors used for motor control. Furthermore, opportunities for continuous operation under high-load conditions have also increased, resulting in larger continuously flowing currents. Bus bars, which are the current paths for the measured current, generate heat in an amount proportional to the square of the magnitude of the current. Therefore, as the continuously flowing measured current increases, the amount of heat generated by the bus bars increases, resulting in a problem of high temperatures for electronic components, such as magnetic detectors, located near the bus bars.

[0003] Japanese Patent Application Laid-Open No. 2017-102024

[0004] Patent Document 1 describes a current sensor in which a substrate equipped with a magnetic detection unit is provided within a case member in which a bus bar is insert-molded. In this current sensor, both sides of the bus bar are covered with resin, taking into account the fluidity of the resin when molding the case member. Therefore, heat generated in the bus bar is transferred to the magnetic detection unit via the resin-based material covering the opposing surface facing the magnetic detection unit. As the current to be measured increases, the amount of heat generated by the bus bar increases, causing the temperature in the storage space to exceed the heat-resistant temperature of the magnetic detection unit, which can lead to problems such as reduced measurement accuracy and a shortened product life. Therefore, an object of the present invention is to provide a current sensor suitable for measuring large currents, in which heat generated by the bus bar prevents electronic components such as the magnetic detection unit from becoming too hot.

[0005] The present invention provides a current sensor that solves the above-described problems, comprising: a bus bar through which a current to be measured flows, a magnetic detection unit capable of detecting magnetic fields generated by the bus bar, and a case formed integrally with the bus bar and having a storage space for storing the magnetic detection unit, wherein the magnetic detection unit is disposed at a position facing the bus bar while being spaced apart from the bus bar, the bus bar is provided on a first surface of the storage space that defines the storage space and faces the magnetic detection unit along a first direction, and a low-thermal-conductivity material having a lower thermal conductivity than a resin-based material forming the case is provided between the bus bar and the magnetic detection unit so as to be in contact with a surface of the bus bar that faces the magnetic detection unit.

[0006] The low thermal conductivity material provided between the bus bar and the magnetic detection unit makes it difficult for heat generated by the bus bar to be transmitted to the magnetic detection unit via the storage space, thereby reducing the heat transmitted from the bus bar to the magnetic detection unit. This prevents the temperature around the magnetic detection unit from increasing due to heat from the bus bar, thereby preventing a decrease in the detection accuracy of the magnetic sensor.

[0007] Only an air layer may be provided as the low thermal conductivity material between the bus bar and the magnetic detection unit. Air has a relatively low thermal conductivity, and the air layer is a good heat insulating layer. Therefore, the simple configuration of providing an air layer between the bus bar and the magnetic detection unit can suppress a rise in temperature around the magnetic detection unit. The low thermal conductivity material may be provided so that the air constituting the air layer is in contact with the opposing surface.

[0008] The bus bar may have the facing surface exposed in the storage space, and the opposite surface of the bus bar opposite the facing surface embedded in the case. In the area where the bus bar faces the magnetic detection unit, air between the facing surface of the bus bar and the magnetic detection unit can reduce heat transfer from the facing surface of the bus bar to the magnetic detection unit through the storage space. Furthermore, by embedding the opposite surface of the bus bar in this area in a case with a higher thermal conductivity than air, heat from the bus bar can be guided to the case on the opposite side of the magnetic detection unit. This prevents the temperature around the magnetic detection unit from rising due to heat from the bus bar.

[0009] The distance in the first direction between the opposing surface of the bus bar and the magnetic detection unit may be equal to or less than the distance in the first direction between the first surface of the storage space and the magnetic detection unit. By arranging the bus bar so that the distance from the magnetic detection unit in the first direction is greater from the first surface of the storage space than from the opposing surface of the bus bar, heat transferred from the bus bar to the magnetic detection unit through the storage space from the first surface of the storage space can be reduced, thereby suppressing an increase in temperature around the magnetic detection unit.

[0010] The facing surface of the bus bar and the first surface of the storage space may be flush with each other. By making the facing surface of the bus bar and the first surface of the storage space flush with each other, it becomes easier to form and process the case and the bus bar.

[0011] The current sensor may further include a magnetic shield. The magnetic shield may be a pair of flat magnetic shields aligned in the first direction, and the bus bar and the magnetic detection unit may be disposed between the pair of flat magnetic shields. The flat magnetic shield disposed proximal to the bus bar may be integrally formed with the case together with the bus bar. The magnetic shield can block external magnetic field noise from reaching the magnetic detection unit, thereby improving the external magnetic field noise resistance of the magnetic detection unit.

[0012] The magnetic shield may have a base portion disposed on the opposite side of the bus bar from the magnetic detection portion in the first direction, and sidewall portions extending from both ends of the base portion along the first direction. By disposing the magnetic shield having a U-shaped cross section so as to surround the bus bar, the resistance of the current sensor to external magnetic field noise is improved.

[0013] The magnetic detection unit may include a first magnetic detection unit and a second magnetic detection unit, and may detect the magnetic field generated by the bus bar based on an output of the first magnetic detection unit and an output of the second magnetic detection unit. By detecting the magnetic field based on the outputs of the first magnetic detection unit and the second magnetic detection unit, it is possible to eliminate the influence of external magnetic field noise common to the first and second magnetic detection units, thereby improving the resistance of the current sensor to external magnetic field noise.

[0014] The cross-sectional shape of the bus bar perpendicular to the extension direction of the bus bar may have a dimension in the first direction larger than a dimension in a second direction perpendicular to the first direction. By using a bus bar having a cross-sectional shape whose dimension in the first direction is larger than the dimension in the second direction, an elongated elliptical magnetic field is generated in the cross section, with a major axis whose component in the first direction is larger than the component in the second direction. Therefore, a magnetic field with a larger component in the first direction and an opposite direction is formed near the magnetic detection unit, and the magnetic field from the bus bar can be detected accurately.

[0015] The magnetic detection unit may include an output terminal unit, the output terminal unit may be held by a substrate, and the output terminal unit may be sealed. By sealing the output terminal unit by potting with a sealant, discharge from the bus bar to the output terminal unit is less likely to occur, and the voltage resistance of the current sensor is improved.

[0016] The magnetic detection unit may further include a cover that covers the storage space, the magnetic detection unit may include an output terminal unit, the output terminal unit may be held by a substrate, and the substrate may be held by the cover. When heat from the bus bar is transferred to the substrate via a resin-based material, heat transfer is reduced at the contact point between the case and the cover, so that it is possible to prevent the heat from the bus bar from being transferred to the magnetic detection unit and the temperature of the magnetic detection unit from increasing.

[0017] According to the present invention, it is possible to reduce the temperature rise of the magnetic sensor caused by heat from the bus bar being transferred to the magnetic detection unit through the resin material of the case, thereby providing a current sensor suitable for measuring large currents in which deterioration of measurement accuracy due to an increase in the temperature of the magnetic detection unit caused by heat from the bus bar is suppressed.

[0018] FIG. 1 is a perspective view of a current sensor according to an embodiment of the present invention; FIG. 2 is a cross-sectional view of the current sensor according to the first embodiment taken along line AA in FIG. 1; FIG. 3 is a plan view of the current sensor of FIG. 2; FIG. 4 is a cross-sectional view of a modified example of the current sensor according to the first embodiment; FIG. 5 is a cross-sectional view of another modified example of the current sensor according to the first embodiment; FIG. 6 is a cross-sectional view of the current sensor according to the second embodiment; FIG. 7 is a cross-sectional view of a modified example of the current sensor according to the second embodiment; FIG. 8 is a cross-sectional view of the current sensor according to the third embodiment; FIG. 9 is a cross-sectional view of the current sensor according to the fourth embodiment; FIG. 10 is a cross-sectional view of the current sensor according to the fifth embodiment; FIG. 11 is a cross-sectional view of the current sensor according to the sixth embodiment; FIG. 12 is a cross-sectional view of a conventional current sensor;

[0019] 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 indicated in each drawing as appropriate to indicate the positional relationship of each component. The reference coordinates are defined as the X-axis direction, the Y-axis direction on the bus bar surface that is perpendicular to the X-axis direction, and the Z-axis direction, the normal to the bus bar surface.

[0020] 1 is a perspective view of a current sensor 10 according to this embodiment. The current sensor 10 has three bus bars 11 integrally molded with a case member 12, three magnetic detection units 13 (see FIG. 3) on a substrate 19, and three measurement channels. Note that the present invention can also be implemented as a current sensor having one or more measurement channels other than three.

[0021] 12 is a cross-sectional view of conventional current sensor 100, showing a cross section of a portion including a set of busbar 101 and magnetic detection unit 103, corresponding to a cut along line A-A in FIG. 1 in the YZ plane. As shown in the figure, current sensor 100 has a resin-based material provided on both sides of busbar 101 in the Z-axis direction, taking into account the fluidity of the resin-based material when busbar 101 is insert-molded into case member 102. In this way, in conventional current sensor 100, the resin-based material of case member 102 is formed between busbar 101 and magnetic detection unit 103, and busbar 101 is not exposed in storage space 104 for magnetic detection unit 103.

[0022] The thermal conductivity of the resin-based material forming the case member 102 is greater than that of air. For example, the thermal conductivity of polyphenylene sulfide (PPS) is approximately 0.3 W / mK, which is greater than the thermal conductivity of air, 0.0241 W / mK. In the conventional current sensor 100, a resin-based material that conducts heat generated in the busbar 101 more easily than air is provided between the busbar 101 and the magnetic detection unit 103. Therefore, heat generated in the busbar 101 is easily conducted to a position close to the magnetic detection unit 103 through the resin layer of the resin-based material, and the temperature around the magnetic detection unit 103 is likely to rise. In addition, heat is easily conducted from the resin-based material to the sidewall of the case member 102, so heat is easily conducted to the magnetic detection unit 103 via the case member 102 and the substrate 109. Therefore, if the current to be measured flowing through the busbar 101 becomes large and the amount of heat generated increases, there is a risk that the magnetic detection unit 103 will become too hot and exceed its heat-resistant temperature.

[0023] Fig. 2 is a cross-sectional view of the current sensor 10 according to this embodiment taken along the YZ plane at line AA in Fig. 1. Fig. 3 is a plan view of the current sensor 10 in Fig. 2. In Fig. 3, the terminals of the magnetic detection unit 13 and the substrate 19 are omitted in order to show the positional relationship between the bus bar 11, the case member 12, and the magnetic detection unit 13 when viewed from the substrate 19 toward the bus bar 11 along the Z axis.

[0024] The current sensor 10 includes a bus bar 11, a case member 12, and a magnetic detection unit 13. The bus bar 11 is a plate-shaped conductive material, and a portion of it is formed integrally with the case member 12 by insert molding. The bus bar 11 is made of, for example, copper, brass, or aluminum, and a measurement current to be detected flows through the bus bar 11. The bus bar 11 is provided such that two opposing plate surfaces correspond to the top and bottom of the case member 12 (both sides in the Z-axis direction).

[0025] Note that both ends of busbar 11 in the X-axis direction, which are the connection portions with the outside, do not necessarily have to be line-symmetrical with respect to the Y-axis. Also, the portion of busbar 11 facing magnetic detection unit 13 may be set to have a smaller dimension in the Y-axis direction than other portions. Portions of busbar 11 other than the portion facing magnetic detection unit 13 do not have to be flat, and may be bent, for example.

[0026] The magnetic detection unit 13 is disposed at a position away from the bus bar 11 and facing the bus bar 11. In FIG. 3 , the magnetic detection unit 13 is disposed so that the center of the width of the magnetic detection unit 13 in the Y-axis direction overlaps with the center of the width of the bus bar 11 in the Y-axis direction when viewed along the Z-axis. However, the magnetic detection unit 13 only needs to be positioned so that it can measure the magnetic field generated when a current to be measured flows through the bus bar 11. Therefore, the magnetic detection unit 13 may be disposed at a position offset from the bus bar 11 rather than being entirely overlapped with it. However, it is preferable that a portion of the magnetic detection unit 13 overlaps with the opposing bus bar 11 when viewed along the Z-axis.

[0027] In the current sensor 10, a substrate 19 on which the magnetic detection unit 13 is mounted is fixed to a case member 12 in which the bus bar 11 is insert-molded. This allows the bus bar 11 and the magnetic detection unit 13 to be positioned with high precision.

[0028] A portion of the bus bar 11 is embedded in a first surface 14a of the storage space 14. The first surface 14a is a part of a surface that defines the storage space 14 and faces the magnetic detection unit 13 along a first direction (Z-axis direction). At the first surface 14a, the facing surface 11a of the bus bar 11 that faces the magnetic detection unit 13 is exposed, and therefore, air, which serves as a low thermal conductivity material, is present between the bus bar 11 and the magnetic detection unit 13, and the air is in contact with the facing surface 11a. The facing surface 11a of the bus bar 11 in the current sensor 10 is in contact with the air, which serves as a low thermal conductivity material, over its entire surface.

[0029] In the current sensor 10, only an air layer 15 is provided between the facing surface 11a of the busbar 11 and the magnetic detection unit 13. Air has a lower thermal conductivity than the resin-based material forming the case member 12. By bringing the air layer 15 into contact with the facing surface 11a of the busbar 11, heat from the busbar 11 is less likely to be transferred across the storage space 14 and directly to the magnetic detection unit 13. Furthermore, because heat is less likely to be transferred from the facing surface 11a of the busbar 11 to the sidewall of the storage space 14, heat transferred to the magnetic detection unit 13 via the sidewall of the storage space 14 and the substrate 19 is also less than in the conventional current sensor 100 (see FIG. 12 ). This reduces the influence of heat from the busbar 11 and allows the ambient temperature of the magnetic detection unit 13 to be kept lower than in the conventional current sensor 100. Therefore, the current to be measured that flows through the busbar 11 can be increased. Resin-based materials include materials made of resin and materials containing fillers or the like added to resin.

[0030] In the storage space 14, the bus bar 11 has an exposed facing surface 11a that faces the magnetic detection unit 13, and an opposite surface 11b opposite to the facing surface 11a that is embedded in the case member 12. From the viewpoint of suppressing heat transfer from the bus bar 11 from the facing surface 11a side to the magnetic detection unit 13, it is preferable that the entire facing surface 11a of the bus bar 11 is exposed and the entire opposite surface 11b is embedded in the case member 12. From the viewpoint of improving manufacturing efficiency by facilitating the formation and processing of the case member 12 and the bus bar 11, it is preferable that the facing surface 11a of the bus bar 11 and the first surface 14a of the storage space 14 form the same plane.

[0031] FIG. 4 is a cross-sectional view of a modified current sensor. Current sensor 20 according to the modified example differs from current sensor 10 in that the facing surface 11a and the first surface 14a are not flush with each other. In current sensor 10 shown in FIG. 2, the distance L1 between the facing surface 11a of busbar 11 and magnetic detection unit 13 in the first direction (Z-axis direction) is equal to the distance L2 between the first surface 14a of storage space 14 and magnetic detection unit 13 in the first direction (Z-axis direction). In contrast, in current sensor 20 shown in FIG. 4, the distance L1 between the facing surface 11a of busbar 11 and magnetic detection unit 13 is shorter than the distance L2 between the first surface 14a of storage space 14 and magnetic detection unit 13. By making the distance L1 shorter than the distance L2, heat transfer from busbar 11 to magnetic detection unit 13 via the resin-based material of case member 12 can be reduced.

[0032] 5 is a cross-sectional view of another modified example of a current sensor. In a current sensor 30 according to the other modified example, a distance L1 between the facing surface 11 a of the bus bar 11 and the magnetic detection unit 13 is greater than a distance L2 between the first surface 14 a of the storage space 14 and the magnetic detection unit 13. However, because the entire facing surface 11 a of the bus bar 11 is exposed in the storage space 14, air acts as a low thermal conductivity material, thereby suppressing the transfer of heat from the bus bar 11 to the magnetic detection unit 13.

[0033] 6 is a cross-sectional view of a current sensor 40 according to this embodiment. The current sensor 40 differs from the current sensor 10 in the configuration in which a magnetic shield 45 is disposed. The magnetic shield 45 includes a pair of flat plate-shaped magnetic shields 45A and 45B aligned in the Z-axis direction. The magnetic detection unit 13 and the bus bar 11 are disposed between the magnetic shields 45A and 45B in the Z-axis direction.

[0034] The magnetic shield 45A, which is arranged near the bus bar 11, is formed integrally with the case member 12 together with the bus bar 11, and is provided on the side of the bus bar 11 opposite to the side on which the magnetic detection unit 13 is arranged. The magnetic shield 45B, which is arranged near the magnetic detection unit 13, is formed integrally with the cover member 42, and is provided on the side of the magnetic detection unit 13 opposite to the side on which the bus bar 11 is arranged.

[0035] The magnetic shields 45A and 45B are, for example, formed by stacking multiple metal plates of the same shape. The magnetic shields 45A and 45B can block external magnetic field noise, improving the external magnetic field noise resistance of the magnetic detection unit 13. However, because only one of the magnetic shields 45A or 45B is effective in blocking external magnetic field noise, only one may be provided instead of a pair.

[0036] 7 is a cross-sectional view of a modification of the current sensor according to the present embodiment. Current sensor 50 according to this modification differs from current sensor 40 in that it includes a magnetic shield 55 that surrounds bus bar 11 and magnetic detection unit 13 and has a U-shaped cross section in the YZ plane that is orthogonal to the extension direction (X-axis direction) of bus bar 11.

[0037] The magnetic shield 55 has a base 55a disposed on the opposite side of the bus bar 11 from the magnetic detection unit 13, and side wall portions 55b extending from both ends of the base 55a along the Z-axis direction. The magnetic shield 55 is disposed so as to surround the bus bar 11 and the magnetic detection unit 13, i.e., so that the bus bar 11 and the magnetic detection unit 13 overlap with the base 55a when viewed along the Z-axis direction, and so that the bus bar 11 and the magnetic detection unit 13 overlap with the side wall portion 55b when viewed along the Y-axis direction. Therefore, the magnetic shield 55 can effectively block external magnetic field noise from reaching the bus bar 11 and the magnetic detection unit 13, improving the external magnetic field noise resistance of the current sensor 50.

[0038] 8 is a cross-sectional view of a current sensor 60 according to this embodiment. The current sensor 60 differs from the current sensor 10 in the shape of the bus bar 61 and the configuration of the magnetic detection unit 63, which performs differential detection. The current sensor 60 includes a first magnetic detection unit 63A and a second magnetic detection unit 63B as the magnetic detection unit 63, and is capable of detecting the magnetic field generated from the bus bar 61 based on the output of the first magnetic detection unit 63A and the output of the second magnetic detection unit 63B. The first magnetic detection unit 63A and the second magnetic detection unit 63B are formed by using Hall elements or magnetic resistance elements (GMR elements, TMR elements, etc.) having detection axes oriented in the same or opposite directions in the Z-axis direction.

[0039] In this embodiment, the busbar 61 has a cross-sectional shape perpendicular to the extension direction (X-axis direction), with a dimension D1 in the Z-axis direction (first direction) larger than a dimension D2 in the Y-axis direction (second direction) perpendicular to the Z-axis direction. That is, the busbar 61 has a plate-like shape with a narrower width in the Y-axis direction than in the Z-axis direction. Therefore, when a current to be measured flows, as shown by the dashed-dotted line in FIG. 8 , an elongated elliptical magnetic field is generated, with the Z-axis (first direction) component having a longer major axis than the Y-axis (second direction) component. Therefore, near the magnetic detection unit 63, the component in the first direction (Z-axis direction) is larger, forming a magnetic field in the opposite direction. However, instead of the busbar 61 having a dimension D1 larger than the dimension D2 (dimension D1 > dimension D2), a busbar having a dimension D1 equal to or smaller than the dimension D2 (dimension D1 ≦ dimension D2) may be used.

[0040] The differential current sensor 60 uses a first magnetic detection unit 63A and a second magnetic detection unit 63B, which are highly sensitive to magnetic fields in a specific direction (sensitivity direction), as the magnetic detection unit 63. The first magnetic detection unit 63A and the second magnetic detection unit 63B are arranged so that their sensitivity directions are approximately parallel. Furthermore, to achieve high measurement sensitivity, the first magnetic detection unit 63A and the second magnetic detection unit 63B are arranged in positions where the directions of the magnetic field caused by the current to be measured are approximately opposite, with their sensitivity directions approximately parallel to the direction of the magnetic field.

[0041] The magnetic fields of the current to be measured at the locations where the pair of first and second magnetic detection units 63A and 63B are located have vectors in opposite directions, and the difference between the magnetic fields as vectors is large. In the differential current sensor 60, the current measurement result is obtained based on the magnetic fields as vectors detected by the first and second magnetic detection units 63A and 63B.

[0042] 8, when the first magnetic detection unit 63A and the second magnetic detection unit 63B have the same sensitivity direction, the current measurement result is obtained based on the difference between the two detection signals from the first magnetic detection unit 63A and the second magnetic detection unit 63B. When the first magnetic detection unit 63A and the second magnetic detection unit 63B have opposite sensitivity directions, the current measurement result is obtained based on the sum of the two detection signals from the first magnetic detection unit 63A and the second magnetic detection unit 63B.

[0043] By detecting the magnetic field of the bus bar 61 based on the outputs of the first magnetic detection unit 63A and the second magnetic detection unit 63B, it is possible to eliminate the influence of external magnetic field noise common to the first magnetic detection unit 63A and the second magnetic detection unit 63B. Therefore, the current sensor 60 can accurately detect the induced magnetic field of the bus bar 61.

[0044] 9 is a cross-sectional view of a current sensor 70 according to this embodiment. The current sensor 70 differs from the current sensor 10 in that the magnetic detection unit 13 includes an output terminal portion 73, the output terminal portion 73 is held by a substrate 19, and the output terminal portion 73 is sealed with a sealant 74. By potting and sealing the output terminal portion 73 with the sealant 74, discharge from the bus bar 11 to the output terminal portion 73 is less likely to occur, and the voltage resistance of the current sensor 70 is improved.

[0045] The sealant 74 is provided to cover the output terminal portion (electrode terminal) 73 but not to cover the opposing surface 13a of the magnetic detection unit 13 that faces the bus bar 11. This makes it possible to reduce the heat of the bus bar 11 that is transferred to the magnetic detection unit 13 via the sealant 74, which has a higher thermal conductivity than the air in the storage space 14. This prevents the temperature of the magnetic detection unit 13 from increasing due to the heat of the bus bar 11.

[0046] 10 is a cross-sectional view of a current sensor 80 according to this embodiment. The current sensor 80 includes a cover member 82 that covers the storage space 14, a magnetic detection unit 13 that includes an output terminal portion 83 that is held by a substrate 19, and a holding member 84 that holds the substrate 19 to the cover member 82.

[0047] When heat from the busbar 11 is transferred to the circuit board 19 via the resin-based material that constitutes the case member 12 and the cover member 82, heat transfer is reduced at the contact point between the case member 12 and the cover member 82. Furthermore, since the circuit board 19 is held by the cover member 82 via the holding member 84 and an air layer is formed between the circuit board 19 and the cover member 82, heat is less likely to be transferred from the cover member 82 to the circuit board 19. Furthermore, the path along which heat is transferred via the resin-based material is longer. Therefore, it is possible to suppress a temperature rise in the magnetic detection unit 13 due to the heat from the busbar 11.

[0048] 11 is a cross-sectional view of a current sensor 90 according to this embodiment. The current sensor 90 differs from the current sensor 10 in that a low thermal conductivity material 95 other than the air layer 15 (see FIG. 2 ) is provided in contact with the opposing surface 11 a of the bus bar 11.

[0049] By providing a low thermal conductivity material 95 having a lower thermal conductivity than the resin-based material forming the case member 12, the temperature rise of the magnetic detection unit 13 caused by the heat of the bus bar 11 being transferred to the magnetic detection unit 13 can be reduced.

[0050] An example of the low thermal conductivity material 95 is porous ceramic. The thermal conductivity of porous ceramic varies depending on the type, but some are, for example, approximately 0.003 W / mK. This value is slightly higher than the thermal conductivity of air, but is sufficiently lower than the thermal conductivity of resin-based materials such as polyphenylene sulfide. Therefore, by providing the low thermal conductivity material 95, it is possible to reduce the heat transferred from the bus bar 11 to the magnetic detection unit 13, just like an air layer.

[0051] 11 , the low thermal conductivity material 95 does not need to be provided so as to cover the entire opposing surface 11 a of the bus bar 11 and the first surface 14 a of the storage space 14. For example, the low thermal conductivity material 95 may be provided so as to cover only the opposing surface 11 a. Alternatively, a configuration may be adopted in which a portion of the opposing surface 11 a of the bus bar 11 is covered with the low thermal conductivity material 95, and the remaining portion is covered with the air layer 15.

[0052] 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-mentioned embodiments alone, and is intended to include all modifications within the meaning and scope of the claims.

[0053] A simulation was performed on the ease of heat transfer from the busbar 11 to the magnetic detection unit 13 for the current sensor 10 according to the first embodiment shown in Fig. 2. A simulation was also performed on the ease of heat transfer from the busbar 101 to the magnetic detection unit 103 for the conventional current sensor 100 shown in Fig. 12. In these simulations, the current to be measured was continuously passed through the busbars 11 and 101 at 200 A, and the temperatures of the magnetic detection units 13 and 103 were determined when the temperatures of the busbars 11 and 101 reached 146°C.

[0054] The current sensor 10 was evaluated with the entire facing surface 11a of the busbar 11 exposed, and the distances L1 and L2 in the Z-axis direction between the facing surface 11a of the busbar 11 and the magnetic detection unit 13 being 4.2 mm. The conventional current sensor 100 differs from the current sensor 10 only in that the entire facing surface 101a of the busbar 101 is covered with a resin-based material having a thickness of 1.2 mm, and the conventional current sensor 100 was evaluated with the distances L1 being 3.0 mm and the distances L2 being 1.2 mm. The resin-based material constituting the case members 12 and 102 was polyphenylene sulfide (PPS).

[0055] As a result of the simulation, the temperature of the magnetic detection unit 13 of the current sensor 10 was 121.8°C, while the temperature of the magnetic detection unit 103 of the current sensor 100 was 129.0°C. In this way, by removing the resin-based material from the opposing surface 11a of the bus bar 11 and exposing the opposing surface 11a, the present invention was able to reduce the temperature rise in the magnetic detection unit 13 due to the influence of heat from the bus bar 11. From this simulation result, it can be seen that the current sensor 10 of the present invention can use a magnetic detection unit 13 with a heat-resistant temperature of 125°C, which cannot be used with the conventional current sensor 100.

[0056] INDUSTRIAL APPLICABILITY The present invention is useful as a current sensor provided with a bus bar through which a large current flows as a current to be measured.

[0057] 10: Current sensor 11: Bus bar 11a: Opposing surface 11b: Opposite surface 12: Case member (case) 13: Magnetic detection unit 13a: Opposing surface 14: Storage space 14a: First surface 15: Air layer (low thermal conductivity material) 19: Substrate 20: Current sensor 30: Current sensor 40: Current sensor 42: Cover member 45: Magnetic shield 45A: Magnetic shield 45B: Magnetic shield 50: Current sensor 55: Magnetic shield 55a: Base 55b: Side wall 60: Current sensor 61: Bus bar 63: Magnetic detection unit 63A: First magnetic detection unit 63B: Second magnetic detection unit 70: Current sensor 73: Output terminal portion 74: Sealant 80 : Current sensor 82 : Cover member 83 : Output terminal portion 84 : Holding member 90 : Current sensor 95 : Low thermal conductivity material 100 : Current sensor 101 : Bus bar 101a : Opposing surface 102 : Case member 103 : Magnetic detection portion 104 : Storage space 109 : Board D1 : Dimension D2 : Dimension L1 : Distance L2 : Distance

Claims

1. A bus bar through which a current to be measured flows; a magnetic detection unit capable of detecting magnetism generated by the bus bar; a case formed integrally with the bus bar and having a storage space for storing the magnetic detection unit, the magnetic detection unit is disposed at a position spaced apart from the bus bar and facing the bus bar, the bus bar is provided on a first surface of the storage space that defines the storage space and faces the magnetic detection unit along a first direction, a low thermal conductivity material having a thermal conductivity lower than that of a resin-based material forming the case is provided between the bus bar and the magnetic detection portion so as to be in contact with a surface of the bus bar facing the magnetic detection portion, the magnetic detection unit includes an output terminal unit, The output terminal portion is held by a substrate, A current sensor characterized in that the output terminal portion is sealed with a sealant having a thermal conductivity higher than that of air, and the sealant does not cover an opposing surface of the magnetic detection portion that faces the bus bar.

2. The current sensor according to claim 1 , wherein only an air layer is provided as the low thermal conductivity material between the bus bar and the magnetic detection portion.

3. The current sensor according to claim 2 , wherein the facing surface of the bus bar is exposed in the storage space, and a surface opposite to the facing surface is embedded in the case.

4. The current sensor according to claim 3 , wherein a distance in the first direction between the opposing surface of the bus bar and the magnetic detection portion is equal to or less than a distance in the first direction between the first surface of the storage space and the magnetic detection portion.

5. The current sensor according to claim 3 , wherein the opposing surface of the bus bar and the first surface of the storage space form a same plane.

6. The current sensor of claim 1 further comprising a magnetic shield.

7. the magnetic shield is a pair of flat plate-shaped magnetic shields arranged in the first direction, The current sensor according to claim 6 , wherein the bus bar and the magnetic detection portion are disposed between a pair of the magnetic shields each having a flat plate shape.

8. The current sensor according to claim 7 , wherein the magnetic shield, which has a flat plate shape and is disposed proximal to the bus bar, is integrally formed with the case together with the bus bar.

9. 7. The current sensor according to claim 6, wherein the magnetic shield has a base portion arranged on the opposite side of the bus bar from the magnetic detection portion in the first direction, and side wall portions extending from both ends of the base portion along the first direction.

10. 2. The current sensor according to claim 1, wherein the magnetic detection unit includes a first magnetic detection unit and a second magnetic detection unit, and is capable of detecting the magnetic field generated by the bus bar based on an output of the first magnetic detection unit and an output of the second magnetic detection unit.

11. The current sensor according to claim 10 , wherein a dimension of a cross-sectional shape of the bus bar perpendicular to an extension direction of the bus bar in the first direction is larger than a dimension of the cross-sectional shape in a second direction perpendicular to the first direction.

12. A cover for covering the storage space is provided, the magnetic detection unit includes an output terminal unit, The output terminal portion is held by a substrate, The current sensor of claim 1 , wherein the substrate is held by the cover.