Current sensor

Abstract

A current sensor 1 according to the present invention, which is suitable for reduction in height and size and is high in measurement accuracy, comprises: a magnetic sensor 2 including a magnetic device 21; a bus bar 3; a magnetic shield 4; and a cancel member 5 made of a magnetic body. The cancel member 5 is disposed at a position where a residual magnetic field generated by the magnetic shield 4 is weakened by a residual magnetic field generated by the cancel member 5. Thus, an offset error in a state where current is not flowing through the bus bar 3 can be reduced without complicated calculation when detecting magnetism.

Description

Current Sensor

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

[0002] In recent years, current sensors have been used to measure the current flowing through various devices in order to control the power supply systems of vehicles and other devices equipped with such devices. For example, some current sensors include a magnetic detection unit that detects the magnetic field generated from a bus bar and a magnetic shield that blocks external magnetic fields that may disturb the magnetic detection unit.

[0003] Patent Document 1 discloses a current sensor having a shield portion that shields magnetism in order to reduce offset errors included in the sensor output when no current flows through the bus bar. The current sensor has a first shield portion that generates a first magnetic field when no current flows through the bus bar, and a second shield portion that generates a second magnetic field that is opposite in direction to the first magnetic field, and is arranged so that the first magnetic field and the second magnetic field cancel each other out on the detection surface.

[0004] Patent Document 2 discloses a magnetic sensor that aims to solve the problem of reduced detection accuracy of the magnetic sensor due to hysteresis error caused by residual magnetic flux that occurs when a magnetic shield or the like is magnetized by detected magnetic flux, disturbance magnetic flux, etc. The magnetic sensor acquires a corrected physical quantity in which the hysteresis error caused by the residual magnetic flux is corrected based on the difference between a first output value from a first magnetic detection unit and a second output value from a second magnetic detection unit.

[0005] JP 2021-47147 A JP 2023-54490 A

[0006] The current sensor described in Patent Document 1 has a first shield portion and a second shield portion, and reduces offset errors by adjusting the positions of these two shield portions. However, because the current sensor has two shield portions, it is difficult to reduce its height and size. The magnetic sensor described in Patent Document 2 corrects hysteresis errors caused by residual magnetic flux based on the difference in output values ​​from the two magnetic detection portions, which results in a problem of complex calculations when detecting magnetism. Therefore, an object of the present invention is to provide a current sensor with good measurement accuracy that is suitable for reducing its height and size, and that can reduce offset errors when no current is flowing through the bus bar without complicating calculations when detecting magnetism.

[0007] As a means for solving the above-mentioned problems, the present invention has the following configuration: A current sensor including a magnetic sensor containing a magnetic device, a bus bar, and a magnetic shield, the current sensor including a canceling member made of a magnetic material, the canceling member being positioned so that the residual magnetic field generated by the magnetic shield is weakened by the residual magnetic field generated by the canceling member. The canceling member provided separately from the magnetic shield can weaken the residual magnetic field generated by the magnetic shield, thereby suppressing the influence of the residual magnetic field on magnetic field measurement.

[0008] The canceling member may be formed integrally with the magnetic sensor. By forming the canceling member and the magnetic sensor integrally, misalignment between the canceling member and the magnetic device of the magnetic sensor is less likely to occur. Therefore, compared to when the canceling member and the magnetic sensor are formed separately, there is less risk of errors occurring due to misalignment, resulting in a current sensor with good measurement accuracy.

[0009] The canceling member may be disposed inside a package that forms the outer shape of the magnetic sensor. The canceling member may be disposed on a surface of the magnetic device that faces the bus bar. The magnetic sensor may have a frame on which the magnetic device is mounted, and the canceling member may be disposed on the surface of the frame that is opposite the surface on which the magnetic device is mounted. The canceling member may be disposed on the outer peripheral surface of a package that forms the outer shape of the magnetic sensor. In a packaging process for manufacturing a magnetic sensor, the canceling member disposed in the above-mentioned portion can be easily formed by plating, bonding, or the like. This enables efficient manufacturing of current sensors.

[0010] The magnetic device may be a magnetoresistive element.

[0011] According to the present invention, the provision of a canceling member weakens the residual magnetic field generated by the magnetic shield, thereby suppressing the effects of hysteresis with a simple configuration. Furthermore, by locating the canceling member near the magnetic device, the effects of the residual magnetic field of the magnetic shield can be suppressed with a small canceling member. Therefore, a current sensor with good measurement accuracy that reduces errors caused by the hysteresis of the magnetic shield and is suitable for low-profile and miniaturization can be provided.

[0012] 1 is a perspective view schematically showing the configuration of a current sensor according to an embodiment of the present invention. FIG. 1 is a cross-sectional view schematically showing the configuration of the current sensor taken along line A-A of FIG. 1. FIG. 2 is a cross-sectional view schematically showing the configuration of a modified example of the current sensor of FIG. 2. FIG. 3 is a cross-sectional view schematically showing the configuration of a magnetic sensor in the current sensor of FIG. 3. FIG. 4 is a cross-sectional view schematically showing the configuration of a modified example of the magnetic sensor of FIG. 4. FIG. 4 is a cross-sectional view schematically showing the configuration of another modified example of the magnetic sensor of FIG. 4. FIG. 3 is a cross-sectional view schematically showing the configuration of a modified example of the current sensor of FIG. 3. FIG. 3 is a cross-sectional view schematically showing the configuration of another modified example of the current sensor of FIG. 3. FIG. 4 is a perspective view showing essential members, explaining the sizes of members constituting the current sensor of the example. FIG. 5 is a graph showing the results of measuring the influence of hysteresis on measurement for current sensors of the example and comparative example. FIG. 6 is a perspective view schematically showing the configuration of a conventional current sensor.

[0013] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. The same components in each drawing are designated by the same reference numerals, and descriptions thereof will be omitted where appropriate. Reference coordinates are shown in each drawing as appropriate to indicate the positional relationship of each component. In the reference coordinates, the extension direction of the bus bar is defined as the X direction, the width direction of the bus bar perpendicular to the X direction is defined as the Y direction, and the stacking direction of the bus bar and magnetic sensor perpendicular to the X and Y directions is defined as the Z direction. The Y direction is the direction of the sensitivity axis of the magnetic sensor, and the X and Z directions are perpendicular to the sensitivity axis.

[0014] Fig. 1 is a perspective view schematically illustrating the configuration of a current sensor 1 according to this embodiment. Fig. 2 is a cross-sectional view schematically illustrating the configuration of the current sensor 1 taken along line A-A in Fig. 1. As shown in these figures, the current sensor 1 includes a magnetic sensor 2, a bus bar 3, and a magnetic shield 4, and also includes a canceling member 5 that weakens the residual magnetic field from the magnetic shield 4. For ease of explanation, the first case 6 and the second case 7 shown in Fig. 1 are omitted from Fig. 2 and other figures referred to later.

[0015] The magnetic sensor 2 includes a magnetic device 21 and is mounted on a substrate (not shown). The magnetic device 21 is disposed opposite the bus bar 3 in the Z direction and detects a magnetic field (magnetism) emitted by the bus bar 3 when a current to be measured flows through the bus bar 3. A current flows through the bus bar 3 in the X direction. When the magnetic field generated when a current to be measured flows through the bus bar 3 is viewed along the Z direction, a magnetic field parallel to the Y direction is generated at a position overlapping the bus bar 3. Therefore, by aligning the detection surface of the magnetic sensor 2 (magnetic device 21) directly opposite the bus bar 3 in the Z direction so that the sensitivity axis of the magnetic sensor 2 is parallel to the Y direction, the magnetic field emitted by the bus bar 3 as an induced magnetic field can be accurately detected by the magnetic device 21.

[0016] For example, a magnetoresistive effect element, a Hall element, etc. can be used as the magnetic device 21. Note that the above-described configuration is an example in which a magnetoresistive effect element is used as the magnetic device 21, but when using another magnetic device 21, it is necessary to appropriately change the orientation of the detection surface, etc., and position the device.

[0017] The bus bar 3 extends in the X direction among the mutually orthogonal X, Y, and Z directions. The bus bar 3 is a plate-shaped conductor through which the current to be measured flows along the X direction, and is made of, for example, copper, brass, aluminum, etc. The normal direction of the surface of the bus bar 3 facing the magnetic sensor 2 is the Z direction.

[0018] 1 is held by being sandwiched between the first case 6 and the second case 7 from both sides in the Z direction. In the current sensor 1, the bus bar 3 configured as a separate body is incorporated into the first case 6 and the second case 7. However, the bus bar 3 may be molded integrally with the first case 6 or the second case 7 by insert molding or the like.

[0019] 2, at least a portion of the U-shaped magnetic shield 4 is insert-molded into the second case 7. The magnetic shield 4 is a metal plate-like body, and can be formed, for example, by stacking multiple plates of the same shape (U-shape). When viewed along the X direction, the magnetic shield 4 is configured in a U-shape including a bottom portion 41 and two sidewall portions 42 extending from both ends of the bottom portion 41 toward the Z2 side.

[0020] The bottom 41 has a plate surface parallel to the XY plane and is disposed on the Z1 side in the Z direction relative to the bus bar 3. The side wall 42 has a plate surface parallel to the XZ plane and extends from each of both ends of the bottom 41 in the Y direction toward the Z2 side in the Z direction. The magnetic shield 4 is disposed so as to surround both ends of the bus bar 3 in the Y direction and the Z1 side in the Z direction, and the magnetic sensor 2 is disposed between the side wall 42 at both ends of the magnetic shield 4 when viewed along the Z axis.

[0021] The provision of the magnetic shield 4 can suppress external magnetic noise to the magnetic sensor 2. However, since the magnetic shield 4 is made of a soft magnetic material, it may be magnetized by the magnetic field to be detected that is generated when the magnetic field to be measured flows through the bus bar 3, or by the disturbance magnetic field of the shielded object.

[0022] As described above, the magnetic shield 4 made of a soft magnetic material may have a different magnetic state when no magnetic field is applied, due to the influence of magnetic fields previously applied. This change in the magnetic state when no magnetic field is applied due to the influence of magnetic fields previously applied is called hysteresis (history phenomenon). The residual magnetic field from the magnetic shield 4 becomes noise when the magnetic device 21 detects magnetic fields, and therefore reduces the measurement accuracy of the current sensor 1.

[0023] Fig. 11 is a cross-sectional view schematically illustrating the configuration of a conventional current sensor 100. For example, when a current to be measured flows through the bus bar 3 as shown in Fig. 11, an induced magnetic field is generated as indicated by the dashed arrow in the figure. If the magnetic shield 4 is magnetized under the influence of the induced magnetic field as shown in Fig. 11, a residual magnetic field of the magnetic shield 4, indicated by the black arrow in the figure, is generated in the magnetic shield 4 even when no current flows through the bus bar 3, and this magnetic field affects the magnetic device 21 of the magnetic sensor 2. In particular, the U-shaped magnetic shield 4 has a larger hysteresis than a flat-plate-shaped magnetic shield, which will be described later, and this has a significant impact on degrading the measurement accuracy of the current sensor 1.

[0024] Therefore, in the current sensor 1, in order to reduce the influence of the residual magnetic field generated by the hysteresis of the magnetic shield 4, a cancel member 5 made of a magnetic material is provided separately from the magnetic shield 4. The cancel member 5 is disposed in a position where the residual magnetic field generated by the magnetic shield 4 is weakened by the residual magnetic field generated by the cancel member 5. In other words, the cancel member 5 is disposed in a position where the magnetic field generated by the magnetic shield 4 that passes through the magnetic device 21 and the magnetic field generated by the cancel member 5 that passes through the magnetic device 21 cancel each other out.

[0025] 2, the solid arrows indicate the residual magnetic field generated by the hysteresis of the magnetic shield 4, and the hollow arrows indicate the residual magnetic field generated by the canceling member 5. In other drawings, the residual magnetic field from the magnetic shield 4 is indicated by a solid arrow, and the residual magnetic field from the canceling member 5 is indicated by a hollow arrow, as appropriate.

[0026] As shown in the figure, by disposing the cancel member 5 between the magnetic device 21 and the bus bar 3, the direction of the residual magnetic field generated by the cancel member 5 and the direction of the residual magnetic field generated by the magnetic shield 4 are opposite to each other near the magnetic device 21. Therefore, the cancel member 5 weakens the residual magnetic field from the magnetic shield 4, and it is possible to suppress the effect of the hysteresis of the magnetic shield 4 on the magnetic device 21. Therefore, it is possible to suppress the effect of the hysteresis of the magnetic shield 4 and provide a current sensor 1 with high measurement accuracy.

[0027] 2 is an example, and the position at which the canceling member 5 is arranged in the magnetic sensor 2 is not limited to this. The canceling member 5 may be arranged at a position on the magnetic detection surface of the magnetic device 21 where the residual magnetic field from the canceling member 5 weakens the residual magnetic field generated by the magnetic shield 4. For example, the canceling member 5 may be arranged on the opposite side of the magnetic device 21 from the bus bar 3.

[0028] 2, only the counterclockwise magnetic field is shown on the Z2 side of the cancel member 5 by the white arrow, but a clockwise magnetic field is generated on the Z1 side of the cancel member 5. Therefore, even if the cancel member 5 is placed on the opposite side of the bus bar 3 with the magnetic device 21 in between, the residual magnetic field generated by the cancel member 5 faces the Y1 side near the magnetic device 21, and therefore the residual magnetic field generated by the magnetic shield 4 can be weakened.

[0029] Fig. 3 is a cross-sectional view schematically showing the configuration of a modified example of the current sensor 1 of Fig. 2. In the current sensor 1 shown in the figure, the magnetic sensor 2 and the canceling member 5 are integrally formed. By integrating them, misalignment between the magnetic device 21 of the magnetic sensor 2 and the canceling member 5 is less likely to occur. Therefore, the influence of the residual magnetic field of the magnetic shield 4 can be accurately canceled, making it possible to provide a current sensor 1 with high measurement accuracy.

[0030] Fig. 4 is a cross-sectional view schematically showing the configuration of the magnetic sensor 2 in the current sensor 1 of Fig. 3. In the magnetic sensor 2 shown in the figure, the canceling member 5 is disposed inside a package 22 made of molded resin or the like that forms the outer shape of the magnetic sensor 2. More specifically, the canceling member 5 is disposed on the surface of a surface 21S of a magnetic device 21 provided on an integrated circuit 24 on a frame 23 within the package 22 that faces the bus bar 3 (see Fig. 3).

[0031] As described above, by arranging the canceling member 5 inside the package 22, it is possible to reduce the distance between the canceling member 5 and the magnetic device 21. Therefore, the residual magnetic field from the canceling member 5 can efficiently suppress the influence of the residual magnetic field of the magnetic shield 4.

[0032] Furthermore, the canceling member 5 can be easily formed on the surface 21S of the magnetic device 21 in the process of forming the magnetic device 21. Methods for forming the canceling member 5 include plating, sputtering, and bonding.

[0033] The current sensor 1 of this embodiment includes a canceling member 5 for canceling the influence of hysteresis of the magnetic shield 4. In this way, the canceling member 5 for suppressing the influence of hysteresis of the magnetic shield 4 is disposed near the magnetic device 21 as a separate member from the magnetic shield 4 that shields magnetism. Therefore, it is possible to configure the canceling member 5 using a magnetic material that is smaller than the magnetic shield 4, thereby realizing the miniaturization of the current sensor 1 and suppressing the influence of hysteresis caused by residual magnetization of the magnetic shield 4.

[0034] 5 is a cross-sectional view schematically illustrating the configuration of a modified example of the magnetic sensor 2 of FIG. 4. In the magnetic sensor 2 shown in the figure, the canceling member 5 is formed on the surface of the frame 23. That is, the magnetic sensor 2 has a frame 23 on which the magnetic device 21 and the integrated circuit 24 are mounted, and the canceling member 5 is disposed on a surface 23S2 of the frame 23 that is behind the surface 23S1 on the Z1 side on which the magnetic device 21 is mounted. The canceling member 5 can be easily formed on the surface of the frame 23 by plating, bonding, or the like in the packaging process for manufacturing the magnetic sensor 2. Therefore, the current sensor 1 can be manufactured efficiently.

[0035] Fig. 6 is a cross-sectional view schematically showing the configuration of another modified example of the magnetic sensor 2 of Fig. 4. The magnetic sensor 2 shown in Fig. 6 has a configuration in which the canceling member 5 is arranged on the outer peripheral surface of the package 22. As with the aspects shown in Figs. 4 and 5, the canceling member 5 can be easily formed on the outer peripheral surface of the package 22 by plating, bonding, or the like in the packaging process for manufacturing the magnetic sensor 2. This allows the current sensor 1 including the canceling member 5 to be manufactured efficiently.

[0036] 7 is a cross-sectional view schematically illustrating the configuration of a modified example of the current sensor 1 of FIG. 3. As shown in the figure, a C-shaped (core-shaped) magnetic shield 4 may be used for the current sensor 1 instead of the U-shaped magnetic shield 4. Even when a C-shaped magnetic shield 4 is used, the provision of a cancellation member 5 can suppress the effect of the residual magnetic field of the magnetic shield 4 on the magnetic device 21, thereby improving the measurement accuracy of the current sensor 1.

[0037] 8 is a cross-sectional view schematically illustrating the configuration of another modified example of the current sensor 1 of FIG. 3. As shown in the figure, a parallel plate type may be used as the magnetic shield 4 of the current sensor 1 instead of the U-shaped type. Even when a parallel plate type magnetic shield 4 is used, the provision of the canceling member 5 can suppress the influence of hysteresis of the magnetic shield 4, thereby improving the measurement accuracy of the current sensor 1.

[0038] Fig. 9 is a perspective view showing essential components for explaining the dimensions (sizes) of the components constituting the current sensor 1 of the embodiment. Note that Fig. 9 and other drawings are schematic diagrams whose size has been adjusted for convenience of explanation, and the dimensions of the components constituting the current sensor 1 do not correspond to the actual size.

[0039] The dimensions of each part of the current sensor 1 of the example are as follows: The magnetic shield 4 used had a bottom 41 with a width A in the Y direction (gap A in the Y direction between the two side walls 42) of 10 mm, a thickness B of the bottom 41 and the side walls 42 of 2 mm, a depth C of the bottom 41 and the side walls 42 in the X direction of 6 mm, and a length D of the side walls 42 protruding in the Z direction from both sides of the bottom 41 of 6 mm.

[0040] The canceling member 5 used had a width a in the Y direction of 1 mm, a thickness b in the Z direction of 0.03 mm, and a depth c in the X direction of 0.1 mm. The gap E in the Z direction between the magnetic shield 4 and the magnetic device 21 (the gap between the Z2-side end of the side wall portion 42 and the Z1-side detection surface of the magnetic device 21) was 0.5 mm, and the gap e in the Z direction between the canceling member 5 and the magnetic device 21 was 0.05 mm.

[0041] The current sensor 100 of the comparative example differs from the current sensor 1 of Example 1 in that it does not have a cancellation member 5, and the dimensions of the width A, thickness B, depth C and length D of the magnetic shield 4, as well as the gap E in the Z direction between the magnetic shield 4 and the magnetic device 21, are the same as those of the current sensor 1.

[0042] For the current sensor 1 and current sensor 100 described above, the current to be measured input to the busbar 3 was changed stepwise at room temperature from 0 A to +450 A, from +450 A to 0 A, from 0 A to −450 A, and from −450 A to 0 A, and the output from the current sensor 1 was measured. Note that the + and − current values ​​indicate the direction of the current to be measured in the busbar 3. That is, the current to be measured was increased or decreased in the range from 0 to 450 A, and then the current to be measured was increased or decreased in the opposite direction in the range from 0 to 450 A, and measurements were taken.

[0043] 10 is a graph showing the linearity (%) of the measured output, calculated by comparing the measured output with an approximate line based on all the measured values. For example, if the output value measured for a certain current is 101 and the calculated output value based on the approximate line calculated based on all the measured values ​​is 100, the linearity is +1% = (101 - 100) / 100 x 100.

[0044] The graph in Figure 10 shows the results of measuring the effect of hysteresis of the magnetic shield 4 for the current sensor 1 of the embodiment shown in Figure 3 and the current sensor 100 of the comparative example shown in Figure 11, where the solid line shows the embodiment and the dashed line shows the comparative example.

[0045] As shown in the graph of FIG. 10, by disposing the canceling member 5 on the magnetic sensor 2, the influence of the residual magnetic field due to the hysteresis of the magnetic shield can be suppressed, and the linearity of the measurement by the current sensor 1 is improved.

[0046] The graph shown in Fig. 10 is discontinuous at a current of 0 A. This is because the evaluation result when the current is changed and then returned to 0 A differs from the evaluation result at 0 A at the start point due to the influence of hysteresis.

[0047] In the current sensor 1 of the embodiment, the canceling member 5 is disposed near the magnetic device 21, and the influence of the residual magnetic field is suppressed by the small canceling member 5. The small canceling member 5 improves the linearity of the measurement by the current sensor 1, which is advantageous for making the current sensor 1 smaller, thinner, and lighter.

[0048] According to the results of the current sensor 1 of the embodiment, by arranging the cancel member 5 near the magnetic device 21 so that the gap e between the magnetic device 21 of the magnetic sensor 2 and the cancel member 5 is 1 / 20 to 4 / 20 of the gap E between the magnetic device 21 and the magnetic shield 4, or 0.25 to 0.10 mm, and by using a small cancel member 5 whose width a is 1 / 20 to 4 / 20 of the width A of the bottom 41 of the magnetic shield 4, whose thickness b is 1 / 200 to 6 / 200 of the thickness B of the magnetic shield 4, and whose depth c is approximately 1 / 120 to 4 / 120 of the depth C of the magnetic shield 4, it can be said that the linearity in the measurement of the current sensor 1 can be improved.

[0049] 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.

[0050] The present invention is useful as a current sensor for measuring a current to be measured flowing through equipment, for example, in order to control the power supply system of a vehicle or the like equipped with various equipment.

[0051] 1: Current sensor 2: Magnetic sensor 21: Magnetic device 21S: Surface 22: Package 23: Frame 23S1: Face 23S2: Face 24: Integrated circuit 3: Bus bar 4: Magnetic shield 41: Bottom 42: Side wall 5: Cancel member 6: First case 7: Second case 100: Current sensor A: Width B: Thickness C: Depth D: Length E: Gap a: Width b: Thickness c: Depth e: Gap

Claims

1. A current sensor comprising a magnetic sensor containing a magnetic device, a bus bar, and a magnetic shield, the current sensor having a cancellation member made of a magnetic material, the cancellation member being positioned at a position where the residual magnetic field generated by the magnetic shield is weakened by the residual magnetic field generated by the cancellation member.

2. The current sensor according to claim 1, wherein the canceling member is formed integrally with the magnetic sensor.

3. The current sensor according to claim 2, wherein the canceling member is disposed inside a package that defines the outer shape of the magnetic sensor.

4. The current sensor according to claim 2, wherein the canceling member is disposed on a surface of the magnetic device facing the bus bar.

5. The current sensor according to claim 2, wherein the magnetic sensor has a frame on which the magnetic device is mounted, and the canceling member is disposed on a surface of the frame opposite to a surface on which the magnetic device is mounted.

6. The current sensor according to claim 2, wherein the canceling member is disposed on an outer peripheral surface of a package that defines the outer shape of the magnetic sensor.

7. The current sensor according to claim 1, wherein the magnetic device is a magnetoresistance effect element.

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