JP5678287B2 - Current sensor - Google Patents

Description

  The present invention relates to a current sensor that measures current without contact. In particular, the present invention relates to a current sensor having a failure determination function.

  In fields such as motor drive technology in electric vehicles and hybrid cars, a relatively large current is handled, and thus a current sensor capable of measuring a large current in a non-contact manner is required for such applications. As such a current sensor, a method of detecting a change in magnetic field caused by a current to be measured by a magnetic sensor has been proposed. For example, Patent Document 1 discloses a current sensor using a magnetoresistive element as an element for a magnetic sensor.

  By the way, in the non-contact current sensor as described above, the current detection performance may be deteriorated due to aging of the magnetic sensor element or the like. For this reason, it may be necessary to determine the failure of the current sensor. Patent Document 2 discloses a current sensor that has a failure determination function, and performs a failure determination by passing an inspection current through a coil when a current to be measured is stopped.

JP 2002-156390 A JP 2006-145426 A

  In the current sensor disclosed in Patent Document 2, an inductive magnetic field corresponding to the inspection current is generated by flowing an inspection current through the coil, and failure determination is performed based on the detected measurement value. For this reason, in the above-described current sensor, if even a small amount of current to be measured flows, it is affected by an induced magnetic field generated by the current to be measured, and failure determination cannot be performed accurately. That is, in the above-described current sensor, there is a problem that the failure determination is limited to a case where the current to be measured which is a measurement target of the current sensor is not conductive.

  The present invention has been made in view of such a point, and an object thereof is to provide a current sensor having a failure determination function capable of determining a failure even when a current to be measured is passed.

In the current sensor of the present invention, the sensitivity axis of the first magnetic sensor element and the second magnetic sensor element whose absolute value of sensitivity is substantially equal to the first magnetic sensor element are opposite to each other. A series circuit connected in series; a composite characteristic measuring unit that calculates a composite characteristic of the series circuit;
Have a, a malfunction determining unit for determining a failure if the combined characteristic calculated in the composite characteristic measuring unit is out of the predetermined range, the first magnetic sensor element, and the second magnetic sensor element is a magnetic The combined characteristic measuring unit calculates a combined resistance value of the series circuit as the combined characteristic .

  According to this configuration, the first magnetic sensor element and the second magnetic sensor element constituting the current sensor are arranged so that the absolute values of the sensitivity are equal to each other and the sensitivity axes are opposite to each other. . Thereby, the composite characteristic of the series circuit in which the first magnetic sensor element and the second magnetic sensor element are connected becomes substantially constant regardless of whether or not the current to be measured is flowing. For this reason, it is possible to perform failure determination in real time by calculating the composite characteristics of the series circuit. That is, it is possible to provide a current sensor having a failure determination function capable of determining a failure even when a current to be measured is passed.

In the current sensor of the present invention, a constant voltage source may be connected to the series circuit, and the combined characteristic measurement unit may calculate the combined resistance value from a current value flowing through the series circuit. In the current sensor of the present invention, a constant current source may be connected to the series circuit, and the combined characteristic measurement unit may calculate the combined resistance value from a voltage generated in the series circuit.

  In the current sensor of the present invention, the first magnetic sensor element and the second magnetic sensor element are Hall elements, and the composite characteristic measurement unit may calculate a voltage value of the series circuit as the composite characteristic. good.

  In the current sensor of the present invention, the first magnetic sensor element and the second magnetic sensor element whose absolute value of sensitivity is substantially equal to the first magnetic sensor element are arranged so that the sensitivity axes are opposite to each other. And a third magnetic sensor element and a fourth magnetic sensor element having an absolute value of sensitivity substantially equal to the third magnetic sensor element are arranged so that the sensitivity axes are opposite to each other, The magnetic sensor element and the third magnetic sensor element are arranged so that sensitivity axes are opposite to each other, and one end of the first magnetic sensor element and one end of the second magnetic sensor element are Connected, one end of the third magnetic sensor element and one end of the fourth magnetic sensor element are connected, and the other end of the first magnetic sensor element and the other end of the third magnetic sensor element are connected Connected, the other end of the second magnetic sensor element and the A bridge circuit formed by connecting the other end of each of the four magnetic sensor elements; a composite characteristic measurement unit that calculates a composite characteristic of the bridge circuit; and a composite characteristic calculated by the composite characteristic measurement unit is out of a predetermined range. A failure determination unit that determines a failure in some cases.

  According to this configuration, the first magnetic sensor element and the second magnetic sensor constituting the current sensor are arranged such that the absolute values of the sensitivity are equal to each other and the sensitivity axes are opposite to each other. The third magnetic sensor element and the fourth magnetic sensor are arranged so that the absolute values of sensitivity are equal to each other and the sensitivity axes are opposite to each other. The first magnetic sensor element and the third magnetic sensor element are arranged so that the sensitivity axes are opposite to each other. As a result, the combined characteristics of the bridge circuit formed by connecting the first magnetic sensor element, the second magnetic sensor element, the third magnetic sensor element, and the fourth magnetic sensor element are obtained when the current to be measured flows. It becomes substantially constant regardless of whether or not it exists. For this reason, it is possible to perform failure determination in real time by calculating the composite characteristics of the bridge circuit. That is, it is possible to provide a current sensor having a failure determination function capable of determining a failure even when a current to be measured is passed.

  In the current sensor of the present invention, the first magnetic sensor element, the second magnetic sensor element, the third magnetic sensor element, and the fourth magnetic sensor element are magnetoresistive elements, and the combined characteristics The measurement unit may calculate a combined resistance value of the bridge circuit as the combined characteristic. In the current sensor of the present invention, a constant voltage source may be connected to the bridge circuit, and the combined characteristic measurement unit may calculate the combined resistance value from a current value flowing through the bridge circuit. In the current sensor of the present invention, a constant current source may be connected to the bridge circuit, and the combined characteristic measurement unit may calculate the combined resistance value from a voltage generated in the bridge circuit.

  In the current sensor of the present invention, the first magnetic sensor element and the fourth magnetic sensor element are arranged at one end of a substantially U-shaped current path through which a current to be measured flows, and the second magnetic sensor element The magnetic sensor element and the third magnetic sensor element may be disposed at the other end of the substantially U-shaped current path.

  According to this configuration, since the direction of the induced magnetic field is reversed between one end and the other end of the substantially U-shaped current path, the sensitivity axes of the first to fourth magnetic sensor elements are all in the same direction. can do. Thereby, since one kind of magnetic sensor element is sufficient in the manufacturing process, the process of arranging the magnetic sensor element can be simplified.

  In the current sensor of the present invention, at least a pair of magnetic sensor elements constituting the current sensor are arranged such that absolute values of sensitivity are equal to each other and sensitivity axes are opposite to each other. Thereby, the composite characteristic of the circuit including these magnetic sensor elements becomes substantially constant regardless of whether or not the current to be measured is flowing. For this reason, it is possible to perform failure determination in real time by using the composite characteristic of the circuit for failure determination. That is, it is possible to provide a current sensor having a failure determination function capable of determining a failure even when a current to be measured is passed.

It is a circuit diagram shown about the structural example of the current sensor which concerns on embodiment. It is a circuit diagram shown about another structural example of the current sensor which concerns on embodiment. It is a schematic diagram which shows the specific structural example of a bridge circuit. It is a flowchart which shows the failure determination process of the current sensor which concerns on embodiment.

  Hereinafter, embodiments will be described in detail with reference to the drawings.

  FIG. 1 is a circuit diagram (circuit block diagram) illustrating a configuration example of a current sensor according to the present embodiment. A current sensor 1 shown in FIG. 1 includes a series circuit (half-bridge circuit) 11 including two magnetic sensor elements 11a and 11b, which are magnetic detection elements, and characteristics of the series circuit 11 (combined characteristics of the magnetic sensor elements 11a and 11b). ) For measuring and calculating), a failure determination unit 13 for determining whether or not the current sensor 1 has failed based on the combined characteristic calculated by the combined characteristic measuring unit 12, and supplying power to the series circuit 11 And a power supply circuit 14 for performing the operation. Here, the arrow attached to the magnetic sensor elements 11a and 11b represents the direction of the sensitivity axis of each magnetic sensor element. The power supply circuit 14 is provided outside the current sensor 1 and may not be included in the configuration of the current sensor 1.

  In the series circuit 11, one end of the magnetic sensor element (first magnetic sensor element) 11a and one end of the magnetic sensor element (second magnetic sensor element) 11b are electrically connected, and the output terminal of the sensor output Out It has become. Further, the other end of the magnetic sensor element 11 a and the other end of the magnetic sensor element 11 b are external connection ends of the series circuit 11. The composite characteristic measuring unit 12 is connected to the series circuit 11 so that the composite characteristic of the series circuit 11 can be measured. The connection relationship between the composite characteristic measuring unit 12 and the series circuit 11 is not limited to that shown in FIG. The failure determination unit 13 is connected to the composite characteristic measurement unit 12 so that failure determination can be performed based on information from the composite characteristic measurement unit 12. The series circuit 11 is connected to a power supply circuit 14 that is a power supply source.

  In the current sensor 1, the magnetic sensor element 11a and the magnetic sensor element 11b are elements whose characteristics are changed by an induced magnetic field generated by a current to be measured flowing through a current line (not shown). Examples of such a magnetic sensor element include a magnetoresistive element and a Hall element. When the above-described series circuit 11 is configured using the magnetic sensor element having such a property, the electrical characteristic (for example, voltage) of the connection point between one end of the magnetic sensor element 11a and one end of the magnetic sensor element 11b is as follows. It fluctuates according to the magnitude of the induced magnetic field generated by the current to be measured. Therefore, by extracting the electrical characteristics of the connection point as the sensor output Out, the magnitude of the induced magnetic field can be calculated from the fluctuation of the electrical characteristics, and the magnitude of the current to be measured can be calculated.

  Here, in the current sensor 1, the magnetic sensor element 11a and the magnetic sensor element 11b have the same absolute value of sensitivity. The magnetic sensor element 11a and the magnetic sensor element 11b are arranged so that the sensitivity axes are opposite to each other. For this reason, the composite characteristic of the series circuit 11 including the magnetic sensor elements 11a and 11b in a normal state is substantially constant without depending on the value of the current to be measured.

  For example, consider using a magnetoresistive effect element whose electrical resistance (sometimes simply referred to as resistance) changes according to an external magnetic field for the magnetic sensor element 11a and the magnetic sensor element 11b. Since the magnetoresistive effect element has a property that the electric resistance changes in accordance with an external magnetic field, the electric resistance is suitable as a characteristic used for failure determination. Therefore, here, combined resistance is adopted as the combined characteristic. Assuming that the initial value of the electric resistance of the magnetic sensor element 11a (value in the absence of magnetic field) and the initial value of the electric resistance of the magnetic sensor element 11b (value in the absence of magnetic field) are R, these two magnetic sensor elements 11a and 11b are The initial value (value in the absence of a magnetic field) of the combined resistance of the series circuit 11 connected in series is 2R. The magnetic sensor elements 11a and 11b do not have to have the same initial resistance value as long as the absolute value of sensitivity (here, the absolute value of the resistance change) is substantially equal.

  It is assumed that the resistance of the magnetic sensor element 11a changes by ΔR due to the induced magnetic field of the current to be measured and becomes R + ΔR. Since the absolute value of the sensitivity of the magnetic sensor element 11b is equal to that of the magnetic sensor element 11a and the direction of the sensitivity axis is opposite to that of the magnetic sensor element 11a, the resistance change in the magnetic sensor element 11b is −ΔR. That is, the resistance of the magnetic sensor element 11b at this time is R−ΔR. Therefore, the combined resistance is (R + ΔR) + (R−ΔR) = 2R, and there is no change from the initial value. In order to establish the equation, specifically, two elements having the same characteristics may be arranged in opposite directions. Alternatively, two elements whose resistance increase and decrease are opposite to each other with respect to the same induced magnetic field (for example, when one is + ΔR and the other is −ΔR) may be arranged in the same direction. As described above, in the current sensor 1, appropriate failure determination is possible as long as the above equation can be established. Therefore, the specific arrangement of the magnetic sensor elements 11 a and 11 b in the current sensor 1 is particularly important. It is not limited. Further, the conditions for establishing the above equation are collectively referred to as “the sensitivity axis is in the reverse direction”. An example of an element in which the increase / decrease in resistance is reversed as described above is a GMR element in which the direction of the pinned layer is reversed.

  As described above, the magnetic sensor element 11a and the magnetic sensor element 11b are arranged so that the absolute values of the sensitivity are equal to each other and the sensitivity axes are opposite to each other. In the case of using an effect element, the combined resistance) is generally constant regardless of the external magnetic field. On the other hand, if an abnormality due to secular change or the like occurs in the magnetic sensor element 11a or 11b and the sensitivity of the magnetic sensor element 11a or 11b changes, the balance between the magnetic sensor element 11a and the magnetic sensor element 11b is lost, and the series circuit 11 composite characteristics are not constant. For this reason, the failure determination unit 13 determines whether or not the composite characteristic is within a predetermined range, thereby detecting an abnormality in the magnetic sensor element 11a or the magnetic sensor element 11b and determining whether or not there is a failure. it can.

  Note that the “predetermined range” used for failure determination in the failure determination unit 13 is determined in consideration of factors such as measurement error, element characteristic variation, and measurement current range. For example, the failure determination can be performed by setting a range of about ± 2% with respect to the reference value (initial value) of the composite characteristic as a “predetermined range”. It should be noted that a plurality of the “predetermined ranges” may be provided and the determination at another stage may be performed. Specifically, as the “predetermined range”, a “wide predetermined range” (for example, a range of about ± 3% relative to the reference value of the composite characteristic) and a “narrow predetermined range” (for example, the reference value of the composite characteristic) If the measured composite characteristics exceed “narrow predetermined range”, perform “Caution” and exceed “wide predetermined range”. A configuration may be adopted in which “failure determination” is performed in the case of a failure. Further, the “predetermined range” is not limited to having a range. For example, the “predetermined range” may be set as one point only for the reference value of the composite characteristic, and “failure determination” may be performed immediately when the reference value of the composite characteristic is deviated.

  In the current sensor 1, the method of measuring the combined resistance as the combined characteristic differs depending on whether the power supply circuit 14 is a constant current source or a constant voltage source. For example, when the power supply circuit 14 is a constant current source, the combined characteristic measurement unit 12 can calculate the combined resistance by measuring the voltage applied to the series circuit 11. When the power supply circuit 14 is a constant voltage source, the composite characteristic measuring unit 12 can calculate the combined resistance by measuring the current flowing through the series circuit 11. As described above, the parameters measured by the composite characteristic measuring unit 12 vary depending on the type of the power source, etc. Therefore, the connection relationship between the series circuit 11 and the composite characteristic measuring unit 12 calculates the composite resistance by appropriate measurement. Anything is possible.

  In the magnetoresistive effect element, for a magnetic field exceeding a linear region (a measurement region in which the output changes substantially linearly with respect to the magnetic field), the resistance change tends to be saturated and the resistance change amount tends to be small. It is also possible to detect whether or not appropriate current measurement is performed using this. For example, the linear regions of the two magnetic sensor elements are differentiated in advance. In this state, if a large current to be measured flows and a large induction magnetic field is generated, one of the magnetic sensor elements is saturated first, and the resistance change becomes small. Then, the balance of the composite characteristic (combined resistance) of the two magnetic sensor elements is lost. Thus, by making the linear regions of the two magnetic sensor elements different, it is possible to detect that one of the magnetic sensor elements is saturated and it is difficult to perform appropriate current measurement.

  In addition, if it is the structure which can implement | achieve the function of the said current sensor 1, about the specific mounting aspect, such as the synthetic | combination characteristic measurement part 12, the failure determination part 13, and the power supply circuit 14, will not be restricted especially. For example, these may be provided outside the current sensor. More specifically, various circuits such as the composite characteristic measurement unit 12, the failure determination unit 13, and the power supply circuit 14 may be provided in an IC outside the current sensor. Thus, by realizing various circuits with an IC outside the current sensor, an excellent current sensor can be realized while suppressing an increase in cost.

  In the above, the case where magnetoresistive effect elements are used as the magnetic sensor element 11a and the magnetic sensor element 11b has been described as an example. However, the magnetic sensor elements that can be used as the magnetic sensor element 11a and the magnetic sensor element 11b are described here. Not limited. For example, Hall elements can be used as the magnetic sensor element 11a and the magnetic sensor element 11b. Hereinafter, a case where Hall elements are used as the magnetic sensor element 11a and the magnetic sensor element 11b will be briefly described.

  The Hall element is an element utilizing a phenomenon (Hall effect) in which Lorentz force acts on charged particles flowing through the element in a magnetic field, thereby generating an electromotive force. Since the Hall element has a property that an electromotive force (voltage or potential difference) changes according to an external magnetic field, an electromotive force (voltage or potential difference) is suitable as a characteristic used for failure determination. Therefore, in the case where Hall elements are used as the magnetic sensor element 11a and the magnetic sensor element 11b, an electromotive force (voltage or potential difference) of a series circuit is employed as a composite characteristic. Note that the initial value of the electromotive force of the magnetic sensor element 11a (value in the absence of magnetic field) and the initial value of the electromotive force of the magnetic sensor element 11b (value in the absence of magnetic field) are usually zero. For this reason, the initial value (value in the absence of a magnetic field) of the electromotive force of the series circuit 11 in which these two magnetic sensor elements 11a and 11b are connected in series is zero.

  It is assumed that the electromotive force of the magnetic sensor element 11a changes by ΔV due to the induced magnetic field of the current to be measured and becomes ΔV. Since the absolute value of the sensitivity of the magnetic sensor element 11b is equal to that of the magnetic sensor element 11a and the direction of the sensitivity axis is opposite to that of the magnetic sensor element 11a, the change in electromotive force in the magnetic sensor element 11b is −ΔV. . That is, the electromotive force of the magnetic sensor element 11b at this time is −ΔV. For this reason, the electromotive force of the series circuit 11 is ΔV + (− ΔV) = 0, and there is no change from the initial value.

  As described above, even when Hall elements are used as the magnetic sensor element 11a and the magnetic sensor element 11b, the combined characteristics (here, electromotive force) of the series circuit 11 are generally constant regardless of the external magnetic field. For this reason, the failure determination unit 13 determines whether or not the composite characteristic is within a predetermined range, thereby detecting an abnormality in the magnetic sensor element 11a or the magnetic sensor element 11b and determining whether or not there is a failure. it can.

  As described above, in the current sensor 1 of the present embodiment, the first magnetic sensor element 11a and the second magnetic sensor 11b constituting the current sensor 1 have the same absolute value of sensitivity, and the sensitivity axis. Are arranged in opposite directions. Thereby, the composite characteristic of the series circuit 11 formed by connecting the first magnetic sensor element 11a and the second magnetic sensor element 11b becomes substantially constant regardless of whether or not the current to be measured is flowing. For this reason, by calculating the composite characteristic of the series circuit 11 in the composite characteristic measuring unit 12, the failure determination unit 13 can perform the failure determination in real time. That is, it is possible to provide a current sensor having a failure determination function capable of determining a failure even when a current to be measured is passed.

  FIG. 2 is a circuit diagram (circuit block diagram) illustrating a configuration example of a current sensor having a mode different from that in FIG. The current sensor 2 shown in FIG. 2 includes a bridge circuit 21 including four magnetic sensor elements 21a, 21b, 21c, and 21d, which are magnetic detection elements, and characteristics of the bridge circuit 21 (magnetic sensor elements 21a, 21b, 21c, and 21d). A composite characteristic measuring unit 22 for measuring and calculating a composite characteristic), a failure determining unit 23 for determining whether the current sensor 2 has a failure based on the composite characteristic calculated by the composite characteristic measuring unit 22, and a bridge circuit 21. And a power supply circuit 24 for supplying electric power. Here, the arrows attached to the magnetic sensor elements 21a, 21b, 21c, and 21d indicate the directions of the sensitivity axes of the magnetic sensor elements. The power supply circuit 24 is provided outside the current sensor 2 and may not be included as a configuration of the current sensor 2.

  In the bridge circuit 21, one end of the magnetic sensor element (first magnetic sensor element) 21a and one end of the magnetic sensor element (second magnetic sensor element) 21b are electrically connected, and the output terminal of the sensor output Out1. It has become. One end of the magnetic sensor element (third magnetic sensor element) 21c and one end of the magnetic sensor element (fourth magnetic sensor element) 21d are electrically connected and serve as an output end of the sensor output Out2. Further, the other end of the magnetic sensor element 21a and the other end of the magnetic sensor element 21c are electrically connected, and the other end of the magnetic sensor element 21b and the other end of the magnetic sensor element 21d are electrically connected to each other. This is an external connection end of the circuit 21. The composite characteristic measurement unit 22 is connected to the bridge circuit 21 so that the composite characteristic of the bridge circuit 21 can be measured. The connection relationship between the composite characteristic measuring unit 22 and the bridge circuit 21 is not limited to that shown in FIG. The failure determination unit 23 is connected to the composite characteristic measurement unit 22 so that failure determination can be performed based on information from the composite characteristic measurement unit 22. The bridge circuit 21 is connected to a power supply circuit 24 that is a power supply source.

  In the current sensor 2, the magnetic sensor elements 21a, 21b, 21c, and 21d are elements whose characteristics are changed by an induced magnetic field generated by a current to be measured flowing through a current line (not shown). This is the same as the current sensor 1 in FIG.

  In the current sensor 2, the magnetic sensor element 21a and the magnetic sensor element 21b have the same absolute value of sensitivity, and the magnetic sensor element 21c and the magnetic sensor element 21d have the same absolute value of sensitivity. . The magnetic sensor element 21a and the magnetic sensor element 21b are arranged so that the sensitivity axes are opposite to each other, and the magnetic sensor element 21c and the magnetic sensor element 21d are such that the sensitivity axes are opposite to each other. Is arranged. For this reason, the composite characteristic of the bridge circuit 21 including the magnetic sensor elements 21a, 21b, 21c, and 21d in a normal state does not depend on the value of the current to be measured and is substantially constant.

  For example, consider that a magnetoresistive effect element whose electric resistance changes according to an external magnetic field is used for the magnetic sensor elements 21a, 21b, 21c, and 21d, and that a combined resistance is adopted as a combined characteristic. When the initial value of the electric resistance of the magnetic sensor elements 21a, 21b, 21c, and 21d (value in the absence of magnetic field) is R, the initial value of the combined resistance of the series circuit in which the magnetic sensor elements 21a and 21b are connected in series (in the absence of magnetic field) Value) is 2R, and the initial value (the value in the absence of a magnetic field) of the combined resistance of the series circuit in which the magnetic sensor elements 21c and 21d are connected in series is 2R. For this reason, in the bridge circuit 21 having a configuration in which two series circuits are connected in parallel, the initial value of the combined resistance (value in the absence of a magnetic field) is R. The magnetic sensor elements 21a and 21b or the magnetic sensor elements 21c and 21d are not equal in their initial resistance values if the absolute values of sensitivity (here, the absolute values of resistance changes) are substantially equal. Good.

  It is assumed that the resistance of the magnetic sensor element 21a is changed by ΔR1 due to the induced magnetic field of the current to be measured and becomes R + ΔR1. Further, it is assumed that the resistance of the magnetic sensor element 21c changes by −ΔR2 to R−ΔR2. Since the absolute value of the sensitivity of the magnetic sensor element 21b is equal to that of the magnetic sensor element 21a and the direction of the sensitivity axis is opposite to that of the magnetic sensor element 21a, the resistance change in the magnetic sensor element 21b is −ΔR1. At this time, the resistance of the magnetic sensor element 21b is R-ΔR1. For this reason, the combined resistance of the series circuit in which the magnetic sensor elements 21a and 21b are connected in series is (R + ΔR1) + (R−ΔR1) = 2R. Similarly, since the absolute value of the sensitivity of the magnetic sensor element 21d is equal to that of the magnetic sensor element 21c and the direction of the sensitivity axis is opposite to that of the magnetic sensor element 21c, the resistance change in the magnetic sensor element 21d is ΔR2. Become. At this time, the resistance of the magnetic sensor element 21d is R + ΔR2. For this reason, the combined resistance of the series circuit in which the magnetic sensor elements 21c and 21d are connected in series is (R−ΔR2) + (R + ΔR2) = 2R. That is, the combined resistance of the bridge circuit 21 having a configuration in which two series circuits are connected in parallel is R, and there is no change from the initial value.

  As described above, since the magnetic sensor elements 21a, 21b, 21c, and 21d have the above-described relationship, the combined characteristic of the bridge circuit 21 (the combined resistance in the case of using the magnetoresistive effect element) is usually external. It is almost constant regardless of the magnetic field. On the other hand, if the magnetic sensor elements 21a, 21b, 21c, and 21d are abnormal due to secular change or the like, and the sensitivity of the magnetic sensor elements 21a, 21b, 21c, and 21d is changed, the magnetic sensor elements 21a, 21b, 21c, The balance of 21d is lost, and the composite characteristics of the bridge circuit 21 are not constant. For this reason, the failure determination unit 23 determines whether or not the composite characteristic is within a predetermined range, thereby detecting the abnormality of the magnetic sensor elements 21a, 21b, 21c, and 21d and determining the presence or absence of the failure. Can do.

  In the current sensor 2, the direction of the sensitivity axis of the magnetic sensor element 21a and the direction of the sensitivity axis of the magnetic sensor element 21c are opposite to each other, and the direction of the sensitivity axis of the magnetic sensor element 21b and the sensitivity of the magnetic sensor element 21d. Each magnetic sensor element is arranged so that the directions of the axes are opposite to each other. By adopting such a configuration, the difference in voltage between the sensor output Out1 and the sensor output Out2 is increased, so that the accuracy of current measurement can be increased.

  In the current sensor 2, the method of measuring the combined resistance as a combined characteristic differs depending on whether the power supply circuit 24 is a constant current source or a constant voltage source. For example, when the power supply circuit 24 is a constant current source, the combined characteristic measurement unit 22 can calculate the combined resistance by measuring the voltage applied to the bridge circuit 21. When the power supply circuit 24 is a constant voltage source, the composite characteristic measuring unit 22 can calculate the combined resistance by measuring the current flowing through the bridge circuit 21. As described above, the parameters measured by the composite characteristic measurement unit 22 vary depending on the type of the power source and the like. Therefore, the connection relationship between the bridge circuit 21 and the composite characteristic measurement unit 22 calculates the composite resistance by appropriate measurement. Anything is possible.

  In the above description, the case where magnetoresistive elements are used as the magnetic sensor elements 21a, 21b, 21c, and 21d has been described as an example. However, the magnetic sensor elements that can be used as the magnetic sensor elements 21a, 21b, 21c, and 21d are as follows. It is not limited to this. For example, Hall elements can be used as the magnetic sensor elements 21a, 21b, 21c, and 21d. Hereinafter, a case where Hall elements are used as the magnetic sensor elements 21a, 21b, 21c, and 21d and the voltage of the bridge circuit 21 is employed as a composite characteristic will be briefly described.

  When Hall elements are used as the magnetic sensor elements 21a, 21b, 21c, and 21d, the initial value (value in the absence of a magnetic field) of the electromotive force as the magnetic sensor elements 21a, 21b, 21c, and 21d is normally zero. Therefore, the initial value (value in the absence of a magnetic field) of the series circuit in which the magnetic sensor elements 21a and 21b are connected in series is zero, and the electromotive force of the series circuit in which the magnetic sensor elements 21c and 21d are connected in series. The initial value (value in the absence of a magnetic field) is zero. That is, the initial value (value in the absence of a magnetic field) of the electromotive force of the bridge circuit 21 configured such that these two series circuits are connected in parallel is also zero.

  It is assumed that the electromotive force of the magnetic sensor element 21a changes by ΔV1 due to the induced magnetic field of the current to be measured and becomes ΔV1. Further, it is assumed that the electromotive force of the magnetic sensor element 21c changes by −ΔV2 to −ΔV2. Since the absolute value of the sensitivity of the magnetic sensor element 21b is equal to that of the magnetic sensor element 21a and the direction of the sensitivity axis is opposite to that of the magnetic sensor element 21a, the change in electromotive force in the magnetic sensor element 21b is −ΔV1. . The electromotive force of the magnetic sensor element 21b at this time is −ΔV1. For this reason, the electromotive force of the series circuit in which the magnetic sensor elements 21a and 21b are connected in series is ΔV1 + (− ΔV1) = 0. Similarly, since the absolute value of the sensitivity of the magnetic sensor element 21d is equal to that of the magnetic sensor element 21c and the direction of the sensitivity axis is opposite to that of the magnetic sensor element 21c, the change in electromotive force in the magnetic sensor element 21d is ΔV2. It becomes. The electromotive force of the magnetic sensor element 21d at this time is ΔV2. For this reason, the electromotive force of the series circuit in which the magnetic sensor elements 21c and 21d are connected in series is −ΔV2 + (ΔV2) = 0. That is, the electromotive force of the bridge circuit 21 having a configuration in which two series circuits are connected in parallel is zero, and there is no change from the initial value.

  As described above, even when Hall elements are used as the magnetic sensor elements 21a, 21b, 21c, and 21d, the combined characteristic (here, electromotive force) of the bridge circuit 21 is generally constant regardless of the external magnetic field. . For this reason, the failure determination unit 23 determines whether or not the composite characteristic is within a predetermined range, thereby detecting the abnormality of the magnetic sensor elements 21a, 21b, 21c, and 21d and determining the presence or absence of the failure. Can do.

  In the current sensor 2, since the failure determination is performed using the combined characteristic of the bridge circuit 21, a failure mode in which the characteristics of the magnetic sensor element 21a and the magnetic sensor element 21d change to the same extent, the magnetic sensor element 21c, and the magnetic sensor element It is also possible to detect a failure mode in which the characteristics of 21b change to the same extent. For example, when a large current flows through the magnetic sensor element, the characteristics of the magnetic sensor element may change (deteriorate) due to magnetic hysteresis. The degree of the change may appear in the same manner in the magnetic sensor elements (the magnetic sensor elements 21a and 21d or the magnetic sensor elements 21b and 21c in the current sensor 2) having the same sensitivity axis direction. Such a failure mode is difficult to detect from the output waveform of the current sensor. In the current sensor 2 according to the present embodiment, the failure determination is performed using the composite characteristic of the bridge circuit 21. Therefore, it is possible to detect the resistance value fluctuation that appears in the same manner in the two magnetic sensor elements, and the detection is relatively easy. It is possible to detect a failure mode as described above, which is difficult. For this reason, appropriate current measurement can be realized by taking a countermeasure such as demagnetization based on such a detection result.

  FIG. 3 is a schematic diagram illustrating a specific configuration example of the bridge circuit 21 of the current sensor 2. As shown in FIG. 3, in order to eliminate the influence of an external magnetic field in the current sensor 2, for example, two magnetic sensor elements 21a and 21d are arranged at one end 31a of a substantially U-shaped current path 31, and others. Another two magnetic sensor elements 21b and 21c may be arranged at the end 31b to constitute the bridge circuit 21. In this case, the combined magnetic field of the induced magnetic field A generated by the current to be measured flowing through the current path 31 and the external magnetic field B differs between the left and right sides of the current path 31. Therefore, even if all the sensitivity axes of the four magnetic sensor elements are installed in the same direction, the same effect as that obtained when the orientation of the sensitivity axes is changed as shown in FIG. 2 can be obtained. The fact that all the sensitivity axes can be made the same means that one type of element can be used in the manufacturing process, and there is an advantage that the process of arranging the elements becomes simple.

  For example, as shown in FIG. 3, the induced magnetic field A and the external magnetic field B are in the same direction on the left side of the current path 31, whereas the induced magnetic field A and the external magnetic field are on the right side of the current path 31. B is facing a different direction. For this reason, in the case shown in FIG. 3, the influence of the magnetic hysteresis may appear strongly on the left side of the current path 31. Thus, since the balance of the composite characteristics may be lost due to the influence of magnetic hysteresis, such a state can also be detected. When such a state is detected, it can be demagnetized by a method of applying a large reverse magnetic field or a method of applying a decaying alternating magnetic field.

  FIG. 4 is a flowchart showing a failure determination process of the current sensor 1 in the present embodiment. Although the flow of the failure determination process in the current sensor 1 will be described here, the failure determination can also be performed in the current sensor 2 by the same process.

  When the failure determination process is started, in step 101, the composite characteristic measurement unit 12 measures and calculates the composite characteristic of the series circuit 11. When the magnetic sensor elements 11a and 11b are magnetoresistive elements, the composite characteristic measuring unit 12 measures the voltage applied to the series circuit 11 or the current flowing through the series circuit 11, and calculates the combined resistance of the series circuit 11. To do. When the magnetic sensor elements 11 a and 11 b are Hall elements, the composite characteristic measuring unit 12 measures the electromotive force (voltage, potential difference) of the series circuit 11.

  Thereafter, in step 102, the failure determination unit 13 determines whether or not the combined characteristic measured and calculated by the combined characteristic measurement unit 12 is within a reference range. The reference range can be set as appropriate from the accuracy and reliability required for the current sensor 1. For example, ± 3% of the reference value (for example, the initial value of the composite characteristic in the absence of a magnetic field) is set to the lower limit value and It is set as an upper limit value and can be determined by whether or not it is within the range.

  When the composite characteristic is within the reference range in step 102, in step 103, failure determination unit 13 determines that current sensor 1 is normal (no failure). On the other hand, if the composite characteristic is not within the reference range in step 102, the failure determination unit 13 determines that the current sensor 1 has a failure in step 104. The failure determination process ends when the determination is made.

  If it is determined by the above-described failure determination process that the current sensor 1 or the current sensor 2 is defective, measures such as demagnetization can be taken for the current sensor 1 or the current sensor 2. Further, processing such as issuing a warning to the system including the current sensor 1 or the current sensor 2 may be performed.

  As described above, in the current sensor of the present invention, at least a pair of magnetic sensor elements constituting the current sensor are arranged such that the absolute values of sensitivity are equal to each other and the sensitivity axes are opposite to each other. ing. Thereby, the composite characteristic of the circuit including these magnetic sensor elements becomes substantially constant regardless of whether or not the current to be measured is flowing. For this reason, it is possible to perform failure determination in real time by using the composite characteristic of the circuit for failure determination. That is, it is possible to provide a current sensor having a failure determination function capable of determining a failure even when a current to be measured is passed.

  In addition, this invention is not limited to the said embodiment, A various change can be implemented. For example, the connection relationship, size, and the like of each element in the above embodiment can be changed as appropriate without changing the gist of the invention. In addition, the structures, methods, and the like described in the above embodiments can be combined as appropriate. In addition, the present invention can be implemented with appropriate modifications without departing from the scope of the present invention.

  The current sensor of the present invention can be used, for example, to detect the magnitude of a current for driving a motor of an electric vehicle or a hybrid car.

DESCRIPTION OF SYMBOLS 1, 2 Current sensor 11 Series circuit 11a, 11b Magnetic sensor element 12 Composite characteristic measurement part 13 Failure determination part 14 Power supply circuit 21 Bridge circuit 21a, 21b, 21c, 21d Magnetic sensor element 22 Composite characteristic measurement part 23 Failure determination part 24 Power supply circuit

Claims (8)

A series in which a first magnetic sensor element and a second magnetic sensor element having an absolute value of sensitivity substantially equal to the first magnetic sensor element are connected in series so that sensitivity axes are opposite to each other. Circuit,
A composite characteristic measuring unit for calculating a composite characteristic of the series circuit;
Have a, a malfunction determining unit that combined characteristic calculated in the composite characteristic measuring unit determines a failure if out of a predetermined range,
The first magnetic sensor element and the second magnetic sensor element are magnetoresistive elements,
The combined characteristic measuring unit calculates a combined resistance value of the series circuit as the combined characteristic . A constant voltage source is connected to the series circuit,
The current sensor according to claim 1 , wherein the composite characteristic measurement unit calculates the composite resistance value from a current value flowing through the series circuit. A constant current source is connected to the series circuit,
The current sensor according to claim 1 , wherein the combined characteristic measurement unit calculates the combined resistance value from a voltage generated in the series circuit. A series in which a first magnetic sensor element and a second magnetic sensor element having an absolute value of sensitivity substantially equal to the first magnetic sensor element are connected in series so that sensitivity axes are opposite to each other. Circuit,
A composite characteristic measuring unit for calculating a composite characteristic of the series circuit;
A failure determination unit that determines a failure when the combined characteristic calculated in the combined characteristic measurement unit is out of a predetermined range;
The first magnetic sensor element and the second magnetic sensor element are Hall elements,
The combined characteristic measuring unit calculates a voltage value of the series circuit as the combined characteristic. The first magnetic sensor element and the second magnetic sensor element whose absolute value of sensitivity is substantially equal to the first magnetic sensor element are arranged so that the sensitivity axes are opposite to each other,
A third magnetic sensor element and a fourth magnetic sensor element having an absolute value of sensitivity substantially equal to the third magnetic sensor element are arranged such that the sensitivity axes are opposite to each other;
The first magnetic sensor element and the third magnetic sensor element are arranged such that sensitivity axes are opposite to each other,
One end of the first magnetic sensor element and one end of the second magnetic sensor element are connected,
One end of the third magnetic sensor element and one end of the fourth magnetic sensor element are connected,
The other end of the first magnetic sensor element and the other end of the third magnetic sensor element are connected,
A bridge circuit in which the other end of the second magnetic sensor element and the other end of the fourth magnetic sensor element are connected;
A synthesis characteristic measuring unit for calculating a synthesis characteristic of the bridge circuit;
A failure determination unit that determines a failure when the combined characteristic calculated in the combined characteristic measurement unit is out of a predetermined range;
The first magnetic sensor element, the second magnetic sensor element, the third magnetic sensor element, and the fourth magnetic sensor element are magnetoresistive elements,
The combined characteristic measuring unit calculates a combined resistance value of the bridge circuit as the combined characteristic. A constant voltage source is connected to the bridge circuit,
The current sensor according to claim 5 , wherein the composite characteristic measurement unit calculates the composite resistance value from a current value flowing through the bridge circuit. A constant current source is connected to the bridge circuit,
The current sensor according to claim 5 , wherein the composite characteristic measurement unit calculates the composite resistance value from a voltage generated in the bridge circuit. The first magnetic sensor element and the fourth magnetic sensor element are arranged at one end of a substantially U-shaped current path through which a current to be measured flows.
The current according to claim 5 , wherein the second magnetic sensor element and the third magnetic sensor element are arranged at the other end of the substantially U-shaped current path. Sensor.

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