JP2005188932A - Voltage-drop type current measuring device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a voltage-drop type current measuring device suitable to reduce the setting space and the number of part items. <P>SOLUTION: The voltage-drop type current measuring device 1 is to be incorporated into an electric connection box, a bus bar 13 takes on the function as a shunt resistance and the function as a base for a circuit board 15. In the electric connection box, the current measuring device 1 is incorporated within a case body 7 with a fuse member (fusible link) 3 and a switching circuit part (relay) 5. The connection of the current measuring device 1 with the fuse member 3 is performed by bolting or the like. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a voltage drop type current measuring device and a technology related thereto.

  For example, when driving various loads mounted on an automobile or the like, the current is measured by a current sensor and used as a control parameter for a generator.

  Some current sensors used in this case use Hall elements, but the component size is relatively large according to the size of the conductor through which a large current flows, and this does not meet the requirements for miniaturization. There is. Therefore, a shunt resistor is arranged in the current path, and a current flowing through the shunt resistor is measured.

  However, a conventional current sensor using a shunt resistor often employs a configuration in which a shunt resistor is provided on a predetermined circuit board. In such a configuration, the number of components increases as much as the shunt resistor is required as a dedicated component, leading to an increase in the size of the device configuration. Further, if the voltage drop type current measuring device is configured separately from other electrical components such as other relay boxes, the installation space and the number of parts increase.

  Accordingly, a first problem to be solved by the present invention is to provide a voltage drop type current measuring device suitable for reducing the installation space and the number of parts.

  The second problem to be solved by the present invention is that the current flowing through the shunt resistor can be easily measured without being affected by the temperature change without considering the rate of change of the resistance value with respect to the temperature change by calculation or the like. A voltage drop type current measuring device is provided.

  The means for solving the problem is a voltage drop type current measuring device that is interposed in a path through which a current to be measured flows and measures the current to be measured, and is a conductive wiring material interposed in the path And a circuit board provided on the wiring material and provided with at least a part of a circuit for measuring the current to be measured based on a voltage drop amount generated between two predetermined points of the wiring material. In other electrical components that are electrically connected to the path.

  Preferably, the electrical component includes a fuse member interposed in the path, and a case body that accommodates the fuse member, and the voltage drop type current measuring device is accommodated in the case body of the electrical component. It is good to be done.

  Preferably, the electrical component includes a switching circuit unit that is interposed in the path and controls a current flowing through the path, and a case body that houses the switching circuit unit, and the voltage drop type current measurement. The device may be housed in the case body of the electrical component.

  Further preferably, the circuit for measuring the current to be measured is composed of the wiring material and a material having the same resistance temperature coefficient as the wiring material, and is electrically connected to the wiring material at a predetermined connection point. A potential difference between the sense conductor having a predetermined distance from the connection point in the wiring material and a second point having a predetermined distance from the connection point in the sense conductor. Based on the signal from the potential difference comparison circuit and the potential difference comparison circuit, the sense conductor is connected to the second point from the connection point until the potentials of the first point and the second point become equal. A current control circuit for flowing a measurement current toward the current measurement circuit, and a current measurement circuit for measuring the current to be measured based on the measurement current. The circuit board includes the wiring material excluding the wiring material. Measure current to be measured Better to the sense conductor provided at least of the components of a circuit for.

  According to the first aspect of the present invention, the wiring material is used as a shunt resistor and is also used as a base of a circuit board on which at least a part of a circuit for current measurement is provided. Compared with the configuration in which the shunt resistor and the circuit board base are provided, it is possible to make the configuration more suitable for reducing the number of parts and reducing the size.

  In addition, since the voltage drop type current measuring device is incorporated into other electrical components, the installation space and the number of parts can be reduced compared to a configuration in which the voltage drop type current measuring device is provided separately from the electrical components. .

  According to the second aspect of the present invention, since the voltage drop type current measuring device and the fuse member are often interposed in series in the current path, the voltage drop type current measuring device is placed in the case body together with the fuse member. By incorporating it easily, the configuration of the connection circuit and the like can be reduced.

  According to the third aspect of the present invention, since the voltage drop type current measuring device and the switching circuit unit are often interposed in series in the current path, the voltage drop type current measuring device is installed together with the switching circuit unit in the case. By easily incorporating into the body, the configuration of the connection circuit and the like can be reduced.

  According to the invention described in claim 4, the voltage drop in the wiring material and the voltage drop in the sense conductor made of the material having the same resistance temperature coefficient as the wiring material are subjected to the resistance value change due to the same temperature change. Is used to measure the current to be measured flowing from the sense conductor, thereby measuring the current to be measured flowing in the wiring material. The main current flowing out of the can be easily measured.

  FIG. 1 is a perspective view of an electrical junction box in which a voltage drop type current measuring device (hereinafter simply referred to as “current measuring device”) according to an embodiment of the present invention is incorporated. As shown in FIG. 1, the electrical connection box (electrical component) is configured by incorporating the current measuring device 1 into a resin case body 7 together with the fuse member 3 and the switching circuit unit 5, and is not illustrated. Electrically connected to the positive terminal of the battery. As a modification, a configuration in which any one of the fuse member 3 and the switching circuit unit 5 is omitted may be employed.

<Current measuring device>
As shown in FIGS. 2 and 3, the current measuring device 1 includes a metal bus bar (wiring material) 13 and a circuit board 15.

<Circuit configuration>
In general, in an environment that handles a small current to a large current such as an automobile, a plate-shaped metal piece made of copper, copper alloy, or aluminum called a bus bar is used for power distribution in wiring parts called a junction box. This bus bar can be used as a shunt resistor for measuring the current applied to the load. Therefore, in this embodiment, the bus bar 13 interposed in the path of the current to be measured is used as a shunt resistor and also used as a base of the circuit board 15.

  For example, when copper is used as the metal material of the bus bar, the resistance temperature coefficient of the copper is approximately 0.004 / ° C. And when using shunt resistance in the circuit in a motor vehicle, atmospheric temperature is -40 degreeC-+85 degreeC or +125 degreeC, and the width | variety of a temperature change is as large as 100 degreeC or more. Thus, if the temperature difference of the ambient temperature is 100 ° C., the resistance value becomes 1.4 times. Therefore, in order to know an accurate current value using the bus bar 13 as a shunt resistor, it is necessary to correct the resistance value by some means.

  Therefore, in the present embodiment, the sense conductor 21 (FIG. 4) as a temperature compensating resistor composed of a material (including the same material) having the same resistance temperature coefficient as that of the bus bar 13 used as a shunt resistor on the circuit board 15. And the sense conductor 21 is arranged close to the bus bar 13, and the temperature of the resistance value of the bus bar 13 is utilized by utilizing the fact that the temperature changes of the bus bar 13 and the sense conductor 21 are equal to each other. The change is corrected.

  Specifically, the current measuring device 1 has a circuit configuration for current measurement, as shown in FIGS. 4 and 5, as a shunt resistor interposed in a path through which a main current (current to be measured) I1 flows. Bus bar 13, a sense conductor 21 as a temperature compensating resistor connected to a predetermined connection point Pcn in the bus bar 13, and a predetermined distance in the bus bar 13 from the connection point Pcn in the direction in which the main current I1 flows. A potential difference comparison circuit 23 for comparing the potential at a remote point A (first point) with the potential at a point B (second point) separated from the connection point Pcn within the sense conductor 21 by a predetermined distance; A current control circuit 25 that causes the measurement current I2 to flow from the connection point Pcn to the point B through the sense conductor 21 until the potential at B and the potential at point A become equal, and the main current based on the measurement current I2 A current measuring circuit 27 for measuring the flow I1 is provided. In the circuit configuration for current measurement excluding the bus bar 13, at least the sense conductor 21 is provided on the circuit board 15. In the present embodiment, the circuit board 15 is provided with a sense conductor 21, a potential difference comparison circuit 23, a current control circuit 25, and a current measurement circuit 27.

  Next, the electrical configuration and function of each circuit element will be briefly described. As will be described in detail later, the bus bar 13 is a plate-like body formed of a metal material (here, copper), and functions as a shunt resistor, a base of the circuit board 15, and the like.

  The sense conductor 21 is connected to a predetermined connection point Pcn in the bus bar 13 through a predetermined connection conductor, for example, and the sense conductor 21 is a metal material (for example, copper) having the same resistance temperature coefficient as the bus bar 13. Is used. The resistance value of the sense conductor 21 may be set differently from the resistance value of the bus bar 13, and is set to a predetermined ratio such as 10,000: 1.

  The sense conductor 21 on the circuit board 15 is disposed so as to be close to the bus bar 13 in order to make changes in the temperature of the bus bar 13 and the sense conductor 21 almost equal. Thereby, if the current of the sense conductor 21 is measured, the measurement considering the rate of change of the resistance value with respect to the temperature change of the bus bar 13 can be performed. Therefore, the temperature coefficient of the bus bar 13 and the sense conductor 21 can be canceled at the time of measurement. Can do.

  The potential difference comparison circuit 23 is, for example, an operational amplifier (op-amp), and the non-inverting input terminal shown in FIG. 5 is a connection point A that is an intermediate point on the load M side with respect to the connection point Pcn in the bus bar 13 as shown in FIG. 5, the inverting input terminal shown in FIG. 5 is connected to the point B of the sense conductor 21 as shown in FIG. 4, and the difference in voltage applied to both input terminals is output from the output terminal as shown in FIG. Is done.

  In FIG. 4, the separation distance between the connection point Pcn and the connection point A defines the resistance value with respect to the current flowing therethrough, but a predetermined voltage is applied between the connection point Pcn and the connection point A when energized. The separation distance between the connection point Pcn and the connection point A is set so as to have a resistance value suitable for the voltage detection accuracy in the potential difference comparison circuit 23. As described above, since the intermediate position of the bus bar 13 is set to the connection point Pcn and the connection point A, in order to determine the resistance value when realizing a voltage drop adapted to the voltage detection accuracy in the potential difference comparison circuit 23. This is convenient because the distance between the connection point Pcn and the connection point A can be set very easily.

  The current control circuit 25 is, for example, a P-channel FET, and the source is connected to the point B of the sense conductor 21 and the drain is connected to the current measurement circuit 27. The gate of the current control circuit 25 is connected to the output terminal of the potential difference comparison circuit 23. That is, a circuit branched from the point B into two paths, that is, a path to the inverting input terminal of the potential difference comparison circuit 23 and a path to the current control circuit 25 is configured.

  Thereby, the potential difference comparison circuit 23 controls the gate input of the current control circuit 25 by the voltage drop in the bus bar 13 generated when the main current I1 flows through the bus bar 13 in FIGS. The current I2 flows through the point B so that the voltage drops are equal.

  For example, as shown in FIG. 5, the current measurement circuit 27 includes a resistor 31 for converting the measurement current I2 into a voltage, and an A / D converter (detection circuit) for measuring the potential at one end of the resistor 31. 33. The other end of the resistor 31 is connected to the reference potential (ground level) of the A / D converter 33. As the resistor 31, a resistor whose temperature coefficient of resistance is sufficiently smaller than the temperature coefficient of resistance of the bus bar 13 is used. For this reason, even if the resistor 31 is arranged on the circuit board 15 as in the present embodiment, the change in the resistance value of the resistor 31 when the temperature changes is compared to the change in the resistance value of the bus bar 13. And can be kept small enough.

  Next, the operation of the above circuit configuration will be described.

  When the power supply voltage from the original power supply (+ B) in FIGS. 4 and 5 is supplied, the main current I1 flows through the bus bar 13, and the main current I1 is supplied to the load M.

  Here, when the main current I1 flows through the bus bar 13, the voltage drop at the bus bar 13 causes the non-inverting input terminal of the potential difference comparison circuit 23 to go low as shown in FIG. Then, the output terminal of the potential difference comparison circuit 23 becomes low, and this is given to the gate of the current control circuit 25 which is a P-channel FET, and this gate input is controlled, so that the potential difference comparison circuit 23 in FIG. A current I2 for measurement flows through the sense conductor 21 so that the voltage drops at the points A and B are equal.

  In this case, the potential difference comparison circuit 23 controls the current control circuit 25 so that “R1 × I1 = R2 × I2”, where R1 is the resistance value of the bus bar 13 and R2 is the resistance value of the sense conductor 21. In this operation, since no current flows into each input terminal of the potential difference comparison circuit 23, all the measurement current I 2 as a shunt current is output to the current measurement circuit 27 as the drain current of the current control circuit 25.

  When the measurement current I2 flows through the resistor 31 of the current measurement circuit 27, a voltage generated at one end of the resistor 31 is applied to the A / D converter 33, thereby measuring the measurement current I2 so that the main current I2 is measured. The current I1 is measured.

  In this case, assuming that the resistance value of the resistor 31 is Rout and the voltage across the resistor 31 is Vout, “Vout = Rout × I2” and “I2 = (R1 / R2) × I1”. Vout = Rout × (R1 / R2) × I1 ”. Therefore, the main current I1 can be obtained by calculation based on the expression “I1 = Vout × (R2 / R1) / Rout” based on Vout measured by the A / D converter 33.

<About structure>
As shown in FIGS. 2 and 3, the bus bar 13 of the current measuring device 1 is a plate-like body having a predetermined thickness (for example, 1 to 2 mm) formed of a predetermined metal material (here, copper). As described above, it functions as a shunt resistor and functions as a base of the circuit board 15 and the like. The bus bar 13 has a slightly elongated rectangular plate shape along the flow direction of the main current I1, which is a current to be detected, and the circuit board 15 is disposed on one side of the intermediate portion. At both ends of the bus bar 13 in the longitudinal direction, through holes 43 through which electric connection and fixing bolts 41 are inserted are provided as necessary.

  As the circuit board 15, a board (PCB in this embodiment) such as a PCB (Printed Circuit Board) or an FPC (Flexible Printed Circuit) is used. 13, at least the sense conductors 21 (in this embodiment, the sense conductor 21, the potential difference comparison circuit 23, the current control circuit 25, and the current measurement circuit 27) are provided. The circuit board 15 and the bus bar 13 are fixed by soldering or the like that also serves as an electrical connection of the contact of the circuit board 15 to the bus bar 13.

<Other configuration of electrical junction box>
A fuse member 3 shown in FIG. 1 is interposed in a current path connected to the positive terminal of the battery, and protects against an overcurrent in the current path. For example, a fusible link (a fuse may be used). ) Is used. In addition, the switching circuit unit 5 is interposed in a current path connected to the positive terminal of the battery, and controls the current flowing through the current path (on, off, etc.). For example, a relay is used. A circuit unit using a semiconductor switching element may be used.

  As shown in FIG. 1, the case body 7 includes a case main body 51 and a cover 53 attached thereto. In the case main body 51, a plurality of (for example, four) accommodating portions 51 a to 51 d are provided that are partitioned by a partition portion. The fuse members 3 and the current measuring device 1 are accommodated in the accommodating portions 51a and 51b, and the switching circuit portion 5 and the current measuring device 1 are accommodated in the accommodating portions 51c and 51d. The cover 53 is provided with a main body portion 53a that is attached to the case main body 51 and covers each of the housing portions 51a to 51d, and a terminal cover portion 53b that covers a conductive fitting 55 and a battery positive terminal described later.

  Further, the connection between the electrical junction box and the positive terminal of the battery is performed using the conductive metal fitting 55. One end portion 55a of the conductive metal fitting 55 has a substantially ring-shaped structure, and is externally fitted to the positive terminal of the battery, and is fastened and fixed and electrically connected by a bolt and a nut (not shown). The other end of the conductive metal fitting 55 is inserted into the case main body 51 and branched into a plurality (for example, four). Electric wires 57 are respectively connected to the branched other end portions via one of the fuse member 3 or the switching circuit portion 5 and the current measuring device 1. That is, in the present embodiment, one of the fuse member 3 or the switching circuit unit 5 and the current measuring device 1 are interposed in series in the current path branched into a plurality by the conductive metal fitting 55.

  The connection between the current measuring device 1 and the fuse member 3 or the like is performed as follows, for example. That is, as shown in FIG. 3, the connection portion 3 a of the fusible link 3 is provided with a through hole for insertion of the bolt 41 and is set on the upper side (or lower side) of the bus bar 13 of the current measuring device 1. In this state, the bolt 41 is inserted into the through hole 43 of the bus bar 13 through the through hole, and is screwed and fastened to the nut 59, thereby being electrically connected and fixed to the bus bar 13 of the current measuring device 1.

  Further, a terminal 61 is connected to the terminal portion of the electric wire 57 by crimping or the like, and the terminal has, for example, a ring-shaped connection end 61a, and is above (or below) the bus bar 13 of the current measuring device 1. The bolt 41 is inserted into the through hole 43 of the bus bar 13 through the through hole of the connection end 61a, and is screwed and fastened to the nut 59. Electrical connection and fixed.

  In addition, the connection form using this volt | bolt 41 is only an illustration, The form using the terminal structure which male-female fits, welding, etc. are employable.

  As described above, according to the present embodiment, the bus bar 13 in the current measuring device 1 is used as a shunt resistor and is also used as a base of the circuit board 15 on which at least a part of a current measuring circuit is provided. Therefore, as compared with a configuration in which a dedicated shunt resistor or a circuit board base is provided, a configuration that is more suitable for reducing the number of components and reducing the size can be achieved.

  Moreover, since it is the structure which incorporates the electric current measurement apparatus 1 in the electrical junction box which is another electrical component, it reduces installation space and a number of parts compared with the structure which provides the electrical current measurement apparatus 1 separately from an electrical junction box. Can do.

  Furthermore, since the current measuring device 1 and the fuse member 3 are interposed in series in the current path, the current measuring device 1 can be easily incorporated together with the fuse member 3 in the case body 7 of the electrical junction box, thereby providing a connection circuit. Etc. can be reduced.

  Moreover, since the current measuring device 1 and the switching circuit unit 5 are interposed in series in the current path, the current measuring device 1 can be easily incorporated into the case body 7 of the electrical junction box together with the switching circuit unit 5. The configuration of the connection circuit and the like can be reduced.

  Furthermore, it is utilized that the voltage drop in the bus bar 13 in the current measuring device 1 and the voltage drop in the sense conductor 21 made of the material having the same resistance temperature coefficient as the bus bar 13 are subjected to the resistance value change due to the same temperature change. Since the main current flowing through the bus bar 13 is measured by measuring the measurement current flowing out from the sense conductor 21, the main flowing out from the bus bar 13 can be obtained without considering the rate of change of the resistance value with respect to the temperature change by calculation or the like. Current can be easily measured.

It is a perspective view of the electrical junction box in which the voltage drop type current measuring device concerning one embodiment of the present invention was built. It is a top view of a voltage drop type current measuring device. It is sectional drawing of the part in which the voltage drop type electric current measuring apparatus of FIG. 1 was integrated. It is a schematic block diagram of a voltage drop type current measuring device. It is a block diagram of a voltage drop type current measuring device.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Voltage drop type current measuring device 3 Fuse member 5 Switching circuit part 7 Case body 13 Bus bar 15 Circuit board 21 Sense conductor 23 Potential difference comparison circuit 25 Current control circuit 27 Current measurement circuit

Claims (4)

A voltage drop type current measuring device that is interposed in a path through which a current to be measured flows and measures the current to be measured,
A conductive wiring member interposed in the path;
A circuit board provided on the wiring member and provided with at least a part of a circuit for measuring the measured current based on a voltage drop amount generated between two predetermined points of the wiring member;
With
A voltage drop type current measuring device incorporated in another electrical component electrically connected to the path. In the voltage drop type current measuring device according to claim 1,
The electrical component is
A fuse member interposed in the path;
A case body for housing the fuse member;
With
The voltage drop type current measurement device, wherein the voltage drop type current measurement device is accommodated in the case body of the electrical component. In the voltage drop type current measuring device according to claim 1,
The electrical component is
A switching circuit unit interposed in the path and controlling a current flowing through the path;
A case body that houses the switching circuit portion;
With
The voltage drop type current measurement device, wherein the voltage drop type current measurement device is accommodated in the case body of the electrical component. In the voltage drop type current measuring device according to any one of claims 1 to 3,
The circuit for measuring the measured current is:
The wiring material;
A sense conductor composed of a material having the same resistance temperature coefficient as the wiring material and electrically connected to the wiring material at a predetermined connection point;
A potential difference comparison that compares a potential difference between a first point that is a fixed distance away from the connection point in the wiring material in the direction in which the current to be measured flows and a second point that is a predetermined distance away from the connection point in the sense conductor. Circuit,
Based on a signal from the potential difference comparison circuit, a current that causes a measurement current to flow from the connection point to the second point through the sense conductor until the potentials of the first point and the second point become equal A control circuit;
A current measurement circuit for measuring the measured current based on the measurement current;
Configured with
The voltage drop type current measuring device, wherein the circuit board is provided with at least the sense conductor among the components of the circuit for measuring the measured current excluding the wiring material.