JP2005188972A - Voltage-drop type current measuring device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a voltage-drop type current measuring device capable of moderating the stress in the connection part between a bus bar and a wiring material to be attached thereto. <P>SOLUTION: This device comprises the bus bar 1 interposed in a current passage that is a measuring object, and a flexible wiring board 24 integrated with a current measuring circuit. In the state where the flexible wiring board 24 is superposed with the bus bar 1, a wiring pattern constituting the current measuring circuit in the flexible wiring board 24 is electrically and mechanically connected to the bus bar 1 by soldering or the like. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a voltage drop type current measuring device.

  For example, when various loads mounted on an automobile or the like are driven, the current is measured by a current sensor, and the measured current value is 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.

  In this case, a bus bar constituting the current path is used as a shunt resistor, a PCB (printed circuit board) is disposed so as to be superimposed on the bus bar, and a predetermined current detection circuit is incorporated on the PCB, It can be considered that the wiring of the PCB and the bus bar are connected by soldering or the like.

  However, in the configuration in which the PCB is superimposed on the bus bar and soldered together as described above, for example, in an environment where the temperature change is severe in the vehicle or the like, the connection between them due to the difference in the thermal expansion coefficient between the two Stress may be applied to the portion, and in some cases, the connecting portion may be damaged.

  Accordingly, an object of the present invention is to provide a voltage drop type current measurement that can relieve stress acting on a connecting portion between a plate-like wiring member through which a current to be measured flows and a circuit board for current measurement attached thereto. To provide an apparatus.

  In order to solve the above-mentioned problem, the invention according to claim 1 is a voltage drop type current measuring device for measuring a current to be measured flowing through a predetermined path, which has conductivity and is a wiring 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 measured current based on a voltage drop amount generated between two predetermined points of the wiring material. The circuit board is made of a material that is more flexible than the wiring material, and is electrically connected and fixed to the wiring material at the predetermined two points.

  According to a second aspect of the present invention, a lead wire for external connection may be integrally formed on the circuit board.

  Further, according to a third aspect of the present invention, 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 connected to the wiring material at a predetermined connection point. A sense conductor that is electrically connected, a first point that is a predetermined distance away from the connection point in the wiring material in a 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. The potential difference comparison circuit for comparing the potential difference between the first point and the connection point to the sense conductor so that the potential difference between the first point and the second point becomes equal based on a signal from the potential difference comparison circuit. A current control circuit for flowing a measurement current toward the second point, and a current measurement circuit for measuring the measured current based on the measurement current, and the circuit board includes: Excluding the wiring material The sense conductor of the components of a circuit for measuring the measured current may be provided with at least.

  As described above, according to the voltage drop type current measurement device according to claims 1 to 3, the difference in shape change caused by the difference in thermal expansion coefficient between the wiring material and the circuit board is relatively flexible. It is absorbed by the deformation of the circuit board. Therefore, the stress at the connection portion between the wiring material and the circuit board can be relaxed.

  Furthermore, according to the second aspect of the present invention, connection to an external circuit can be easily performed via the lead wire.

  According to the invention of claim 3, 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. Therefore, the current to be measured flowing through the wiring material is measured by measuring the measurement current flowing out from the sense conductor. The measurement current can be easily measured.

  Hereinafter, a voltage drop type current measuring device according to an embodiment of the present invention will be described.

  FIG. 1 is a perspective view showing a voltage drop type current measuring device 20, and FIG. 2 is a side view showing the voltage drop type current measuring device 20.

  This voltage drop type current measuring device 20 measures a current flowing through a predetermined current path to be measured. For example, in a vehicle or the like, by detecting an energization current from the battery to the starter motor, Used for determining the state of charge.

  The voltage drop type current measuring device 20 includes a bus bar 1 which is a wiring material, and a flexible wiring board 24 as a circuit board attached to the bus bar 1.

  The bus bar 1 is a plate-like conductive piece formed of a conductive material such as copper, a copper alloy, or aluminum. The bus bar 1 is inserted in a current path that supplies power to a predetermined load. The voltage drop type current measuring device 20 measures the current flowing through the bus bar 1. In FIG. 1, holes 1 h provided for connection to a predetermined load or a wiring material on the battery side are formed at both ends of the bus bar 1.

  The flexible wiring board 24 is a flexible wiring board (FPC) in which a predetermined wiring pattern formed of a copper foil or the like is sandwiched between a pair of flexible resin films, for example, and has a flexible wiring board. It is. As the circuit board, in addition to the flexible wiring board 24, for example, a circuit board that is superior in flexibility (or softness) to a general printed board using a resin board having a predetermined thickness can be used.

  On the flexible wiring board 24, a predetermined wiring pattern is formed and a predetermined electronic component is mounted, so that a circuit for current measurement is at least partially formed. An example of a circuit for measuring current will be described later.

  A wiring pattern which is a wiring member constituting the current measurement circuit is electrically and mechanically connected to the bus bar 1. The connection between the wiring pattern and the bus bar 1 is performed by, for example, soldering, welding, screwing, or the like. In the present embodiment, the wiring pattern and the bus bar 1 are electrically and mechanically connected via the soldering portion 22 in a state where the flexible wiring board 24 is disposed so as to overlap one side of the bus bar 1. ing. Here, the connection point between the wiring pattern and the bus bar 1 corresponds to a point A and a point Pcn described later.

  Here, a circuit example for current measurement applied in the voltage drop type current measurement device 20 will be described with reference to FIG.

  This circuit for measuring current measures the main current I1 that flows through the load M by measuring the voltage drop. In general, the voltage drop at the bus bar 1 that is a shunt resistor, and the bus bar By utilizing the fact that the voltage drop in the temperature compensating resistor 2 (sense conductor) of the material having the resistance temperature coefficient substantially the same as 1 is affected by the substantially same resistance value change due to the temperature change, the bus bar 1 The measuring current I2 flowing out from the temperature compensating resistor 2 connected in close proximity to the measuring current I2 is measured, so that the main current I1 flowing through the bus bar 1 is measured.

  Specifically, the voltage drop type current measuring device 20 includes a bus bar 1 as a shunt resistor inserted in a current path from the battery to the load M, and a temperature compensation connected to a predetermined connection point Pcn of the bus bar 1. The resistor 2 is separated from the connection point Pcn in the bus bar 1 by a predetermined distance from the connection point Pcn in the direction in which the main current I1 flows, and the temperature assurance resistor 2 is separated from the connection point Pcn by a predetermined distance. The potential difference comparison circuit 3 that compares the potential at the point B, and the current I2 for measurement from the connection point Pcn to the point B are applied to the temperature compensation resistor 2 until the potential at the point B and the potential at the point A become equal. A current control circuit 4 is provided, and a current measurement circuit 5 that measures the main current I1 based on the measurement current I2.

  The temperature compensating resistor 2 is constituted by, for example, a wiring pattern included in the flexible wiring board 24.

  Further, the potential difference comparison circuit 3 is configured by, for example, an operational amplifier (op-amp), and its non-inverting input terminal is connected to the point A on the bus bar 1 side, and the inverting input terminal is on the temperature compensation resistor 2 side. It is connected to the point B, and the difference between the voltages applied to both input terminals is output from the output terminal.

  The current control circuit 4 is composed of a P-channel FET, the source is connected to the point B of the temperature compensating resistor 2, the drain is connected to the current measurement circuit 5, and the gate is the output of the potential difference comparison circuit 3. Connected to the terminal.

  Thereby, the potential difference comparison circuit 3 controls the gate input of the current control circuit 4 by the voltage drop in the bus bar 1 generated when the main current I1 flows through the bus bar 1, and the voltage drops at the points A and B become equal. Thus, the current I2 flows through the point B.

  The current measurement circuit 5 includes a resistor 11 for converting the measurement current I2 into a voltage, and an A / D converter (detection circuit) 12 for measuring the potential at one end of the resistor 11.

  The potential difference comparison circuit 3, the current control circuit 4, and the current measurement circuit 5 may be mounted on the flexible wiring board 24 or may be mounted on a substrate different from the flexible wiring board 24.

  The circuit operation of the voltage drop type current measuring device 20 will be described.

  First, when the power supply voltage from the battery (+ B) is supplied, the main current I1 flows through the bus bar 1, and the main current I1 flows through the load M.

  Here, when the main current I1 flows through the bus bar 1, the non-inverting input terminal of the potential difference comparison circuit 3 becomes low due to the voltage drop at the bus bar 1. Then, the output terminal of the potential difference comparison circuit 3 becomes low, and this is given to the gate of the current control circuit 4 which is a P-channel FET, and the gate input is controlled. A measurement current I2 flows through the temperature compensating resistor 2 so that the voltage drops at point B are equal.

  In this case, assuming that the resistance value of the bus bar 1 is R1 and the resistance value of the temperature compensating resistor 2 is R2, the potential difference comparison circuit 3 controls the current control circuit 4 so that “R1 × I1 = R2 × I2”. Will do. In this operation, since no current flows into each input terminal of the potential difference comparison circuit 3, all the measurement current I 2 as a shunt current is output to the current measurement circuit 5 as the drain current of the current control circuit 4.

  When the measurement current I2 flows through the resistor 11 of the current measurement circuit 5, a voltage generated at one end of the resistor 11 is applied to the A / D converter 12, and thereby the measurement current I2 is measured. The current I1 is measured.

  That is, assuming that the resistance value of the resistor 11 is Rout and the voltage across the resistor 11 is Vout, “Vout = Rout × I2” and “I2 = (R1 / R2) × I1”. = 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 12.

  Here, if the bus bar 1 and the temperature compensating resistor 2 are made of materials having substantially the same resistance temperature coefficient, and they are arranged close to each other, the change in resistance value with respect to the temperature change becomes substantially the same. That is, (R2 / R1) is a substantially constant value in the above-described equation for deriving the current I1. Therefore, by measuring the measurement current I2 flowing out from the temperature compensating resistor 2, the main current I1 flowing out from the bus bar 1 can be measured without taking into account the rate of change of the resistance value with respect to the temperature change by calculation or the like. It will be possible.

  That is, when the circuit block using the principle shown in FIG. 3 is applied as the voltage drop type current measuring device 20, the resistance value change rates of the bus bar 1 and the temperature compensating resistor 2 with respect to the temperature change are substantially the same. In order to achieve this, it is preferable that the bus bar 1 and the temperature compensating resistor 2 are arranged close to each other. For this reason, when the temperature compensating resistor 2 which is a component of the circuit for current measurement is assembled in the flexible wiring board 24 and the flexible wiring board 24 is arranged so as to overlap the bus bar 1, The rate of change in resistance with the temperature compensating resistor 2 can be made substantially the same.

  According to the voltage drop type current measuring device 20 configured in this way, when the ambient temperature changes, the amount of change between the two due to the difference in the thermal expansion coefficient between the bus bar 1 and the flexible wiring board 24 or the like. Even when the difference occurs, the difference in the amount of change is absorbed by the deformation of the flexible wiring board 24 that is relatively flexible. Therefore, the stress at the connection portion between the wiring member of the flexible wiring board 24 and the bus bar 1 can be relaxed.

  4 and 5 show examples of mounting the voltage drop type current measuring device 20.

  FIG. 4 shows an example in which the voltage drop type current measuring device 20 is disposed so as to overlap with the bottom surface 30a in the housing 30 such as a relay box, and FIG. The example which has arrange | positioned the voltage drop type | formula current measuring device 20 so that it may match is shown.

  As shown in these drawings, the voltage drop type current measuring device 20 has a thin configuration in which the flexible wiring board 24 is superposed on the plate-like bus bar 1. And can be assembled in a space-saving manner so as to overlap the side surface 30b. In particular, since the flexible wiring board 24 itself is thin, it contributes to thinning of the overall configuration of the voltage drop type current measuring device 20.

  In the example shown in FIGS. 4 and 5, one side portion of both end portions of the bus bar 1 is bent, and the bent piece 1b is penetrated through the housing 30 and led out outward (see FIG. 5). And the wiring which reaches a battery and load M is suitably connected to the derivation end of the bent piece 1b.

  The flexible wiring board 24 is integrally formed with a lead wire 25 for external connection. The lead line 25 includes, for example, a signal line for outputting a detection signal of a current detection circuit to the outside. Then, a current measurement circuit is connected to a predetermined control unit via the lead line 25.

  Thus, by integrally forming the lead wire 25 on the flexible wiring board 24, the current detection circuit and the external circuit can be easily connected via the lead wire 25.

  For this reason, particularly when the potential difference comparison device 3, the current control device 4, and the current measurement device 5 are mounted on a substrate different from the flexible wiring board 24, the flexible substrate 24 and the other substrate are connected. It is valid.

1 is a perspective view showing a voltage drop type current measuring device according to an embodiment of the present invention. It is a side view which shows a voltage drop type current measuring device same as the above. It is a circuit block diagram of a current center device. It is a perspective view showing an example of attachment of a voltage drop type current measuring device. It is a perspective view showing an example of attachment of a voltage drop type current measuring device.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Bus bar 2 Resistor for temperature compensation 3 Potential difference comparison circuit 4 Current control circuit 5 Current measuring device 20 Voltage drop type current measuring device 24 Flexible wiring board

Claims (3)

A voltage drop type current measuring device that measures a current to be measured flowing through a predetermined path,
A wiring material having conductivity and 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 current to be measured based on a voltage drop amount generated between two predetermined points of the wiring member;
The voltage drop type current measuring device, wherein the circuit board is configured to be more flexible than the wiring material, and is electrically connected and fixed to the wiring material at the predetermined two points. The voltage drop type current measuring device according to claim 1,
A voltage drop type current measuring device in which a lead wire for external connection is integrally formed on the circuit board. The voltage drop type current measuring device according to claim 1 or 2,
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 for measurement is applied to the sense conductor from the connection point toward the second point so that the potential difference between the first point and the second point becomes equal. A current control circuit to flow;
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 components of a circuit for measuring the measured current excluding the wiring member.