JP2018173360A - Current detector - Google Patents

Abstract

A shunt resistor connected in parallel accurately detects a large current with high accuracy, reduces a CPU load of a microcomputer for calculating a current value, and quickly detects an excessive peak current. A plurality of current detection circuits 5 are connected to each shunt resistor 2 connected in parallel, and a microcomputer 6 calculates the current value output at a predetermined cycle from each current detection circuit 5 and all microcomputers 6 A current detector that calculates the total current of the resistor. The current detection circuit 5 includes a first current detection circuit 5A that outputs a current signal to the microcomputer in a short cycle and a first current detection circuit 5A that outputs a current signal to the microcomputer 6 in a long cycle. The microcomputer calculates a total current from current signals input from the first current detection circuit 5A and the second current detection circuit 5B. [Selection] Figure 3

Description

  The present invention relates to a current detector that mainly detects a large current, and more particularly to a current detector that is optimal for detecting a current that charges and discharges a battery for traveling that supplies power to a traveling motor for a vehicle.

A current detector that detects a fluctuating large current is used in various applications. For example, batteries and peripheral systems that supply power to the running motors of hybrid cars and electric vehicles detect charging currents and calculate remaining capacity, and charge and discharge currents so that the remaining capacity is within the set range. The battery is controlled with a protection circuit and a fuse by detecting an instantaneous excessive current. A current detector using a shunt resistor is used as a large current detector. (See Patent Document 1)
This current detector can detect the current (I) from the voltage drop (E) of the shunt resistor. This is because the current (I) can be calculated by voltage drop (E) / resistance value (R).

This current detector tends to increase the error when the maximum current that can be detected exceeds 100A. This is because when a large current flows through the shunt resistor, the temperature of the shunt resistor rises, and when the temperature rises, the resistance value changes. Since the shunt resistor increases the power loss in proportion to the square of the flowing current, if the maximum current detected with a constant resistance value is increased, the power loss of the shunt resistor increases abruptly. In addition, the power loss leads to heat generation, and the heat generation raises the temperature of the shunt resistor, so that a resistance value change corresponding to the resistance temperature coefficient occurs, and thus an error increases. Although heat generation can be suppressed by lowering the design resistance value (R1) of the shunt resistor, the error value (R2) generated from the manufacturing process of the shunt resistor cannot be made zero, and the manufacturing process. The resistance error coefficient (α = (R1 + R2) / R1) generated in (1) increases as the design resistance value decreases. Therefore, there is a limit to lowering the design resistance value.
From this, the current detector using the shunt resistor can detect the current with high accuracy by setting the maximum current to about 100A.

JP 2013-174555 A

  A plurality of shunt resistors are connected in parallel, the current of each shunt resistor is detected, and the maximum current that can be detected can be increased by adding the detected currents. This current detector is connected to multiple shunt resistors in parallel, and each shunt resistor is connected to a current detection circuit that detects current from the voltage drop across the shunt resistor, and further detected by each current detection circuit. Current signals output to the microcomputer, and the microcomputer adds the current signals output from the current detection circuits to detect the total current. The current detector can increase the maximum current that can be detected by connecting a plurality of shunt resistors in parallel and increasing the number of shunt resistors connected in parallel.

This current detector can also detect a total current flowing through a plurality of shunt resistors with a set of current detection circuits. This current detection circuit detects the total current from the resistance value and voltage drop of shunt resistors connected in parallel.
The resistance value of shunt resistors connected in parallel is
It can be calculated by [resistance value of one shunt resistor / number of parallel connections].
For example, when four 0.1 mΩ shunt resistors are connected in parallel, the resistance value of the shunt resistors connected in parallel is 0.1 / 4 mΩ, which is 0.025 mΩ. Therefore, the total current can be detected by calculating the voltage drop (E) /0.025 mΩ of the shunt resistor.

  However, a current detector in which a plurality of shunt resistors are connected in parallel and the total current is detected by a single current detection circuit cannot detect the total current with high accuracy. This is because a shunt resistor having a resistance value as small as possible in order to suppress the temperature rise is affected by the resistance value of the path connecting the shunt resistors. In order to suppress the influence of the resistance value of the path as much as possible, it is necessary to measure the voltage drop across each shunt resistor.

  Connect multiple shunt resistors in parallel, connect a current detection circuit to each shunt resistor, detect the current of each shunt resistor with each current detection circuit, and add the current detected by each current detection circuit with a microcomputer Thus, the current detector that detects the total current has a feature that can detect the total current with high accuracy. However, since this current detector calculates the current value from the voltage drop of the shunt resistor in a predetermined cycle, the microcomputer calculates a plurality of current values as the number of shunt resistors and current detection circuits is increased. Therefore, high processing capability is required, and it is necessary to use a microcomputer capable of high-speed processing for the microcomputer, resulting in an increase in component costs. The cycle of calculating and outputting the total current from a plurality of current values can be lengthened to reduce the processing capacity of the microcomputer. However, if the period for detecting the total current is long, there is a problem that the peak current that temporarily increases in a short time cannot be detected quickly. A current detector that cannot quickly detect the peak current cannot ensure sufficient safety in a protection circuit or the like. For example, a current detector that cannot quickly detect an excessive short-circuit current has various problems such as a short-circuit cannot be detected and the current cannot be quickly cut off.

  The present invention has been developed for the purpose of solving the above-mentioned drawbacks. An important object of the present invention is to detect a large current with high accuracy while increasing the maximum current that can be detected by connecting a plurality of shunt resistors in parallel, and to reduce the CPU load of the microcomputer. An object of the present invention is to provide a current detector capable of quickly detecting a peak current.

Means for Solving the Problems and Effects of the Invention

  A current detector according to an aspect of the present invention includes a plurality of shunt resistors connected in parallel to each other, and connected to each shunt resistor to calculate a current value from a voltage drop, and to output a current signal at a predetermined cycle. A plurality of current detection circuits for outputting, and a microcomputer for calculating a current signal input from each current detection circuit and calculating a total current of all shunt resistors. The current detection circuit includes a first current detection circuit and a second current detection circuit that output current signals at different cycles, and the first current detection circuit has a shorter cycle than the second current detection circuit. The signal is output to the microcomputer, the second current detection circuit outputs the current signal to the microcomputer with a longer period than the first current detection circuit, and the microcomputer receives the current signal input from the first current detection circuit and The total current is calculated from the current signal input from the second current detection circuit.

  These current detectors can accurately detect large currents with high accuracy while increasing the maximum current that can be detected by multiple shunt resistors, and further reduce the CPU load to quickly detect excessive peak currents. There are features that can be done. The reason why the maximum current that can be detected is increased and the large current can be detected accurately with high accuracy is that multiple shunt resistors are connected in parallel and the current of each shunt resistor is detected to detect the total current. is there.

  The fact that the current that fluctuates can be detected quickly by reducing the CPU load of the microcomputer is composed of a first current detection circuit and a second current detection circuit that output current signals at different periods, The first current detection circuit outputs a current signal to the microcomputer with a shorter period than the second current detection circuit, and the second current detection circuit outputs the current signal to the microcomputer with a longer period than the first current detection circuit. This is because the microcomputer calculates the total current from the current signal input from the first current detection circuit and the current signal input from the second current detection circuit. Furthermore, the ability to accurately detect an instantaneous current while reducing the CPU load of the microcomputer also realizes a feature that can reduce the component cost without degrading the accuracy of current detection.

  The current detector according to an aspect of the present invention can include more second current detection circuits than the first current detection circuit, and can include three or more sets of second current detection circuits.

  In a current detector according to an aspect of the present invention, a shunt resistor is connected in series with a traveling battery that supplies power to a traveling motor of a vehicle, and a remaining battery capacity is calculated from a total current detected by a microcomputer. A circuit configuration including a remaining capacity calculation circuit can be provided.

  The current detector according to an aspect of the present invention can calculate the remaining capacity of the battery in a long cycle with the remaining capacity calculation circuit.

  Furthermore, in the current detector according to an aspect of the present invention, the resistance value of each shunt resistor can be 0.01 mΩ or more and 1.0 mΩ or less.

  Furthermore, in the current detector according to an aspect of the present invention, the current detection circuit is provided with a correction circuit that corrects the resistance value based on the temperature of the connected shunt resistor, and the current detection circuit is corrected by the correction circuit. The current flowing through the shunt resistor can be detected by the resistance value.

  In the current detector according to an aspect of the present invention, a short cycle in which the first current detection circuit outputs a current signal is set to 1/10 or less of a long cycle in which the second current detection circuit outputs a current signal. be able to.

It is a block diagram which shows an example of the current detector of this invention. It is a block diagram which shows an example of the other current detector of this invention. 3 is a graph showing timing of current values output from the current detection circuit shown in FIGS. 1 and 2.

  Embodiments of the present invention will be described below with reference to the drawings. However, the embodiment shown below exemplifies a current detector for embodying the technical idea of the present invention, and the present invention does not specify the current detector as follows.

  Further, in this specification, in order to facilitate understanding of the scope of claims, the numbers corresponding to the members shown in the embodiments are referred to as “Claims” and “Effects of Means for Solving the Problems and the Invention”. It is appended to the members shown in. However, the members shown in the claims are not limited to the members in the embodiments.

  FIG. 1 shows a current detector that is mounted on an electric vehicle such as a hybrid car or an electric vehicle and charges a traveling battery 1 and detects a discharging current. The application of the current detector according to the present invention is described below. It is not specified as a detector that detects battery current. This is because it can be used for all other applications that detect a large current exceeding 100 A and a current that fluctuates greatly.

  The current detector shown in FIG. 1 includes a plurality of shunt resistors 2 that detect the current of the battery 1, and a plurality of current detectors that detect a current value flowing through each shunt resistor 2 and output a current signal at a predetermined period. The circuit 5 includes a microcomputer 6 that calculates current signals input from all the current detection circuits 5 and calculates the total current of all the shunt resistors 2.

  The current detector shown in the figure has a plurality of shunt resistors 2 connected in parallel by lead wires 8. The number of shunt resistors 2 connected in parallel is specified in consideration of the maximum current that can be detected by the current detector and the maximum current that can be detected by one shunt resistor 2 with high accuracy. The current detector shown in the figure has four sets of shunt resistors 2 connected in parallel, but the current detector can increase the maximum current that can be detected by increasing the number of shunt resistors 2 connected in parallel. A current detector in which four sets of shunt resistors 2 are connected in parallel is suitable for setting the maximum current that can be detected to several hundred A.

  The shunt resistor 2 detects the voltage by detecting the voltage drop by the current detection circuit 5. Since the voltage drop (E) of the shunt resistor 2 is the product of the resistance value (R) and the current (I), the shunt resistor 2 can increase the resistance value and increase the voltage drop to increase detection accuracy. . However, since the power loss of the shunt resistor 2 increases in proportion to the resistance value, it is required to reduce the resistance value as much as possible in order to reduce the power loss. In particular, since the power loss increases in proportion to the product of the square of the current and the resistance value, the shunt resistor 2 that detects a large current sets the resistance value as small as possible in consideration of a decrease in accuracy. . For this reason, the shunt resistor 2 having a considerably large detection current of several hundreds A or more has a low resistance value, for example, 0.01 mΩ or more and 1.0 mΩ or less, more preferably 0.07 mΩ or more, and 0.03 mΩ or more. Set to 3 mΩ or less, optimally about 0.1 mΩ.

  The shunt resistor 2 is provided with a terminal portion 2B for connecting the lead wire 8 at both ends, and the portion between the terminal portions 2B is a resistance portion 2A. This shunt resistor 2 specifies the resistance value of the shunt resistor 2 by using the resistance portion 2A as a metal plate having a lower conductivity than the terminal portion 2B, and setting the resistance value of the resistance portion 2A as a constant resistance value. The low-resistance terminal portion 2B is connected to both ends. This shunt resistor 2 has a structure in which a resistor plate 2A and a terminal portion 2B are integrally formed by connecting a metal plate to be a terminal portion 2B to both ends of a metal plate to be a resistor portion 2A by a method such as welding or pressure welding. It is a sheet of metal plate.

  The terminal portion 2 </ b> B is provided with through holes 7 for connection on both surfaces, and lead wires 8 are connected via set screws that are inserted through the through holes 7. The shunt resistor 2 in FIG. 1 has a lead wire 8, a temperature detection wire 12 and a voltage detection wire 14 connected to the terminal portion 2B, but the shunt resistor 2 in FIG. 2 has a lead wire 8 connected to the terminal portion 2B. And a second terminal portion 2b for connecting the temperature detection line 12 and the voltage detection line 14 are provided.

  The lead wire 8 is connected to the battery 1 by connecting a plurality of shunt resistors 2 in parallel. The plurality of shunt resistors 2 connected in parallel are connected to the battery 1, the motor 9, and the generator 10, and detect currents of the motor 9 and the generator 10. The hybrid car connects the shunt resistor 2 connected in parallel to the battery 1, the motor 9, and the generator 10, and the electric vehicle connects the shunt resistor 2 connected in parallel to the battery 1, the motor 9, and a charger (not shown). Connect to. The motor 9 and the generator 10 are connected to the battery 1 via the control circuit 11. The control circuit 11 controls the discharge current of the motor 9 and the charging current of the generator 10 so that the remaining capacity of the battery 1 input from the microcomputer 6 falls within the set range when the vehicle is running.

  1 and 2, the shunt resistor is connected to a parallel circuit of a motor and a generator in series with a shunt resistor to detect the current flowing through the motor and the generator. Since the current flowing through the circuit connected to the path is detected, in an electric vehicle, although not shown, it is connected in series with the motor to detect the current of the motor, and connected to the charger in series with the current of the charger. And the current flowing through the battery connected to the negative side or the positive side of the battery can be detected.

  The current detection circuit 5 is connected to each shunt resistor 2, calculates a current from the voltage drop of each shunt resistor 2, and outputs a current signal to the microcomputer 6 at a predetermined cycle. In order to detect the voltage drop of each shunt resistor 2 separately and independently, a current detection circuit 5 is connected to each shunt resistor 2. The current detector shown in the figure includes four sets of shunt resistors 2, and thus includes four sets of current detection circuits 5 in order to detect the current flowing through each shunt resistor 2.

  All the current detection circuits 5 do not output a current signal to the microcomputer 6 in the same cycle. This is because if all current detection circuits 5 output current signals to the microcomputer 6 in a short cycle, the CPU load of the microcomputer 6 increases and the component cost increases. The plurality of current detection circuits 5 include a first current detection circuit 5A and a second current detection circuit 5B that output current signals to the microcomputer 6 at different periods. The first current detection circuit 5A outputs a current signal to the microcomputer 6 with a shorter cycle than the second current detection circuit 5B, and the second current detection circuit 5B has a longer cycle than the first current detection circuit 5A. A signal is output to the microcomputer 6.

  The timing chart of FIG. 3 shows the timing at which one set of first current detection circuits 5A outputs current values in a short cycle and the timing at which three sets of second current detection circuits 5B output current values in a long cycle. Show. However, this figure shows the timing of outputting a current signal as a pulse signal, and the current signal output in a short cycle and the current signal output in a long cycle are digital signals. This current detection circuit specifies a current value with an 8-bit or 16-bit digital signal, and outputs a current signal specifying the current value with a digital signal to the microcomputer in a short cycle or a long cycle. However, the current detection circuit of the present invention can also output a current signal output in a short cycle or a long cycle to the microcomputer as an analog signal. A microcomputer to which a current signal is input as an analog signal converts the analog signal into a digital signal by an A / D converter provided on the input side, and performs calculation. In FIG. 3, in order to make it easy to understand the short period and the long period, the ratio of the short period and the long period, which is the ratio of the short period and the long period, is 1/10. An instantaneous current change can be detected quickly while reducing the CPU load of the microcomputer 6 by setting it to 1/10 or less, preferably 1/30 or less, more preferably 1/50 or less, and most preferably about 1/100.

  The period in which the first current detection circuit 5A and the second current detection circuit 5B output the current signal is set to an optimum period in consideration of the application. The current detector that detects the current of the battery connected to the motor or generator mounted on the vehicle detects the current in a short period, detects the short circuit or output power from the instantaneous current value, The remaining capacity of the battery 1 is calculated by integrating the current values detected in a long cycle. Short and output power are not required to be highly accurate compared to the calculation of the remaining capacity, but must be detected in the shortest possible cycle. This is to detect the short-circuit current and quickly activate the protection circuit, and to prevent the output power from instantaneously exceeding the allowable value and overloading the battery 1. On the other hand, the calculation of the remaining capacity of the battery 1 does not need to be detected in such a short cycle, but requires as high accuracy as possible. This is because the remaining capacity error limits the capacity of the battery 1 that can be charged and discharged.

  In the current detectors of FIGS. 1 and 2, the first current detection circuit 5A outputs a current signal to the microcomputer 6 in a short cycle and outputs instantaneously varying current to the microcomputer 6 without time delay. In order to quickly detect a current that fluctuates instantaneously, the short period in which the first current detection circuit 5A outputs a current signal is, for example, 100 msec or less, preferably 50 msec or less, more preferably 30 msec or less, optimally about 10 msec. Even if the short cycle of the first current detection circuit 5A is too small, the CPU load of the microcomputer 6 increases. Therefore, the short cycle in which the first current detection circuit 5A outputs a current signal is, for example, 0.1 msec or more, preferably Is 1 msec or more, more preferably 5 msec or more.

In order to detect the current value with high accuracy, the second current detection circuit 5B is larger than the number of the first current detection circuits 5A. Preferably, the number of the second current detection circuit 5B is three or three or more as shown in the figure. Provided. Since the first current detection circuit 5A and the second current detection circuit 5B are respectively connected to the independent shunt resistor 2, the shunt resistor connected to the first current detection circuit 5A and the second current detection circuit 5B. A vessel 2 is provided. The current detector increases the number of second current detection circuits 5B and detects the current value with high accuracy. To reduce the load on the microcomputer, the second current detection circuit 5B The current detection circuit 5A detects the current signal with a longer period than the short period in which the current value is output, and outputs it to the microcomputer 6. The long period in which the second current detection circuit 5B outputs a current value is, for example, 100 msec or more, preferably 200 msec or more, and more preferably 500 msec or more. If the long period is too large, the change in the remaining capacity cannot be calculated quickly. For example, it is 50 sec or less, preferably 20 sec or less, more preferably 10 sec or less, and optimally about 1 sec.
In the first current detection circuit and the second current detection circuit, the sampling period for detecting the voltage of the shunt resistor is shorter than the period for outputting the current signal, for example, 1/100 to 1 of the period for outputting the current signal. / 3 can increase the current detection accuracy. This is because a current value can be detected by reducing the influence of noise and the like by calculating a current value from a plurality of detection voltages. The current detection circuit which sets the sampling period of voltage detection to 1/10 of the period of outputting the current signal calculates the current value very accurately by averaging or integrating the detection voltage of 10 times. The current value can be output to the microcomputer as a current signal. In particular, since the second current detection circuit outputs a current signal with a long cycle, the time interval for outputting the current signal, that is, the pause timing (Ts) at which the current signal is not output is long, and the shunt resistor is repeatedly applied many times at the pause timing. Can be detected and averaged or integrated to increase the current detection accuracy. For example, the second current detection circuit that outputs a current signal with a long cycle 10 times the short cycle detects the voltage of the shunt resistor with the same sampling cycle as the first current detection circuit, while the first current detection circuit The detection voltage that is 10 times as many times within one cycle of the second current detection circuit is averaged or integrated within one cycle of the second current detection circuit, and the current value can be calculated and output as a current signal with extremely high accuracy. is there. This current detection circuit has an arithmetic circuit (not shown) that detects the voltage drop of the shunt resistor multiple times with a sampling period shorter than the period of outputting the current signal, and calculates the current value. The current value thus output is output as a current signal to the microcomputer in a short cycle or a long cycle.

  1 and 2 includes a correction circuit 4 that detects the temperature of the shunt resistor 2 and corrects the resistance value. The correction circuit 4 is connected to a temperature sensor 3 that detects a correction temperature for correcting a change in resistance value due to the temperature of the shunt resistor 2, detects the temperature with an input signal from the temperature sensor 3, and shunts at the detected temperature. The resistance value of the resistor 2 is corrected.

  As the temperature sensor 3, any sensor capable of detecting the temperature of the shunt resistor 2, such as a thermistor or a thermocouple, can be used, but a thermocouple is preferable. In the thermocouple, a pair of thin temperature detection wires 12 made of different metal wires are connected at a measurement point 13 at the tip. The thermocouple is a temperature sensor 3 that detects the temperature using the Seebeck effect. A pair of temperature detection wires 12 made of different metal wires are electrically connected at a measurement point 13 at the front end, and the rear end is opened to heat the thermocouple. The temperature can be detected by detecting the potential difference due to the electromotive force. The thermocouple can detect the open voltage by opening the rear ends of the pair of temperature detection lines, and can detect the temperature of the measurement point by connecting the temperature detection lines and detecting the current flowing in the closed loop. The type of thermocouple that is a temperature sensor is defined by the JIS standard depending on the type of dissimilar metal wire. The thermocouple of the symbol (T) of the JIS standard type is an alloy (constantan) mainly composed of copper in the + leg and copper and nickel in the − leg. Since this thermocouple uses copper as the + leg, it is most suitable for use as a voltage detection line. However, the present invention does not specify the thermocouple as JIS standard (T), and for example, JIS standard J, K, etc. can be used.

  In the thermocouple of the temperature sensor 3, the measurement point 13 is electrically connected to the terminal 2 </ b> B of the shunt resistor 2, and one temperature detection line 12 is used as the voltage detection line 14. This thermocouple uses the + leg temperature detection line 12, which is a copper wire, together with the voltage detection line 14 to accurately detect the voltage of the shunt resistor 2. This is because both voltage detection lines 14 are connected to both ends of the shunt resistor 2. The thermocouple can increase the temperature detection accuracy by connecting the measurement point to the center of the resistance portion 2A. This is because the temperature at the center of the shunt resistor 2 is the highest. In order to make the measurement point approach the central portion of the shunt resistor 2, the thermocouple in the figure has the measurement point 13 connected to the portion of the terminal portion 2B close to the boundary with the resistance portion 2A. The thermocouple connecting the measurement point 13 to this position has a feature that the temperature can be accurately detected by using the temperature detection line 12 together with the voltage detection line 14 while accurately detecting the temperature of the entire shunt resistor 2. .

  The shunt resistor 2 has the highest temperature at the center, because the lead wire 8 is connected to the terminal portions 2B at both ends and heat is radiated to the lead wire 8. From this, the thermocouple can detect the temperature of the shunt resistor 2 with higher accuracy by bringing the connection position of the measurement point closer to the center of the shunt resistor 2, but the thermocouple measurement point can be detected by the resistor 2A. Since the temperature detection line can be used together with the voltage detection line and the voltage across the shunt resistor 2 cannot be accurately detected, the measurement point of the thermocouple is preferably the terminal part 2B and the resistance part 2A. Connected to a nearby area. Since the resistance value of the terminal portion 2B is smaller than that of the resistance portion 2A, the accuracy of voltage detection generated at both ends of the shunt resistor 2 is not greatly lowered regardless of the position of the measurement point on the terminal portion 2B. However, in the thermocouple, the temperature detection line can be used together with the voltage detection line, with the measurement point being the end portion of the resistance portion 2A and the region close to the terminal portion 2B. This is because the resistance difference between the resistance portion 2A and the terminal portion 2B decreases as the end portion approaches.

  The measuring point 13 of the thermocouple is welded and electrically connected to the shunt resistor 2 in an ideal state. However, the method of electrically connecting the measurement point to the shunt resistor is not specified for welding. This is because it can be electrically connected by a method other than welding, for example, pressure welding, caulking structure, adhesion using a conductive adhesive, screwing, or the like. The thermocouple connects the tips of a pair of temperature detection wires 12 as a measurement point 13, connects this measurement point 13 to the shunt resistor 2, or closes the tips of the temperature detection wire 12 to each other to connect the shunt resistor 2. To the measurement point 13 by connecting via the shunt resistor 2.

  The correction circuit 4 calculates the temperature of the measurement point 13 from the thermoelectromotive force at the open end of the thermocouple that is a temperature sensor. This is because the thermoelectromotive force at the open end is specified by the type and temperature of the thermocouple. Since the thermoelectromotive force of the thermocouple is specified from the temperatures at both ends of the temperature detection line 12, the correction circuit 4 also includes a circuit that detects the temperature at the open end of the thermocouple as a reference temperature. The reference temperature is detected by a thermistor or a thermocouple (not shown) built in the correction circuit because the temperature does not change with current unlike a shunt resistor. Note that the reference temperature can be detected not by the thermistor or thermocouple built in the correction circuit but by using the fact that the voltage between the base / emitter of the transistor and the forward voltage of the diode change depending on the temperature. In this configuration, it is not necessary to incorporate a thermistor or thermocouple in the correction circuit. The correction circuit 4 calculates the temperature at the measurement point 13 from the thermoelectromotive force at the open end of the thermocouple and the reference temperature. The correction circuit when using a thermistor for the temperature sensor 3 is not shown, but a reference resistor is connected in series with the thermistor, the thermistor or the reference resistor voltage is detected, and the electrical resistance of the thermistor is detected from the detected voltage value. To detect the reference temperature. This is because the electric resistance of the thermistor changes with temperature. The thermistor has a large change in resistance value with respect to temperature, and has a feature that can detect a reference temperature with a simple circuit configuration.

The current detection circuit 5 calculates the current flowing through the shunt resistor 2 from the voltage generated at both ends of the shunt resistor 2. The current detection circuit 5 corrects the electric resistance of the resistor portion 2A with the correction temperature of the shunt resistor 2 detected by the correction circuit 4, and generates a current from the corrected electric resistance and the voltage drop across the shunt resistor 2. To detect. The correction circuit 4 of the current detection circuit 5 includes a memory that stores the electrical resistance with respect to the temperature of the shunt resistor 2 as a function of temperature or as a lookup table. Based on the function and lookup table stored in the memory, the correction circuit 4 The electric resistance is corrected from the temperature of the resistor. The current detection circuit 5 calculates a current from the corrected electric resistance and a voltage drop generated at both ends of the shunt resistor. The current detection circuit 5 calculates the current (I) of the shunt resistor 2 from the electric resistance (R) corrected by the temperature of the shunt resistor 2 and the voltage drop (E) generated in the shunt resistor 2 by the following formula. To do.
I = E / R

  The current value detected by the current detection circuit 5 is output to the microcomputer 6. The microcomputer 6 detects an instantaneous change in the current flowing through the battery 1 with a current signal input in a short cycle from the first current detection circuit 5A, and outputs it to the control circuit on the vehicle side. When the instantaneous battery current input from the microcomputer 6 exceeds the preset maximum current, the control circuit determines that a short circuit has occurred and switches the breaker or relay to the OFF state to interrupt the current. The current of the motor and generator is controlled so that the battery current does not exceed the preset maximum output power setting. Instantaneous current detection is used to control a short circuit and output power, and therefore, it is required to detect the current more quickly without time delay than accuracy. The current detector shown in the figure includes a set of first current detection circuits 5A that output a current signal in a short cycle.

  The microcomputer 6 calculates the remaining capacity of the battery 1 by integrating the current signals input from the three sets of the second current detection circuits 5B and the one set of the first current detection circuits 5A. The microcomputer 6 calculates the total current by adding the current values input from all the current detection circuits 5, and calculates the remaining capacity of the battery 1 by integrating the total current. Since the microcomputer 6 adds up the current signals input from all the current detection circuits 5 and calculates the total current, the microcomputer 6 calculates the total current with a long period input from the second current detection circuit 5B and calculates the remaining capacity. Calculate. The microcomputer 6 adds the integrated value of the charging current of the battery 1 to the remaining capacity and subtracts the integrated value of the discharging current of the battery 1 to calculate the varying remaining capacity of the battery 1.

The microcomputer 6 detects an overcurrent and outputs it to the protection circuit 16 that cuts off the battery current, and further outputs the calculated current value and remaining capacity to the control circuit 11 that controls the motor 9 and the generator 10. The microcomputer 6 may calculate the remaining capacity using the battery voltage when the vehicle is stopped for a certain period of time and the battery voltage is stable, but the voltage drop is caused by the internal resistance and current of the battery while the vehicle is running. Therefore, it is difficult to calculate the remaining capacity with voltage. Therefore, the microcomputer 6 calculates the remaining battery capacity by integrating the charge / discharge current input from the current detection circuit while the vehicle is running. The microcomputer 6 calculates the remaining battery capacity by adding the integrated value of the charging current and subtracting the integrated value of the discharging current. When the current value input from the microcomputer 6 exceeds the maximum set current, the protection circuit 16 protects the battery by cutting off the current with a protection element (not shown) such as a breaker, relay, or fuse. The control circuit 11 controls the current of the motor 9 and the generator 10 while monitoring the current value input from the current detection circuit.

  The current detector of the present invention is optimally used for applications in which a large current is accurately detected by a plurality of shunt resistors connected in parallel, such as a charge / discharge current of a battery for traveling mounted on a vehicle. .

DESCRIPTION OF SYMBOLS 1 ... Battery 2 ... Shunt resistor 2A ... Resistance part 2B ... Terminal part 2a ... 1st terminal part 2b ... 2nd terminal part 3 ... Temperature sensor (thermocouple)
DESCRIPTION OF SYMBOLS 4 ... Correction circuit 5 ... Current detection circuit 5A ... 1st current detection circuit 5B ... 2nd current detection circuit 6 ... Microcomputer 7 ... Through-hole 8 ... Lead wire 9 ... Motor 10 ... Generator 11 ... Control circuit 12 ... Temperature Detection line 13 ... Measurement point 14 ... Voltage detection line 16 ... Protection circuit

Claims (9)

A plurality of shunt resistors connected in parallel to each other;
A plurality of current detection circuits connected to each shunt resistor to calculate a current value from a voltage drop and output a current signal in a predetermined cycle;
A current detector comprising a microcomputer that calculates a current signal input from each of the current detection circuits and calculates a total current of all shunt resistors,
The current detection circuit includes a first current detection circuit and a second current detection circuit that output current signals at different periods,
The first current detection circuit outputs a current signal to the microcomputer with a shorter cycle than the second current detection circuit,
The second current detection circuit outputs a current signal to the microcomputer with a longer period than the first current detection circuit,
The current detector, wherein the microcomputer calculates a total current from a current signal input from the first current detection circuit and a current signal input from the second current detection circuit. A current detector according to claim 1, comprising:
The current detector, wherein the number of the second current detection circuits is larger than that of the first current detection circuits. A current detector according to claim 2, comprising:
A current detector comprising three or more sets of second current detection circuits. A current detector according to any one of claims 1 to 3,
The current detection circuit has an arithmetic circuit for calculating a current value by detecting a voltage drop of the shunt resistor a plurality of times in a sampling cycle shorter than a cycle of outputting a current signal;
A current detector that outputs a current value calculated by the arithmetic circuit as a current signal. A current detector according to claims 1 to 4, comprising:
The shunt resistor is connected in series with a battery for traveling that supplies power to a traveling motor of a vehicle, and includes a remaining capacity calculation circuit that calculates a remaining capacity of the battery from a total current detected by the microcomputer. Current detector. A current detector according to claim 5, comprising:
The current detector is characterized in that the remaining capacity calculation circuit calculates the remaining capacity of the battery in a long cycle. The current detector according to claim 1, comprising:
A current detector, wherein a resistance value of the shunt resistor is 0.01 mΩ or more and 1.0 mΩ or less. A current detector according to any one of claims 1 to 7,
The current detection circuit includes a correction circuit that corrects a resistance value at a temperature of the shunt resistor connected thereto,
The current detector detects the current flowing through the shunt resistor with the resistance value corrected by the correction circuit. A current detector according to any one of claims 1 to 8,
The current detector, wherein a short cycle in which the first current detection circuit outputs a current signal is 1/10 or less of a long cycle in which the second current detection circuit outputs a current signal.

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