JP2014204575A - Shut-off device - Google Patents

Abstract

An object of the present invention is to provide a breaker capable of reliably preventing the ignition of an electric wire and having a long use period and being inexpensive. A CPU 63 repeatedly calculates a temperature difference between the ambient temperature of the electric wire 4 and the temperature of the electric wire 4 over time. When the temperature obtained by adding the temperature difference calculated by the CPU 63 to the ambient temperature is equal to or higher than the predetermined temperature, the control circuit 53 blocks the current flowing through the wire 4 by turning off the FET 51. The CPU 63 sets an initial temperature difference that is a positive value based on the ambient temperature. The CPU 63 uses the set initial temperature difference for the first temperature difference calculation, and uses the previously calculated temperature difference for the subsequent temperature difference calculation. [Selection] Figure 1

Description

  The present invention relates to a breaker that calculates a wire temperature and blocks a current flowing through the wire when the calculated wire temperature is equal to or higher than a threshold value.

  When a current flows through an electric wire of a wire harness that connects many electric devices mounted on a vehicle, the electric wire generates Joule heat. For example, even if the current flowing through the electric wire is not an overcurrent, the Joule heat generated by the current flowing through the electric wire may exceed the heat radiation amount of the electric wire. When Joule heat generated from the electric wire exceeds the heat radiation amount of the electric wire, the electric wire temperature rises. And when an electric wire temperature exceeds fixed temperature, an electric wire ignites.

  Patent Document 1 discloses a breaker that can prevent the ignition of such an electric wire. This circuit breaker detects the current flowing through the electric wire, and repeatedly calculates the temperature difference between the ambient temperature of the electric wire and the temperature of the electric wire over time. The circuit breaker disclosed in Patent Literature 1 calculates a temperature difference between the ambient temperature and the wire temperature using the detected current value and the previously calculated temperature difference, and adds the calculated temperature difference to the ambient temperature. That is, the current flowing through the electric wire is cut off when the electric wire temperature is equal to or higher than a predetermined temperature. Thereby, before an electric wire ignites, the electric current which flows into an electric wire can be interrupted | blocked and the ignition of an electric wire can be prevented.

Japanese Patent No. 4624400

  In the circuit breaker described in Patent Document 1, the temperature difference between the ambient temperature of the electric wire and the electric wire temperature is usually calculated by a CPU (Central Processing Unit) of a microcomputer (hereinafter referred to as a microcomputer). In order to calculate the temperature difference, the calculated temperature difference is temporarily stored in a RAM (Random Access Memory) of the microcomputer. Many microcomputers are configured to be reset and initialized when a malfunction occurs.

  When the microcomputer is initialized, the temperature difference stored in the RAM is erased, and the CPU resumes calculating the wire temperature assuming that the temperature difference is zero, that is, the wire temperature matches the ambient temperature. To do. For this reason, for example, when the microcomputer is initialized in a state where the electric wire temperature is high, the electric wire temperature calculated by the CPU thereafter is lower than the actual electric wire temperature. Therefore, even when the actual electric wire temperature is equal to or higher than the predetermined temperature, the electric current flowing through the electric wire is not interrupted, so that the electric wire may ignite, and there is a problem that the electric wire cannot be reliably ignited.

  Even in the above cases, as a shut-off device that can prevent the ignition of the electric wire, a non-volatile memory that always keeps memory is provided, and each time the CPU calculates the temperature difference, the non-volatile memory is calculated. A shut-off device for writing the temperature difference is conceivable. In this case, however, the manufacturing cost increases because a non-volatile memory for storing the temperature difference must be provided. Furthermore, the number of times of temperature difference writing becomes enormous and the non-volatile memory deteriorates early, so that there is a problem that the device usage period is short.

  This invention is made | formed in view of such a situation, The place made into the objective is providing the interruption device which can prevent the ignition of an electric wire reliably and has a long use period and is inexpensive.

  The circuit breaker according to the present invention includes a calculation unit that repeatedly calculates a temperature difference between the ambient temperature of the wire and the temperature of the wire over time, and the temperature obtained by adding the temperature difference calculated by the calculation unit to the ambient temperature is In the interrupting device that interrupts the current flowing through the wire when the temperature is equal to or higher than a predetermined temperature, the interrupting device includes a setting unit that sets an initial temperature difference that is a positive value based on the ambient temperature, and the calculating unit includes the initial temperature In the calculation of the difference, the initial temperature difference set by the setting means is used, and in the subsequent calculation of the temperature difference, the previously calculated temperature difference is used.

  In the present invention, the temperature difference from the ambient temperature of the wire to the wire temperature is repeatedly calculated over time. When starting the calculation of the temperature difference, first, an initial temperature difference that is a positive value is set based on the ambient temperature of the electric wire. In the initial temperature difference calculation, the temperature difference between the ambient temperature and the wire temperature is calculated using the set initial temperature difference, and in the subsequent temperature difference calculation, the ambient temperature is calculated using the previously calculated temperature difference. And the temperature difference between the wire temperature. Then, when the temperature obtained by adding the calculated temperature difference to the ambient temperature, that is, when the wire temperature is equal to or higher than the predetermined temperature, the current flowing through the wire is cut off.

  For this reason, for example, even when the microcomputer that calculates the temperature difference between the ambient temperature and the wire temperature is initialized and the calculation of the temperature difference starts again from the beginning, it is a positive value based on the ambient temperature. By appropriately setting the initial temperature difference, it is possible to keep the calculated wire temperature exceeding the actual wire temperature.

  Accordingly, since the current flowing through the electric wire can be surely interrupted before the actual electric wire temperature becomes equal to or higher than the predetermined temperature, ignition of the electric wire is reliably prevented. Furthermore, since it is not necessary to use a non-volatile memory that always stores the calculated temperature difference, and it is not necessary to write the temperature difference in the non-volatile memory, the device is inexpensive and the device usage period is long. .

  The shut-off device according to the present invention is characterized in that the setting means is configured to set the initial temperature difference to a larger value as the ambient temperature is lower.

  In the present invention, when the ambient temperature is low, the initial temperature difference is set to a large value, and when the ambient temperature is high, the initial temperature difference is set to a small value so that the wire temperature is always high. Under this assumption, the calculation of the wire temperature can be started. For example, when the predetermined temperature is 150 ° C., the calculation of the wire temperature can be started on the assumption that the wire temperature is 130 ° C. For this reason, it becomes possible to reliably exceed the calculated electric wire temperature above the actual electric wire temperature. By causing the calculated electric wire temperature to exceed the actual electric wire temperature, the current flowing through the electric wire is interrupted before the actual electric wire temperature becomes equal to or higher than the predetermined temperature, so that the ignition of the electric wire is more reliably prevented.

The interrupting device according to the present invention further includes detection means for detecting a current flowing through the electric wire, and the calculation means is a current value I1 (A) detected by the detection means and a temperature difference ΔT1 (° C.) calculated last time. The temperature difference ΔT2 (° C.) is calculated by substituting into the following equation.
ΔT2 = ΔT1 × exp (−Δt / τ)
+ Rth × R1 × I1 ² × (1-exp (−Δt / τ))
R1 = Ro × (1 + κ × (Ta + ΔT1-To))
However, Rth: Wire thermal resistance (° C / W)
Ro: Wire resistance (Ω) at a predetermined temperature To (° C.)
Ta: the ambient temperature (° C.)
τ: Electric wire heat dissipation time constant (s)
κ: Wire resistance temperature coefficient (/ ° C)
Δt: Calculation interval (s) of the calculation means

  In the present invention, by detecting the current flowing through the wire and substituting the detected current value and the previously calculated temperature difference into the above formula, the wire temperature closer to the actual wire temperature is calculated. The

  According to the present invention, since the initial temperature difference, which is a positive value, is set based on the ambient temperature of the electric wire, it is possible to reliably prevent the electric wire from being ignited, and to realize an inexpensive circuit breaker having a long use period. be able to.

It is a block diagram which shows the structure of the interruption | blocking apparatus which concerns on this invention. It is a flowchart which shows the procedure of the operation | movement which CPU performs. It is a graph which shows the relationship between the ambient temperature of an electric wire, and an initial temperature difference. It is explanatory drawing of the effect in a cutoff device. It is another explanatory drawing of the effect in a blocking device.

Hereinafter, the present invention will be described in detail with reference to the drawings illustrating embodiments thereof.
FIG. 1 is a block diagram showing a configuration of a shut-off device according to the present invention. This interruption device 1 is suitably mounted on a vehicle, and is connected by a wire 4 between the positive terminal of the battery 2 and one end of the load 3. The negative terminal of the battery 2 and the other end of the load 3 are grounded. The circuit breaker 1 detects the current flowing through the electric wire 4 and the ambient temperature of the electric wire 4, and calculates the electric wire temperature of the electric wire 4 using the detected current value and the ambient temperature. The interruption | blocking apparatus 1 interrupts | blocks the electric current which flows into the electric wire 4, when the calculated electric wire temperature is more than a threshold value.

  The shut-off device 1 includes an IPD (Intelligent Power Device) 11, a temperature detection unit 12, a microcomputer 13, and a watch dog 14. The IPD 11 is connected by a wire 4 between the positive terminal of the battery 2 and one end of the load 3, and further connected to the microcomputer 13. The temperature detector 12 is disposed in the vicinity of the electric wire 4 and is connected to the microcomputer 13. The microcomputer 13 is connected to the watch dog 14 in addition to the IPD 11 and the temperature detection unit 12.

The IPD 11 detects the current flowing through the electric wire 4 and outputs current information indicating the detected current value to the microcomputer 13 when receiving an instruction to output a current value from the microcomputer 13. Further, when receiving an instruction for interrupting the current flowing through the electric wire 4 from the microcomputer 13, the IPD 11 interrupts the current flowing through the electric wire 4.
The temperature detector 12 detects the ambient temperature of the electric wire 4 and outputs temperature information indicating the detected ambient temperature to the microcomputer 13.

  The microcomputer 13 acquires current information from the IPD 11 and outputs temperature information from the temperature detection unit 12 by outputting an output instruction to the IPD 11. The microcomputer 13 repeatedly calculates the wire temperature of the wire 4 over time using the current value and the temperature indicated by the current information and the temperature information acquired from the IPD 11 and the temperature detection unit 12, respectively. When the calculated wire temperature is equal to or higher than the threshold value, the microcomputer 13 outputs a cut-off instruction to the IPD 11 and cuts off the current flowing through the wire 4.

Further, the microcomputer 13 outputs pulses to the watch dog 14 at a predetermined cycle while operating normally. When the microcomputer 13 receives a reset signal instructing resetting from the watchdog 14, the microcomputer 13 performs initialization.
The watch dog 14 receives a pulse output from the microcomputer 13. For example, when a pulse is not input from the microcomputer 13 for a certain period due to a malfunction of the microcomputer 13, the watch dog 14 outputs a reset signal to the microcomputer 13.

  The IPD 11 includes an N-channel FET (Field Effect Transistor) 51, a current detection unit 52, and a control circuit 53. Regarding the FET 51, the drain is connected to the positive terminal of the battery 2 by the electric wire 4, the source is connected to one end of the load 3 by the electric wire 4, and the gate is connected to the control circuit 53. The control circuit 53 is connected to the current detection unit 52 and the microcomputer 13 in addition to the gate of the FET 51.

The FET 51 functions as a switch. When a voltage higher than a predetermined voltage is applied to the gate, the current flows from the drain to the source and turns on. When the voltage applied to the gate is lower than the predetermined voltage, the current is drained. Turns off without flowing from source to source.
The current detection unit 52 detects the current flowing through the electric wire 4 and outputs the detected current value to the control circuit 53. The current detection unit 52 functions as detection means.

  The control circuit 53 adjusts the voltage applied to the gate of the FET 51 to turn on / off the FET 51, and normally keeps the FET 51 on. Further, the control circuit 53 receives an output instruction and a cutoff instruction from the microcomputer 13. When receiving the output instruction, the control circuit 53 outputs current information indicating the current value detected by the current detection unit 52 to the microcomputer 13. When the control circuit 53 receives the cutoff instruction, the control circuit 53 turns off the FET 51 and cuts off the current flowing through the electric wire 4.

The microcomputer 13 includes an input unit 61, an output unit 62, a CPU 63, a storage unit 64, and a RAM 65, which are connected to a bus 66.
The input unit 61 receives current information and temperature information from the control circuit 53 and the temperature detection unit 12 of the IPD 11, and the input unit 61 sends the current value and ambient temperature indicated by the input current information and temperature information to the CPU 63. Notice. The output unit 62 outputs an output instruction and a cutoff instruction to the control circuit 53 in accordance with an instruction from the CPU 63. Furthermore, the output unit 62 outputs pulses to the watch dog 14 at a predetermined cycle while the CPU 63 is operating normally.

CPU63 loads the control program memorize | stored in the memory | storage part 64 to RAM65, and performs control of operation | movement of the output part 62, calculation of electric wire temperature, etc. by executing the loaded control program. The storage unit 64 is a nonvolatile memory, and the content stored in the storage unit 64 is read by the CPU 63. The RAM 65 is a memory that temporarily stores information, and the CPU 63 performs writing to the RAM 65 and reading from the RAM 65.
When the watchdog 14 outputs a reset signal to the microcomputer 13, the operations of the input unit 61, the output unit 62, the CPU 63, and the RAM 65 are initialized.

  FIG. 2 is a flowchart showing a procedure of operations executed by the CPU 63. First, CPU63 acquires the ambient temperature of the electric wire 4 which the temperature information input into the input part 61 from the temperature detection part 12 shows (step S1). Next, CPU63 sets the initial temperature difference which is a positive value used for calculation of the first electric wire temperature based on the ambient temperature acquired at step S1 (step S2). The CPU 63 functions as setting means.

  FIG. 3 is a graph showing the relationship between the ambient temperature of the electric wire 4 and the initial temperature difference. The relationship between the ambient temperature and the initial temperature difference shown in FIG. In step S2, the CPU 63 sets the initial temperature difference used for the calculation of the wire temperature to the initial temperature difference corresponding to the ambient temperature acquired in step S1, using the graph shown in FIG. In the relationship between the ambient temperature and the initial temperature difference shown in FIG. 3, the initial temperature difference decreases as the ambient temperature of the electric wire 4 increases. Therefore, in step S <b> 2, the CPU 63 causes the initial temperature difference to decrease. Set the temperature difference to a large value. The initial temperature difference set by the CPU 63 is stored in the RAM 65. In the graph of FIG. 3, the initial temperature difference is a positive value and always exceeds zero.

  After executing step S2, the CPU 63 causes the output unit 62 to output an output instruction to the control circuit 53, thereby acquiring the current value indicated by the current information input from the control circuit 53 to the input unit 61 (step S3).

  After executing step S3, the CPU 63 calculates a temperature difference between the ambient temperature acquired in step S1 or step S7 described later and the wire temperature of the wire 4 (step S4). As will be described later, while the calculated wire temperature is lower than the threshold, the CPU 63 repeatedly executes steps S3, S4, S5, and S7.

  In the calculation of the first temperature difference performed in step S4, the CPU 63 uses the ambient temperature acquired in step S1, the initial temperature difference set in step S2, and the current value acquired in step S3, in step S1. The temperature difference between the acquired ambient temperature and the wire temperature is calculated. In the calculation of the temperature difference after the second time performed in step S4, the CPU 63 obtains the ambient temperature acquired in the same manner as in step S1 in step S7, the temperature difference calculated in the previous step S4, and the current value acquired in step S3. Is used to calculate the temperature difference between the ambient temperature acquired in step S7 and the wire temperature. The CPU 63 also functions as a calculation unit.

  Next, the CPU 63 calculates the wire temperature of the wire 4 by adding the temperature difference calculated in step S4 to the ambient temperature acquired in step S1 or step S7 (step S5). In the calculation of the first wire temperature performed in step S5, the wire temperature is calculated by adding the temperature difference calculated in step S4 to the ambient temperature acquired in step S1, and the second and subsequent wire temperatures calculated in step S5. In the calculation, the wire temperature is calculated by adding the temperature difference calculated in step S4 to the ambient temperature acquired in step S7.

  And CPU63 determines whether the electric wire temperature calculated by step S5 is more than a threshold value (step S6). When the CPU 63 determines that the electric wire temperature is lower than the threshold (step S6: NO), the CPU 63 obtains the ambient temperature of the electric wire 4 indicated by the temperature information input from the temperature detection unit 12 to the input unit 61 as in step S1. (Step S7), and the process returns to Step S3. Steps S3, S4, S5, and S7 are repeatedly executed until the wire temperature becomes equal to or higher than the threshold value.

  CPU63 performs step S3, S4, S5, and S7 for every predetermined period, while repeatedly determining with electric wire temperature being less than a threshold value by step S6. As described above, the CPU 63 repeatedly calculates the temperature difference between the ambient temperature of the electric wire 4 and the electric wire temperature of the electric wire 4 over time, specifically, every predetermined period.

When the CPU 63 determines that the electric wire temperature calculated in step S5 is equal to or higher than the threshold (step S6: YES), the CPU 63 instructs the output unit 62 to output a shut-off instruction to the control circuit 53, whereby the current flowing through the electric wire 4 is determined. Shut off (step S8). When the output unit 62 outputs a cutoff instruction to the control circuit 53, the control circuit 53 turns off the FET 51 and cuts off the current flowing through the electric wire 4 as described above. Here, the threshold corresponds to a predetermined temperature.
CPU63 complete | finishes operation | movement, after performing step S7.

In the calculation of the temperature difference for the second and subsequent times in step S4, the CPU 63 calculates the current value acquired in the immediately preceding step S3, the temperature difference calculated in the previous step S4, and the ambient temperature acquired in step S7 (1) And a temperature difference is calculated by substituting into (2) Formula.
ΔT2 = ΔT1 × exp (−Δt / τ) + Rth × R1
× I1 ² × (1-exp (−Δt / τ)) (1)
R1 = Ro × (1 + κ × (Ta + ΔT1-To)) (2)

  The variables and constants used in the equations (1) and (2) will be described below. In the description of variables and constants, the unit of the variable or constant is shown in parentheses. ΔT1 is the temperature difference (° C.) calculated in the previous step S4, and ΔT2 is the temperature difference (° C.) calculated in step S4. Δt is an interval (s) for calculating the temperature difference ΔT2 in step S4, and τ is a wire heat dissipation time constant (s) of the wire 4.

  Rth is the wire thermal resistance (° C./W) of the wire 4, and R1 is the wire resistance (Ω) of the wire 4 when the wire temperature of the wire 4 is the wire temperature calculated in the previous step S5. To is a predetermined temperature (° C.), and Ro is a wire resistance (Ω) at the temperature To. Ta is the ambient temperature (° C.) acquired in step S 7, and κ is the wire resistance temperature coefficient (/ ° C.) of the wire 4. I1 is the current value (A) acquired in step S3. ΔT1, ΔT2, I1 and Ta are variables, and Δt, τ, Rth, Ro, κ and To are preset constants.

  In the calculation of the first temperature difference in step S4, the CPU 63 substitutes the ambient temperature acquired in step S1 for Ta and the initial temperature difference set in step S2 for ΔT1 into the expressions (1) and (2). Thus, the temperature difference ΔT2 between the ambient temperature acquired in step S1 and the wire temperature is calculated. For other variables and constants in the first temperature difference calculation, as in the second and subsequent temperature difference calculations, I1 is the current value obtained in the immediately preceding step S3, and Δt, τ, Rth, Ro, κ. And To are preset constants.

  The (right side) of equation (1) is composed of the sum of the first term and the second term. Since exp (−Δt / τ) becomes smaller as the temperature difference calculation interval Δt becomes longer, the first term is a term representing heat radiation of the electric wire 4. Further, (1-exp (−Δt / τ)) becomes larger as the temperature difference calculation interval Δt becomes longer, so the second term is a term representing heat generation of the electric wire 4.

  In the shut-off device 1, as described above, the CPU 63 sets the initial temperature difference to a larger numerical value as the ambient temperature is lower. For this reason, the CPU 63 can always start calculating the wire temperature under the assumption that the wire temperature is high. For example, assuming that the threshold for determining whether or not to interrupt the current is 150 ° C., the wire temperature is 130 ° C. by setting the initial temperature difference to a larger value as the ambient temperature is lower. The calculation of the wire temperature can be started. Therefore, the electric wire temperature calculated by the CPU 63 can be surely exceeded the actual electric wire temperature. Thereby, since the electric current which flows into the electric wire 4 is interrupted | blocked before actual electric wire temperature becomes more than a threshold value, the ignition of the electric wire 4 which arises by the raise of electric wire temperature can be prevented more reliably.

  Further, even when the calculation of the wire temperature is started under the assumption that the wire temperature is high, by calculating the wire temperature using the equations (1) and (2), the CPU 63 The wire temperature close to the actual wire temperature can be calculated.

  FIG. 4 is an explanatory diagram of effects in the blocking device 1. In FIG. 4, the transition of the wire temperature calculated by the CPU 63 is indicated by a bold line, and the transition of the actual wire temperature is indicated by a thin line. As shown in FIG. 4, as time elapses, that is, as the number of times the CPU 63 calculates the wire temperature increases, the wire temperature calculated by the CPU 63 approaches the actual wire temperature. The reason for this will be described below.

  When the initial temperature difference is set to a value larger than the actual temperature difference in the electric wire 4, ΔT1 in the equation (1) into which the initial temperature difference is substituted in the first calculation is a very large value. For this reason, the value of the first term described on the right side of the equation (1) is greatly reduced. The second term described on the right side of the equation (1) is low because it is the current value detected by the current detection unit 52, that is, the value of the current that actually flows through the electric wire 4. Thus, the CPU 63 repeats the calculation of the wire temperature using the equations (1) and (2), thereby reducing the calculated temperature difference ΔT2 and calculating the wire temperature close to the actual wire temperature. When an appropriate constant current continues to flow through the electric wire 4, when the CPU 63 further repeats the calculation of the electric wire temperature, the amount of decrease in the first term of the equation (1) and the second term of the equation (1) As shown in FIG. 4, the temperature difference ΔT2 calculated by the CPU 63 is constant.

For this reason, in the interruption device 1, only when the actual wire temperature is sufficiently high and close to the threshold value, an interruption instruction is output from the output unit 62 to the control circuit 53, the FET 51 is turned off, and the current flowing through the wire 4 is interrupted. Is done.
The same effect is obtained when the equation used to calculate the temperature difference ΔT2 is the sum of the term of heat dissipation that depends on the previously calculated temperature difference ΔT1 and the term of heat generation that depends on the value I1 of the current flowing through the wire 4. Is obtained.

  Even when the CPU 63 repeatedly calculates the wire temperature, the watch dog 14 outputs a reset signal to the microcomputer 13 so that the CPU 63 is initialized and the calculation of the wire temperature is resumed. The electric current flowing through the electric wire 4 can be interrupted before the electric wire temperature becomes equal to or higher than the threshold value.

  FIG. 5 is another explanatory view of the effect in the blocking device 1. In FIG. 5, the transition of the wire temperature calculated by the CPU 63 is indicated by a bold line, the transition of the actual wire temperature is indicated by a thin line, and the transition of the wire temperature calculated in the conventional breaker is indicated by a one-dot chain line. It is shown.

  Here, as shown in FIG. 5, the case where the actual electric wire temperature rises with time and reaches a threshold value will be described. In the conventional interruption device in which the initial temperature difference is set to zero, as shown in FIG. 5, when the CPU is initialized in the middle of the calculation, the calculation of the wire temperature is resumed because the initial temperature difference is zero. The wire temperature calculated later is lower than the actual wire temperature. For this reason, when the actual electric wire temperature becomes a threshold value, the calculated electric wire temperature is less than the threshold value, and the current flowing through the electric wire is not interrupted, so that the electric wire may ignite.

  As shown in FIG. 5, since the initial temperature difference that is a value exceeding zero, that is, a positive value is set in the interrupting device 1, under the assumption that the wire temperature of the wire 4 is sufficiently high. The calculation of the wire temperature of the wire 4 is started. When the initial temperature difference is set to a sufficiently large value, as described above, the wire temperature calculated by the CPU 63 decreases with time and approaches the actual wire temperature. Further, when the CPU 63 is initialized in the middle of the calculation and the calculation of the wire temperature is resumed, an initial temperature difference having a large numerical value is set again, so that the wire temperature calculated by the CPU 63 is higher than the actual wire temperature.

  As a result, as shown in FIG. 5, the CPU 63 can reliably cut off the current flowing through the electric wire 4 before the actual electric wire temperature becomes equal to or higher than the threshold value, and can reliably prevent the electric wire 4 from firing. . Furthermore, since it is not necessary to use a non-volatile memory that always stores the temperature difference calculated by the CPU 63 and it is not necessary to write the temperature difference in the non-volatile memory, the shut-off device 1 is inexpensive and the shut-off device The period of use of 1 is long.

  The CPU 63 calculates the temperature difference between the ambient temperature of the electric wire 4 and the electric wire temperature, and is not limited to the equations (1) and (2). The CPU 63 only needs to be an expression configured by the sum of the term of heat dissipation that depends on the previously calculated temperature difference ΔT1 and the term of heat generation that depends on the value I1 of the current flowing through the electric wire 4.

  Further, the CPU 63 does not have to set the initial temperature difference to a larger value as the ambient temperature is lower. The CPU 63 does not set the initial temperature difference based on the ambient temperature so that the calculated wire temperature exceeds the actual wire temperature. Should be set. Furthermore, the method of setting the initial temperature difference based on the ambient temperature by the CPU 63 is not limited to the method of setting the initial temperature difference using a graph showing the relationship between the ambient temperature and the initial temperature difference. For example, the CPU 63 may calculate the initial temperature difference by substituting the ambient temperature detected by the temperature detection unit 12 into an arithmetic expression indicating the relationship between the ambient temperature and the initial temperature difference.

  The CPU 63 calculates the temperature difference between the ambient temperature and the wire temperature using the initial temperature difference or the previously calculated temperature difference and the current value of the wire 4 detected by the current detection unit 52. The current value may not be used. The CPU 63 uses the initial temperature difference or the previously calculated temperature difference and a value related to the current flowing in the electric wire 4, for example, the voltage between both ends of the resistor provided in the electric wire 4 to calculate the ambient temperature and the electric wire temperature. A temperature difference may be calculated.

  Since the FET 51 only needs to function as a switch, a switch such as a P-channel FET, a bipolar transistor, or a relay contact may be used instead of the FET 51. Furthermore, the configuration for interrupting the current flowing through the electric wire 4 is not limited to the configuration in which a switch is provided in the middle of the electric wire 4 and the switch is turned off.

  The disclosed embodiments are to be considered in all respects as illustrative and not restrictive. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

1 Circuit breaker 4 Electric wire 51 FET
52 Current Detection Unit 53 Control Circuit 63 CPU

Claims (3)

A calculation means for repeatedly calculating the temperature difference between the ambient temperature of the electric wire and the temperature of the electric wire over time, and when the temperature obtained by adding the temperature difference calculated by the calculation means to the ambient temperature is a predetermined temperature or more In the interrupting device that interrupts the current flowing in the wire,
Setting means for setting an initial temperature difference which is a positive value based on the ambient temperature;
The calculating means includes
In the first calculation of the temperature difference, the initial temperature difference set by the setting means is used.
In the subsequent calculation of the temperature difference, the interruption device is configured to use the previously calculated temperature difference. The blocking device according to claim 1, wherein the setting unit is configured to set the initial temperature difference to a larger value as the ambient temperature is lower. It further comprises detection means for detecting the current flowing through the electric wire,
The calculation means is configured to calculate a temperature difference ΔT2 (° C.) by substituting the current value I1 (A) detected by the detection means and the previously calculated temperature difference ΔT1 (° C.) into the following equation. The shut-off device according to claim 1 or 2, wherein the shut-off device is provided.
ΔT2 = ΔT1 × exp (−Δt / τ)
+ Rth × R1 × I1 ² × (1-exp (−Δt / τ))
R1 = Ro × (1 + κ × (Ta + ΔT1-To))
However, Rth: Wire thermal resistance (° C / W)
Ro: Wire resistance (Ω) at a predetermined temperature To (° C.)
Ta: the ambient temperature (° C.)
τ: Electric wire heat dissipation time constant (s)
κ: Wire resistance temperature coefficient (/ ° C)
Δt: Calculation interval (s) of the calculation means

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