JP2014027875A - Protector of load circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a protector of a load circuit, which can detect a temperature rise of a wire and can surely block the load circuit when a rare short-circuit occurs.SOLUTION: When a current flowing in a load 4 rises, a rise temperature of a wire 7 is calculated on the basis of a thermal characteristic (thermal resistance and heat capacity) of the wire 7 or a contact conductor, and calculates a drop temperature of the wire 7 in response to the thermal characteristic of the wire 7 when the current flowing in the load 4 is zero or decreases. The rise temperature and the drop temperature, which are calculated for each sampling time, are successively integrated and an integrated result is stored in a memory 64a as an estimated temperature. When the estimated temperature exceeds a prescribed permissible temperature, the load circuit is blocked. Thus, the circuit can highly precisely be protected on the basis of the temperature rise of the wire 7.

Description

  The present invention relates to a load circuit protection device that detects a temperature of an electric wire when it rises and protects the load circuit.

  For example, a load circuit that supplies electric power to a load such as a lamp or a motor mounted on a vehicle includes a battery and an electronic switch (such as a semiconductor switch) provided between the battery and the load. The electronic switch and the load are connected to each other through a conductor including an electric wire. Further, a control circuit for turning on and off the electronic switch is provided. The drive and stop signals output from the control circuit are used to turn on and off the electronic switch to switch between driving and stopping of the load.

  In such a load circuit, an overcurrent protection function such as a fuse is provided to quickly shut down the circuit when an overcurrent flows through the load and protect the load, electric wire, electronic switch, etc. When an overcurrent exceeding a certain threshold current flows, this is detected and the electronic switch is turned off to shut off the circuit.

  However, in such a load circuit, when an overcurrent exceeding the above-mentioned threshold current flows, that is, when a dead short occurs, this can be detected immediately and the circuit can be protected. When a current that does not exceed the current flows, that is, when a rare short occurs, this may not be detected.

  When such a short-circuit occurs, the temperature of the wire rises due to the Joule heat generated in the wire, and if the amount of heat generated by the wire exceeds the amount of heat released, the wire temperature gradually increases, causing problems such as smoke generation and burning. Sometimes.

  In order to solve such a problem, for example, what is described in JP 2002-84654 A (Patent Document 1) is known. In Patent Document 1, when current flows through the load, the current value at this time is read to calculate Joule heat, and when current does not flow through the load, the amount of heat released from the wire is calculated, and the power is turned off. Immediately after that, the amount of arc heat generated as the power is turned off is calculated. Then, it is disclosed that these total heat amounts are obtained, and when the obtained total heat amount exceeds a predetermined threshold, the circuit is shut off to protect the entire circuit.

JP 2002-84654 A

  However, the load circuit protection device described in Patent Document 1 described above integrates the heat generation amount and the heat dissipation amount, and determines whether or not to shut off the circuit according to the integrated value. It does not take into account the temperature rise of the wire. That is, even when the heat generation amount is large, when a thick wire is used, the heat dissipation amount exceeds the heat generation amount, and a large temperature rise does not occur. Therefore, in such a case, there is a problem that the circuit is interrupted although continuous energization is possible.

  On the other hand, when a thin wire is used, even if the calorific value is small, a large temperature rise occurs, and although there is a risk of causing smoke or burnout, smooth circuit interruption The problem that is not done occurs.

  The present invention has been made to solve such a conventional problem, and the object of the present invention is to determine whether or not to interrupt the circuit based on the temperature rise of the electric wire when a rare short occurs. It is an object of the present invention to provide a load circuit protection device.

  In order to achieve the above object, the present invention provides a load circuit protection device for detecting a current flowing through the load of a load circuit including a power source, a switch, and a load, and cutting off the load circuit based on the detected current value. Current detection means for detecting a current flowing through the load, and when a current is detected by the current detection means, based on the detected current value and the thermal characteristics of the conductor connecting the load and the power source, A rising temperature calculating means for calculating a rising temperature of the conductor, and when the current is not detected by the current detecting means, or when the detected current drops, the falling temperature of the conductor based on the thermal characteristics of the conductor; Falling temperature calculating means for calculating the rising temperature, rising temperature for each predetermined sampling time calculated by the rising temperature calculating means, and for every predetermined sampling time calculated by the falling temperature calculating means The temperature drop is integrated at every predetermined sampling time, the estimated temperature of the conductor as a result of the integration is calculated, and further calculated by the estimated temperature calculating means having a memory for storing the estimated temperature, and the estimated temperature calculating means Temperature determining means for determining whether or not the temperature of the conductor to be exceeded exceeds a predetermined threshold temperature, and when the temperature determining means determines that the temperature of the conductor has exceeded a predetermined threshold temperature, the load And a shut-off control means for shutting off the circuit.

  The thermal characteristics are a thermal resistance R indicating the ease of heat transfer and a heat capacity C required to increase the unit temperature.

  In the invention of claim 1, when the current is detected by the current detection means and the current value is increased or maintained at a constant current, the current value and the thermal characteristics of the conductor (the electric wire and the contact conductor) are determined. The rising temperature of the electric wire is required. Further, when no current is detected by the current detecting means, or when the detected current is decreasing, the descending temperature of the electric wire corresponding to the thermal characteristics of the conductor is obtained. Then, the estimated temperature of the conductor is calculated by integrating the rising temperature or the decreasing temperature of the electric wire calculated every predetermined sampling time, and is stored in the memory. That is, the estimated temperature stored in the memory is sequentially updated based on the rising temperature or the falling temperature calculated every sampling time. Then, when the estimated temperature of the conductor exceeds a predetermined threshold, it is determined that the electric wire is smoking, and the load circuit is shut off. Therefore, since it is determined whether or not to interrupt the circuit based on the temperature of the electric wire, it is possible to perform highly accurate circuit interruption control according to the electric wire temperature.

  In the invention of claim 2, since the thermal resistance of the electric wire, the thermal resistance R of the conductor including the thermal capacity, and the thermal capacity C are used as the thermal characteristics, it is possible to detect the temperature with extremely high accuracy according to the specific characteristics of the electric wire. As a result, high-accuracy circuit interruption control becomes possible.

  According to the third and fourth aspects of the present invention, the rising temperature or the falling temperature of the electric wire using the mathematical expression indicating the heat resistance of the electric wire, the heat resistance R of the conductor including the heat capacity, the heat generation characteristic using the heat capacity C, and the heat dissipation characteristic. Therefore, it is possible to detect the temperature with high accuracy, and consequently, it is possible to control the interruption of the circuit with high accuracy.

It is a circuit diagram which shows the structure of the load circuit where the protection apparatus of the load circuit which concerns on one Embodiment of this invention was used. FIG. 2 is a functional block diagram showing a specific configuration of a control circuit shown in FIG. 1. It is a flowchart which shows the processing operation of the protection apparatus of the load circuit which concerns on one Embodiment of this invention. It is a characteristic view which shows the change of the electric wire temperature with progress of time, (a) is the time of an electric current rise, (b) shows the electric current zero after temperature saturation, or the time of electric current decrease. It is a characteristic view which shows the change of the electric wire temperature with progress of time, (a) is a time of an electric current rise, (b) shows a change when an electric current reduces before temperature is saturated. It is explanatory drawing which shows the arc corresponding | compatible map set to the arc raise temperature calculation part.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a circuit diagram illustrating a configuration of a load circuit including a load circuit protection device according to an embodiment of the present invention. For example, the load circuit is mounted on a vehicle such as a lamp or a motor mounted on the vehicle. It is a circuit for supplying power from a battery for driving.

  As shown in FIG. 1, a load circuit 1 is provided between a battery (power source) 2 mounted on a vehicle, a load 4 such as a lamp or a motor, and between the battery 2 and the load 4. And an electronic switch (switch) 3 such as a MOSFET for switching between supply and stop.

  Further, an ammeter (current detection means) 5 for detecting a current flowing through the load 4 and a control circuit 6 for controlling on / off of the electronic switch 3 are provided. Furthermore, a wire 7 connects between the battery 2 and the electronic switch 3 and between the electronic switch 3 and the load 4. Here, the load circuit protection device 10 according to the present embodiment includes an electronic switch 3, an ammeter 5, and a control circuit 6.

  FIG. 2 is a functional block diagram showing a detailed configuration of the control circuit 6. As shown in FIG. 2, the control circuit 6 includes a rising temperature calculation unit 61, a falling temperature calculation unit 62, and an arc rising temperature calculation unit. 63, the estimated temperature calculation part 64, the temperature determination part 65, and the switch control part (shut-off control means) 66 are provided.

  The rise temperature calculation unit (rise temperature calculation means) 61 includes a load current detected by the ammeter 5 when the electronic switch 3 is turned on and a current is flowing through the load 4, and a preset electric wire 7 Based on the thermal characteristics (thermal resistance R and thermal capacity C described later) of the conductor made of the contact conductor, the rising temperature of the electric wire 7 is calculated every predetermined sampling time (for example, 5 msec).

  The descending temperature calculating section (decreasing temperature calculating means) 62 is configured to detect the current detected by the ammeter 5 when the current is not detected by the ammeter 5 due to the contact conductor in the circuit and the electric wire 7 being separated from each other. , When no current is detected, or when the current starts to drop, based on the estimated temperature of the wire 7 and the thermal characteristics of the conductor including the wire 7, the wire at a predetermined sampling time 7 descending temperature is calculated.

  The arc rising temperature calculation unit 63 sets the rising temperature of the electric wire 7 due to the arc generated immediately after the contact conductor and the electric wire are separated and the current value returns to the normal operating current of the load, to the normal operating current of the load. Based on the current value flowing immediately before returning, the calculation is performed at predetermined sampling times. Specifically, as shown in FIG. 6, an arc correspondence map showing the relationship between the current value i and the rising temperature Q (i) is provided, and when the current value flowing through the load returns to the normal operating current of the load. In this case, the rising temperature is obtained by applying the current value immediately before this to the arc correspondence map.

  The estimated temperature calculation unit (estimated temperature calculation means) 64 includes a memory 64a, and a predetermined temperature calculated by the rising temperature / lowering temperature calculation unit 62 calculated for each predetermined sampling time calculated by the rising temperature calculation unit 61 described above. The estimated temperature of the electric wire 7 at the present time is calculated by integrating the falling temperature for each sampling time and the rising temperature for each predetermined sampling time calculated by the arc rising temperature calculation unit 63. That is, the memory 64a uses the ambient temperature as a reference, and accumulates (adds or subtracts) the rising temperature and the falling temperature for each sampling time with respect to the ambient temperature and stores and saves them.

Therefore, the current estimated temperature of the electric wire 7 is stored in the memory 64a. For this reason, even when the electric wire 7 changes from heat generation to heat dissipation, or from heat dissipation to heat generation, or when heat generation and heat dissipation are repeated in a short time, the estimated temperature of the electric wire 7 at that time is stored in the memory 64. As a result, the current estimated temperature of the electric wire 7 can be calculated.

  The temperature determination unit 65 compares the estimated temperature Tnow of the electric wire 7 calculated by the estimated temperature calculation unit 64 described above with a preset allowable temperature (predetermined threshold temperature) Tth, and the estimated temperature Ton determines the allowable temperature Tth. When it is determined that it has exceeded (Tnow> Tth), a circuit cutoff command signal is output to the switch control unit 66.

  The switch control unit (shut-off control means) 66 turns off the electronic switch 3 to stop the energization when the above-described circuit shut-off command signal is output from the temperature determination unit 65, thereby protecting the circuit.

  Note that the functional configuration of the control circuit 6 described above shows only a circuit configuration for dealing with a rare short circuit occurring in the load circuit, and a cut-off circuit when a dead short circuit occurs is omitted.

  Next, a method for calculating the rising temperature or the falling temperature in the rising temperature calculation unit 61, the falling temperature calculation unit 62, and the arc rising temperature calculation unit 63 will be described.

(A) Calculation of rising temperature in rising temperature calculation part 61 Temperature T1 of the electric wire 7 accompanying the heat_generation | fever by an electric current flowing through the electric wire 7 is shown by following (1) Formula.

  Here, each symbol is as follows.

T1: Wire temperature [° C]
T2: Ambient temperature [℃]
i: Current [A]
r: Resistance of conductor [Ω]
R: Thermal resistance of conductor [° C / W]
C: Heat capacity of conductor [J / ° C] or [W · sec / ° C]
t: Elapsed time [sec]
In the equation (1), the ambient temperature T2 is the temperature of the electric wire 7 when the electronic switch 3 is turned on, and is a fixed value in the initial state, for example, 25 ° C. in a normal environment, and a high temperature environment such as an engine room. Below, it is set to 85 ° C. or the like. The current i is a value measured by the ammeter 5. The resistance r is a constant. The thermal resistance R is a value indicating the ease of heat transfer of the conductor including the electric wire 7 and is a value of the conductor including a specific value based on the material, thickness, shape, and the like of the electric wire 7. The heat capacity C is the amount of heat necessary to raise the temperature of the conductor including the electric wire 7 by 1 ° C., and is a value of the conductor including specific values based on the material, thickness, shape, etc. of the electric wire.

  Therefore, when the current i and the time t are determined, the current temperature T1 of the electric wire 7 can be obtained by using the equation (1).

(B) Calculation of descending temperature in descending temperature calculation unit 62 When the current is not detected by the ammeter 5 or when the detected current value decreases, the temperature T1 of the electric wire accompanying heat radiation is expressed by the following equation (2). Indicated by

  Here, each symbol in the formula (2) is as follows.

T1: Wire temperature [° C]
T2: Ambient temperature [℃]
r: Resistance of conductor [Ω]
R: Thermal resistance of conductor [° C / W]
C: Heat capacity of conductor [J / ° C] or [W · sec / ° C]
t: Elapsed time [sec]
In the equation (2), the ambient temperature T2 is the temperature of the electric wire 7 when no current is detected by the ammeter 5 or when the detected current value decreases. “I” indicates that the heat generation is saturated at the temperature of the electric wire 7 when the current is not detected by the ammeter 5 or when the detected current value is lowered (the temperature T1 obtained by the above equation (1)). When the temperature of the electric wire 7 is saturated, the current [A] is detected when no current is detected by the ammeter 5 or immediately before the detected current value is lowered. Details will be described later. Therefore, when the current i and the time t are determined, the current temperature T1 of the electric wire 7 can be obtained by using the equation (2).

(C) Calculation of rising temperature in arc rising temperature calculation unit 63 The relationship between the rising temperature Q (i) and the current i immediately before the contact conductor and the electric wire 7 are separated and the current value returns to the normal operating current of the load. The arc correspondence map shown (see FIG. 6) is stored in advance, and when the contact conductor is separated from the electric wire 7 and the current value returns to the normal operating current of the load, the arc is determined based on the current i immediately before the return. The rising temperature Q (i) is obtained with reference to the correspondence map, and the temperature T1 of the electric wire 7 is obtained using the following equation (3).

T1 = T2 + Q (i) (3)
Here, the ambient temperature T2 is the temperature of the electric wire 7 when the contact conductor is separated from the electric wire 7 and the current value returns to the normal operating current of the load.

  Next, the operation of the load circuit 1 according to the present embodiment configured as described above will be described with reference to the flowchart shown in FIG. Note that the processing shown in this flowchart is periodically executed with a sampling time of, for example, 5 [msec].

  First, in step S1, it is determined by the ammeter 5 whether a load current is flowing. That is, the electronic switch 3 is turned on, the battery 2 and the load 4 are electrically connected, and it is determined whether or not a current is flowing through the electric wire 7.

  If it is determined that a current is detected (YES in step S1), in step S2, the detected current at the current sampling is compared with the detected current at the previous sampling.

  If it is determined that the current detection current is greater than or equal to the previous detection current (YES in step S2), that is, it is determined that the current flowing through the load 4 is rising or stable at a constant current. In step S4, the rising temperature calculation unit 61 operates the timer to measure the time elapsed, and based on the current value i detected by the ammeter 5 and the elapsed time measured by the timer, The temperature T1 of the electric wire 7 is calculated using the equation (1) described above. The ambient temperature T2 in the equation (1) is set to a value such as 25 ° C. as an initial temperature.

  Next, in step S7, the estimated temperature calculation unit 64 stores and saves the temperature T1 calculated in step S4 in the memory 64a as the current estimated temperature Tnow of the electric wire 7.

  In step S8, the temperature determination unit 65 compares the estimated temperature Tnow of the electric wire 7 stored in the memory 64a with the allowable temperature (predetermined threshold temperature) Tth set to such an extent that the electric wire 7 does not smoke. If the estimated temperature Tnow is equal to or lower than the allowable temperature Tth (estimated temperature Tnow ≦ allowable temperature Tth), the process is returned (YES in step S8).

  And when the electric current which flows into said load 4 rises or is stabilized with a constant current, the process of step S1, S2, S4, S7 is repeated and the temperature of the electric wire 7 is t = infinity in (1) Formula. As a result, the temperature converges to the temperature T1 shown in the following equation (4).

T1 = T2 + i ² · r · R (4)
Here, when a short circuit occurs in the load circuit 1 and the current i flowing through the load 4 increases, the temperature of the electric wire 7 rises, and the current estimated temperature Tnow of the electric wire 7 exceeds the allowable temperature Tth. In step S8, the result is NO, and in step S9, the switch control unit 66 turns off the electronic switch 3 to shut off the circuit and protect the load circuit 1 from heat generation.

  If the detected current at the current sampling is less than the detected current at the previous sampling (NO at step S2), the current detected at the previous sampling is the normal operating current range of the load at step S3. It is determined whether the current detected during the current sampling is within the normal operating range of the load. In this determination process, a YES determination is made when an arc current occurs. If the determination in step S3 is YES, in step S5, the arc rising temperature calculation unit 63 calculates the rising temperature of the electric wire 7 using the above-described equation (3) based on the arc correspondence map. That is, by applying the current value i immediately before the detected current returns to the normal operating current of the load 4 to the arc correspondence map as shown in FIG. 6, the rising temperature Q (i) is obtained.

  And in step S7, the estimated temperature calculation part 64 adds the temperature rise Q (i) calculated | required by said process to the temperature of the electric wire 7 memorize | stored in the memory 64a, and updates the temperature of the electric wire 7. FIG. . That is, the temperature of the electric wire 7 obtained in the previous sampling period stored in the memory is set as the ambient temperature T2, and the above-described increased temperature Q (i) is added to the ambient temperature T2 (that is, the above-described ( 3) The current temperature T1 of the electric wire 7 is obtained by the equation (3), and this is stored in the memory 64a as the estimated temperature Tnow.

  Next, if the estimated temperature Tnow of the electric wire 7 is equal to or lower than the allowable temperature Tth at this time (YES in step S8), the process returns to step S1, and if NO in step S8, the process returns to step S9. The switch control unit 66 turns off the electronic switch 3 to cut off the circuit and protect the load circuit 1 from heat generation.

  Further, in the case of NO in the process of step S3, that is, the condition that “the detected current at the previous sampling is out of the normal operating current range of the load and the detected current at the current sampling is within the normal operating range of the load” is satisfied. If not, in other words, it is not caused by a sudden current such as an arc, but the current value is simply decreasing, and if NO in step S1, that is, the current value flowing through the load 4 is zero. If there is, the process proceeds to step S6.

  In step S6, the descending temperature calculation unit 62 resets the timer and starts counting the timer as an initial process. Further, the current temperature T1 of the electric wire 7 is calculated by substituting the elapsed time t, the current i, and the ambient temperature T2 measured by the timer into the above-described equation (2). At this time, as described above, the current “i” in the equation (2) is the current [A] at which the heat generation is saturated at the temperature T1 when the current is not detected or when the current starts to decrease. . When the temperature of the electric wire 7 is already saturated, the current “i” is the current [A] when no current is detected or immediately before the current starts to decrease.

  Hereinafter, the current “i” in the equation (2) will be described in detail. Now, when the ambient temperature (the initial temperature of the electric wire 7) is T21, if the current I1 continues to rise, the temperature of the electric wire 7 rises with the characteristic shown in the above-described equation (1), and is constant. Saturates at the temperature T11. If this is shown in a characteristic diagram, it becomes like a curve s1 shown in FIG. 4A, and the temperature gradually rises from the temperature T21 with time and converges to the temperature T11. That is, it is saturated at the temperature T11.

  Then, when the temperature of the electric wire 7 is saturated at the temperature T11, if the current is not detected by the ammeter 5 or the current starts to decrease, the electric wire at the temperature T11 is expressed by the equation (2). The current at which the temperature of 7 is saturated, that is, the current I1 when the current is not detected or immediately before the current starts to drop is set as “i”. Therefore, as shown by a curve s2 in FIG. 4B, the temperature of the electric wire 7 decreases with the characteristic that the curve s1 in FIG. 4A is turned upside down, and finally converges to the ambient temperature T21. Change.

  Further, when the temperature of the electric wire 7 is not saturated, when the current is not detected by the ammeter 5 or the current starts to drop, that is, as shown in FIG. For example, when the current is not detected at the time t1 before the temperature T11 converges or the current starts to decrease, the current at which the temperature of the electric wire 7 is saturated at the temperature T12 at this time is the current “i”. Set as That is, the current I2 at which the temperature of the electric wire 7 is saturated at the temperature T12 is obtained (see the curve s3), and this current I2 becomes the current “i” in the equation (2).

  Therefore, the heat dissipation characteristic has a characteristic in which the curve s3 is turned upside down, and becomes a characteristic curve in which the temperature of the electric wire 7 decreases as shown by a curve s4 shown in FIG. 5B.

  Then, when the descending temperature is calculated by the above-described equation (2) in step S6 of FIG. 3, the current estimated temperature Tow of the electric wire 7 stored in the memory 64a of the estimated temperature calculation unit 64 is calculated in step S7. Updated.

  That is, the estimation of the electric wire 7 is obtained in the memory 64a by considering all of the temperature rise when the load current is rising, the temperature rise when the arc is generated, and the heat radiation when the load current is off or decreasing. The temperature Tnow is stored and saved. In step S8, the estimated temperature Tnow of the electric wire 7 is compared with the allowable temperature Tth, and when the estimated temperature Tnow becomes equal to or higher than the allowable temperature Tth, the electronic switch 3 is turned off to cut off the circuit. Thus, when a short circuit occurs and the temperature of the electric wire 7 rises, the circuit can be shut off immediately.

  Thus, in the load circuit protection device according to the present embodiment, when the current flowing through the load 4 is rising, the temperature of the electric wire 7 is detected using the above-described equation (1), and the current is When zero or the current is decreasing, the temperature of the electric wire 7 is detected using the above equation (2), and the temperature rise when the arc is generated is added according to the equation (3) to obtain a total. The current temperature of the electric wire 7 is estimated.

  Then, when the estimated temperature Tnow of the current electric wire 7 reaches the allowable temperature Tth that generates smoke, the electronic switch 3 is turned off to protect the circuit. That is, since the actual temperature of the electric wire 7 is estimated using the characteristic of the electric wire 7 such as the thermal resistance R and the heat capacity C of the electric wire 7 and it is determined whether or not the circuit is interrupted, the electric wire 7 emits smoke. The load circuit and the electric wire 7 can be protected by reliably interrupting the circuit at the previous time. In addition, it is possible to avoid the occurrence of trouble that the load circuit 1 is interrupted unnecessarily with very little heat generation, which allows continuous energization.

  Furthermore, when the current flowing through the load 4 is zero or starts decreasing, the current value saturated at the temperature immediately before this condition is applied to the above equation (2) to calculate the temperature drop due to heat dissipation. The temperature can be calculated with high accuracy, and the temperature of the electric wire 7 can be obtained with high accuracy. As a result, even if a rare short circuit occurs, the circuit is reliably interrupted before the electric wire 7 smokes. can do.

  Although the load circuit protection device of the present invention has been described based on the illustrated embodiment, the present invention is not limited to this, and the configuration of each part is an arbitrary configuration having the same function. Can be replaced.

  For example, in the above-described embodiment, the case where the load circuit protection device is used in the load circuit 1 that drives a load such as a lamp or a motor mounted on the vehicle has been described as an example. The present invention is not limited, and can be applied to other load circuits.

  When a rare short occurs, it is extremely useful for reliably detecting this and protecting the circuit.

DESCRIPTION OF SYMBOLS 1 Load circuit 2 Battery 3 Electronic switch 4 Load 5 Ammeter (Current detection means)
6 Control Circuit 7 Electric Wire 10 Protective Device for Load Circuit 61 Rise Temperature Calculation Unit (Rise Temperature Calculation Means)
62 Falling temperature calculation unit (falling temperature calculation means)
63 Arc rising temperature calculation unit 64 Estimated temperature calculation unit (estimated temperature calculation means)
64a memory 65 temperature determination unit (temperature determination means)
66 Switch control unit (cut-off control means)

Claims (4)

In a load circuit protection device for detecting a current flowing through the load of a load circuit including a power source, a switch, and a load, and cutting off the load circuit according to the detected current value.
Current detection means for detecting a current flowing through the load;
When a current is detected by the current detection means, the temperature rise means for calculating the temperature rise of the conductor based on the detected current value and the thermal characteristics of the conductor connecting the load and the power source;
A descending temperature calculating means for calculating a descending temperature of the conductor based on a thermal characteristic of the conductor when no current is detected by the current detecting means or when the detected current falls;
A result of accumulating the rising temperature for each predetermined sampling time calculated by the rising temperature calculating means and the falling temperature for each predetermined sampling time calculated by the falling temperature calculating means for each predetermined sampling time. An estimated temperature calculating means having a memory for calculating the estimated temperature of the conductor and storing the estimated temperature;
Temperature determination means for determining whether the temperature of the conductor calculated by the estimated temperature calculation means exceeds a predetermined threshold temperature;
An interruption control means for interrupting the load circuit when the temperature determination means determines that the temperature of the conductor exceeds a predetermined threshold temperature;
A load circuit protection device comprising:   2. The load circuit protection device according to claim 1, wherein the thermal characteristics are a thermal resistance R indicating ease of heat transfer and a heat capacity C required to increase a unit temperature. 3. The load circuit protection device according to claim 2, wherein the rising temperature calculation means calculates the temperature of the conductor by the following formula using the thermal resistance R and the thermal capacity C. 4.

However, each symbol is as follows.
T1: Wire temperature [° C]
T2: Ambient temperature [° C]
i: Current [A]
r: Conductor resistance [Ω]
R: Thermal resistance of conductor [° C / W]
C: Heat capacity of conductor [J / ° C] or [W · sec / ° C]
t: Elapsed time [sec] 4. The load circuit according to claim 2, wherein the descending temperature calculation means calculates the temperature of the conductor by the following formula using the thermal resistance R and the thermal capacity C. 5. Protective device.

However, each symbol is as follows.
T1: Wire temperature [° C]
T2: Ambient temperature [° C]
i: Current at which heat generation is saturated at temperature T1 when no current is detected or when current decreases [A]
r: Conductor resistance [Ω]
R: Thermal resistance of conductor [° C / W]
C: Heat capacity of conductor [J / ° C] or [W · sec / ° C]
t: Elapsed time [sec]

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