Electronic control device

Abstract

A main element 5 controls current flowing through a wire harness 4, and a current corresponding to the current flows through a sense element 6. A detection resistor 7 generates a sense voltage corresponding to the current flowing through the sense element 6. A charge / discharge circuit 24 charges and discharges a capacitor 42 on the basis of the sense voltage. A charge / discharge control unit 46 forcibly switches the charge / discharge circuit 24 to a discharge state when a charge state continues beyond an upper limit value. An integration circuit 48 integrates a multiplication signal obtained according to the voltage during discharging of the capacitor 42, and a subtraction circuit 49 subtracts a subtraction value corresponding to the heat dissipation characteristics of the harness 4 from the integration result. A control circuit 12 cuts off the current flowing through the harness 4 when the value subtracted by the subtraction circuit 49 exceeds an integration threshold value corresponding to the heat generation characteristics of the harness 4. When switched to the discharge state, the charge / discharge control unit 46 integrates a cutoff acceleration value instead of the multiplication signal.

Description

Electronic control unit CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application is based on Japanese Application No. 2024-88007, filed on May 30, 2024, the contents of which are incorporated herein by reference.

[0002] The present disclosure relates to an electronic control device for protecting a wire harness.

[0003] For example, Patent Document 1 proposes an electronic control device that protects a wire harness to which a load is connected. This device is configured to supply current to the load connected to the wire harness via an intelligent power device (IPD) consisting of a main element and a sense element. A multiplication circuit that calculates the power supplied to the load obtains multiplication characteristics by charging and discharging a capacitor.

[0004] The integrating circuit generates a signal with a pulse width corresponding to the capacitor's discharge time, counts the pulse width, and integrates the counted value. If the result of subtracting a value corresponding to the heat dissipation characteristics of the wire harness from the integrated value exceeds a threshold, the circuit protects the wire harness by cutting off the power supply to the load via the IPD. Hereinafter, this type of wire harness protection operation may be referred to as "e-Fuse."

[0005] JP 2023-18957 A

[0006] However, in the configuration of Patent Document 1, as shown in FIG. 14, when the voltage VS corresponding to the detected current IM exceeds the input range defined by the output signal Vsaw of the DAC, the charging of the capacitor indicated by the signal Vcx continues and does not switch to discharging, so that a pulse width signal Vout2 corresponding to the discharge time cannot be generated and multiplication characteristics cannot be obtained.

[0007] As shown in Figure 15, in practice, a wiring harness whose smoke-generating characteristics are greater than or equal to the current range to be used is selected, and the e-Fuse cutoff threshold is set within a range that is greater than or equal to the current range to be used but less than or equal to the smoke-generating characteristics. The cutoff threshold set by the e-Fuse is constant, but the time t1 required to reach the cutoff threshold is short when the current is large, and the time t2 required to reach the cutoff threshold is longer when the current is small.

[0008] Furthermore, the multiplication circuit of Patent Document 1 does not have a means for detecting when the input current exceeds the detection range, as shown in the area surrounded by a dashed line in Fig. 14. Therefore, as shown in Fig. 15, there is a problem in that the range below the overcurrent threshold that protects the IPD itself and above the current detection range of the e-Fuse are dead zones or unprotectable areas that cannot protect the wire harness.

[0009] The present disclosure has been made in consideration of the above circumstances, and an object of the present disclosure is to provide an electronic control device that can protect a wire harness even when a current exceeds a detection range.

[0010] According to the electronic control device of claim 1, the main element controls the current flowing through the wire harness, and a current corresponding to the current flowing through the main element flows through the sense element. The detection resistor generates a sense voltage corresponding to the current flowing through the sense element. The charge / discharge circuit charges and discharges the charge / discharge capacitor based on the sense voltage. The forced discharge circuit forcibly switches the charge / discharge circuit to a discharge state when the charge state of the charge / discharge circuit continues to exceed an upper limit value.

[0011] The integration circuit integrates a multiplication signal obtained according to the voltage at the charge / discharge capacitor when discharging, and the subtraction circuit subtracts a subtraction value according to the heat dissipation characteristics of the wire harness from the integration result of the integration circuit. The control circuit controls the on / off of the main element, and cuts off the current flowing through the wire harness when the value subtracted by the subtraction circuit exceeds an integration threshold according to the heat dissipation characteristics of the wire harness. When the forced discharge circuit switches to the discharge state, it causes the integration circuit to integrate a cutoff acceleration value instead of the multiplication signal.

[0012] The charging time of the charge / discharge capacitor is determined by the magnitude of the sense voltage generated by the detection resistor, and the longer the charging time, the longer the discharge time. Therefore, when the charging state by the charge / discharge circuit continues to exceed the upper limit, it can be determined that the value of the current flowing through the sense element has increased to a certain extent and is in an over-range state that exceeds the range of the current to be detected.

[0013] Therefore, the forced discharge circuit causes the integration circuit to integrate a cutoff acceleration value instead of the multiplication signal, thereby increasing the rate at which the integrated value increases and exceeds the integration threshold more quickly, causing the control circuit to turn off the main element and cut off the current flowing through the wire harness. This makes it possible to protect the wire harness even when the detected current is in an over-range state, or a so-called overcurrent state.

[0014] According to the electronic control device of claim 2, the forced discharge circuit stops subtraction by the subtraction circuit when the integration circuit accumulates the cutoff acceleration value, thereby making it possible to cut off the current earlier.

[0015] According to the electronic control device of claim 3, the comparison value setting unit gradually increases the comparison value over time. The charge / discharge switching unit switches the charging state of the charge / discharge circuit to a discharging state when the comparison value exceeds the sense voltage. As a result, the charge / discharge circuit is in a charging state while the sense voltage is above the comparison value, and switches to a discharging state when the comparison value exceeds the sense voltage. If the sense voltage remains above the comparison value for a certain period of time, the charging state of the charge / discharge circuit has continued beyond the upper limit, and the forced discharge circuit forcibly switches the charge / discharge circuit to a discharging state.

[0016] The above and other objects, features and advantages of the present disclosure will become more apparent from the following detailed description taken in conjunction with the accompanying drawings. 1 is a diagram showing the configuration of an electronic control device in a first embodiment, FIG. 2 is a flowchart mainly showing the processing contents by the charge / discharge control unit, FIG. 3 is an operation timing chart, FIG. 4 is a diagram explaining the relationship between the integrated value TINT, the multiplication result ADD, and the subtraction value CSUB, FIG. 5 is a diagram showing the change in the integrated value TINT over time, FIG. 6 is a diagram explaining the relationship between the range of current to be detected and the smoke generation characteristics of a wire harness, FIG. 7 is a diagram showing the configuration of an electronic control device in a second embodiment, FIG. 8 is a flowchart mainly showing the processing contents by the charge / discharge control unit, FIG. 9 is a diagram showing input / output characteristics depending on whether the gain of an amplifier is switched or not, FIG. 10 is an operation timing chart, FIG. 11 is an operation timing chart showing a third embodiment, FIG. 12 is a flowchart mainly showing the processing contents by the charge / discharge control unit, FIG. 13 is an operation timing chart showing a fourth embodiment, FIG. 14 is an operation timing chart showing a conventional technique, and FIG. 15 is a diagram showing the protection characteristics of a wire harness and the interruption characteristics within a detection current range.

[0017] 1, an electronic control unit 1 of this embodiment is disposed between a power source 2 and a load 3 via a wire harness 4, and is connected to an external control unit 60. The electronic control unit 1 includes a main element 5, a sense element 6, a detection resistor 7, a multiplication circuit 8, control logic 9, a diagnostic circuit 10, and the like. The electronic control unit 1 is configured such that the above components are integrally packaged to form an intelligent power device (IPD).

[0018] In this embodiment, the main element 5 and the sense element 6 are configured as n-channel metal oxide semiconductor (MOSFETs), but may also be insulated gate bipolar transistors (IGBTs) or the like. The gates of the main element 5 and the sense element 6 are connected to a drive circuit 11 that applies a predetermined gate voltage. The main element 5 and the sense element 6 are switched between an ON state in which current flows and an OFF state in which current is blocked by the applied gate voltage. The drive circuit 11 is connected to a control circuit 12, which will be described later, and controls the ON and OFF states of the main element 5 and the sense element 6 based on drive instructions from the control circuit 12.

[0019] The main element 5 and the sense element 6 are formed to have a predetermined area ratio, and the currents flowing through the main element 5 and the sense element 6 are values ​​according to the area ratio. In this embodiment, the main element 5 and the sense element 6 are formed on a common semiconductor substrate, although details are not particularly shown. The detection resistor 7, multiplication circuit 8, control logic 9, diagnostic circuit 10, etc. are formed on a semiconductor substrate separate from the semiconductor substrate on which the main element 5 and the sense element 6 are formed. The electronic control device 1 is packaged by integrating the semiconductor substrate on which the main element 5 and the sense element 6 are formed and the semiconductor substrate on which the detection resistor 7, etc. are formed, with a sealing member.

[0020] The drains of the main element 5 and the sense element 6 are connected to the power supply 2. The source of the main element 5 is connected to the load 3 via the wire harness 4 and is also connected to the inverting input terminal of a current detection amplifier 14 (described later). The source of the sense element 6 is connected to the non-inverting input terminal of the current detection amplifier 14.

[0021] The detection resistor 7 is connected to the sense element 6 via a current detection amplifier 14 and a P-channel MOSFET 15. The source of the FET 15 is connected to the source of the sense element 6 and the non-inverting input terminal of the current detection amplifier 14, and the drain is connected to the detection resistor 7. The gate of the FET 15 is connected to the output terminal of the current detection amplifier 14.

[0022] The multiplication circuit 8 includes an amplifier 21, a comparator 22, a D latch 23, a charge / discharge circuit 24, a comparator 25, and an AND gate 26. The input terminal of the amplifier 21 is connected to a detection resistor 7. The detection resistor 7 generates a sense voltage corresponding to the value of the current flowing through it. The sense voltage is amplified by the amplifier 21 at a predetermined amplification factor and is provided to the non-inverting input terminal of the comparator 22 and to the charge / discharge circuit 24 via a switch 27.

[0023] The charge / discharge circuit 24 includes a series circuit of a resistor element 29 and a PNP transistor 30, a current source 31, a series circuit of an NPN transistor 32 and a resistor element 33, and a series circuit of current sources 34 and 35, all of which are connected between a power supply 28 and ground. In addition to the switch 27, a reference power supply 37 is connected to the base of the transistor 30 via a switch 36. The on / off of the switches 27 and 36 is controlled by the D latch 23.

[0024] An input terminal D of the D latch 23 is pulled up to the power supply 28. A trigger signal ICHG_EN is input to a clock terminal C of the D latch 23 from the control logic 9. An output terminal of an AND gate 38 is connected to a negative logic reset terminal RB of the D latch 23. One of the input terminals of the AND gate 38 is connected to the output terminal of the comparator 22, and a signal OUT_CUT is input to the other input terminal from the control logic 9.

[0025] NOT gates 39 and 40 are connected in series to the output terminal Q of the D latch 23. In addition to the switch 27, the on / off of switch 41 constituting the charge / discharge circuit 24 is controlled by the output signal of the NOT gate 40, and the on / off of switch 36 is controlled by the output signal of the NOT gate 39. In other words, the on / off of switches 27 and 41 and the on / off of switch 36 are controlled by signals of opposite phases. The output signal of the NOT gate 39 is input to the control logic 9 as the signal CHG_DIS_OUT, and is also provided to one of the input terminals of the AND gate 26. The comparator 22, the D latch 23, the AND gate 38, and the NOT gates 39 and 40 constitute a charge / discharge switching unit 51.

[0026] The common connection point of the current sources 34 and 35 is connected to ground via a charge / discharge capacitor 42 and is also connected to the non-inverting input terminal of the comparator 25. A reference power supply 43 is applied to the inverting input terminal of the comparator 25. The output terminal of the comparator 25 is connected to the other input terminal of the AND gate 26.

[0027] The control logic 9 includes a pulse width counter 44, a multiplexer 45, a charge / discharge control unit 46, a DAC output unit 47, an integrator circuit 48, and a subtractor circuit 49. The pulse width counter 44 counts the length of the period during which the output signal ADD of the AND gate 26 indicates a high level, and inputs the count result to the multiplexer 45. Although an "addend 1" and an "addend 2" are also input to the multiplexer 45, only the "addend 2" is used in this embodiment. In the following description, the "addends 1 and 2" may also be referred to as "acceleration values ​​1 and 2." The input selection of the multiplexer 45 is controlled by the charge / discharge control unit 46.

[0028] The output signal of the multiplexer 45 is input to an integrating circuit 48. A subtracting circuit 49 and the above-mentioned diagnostic circuit 10 and control circuit 12 are connected to the integrating circuit 48. A diagnostic signal output by the diagnostic circuit 10 is input to an external control unit 60. An output signal from the external control unit 60 is input to the control circuit 12. The charge / discharge control unit 46 controls a DAC output unit 47 to input a digital value to a DAC (D / A converter) 50. The DAC 50 generates an analog voltage signal VDAC corresponding to the input digital value and outputs it to the inverting input terminal of the comparator 22. The charge / discharge control unit 46 corresponds to a forced discharge circuit. The charge / discharge control unit 46, the DAC output unit 47, and the DAC 50 correspond to a comparison value setting unit.

[0029] The external control unit 60 is configured with a microcomputer or the like equipped with a central processing unit (CPU) and storage units such as read-only memory (ROM), random access memory (RAM), and non-volatile RAM. The external control unit 60 performs various control operations by having the CPU read and execute programs from the ROM or non-volatile RAM. The ROM or non-volatile RAM stores in advance various data used when executing the programs, such as initial values, look-up tables, and maps.

[0030] Next, the operation of this embodiment will be described. As shown in FIG. 2, when the charge / discharge control unit 46 outputs a high-level pulse as the signal ICHG_EN (S1), it controls the DAC output unit 47 to start outputting the voltage signal VDAC (S2). This causes the sawtooth wave voltage tDAC shown in FIG. 3 to be output. Next, it is determined whether the signal CHG_DIS_OUT output from the D latch 23 via the NOT gate 39 is high (S3). If the signal CHG_DIS_OUT is low (NO), it is determined whether the voltage signal VDAC has reached its maximum amplitude (S9). If it has not reached its maximum amplitude (NO), the process returns to step S3. While the signal CHG_DIS_OUT indicates a low level, the charge / discharge capacitor 42 is being charged.

[0031] When the signal CHG_DIS_OUT goes high (S3; YES), the pulse width counter 44 starts counting the pulse width of the signal ADD output by the AND gate 26 (S4). At this time, the charge / discharge capacitor 42 switches to discharging. When the signal ADD goes low, the counting ends and the pulse width value is integrated by the integration circuit 48 (S5). At this time, the charge / discharge control unit 46 switches the input selection of the multiplexer 45 to the pulse width counter 44 side. Then, the subtraction circuit 49 subtracts a value corresponding to the heat dissipation characteristics of the wire harness 4 from the integrated value (S6). TINT shown in FIG. 3 is the integrated value in the integration circuit 48.

[0032] As shown in FIG. 4, the integrated value TINT(n) is obtained by adding the pulse width count value ADD to the previous integrated value TINT(n-1) and subtracting the subtraction value CSUB from the result. The subtraction value CSUB is (1-e －Δｔ／π ) and is a heat dissipation characteristic obtained from the thermal time constant of the wire harness 4. FIG. 5 shows a case where the integrated value TINT reaches the cutoff threshold value while the input voltage is within the detection range.

[0033] If the integrated value does not exceed the cutoff threshold for e-Fuse operation (S7; NO), the process returns to step S1. If the integrated value exceeds the cutoff threshold (YES), the control circuit 12 turns off the main element 5 and the sense element 6 using the drive circuit 11, thereby cutting off the power supply to the load 3 (S8). The cutoff threshold corresponds to the integrated threshold.

[0034] If the voltage signal VDAC reaches the MAX amplitude in step S9 (YES), the charge / discharge control unit 46, which is a forced discharge circuit, outputs a low-level pulse as the OUT_CUT signal (S10). This forcibly switches the charge / discharge capacitor 42 to discharge when the dead zone indicated by the dashed line in FIG. 3 is entered. The input selection of the multiplexer 45 is then integrated by the integration circuit 48 as an acceleration value (2) (S11). Then, the process proceeds to step S7. The time it takes for the voltage signal VDAC to reach the MAX amplitude corresponds to the upper limit. The acceleration value (2) corresponds to the cutoff acceleration value.

[0035] Here, the reason for integrating the acceleration value will be explained. When the upper limit of the range of the pulse width of the signal ADD is added in the over-range state, the result becomes as shown in a in Figure 6. Since the interruption time is constant for currents above the detection range, as the current increases, it exceeds the smoke generation characteristics of the wire harness 4. This is the dead band area. The smoke generation characteristics of wire harnesses are also described in detail in paragraphs

[0021] to

[0024] of Patent Document 1.

[0036] Therefore, when the current value exceeds the detection range, the acceleration value is integrated instead of the pulse width to cut off the current more quickly, as shown by b in the figure. The acceleration value is set so that the cutoff threshold does not exceed the smoke generation characteristics of the wire harness 4 in the dead band area. If the e-Fuse processing calculation is executed once every 4 ms, for example, and it is necessary to cut off the current within 100 ms, the acceleration value is set so that the cutoff threshold is reached after 25 integrations.

[0037] As described above, according to this embodiment, in the electronic control device 1, the main element 5 controls the current flowing through the wire harness 4, and a current corresponding to the current flowing through the main element 5 flows through the sense element 6. The detection resistor 7 generates a sense voltage corresponding to the current flowing through the sense element 6. The charge / discharge circuit 24 charges and discharges the charge / discharge capacitor 42 based on the sense voltage. If the charge state of the charge / discharge circuit 24 continues to exceed an upper limit, the charge / discharge control unit 46 forcibly switches the charge / discharge circuit 24 to a discharging state.

[0038] The integration circuit 48 integrates a multiplication signal obtained according to the voltage at the time of discharge in the charge / discharge capacitor 42, and the subtraction circuit 49 subtracts a subtraction value according to the heat dissipation characteristics of the wire harness 4 from the integration result of the integration circuit 48. The control circuit 12 controls the on / off of the main element 5, and cuts off the current flowing through the wire harness 4 when the value subtracted by the subtraction circuit 49 exceeds an integration threshold according to the heat generation characteristics of the wire harness 4. When the charge / discharge control unit 46 switches to the discharge state, it causes the integration circuit 48 to integrate a cutoff acceleration value instead of the multiplication signal.

[0039] More specifically, the charge / discharge control unit 46 gradually increases the voltage signal VDAC, which is the comparison value, over time via the DAC output unit 47 and the DAC 50. When the comparison value exceeds the sense voltage, the charge / discharge switching unit 51 switches the charging state of the charge / discharge circuit 24 from a charging state to a discharging state. The charging time of the charge / discharge capacitor 42 is determined by the magnitude of the sense voltage generated by the detection resistor 7, and the discharging time increases as the charging time increases. Therefore, when the charging state of the charge / discharge circuit 24 continues to exceed the upper limit value, the value of the current flowing through the sense element 6 increases to a certain extent, entering an over-range state that exceeds the range of the current to be detected.

[0040] Therefore, the charge / discharge control unit 46 causes the integration circuit 48 to integrate the cutoff acceleration value instead of the multiplication signal, thereby increasing the rate at which the integrated value increases and exceeds the integration threshold more quickly, and causes the control circuit 12 to turn off the main element 5 and cut off the current flowing through the wire harness 4. This makes it possible to protect the wire harness 4 even when the detected current is in an over-range state, a so-called overcurrent state. In addition, at that time, the subtraction by the subtraction circuit 49 is stopped, so that the current can be cut off more quickly.

[0041] Second Embodiment Hereinafter, the same components as those in the first embodiment are denoted by the same reference numerals, and their descriptions will be omitted, and only differences will be described. As shown in FIG. 7 , an electronic control device 61 of the second embodiment includes a multiplication circuit 62 instead of the multiplication circuit 8. The multiplication circuit 62 includes a series circuit of an amplifier 63 and a switch 64 and a series circuit of an amplifier 65 and a switch 66, connected in parallel, instead of the amplifier 21. The amplification factors, i.e., gains, of the amplifiers 63 and 65 are set to 1 and 2, respectively. The on / off of the switches 64 and 66 is controlled by a charge / discharge control unit 67, which replaces the charge / discharge control unit 46. In the second embodiment, the two amplifiers 63 and 65 are selected by turning the switches 64 and 66 on and off, and are therefore considered to be "amplifiers with adjustable amplification factors."

[0042] Next, the operation of the second embodiment will be described. Hereinafter, the output signal of amplifier 63 or 65 will be referred to as Vamp. As shown in Fig. 8 , charge / discharge control unit 67 first turns on switch 64 and turns off switch 66 to select amplifier 63, which has a gain of 1 (S21). Then, DAC output unit 47 is controlled to set the level of voltage signal VDAC to selection threshold value VTH shown in Fig. 10 (S22).

[0043] In this case, the comparator 22 compares the output signal Vamp of the amplifier 63 with the level of the voltage signal VDAC, i.e., the selection threshold VTH (S23). If (Vamp>VTH) (YES), the charge / discharge control unit 67 maintains the on / off states of the switches 64 and 66 to continue selecting the amplifier 63 with a gain of 1 (S24). On the other hand, if (Vamp≦VTH) (NO), the charge / discharge control unit 67 turns off the switch 64 and turns on the switch 66 to select the amplifier 65 with a gain of 2 (S25). Note that details of the logic for switching between the amplifiers 63 and 65 in this manner are omitted from FIG. 7.

[0044] Next, after steps S1 to S4 are executed, it is determined whether the gain is set to 2x (S26). If the gain is set to 2x (YES), step S5 is executed. If the gain is set to 1x (NO), a value 4x the pulse width of the signal ADD is added to correct for the difference from the 2x case (S27). Then, steps S6 to S10 are executed.

[0045] When an over-range condition occurs and step S10 is executed, a determination similar to step S26 is made (S28). If the gain setting is 2x (YES), the charge / discharge control unit 67 controls the multiplexer 45 to accumulate an acceleration value 1 as shown in FIG. 9 (S29). The acceleration value 1 here corresponds to the upper limit of the input range of the sense voltage. On the other hand, if the gain setting is 1x (NO), an acceleration value 2 is accumulated (S30). As a result, when an over-range condition occurs, the current can be shut off early by accumulating an acceleration value according to the gain setting.

[0046] 11 and 12, the charge / discharge control unit 46 of the first embodiment switches to forced discharge using a time filter function. As shown in FIG. 12, when the charge / discharge control unit 46 starts outputting the voltage signal VDAC (S2), it starts counting a fixed time tDAClim. The internal signal tDAClim indicates a high level during the counting period and changes to a low level after the fixed time tDAClim has elapsed. If the internal signal tDAClim is at a high level (S31; YES), steps S3 to S11 are executed. If the internal signal tDAClim changes to a low level (S31; NO), the process proceeds to step S10, where the charge / discharge control unit 46 switches to forced discharge.

[0047] Fourth Embodiment In a fourth embodiment shown in FIG. 13, the waveform of the voltage signal VDAC is not a sawtooth wave, but rather a waveform in which, once the voltage rises to a certain value, the voltage is maintained at that certain value thereafter.

[0048] (Other Embodiments) Step S6 may be executed when the acceleration value is integrated. In the second embodiment, the amplification factor of a single amplifier may be changed. Also, in the second embodiment, the gain may be set in three or more stages. As in Patent Document 1, the subtraction factor used in the subtraction circuit 49 may be adjusted to suit the heat dissipation characteristics of the wire harness 4 to be used by inputting a subtraction factor adjustment signal from the outside to the external control unit 60 via a communication circuit (not shown).

[0049] Although the present disclosure has been described with reference to the embodiments, it is understood that the present disclosure is not limited to the embodiments or structures. The present disclosure also encompasses various modifications and equivalent modifications. In addition, various combinations and forms, including only one element, more than one element, or less than one element, are also within the scope and spirit of the present disclosure.

Claims

1. An electronic control device for controlling a current flowing through a wire harness (4), comprising: a main element (5) for controlling the current flowing through the wire harness; a sense element (6) through which a current corresponding to the current flowing through the main element flows; a detection resistor (7) connected to the sense element and generating a sense voltage corresponding to the current flowing through the sense element; a charge / discharge circuit (24) for charging and discharging a charge / discharge capacitor (42) based on the sense voltage; a forced discharge circuit (46, 67) for forcibly switching the charge / discharge circuit to a discharge state when the charge state of the charge / discharge circuit exceeds an upper limit value and continues; an integration circuit (48) for integrating a multiplied signal obtained according to the voltage at the time of discharge in the charge / discharge capacitor; a subtraction circuit (49) for subtracting a subtraction value corresponding to the heat dissipation characteristics of the wire harness from the integration result of the integration circuit; and a control circuit (12) for controlling the on / off of the main element, and for cutting off the current flowing through the wire harness when the value subtracted by the subtraction circuit exceeds an integration threshold corresponding to the heat dissipation characteristics of the wire harness. When the forced discharge circuit is switched to the discharge state, the electronic control device causes the integrating circuit to integrate a cutoff acceleration value instead of the multiplication signal.

2. The electronic control device according to claim 1, wherein said forced discharge circuit stops subtraction by said subtraction circuit when said integrating circuit integrates said cutoff acceleration value.

3. An electronic control device as claimed in claim 1 or 2, comprising: a comparison value setting unit (46, 47, 50) that gradually increases the comparison value over time; and a charge / discharge switching unit (51) that switches the charge state of the charge / discharge circuit to a discharge state when the comparison value exceeds the sense voltage.

4. An electronic control device according to claim 3, comprising an amplifier (63, 65) for amplifying the sense voltage and capable of changing the amplification factor, wherein the forced discharge circuit (67) sets the amplification factor according to the level of the sense voltage, and when the amplification factor is set to the minimum, causes the control circuit to integrate the cut-off acceleration value, and when the amplification factor is not set to the minimum, causes the control circuit to integrate the upper limit value of the input range of the sense voltage.

5. An electronic control device as described in claim 4, wherein the comparison value setting unit outputs a selection threshold for selecting the amplifier for a fixed period of time before gradually increasing the comparison value over time, and the forced discharge circuit compares the sense voltage with the selection threshold to select the amplifier.

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