JP2022120236A - Insulation resistance deterioration detector and failure diagnosis method for insulation resistance deterioration detector - Google Patents

Abstract

To accurately detect state change of an insulation resistance deterioration detector.SOLUTION: An insulation resistance deterioration detector detects deterioration in insulation resistance between a frame of a vehicle and a high voltage circuit mounted on the vehicle. The insulation resistance deterioration detector includes a controller, a pulse generator for generating a pulse with a predetermined period, detection resistance provided between the pulse generator and the frame, electric leak resistance connected to a measuring node between the detection resistance and the frame, and a switch controlled to be in an OFF state for cutting off between the electric leak resistance and ground or an ON state for connecting the electric leak resistance and the ground. The controller detects a resistance value of the insulation resistance on the basis of the voltage of the measuring node when the switch is in the OFF state and determines whether or not the insulation resistance deterioration detector is normal on the basis of the detected resistance value and the voltage of the measuring node when the switch is in the ON state.SELECTED DRAWING: Figure 1

Description

The present invention relates to an insulation resistance drop detection device for detecting a drop in insulation resistance between a high voltage circuit mounted on a vehicle and a vehicle frame, and a fault diagnosis method for the insulation resistance drop detection device.

In many cases, electrical circuits mounted on a vehicle are electrically insulated from the body of the vehicle (hereinafter referred to as vehicle frame). For example, a fuel cell vehicle is equipped with a high voltage circuit including a fuel cell, a DC/DC converter and a load. In this case, this high voltage circuit is isolated from the vehicle frame. Moreover, such a vehicle is provided with an insulation resistance drop detection device for detecting a drop in insulation resistance. Note that the insulation resistance drop detection device is sometimes called an earth leakage detection device.

An insulation resistance drop detector includes, for example, a pulse generator, a detection resistor, a decoupling capacitor, and a controller. In this case, the pulse signal generated by the pulse generator is transmitted to the ground of the high-voltage circuit mounted on the vehicle via the detection resistor, decoupling capacitor, and insulation resistor. Then, the controller measures the crest value of the pulse signal using the detection resistor, and determines whether the insulation resistance is normal based on the crest value.

The insulation resistance drop detector may have a self-diagnostic function. The self-diagnostic function determines whether the insulation resistance drop detection device is operating normally. For example, during self-diagnosis, a pseudo-leakage condition is induced. Then, the controller measures the crest value of the pulse signal in the pseudo electric leakage state, and determines whether or not the insulation resistance drop detection device is operating normally based on the crest value.

An insulation resistance drop detector capable of performing self-diagnosis is described in Patent Document 1, for example.

JP 2007-187454 A

The self-diagnostic function described above diagnoses the insulation resistance drop detector by measuring the crest value of the pulse signal while generating a pseudo electric leakage state. That is, the self-diagnosis utilizes the insulation resistance between the vehicle frame and the high voltage circuit. Here, the resistance value of the insulation resistor can change according to the environment. Therefore, when performing self-diagnosis considering the change in the resistance value of the insulation resistance, a margin corresponding to the change in the resistance value of the insulation resistance is set. The threshold range for judging whether or not is widened. If this threshold range widens, it becomes difficult to detect a sign of failure or a minor failure of the insulation resistance drop detection device. In other words, it is difficult for the conventional technology to accurately detect the state change of the insulation resistance drop detection device.

An object according to one aspect of the present invention is to provide a method for accurately detecting a state change of an insulation resistance drop detection device.

An insulation resistance drop detector according to one aspect of the present invention detects a drop in insulation resistance between a vehicle frame and a high voltage circuit mounted on the vehicle. This insulation resistance drop detector includes a controller, a pulse generator that generates pulses at a predetermined cycle, a detection resistor provided between the pulse generator and the frame, and a measurement node between the detection resistor and the frame. A connected earth leakage resistance and a switch controlled to be in an OFF state for disconnecting between the earth leakage resistance and the ground or an ON state for connecting between the earth leakage resistance and the ground. Then, the controller detects the resistance value of the insulation resistor based on the voltage of the measurement node when the switch is in the off state, and based on the detected resistance value and the voltage of the measurement node when the switch is in the on state, It is determined whether or not the insulation resistance drop detection device is normal.

Thus, the insulation resistance drop detector detects the resistance value of the insulation resistance before self-diagnosis. Then, self-diagnosis is performed using the resistance value of the insulation resistance. Therefore, even if the resistance value of the insulation resistor fluctuates, self-diagnosis can be performed based on the current resistance value. Therefore, it is possible to detect a sign of failure or a minor failure of the insulation resistance drop detection device. That is, according to the embodiment of the present invention, it is possible to accurately detect the state change of the insulation resistance drop detection device.

In the above-described aspect, a characteristic graph showing the correspondence relationship between the resistance value of the insulation resistance and the evaluation value obtained based on the voltage of the measurement node when the insulation resistance drop detection device is normal and the switch is in the ON state. Prepared in advance, the controller detects the resistance value of the insulation resistance based on the voltage of the measurement node when the switch is in the off state, and uses the characteristics graph to obtain the evaluation value corresponding to the detected resistance value. and the difference between the evaluation value obtained using the characteristic graph and the evaluation value obtained based on the voltage of the measurement node when the switch is in the ON state falls within a preset threshold range for the characteristic graph. If it is within, it may be determined that the insulation resistance drop detection device is normal.

According to this configuration, the evaluation value corresponding to the resistance value of the insulation resistance detected before the self-diagnosis is specified, and the self-diagnosis is performed using the threshold range set for the evaluation value. Therefore, since the threshold range can be narrowed, the state change of the insulation resistance drop detection device can be detected with high accuracy.

According to the above aspect, it is possible to accurately detect the state change of the insulation resistance drop detection device.

1 is a diagram showing an example of an insulation resistance drop detector according to an embodiment of the present invention; FIG. It is a figure which shows an example of the voltage waveform measured by a voltage sensor. 4 is a diagram showing changes in evaluation values with respect to resistance values of insulation resistance; FIG. It is a figure which shows an example of a self-diagnosis and an earth-leakage determination. It is a figure which shows an example of the self-diagnosis and earth-leakage determination which concern on embodiment of this invention. It is a figure which shows the Example of a self-diagnosis and an earth-leakage determination.

FIG. 1 shows an example of an insulation resistance drop detector according to an embodiment of the present invention. An insulation resistance drop detection device 30 according to an embodiment of the present invention is mounted on a vehicle 1 and detects a drop in insulation resistance Ri between a high voltage circuit 10 and a vehicle frame 20 . The vehicle 1 is, for example, an industrial vehicle such as a forklift, although it is not particularly limited. However, the vehicle 1 is not limited to an industrial vehicle, and may be a passenger car or the like. The vehicle 1 is not particularly limited, but is, for example, a fuel cell vehicle equipped with a fuel cell. However, the vehicle 1 is not limited to a fuel cell vehicle.

High voltage circuit 10 includes fuel cell 11 , DC/DC converter 12 , and load 13 . Note that the high voltage circuit 10 may include other circuits or functions not shown in FIG.

The fuel cell 11 uses fuel gas (eg, hydrogen) to generate electric power. The DC/DC converter 12 steps up and/or steps down the output voltage of the fuel cells 11 . The load 13 is, for example, a running motor of the vehicle 1 and is applied with a DC voltage via the DC/DC converter 12 . That is, the load 13 is driven by the electric power generated by the fuel cells 11 .

High voltage circuit 10 is electrically isolated from vehicle frame 20 . That is, an insulation resistor Ri is provided between the high voltage circuit 10 and the vehicle frame 20 . Here, the minimum resistance value of the insulation resistance Ri is determined by standards or the like. Therefore, the insulation resistance drop detector 30 monitors the drop in the resistance value of the insulation resistor Ri.

The insulation resistance drop detector 30 includes a pulse generator 31 , a detection resistor Rd, a decoupling capacitor C, an earth leakage resistor Rx, a switch SW, a voltage sensor 32 and a controller 33 . The insulation resistance drop detection device 30 may have other circuits or functions not shown in FIG.

The pulse generator 31 generates a pulse having a predetermined crest value with a predetermined cycle T. FIG. The period T is set to allow the pulse train to pass through the decoupling capacitor C. It is also assumed that the crest value of the pulse is proportional to the power supply voltage Vcc. The pulse is, for example, a rectangular wave, although not particularly limited. In this case, the pulse duty is not particularly limited. A pulse generated by the pulse generator 31 is applied to one terminal of the detection resistor Rd.

The other terminal (output terminal) of the detection resistor Rd is electrically connected to one terminal of the decoupling capacitor C. As shown in FIG. The other terminal of decoupling capacitor C is electrically connected to vehicle frame 20 . A decoupling capacitor C is provided to remove a DC voltage component.

One terminal of the leakage resistance Rx is electrically connected to the output terminal of the detection resistance Rd. The other terminal of the leakage resistance Rx is electrically connected to the ground via the switch SW. That is, the leakage resistance Rx and the switch SW are provided in series between the output terminal of the detection resistance Rd and the ground. The state of the switch SW is controlled by the controller 33 . Specifically, the switch SW is controlled by the controller 33 to be in an OFF state for disconnecting the leakage resistance Rx from the ground, or to an ON state for connecting between the leakage resistance Rx and the ground.

A voltage sensor 32 measures the voltage at the output terminal of the detection resistor Rd. A voltage value measured by the voltage sensor 32 is sent to the controller 33 . In the following description, the node whose voltage is measured by the voltage sensor 32 may be called "measurement node M".

The controller 33 detects the resistance value of the insulation resistor Ri. The controller 33 also determines whether the insulation resistance drop detector 30 is operating normally. That is, the controller 33 performs self-diagnosis of the insulation resistance drop detection device 30 . Note that the controller 33 is realized by, for example, a processor and memory. In this case, the memory stores a program for detecting the resistance value of the insulation resistance Ri and a self-diagnostic program for diagnosing the insulation resistance drop detector 30 . By executing these programs by the processor, the resistance value of the insulation resistance Ri is detected, and self-diagnosis of the insulation resistance drop detection device 30 is realized.

In the vehicle 1 configured as described above, when detecting the resistance value of the insulation resistor Ri, the controller 33 turns off the switch SW. That is, the connection between the leakage resistance Rx and the ground is cut off. Further, the controller 33 causes the pulse generator 31 to generate pulses with a predetermined cycle T. FIG. Then, the pulse train generated by the pulse generator 31 is applied to the vehicle frame 20 via the detection resistor Rd and the decoupling capacitor C. As shown in FIG. Furthermore, this pulse train reaches the high voltage circuit 10 via the insulation resistor Ri and is terminated at the ground of the high voltage circuit 10 .

Voltage sensor 32 measures the voltage of measurement node M at this time. Then, the controller 33 acquires the voltage value measured by the voltage sensor 32 at predetermined sampling intervals. The sampling interval is assumed to be sufficiently short with respect to the period T of the pulse.

FIG. 2 shows an example of voltage waveforms measured by the voltage sensor 32 . In this embodiment, as shown in FIG. 2(a), the peak value of the pulse appearing at the measurement node M is V1. The crest value V1 is proportional to the voltage obtained by dividing the power supply voltage Vcc by the detection resistor Rd and the insulation resistor Ri. Here, the resistance value of the insulation resistor Ri is required to be greater than or equal to a predetermined minimum resistance value. Therefore, the controller 33 is set with a threshold value Vth representing the crest value obtained at the measurement node M when the resistance value of the insulation resistor Ri is assumed to be this minimum resistance value. Then, the controller 33 determines the state of the insulation resistance Ri by comparing the crest value V1 obtained by the measurement with the threshold value Vth. In the example shown in FIG. 2A, the crest value V1 obtained by measurement is higher than the threshold value Vth. In this case, the controller 33 determines that the insulation resistance Ri is normal. That is, it is determined that no electric leakage has occurred.

In the example shown in FIG. 2B, the resistance value of the insulation resistor Ri is lowered. In this case, the influence of the inductance component included in the high voltage circuit 10 becomes dominant, and the voltage waveform becomes dull. Therefore, the timing at which the crest value of the pulse appearing at the measurement node M exceeds the threshold Vth is delayed compared to the case shown in FIG. 2(a). Therefore, when monitoring the decrease in the resistance value of the insulation resistor Ri based on the comparison between the crest value of the pulse appearing at the measurement node M and the threshold value Vth, when the predetermined time t has passed since the pulse was applied, Preferably, the two voltages are compared. Specifically, if the crest value V2 of the pulse appearing at the measurement node M after a predetermined time t has elapsed since the pulse was applied is lower than the threshold value th, the controller 33 determines that the insulation resistance Ri has decreased. judge. That is, it is determined that an electric leak has occurred. Note that the voltage at the rising edge of the pulse is represented by Vcc*Ri/(Rd+Ri). Therefore, for example, when the insulation resistance of 50 kΩ is used as the threshold, the threshold Vth can be set by setting Vth=Vcc*50 kΩ/(Rd+50 kΩ).

In the example shown in FIG. 2, the controller 33 acquires the crest value of the pulse appearing at the measurement node M and determines the state of the insulation resistance Ri based on the crest value, but the present invention is limited to this configuration. not something. For example, the controller 33 may determine the state of the insulation resistance Ri based on the integrated value of the voltage value appearing at the measurement node M. In this case, the controller 33 repeatedly obtains the voltage value appearing at the measurement node M at predetermined sampling intervals over a predetermined measurement period, and calculates the sum of a plurality of voltage values obtained by this sampling operation. get Then, the controller 33 determines the state of the insulation resistance Ri based on this voltage integrated value.

Thus, the crest value of the pulse appearing at the measurement node M or the integrated value of the voltage appearing at the measurement node M depends on the resistance value of the insulation resistor Ri. Therefore, it is possible to calculate the resistance value of the insulation resistor Ri from the crest value or the integrated voltage value. Note that the peak value and the integrated voltage value are examples of evaluation values obtained based on the voltage of the measurement node M, respectively. In the following description, the insulation resistance drop detection device 30 performs resistance detection and self-diagnosis using the voltage integrated value, but the present invention is not limited to this configuration. That is, the insulation resistance drop detection device 30 can perform resistance detection and self-diagnosis based on the voltage of the measurement node M. FIG.

FIG. 3 shows changes in the evaluation value with respect to the resistance value of the insulation resistance Ri. In the description below, the evaluation value is the integrated value of the voltage appearing at the measurement node M. FIG.

FIG. 3(a) shows the correspondence relationship between the resistance value of the insulation resistor Ri and the integrated value of the voltage at the measurement node M when the switch SW is controlled to be turned off. That is, the characteristic graph G1 shown in FIG. 3(a) represents the integrated voltage value with respect to the resistance value of the insulation resistor Ri in a state in which no pseudo electric leakage is caused. It should be noted that the characteristic graph G1, for example, is obtained by holding the switch SW in an off state when the insulation resistance drop detection device 30 is verified to be normal, and changing the resistance value of the insulation resistance Ri while changing the voltage at the measurement node M. is created in advance by sampling the Then, the characteristic graph G1 is stored in the controller 33. FIG.

The controller 33 can detect the resistance value of the insulation resistor Ri using the characteristic graph G1. Specifically, the controller 33 calculates the integrated voltage value while controlling the switch SW to be in the OFF state. Then, the controller 33 detects the resistance value of the insulation resistance Ri by referring to the characteristic graph G1 with the calculated integrated voltage value.

When performing self-diagnosis of the insulation resistance drop detection device 30, the controller 33 controls the switch SW to the ON state. That is, the earth leakage resistance Rx is connected to the ground, causing a pseudo earth leakage. Further, the controller 33 causes the pulse generator 31 to generate pulses with a predetermined cycle T. FIG. The controller 33 then measures the voltage of the measurement node M and calculates the integrated voltage value. At this time, the measurement node M is grounded by the insulation resistance Ri and the leakage resistance Rx provided in parallel. Therefore, the integrated voltage value obtained during self-diagnosis is basically smaller than the integrated voltage value obtained during detection of the resistance value of the insulation resistor Ri.

FIG. 3B shows the correspondence relationship between the resistance value of the insulation resistor Ri and the integrated value of the voltage of the measurement node M when the switch SW is controlled to be on. That is, the characteristic graph G2 shown in FIG. 3(b) represents the integrated voltage value with respect to the resistance value of the insulation resistor Ri in the state in which the pseudo electric leakage is caused. It should be noted that the characteristic graph G2 is obtained by, for example, holding the switch SW in the ON state when the insulation resistance drop detection device 30 is verified to be normal, and changing the resistance value of the insulation resistance Ri while the voltage at the measurement node M is changed. is created in advance by sampling the Then, the characteristic graph G2 is stored in the controller 33. FIG.

The controller 33 can diagnose whether the insulation resistance drop detector 30 is normal using the characteristic graph G2. Specifically, the controller 33 measures the voltage of the measurement node M while controlling the switch SW to the ON state, and calculates the integrated voltage value. Here, if the insulation resistance drop detector 30 is normal, the calculated voltage integrated value should be close to the voltage integrated value represented by the characteristic graph G2. Therefore, if the calculated voltage integrated value is detected within a predetermined range with respect to the voltage integrated value represented by the characteristic graph G2, the controller 33 determines that the insulation resistance drop detection device 30 is normal. On the other hand, if the calculated voltage integrated value is out of the above range, the controller 33 determines that the insulation resistance drop detector 30 is out of order.

FIG. 4 shows an example of self-diagnosis and earth leakage determination. In this example, the controller 33 detects the resistance value of the insulation resistance Ri after performing self-diagnosis of the insulation resistance drop detection device 30 .

That is, in S1 to S2 shown in FIG. 4A, the controller 33 performs self-diagnosis. At this time, the controller 33 determines whether or not the integrated value of the voltage of the measurement node M is within a predetermined threshold range set for the characteristic graph G2. However, at this time, the resistance value of the insulation resistor Ri is unknown. Therefore, in this method, the threshold range for determining whether or not the integrated voltage value is close to the characteristic graph G2, as shown in FIG. set to cover. When it is determined in the self-diagnosis that the insulation resistance drop detection device 30 is normal, the controller 33 detects the resistance value of the insulation resistance Ri in S3.

Thus, in the procedure shown in FIG. 4, the threshold range for determining whether or not the voltage integrated value is close to the characteristic graph G2 becomes wide. Therefore, the reliability of self-diagnosis is lowered. For example, it is assumed that the voltage integrated value obtained by measurement is 12000. In this case, since this voltage integrated value is within the threshold range, the judgment result is "normal". At this time, assuming that the resistance value of the insulation resistance Ri is 150Ω, the difference D1 between the integrated voltage value and the characteristic graph G2 is sufficiently small, so the reliability of the determination result is high. However, for example, if the resistance value of the insulation resistor Ri is 800Ω, the difference D2 between the integrated voltage value and the characteristic graph G2 is relatively large, and the reliability of the determination result is low. Therefore, in the procedure shown in FIG. 4, a sign of failure or a minor failure of the insulation resistance drop detection device 30 may not be detected.

It should be noted that the resistance value of the insulation resistor Ri not only changes depending on the temperature, but also may change greatly when moisture adheres to the insulation resistor Ri due to rain or snow. A sign of failure or a minor failure of the insulation resistance drop detection device 30 is not particularly limited, but for example, fluctuation in the gain of an amplifier that amplifies the output signal of the voltage sensor 32 is assumed.

FIG. 5 shows an example of self-diagnosis and earth leakage determination according to the embodiment of the present invention. In the embodiment of the present invention, the controller 33 performs self-diagnosis and earth leakage determination according to the flowchart shown in FIG. 5(a). In this embodiment, it is assumed that the characteristic graph G1 shown in FIG. 3A and the characteristic graph G2 shown in FIG.

In S11, the controller 33 detects the resistance value of the insulation resistor Ri. At this time, the controller 33 turns off the switch SW and causes the pulse generator 31 to generate a pulse. Subsequently, the controller 33 measures the voltage of the measurement node M to calculate the integrated voltage value. Then, the controller 33 detects the resistance value of the insulation resistor Ri by referring to the characteristic graph G1 shown in FIG. 3(a) using this integrated voltage value.

In S12-S13, the controller 33 performs self-diagnosis of the insulation resistance drop detection device 30. FIG. At this time, the controller 33 turns on the switch SW. That is, a pseudo electric leakage state is generated. The controller 33 also causes the pulse generator 31 to generate pulses. Subsequently, the controller 33 measures the voltage of the measurement node M to calculate the integrated voltage value. Further, the controller 33 determines whether or not this voltage integrated value is close to the characteristic graph G2 shown in FIG. 3(b). Here, in the embodiment of the present invention, as shown in FIG. 5B, a threshold range is set for determining whether or not the voltage integrated value is close to the characteristic graph G2.

The threshold range set in the embodiment of the present invention is narrower than the threshold range set in the case shown in FIG. Also, the width of the threshold range is set based on, for example, the integrated voltage value represented by the characteristic graph G2. As an example, the width of the threshold range is 6 percent of the integrated voltage value represented by characteristic graph G2. In this case, the threshold range is represented by "voltage integrated value represented by characteristic graph G2 ±3%". Therefore, for example, if the characteristic graph G2 represents "integrated voltage value=13000" for "resistance=500", the threshold range for "resistance=500" is "13000±390". Also, if the characteristic graph G2 represents "integrated voltage value=12000" for "resistance=100", the threshold range for "resistance=100" is "12000±360". Thus, a threshold range corresponding to the resistance value of the insulation resistor Ri is set. Alternatively, the width of the threshold range may be a fixed value independent of the resistance value of the insulation resistor Ri. In this case, the threshold range is set to, for example, "the integrated voltage value represented by the characteristic graph G2 ±300".

Then, the controller 33 uses the resistance value detected in S11 and the threshold range shown in FIG. 5B to determine whether the insulation resistance drop detection device 30 is normal. Specifically, if the voltage integrated value calculated in S12 is within the threshold range corresponding to the resistance value detected in S11, the controller 33 determines that the insulation resistance drop detector 30 is normal. On the other hand, if the voltage integrated value calculated in S12 is out of the threshold range corresponding to the resistance value detected in S11, the controller 33 determines that the insulation resistance drop detection device 30 is not operating normally. .

When determining that the insulation resistance drop detection device 30 is normal, the controller 33 performs leakage determination in S14. Specifically, if the resistance value of the insulation resistor Ri detected in S11 is equal to or greater than a predetermined minimum resistance value, it is determined that no electrical leakage has occurred. On the other hand, when the resistance value of the insulation resistor Ri detected in S11 is smaller than the predetermined minimum resistance value, it is determined that an electrical leak has occurred. Note that when it is determined that the insulation resistance drop detection device 30 is not operating normally, the controller 33 does not need to perform the earth leakage determination. In this case, the controller 33 may output an alarm indicating that the insulation resistance drop detector 30 is not operating normally.

FIG. 6 shows an embodiment of self-diagnosis and earth leakage determination. In this embodiment, it is assumed that the characteristic graph G2 shown in FIG. 6 is created.

Since the characteristic graph G2 is a function of the resistance value of the insulation resistance Ri, it is represented by the following equation (1). The function F is determined in advance by measurement, for example. Also, the threshold range is assumed to be "±3 percent" with respect to the characteristic graph G2, as shown in the following equation (2).
Characteristic graph: G2=F(Ri) (1)
Threshold range: 0.97×G2 to 1.03×G2 (2)

Case 1 (resistance value of insulation resistance Ri = 600 ohms, integrated voltage value: 13500)
Case 1 corresponds to decision point E1 shown in FIG. Here, by giving "Ri=600" to the equation (1) and giving the result to the equation (2), the threshold range corresponding to the resistance value of the insulation resistance Ri is set. Then, since the determination point E1 is within the threshold range, the controller 33 determines that the insulation resistance drop detector 30 is normal. It is also assumed that the minimum resistance value for determining the presence or absence of electric leakage is 500 ohms. In this case, since the resistance value of the insulation resistor Ri is greater than the minimum resistance value, it is determined that no electrical leakage has occurred.

Case 2 (resistance value of insulation resistance Ri = 600 ohms, integrated voltage value: 12000)
Case 2 corresponds to decision point E2 shown in FIG. The threshold range is the same for Case 1 and Case 2. Then, since the determination point E2 is not within the threshold range, the controller 33 determines that the insulation resistance drop detection device 30 is not operating normally. In this case, the controller 33 does not need to perform earth leakage determination.

Case 3 (resistance value of insulation resistance Ri = 150 ohms, integrated voltage value: 13500)
Case 3 corresponds to decision point E3 shown in FIG. Here, by giving "Ri=150" to the equation (1) and giving the result to the equation (2), the threshold range corresponding to the resistance value of the insulation resistance Ri is set. Then, since the determination point E3 is not within the threshold range, the controller 33 determines that the insulation resistance drop detection device 30 is not operating normally. In this case, the controller 33 does not need to perform earth leakage determination.

Case 4 (resistance value of insulation resistance Ri = 150 ohms, integrated voltage value: 12000)
Case 4 corresponds to decision point E4 shown in FIG. The threshold range is the same for cases 3 and 4. Then, since the determination point E4 is within the threshold range, the controller 33 determines that the insulation resistance drop detector 30 is normal. However, since the resistance value of the insulation resistor Ri is smaller than the minimum resistance value (here, 500 ohms), it is determined that an electric leak has occurred.

Thus, the insulation resistance drop detection device 30 according to the embodiment of the present invention detects the resistance value of the insulation resistance Ri before self-diagnosis. Self-diagnosis is performed using the resistance value of the insulation resistor Ri. At this time, a threshold range for determining whether the insulation resistance drop detection device 30 is normal is set for the resistance value of the insulation resistance Ri. Therefore, the threshold range does not need to include a margin considering variations in the resistance value of the insulation resistor Ri. That is, even when the resistance value of the insulation resistor Ri fluctuates, a narrow threshold range can be set. As a result, it is possible to detect a sign of failure or a minor failure of the insulation resistance drop detection device. That is, according to the embodiment of the present invention, it is possible to accurately detect the state change of the insulation resistance drop detection device.

In the above embodiment, the characteristic graph G1 is used to map the integrated voltage value to the resistance value of the insulation resistor Ri, but the present invention is not limited to this method. For example, an approximation formula representing the characteristic graph G1 may be created in advance, and the resistance value of the insulation resistance Ri may be calculated by giving the voltage integrated value to this approximation formula.

Also, the threshold range may be defined by a table in which the upper limit value and the lower limit value of the integrated voltage value are recorded with respect to the resistance value of the insulation resistor Ri. In this case, the threshold range is specified by searching the table with the resistance value of the insulation resistor Ri. Alternatively, it may be defined by an approximation formula representing the upper limit value and an approximation formula representing the lower limit value of the integrated voltage value. In this case, the threshold range is specified by giving the resistance value of the insulation resistance Ri to each approximate expression.

1 vehicle 10 high voltage circuit 20 vehicle frame 30 insulation resistance drop detector 31 pulse generator 32 voltage sensor 33 controller

Claims (4)

An insulation resistance drop detection device for detecting a drop in insulation resistance between a vehicle frame and a high voltage circuit mounted on the vehicle,
a controller;
a pulse generator that generates pulses at a predetermined period;
a sensing resistor provided between the pulse generator and the frame;
a leakage resistor connected to a measurement node between the sensing resistor and the frame;
a switch that is controlled to an OFF state that cuts off between the leakage resistance and ground or an ON state that connects between the leakage resistance and ground,
The controller is
detecting the resistance value of the insulation resistor based on the voltage of the measurement node when the switch is in an off state;
An insulation resistance drop detector that determines whether the insulation resistance drop detector is normal based on the detected resistance value and the voltage of the measurement node when the switch is in an ON state. A characteristic graph representing a correspondence relationship between a resistance value of the insulation resistance and an evaluation value obtained based on the voltage of the measurement node when the insulation resistance drop detection device is normal and the switch is in an ON state is prepared in advance. is created and
The controller is
detecting the resistance value of the insulation resistor based on the voltage of the measurement node when the switch is in an off state;
Acquiring an evaluation value corresponding to the detected resistance value using the characteristic graph,
The difference between the evaluation value obtained using the characteristic graph and the evaluation value obtained based on the voltage of the measurement node when the switch is in an ON state is a threshold preset for the characteristic graph. 2. The insulation resistance drop detection device according to claim 1, wherein if it is within the range, the insulation resistance drop detection device is determined to be normal. 2. The controller determines whether or not the resistance value of the insulation resistance has decreased below a predetermined threshold when determining that the insulation resistance drop detection device is normal. 3. The insulation resistance drop detector according to 2. A method for diagnosing a failure of an insulation resistance drop detection device that detects a drop in insulation resistance between a vehicle frame and a high voltage circuit mounted on the vehicle, comprising:
The insulation resistance drop detection device includes a pulse generator that generates pulses at a predetermined cycle, a detection resistor provided between the pulse generator and the frame, and a measurement node between the detection resistor and the frame. and a switch that is controlled to an OFF state that disconnects between the leakage resistance and the ground or an ON state that connects between the leakage resistance and the ground,
detecting the resistance value of the insulation resistor based on the voltage of the measurement node when the switch is in an off state;
Determining whether the insulation resistance drop detection device is normal based on the detected resistance value and the voltage of the measurement node when the switch is in the ON state. fault diagnosis method.

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