JP2010004631A - Electric vehicle and ground fault detection method in the electric vehicle - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electric vehicle and a ground fault detection method in the electric vehicle capable of correctly and rapidly detecting a ground fault. <P>SOLUTION: If an insulation resistance R is lower than an idling stop inhibition threshold Rth2 (R<Rth2) when a fuel cell is in a state of repetition between normal driving and idling stop such as driving in a traffic jam, the idling stop of the fuel cell is inhibited, namely, the shift from normal driving to idling stop is inhibited, alternatively the idling stop is released to shift to the normal driving. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an electric vehicle including a ground fault detection device that detects a ground fault between a fuel cell and a drive circuit of an electric motor, and a ground fault detection method in the electric vehicle.

  Conventionally, a ground fault detection device is connected in parallel to the output side of a non-grounded fuel cell, and when a ground fault occurs on the output side, current is passed through the resistor in the ground fault detection device to the resistor. If the generated voltage is higher than a set voltage, it has been proposed to operate a circuit breaker connected to the output side to perform ground fault protection for the fuel cell (see Patent Document 1).

Japanese Patent Laid-Open No. 2-15569

  By the way, in an electric vehicle that travels by the rotation of a wheel by an electric motor, for example, when a normal operation of a fuel cell and a pause of a fuel cell operation (hereinafter referred to as idle stop) are repeated as in a traffic jam, Since the output voltage of the fuel cell at the time of idling stop is lower than the output voltage at the time of normal operation, when the ground fault detection device of Patent Document 1 is applied to the electric vehicle, the normal operation and the idling stop are performed. The ground fault generated between the fuel cell and the drive circuit cannot be detected accurately and promptly due to the voltage change in the resistor due to the change in the output voltage due to the repetition of the above.

  The present invention has been made in consideration of such problems, and an object thereof is to provide an electric vehicle capable of accurately and quickly detecting a ground fault and a ground fault detection method in the electric vehicle. .

  The present invention includes a fuel cell, an electric motor connected to the fuel cell via a drive circuit and rotating a wheel, a ground fault detection device for detecting a ground fault between the fuel cell and the drive circuit, In an electric vehicle including a fuel cell, the drive circuit, and a control unit that controls the electric motor, the ground fault detection device calculates an insulation resistance between the occurrence point of the ground fault and the ground, and calculates the calculated insulation If the resistance is lower than the idle stop prohibition threshold, the detection result indicating that the insulation resistance is lower than the idle stop prohibition threshold is output to the control unit, and the control unit is based on the input detection result. The fuel cell is prohibited from being idled.

  The ground fault detection method for an electric vehicle according to the present invention is an electric vehicle in which an electric motor for rotating a wheel is connected to a fuel cell via a drive circuit, and the ground fault between the fuel cell and the drive circuit. Is detected, the insulation resistance between the ground fault occurrence point and the ground is calculated, and if the calculated insulation resistance is lower than the idle stop prohibition threshold, the fuel cell is prohibited from idling. It is a feature.

  According to these inventions, if the insulation resistance is lower than the idle stop prohibition threshold, the idle stop is prohibited, so that the ground fault can be detected accurately and promptly.

  Here, the control unit prohibits the transition from the operating state of the fuel cell to the idle stop based on the detection result, or performs the idle stop based on the detection result. It is preferable to cancel and start the operation of the fuel cell.

  As a result, when the ground fault occurs, the ground fault can be reliably detected. On the other hand, when the ground fault does not occur, the ground fault is erroneously detected. Can be reliably prevented.

In addition, the ground fault detection device measures a charging voltage of the capacitor and a series circuit of a resistor and a capacitor connected in parallel to the fuel cell, and generates the ground fault based on the measured charging voltage. A ground fault detection unit to detect,
The ground fault detection unit measures in advance a charging voltage when the ground fault has not occurred (hereinafter referred to as a first charging voltage), and a charging voltage when the ground fault has occurred (hereinafter referred to as a second charging). The insulation resistance is calculated based on a ratio between the first charging voltage and the second charging voltage, and the detection is performed when the calculated insulation resistance is lower than the idle stop prohibition threshold. The result is output to the control unit, and the control unit is notified of the occurrence of the ground fault when the insulation resistance is lower than the ground fault determination threshold value set lower than the idle stop prohibition threshold value.

  Thereby, the ground fault can be detected with high accuracy.

  In addition, a diode for supplying power from the fuel cell to the electric motor via the drive circuit is disposed between the fuel cell and the drive circuit, and the drive circuit is controlled by the control unit. When a power storage device is connected in parallel to the diode and the fuel cell via a DC / DC converter, the ground fault detection device is connected between the fuel cell and the diode, Or if it connects between the said diode and the said drive circuit, generation | occurrence | production of the said ground fault between the said fuel cell and the said drive circuit can be detected more reliably.

  According to the present invention, if the insulation resistance is lower than the idle stop prohibition threshold, the idle stop is prohibited, so that a ground fault can be detected accurately and promptly.

  Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

  FIG. 1 is a circuit diagram of a fuel cell vehicle (electric vehicle) 10 according to an embodiment of the present invention.

  The fuel cell vehicle 10 basically includes a fuel cell 12 as a power generation device that generates the first voltage V1, an inverter (drive circuit) 16 connected to output lines 14a and 14b of the fuel cell 12, and an inverter 16 Connected to the motor (electric motor) 18, the battery 38, the DC / DC converter 36 connected to the output lines 42 a and 42 b of the battery 38 and the output lines 40 a and 40 b connected to the output lines 14 a and 14 b, and fuel And a control unit 46 that controls the battery 12, the inverter 16, the motor 18, and the DC / DC converter 36. In this case, in the fuel cell vehicle 10, the fuel cell 12 to the motor 18 and the fuel cell 12 and the motor 18 to the battery 38 are not grounded.

  A contactor 34 and a backflow prevention diode 28 are arranged on the output line 14a, a contactor 44 is arranged on the output line 42a, and the first voltage V1 and the second voltage V2 are detected between the output lines 14a and 14b, respectively. Thus, the voltage sensors 30 and 32 output to the control unit 46 are connected in parallel to the fuel cell 12 and the inverter 16.

  The fuel cell 12 has, for example, a stack structure in which cells formed by sandwiching a solid polymer electrolyte membrane from both sides between an anode electrode and a cathode electrode are stacked. When the contactor 34 is closed by the control unit 46, The first current I1 (generated current) generated by the electrochemical reaction between hydrogen (fuel gas) and air (oxidant gas) is supplied to the inverter 16 and / or the DC / DC converter 36 via the diode 28. The inverter 16 performs DC / AC conversion and supplies the second current I2 (motor current) to the motor 18, while the second current I2 after AC / DC conversion accompanying the regenerative operation is supplied to the battery through the DC / DC converter 36. 38.

  The motor 18 is rotated by supplying power from the fuel cell 12 via the diode 28 and the inverter 16 or by supplying power from the battery 38 via the DC / DC converter 36 and the inverter 16. It is transmitted to the wheel 24 through the speed reducer 20 and the shaft 22 to rotate the wheel 24. The battery 38 is, for example, a lithium ion secondary battery, a nickel hydride secondary battery, or a capacitor. The battery 38 generates the third voltage V3 (battery voltage), and when the contactor 44 is closed by the control unit 46, the motor 18 When the motor 18 is rotating, electric power is supplied to the motor 18, while charging is performed when the motor 18 is regenerated.

  The second current I2 is a combined current (I2 = I1 + I3 ′) of the first current I1 and the current I3 ′ obtained by converting the third current I3 (battery current) flowing out of the battery 38 by the DC / DC converter 36. . Further, the control unit 46 determines the distribution of the power sharing of the fuel cell 12, the power sharing of the battery 38, and the power sharing of the motor 18, and based on this determination, the fuel cell 12, the DC / DC converter 36, the inverter By controlling the motor 16 and the motor 18, the voltages V1 to V3 and the currents I1 to I3 ′ are controlled. The vehicle speed sensor 48 supplies a vehicle speed signal Ss indicating the vehicle speed of the fuel cell vehicle 10 to the control unit 46.

  Furthermore, the fuel cell vehicle 10 includes an insulation resistance R (insulation resistances R1 and R2 in FIGS. 1 to 3) between the ground fault occurrence point and the ground when a ground fault occurs in the output lines 14a and 14b. A ground fault sensor 26 that detects (detects) a decrease in the insulation resistance of the fuel cell vehicle 10 as a whole and supplies the detection result to the control unit 46 as a detection signal Sd is provided between the output lines 14a and 14b. 12 and the inverter 16 are connected in parallel. In this case, the control unit 46 prohibits the fuel cell 12 from being idled based on the input detection signal Sd, or warns the outside of the occurrence of a ground fault.

  In FIG. 1, a ground fault sensor 26 is connected between the output lines 14 a and 14 b between the diode 28 and the inverter 16. In the output line 14 a, the fuel cell 12 and the diode 28, and the diode 28 The case where the ground fault has each generated between the inverters 16 (the ground fault generation | occurrence | production locations 54 and 56 exist) is shown in figure. In FIG. 1, a virtual resistor 50 having an insulation resistance R1 is illustrated between the ground fault occurrence point 54 and the ground, while an insulation resistance R2 is provided between the ground fault occurrence point 56 and the ground. It is illustrated as a virtual resistor 52 having. In this embodiment, as shown in FIG. 2, a ground fault sensor 26 may be connected between the output lines 14 a and 14 b between the fuel cell 12 and the diode 28. As shown in FIG. 3, the diode 28 may be a diode in a DC / DC converter 58 arranged between the output lines 14a and 14b.

  Next, the insulation resistance R between the ground fault occurrence location and the ground when the ground fault occurs (if there are a plurality of ground fault occurrence locations 54 and 56 as described above, the fuel including the insulation resistances R1 and R2) The detection principle of the insulation resistance R) of the battery vehicle 10 as a whole will be described with reference to FIGS.

  As shown in FIG. 4, the ground fault sensor 26 includes a series circuit of a resistor 60 and a capacitor 62 connected in parallel to the fuel cell 12, a ground fault detector 64 connected to the capacitor 62, and an output line. A switch 66a for connecting 14a and the resistor 60, a switch 66b for connecting the capacitor 62 and the output line 14b, and a switch 66c for grounding the negative electrode side of the capacitor 62.

  First, the ground fault sensor 26 measures the first voltage V1 in a state where no ground fault occurs in the output lines 14a and 14b (see FIG. 4). Specifically, when the contactor 34 and the switches 66a and 66b are closed and the switch 66c is open, the contactor 34, the switch 66a, the resistor 60, the capacitor 62, and the switch are connected from the positive electrode of the fuel cell 12. The first charging voltage Vc1 generated in the capacitor 62 by the current I flowing in the order of 66b and the negative electrode of the fuel cell 12 is measured. As shown in FIG. 7, the characteristic 72 of the first charging voltage Vc1 increases with the elapse of time t, and when the time elapses, the voltage value becomes substantially the first voltage V1.

  After the measurement of the first voltage V1, as shown in FIG. 5, for example, when a ground fault occurs in the output line 14b and the insulation resistance between the ground fault occurrence point 68 and the ground is R, that is, the ground When a virtual resistor 70 having an insulation resistance R is formed between the occurrence point 68 and the ground, the ground fault sensor 26 closes the switches 66a and 66c and opens the switch 66b, respectively. A second charging voltage Vc2 generated in the capacitor 62 by the current I ′ flowing in the order from the positive electrode of the battery 12 to the contactor 34, the switch 66a, the resistor 60, the capacitor 62, the switch 66c, the ground, the resistor 70, and the negative electrode of the fuel cell 12 is obtained. measure. As shown in FIG. 7, the characteristic 74 of the second charging voltage Vc2 increases with the elapse of time t, and when the time elapses, the voltage value becomes a predetermined voltage V1 ′.

  The voltage V1 ′ is obtained by subtracting the voltage R × I ′ generated in the resistor 70 when the current I ′ flows from the first voltage V1 (V1 ′ = V1−R × I ′). Therefore, when the insulation resistance R becomes high resistance, the voltage V1 ′ decreases. On the other hand, when the insulation resistance R becomes low resistance, the voltage V1 ′ increases. Therefore, the ground fault detection unit 64 determines the overall insulation resistance in the fuel cell vehicle 10 (insulation in FIG. 5) based on the ratio between the first voltage V1 measured in advance and the voltage V1 ′ measured when the ground fault occurs. Resistance R) is calculated.

  As described above, since the fuel cell 12 and the like are not grounded, as shown in FIG. 6, even when the switches 66a and 66c are in the closed state, as shown in FIG. No current flows in the direction of the ground from the positive electrode via the contactor 34, the switch 66a, the resistor 60, the capacitor 62, and the switch 66c.

  Next, with reference to FIG. 8A to FIG. 14, an output process of the detection signal Sd from the ground fault sensor 26 to the control unit 46 and a ground fault determination process at the control unit 46 when the detection signal Sd is input will be described. Will be described (ground fault detection method in the fuel cell vehicle 10).

  Here, the ground fault detection problem (first and second problems) in the case where the insulation resistances R1 and R2 are different and V1 <V2, and the contents of this embodiment for solving the problem (first problem) The first embodiment and the second embodiment) will be described.

  First, the first problem will be described.

  8A and 8B show the fuel cell vehicle 10 of FIG. 1 during normal operation of the fuel cell 12 (for example, when the fuel cell vehicle 10 travels due to power supply from the fuel cell 12 to the motor 18) and the fuel cell. 12 is a graph showing a change in the second charging voltage Vc2 at 12 idle stops (for example, when the fuel cell vehicle 10 is stopped). Here, Vcth is a ground fault determination threshold value for determining the occurrence of a ground fault (a voltage value for determining that a ground fault has occurred when Vc2 ≧ Vcth).

  8A, power is supplied from the fuel cell 12 and the battery to the motor 18 under the control of the control unit 46, respectively. Therefore, in this case, since V1 = V2, the characteristic 80 of the second charging voltage Vc2 when the insulation resistance R is high resistance (normal range) regardless of the magnitude relationship between the insulation resistances R1 and R2 is: On the other hand, the characteristic 78 of the second charging voltage Vc2 when the insulation resistance R is low (ground fault state) is a characteristic that does not increase to the ground fault determination threshold Vcth (Vc21 <Vcth). (Vcth <Vc22). The characteristic 76 is a characteristic of the first voltage V1 when no ground fault has occurred.

  8B, only the power supply from the battery 38 to the motor 18 is performed by the control of the control unit 46, and the power supply from the fuel cell 12 to the motor 18 is stopped by the temporary suspension of the fuel cell 12. . As a result, V1 <V2 and the diode 28 is turned off. Further, when R1 << R2, the characteristic 86 of the second charging voltage Vc2 is a relatively low voltage characteristic that does not rise to the ground fault determination threshold Vcth (Vc23 <Vcth), and the ground fault occurrence location 54 There is a risk that a ground fault may become undetected despite the occurrence of a fault.

  This is because the insulation resistance R of the fuel cell vehicle 10 as a whole is a combined resistance of the insulation resistances R1 and R2 {the combined resistance when the resistors 50 and 52 are considered to be connected in parallel to the ground fault sensor 26. In spite of R = R1 × R2 / (R1 + R2)}, the position of the output line 14a from the fuel cell 12 to the diode 28 due to the open state of the contactor 34 and the diode 28 being turned off, and the output line 14a This is because the ground fault detection unit 64 can measure only the second charging voltage Vc2 (characteristic 86) corresponding only to the insulation resistance R2. In addition, since R1 << R2, R = R1 × R2 / (R1 + R2) ≈R1, that is, R1 is dominant in the insulation resistance R, and R1≈R << R2, and the ground fault detection unit 64 is The second charging voltage Vc2 is measured lower.

  The above is a schematic description regarding the first problem.

  The characteristic 82 is a characteristic when the ground fault sensor 26 measures the power supply voltage (the second voltage V2 obtained by converting the third voltage V3 of the battery 38 by the DC / DC converter 36). The characteristic 84 is a characteristic indicating the measurement result of the second charging voltage Vc2 when the ground fault sensor 26 is arranged at the position shown in FIG. 2, and in this case, the second charging voltage according to the insulation resistance R1. Vc2 (first voltage V1) is measured, and the ground fault sensor 26 can detect the occurrence of a ground fault at the ground fault occurrence location 54.

  Next, the first problem will be described more specifically with reference to FIG.

  FIG. 9 shows, for example, a vehicle speed characteristic 90, a first voltage V1 characteristic 94, a second voltage V2 characteristic 92, an insulation resistance when the fuel cell 12 repeats idle stop and normal operation as in a traffic jam. 11 is a graph of R characteristics 96 and 98, a characteristic 100 indicating a counter value of a confirmation counter (not shown) of the control unit 46, and a characteristic 102 indicating a warning from the control unit 46 to the outside.

  In FIGS. 8A and 8B, the ground fault sensor 26 performs a ground fault generation process using the second charging voltage Vc2 and the ground fault threshold value Vcth. On the other hand, in FIG. 9, the ground fault sensor 26 calculates the insulation resistance R based on the second charging voltage Vc2, and the calculated insulation resistance R is greater than the ground fault determination threshold value Rth1 corresponding to the ground fault determination threshold value Vcth. Is lower (R <Rth1), the detection signal Sd indicating the occurrence of the ground fault is output to the control unit 46, and the control unit 46 starts counting by the confirmation counter based on the input detection signal Sd. When the value reaches a predetermined count threshold TH, a warning is given to the outside.

  The characteristic 96 is a characteristic of the calculated value of the insulation resistance R calculated by the ground fault detector 64, and the characteristic 98 is a true value of the insulation resistance R (the value of the insulation resistance of the fuel cell vehicle 10 as a whole). 1 to 3, the combined resistance value of the insulation resistances R1 and R2).

  During normal operation of the fuel cell 12, the characteristic 92 of the first voltage V1 and the characteristic 94 of the second voltage V2 are substantially the same under the control of the control unit 46. On the other hand, when the fuel cell 12 is idling stopped, the characteristic 94 is time. Since it decreases with the elapse of t, the characteristic 92 does not match. Note that the characteristic 92 is maintained at a substantially predetermined voltage during idling stop. The characteristics 92 and 94 change in accordance with changes in the vehicle speed characteristic 90.

  At time t1, when the characteristic 96 falls below the ground fault determination threshold Rth1 (R <Rth1), the ground fault detection unit 64 outputs a detection signal Sd for notifying the occurrence of the ground fault to the control unit 46, The control unit 46 starts counting by the confirmation counter based on the input of the detection signal Sd. Switching from normal operation to idle stop at time t2 and when V1 <V2 due to contactor 34 opening and diode 28 off at time t3, the calculated value characteristic 96 does not match the true value characteristic 98. It becomes. That is, at the time of idling stop, the ground fault detection unit 64 calculates the insulation resistance R higher than the true value. Therefore, when the characteristic 96 exceeds the ground fault determination threshold Rth1 at time t4 and the output of the detection signal Sd from the ground fault detection unit 64 to the control unit 46 is stopped, the control unit 46 is based on the stop of the input of the detection signal Sd. The count value of the confirmation counter is reset to 0.

  The count start and reset of the confirmation counter during the occurrence of the ground fault as described above is also performed in the time period from time t5 to time t6, and then the count is started again at time t7, and the confirmation counter is counted at time t8. When the threshold value TH is reached, the control unit 46 warns the outside that the occurrence of the ground fault has been confirmed.

  Thus, when the fuel cell 12 repeats idling stop and normal operation, if V1 <V2, even if a ground fault occurs, the insulation resistance R is accurately calculated due to a decrease in the first voltage V1. As a result, the timing for warning the occurrence (determination) of the ground fault to the outside is delayed. The above is the specific description regarding the first problem.

  Next, the second problem will be described.

  The second problem is that in the fuel cell vehicle 10 of FIG. 2, when R1 << R2 (R1 is dominant with respect to the insulation resistance R) and V1 <V2, the ground fault detection unit 64 (see FIG. 4) is Contrary to the case of the first problem, since the insulation resistance R is calculated to be low, there is a possibility of erroneously detecting a ground fault.

  Referring to the graph of FIG. 10, when the characteristic 134 of the first voltage V1 and the characteristic 132 of the second voltage V2 change corresponding to the vehicle speed characteristic 130, idle time from time t30 to time t34 is illustrated. At the time of stopping, after time t31, due to the mismatch between the characteristics 132 and 134, the true value characteristic 138 and the calculated value characteristic 136 of the insulation resistance R are mismatched (the characteristic 136 is calculated lower than the characteristic 138). . As a result, R <Rth1 at time t32, and when the confirmation counter starts counting, the count value (characteristic 140) reaches the count threshold value TH at time t33, and the control unit 46 confirms the occurrence of the ground fault externally. (A flag for the warning characteristic 142 is set). That is, despite the fact that the true value characteristic 138 is higher than the ground fault determination threshold value Rth1 (no ground fault has occurred), the control unit 46 incorrectly warns the occurrence of a ground fault to the outside.

  This is the second problem.

  Therefore, in the first example of this embodiment, in order to solve the first problem, as shown in FIGS. 11 and 12, the ground fault detection unit 64 includes the idle fault determination threshold value Rth 1 If the stop inhibition threshold value Rth2 is provided as a threshold value and the calculated insulation resistance R (characteristics 112 and 122) is lower than the idle stop threshold value Rth2 (R <Rth2), the control unit 46 is requested to prohibit the idle stop. If the calculated insulation resistance R is lower than the ground fault determination threshold value Rth1 (R <Rth1), a new detection signal Sd indicating the occurrence of a ground fault to the control unit 46 is output. Is output.

  That is, in FIG. 11, in the idle stop time period from time t10 to time t12, the calculated value characteristic 112 and the true value characteristic 114 do not match from time t11 to approximately time t12, and then at time t13, R <Rth2, and when the ground fault detection unit 64 outputs the detection signal Sd requesting the prohibition of the idle stop to the control unit 46, the control unit 46 switches to the idle stop based on the input of the detection signal Sd. Prohibit migration. At time t14, when R <Rth1, and the ground fault detection unit 64 outputs a new detection signal Sd indicating the occurrence of the ground fault to the control unit 46, the control unit 46 sets the new detection signal Sd. Based on the input, and at time t15, when the count value (characteristic 116) reaches the count threshold value TH, a warning is given to the outside that the occurrence of the ground fault is confirmed (warning characteristic 118). Flag).

  As described above, since the control unit 46 prohibits the transition to the idle stop at time t13, the fuel cell 12 shifts to the idle stop even when the vehicle speed (its characteristic 110) becomes 0 at the time t16. No, continue normal operation (fuel cell operation).

  On the other hand, in FIG. 12, even when the calculated value characteristic 122 and the true value characteristic 124 do not match from the time t21 to the time t22 in the idle stop time period starting from the time t20, R < When Rth2 is reached, the ground fault detection unit 64 outputs a detection signal Sd requesting prohibition of idle stop to the control unit 46, and the control unit 46 prohibits idle stop based on the input of the detection signal Sd. To do. Thereby, even after the time t22, even if the vehicle speed (its characteristic 120) is 0, the fuel cell 12 cancels the idle stop and shifts from the idle stop to the normal operation state. At time t23, when R <Rth1, the ground fault detection unit 64 outputs a new detection signal Sd indicating the occurrence of the ground fault to the control unit 46, and the control unit 46 outputs the detection signal Sd. Based on the input, the count of the confirmation counter is started. When the count value (characteristic 126) reaches the count threshold value TH at time t24, a warning is given to the outside that the occurrence of the ground fault has occurred (flag of the warning characteristic 128) Stand up).

  Therefore, in the first embodiment, as the threshold value for the insulation resistance R, both the ground fault determination threshold value Rth1 for determining the occurrence of the ground fault and the idle stop prohibiting threshold value Rth2 for determining the prohibition of the idle stop are provided. Thus, the control unit 46 can promptly warn the outside that the occurrence of the ground fault has been confirmed.

  Further, in this embodiment (second example), in order to solve the second problem, as shown in FIG. 13, the normal operation and the idle stop are shifted at time t40 and t42, and from time t41. When the characteristic 152 of the calculated value of the insulation resistance R and the characteristic 154 of the true value do not match in the time zone up to the time t43, when R <Rth2 at the time t44, the ground fault detection unit 64 A detection signal Sd requesting prohibition of idle stop is output to the control unit 46, and the control unit 46 prohibits transition to idle stop based on the input of the detection signal Sd. As a result, even when the vehicle speed (its characteristic 150) becomes 0 at time t46 after time t44, the fuel cell 12 does not shift from normal operation to idle stop. Further, since the transition to the idle stop after the time t44 is prohibited, the occurrence of the mismatch between the calculated value characteristic 152 and the true value characteristic 154 can be reliably prevented, and the count value characteristic 156 increases. Since the flag of the warning characteristic 158 is prevented from being raised, it is possible to avoid accidental warning to the outside even when a ground fault has not occurred.

  FIG. 14 is a flowchart showing a process for determining whether or not to perform idle stop. In step S1, the control unit 46 determines whether or not there is an idle stop request (input of the detection signal Sd indicating), and if there is an idle stop request (YES in step S1), then R < It is determined whether it is Rth2 (step S2).

  When R <Rth2 is not satisfied, that is, when R ≧ Rth2, and there is no input of a new detection signal Sd indicating the occurrence of a ground fault (NO in step S2), it is determined that no ground fault has occurred. The control unit 46 performs idle stop (step S3).

  On the other hand, when there is no idle stop request in step S1 (NO in step S1), or in step S2, a new detection signal Sd indicating the occurrence of a ground fault is input, and it is found that R <Rth2. (YES in step S2), the control unit 46 performs normal operation (prohibits transition to idle stop or cancels idle stop and shifts to normal operation) (step S4).

  As described above, in this embodiment, when the insulation resistance R is lower than the idle stop prohibition threshold Rth2 (R <Rth2), the idle stop is prohibited, so that the ground fault can be detected accurately and promptly. In this case, if a ground fault has occurred by prohibiting the transition from the normal operation to the idle stop or canceling the idle stop and shifting to the normal operation, the ground fault is surely prevented. On the other hand, when a ground fault does not occur, it is possible to reliably prevent the ground fault from being erroneously detected.

  In addition, the ground fault detection unit 64 calculates the insulation resistance R based on the ratio of the first charging voltage Vc1 and the second charging voltage Vc2 of the capacitor 62, and calculates the calculated insulation resistance R, the ground fault determination threshold value Rth1, and idle stop prohibition. Based on the comparison with the threshold value Rth2, a request for prohibiting the occurrence of a ground fault or idling stop is output to the control unit 46 as the detection signal Sd. Thereby, a ground fault can be detected accurately.

  Also, as shown in the circuit diagrams of FIGS. 1 to 3, the ground fault sensor 26 may be disposed at any position between the output lines 14 a and 14 b, so that a ground fault between the fuel cell 12 and the inverter 16 is possible. Can be detected more reliably.

  Note that this embodiment is not limited to the above description, and it is needless to say that various configurations can be adopted based on the description in the specification and the drawings.

1 is a circuit diagram of a fuel cell vehicle according to an embodiment of the present invention. It is a circuit diagram at the time of changing the arrangement position of a ground fault sensor. It is a circuit diagram in case a diode is included in a DC / DC converter. It is a circuit diagram which shows measurement of the 1st charging voltage by a ground fault sensor. It is a circuit diagram which shows the measurement of the 2nd charging voltage by a ground fault sensor. It is a circuit diagram when a ground fault has not occurred. It is a graph of the 1st and 2nd charging voltage. 8A and 8B are graphs of first and second charging voltages for explaining the first problem. It is a graph for demonstrating a 1st problem. It is a graph for demonstrating a 2nd problem. It is a graph for demonstrating 1st Example. It is a graph for demonstrating 1st Example. It is a graph for demonstrating 2nd Example. It is a flowchart of the determination process of a normal driving | operation and an idle stop.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Fuel cell vehicle 12 ... Fuel cell 14a, 14b, 40a, 40b, 42a, 42b ... Output line 16 ... Inverter 18 ... Motor 26 ... Ground fault sensor 28 ... Diode 30, 32 ... Voltage sensor 34, 44 ... Contactor 36, 58 ... DC / DC converter 38 ... Battery 46 ... Control unit 50, 52, 60, 70 ... Resistors 54, 56, 68 ... Ground fault occurrence location 62 ... Capacitor 64 ... Ground fault detection unit 66a-66c ... Switch

Claims (6)

A fuel cell;
An electric motor connected to the fuel cell via a drive circuit and rotating a wheel;
A ground fault detection device for detecting a ground fault between the fuel cell and the drive circuit;
A control unit for controlling the fuel cell, the drive circuit and the electric motor;
In an electric vehicle comprising:
The ground fault detection device calculates an insulation resistance between the occurrence point of the ground fault and the ground, and if the calculated insulation resistance is lower than an idle stop prohibition threshold, the insulation resistance is lower than the idle stop prohibit threshold. Output a detection result indicating that the
The electric vehicle, wherein the control unit prohibits the fuel cell from being idled based on the input detection result. The electric vehicle according to claim 1,
The control unit prohibits transition from the state in which the fuel cell is operated to the idle stop based on the detection result. The electric vehicle according to claim 1,
The control unit releases the idle stop and starts operation of the fuel cell based on the detection result. The electric vehicle according to any one of claims 1 to 3,
The ground fault detection device is
A series circuit of a resistor and a capacitor connected in parallel to the fuel cell;
A ground fault detector that measures the charging voltage of the capacitor and detects the occurrence of the ground fault based on the measured charging voltage;
Have
The ground fault detector is
A charging voltage when the ground fault has not occurred (hereinafter referred to as a first charging voltage) is measured in advance,
Measure the charging voltage (hereinafter referred to as the second charging voltage) when the ground fault occurs,
The insulation resistance is calculated based on a ratio between the first charging voltage and the second charging voltage, and when the calculated insulation resistance is lower than the idle stop prohibiting threshold, the detection result is output to the control unit. And
The electric vehicle characterized by notifying the controller of the occurrence of the ground fault when the insulation resistance is lower than a ground fault determination threshold set lower than the idle stop prohibition threshold. The electric vehicle according to any one of claims 1 to 4,
Between the fuel cell and the drive circuit, a diode for supplying electric power from the fuel cell to the electric motor via the drive circuit is disposed,
In the drive circuit, a power storage device is connected in parallel to the diode and the fuel cell via a DC / DC converter controlled by the controller.
The electric vehicle characterized in that the ground fault detection device is connected between the fuel cell and the diode, or connected between the diode and the drive circuit. In an electric vehicle in which an electric motor that rotates a wheel is connected to a fuel cell via a drive circuit, when detecting a ground fault between the fuel cell and the drive circuit,
An electric vehicle that calculates an insulation resistance between the occurrence point of the ground fault and grounding, and prohibits idle stop of the fuel cell if the calculated insulation resistance is lower than an idle stop prohibition threshold. Ground fault detection method.

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