Failure detection device

Abstract

To provide a failure detection device capable of detecting an ON failure while suppressing the number of switching means.SOLUTION: A failure detection device comprises: switching means SW1 to SW3 in which three drain terminals D are connected to a connection point P, and two source terminals S are connected to a main battery and a sub battery; and a failure detection unit 50a which detects an ON failure of the first switching means SW1 and the second switching means SW2. The failure detection unit 50a includes: a voltage application part 50V that applies a predetermined voltage to the connection point P in a superimposed manner when all the switching means SW1 to SW3 are controlled to be turned off; a voltage detection part 51b that detects the voltage at the connection point P in the application state by the voltage application part 50V; and an ON failure determination part 51c that determines that at least one of the first switching means SW1 and the second switching means SW2 is in an ON failure state when the voltage detected by the voltage detection part 51b is not equal to or greater than a threshold.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a fault detection device. [Background technology]

[0002] 2. Description of the Related Art Conventionally, a fault detection device has been proposed that detects sticking of a switch means such as an FET (Field Effect Transistor) in an ON fault or an OFF fault (see Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent Publication No. 2021-85733 Summary of the Invention [Problem to be solved by the invention]

[0004] The fault detection device described in Patent Document 1 detects faults in back-to-back MOSFETs (Metal Oxide Semiconductor Field Effect Transistors). In this case, the diode-OR configuration using drain-connected MOSFETs cannot detect on-faults because a detour exists due to a parasitic diode even if the MOSFET is turned off, and the MOSFET cannot be completely turned off.

[0005] As a countermeasure to this, if a DC / DC converter is provided as a power supply on both sides of the diode-OR configuration, it is possible to create a potential difference between the MOSFETs by stepping up or stepping down the output voltage, making it possible to detect on-failures. However, in reality, the output voltage in vehicle equipment and other devices is determined by the equipment to which the voltage is supplied, and furthermore, these devices basically operate at the same voltage, so the voltage cannot be stepped up or down arbitrarily and on-failures cannot be detected.

[0006] This requires a diode-OR configuration in which two pairs of switch means are combined back to back, and therefore at least four switch means are required, increasing the number of switch means.

[0007] Therefore, the present disclosure provides a failure detection device that is capable of detecting on-failures while reducing the number of switch means. [Means for solving the problem]

[0008] In order to solve the above problem, a fault detection device according to an embodiment of the present disclosure includes a first switch means having a first terminal connected to a first battery outputting a predetermined voltage, a second terminal connected to a connection point, and a parasitic diode that blocks a current from flowing from the second terminal to the first terminal, a second switch means having a first terminal connected to a second battery outputting the predetermined voltage, a second terminal connected to the connection point, and a parasitic diode that blocks a current from flowing from the second terminal to the first terminal, a third switch means having a first terminal connected to a load, a second terminal connected to the connection point, and a parasitic diode that blocks a current from flowing from the second terminal to the first terminal, and an ON / OFF switch between the first switch means and the second switch means. and a fault detection means for detecting an on-failure, the fault detection means comprising: a voltage application means for superimposing a specified voltage on the connection point when the first switch means, the second switch means, and the third switch means are all controlled to be off; a voltage detection means for detecting the voltage of the connection point in a state where the voltage is applied by the voltage application means; and an on-failure determination means for determining that at least one of the first switch means and the second switch means has an on-failure when the voltage detected by the voltage detection means exceeds the specified voltage and is not equal to or greater than a threshold value that is set to be less than a value obtained by adding the specified voltage to the specified voltage and subtracting a voltage drop due to a parasitic diode of the first switch means and the second switch means. Effect of the Invention

[0009] According to the present disclosure, it is possible to provide a failure detection device capable of detecting an on failure while reducing the number of switch means. [Brief description of the drawings]

[0010] [Figure 1] 1 is a block diagram showing a power supply system including a fault detection device according to an embodiment of the present invention. [Diagram 2] 2 is a block diagram showing details of a changeover switch shown in FIG. 1. [Diagram 3] 3 is a circuit diagram showing a detailed example of the one-pulse boost circuit shown in FIG. 2. [Figure 4] 11 is a timing chart showing a voltage state when an on-failure does not occur. [Diagram 5] 11 is a timing chart showing a voltage state when an on-failure occurs. [Figure 6] 5 is a flowchart showing a method for determining an on-failure in an MCU of the changeover switch according to the present embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] The present invention will be described below along with preferred embodiments. Note that the present invention is not limited to the embodiments shown below, and can be modified as appropriate within the scope of the present invention. In addition, in the embodiments shown below, some configurations are omitted from illustration and description, but it goes without saying that publicly known or well-known technologies are appropriately applied to the details of the omitted technologies within the scope of the contents described below.

[0012] Fig. 1 is a block diagram including a power supply system including a fault detection device according to this embodiment. The power supply system 1 shown in Fig. 1 supplies power to a load L, and includes a high / low voltage DC power supply 10, a main battery (first battery) MB, a battery fuse terminal (hereinafter referred to as BFT) 20, a sub-battery (second battery) SB, a BFT 30, an ECU (Electronic Control Unit) 40, and a changeover switch (fault detection device) 50.

[0013] The high / low voltage DC power supply 10 is composed of a DC / DC converter that steps down the voltage from a high voltage power supply. This high / low voltage DC power supply 10 steps down the voltage from the high voltage power supply to a predetermined voltage (e.g., 12 V) that serves as the operating voltage of the load L. After stepping down the voltage, the high / low voltage DC power supply 10 supplies power to the changeover switch 50 via a first fuse F1 in the BFT 20.

[0014] The main battery MB is capable of supplying a predetermined voltage (for example, 12 V) that serves as an operating voltage to the load L, and is configured, for example, as a lead storage battery. This main battery MB supplies power to the changeover switch 50 via a second fuse F2 in the BFT 20.

[0015] The sub-battery SB is capable of supplying a predetermined voltage (e.g., 12 V) that serves as an operating voltage to the load L, and is composed of, for example, a lead-acid battery or a lithium-ion battery. The sub-battery SB is capable of supplying the same voltage as the main battery MB, and supplies power to the changeover switch 50 via the third fuse F3 in the BFT 30.

[0016] The ECU 40 corresponds to a higher-level device that controls the changeover switch 50. The changeover switch 50 switches the power supply path to the load L. In this embodiment, the load L is assumed to be, for example, an important load that is essential for the vehicle to run. The power supply system 1 includes the changeover switch 50 to avoid a situation in which power cannot be supplied to the load L. For example, when power cannot be supplied from the main battery MB (including the high-voltage / low-voltage DC power supply 10), the power supply system 1 controls the changeover switch 50 to supply power from the sub-battery SB to the load L.

[0017] The changeover switch 50 includes first to third switch means SW1 to SW3, an MCU (Memory Control Unit) 51, and a one-pulse boost circuit (boosting means) 52. The MCU 51 and the one-pulse boost circuit 52 constitute a failure detection section (failure detection means) 50a that detects whether at least one of the first switch means SW1 and the second switch means SW2 has an on-failure.

[0018] The first switch means SW1 is configured with a MOSFET, with a source terminal (first terminal) S connected to the BFT 20 side, i.e., the main battery MB, and a drain terminal (second terminal) D connected to a connection point P. A gate terminal G is configured to receive a gate signal from the ECU 40 or the MCU 51 that receives an instruction from the ECU 40. The first switch means SW1 also has a parasitic diode BD1 that allows a current to flow from the source terminal S to the drain terminal D and blocks a current to flow from the drain terminal D to the source terminal S.

[0019] The second switch means SW2 is configured with a MOSFET, with a source terminal (first terminal) S connected to the BFT 30 side, i.e., the sub-battery SB, and a drain terminal (second terminal) D connected to the connection point P. Similarly to the first switch means SW1, the gate terminal G is configured to receive a gate signal from the ECU 40 or MCU 51. The second switch means SW2 also has a parasitic diode BD2 that allows a current to flow from the source terminal S to the drain terminal D and blocks a current to flow from the drain terminal D to the source terminal S. The first switch means SW1 and the second switch means SW2 configure a diode OR circuit.

[0020] The third switch means SW3 is also configured with a MOSFET, with a source terminal (first terminal) S connected to the load L and a drain terminal (second terminal) D connected to the connection point P. Similarly to the first switch means SW1, a gate signal is input to the gate terminal G from the ECU 40 or MCU 51. The third switch means SW3 also has a parasitic diode BD3 that allows a current to flow from the drain terminal D to the source terminal S and blocks a current to flow from the drain terminal D to the source terminal S.

[0021] Fig. 2 is a block diagram showing details of the changeover switch 50 shown in Fig. 1. As shown in Fig. 2, the MCU 51 of the changeover switch 50 includes an output section (output means) 51a, a voltage detection section (voltage detection means) 51b, and an ON failure determination section (ON failure determination means) 51c in order to determine ON failures of the first switch means SW1 and the second switch means SW2.

[0022] The output unit 51a outputs a voltage to be superimposed on the connection point P, for example, a voltage of 5V. This output unit 51a outputs a one-pulse voltage that is on for only a very short time. The one-pulse boost circuit 52 boosts the one-pulse voltage from the output unit 51a and superimposes it on the connection point P. The output unit 51a and the one-pulse boost circuit 52 constitute a voltage application unit (voltage application means) 50V. When the first switch means SW1, the second switch means SW2, and the third switch means SW3 are all controlled to be off by the ECU 40 (see FIG. 1) or the MCU 51, the voltage application unit 50V superimposes and applies a boosted voltage based on the one-pulse voltage as a specified voltage to the connection point P.

[0023] Fig. 3 is a circuit diagram showing a detailed example of the one-pulse boost circuit 52 shown in Fig. 2. As shown in Fig. 3, for example, the one-pulse boost circuit 52 includes an NPN transistor Q1, resistors R1 and R2, a capacitor C1, and Schottky barrier diodes SD1 and SD2.

[0024] A single pulse voltage from the output section 51a (see FIG. 2) is input to the base B of the NPN transistor Q1 via a resistor R1. The collector C of the NPN transistor Q1 is connected to the main battery MB via a resistor R2. The emitter E of the NPN transistor Q1 is connected to ground.

[0025] In addition, a connection point P1 between the main battery MB and the resistor R2 is connected to the anode of a Schottky barrier diode SD1. The cathode of the Schottky barrier diode SD1 is connected to the anode of another Schottky barrier diode SD2. The cathode of the Schottky barrier diode SD2 serves as a boost output section (a section that outputs a specified voltage).

[0026] A connection point P2 between the two Schottky barrier diodes SD1 and SD2 is connected via a capacitor C1 to a connection point P3 between the resistor R2 and the collector C of the NPN transistor Q1.

[0027] Referring again to FIG. 2, the voltage detection unit 51b detects the voltage applied to the connection point P. The on-failure determination unit 51c determines whether an on-failure occurs in the first switch means SW1 or the second switch means SW2 based on the voltage detected by the voltage detection unit 51b ... threshold is set to a value that exceeds a predetermined voltage, which is the output voltage of the batteries MB and SB, and is less than a value obtained by adding the above-mentioned specified voltage to the predetermined voltage and subtracting a voltage drop caused by the parasitic diodes BD1 and BD2, which will be described later. If the detected voltage is equal to or greater than the threshold, the on-failure determination unit 51c determines that an on-failure does not occur in either the first switch means SW1 or the second switch means SW2. On the other hand, if the detected voltage is not equal to or greater than the threshold, the on-failure determination unit 51c determines that an on-failure occurs in at least one of the first switch means SW1 and the second switch means SW2.

[0028] Next, an outline of an on-failure determination method by the on-failure determination unit 51c will be described with reference to Figures 2, 4, and 5. Figure 4 is a timing chart showing the voltage state when no on-failure occurs, and Figure 5 is a timing chart showing the voltage state when an on-failure occurs.

[0029] First, a case where an ON failure does not occur will be described. As shown in Fig. 2, the first switch means SW1 and the second switch means SW2 each have a parasitic diode BD1, BD2, and the parasitic diodes BD1, BD2 are oriented to allow a current from each battery MB, SB toward the connection point P. If the voltage (predetermined voltage) of the main battery MB and the sub-battery SB is 12V, a voltage obtained by subtracting the voltage drop of the parasitic diodes BD1, BD2 from 12V is applied to the connection point P. For example, if the voltage drop of the parasitic diodes BD1, BD2 is 0.6V, a voltage of 12V-0.6V=11.4V is applied to the connection point P.

[0030] Further, the voltage application unit 50V applies a prescribed voltage to the connection point P to which such a voltage is applied. Here, it is assumed that the output unit 51a outputs a 5V voltage at time t11 shown in FIG. 4. The 5V voltage is boosted to 12V over time. Therefore, a voltage of 11.4V+12V (=23.4V) is finally applied to the connection point P. Here, the threshold value is set to less than 23.4V. In the example shown in FIG. 4, the voltage detected by the voltage detection unit 51b is equal to or greater than the threshold value at least at time t12. The state in which the detected voltage is equal to or greater than the threshold value continues at least until time t13 when the one-pulse voltage is turned off. Therefore, the on-failure determination unit 51c determines that no on-failure has occurred in either the first switch means SW1 or the second switch means SW2 when the detected voltage is equal to or greater than the threshold value.

[0031] On the other hand, when an on-failure occurs, the connection point P is in a conductive state with at least one of the main battery MB and the sub-battery SB. Therefore, the voltage of the connection point P is fixed to a predetermined voltage. Therefore, even if the output unit 51a outputs a voltage of 5V at time t21 shown in FIG. 5, the voltage is maintained at 12V until time t22 when the one-pulse voltage is turned off. Here, the threshold value is set to a value exceeding 12V. Therefore, the on-failure determination unit 51c determines that an on-failure has occurred in at least one of the first switch means SW1 and the second switch means SW2 when the detected voltage is not equal to or higher than the threshold value.

[0032] As shown in Fig. 4, the detected voltage is at a maximum value near time t13 when the one-pulse voltage is turned off. For this reason, it is preferable that the voltage detection unit 51b detects the voltage at the connection point P near time t13, which is the time when the one-pulse voltage is turned off. This is because it is possible to prevent the voltage detection unit 51b from erroneously judging the voltage at a timing before time t12 when the voltage has not been fully boosted. Here, for example, the vicinity of time t13 refers to the period from time t13-α to time t13+α, assuming that the time α is half the time from time t12, when the detected voltage matches the threshold value in the absence of an on-failure, to time t13.

[0033] 6 is a flowchart showing a method for determining an on-failure in the MCU 51 of the changeover switch 50 according to this embodiment. As shown in FIG 6, first, the MCU 51 sets the number of retries N (S1). For example, in this embodiment, the number of retries N is assumed to be "3".

[0034] Next, the MCU 51 turns off all the switch means SW1 to SW3 (S2). Next, the output section 51a of the MCU 51 outputs a one-pulse voltage (S3). The one-pulse voltage is boosted by the one-pulse boost circuit 52 and applied to the connection point P.

[0035] Thereafter, the voltage detection unit 51b detects the voltage (drain voltage) at the connection point P through A / D input (S4). Next, the on-failure determination unit 51c determines whether the voltage detected in step S4 is equal to or greater than a threshold value (S5).

[0036] If the detected voltage in step S4 is not equal to or greater than the threshold (S5: NO), the MCU 51 determines whether the retry count N is "0" (S6). If the retry count N is not "0" (S6: NO), the MCU 51 decrements the retry count N (S7), and the process proceeds to step S3. If the retry count N is "0" (S6: YES), the on-failure determination unit 51c determines that at least one of the first switch means SW1 and the second switch means SW2 has an on-failure, and outputs a notice to that effect to the ECU 40 (S8). Thereafter, the process shown in FIG. 6 ends.

[0037] On the other hand, if the detected voltage in step S4 is equal to or higher than the threshold value (S5: YES), the on-failure determination unit 51c determines that no on-failure has occurred in either the first switch means SW1 or the second switch means SW2 (S9). After that, the process shown in FIG. 6 ends.

[0038] In this way, according to the changeover switch 50 of this embodiment, when an on-failure does not occur, a voltage based on each battery MB, SB (a voltage slightly lower than the predetermined voltage) is applied to the connection point P in terms of the orientation of the parasitic diodes BD1, BD2 of each switch means SW1, SW2. Furthermore, when an on-failure is determined, a specified voltage applied by the voltage application unit 50V is applied to the connection point P. Therefore, when an on-failure does not occur, a voltage obtained by adding the specified voltage to a voltage slightly lower than the predetermined voltage should be detected. Therefore, by appropriately setting the threshold value, the on-failure determination unit 51c can determine that an on-failure does not occur in each switch means SW1, SW2 when the detected voltage at the connection point P is equal to or higher than the threshold value.

[0039] On the other hand, in the event of an on-fault, the connection point P is shorted to the main battery MB or the sub-battery SB, and the connection point P is at a predetermined voltage. Therefore, when the voltage of the connection point P is not equal to or higher than the threshold value exceeding the predetermined voltage, the on-fault determination unit 51c can determine that at least one of the first switch means SW1 and the second switch means has an on-fault.

[0040] In addition, since the ON failure can be determined by using at least three switch means SW1 to SW3, the number of switch means can be reduced, and therefore it is possible to provide a failure detection device that can detect ON failures while reducing the number of switch means SW1 to SW3.

[0041] Furthermore, the voltage application unit 50V has an output unit 51a that outputs a voltage to be applied to the connection point P, and a one-pulse boost circuit 52 that boosts the voltage output by the output unit 51a. Therefore, for example, a voltage of 5V can be output to be applied from the MCU 51 to the connection point P, and the output voltage can be boosted to apply a relatively high voltage. This increases the voltage difference at the connection point P between when an ON fault occurs and when there is no ON fault, making it possible to more appropriately detect an ON fault.

[0042] Furthermore, since the output section 51a outputs one pulse voltage, unnecessary power consumption can be minimized.

[0043] The present invention has been described above based on an embodiment, but the present invention is not limited to the above embodiment, and modifications may be made without departing from the spirit of the present invention, and if possible, known or well-known technologies may be combined.

[0044] For example, in the above embodiment, the output section 51a outputs a one-pulse voltage, but this is not a limitation and the voltage is not limited to one pulse voltage as long as it can be applied to the connection point P in a superimposed manner. Also, the changeover switch 50 includes a one-pulse boost circuit 52, which boosts the voltage of 5V or the like from the output section 51a to 12V or the like and applies it to the connection point P, but this is not a limitation and the voltage may be applied without being boosted. It goes without saying that the specified voltage applied in this case is a voltage larger than the voltage drop caused by the parasitic diodes BD1 and BD2. [Explanation of symbols]

[0045] 1: Power System 50: Changeover switch (fault detection device) 50a: Fault detection unit (fault detection means) 50V: Voltage application section (voltage application means) 51a: Output section (output means) 51b: Voltage detection unit (voltage detection means) 51c: ON failure determination unit (ON failure determination means) 52:1 pulse boost circuit (boosting means) BD1 to BD3: Parasitic diodes D: Drain terminal (second terminal) L: Load MB: Main battery (first battery) P: Connection point S: Source terminal (first terminal) SB: Sub-battery (second battery) SW1: First switch means SW2: Second switch means SW3: Third switch means

Claims

1. a first switch means having a first terminal connected to a first battery outputting a predetermined voltage and a second terminal connected to a connection point, the first switch means having a parasitic diode for preventing a current from flowing from the second terminal to the first terminal; a second switch means having a first terminal connected to a second battery that outputs the predetermined voltage and a second terminal connected to the connection point, the second switch means having a parasitic diode that blocks current from flowing from the second terminal to the first terminal; a third switch means having a first terminal connected to the load and a second terminal connected to the connection point, the third switch means having a parasitic diode for preventing a current from flowing from the second terminal to the first terminal; a failure detection means for detecting an on-failure of the first switch means and the second switch means, The failure detection means includes: a voltage application means for applying a specified voltage to the connection point in a superimposed manner when the first switch means, the second switch means, and the third switch means are all controlled to be turned off; a voltage detection means for detecting a voltage at the connection point in a state where the voltage is applied by the voltage application means; and an on-failure determination means for determining that at least one of the first switch means and the second switch means has an on-failure when the voltage detected by the voltage detection means exceeds the predetermined voltage and is not equal to or greater than a threshold value set to be less than a value obtained by adding the regulated voltage to the predetermined voltage and subtracting a voltage drop due to a parasitic diode of the first switch means and the second switch means. A fault detection device comprising:

2. The voltage application means includes an output means for outputting a voltage to be applied to the connection point, and a boosting means for boosting the voltage output by the output means.

2. The fault detection device according to claim 1.

3. The output means outputs one pulse voltage.

3. The fault detection device according to claim 2.

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