JP2013038042A - Circuit fault detection device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a circuit fault detection device which can surely detect an open fault in an environment where foreign matter could get mixed in a switch which switches power supply to a drive circuit.SOLUTION: A circuit fault detection device 1 comprises: a drive circuit 10 which supplies power to a load 2a; a main switch 21 which switches power supply to the drive circuit 10 on or off; and a fault determination unit 31 which determines whether there is a fault in the main switch 21. The drive circuit 10 includes a drive switch 13 which switches the electrical continuity of the load 2a and a capacitor 12 which stores charges therein when power is supplied to the drive circuit 10. The fault determination unit 31 changes the drive switch 13 to a closed state for a prescribed time T1 after the main switch 21 is changed to a closed state, thereby making charges stored in the capacitor 12 ejected, and determines whether there is a fault in the main switch 21 on the basis of a voltage value Vb at a ground side terminal of the main switch 21.

Description

  The present invention relates to a circuit failure detection device for detecting a switch failure in a drive circuit.

  There is known a control device that controls a drive circuit using an electromagnetic relay as a switch for switching power supply. Such a control device is applied to, for example, a driving force transmission device or an electric power steering device mounted on a vehicle. Some control devices include a circuit failure detection device that detects failure of an electromagnetic relay when an ignition switch of a vehicle is turned on. As failure detection of an electromagnetic relay, for example, Patent Literature 1 discloses welding detection for detecting a welding state of a contact, and Patent Literature 2 discloses open failure detection for detecting an open failure where a contact does not close. In addition, when the failure of the electromagnetic relay is detected by the circuit failure detection device, the control device attempts to ensure the safety of the entire device by executing fail-safe processing or the like.

JP 2007-26741 A JP-A-60-254530

  By the way, in such a failure detection of the electromagnetic relay, for example, there is a case where, even if foreign matter is mixed between the electrodes of the relay switch, it is instantaneously connected when switched to the closed state. In such a case, depending on the configuration of the drive circuit, an open failure may be overlooked and erroneously determined as normal.

  The present invention has been made in view of the above problems, and provides a circuit failure detection device capable of reliably detecting an open failure even in an environment where foreign matter may enter a switch that switches power supply to a drive circuit. The purpose is to do.

  In order to solve the above-described problem, according to a circuit detection device according to claim 1, a drive circuit that supplies power to a load provided in an electric circuit between a power supply and a ground, and supply of power to the drive circuit A main switch that switches between shut-off and a failure determination unit that determines the presence or absence of a failure of the main switch, and the drive circuit is connected in series with the load, and a drive switch that switches a conduction state of the load, A capacitor that is connected in parallel with the load and stores electric charge when electric power is supplied to the drive circuit, and the failure determination unit keeps the drive switch constant after the main switch is switched to a closed state. The electric charge stored in the capacitor is released by switching to the closed state for a time, and the main switch It determines the presence or absence of disabilities.

  According to a second aspect of the present invention, in the first aspect, the main switch is a relay switch that constitutes an electromagnetic relay that opens and closes according to the excitation state of the coil, and is fixed when switching from the open state to the closed state. A wiping mechanism is provided that moves the contact between both electrodes while the movable electrode is electrically connected to the electrode.

  According to the first aspect of the present invention, the failure determination unit releases the electric charge stored in the capacitor of the drive circuit after the main switch, which is a failure determination target, is switched to the closed state. Then, the determination is made based on the voltage value at the ground side terminal of the main switch. Here, when the main switch is operated in an environment in which foreign matter may be mixed, if foreign matter enters between the electrodes of the main switch, an open failure that does not conduct even when switched to the closed state may occur. However, the conventional failure detection apparatus sometimes overlooks such an open failure. One reason for this is that depending on the shape and size of the contaminated foreign matter, the main switch may be turned on momentarily when it is switched to the closed state, and the instantaneously supplied power is detected. As mentioned.

  Furthermore, it has been found that another cause is due to the action of the capacitor of the drive circuit. That is, when the drive circuit has a capacitor, the capacitor stores electric charge by the instantaneously supplied power. Then, when the voltage at the ground side terminal of the main switch that has become non-conductive thereafter is detected, a predetermined voltage value is detected by the charge discharged from the capacitor. If this happens, if this voltage value exceeds the threshold for determining the presence or absence of an open fault, the main switch may be erroneously determined to be conducting normally, and an open fault may be overlooked. It was.

  Therefore, in the present invention, as described above, the drive switch of the drive circuit is switched to the closed state for a certain time before detecting the voltage value at the ground side terminal of the main switch switched to the closed state. Then, before the voltage value is detected, the charge stored in the capacitor is discharged in advance. Here, in the case of an open failure that conducts instantaneously when the main switch is switched to the closed state, the capacitor charge is sufficiently removed, so that the correct voltage value is not affected by the action of the capacitor. Can be detected. Thereby, it is possible to detect a failure that has not been detected by the conventional failure detection device. The “certain time” for switching the drive switch to the closed state is a predetermined time, and may be set by the capacitance of a capacitor provided in the drive circuit.

  On the other hand, if an open failure that does not cause the main switch to conduct even momentarily has occurred, no charge is stored in the capacitor, so the failure determination can be performed as in the conventional case. Similarly, whether or not the main switch has failed can be more reliably determined even when electric charges are stored in the capacitor due to other factors, such as when the drive circuit is repeatedly activated in a short time. When the main switch is in a normal state where no open failure has occurred, the main switch is switched to the closed state, so even if power is supplied to the drive circuit, the charge is stored again in the capacitor. . Since the voltage is normally applied to the ground side terminal of the main switch, it is confirmed that the main switch is conductive based on the voltage value at the terminal, and it can be determined that there is no failure in the main switch.

  According to the invention which concerns on Claim 2, the main switch is made into the relay switch which comprises an electromagnetic relay. Here, an electromagnetic relay that opens and closes by mechanically operating an electrode according to the excitation state of the coil may cause an inrush current larger than a steady current to flow due to the configuration of the drive circuit when the electrode is closed. is there. As a result, arc discharge may occur at the contact between the electrodes of the relay switch. If this arc discharge repeatedly occurs, there is a risk that defects such as welding occur at the contact of the relay switch. Therefore, in addition to improving durability by changing the shape and material of the electrode, a relay switch that prevents contact welding by a wiping mechanism is known. The wiping mechanism is a mechanism for moving (wiping) a contact between the electrodes while the movable electrode is brought close to and electrically connected to the fixed electrode. As a result, welding between the contacts is prevented and contact reliability between the electrodes is improved.

  However, in an electromagnetic relay having such a wiping mechanism, if foreign matter enters the relay switch, the foreign matter may be caught between both electrodes during wiping, resulting in an open failure. Then, power is supplied to the drive circuit during a period from when the electrodes are first electrically connected to when the foreign object is caught. As a result, electric charge is stored in the capacitor of the drive circuit, and a predetermined voltage value is detected by the electric charge released from the capacitor in subsequent failure determination, causing erroneous determination. On the other hand, in the present invention, before the voltage value at the ground side terminal of the relay switch is detected, the electric charge stored in the capacitor is discharged in advance, so that an open failure that bites a foreign object during wiping is also ensured. Can be detected. Thus, it is particularly useful to apply the present invention to an electromagnetic relay having a wiping mechanism.

It is a block diagram which shows the structure of the circuit failure detection apparatus in embodiment. It is a schematic diagram which shows the wiping of an electromagnetic relay It is a flowchart which shows the process at the time of starting of a drive transmission apparatus. It is a flowchart which shows the process of an open failure detection of an electromagnetic relay. It is a time chart at the time of the charge removal process of a capacitor | condenser.

  Hereinafter, an embodiment in which a circuit failure detection device of the present invention is embodied in a vehicle control device 1 will be described with reference to the drawings.

<Embodiment>
(Configuration of control device)
The control device 1 is a device that controls the driving force distribution of the driving force transmission device 2 mounted on the vehicle. The driving force transmission device 2 is a joint device that is provided on a propeller shaft that connects a front and rear driving shafts of a vehicle (not shown) and has a wet electromagnetic clutch mechanism. The electromagnetic clutch mechanism includes a plurality of clutch plates that can be engaged with each other by friction, and an electromagnetic coil 2a. In the driving force transmission device 2, a current according to a control signal from the control device 1 is supplied to the electromagnetic coil 2a, and the clutch plates engage with each other to transmit the driving force. The vehicle is four-wheel drive when the driving force transmission device 2 is engaged with the clutch, and is two-wheeled when the driving force transmission device 2 is disengaged from the clutch. Further, the engaging force of each clutch plate varies according to the amount of current supplied to the electromagnetic coil 2a. Therefore, the control device 1 enables variable control of the driving force distribution in the driving force transmission device 2 by the control signal.

  The battery 3 is an in-vehicle battery, and is a DC power source that supplies power to the driving force transmission device 2 via the control device 1 at a predetermined voltage. The ignition switch 4 is a vehicle power switch that switches between supply and interruption of the power of the battery 3 to the control device 1. When the ignition switch 4 is turned on, power is supplied to the control device 1 and various control programs are executed.

  Moreover, the control apparatus 1 has the drive circuit 10, the electromagnetic relay 20, and ECU30, as shown in FIG. The drive circuit 10 is a circuit that supplies power to the electromagnetic coil 2a of the drive force transmission device 2 that is a load provided on an electric path between the battery 3 that is a power source and the ground. The drive circuit 10 includes a coil 11, a capacitor 12, a transistor 13, and a diode 14. The coil 11 and the capacitor 12 constitute a filter circuit that removes noise in the drive circuit 10. The capacitor 12 is connected in parallel with the electromagnetic coil 2 a of the driving force transmission device 2 that is a load, and stores electric charge when electric power is supplied to the driving circuit 10.

  The transistor 13 is a drive switch that is connected in series with the electromagnetic coil 2a of the driving force transmission device 2 that is a load and switches the conduction state of the electromagnetic coil 2a. The transistor 13 is on / off controlled by a control signal from the ECU 30. The diode 14 is connected in parallel with the electromagnetic coil 2a, and protects the transistor 13 and the like from high voltage generated in the inductive electromagnetic coil 2a when power to the drive circuit 10 is cut off.

  As shown in FIG. 2, the electromagnetic relay 20 includes a relay switch 21 and a coil 22. The relay switch 21 is a switch that opens and closes according to the excitation state of the coil 22 and switches between supply and interruption of power to the drive circuit 10. Thus, the relay switch 21 constitutes the electromagnetic relay 20 that is operated by the coil 22 and corresponds to the “main switch” of the present invention. In addition, the relay switch 21 forms a wiping mechanism by the fixed electrode 23 connected to the drive circuit 10 and the movable electrode 24 connected to the power source 3. As shown in FIG. 2, the wiping mechanism further moves the contact between the electrodes while the movable electrode 24 is brought close to and electrically connected to the fixed electrode 23 when switching from the open state to the closed state. (Wiping) mechanism.

  Here, when the electromagnetic relay 20 is switched to the closed state, an inrush current larger than the steady current may flow due to the configuration of the drive circuit 10 or the like. As a result, arc discharge may occur at the contact between the electrodes of the relay switch 21. If this arc discharge is repeatedly generated, there is a possibility that problems such as welding occur at the contact of the relay switch 21. For this reason, in the present embodiment, the above-described wiping mechanism is used to prevent welding at the contacts and to improve contact reliability between the electrodes.

  The ECU 30 is a microcomputer that includes a CPU that performs arithmetic processing and RAM, ROM, and the like as storage devices. The ECU 30 inputs signals from sensors such as the engine speed, vehicle speed, and accelerator pedal sensor, and acquires various vehicle information. The ECU 30 calculates the driving force distribution in the driving force transmission device 2 based on the vehicle information and outputs a control signal to the transistor 13 of the driving circuit 10. The driving force transmission device 2 supplies current to the electromagnetic coil 2a in accordance with the on / off control of the transistor 13, and distributes a predetermined driving force to the front and rear wheels.

  Further, the ECU 30 outputs a control signal to the electromagnetic relay 20 to switch the excitation state and the non-excitation state of the coil 22. As shown in FIG. 1, the ECU 30 inputs a voltage value Vb at the ground side terminal of the electromagnetic relay 20. The failure determination unit 31 of the ECU 30 executes processing for determining whether or not the relay switch 21 of the electromagnetic relay 20 has a failure based on the input voltage value Vb. Details of the failure detection will be described later.

(Electromagnetic relay failure detection)
The failure detection of the electromagnetic relay 20 by the failure determination unit 31 of the ECU 30 will be described with reference to FIG. First, when electric power is supplied to the ECU 30 whose ignition switch 4 is turned on, the ECU 30 performs initial settings such as a check process for RAM, ROM, etc. (S10).

  Subsequently, the failure determination unit 31 performs welding detection of the relay switch 21 for the failure of the electromagnetic relay 20 (S20). In the welding detection, first, the ECU 30 outputs a control signal to the electromagnetic relay 20 so as to be in an open state, and after waiting for a predetermined time, the transistor 13 is turned on to measure the voltage value Vb. Then, it is determined whether or not welding has occurred in the relay switch 21 by comparing the voltage value Vb with a preset threshold value Vs (S30). When the voltage value Vb is larger than the threshold value Vs (S30: Yes), it is determined that welding has occurred because the electromagnetic relay 20 is in an open state, and the fail-safe process is performed. Is executed (S80). On the other hand, when the voltage value Vb is equal to or less than the threshold value Vs (S30: No), it is determined that no welding has occurred since the electromagnetic relay 20 is not conductive.

  When welding is not detected in the electromagnetic relay 20, the open failure of the relay switch 21 is subsequently detected (S40). Details of this open failure detection will be described later. If an open failure has occurred (S50: Yes), fail-safe processing is executed (S80). On the other hand, if no open failure has occurred (S50: No), no welding or open failure has occurred in the electromagnetic relay 20, and therefore the drive circuit 10 is allowed to start (S60). And the control apparatus 1 performs normal control of the driving force transmission apparatus 2 (S70). That is, the control device 1 performs control so as to distribute a predetermined driving force to the front and rear wheels based on the acquired various vehicle information.

  Here, the open failure detection in S40 will be described in detail with reference to FIG. During the open failure detection process, the transistor 13 and the electromagnetic relay 20 of the drive circuit 10 are both off (open) as an initial state. First, as shown in FIG. 4, the ECU 30 outputs a control signal to the electromagnetic relay 20, and switches the relay switch 21 to the open state (S401). Thereafter, the ECU 30 resets a timer (not shown) to switch the transistor 13 to the closed state (S402) and starts the timer. Thereby, the electromagnetic coil 2a of the driving force transmission device 2 is in a conductive state.

  Then, the ECU 30 compares the value of the timer with a certain time T1 (S403), and when the certain time T1 has not elapsed (S403: No), the ECU 30 maintains the transistor 13 in a closed state and stands by. The ECU 30 returns the transistor 13 to the open state (S404) when a predetermined time T1 has elapsed since the transistor 13 was switched to the closed state (S403: Yes). Thereby, the electromagnetic coil 2a of the driving force transmission device 2 is not in a conductive state.

  In S402 to S404, the electromagnetic coil 2a of the driving force transmission device 2 is in a conductive state by closing the transistor 13 for a certain time T1. This series of processes is intended to release the charge stored in the capacitor 12 once. Therefore, the “certain time T1” for maintaining the closed state of the transistor 13 is a predetermined time and is appropriately set depending on the capacitance of the capacitor 12.

  Subsequently, the ECU 30 resets and starts the timer again. The failure determination unit 31 receives the voltage value Vb measured at the ground-side terminal of the electromagnetic relay 20 and compares the voltage value Vb with the threshold value Vp to determine whether an open failure has occurred in the relay switch 21. (S405). When the voltage value Vb is larger than the threshold value Vp (S405: Yes), the electromagnetic relay 20 is closed and a voltage exceeding at least the threshold value Vp is applied to the drive circuit 10 so that no open failure has occurred. And the open failure detection process is terminated.

  On the other hand, if the voltage value Vb is less than or equal to the threshold value Vp (S405: No), it is determined whether a certain time T2 has elapsed since the timer was started (S406). If the predetermined time T2 has not elapsed (S406: No), the failure determination unit 31 inputs the voltage value Vb measured again and compares the voltage value Vb with the threshold value Vp again (S405). The failure determination unit 31 repeats this until a predetermined time T2 elapses (S406: Yes). If the voltage value Vb exceeds the threshold value Vp during this fixed time T2, it is determined that no open failure has occurred. If the voltage value Vb is always equal to or less than the threshold value Vp, the electromagnetic relay 20 is closed. Despite being set, it is not conducting and there is a risk of an open failure.

  Here, the open failure of the relay switch 21 is considered to be caused by, for example, the biting of an insulating material or the formation of an oxide film on the electrode. Therefore, the ECU 30 opens and closes the relay switch 21 and performs N retries in order to try to eliminate the cause of the open failure by mechanical operation at the contact. That is, the ECU 30 switches the electromagnetic relay 20 to the open state (S407) and increments a counter (not shown) (S408). Then, the ECU 30 compares the counter with the retry upper limit value N (S409). If the counter has not reached N times (S409: Yes), a control signal is output to the electromagnetic relay 20, and the relay switch 21 is switched to the open state (S401). Then, the ECU 30 resets and starts the timer again, and repeats S401 to S409.

  If the voltage value Vb exceeds the threshold value Vp during N retries, it is determined that no open failure has occurred. If the voltage value Vb is always equal to or less than the threshold value Vp, the electromagnetic relay 20 is closed. However, it is determined that an open failure has occurred (S410). And the failure determination part 31 memorize | stores the determination result about the presence or absence of an open failure, and complete | finishes a process. The ECU 30 determines whether to perform fail-safe processing based on the stored determination result (S50).

(Operation and effect of the embodiment)
The operation and effect of the control device 1 having the above-described configuration will be described with reference to FIG. Here, in the processing of S401 to S406 in the open failure detection by the failure determination unit 31, the control signals and voltage values of the respective units are shown in the time chart of FIG. For example, when the relay switch 21 is normal, the voltage value Vb at the ground side terminal of the electromagnetic relay 20 is used to switch the electromagnetic relay 20 to the closed state, as indicated by the thin solid line L1 at the bottom of FIG. As a result, the voltage becomes a predetermined voltage value and the state is maintained.

  Further, when the relay switch 21 is operated in an environment in which foreign matter may be mixed, foreign matter may be mixed between the electrodes of the relay switch 21 and an open failure may occur. When the mixed foreign matter adheres to the electrode of the relay switch 21, the relay switch 21 is not conductive at all. However, depending on the shape and size of the mixed foreign matter, the relay switch 21 is switched to the closed state. May conduct momentarily. Thereafter, the relay switch 21 becomes non-conductive again due to a foreign substance, but the capacitor 12 stores electric charge instantaneously by the electric power supplied to the drive circuit 10. Further, since the capacitor 12 is located on the ground side of the electromagnetic relay 20, when the voltage value Vb at the ground side terminal of the electromagnetic relay 20 is measured, there is a possibility that the charge stored in the capacitor 12 may affect the measured value. is there. Then, it may become a factor of erroneous determination in failure determination based on the voltage value Vb.

  Therefore, the failure determination unit 31 closes the transistor 13 for a predetermined time T1 in S402 to S404 after the relay switch 21 to be determined is switched to the closed state during the open failure detection process (S401). The electric charge stored in the capacitor 12 is released by switching. After that, the failure determination is made based on the voltage value Vb at the ground side terminal of the relay switch 21. As a result, the voltage value Vb is instantaneously conducted with the switching to the closed state of the electromagnetic relay 20 and rises to a predetermined voltage value as shown by the bottom solid line L2 in FIG. 12 and is reduced to 0 [V] around a certain time T1.

  Thereby, the voltage value Vb measured during the predetermined time T2 in S405 and S406 can be correctly detected without being influenced by the action of the capacitor 12 even in the case of the open failure due to the foreign matter as described above. . Therefore, an open failure can be detected more reliably. Similarly, even when the electric charge is stored in the capacitor 12 due to other factors, such as the activation of the drive circuit 10 being repeated in a short time, the presence or absence of the failure of the relay switch 21 can be determined more reliably. Further, since it is not necessary to consider the electric charge of the capacitor 12, the threshold value Vp in the failure determination can be set smaller than the conventional one. Therefore, it is possible to improve the accuracy of failure determination.

  Here, for reference, a case where the same foreign matter is mixed in the conventional failure detection apparatus will be described. At this time, as indicated by the lowermost broken line L3 in FIG. 5, the voltage value Vb instantaneously conducts as the electromagnetic relay 20 is switched to the closed state and rises to a predetermined voltage value. The voltage value Vb gradually decreases as 12 gradually discharges the electric charge. When the voltage value Vb is compared with the threshold value Vp before the voltage value Vb sufficiently drops, it is erroneously determined that no open failure has occurred because the voltage value Vb is larger than the threshold value Vp. As described above, in the conventional failure detection apparatus, an open failure due to the mixing of foreign matter may be overlooked. On the other hand, the control device 1 of the present embodiment can reliably determine the presence or absence of a failure by removing the charge from the capacitor 12.

  Further, the electromagnetic relay 20 is configured to prevent welding between the contacts and improve contact reliability between the electrodes by a wiping mechanism. However, in the electromagnetic relay 20 having such a wiping mechanism, when foreign matter enters the relay switch 21, foreign matter may be caught between both electrodes during wiping, resulting in an open failure. Then, electric power is supplied to the drive circuit 10 and electric charge is stored in the capacitor 12 during a period from when the electrodes are first electrically connected to when the foreign object is caught. On the other hand, in the present embodiment, by performing the charge removal processing of the capacitor 12 in advance before measuring the voltage value Vb, it is possible to reliably detect an open failure such as a foreign matter being caught during wiping. . In this way, when the electromagnetic relay 20 having the wiping mechanism is a target for failure determination, the charge removal processing of the capacitor 12 is particularly useful.

<Modification of Embodiment>
In the present embodiment, the driving circuit 10 is exemplified as a circuit that supplies power to the driving force transmission device 2. In addition, for example, the present invention may be applied to a circuit for driving an electric power steering device or the like. Further, the transistor 13 is opened and closed as a drive switch in order to perform the charge removal processing of the capacitor 12. On the other hand, the drive circuit 10 may have a configuration in which a dedicated switch for performing charge removal processing of the capacitor 12 is provided.

  Furthermore, in this embodiment, the main switch that is the target of failure determination is the relay switch 21 of the electromagnetic relay 20. On the other hand, any switching element that switches between supply and interruption of power to the drive circuit 10 may be used. In addition, any configuration in the above-described modified embodiment has the same effect as that of the present embodiment.

1: Control device (circuit failure detection device) 2: Driving force transmission device 2a: Electromagnetic coil (load) 3: Battery (power source) 4: Ignition switch 10: Drive circuit 11: Coil 12: Capacitor 13: Transistor (drive switch), 14: Diode 20: Electromagnetic relay, 21: Relay switch (main switch), 22: Coil 23: Fixed electrode, 24: Movable electrode 30: ECU, 31: Failure determination unit

Claims (2)

A drive circuit for supplying power to a load provided in an electric circuit between the power source and the ground;
A main switch for switching between power supply and cut-off to the drive circuit;
A failure determination unit that determines the presence or absence of a failure of the main switch,
The drive circuit is
A drive switch connected in series with the load and switching a conduction state of the load;
A capacitor that is connected in parallel with the load and stores electric charge when power is supplied to the drive circuit;
The failure determination unit switches the drive switch to a closed state for a certain period of time after the main switch is switched to a closed state to release the charge stored in the capacitor, and a voltage value at the ground side terminal of the main switch A circuit failure detection device for determining whether or not there is a failure in the main switch based on the above. In claim 1,
The main switch is
A relay switch that constitutes an electromagnetic relay that opens and closes according to the excitation state of the coil,
A circuit failure detection device having a wiping mechanism for moving a contact between both electrodes while the movable electrode is electrically connected to the fixed electrode when switching from the open state to the closed state.

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