JP2009204558A - Capacitance diagnosis method for backup capacitor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a capacitance diagnosis method for backup capacitor for diagnosing the capacitance of the backup capacitor, in a short time. <P>SOLUTION: This capacitance diagnosis method includes a first step of increasing the voltage to a target increase voltage, based on the voltage of a power supply and charging the back up capacitor; a second step of determining whether the voltage is stable within an increased voltage defined range; a third step of stopping the voltage increase and starting discharge to a predetermined load, when it is determined in the second step that the voltage is stable within the increased voltage defined range; a fourth step of acquiring the first voltage of the back up capacitor, at starting of the discharge in the third step; a fifth step of acquiring the second voltage of the back up capacitor at a time, after the lapse of a first certain time after start of the discharge; a sixth step of calculating the potential difference between a first voltage and a second voltage, and a seventh step of comparing the potential difference calculated in the sixth step with a threshold potential difference and determining whether the capacitance of the backup capacitor is normal. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a backup capacitor capacity diagnosis method for diagnosing the capacity of a backup capacitor that backs up a power source for operating an airbag device.

  In order to protect an occupant from a secondary collision, an air bag device is installed in the vehicle as an occupant protection device. The airbag device detects the impact caused by the collision and deploys the airbag to protect the passengers in the vehicle. If the airbag device power supply is damaged by the collision, an ignition circuit (squib) of the airbag device is used. ), The squib does not ignite and the airbag cannot be deployed. Therefore, the occupant protection device is provided with a backup capacitor to back up the power supply, and even if the power supply is damaged in the event of a collision by charging the backup capacitor to a voltage necessary for the squib to ignite for a predetermined time. The power required for deploying the airbag is supplied from the backup capacitor.

  However, if the capacity of the backup capacitor is insufficient due to manufacturing defects or aging deterioration, it is not possible to charge the charge necessary to deploy the airbag. For example, when a malfunction related to the backup capacitor occurs, a warning lamp is lit to notify the passenger of the malfunction of the backup capacitor.

As a prior art for diagnosing the capacity of a backup capacitor, there is Patent Document 1. In Patent Document 1, after charging a backup capacitor to a certain voltage, the discharge of the backup capacitor is started, and the failure diagnosis time until the voltage drop from the start of discharge becomes a certain potential difference is measured. Based on this, it is described that it is determined whether or not the capacity of the backup capacitor is normal.
JP 2003-127822 A

  However, in Patent Document 1, the failure diagnosis time from when the voltage of the backup capacitor starts to discharge until the voltage drops to a constant potential difference is measured. However, the failure diagnosis time varies depending on the capacity of the backup capacitor. The type of airbag device varies depending on the type of vehicle on which it is installed, and the capacity of the backup capacitor required to ignite the squib and deploy the airbag also varies depending on the vehicle type. It is necessary to use a high-performance capacitor having a large capacity. Further, when discharging the backup capacitor, the load of the acceleration sensor or the like mounted on the airbag device differs depending on the vehicle type, so that the load current is different and the failure diagnosis time is different.

  For this reason, there is a problem in that a backup capacitor with higher backup performance has a longer failure diagnosis time and delays the start of collision determination performed after failure diagnosis. For example, in the case of a high-performance backup capacitor having a capacity of 9400 μF, the fault diagnosis time takes a long time of 1.5 seconds at the maximum. Therefore, it is necessary to establish a system startup time schedule assuming the longest failure diagnosis time as the diagnosis time, and there is a problem that the collision start determination is uniformly delayed.

  SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and a backup capacitor capacity diagnosis method capable of performing a capacity diagnosis of a backup capacitor in a fixed short time without depending on the capacity and load of the backup capacitor. The purpose is to provide.

  According to the first aspect of the present invention, there is provided a method for diagnosing a capacity of a backup capacitor for backing up a power source for operating an airbag device, wherein when a voltage is supplied from the power source, the capacitance is determined based on the voltage of the power source. The first step of boosting to the target boost voltage and charging the backup capacitor, the second step of determining whether or not the voltage of the backup capacitor is stable within the boost voltage regulation range, and the second step When it is determined that the voltage of the backup capacitor is stable within the specified boosted voltage range, the step of stopping the boosting and starting discharging the charge of the backup capacitor to a predetermined load; and the third step The first of the backup capacitor at the time when the discharge of the charge of the backup capacitor starts A fourth step of acquiring a pressure, a fifth step of acquiring a second voltage of the backup capacitor at a time when a first fixed time has elapsed since the discharge of the backup capacitor was started, the first voltage and the second A sixth step of calculating a potential difference from the voltage; a seventh step of comparing the potential difference calculated in the sixth step with a threshold potential difference to determine whether or not the capacity of the backup capacitor is normal; A method of diagnosing the capacity of a backup capacitor having the above is provided.

  According to a second aspect of the present invention, in the first aspect of the invention, the second step includes a second constant time after the voltage of the backup capacitor reaches a predetermined voltage within the boost voltage regulation range, Provided is a capacity diagnosis method for a backup capacitor that determines that the backup capacitor is stable when the boost voltage is within a specified range.

  According to a third aspect of the present invention, in the first aspect of the invention, the voltage of the backup capacitor is stabilized by the second step even after a third fixed time has elapsed since the voltage was supplied from the power source. If it cannot be determined that the backup capacitor is present, a backup capacitor capacitance diagnosis method further comprising a step of stopping diagnosis of the backup capacitor and notifying the fact.

  According to a fourth aspect of the present invention, in the first aspect of the invention, the threshold potential difference is a voltage within the boost voltage regulation range as a discharge start voltage, and the discharge start voltage and an allowable capacity lower limit of the backup capacitor. A capacity diagnosis method for a backup capacitor that is set based on a potential difference between the capacitor having a value and the voltage of the capacitor when the first constant time elapses when the capacitor is discharged under a load resistance of the predetermined load. Provided.

  According to the first aspect of the present invention, when the voltage of the backup capacitor is stabilized, the boosting of the backup capacitor is stopped, the charge of the backup capacitor is discharged for the first fixed time, and the backup capacitor until the first fixed time elapses. Based on the potential difference between the backup capacitor, it is determined whether or not the capacity of the backup capacitor is normal. Therefore, the capacity diagnosis time of the backup capacitor becomes a fixed time without depending on the backup capacitor or load resistance, and the diagnosis time is shortened. be able to.

  According to the second aspect of the present invention, it is determined that the backup capacitor is stable when the voltage of the backup capacitor is within the boost voltage regulation range for the second predetermined time after the voltage of the backup capacitor reaches the predetermined voltage in the boost voltage regulation range. Even if the voltage of the backup capacitor slightly fluctuates within the specified boosted voltage range, the backup capacitor can be started to be discharged, and the diagnosis time can be shortened.

  According to the third aspect of the present invention, when the backup capacitor whose boosted voltage changes drastically outside the boost specified voltage range is not connected or when the voltage of the backup capacitor does not reach the boost voltage specified range due to a malfunction of the boost circuit. Thus, it is possible to detect that the voltage of the backup capacitor is not stable, stop the diagnosis of the backup capacitor, and notify the passenger to that effect.

  According to the fourth aspect of the present invention, when the voltage within the specified boosted voltage range is set as the discharge start voltage, the capacitor having the lower limit value of the allowable capacity of the backup capacitor and the capacitor is discharged under the load resistance of the predetermined load. 1 The threshold voltage difference is set based on the capacitor voltage when a certain period of time has passed, so that the lower limit of the allowable capacity is guaranteed, so even if there is a change in the load resistance or the backup capacitor discharge start voltage, It can be determined whether or not the capacity of the backup capacitor is normal.

  FIG. 1 is a schematic configuration diagram of a diagnostic apparatus for carrying out a capacity diagnostic method for a backup capacitor according to an embodiment of the present invention. As shown in FIG. 1, the capacity diagnosis device for a backup capacitor includes diodes D1 and D2, a smoothing capacitor C0, a booster circuit 2, a voltage sensor 4, a diode D3, an A / D converter 6, a step-down circuit 7, a CPU 8, and a squib 10. It comprises.

  The diode D1 is a diode for blocking a reverse current from the backup capacitor C1, and has an anode connected to the terminal VA and a cathode connected to the CPU 8 and the squib 10 through the step-down circuit 7. The terminal VA is connected to the positive electrode of a battery (for example, a 13.5 V battery) B through an ignition switch IG_SW.

  The diode D2 is a diode for blocking a reverse current from the smoothing capacitor C0, and has an anode connected to the terminal VB and a cathode connected to the positive electrode of the smoothing capacitor C0 and one end of the inductor L. The terminal VB is connected to the positive electrode of the battery B through the ignition switch IG_SW.

  The booster circuit 2 includes an inductor L, resistors R1 and R2, a switching element Q, a diode D3, and a backup capacitor C1. The inductor L has one end connected to the positive electrode of the smoothing capacitor C0 and the cathode of the diode D2, and the other end connected to the drain of the switching element Q and the anode of the diode D3. The resistor R1 has one end connected to the CPU 8 and one end of the resistor R2, and the other end grounded. The resistor R2 has one end connected to one end of the resistor R1 and the CPU 8, and the other end connected to the gate of the switching element Q.

  The switching element Q has a drain connected to the other end of the inductor L and the anode of the diode D3, and a source grounded. A pulse control signal for boosting is input from the CPU 8 to the gate through the resistor R2, and the switching element Q is turned ON / OFF under the control of the CPU 8. The anode of the diode D3 is connected to the other end of the inductor L and the drain of the switching element Q, and the cathode is connected to the positive electrode of the backup capacitor C1 and the anode of the diode D4. The backup capacitor C1 has a positive electrode connected to the cathode of the diode D3 and an anode of the diode D4, and a negative electrode grounded.

  The operation of the booster circuit 2 is as follows. When the ignition switch IG_SW is turned on, the battery B is connected to the terminal VB, the diodes D2 and D3 are turned on, and the smoothing capacitor C0 and the backup capacitor C1 are charged until they become equal to the voltage of the battery B at the terminal VB. When a high level pulse control signal is input to the switching element Q, the switching element Q is turned ON. When the switching element Q is turned on, a current flows from the terminal VB through the inductor L and the switching element Q.

  When a low level pulse control signal is input to the switching element Q, the switching element Q is turned OFF. When the switching element Q is turned off, the magnetic energy accumulated in the inductor L generates a back electromotive force in the direction in which the other end on the anode side of the diode D3 of the inductor L is positive, boosted, and the diode D3 is turned on. The backup capacitor C1 is charged.

  Assuming that the voltage V1 and the boosted voltage V2 at the terminal VB at this time are given, the boost ratio (= V2 / V1) is ((Ton + Toff) / Toff), and is determined by the duty ratio for turning on / off the switching element Q. Ton is the time during which the switching element Q is ON within the switching period, and Toff is the time during which the switching element Q is OFF within the switching period. The CPU 8 determines the duty ratio so that the voltage of the backup capacitor C1 becomes the target boost voltage, and outputs a pulse control signal for turning on / off the switching element Q to the gate of the switching element Q based on the duty ratio. The boosting operation of the booster circuit 2 is controlled.

  The voltage sensor 4 is connected in parallel to the backup capacitor C1, detects the voltage across the backup capacitor C1 (Vup voltage), and outputs an analog detection signal corresponding to the voltage to the A / D converter 6. The diode D4 is a diode for preventing a reverse current from the terminal VA. The anode is connected to the positive electrode of the backup capacitor C1 and the cathode of the diode D3, and the cathode is connected to the step-down circuit 7 and the squib 10.

  The A / D converter 6 samples the analog detection signal from the voltage sensor 4 at a constant sampling period, converts it to a digital signal of a predetermined bit, and inputs the digital signal to the CPU 8. The step-down circuit 7 steps down the voltage from the diode D4 or D1 to the operating voltage of the CPU 8, and supplies power to the CPU 8. When the voltage of the backup capacitor C1 is boosted by the booster circuit 2 and becomes higher than the voltage of the terminal VA, the diode D1 is reverse-biased and turned OFF, and the voltage is supplied to the step-down circuit 7 from the backup capacitor C1 through the diode D4. . The voltage sensor 4 and the A / D converter 6 are supplied with a voltage from the backup capacitor C1 or the battery B.

  The squib 10 is supplied with power from the backup capacitor C1 through the diode D4 or from the battery B through the diode D1. For this reason, when the battery B to which the terminal VA is connected is damaged at the time of collision, power is supplied from the backup capacitor C1 to the CPU 8 from the step-down circuit 7 through the diode D4 and also to the squib 10. Therefore, even if the battery B is damaged and becomes unusable at the time of a collision, the airbag can be deployed. In addition to the CPU 8 and the squib 10, the backup capacitor C1 includes a front crash sensor for detecting longitudinal acceleration (not shown) for determining a frontal collision and a side collision, a side impact sensor for detecting lateral acceleration, and a longitudinal / lateral acceleration. Power is also supplied to the unit sensor that detects.

  As will be described later, when the ignition switch IG_SW is turned on, the CPU 8 initializes the diagnosis phase for executing the capacity diagnosis of the backup capacitor C1 and the initialization for executing the collision determination, and then performs the backup capacitor When the capacity of C1 is diagnosed and the Vup voltage of the backup capacitor C1 is not stable, a warning lamp indicating that the backup capacitor C1 is not connected is lit, and the capacity of the backup capacitor C1 is below the allowable lower limit value and normal If it is diagnosed, the warning lamp indicating that the capacity of the backup capacitor C1 has decreased is turned on. After the diagnosis of the capacity of the backup capacitor C1, the collision determination is started. When it is determined that the vehicle is a collision, an ignition signal is output to the squib 10 to deploy an airbag (not shown).

  When an ignition signal is output from the CPU 8, the squib 10 is energized and heated by the power supplied from the backup capacitor C1 and the battery B, and ignites the enhancer to burn the gas generating agent. Nitrogen gas generated in the combustion enters the airbag from the inflator, and the airbag is deployed to protect the occupant.

  FIG. 2 is a functional block diagram of the CPU 8 according to the capacity diagnosis of the backup capacitor C1 according to the embodiment of the present invention. As shown in FIG. 2, the functional block includes boost start control means 20, boost stability confirmation means 22, discharge control means 24, potential difference calculation means 26, potential difference comparison means 28, and retry control means 30.

The boost start control means 20 controls the start of the boost operation of the boost circuit 2 for the capacity diagnosis of the backup capacitor C1. When the ignition switch IG_SW is turned on and power is supplied from the terminal VA to the CPU 8, the diagnosis is performed. Transition to phase 0 enters a state in which the diagnosis of the capacity of the backup capacitor C1 is started. Thereafter, in order to start diagnosis in transition to diagnosis phase 1, the voltage at the terminal VB (for example, 13.5 V) and the boost target voltage within the boost voltage regulation range from the boost lower limit voltage V _L to the boost upper limit voltage V _H ( For example, the switching element Q is turned ON / OFF at a duty ratio based on an intermediate voltage 22.5 V between V _L and V _H 2, the booster circuit 2 is operated, and charging of the backup capacitor C 1 is started.

The boosting stability check means 22 boosts the Vup voltage to the boosting lower limit voltage V _L and the boosting upper limit voltage V _H by the boosting operation of the boosting circuit 2 in accordance with the Vup voltage of the backup capacitor C1 output from the A / D converter 6. Whether the voltage is stable within the voltage regulation range, for example, whether the Vup voltage is within the boost voltage regulation range for a certain time after reaching a predetermined voltage within the boost voltage regulation range, for example, the boost lower limit voltage V _L Whether or not the Vup voltage is a stable voltage is determined based on whether or not, and if the Vup voltage is a stable voltage, a warning lamp indicating that the backup capacitor C1 is poorly connected or the like is turned on.

When the Vup voltage is not stable, the Vup voltage of the backup capacitor C1 does not reach the boosted voltage specified range due to the connection failure of the backup capacitor C1 due to the Vup voltage fluctuating beyond the specified boosted voltage range or a failure of the booster circuit 2. In this case, since the air bag device cannot be operated normally by the backup capacitor C1, a warning lamp indicating that fact is turned on. It is determined whether the Vup voltage is a stable voltage depending on whether the Vup voltage is within the specified boost voltage range for a certain time after the Vup voltage becomes the boost lower limit voltage V _L. In the case of fluctuation within the range, the capacity diagnosis of the backup capacitor C1 can be started, and erroneous determination due to disturbance such as noise can be avoided.

  When the boost control confirmation unit 22 confirms that the Vup voltage is a stable voltage, the discharge control unit 24 transitions to the diagnosis phase 2 and turns off the switching element Q, and performs the boost operation of the boost circuit 2 for a certain time ( For example, 50 msec) is stopped, and the discharge time of the backup capacitor C1 is controlled.

  Under the control of the discharge control means 24, the potential difference calculating means 26 samples the output of the A / D converter 6 at the time when the discharge of the backup capacitor C1 is started as the discharge start voltage Vupst, and for a predetermined time (for example, 50 msec) The output of the A / D converter 6 at the elapsed time is sampled as the discharge end voltage Vup50. Then, the potential difference dVup is calculated from the following equation (1).

dVup = Vupst−Vup50 (1)
The potential difference comparing unit 28 determines whether or not the potential difference dVup calculated by the potential difference calculating unit 26 is smaller than the threshold potential difference dVth. If the potential difference dVth is smaller than the threshold potential difference dVth, the backup capacitor C1 has an allowable lower limit capacity. It is set that the diagnosis result is normal with a capacity exceeding that, and the process proceeds to an end phase to operate the booster circuit 2 to boost the backup capacitor C1 to the target boost voltage (22.5 V). If the potential difference dVup is greater than or equal to the threshold potential difference Vth, it is set that the diagnosis result is abnormal.

  The threshold potential difference dVth is set as follows. Assuming that the voltage at the time (t = 0) at which discharge of the backup capacitor C1 is started is V0, the voltage V (t) of the backup capacitor C1 after t seconds is expressed by Expression (2).

V (t) = V0 × exp (−t / RC) (2)
Here, R is a load resistance of the CPU 8 or the like that is fed by the backup capacitor C1, and C is the total capacity of the backup capacitor C1.

  When V0 is a voltage within the specified boosted voltage range and C is the entire allowable lower limit capacitance value of the backup capacitor C1, the potential difference (V0−V (50 msec)) in the discharge period (50 msec) is calculated from the equation (2). . From the voltage drop of the capacitor during the discharge period (50 msec) when V0 is changed within the specified boosted voltage range and the load resistance is changed due to a temperature change or the like, the capacity of the backup capacitor C1 is greater than or equal to the allowable lower limit capacity. The threshold potential difference dVth is set so as to be guaranteed.

  Since the voltage (for example, 19 V or more) in the discharge period of the backup capacitor C1 is higher than the voltage (13.5 V) of the terminal VA, the diode D1 is reverse-biased and turned off, and the diode D4 is passed from the backup capacitor C1 through the step-down circuit. 7 is supplied to the CPU 8.

  The configuration of the airbag device differs depending on the vehicle type on which the backup capacitor failure diagnosis program is installed, and the allowable lower limit capacity and load resistance R of the backup capacitor C1 vary. Therefore, the threshold potential difference dVth is such as the backup capacitor C1 and the sensor. Set according to the type of load.

  When the potential difference dVup is larger than the threshold potential difference dVth, the retry control unit 30 determines whether or not the number of diagnoses has been performed up to a predetermined value, for example, 3 times, and the diagnosis is performed up to 3 times. If not, the process proceeds to diagnosis phase 1 and the number of retries is added to boost the booster circuit 2 to the target boost voltage.

  Whether or not the boosted voltage of the backup capacitor C1 is stable is determined by the boost stability confirmation unit 22, the discharge control unit 24 controls the discharge of the backup capacitor C1, and the potential difference calculation unit 26 calculates the potential difference in the discharge period. The potential difference comparison means 28 compares the potential difference in the discharge period with the threshold potential difference dVth to determine whether or not the diagnosis result is normal. If the diagnosis result is abnormal, the process is repeated until the number of diagnoses reaches a predetermined number. If the diagnosis result is abnormal even if the diagnosis is repeated up to a predetermined number of times, it is determined that the backup capacitor C1 is faulty. As described above, if the diagnosis result is abnormal, the retry is performed up to a predetermined number of times due to an error signal included in the discharge start voltage Vupst and the discharge end voltage Vup50 due to noise included in the output of the A / D converter 6. This is because the variation due to the influence and the voltage variation of the battery B is taken into consideration.

  3 to 7 are diagrams illustrating a method of diagnosing the backup capacitor C1 according to the embodiment of the present invention. Hereinafter, a diagnosis method for the backup capacitor C1 will be described with reference to these drawings. When the ignition switch IG_SW is turned on at time t0 in the time charts shown in FIGS. 5 to 7, an initialization program (not shown) is started, and initialization processing for operating the passenger protection program and the failure diagnosis program is executed. Is done. As an initialization process related to the capacity diagnosis of the backup capacitor C1, diagnosis phase 0 is set. After the initialization is completed, the capacity of the backup capacitor C1 is diagnosed (the flow in FIG. 3). The flow of FIG. 3 is executed at a constant cycle.

  In step S2 in FIG. 3, the diagnosis phase is determined. If the diagnosis phase is 0, the process proceeds to step S4. If the diagnosis phase is 1, the process proceeds to step S6. If the diagnosis phase is 2, the process proceeds to step S24. If the diagnosis phase ends, the process ends.

In step S4, an unexecuted state is set in the diagnosis result. The backup capacitor capacity diagnosis start of FIG. 4 is executed when the diagnosis start condition is satisfied. In step S100, 1 is set in the diagnosis phase. In step S102, the booster circuit 2 is operated to start boosting to the target boost voltage (22.5V) within the boost voltage regulation range from the boost lower limit voltage V _L to the boost upper limit voltage V _H. The booster circuit 2 operates at time t1 in FIGS. 5 to 7, the backup capacitor C1 is charged, and the Vup voltage rises. In step S104, a diagnostic timer is started.

If it is determined in step S2 in FIG. 3 that the diagnosis phase is 1, the process proceeds to step S6. In step S6, the output of the A / D converter 6 is sampled to check whether the Vup voltage is stable. For example, as shown in FIG. 5, the Vup voltage is within the boost voltage regulation range V _{L to} V _H for a certain time (t 3 -t 2) from time t 2 when the Vup voltage becomes the boost lower limit voltage V _L. Is determined to be stable. If the Vup voltage becomes boosted voltage specified range V _L ~V _H out, a predetermined time from when Vup voltage is again boosted voltage within a specified range V _L ~V _H, boosting Vup voltage voltage specified range V _L ~ When it is within V _H , it is determined that the Vup voltage is stable.

  In step S8, it is determined whether or not the Vup voltage is stable within the specified boosted voltage range. If a positive determination is made, the process proceeds to step S10. If a negative determination is made, the process proceeds to step S18. In step S10, the Vup voltage output from the A / D converter 6 is sampled and substituted into the discharge start voltage Vupst. For example, it is determined that the Vup voltage is a stable voltage at time t3 in FIGS.

  In step S12, the switching element Q of the booster circuit 2 is turned off to stop the boosting operation. In step S14, 2 is set in the diagnosis phase. In step S16, the boost stop timer is started. When the boosting of the booster circuit 2 is stopped, the backup capacitor C1 starts discharging to the CPU 8 and the like through the step-down circuit 7, and the Vup voltage of the backup capacitor C1 is changed to the load resistance R and the backup as shown in the equation (2). The voltage drops according to the capacitance C of the capacitor C1 and the discharge start voltage Vupst. For example, the backup capacitor C1 starts discharging at time t3 in FIG. 5, and the Vup voltage drops.

If it is determined in step S8 that the voltage Vup is not stable within the specified boost voltage range, it is determined in step S18 whether or not the diagnostic timer has timed out. If a positive determination is made, the process proceeds to step S20. If a negative determination is made, the process ends. In step S20, a timeout is set in the diagnosis result. For example, as shown in FIG. 6A, when the backup capacitor C1 is not connected, the Vup voltage fluctuates violently beyond the boost voltage regulation range V _{L to} V _H , and the Vup voltage is not stabilized. The diagnostic timer times out. As shown in FIG. 6B, even when the Vup voltage does not exceed the boost lower limit voltage V _L due to a failure of the booster circuit 2 or the like, the diagnosis timer times out without being determined that the Vup voltage is stable. In step S22, the diagnosis phase is set to end, and the capacity diagnosis of the backup capacitor C1 is ended.

  If it is determined in step S2 that the diagnosis phase is 2, the process proceeds to step S24. In step S24, it is determined whether or not the boost stop timer has elapsed a predetermined time, for example, 50 msec. If a positive determination is made, the process proceeds to step S26. If a negative determination is made, the process ends. In step S26, the Vup voltage output from the A / D converter 6 at the time when the boost stop timer has elapsed for a predetermined time is sampled and substituted into Vup50.

  In step S28, the voltage Vup50 after the elapse of a fixed time (50 msec) is subtracted from the voltage VupSt at the discharge start time (VupSt−Vup50), and (VupSt−Vup50) is substituted for the potential difference dVup. For example, the potential difference dVup is calculated at time t4 when 50 msec has elapsed from time t3 in FIG.

  In step S30, it is determined whether or not the potential difference dVup is smaller than the threshold potential difference dVth. If a positive determination is made, the process proceeds to step S32. If a negative determination is made, the process proceeds to step S38. In step S32, it is determined that the backup capacitor C1 has a lower limit capacitance value or more, and a normal state is set in the diagnosis result. In step S34, the diagnosis phase is set to end. In step S36, the booster circuit 2 is operated to boost the voltage to the target boosted voltage (22.5V), and the normal operation for executing the collision determination is started. At this time, since it is diagnosed as normal, it is ensured that the backup capacitor C1 has a capacity necessary for ignition of the squib 10, and even when the battery B connected to the terminal VA is damaged by the collision, the backup capacitor C1 is backed up. Power is supplied from the capacitor C1 to the squib 10 and the CPU 8, and the airbag is deployed.

  In step S38, an abnormal state is set in the diagnosis result. In step S40, it is determined whether or not the diagnosis has been performed a predetermined number of times, for example, three times. If a negative determination is made, the process proceeds to step S42. If a positive determination is made, the process proceeds to step S48. For example, if the potential difference dVup1 is greater than the threshold potential difference dVth at time t4 in FIG. 7 and the diagnosis has not been performed three times, the process proceeds to step S42.

In step S42, 1 is set in the diagnosis phase. In step S44, the number of retries is added. In step S46, the booster circuit 2 is operated to boost the voltage to a target boosted voltage (22.5V) within the specified boosted voltage range V _{L to} V _H. In step S2, it is determined that the diagnosis phase is 1, and the process proceeds to step S6. In step S6 to S16, the Vup voltage stability check and discharge start are performed. In steps S24 to S30, the potential difference dVup is calculated, and the potential difference Vth and the threshold potential difference dVth. It is determined whether or not the diagnosis result is normal. When it is determined that the diagnosis result is normal, the diagnosis result is set to normal in steps S32 to S36, and the pressure increase is resumed.

  If it is determined that the diagnosis result is abnormal, it is set in step S38 that the diagnosis result is abnormal. In step S40, it is determined whether or not the diagnosis has been performed a predetermined number of times until the diagnosis result reaches the predetermined number of times. The diagnosis is retried. For example, potential differences dVup2 and dVup3 are calculated at times t7 and t10 by diagnosis through retry.

  In step S48, the diagnosis has been performed a predetermined number of times, but since the potential difference dVup is equal to or greater than the threshold potential difference dVth, failure confirmation is set in the diagnosis result in step S48. In step S50, the diagnosis phase is set to end. In step S52, the booster circuit 2 is operated to restart boosting. For example, the failure is determined at time t10 in FIG. 7, and a failure signal is output.

  According to the present embodiment described above, since the discharge time is set to a fixed time, a diagnosis can be made with a fixed diagnosis time even if the capacitance value or load current of the backup capacitor C1 differs depending on the vehicle type on which the airbag device is mounted. Further, since the discharge time is 50 msec, diagnosis can be performed at high speed. Further, since the discharge time is made constant by eliminating the variation factor of the diagnosis time, there is no influence on the execution timing of the normal operation of the boost circuit and the ignition circuit after the backup capacitor capacity diagnosis and the collision determination. Furthermore, since the discharge time is fixed, the sampling points of the A / D converter are two points, and diagnosis can be realized with simple control.

It is a schematic block diagram of the capacity | capacitance diagnostic apparatus of the backup capacitor of this invention. It is a functional block diagram concerning capacity diagnosis of a backup capacitor according to an embodiment of the present invention. It is a flowchart which shows the capacity | capacitance diagnosis start method of the backup capacitor of this invention. It is a flowchart which shows the capacity | capacitance diagnosis start method of the backup capacitor of this invention. It is a time chart which shows the capacity | capacitance diagnostic method of the backup capacitor of this invention. It is a time chart which shows the capacity | capacitance diagnostic method of the backup capacitor of this invention. It is a time chart which shows the capacity | capacitance diagnostic method of the backup capacitor of this invention.

Explanation of symbols

2 Booster circuit C1 Backup capacitor 6 A / D converter 7 Step-down circuit 8 CPU
10 Squibb 10
20 Boost start control means 22 Boost stability confirmation means 24 Discharge control means 26 Potential difference calculation means 28 Potential difference comparison means 30 Retry control means

Claims (4)

A capacity diagnosis method for a backup capacitor for backing up a power source for operating an airbag device,
When a voltage is supplied from the power source, the first step of boosting to a target boost voltage based on the voltage of the power source and charging the backup capacitor;
A second step of determining whether or not the voltage of the backup capacitor is stable within a specified boost voltage range;
When it is determined in the second step that the voltage of the backup capacitor is stable within the specified boosted voltage range, the boosting is stopped and discharging of the backup capacitor charge to a predetermined load is started. When,
A fourth step of obtaining a first voltage of the backup capacitor at a time when discharging of the charge of the backup capacitor is started in the third step;
A fifth step of obtaining a second voltage of the backup capacitor at a time when a first fixed time has elapsed from a time when discharge of the backup capacitor is started;
A sixth step of calculating a potential difference between the first voltage and the second voltage;
A seventh step of comparing the potential difference calculated in the sixth step with a threshold potential difference to determine whether or not the capacity of the backup capacitor is normal;
A capacity diagnosis method for a backup capacitor comprising   In the second step, the backup capacitor is stable when the voltage of the backup capacitor is within the boost voltage regulation range for a second fixed time after reaching the predetermined voltage within the boost voltage regulation range. The method of diagnosing the capacity of a backup capacitor according to claim 1, wherein   If it is not possible to determine that the voltage of the backup capacitor is stable by the second step even after a third fixed time has elapsed since the voltage was supplied from the power source, the backup capacitor diagnosis is stopped, The method for diagnosing a capacity of a backup capacitor according to claim 1, further comprising a step of notifying the fact.   The threshold potential difference is a voltage within the boost voltage regulation range as a discharge start voltage, and the capacitor is under the discharge start voltage, a capacitor having an allowable capacity lower limit value of the backup capacitor, and a load resistance of the predetermined load. 2. The method for diagnosing a capacity of a backup capacitor according to claim 1, wherein the capacitance diagnosis method is set based on a potential difference with respect to the voltage of the capacitor when the first fixed time has elapsed after discharging.

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