JP3683522B2 - Backup capacitor capacity diagnosis method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a backup capacitor capacity diagnosis method for diagnosing a backup capacitor capacity for backing up a power supply of an in-vehicle airbag device.
[0002]
[Prior art]
Conventionally, an air bag device is installed in a vehicle as an occupant protection device. This air bag device detects an impact caused by a collision and deploys the air bag to protect passengers in the vehicle. For example, if the air bag device power supply is damaged by the collision, the air bag device functions. The air bag will not be deployed. Therefore, this type of occupant protection device is provided with a backup capacitor for backing up the power supply. By charging this backup capacitor, even if the power supply is damaged in the event of a collision, the airbag device The power necessary for the power supply is surely supplied.
[0003]
As described above, the backup capacitor is an important component in terms of safety, but inherently has a property that its capacity deteriorates over time due to a decrease in the electrolyte and the like. Therefore, in this type of system, it is usual to diagnose whether the capacity of the backup capacitor has deteriorated. As a conventional technique for diagnosing the capacity of a backup capacitor, for example, a technique disclosed in Japanese Patent Publication No. 2653744 is known. According to this prior art, the abnormality of this capacitor is diagnosed by measuring the charging time of the capacitor.
[0004]
[Problems to be solved by the invention]
By the way, when the capacity is accurately diagnosed by the charging time of the backup capacitor, it is necessary to keep the charging current constant. However, in general, since the backup capacitor is charged with the boosted voltage, the charging current is not constant due to the surge voltage at the time of boosting. For this reason, according to the prior art in which the charge time during boosting is measured to diagnose the capacity, there is a problem that it is difficult to accurately diagnose the capacity of the backup capacitor. Further, the charging time may be shortened due to the surge voltage at the time of boosting. In such a case, there is a problem that the diagnosis is normal even though the capacity is deteriorated.
[0005]
The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a backup capacitor capacity diagnosis method capable of accurately diagnosing the capacity of a backup capacitor and preventing erroneous diagnosis.
[0006]
[Means for Solving the Problems]
In order to solve the above problems, the present invention has the following configuration.
That is, the backup capacitor capacity diagnosis method according to the present invention is a method for diagnosing the capacity of a backup capacitor for backing up a power supply for starting an air bag device. (A) When the power supply is turned on, the backup capacitor capacity diagnosis method is constant. A first step of prohibiting the boosting operation over a period of time and boosting the backup capacitor to a normal voltage in a quadratic curve; and (b) performing an initial check related to boosting when boosting to the normal voltage. A second step to perform; (c) after the initial check, a third step for boosting in a quadratic curve to a voltage higher than the normal voltage; and (d) from the normal voltage (for example, 20.5 V) a fourth step of maintaining a predetermined time the voltage after boosting quadratically even higher voltage (22.5V), (e) the Tsu a fifth step of linearly discharging at a constant gradient click up capacitor at a substantially constant current (e.g., current consumption will be described later CPU), the process for linearly discharging said backup capacitor (f) at a constant gradient , A discharge time (for example, discharge time Td described later) required for the terminal voltage of the backup capacitor to drop by a predetermined voltage (for example, 1.5 V as a voltage change described later) and a voltage drop are measured . And (g) determining whether or not the capacity of the backup capacitor is normal based on the discharge time and voltage change .
[0007]
Further, in the backup capacitor capacity diagnosis method, by performing the first to sixth steps , it is determined that the capacity of the backup capacitor is not normal as a result of performing an initial diagnosis on the capacity of the backup capacitor. In this case, the first to sixth steps are executed again to diagnose the capacity of the backup capacitor.
Further, in the backup capacitor capacity diagnosis method, if the backup capacitor capacity is determined to be not normal as a result of diagnosing the backup capacitor capacity again, it is determined that the capacity of the backup capacitor has deteriorated. It is characterized by.
Furthermore, in the backup capacitor capacity diagnosis method, a CPU for controlling the operation of the airbag device is connected as a load of the backup capacitor, and the backup capacitor is discharged.
[0008]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings.
In addition, although this invention is applied to an airbag apparatus, it demonstrates focusing on the booster circuit for charging the capacitor | condenser (backup capacitor) for backing up the power supply of an airbag apparatus for convenience.
FIG. 1 shows the configuration of the booster circuit according to this embodiment. In the figure, a power source VA is a power source and is supplied to the ignition circuit side (not shown) of the airbag via a backflow preventing diode D0.
[0009]
The power source VB is a power source provided separately from the above-described power source VA. Between the power source VB and the ignition circuit, a diode D1, a boosting coil L, a diode D2, and a diode D3 are provided. The diodes are connected in order, and the diodes are connected such that the direction from the power supply VB toward the ignition circuit is the forward direction. The power sources VA and VB supply power to electrical devices other than the air bag device. By providing a separate power source in this way, even if one of the power sources breaks down, regular power supply and backup are performed. It is possible to avoid a situation in which both of the power supplies are down.
[0010]
One electrode of a smoothing capacitor C1 is connected to a connection point between the diode D1 and the coil L, and the other electrode of the capacitor C1 is grounded. A current path of a transistor (FET) T is connected between the other end of the coil L and the ground, and a pulse signal PLS from a CPU (not shown) is applied to its gate via a resistor R1. The resistor R1 is for suppressing noise when the transistor T is switched. Further, the gate of the transistor T is grounded via the resistor R1 and the resistor R2. This resistor R2 is for, for example, fixing the transistor T in the OFF state when a situation where the wiring of the pulse signal PLS is disconnected occurs, and avoiding a situation where the power supply VB is short-circuited to the ground.
[0011]
A backup capacitor C2 and a backup capacitor C3 are connected in parallel between the cathode side of the diode D2 and the ground. This is because the backup capacitor is divided into two parts so that the function as the backup capacitor is not lost even if one of them is damaged. In this embodiment, the capacities of the backup capacitors C2 and C3 are 4700 μF, respectively. Therefore, the capacity as a backup capacitor is 9400 μF in total.
[0012]
Although not specifically shown, the airbag apparatus according to this embodiment includes means for detecting boosted voltage Vup (that is, terminal voltages of backup capacitors C2 and C3), and means for detecting this voltage change. Is provided. However, a known technique can be used for these means. Although not shown in FIG. 1, the voltage output to the cathodes of the diodes D0 and D3 is also supplied as a power source for the CPU for controlling the overall operation of the airbag apparatus.
[0013]
According to the charging booster circuit configured as described above, when the transistor T is switched by the pulse signal PLS, the energy accumulated in the coil L is released in the switching process, and the voltage of the anode of the diode D2 rises. As a result, the boosted voltage Vup appears at the cathode of the diode D2, and the backup capacitors C2 and C3 are charged. Normally, power is supplied from the power source VA to the ignition circuit side. For example, when the power supply from the power source VA is interrupted due to an impact at the time of a collision, the charges accumulated in the backup capacitors C2 and C3 are passed through the diode D3. The power supply to the ignition circuit side is maintained. Therefore, even if the power supply VA becomes unusable at the time of a collision, the airbag can be deployed.
[0014]
Next, a diagnosis method for the backup capacitors C2 and C3 according to this embodiment will be described along the flow shown in FIG. 2 and with reference to the waveform diagram shown in FIG.
When an occupant turns on the ignition switch of a vehicle, the airbag device performs a series of self-diagnosis as an initial check for acceleration sensors for detecting impacts, squib resistance for ignition, etc. The capacity diagnosis is performed as one item in the initial check . In this embodiment, description of diagnostics other than the backup capacitor is omitted.
[0015]
First, when the power supply VB is turned on at time t0 shown in FIG. 3, an initial check (self-diagnosis) is first performed as an overall operation, and then an air bag is deployed when a strong impact exceeding a specified value is detected. For normal operation. In the initial check, as will be described in detail below, diagnosis is performed on the capacities of the backup capacitors C2 and C3 shown in FIG.
That is, when the power supply VB is turned on, after the boosting operation is prohibited for a certain period, the boosting operation by the boosting circuit shown in FIG. 1 is started at time t1, and the boosting voltage Vup starts to rise. Then, a CPU (not shown) that controls the overall operation of the airbag device sequentially determines whether or not the current status is a status for performing a capacity diagnosis of the backup capacitor (B / U capacitor check status) (step S1).
[0016]
Here, when the status becomes “00H” at time t2 when the boosted voltage Vup is stabilized at 20.5 V, the CPU executes a determination process to start the capacity diagnosis of the backup capacitor (step S2). Thus, further boosting is performed by the booster circuit shown in FIG. 1 at time t2, and the boosted voltage Vup begins to rise to a voltage higher than the normal boosted voltage of 20.5V. If the status becomes “01H” during the step-up operation, a process for setting the step-up voltage Vup to the check start voltage of 22.5 V is executed (step S3). Thereafter, the boosted voltage Vup reaches 22.5 V and stabilizes.
[0017]
When 500 ms elapses after the boosted voltage Vup reaches 22.5 V and the status becomes “02H”, the boosting operation is stopped and the discharge time measurement process is executed (step S4). At this time, the backup capacitors C2 and C3 are discharged with the CPU as a load. Since the current consumption of the CPU is sufficiently smaller than the switching frequency of the transistor T constituting the booster circuit, the CPU behaves as a load for passing a substantially constant current. For this reason, the terminal voltages (that is, the boosted voltage Vup) of the backup capacitors C2 and C3 are linearly decreased with a constant gradient. The CPU measures the discharge time Td of the backup capacitor.
[0018]
Subsequently, it is determined according to the determination condition shown in FIG. 4 whether the capacities of the backup capacitors C2 and C3 are normal or abnormal based on the discharge time Td.
That is, in the example shown in FIG. 4, when the discharge time Td until the voltage change ΔV of the terminal voltage drops to 1.5 V (predetermined voltage) is 93 ms or more, or the discharge time Td exceeds 1500 ms. However, if the voltage change ΔV is 1.5 V or less, it is determined that the capacities of the backup capacitors C2 and C3 are normal (OK). On the other hand, if the voltage change becomes 1.5 V or more before the discharge time Td is 93 ms, it is determined that the capacities of the backup capacitors C2 and C3 may be deteriorated, and the check start voltage of 22 again. Raise the boost voltage Vup to .5V and measure the discharge time Td again. In any of these two diagnoses, if it is determined that the capacity of the backup capacitor has deteriorated, it is determined that there is an abnormality (NG), and the determination that there is a failure is established. When such a determination is made, the CPU issues a warning to the passenger that there is an abnormality in the airbag device.
[0019]
Next, in step S4, when the time allotted for the initial check has elapsed, or when the backup capacitor diagnosis result is determined to be abnormal, the status becomes “03H”, and a series of backup capacitor diagnosis processes are in progress. (Step S5). Then, the boosted voltage Vup is reset to the specified 20.5V, and the backup capacitors C2 and C3 are charged to the specified voltage (20.5V) while the capacitance is abnormal. In this case, since the backup capacitors C2 and C3 may be deteriorated, there is a possibility that the power supply VA cannot be backed up in the event of a collision. Therefore, the vehicle occupant can fully back up the power supply by replacing the backup capacitors C2 and C3 at an early stage in accordance with the above-described alarm. On the other hand, if it is determined in step S4 that the diagnosis result is normal, the status is “04H”, and the series of backup capacitor diagnosis processing ends normally (step S6). The embodiment has been described above.
[0020]
According to the above-described embodiment, even when the backup capacitors C2 and C3 are manually inserted components, it is possible to check for an open mode failure or a failure due to a decrease in capacitance. In addition, since the backup capacitor is discharged, it is not affected by a surge voltage or the like caused by boosting. Therefore, it becomes possible to diagnose the capacity of the backup capacitor with high accuracy.
[0021]
Although the embodiment of the present invention has been described above, the present invention is not limited to the above-described embodiment, and any design change or the like without departing from the gist of the present invention is included in the present invention. . For example, in the above-described embodiment, the discharge time Td required until the terminal voltage of the backup capacitor drops from 22.5 V to 1.5 V is measured, but this voltage is limited to the extent that necessary accuracy can be obtained. The relationship between the change amount and the discharge time may be set in any way. In the above-described embodiment, when an abnormality is diagnosed in the first diagnosis, the diagnosis is performed again and the diagnosis is performed twice. However, the present invention is not limited to this. May be. Further, if the diagnosis result is normal only once, it is determined that there is no abnormality. However, if all the diagnosis results of a plurality of times are normal, it may be determined that there is no abnormality.
[0022]
【The invention's effect】
As described above, according to the present invention, when the power is turned on, the voltage for charging the backup capacitor is boosted to a voltage higher than the normal voltage, and the backup capacitor is supplied with a substantially constant current. In the process of discharging and discharging the backup capacitor, the discharge time required for the terminal voltage to drop by a predetermined voltage is measured, and based on the discharge time, it is determined whether or not the capacity of the backup capacitor is normal. Therefore, the capacity of the backup capacitor can be diagnosed with high accuracy, and erroneous diagnosis can be prevented.
[Brief description of the drawings]
FIG. 1 is a circuit diagram showing a configuration of a boosting circuit for charging according to an embodiment of the present invention.
FIG. 2 is a flowchart showing a flow of a capacity diagnosis method for a backup capacitor according to the embodiment of the present invention.
FIG. 3 is a waveform diagram for explaining the operation of the charge booster circuit according to the embodiment of the present invention;
FIG. 4 is a view for explaining normal / abnormal judgment conditions in the capacity diagnosis method for a backup capacitor according to the embodiment of the present invention;
[Explanation of symbols]
C1: Capacitor (for smoothing)
C2, C3: Backup capacitors D0 to D3: Diode L: Coil (inductor)
R1, R2: Resistance T: Transistor (FET)
Td: discharge time VA, VB: power supply (battery)

Claims (4)

In a method of diagnosing the capacity of a backup capacitor for backing up a power source for starting an airbag device,
(A) a first step of prohibiting a boosting operation for a predetermined time when the power is turned on and boosting the backup capacitor to a normal voltage in a quadratic curve ;
(B) a second step of performing an initial check related to boosting when boosted to the normal voltage;
(C) after the initial check, a third step of boosting in a quadratic curve to a voltage higher than a normal voltage;
(D) a fourth step of maintaining the voltage for a predetermined time after boosting in a quadratic curve to a voltage higher than the normal voltage;
(E) a fifth step of discharging the backup capacitor linearly at a constant gradient with a substantially constant current;
(F) a sixth step of measuring a discharge time and a voltage drop required for the terminal voltage of the backup capacitor to drop by a predetermined voltage in the process of discharging the backup capacitor linearly with a constant gradient ;
(G) determining whether the capacity of the backup capacitor is normal based on the discharge time and voltage drop ;
A backup capacitor capacity diagnosis method comprising: If it is determined that the capacity of the backup capacitor is not normal as a result of performing a first diagnosis on the capacity of the backup capacitor by executing the first to sixth steps, the first to sixth steps are again performed . The backup capacitor capacity diagnosis method according to claim 1, wherein the capacity of the backup capacitor is diagnosed by executing the following steps.   3. The method according to claim 2, wherein, as a result of diagnosing the capacity of the backup capacitor again, if it is determined that the capacity of the backup capacitor is not normal, it is determined that the capacity of the backup capacitor is deteriorated. Backup capacitor capacity diagnosis method.   4. The backup capacitor capacity diagnosis according to claim 1, wherein a CPU for controlling the operation of the airbag device is connected as a load of the backup capacitor to discharge the backup capacitor. Method.

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