JP2003127822A - Diagnosis method of backup capacitor capacity - Google Patents

Abstract

(57) [Summary] [PROBLEMS] To provide a backup capacitor capacity diagnosis method capable of accurately diagnosing the capacity of a backup capacitor. SOLUTION: A voltage Vup for charging a backup capacitor is boosted to a voltage higher than a normal voltage (time t2). After a lapse of a certain time, the backup capacitor is discharged with a substantially constant current (time t3). In the process of discharging the backup capacitor,
The discharge time Td required for the terminal voltage of the backup capacitor to drop by a predetermined voltage is measured. Then, it is determined whether or not the capacity of the backup capacitor is normal based on the discharge time Td.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a backup capacitor capacity diagnosing method for diagnosing a backup capacitor capacity for backing up a power source of an in-vehicle air bag device.

[0002]

2. Description of the Related Art Conventionally, an air bag device is installed in a vehicle as a passenger protection device. This airbag device protects an occupant in a vehicle by deploying the airbag by detecting the impact of a collision. However, if the power source of the airbag device is damaged by the collision, the airbag device will function. And the airbag will not be deployed. Therefore, this type of occupant protection device is provided with a backup capacitor for backing up the power supply, and by charging this backup capacitor, even if the power supply is damaged during a collision, the airbag device The electric power required for is surely supplied.

In this way, the backup capacitor is
Although it is an important component for security, it inherently has the property that its capacity deteriorates over time due to a decrease in electrolyte solution. Therefore, in this type of system, it is customary 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, Japanese Patent Publication No. 26
The technique disclosed in No. 53744 is known. According to this conventional technique, the abnormality of this capacitor is diagnosed by measuring the charging time of the capacitor.

[0004]

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 surge voltage during boosting. Therefore, according to the conventional technique of measuring the charging time at the time of boosting and diagnosing the capacity, 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, and in such a case, there is also a problem that the capacity is deteriorated but is normally diagnosed as normal.

The present invention has been made in view of the above circumstances, and an object thereof is to provide a backup capacitor capacity diagnosing method capable of accurately diagnosing the capacity of a backup capacitor and preventing erroneous diagnosis. And

[0006]

In order to solve the above problems, the present invention has the following constitution. That is, the backup capacitor capacity diagnosing method according to the present invention is a method for diagnosing the capacity of a backup capacitor for backing up a power supply for activating an airbag device, wherein (a) the power supply is turned on, The voltage for charging the backup capacitor is higher than the normal voltage (for example, 20.5V) (for example, 2V).
A first step of boosting the voltage to 2.5 V), and (b) a second step of discharging the backup capacitor with a substantially constant current (for example, current consumption of a CPU described later),
(C) In the process of discharging the backup capacitor, a discharge time (for example, a discharge time Td described later) required for the terminal voltage of the backup capacitor to drop by a predetermined voltage (for example, 1.5V as a voltage change described below). And a step of (d) determining whether or not the capacity of the backup capacitor is normal based on the discharge time.

In the backup capacitor capacity diagnosing method, the capacity of the backup capacitor is not normal as a result of performing the first diagnosis of the capacity of the backup capacitor by executing the first to third steps. If it is determined that the backup capacitor is diagnosed, the first to third steps are executed again. Further, in the backup capacitor capacity diagnosing method, when the capacity of the backup capacitor is judged to be not normal as a result of diagnosing the capacity of the backup capacitor again, it is judged that the capacity of the backup capacitor is deteriorated. Is characterized by. Furthermore, in the backup capacitor capacity diagnosing method, a CPU for controlling the operation of the airbag device is connected as a load of the backup capacitor to discharge the backup capacitor.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. Although the present invention is applied to an airbag device, for convenience sake, the description will focus on a booster circuit for charging a capacitor (backup capacitor) for backing up the power source of the airbag device. FIG. 1 shows the configuration of the booster circuit according to this embodiment. In the figure, a power supply VA is a power supply, and is supplied to the ignition circuit side (not shown) of the airbag via a backflow prevention diode D0.

The power source VB is a power source provided separately from the above-mentioned power source VA, and a diode D1, a boosting coil L, a diode D2, and a diode are provided between the power source VB and the ignition circuit. D3 is connected in this order, and the diodes are connected so that the direction from the power supply VB to the ignition circuit is the forward direction. The power supplies VA and VB also supply power to electric devices other than the airbag device. By separately providing power supplies in this way, even if one of the power supplies fails, normal power supply and backup are provided. It is possible to avoid a situation where both of the power feeds go down.

To the connection point between the diode D1 and the coil L, one electrode of the smoothing capacitor C1 is connected,
The other electrode of this capacitor C1 is grounded. Between the other end of the coil L and the ground, a transistor (FET) T
Is connected to a current path of a pulse signal PLS from a CPU (not shown) via a resistor R1. The resistor R1 is for suppressing noise when the transistor T switches. Further, the gate of the transistor T is grounded via the resistors R1 and R2. This resistor R2 is, for example, a pulse signal P
This is for fixing the transistor T in the off state in the case where the wiring of the LS is disconnected, so as to prevent the power supply VB from being short-circuited to the ground.

A backup capacitor C2 and a backup capacitor C3 are connected in parallel between the cathode side of the diode D2 and the ground. By thus dividing the backup capacitor into two, even if one is damaged, the function as the backup capacitor is not lost. In this embodiment, the capacities of the backup capacitors C2 and C3 are 4 respectively.
It is set to 700 μF. Therefore, the total capacity of the backup capacitors is 9400 μF.

Although not particularly shown, the airbag apparatus according to this embodiment has a means for detecting the boosted voltage Vup (that is, the terminal voltage of the backup capacitors C2, C3) and a means for detecting this voltage change. And means. However, known techniques can be used for these means. Also, although not shown in FIG.
The voltage output to the cathode side of the diodes D0 and D3 is also supplied as the power source of the CPU for controlling the overall operation of the airbag device.

According to the charging booster circuit thus constructed, when the transistor T is switched by the pulse signal PLS, the energy accumulated in the coil L is released during the switching process, and the voltage of the anode of the diode D2 is discharged. 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, the power supply VA
The electric power is supplied from the power source VA to the ignition circuit side. However, for example, when the power supply from the power source VA is interrupted due to the impact at the time of a collision, the charge accumulated in the backup capacitors C2 and C3 is diode D.
3 is discharged to the ignition circuit side, and 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.

Next, a method of diagnosing 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 chart shown in FIG.
When the occupant turns on the ignition switch of the vehicle, in the airbag device, a series of self-diagnosis is executed as an initial check for the acceleration sensor for detecting impact, the squib resistance for ignition, etc.
The capacity diagnosis of the backup capacitor is carried out as one item in the initial check. In this embodiment, description of the diagnosis other than the backup capacitor is omitted.

First, at time t0 shown in FIG.
When B is turned on, an initial check (self-diagnosis) is first performed as a whole operation, and then, when a strong impact of a specified value or more is sensed, the operation shifts to a normal operation for deploying the airbag. In the initial check,
As will be described in detail below, diagnosis of the capacities of the backup capacitors C2 and C3 shown in FIG. 1 is performed. 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 boosted voltage Vup starts to rise. Then, the 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 capacity diagnosis of the backup capacitor (B / U capacitor check status) (step S1).

When the status becomes "00H" at time t2 when the boosted voltage Vup stabilizes at 20.5V, the CPU executes a judgment process to start the capacity diagnosis of the backup capacitor (step S2). As a result, at time t2, the booster circuit shown in FIG. 1 performs further boosting, and the boosted voltage Vup starts to rise to a voltage higher than the normal boosted voltage of 20.5V. In the process of the boosting operation, when the status becomes “01H”, the boosting voltage Vup is set to the check start voltage of 22.5V.
Processing for setting to (step S3). After this, the boosted voltage Vup reaches 22.5V and stabilizes.

When 500 ms have passed since the boosted voltage Vup reached 22.5 V and the status becomes "02H", the boosting operation is stopped and the discharge time measuring process is executed (step S4). At this time, the backup capacitors C2 and C3 are discharged using the CPU as a load. CPU
Consumption current is sufficiently smaller than the switching frequency of the transistor T that constitutes the booster circuit, so that it behaves as a load in which a substantially constant current flows. Therefore, the terminal voltage of the backup capacitors C2 and C3 (that is, the boosted voltage Vu
p) decreases linearly with a constant slope. The CPU measures the discharge time Td of this backup capacitor.

Then, it is judged whether the capacities of the backup capacitors C2 and C3 are normal or abnormal based on the above-mentioned discharge time Td according to the judgment condition shown in FIG. That is,
In the example shown in FIG. 4, the voltage change ΔV of the terminal voltage is 1.5
Discharge time Td before dropping to V (predetermined voltage) is 93 m
s or more, or the discharge time Td is 1500 m
If the voltage change ΔV is 1.5 V or less even after exceeding s, it is determined that the capacities of the backup capacitors C2 and C3 are normal (OK). On the other hand, the discharge time T
If the voltage change is 1.5 V or more before d is 93 ms, it is determined that the capacities of the backup capacitors C2 and C3 may be deteriorated, and the boost voltage is increased to the check start voltage of 22.5 V again. Vup is increased and the discharge time Td is measured again. In any of these two diagnoses, when it is determined that the capacity of the backup capacitor is deteriorated, it is determined to be abnormal (NG), and the determination of failure is confirmed. When such a determination is made, the CPU issues a warning to the occupant that there is an abnormality in the airbag device.

Next, in step S4, if the time allotted for the initial check has elapsed or if the diagnosis result of the backup capacitor is determined to be abnormal, the status becomes "03H", and a series of backup capacitor diagnosis is performed. The process is terminated on the way (step S5). Then, the boosted voltage Vup is set to 20.
The voltage is reset to 5V, and the backup capacitors C2 and C3 are charged to the specified voltage (20.5V) while the capacity is abnormal. In this case, backup capacitor C
Since C2 and C3 may be deteriorated, there is a possibility that the power supply VA cannot be backed up at the time of collision. Therefore, the vehicle occupant can complete the backup of the power supply by replacing the backup capacitors C2 and C3 at an early stage according to the above-mentioned warning. On the other hand, if it is determined in step S4 that the diagnosis result is normal, the status becomes "04H", and the series of backup capacitor diagnosis processing ends normally (step S6). The embodiment has been described above.

According to the above embodiment, even when the backup capacitors C2 and C3 are manually inserted parts,
It is possible to check the defects in the open mode and the defects due to the capacity decrease. Further, since the backup capacitor is discharged, it is not affected by surge voltage due to boosting. Therefore, the capacity of the backup capacitor can be accurately diagnosed.

Although the embodiments of the present invention have been described above, the present invention is not limited to the above-mentioned embodiments, and the present invention is applicable even if there are design changes and the like within the scope not departing from the gist of the present invention. include. For example, in the above embodiment, the terminal voltage of the backup capacitor is 22.5V.
Although the discharge time Td required for the voltage to drop by 1.5 V from the above is measured, the relationship between this voltage change and the discharge time may be set in any manner within the limit that the required accuracy can be obtained. Further, in the above-described embodiment, when the 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, and the diagnosis is performed three times or more. May be. Furthermore, if the diagnosis result is normal only once, it is decided that there is no abnormality.
It may be determined that there is no abnormality when all of the results of a plurality of diagnoses are normal.

[0022]

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 Discharge with a substantially constant current, measure the discharge time required for the terminal voltage to drop by a predetermined voltage in the process of discharging the backup capacitor, and judge whether the capacity of the backup capacitor is normal based on the discharge time. By doing so, the capacity of the backup capacitor can be accurately diagnosed, and erroneous diagnosis can be prevented.

[Brief description of 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 backup capacitor capacity diagnosis method according to the embodiment of the present invention.

FIG. 3 is a waveform diagram for explaining the operation of the booster circuit for charging according to the embodiment of the present invention.

FIG. 4 is a diagram for explaining a normal / abnormal determination condition in the backup capacitor capacity diagnosing method according to the embodiment of the present invention.

[Explanation of symbols]

C1: Capacitor (for smoothing) C2, C3: Backup capacitor D0 to D3: Diode L: Coil (inductor) R1, R2: resistance T: Transistor (FET) Td: Discharge time VA, VB: Power source (battery)

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Tsutomu Takahashi             Saginoya Higashi, Hoshoji Temple, Takanezawa Town, Shioya District, Tochigi Prefecture             Address 2021 Keihin Tochigi Development Center Co., Ltd.             In the center (72) Inventor Masahide Kimishima             Miyagi Prefecture Kakuda City Sakura character Miyagiya 4 number 3 stock             Ceremony Company Keihin Kakuda Third Factory F term (reference) 2G028 AA01 BB06 CG07 DH03 MS03                       MS05                 2G036 AA04 AA24 AA27 BA12 BA37                       BA45 BB02 CA10                 3D054 EE55

Claims (4)

[Claims] 1. A method for diagnosing the capacity of a backup capacitor for backing up a power source for starting an airbag device, comprising: (a) a voltage for charging the backup capacitor when the power source is turned on. Is boosted to a voltage higher than the normal voltage, (b) a second step of discharging the backup capacitor with a substantially constant current, and (c) a process of discharging the backup capacitor, A third step of measuring a discharge time required for the terminal voltage of the backup capacitor to drop by a predetermined voltage, and (d) a step of determining whether or not the capacity of the backup capacitor is normal based on the discharge time. A method for diagnosing a backup capacitor capacity, which includes: 2. When the capacity of the backup capacitor is judged to be not normal as a result of performing the first diagnosis of the capacity of the backup capacitor by executing the first to third steps, the above-mentioned method is performed again. The first to third steps are executed to diagnose the capacity of the backup capacitor.
Backup capacitor capacity diagnostic method described in. 3. When the capacity of the backup capacitor is judged to be abnormal as a result of diagnosing the capacity of the backup capacitor again, it is judged that the capacity of the backup capacitor is deteriorated. The method for diagnosing the backup capacitor capacity according to item 2. 4. A CPU for controlling the operation of the airbag device as a load of the backup capacitor.
The backup capacitor capacity diagnosing method according to any one of claims 1 to 3, wherein the backup capacitor is discharged by connecting the above.