JP2000219097A - Air bag system and its examining method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an air bag system and its examining method allowing the capacity of a backup capacitor to be examined with high precision even if a discharging diode and a charging resistance are omitted. SOLUTION: This examining method involves the use of an igniting circuit 3, a backup capacitor 6, a control circuit 9 including a computer and a current measuring circuit 10 for measuring a discharge current in the backup capacitor 6. The output voltage of a boosting circuit 5 is boosted from a first voltage up to a second voltage in accordance with the control of the control circuit 9 and set back to the first voltage after the terminal voltage of the backup capacitor 6 arrives at the second voltage. The capacity of the backup capacitor is computed in accordance with the drop of the terminal voltage of the backup capacitor 6 after a time passed and with a current flowing from the backup capacitor 6 into a load, whereby the capacitor of the backup capacitor is examined to be proper or not.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an airbag system and a method of diagnosing the airbag system, and more particularly to a method for reliably supplying power from a battery power supply to an ignition circuit from a backup capacitor in the event of a vehicle collision. The present invention relates to an improvement in a method for diagnosing the suitability of the capacity of a backup capacitor in an airbag system configured as described above.

[0002]

2. Description of the Related Art A conventional airbag system of this type is constructed as shown in FIG. In the figure,
Reference numeral 1 denotes a battery power supply, to which an ignition circuit 3 is connected via a diode 2. This ignition circuit 3
For example, a mechanical switch MS such as a roll-mite type switch and a lead switch, a diode Da and a squib R
a, a semiconductor switching means, for example, a first series circuit of a field effect transistor Qa, and a second series circuit of a diode Db, a squib Rb and a field effect transistor Qb.

A booster circuit 5 is connected to the battery power supply 1 via a diode 4. The booster circuit 5 operates to compensate for the decrease in the voltage of the battery power supply 1 when the voltage of the battery power supply 1 decreases. For example, the coil L and the diode
And a semiconductor switching means connected to a connection point between the coil L and the diode D1, for example, a field effect transistor Q1, and a smoothing capacitor C1 connected to an output terminal of the series circuit. Have been.

A resistor R1 is connected to the output side of the booster circuit 5.
The backup capacitor 6 is connected through a parallel circuit of the resistor R1 and the diode D2.
A diode 7 is connected between the diode and the anode side so as to be forward with respect to the diode 2. In addition, the backup capacitor 6 is connected to a forced discharge circuit DC.

Further, a drive power supply 8 of a control circuit including a computer, which will be described later, is connected to the output side of the booster circuit 5. The drive power supply 8 is configured by, for example, reducing the output voltage of the booster circuit 5 to 5V. The variable control of the output voltage by controlling the field-effect transistor Q1 in the booster circuit 5, the control of the forced discharge circuit DC, the control of the field-effect transistors Qa and Qb in the ignition circuit 3, and the like include control including a computer. This is performed by the circuit 9. The control circuit 9 is provided with a function of taking in the terminal voltage of the backup capacitor 6 and judging whether or not the capacitor capacity is appropriate.

In this configuration, when the vehicle does not collide, the ignition circuit 3 does not perform an ignition operation because both the switch MS and the field effect transistors Qa and Qb are kept OFF. On the other hand, the backup capacitor 6 is charged via the resistor R1 by the output voltage of the booster circuit 5 boosted to, for example, about 15V.
The operation of the control circuit 9 is ensured by the drive power supply 8 configured to reduce the voltage to, for example, about 5 V using the DC output voltage of the booster circuit 5.

[0007] Once a vehicle collides, the switch MS of the ignition circuit 3 is closed by the action of acceleration (deceleration) G, and the field effect transistors Qa and Qb are based on a detection signal from an electronic acceleration sensor. The output signal of the control circuit 9 is turned on by being applied to the gate.

When the switch MS and the field effect transistors Qa and Qb are both turned on, the switch MS-diode Da, Db-squib Ra and Rb-electric field from the battery power source 1 via the diode 2. A large ignition current flows through the effect transistors Qa and Qb. As a result, the inflator operates based on the heating of the squibs Ra and Rb, the airbag is deployed in a short time, and the occupant is reliably protected.

However, in the event that the battery power source 1 comes off the circuit due to an impact such as a collision, the power supply from the battery power source 1 to the ignition circuit 3 becomes impossible, but the backup capacitor 6 (and the smoothing capacitor) is not provided. The charge of C1) is promptly supplied to the ignition circuit 3 via the diode D2-diode 7-diode 2. Therefore, the ignition circuit 3 operates to protect the occupant in the same manner as the power supply from the battery power supply 1.

[0010]

As described above, when the power supply from the battery power supply 1 to the ignition circuit 3 becomes impossible, the charge stored in the backup capacitor 6 (and the smoothing capacitor C1) is reduced. The charge amount is used as the ignition current of the ignition circuit 3, and this charge amount depends on the capacitance of the capacitor.

For example, when the capacitance of the capacitor is reduced due to temperature influence from the use environment, deterioration of the capacitor itself, etc., the amount of charge that can be charged to the backup capacitor is also reduced.
Cannot supply sufficient ignition current, and the deployment of the airbag is also uncertain, and the protection of the occupant cannot be guaranteed. For this reason, in the airbag system, it is extremely important to constantly diagnose the capacitor capacity of the backup capacitor 6 and to grasp that the capacity is maintained at a predetermined value or more in order to maintain the high reliability of this type of system. It is an important diagnostic item.

Therefore, conventionally, various methods have been adopted for diagnosing the capacitance of the backup capacitor 6. For example, in FIG. 4, a charging curve (change in terminal voltage) when the backup capacitor 6 is charged from the booster circuit 5 via the resistor R1 is taken into the control circuit 9, and the capacitor is obtained by an arithmetic processing based on the data. The suitability of the capacity has been determined.

Although this diagnostic method is excellent as a simple diagnostic method, the diagnostic accuracy of the capacitance of the capacitor varies depending on the charging timing of the backup capacitor 6, that is, the amount of charge remaining in the capacitor.
There is a problem that it is difficult to always obtain stable diagnostic accuracy.

Further, as shown in FIG. 1, a forced discharge circuit DC is added to the backup capacitor 6, and when the capacity of the capacitor is diagnosed, the electric charge remaining in the backup capacitor 6 is immediately discharged immediately before the diagnosis. A method has also been put into practical use in which the effect of residual charges is minimized by forcibly discharging using the circuit DC to improve diagnostic accuracy.

According to this diagnostic method, although relatively high diagnostic accuracy can be obtained, not only the circuit becomes complicated, but also
A discharge diode D2 and a discharge diode 7 are provided in a path for supplying the charge of the backup capacitor 6 to the ignition circuit 3.
Is present and a voltage drop occurs, so the capacity of the backup capacitor 6 must be increased,
In addition to increasing the size of the capacitor and increasing the cost,
There is a problem that the number of parts increases.

On the other hand, if the discharging diode D2 and the charging resistor R1 are omitted, the above-mentioned problem can be solved. On the contrary, the capacitor of the backup capacitor 6 is replaced by the resistor R1 as described above. The diagnosis based on the used charging cannot be performed. Therefore, there is a demand for an appropriate diagnosis method that can perform diagnosis with the same accuracy as that at the time of charging.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide an airbag system capable of diagnosing the capacity of a backup capacitor with high accuracy even if a discharging diode and a charging resistor are omitted, and a diagnostic method therefor. It is in.

[0018]

SUMMARY OF THE INVENTION Therefore, in order to achieve the above-mentioned object, the present invention provides a battery power source, and an ignition circuit including a squib connected to the battery power source via a diode and semiconductor switching means. A booster circuit connected to the battery power supply via a diode, a backup capacitor connected to the output side of the booster circuit and electrically connected to the ignition circuit, and a backup capacitor connected to the output side of the booster circuit. A current measuring circuit for measuring a current, and a control circuit including a computer for controlling at least an output voltage of the booster circuit to an arbitrary voltage and for turning on a semiconductor switching means of the ignition circuit based on a collision signal of the vehicle. Wherein the control circuit increases the terminal voltage of the backup capacitor from the first voltage to the second voltage by the booster circuit.
After the voltage has been raised to the first voltage, the capacity of the backup capacitor is calculated based on the voltage drop of the terminal voltage of the backup capacitor and the current measured by the current measuring circuit after T time when the voltage is returned to the first voltage again. According to a second aspect of the present invention, the current measuring circuit includes at least a resistor connected in series to a load, and both ends of the resistor connected to respective input terminals. And a differential amplifier.

A third aspect of the present invention provides a battery power source, a squib connected to the battery power source via a diode, an ignition circuit including semiconductor switching means, and a battery power source via a diode. Connected booster circuit,
A backup capacitor connected to the output side of the booster circuit and electrically connected to the ignition circuit; a current measuring circuit for measuring a discharge current of the backup capacitor connected to the output side of the booster circuit; and at least an output voltage of the booster circuit. A control circuit including a computer for controlling the semiconductor switching means of the ignition circuit to an arbitrary voltage and turning on the semiconductor switching means based on a collision signal of the vehicle, wherein the control circuit controls the control circuit. Boosting the output voltage of the booster circuit from the first voltage to the second voltage based on the voltage of the booster circuit, and after the terminal voltage of the backup capacitor reaches the second voltage,
The voltage is returned to the first voltage again, and the voltage drop ΔV of the terminal voltage of the backup capacitor after the elapse of the time T and the current I flowing to the load from the backup capacitor are detected. / △ V
The diagnostic method of the airbag system is characterized in that the appropriateness of the capacity of the backup capacitor is diagnosed by calculating based on the following equation.

Further, according to a fourth aspect of the present invention, there is provided a battery power source, a squib connected to the battery power source via a diode, an ignition circuit including semiconductor switching means, and a battery power source via a diode. A booster circuit connected thereto, a backup capacitor connected to the output side of the booster circuit, and electrically connected to the ignition circuit, and a current measuring circuit for measuring a discharge current of the backup capacitor connected to the output side of the booster circuit; A control circuit including a computer for controlling the output voltage of the booster circuit to an arbitrary voltage and turning on the semiconductor switching means of the ignition circuit based on a vehicle collision signal; From the voltage to the second voltage, and after the terminal voltage of the backup capacitor reaches the second voltage,
The voltage is returned to the first voltage, and after a lapse of T time, the voltage drop ΔV of the terminal voltage of the backup capacitor and the current I flowing from the backup capacitor to the load are detected. And a non-volatile memory storing the capacitance of the capacitor as initial data, and boosting the output voltage of the booster circuit from the first voltage to the second voltage based on the control of the control circuit. Then, after the terminal voltage of the backup capacitor reaches the second voltage, the voltage is returned to the first voltage again, and T
By comparing the capacity of the backup capacitor calculated based on the voltage drop ΔV of the terminal voltage of the backup capacitor after a lapse of time and the current I measured by the current measuring circuit with the initial data stored in the nonvolatile memory, the backup capacitor is obtained. A method for diagnosing an airbag system, characterized in that the capacity of the airbag system is diagnosed.

[0021]

Next, an embodiment of an airbag system according to the present invention will be described with reference to FIG.
The same parts as those in the conventional example shown in FIG. 4 are denoted by the same reference numerals, and detailed description thereof will be omitted. The feature of this embodiment is that a backup capacitor 6 is directly connected to the output side of the booster circuit 5 without passing through a charging resistor and a discharging diode, and the output of the booster circuit 5 A current measuring circuit 10 for measuring the discharge current of the backup capacitor 6 is provided on the side, and a control circuit 9 including a computer is provided with a booster circuit 5 to increase the terminal voltage of the backup capacitor 6 from the first voltage to the second voltage. Then, the voltage drop ΔV of the terminal voltage of the backup capacitor 6 after the elapse of the T time when the voltage is returned to the first voltage again, and the current I flowing from the backup capacitor 6 to the load are detected. Change the capacity C of the backup capacitor 6 to C
= I · T / △ V, and the function of judging the suitability is provided.

The control circuit 9 comprises, for example, a microcomputer, a drive power supply 8 for the microcomputer, and peripheral circuits thereof. The control circuit 9, especially the microcomputer, has the drain and gate of the field effect transistor Q1 and the gate of the field effect transistors Qa and Qb of the ignition circuit 3 has the terminal of the backup capacitor 6. However, the output side of the current measuring circuit 10 and the like are connected, and various signals are received and control signals are transmitted.

A non-volatile memory 11 is connected to the microcomputer, and the non-volatile memory 11 is connected to a program for measuring and diagnosing the capacity of the backup capacitor 6 and the capacity of the capacitor when the backup capacitor 6 is mounted. Are stored as initial data.

Further, the current measuring circuit 10 includes, for example, a resistor R having a known resistance value and connected in series to a load circuit.
And a differential amplifier O which receives the terminal voltage across the resistor R as an input.
The terminal of the resistor R on the backup capacitor side is connected to the inverting input terminal of the differential amplifier OP, and the terminal on the driving power supply side is connected to the non-inverting input terminal. The differential amplifier OP outputs a current I measured based on the terminal voltage difference of the resistor R as measurement data.

Next, the operation of the airbag system will be described with reference to FIGS. First, FIG.
As shown in FIG. 5, when the battery power supply 1 is connected to the circuit at time T0 by closing a switch (not shown), the booster circuit 5 operates under the control of the control circuit 9 and the first voltage V1 (for example, 15 V). Is output. The terminal voltage of the backup capacitor 6 connected to the booster circuit 5 is charged by the first voltage, and as shown in FIG.
It is charged to the first voltage V1.

Next, at time T1 when the output voltage of the battery-power supply 1 is stabilized, the control circuit 9 changes the output voltage of the booster circuit 5 to a second voltage V2 (for example, 17.2 V). Then, the terminal voltage of the backup capacitor 6 rises as shown in FIG.
Up to Thereafter, when the output voltage of the booster circuit 5 is returned from the second voltage V2 to the first voltage V1 under the control of the control circuit 9, the charge stored in the backup capacitor 6 is discharged via the current measuring circuit 10, The voltage is eventually reduced to the first voltage V1.

Next, at the time T2 when the terminal voltage of the backup capacitor 6 decreases by ΔV (that is, the second voltage V2
At a time T1 after the time T1 when the voltage is returned to the first voltage V1), the discharge current I of the backup capacitor 6 is measured by the current measuring circuit 10. The current I and the voltage drop ΔV are taken into the microcomputer of the control circuit 9.

Then, the microcomputer determines whether or not the capacity of the backup capacitor 6 is appropriate based on the acquired data. Specifically, the capacitance C of the backup capacitor 6 is equal to the elapsed time T,
Utilizing the current I and the voltage drop ΔV, it can be obtained by a calculation formula of C = IT · ΔV. Therefore, the time T
If the voltage drop ΔV is set to a known value, the capacitance C of the capacitor can be calculated only by detecting the current I described above.

In the microcomputer, arithmetic processing is performed based on the various data taken in, the capacitance C of the backup capacitor 6 is calculated, and then compared with the initial data read from the nonvolatile memory 11. -Judgment is made and its suitability is finally diagnosed.

In particular, when a diagnosis result is obtained that the backup capacitor 6 lacks suitability as a backup capacitor, the driver is notified by turning on an alarm lamp (warning lamp) or the like. Therefore, if the backup capacitor 6 is replaced with a normal one based on the result of the diagnosis, the airbag system can be reliably made differential in the event of a vehicle collision.

When the capacity of the backup capacitor 6 at the start of use is stored in the nonvolatile memory 11 as initial data, the detection of the capacity of the capacitor is performed in the same manner as the calculation of the capacity of the capacitor in the above-described diagnosis process. Done.

Next, a specific diagnosis method for the capacity of the backup capacitor 6 in the airbag system will be described with reference to FIG.

First, in step S1, when the battery power supply 1 is connected to the circuit as shown in FIG. 2 (a), the booster circuit 5 operates to output the first voltage V1 (for example, 15V), thereby providing a backup. The terminal voltage of the capacitor 6 is also charged to the first voltage V1, as shown in FIG. Then, in step S2, it is determined whether the terminal voltage of the backup capacitor 6 has reached the first voltage V1. If it is determined that it has reached, the process proceeds to step S3.

In step S3, at the time T1 when the first voltage V1 is stabilized, the output voltage of the booster circuit 5 is boosted to the second voltage V2 (for example, 17.2 V) by the control circuit 9, and the terminal voltage of the backup capacitor 6 is increased. Figure 2
As shown in (b), the voltage is increased to the second voltage V2. In step S4, it is determined whether the terminal voltage of the backup capacitor 6 has been boosted to the second voltage V2. If the pressure has not been increased, the process returns to step S3. Second voltage V
If the pressure has been increased to 2, the process proceeds to step S5.

In step S5, the output voltage of the booster circuit 5 is returned from the second voltage V2 to the first voltage V1 under the control of the control circuit 9. In step S6, the second voltage V
The voltage drop ΔV after a lapse of T time from the point of time T1 when the voltage is returned from T2 to the first voltage V1 and the discharge current I of the backup capacitor 6 flowing to the load (drive power supply 8) are measured by the current measuring circuit 1.
The measured data is taken into the microcomputer of the control circuit 9 and the capacitance C of the backup capacitor 6 is calculated.

In step S8, it is determined whether the calculated capacitor capacity is normal. If it is determined that the airbag system is normal, the normal operation of the airbag system is guaranteed at the time of the vehicle collision. If the capacity of the capacitor is insufficient,
If it is determined that there is an abnormality due to an open connection or the like, a warning light is displayed, the driver is notified of the fact, and the diagnosis is completed.

According to this configuration, in the conventional system, the resistor R1 and the diode D2 required for charging and discharging the backup capacitor 6 can be omitted, so that the voltage drop due to the discharging diode D2 can be reduced. Can be avoided. Therefore, it is not necessary to increase the capacitance of the backup capacitor 6 in anticipation of the voltage drop, and it is possible to reduce the size and cost.

After the output of the booster circuit 5 is returned from the second voltage to the first voltage, the backup capacitor 6
The voltage drop ΔV after the lapse of time and the discharge current I of the backup capacitor 6 at that time are measured, and based on the measured data, the capacitance C of the capacitor is calculated by a calculation formula of C = IT / ΔV. By judging whether or not the capacitance of the capacitor is within a range capable of exhibiting the function as a backup capacitor, the suitability of the capacitor is diagnosed. Therefore, not only high-precision diagnosis is possible, but also
It is possible to obtain higher diagnostic accuracy than the conventional diagnostic method using the charging resistor R1.

The present invention is not limited to the above-described embodiment. For example, the semiconductor switching means is not limited to a field-effect transistor, but may be a transistor or an SCR. Also, the electrical connection between the backup capacitor and the ignition circuit can be made directly without going through a diode. Further, the smoothing capacitor of the booster circuit can be integrated with the backup capacitor. Further, a computer built-in memory can be used as the external nonvolatile memory.

[0040]

As described above, according to the present invention, the resistor for charging the backup capacitor and the diode for discharging can be completely omitted, so that the voltage drop due to the discharging diode can be avoided. Therefore, it is not necessary to increase the capacitor capacity of the backup capacitor in anticipation of the voltage drop, and the size and cost can be reduced.

The backup capacitor was evaluated by measuring the voltage drop ΔV after a lapse of T time since the output of the booster circuit was returned from the second voltage to the first voltage, and the discharge current I of the backup capacitor at that time. Then, the capacitor capacitance C is calculated based on these measurement data, and the diagnosis is performed by diagnosing the suitability of the capacitor capacitance based on the calculated data. Obtainable.

[Brief description of the drawings]

FIG. 1 is an electric circuit diagram showing an embodiment of an airbag system according to the present invention.

FIG. 2 is an operation timing chart at the time of diagnosis of a backup capacitor.

FIG. 3 is a diagnostic flowchart of a backup capacitor.

FIG. 4 is an electric circuit diagram of a conventional airbag system.

[Explanation of symbols]

 Reference Signs List 1 battery power supply 2, 4, Da, Db, D1 diode 3 ignition circuit 5 booster circuit 6 backup capacitor 8 drive power supply 9 control circuit 10 current measurement circuit 11 nonvolatile memory Qa, Qb, Q1 semiconductor switching means MS switch Ra, Rb Squib L coil C1 Smoothing capacitor R Resistance OP Differential amplifier

Claims (4)

[Claims] An ignition circuit including a squib connected to the battery power supply via a diode, a semiconductor switching means, a booster circuit connected to the battery power supply via a diode, and a booster circuit. A backup capacitor connected to the output side and electrically connected to the ignition circuit, a current measurement circuit for measuring a discharge current of the backup capacitor connected to the output side of the booster circuit, and at least an output voltage of the booster circuit to an arbitrary voltage And a control circuit including a computer for turning on and off the semiconductor switching means of the ignition circuit based on the collision signal of the vehicle. The control circuit controls the terminal voltage of the backup capacitor by a booster circuit. After the voltage is raised from the first voltage to the second voltage, the backup is performed again after T time when the voltage is returned to the first voltage again. An airbag system having a function of calculating the capacity of a backup capacitor based on a drop voltage of a terminal voltage of a capacitor and a current measured by a current measuring circuit, and determining whether or not the capacity is appropriate. 2. The current measuring circuit according to claim 1, wherein the current measuring circuit includes at least a resistor connected in series to the load, and a differential amplifier having both ends of the resistor connected to respective input terminals. The airbag system as described. 3. An ignition circuit including a battery power supply, a squib connected to the battery power supply via a diode, and a semiconductor switching means, a booster circuit connected to the battery power supply via a diode, and a booster circuit. A backup capacitor connected to the output side and electrically connected to the ignition circuit, a current measurement circuit for measuring a discharge current of the backup capacitor connected to the output side of the booster circuit, and at least an output voltage of the booster circuit to an arbitrary voltage And a control circuit including a computer for controlling the semiconductor switching means of the ignition circuit to be turned on based on a collision signal from the vehicle, and boosting the pressure based on the control of the control circuit. The output voltage of the circuit is changed from the first voltage to the second voltage.
And after the terminal voltage of the backup capacitor reaches the second voltage, the voltage is returned to the first voltage again, and after a lapse of the T time, the terminal voltage of the backup capacitor drops from the voltage ΔV and from the backup capacitor. An airbag system characterized in that a current I flowing to a load is detected and a capacity C of the backup capacitor is calculated based on the current I based on C = IT / ΔV to thereby determine whether the capacity of the backup capacitor is appropriate. Diagnostic method. 4. A battery power source, a squib connected to the battery power source via a diode, an ignition circuit including semiconductor switching means, a booster circuit connected to the battery power source via a diode, and a booster circuit. A backup capacitor connected to the output side and electrically connected to the ignition circuit, a current measurement circuit for measuring a discharge current of the backup capacitor connected to the output side of the booster circuit, and at least an output voltage of the booster circuit to an arbitrary voltage A control circuit including a computer that controls the semiconductor switching means of the ignition circuit based on a vehicle collision signal;
The output voltage of the booster circuit is boosted from the first voltage to the second voltage, and after the terminal voltage of the backup capacitor reaches the second voltage, the voltage is returned to the first voltage again, and the backup after the elapse of the time T has elapsed. Voltage drop of terminal voltage of capacitor △ V
And a non-volatile memory which detects the current I flowing from the backup capacitor to the load, calculates the capacity C of the backup capacitor from these by C = IT / △ V, and stores the capacity of the capacitor as initial data. Then, the output voltage of the booster circuit is boosted from the first voltage to the second voltage based on the control of the control circuit, and after the terminal voltage of the backup capacitor reaches the second voltage, the first The initial data stored in the non-volatile memory is returned to the voltage, and the capacity of the backup capacitor calculated based on the voltage drop ΔV of the terminal voltage of the backup capacitor after the lapse of T time and the current I measured by the current measuring circuit is stored in the nonvolatile memory.
A method of diagnosing the suitability of the capacity of the backup capacitor by comparing the capacity of the airbag system with the capacity of the backup capacitor.