JPH0424145A - Igniting electric power device for vehicle air bag - Google Patents

Abstract

PURPOSE:To obtain a small-sized, inexpensive electric power unit by providing a capacitor for backup and for a filter of a DC-DC converter, providing a switching means between the capacitor and a load except an ignition system so as to prevent generation of electric supply from the capacitor to the load at the time of stopping output from a battery. CONSTITUTION:In a device equipped with G sensors 4, 5 detecting collision of automobiles to let ignition current flow to a starting means 3 and making an air bag develop while equipped with a boosting DC-DC converter, a capacitor 17 for a filter connected between the output side of the DC-DC converter 8 and the earth is provided while a switching transistor 18 for connecting and disconnecting the capacitor 17 and a load 10 is provided. An electric power supply condition detecting transistor 14 is provided. When electric power from a battery 1 is cut off, the transistors 14, 18 are made to OFF state, charging voltage for the capacitor 17 is maintained at a specified voltage even if output of the DC-DC converter 8 is cut off, and sufficient ignition current for the starting means 3 can be supplied at the time of closing the G sensors 4, 5.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a power supply device for igniting an airbag for a vehicle, and particularly to a charging/discharging circuit for a backup capacitor thereof.

[Conventional technology]

FIG. 2 shows a conventional automobile airbag ignition type f1. The configuration of the device is shown: 1 is a car battery, 2 is an ignition switch, 3 is a starting means for deploying an air bag, and 4.5 detects a car collision and closes the contacts in response. A G sensor 6 causes an ignition current to flow to the starting means 3 and deploys the air nozzle, and 6 is a G sensor for a certain period of time after the battery 1 or the wiring from the battery 1 is disconnected, and after the ignition switch 2 is turned off. 7 is a diode that prevents the charge charged in the capacitor 6 from flowing back to the battery 1 side, and 8 is not affected by the voltage level of the battery 1. 9 is a step-up DC-DC converter that always charges the capacitor 6 with a constant voltage; 9 is a filter capacitor in the output stage of the DC-DC converter 8; 10 is a circuit for diagnosing air bag system failures, a microcomputer, etc. A load 11 other than the ignition system is a diode that prevents the charge charged in the capacitor 6 from being discharged to the load 10 side.

Next, the operation will be explained. When the car collides, the G sensors 4 and 5 close their contacts, and the starting means 3 passes from the hafting system 1 to the ignition switch 2 and the diode 7.
A current flows to the starting means 3, which inflates an airbag for protecting the occupants of the automobile. Therefore, in order to allow current to flow to the starting means 3, the ignition switch 2 must be closed. However, in the event of a car collision, battery 1
There is a possibility that various failures may occur instantaneously, such as damage to the circuit or disconnection of the wiring from the haft relay 1, and even in such cases, a capacitor is used to supply current to the starting means 3 for a certain period of time. 6 is provided, and the capacitor 6 always stores a constant charge.

The capacitor 6 is charged with the voltage boosted by the DC-DC converter 8, and this is because the capacitor 6 is charged with a constant voltage even when the battery 1 is at a low voltage due to discharge. Further, the capacitor 9 is a filter capacitor inserted in the output stage of the DC-DC converter 8, and is a well-known capacitor. Load weight 0 is, for example, a failure diagnosis circuit that detects when one of the systems fails and notifies the driver of the failure in order to improve the reliability of the airbag system. DC-D is used as the circuit power supply to enable stable failure detection even when the voltage is low.
The output of C converter 8 is used. Also, battery 1
If the electric charge stored in the capacitor 6 leaks to the load 10 or the output side of the DC-DC converter 8 when the diode 7 is damaged or disconnected, there is a risk that the operating current to the starting means 3 cannot be supplied. 11 is inserted. Note that the capacitor 6 has a current of 2 to 3 A flowing to the starting means 3.
(time is several m5ec), so a large capacity (
1,000 to 10,000 tries) and low impedance are used. Also, the capacitor 9 is also DC-D.
In order to sufficiently reduce ripples and spikes during switching, a filter capacitor with a large capacity (several hundred to 1000 p) and low impedance is used as the filter capacitor for the output stage of the C converter 8.

[Problem to be solved by the invention]

The conventional ignition power supply device for car airbags is configured as described above, and a large and expensive electrolytic capacitor must be used as the capacitor 6.9, making the device as a whole large and expensive. It became something.

The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to obtain a small and inexpensive power supply device for igniting a vehicle airbag.

[Means to solve the problem]

The ignition power supply device for a vehicle airbag according to the present invention includes:
It functions as a filter between the output side of the DC-DC converter and the ground, and is charged by the output, and supplies ignition current to the starting means through the contact of the collision detection means when the output from the battery is stopped. capacitor and
A switching means is provided between the capacitor on the output side of the DC/DC converter and a load other than the ignition system, and cuts off the connection when the output of the battery is stopped.

[For production]

The capacitor in this invention functions as a filter for the output stage of the DC-DC converter and as a backup power source. Further, when the output of the battery is stopped, the connection between the capacitor on the output side of the DC-DC converter and loads other than the ignition system is cut off.

〔Example〕

Embodiments of the present invention will be described below with reference to the drawings. 1st
The figure shows the configuration of the power supply device according to this embodiment, with reference numerals 1 to 1.
The parts indicated by 5, 7, and 8.10 are the same as the conventional one. 1
7 is a filter capacitor connected between the output side of the DC-DC converter 8 and the ground, 18 is a switching transistor that connects and disconnects the capacitor 17 and the load 10, and 12.13 is a resistor for the switching transistor 18. , 14 is the ignition switch 2
a power state detection transistor that is in an on state when the battery 1 is in an on state, the battery 1 is normal, and the wiring is also normal;
15 and 16 are resistors for controlling the transistor 14.

Next, the operation will be explained. The output stage filter capacitor 17 of the DC-DC converter also serves as a back amplifier that allows current to flow to the starting means 3 for a certain period of time in the event of a failure or disconnection of the battery 1, and the capacitance and impedance of the capacitor 17 causes the starting means 3 to ignite. It is determined by the current (2 to 3 A) required for this purpose, the energization time (several gsec), and the maximum time until ignition occurs after the output of the DC-DC converter 8 fails due to failure of the battery 1, etc. The characteristics of the capacitor 17 are also determined by the switching current in the DC-DC converter 8, the maximum current of the load, the switching frequency, the allowable ripple voltage, etc.

However, the capacitance of capacitor 17 is the same as that of conventional capacitor 6.
It should be smaller than the total capacitance of capacitors 9 and 6.
Since the capacitance of the capacitor 17 is very large, the capacitance of the capacitor 17 can be made almost equal to the capacitance of the capacitor 6. or,
The impedance of capacitor 17 can also be made approximately equal to the impedance of capacitor 6, which is DC-
This is because the impedance required for the ignition capacitor is smaller than the impedance required by the DC converter 8. However, since the output of the DC-DC converter 8 is also supplied to loads 10 other than the ignition system, if the following occurs, there is a risk that the capacitor F will not be able to discharge the current necessary for ignition. . That is,
Before the car collides and G sensor 4.5 closes its contacts,
If battery 1 is damaged or disconnected, DC-D
C converter 8 becomes inoperable and capacitor 17 is no longer charged. However, since the load 10 is connected to the capacitor 17, the charge on the capacitor 17 is
There is a risk of being discharged to. The later the timing of closing the contacts of the G sensors 4 and 5 is, and the larger the extinction current of the load 10 is, the more the charge in the capacitor 17 is discharged, making it impossible to supply the necessary ignition current to the starting means 3. However, in this embodiment, when power is no longer supplied from the battery 1, the transistor 14 is turned off, and the transistor 18 is also turned off because the base current no longer flows. In addition, resistance 13
．． 15 is a base current limiting resistor, 12.16 is a base current limiting resistor, and 12.16 is a base current limiting resistor.
This is the bleeder resistance between the emitters. Therefore, the discharge of the capacitor 17 results in the backflow into the DC-DCC converter 8 and the leakage of the capacitor 17 itself, and even if the output of the DCDC converter 8 disappears, the capacitor 17 remains charged.
The pressure is maintained at a predetermined voltage, and sufficient ignition current is supplied to the starting means 3 when the contacts of the G sensor 4.5 are closed. In addition, under normal conditions, ignition switch 2
When the capacitor 17 is closed, the capacitor 17 acts as a filter for the output of the DC-DC converter and is charged by the output to a predetermined voltage, and the transistors 14 and 18
When turned on, the output of the DC-DC converter 8 is supplied to the load 10. Moreover, when the battery 1 is normal, the starting means 3
is supplied with power by the battery 1, and is supplied with power by the capacitor 17 when the battery 1 is abnormal. Here, when comparing the conventional example with this embodiment, a transistor 14.18 and a resistor 12.1 are used instead of the conventional capacitor 9 and diode 11.
315.16 (as mentioned above, capacitor 17 substantially corresponds to capacitor 6).
However, transistors 14, 18 and resistors 12, 13, 15, .
16 can be made very small as a surface mount component, and capacitor 9 has a much larger volume.

(Effects of the Invention) As described above, according to the present invention, the backup and DC
- In addition to providing a filter capacitor for the DC converter, a switching means is also provided between this capacitor and a load other than the ignition system to prevent power from being supplied to the load from the capacitor when the battery output is stopped. Power can be supplied to the starting means without any trouble, the number of large and expensive capacitors can be reduced, and a small and inexpensive power supply device can be obtained.

[Brief explanation of drawings]

FIG. 1 is a block diagram of the inventive device, and FIG. 2 is a block diagram of a conventional device. 1...Battery, 3...Starting means, 4, 5...G
Sensor, 8... DC-DC converter, 10... Load other than the ignition system, 14.18... Transistor, 17
...Capacitor. Note that the same reference numerals in the figures indicate the same or equivalent parts.

Claims (1)

[Claims] a battery, a DC-DC converter connected to the battery to stabilize the output of the battery, a collision detection means whose contacts close when detecting a collision of the vehicle, and connected to the battery via a contact of the collision detection means, a starting means for deploying an airbag for occupant protection when ignition current is applied, and connected between the output side of the DC-DC converter and ground;
A capacitor which functions as a filter for the output and is charged by the output and supplies ignition current to the starting means via the contact of the collision detection means when the output from the battery 1 is stopped; and a capacitor on the output side of the DC-DC converter. A vehicle image characterized by comprising a connected load other than the ignition system, a switching means provided between the capacitor on the output side of the DC-DC converter and the load, and shutting off the connection when the output of the battery is stopped. Power supply device for ignition of airbags.