JPH04278862A - Air bag driving circuit - Google Patents

Abstract

PURPOSE:To prevent the breakage of a switching element, etc., by the excessive electric current which flows in the case where a squib is short-circuited in ignition, in an air bag driving circuit. CONSTITUTION:When a microcomputer MC detects the collision of a vehicle, a switching element SW is turned ON by the gate driving voltage VG outputted from the microcomputer, and an ignition electric current flows in a squib SQ. At this time, each electric potential VA, VB at both the edges of the squib is taken into the microcomputer through an A/D converter, and when it is detected that the difference between VA and VB becomes less than a prescribed value (the squib is short-circuited), the duty ratio of the gate driving voltage VG is lowered, and the switching element is duty-driven with the duty ratio, and the excessive increase of the ignition electric current is restricted.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an airbag drive circuit, and more particularly to an airbag drive circuit which limits the ignition current flowing through a squib (airbag ignition filament) from becoming excessively large.

0002

[Prior Art] Generally, in this type of airbag drive circuit, when a vehicle collision is detected, a switching element (for example, FET) is turned on to flow an ignition current to an airbag ignition filament (squib). It is configured as follows.

However, the squib (usually having a resistance value of several ohms) may melt due to the current flowing during such ignition, resulting in a short-circuit condition. In such a state, the ignition current, which is normally 10 amperes or less, becomes an overcurrent reaching, for example, 30A, and this overcurrent flows into the ignition circuit, causing the switching element (for example, FET) or the switching element to be mounted. There was a problem that the airbag ECU that was installed in the engine could be destroyed or burnt out.

0004

[Problems to be Solved by the Invention] The present invention has been made to solve this problem, and it is an object of the present invention to prevent the ignition from occurring due to the overcurrent that flows when the squib is short-circuited as described above during ignition. This is to prevent switching elements, airbag ECUs, etc. from being destroyed or ignited and burnt out.

[0005]

[Means for Solving the Problems] In order to solve the problems, the present invention provides means for detecting a potential difference between both ends of a squib in a state where an ignition current is flowing through the squib, and a means for detecting a potential difference between the two ends of the squib. An airbag drive circuit is provided that includes means for limiting the ignition current flowing through the squib when the ignition current is below a predetermined value.

[0006]

[Operation] According to the above configuration, it is possible to detect whether or not the squib is in a short-circuit condition by detecting the potential difference between both ends of the squib at the time of ignition, and if it is determined that the squib is in a short-circuit condition, the ignition By limiting the current, it is possible to prevent destruction of the ignition switching element or the like or an accidental ignition.

[0007]

[Embodiment] Fig. 1 shows an airbag drive circuit as an embodiment of the present invention, where B is a battery, D is a diode, SQ is a squib, and SW is an ignition switching element (
For example, when the microcomputer MC determines that there is a car collision based on the detection signal from the collision detection sensor S, the switching element SW is turned on by the gate drive voltage VG output from the microcomputer MC, Ignition current flows through the squib SQ.

[0008] The above-mentioned ignition circuit usually has a so-called safety system that turns off the ignition circuit by a signal from the microcomputer when the squib SQ short-circuits with the ground side or when the collision detection sensor S malfunctions. A transistor, a safety sensor, etc. are provided to prevent the ignition current from immediately flowing into the ignition circuit even if a short circuit occurs in the squib or a malfunction of the collision detection sensor occurs, but these are omitted in Figure 1 above. has been done.

In the present invention, the voltages VA and VB across the squib SQ are converted into corresponding digital values DVA and DVB by the A/D converter ADC, and when the squib SQ is ignited (that is, the switching element When the SW is on), the digital value DV
A and DVB are taken into the microcomputer MC.

[0010]The microcomputer MC then compares the digital values DVA and DVB and determines whether the difference between them is less than a predetermined value. The squib S
It is detected that Q is shorted.

[0011] When the short-circuit state of the squib SQ is detected in this way, the duty ratio of the gate drive voltage VG outputted from the microcomputer MC to the switching element SW is lowered, whereby the switching Since the element SW is driven by the reduced duty ratio, the current value of the ignition current is limited.

FIG. 2 shows voltage changes at various parts in the device shown in FIG.
The switching element SW is turned on by the gate drive voltage VG output from C, and the ignition operation is started. At this time, if there is a difference greater than a predetermined value between the voltages VA and VB across the squib, the gate drive voltage VG
Accordingly, the switching element SW is driven with a duty ratio of 100%.

Next, as described above, in the microcomputer MC, it is determined that VA and VB almost match (that is, the difference between them is less than a predetermined value).
is detected (that is, a short-circuit condition of the squib is detected), the duty ratio of the gate drive voltage VG output from the microcomputer decreases, thereby causing the switching element SW to Duty driving is performed at a reduced duty ratio to limit the ignition current value.

FIG. 3 is a flowchart showing the operating procedure of the microcomputer in the device shown in FIG. 1. In step 1, a constant check is started, and in step 2, a car collision is detected by a detection signal from a collision detection sensor. If so, the process proceeds to step 3, where the switching element SW is turned on and ignition current flows through the squib. When such a squib is ignited, the A/D conversion values DVA and DV of the voltages VA and VB across the squib are determined in subsequent steps 4 and 5, respectively.
B is taken into the microcomputer.

Then, in step 6, it is detected whether the squib is in a short-circuit condition by comparing the values of DA and DB. If the squib is not in a short-circuit state, the process proceeds to step 7 and the switching element SW is driven at a duty ratio of 100%. On the other hand, if it is detected that the squib is short-circuited because the difference between DA and DB is less than the predetermined value, the process proceeds to step 8, where the duty ratio of the gate drive voltage VG to the switching element SW is is lowered, and the switching element SW is driven by the lowered duty ratio to limit the ignition current value.

[0016]

According to the present invention, even if the squib is short-circuited during ignition, excessive ignition current is prevented from flowing, thereby reducing the ignition switching element and the circuit pattern connecting it. Furthermore, it is possible to prevent destruction or fire accidents of the airbag ECU in which the switching element and the like are mounted.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing an airbag drive circuit as one embodiment of the present invention.

FIG. 2 is a timing chart showing voltage changes at various parts of the device in FIG. 1;

FIG. 3 is a flowchart showing the operation procedure of the microcomputer in the apparatus of FIG. 1;

[Explanation of symbols]

SQ…Squib SW…Ignition switching element ADC...A/D converter MC...Microcomputer S...Collision detection sensor

Claims (1)

[Claims] 1. Means for detecting a potential difference between both ends of the squib while an ignition current is flowing through the squib, and means for limiting the ignition current flowing through the squib when the detected potential difference becomes less than a predetermined value. An airbag drive circuit characterized by having