US 4,851,705 AGranted

Firing circuit for a vehicle passenger restraint system

AssigneeAutomotive Systems Laboratory, Inc.

InventorsKevin E. Musser, Craig W. White

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Abstract

A firing circuit for deploying a pair of air bags comprises two circuit legs connected in parallel across a voltage supply. Each circuit leg comprises in series a safing sensor, a squib, and a crash sensor, with each sensor being shunted by a like resistor having a nominal resistance substantially greater than the nominal resistance of the squibs. Two separate diode bridges, each comprising a pair of oppositely biased diodes, bridge the circuit legs at junctions thereon between the safing sensors and the squibs, and the squibs and the crash sensors, respectively, to provide multiple firing paths for both squibs. A microprocessor checks the integrity of the firing circuit and diagnoses the presence of faults therein by reading the voltage potentials at each junction; comparing the voltage potential at one or more junctions with the supply voltage; comparing the voltage drop across the diode bridges with the diode forward-biased conduction voltages; and, if a specific fault has not yet been identified, determining the effect on the voltage potential at one or more junctions when increasing the supply voltage applied across the firing circuit. The microprocessor periodically determines the instantaneous forward-biased conduction voltages of the bridging diodes for use in the above diagnostic sequence by operating a current switch connected to a junction on each circuit leg and determining the resulting voltage drops across the diode bridges.

Claims22

Dependent claims

A firing circuit for actuating a first and second instrumentality of a vehicle passenger restraint system comprising

a first circuit leg comprising in series a first normally open sensor for detecting a first condition requiring actuation of said instrumentalities, a first trigger means having an internal resistance for actuating said first instrumentality, and a second normally open sensor for a second condition requiring actuation of said instrumentalities, said first and second sensor being shunted by a first and second resistor, respectively, said first and second resistors having a resistance substantially greater than the internal resistance of said first trigger means;
a second circuit leg connected in parallel with said first circuit leg comprising in series a third normally open sensor for detecting the first condition requiring actuation of said instrumentalities, a second trigger means having an internal resistance substantially equal to the internal resistance of said first trigger means for actuating said second instrumentality, and a fourth normally open sensor detecting the second condition requiring actuation of said instrumentalities, said third and fourth sensor being shunted by a third and fourth resistor, respectively, said third and fourth resistors having a resistance substantially greater than the internal resistance of said second trigger means;
a first diode bridge comprising a pair of oppositely biased diodes connecting a first junction on said first circuit leg between said first sensor and said first trigger means with a first junction on said second circuit leg between said third sensor and second trigger means;
and
a second diode bridge comprising a pair of oppositely biased diodes connecting a second junction on said first circuit leg between said first trigger means and said second sensor with a second junction on said second circuit leg between said second trigger means and said fourth sensor;
and
means for applying a first voltage across said circuit legs.

4 more elements

A firing circuit for actuating a plurality of instrumentalities of a vehicle passenger restraint system comprising

a first circuit leg comprising in series a first normally open sensor for detecting a first condition requiring actuation of said instrumentalities, trigger means having an internal for actuating said instrumentalities and a second normally open sensor for a second condition requiring actuation of said instrumentalities, said first and second sensor being shunted by a first and second resistor, respectively, each having a resistance substantially greater than the internal resistance of said trigger means:
a second circuit leg connected in parallel with said first circuit leg comprising in series a third normally open sensor for detecting the first condition requiring actuation of said instrumentalities and a third resistor having a resistance substantially greater than the internal resistance of said trigger means:
a third circuit leg connected in parallel with said first and second circuit legs comprising in series a fourth resistor and a fourth normally open sensor for detecting the second condition requiring actuation of said instrumentalities, said fourth resistor having a resistance substantially greater than the resistance of said trigger means;
a first diode bridge comprising a pair of oppositely biased diodes connecting a first junction on said first circuit leg between said first sensor and said trigger means with a junction on said second circuit leg between said third sensor and said third resistor;
and
a second diode bridge comprising a pair of oppositely biased diodes connecting a second junction on said first circuit leg between said first trigger means and said second sensor thereof with a junction on said third circuit leg between said fourth resistor and said fourth sensor;
and
means for applying a first voltage across said circuit legs.

5 more elements

Dependencies are inferred from the claim text.