Automotive Systems Laboratory, Inc.

Kevin E Musser

Craig W White

Leonard W Behr

James R Paye

A method and system for improving reliability of a vehicle crash discrimination system by minimalizing the effect of resonance inherently produced by structural elements of the vehicle includes using at least two accelerometers (18,20) mounted to different structural elements (22, 24) of the vehicle. The accelerometers are preferably mounted in close proximity to each other to produce similar acceleration data, but corrupted by dissimilar structural resonance. Signal analysis processing (36) is performed to extrapolate the common acceleration data to generate an output (38) substantially uncorrupted by structural resonance for use in the vehicle crash discrimination system. Detection of operability of the accelerometers (34) can also be performed to provide for switching to a backup mode filtering process (44) to insure operability of the discrimination system upon failure of one of the accelerometers.

Method for minimalizing structural resonance on vehicle acceleration data

An acceleration sensor having a sensing mass supported relative to a frame by a plurality of beams having a plurality of resistors integral therewith. The resistance of the beam resistors varies as the sensing mass is displaced relative to the frame in response to acceleration of the frame in a direction generally normal to the plane of beam extension. The displacement of the sensing mass due to such acceleration produces a corresponding change in the output of a Wheatstone bridge incorporating the beam resistors in the legs thereof. At least one leg of the bridge additionally has a resistor of variable resistance in series with the beam resistor thereof, the resistance of which is controlled by a microprocessor, whereby the bridge output is adjusted to compensate for temperature effects and manufacturing tolerances. The output of the electrical control circuit for the sensor is periodically calibrated by electrostatically deflecting the sensing mass relative to the frame, whereby the sensing mass is subjected to the equivalent of a known accelerating field, and using the resultant change in bridge output as a reference value for calibrating the instantaneous changes in bridge output resulting from the acceleration of the sensor frame.

Method for calibrating an accelerometer

An air bag firing circuit comprises a firing path which includes in series a safing sensor, a squib, and a FET operated under microprocessor control in response to the output of an electronic crash sensor. A power supply maintains a known voltage across the firing path sufficient to explode the squib upon simultaneous 'closure' of both the safing sensor and the FET operated by the microprocessor in response to crash sensor output. Normally, upon detection of a failure in the electronic crash sensor, its supporting electronics, or the FET actuated in response thereto, the microprocessor reconfigures the firing threshold of the safing sensor, as by applying a current to its integral test coil to increasingly bias the sensor's inertial mass away from its switch contacts. However, if a failure of the safing sensor is detected, reconfiguration of its threshold is inhibited notwithstanding the failure of other circuit components to prevent inadvertent deployment of the air bag. Once the safing sensor is reconfigured, the microprocessor turns on another FET to pull one side of the squib to ground, thereby removing the inoperable FET from the firing path and ensuring continued protection of the vehicle passengers until the sensor is serviced or replaced.

Reconfigurable air bag firing circuit

An acceleration sensor having a sensing mass supported relative to a frame by a plurality of beams having a plurality of resistors integral therewith. The resistance of the beam resistors varies as the sensing mass is displaced relative to the frame in response to acceleration of the frame in a direction generally normal to the plane of beam extension. The displacement of the sensing mass due to such acceleration produces a corresponding change in the output of a Wheatstone bridge incorporating the beam resistors in the legs thereof. At least one leg of the bridge additionally has a resistor of variable resistance in series with the beam resistor thereof, the resistance of which is controlled by a microprocessor, whereby the range of bridge outputs is adjusted to initially compensate for manufacturing tolerances and thereafter compensate for temperature effects and component aging. The resistance is varied by way of the microprocessor switching fixed resistors in paarallel connection with the leg of the bridge.

Self-compensating accelerometer

Self-calibrating accelerometer

A firing circuit for deploying a pair of air bags comprises four circuit legs connected in parallel across a voltage supply via a diode shunted with a resistor. The first and second circuit legs each comprise in series a safing sensor, a squib, and a crash sensor, with each sensor being shunted by a like resistor whose resistance is substantially greater than the nominal resistance of the squibs. The third and fourth circuit legs each preferably comprise a resistor in series with a capacitor, with the resistance of the series resistor being significantly greater than that of the resistor shunting the grounded diode. Five bridges interconnect the four circuit legs so as to provide multiple firing paths and continued circuit viability notwithstanding the presence of one or more 'faults' in the instant firing circuit. The addition, for example, of voltage detecting and comparing means about the four circuit legs, diodes and/or current-limiting devices in the bridges between the circuit legs further, and means operative to draw current from a junction on the first and second circuit legs, respectively, renders the instant firing circuit fully diagnosable in situ.

Passenger restraint firing circuit

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.

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Farmington, MI, United States of America

Kevin E Musser