Reconfigurable air bag firing circuit

• US 5,261,694 A
• Filed: 06/14/1991
• Issued: 11/16/1993
• Est. Priority Date: 06/14/1991
• Status: Expired due to Fees

• Current Assignee: Automotive Systems Laboratory, Incorporated (Ningbo Junsheng Investment Group Co., Ltd.)
• Original Assignee: Automotive Systems Laboratory, Incorporated (Ningbo Junsheng Investment Group Co., Ltd.)
• Inventors: Paye, James R., White, Craig W., Musser, Kevin E.
• Primary Examiner(s): Tyson, Karin L.
• Application Number:
  US07/715,344
• Time in Patent Office: 886 Days
• Field of Search: 280/735, 180/274, 180/282, 307/10.1, 340/436, 340/438
• US Class Current: 280/735
• CPC Class Codes: B60R 21/0173 Diagnostic or recording means therefor

Abstract

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.

Claims

1. A control circuit for a vehicle passenger restraint comprising:

a firing path including in series;

a first, normally-open, acceleration-responsive switch which closes in response to an acceleration input exceeding a first threshold, said first switch being shunted by a first shunting resistor;

trigger means for actuating said restraint, said trigger means having internal electrical resistance substantially less than said resistance of said first shunting resistor; and

a second and third normally-open, electrically-operated switch, said second switch being shunted by a second shunting resistor having a resistance substantially greater than the internal resistance of said trigger means;

means for applying a voltage across said firing path;

an electronic sensor for sensing an acceleration exceeding a second threshold, said second threshold being nominally greater than said first threshold;

a microprocessor responsive to said electronic sensor for operating said controlling said second switch, said microprocessor closing said second switch when said electronic sensor senses an acceleration exceeding said second threshold;

failure-detecting means for detecting a failure of first switch, said electronic sensor, said microprocessor, or said second switch;

first means responsive to said failure-detecting means for increasingly biasing said first switch in said normally-open position; and

second means responsive to said failure-detecting means for operating said third switch.

2. The circuit of claim 1 wherein said first means responsive to said failure-detecting means includes

a constant current source;

and

a coil connected to said constant current source.

3. A method of operating the circuit of claim 1, said operating method including the steps of:

detecting a failure of at least one of said group consisting of said electronic sensor, said microprocessor, and said second switch;

confirming the continued operability of said first sensor by not detecting a failure thereof with said failure-detecting means;

operating said first means responsive to said failure-detecting means to increasingly bias said first switch in said normally-open position after confirming the continued operability of said first sensor; and

operating said second means responsive to said failure-detecting means to close said third switch after said first switch is increasingly biased in said normally-open position.

4. A circuit for actuating a safety restraint in a motor vehicle comprising:

sensor means for generating a first signal representative of instantaneous vehicle acceleration;

processor means responsive to said first signal for generating a second signal when said first signal indicates a condition requiring actuation of said safety restraint;

a firing path having in series a first normally-open switch means which closes in response to vehicle acceleration exceeding a threshold value therefor, a current-responsive trigger means for actuating said safety restraint, and a second normally-open switch means in communication with said processor means which closes in response to generation of said second signal;

failure detecting means for detecting a failure of said first switch means and any one or more of the group consisting of said sensor means, said processor means and said second switch means;

threshold-adjusting means responsive to said failure detecting means for increasing the threshold value of said first switch means, wherein said threshold-adjusting means operates to increase the threshold value of said first switch means upon detection of a failure of any one of the group consisting of said sensor means, said processor means, and said second switch means, and wherein operation of said threshold-adjusting means is inhibited upon detection of a failure of said first switch means; and

shunt means, responsive to said failure detecting means and operation of said threshold-adjusting means, for shunting said second switch means, wherein said shunt means operates to shunt said second switch means after operation of said threshold-adjusting means upon detection of a failure of any one of the group consisting of said sensor means, said processor means, and said second switch means.

5. A method for operating a control circuit for a safety restraint in a motor vehicle, said control circuit including sensor means for generating a first signal representative of instantaneous vehicle acceleration;

processor means responsive to said first signal for generating a second signal when said first signal indicates a condition requiring actuation of said safety restraint;

a firing path having in series a first normally-open switch means which closes in response to vehicle acceleration exceeding a threshold value therefor, a current-responsive trigger means for actuating said safety restraint, and a second normally-open switch means in communication with said processor means which closes in response to generation of said second signal;

means for detecting a failure of any one or more of the group consisting of said sensor means, said processor means, said first switch means, and said second switch means;

threshold-adjusting means for increasing the threshold value of said first switch means; and

shunt means for shunting said second switch means, said method comprising the steps of;

detecting a failure of any one or more of the group consisting of said sensor means, said processor means, and said second switch;

confirming the continued operability of said first switch means by not detecting a failure thereof;

operating said threshold-adjusting means after confirming continued operability of said first switch means to increase the threshold value of said first switch means;

confirming the operation of said threshold-adjusting means; and

operating said shunt means to shunt said second switch means only after confirming the operability of said threshold-adjusting means.