General System Description

DESCRIPTION
The Supplemental Inflatable Restraint (SIR) system supplements the normal restraint of the driver's seat belt by deploying an airbag from the center of the steering wheel during an accident. The airbag deploys when the vehicle is involved in a front end collision of sufficient force. To further absorb the energy of an accident, there is a knee bolster (tie bar) located below the instrument panel in the driver area. The steering column is collapsible to also absorb force.

OPERATION
The main portions of the SIR system are the deployment loop and the diagnostic energy reserve module (DERM). The main function of the deployment loop is to supply current through the inflator module in the steering wheel which will cause deployment of the airbag in the event of an accident severe enough to warrant airbag deployment.
The deployment loop consists of the arming sensor, coil assembly, inflator module and discriminating sensors. The arming sensor switches power to the inflator module on the high side of the deployment loop. Either of the discrimination sensors can supply ground to the inflator module on the low side of the deployment loop. The inflator module is only supplied sufficient current to deploy when the arming sensor and at least one of the two discriminating sensors close simultaneously.
The diagnostic energy reserve module (DERM) supplies the deployment loop with a 36 volt loop reserve (36VLR) to assure sufficient energy to deploy the airbag if the ignition voltage is cut during an accident.