Description & Operation

The Supplemental Inflatable Restraint (SIR) system supplements protection offered by seat belts. The air bags will deploy when the vehicle is involved in a frontal crash of sufficient force, up to 30 degrees left or right of the center line of the vehicle. For additional absorption of crash energy, there are knee bolsters located beneath the instrument panel for both the driver and the passenger. The steering wheel is collapsible as well.

The SIR system is composed of the Sensing and Diagnostic Module (SDM), the driver inflator module, the SIR coil assembly, the passenger inflator module and the AIR BAG warning light in the instrument cluster. The SDM, SIR coil assembly (driver's side only), driver inflator module, passenger inflator module and connecting wires make up the deployment loops. The main function of the deployment loops is to supply current through the inflator modules, which cause deployment of the air bags in the event of a frontal collision. The inflator modules are only supplied with sufficient current to deploy when the SDM detects vehicle velocity changes severe enough to necessitate deployment.

The SDM employs a sensing device which converts the vehicle acceleration changes to an electrical signal. The signal generated is processed by the SDM and then compared to values stored in EEPROM. When the proper variances are exceeded, the SDM will cause current to flow through the inflator module deploying the air bags.