SIR System

The Supplemental Inflatable Restraint (SIR) system consists of the following deployment loops, along with the Sensing And Diagnostic Module (SDM), an AIR BAG telltale in the instrument cluster, and connecting wires:
^ Driver Frontal Deployment Loop - Roll connector, driver inflator module.
^ Passenger Frontal Deployment Loop - Passenger inflator module.
^ Left Curtain Deployment Loop - Left Side Impact Sensor (Left SIS), left curtain inflator module.
^ Right Curtain Deployment Loop - Right Side Impact Sensor (Right SIS), right curtain inflator module.

The frontal air bags deploy when the vehicle is involved in a frontal crash of sufficient force. The function of the frontal deployment loops is to supply enough current to deploy the frontal inflator modules when the SDM detects vehicle velocity changes severe enough to warrant deployment. To detect changes in forward velocity, the SDM contains a sensing device (accelerometer) that converts the vehicle velocity changes to an electrical signal. The electrical signal generated is processed by the SDM and then compared to the values stored in memory (EEPROM). When the proper threshold values are exceeded, the SDM will cause current to flow through the initiator, which ignites the material in the frontal inflator modules. The gas produced from this reaction rapidly inflates the frontal air bags. The frontal air bags (1) are deployed during certain frontal crashes to supplement the protection offered by the driver and front passenger seat belts (2). To further absorb crash energy, there are knee bolsters (3) located beneath the instrument panel for both the driver and passenger. Additionally, the steering column is collapsible.

The optional side curtain air bags deploy when the vehicle is involved in a side crash of sufficient force. The function of the side curtain deployment loops is to supply enough current to deploy the curtain inflator module on the side of impact when the SIS detects a side impact severe enough to warrant deployment. The SIS contains a sensing device (accelerometer) that converts acceleration into an electrical (analog) signal. This signal is converted by a microprocessor in the SIS into acceleration and velocity data. This data is used by a sensing algorithm and compared to various predetermined boundary conditions. When the acceleration value exceeds the predetermined threshold and the velocity boundary is crossed, the SIS signals the SDM to cause current to flow through the initiator, which ignites the material in the curtain inflator module. The gas produced from this reaction rapidly inflates the curtain air bag from the roof rail on the side of impact. The curtain air bag supplements the protection offered by the door and the vehicle structure.