SIR System Operation

SIR SYSTEM OVERVIEW

SIR System Overview:

The Supplemental Inflatable Restraint (SIR) system supplements the protection offered by the occupant's seat belt system (2). The SIR system may contain several inflator modules located throughout the vehicle, i.e. steering wheel module (1), instrument panel (IP) module (1), side impact modules, or roof rail modules. In addition to inflator modules, the vehicle may contain seat belt pretensioners that tighten the seat belt in the event of a collision, thus reducing the distance between the occupant and the seat belt when an inflator module is deployed. Each inflator module has a deployment loop that is controlled by the sensing and diagnostic module (SDM) mounted inside the vehicle. The SDM determines the severity of a collision with the assistance of various sensor inputs located at strategic points on the vehicle. When the SDM detects a collision of sufficient force it will process the information provided by the sensors to further support air bag deployment. The SDM performs continuous diagnostic monitoring of the SIR system electrical components. Upon detection of a circuit malfunction, the SDM will set a DTC and inform the driver by turning the AIR BAG indicator ON. The steering column (1) and knee bolsters (3) are designed to absorb energy and compress during frontal collisions in order to limit leg movement and decrease the chance of injury to the driver and passenger.

After an Air Bag deployment, the SDM will send out a post-air message to the Rear Integration Module (RIM) through the class 2 serial data circuit. The RIM will unlock the doors and turn ON the interior lights 15 seconds after receipt of this message.

FRONTAL SIR SYSTEM DESCRIPTION
The frontal SIR system consists of the following components:
^ AIR BAG indicator located in the Instrument Panel Cluster (IPC)
^ Inflatable restraint Electronic Frontal Sensor (EFS), if vehicle is equipped with dual stage air bags
^ Inflatable restraint IP module
^ Inflatable restraint Sensing And Diagnostic Module (SDM)
^ Inflatable restraint steering wheel module
^ Inflatable restraint steering wheel module coil
^ Inflatable restraint wiring harnesses
^ Steering wheel and column

A frontal collision of sufficient force will deploy the frontal air bags. The SDM contains a sensing device (accelerometer) that converts vehicle velocity changes to an electrical signal. In the event of a frontal collision, the SDM receives a signal from the electronic frontal sensor, which assists the SDM in determining the severity of the collision. The SDM compares these signals to a value stored in memory. When the generated signals exceed the stored value, the SDM will cause current to flow through the frontal deployment loops simultaneously deploying the frontal air bags. The SDM, IP module, steering wheel module, steering wheel module coil and the connecting wires makeup the frontal deployment loops. The SDM continuously monitors the deployment loops for malfunctions and turns the AIR BAG indicator ON if a fault is detected.