SIR System

SIR SYSTEM OPERATION

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), and Instrument Panel (IP) module (1). 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. 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.

SIR SYSTEM DESCRIPTION
The SIR system consists of the following components:
^ AIR BAG indicator located in the Instrument Panel Cluster (IPC)
^ Driver and passenger knee bolsters
^ Inflatable restraint front end discriminating sensor
^ 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 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 front end discriminating sensor which assists the SDM in determining the severity of some frontal collisions. The SDM contains a microprocessor that performs calculations using the measured accelerations. The SDM compares these calculations to a value stored in memory. When the generated calculations exceed the stored value, the SDM will cause current to flow through the frontal deployment loops deploying the air bags. Once the air bags are inflated they quickly deflate through the air bag vent holes. After the air bags have deployed, the SDM sets a Diagnostic Trouble Code (DTC) and turns the AIR BAG indicator ON. The SDM, IP module, steering wheel module, steering wheel module coil and the connecting wires makeup the deployment loops. The SDM continuously monitors the deployment loops for malfunctions and turns the AIR BAG indicator ON if a fault is detected.