Air Bag Systems: Description and Operation

Air Bag Supplemental Restraint System (SRS)

The SRS is designed to provide increased collision protection for front seat occupants in addition to that provided by the three-point safety belt system. Safety belt use is necessary to obtain the best occupant protection and to receive the full advantages of the SRS.

The SRS components are shown in the following illustration.

Air Bag Supplemental Restraint System (SRS) Components







Restraints Control Module (RCM)

The restraints control module (RCM):
- The primary purpose of the restraints control system is to discriminate between an event that warrants supplemental restraints system deployment and an event that does not. The air bag control module, located under the floor console, governs the operation of the whole system and performs continual system diagnostics. Information on the severity of an impact is received from the crash sensor. In the event of a side impact, in excess of a predetermined limit, the air bag control module will evaluate the signal received from either of the side impact sensors against stored data and deploy the corresponding side air bag module and the side air curtain module. In the event of a frontal impact, in excess of a predetermined limit, the air bag control module will evaluate the signal received from the front crash sensor against stored data and deploy the front air bag modules and the safety belt buckle pretensioners. Variations in the deployment of the front air bag modules are dependent on the status of the driver seat track position, passenger weight sensor and the front safety belt buckles.

Driver Air bag Module

The drivers air bag module:
- The driver air bag module is replaced as an assembly.
- There is no routine maintenance required for this part and there is no serviceable parts.
- The driver air bag module is fitted to the steering wheel, the cover forming the outer surface of the steering wheel boss. The cover has invisible split lines molded in its surface allowing the air bag to easily exit through the cover when the system deploys.

Passenger Air Bag Module

The passenger air bag module:
- The passenger air bag module is replaced as an assembly.
- There is no routine maintenance required for this part and there is no serviceable parts.
- The passenger air bag module is located above the glove compartment behind the finish panel. The air bag control module will only deploy the passenger air bag provided that the passenger weight sensor senses that the seat is occupied.


Deployment Door

The deployment door:
- Is an integral part of the instrument panel with a textured finish.
- Has a tear seam that separates when the air bag inflates, and hinges out of the way during deployment.
- Must not be repainted for any reason.
- Is a component of the passenger air module and is not replaced separately.

Inflator

The inflator:
- Both driver and passenger air bag inflators have a two stage inflation system, this means there are two air bag connections to be made. The two connectors are coded to ensure that the connection is made correctly.
- Receives electrical charge when the air bag sensor is activated.
- Contains an igniter that converts the electrical signal to thermal energy (heat), causing the ignition of the inflator gas generant.
- Inflates the air bag after the sodium azide/copper oxide combustion occurs.
- Is a component of the driver air bag module and passenger air bag module and is not replaced separately.

Side Air Curtain Module

The side air curtain module:
- Is replaced as an assembly.
- The side air curtain modules are fixed between the A-pillar and C-pillar under the headliner and deployed at the same time as the corresponding seat mounted side air bag. If the passenger air bag is deactivated the corresponding side air bag is also deactivated. When deployed, the side air curtain module extends down to approximately shoulder height to protect both the front and rear occupants heads. The side air curtain module is stabilized at the A-pillar and C-pillar by tethers. The side curtain module uses compressed argon to inflate the air bag.

Side Air Bag Module - Front Seat

The side air bag module:
- Is replaced as an assembly.
- The side air bag module is mounted in the outboard bolster of each front seat and uses compressed argon to inflate. It provides protection for the thorax (the part of the torso between the neck and the abdomen). To ensure that the air bag emerges at the same point, a chute has been designed into the inside of the seat trim cover and wrapped around the air bag module. In a side air bag module deployment situation, the air bag module deploys through a stitched seam in the side bolster.

Air Bag Sliding Contact

The air bag sliding contact:
- The air bag sliding contact does not contain any serviceable components.
- The air bag sliding contact is mounted on the steering column, behind the steering wheel.
- The air bag sliding contact continuously transfers electrical signals from the driver air bag module to the air bag sensor.

Side Impact Sensors

The side impact sensors:
- The side impact sensors are mounted at the base of the B-pillars to facilitate lateral impact sensing. In the event of a side impact, the air bag control module processes the crash data sent by the side impact sensor against stored data. The air bag control module will deploy the side air bag and, if equipped, the side air curtain on the side the deployment request was initiated.

Crash Sensor

The crash sensor:
- The front crash sensor is located under the grill opening panel to facilitate impact sensing along the longitudinal axis. The air bag control module processes the crash data sent by the front crash sensor against stored data, and deploys the front air bags.

Seat Track Position Sensor

The seat track position sensor:
- The seat track position sensor is located on the driver seat track. The seat position sensor determines the position of the driver seat, which is then communicated to the restraints control module. If the driver seat is in the forward position, the driver air bag second stage is disabled.

Passenger Weight Sensor

The passenger weight sensor:
- The occupant classification sensor detects, by integrated pressure sensors, the presence of a passenger or object on the seat cushion. The occupant classification sensor cannot discriminate between a passenger and an object. The electronic control unit processes the pressure information and, if the pressure exceeds a threshold, an occupied seat state is communicated through the wiring harness to the air bag control module. If the seat is empty or occupied by a very light object an empty seat state is transmitted to the air bag control module and the passenger air bag will be deactivated to avoid unnecessary repair costs. If the seat is empty and the safety belt is buckled the passenger air bag deactivation indicator will be illuminated. The occupant classification sensor system is not affected by the position of the passenger seat.

Passenger Air Bag Deactivation (PAD) Indicator

The Passenger air bag deactivation (PAD) Indicator:
- The passenger air bag deployment door has a built in lens that displays the passenger air bag module deactivated symbol. The symbol is backlit by the PAD indicator. The illumination of the symbol informs the front seat occupants whether or not the passenger air bag has been deactivated by the occupancy sensing system. The PAD indicator is located under the vent finish panel in front of the passengers seat.