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AIRBAG logo embossed onto the seat cover
The supplementary restraint system (SRS) has been specifically designed to protect the driver and passenger from sustaining severe facial and upper body injuries in the event of a serious impact. The SRS is designed to deploy only in the event of a collision, with the ignition in the RUN position and where the safety belts on their own are no longer sufficient to protect the occupants. However, the SRS will deploy regardless of whether or not an occupant is wearing a safety belt.
Optimum protection can only be achieved when used in conjunction with a conventional three-point safety belt. The safety belts form an integral part of the SRS.
Vehicles built up to 09/1999 utilize a direct current (DC) firing strategy. Vehicles built 09/1999 onwards utilize an alternating current (AC) firing strategy.
The driver, wearing the safety belt provided, should position the seat as far back as is practical, so that the steering wheel can be reached with arms slightly angled, thereby leaving a gap between the steering wheel and the driver.
The passenger, wearing the safety belt provided, should not position himself or herself so that the air bag cover is in direct contact with the occupants' body.
The front air bags and safety belt buckle pretensioners will deploy in the event of a direct front impact or when the impact angle is up to 30 degrees from the left or right of the vehicle center line.
The air bag(s) and safety belt buckle pretensioners will deploy only once. In a collision in which they deployed at the first impact, the air bags and safety belt buckle pretensioners will not reduce the risk of injury in a subsequent impact.
In the event of a side impact, in which the side air bags deploy, the front air bags will still deploy in a subsequent front impact, provided that the front impact exceeds the triggering threshold.
Under certain circumstances, although the damage sustained by the vehicle may look extensive, the impact may remain below the triggering threshold of the SRS and the air bags will not deploy. In such circumstances the safety belts would provide sufficient protection for the occupants.
The visible VIN plate, which shows the air bag symbol and either X1 or X2 dependant on the number of air bags fitted, is attached to the windshield edge of the instrument panel.
Vehicles equipped with side air bag modules can be identified by an embossed AIRBAG logo on the seat fabric adjacent to the air bag module.
The SRS consists of the following components:
- air bag control module
- wiring harness
- air bag sliding contact
- warning indicator
- air bag module(s)
- side impact sensors (when equipped with side air bags)
- safety belt buckle and pretensioners
The air bag control module governs the operation of the whole system, including the diagnostics element. It contains two frontal impact sensors; a crash sensor and a safing sensor. The crash sensor produces a signal corresponding to the rate of deceleration. The safing sensor detects only deceleration. These two sensors are connected in series and if they both sense a deceleration in excess of a predetermined limit, the air bag control module will deploy the front air bag module(s) and the safety belt buckle pretensioners. The front air bags are not designed to deploy in side or rear impacts where the air bag(s) will not offer additional protection to the occupant(s). In exceptional circumstances the front air bags may deploy in a side impact which results in a sudden total loss of forward motion. The air bag control module will always deploy the safety belt buckle pretensioner before or at the same time as the air bag(s) and in that sequence only.
In the event of a side impact, the air bag control module will deploy the corresponding side air bag, even if the respective seat is not occupied, when the level of impact is sufficiently great that the air bag could reduce the risk of injury. Deployment is dependent on the signal received from the side impact sensor. The side air bags are not designed to deploy in a mainly frontal or rear impact where the side air bag will not offer additional protection to the occupant.
The air bag control module performs continual system diagnostics. In the event of a fault being detected the warning indicator is illuminated either constantly or intermittently. The behavior of the warning indicator depends on the type of fault present. The warning indicator is located in the instrument cluster.
The safety belt buckle pretensioners reduce any slack, which may exist in the safety belt webbing, keeping the occupant in their seat during the impact and air bag deployment.
The wiring harness provides power to the air bag control module from the vehicle supply and hence to the air bag module(s), side impact sensors (if equipped with side air bags), safety belt buckle pretensioners and the warning indicator.
The air bag sliding contact is designed to carry signals between the air bag control module and the driver air bag module. The air bag sliding contact is fitted to the steering column and consists of fixed and moving parts connected by a coiled Mylar tape with integral conducting tracks. The Mylar tape is able to `wind up' and `unwind' as the steering wheel (to which the moving part is attached) is turned, maintaining electrical contact at all times between the air bag control module and the driver air bag module. The air bag sliding contact is used in order to achieve the high degree of circuit integrity required critical safety system SRS
When the air bag(s) deploy, they remain fully inflated for only a fraction of a second and start to deflate immediately, cushioning the occupant. The high speed of inflation along with the surrounding events and noise from the impact can give the impression that the air bag(s) did not deploy to their full extent.
In certain circumstance slight grazing or minor friction burns can result from air bag deployment.
There are two processes which are involved:
- Friction can occur between the fabric of the air bag and unprotected areas of the skin, either during its very rapid deployment or when the occupant contacts the air bag.
- Hot gases from the charge used to inflate the air bag vent as it starts to deflate. Depending on the position of the drivers hands, or how close the occupant is to the air bag, it is not always possible to exclude the possibility of these gases contacting areas of the skin unprotected by clothing.
The driver, passenger and side air bag modules consist of the following components which cannot be disassembled:
- inflator
- bag
- container
- cover
Driver and passenger air bag module inflator
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Passenger inflator unit
The inflator is screwed into a metal cup-shaped container. The air bag is then folded on top of the inflator and the whole sub-assembly is closed by the cover.
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' moulded in its surfaces allowing the air bag to easily exit though the cover when the system deploys.
The passenger air bag module is located above the glove compartment and is integrated into the instrument panel to provide an unobtrusive appearance. The cover is a one-piece moulding held by five clips and a short retaining strap. As the air bag deploys, the cover is forced free of the clips, but remains attached to the instrument panel by the short retaining strap.
Side air bag module
The side air bag modules are integrated into the front seat backrests providing an unobtrusive appearance. The unique seat cover has been designed to accommodate air bag deployment. When the side air bag is deployed the stitched seam of the seat cover adjacent to the side air bag module splits, allowing the air bag to exit the seat back unobstructed.
The purpose of the inflator is to generate the gas needed to fill the air bag. It consists of a high strength steel casing filled with a solid propellant charge and an electrically activated igniter. The igniter is activated by a signal from the air bag control module, which in turn ignites the propellant charge. The very rapid burning of the propellant produces sufficient gas to fill the air bag(s). As the gases expand they cool, preventing heat damage to the air bag. The driver air bag module has one inflator and an air bag, with a filled volume of 30 liters. The passenger air bag module had two inflators and an air bag on vehicles built up to 04/1997, revised to a single inflator and an air bag on vehicles built 04/1997 onwards. The passenger air bag has a filled volume of 60 liters.
The side air bag modules each have one inflator and an air bag which has a filled volume of 12 liters.
The air bag(s) are a one-piece woven item with a silicon coating to provide flame and heat protection in the vicinity of the inflator. The shapes of the passenger and side air bags (when equipped) are tailored to the vehicles proportions. In order to prevent the folds of the air bag from sticking together in its tightly stowed position, the fabric may be treated with talcum powder. When the air bag(s) deploy, some of the fine powder is blown into the vehicle. This powder is visible as a dust cloud and also has a characteristic odour. The particles soon settle and do not represent a health risk. The dust cloud is not a sign of external combustion outside the air bag inflator cartridge.
The SRS will communicate concerns detected during a driving cycle or after initial key ON by means of a warning indicator located in the instrument cluster.
