Audi A3 Sportback, Service, Page: 16 / 60

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Occupant protection
Airbag
Front airbags
Dual-stage gas generators are employed in the front airbags.
The impact load acting on the driver and front passenger during an accident is reduced by radial inflation of
the driver side airbag and by time-staggered ignition of the propellant charges. The airbag control unit
controls the time interval between the two deployments depending on the severity and nature of the accident.
The time interval can vary between approx. 5 ms and 40 ms.
In any event, both propellant charges are ignited. This ensures that no propellant charge remains active after
an airbag deployment.
Driver airbag, N95, N250
The driver airbag uses two pyrotechnic propellant charges.
The airbag control unit activates the electrical detonator of the first propellant charge. The detonator ignites
the priming charge, which in turn detonates the actual propellant charge through nozzle holes in the gas
chamber. The combustion of the propellant charge produces a pressure inside the gas generator. If the gas
pressure exceeds a defined threshold, then the gas generator housing deforms and allows the gas to flow
through the metal filter to the airbag. The airbag unfolds and is inflated by the gases resulting from
combustion of the propellant charge. After a preset time delay, the airbag control unit energises the second
electrical detonator, which directly ignites the secondary propellant charge. When a preset pressure is
reached, the developing gas lifts the cap off the second-stage chamber and flows into the first-stage
combustion chamber. From here, the gas flows through the filter to the airbag.
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Housing
Propellant charge 1
Cap Propellant charge 1
Metal filter
Priming charge Detonator 2
Nozzle holes
Detonator 1
Propellant charge 2