US Patent 7942443 Airbag system

An airbag module for a vehicle includes an airbag cushion, an inflator to inflate the airbag cushion, a sleeve connected to the airbag cushion and a tether configured to pass through the sleeve. A first end of the tether is anchored to a portion of the airbag cushion, module, or a structure of the vehicle and a second, opposite end of the tether is capable of passing through at least a portion of the sleeve during deployment of the airbag. The tether and sleeve are configured to initially restrain the deployment of the airbag cushion to provide a knee bolster, after which the tether is configured to unlace within the sleeve to release the restraint on the airbag cushion.