US Patent 8376396 Multi-chamber knee airbag

An airbag module for a vehicle includes a gas generator for generating a gas and a multi-chamber airbag operatively connected to the gas generator for receiving the gas. The airbag defines a first inflation chamber, at least one second inflation chamber, at least one third inflation chamber and a fourth inflation chamber. The airbag includes internal vents configured to allow selective communication between the first chamber and each of the at least one second chamber and the at least one third chamber and selective communication between the at least one second chamber and the fourth chamber. The internal vents are configured to maintain a higher pressure in selective chambers by restricting ability of the gas to escape the selective chamber. The order of internal venting between the respective inflation chambers controls the pressure and timing of inflation of the multi-chamber airbag.