Roof-mounted occupant restraint system

A restraint system for helping to protect an occupant of a vehicle having a roof and a cabin with a seat for the occupant, comprising:

• an airbag mounted to the vehicle roof, the airbag having a stored condition and being inflatable to a deployed condition, the airbag when deployed having a front-facing occupant receiving portion and an opposite rear-facing portion facing away from the occupant;
• an inflator configured to direct inflation fluid into the airbag to inflate and pressurize the airbag;
• wherein the airbag has a generally U-shaped configuration with a first leg comprising the occupant receiving portion and a second leg comprising the rear-facing portion, the first leg having a terminal end portion with a connection to the vehicle roof, wherein the airbag is configured to pivot about the connection to the vehicle roof in response to the occupant receiving portion being acted upon by an impacting occupant;
• wherein a terminal end portion of the second leg is free from connections to the vehicle and configured to move into engagement with the vehicle roof in response to the airbag pivoting about the connection to cause the vehicle roof to act as a reaction surface for resisting pivoting movement of the airbag about the connection in response to the impacting occupant so that the airbag cushions the impacting occupant without relying on the rear-facing portion of the airbag engaging vehicle structure other than the roof as a reaction surface for supporting the airbag;
• wherein the restraint system further comprises at least one tether that connects the end portion of the first leg to the end portion of the second leg, wherein the first and second legs are configured to move away from each other in response to pressurization and the at least one tether is configured to limit the first and second legs from moving away from each other in response to pressurization so that pressurization of the first and second legs tensions the at least one tether, which pre-loads the first and second legs against movement toward each other;
• wherein the inflator is configured to deliver a volume of inflation fluid to the airbag sufficient to pressurize the first and second legs such that the pre-load resists movement of the first leg toward the second leg to a degree sufficient to absorb impact forces and provide a ride-down effect to the occupant due to the vehicle roof receiving the end of the second leg and acting as a reaction surface that resists further pivotal movement of the airbag about the connection of the first leg to the vehicle roof.