1. Field of the Invention
The present invention relates to a curtain airbag that reduces the probability of ejection of a vehicle occupant during rollover (overturning) of a vehicle.
2. Related Technology
In recent years, high levels of safety performance have been required of vehicles. This trend is shared across countries around the world, where most vehicles are currently standard-equipped with airbags as vehicle safety devices. Firms involved in vehicle development have adopted ongoing safety improvements as a major development guideline. In keeping with this, new airbags are continually being developed.
Standards for evaluating vehicle safety differ from country to country, and firms approach product development such that products can meet evaluation standards in multiple countries. In the United States, for instance, which has the largest automobile fleet in the world, Federal Motor Vehicle Safety Standards (FMVSS) are issued by the National Highway Traffic Safety Administration (NHTSA). In a Notice of Proposed Rulemaking (NPRM, Docket Number: NHTSA-2009-0183) for FMVSS, scheduled to be issued by the NHTSA, a requirement is proposed that aims at “reducing the probability of occupant ejection from a vehicle through a side window using an ejection mitigation system in the event of a side impact crash or rollover (overturning)”. The requirement can be met by providing a curtain airbag as a device intended to reduce ejection from a vehicle, such that the curtain airbag constitutes herein the ejection mitigation system.
A curtain airbag is an airbag disposed above a door and that inflates and deploys along vehicle side windows, upon occurrence of an impact, to protect an occupant thereby. An ordinary curtain airbag is designed to have a pressure duration, when inflated and deployed, longer than that of a front airbag or the like. That is because the time during which an impact unfolds is lengthened if, for instance, rollover follows the lateral collision. Thus, the curtain airbag is intended to maintain the inflated state until and during rollover, to restrain thereby the occupant, and prevent the occupant from being ejected from the vehicle.
For instance, a curtain airbag that deploys along a vehicle side face comprises a series of chambers, as disclosed in Japanese Patent Application Publication No. 2002-302005. These chambers mitigate the impact that an occupant receives upon lateral collision of the vehicle, and prevents the occupant from being ejected out of the vehicle during vehicle rollover.
Upon collision of an impactor against an impact point prescribed in FMVSS 226, tension lines form radially from that impact point up to a respective tab that fixes the curtain airbag to the vehicle body. Herein, a tension line denotes a taut line that joins the center of impact, occurring upon impact against a given impact point, with a respective fixed point. Tension lines that are subject to the highest possible tension are formed in order to enhance the ejection mitigation function of the curtain airbag. That is because the higher the tension that is applied to the curtain airbag upon collision, the greater are the forces that oppose ejection of the occupant.