In the past 20 years，newly produced automobiles have been equipped with occupantrestraint systems, such as airbags, to reduce passenger injuries and fatalities in the eventof a crash. An airbag is a passive restraint system-an automatic safety system thatrequires no action by the occupant. Government regulations，industrial participation, andsocial consciousness of safety have popularized the use of occupant restraints in vehiclesworldwide. Using advanced technologies, additional restraints and enhanced functionalities arebeing implemented.
History
Automobiles entered the market more than 100 years ago. Since then, tremendousprogress in reliability, usability, and safety of roadway vehicles has been made. However,the availability of passive safety systems was slow in coming, despite the initial conceptionin 1950s and experimental production in 1970s. It was not until the late 1980s that airbagsbecame standard equipment，beginning in the United States. Over the last 20 years，theautomotive safety industry has gone through considerable changes.
In recent years，passive restraint systems have been one of the fastest-growing sectorswithin the automotive industry. One reason for this growth is the inclusion of additionalrestraint devices on vehicles. For example，the average number of airbag modules hasincreased from one to two per vehicle in the early 1990s to four to six per vehicle for thelatest models, with more expected to come. Another reason for this growth is an increasein the complexity and sophistication of the safety systems' functional requirements. Forexample, to minimize out-of-position occupant injuries, a smart airbag system needs to beequipped with occupant-sensing capabilities.
Particularly notable in the evolution of restraint systems has been the phenomenon ofincreasing use of electronics, which has occurred in parallel in the automotive world，aswell as most technology fields. Increasingly, sensing, actuation, and control functions ofairbag systems are being implemented with electronic filters, conditioners，memoryintegrated circuits, microprocessors， and microcontrollers. Upcoming productsimplemented in electronics，such as rollover and other sensors, are being added into anintegrated vehicular safety system.
Technology Trends
Over the years, a transition in technology has occurred at several levels among theprimary components of occupant restraint systems, including sensors, airbag modules,and seat belts. In addition, product design and implementation methods have changeddramatically. The functional requirements of passive restraint systems have been elevatedfrom a simple on-or-off deployment decision to a staged- or graded-control command,which provides a tailored choice for optimal protection in a smart system.
In the area of sensing technology, electronic sensors have become dominant andreplaced first-generation mechanical and electromechanical devices. Electronic control units(ECU) have been equipped with sophisticated capabilities to allow reliable diagnosis androbust control. The ECU is coupled with a network of satellite and auxiliary sensors toacquire all the necessary information to make an appropriate crash-status decision. Inaddition, data from occupant sensors and seat-belt-buckle switches are fed into the ECU toprovide occupant-seating conditions as a critical part of smart restraints. Through a sensornetwork distributed across the vehicle platform, intelligent decisions can be made forselective deployment of the proper restraints. Airbag modules are moving quickly towardthe use of dual- or multiple-stage inflators.
These partitioned and staged inflators provide the benefits of minimizing loads on theoccupants and offering the flexibility of meeting the protection requirements in variouscrash conditions. Seat belts have been engineered with versatile options such as pretensioning and load-limiting features.
Togetherr sensors, actuators，and protective devices constitute the foundation ofsmart airbags. An optimal protection sequence begins with the pretensioning of the seatbelts to engage the occupant, followed by a seat-belt load-limiting feature to minimize therestraining load, and then an effective dissipation of occupant movements with an airbagcushion inflated with an adjusted and controlled level of deployment power. All therestraining devices in the' vehicle work in a smart and coordinated manner to manage thekinetic energy carried by occupants in a collision.
Outlook
The airbag industry has experienced tremendous growth in the last two decades，andis already maturing in several subsectors despite its relatively short history, compared withother sectors of the automotive industry. The concept of vehicular safety, however，isbeing rejuvenated with a variety of new developments.
For example, global positioning systems are being integrated with wireless communicationand crash-sensing systems into emergency notification and response services. Parallel tothe rapid progress in passive restraint systems, significant strides have been made in activesafety systems. Passive safety systems are“reactive" with the purpose of mitigatingaccident consequences，while active safety systems are“preventive”and target thepotential to avoid accidents. In active safety systems，the actions occur prior to theaccident. One example is the mild level of braking exerted automatically in some advancedcruise control system when the vehicle-following distance falls below a threshold. Anotherexample is the use of a steering-assist function to prevent road-departure accidents.
The introduction of active safety systems will provide the foundation for integratingselective components and capabilities into automotive safety systems. The focus of safetyimprovements will shift from collision mitigation to collision avoidance, although the twofunctions are not separable. The passive restraints, originating from the concept of asimple airbag deployment, will evolve into a part of the smart-vehicle interior thataccommodates all customer-appealing features inside a protective vehicle environment.
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