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1、How Seatbelts Work,Introduction,According to NHTSA seatbelts save 13,000 lives in US each year7,000 US car accident fatalities could have been avoided if victims had been wearing beltsSeatbelts reduce the risk of death for a front seat car occupant by about 50 percent,Seatbelts,Seatbelt spreads the
2、crash forces across stronger parts of the body to minimize injury.Consists of lap belt and a shoulder beltBelts extend across the pelvis,rib cage and shoulder.Force is not concentrated in a small area,so injury is reduced.,Crashworthiness,Crumple zones front and rear of the car that collapse relativ
3、ely easilyCar seatbelts have the ability to extend and retractYou can lean forward easily,belt stays fairly tautIn a collision,belt tightens up and holds you in place,Seat Belt Retractors,Retractor mechanism,A spiraled spring rotates the spool to keep the seatbelt webbing taut,Retractor has a lockin
4、g mechanism,Two types of locking mechanisms:Systems triggered by the cars movementSystems triggered by the belts movement,Weighted pendulum triggered by car movement,When the car comes to a sudden stop the inertia causes the pendulum to swing forward.The pawl on the other end of the pendulum catches
5、 the tooth ratchet gear attached to the spool.The gear and spool can no longer rotate counterclockwise.,1),Centrifugal clutch triggered by belt movement,Centrifugal clutch.When the spool rotates quickly,centrifugal force drives the weighted end of a pivoting lever outward.The lever pushes a cam conn
6、ected to a pawl.The pawl moves into the spinning ratchet gear stopping the belt.,2),Pretensioner,Tightens up slack in the belt webbing in the event of a crashPulls in on the beltSome pretensioners pull the entire retractor mechanism backward and some rotate the spool itselfThey are the same central
7、control processor that activates the cars air bags,Pretensioners,Processor monitors mechanical or electronic motion sensors that respond to sudden deceleration of impactPretensioners built around electric motors or solenoids Popular designs today-pyrotechnics,When the gas is ignited,the pressure pus
8、hes the piston up to rotate the retractor,Pretensioners,Central element combustible gasWhen collision detected,it immediately applies electrical current across electrodesSpark from electrodes ignites the igniter material,which combusts to ignite the gasPressure pushes piston,driving it upwardRetract
9、or mechanism speeding rack rotates spool forcefully,winding up any slack belt webbing,Load Limiters,Minimize belt-inflicted injuryEarlier load limiters had stitching aling the belt that broke to limit the load as the belt tightened.Advanced load limiters rely on torsion barWhen great deal of force is applied to the webbing,torsion bar twists slightlyAllows webbing to extend a little bit farther,From:http:/,
