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1、How Seatbelts Work,Introduction,According to NHTSA seatbelts save 13,000 lives in US each year 7,000 US car accident fatalities could have been avoided if victims had been wearing belts Seatbelts reduce the risk of death for a front seat car occupant by about 50 percent,Seatbelts,Seatbelt spreads th
2、e crash forces across stronger parts of the body to minimize injury. Consists of lap belt and a shoulder belt Belts 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
3、relatively easily Car seatbelts have the ability to extend and retract You can lean forward easily, belt stays fairly taut In 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
4、has a locking mechanism,Two types of locking mechanisms: Systems triggered by the cars movement Systems 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 p
5、endulum catches 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 leve
6、r pushes a cam connected 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 crash Pulls in on the belt Some pretensioners pull the entire retractor mechanism backward and some rotate the spool itself The
7、y are the same central control processor that activates the cars air bags,Pretensioners,Processor monitors mechanical or electronic motion sensors that respond to sudden deceleration of impact Pretensioners built around electric motors or solenoids Popular designs today - pyrotechnics,When the gas i
8、s ignited, the pressure pushes the piston up to rotate the retractor,Pretensioners,Central element combustible gas When collision detected, it immediately applies electrical current across electrodes Spark from electrodes ignites the igniter material, which combusts to ignite the gas Pressure pushes
9、 piston, driving it upward Retractor mechanism speeding rack rotates spool forcefully, winding up any slack belt webbing,Load Limiters,Minimize belt-inflicted injury Earlier load limiters had stitching aling the belt that broke to limit the load as the belt tightened. Advanced load limiters rely on torsion bar When great deal of force is applied to the webbing, torsion bar twists slightly Allows webbing to extend a little bit farther,From: http:/ safety-regulatory-devices/seatbelt.htm,