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Seat_Belt_for_Automotive.pptx
- 1. Seat Belt ForAutomotive Presented by Subin Stanly
- 2. Introduction A seat beltis a safety belt that is designed to protect the occupant of the vehicle against harmful movement during a crash or a sudden stop.
- 6. The seat belt’sfunction is to spread the inertial force across rigid part of the body in order to minimize the damage.
- 7. • To reducethe risk of contact with the interior of the vehicle or reduce the severity of injuries if this occurs; • distribute the forces of a crash over the strongest parts of the human body; • prevent the occupant from being ejected from the vehicle in an impact; • prevent injury to other occupants (for example in a frontal crash, unbelted rear-seated passengers can be catapulted forward and hit other occupants).
- 8. Seat-belt designs should complywith national or international standards. Designs that ensure ease of use will serve to increase wearing rates.
- 9. Group Description 0 Forchildren of a mass less than 10 kg 0+ For children of a mass less than 10 kg I For children of a mass less than 13kg II For children of a mass from 9 kg to 18 kg III For children of a mass from 22 kg to 36kg
- 10. In a typicalseatbelt system, the belt webbing is connected to a retractor mechanism. • The central element in the retractor is a spool, which is attached to one end of the webbing. • When the webbing is pulled out, the spool rotates counter-clockwise, which turns the attached spring in the same direction. • The spring applies a rotation force, or torque, to the spool in clockwise direction so that it winds up any loose webbing.
- 11. The retractor hasa locking mechanism that stops the spool from rotating when the car is involved in a collision. There are two sorts of locking systems in common use today: • systems triggered by the car's movement • systems triggered by the belt's movement
- 12. 2 Systems triggeredby the belt's movement
- 13. Pretensioner • In somelatest seat belt a pretensioners also works in order to tighten the belt in the event of crash. • They are connected to a central control processor that is also responsible for activating the car’s airbag system. • When an impact signal is received the processor actuates the pretensioner and then the air bag system.
- 14. Load limiters A loadlimiter release a little more belt webbing when a high force is applied to the belt in order to prevent injury from the seat belt
- 15. Safety Clutch typeload limiter
- 16.
- 17.
Editor's Notes
- #3 Suppose if a car hits a tree at a speed 60km/hr, it would be obvious that the occupant’s inertia and car were absolutely independent, it would hit the tree at the same force as it would hit the ground falling off from a five-story building, the force of the tree would bring the car to an abrupt stop, but occupant speed would remain the same If the occupant was wearing the seat belt the severity of the injury is reduced by preventing the occupant from hitting hard against inertial elements of the vehicle or other passengers, and positioning the occupant correctly for maximum benefit from the air bag and also prevent the occupant from being ejected from the vehicle.
- #4 without the seat belt the occupant would go flying through the windshield at 60km/hr, just as the tree slowed the car down, the dashboard windshield or the road would,
- #5 At that time conventional wisdom said it was better to get thrown out of the car to have a better chance of survival than to be trapped inside. So seat belt didn’t catch until the time of Indianapolis motor speedway in 1956 during which Ray Crawford opted for a car with seat belts and he had a head on collision and walked away from it unscratched which proved that seat belts where better than getting ejected from the car.
- #6 Before 1959, only two-point lap belts were available in automobiles; for the most part, the only people who regularly buckled up were race car drivers. The two-point belts strapped across the body, with a buckle placed over the abdomen, and in high-speed crashes had been known to cause serious internal injuries. Bohlin had also designed ejector seats for Saab fighter airplanes in the 1950s. In designing the new seat belt, he concentrated on providing a more effective method of protecting driver and passenger against the impact of the swift deceleration that occurred when a car crashed.
- #7 Typically seat belt consists of a shoulder belt, extends across the occupant’s chest and a lap belt that rests over the occupants pelvis. Two belt sections are tightly secured to the frame of the vehicle. When the occupant wears the belt correctly most of the force are applied to his rib cage and pelvis, which are relatively sturdier parts of the body. Since the belt is extended to wide part of the body, the forces aren’t concentrated in small area to do much damage. Additionally the seat belt material is made of more flexible webbing, it stretches quite a bit that is it doesn’t stop abruptly. The seat belt shouldn’t be given more than a little flexibility or else the occupant might bang into steering wheel or side door. The safe designed seat belt will only let the occupant shift forward slightly.
- #8 Seat belt webbing is woven from thousands of strands of polyester. The impact in an accident reduces the effectiveness of the belt because it permanently elongates the webbing – by as much as 13%. If the belt is not replaced following this elongation, the wearer’s body would take the full shock load in subsequent accidents -approximately equal to the weight of a three tonne elephant against the belt.
- #9 The three-point lap and diagonal seat-belt is the safest and most commonly used in cars, vans, minibuses, trucks and the driver’s seat of buses and coaches, while the two-point lap belt is most commonly used in buses and coaches. Seat-belt standards set out requirements for the width of webbing and buckles, and the ease of operation and adjustment. In more recent years seat-belts have become integrated into overall vehicle safety systems that include such devices as pretensioners, load limiters and airbags. Single diagonal belt has been shown to be poorer at preventing ejection and submarining (slipping under the seat-belt). Full harness The full harness (double shoulder, lap and thigh straps with central buckle device) gives very good protection both from ejection and from interior contact. However, it is somewhat cumbersome to put on, and cannot be easily operated with one hand. This is an important factor in achieving a high wearing rate, and thus the harness only tends to be installed in vehicles used for motor sport, where drivers and co-drivers are at high risk.
- #10 Infants under the age of 1 year (Group 0 or 0+) At birth, the infant head is around a quarter of their total length and about a third of their body weight. An infant’s skull is very flexible, so a relatively small impact can result in significant deformation of the skull and brain. A rear-facing child restraint system (sometimes called an “infant car seat”) provides the best protection for infants until they are both 1 year of age and at least 13 kilograms (kg) weight. Children aged 1–4 years (Group I) The bone-forming process is not complete until the age of 6 or 7 years, and throughout childhood a child’s skull remains less strong than that of an adult. A restraint system needs to limit forward head movement in a frontal impact and provide protection from intrusion in a side impact. The integral harness secures the child and spreads the crash forces over a wide area. This seat will last them until either their weight exceeds 18 kg or they grow too tall for the height of the adjustable harness. Children aged 4–6 years (Group II) Booster seats raise the seating position of the child so that the adult seat-belt lies properly across the chest, crossing diagonally at the child's shoulder rather than the neck, and low across the pelvis. 6–11 years (Group III) Booster cushions without backs are designed for weights from 22 kg to 36 kg, but manufacturers are now producing booster cushions with backs that cover the full 15 kg to 36 kg range.
- #11 In usual seat belt system, the retractor mechanism is connected to the belt webbing
- #12 For this mechanism the central operating element is a weighted pendulum. During rapid deceleration the pendulum swing forward due to inertia. The ratchet gear attached to the spool get caught by the pawl on the other end of the pendulum. Hence the gear as well as spool can’t rotate counter clockwise. After the crash the gear rotates clockwise as the webbing loosens and thus pawl disengages.
- #13 In this design the central operating element is centrifugal clutch which consist of weighted pivoted lever mounted to the rotating spool. This pivoted lever doesn’t pivot when the spool spins at low speeds since the centrifugal force is not enough to lock the spool. When a sudden jerk is given to the belt, spool rotates at high speed which provides a sufficient amount of centrifugal force to drive the weighted end of the lever outward and push the cam piece mounted at the retractor housing.
- #14 pretensioners works along with retractor in order to tighten the belt in the event of crash. In general pretensioner are connected to a central control processor that is also responsible for activating the car’s airbag system. The processor receives the motion sensor’s input that respond during a sudden deceleration of an impact. When an impact signal is received the processor actuates the pretensioner and then the air bag system. Pretensioner system are of different type, some may be built around electric motors or solenoids, but the most common design at present is the pyrotechnic to pull the seat belt webbing.(
- #15 limiters: In many crashes when the car collides with extremely high impact, the seat belt can cause some serious injuries, since the passenger’s inertial force is more it takes greater force to bring back the passenger to position. That is, the heavier the stopping force, the tighter the seatbelt will push. Therefore some seatbelt system uses load limiter to reduce this effect. Toothed plate type load limiter consists of a set of open metal teeth in the form of ladder. The retractor is held in the bottom of the toothed plate and is restricted to move due to the presence of teeth. When seat belt impact force is high the teeth starts to deform allowing the retractor to move forward hence letting the belt webbings to extend a little more.
- #16 A cylinder cut at an angle forms a load limiter. Here the spring tension sets the load limit.
- #17 First introduced in 2011, the inflatable seatbelt available in select Lincoln models is one of the top innovations in safety belt technology in recent years. Inflatable seatbelts are designed to deploy in a collision and dissipate impact by spreading the crash force over a larger area to help reduce chest and ribcage injury. Noticeably thicker than a traditional seatbelt, inflatable seatbelts will activate in a matter of milliseconds and help to distribute up to five times more impact