Seat Belt

Seat Belt

A seat belt, sometimes called a safety belt, is a safety harness designed to secure the occupant of a vehicle against harmful movement that may result from a collision or a sudden stop. As part of an overall occupant restraint system, seat belts are intended to reduce injuries by stopping the wearer from hitting hard interior elements of the vehicle or other passengers and by preventing the wearer from being thrown from the vehicle.

Types of seat belts

* Lap: Adjustable strap that goes over the waist. Used frequently in older cars, now uncommon except in some rear middle seats. Passenger aircraft seats also use lap seat belts.

* Sash: Adjustable strap that goes over the shoulder. Used mainly in the 1960s, but of limited benefit because it is very easy to slip out of in a collision.

* Lap and Sash: Combination of the two above (two separate belts). Mainly used in the 1960s and 1970s. Generally superseded by three-point design.

* Three-point: Similar to the lap and sash, but one single continuous length of webbing. Both three-point and lap-and-sash belts help spread out the energy of the moving body in a collision over the chest, pelvis, and shoulders. Until the 1980s three-point belts were commonly available only in the front seats of cars, the back seats having only lap belts. Evidence of the potential for lap belts to cause separation of the lumbar vertebrae and the sometimes associated paralysis, or "seat belt syndrome", has led to a revision of passenger safety regulations in nearly all of the developed world requiring that all seats in a vehicle be equipped with three-point belts. By September 1, 2007, all new cars sold in the US will require a lap and shoulder belt in the center rear.

* Criss-cross: Experimental safety belt presented in the Volvo SCC. It forms a cross-brace across the chest.

* Five-point harnesses: Safer but more restrictive than most other seat belt types. They are typically found in child safety seats and in racing cars. The lap portion is connected to a belt between the legs and there are two shoulder belts, making a total of five points of attachment to the seat. (Strictly speaking, harnesses are never to be fastened to the seat - they should be fastened to the frame/sub-frame of the automobile.)

* Six-point harnesses: Similar to a five-point harness but includes an extra belt between the legs, which is seen by some to be a weaker point than the other parts. These belts are used mainly in racing. In NASCAR, the six-point harness became popular after the death of Dale Earnhardt. Earnhardt was wearing a five-point harness when he crashed and died. Because it was thought at first that his belt had broken, some teams ordered a six-point harness.

Seat belts were invented by George Cayley in the 1800s.[citation needed] They were introduced in aircraft for the first time in 1913, by Adolphe Pegoud, who became the first man to fly a plane upside-down. However, seat belts did not become common on aircraft until the 1930s.

Safety belts were tested by Col John P. Stapp, using a rocket sled and himself as the guinea pig, among others. His studies explained the phenomenon that most people injured or killed in plane crashes didn't die when the plane hit the ground, but when the person hit the inside of the plane.

Edward J. Claghorn was granted U.S. Patent 312,085 on February 10, 1885 for a safety belt providing protection for a person ascending or descending a ladder or pole.

Edward J. Hock invented the safety belt first used by the Ford Motor Company as standard equipment, while he was on active duty with the military as a flight instructor. In 1955 his idea was accepted by the naval authorities, and Hock was awarded $20.50 for his invention. The original schematic and blueprints shows that he utilized scrap parachute strapping to implement his idea. He was never awarded anything other than the $20.50 award, a letter of recognition, a picture with military 'brass', and a newspaper article to his credit.

Nils Bohlin of Sweden invented the three point seat belt for Volvo, who introduced it in 1959 as standard equipment. Bohlin was granted U.S. Patent 3,043,625 for the device.

Most US automobiles were sold with front seat belts standard in the 1964 model year. Rear seat belts were made standard in 1968.

Most seat belts are equipped with locking mechanisms (or inertia reels) that tighten the belt when pulled hard (e.g. by the force of a passenger's body during a crash) but do not tighten when pulled slowly. This is implemented with a centrifugal clutch, which engages as the reel spins quickly. Alternatively, this function may be secured by a weighted pendulum or ball bearing: when these are deflected by deceleration or roll-over they lock into pawls on the reel.

Types of inertia reel type seatbelts:

NLR (No Locking Retractor) - Commonly used in recoiling lap belts

ELR V (Emergency Locking Retractor - Vehicle sensitive) - Single sensitive mechanism, comprised of a locking mechanism activated in an emergency by deceleration or rollover of the vehicle. Thus, the seatbelt is sensitive to the vehicle's motion.

ELR VW (Emergency Locking Retractor - Vehicle and Webbing sensitive) - Dual sensitive means a seatbelt retractor that, during normal driving conditions, allows freedom of movement by the wearer of the seatbelt by means of length-adjusting components that automatically adjust the strap to the wearer, with a locking mechanism that is activated by two or more of the following:

* deceleration or rollover of the vehicle,

* acceleration of the strap (webbing) from the retractor, or

* other means of activation.