Prepared by
JYOTI RANJAN NAYAK

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Introduction
An anti-lock braking system (ABS) is a safety system on motor vehicles which prevents the wheels from locking while braking.
A rotating road wheel allows the driver to maintain steering control under heavy braking, by preventing a locked wheel or skid, and allowing the wheel to continue to forward roll and create lateral control, as directed by driver steering inputs. Disadvantages of the system include increased braking distances under some limited circumstances (snow, gravel, "soft" surfaces), and the creation of a "false sense of security" among drivers who do not understand the operation, and limitations of ABS.
History
• Anti-lock braking systems were first developed for aircraft in 1929, by the French automobile and aircraft pioneer, Gabriel Voisin, as threshold braking an airplane is nearly impossible.
• An early system was Dunlop's Maxaret system, introduced in the 1950s and still in use on some aircraft models.
• A fully mechanical system saw limited automobile use in the 1960s in the Ferguson P99 racing car, the Jensen FF and the experimental all wheel drive Ford Zodiac, but saw no further use; the system proved expensive and, in automobile use, somewhat unreliable.
• However, a limited form of anti-lock braking, utilizing a valve which could adjust front to rear brake force distribution when a wheel locked, was fitted to the 1964 Austin 1800.
• Chrysler, together with the Bendix Corporation, introduced a crude, limited production ABS system on the 1971 Imperial. Called "Sure Brake", it was available for several years, and had a satisfactory performance and reliability record.
• Ford also introduced anti lock brakes on the Lincoln Continental Mark III and the Ford LTD station wagon, called "Sure Trak" in 1975.
• The German firms Bosch and Mercedes-Benz had been co-developing anti-lock braking technology since the 1930s, and introduced the first completely electronic 4-wheel multi-channel ABS system in trucks and the Mercedes-Benz S-Class in 1978.
• ABS Systems based on this more modern Mercedes design were later introduced on other cars and motorcycles. General Motors introduced the "Trackmaster" ABS on their Cadillac models in 1971 as an option that was operational on the rear wheels for RWD models.
In 1988 BMW became the world's first motorcycle manufacturer to introduce an electronic/hydraulic ABS system, this on their BMW K100.
• In 1992 Honda launched its first ABS system, this on the ST1100 Pan European.
• In 1997 Suzuki launched its GSF1200SA (Bandit) with ABS
• Today ABS has become a standard equipment even for small cars
Theory
When the car brakes (normally), the momentum of the car must be reduced, so a backwards force needs to be transmitted to the car. This is achieved by the wheels exerting a forward force on the street which lies below the threshold of maximum static sliding friction. The wheels keep sticking to the road because of this friction.
If the driver brakes very hard (or accelerates extremely) it can occur that the maximum static friction is surpassed and the wheels lose their grip and begin sliding (or spinning). In this case the dynamic sliding friction (which is less than the maximum static friction) takes over
The amount of traction which can be obtained for an auto tire is determined by the coefficient of static friction between the tire and the road. If the wheel is locked and sliding, the force of friction is determined by the coefficient of kinetic friction and is usually significantly less. A tire that is just on the verge of slipping (10 to 20% slippage) produces more friction with respect to the road than one which is locked and skidding (100% slippage). Once traction is lost, friction is reduced, the tire skids and the vehicle takes longer to stop. So locked wheels are less effective in stopping on a road
But in gravel, sand and deep snow, locked wheels dig in and stop the vehicle more quickly. A locked tire allows a small wedge of snow to build up ahead of it which allows it to stop in a somewhat shorter distance than a rolling tire. That is why some vehicles have an on/off switch for deactivating the antilock system when driving on snow.
So, antilock brakes do not necessarily reduce the stopping distance, and in fact may actually increase stopping slightly on dry pavement. But on wet or slick pavement, antilock brakes may reduce the stopping distance up to 25% or more, which could be the difference between a safe stop and an accident
But what ABS provides is Directional stability which is very crucial.
Directional stability also depends on traction. As long as a tire does not slip, it will roll only in the direction it turns. But once it skids, it has about as much directional stability as a hockey puck on ice because, regardless of the angle of the front wheels, the vehicle continues to skid in whatever direction its momentum sends it until either the driver releases the brakes. By minimizing the loss of traction, antilock braking helps maintain directional stability and steering control