28-12-2012, 06:33 PM
Antilock Braking System
1Antilock Braking.ppt (Size: 1.98 MB / Downloads: 101)
Introduction
An Anti-lock Braking System (ABS) is a safety system that allows the wheels on a motor vehicle to continue interacting tractively with the road surface as directed by driver steering inputs while braking, preventing the wheels from locking up (that is, ceasing rotation) and therefore avoiding skidding.
History
The ABS was first developed for aircraft used in 1929 by the French automobile and aircraft pioneer.
An early system was Dunlop's Maxaret system, which was introduced in the 1950s and is still in use on some aircraft models.
In 1958, a Royal Enfield Super Meteor motorcycle was used by the Road Research Laboratory to test the Maxaret anti-lock brake. The experiments demonstrated that anti-lock brakes can be of great value to motorcycles, for which skidding is involved in a high proportion of accidents.
Stopping distances were reduced in most of the tests compared with locked wheel braking, particularly on slippery surfaces, in which the improvement could be as much as 30 percent. Experts saw little future in the system, however it was not put into production by the company.
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 unreliable in automobile use.
Modern systems
Bendix Corporation, introduced a computerized, three-channel, four-sensor all-wheel ABS called "Sure Brake" for its 1971 Imperial .It was available for several years thereafter, functioned as intended, and proved reliable.
In 1971, General Motors introduced the "Trackmaster" rear-wheel only ABS as an option on their Rear-wheel drive Cadillac models.
In the same year, Nissan offered an EAL (Electro Anti-lock System) as an option on the Nissan President, which became Japan's first electronic ABS.
In 1975, Robert Bosch took over the European company Teldix and all patents registered by the joint-venture and used this acquisition to build the base of the ABS introduced on the market some years later.
In 1978, the German firms Bosch and Daimler-Benz co-developed an ABS technology that begun in the early 1970s, and introduced the first completely electronic four-wheeled multi-channel ABS in trucks and the Mercedes-Benz S-Class.
Main Components
Speed sensors :-
The anti-lock braking system needs some way of knowing when a wheel is about to lock up. The speed sensors, which are located at each wheel, or in some cases in the differential, provide this information.
Valves :-
There is a valve in the brake line of each brake controlled by the ABS. On some systems, the valve has three positions: In position one, the valve is open; pressure from the master cylinder is passed right through to the brake.
In position two, the valve blocks the line, isolating that brake from the master cylinder. This prevents the pressure from rising further should the driver push the brake pedal harder.
In position three, the valve releases some of the pressure from the brake.
Pump :-
Since the valve is able to release pressure from the brakes, there has to be some way to put that pressure back. That is what the pump does; when a valve reduces the pressure in a line, the pump is there to get the pressure back up.
Controller :-
The controller is an ECU type unit in the car which receives information from each individual wheel speed sensor, in turn if a wheel loses traction the signal is sent to the controller, the controller will then limit the brake force (EBD) and activate the ABS modulator which actuates the braking valves on and off.