Anti-lock brakes began on aircraft and railways long before they reached cars
Skilled drivers once pumped the brake pedal to stop a skid. Anti-lock brakes automate that trick, easing pressure on any wheel about to lock many times faster than a human could, and the idea was flying on jet bombers and airliners decades before it became standard on family cars.
The system rests on a simple comparison. A control unit watches a speed sensor on each wheel, and if one is turning much slower than the car is moving, meaning it is about to lock, valves bleed off hydraulic pressure to that brake until the wheel spins up again. Small differences are ignored, because on a bend the inner wheels naturally turn more slowly than the outer ones. A fault switches the system off and lights a warning lamp.
Early versions were mechanical. J.E. Francis built a slip regulator for rail vehicles in 1908, and around 1920 Gabriel Voisin used a flywheel and valve to stop aircraft tyres skidding, since pilots can barely modulate brakes themselves. Karl Wässel patented a design in 1928 and Bosch another eight years later, though neither built a working product. By the early 1950s Dunlop's Maxaret was fitted to British aircraft such as the Vulcan and the Comet.
Road tests lagged. In 1958 a Royal Enfield motorcycle fitted with Maxaret stopped up to 30 percent shorter on slippery surfaces, yet Enfield's technical director saw no future in it. A mechanical version appeared on the Jensen FF in the 1960s but proved costly and unreliable. The first fully electronic system was built for Concorde, and in 1971 Mario Palazzetti at Fiat's research centre devised the modern design, selling the patent to Bosch.
Adoption then spread steadily. Chrysler's 1971 Imperial was the first production car with computer-controlled braking on all four wheels. Mercedes offered Bosch's system from 1978 and fitted it to every car from 1984, and the Ford Scorpio won European Car of the Year partly for making it standard. There is a catch: on loose gravel or snow it can lengthen stopping distances, though steering still improves.
Source: Anti-lock braking system
