Antilock

Anti-lock braking system (ABS) is an automobile safety system that prevents wheels from locking up during hard braking. By maintaining traction, ABS helps preserve steering control and reduces the risk of skidding on wet, icy, or loose surfaces.

ABS works by continuously monitoring the rotational speed of each wheel with wheel-speed sensors. If a wheel decelerates too rapidly, the system signals a hydraulic modulator to momentarily reduce brake pressure on that wheel, allowing it to recover traction. The process may repeat many times per second, creating a pulsing brake feel that drivers may notice through the pedal or brake pedal vibration.

Development and deployment: Electronic ABS first appeared in the late 1970s, with early commercial systems in high-end cars from manufacturers such as Bosch and Mercedes-Benz. Over the 1980s and 1990s, ABS became increasingly common, and by the early 21st century was standard on many passenger vehicles worldwide.

Effectiveness and limits: ABS improves steering control during emergency braking on a variety of surfaces and can shorten stopping distances on wet pavement, but it does not guarantee shorter overall stopping distances on all surfaces. On loose gravel, snow, or mud, stopping distance may be longer. Performance also depends on tire condition and road friction.

Related technologies: ABS is often integrated with electronic stability control (ESC), traction control, and electronic brake-force distribution (EBD). Regular maintenance includes checking wheel-speed sensors and the hydraulic modulator; fault indicators can illuminate a dashboard warning light, and replacement should be performed by qualified technicians.