An anti-lock braking system or ABS is a safety “electronic” controlled 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 (ice, 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.

The anti-lock brake controller is also known as the CAB (Controller Anti-lock Brake). A typical ABS is composed of a central electronic control unit (ECU), four wheel speed sensors (one for each wheel), and two or more hydraulic valves within the vehicle brake circuit. The ECU constantly monitors the rotational speed of each wheel. When it senses that any number of wheels are rotating considerably slower than the others (a condition that is likely to bring it to lock – see note below),it actuates the valves to decrease the pressure on the specific braking circuit for the individual wheel, effectively reducing the braking force on that wheel. This process is repeated continuously, and this causes the characteristic pulsing feel through the brake pedal. The sensors can become contaminated with metallic dust, or other contaminants, and fail to correctly detect wheel slip; this is not always picked up by the internal ABS controller diagnostic. In this occurrence, the ABS warning light will usually be illuminated on the instrument panel, and the ABS will be disabled until the fault is rectified.

Automatic, electronic regulation of brake pressure to prevent the wheels from locking up during braking. driver maintains the ability to steer vehicle.

HYDRAULIC COMPONENTS OF ABS:

The hydraulic components of ABS of vehicle are shown in this figure. It consists of brake calipers, lines or hoses a master cylinder and hydraulic control unit. The hydraulic control is controlled by the ABS “electronic control unit”.