Anti-lock Brake System (ABS) - General Information

When a vehicle is equipped with a conventional brake system, sudden application of the foot brake pedal causes the wheels to lock. As a result, the tire tread loses grip with the road surface, and the vehicle may skid and lose steering control. The Anti-lock Brake System (ABS) prevents premature wheel lock by continuously controlling wheel rotational speed during braking through modulation of brake fluid pressure at each of the brake units.

ABS consists of two main subsystems: electrical and hydraulic. The electrical part of the system includes four wheel speed sensors, a control module, and a set of connecting wiring. The hydraulic part includes a pressure modulator, disc brake calipers, and the hydraulic lines connecting these components.

The operating principle of the system is fairly simple. Each wheel is equipped with an individual speed sensor. The sensor consists of a tone ring (a ring with evenly spaced teeth around its circumference) and a sensing element in the form of a magnetized coil. The sensing element detects the passing of the tone ring teeth and converts this information into electrical signals, which are continuously sent to the ABS control module. Based on processing of the incoming signals, the module obtains information about the relative rotational speed of each wheel. While all four wheels rotate at the same speed, the ABS remains in standby mode. As soon as any wheel begins to lock, the module detects the change in the incoming signal and issues a command to actuate the modulator, which immediately releases brake fluid pressure in the brake unit of the corresponding wheel. As soon as normal wheel rotation is restored, the module stops operation of the modulator.

The actual operation of the ABS is much more complex than it may appear, so the authors of this Manual do not recommend that vehicle owners attempt to repair the system themselves. If a malfunction occurs, it is best to contact a qualified service center.