How Do ABS Brakes Work?

Before ABS application

Pressing your car's brake pedal triggers a series of actions to provide safe stopping ability for your car. ABS (anti-lock braking system) works in conjunction with your regular braking system to provide computerized stopping assistance when your car loses control. Understanding how a car's brake system works will help you envision how ABS improves braking ability in difficult driving conditions.

When you apply the brakes, this sends a message to the master cylinder which forces fluid into the brake lines of your car. When the master cylinder compresses to force fluid into the lines, this creates friction that heats up the lines and brake pads. The heated pads press against the brake discs or drums, slowing the car and eventually stopping forward motion.

Detection

ABS systems contain a controller that functions as a computer. Controllers measure speed and control the valves and pump of the ABS system. If the controller senses a difference in wheel speed in the speed sensors, the ABS overrides your pressure on the brake pedal. This complicated process begins with detection at your computer and speed sensors. The computer evaluates the speed of the slipping wheel and controls the valves to provide a measured response. The controller evaluates wheel speed and rotation as well as continuity between the wheels.

Based on this evaluation, the controller decides whether the car can regain control without ABS, if the system requires complete takeover to return control to the car, or if the valve should release pressure to return the brake system to normal. The controller performs this assessment within seconds.

Triggering ABS application

Valves control the amount of fluid available to the lines and brake system. Once the controller tells the valves of the ABS that the system needs to control the skid, this engages a pump on the ABS. The pump releases and applies variable pressure to the braking system to stop the car or regain traction. The pumping system also varies the application of the brakes at a rate to control the skid.

If multiple wheels lose control, the controller sends different messages to each wheel based on its assessment of stopping requirements. ABS varies the rate of brake application based on information collected from the wheel sensors. ABS automatically applies the brakes based on each individual wheel evaluation to reestablish control.

ABS pumps your brakes at a much greater speed that humanly possible. This feels like a pulsing in the brake pedal when ABS is engaged. Some ABS systems can apply brakes up to 30 to 40 times per second, much faster than humanly possible.

Returning to normal

Activating your ABS system temporarily prevents the initiation of regular braking. As soon as the ABS system gains traction, the controller notifies the valves to release pressure from the brake lines. This restores the normal braking system to the vehicle. The pump restores normal pressure to the brake lines after application of the ABS.