FAQ: How Do Autonomous Brake Systems Work?

READER QUESTION: How to autonomous brake systems work on my Audi Pre-Braking system?

Autonomous braking is performed with technology that has been of vehicles for more than 25 years, the ABS braking system. The ABS controller/modulator is the heart of the system. The modulator gets the brake pressure from the master cylinder when the driver applies the brakes. When the autonomous brakes activate, the electric pump and accumulators supply pressure.

Inside are the valves and electrical solenoids that control the pressures to apply or release the brakes. During normal operation, the pressure from the master cylinder goes through the HCU unaltered. When the vehicle is braked automatically, the master cylinder is isolated from the system using these valves

Old ABS four-channel system will have eight solenoids (four isolation/four dump), or two for each wheel. With these old systems, the brake pedal would shake a vibrate. Modern vehicles with autonomous systems may have 12 or more valves. The four additional valves work to channel hydraulic pressure to a specific wheel from the pump and accumulator.

If you have the traffic jam pilot engaged to make your commute more bearable, the pump and valves inside the HCU do all the work. When the brakes are requested, two valves close to isolate the master cylinder and brake pedal from the brake system. The valves for the wheels open up and the pump is turned on to provide hydraulic pressure to the calipers.

The process takes milliseconds to activate. The decision to apply the brakes require cameras and radar sensors to detect the road and other vehicles. A very fast computer classifies objects to determine the correction and amount of brake pressure applied.

The one thing that can prevent the system is worn brake pads or damaged sensors. If the system does not detect that the application of the brakes is not stopping the vehicle, it will apply more pressure. If the brake pads are worn to the backing plates and not producing predictable levels of friction, the system could set a code for hydraulic failure.