After ABS, What?

ABS is in concept a simple idea. Measure wheel speed, and if any or all stop rotating, send a signal to a solenoid operated valve to reduce line pressure. Thanks to the wonder of electronics, it all happens fast enough to create pedal pulsations not unlike those resulting from a warped brake rotor. ABS isn’t new, but most technicians have at least one experience of a customer who uses their vehicle’s ABS capability for the first time, then brings the vehicle in to service the “faulty” pulsating brakes. Mechanically, they’re much the same as conventional brakes and traditional service procedures still apply. Dynamic stability control and brake assist, however, are changing the game with more hardware in the system and software in the chassis computers. An example is the ESC MK25 E5 system from Continental Teves installed in new Mercedes-Benz S-Class cars.

In addition to the master cylinder pressure sensor, the system employs four additional pressure sensors. Infinitely variable cut-off and block valves meter the brake pressures with extreme sensitivity, shortening stopping distances while reducing the pedal pulsation noticeable by the driver. Included is a hill start assist in combination with the standard automatic transmission, automatic wet brake disc drying in wet weather and the preventive application of the brake pads when danger is anticipated. ABR Adaptive Brake, an electronic brake control system developed in cooperation with Mercedes-Benz for its new S-Class, adds several additional features. The modular electronic stability control system includes the basic controller, anti-lock brake system (ABS), anti-slip control (ASC) and a yaw ratio controller (YRC). While ABS and ASC primarily improve the vehicle’s forward dynamics, YRC controls its side-to-side dynamic response. In critical driving situations, ESC maintains the vehicle’s stability by applying brake ad throttle inputs independently of the driver. An electric parking brake releases automatically without any manual intervention. Eliminating the lever mechanism in the driver’s foot space is an additional safety feature providing more legroom for the driver. The system also detects possible malfunctions and displays them as a warning in the instrument cluster. Adaptive cruise control isn’t new, but when integrated with the advanced ABS and stability system, the S-Class can be driven in stop-and-go traffic with the system braking the vehicle to a full stop, then maintaining brake pressure until the vehicle ahead moves. The driver simply taps the throttle or pushes a button and the vehicle accelerates automatically in stop-and-go conditions. The system can even anticipate a serious crash, apply the brakes and retract the master cylinder to reduce possible leg injuries. What’s the impact from a service perspective? Compared to conventional ABS, these systems now have actuators that apply brake pressure, as well as radar systems to feed distance and obstacle closing rate information to the computer. More inputs, more processors and new actuators will probably require additional test equipment. Time will tell.