Anti-lock braking system for motorcycles
The Motorcycle Anti-lock Brake System (ABS) prevents the wheels of a powered two wheeler from locking during braking situations. Based on information from wheel speed sensors the ABS unit adjusts the pressure of the brake fluid in order to keep traction and avoid fall downs (e.g. maintain deceleration). Motorcycle ABS helps the rider to maintain stability during braking and to decrease the stopping distance. It provides traction even on low friction surfaces. While older ABS models are derived from cars, recent ABS are the result of research, oriented on the specifics of motorcycles in case of size, weight and functionality. National and international organizations evaluate Motorcycle ABS as an important factor to increase safety and reduce motorcycle accident numbers. The European Commission passed legislation in 2012 that made the fitment with ABS for all new motorcycles above 125 cm3 to be mandatory from 1 January 2016.
In 1988, BMW introduced an electronic/hydraulic ABS for motorcycles, ten years after Daimler Benz and Bosch released the first four-wheel vehicle ABS for series production. Motorcycles of BMW K100 series were optionally equipped with the ABS, which added 11 kg to the bike. It was developed together with FAG Kugelfischer and regulated the pressure in the braking circuits via a plunger piston. Japanese manufacturers followed with an ABS option by 1992 on the Honda ST1100 and the Yamaha FJ1200.
Continental presented its first Motorcycle Integral ABS (MIB) in 2006. It has been developed in cooperation with BMW and weighed 2.3 kg. While the first generation of motorcycle ABS weighed around 11 kg. The current generation (2011) presented by Bosch in 2009 weighs 0.7 kg (ABS base) and 1.6 kg (ABS enhanced) with integral braking.
Wheel speed sensors mounted on front and rear wheel constantly measure the rotational speed of each wheel and deliver this information to an Electronic Control Unit (ECU). The ECU detects on the one hand if the deceleration of one wheel exceeds a fixed threshold and on the other hand whether the brake slip, calculated based on information of both wheels, rises above a certain percentage and enters an unstable zone. These are indicators for a high possibility of a locking wheel. To countermeasure these irregularities the ECU signals the hydraulic unit to hold or to release pressure. After signals show the return to the stable zone, pressure is increased again. Past models used a piston for the control of the fluid pressure. Most recent models regulate the pressure by rapidly opening and closing solenoid valves. While the basic principle and architecture has been carried over from passenger car ABS, typical motorcycle characteristics have to be considered during the development and application processes. One characteristic is the change of the dynamic wheel load during braking. Compared to cars, the wheel load changes are more drastic, which can lead to a wheel lift up and a fall over. This can be intensified by a soft suspension. Some systems are equipped with a rear wheel lift off mitigation functionality. When the indicators of a possible rear lift off are detected, the system releases brake pressure on the front wheel to counter this behavior. Another difference is that in case of the motorcycle the front wheel is much more important for stability than the rear wheel. If the front wheel locks up between 0.2-0.7s, it loses gyrostatic forces and the motorcycle starts to oscillate because the increased influence of side forces operating on the wheel contact line. The motorcycle becomes unstable and falls.
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Wikipedia