F2008-03-025
A Semi Active Suspension System for Motorbikes
A semi active suspension system would be developed for motorbikes, based on conventional coil/spring dampers. In this system the dampers are continuously adjustable in compression, rebound, and spring preload. The adjustment range is 25 percent of the total damping for rebound and compression. The spring preload (motorbike height) is limited to 30mm height change. Compression and rebound are controlled by step motors coupled to the dampers. A hydraulik pump controls the spring preload of both dampers, via 2 valves, and 2 single acting cylinders located above the springs. Linear potentiometer are returning the spring preload to the electronic control unit (ECU). This system performs the 30mm height change and 25 percent damping change in less than 0,5 seconds. The ECU uses a GPS reciever and damper travel sensors to record the spring travel over the distance. The collected data is compared to the stored simulation modell of the motorbike and the dampers characteristic curves. The controller divides then the recorded track in sectors, and determinates the best possible damper settings for each track sector. Sectors are chosen by the driven line characteristic and the motorcycle state, such as bumps, straight-line, curve, acceleration, braking. This system performs, in real time, adjustments for the motorcycle height and minor time delays in the settings changes, especially for the braking and acceleration points, for a seamless transition between 2 different settings. The controller can also react to changes from the driver or from the motorcycle, for exemple a different tyre type, different weather conditions, driven line or drive speed. The adjustment takes place after 2 consecutive laps with a similar changing pattern in 1 or more sectors. The system, built in a BMW K1200S for racetrack purpose, results in improvements in traction, straight-line acceleration and high speed maniability, without loss of stability. The test has showed that the performance of the motorbike would be improved greatly with respect to comfort on bumps and rough surfaces, handling in corner entries, traction in corner exits. The straight-line acceleration performance would be improved too by lowering the bike for a lesser aerodynamic drag. The established system, which considerate the chassis geometry, roadsurface and shock-absorber work is the base for a future active suspension system designed for road use.
Poster presentation: Chassis development for passenger cars, trucks and buses