F2008-03-056
Reducing Braking Distance of Cars and Motorcycles by Control of Semi-Active Suspension without ABS Interaction
SCOPE AND STATE OF THE ART In today´s series cars active dampers are usually normally used to improve riding comfort realize by a skyhook control strategy to improve riding comfort. NIEMZ proved experimentally supplied evidence that his control algorithm called "MiniMax" reduces the average braking distance of ABS controlled full braking tests of a passenger car by minimizing the wheel load induced slip oscillations. On a road with an unevenness comparable to the one that is found orepresentative nto a typical German Autobahn a reduction of typically 1-2 %, compared to the best passive damping (hard), has been achieved with an initial speed of 70 km/h. The pPerformance and stability of this control strategy have not been investigated for other conditions and other types of vehicles (e.g. motorcycles) was not investigated yet.
PAST EXPERIENCE OF AUTHORS´ INSTITUTION In former research the authors´ Chair of Automotive Engineering demonstrated that the control of active dampers has a significantly influences of the braking process. In braked driving tests with constant velocity REICHEL showed that the control of active dampers has a significant positive influence on the braking torque. Based on these results NIEMZ proved that his control algorithm "MiniMax" reduces the average braking distance of ABS controlled full braking tests.
APPROACH, METHODS AND TOOLS Goal Aim of this paper is to proof prove the robustness of the "MiniMax" control strategy for various driving situations of cars and to analyze the feasibility of a "MiniMax" controller for motorcycles. For the investigation of the MiniMax control performance and stability in various braking conditions of a passenger car, the following parameters initial velocity, friction coefficient, type of pavement and different types of tires are examined experimentally and with statistical methods: initial velocity, friction coefficient, type of pavement and different types of tires. As a consequence of the promising results for various driving situations, the potential for to improveing motorcycle braking performance is investigated. Relevant parameters (e.g. the transfer function of road excitation to wheel load integral and thus wheel slip, damper switching time delay, the validity of assuming a quarter-car model) are identified for a typical motorcycle with in simulation studies and two-post test rig experiments. The feasibility of a "MiniMax" controller for motorcycles is proved assumed by if finding no significant differences between the relevant parameters of the reference car and the motorcycle can be found.
RESULTS, CONCLUSIONS AND THEIR SIGNIFICANCE Almost one thousand ABS-controlled braking tests with a passenger car, which were evaluated with statistical methods, demonstrate the possibility to improve a variety of car´s braking situations by control of semi-active suspension. Simulation studies and two-post test rig experiments with a motorcycle suggest at least a comparable reduction in braking distance for motorcycles. The defined quantities show no significant differences between the reference car and a typical touring type motorcycle. In addition, due to the large pitching movement, the ratio between vehicle body induced dynamic wheel load and seismic excitation dynamic wheel load is larger higher compared to that of the reference car due to the large pitching movement. Therefore, even larger improvements in braking performance are expected.
REFERENCES Niemz, Tobias (2007): "Reducing Braking Distance by Control of Semi-Active Suspension" Reichel, Jochen (2003): "Untersuchungen zum Einfluss stufenlos verstellbarer Schwingungsdämpfer auf das instationäre Bremsen von Personenwagen"
Poster presentation: Chassis development for passenger cars, trucks and buses