Suspension
From c,mm,n
The following text is the summary of a graduation thesis by Martin Leegwater. He graduated in september 2007 on this study about an active suspension system at the Eindhoven University of Technology.
Abstract
During the design of a suspension system, a number of conflicting requirements has to be met. The suspension setup has to ensure a comfortable ride and good cornering characteristics at the same time. Also, optimal contact between wheels and road surface is needed in various driving conditions in order to maximize safety. Instead of a passive suspension, present in most of today’s cars, an active suspension can be used in order to better resolve the trade-off between these conflicts. However, this is generally accompanied by considerable energy consumption.
In this report an active suspension is investigated which is capable of leveling the car during cornering theoretically without consuming energy. Simulations using a full-car model show that this maximizes the car’s cornering velocity. As extreme cornering may be required to remain on the road or to avoid an obstacle, implementing the active suspension system improves safety. As the active part of the suspension takes care of realizing good cornering behaviour and of static load variations, the primary suspension springs can be tuned purely for optimizing comfort and road holding. Simulations show that the required energy for leveling the car during cornering is negligible, so it can be concluded that the active suspension system is able to economically level the car.
Furthermore, the active suspension’s potential for improving comfort is examined using a quarter-car model in combination with the skyhook damping principle. Performing simulations with an unrestricted actuator shows that comfort can slightly be improved with little actuator action and without deteriorating road holding and suspension travel. Further improving the comfort level requires more actuator action and results in considerable degradation of road holding and suspension travel. Performing simulations including actuator dynamics and force limitation shows that comfort can be improvement with only 5 [%] with this active suspension. However, improving comfort with the active suspension does not require but actually produces a small amount of energy as it functions as a skyhook damper.
The groundhook damping principle in combination with a quarter-car model is used to investigate the possibilities of improving road holding with the active suspension. Performing simulations with an unrestricted actuator on a deterministic road surface shows that variations in force between tire and road are reduced considerably at the expense of deteriorating comfort. However, performing simulations including actuator dynamics and force limitation show that the active suspension is hardly able to improve road holding because of the large required forces to be produced by the actuator. Moreover, because the enormous peaks in power require extremely powerful electric actuators it is not very interesting to apply the presented active suspension system in combination with the groundhook damping principle. Furthermore, the improvement when driving over a stochastic road surface is marginal and accompanied by an unacceptable deterioration in comfort.
