An Investigation of the Effectiveness of Skyhook Suspensions for Controlling Roll Dynamics of Sport Utility Vehicles Using Magneto-Rheological Dampers
In recent years, many investigators have predicted that with a semiactive suspension it is possible to attain performance gains comparable to those possible with a fully active suspension. In achieving this, the method by which the damper is controlled is one of the crucial factors that ultimately determines the success or failure of a particular semiactive suspension. This study is an investigation into the effectiveness of a number of basic control strategies at controlling vehicle dynamics, particularly vehicle roll. The test vehicle is a Sport Utility Vehicle (SUV), a class of vehicle that regularly sees widely varying vehicle weight (as a result of passengers and load) and can exhibit undesirable levels of vehicle roll. This study includes a suspension system comprised of four controllable magneto-rheological dampers, associated sensors, and controller. There are three distinct phases in this investigation, the first of which is a numerical investigation performed on a four-degree-of-freedom vehicle roll-plane model. The model is subjected to a variety of road and driver induced inputs, and the vehicle response is characterized, with each semiactive control policy. The second phase of this study consists of laboratory testing performed on a Ford Expedition, with the front axle of the vehicle placed on a two-post dynamic rig (tire coupled), and a variety of road inputs applied. The third phase of this testing involves road testing the test vehicle to further evaluate the effectiveness of each of the semiactive control policies at controlling both vehicle comfort (vibration) and stability (roll). In each phase, the semiactive control policies that are investigated are tuned and modified such that the best possible performance is attained.
The performance of each of these optimal semiactive systems is then compared.
In the first phase of this investigation, two basic skyhook control strategies are investigated and two modified strategies are proposed. Upon numerically investigating the effectiveness of the four control strategies, it is found that the performance achievable with each of the control strategies is heavily dependent on the properties of the controllable damper. The properties of the controllable damper that were particularly important were the upper and lower levels of force that the controllable damper was able to apply. Based on numerical results, the controllable dampers were tuned for each control system. The results indicate that a velocity-based skyhook control policy, in conjunction with force control, is most effective at controlling both road-induced vibration and driver-induced roll. In the second phase of this investigation, the effects of the two skyhook control strategies were again examined. Multiple system inputs including step inputs, chirp inputs, and multi-sine inputs were used, and the results indicate that significant performance gains using the basic skyhook policies are unlikely. The third phase involved road testing the vehicle through specific maneuvers modeling a wide variety of common driving situations. In addition to the two basic skyhook policies, two additional policies augmented with steering wheel position feedback were also examined. It was found that the velocity based skyhook control policy augmented with steering wheel position feedback achieved performance superior to both the stock passive dampers and other control policies tested here.