Physical model of a quarter-car active suspension system

The potential advantages of a modern active suspension system are recognized for race cars, on road cars or even for great series cars. Beside the passenger ride comfort, the control of the vehicle vertical acceleration directly affects the road holding. In the case of passive suspension models, the car structure is optimized in initial stage of design, taking into consideration the spring stiffness, damper coefficient, sprung and unsprung mass, various tires performance and different velocities, etc. The performance of the passive suspension system is limited, in the first line, by the inherent variation of these parameters. The active suspension system preserves the advantage of a close loop control system, because these actuators are controlled by devices which receive and process the direct information from proper sensors. In order to evaluate the active suspension system performance, more possibilities are known: mathematical analog or digital models, the design and implementation of test set-up versions or physical test models. Obviously, the physical test models are able to act as the common car structure, but these manufactured equipments are not available on the market. In this sense, the authors conceived, designed and built a test setup version, a “physical model”, as a robust, simplified solution, with only one acceleration/speed transducer in the control loop. The actuator is an electromagnet operating against an internal spring. The structure comprises a cam, driven by a DC motor, which simulates the road conditions, an articulated wheel with tire, a spring and damper. The car body is simulated by an articulated plate. To test the active suspension system performances are attached two position sensors, one for wheel and one for the car body. Based on this structure, various modern designed control strategies can be implemented and tested.