Abstract
Keywords: Semi-active suspension. Vibrating test bench. Damping coefficient. Periodical Motor Vehicle Inspection.
The development of semi-active suspension systems could significantly contribute to improve the dynamic performance and safety behavior of modern vehicles (Motta, 2000). These systems are required to provide a high riding comfort level while maintaining a reasonable ability to ensure safety performances by keeping the vehicle on the road.
A semi-active damping system is basically a shock absorber in which the dissipation law can be actively modulated through a control law. Several control laws have appeared in the literature; one of the most used is the semi-active on-off system proposed by Karnopp (Karnopp, 1974), in which hard and soft damping coefficients are switched depending on the sign of the product of body velocity and damper velocity.
Current passive systems are still very competitive because they are simple, reliable and do not need a power supply, but their behavior must maintain a commitment between ride comfort and safety (Ward, 2001).
When the designers develop the suspension system, the behavior of the vehicle is optimized in order to obtain the best commitment between high ride comfort and high tire grip force. Several authors (Motta, 2000), (Heo, 2003), (Yosimura, 2001) agree on using the following parameters to evaluate the suspension system performances:
o Body vertical acceleration is used to evaluate the ride comfort performances.
o Tire adherent force is used to evaluate the safety performances.
However, along the life of the vehicle, the damper performances will became worse due to the usual wearing out of the internal components and oil degradation, as consequence the vehicle behavior gradually drifting from optimum design condition.