Nonlinear design of active suspensions

This article develops a new nonlinear backstepping design for the control of active suspension systems, which improves the inherent tradeoff between ride quality and suspension travel. The novelty is in the use of a nonlinear filter whose effective bandwidth depends on the magnitude of the suspension travel. This intentional introduction of nonlinearity, which is readily accommodated by backstepping, results in a design that is fundamentally different from previous ones: as the suspension travel changes, the controller smoothly shifts its focus between the conflicting objectives of ride comfort and rattlespace utilization, softening the suspension when suspension travel is small and stiffening it as it approaches the travel limits. Thus, our nonlinear design allows the closed-loop system to behave differently in different operating regions, thereby eliminating the dilemma of whether to use a soft or stiff suspension setting. The improvement achieved with our design is illustrated through comparative simulations.