Inerter-based semi-active suspensions with low-order mechanical admittance via network synthesis

In this paper, the semi-active suspension design problem is concerned by proposing a novel design method incorporating inerters, where the overall semi-active suspension is divided into a passive part and a semi-active part. A mechanical network composed of springs, dampers and inerters is employed as the passive part, and a semi-active damper constitutes the semi-active part. For the conventional semi-active suspensions, the passive part is merely a parallel connection of a spring and a damper, and the main focus is on improving the semi-active part by proposing more effective control algorithms. In contrast, in this paper, the main idea is to improve the overall vehicle performance by improving the passive part instead of the semi-active part. Low-order admittance networks are employed in the passive parts, where some low-order positive real admittance functions are optimized, and then realized as specific mechanical networks by using network synthesis. A suboptimal control law, called steepest gradient control, is utilized in the semi-active part for the control of the semi-active damper. The proposed method is illustrated based on a quarter-car model, and numerical simulations based on a quarter-car and full-car model are performed to show the effectiveness of the proposed method. In contrast to the conventional semi-active suspensions without inerters, the proposed method can provide significant improvements (over 10% and 8% improvements for the quarter-car and full-car model cases, respectively) for the overall suspension performance involving ride comfort, suspension deflection, and road holding.