Modeling and Control Design of a Camless Valve Actuation System

This paper presents the modeling and control design of a new fully flexible engine valve actuation system which is an enabler for camless engines. Unlike existing electromechanical or servo actuated electro-hydraulic valve actuation systems, precise valve motion control is achieved with a hydro-mechanical internal feedback mechanism. This feedback mechanism can be turned on or off in real-time using simple two state valves which helps reduce the system cost and enables mass production. Since the external control only activates or deactivates the internal feedback mechanism, the trajectory of the entire closed-loop system is purely dependent on the design parameters of the internal feedback system. A mathematical model of the system is developed to evaluate the effect of each of the design parameters. The "Area-schedule" is identified as the key design feature which affects the trajectory of the closed-loop system. It needs to be designed systematically to optimize the performance of the system as well as improve its robustness. By treating this feature as the feedback control variable, the design problem is transformed into a nonlinear optimal control problem which is later solved using the numerical dynamic programming method. The effectiveness of the designed area-schedules is verified with simulations.