Design, modeling, and control of a camless valve actuation system with internal feedback

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 electrohydraulic valve actuation systems, precise valve motion control is achieved using a very stiff hydromechanical internal-feedback mechanism. The entire feedback mechanism is built into the physical design of the system. The external control only activates or deactivates the feedback mechanism in real time using simple two-state valves. This helps reduce the system cost, and thus enables mass production. The trajectory of the closed-loop system is purely dependent on the design parameters of the internal-feedback system. A mathematical model of the system has been developed and validated with experimental results from a prototype system. The area-schedule is identified as the most critical design feature, which affects the trajectory of the closed-loop system and, therefore, 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 and solved numerically using dynamic programming. The effectiveness of the proposed design procedure is verified with case studies.