Simulation of a Camless Engine Valve Actuator With Mechanical Feedback

Fully flexible engine valve actuation systems are enablers for improvements in engine fuel consumption and power delivery, as well as the implementation of advanced combustion strategies like homogeneous charge compression ignition (HCCI). Hydraulically actuated valve actuation systems provide the greatest operating flexibility but have generally required precision flow control (i.e., servovalves) for viable operation while consuming more power than conventional cam-driven valvetrains. This paper describes an electrohydraulic fully flexible engine valve actuator with a mechanical feedback linkage between the engine valve and the spool in the hydraulic flow control valve. This feedback linkage is intended to simplify the control of the engine valve motion and eliminate the need for servovalve-class performance in the hydraulic control valve. The feedback mechanism reduces the control effort needed to operate the flow control valve since the spool position is not solely a function of the control input. With the assistance of mechanical feedback, the flow through the control valve is throttled in proportion to the engine valve motion. Thus, while throttling losses are not eliminated, there is no excessive flow throttling. This will have a beneficial impact on the energy consumption of the actuator. For preliminary study and validation of the concept, a model of the actuator was developed using ADAMS mechanical system simulation software and AMESim hydraulic simulation software. Results for the combined mechano-hydraulic model are presented to illustrate potential performance benefits and pitfalls of the concept, including effects of dimensional tolerances in the flow control valve. The simulation data was also used to size an electromechanical actuator that would be used to the flow control valve in conjunction with the feedback mechanism.