Repetitive control of an electro-hydraulic engine valve actuation system

Fully flexible engine valve systems serve as powerful rapid prototyping tools in research laboratories. With the ability to quickly design innovative valve strategies, researchers can explore the possibilities of improving fuel efficiency, power output and emissions through appropriately varying the valve lift, phasing and timing. One means of achieving variable valve motion is through an electro-hydraulic valve system (EHVS). However, with an EHVS, it is difficult to achieve the high acceleration necessary for tracking cam profiles while maintaining the same level of accurate position control that a mechanical cam provides. In particular, the response time delay and the nonlinear dynamics of the hydraulic system can lead to error in position control. The paper first describes an identification method for obtaining a mathematical model of the EHVS. Based on the model, a linear feedback controller is developed. Finally, a repetitive feed-forward controller is added to augment the feedback controller, improving root- mean-square tracking performance to below forty micrometers.