Implementation and Analysis of a Repetitive Controller for an Electro-Hydraulic Engine Valve System

Variable valve actuation plays an important role in modern engine design. Fuel economy, emissions, and power output can be improved through appropriately varying valve lift and timing. One means of independently and continuously adjusting these valve profile parameters is with an electro-hydraulic valve system (EHVS). However, with an EHVS, it is very difficult to achieve 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 valve position control. The paper first describes the identification method used to obtain a mathematical model of the EHVS. Based on the model, two linear feedback controllers are developed and compared. To further improve the tracking performance, a repetitive feed-forward controller is added to augment the feedback controller and the root mean square tracking error is improved to under 40 μ m. Stability and steady-state tracking error variance analyses complete the mathematical framework of this work.