Nonlinear Control of Hydraulic Actuators in Variable Cam Timing Engines

Abstract

This study demonstrates, from both mechanical considerations and test
data, the presence of a significant nonlinearity in the variable
cam timing (VCT) actuators. This motivates the inclusion of a simple nonlinear compensation term in the VCT controller allowing faster valve timing control loops than linear controllers with better robustness in practice. Nonlinear models of hydraulic VCT actuators are identified on a dual-independent VCT engine under closed-loop operation. It is shown by simulation and also verified experimentally that simple nonlinear control schemes achieve superior performance compared to linear PIDs even though the identified nonlinearity is likely to be only a basic approximation of the true behaviour.