Inherent limitations and control design for camless engine idle speed dynamics

The idle speed control problem of a spark-ignited engine equipped with a ca mless valvetrain is considered. The camless valvetrain allows control of th e individual intake and exhaust valves of each cylinder and can be used to achieve unthrottled operation, and consequently, optimize the engine perfor mance. We formulate the speed control problem for this engine and show that it exhibits unstable open-loop behaviour with a significant delay in the f eedback loop. The instability is intrinsic to the unthrottled operation and specific to the camless actuation used to achieve the unthrottled operatio n. The delay is caused by the discrete combustion process and the sensor/co mputer/actuator interface. We demonstrate the inherent system limitations a ssociated with the unstable dynamics and the delay and provide insight on t he structural (plant) design that can alleviate these limitations. Finally, stabilizing controllers using classical and modern robust design technique s are presented and tested on a nonlinear simulation model. Copyright (C) 2 001 John Wiley & Sons, Ltd.