Idle speed control: an old problem in a new engine design

The idle speed control problem of a spark ignited engine equipped with camless valvetrain is considered. The camless valvetrain allows control of the individual cylinder valves and can be used to achieve unthrottled operation, and consequently, improve dramatically fuel economy. We formulate the speed control problem for this engine and show that it exhibits unstable open loop behavior with a significant delay in the feedback loop. The instability is intrinsic to the unthrottled operation and specific to the camless actuation used to achieve the unthrottled operation. The delay is caused by the discrete combustion process and the actuator/sensor interface. We demonstrate the inherent system limitations associated with the unstable dynamics and the delay and provide insight on the structural (plant) changes that can alleviate these limitations. Finally, a stabilizing controller is designed and tested on a crankangle-based simulation model.