Design and control of fully flexible valve actuation systems for camless engines

Abstract

The motivation to improve the fuel efficiency and reduce emissions of the internal combustion engine comes from the dwindling oil reserves and the increased concerns about climate change. A key step towards realizing these improvements is to introduce flexibilities into the mechanisms used for air and fuel management by replacing the mechanical devices with mechatronic systems. The introduction of fuel injection systems in place of the carburetors resulted in significant improvements due to the additional flexibilities in fuel management. The traditional air management systems use camshaft based mechanisms to actuate the intake/exhaust valves. The benefits offered by fully flexible valve actuation and the limitations of the camshaft based systems motivate the development of a "Camless valve actuation system". Research in this area during the past two decades has led to the development of several concepts. However, the stringent performance requirements to ensure reliable operation and the shortcomings of the previously developed concepts has impeded the widespread deployment of these systems. In this research, we propose to address the problem from two perspectives. A design based solution capable of achieving fully flexible operation using inexpensive components while requiring simplified controllers is first introduced. It is followed by the development of a systematic procedure for optimizing the design of a key component in this system to improve it performance and robustness. The second topic focuses on the implementation aspects of a new control algorithm to enable precise tracking of the engine valve reference profile. The effectiveness of the linear time invariant controllers based on the internal model principle for steady state operation of the engine is leveraged to enable tracking control during engine speed transients by extending the control framework to the time-varying setting. The challenges associated with the time-varying nature of the controller are revealed and the developed solutions help its implementation and validation on experimental hardware. The proposed framework can easily be extended to other engine subsystems as well as other general rotational machinery.