A comprehensive mathematical theory and optimized design of a high-frequency electro-pneumatic variable valve actuator for a camless IC engine

Abstract

This paper discusses the development of a detailed mathematical theory and its use for the design of an electronically controlled, double-acting Variable Valve Actuation (VVA) mechanism for a camless internal combustion engine, that offers a comprehensive control over the timings and the motion of the valves such that any arbitrary time-variation of the valve lift profile can be obtained at variable rotational speeds of the engine shaft. The developed theory encompasses the thermo-fluid-dynamic as well as the applied-mechanical aspects of the actuator cylinder-engine valve system performance, the dynamics of the valve actuation being characterized by parameters such as valve opening duration, peak lift and seating velocity. The prediction of the mathematical theory compares well with several experimental data sets obtained from an in-house pneumatic VVA set-up. A new design methodology is formulated for determining the appropriate dimensions of the actuator, operating thermodynamic parameters and the electronic control of the various valve events for a desired range of engine rotational speed. Several parameters in the new design philosophy are kept within acceptable ranges established from time-tested data obtained from conventional cam-based valve actuation. For example, a new pneumatic cushioning strategy has been developed that is simple, effective and energy-efficient, and is able to keep the valve seating velocity within an acceptable range (0.08–1.13 m/s). The work also discusses the implementation of several constraints that are necessary for the design of a practically viable pneumatic actuator. The evolution of a design matrix map for the electro-pneumatic VVA is quantified for the engine rotational speed varying up to 5500 rpm.