Valve Events and Engine Operation

In SI automotive engines valve events exert a major influence on charge composition under highly throttled conditions such as idle and also on WOT performance. In the interest of promoting maximum idle quality with minimum idle fuel consumption, minimization of valve overlap is desireable. Maximizing engine performance via valve events within the aforementioned constraint is the substance of this paper. Valve events are discussed on the basis of instantaneous changes in cylinder volume in a phased relationship with flow area created by valve lift. Indicator (P-V) diagrams focused on pumping loops at WOT over a broad speed range provide a rational basis for selecting exhaust valve timing points. Key to achieving the stated objective of minimizing valve overlap is delaying the timing of intake-valve opening while establishing the timing of intake-valve closing on the basis of the desired balance between low-speed torque and power.