A Survey of Variable-Valve-Actuation Technology 891674
In the conventional homogeneous-charge spark-ignition engine, fixed lift characteristics and timings for opening and closing of the intake and exhaust valves compromise efficiency and maximum power. In order to minimize the compromise, numerous variable-valve-actuation (VVA) systems have been proposed in the past that give adjustable valve operation depending on the engine-operating condition. A literature survey was conducted of the vast array of VVA devices that have been tested and/or analyzed in order to compare attributes of different systems.
The review indicates that the chief benefit of phase-shift systems, the ability to extract more power from a given-displacement engine without compromising idle stability, has been demonstrated conclusively. However, assessments of the potential benefits of the devices with variable-lift capability are less reliable because of the limited scope of past studies, lack of effort to separate the effects of different variables, and unreliability of data.