2010 Volume 52 Issue 161 Pages 181-188
Various methods of variable valve actuation mechanisms has been studied during the past decades until today, a simple phase shift mechanisms and cam robe switching mechanisms are commonly used and Variable Valve Lift & Duration (VVLD) was put into practical use in 2001. These technologies drastically expanded the degree of freedom in valve timing variation. In this paper, the principle of variable valve actuation mechanism, particularly of VVLD is explained by introducing some mass-produced and studied systems. In addition, “Exhaust Secondary Cam” mechanism, which an exhaust valve reopens at the beginning of the compression stroke, is introduced and its simulation and experiment results in several usages are shown for detail. Unlike fuel injection which controls local air-fuel mixture characteristics in the combustion chamber, a variable valve actuation system can control the cylinder average air-fuel mixture characteristics such as cylinder pressure, temperature, fuel density (opposite of mixture quantity) and oxygen density. Their impact on local combustion are not high, however they play an important roll on the overall combustion cycle performance. Combustion studies focused on how to take the advantages of variable valve timings are now expected to be performed widely.
