Abstract
Depending on the engine speed, the variable valve timing system can correspondingly change the valve open and close timing as well as the valve lifting position. As a result, not only the volumetric efficiency and the output torque can be effectively enhanced, but also the fuel consumption and emissions can be reduced. The purpose of this work is to develop a new variable valve timing mechanism using the creative design method. This new mechanism is expected to improve the valve open and close timing as well as the valve lifting position, using more efficient mechanism with a less number of the mechanism links. As a first step, the creative design method is used to find all the new and feasible variable valve timing mechanisms, which are capable of achieving the same function as the existing single over-head cam-shaft mechanism. Then, based on imposed constraints, we can select acceptable variable valve timing mechanisms with five-bar cam-link features. Furthermore, an appropriate new mechanism can be chosen to potentially offer superior performance. After the link lengths and the follower motion program are specified, the cam profile parametric equations are derived by applying the concept of velocity instant center. Consequently, the follower displacement, velocity, and acceleration with respect the input link rotation angle of the chosen new mechanism are calculated. Finally, under different adjusted phase angle conditions, the proposed variable valve timing mechanism can be used to study the effects on the existing mechanism. These effects include the variable valve timing and lift, the resulting valve displacement, velocity, and acceleration. Additionally the overlapping area of the valve opening and closing are calculated and compared. This proposed variable valve timing mechanism can provide two available phase angle adjusting conditions, and this new mechanism can achieve the expected variable timing and lift effect improvement.