The Design And Dynamic Analysis Of Continuous Variable Valve Actuation System

The valve timing of traditional gasoline engine is a compromise plan of engine performance which is selected by a variety of different valve phase experiments. Besides, because of the throttle of intake manifold, pumping loss of exchange process significantly increased. As a result of that, studying on a continuously variable valve train has great practical significance to the energy saving and emission reduction.This paper presents a continuous variable valve timing train. In this mechanism, the rising process of intake valve is controlled by cam profile while the falling process of intake valve is controlled by hydraulic system. By controlling the relieving time of hydraulic system, we can decide the intake duration and then realize variable valve timing. The mass flow in the cylinder can be controlled by late closing of intake valve.This paper chooses K157 as the research object. By redesigning the valve train of the engine, it can achieve the continuous variable valve timing. The main tasks include the following:First, use the polynomial profile to design the cam of valve train. Meanwhile, the angle of repose increases in order to meet the different duration of the greatest valve lift with different speed and hydraulic system, then we can obtain a series of continuously variable cam profile.Second, according to the structure of K157 motorcycle engine, design the variable valve train driven by hydraulic. Between the valve and cam ,design hydraulic-driven train. Through the cam, tappet, hydraulic piston, the mechanism can control the open process of intake valve; while the seating process is controlled by the effect of flow restriction which will allow the valve working smoothly and steadily.Third, design hydraulic controlled system. Make the hydraulic cylinder filled with oil in order to provide medium for force transmission. Control the relieving time to make the intake valve fallback in time to achieve continuously variable intake valve timing.Forth, through the fluid continuity equation which is based on the law of mass conservation and the motion differential equation of momentum theorem, set up kinetic equation of variable valve system and analyze the result of a variety of conditions.Last, study the influence to the intake performance with new designed structure through the experiments. The experimental results show that the new developed valve train can effectively improve the intake performance.