Valve Motion Characteristics and Application on Engine Based on a New Variable Valve Actuation System

A new mechanical-hydraulic variable valve actuation (VVA) system was developed and a thin-wall orifice velocity control system were analyzed. Meanwhile, influence of speed, needle valve overflow area, oil temperature and oil supply pressure on valve motion characteristics were explored, as well as the VVA system have been applied on a single-cylinder engine preliminary. By the VVA system, valve lifts can be adjusted from maximum of 8.7 mm to fully closing. Valve seating velocity decreased with orifice diameter reducing. Seating velocity can be maintained below 0.5 m/s with 0.8 mm diameter of thin-wall orifice and 3 mm check valve moving distance. Besides that, velocity control system also can help improve the coefficient of cyclic variation of maximum valve lift. Except for the needle valve closing state, valve lift decreased with oil temperature increasing and operating speed reducing under the same needle valve state. Oil supply pressure hardly had no influence on valve lifts, but delayed valve opening timing with pressure decreasing. Thin-wall orifice seating velocity control system was not sensitive to variable oil temperature and supply pressure. Compared with conventional engine, adjusting intake valve by VVA system under un-throttle internal EGR strategy, can improve BSFC and NOx emissions significantly about 13.8 % and 19.8 % on 6 bar IMEP.