For the optimization and extension of operating range of future combustion systems aiming at ultra-low emissions and high efficiency, the control of gas exchange plays a major role. Important parameters for optimization are e.g. volumetric efficiency, residual gas control, in-cylinder charge motion and precise control of the level of homogeneity or inhomogeneity of the charge as required by the particular combustion mode. In addition, advanced operating modes such as Miller or Atkinson cycle or gasoline compression ignition demand a high degree of variability in cam timing. A highly flexible variable valvetrain has been designed for the investigation and development of such new combustion processes. This novel valvetrain is based on a mechanically fully variable actuation concept using two independently rotating cam disks per valve. By this arrangement, new degrees of freedom in the design of the valve opening curve arise. For a single cylinder research engine using a four-valve cylinder head, this valvetrain has been designed in a way so that all four valves can be controlled independently, offering the possibility of e.g. inlet valve phasing combined with a second event on the exhaust. The new valvetrain has been manufactured and tested on a mechanical component test bench. In a “backward” design approach, the valve lift curves and the timing variation range required for the generation of particular variations of in-cylinder charge motion were defined by 3D CFD simulation. On this basis, the layout of the valvetrain components for realization in the research engine was defined. The new valvetrain will be employed for the development of highly efficient low-emission combustion systems on the test bench.
