Mechanical Fully-Flexible Valve Control with delta-st 970251
Nowadays fully-flexible valve control is considered to be the most promising improvement measure for SI-engines besides or in combination with direct fuel injection. Engine producers investigate the readability of a huge variety of systems, but at present only simple systems are applied in production engines, which fulfil only a part of the requirements. Although hydraulic systems are very suitable for finding optimum valve control strategies, the advantages of mechanical systems for series requirements are obvious. Thus, after development of mechanical phase shifters and mechanical systems with up to three selectable valve lift curves, it seems to be logical to use the advantages and experiences with mechanical systems to realize a fully-flexible valve control as well.
In this context a new mechanical valve gear called delta-st (delta-st = delta control) for continuous adjustment of valve lift, opening duration and phase angle was developed at the University of Karlsruhe, Germany. As a special feature of this valve gear, only one (triangular) gear part has to be added to a conventional drag lever or tappet valve gear.
The first section of our paper provides information about the system itself, its operating principle and its possibilities to improve gas exchange. The different variants of delta-st are shown, also pointing out the specific properties and the boundary conditions important for cylinder head design. The second section gives a survey on the valve gear layout process and the tools developed in order to do the different tasks concerning kinematics and dynamics. Finally in the third section the application of delta-st in a production engine is presented and the most important test results are shown.