Comparison of Three Different Concepts for a Variable Valvetrain for Huge Combustion Engines

Emissions reduction and performance improvements of combustion engines is a permanent topic in R&D not only for engines of passenger cars but also for huge engines for trucks, locomotives, or for power generation. One decisive step forward in this respect is the realization of variable valvetrains for engine valves. Such systems offer much higher flexibility to adopt the inflow of air and the outflow of the exhaust gases in order to reduce throttling losses, improve the mixing of air with the fuel, or to handle specific modes of operation, like the Miller Cycle. Thus, a high potential exists to increase power density and the combustion cycle efficiency. We will compare several electrohydraulic systems with respect to power consumption, flexibility, and reliability for valvetrain systems found in patent or other literature and a system developed by the authors. The latter is a novel energy saving system exploiting a hydraulic spring concept. Detailed experimental results obtained from a functioning test rig of the authors' system allow to tune the simulation models and yielded a good insight in the main technical difficulties with electrohydraulic variable valvetrains.