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The VVH System - Variabler (variable) Ventil (valve) Hub (lift) - is a variable valve timing system suitable for an unthrottled load control of spark ignition engines. This mechanical valve train system allows a continuously variable intake valve lift from zero to maximum with a corresponding variable intake closing. Based on a first introduction of the VVH system during the SAE '98 Annual Congress this paper gives a more detailed description of this technology and reports about the progress of development. In a first part of this paper a systematic design study showing application variants of the principle design proves that the VVH technology can be designed for all kinds of combustion engines with poppet valves including two and multi-valve cylinder heads, engines with over-head cam drive or pushrod valve train, inline or V-engines.

A continuously variable valve timing system called the “Meta VVH System” is presented. It allows the unthrottled load control of spark ignition engines. Two camshafts rotating at the same speed are acting on the intake valve(s) via a follower and a transmission element in such a way, that the output displacement is the sum of the effective displacements of the two cams. The first camshaft which operates as an opening cam is driven directly by the crankshaft. The second camshaft operating as the closing cam is driven by the opening cam via a four wheel gear drive. This gear drive allows a phasing between both camshafts in a range necessary to vary lift and duration of the valve(s) from zero to maximum. This system not only offers the flexibility and range required for an unthrottled load control but also shows benefits concerning its friction losses even in comparison to modern state of the art valve trains like the roller finger follower.

This paper reports the results of theoretical and experimental investigations in the field of variable intake - valve control of spark-ignition engines. Different degrees of freedom for a variable intake profile such as variable intake opening and closing events, variable valve lift, as well as the deactivation of one of the intake valves per cylinder of a multi-valve engine are considered and evaluated concerning their potential to reduce pumping losses, to support mixture formation, and to improve combustion. The investigations show that additional efforts are necessary to convert the potential of minimized pumping losses due to unthrottled SI-engine load control into reduced fuel consumption and good driveability. Increased gas velocities during intake for low engine speed and load and adjusted residual-gas fractions according to the different operating conditions prove to be very efficient parameters to improve engine performance under unthrottled conditions.