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Variable valve timing represents one of the key technologies in further development of automotive engines. Different valve lift profiles and variable valve timing in the engine operation map offer the flexibility to better meet the load specific engine requirements regarding the intake flow conditions, the exhaust gas control and the efficiency of load exchange, mixture preparation and combustion.

Variable valve timing is one of the key technologies in the further development of automotive engines. A variation of valve lift profiles and variable valve timing in the engine operation map offer the flexibility to better meet the load specific engine requirements regarding the intake flow conditions, the exhaust gas control and the efficiency of load exchange, mixture preparation and combustion. This paper describes solutions of variable valve lift systems for both a two or three-step switchable system as well as the actual design of the continuously variable valve lift system VVH. The system properties will be described and analyzed regarding their specific benefits in fuel economy, emission behavior and performance as well as regarding the systems trade-off. Optimization strategies regarding a two or three-step variable maximum valve lift are pointed out and will be compared to the continuously variable intake valve timing.

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.