Abstract
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 combination with cam-phasing devices will be discussed for both the multi-step and the continuously variable valve lift system on the base of load exchange calculations as well as dyno test results. Finally, it will be shown that the combination of variable valve lift and exhaust turbo-charging offers a considerable potential to further improve both low-end-torque and maximum power.
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