Variable valve actuation - switchable and continuously variable valve lifts

You are here: Homepage > Search

Variable valve actuation - switchable and continuously variable valve lifts

Kreuter, P. / Heuser, P. / Reinicke-Murmann, J. / Erz, R. / Peter, U. / Böcker, O.

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 efficiency of load exchange, mixture preparation, and combustion. This paper describes solutions of variable valve lift systems and illustrates the potential for naturally aspirated and turbo-charged SI (spark ignition) engines. An optimisation strategy for a two- and a three-step switchable system with double-cam-phaser is presented and the mechanism is illustrated. Based on steady state dyno measurements with a 4-cylinder SI engine, an improvement in fuel economy of 4.5 - 5.5% in the FTP75 cycle was demonstrated with these switchable systems. The improvement in low-end-torque amounts to 5 - 8% and a specific power of more than 70 kW/l was realised. Furthermore the actual development status of the continuously variable valve lift system (VVH) and the benefit of combining it with a cam-phasing device is presented. Actual dyno measurements show an improvement in fuel economy of 11.5% for the FTP75 cycle. The full load performance can be improved by 15 - 25% over the entire speed range. A VVH version with focus on low-end torque combines a BMEP of 10.3 bar at 1000 rpm with an excellent peak torque of more than 110 Nm/l and a power output of more than 50 kW/l. A version with focus on peak power realises more than 75 kW/l and an increasing torque curve versus speed on a high level. It is demonstrated that the variable valve timing is supporting a turbocharged engine concerning transient response, low-end torque, exhaust gas control and fuel consumption.