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Erschienen in:
2019 | OriginalPaper | Buchkapitel
Efficient Utilization of the Gas Exchange Advantages of an Infinite Variable Mechanical Valve Train System
verfasst von : Michael Breuer, Stefan Moormann, Stephan Schmitt, Paul Freeland, Gareth Jones
Erschienen in: Ladungswechsel und Emissionierung 2018
Verlag: Springer Fachmedien Wiesbaden
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Abstract
Since 2010 Pierburg has been involved in development, application and production of variable valve actuation (VVA) systems. UniValve, UpValve and FlexValve are recognized, fully variable mechanical VVA upgrades for SI- as well as for Diesel engines. This paper reports on layout and application of UpValve and highlights potentials to utilize its gas exchange advantages.
The paper briefly recaps the UpValve principle, architecture and layout. The clearance between valve head and piston (pockets) limits the valve lift around TDC of overlap. Different possibilities to minimize the intake pumping work while meeting those constrains are discussed. Obviously VVA introduces additional parts into the valve train. Hence, VVA friction is often considered as an issue. However, UpValve test results reveal a very favorable torque to turn behaviour. A plain simulation is used to understand this outcome.
Special attention must be given to the lift balance across the cylinder head, as the volumetric efficiency is significantly correlated to (early) IVC timing. It is demonstrated how this challenge is addressed during production and assembly. Finally dyno results are disclosed, which are acquired on a state-of-the-art SI engine with UpValve on the intake side. This concept engine also makes use of the inherent UpValve capability to shut down specific valves for cylinder deactivation.
Initially, VVA was introduced to minimize the part load pumping losses. While part of this potential is also utilized by downsizing, the freedom of variable inlet timings can be used as well to mitigate knock (Miller cycle) and to decrease transient AFR excursions due to the better air path controllability. The anti-knock effect allows for less overfueling and higher compression ratios associated with further efficiency gains, and the improved response reduces the need for spark retardation. Even the additional potential of exhaust side VVA was already demonstrated [1, 2].