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ABSTRACT
After a brief historical review, the parameters of the variable valve train system are presented. The concepts of VVA (Variable Valve Actuation) and VVT (Variable Valve Timing) are defined and their main capabilities are briefly outlined. The simplest method of modifying the valve timing is to use variable cam phasing devices. More sophisticated systems can act on lifting and/or duration. The strategy of Early Inlet Valve Closure (EIVC) or Late Inlet Valve Closure (LIVC) to achieve the Miller/Atkinson cycle is discussed. A large chapter is devoted to constructive achievements and to explaining their function. Cam phasing devices are first presented: chain, helical, and vane types followed by the technologies used to vary lifting and/or duration: switchable systems or systems with a continuously variable lift and finally systems without camshaft: "Camless" Electromechanical Valve Actuation (EVA) or Hydraulic Valve Actuation (HVA).
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Read the articleAUTHORS
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Pierre PODEVIN: Research engineer at the Conservatoire national des arts et métiers
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Adrian CLENCI: Lecturer at the University of Pitesti (Romania) - Associate researcher at the Conservatoire national des arts et métiers
INTRODUCTION
In today's automotive environment, the internal combustion engine must be :
less and less polluting: compliance with increasingly stringent standards;
less and less greedy in order to limit CO 2 emissions: compliance with future European regulations and/or commitment by car manufacturers encouraged by tax legislation ;
increasingly efficient: engine displacement is reduced, while maintaining the performance of a larger engine (downsizing). The specific power of the latest-generation engines - the ratio of engine shaft-end power to cubic capacity - is now as high as 70 kW/L, a value previously found only in engines designed for motor racing. Variable valve timing provides the internal combustion engine with an additional degree of flexibility, enabling it to increase its performance over its operating range. As a result, this technique is mainly used on engines for road transport vehicles.
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KEYWORDS
variable valve timing | variable valve actuation | cam phasing devices | camless | VVT | VVA | EIVC | LIVC | EVA | HVA
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Variable valve timing technologies for internal combustion engines
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