The Meta VVH System - A Continuously Variable Valve Timing System 980765
A continuously variable valve timing system called the “Meta VVH System” is presented. It allows the unthrottled load control of spark ignition engines. Two camshafts rotating at the same speed are acting on the intake valve(s) via a follower and a transmission element in such a way, that the output displacement is the sum of the effective displacements of the two cams. The first camshaft which operates as an opening cam is driven directly by the crankshaft. The second camshaft operating as the closing cam is driven by the opening cam via a four wheel gear drive. This gear drive allows a phasing between both camshafts in a range necessary to vary lift and duration of the valve(s) from zero to maximum.
This system not only offers the flexibility and range required for an unthrottled load control but also shows benefits concerning its friction losses even in comparison to modern state of the art valve trains like the roller finger follower. The experience with this system applied to different SI engines shows no restrictions for the use on production engines neither concerning its function (including seating velocities, stresses, cycle-to-cycle and cylinder-to-cylinder variations) nor with respect to the complexity (number of parts, space, weight, costs etc.). The variation in lift and duration realized by this mechanism provides the conditions to avoid pumping losses at part load conditions and to improve the maximum volumetric efficiency over the whole engine speed range. Additionally the mixture preparation under atmospheric conditions is supported by high intake flow velocities at part load, thus leading to an improved combustion even at low loads under steady state, cold start and warm up conditions.
Results of extensive thermodynamic investigations with the variable valve timing system and its potentials will be presented and discussed in this paper.