SAE 2017-01-0635 : 2017

This paper provides an overview of the analysis and design of the DigitalAir™ camless valve train including the architecture and design of the valve and head; the details of the electric valve actuator, and the flow characteristics of the valves and resulting charge motion in a motoring engine. This valve train is a completely new approach to fully variable valve actuation (FVVA), which allows almost unlimited continuously variable control of intake and exhaust valve timing and duration without the use of a camshaft. This valve train replaces conventional poppet valves with horizontally actuated valves located above the combustion deck. As the valves move, they open and close a number of slots connecting the cylinder with the intake and exhaust ports. The valve stroke necessary to provide the full flow area is approximately 25% of the stroke of the equivalent poppet valve, thus allowing direct electrical actuation with very low power consumption. This design arrangement avoids the risk of poppet valve to piston collision, or the need for cut-outs in the piston crown, since the valves do not open into the cylinder. The results from the analytical models used to predict the performance of the valve train are presented and compared with experimental data (when available). JP SCOPE Inc. has been running engines with this valve train for several years and has successfully completed preliminary performance and durability tests. Part 2 of this paper [ 1 ] will present analytical and experimental data which confirms that the proposed FVVA system can meet the basic performance requirements of modern GTDI engines.

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