Charlton, S., Price, C., Rogers, J., Turner, J. et al., "DigitalAir™ Camless FVVA System - Part 2, Gasoline Engine Performance Opportunities," SAE Int. J. Engines 10(3):2017, doi:10.4271/2017-01-0641.
The paper describes a completely new approach to fully variable valve actuation (FVVA), which allows almost unlimited continuously variable control of intake and exhaust valve opening and closing events, and duration without the use of a camshaft.DigitalAir replaces conventional poppet valves with horizontally actuated valves located directly above the combustion deck of the cylinder head, which open and close a number of slots connecting the cylinder with the intake and exhaust ports, Figure 1. The stroke of the valves 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 also 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 paper will present analytical and experimental data which confirms that the proposed FVVA system can meet the basic performance requirements of modern GDI engines with respect to breathing characteristics across the speed range, throttleless operation at and above idle, opening and closing event optimization, cylinder deactivation, control of residual gas fraction / scavenging and exhaust thermal management.Analytical results were developed using GT-POWER Cycle Simulation and CONVERGE computational fluid dynamics (CFD). Cycle simulation was used to study the system level performance, such as full load capability and transient response, and in particular to quantify the fuel consumption benefits of throttleless operation. CFD was used to better understand the opportunities for in-cylinder charge motion - tumble, swirl and turbulence.JP SCOPE Inc. has been running experimental engines with DigitalAir for several years and has successfully completed performance and durability tests. The mechanical and thermal design of the cylinder head, and the design of the actuator will be covered in Part 1 of this paper .