Freevalve thinks so
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Wait long enough, and Moore’s Law of increased computing power in smaller packages (or just good ol’ human ingenuity) eventually makes all great ideas practical. The latest to catch my attention: engine valves that operate without camshafts. For decades the idea of electronically controlled electromagnetic, hydraulic, or pneumatic valve actuation has been studied, developed, and ultimately abandoned by big-name engineering firms such as Lotus and Ricardo—as well as familiar automakers including BMW, Fiat, Ford, GM, and Renault. Now a spinoff of hypercar maker Koenigsegg called Freevalve appears poised to bring the concept to production.
Freevalve seems to be taking an all-of-the-above approach with its so-called pneumatic-hydraulic-electronic actuators. But air does the work. The team first employed this solution on the Scuderi Split-Cycle air-hybrid engine I first covered in June 2006. That design demanded valves that opened far more quickly than a traditional cam-driven design could manage. Because the engine recovered braking energy as compressed air, that energy source was abundantly available. So compressed air opens the valve almost instantly, electronically controlled hydraulic pressure holds it open, a coil spring closes it, and passive hydraulic pressure cushions its “landing.” An electric coil provides highly precise sensing of each valve’s position.
The first thing everybody frets about with such systems (or with an old car overdue for a new timing belt) is what happens if the valves go out of sync and try to stay open when the piston is rising. Actually, not much, explains Freevalve marketing director Andreas Möller: “There is no rigid mechanical structure behind the valve, so the piston can push the valve assembly back with no counter forces.” The hydraulic hold-open circuit automatically releases if faced with such a force. Sure, if the valves are inclined at a steep angle, the piston could bend a valve and cause some mayhem. But Möller notes that “a combustion chamber designed from scratch with the Freevalve system is likely to have a higher compression ratio [allowing valve timing to reduce effective compression] and a smaller area-to-volume ratio with more upright valves that are less prone to bending in case of piston contact.”
The second major concern is the one that generally doomed these systems in the past: energy draw. Möller says that although the compressor (featuring standard AC-compressor innards capable of peak pressures near 300 psi) generally consumes more energy than camshafts, this is partially offset by a reduction of the engine oil flow and pressure required to lubricate cams and valves. (Freevalve’s head employs a dedicated hydraulic circuit.) And Freevalve’s high-speed friction penalty is countered by the fact that at idle and lower speeds its parasitic losses undercut those of several VVT systems.
The whole point of infinitely variable valve lift and duration is to enable opportunities for improved combustion efficiency, some familiar—Atkinson/Miller cycle timing, elimination of the throttle valve and its pumping losses, in-cylinder exhaust-gas recirculation—to novel ideas such as divided exhaust ports (DEP). These route the flow from half the exhaust valves to the turbo while the rest bypasses it, eliminating the need for a turbo wastegate. Bypassing the turbo at startup heats the main catalyst quickly enough to eliminate a close-coupled cat. DEP also improves scavenging of residual exhaust.