Ultimate Atkinson Cycle

Well, Atkinson Cycle engines are somewhat interesting. What happens is the intake charge is sucked into the engine, then the intake valve remains open for a short period of time on the compression stroke so some of the charge is pushed out. This allows for greater efficiency with the trade-off of reduced power. But I believe there is a lot of un-harnessed potential in the Atkinson Cycle.

First off, in my design it would have to be variable. I propose a system like VTEC in Honda engines where there are separate rocker arms that lock together to control the same valves (in this case there would be two rocker arms for two valves and one in the center for the atkinson affect). Then, the center rocker arm would be controlled by a device like Valvetronic found in some BMW engines to continuosly vary valve lift. This is all possible stuff, hardly inventitive however necissary to the engine, as it allows the variable lift to be isolated to only the Atkinson effect, while the other two lobes control the intake function normally.

Next, there is a feature similar to my proposed idea for variable squish tabs, which would have a small tab in each cylinder that allows for a very high compression ratio when at the top of the head, but can be raised even further up to create a cavity and therefore a lower compression ratio but increased volume. This would seem like a half-assed rather than half-baked way of controlling compression ratio, however with a variable Atkinson Cycle, the extra volume added by raising the tab could be expelled in the compression stroke when necissary, effectively maintaining a constant displacement for the engine. This would be useful because it would allow for much greater power at high RPMs, as engines can handle a higher compression ratio at higher RPMs without detonation because there is less time for it in the compression stroke. It goes without saying that this would be direct-injected, so picture something like a starting compression ratio of around 12:1 with the cavity as high up as possible, increasing to as high as 15:1 in its lowest position (which would be at the top of the head as mentioned, not protruding into the cylinder).

And with greater power would come greater efficiency. A continuosly variable Atkinson Cycle would mean that the intake lobes could provide maximum lift (meaning minimum resistance) so that the pistons would suck in the charge using much less energy than with a restrictive throttle or even variable valve lift device on its own, since a lower valve lift would still create a non-trivial amount of resistance. Of course the amount of charge that would stay in the cylinder to be compressed would rely on the throttle position, which would control how much valve lift there is on the Atkinson lobe (the more lift, the more is pushed out; the less lift, the less is pushed out). The neat thing about devices like Valvetronic is that they allow for a wide range of lift.

In a nutshell, this would undoubtebly provide better efficiency and better power capability than an equivalent Otto Cycle. Oh and as a side-note, there would be a sparkplug on the tab itself in addition to the one in the head simply for better combustion.