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You may have been to a fair where collectors run antique Hit 'N Miss engines (slightly different from Make 'N Brake). The reason they're called "Hit 'n miss" is because the engine does not fire on every "power stroke" because of a unique system for governing engine speed.
The idea is very simple,
if an engine is not under load, the engine only fires enough to keep the engine running - that is when the engine is not under load, a govenor opens up the exhaust valves and the engine will not fire because there is no compression, when the engine speed falls too low the exhaust valves close and the engine fires - now that it is moving quickly again, the exhaust valves open up again. When the engine is under load, the exhaust valves operate normally (no power strokes are missed).
Now, my idea is simple, modify this system for use in a modern car to save fuel - to make it more efficeint, the fuel injectors will not spray any fuel when the govenor is holding the exhaust valves open, there for not wasting any fuel (On the carbureted engines, raw fuel would be spit out of the exhaust when the engine wasn't firing - imagine what the EPA would have to say about that!)
Coupled with a free-wheeling transmission I think this sort of engine would be very effective.
Engine with varying cylinder sizes
[Gordon Comstock, Oct 04 2004]
Hit N' Miss engine
[normzone, Aug 13 2009]
||Mercedes-Benz have a system where half of the cylinders of an engine (e.g. a V12) are turned off when no great power is needed, like in city traffic.
I don't know exactly though how they turn them off, though.
||They're not just thinking about doing it. They're doing it, coming soon, to both GM and Ford big trucks. I interviewed for a position related to Ford's efforts, which are electro-hydraulically controlled by little relays in the pan, controlling cheesy little DC motors to operate a regulator needle valve, (the very same motors you see in little RC cars).
||That Cadillac 4-6-8 system was in the 80's.
||I don't think having a valve open when a piston reaches TDC in a modern engine is a very good idea.
We sort of covered this concept in "Engine with varying cylinder sizes", see link.
||I disagree that this is covered in "varying cylinder sizes." It strikes me that this is applying very old and valid technology to a modern problem, simply turning the engine on and off as needed, the way hybrids do at stoplights.
I imagine the engine would run much cooler. The cruise control would have to operate the hit-miss operation, since the ride might be jerky indeed at lower speeds.
You don't want an overrunning clutch, though: if the car is allowed to roll along, and the engine is allowed to stop, what then restarts the engine if the clutch is simply overspeeding the engine? You have to retain that rigid connection to keep the engine turning, then the cruise control fires the cylinders a few times to keep revs up.
I think the Honda approach of turning off one bank of the V6 is insufficient. If the car will maintain speed on just one cylinder, then do that. Fire up a different cylinder once in a while to even out the heating and wear.