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For example, take a 4 cylinder motor, and add 4 more smaller cylinders on the outside of the block, that would also drive the crank, but in between the firing of the other pistons. Eseentially this would be an 8 stroke motor. The idea is that the smaller pistons would fire right before the bigger ones,
increasing engine speed, and smoothing out the torque curve of the motor.
1e and a 2e and a 3e and a 4e instead of 1 and 2 and 3 and 4.... dig?
Giblet.
(?) Mayflower engine
http://www.mayflowere3.com/
dynamically varying cylinder sizes [drew, Jun 03 2002, last modified Oct 04 2004]
an even better solution: continuous cylinder size
http://www.greenbus...l%20Compressors.pdf
Wasn't easy but found it at last. (Saw it years ago) [pashute, Oct 04 2004]
[link]
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The first reasonable idea I've seen from you. |
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I don't understand why you would want the in-between cylinders to be smaller. |
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I understand how the addition of cylinders, in a classic design, would improve torque but I fail to understand how this arrangement would affect engine "speed" (rpm?). As for the additional cylinders added as in-between assistance in smoothing the power pulses, perhaps a one way of thinking about this is as an "active flwheel," since an enhanced flywheel effect seems to be what you are seeking with this proposal. |
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I'm sorta with [jutta] on this one. Why not just buy an 8 cylinder engine? Or suggest an engine with 64 itty bitty cylinders? |
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Saab has come a long way in development of a variable compression engine that increases fuel economy among other advantages. The whole upper engine block can tilt on "hinges" relative to the crankshaft. |
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FJ: I've seen the Saab effort, and it's an interesting idea, but limited. The Mayflower engine has one very important advantage - you can effectively fit two engines for the (admittedly more expensive) price of one; a small engine for town use, and a big engine when you feel the need for etc. Economy or power - you flex your foot and take your choice. |
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That Mayflower thing is amazingly neat. I wonder how well it works in real life... |
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I don't know, StarChaser - but now Mayflower have got in on the act, I think it will become reality. The one-man designer trying to make it would never work. Mayflower is a large, serious company, and they see huge potential earnings from this engine. With ever more stringent emissions regulations, I can certainly see this as a major development. |
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i can't recal exactly which company was working on this, but one of the american makers is developing an engine which more or less stops using a half the cylinders when cruising for efficiency. they've got in one of their oversized pickups i believe. |
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Love the Mayflower site (fast flash graphics, at one point even spells out "the" "f" "word"). Schematic looks like a standard internal combustion shell with stroke limiting internal links. Next step, bye bye transmission? |
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Nothing new in that - I've had several cars where the engine has managed to comprehensively remove the transmission. |
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American cars no doubt... :-) |
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jiggerspalt : Cadillac had an eight cylinder engine that would run on just four or six cylinders depending on circumstances, but I'm not sure if it's still in use. I suspect that friction and complexity were problems.
I can almost see the point in having secondary expansion, shorter, fatter cylinders to take the exhaust from the primary cylinders to extract more power from the hot gas (like later steam engines) but I think the size and weight increase (not so important on a ship or railway loco) would be an insurmountable problem. Oh and turbochargers use this wasted energy in a much smaller neater package. |
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What may work better is to design the flyweel to be a rotary engine giving that extra boost to mellow torque and increase rpms. |
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Gordon - re: the Caddie - yep , they gave it up for exactly
those reasons - even if you weren't using eight cylinders
you were still carrying all that dead weight, and a friend
of mine who had one said the damn thing would always
find some way of screwing up between 4/6/8... usually
some kind of gawdawful clunk. Of course, he also found
some genius of a woodworker had replaced a faulty piston
with a perfectly machined wooden one, wh: may have
contributed to the whole mess... but then what do you
want out of a $200 Caddie? |
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I've read recently that GM has revitalized their efforts in creating a 'displacement on demand' engine...and it's coming along very well. The switch between the various cylinder configurations is very smooth and almost entirely unfelt; it happens within one-half to one revolution of the camshaft, which at a normal operating speed of 1500 rpm would work out to around 1/1500 to 1/750 of a second. That's a very short transition time. They've even implemented this concept on various Corvette and truck engines for testing, and the results were an engine with an equal amount of performance and much better fuel economy. |
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Interesting idea, four smaller cylinders act like lil helper cylinders for the four larger ones. One word. Mass. The four lil cylinders will be a drain on the larger ones, to help the big one go down they would have to be of equal mass to accomplish this, not to mention the timing nightmare... imagine what your distributor would look like..it would be completely unbalanced, and if you did actually achieve balance, all the pistons, and sections of crankshaft would all weight the same, so negating the fact of having helping cylinders. The crank you describe in which the smaller pistons piggy back on, would be so offset that it would rattle the poor lil motor and possibly the car it was in to pieces. with current technology, the only way to smooth out your power curve is to have more cylinders firing and a larger flywheel to negate the standard up and down. Or another alternative is go Rotary, less moving parts and Mazda has in fact come close to perfecting that lil motor. Fewer moving parts = less weight = less wear and better fuel mileage. Interesting idea and even doable... just will end up with an engine that functions even less smoothly than your intent was to begin with. |
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See link. At the time I first saw it (probably around '95) they were talking about the motor industy, and if I remember correctly, they were complaining that it is very hard to enter this industry with revolutionary changes. From the current link I learn they are in the pumping industry only. (Running burning fuel through the spirals would turn this "pump" into an engine, and a very efficient one at that. |
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How about a small mayflower, compressor/ rotary engine mounted in each wheel hub with multiple cylinders for smooth power delivery directly where it is needed. Controled by modern electronics you could do away with most of the transmission losses and drive train. Like others I like the idea of the Mayflower engine but can't understand why it's not out there yet? |
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thats what a flywheel is there for, to provide the inertia between power strokes which then smoothes out power pulses |
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That Mayflower idea is worth about a million croissants. |
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That slider-crank arrangement is a basic kinematic linkage taught in Mechanical Engineering 101. Why nobody ever applied it to a ICE before I'll never know. |
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I see what you mean about the flywheel, but the flywheel only stores kinetic energy, doesn't create antything. |
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The smaller pistons would fire to push the other ones, creating energy. The issues of timing might be solved electronically for the spark. instead of a traditional mechanical distributor. |
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The engine speed would be increased I think as the the moment immediately following the firing of the big cylinder, it begins to lose enegy and speed, so the second smaller firing would help push the big one along, thus effectively increasing engine speed. However, like mentioned the extra mass may negate any advantage gained. |
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The vibration issues I beleive could be solved with counter-weights like on 4 cylinders. |
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As well, doesn't have to be an 8 cylinder. Might be more practical in a 4 banger. |
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The idea 'in my head' envisions the 4 cylinder being a formula, and the other 4 cylinders inserted in between the other ones, and in between the timing. |
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Ideas come from weird places. This one came to me as I was tuning my guitar. The beat frequency produced as the strings were out was vibrating, and each half of the vibiration was slightly louder then the other. |
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One note inserted in to another. |
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ok so we have 8 cylinders... how would this be better than any other v-8 with the same displacement divided between the 8. |
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The simplest points can put it into perspective Shad. |
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Put that simply, I can't see any advantage dividing up the displacment and timing unevenly. |
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I guess my goal to find an engine concept with the advantages of 4 and 8 cylinders without shutting down half of an 8 is fruitless for now... |
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If you had different sized cylinders, you'd have to have a different Air/Fuel ratio for those, and that would be OVERLY complicated to acheive in the same system. That's just ONE problem with this idea. |
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