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Designed to accomodate a Donut Piston¹ without sideloading² during the combustion and intake strokes, a Squiggle Cylinder's shape curves to always match the conrod angle during travel from TDC to BDC, mitigating sideloading completely. In the case of a standard geometry³ the cylinder would curve up
to 18º then return.
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As a possibly beneficial side-effect, the combustion and intake strokes are slightly longer in duration than the compression and exhaust strokes.
Of course the compression and exhaust strokes now have increased sideloading, but that's not the point.
A negligibly small amount of sideloading and added reciprocation is caused by the squiggly travel path.
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1 - The piston and rod form one piece like a golf tee, rather than being articulated. Since the piston head is shaped as a spheric equatorial section, the piston wall remains in contact (as a circular line) with the cylinder wall at all times, no matter what the rod angle is.
2 -Sideloading is caused by the forces pushing straight downwards on the piston head being transferred to the connecting rod which is at an angle; the result is that the piston is pushed against the side of the cylinder causing friction, and wear on both.
3 - 4" stroke, 3.5" bore width, 6" connecting rod
Donut_20Piston
[FlyingToaster, Sep 08 2011]
sphericon
http://www.youtube....watch?v=HeSRbfcwqvo
[JesusHChrist, Sep 09 2011]
sphericon machine
http://gatesof.tvheaven.com/custom.html
[JesusHChrist, Sep 09 2011]
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1) How does you piston seal to the bore? At any time, there is only line contact between the piston and bore. The position of that line changes as the piston 'rocks' relative to the bore axis. |
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2) There will be almost no reduction in overall side load. While you may be able to reduce side load at some points in the cycle, the total resolution of forces must remain the same. |
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3) The reason pistons have skirts is so that side loads can be reacted over a large, lubricated area. A donut piston contacts the bore over a very small area directly adjacent to the combustion chamber with no prospect of useful lubrication. |
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This kind of piston arrangement exists, but is better suited to water pistols than engines. |
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1) Sealing: covered in the previous post; recap: a moulded-to-the-pistonwall compression collar is fitted instead of rings. It's sprung enough to seal during intake and exhaust, and during compression and combustion, it's forced outwards even more by the pressure differential between combustion chamber and crankcase. |
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Contact Circle: the point of the Donut Piston is that the contact area is a circular line instead of a cylinder, ie: much less friction. |
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The point of the Squiggle Cylinder is that during the geometric expansion strokes the contact circle does *not* change. The piston does *not* rock relative to the bore. The conrod is kept perfectly in line directly underneath it. |
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2) Sideload: there's no potential for sideloading during the geometric expansion strokes. There's increased potential for sideloading during the geometric contraction strokes. The reason I'm saying "potential" is so I can slip a word in edgewise that the combustion stroke is more powerful than the compression stroke, and the reasons engines work is that the resolution of forces is *not* the same. |
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3) Lubrication: vaguely covered in the previous post. |
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[JHC] any particular relevance to the links ? |
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The zz machine and Mezmerizing links to Donut
Piston reminded me of the sphericon machine in the
second link here which has a squiggly motion that
translates round and round motion into back and
forth motion. Not sure if that is on topic or not. |
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Oh, okay... just that "sphericon" got posted on the other idea, and I was wondering if there's something I was missing, like it's a baked idea or something. Personally I don't see it (yet) if it is. |
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By way of re-explaining this post... |
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If you look at a diagram of a piston & cylinder in a regular engine, you'll notice that the rod that joins the piston to the crankshaft is only lined up with the cylinder when the piston is at the very top or the very bottom of the stroke. Most of the time it's angled off to one side or the other. The angling means that (especially) during the combustion stroke, the force pushing the piston down, combined with the rod that's off at an angle, ends up pushing the piston into the wall on one side of the cylinder. This is called "sideloading" and it makes for wear and tear on both cylinder and piston. The reason it's not considered a serious problem in most engines is because the pistons slide up and down in the cylinder with quite a large contact patch: the piston is a cylinder shape inside a bigger cylinder; this spreads the sideloading. But it also causes friction. |
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The previous idea <linked> called a "Donut Piston" is designed to be as close to frictionless as is possible: the contact area is only a circular line. This is good except, since the contact patch is so small, it would be really really sensitive to sideloading wear and tear, since all that force would be concentrated on a line. |
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The connecting rod's angle as it goes about its business isn't open to debate: it's caused by the other end of the rod rotating in a circle. Cylinders are usually straight from one end to the other, but this idea is for a cylinder which curves from one end to the other, following the angle of the connecting rod as it goes from top-dead-center to bottom-dead-center. Since this causes the connecting rod to *always* be at a square angle to the contact circle between piston and cylinder, there is no sideloading. This only works on a ball or donut piston since a regular cylindrical contact patch couldn't get through a changing curve. |
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However it only works in one direction; when reversed the connecting rod angle ends up greater than it would normally be. So it ain't perfect. |
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Since combustion has the greatest potential for sideloading by far, the squiggle is oriented to help out with expansion strokes. |
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None of the 'explanations' are satisfactory: |
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Sealing at line contact is not practical. I am not aware of any 'mouldable' or otherwise compliant material that can tolerate IC engine conditions and support the loads required. Piston rings 'seal' by restricting leakage to a thin laminar path. For this to work, they need some thickness over which to spread pressure, maintaining a balance between minimum seal gap and the limitations of the materials and lubricant.
Conventional rings carry only compression loads, not side load. |
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The resolution of forces through the cycle of an engine must be the same whatever the intermediate geometry between piston and crank. You can shuffle the peak loads about, but the total (force x time) side load must remain consistent. |
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If you simply intend to bias sideload to reduce the peak during the combustion cycle, this can easily be achieved by offsetting the cylinder axis from the crank axis. |
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Lubrication is subject to limitations of temperature and pressure. Line contact does not reduce friction, but it does increase pressure which excludes lubricant from the seal gap. Combine that with the proximity between loaded surfaces and combustion and the lubricant will be in real trouble. |
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A little research into friction, sealing and lubrication would not go amiss. |
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I think there will be more friction on the combustion stroke! The piston will have inertia whch will force it into the curved surface... |
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What [Twizz] said, with additional not-entirely-relevant mutterings about coefficients of expansion, tribology, asymmetric wear and the problems of internally machining a perfectly smooth surface in a non-cylindrical bore, requiring high precision in a 6-axis machine - a problem so far successfully addressed only for very small gas turbine blades and the very large propellers of nuclear submarines, and that's external machining, on a one-off basis ... |
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This invention is actually the same as "tilting the cylinder", but taking advantage of the circular contact patch to do so precisely. |
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//inertial sideloading// yup, that's a function of RPM though, not how much power is being produced by the engine. This post, I'm just trying to diminish the sideloading that's a function of the pressure differential between combustion chamber and crankcase, ie: that shows up the most in the combustion stroke and a bit in the compression stroke, and not so much at all in intake and exhaust strokes. |
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[Twizz] picture the pistonhead - a hockey puck with very slightly rounded sides. The collar fits over the sides snugly and is hermetically sealed at the bottom. There's some holes that go from the top of the piston to the space between collar and piston (noting that "space" can be zero). When the fuel and air goes boom it forces the collar outwards from the contact circle down. |
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Considering the dog's breakfast that the current solutions to seal and lubrication issues are, I assume that if worst comes to worst, something equally as kludgy could be worked up to function at least as well. |
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// "tilting the cylinder" // |
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There are plenty of "oscillating cylinder" model steam engines which are effectively "valveless". And there are both hydraulic pumps and hydraulic motors which use the "oscillating cylinder" concept, with the working fluid fed through the trunnions. |
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If you are enamoured of the idea of a one-piece piston and con-rod, then why not consider a simple tubular cylinder with trunnions (containing the inlet and outlet valves) at the top end ? A secondary sliding "spider" on the con-rod would provide angular guidance to the cylinder wall. |
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All you have to work out then is what to do about blow-by when the crankcase is of necessity "open" ... |
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