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A Good Bearing for Sinusoidal Piston Movement?

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Maat_Mons:
I've been learning about rod ratios, why traditional engine designs don't have perfectly sinusoidal movement, and how that creates net forces that could lead to vibration if not compensated for. 

I've been looking for good ways to make piston movement sinusoidal, but so far nothing I've found has seemed great.  Rolling it around in my head, I did think of something that seems mathematically kind of cool:


I hope that animated gif shows up.  Sorry if it takes a long time to load.  Maybe a resolution of 1350x1080 was overkill. 

Anyway, looking at that graphic, I'm sure you can see that there would need to be something forcing the crankshaft to stay in contact with the piston rods in order for it to actually function.  But I can't think of anything that wouldn't either have more friction than a normal engine, or greater complexity than a normal engine. 

The simplest solution would just be a circle with a slot cut into it. 

But I feel like that would have a lot of friction.  Some sort of rolling bearing could reduce the friction, but then you'd need to fabricate all the little individual rollers.  Something inspired by a planetary gearbox might work, but that still seems like a lot of moving parts. 

The crankshaft and piston rods could meet with geared teeth, which would mean, with the piston being confined to up-and-down motion, they could only come apart at the top or bottom.  Would it be easier to build a mechanism that only locks the parts together at those two extremes?  Would gear teeth substantially increase friction? 

I've even considered double crankshafts, which always push in opposite directions, but that would mean the widest part of the piston would need to be more than twice the stroke. 


Any insights would be greatly appreciated. 

Also, I've read that pretty much every engine idea has already been tried.  Is this one of them?  If so, what's it called? 

A7er:
If the slot in the big end was a rectangle with a square bearing that could slide horizontally (side to side) with a hole in the middle of the bearing the diameter of the crankshaft, this would, I think, take care of the movement requirements, but I dont know how much friction it would generate. The crankshaft would need counter balances to smooth out the forces of the bearing.

BillTodd:
What you have there is an epicyclic motion similar to that used in the esso dross engine

tvoght:
What A7er is describing above is a variation of the Scotch Yoke mechanism which does produce sinusoidal motion.
https://en.wikipedia.org/wiki/Scotch_yoke
And a A7er suggests, engine designs using it have suffered from problems of friction and wear.

Interestingly, that wikipedia article calls into question whether pure sinusoidal motion is really desirable for internal combustion engines.
A mechanism that has interested me for a few years -and which can provide pure sinusoidal motion is the Stiller-Smith mechanism as described in US patent 5046459.  I tried to attach a PDF but it was too large.I also have some SAE papers on the mechanism, but I can't share them because of copyright.
This mechanism does not have the sliding contact that the Scotch Yoke has, but will involve gears or toothed belts or the like.
The variation of it that I have been interested in is shown in Figure 13 of the patent. See the attachment.

--Tim

steamer:
Wot Bill said!


So some thin Torque tube bearings would work I think...at least for a model

The bearings for my V12 build are 32mm OD  x 25mm ID x 4mm wide.   You could put 2 side by side....  don't know your scale....

Dave

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