Author Topic: A Good Bearing for Sinusoidal Piston Movement?  (Read 1150 times)

Offline Maat_Mons

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A Good Bearing for Sinusoidal Piston Movement?
« on: June 18, 2022, 09:18:38 AM »
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? 

Offline A7er

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Re: A Good Bearing for Sinusoidal Piston Movement?
« Reply #1 on: June 18, 2022, 11:18:33 AM »
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.

Offline BillTodd

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Re: A Good Bearing for Sinusoidal Piston Movement?
« Reply #2 on: June 18, 2022, 12:59:23 PM »
What you have there is an epicyclic motion similar to that used in the esso dross engine


Offline tvoght

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Re: A Good Bearing for Sinusoidal Piston Movement?
« Reply #3 on: June 18, 2022, 02:14:24 PM »
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

Offline steamer

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Re: A Good Bearing for Sinusoidal Piston Movement?
« Reply #4 on: June 18, 2022, 04:59:11 PM »
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
« Last Edit: June 18, 2022, 05:07:23 PM by steamer »
"Mister M'Andrew, don't you think steam spoils romance at sea?"
Damned ijjit!

Offline BillTodd

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Re: A Good Bearing for Sinusoidal Piston Movement?
« Reply #5 on: June 18, 2022, 05:44:07 PM »
You should be aware that , to keep the contra rotating , er, thingy   - contra-rotating, there is a sideways force on the 'big-end'  . This force is taken to the cylinder walls by the two pistons of the Esso-Cross engine , and would need to be controlled by something in your inline four design.

http://www.douglas-self.com/MUSEUM/POWER/unusualICeng/RotaryValveIC/RotaryValveIC.htm#esscross
« Last Edit: June 18, 2022, 05:47:33 PM by BillTodd »

Offline BillTodd

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Re: A Good Bearing for Sinusoidal Piston Movement?
« Reply #6 on: June 18, 2022, 06:17:00 PM »
Another thought...

The two contrarotating contraptions are connected together in the EC engine . That allows both cylinder pairs to drive them in quadrature (at 90 degrees) preventing any dead spots that could jam an unconstrained thingy 8-)



Offline Maat_Mons

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Re: A Good Bearing for Sinusoidal Piston Movement?
« Reply #7 on: June 19, 2022, 05:03:42 AM »
Wow, that Esso-Cross engine is pretty much exactly what I was trying to design.  Well, except for how it uses a radial arrangement of pistons.  And the fact that it uses rotary valves.  But the eccentric spinny bits in the middle are spot on.  I’m sad to hear they got less than half the predicted horsepower and then gave up.  I wonder if it was down to too much friction? 

Was “Esso-Dross” a pun or a typo? 

I’m trying to get my head around that Stiller-Smith engine. 

Offline Maat_Mons

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Re: A Good Bearing for Sinusoidal Piston Movement?
« Reply #8 on: June 19, 2022, 07:53:06 AM »
YouTube's algorithm can be scary sometimes.  One day after I make a post here about this engine design, my video suggestions contain an animation of the exact same design.  If their algorithm were just slightly better, maybe they could have shown me that video before I made a post about it. 

Actually, that guy's design is different from mine in a few ways.  For one thing, he's using both a geared crankshaft and circle doohickeys.  I only considered a geared crankshaft in the hopes of doing away with the circle doohickeys.  I think his design would still work fine without the gear teeth.  I mean, the Esso-Cross engine worked without any such thing, albeit at less than half the desired horsepower. 

The same guy also has this video, which I really dig.  Though, again, I don't think he needs those teeth.  But man, that is a compact 8-cylinder. 

Offline A7er

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Re: A Good Bearing for Sinusoidal Piston Movement?
« Reply #9 on: June 19, 2022, 08:30:25 AM »
Maat_Mons
I just watched the video with the 8 cylinder. I wonder if the pistons would actually drive the crankshaft? It seems to my simple mind that this would work better as a pump, with the crankshaft driving the pistons. But then, the Wankel engine works OK!

Offline BillTodd

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Re: A Good Bearing for Sinusoidal Piston Movement?
« Reply #10 on: June 19, 2022, 09:11:44 AM »
The problem that both of those engines would have is the contra rotating 'big-end,  has a 'tdc'  problem : i.e. it could be driven in the same direction as the crank . The EC engine , and other epicyclic designs , have some means  (e.g. gears) to overcome this.

Offline BillTodd

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Re: A Good Bearing for Sinusoidal Piston Movement?
« Reply #11 on: June 19, 2022, 09:15:25 AM »
Wow, that Esso-Cross engine is pretty much exactly what I was trying to design.  Well, except for how it uses a radial arrangement of pistons.  And the fact that it uses rotary valves.  But the eccentric spinny bits in the middle are spot on.  I’m sad to hear they got less than half the predicted horsepower and then gave up.  I wonder if it was down to too much friction? 

Was “Esso-Dross” a pun or a typo? 

I’m trying to get my head around that Stiller-Smith engine.

Unlikely to be friction, that just creates heat. Most likely poor breathing and heating of the intake gases by the close proximity of the exhaust.

Esso dross  - typo  8-) I think its a clever design  and I really like Cross's valve clamping mechanism.
« Last Edit: June 19, 2022, 09:19:45 AM by BillTodd »

Offline Maat_Mons

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Re: A Good Bearing for Sinusoidal Piston Movement?
« Reply #12 on: June 19, 2022, 10:50:34 AM »
Do you just mean that, at top dead center, pushing down on the piston could cause the crankshaft to rotate in either direction?  I'm pretty sure normal 4 cylinder engines have that property too.  I thought the usual way of handling it was that things are worked out such that the force starts ever so slightly after top dead center. 

Offline BillTodd

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Re: A Good Bearing for Sinusoidal Piston Movement?
« Reply #13 on: June 19, 2022, 11:19:46 AM »
No , not the crank , the bit that contrarotates between the crank and the big-end  thishas the same radius as the crank and so could rotate invthe same direction as the crankshaft leaving the piston still and unable to move the crank shaft .

Offline Maat_Mons

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Re: A Good Bearing for Sinusoidal Piston Movement?
« Reply #14 on: June 19, 2022, 08:35:55 PM »
Oh, I see what you mean.  Yeah, that could be a problem. 

Offline Maat_Mons

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Re: A Good Bearing for Sinusoidal Piston Movement?
« Reply #15 on: June 21, 2022, 01:40:50 AM »
Okay, I think I understand the Stiller-Smith mechanism now.  And also something I hadn't noticed about the Esso-Cross engine.  They're both kind of ellipsographs

 

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