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Coomber Engine Ideas

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vederstein

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On to my next engine.

I was looking at Elmer's #46. The Coomber engine. (I don't know if it's "Coomber" or "Comber". I've seen it spelled both ways.)

Anyway, these designs always have the cam ring with the cam rollers on the inside. I was thinking what would happen if I put the cam rollers on the outside:

1. The cam would be easier to make with manual equipment. It would like machining a large cam profile for a gas engine.
2. The cam would be overall smaller because the rollers are on the outside and not the inside, making for a smaller part.

So I proceeded to do some conceptual design work to just flesh out the idea a bit.

At this stage I like that the elliptical shape of the cam is more accentuated from a circle and its shape can be more identified as not circular.

Here's a short video of the idea.

(As usual, if this engine goes to completion, I'll post the design files on this forum.)

What do you all think?

 

johnmcc69

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Looks good Ved! I'm looking forward to seeing how you do the valving.

John
 

vederstein

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I'm looking forward to seeing how you do the valving.
The bronze bearing on the axle has two 1/8" wide slots along the perimeter. It's a similar setup to a wobbler's radial slots except the slots are on the circumference pointed to the center axis instead of curved slot around the center of rotation.

When I get around to finishing the prototype, I'll post the drawings and it'll make sense.

Externally, it won't look much different though. All valving is internal.

Thanks for the inquiry.

...Ved.
 

vederstein

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I believe I've worked out the final issues.

I've modified the base, removing the undercut, thus making is sand castable. I added fasteners and adjusted a couple of items that didn't work out. So I'm off to creating the first set of drawings.

From these drawings, I'll make the first one. If all works out, I'll post the design.

I-Coomber.JPG
 

johnmcc69

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Will you have to make any provision to stop the piston rod from turning on its axis?

John
 

vederstein

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Nope. If there is an issue and the rod rotates, I can add a flange to the cam rollers.
 

Peter Twissell

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I can guarantee that the rod will rotate. Contact between the rollers and the cam is not normal to the rod axis (except at TDC/BDC), so it will exert a moment about that axis.
 

vederstein

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I've managed to get my inverted Coomber prototype running. It's not particularly pretty, but it does run. Here's the final design.


Capture.JPG


First the design assembly files:
 

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vederstein

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1952 MG TD

Ive had it about three months now. It's my "unicorn."
 

ICEpeter

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1952 MG TD

Ive had it about three months now. It's my "unicorn."
My first car was a 1958 MGA, a lovely car that I drove for a number of years - never mind the leaks and draft through the soft top and inadequate side windows. Wish I still had it!

Peter J.
 

Anatol

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I can guarantee that the rod will rotate. Contact between the rollers and the cam is not normal to the rod axis (except at TDC/BDC), so it will exert a moment about that axis.
surely, IIUC the rotating piston rod and cylinder would be a feature not a bug - like precessing valves, preventing wear asymmetries in cylinder wall...?
 

Anatol

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I've managed to get my inverted Coomber prototype running. It's not particularly pretty, but it does run. Here's the final design.
fascinating. The valve system remains a mystery, I'm assuming its a wobbler style, but rotary - very simple. How are you sealing ?
Also, is there a good reason for the overhung cam-rollers? A clevis style would be more balanced, no?
 

vederstein

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Sealing?!?!?! This thing leaks all over the place. It was more important to have it freewheeling than well sealed. It doesn't have a lot of power, so it cannot have much drag. I'm sure the design can be improved, but it's a first of its kind.
 

Anatol

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To be clear, I think its a really interesting topology especially because of the reduced moving parts count.
Are you saying that the mechanism, in your opinion, is a novelty that would be unlikely to have practical use?
 
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