Eliptical engine cylinders

[xpensive]

Never get me wrong DK, this latest picture was xtremely impressive, but not to the xtent if the cross-section would have been cut to the classical (x^2/a^2)+(y^2/b^2)=1,
where the eliptical width is 2a and eliptical height is 2b.

That, whould have been a truly nightmare to manufacture and seal to any precision.

[riff_raff]

xpensive,

If you look carefully at the piston shape used in the later versions of Honda's NR engine, you'll note that the long skirt sides are actually oval profiled, and not flat.

http://world.honda.com/history/challeng ... pho_02.jpg

While the rings and piston skirt can be cam ground to any shape desired, producing an elliptical cylinder bore to match is the thing that impresses me. I can't see any way that they could hone it, so it must be produced by a finish process like broaching.

They're very clever, these Honda guys.

[flynfrog]

I consider this effort by Honda as very impressive. Imagine, they took the rules in place, and attempted to design an engine that produced superior power by innovative and imaginative design. If ever the term "thinking outside the box" is to be applied, this is a great example.
I'm sure it was a tough battle, but the engineers involved must have really enjoyed the challenge in front of them. What really blows me away is how they overcame the sealing problem. I would love to know the history and development path required to make effective piston rings.

I see it as doing things the hard way to avoid using the simple solution (in this case a two stroke). Yeah its neat but in the end they scrapped the project with limited success and went to the kiss principal

[xpensive]

For Terry and DK,
Admit to be a little confused here, is the cross section of the Honda piston two equal curves connected by two flats, or four curves of two different radiuses?

[riff_raff]

xpensive,

To answer your question, it was both.

The earlier models were flat-sided and the production NR engine piston profile was elliptical in the later models. That is it was radiused on all sides, or defined by four tangent radii. The radiused sides and ends shaped bore was easier to make piston rings for than a flat sided bore shape. The convex profile piston rings always tended to produce a positive cylinder wall contact conformity, that the flat sided rings did not.

I still have no clue as to how they produced an elliptical finished bore shape.

[xpensive]

Thanks Teerry, most affirmative as well as informative.

The manufacturing of the bore is a mistery to me as well, could it have been ,
what's it called in english? You know the kind of "spark-erosion" as the direct
Swedish translation would be?

[alexbarwell]

Thanks for the pics guys, quite fascinating, although my understanding from mathematical principals is that a circular bore offers the minimum circumference for a given cross-sectional area so most effective bore with the least friction (because of the minimal surface are swept up the stroke of the bore). Not least, round is a darn sight easier to machine than oval/elliptical.

[xpensive]

That one is rather obvious, Alex. While technically xiting and taking nothing away from the Honda-engineers, I still fail to see the advantages of such a design other than perhaps external packaging and a more optimized valve-area?

[flynfrog]

Thanks Teerry, most affirmative as well as informative.

The manufacturing of the bore is a mistery to me as well, could it have been ,
what's it called in english? You know the kind of "spark-erosion" as the direct
Swedish translation would be?

EDM electro discharge machining