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A conventional internal combustion engine uses a crankshaft to
convert the back-and-forth movement of the piston(s) into
rotary motion. This results in a lot of thrashing around and
An alternative way to convert linear to rotary motion would be
to use a screw or, more precisely,
a helix. The backside of the
piston is connected (rigidly) to a rod with helical grooves in it,
which in turn slides into a tube with helical rifling. Now, as
the piston moves down, it will cause the rifled tube to rotate.
One problem with this is that the rifled tube will rotate the
other way as the piston travels back up. This, however, can
be solved in numerous ways, including the use of two
intersecting sets of helical grooves of opposite handedness,
meeting each other at the top and bottom ends of the piston
rod. Back-and-forth motion can now be converted to (say)
continuous clockwise rotation.
An advantage of having two (opposite) sets of grooves is that
the engine's output can be reversible without the need for a
reverse gear. If the engine is started "forward", its inertia (or
the inertia of a flywheel) will keep it going forward. If it's
started "reverse", likewise it will keep running in reverse. So,
if you don't mind stopping and restarting the engine (and if the
starter motor can be driven both ways), you can use all your
forward gears in reverse.
A helical drive would be most effective for either single-
cylinder engines, or opposed twin cylinders. However,
multiple in-line (or V) cylinders could be coupled via bevelled
Not well known, but a few around. [neutrinos_shadow, Jan 29 2019]
All sorts of variations... [neutrinos_shadow, Jan 29 2019]
More Axial Engines
Some old patent drawings here. [neutrinos_shadow, Jan 29 2019]
..and it's brethren... [neutrinos_shadow, Jan 29 2019]
The Canda engine
Bizarre and horrible ... [8th of 7, Jan 29 2019]
||With a linear helix, like the type used on screwdrivers, the piston will spend a very short time at top dead centre, which will sap a lot of your efficiency. It might be possible to have the helix bunch up at one end in order to increase the dwell time, but with two helices crossing that might cause problems.
||Using Google is all about knowing what question to ask.
This is a Cam Engine (of a particular type), and has been
experimented with now-and-then around the place
(closely related to the swash-plate engine).
The main advantage is that the "helix" (in reality, a sine
wave wrapper around a cylinder) doesn't need to be the
expected shape, but can be tweaked to allow faster
expansion, longer TDC dwell, smoother intake and
exhaust strokes, etc. And not for single cylinders; most
stack up 4 or 6 around the shaft (pistons move axially,
relative to the shaft alignment).
||// the "helix" (in reality, a sine wave wrapper around a
cylinder)// That's exactly what I would have said if I'd have
||So, once again, reality sneaks in and pre-empts me. Ah well.
||From my experience on worm gears, having metal
sliding around in this manner tends to wear it out
quickly. Doing it at the end of a power cylinder
sounds like metallurgical death in a few hours.
||Not really, because the simple split journal bearings with pressure fed lubrication survive in conventional piston engines for tens of millions of high speed cycles.
||Cam and swashplate engines, along with bizarre rotary hybrids like the Canda engine <link> are Baked & WKTE ...
||I think that's WKTEBNBMB.
||You know, it often occurs to me that if I'd only been born a
hundred years earlier, I'd be dead by now.
||Sadly, fate seems to have decreed otherwise.
||A quick Fermi approximation for a 4-cylinder automotive powerplant that's in a road vehicle that's covered 100,000 km suggests that each big-end bearing has sustained over 500,000,000 load cycles.
||Um, yes, I'm aware of journal bearings, thanks. They
differ a bit in that there isn't any reintroduction of
||<checks job description> sorry I guess that was one
||We just thought it would be wise to point them out before [MB] went to the trouble of re-inventing them.
"fnar fnar" in the manner of Finbarr Saunders.