This is an idea for a kind of Rotary Axial Engine. An axial
engine is one in which the cylinders are arranged parallel
to one another, around a central shaft. A rotary engine is
one in which the engine cylinders rotate around a central
Other people have proposed engines of this kind
but they suffer from high friction at high rpms, because in
those designs, nearly all of the centripetal force keeping
the pistons moving in a circle is supplied by friction
between the cylinder wall and the piston sides.
Eddie Paul's Cylindrical Energy Module can be considered
The purpose of this idea is to supply the necessary
centripetal force by way of simple rigid linkages, and
appropriately chosen bearings.
Consider a piece of metal shaped similarly to a # symbol,
with two vertical bars and two horizontal bars.
Move the horizontal bars a certain amount downwards, for
a reason which I'll explain further down.
Take four pistons, attach them to the tops and bottoms of
the vertical bars. Two of the pistons will of course be
facing upwards, and two facing downwards.
Take four bearings, either tapered roller bearings, or
spherical roller thrust bearings, and attach them to the
ends of the horizontal bars. Attach a spherical wheel to
each of these bearings. Two wheels will have their axles
pointing leftwards, and two pointing rightwards.
Create thin grooves on the inner edge of each vertical bar.
The groove should have a slightly varying depth, and be
deepest near the horizontal bars.
Add a tiny hole through the bar, at the deepest point in
each groove, leading towards the bearing. When oil is
sprayed on the groove when the assembly is spinning,
"centrifugal force" will pull the oil towards the hole, then
through it to the bearing, providing lubrication.
Each vertical rod will *probably* have a counterweight,
because the metal will probably be steel, which is slightly
springy. When the engine is spinning at high speed,
inertial will "pull" the pistons outwards, bending the
verticals bars slightly. A counterweight between the
horizontals might counteract this enough to keep each
piston at the proper radius.
Create a duplicate of this entire assembly, flip it over top-
to-bottom (so it's horizontal beams are "higher" than those
of the first assembly), and interlock it with the first
assembly. Rotate the second assembly 90 degrees to the
first, so two of its wheels are towards you, and two are
away from you.
Create two identical cams. Each cam will encircle our pair
of #-assemblies. One cam will touch the top four wheels,
the other cam will touch the bottom four wheels. Each
cam has a double-sinusoidal curve on it's working surface,
with two peaks and two troughs.
Each cam's working surface has a V-shaped groove in it,
with a slightly varying angle to the V. The variation in the
angle is chosen so that when the engine is spinning, the
rotational speed of each ball shaped wheel will be some
constant multiple of the average RPM, regardless of the
wheel's angle around the engine axis. Without this
variation, the wheel's speed would speed up or slow down,
as it moved along the steeper or more level parts of the
Purpose of the higher horizontal parts (or lower horizontal
parts on the flipped assembly) should now be obvious -- if
the assemblies were identical to one another, they'd collide
as they oscillated vertically.
From here on out, the engine has few if any differences
from Eddie Paul's CEM. While I could provide a link, I
expect most of you would be happier to just read my own
As each #-assembly rotates around its center axis, it
oscillates up and down due to the action of the rollers on
the cams. Because the two #-assemblies are 90 degrees
apart physically, and because the cams have a *double*
curve, the vertical motion of the two #-assemblies will be
180 degrees out of phase, so when one is going up, the
other is going down.
There are two rotating engine heads, one for the top four
pistons, the other for the bottom four. Each head
obviously has four cylinder bores in it. Furthermore, each
bore goes all the way through the head. Each head is
attached to the other in such a way that they can't rotate
relative to one another, but can move slightly closer
together or further apart. The heads are pushed apart by
short, stiff springs.
Each cylinder, on the side of the head away from the
engine's center, has a high-pressure sliding seal around it.
The engine has two stationary port plates, one pressed
against each engine head (or at least, pressed against the
sliding seals of the cylinders). Each port plate has an
intake port, an exhaust port, one or more fuel injectors,
and one or more spark plugs.