Tom Shelley reports on a development that overcomes a
problem that has bugged mechanical engineers since before the
beginning of the steam age
Ingenious mechanisms based on planetary gears allow a
reciprocating piston to turn a shaft through a connecting rod
that remains permanently in line with the direction of piston
motion.
The latest concept to make use of the idea is invented in
Lithuania and eliminates all side forces on pistons, and spreads
or balances out most other reciprocating forces.
It should thus greatly quieten and improve the lifetimes of
internal combustion engines and also, if used in the reverse
sense, improve the functioning of pumps or any device that
requires the conversion of rotary motion to reciprocating motion.
The problem of converting a reciprocating to a rotary motion or
vice versa has been around for a very long time. A method of
converting rotary to reciprocating motion without use of a crank
was invented by the great sixteenth century Italian
mathematician, Girolamo Cardano. If a gear runs round the inside
a ring gear whose diameter is exactly double that of the small
gear, a point exists on the periphery of the small gear which
follows a reciprocating path.
A number of internal combustion engines have been built based on
this principle, converting reciprocating motion to rotary. Their
great advantage is that they do not require the connecting rod to
move out of alignment with the direction of reciprocation. This
simplifies construction, and reduces overall space and weight.
One described on the Internet may be found at
www.wisemanengine.com. It is the claimed invention of one Randall
Wiseman, who apparently lives in Mississippi. Doug Rees, a
retired truck owner, who lives in Chatham, Kent, is building his
Mark II diesel engine based on exactly the same principles. He
makes no claim to have invented the principle, which he says was
originally used in some steam engines in the nineteenth century,
and in experimental petrol engines in the early part of this
century. A unique facet of his particular design is that it
allows for easy variation in compression ratios.
Of his mark 1 engine, he says, "Its main advantage was the
complete lack of vibration. Unless an engine has six cylinders,
it is impossible to balance it using orthodox cranks. I built a
four cylinder engine which was also two stroke diesel. The
prototype did not vibrate, and the oil lubrication was not
involved in the combustion. The engine did not suffer from the
environmental pollution problems normal with two strokes. Also,
it has one injector per two cylinders. In service, it should be
much more economical when not under load. But it gave twice the
expected power when called on due to the two pulses per
revolution. There are no small conventional diesel engines that
do either of these things." (Doug may be contacted at
doug@trukstar.com).
It might also be mentioned at this point that James Watt also
invented a planetary drive for his 'Rotative Engine', a
1788-built working example of which may be seen still driving its
flywheel in London's Science Museum. In this case, the sun and
planet is not used to much to reduce point peak loads, although
it does, but to turn the shaft at a higher speed than is possible
with a simple crank mechanism.
An alternative method of converting rotary to reciprocating
motion and vice versa is by using a gear with teeth on only one
side, placed between two opposing racks.
Despite these viable alternatives, most engineers down the years
have just accepted crankshaft side loads and associated problems
as a necessary evil. Massive linear bearings were provided for
the ends of piston rods on steam railway locomotives and
connecting rods were made as long as possible.
An inventor in Lithuania, however, has now come up with a
mechanism related to that devised by Cardano, which he believes,
converts reciprocating to rotary motion or vice versa, with
greater efficiency than any mechanism has achieved hitherto.
Starting at the output (or input) shaft end, the shaft has a
gear attached to it which meshes with two further gears which are
attached to the ends of what the inventor describes as,
"Immovably fixed crankshafts." The free ends of these
are attached to "Movable crankshafts". The latter are
fitted with gears, which run round the insides of ring gears with
internal and external teeth. The outsides of the ring gears mesh
with each other. By choosing the point at which the ring gears
mesh with each other, the motion of the free ends of the
crankshafts and the positions of the pistons may be selected so
that they can be up to anywhere from 0 to 180 degrees different
from each other.
The radii of the movable crankshafts and the gears attached to
them differ. However, the sums of the radius of each crankshaft
plus gearwheel have to be the same in each case, and equal to the
radius of the inside of the ring gear.
It is clear that by changing relative dimensions, it is possible
to make the new mechanism produce complex cyclic motions from
shaft rotation, but its main interest is in producing or using a
rectilinear motion without producing sideways forces and all
their associated noise and vibration. It does require the use of
seven gears per two pistons but they would normally be spur
gears, and their cost and weight should be offset by strength and
weight reductions elsewhere. We have not been to Lithuania to see
and test the mechanism, but calculations sent to us suggest it
should be both viable and efficient.
The inventor, and agent Dr Arvydas Sutkus, in the Lithuanian
Innovation Centre in Vilnius, consider the invention suitable for
use in internal combustion engines, pumps, machine tools, and in
fixing and raking mechanisms. It should run much more quietly
than conventional mechanisms, although it should be noted that
much of the noise produced by internal combustion engines arises
from the detonations within the cylinders. It should, however,
virtually eliminate piston wear as well as allowing a very
significant reduction in the amount of space taken up by the
crank case. Used in internal combustion engines, efficiency
should be improved significantly, although it has to be
remembered that research has shown that 42% of the energy
generated in such engines is lost to exhaust, and 28% to the
cooling system, and gears are not 100% efficient either. The new
mechanism should be less expensive to manufacture that other
solutions suggested for reducing the inefficiencies of simple
crank mechanisms, particularly the idea of doing away with cranks
by powering cars using small gas turbines.
All aspects of the design are covered by patents either granted
or applied for.
http://www.lic.it Lithuanian
Innovation Centre
mailto:a.sutkus@lic.lt Email
Dr Arvydas Sutkus
http://www.wisemanengine.com
Wiseman Technologies
mailto:doug@trukstar.com
Email Doug Rees
Pointers
* By connecting a piston connecting rod to an internal gear
within a ring gear, or to an internal gear plus crank within a
ring gear, where the single or combined radii of the internal
components are half that of the ring gear, it is possible to
avoid any need for the connecting rod to move from side to side
* This does away with the traditional small end bearing, and
reduces forces at the big end.
* Engines and reciprocating pumps made in this way have the
potential to be more efficient, smaller and much quieter than
traditional designs
For more technical
developments see www.eurekamagazine.co.uk