In the GB2,478,635 patent (click here for more) by a slight modification of the MultiAir electro-hydraulic valve system of FIAT / INA it is achieved an infinity of additional, and more efficient, modes (unlimited Miller cycle, US2,773,490 patent) for the four- stroke engines. The basic idea is to avoid the sub-pressure during the induction stroke and during the compression stroke, and so to reduce the relative pumping loss, which at light loads is a significant part of the indicated power.
The same are applicable to the conventional two-stroke engine (single or multicylinder).
The piston is properly modified:
with a separator the space between the two ends of the piston is divided into two sections;
the separator comprises a passage between the two sections and a valve that controls the passage from fully closed to wide open;
With the two sections having a constant total volume, the passage, depending on the position of the valve, allows a part of the air or mixture from the one section to pass to the other section;
for the load control the engine needs not other control means: all it takes is the valve that controls the passage through which the two sections communicate.
The big difference is at light loads and idling (i.e. wherein an engine of a vehicle - like a motorcycle or a scooter or a car - spends most of its life).
with the valve of the passage wide open,
during the upwards motion of the piston the air / mixture from the lower section passes freely and fills the upper section without creating any vaccum or subpressure (Miller-cycle like);
during the downwards motion of the piston the air or mixture from the upper section passes freely to the lower section;
when the transfer ports open, a small quantity of air or mixture enters into the cylinder and the engine idles stable and clean, with the pumping loss eliminated.
with the valve keeping the passage between the two sections closed, the engine runs at full load just like a conventional two-stroke (or even better because of the smaller dead volume of the upper section as compared to a crankcase), keeping the known two-stroke advantages (lightweight, high power to weight ratio, compact, simple etc).
with tuned-exhaust, the peak power can be achieved with the valve wide open (like having a conventional 2-stroke with infinite crankcase volume).
The piston crown is at the one end of the piston, the wrist pin is at the other end of the piston.
The two ends of the piston are connected to each other by the piston skirt.
Using a conventional oil scraper ring in a ring groove made on the wrist pin end of the piston, the lubrication turns to "four stroke like":
the lubricant in the crankcase recycles as in the four-stroke engines;
the surplus of lubricant on the piston skirt, below the oil scraper ring, enables hydrodynamic lubrication between the cylinder liner and the piston skirt under the oil scraper ring, wherein the thrust loads are taken;
the small leakage of lubricant above the oil scraper ring (just like in the 4-stroke) finds its way to the compression ring(s) of the piston.
Comparison with the "paired cylinders" approach
In the Fig A the curve A is the variation vs. the crankshaft angle of the volume underside the first piston of a paired cylinder 2-stroke (according the US8,683,964 patent), the curve B is the variation vs. the crankshaft angle of the volume underside the second piston of the paired cylinder 2-stroke.
Each of the two pistons is connected to a conventional crankshaft by a conventional connecting rod. The curve C is the sum of the variations of the volumes underside the two pistons vs. the crankshaft angle (i.e. it is the sum of the A and B curves).
With the "connecting rod to stroke ratio" being 1.6, the total volume (curve C) varies more than 16%.
For smaller "connecting rod to stroke" ratios, the variation of the C curve is wider.
The point D on the A curve is where the first piston opens its respective transfer ports.
The point D' on the C curve shows the volume of the combined space underside the two piston crowns the moment the first piston opens its transfer ports.
As the first piston approaches its BDC, the combined space increases, causing some 15% of the burnt gas from inside the first cylinder to return to the combined space (case with wide open bypass passage), contaminating and heating the fresh air or mixture (an open transfer port provides substantially smaller resistance in the motion of a gas than a reed valve).
After the point F at the TDC of the first piston, the volume of the combined space underside the two piston crowns decreases, forcing some 15% of the trapped air or mixture to pass the transfer ports and get into the first cylinder.
After 180 crankshaft degrees the same happen in the second cylinder.
That is, at low-medium revs with the bypass valve wide (or completely) open, some 30% of the one cylinder capacity enters, per crank rotation, into the two cylinders, and some 30% of the residual gas in the one cylinder contaminates the air of mixture in the combined space underside the two piston crowns.
This is an undesired limitation for the idle and the light load operation of the engine because it defines the quality and the revs of the idling; worse even, it makes necessary additional load control means (other than the bypass valve) for the idle and the light load operation, canceling advantages like the reduced pumping loss, the simplicity, the compactness, the low cost.
In the Fig C, the curve A is the variation vs. the crankshaft angle of the volume of the upper section of the space inside the piston of the single cylinder PatTwo engine, the curve B is the variation vs. the crankshaft angle of the volume of the lower section of the space in the piston of the single cylinder PatTwo 2-stroke.
The piston is connected to a conventional crankshaft by a conventional connecting rod.
The curve C is the sum of the A and B curves.
As shown by the curve C in the Fig A and in the Fig C, while in the "paired cylinders" approach (wherein the engine needs two cooperating cylinders) the total volume varies substantially during a crank rotation, in the case of the PatTwo single cylinder the total volume of the two sections remains constant during a complete crankshaft rotation.
PatTwo with reed valve(s). Light load. Click here to enlarge
PatTwo with reed valve(s). Full load. Click here to enlarge
PatTwo with reed valve(s). From various viewpoints. Click here to enlarge
For applications wherein top vibration-free-quality is required (low NVH), the harmonic (click here for more) engine can be modified to PatTwo Harmonic:
The plot in Fig B shows the variation of the volume of the two sections (pure sinusoidal) and the total volume of the combined space which remains contstant.
The basic mechanism is used in the first PatRoVa (rotary valve) prototype (click here for photos and video).
The throttle valve controls the load of the engine.
When fully open, the engine idles.
When fully closed, the engine runs at full load.
In case of tuned-exhaust things get even more interesting: the peak power can be obtained with the throttle valve open.
Below they are shown the moving parts and the stationary ring-gear:
The Harmonic PatTwo engine is:
fuel efficient (Miller cycle at partial loads).
It has "four stroke like" lubrication.
It is as vibration-free as the Wankel Rotary engine.
PatTwo Harmonic. Partial Load.
Click here for another GIF animation
Or click here for a controllable windows exe animation (8Mb)
PatTwo Harmonic. Partial Load. From various viewpoints. Click here to enlarge
PatTwo Harmonic. Reed valves. Partial Load. Click here to enlarge
PatTwo Harmonic. Reed valves. Partial Load. Click here to enlarge
PatTwo Harmonic. From various viewpoints stereoscopically. Click here to enlarge
With its single-piece double-acting piston, this engine has as many combustions as a 4-cylinder 4-stroke, and, in total, only three moving parts:
the first is the rotating, at constant angular velocity, power shaft,
the second is the rotating, also at constant angular velocity, intermediate shaft,
the third is the reciprocating piston.
And here is an even-firing four-cylinder PatTwo Harmonic:
PatTwo Harmonic 4-cylinder even firing. Click here to enlarge
Efficient cooling (as in the radials).
As many combustions as in a 4-stroke eight-cylinder.
The power shaft (blue) comprises a gear wheel that drives the clutch gearwheel (not shown) as in the motorcycles' primary transmission.
The number of the moving parts is 4 in total.
The PatTwo Harmonic can be seen as a "Rotary Reciprocating Engine".