PatRoVa: a disk Rotary Valve with counteracting fronts.
Intellectual Property: patent US 9,677,434
patent GB 2,525,704
The PatRoVa rotary valve comprises a pair of oppositely acting fronts firmly secured to each other.
The fronts seal a pair of oppositely arranged ports (chamber ports) of the combustion chamber.
Click here to enlarge, or here for a side view animation, or here and here for
orbit-animations, or here and here and here for Opposed-Piston versions.
Click here or here for some sealing details.
Click here or here for a V-2 model engine (same vibration-free quality and
same bore to stroke ratio with the Ducati Panigale 1299).
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or here : manufacturing
details of a V-2 model (and not only model) engine (no need for any bolting).
The high pressure inside the cylinder "sees", though the chamber ports, the two fronts and loads them heavily. The rotary valve receives the two strong forces. With the one force counterbalancing the other (through the body of the rotary valve), the overall "pressure" force acting on the rotary valve is from small to zero, leaving its bearings unloaded.
That is, in order to bear the heavy forces applied by the cylinder pressure on its fronts, the PatRoVa "disk rotary valve" needs not the support of a bearing and avoids, this way, both: the inevitable clearance / "play" a bearing introduces and the associated friction / wear.
What the rotary valve does need is a very strong "body" to "connect" the oppositely acting fronts; so strong that the heavy loads applied on the fronts to cause no more than an insignificant deformation of the rotary valve and thereby to keep into the required strict limits the clearance between the chamber ports and the rotary valve fronts (wherein the sealing happens).
Accordingly, a rock-solid structure for the rotary valve is essential; but this is not an issue because the rotary valve performs a smooth rotation at half crankshaft speed; even a substantial increase of the rotary valve mass and inertia is tolerable; in comparison a small increase of the reciprocating mass of a poppet valve causes major side effects.
First PatRoVa prototype main parts (rotary valve external diameter 88mm, cylinder head diameter 120mm):
Click here for a stereoscopic photo of the cylinder head "main parts".
Click here or here for two stereoscopic photos of the engine.
Click on the photo below for the video of the PatRoVa prototype running on gasoline; spot on the flames from the two exhaust ports.
Or click here to download the same video from YouTube.
In the figure below, a pair of sturdy disks are integral with a strong hub / shaft. The hub is not directly supported on the cylinder head; instead, bearings on the cylinder head support a thin shaft extending at the sides of the rotary valve.
The chamber with its ports is arranged between the two disks.
Only the inner flat surfaces of the disks (the two "face to face" fronts) participate in the sealing of the combustion chamber; the external flat surfaces of the two disks isolate the intake passageways from the exhaust passageways of the cylinder head.
The space around the peripheries of the disks is where the intake passageways of the cylinder head end. Exhaust passageways start just after the external flat surfaces of the two disks.
Combustion chamber
The combustion chamber is compact. The piston crown is flat without pockets.
The combustion chamber is rid of hot spots (like, for instance, the hot exhaust poppet valves of the conventional engines, or like the hot chamber ports of the state-of-the-art exhaust rotary valves). Every point of the combustion chamber is equally related with the intake and with the exhaust. On this reasoning the compression ratio can further increase.
There is space for centrally located spark plug and/or injector.
With the proper asymmetric design of the "entrance" of the chamber (cut-view of the cylinder head at top-right of the figure above), the squeeze at the end of the compression stroke can boost the turbulence and swirl as required (for instance, for the high-speed compression-ignition engines).
A cylinder head integral with the cylinder is advantageous (better cooling, lower cost, no gasket issues) and easy to manufacture (there are no valve seats; precise machining is required only on the chamber port lips which are externally accesible).
No need for lubricant in the cylinder head; small (because the loads they bear are small) sealed roller bearings is all it takes for the support of the rotary valve. With the cylinder head running "dry", the lube specific consumption and the emissions decrease, while the lubricant degradation slows down.
Sealing
Considering the flat fronts and the flat lips as parts of spheres (or cylinders) of infinite diameter, the skilled-in-the-art knows how the state-of-the-art "spherical / cylindrical rotary valve sealing technology" is applicable in the case of the PatRoVa rotary valve.
A more ambitious idea is to exploit the inherent characteristics of the PatRoVa rotary valve and seal the combustion chamber without using conventional sealing means.
For the sealing between the pair of flat-fronts and their respective chamber-port-lips only the one of the three dimensions is significant: that one along the rotation axis of the rotary valve (i.e. the distance between the two disks and the width of the combustion chamber); the displacement of the rotary valve along the other two dimensions does not affect the sealing. And because the heavy forces applied on the flat fronts balance one another "internally", such a displacement is easy to be realized and to be controlled (Variable Valve Actuation).
In comparison, the slightest displacement, at any direction, of a spherical rotary valve changes significantly the sealing quality.
The sealing is tolerant to deformations of the cylinder head because, as before, only the one of the three dimensions really matters; significant deformations of the chamber along the other two dimensions do not affect the sealing.
Between its chamber ports the chamber (i.e. the cavity into the cylinder head) is like an open ring (a thin open ring); if the diameter of the ring is for some reason increased (due to the high pressure into the chamber, for instance, or due to the temperature etc) it makes no harm to the sealing. The pressure in the chamber cannot essentially affect the dimension of the "ring" along the rotation axis of the rotary valve.
Besides, the lower part of the chamber is "enclosed" and is strongly supported by the lower end of the cylinder head (which is stiff as being the roof of the cylinder).
With the distance between the chamber-port-lips being small, proportionally small is the effect on the sealing quality of the temperature difference between the rotary valve and the chamber walls.
The limit of the width of the combustion chamber (i.e. of the width of the cavity into the cylinder head) is set by the diameter of the spark plug (or of the injector). For instance, with a distance of 25.4mm (1 in) between the two disks, the estimated thermal (and stress) expansion/contraction is several times smaller as compared to the case wherein the two ports were arranged at the sides of the cylinder.
The smaller the distance between the two disks, the less the thermal expansion, the less the stressing expansion and the less the bending flexing (the major causes affecting the clearance between the flat-fronts and the chamber-port-lips).
In the design above, the distance between the two disks is only 25mm (which means that the cavity, i.e. the combustion chamber in the cylinder head, is only 25mm wide), while the hub diameter (i.e. the diameter of the shaft connecting the two disks) is 40mm.
Cylinder head external dimensions: less than 100mm x 100mm x 100mm for a high revving 500cc cylinder capacity.
The geometry of the intake ports, of the exhaust ports and of the chamber ports defines the overlap and the valve area.
The clearance between the cylinder head and the piston crown defines the compression ratio; for instance, with 25cc cavity volume, 80mm piston stroke, 500cc cylinder capacity and 1.5mm "piston to cylinder head" clearance, the dead volume is (500cc * (1.5mm / 80mm)) + 25cc = 34.4cc and the compression ratio is (500cc + 34.4cc) / 34.4cc = 15.5:1
Multicylinder arrangements
A splined shaft drives all the rotary valves of a row (or bank) of cylinders.
At a thermal expansion (or contraction) each rotary valve slides slightly along the splined shaft and continues its friction-free / wear-free cooperation with the respective ports.
Instead of dealing with the expansion of a, say, 500mm long piece (case with all rotary valves of a bank of cylinders secured on a shaft), with the splined shaft the expansion concerns only the distance between the two disks of each rotary valve (which is in the range of 25mm).
In the above straight-six the crankshaft drives the splined shaft (and all six rotary valves) with a pair of sprockets (purple) and a timing belt (not shown).
Allowing a wider clearance (play) between the splined shaft and the rotary valves, each rotary valve is free to slide and self-align (at all three directions) with the two lips of its respective combustion chamber.
Leakage internally recycled
Without having a pathway to the exhaust, any gas leakage from the combustion chamber during the compression / combustion is recycled: it returns into the cylinder at the next suction cycle.
This built-in "recycling" of the unburned gas leakage is even more important at the warming-up period wherein the clearance between the valve fronts and the chamber ports is not yet minimized.
Variable Valve Actuation
The absence of significant loads on the bearings of the rotary valve, on one hand, and the tolerance of the sealing in radial displacements of the rotary valve, on the other hand, enable a Variable Valve Actuation ( VVA ) wherein the duration and the overlap vary continuously and substantially to meet the instant needs of the engine.
All it takes is the displacement of the rotary valve bearings for a few mm.
In the figure below, both pistons are at the TDC.
At right they are shown, magnified, the ports: the chamber port is in the middle, while the exhaust and intake valve ports - hatched areas - are above and below the chamber port.
At top the overlap is big, the duration is long and the valve-area is large.
At bottom the rotary valve is displaced to the left eliminating the overlap (the intake starts after the end of the exhaust) and reducing substantially the duration and the valve-area.
Valve Area / Power Desnity
The two oppositely arranged ports of the combustion chamber are both used for both: the introduction of the gas into the cylinder and the evacuation of the cylinder from the gas.
The Valve area is already big and can be substantially bigger making even freer the flow of the gas (from another viewpoint: the same cylinder head can be used for a cylinder having substantially smaller capacity).
Besides, a rotary valve like this operates reliably from low to extreme revs.
Accordingly, the red line and the peak power of the engine are limited only by the "underneath" mechanism (piston, connecting rod, cylinder, crankshaft, crankcase).
Load on bearings / shaft as compared to the state-of-the-art
In the following drawing, at right, an intake spherical rotary valve seals a chamber-port of 20cm2 port-area (it substitutes two 36mm diameter intake poppet valves of a conventional 500cc cylinder),
an exhaust spherical rotary valve seals another chamber-port of 20cm2 port-area (it substitutes two exhaust poppet valves of the 500cc cylinder).
A 100bar pressure during the combustion (turbocharged engines operating at substantially higher than 100 bar maximum pressure are quite common) causes an "upwards" force of 2 tons (20cm2*100Kp/cm2) on the intake spherical rotary valve and another "upwards" force of 2 tons on the exhaust rotary valve.
If the same shaft supports both spherical valves, the total force loading the bearings of the rotary valve shaft is 4 tons.
In the case of the PatRoVa rotary valve, at left, two chamber-ports, each having only 10cm2 port-area, offer the same flow capacity
The architecture of the PatRoVa rotary valve allows the same chamber-ports to be used for both,
the intake and the exhaust processes; in the spherical rotary valve architecture there
are chamber ports dedicated to the intake process, and others (necessarily
hot) chamber-ports dedicated to the exhaust.
A 100bar pressure during the combustion causes a side force of 1 ton (100Kp/cm2 * 10cm2) on the one front and an equal and opposite force of 1 ton on the oppositely arranged front of the PatRoVa rotary valve.
The two fronts are firmly secured to each other by a robust shaft / hub.
In total, the bearings supporting the PatRoVa rotary valve can run completely unloaded.
From a practical viewpoint:
Leaving free (i.e. without support bearings) the PatRoVa rotary valve on the cylinder head to seat in place and seal, by its oppositely arranged fronts, the two side chamber-ports, and applying a high pressure (like 100bar) in the combustion chamber, the PatRoVa rotary valve has no tendency to move upwards, or downwards, or to the side.
In comparison, a force of a few tons is required to keep in place a state-of-the-art rotary valve when the same 100bar pressure is in the combustion chamber; the extreme upwards force loads its bearings and causes, among others, the flexing / deformation of the spherical valve, of the shaft of the rotary valve and of the cylinder head wherein the shaft is supported.
The cavity of the PatRoVa architecture eliminates the radial forces acting on the rotary valve and on its bearings, which is a major (if not the worst) problem of the known rotary valve designs.
The ceiling of the PatRoVa cavity receives the heavy radial forces and releases, this way, the rotary valve from them.
The PatRoVa cavity is a buckler that protects the rotary valve from the radial forces.
The oblique flow through the two windows causes a strong in-cylinder tumble (a twin symmetrical tumble at the one direction, and a stronger single tumble at the other direction) without loss of Volumetric Efficiency (as in the Bishop Rotary Valve), enabling very fast burn rates:
Compressors
In the figure below, the rotary valve comprises a single disk integral with the crankshaft of a pulling-rod cross-head compressor (similar architecture with the PatPortLess engine).
The divided chamber (at the two sides of the disk) fits with compressors.
With a shallow groove at the middle of the disk, and a respective "ring" extension of the cylinder head, the space at the periphery of the disk is divided into an intake plenum and an exhaust plenum sealed from each other.
The rotation of the crankshaft causes the reciprocation of the piston.
During the suction stroke, the disk rotary valve allows the communication of the cylinder with the inlet passageways of the cylinder head, and the cylinder fills with gas. During an initial part of the compression stroke, the chamber ports remain closed to prevent compressed gas to return to the cylinder; latter, and for the rest compression stroke, the disk rotary valve opens the chamber ports allowing the communication of the chamber with the exhaust passageways of the cylinder head.
In this case (2-stroke), the rotary valve has only one kind of ports (either intake or exhaust) and rotates in synchronization with the crankshaft (1:1 transmission ratio, preferably at opposite direction).
The timing becomes as asymmetric as necessary (for instance, the exhaust starts substantially before the transfer and ends before the transfer).
In a two-stroke the rotary valve can be used as a counterbalancing shaft, too; for instance, for the balancing - in cooperation with the crankshaft - of the free rocking-couple of the even firing twins (crankpins at 0 and 180 degrees).
The above animation shows the cylinder and the cylinder head of a 2-Stroke PatRoVa comprising two rotary valves on the same spline shaft (one for intake / scavenge, one for exhaust).
The cylinder liner is rid of ports.
The two "cavities" are arranged anti-diametrically.
A big bore-to-stroke ratio (bigger even than the 1.91:1 of the Ducati Panigale 1299) enables a "cross-uniflow" scavenging and a reasonable mean piston speed (i.e. reliability) at way higher revs.
The cylinder head has not rev-limit.
In the animation the exhaust ports are almost closed, the intake / scavenge ports are still substantially open (asymmetric timing: the intake opens later than the exhaust and closes later than the exhaust).
With most of the residual gas concentrated into the exhaust cavity, the cold intake cavity can be used for the combustion.
Animations, photos etc
Racing porting:
Click here for the stereoscopic version (1.1 MB, gif).
Inlet openings can be arranged not only at the "back" side but also at the "front", or spark plug, side of the cylinder head cover:
Click here or here for more details: stereoscopic gif animations.
In the above "racing" design the several inlet passageways make the inlet freer and enable thinner disks further reducing the contact of the rotary valve with the hot exhaust gas.
The extended exhaust openings at the sides of the cylinder-head-cover make the exhaust freer.
The cylinder liner is integral with the cylinder head (the red part).
There is no need for high-pressure cylinder-head gasket.
The red flange (and together with it the PatRoVa assembly) is secured onto the engine casing by bolts.
The same red flange at the top of the cylinder liner is sealing the cooling passages towards the cylinder head and is cooling the cylinder head.
The manufacturing is easy: there are no valve seats; precise machining is required only on the externally accesible chamber port lips.
Click here for a comparison with the "cylinder liner to block" fitting in the Ducati Panigale engine.
All it takes for the modification to PatRoVa is the replacement of the two cylinder liners and of the two desmodromic cylinder heads of Ducati by a pair of PatRoVa assemblies like the above.
In the following animation the PatRoVa rotary valve (blue) in the "transparent" cylinder head is at "overlap":
Click here for the stereoscopic version (4 MB, gif).
The following animation (36 "crankshaft degrees" per slide) shows the above PatRoVa cylinder head from four different viewpoints (full geometrical symmetry):
The exhaust passageways in the PatRoVa rotary valve are shown yellow, the intake passageways in the PatRoVa rotary valve are shown green.
The chamber / cavity, as a buckler, protects the rotary valve from radial forces.
The geometrical symmetry eliminates the total axial force on the rotary valve.
The total force on the PatRoVa rotary valve is permanently zero, no matter what the gas pressure into the combustion chamber is.
The (roller) bearings of the PatRoVa rotary valve run unloaded.
The following animation shows the same cylinder head "exploded":
