With reference to the following slide taken from the above animation:
A: the one inlet port (there is another one for the left piston).
B: inlet hole on the piston skirt.
C: exhaust port.
D: transfer port.
E: opening formed between the tilting valve and the respective piston port (the spherical piston port formed around the wrist pin, (in the case of the left piston it is the K, L)).
F: scavenging pump space
G: passageway between the scavenging pump space F and the transfer passageway H.
H: transfer passageway (it ends at the transfer ports D, which are controlled by the piston skirt)
I, J: lips of the tilting valve of the left piston.
K, L: port formed on the left piston (it is sealed by the tilting valve lips I and J during a part of the cycle).
M: space inside the right piston (permanently in communication with the inlet port A through the hole B on the piston skirt)
N: space inside the left piston.
In the above slide, the pistons are at the beginning of the compression; the exhaust port C is just closed (the transfer port D is already closed).
The space F increases, Air / mixture from the space M inside the piston (wherein the crankshaft is arranged) passes to the space F through the opening E (anti-diametrically there is formed another opening).
The vacuum in the space M inside the piston fills with air / mixture entering through the inlet port A and the hole B on the piston skirt.
After the TDC, the tilting valve seals the respective port on the piston isolating the space M inside the piston from the space F.
During the expansion the volume F decreases, however there is no way the trapped gas to escape.
When the transfer port D is finally opened by the piston, the compressed charge into the F and H spaces enters and scavenges the cylinder.
As the piston moves towards the BDC it pushes the air / mixture from the space F to pass to the combustion cylinder through G, H and D.
Before the closing of the transfer port D, the tilting valve "opens" (E) and air / charge from the space M inside the piston accelerates going to the spaces F and H and, through the transfer port D, into the cylinder until the transfer port D to get closed by the piston.
The vacuum in the space M inside the piston makes air / mixture to enter through the inlet port A into the space M, so, at the end of the transfer there is a significant flow of charge through the inlet port A towards the space M inside the piston and towards the increasing space F at the back side of the piston (like the overlap in the 4-strokes).
During the compression stroke the space F fills with fresh charge, and so on.
TUNING
The "tuning" depends more on the intake and transfer, than on the exhaust.
With the exhaust ports already opened, the transfer ports open and the scavenging begins.
The transfer ports open earlier than in a conventional 2-stroke. The pressure into the "scavenge pump" (sealed by the "back-side" of the piston whereon the tilting valve is still closed) allows such timing.
Later the tilting valve opens and the scavenging continues based on the inertia of the gas column formed along:
the open tilting-valve-port on the piston,
the space into the scavenge pump,
the transfer passageways,
the transfer ports,
the combustion chamber,
the exhaust ports,
and the exhaust.
Fresh charge from the "crankcase" (i.e. from the space inside the piston) feeds this "inertia" column, while the crankcase is fed from the intake, through the intake port, with fresh charge (air-fuel-oil mixture).
When the piston finally closes the transfer ports, the suction of air-fuel-oil-mixture from the intake continues due partly to the subpressure created into the scavenge pump space as the piston (with the tilting valve open) moves towards the TDC, and partly to the inertia of the gas column formed along:
the intake,
the intake port,
the crankcase,
the scavenge pump space,
and the scavenge passageways.
After the TDC the tilting valve closes and the air-fuel-oil-mixture trapped inside the "scavenge pump" is compressed waiting the transfer ports to open again by the piston.
And so on.
PRE tilting valve engine
In the Pulling Rod Engine, below, the "scavenging side" of the piston has bigger diameter enabling over-scavenging.
The compressed air or mixture from the scavenging pump, through ports made on the casing, enters into the combustion cylinder and forces the burnt gas out of the exhaust port.
The dead volume of the scavenging pump is smaller allowing better scavenging efficiency at high or extreme revs.
The pressure inside the crankcase never exceeds the ambient pressure.
During the compression stroke the vacuum inside the scavenging pump causes the flow of air or mixture from the crankcase.
During the expansion stroke, the piston port at the bottom of the piston is closed. The crankcase is sealed from the scavenging pump. The air or mixture in the scavenging pump is compressed waiting the piston to allow the communication of the scavenging pump with the combustion chamber.
The thrust loads are taken at the scavenging end of the piston wherein the cylinder and the piston are substantially cooler (more reliable operation with lower lube consumption).
With the "combustion" side of the piston being rid of thrust loads, and with the wrist pin not hiding the backside of the piston crown, the piston and the cylinder run cooler and more reliable.
The only duty that remains for the "combustion" side of the piston to fulfil is to seal the combustion chamber.
Conventional tilting valve engine
The application of the tilting valve on a simple conventional two-stroke engine could be like:
During the expansion stroke the air or mixture previously entered into the crankcase is compressed (the tilting valve remains closed) waiting the piston to open the transfer port.
During the compression stroke the vacuum into the crankcase causes the suction of air or mixture from the space "inside the piston", through the open piston port at the bottom of the piston.
The space "inside the piston" refills with air or mixture coming through the opening on the piston / cylinder.
Conventional tilting valve overscavenged engine
The application of the tilting valve on a slightly modified conventional two-stroke:
Through the transfer port (at the back of the piston) the crankcase communicates with the combustion chamber when the piston is near the BDC.
The exhaust port (not shown) opens by the piston skirt a little after the middle stroke.
Simplicity, overscavenging, bigger tilting valve area, stong piston structure.
Radial Cross and other tilting valve arrangements
In the Radial Cross engine, below, the four cylinders share the same crankcase. The "fork" connecting rods share the same crank pin. Each piston cooperates with a titling valve integral with its connecting rod.
Besides being even firing, this Cross-Radial engine is also full balanced (inertia forces, inertia moments and inertia torques). It is more vibration-free than the best eight cylinder four stroke engines.
Optionally, articulated connecting rods can be used.
Optionally, in order to avoid the forked connecting rods, the cylinders can be arranged having a small offset along the crankshaft axis. The resulting inertia moment (2nd order) is not too strong.
The power to weight ratio of the Cross-Radial is top.
The flow of air or mixture:
The air or mixture for the scavenging needs not to be compressed into the crankcase (i.e. the crankcase constantly runs at or below the ambient pressure).
Under the control of its tilting valve, each cylinder suctions air or mixture from the crankcase and fills the space between the backside of the piston crown and the "immovable" separating plate (red).
The space inside the cylinder communicates, under the control of the piston skirt, with the space at the backside of the piston crown (this communication happens when the piston is nearing the BDC).
The space at the backside of the piston crown constantly communicates, through recesses cut on the cylinder (blue) and on the casing (cyan), with the space between the tilting valve and the "flat plate of the piston near the wrist pin".
The space between the immovable separating plate (red) and the "flat plate of the piston near the wrist pin" constantly communicates with the crankcase by holes in the casing (cyan) not shown in the animation. This way the pressure inside this space is about the pressure inside the crankcase (optionally this space can be sealed from the crankcase).
As the piston moves towards the TDC the vacuum built in the space between the backside of the piston crown and the immovable plate (red) draws air or mixture from the crankcase, through the open tilting valve and the recesses in the casing (cyan) and in the cylinder (blue), and fills the space at the backside of the piston crown.
After the TDC the titling valve closes sealing the crankcase from the space at the backside of the piston crown. As the piston moves towards the BDC, the air or mixture in the space at the backside of the piston crown is compressed. After the middle stroke the exhaust ports open by the piston skirt and the pressure inside the combustion chamber (i.e. inside the cylinder) drops.
Then, the piston opens the inlet ports through which the cylinder communicates with the space at the backside of the piston crown. The compressed air or mixture scavenges the cylinder. After the BDC the tilting valve opens. The flow of air or mixture from the crankcase towards the cylinder continues ("overlap"). Then the piston closes the inlet ports. The piston motion towards the TDC builds a vacuum in the space at the backside of the piston crown. Air or mixture from the crankcase, through the open tilting valve and the recesses, fills the space . . .
This design does not poses limitations in the arrangement of the inlet and exhaust ports. For instance, the exhaust port can be at the one side of the cylinder only, with the inlet ports covering the rest cylinder.
In the single cylinder tilting valve engine, below, the crankcase constantly runs at, or below, the ambient pressure (like the Cross Radial above).
The space between the red immovable separating plate and the "plate of the piston above the wrist pin" constantly communicates with the crankcase.
The air flow (or mixture flow) throughout the engine (from the throttle valve to the exhaust) is smoothed out (no air oscillations, turbine-like flow).
Here the structure of the piston and the cooperation of the piston with the tilting valve is better shown.
Click here to open the GIF animation of another, more complex, version of the Cross-Radial wherein the scavenging ratio is bigger than 1.
Tilting-Valve small prototype
Capacity: 8cc
Bore: 24mm
Stroke: 19mm
Scavenging bore: 27mm
Connecting rod center to center: 29mm
Tilting valve diameter: 21mm
Wrist pin diameter: 7mm
Height (without the glow plug): 100mm
The Tilting-Valve prototype "resting" on the PatOP (the big one with the cooling fins) prototype:
The Tilting-Valve prototype:
Click on the image below to download the QuickTime video (2.5MB)
ANIMATIONS
Click on any of the following images to download the respective windows exe controllable animation.
