The state-of-the-art Electro-Hydraulic VVA is the MultiAir / TwinAir of Fiat (or UniAir of Schaeffler - INA), currently in mass production (Alfa Romeo Mito and Giulietta, Fiat Punto and Fiat 500 TwinAir, etc).
Click here to download the 170KB PatAir.exe program.
After opening the program press a few times the SpaceBar key for instructions.
The solenoid valve timing can change, the rpm can change, the resulting valve lift
profile is shown, the valve-time area is shown, etc.
The MultiAir of Fiat works according the "Ingoing Air Control": The sooner the intake valve closes, the more "ingoing air" is kept from entering the cylinder during the suction. The later the intake valve closes, the heavier the load.
The MultiAir mechanism:
An "oil push rod" is interposed between the valve and the cam.
The cam pushes the "oil push rod" and the "oil push rod" pushes the valve.
At the right moment a solenoid valve opens, the "oil push rod" collapses and the valve closes under the restoring action of the valve spring.
By a "hydraulic braking mechanism" the landing of the valve on the valve seat becomes acceptably smooth.
The application of the MultiAir / TwinAir in mass production engines proves that the state-of-the-art solenoid valves and the hydraulic system do operate reliably and efficiently.
Things can improve.
The "Ingoing Air Control" (MultiAir / TwinAir) has some inbuilt disadvantages.
After the intake valve closing, the piston continues to move towards the BDC. The charge (air or mixture) inside the cylinder undergoes an expansion. The expansion causes the charge temperature to drop increasing the heat absorption from the hotter walls (cylinder, piston crown, cylinder head, intake and exhaust valves).
After the BDC the piston compresses a hotter charge and restores less mechanical energy than the mechanical energy consumed to expand the charge.
That is, pure mechanical energy (yellow) from the crankshaft-flywheel is consumed inside the cylinder, with only result the increase of the charge temperature. The lighter the load, the bigger this "mechanical energy loss" and the higher the temperature of the cycle. The lighter the load, the more "expensive" the mechanical energy consumed, because it was generated at high BSFC.
The early closing of the intake valve leaves more time to the charge turbulence and swirl to fade before the combustion. The slower the combustion, the less efficient and the less clean the operation of the engine.
The PatAir system
The PatAir system operates either according the pattakon "Outgoing Air Control", or according the Fiat MultiAir / TwinAir "Ingoing Air Control".
According the "Outgoing Air Control" pattakon cycle, the later the intake valve closes, the more "outgoing" air is left to escape from the cylinder back to the intake manifold as the piston moves towards TDC (compression stroke). The engine of Toyota Prius (Atkinson/Miller cycle, overexpansion) operates in a limited "Outgoing Air Control" cycle.
The PatAir principle above, and the MultiAir principle below.
In the "Outgoing Air Control" cycle the vacuum into the cylinder (bad for the pumping energy and worse for the cycle temperatures and efficiency) is avoided.
The retarded closing of the intake valve leaves less time to the charge turbulence and swirl to fade before the combustion, so that the combustion is faster (good for the efficiency and better for the clean exhaust).
The improved homogeny of the charge, because the charge enters and leaves the cylinder a couple of times before it gets burned, further improves the combustion quality.
Thermodynamically the pattakon cycle (Outgoing Air Control) is quite different than the MultiAir Fiat (Ingoing Air Control) cycle.
For instance, the cranking of the PatAir engine takes a few times less torque than the conventional and the MultiAir engines of same capacity, i.e. the PatAir system needs a few times smaller starter and battery (and start-stop system, if any). The manual cranking is also an option, especially for the motorcycle engines (because the "Outgoing Air Control" also serves as an efficient de-compressor during the cranking).
The combination of the "Outgoing Air Control" cycle (breathing optimization, turbulence and swirl optimization, pumping loss minimization) with the Variable Compression Ratio (combustion optimization, emissions control) makes the state-of-the-art internal combustion engine a true Variable-Capacity-Engine (VCE) that operates permanently at the top/optimum thermal efficiency whatever the load and the revs are, thereby leaving no room to the hybrid technology.
The set of the available PatAir modes is a super-set of the available Fiat MultiAir / TwinAir modes: the PatAir can do everything the MultiAir / TwinAir does, and more.
In order to upgrade an existing MultiAir / TwinAir engine up to a PatAir engine, all it takes is a different intake camlobe profile (by machining, for instance, the existing camshaft) and a reprogramming of the "electronic control unit"/ECU. Then the engine can choose between the original MultiAir Fiat cycle and the PatAir pattakon cycle.
Since neither the long duration intake camlobes of the PatAir adds any cost, at all, nor the ECU reprogramming adds any cost, at all, to double the available modes of the MultiAir / TwinAir of Fiat has no manufacturing cost, at all.
The following plot shows the cam-lift vs the crankshaft-angle of the 1st PatAir prototype (blue curve) and of the Original MultiAir engine:
The MultiAir camshaft and the PatAir camshaft (the dark one):
The intake camlobe profiles of the Mito MultiAir and of the Mito PatAir are shown below.
The opening camlobe profile of the PatAir and of the MultiAir are identical;
also the closing camlobe profiles are identical;
but between the opening camlobe profile and the closing camlobe profile of the
PatAir it has been added a constant-lift lobe which, in this case, is of 136 degrees.
The PatAir camshaft assembled into the cylinder head
of the Alfa Romeo Mito pattakon prototype shown, below, at the side of the 1st pattakon prototype car Renault-19 VVA:
The replacement of the camshaft is the only necessary hardware modification.
The reprogramming of the original ECU:
