TheRevva wrote:For others who, like me, might be somewhat intrigued, here's
a semi decent description of MultiAir / Pattakon that has just HELPED my understanding a lot:
http://www.pattakon.com/pattakonHydro.htm
(And yes, the valves do INDEED seem to 'snap shut' a lot more than with a traditional cam profile.)
Edit (I hit SUBMIT a little prematurely... LOL):
What I don't yet grasp is why they've not been able to completely eliminate the camshaft altogether...
The description of the system in the URL above looks to be using a solenoid operated 'relief valve' on a 'hydaulic push rod' between the cam lobe and the valve.
What's stopping them using another such solenoid on a pressurised fluid supply to OPEN the valve too?
I'm envisaging something not entirely different to a high pressure diesel injector employed to push open the valve!
The next 'logical' step from that would be to eliminate the valve springs altogether (along with their associated losses).
Namely, using hydraulics to push the valve OPEN via one solenoid, and hydraulics to push the valve CLOSED with another.
IMNSHO, the effective 'area under the curve' becomes almost infinitely variable
Furthermore, it'd also suit itself VERY well to an ECU. There would be NO need for a cam position sensor since the ECU effectively _IS_ the cam. (Only the crank angle sensor needs to remain)
Quote from
http://www.pattakon.com/pattakonHydro.htm :
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.
The plot below gives the difference between the various modes / strategies of the MultiAir of FIAT:
Quote from
http://www.pattakon.com/pattakonKeyAdv.htm#pattair :
The PatAir, based on very similar hardware (only the duration of the camshaft needs to change), works according:
either the "Ingoing Air Control" of Fiat,
or according the "Outgoing Air Control" of pattakon wherein the load is controllably increased by preventing more "Outgoing Air" from leaving the cylinder. The sooner the intake valve closes after BDC, during the compression stroke, the heavier the load.
The thermodynamic cycles of the "Ingoing Air Control" (Fiat) and of the "Outgoing Air Control" (pattakon) are different.
The "Outgoing Air Control" cycle avoids not only the underpressure, under part load, into the intake manifold (as the throttle-less VVAs, like the Fiat MultiAir and the BMW valvetronic, do) but it also avoids the underpressure into the cylinder by avoiding the expansion of the charge before the compression.
By minimizing the pumping-loss, by avoiding the consumption of mechanical-energy to just expand and warm the charge, by keeping alive the turbulence and swirl during combustion and by improving the mixture homogeny the "Outgoing Air Control" minimizes the mechanical-energy loss and optimizes the combustion.
The PatAir is an evolution of the MultiAir because it can operate not only according the infinite available modes of Fiat MutliAir cycle, but also according the infinite modes of pattakon "Outgoing Air Control" cycle.
The animation below was made to expalin the difference between the MultiAir and the PatAir:
(at
http://www.pattakon.com/hydro_files/PatAir.exe there is a controllable windows exe animation that further explains how things really work).
If the "Outgoing Air Control" seems complicated, please imagine the following:
a) In an empty cup someone adds water by a spoon and stops when 1/4 of the capacity of the cup is filled (Ingoing “Water” Control).
b) In en empty cup someone adds water by a spoon to completely fill the cup, then he pours out of the cup the 3/4 of the water by the same spoon (Outgoing “Water” Control).
Aren’t the above two “cycles” operative and clear?
They look similar. However, when the cylinder takes the place of the cup, and the air takes the place of the water, and the intake valve takes the place of the spoon, the resulting “Ingoing Air Control” cycle and “Outgoing Air Control” cycle differ, from the thermodynamic viewpoint (as explains the description and the Fig 3), as the day from the night.
The plot below is from the first PatAir prototype (adds an infinity of "unlimited" Miller cycles).
At operation with a very little quantity of fresh air, say 10% of the capacity of the cylinder, the “Ingoing Air Control” mode runs as a refrigerator (or heat-pump) working for cooling purposes and indicating negative indicated power output, whilst the same engine running according the “Outgoing Air Control” would indicate its best indicating fuel efficiency. Against the common sense, at “extremely light loads” the “Ingoing Air Control” provides negative indicating power, whereas the “Outgoing Air Control” mode delivers its best indicating efficiency.
What makes the MultiAir of FIAT so good?
There are several VVA systems (electromagnetic, hydraulic, mechanical-hydraulic etc) that, theoretically, provide full control over the intake valve lift, allowing the engine to operate according any mode.
In practice (i.e. in the mass production) the only successful system is the MultiAir of FIAT. It is based on the simplest and cheapest hydro-mechanical mechanism that intergrades (built-in) the indispensable safety
(the valve lift envelope makes the valve-piston-collision as impossible as it is in the best conventional engines).
The direct control of the ECU over the solenoid valves makes the MultiAir engines the first successful true-digitally-controlled engines in mass production. The ECU, based on the feedback, varies the time each solenoid valve is triggered to open (and thereby the moment the intake valve closes), which is an amazingly flexible and an exceptionally accurate control (impossible for the best mechanical systems).
The internal combustion engine turns into a true “digitally controlled device”.
The evolution from the inflexible mechanical valvetronic of BMW (regarded as the state-of-the-art VVA a couple of years ago) to the electro-mechanical-hydraulic MultiAir of FIAT is comparable to the evolution from the “old centrifugal spark advance control” to the modern electronic ignition systems.
However they insist using it the wrong way.
TheRevva wrote: "What's stopping them using another such solenoid on a pressurised fluid supply to OPEN the valve too?"
It is more easy than this. You don't need a second solenoid electromagnetic valve. Take a look at the
HyDesm (Hydraulic Desmodromic) at
http://www.pattakon.com/pattakonHyDesmo.htm
Thanks
Manousos Pattakos