Using the intake valves as the throttle: Fiat Multiair

[85 Cutlass Brougham]

I will say that after seeing this, I am stunned. Fiat (of all companies!) has done something truly brilliant here. They have come up with a way to vary engine speed by controlling the lift and duration of the intake valves and doing away with the conventional throttle blade in the process. This is much different than Honda's VTEC, which only switches between two lobe profiles at a given switch over point. No, this allows an infinite amount of adjustment on the fly using the engine computer and oil pressure as the medium. I cannot even imagine how hard it would be to modify this engine, but I am confident it will be figured out by someone. Why is this relevant to the US market? Well, this technology is used in the Alfa Romeo Mito which is the same car as the Fiat 500 that will be sold in the US at Chrysler dealers some time in the next year or two. So, expect plenty of "Fix It Again Tony" jokes when the Italian electrical systems all fail in rapid succession. Anyhow, here's a link if you want to watch a Flash video or 5 of the system in action. http://www.fptmultiair.com/flash_multiair_eng/home.htm

 

[custom442]

I like this idea, but will it work in the real world? Is there that much to gain on a tiny engine?

 

[joe_padavano]

I will say that after seeing this, I am stunned. Fiat (of all companies!) has done something truly brilliant here. They have come up with a way to vary engine speed by controlling the lift and duration of the intake valves and doing away with the conventional throttle blade in the process.

Actually BMW has had the same system in production since 2001. Works nicely to eliminate the pumping losses of a throttle (one of the reasons why diesels get better mileage than gasoline engines).

http://en.wikipedia.org/wiki/Valvetronic

 

[custom442]

I will say that after seeing this, I am stunned. Fiat (of all companies!) has done something truly brilliant here. They have come up with a way to vary engine speed by controlling the lift and duration of the intake valves and doing away with the conventional throttle blade in the process.

Actually BMW has had the same system in production since 2001. Works nicely to eliminate the pumping losses of a throttle (one of the reasons why diesels get better mileage than gasoline engines).

http://en.wikipedia.org/wiki/Valvetronic

joe - what kind of increase/decrease in duration are they talking about here, just how efficient is it?



off the wiki page:
"The throttle plate also doubles as an emergency backup, should the Valvetronic system fail. In this case, the engine would enter a "limp home" program, and engine speed would once again be controlled by the throttle plate."
oh damn what a shame, having to use the throttle to drive :lol:

 

[85 Cutlass Brougham]

As I read up on this idea further, I found that not only BMW, but Nissan has adopted this idea as well. As for the pumping losses, Fiat states them to be around 10% of engine power-pretty substantial. The Fiat system uses what is basically a race cam, and the Multiair trims the lift and duration until you are at WOT, which is where it allows full lift and duration. They seem to be getting the same power from a 1.4 liter engine as most get from a 1.6 (around 110hp). It's first use is in the Alfa Romeo MiTo, which shares it's subcompact platform with a few Fiats. (Fiat Group consists of Fiat, Lancia, Alfa Romeo, and Ferrari.)

As for the question about engine size, yes there is a lot to gain in a small engine. Remember that the internal combustion engine is not very thermodynamically efficient, and only converts something like 20% (may be more, I have to look it up) of the energy available into motion. The rest is lost to the cooling system, internal losses and the exhaust. So clearly, there is a huge lump of energy waste that has yet to be harvested. Figuring out how to go about it in an economically efficient manner is fascinating to think about.

 

[custom442]

Would it be more efficient if you could take this variable duration and also use throttle action with it? If x amount of duration is efficient, would x amount of duration with half throttle (vs. it staying open entirely) might be more? or is it a negligible gain

 

[85 Cutlass Brougham]

Actually, a throttle would represent a net loss in efficiency. Remember that both the throttle and the valves meter air in a normal engine. By removing the throttle, the engine is no longer fighting against it. Instead, it just ingests the maximum amount of air it can through the valves during a given period in which they are open. There is no throttle to fight against, so it takes less power to operate the engine in terms of pumping losses. Engine vacuum represents a pumping loss. By eliminating manifold vacuum in this way, you eliminate the pumping loss of having the piston pull against the throttle plate.

 

[beermonkey9417]

this is a pritty sweet idea. i wonder if they'll have an aftermarket for this device for other motor types(sbc 😀 ) in a near-er future. im not sure if a 4 barrel carb could be used with this, tho i think i have an idea how it could MAYBE be used. just hope you keep checking yer oil level.

 

[85 Cutlass Brougham]

Logically, no. It would not be adaptable for an economically feasible price to a pushrod engine. It needs to be an OHC engine, and it also needs to have throttle by wire and EFI. Otherwise, you have just introduced a throttle back in to the equation, and negated most of the benefits inherent in this system. The only benefit you would have left is a better idle quality than with a camshaft of equivalent specification.