21 replies to this topic

[desmo]

OK, the Italian press is going all hyperbolic over this new VVT system which can alter the valve timings of individual cylinders by means of electrohydraulic controls. The claims are extravagant, significantly reduced specific fuel consumption and emissions vs. everything else although I haven't heard it will make your bed or walk your dog. Yet.

Any buzz among the engine boffins? Is this a real step forward or just another proprietary VVL/VVT system more or less like any other in practice?

[Greg Locock]

Got to wonder if it might not be worth figuring out why each cylinder needs unique timing, rather than trying to adapt the valve timing to the different cylinders. Having said that, yes OK, there is an argument that on an I6 #5 will always run hot.

Anyway the idea of throttleless engines seems like a good one, although I am still a bit puzzled why a two stage pumping loss is less efficient than a single stage (that is, in order to get a certain small amount of air into an evacuated chamber, why is it more efficient to pump that air just past one obstruction (the valve) than two (the valve and the throttle) for the same net pressure loss?) I guess it is the intremediate expansion stage.

[gruntguru]

Got to wonder if it might not be worth figuring out why each cylinder needs unique timing, rather than trying to adapt the valve timing to the different cylinders. Having said that, yes OK, there is an argument that on an I6 #5 will always run hot.

Anyway the idea of throttleless engines seems like a good one, although I am still a bit puzzled why a two stage pumping loss is less efficient than a single stage (that is, in order to get a certain small amount of air into an evacuated chamber, why is it more efficient to pump that air just past one obstruction (the valve) than two (the valve and the throttle) for the same net pressure loss?) I guess it is the intremediate expansion stage.

Ideal poppet valves do not throttle the intake - they operate as on-off switching devices. Infinite variability of the opening and closing events is something of a holy grail and does offer (among other things) the ability to control intake airflow without pumping losses.

[kikiturbo2]

Got to wonder if it might not be worth figuring out why each cylinder needs unique timing, rather than trying to adapt the valve timing to the different cylinders. Having said that, yes OK, there is an argument that on an I6 #5 will always run hot.

Anyway the idea of throttleless engines seems like a good one, although I am still a bit puzzled why a two stage pumping loss is less efficient than a single stage (that is, in order to get a certain small amount of air into an evacuated chamber, why is it more efficient to pump that air just past one obstruction (the valve) than two (the valve and the throttle) for the same net pressure loss?) I guess it is the intremediate expansion stage.

I'd say that pumping loss is not the point here, but more efficient cylinder filling with varialble lift, timing and possibility to have multiple small valve opening in the same stroke..
I always dreamed of a turbo engine which will go from a normal valve timing and lift at low boost.. right to miller cycle on full boost..

fiat is working on a direct injection version too..

[McGuire]

Got to wonder if it might not be worth figuring out why each cylinder needs unique timing, rather than trying to adapt the valve timing to the different cylinders.

That was my take. Seems like an awfully high component count. I wonder if a Fiat should have that many moving parts... oh wait, they own Chrysler. I for one welcome our new overlords.

[mariner]

The engine boss of Ferari road cars is quoted as saying that they have tried Multiair on the F430 engine but it does not seem to work well at high revs. Apparently better for torque than power , which kind of makes sense.

[gruntguru]

The engine boss of Ferari road cars is quoted as saying that they have tried Multiair on the F430 engine but it does not seem to work well at high revs. Apparently better for torque than power , which kind of makes sense.

From that one would assume the max valve accelerations are not able to match the traditional camshaft system of actuation.

[Powersteer]

No we have got philosophy out of the way, how does it work?

[desmo]

The 1st production cars are just hitting the street. We'll see.

[zac510]

No we have got philosophy out of the way, how does it work?

This article gives the best I have read so far, but to be honest this whole tech slipped past me until I read it in the magazine itself. about the same time this thread popped up!
http://www.autocar.c...erleaf-/243139/

It sounds as though the exhaust valves only have two modes while the intakes can move through more positions.

[gordmac]

Would I be right in thinking BMW have used variable lift inlet valves instead of a butterfly in their petrol engines for years?

[malbear]

Would I be right in thinking BMW have used variable lift inlet valves instead of a butterfly in their petrol engines for years?

Here is a partial quote from an article in my library I am not sure where it came from so I cannot give due credit
Valvetronic
For the first time, a spark ignition engine (petrol engine) does without an intake manifold throttle.

Diesels engines have none: they suck a quantity of air independent of the load, i.e. their power is regulated only by the volume of fuel injected. It is one of the reasons of their better efficiency. A partially closed intake throttle blade increases the pumping losses by strangling the engine to control its power. Thus a spark ignited engine has its best efficiency (inversely proportional to specific consumption – sfc or bsfc) at almost wide open throttle (WOT), in other words close to full load, and this efficiency drops more with the reduction in load than in the case of a diesel. Many OEMs try to solve this problem by means of charge stratification, a technology which consists to use extremely lean air/fuel mixture in the peripheral zones of the combustion chamber when the engine is under low load, so allowing the throttle to remain wide open. The direct injection of gasoline in the combustion chamber at the end of compression stroke makes it possible to concentrate a mixture in flammable proportions close to the spark plug. But it is a difficult way because the production of nitrogen oxides is increased due to the combustion in excess air, and also in consequence of an increased thermal load – in particular on the top ring and land. Moreover, the engines using the stratified charge process require sulfur free gasoline, or else their advantage in fuel economy becomes illusory.

BMW chose a different technology which resolves the problem at its source, while also solving another.

The mass of charge sucked in the cylinder is adjusted by the infinitely variable intake valves lift and duration, so that the manifold throttle could simply be removed. Since very long ago, researchers, engineers and inventors sought a system able to vary the valves opening durations and lifts in order to optimize it according to the revs. In spite of considerable sums of ingeniousness, only some systems varying these parameters either slightly or by steps were marketed. In addition, devices which modify the intake camshaft timing are current nowadays but they produce only some marginal efficiency improvement and they neither change the valve lift nor opening duration. By the way, BMW was the first OEM to use such a mechanism on the exhaust camshaft also (Double Vanos). From now on this system is used together with Valvetronic, so that most of the parameters of the valves actuation become controllable.

The inlet valves are actuated via two levers. One of them rests on an hydraulic socket whereas the other is shifted by the eccentric of a control shaft. This shaft is controlled by an electric motor and a worm gear; 3/10e of seconds is enough to swing from an extreme position to the other. The transient response of the engine is faster than with a conventional throttle since the atmospheric pressure is not decreased in the whole volume of the intake runners. Under low and part load the pumping losses are greatly reduced because the pistons do not have to suck during the entire intake stroke in a depression created by a partially closed throttle blade, but only during a fraction of this stroke. The atmospheric pressure just behind the valve makes it possible to quickly fill the cylinder wit the desired amount of charge and, moreover, as the said valve can be closed before the BDC instead of after, a good part of the energy spent in sucking is recovered when the piston moves up again.
Hence the inlet valves lift changes continuously from about zero to 9.7 mm (4 cylinders 1.8) and the engine output is adjusted in the most logical way. Moreover, under partial load the friction losses in the valvetrain are decreased. The system presents however the disadvantage of a total mass increased by that of the additional lever, so that stronger valve springs are necessary. As a result the red line is set to 6500 t/mn.
cheers Malbeare

Edited by malbear, 14 November 2009 - 21:16.

[gordmac]

Interesting, thanks.

[Powersteer]

MultiAir bravo?

[John Brundage]

MultiAir bravo?

I recall reading about a similar system in a Hot Rod (?) magazine a number of years ago. The company may have been in Colorado.

[gruntguru]

MultiAir bravo?

Very shiny too!

[MatsNorway]

Shiny indeed.

No wonder its no god at a high revving Ferrari, the intake system is hydraulic driven. And on top of that its not made by some hydraulic experts either by the look of it. It got some strange oil intakes on the lifter. the flow might cause some turbulence there on high revs.

I like it tho, you can make the system disengage if the camshaft jumps some teeth on that rubber band or if the chain snaps. ++

Think i heard Peugeot was doing research with electric actuators on the valve control.

a hybrid could be a nice trick to ease the stress on the hydraulic components.

how do i upload pic from my pc? do i have to go over a 3rd part page?

Edited by MatsNorway, 10 March 2010 - 11:43.

[OfficeLinebacker]

I for one welcome our new overlords.

Thanks for that Kent!

[Scorg]

MultiAir bravo?

Yup, out in summer. Being released as a 140bhp model with a CO2 rating of 132 at first, and then later at 129.
Details were released last week at the Geneva motorshow.

http://www.italiaspe...eview/0303.html

[dovatf]

Here is a partial quote from an article in my library I am not sure where it came from so I cannot give due credit
Valvetronic
For the first time, a spark ignition engine (petrol engine) does without an intake manifold throttle.

Hi,

I remember having written this article myself ! Here it is, with pictures : BMW Valvetronic, part 1
BMW Valvetronic, part 2

Cheers,
Francois

[venator]

For the first time??? The very first Cadillacs (of 1903 vintage) used variable valve lifting instead of throttling the intake, and they were by no means the first ones with that idea!

Edited by venator, 28 March 2010 - 22:30.

[dovatf]

For the first time??? The very first Cadillacs (of 1903 vintage) used variable valve lifting instead of throttling the intake, and they were by no means the first ones with that idea!

Thanks for the info, I didn't know that. Any clue how it was done ?