Pneumatic valve train in detail

[ringo]

Yep, so another pneumatic valve train thread.
I've searched the site for other threads that would shed more light on the actual operation of the system but so far, i haven't found much substance on the subject, well not as much as we have on other areas of the F1 car.
I think this part of the engine is most overlooked and taken for granted, and i'm not sure most have a handle on how it actually does what it does.
So i'd like to revisit this topic, seeing as though a lot of time has past since the last pneumatic valve train thread and see if we have any more details on the step by step operation of the valve train.
How the engine is started, how the pressure is maintained, what kind of valving or solenoids are involved.
How the engine is protected (sensors etc), how spring rate is maintained, and if, since around 6 years have passed since the last decent thread on the top, we can see this technology on road cars of today.

As for my contribution, i got nothing really, maybe a few weak sauce weblinks. I'm hoping some of you out there have some new F1 links that really lay it all out on the table. It's been a while and i'm sure there is more material available.

[Harv]

Good piece from Scarbs here. They're not particularly different in terms of operation, although you have to make sure the gas supply is good before starting. Also a bit more detail here, from Ferrari's request to modify their valve system a couple of years ago.





Unlike the electronic system that keeps being rumoured and bandied, this doesn't fall foul of the VVT rules. Are we expecting a return to valve springs with the new 2014 units? The figure for max RPM I keep hearing is 12k, easily within a spring's limts.

[strad]

Hmmmmmm I think we will still see pneumatic valve trains for the more controlled action.

[autogyro]

I think it will depend on the lobe profiles employed.
I cant see why springs cant be used at the lower rpm.
Less complexity and lighter for a start.

[olefud]

I think it will depend on the lobe profiles employed.
I cant see why springs cant be used at the lower rpm.
Less complexity and lighter for a start.

Lighter in reciprocating valve system mass or vehicle weight?

[ringo]

Good drawing, I suspect there are more seals in the cylinder but i guess this is representational.

Is it permitted to vary the stiffness of the valve piston chamber In order to reduce friction loss of the valve train?

There could be some control of the regulators which would be linked to the timing of the cams; reduce valve pressure on compression, then increase pressure on rebound.

I really feel much has changed since we last looked at this system. It may very well mean that pneumatics are here to stay for 2013. I can't see why not.

Looking at the drawing it may very well be that the valves don't have to drop if the engine shuts off. If the outlet regulator is normally closed then there won't be much of a problem.

The nitrogen tank that supplies the gas, I take it that there could be a second tank for the gas returning from the output regulator in addition to little pump maybe?

[Harv]

You will always have a leakdown through the seal and steam seal as well, especially for very high pressures. The whole system is designed only to keep itself inflated for a very short amount of time, using the minimum amount of gas possible. Once the engine is stopped you can connect a giant cylinder or just let the valves drop and re-inflate them before starting (chances are this isn't done, but it's possible.

[autogyro]

I think it will depend on the lobe profiles employed.
I cant see why springs cant be used at the lower rpm.
Less complexity and lighter for a start.

Lighter in reciprocating valve system mass or vehicle weight?

There is little difference in the reciprocating valve system mass.
How much does a Nitrogen tank weigh and the regulators and control system?
I springs can do the job I see no reason for pneumatics.
It would be different if the regs allowed a camless valve system but as usual development is stagnant.

[countersteer]

IIRC, the last of the turbo era Indy/CART engines were spinning upwards of 14k rpm. They lasted for 500 miles at near maximum rpm. We're talking 48 valve, 2.65 liter V-8's so my hunch is the relatively smaller valve sizes (?) and the lower rev limit would make valve springs near bulletproof.

[langwadt]

Good drawing, I suspect there are more seals in the cylinder but i guess this is representational.

Is it permitted to vary the stiffness of the valve piston chamber In order to reduce friction loss of the valve train?

There could be some control of the regulators which would be linked to the timing of the cams; reduce valve pressure on compression, then increase pressure on rebound.

I really feel much has changed since we last looked at this system. It may very well mean that pneumatics are here to stay for 2013. I can't see why not.

Looking at the drawing it may very well be that the valves don't have to drop if the engine shuts off. If the outlet regulator is normally closed then there won't be much of a problem.

The nitrogen tank that supplies the gas, I take it that there could be a second tank for the gas returning from the output regulator in addition to little pump maybe?

unless they constantly change the pressure I don't see why they need an output regulator, if the system volume if much bigger than the pneumatic cylinder volume the pressure will be close to constant whether the valve is open or not
and as long as there is some leak out of the system you'll always need to add gas to maintain pressure

the drawing does look like it has a spring so the valves would still move correctly if you turned over the engine by hand
but even without it, for the valves to drop when there is no pressure, the weight of the valve would have to overcome the
friction of the seals, is that realistic?

[ringo]

They need that regulator, if even as a type of redundant safety.
Remember the stiffness will vary with temperature and as said before the system may leak.
The regulator can work in a way where it keeps the chamber pressure constant with varying temperatures.

Valve dropping looks like something that will happen if there is a complete failure.
The Nitrogen tank, as was reported in the forums, is not powered, ie no pump, so if the engine shuts down it shouldn't affect the pressure delivery of the tank. So the valves will still be under pressure during an engine shut down.

In the event the regulators fail, and air flows out the system then the valve could drop or lag.

I don't have the time now, but i will attempt to model the system with some equations for the air spring.
The air spring may not be simple though, i think it has dynamic stiffness and this is where the regulators are important.

[Harv]

I'm not sure about the valve system still working after electrical disconnection - remember Vettel's alternator failure last year? Horner was on the radio talking about saving the engine. Are alternators chain or belt driven from these engines? The latter would indicate there was a possibility of damage from a lack of electrical power.

[langwadt]

I'm not sure about the valve system still working after electrical disconnection - remember Vettel's alternator failure last year? Horner was on the radio talking about saving the engine. Are alternators chain or belt driven from these engines? The latter would indicate there was a possibility of damage from a lack of electrical power.

I believe all the pumps and the alternator are gear driven

[ringo]

The valve system is supported by pressurized air from a canister. Assuming there is no pumps involved but just a canister of nitrogen, not connected to the egine in anyway mechanically, then the alternator failure would not have an effect on whether the valve "springs" will maintain pressure.

[riff_raff]

The gas supplied to a pneumatic valve spring system is usually something inert, like dry nitrogen. Many of these systems use a bladder or diaphragm to contain the gas volume, since this eliminates leakage past the valve guide. If this sytem were used on a production car engine, it would still require some sort of vestigial mechanical return spring, in order to prevent the valves from dropping into the cylinder after extended periods of inactivity, and thus producing contact with the piston crown at start-up.

Lack of positive valve control at all times is actually one of the major concerns that auto OEMs have with electromechanical valve actuation systems.