15 replies to this topic

[desmo]

I thought it's about time that I posted an illustration of a pneumatic valve spring system. This is an older drawing, but the principle is the same today.

[Yelnats]

Im sorry but I can't make sense of this drawing relative to the much more diagramatic drawings I have seen of Pneumatic valves. Looks more like a hydraulic valve lash system to me.

[desmo]

It does rather resemble a hyraulic tappet doesn't it?

I think the problem with the drawing is that the artist doesn't show any indication of the cylinder that the piston (colored orange in the drawing) rides in. If you picture that, it makes sense. I believe the hardware in the valve/cam area used today in F1 is essentially the same as shown here. Del West S.A. who make the bits for some of the F1 teams show some hardware in their ads in Race Tech mag, and they look almost exactly like the pieces in the drawing. I'm not sure there is any need to re-invent this design, if it keeps the follower on the cam lobe that's really all one can ask of it.

[Top Fuel F1]

I have been hoping to get a good illustration of the pneumatic valve spring system and had searched the availability of back issues of both RACECAR Engineering and RACE TECH for information. RACECAR Engineering Vol. 3 No. 4 had an article: "F1 Engines: Pneumatic Valve Springs". Unfortunitly it is both out of print and out of stock. Maybe some one who archives this magazine could see if it contained any worth while diagrams, illustrations or data in addition to what desmo had already posted earlier this year.

Best Regards; [p][Edited by Top Fuel F1 on 11-08-2000]

[Top Fuel F1]

Re: 1. The illustration posted at the top of this Thread.
2. Pneumatic valve cylinder omitted in the illustration. The piston is orange.
3. Assume the valve stem seals are working perfectly.
4. Assume a higher pressure setting for the Outlet Regulator than for the Input Regulator.

Desmo:

I'm trying to sort out what's going on in detail specific to the illustration and have seached previous Posts on this subject to try to find out. Without complete success let me give two senarios to consider:

A. Case 1
1. Inlet Reg: Are those two elec. wires connected to the Reg. that I see in the illustration? I assume this Reg. is stepping down the very high pressure from the nitrogen storage bottle to what pressure is needed in the gas valve cylinder. If the Reg. is under electronic control it could cut off pressure from the storage bottle when the cam is driving the gas valve piston down (opening the valve) and then restore pressure when the valve is closing .ie less resistance when opening a valve and pressure to close it.
2. Outlet Reg: This I assume is set at a fixed pressure rating and will maintain the proper pressure between the piston and the cam at all times and release the nitrogen displaced by the gas valve piston when it is driven down by the cam.

Case 1. conotates some what of a nitrogen gas pump concept that makes me question how, with all these RPMs and the duration of these races, the storage tank could have enough gas to last out the race.

Case 2:
1. Inlet Reg: Assume the Reg. is not under elec. control and simply regulates pressure down from the high storage tank pressure to what's needed in the gas valve cylinder .ie does not turn on and off like in Case 1.
2. Outlet Reg: The Inlet Reg. is always attempting to supply gas to the gas valve cylinder. When the cam drives the piston down (opening the valve) the nitrogen gas in the cylinder actually compresses to some extent until the Output Reg. pressure setting is over come. The residual gas in the cylinder then rebounds pushing the valve closed and is joined in this effort by replacement gas/pressure it may need from the Input Reg.

Case 2's senario would seem to cut down on the out right pumping of gas. To what extent would depend on how much the nitrogen could be compressed in the cylinder when the cam drives the valve open and how much the Outlet Reg. could limit the expendature of gas to the cam cover area. This might make it more reasonable to believe that the nitrogen storage tank would have enough supply for an entire race.

In one of your Posts, about pneumatic valves, earlier in the year a "ring-main" system was mentioned. This may be a familiar term but I'm not familiar with it. It may be key in explaining this or possibly something else associated with a pneumatic valve sytem. I hoping you can clarify the two Cases I discussed about the illustration and also how a "ring-main" system relates to all of this.

Best Regards;

[desmo]

Case 2 is the correct scenario. The storage tank merely replaces the gas lost through normal leakage past the seals. A ring main is simply plumbing that feeds the individual cylinders from a main feeder that is a complete circuit rather than just a rail. This allows more consistent pressure in the main.

[Halfwitt]

As far as I understand, they use compressed air and not nitrogen, and use a small piston pump to supply a small receiver (tank), which then in turn feeds the underside of the tappet pistons. Looking at the diagram, the tappet piston seems an odd looking thing (i.e. seems to have a cavity or seperate 'inner part'. What is this?

[desmo]

I think the blue part inside the piston is to key the valve to the piston. The piston must "pull" the valve open from the end of the stem. I don't think it makes any difference whether one uses N2 or ambient air, as long as it's dry. I was surprised to read that the Macs were using ambient air to recharge their system lessening the need for a high-volume on board storage tank, or a very high-pressure storage vessel and all the potential reliability concerns that might entail. They must have a very good system for removing water vapor from the air before it is fed to the head.

[Halfwitt]

I didn't mean the blue bit, I was referring to the (apparent) double thickness tappet piston, whcih seems to loop inside itself.

[Yelnats]

McLaren has realised that in a regulated pressure system, temperature and volumetric variations caused by water vapour will be compensated for by the regulator and will have no effect on the pressure levels in the pneumatic valve system. Similarly an air suspension system manages quite well with ambient air as the atmospheric variations are constantly compensated for by the regulator and pump system.

For those new to this topic;
Nitrogen is used to fill tires because it contains no water vapour which has an eratic volumetric response to temperature change and produces major pressure variations in a closed system like a tire. Water vapour is subject to condensation and evaporation effects which produce a non-linier response to temperature and this is compounded by the variations in relative humidity in ambient air. Nitrogen is used because its cheap, inert and free of moisture. Oxygen is cheap and dry but far from inert![p][Edited by Yelnats on 11-01-2000]

[desmo]

Halfwitt, it appears to me that the piston is designed to use the pressure on the underside of the piston to "hold onto" the valve stem thus allowing the bit colored blue to be split for easy assembly. The inside architecture of the piston is almost like a Belleville washer-type spring that reacts to the load of the pressure by compressing the blue split bit. The "seal rubber" would maintain the pressure differential as well as allow for differences in thermal expansion. The piston and the valve stem are not totally fixed to each other. The lower seal (yellow) is made of PTFE (Teflon) and in the exhaust side must be thermally loaded to near it's limit. That seal is being heated by contact with the exhaust valve stem and the valve guide on two of four sides. You're not going to be able to flush alot of oil through those two sides to cool them off.

[Yelnats]

Halfwit- It appears that the piston (Tappett) is two part to enable the top bearing surface to be removed and the split ring accessed for valve removal. At the same time it allows for different bearing surface thicknesses to be used to accomodate valve clearances adjustments. (in place of the shims often used in overhead cam designs).

[Rainer Nyberg]

" The technology of all the current pneumatic valve return systems is that of simply replacing the valve spring with a pneumatic spring, using an inert gas (nitrogen,which behaves substantially the same as air) as the compressive fluid. The camshaft exercises its normal precise control of the motion of each valve, and eachspring maintains the contact force between an individual valve assembly, cam and tappet bucket, during operation. Pneumatic valve spring systems are thus an
improved replacement for mechanical springs. They are not a complete valve control system like a desmodromic operation - which uses no springs.

Pneumatic valve springs operate on a ring-main system with the essential back-up of a compressed gas cylinder, pressure regulators, one-way valves and an oilscavenging system. The principle reduction in valve assembly mass is that of the upper one-third of each valve spring. Although a nett small reduction in valveassembly mass is possible, this is accompanied by added friction of the stem seal ring.

The pneumatic spring is not subject to fatigue failure, or diminished damping, with running time. Valve lift is not constrained by spring wire maximum stress andstress range limits. Renault reports that the rising rate characteristics of the pneumatic spring assists in matching spring force to valve assembly inertia forcerequirements in the particular case of its V10. The fundamental pneumatic spring advantage for very high speed engines is that the natural frequency of thecompressed gas column is in the order of eight times that of a steel wire coil spring.

It was Jean-Pierre Boudy, the Chief Engineer of Engine Development at Renault Sport during the turbocharged V6 race engine era, who invented the first pneumatic valve spring system to be used in a competitive racecar engine. The pneumatic spring equipped Renault engine was first raced, in a Lotus chassis driven by Ayrton Senna, at the beginning of the 1986 GP season.

The Honda RA122E/B (1992 V12 F1) ran at 6-8 bar (87-116 psi) with the gas replenishment cylinder charged, initially, to approx 150 bar (2175 psi). Honda claimed a reduction of valve assembly reciprocating mass of 20 % with similar levels of valve gear friction(as comparedto conventional systems). "

[Top Fuel F1]

Rainer:

Your Post looks exactly like the info " 7.3 How do pneumatic valve return systems work? " previously Posted by desmo in two seperate Threads earlier this year. I think what we were trying to do in this Thread was to glean anything else out of the illustration and to possibly go beyond what was previously Posted. I was also looking for a previous issue of RACECAR Engineering to see what that might add (see my previous Post about that in this Thread}.

Best Regards; [p][Edited by Top Fuel F1 on 11-08-2000]

[Rainer Nyberg]

I wasn´t aware of that it was posted earlier, I am still a newcomer to this, so I guess old threads also will re-appear...

[desmo]

Hey, no harm, no foul. Don't worry about it. When I first started posting here, I wen't back through the previous threads and read them all! Took hours and hours, but it was fun and I learned a lot. If everyone here had read all the posts in this forum not only would there be a lot less repeat posts, the level of discussion would be much, much more informed. I know, it ain't gonna happen but I thought I'd point out the obvious. Turn off that sit-com and read old Tech Forum posts!