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. Changes in combustion chamber design as well as camshaft timing are possible that were not without it. "
Do engines with pneumatic valving use camshafts?
Yes, they do.
"Pneumatic Valves" is somewhat misleading because while it does say air is involved in the valve train, it doesn't say what it does. To understand how "pneumatic valves" work, you have to understand a typical valve train.
As you know, the camshaft opens valves at the appropriate time by having an egg-shaped lobe turn and press the valve downward. That done, you then need something to close it again. Typically, this is done with a spring, or sometimes two or even three, in the case of high performance engines. Figure 1 shows a typical overhead camshaft engine and its valve spring.
[Fig. 1] Typical Double Overhead Camshaft Engine
For street applications, valve springs are fine. They can close valves quickly enough to prevent valves hitting piston heads, in most cases.
However, there are limits to valve spring technology. Springs have a maximum rate at which they can return to their original form after being compressed. The problem is, once you exceed that limit, the spring cannot physically bounce back fast enough to close the valve. The valve stays partly open, even through the compression stroke and possibly even the power stroke.
This condition is called "valve float" and it can ruin an engine. Or at least cost high-end power.
One partial solution is to use stronger springs, and/or more of them, one concentrically inside the other. This strengthens the spring and lets it close more forcefully. The other drawbacks to this are weight, complexity and the fact that the stiffer the spring(s) are, the harder they are to open. That causes more drag on the camshaft, with the possibility of breaking or wearing it and the valve tappet bucket down. However, there is a limit even to multiple stiff springs.
The alternative is to used compressed air as the "spring medium." (See Figure 2.)
[Fig. 2] Pneumatic Valve Closing System.
In a pneumatic valve closing system, air replaces (or suppliments) the valve springs in holding the valves closed.
This system uses a compressor, high pressure air lines, pressure regulators and so on to put air pressure inside the valve's bucket tappet. The advantage of pneumatic valves is that, while air is compressible, it has no natural spring rate. Thus, it has no upper limit to how fast you can compress it and have it rebound. This prevents high-rpm valve float in racing engines, allowing the valves to close tightly even at 10,000 to 20,000 rpm (a rate of over 150 open-and-close cycles per second in a four-stroke engine.)
The disadvantage of pneumatic valve closure is obvious: If you lose air pressure for any reason (broken compressor, leak in the air tank or lines, etc.), your valves won't close. In a race, this means the driver coasts to a stop, says some naughty words on the radio and hikes back to the pits. In a street engine, it can leave you stranded in the middle of nowhere with a blown engine. Or worse, stuck in the "fast lane" in heavy traffic on a six-lanes-wide interstate at 80 mph. The trade-off may be acceptable for Formula One racing, but I think I'll pass on it for a street engine.
Thank you for the excellent post that explains things well.
I had seen pneumatic valving in industry and assumed the valving in F1 motors was completely controlled by electronics operating pneumatic shuttles, but now I see the what pneumatics do.
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Wanted: Winter racing series to avoid off season boredom. Will accept reruns of races long forgotten.
