1 Steam Cars : Phorum
General Steam Car topics
pneumatic valve springs
Posted by: Peter Heid (IP Logged)
Date: February 08, 2002 10:34PM
<HTML>I am a Formula 1 fan, mostly because exciting technological innovations usually happen here first and then outlawed here first. An engineer for Mcclaren said most of his 15 years were spent developing ideas that were later banned. The most intriguing development currently in use is the pneumatic valves (actually just the springs) enabling engine RPM's to exceed 19,000 rpms with no valve float limit in sight. The development started by building springs, one inside the other, with tolerances just right to have drag between the springs to provide needed friction and dampen the valve, but this scheme seemed to have an upper limit of 15,000 RPM. the next step was to replace the coil spring with an air spring, the needed drag was then developed by the drag of the valve cap / plunger on the cylinder that comprises the spring pocket. From what I can gather the pressure is equalized by a pressure reservoir connecting all 40 valve pockets together and the reservoir is charged with compressed air or nitrogen from an onboard tank. You can watch the F1 pit crew recharge the tanks on some cars during a stop, watch for an air hose. The pressure, from the limited information available, seems to be run around 100 psi but each manufacturer probably uses slightly different sized plungers and cylinders. Space is limited and virtually every engine is a V-10 and has 4 valves per cylinder so I would imagine the component sizes are similar from one engine manufacturer to another. The pressure is adjusted on a dyno to give the desired engine response for each track they run.
If the engine spins 19,000 RPM then the cam at 1/2 speed is 9,500 RPM or 158 RPS. A single rotation of the cam would therefor take 0.0063 seconds and if the valve lift duration is 300 degrees of cam rotation the valve action must require 0.0053 seconds. Not bad for a rotating cam against reciprocating parts. Some F1 engineers claim the current valve system is capable of engine speeds in excess of 30,000 RPM and I believe this might be a good design direction to follow for the short cutoffs my engine design would require (theroy).
I have thought of a solenoid opened valve that is of the piston type and it uses the escaping steam from the valve stem leakage to fill an spring chamber. The chamber pressure could be regulated to provide the proper air spring function and the duration of the electrical pulse to the solenoid could be varied to change the cutoff. It would seem hard to acheive long cutoffs, actual time open, because the vapor spring would try to close the valve, working against the air solenoid (need a strong solenoid). The reaction time of the solenoid would have to be very quick, acting through a short stroke. In this case, my calculations (almost a guess) would seem to favor a maximum engine speed around 3000 RPM or greater.
The same technology is easily applied to non-electric valves as in the F1 cars. The cam opens the valves and the gas springs push them back, very simple. Steam could easily supply the pressure needed to operate the gas springs just as in the free piston engine.
Has anyone experimented with such springs for steam valves yet. If anyone is Interested I can supply more information or provide references for research.
Just Another Crazy Idea
Peter Heid</HTML>
If the engine spins 19,000 RPM then the cam at 1/2 speed is 9,500 RPM or 158 RPS. A single rotation of the cam would therefor take 0.0063 seconds and if the valve lift duration is 300 degrees of cam rotation the valve action must require 0.0053 seconds. Not bad for a rotating cam against reciprocating parts. Some F1 engineers claim the current valve system is capable of engine speeds in excess of 30,000 RPM and I believe this might be a good design direction to follow for the short cutoffs my engine design would require (theroy).
I have thought of a solenoid opened valve that is of the piston type and it uses the escaping steam from the valve stem leakage to fill an spring chamber. The chamber pressure could be regulated to provide the proper air spring function and the duration of the electrical pulse to the solenoid could be varied to change the cutoff. It would seem hard to acheive long cutoffs, actual time open, because the vapor spring would try to close the valve, working against the air solenoid (need a strong solenoid). The reaction time of the solenoid would have to be very quick, acting through a short stroke. In this case, my calculations (almost a guess) would seem to favor a maximum engine speed around 3000 RPM or greater.
The same technology is easily applied to non-electric valves as in the F1 cars. The cam opens the valves and the gas springs push them back, very simple. Steam could easily supply the pressure needed to operate the gas springs just as in the free piston engine.
Has anyone experimented with such springs for steam valves yet. If anyone is Interested I can supply more information or provide references for research.
Just Another Crazy Idea
Peter Heid</HTML>
Re: pneumatic valve springs
Posted by: David K. Nergaard (IP Logged)
Date: February 09, 2002 08:22PM
<HTML>I have toyed with the idea of using the cylinder pressure to return the valves to their seats by having "fat" valve stems, working steam pressure on the area of the stem being the force required. Sounds like it should work, but have not yet tried it. Any thoughts?</HTML>
Re: pneumatic valve springs
Posted by: Peter Heid (IP Logged)
Date: February 10, 2002 04:09AM
<HTML>David,
The F1 cars have a small piston attached to the top of the valve, instead of the spring cap, and the spring pocket is pressurized below it. The piston appears to be aluminum, about 12 mm thick with what looks like an oring with back up rings, this also reduces the moving mass. I don't see any reason why a large stem could not do the same to act as the piston. You might want to watch the mass of the valve to provide for fast action and minimal impact when seating or closing against a stop. I have sketched a piston valve that uses a gas spring to return the valve and another to stop the travel, I think it would bounce back and forth without a mechanical device driving it.
The best informaton I have found on the subject is in "spring design and applications" a mcgraw hill text book. I'm quite sure that is the name, I would have to dig through some boxes to find it. It seems to be a rare text and i would be happy to round it up and share the info on gas springs but if you aren't running over 15,000 rpm, the spring math is not very important. You know steam so it's mostly just piston size and PSI. Also you might want a small spring to insure the valve is in the correct position when starting, they pressurize the F1 cars before running them. I make it sound simple don't I ?
Peter Heid</HTML>
The F1 cars have a small piston attached to the top of the valve, instead of the spring cap, and the spring pocket is pressurized below it. The piston appears to be aluminum, about 12 mm thick with what looks like an oring with back up rings, this also reduces the moving mass. I don't see any reason why a large stem could not do the same to act as the piston. You might want to watch the mass of the valve to provide for fast action and minimal impact when seating or closing against a stop. I have sketched a piston valve that uses a gas spring to return the valve and another to stop the travel, I think it would bounce back and forth without a mechanical device driving it.
The best informaton I have found on the subject is in "spring design and applications" a mcgraw hill text book. I'm quite sure that is the name, I would have to dig through some boxes to find it. It seems to be a rare text and i would be happy to round it up and share the info on gas springs but if you aren't running over 15,000 rpm, the spring math is not very important. You know steam so it's mostly just piston size and PSI. Also you might want a small spring to insure the valve is in the correct position when starting, they pressurize the F1 cars before running them. I make it sound simple don't I ?
Peter Heid</HTML>
Re: pneumatic valve springs
Posted by: George K. Nutz (IP Logged)
Date: February 13, 2002 05:48PM
<HTML>Peter,
In a sense (but not totally) the Williams brothers engine used equalized steam "pneumatic" pressures to make their great poppet valve engine work.
There is a August 1968 Machine Design article on it. It states that a professor at the University of Pennsylvania, a Dr. Robert Ayers, tested the engine on a dyno and achieved-as a single acting unaflow- an actual water rate of 6.44#/hp-hr steam and "exceeded its theoretical limits"--so much for professors that profess!!
The brilliant Williams twins came up with an engine of very low clearance volume where excess compression would be put essentially back into the steam chest and at the time of the intake poppet valve opening it had equal pressure on both sides of it to make it a fairly well balanced valve operating at 1000 psi. Its performance was not "greater than theoretical" it just allowed the maximum possible actual expansion ratio as that depends upon the clearance volume. The engine ran at 2500 rpm during the dyno tests.
Jerry Peoples has written extensively about the Williams cycle and it is one great way to make a unaflow work very well with atmospheric exhaust with very little clearance volume. This steam rate certainly beats the heck out of a compound Doble and actually achieves the steam rate of the Doble Triple with reheat but done in a simple unaflow(uniflow) engine. It was their concept of achieving a nearly balanced poppet valve during admission with a very low clearance volume that made a much larger actual expansion ratio that made it run so efficiently. Too bad their remarkable work is another forgotten saga of great efforts. The professor stated that the compression ratio was 26.6/1 and the expansion ratio was 18.6/1.
How much we all try and re-invent the wheel ;>) .
Best, George</HTML>
In a sense (but not totally) the Williams brothers engine used equalized steam "pneumatic" pressures to make their great poppet valve engine work.
There is a August 1968 Machine Design article on it. It states that a professor at the University of Pennsylvania, a Dr. Robert Ayers, tested the engine on a dyno and achieved-as a single acting unaflow- an actual water rate of 6.44#/hp-hr steam and "exceeded its theoretical limits"--so much for professors that profess!!
The brilliant Williams twins came up with an engine of very low clearance volume where excess compression would be put essentially back into the steam chest and at the time of the intake poppet valve opening it had equal pressure on both sides of it to make it a fairly well balanced valve operating at 1000 psi. Its performance was not "greater than theoretical" it just allowed the maximum possible actual expansion ratio as that depends upon the clearance volume. The engine ran at 2500 rpm during the dyno tests.
Jerry Peoples has written extensively about the Williams cycle and it is one great way to make a unaflow work very well with atmospheric exhaust with very little clearance volume. This steam rate certainly beats the heck out of a compound Doble and actually achieves the steam rate of the Doble Triple with reheat but done in a simple unaflow(uniflow) engine. It was their concept of achieving a nearly balanced poppet valve during admission with a very low clearance volume that made a much larger actual expansion ratio that made it run so efficiently. Too bad their remarkable work is another forgotten saga of great efforts. The professor stated that the compression ratio was 26.6/1 and the expansion ratio was 18.6/1.
How much we all try and re-invent the wheel ;>) .
Best, George</HTML>
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