| Author | Message | ||
     Eboos |
The Aprilia Cube (RS3) used pneumatic valves, and they are also used in formula 1 racing. How do they work, and what is the benefit? | ||
| Djkaplan |
They eliminate the valvesprings and the problems associated with valve-float at high rpm. I think the air is still triggered by by a rotating cam mechanism (it was a few years ago on the Renault F1 engine), but it's just a matter of time before lift and duration is totally controlled by computer. | ||
| Eboos |
Like servo actuated? I would think that failure rates would be pretty high as durability would likely be an issue. (Message edited by eboos on August 15, 2006) | ||
| M1combat |
There are a few engines in production that use completely variable valve timing. I'm thinking a BMW is one of them but I can't remember. The pneumatic valves don't "completely" eliminate the valve float issue, they just move the issue up to an RPM that hasn't been achieved yet. I think they were saying something like 26 or 28K RPM. | ||
| Bomber |
so far, they are only found in race engines, where durability isn't too much of a concern (if the perfect racer is one that fall apart completely nanoseconds after crossing the finish line -- benefits include less weight, more exact control, quicker opening/closing speeds | ||
| Blake |
There is no "triggering"; it is just that in places of steel valve springs, the valves are returned to their seats via gas (not air) charged pneumatic cylinders. The advantage as others have stated is that the gas charged cylinders have significantly less sprung mass and so do not contribute to valve float as much as conventional springs. As with spring return systems, opening and closing speeds are dependent on cam profile. | ||
| Bomber |
Blake -- you're absolutely right -- pening and closing speeds ARE dependent on cam profile with gas-charged cyclinders, I would think that opening/closing rates would no longer have to take cam/spring interaction into account . . . . yes? no? something else entirely? | ||
| Blake |
Pneumatic return may well allow more aggressive cam profiles. I'm not intimately familiar with the limiting factor(s) for cam opening and closing ramp profiles. Lateral loading, simple geometric limitations might factor as much or more than inertial concerns. If valve and spring inertia is a governing factor in design of the cam profile opening and closing ramps, then I bet that your observation is dead on accurate. Cool! Now I'm gonna have to do some research. ![: ]](http://www.badweatherbikers.com/buell/clipart/proud.gif) Fun stuff!  | ||
| Tq_freak |
Bomber I think you are right, I think that with the gas charged spring the closing rate would be contingent on the profile of the cam only because, I if I am right, with the lower mass of the air spring it will close the valve faster then a conventional spring could close the valve. But here is my question, what kind of PSI are they using in the air/gas springs? If you have too high of a PSI that would add friction and undo load on the cam. right? or are they useing some other material like teflon to help negate friction. | ||
| Ctyxrnr |
plus if you have no rotating parts in the cylinder head. you don't need oil in the head. especially if you have ceramic valve guides. i would love to see valve actuators instead of cams. the less moving parts the lighter the assy. and more power due to not needing hp to turn said parts. | ||
| Bomber |
Blake -- thanks -- it's GOOD to have a engineer available to answer these things -- my understanding is that valve spring pressure DOES affect opening and closing profiles, but that understanding is definately based on data available during the Nixon administration, and could very well be out of dae by now (sez the man that still owns a dwell meter!) signed Bomber (head dude at the Luddite Lounge) |
