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Camless engine
Actuating valves by exhaust gas pressure instead of hydraulics or solenoids. | |
The auto industry is in something of a frenzy over camless valve actuation in cars. It's been baking for years, but it's the next logical step from current well implemented variable valve timing and cam profile swapping (like you find in many japanese and european cars now). In coming years I'll bet
it'll be the new EFI.
Such systems have already well used on formula one cars, although most still have regular cams, but with a pneumatic valve spring / valve closing system. But the ideal engine would be completely camless, giving absolute maximum performance under all speeds and load conitions, not to mention economy and emissions. You'd be also able to dial up a simulated camshaft if you want to give your engine character in both performance and sound.
I think the approach is all wrong. Most research is looking into electro-hydraulicly actuated valves, some into solenoid actuated. So far all the systems are power hungry without the reliability and longevity required for a practical application. BMW is looking in to a new 48 volt electrical system to support its solenoid actuators for road cars. Lotus believes it will have a electro-hydraulicly activated production item by 2008.
But they have overlooked a power source that doesn't require redesigning the modern engines support systems. Why not use exhaust gas pressure, or perhaps gas directly from the engine's cylinder to power the valve actuation systems?
A small channel could take a shot of hot gas as the engine nears the finish of its power stroke and before the exhaust valves open. This gas would be at a minimum of 250psi, maybe 450-600 psi in a turbo car. Thats a minimum 20-40 bar, and plenty to power to drive a actuation system.
Note: This would take negligable power off the engine, infact it'd take power otherwise wasted and reduce pumping losses a tiny percentage.
A gas collecting tank and heat exchanger (wouldn't need to be very large) would lower the temperature from around 600 degrees C to 100-200 C and then be fed to a very simple double chamber piston arrangement at the top of the valve stems. A position sensor would allow a microprocessor to control the gas flow via a solenoid valve to accelerate and decelerate the valve through its motions.
An electric pneumatic pump and storage bottle would provide air to get the system going when the engine is starting up.
There, you'd have maximum torque at all engine speeds, super perfect output, and you'd have as much power as your engine has ability to rev - and it'd use every last rev too. Want your 5.7 chevy to put out an impossible 35mpg *and* 750hp?
This could all done with existing off the shelf parts and minimal R&D. It's not outside the realm of the DIY enthusiast either: The only two engineering hurdles would be manurfacturing the actuation piston assemblies (it'd be something similar to a small 33cc engine - you could use chainsaw piston rings for arguments sake) and programming the software for a off-the-shelf microcontroller.
Sturman digital valve
http://www.sturmani...-valveactuation.htm
A digitally controlled electrohydraulic example [venomx, Oct 04 2004, last modified Oct 21 2004]
(??) Pistonheads.co.uk
http://www.pistonhe...le.asp?storyId=7005
Lotus on the case [venomx]
Blue Sky Engenuity
http://www.blueskyengenuity.com/
No Cams, no poppet valves, no pushrods, no rockers, no electro-hydraulicly actuated valves! [venomx, Oct 04 2004, last modified Oct 21 2004]
(?) Blue Sky Engenuity
http://www.blueskyengenuity.com/
No Cams, no poppet valves, no pushrods, no rockers, no electro-hydraulicly actuated valves! [Focused, Oct 04 2004]
Quick story on Jalopnik.com; link to full article down the page
http://www.jalopnik...question-223479.php
One link deserves another [discontinuuity, Dec 21 2006]
free pistion engine
https://tec.grc.nas...stirling-convertor/
engine with out a camshaft. [travbm, Oct 29 2015]
[link]
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Unfortunately, the EPA would frown on putting the exhaust-powered valve actuators where they'd do the most good--between the engine and the cat. Though I'll admit I wonder to what extent the cat should be necessary with an electronically-fuel-injected engine using reforumated gasolines. It would seem an engine controller which was calibrated to produce minimal pollution (rather than being calibrated to produce the pollutant mix the cat lines) should be able to do a pretty good job at reducing emissions by itself without an efficiency-robbing cat. |
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You could have a separate catalytic converter for the exhaust gas from the valve-lifter pistons. The mini-cat could be built into the same housing as the main one to keep it hot enough. |
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Obligatory stuff cats through tailpipe Post. |
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Gas turbine engines already make extensive use of "customer bleed air systems" that bleed a minimal amount of air from the compressor and use it for anti-icing. Modern Naval ships use customer bleed air to mask the ships sound, mask the propeller sound and start other turbines. There is no reason this couldn't work. |
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This is more like it. (+ I love the links in the bakery) |
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already have a camless engine on the market it is the ford 6.0L power stroke diesle used in the f series pick up trucks the vales are soleniod actuated |
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Problem with using gas in an active valve control system is that it is too compressible and hence impossible to control at speed (or at least that is the conclusion I came to). Using cylinder gas for returning the valve passively would work though. |
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Hmm why have the cam at all on the intake side --- just have an automatic valve. |
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It opens when the cylinder creates a vacum and closes under pressure... |
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If you think this would have minimal effect on horsepower, try blocking off most of your exhaust pipe and see what it does to power. Gasoline engines, in my experience, are very sensitive to changes in back pressure in the exhaust system. |
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I'm not certain this doesn't violate the second law of thermodynamics. The exhaust gas is powering the valves that keep it pressurized? |
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[RayfordSteele] The gas opening the valve just has to act on a larger area (the little piston) than the gas closing the valve (valve face - if poppet type).
Though if it were the intake valve, then the intake gasses would actually be trying to open the valve for much of the duration, not close it. Closing it would be the more difficult of the two actions.
Im with [WilliamMoore] on this one. Gas is too uncontrollable for timed actuation. Best used for pneumatic springs.
[NoOneYouKnow], if anything, the pressurised gasses extracted from the exhaust for actuation would be reducing back pressure by the very fact that gasses are being extracted... |
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Would this elimiate the timing belt too (one of the most expensive engine maintenance items in my opinion)? |
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Exhaust gasses are much to dirty for this anyway with the amount of carbon and soot in them. The entire system would be clogged in a matter of a few thousand miles. Also new technology is slow to come to the automotive market due to the fact that it has to be taught one by one to each mechanic so that it can be serviced. Hydraulic fluids are also much more easy to control due to the fact that they cannot be compressed like gasses. A small hydraulic pump and the correct solenoids to send fluid to the valves is all that is needed (along with an ECU) for a hydraulic system to work. Simplicity is key for success. |
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[Madness] The problem with your theory is that valves in an engine do not just open at TDC (top dead center) and close at BDC. They are open for several degrees before and after those events. And going with that system what would you do with the exhaust valve since it would not work in the way you are suggesting. |
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It could eliminate the timing belt, but even if it didn't it would reduce the load on the timing train. The timing belt would be performing the same job as before, but only modulating the power impulses without actually being the medium by which those impulses are transmitted. |
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Another bonus: with no rigid connection required between the valve and its timing mechanism, the valves can be canted in their most flow-efficient orientation. If that's straight up, a timing failure simply taps the valve back up into the head. It may nick the cylinder or bend the stem otherwise, but it probably won't crack the head or bend the nonexistent camshaft. The pneumatic cylinder simply absorbs the pressure; a popoff valve will prevent pneumatic cylinder rupture and is an easy reset, no tools required. |
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Maximum Cylinder pressure only occurs at or very near TDC. Near the end of the power stroke the pressure in the cylinder is quite low relatively speaking. Exhaust backpressure is VERY low by comparison and would be whole inadequate to do the Job. Turbo chargers operate on a High Volume, Low Pressure principle and thus your Idea will not Work at all, there would be insufficient pressure available to even overcome spring tension let alone normal valve actuation. |
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Further Electro Hydraulic Works because the incompressability of fluids allows for extremely rapid changes in pressure within the system(just like an ABS system) Pnuematic systems can not generate the highly precise Positve response motions needed to properly control an engines valve train. You would rapidly develop float in the valve train much like a conventional Cam system as the Compressed gas will no longer be able to change pressure fast enough to keep up. |
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BONE BONE BONE Do some research. |
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[Marked for Deletion] Bad Science. (lack of basic understanding of Pnuematics, ICE operating Principles etc.) |
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As much as I like this idea for how it removes a proven convention and tries to replace it with miles of piping, I have to share this: |
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The engine will eventually fail to start. |
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It might start the first time. It might start if started with only brief shutdown intervals. [jhomrighaus] is right, the actuators will never react fast enough to run the engine at any significant speed: low system pressures require large diameter actuators. Those react instantly, but move slowly. Assume instead we take a charge off the cylinder somewhere around mid-stroke, so there's still some pressure on it. Goodbye, 750hp. Let's assume it would be on a constant-speed installation, like a large generator that runs at low revs. Maybe we can engineer an actuator that can keep up with a big, slow grumbly diesel running at 1200 rpm. |
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Now go on a vacation and leave the generator off for a week. The system pressure bleeds down and there is no significant pressure left to operate the actuators. There is a small amount of volume in each cylinder, but is that enough to charge up the system and get it operating? I doubt it. |
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Remember, [venomx]'s idea is to use hot pressurized exhaust gases direct from the cylinder. However, if there isn't enough pressure within the system already - virtually guaranteed if those gases are allowed to cool and thus lose pressure even before leakdown takes place - then intake valves don't open, cylinders don't fire, etc. Break out the bicycle pump and recharge your timing system. |
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Love the idea, not sure how well it'd work. One other type of valve design that was used shortly in a couple of model airplane engines was to use a rotating shaft with holes to allow air into and out of the engine. The problem was the cam didn't last more than a year or 2 due to carbon eating away at the shaft. |
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