alternative valve idea

[motomatt16]

the other day i was thinking of a way to get more flow through a motor thinking about how much extra resistance the valve seat must make for the charge going in and exhasut out when i thought of a butterfly type valve. if you could control it right, while the piston comes down it would make a vacume opening the intake and pulling the charge through. and the piston coming up opening the valve and pressing the exhaust out. the only problem would be the valves opening on the power and compression stroke. if you could figure out a way to hold them shut for those times it could work.? maybe

i'm only 17 so dont shoot me if there is something obvious i am missing it was just a idea

[huskymad127]

Just throwing in my thoughts here, if its opperated by vaccum then you have no way of adjusting them, so its like a step backwards in the powerdepartment, and I'm pretty sure your idea is just more of an obsolete version of reeds on a 2 stroke. Also you would loose your air/fuel mixture when the piston goes up because it some of it would escape before closing the butterfly valve.

[motomatt16]

you would need a long stroke for it to be most effective. it was just an idea

[huskymad127]

I know am I'm just puttin in my opinion. Reeds on a 2 stroke are basically a one way valve like what your saying but without losing anything when they close.

[grayracer513]

The earliest poppet valve four-stroke cycle engines had intake valves that were held closed by a weak spring and opened by the engine's intake vacuum on demand. From a purely performance based standpoint, this is an extremely limiting approach. The intakes need to open well before the intake stroke begins and close well after it ends in order to take advantage of gas inertia and sonic/pressure tuning.

It's also important to bear in mind that any valve used in a 4-stroke will need to be tough enough to seal against compression and combustion forces.

[GCannon]

There are technologies like this in development:

http://www.coatesengine.com/technology.html

http://utsescholarship.lib.uts.edu.au/dspace/handle/2100/248

http://www.northernthunder.com/rotary.html

[1987CR250R]

Beyond the timing issue, using pressure to open and close valves is limited by the speed that the pressure waves can reach the valves, valves need to open before strokes begin in order to allow air to start moving and they need to close after strokes end in order to take advantage of the momentum of the fast moving air. Precise, mechanical timing of valves through cams is currently the best method.

The trouble with modern valvetrain designs isn't the cam, it's the spring. Faster closing rates required to get maxiumum duration and maxiumum power require stiffer springs. Stiffer springs mean thicker coils and thicker coils mean more stress on the surface of the spring for a given valve lift. Thick coils have very finite lifetimes and are prone to failure. Making the valves lighter by running multiple intake and exhaust valves and using exotic materials like titanium has reduced the stiffness of the spring coil required to improve durability.

[grayracer513]

Beyond the timing issue, using pressure to open and close valves is limited by the speed that the pressure waves can reach the valves, valves need to open before strokes begin in order to allow air to start moving and they need to close after strokes end in order to take advantage of the momentum of the fast moving air. Precise, mechanical timing of valves through cams is currently the best method.

Odd, then, don't you think, that the 20,000+ RPM F1 engines use pneumatically operated (opened and closed by air) valve trains with neither cams nor springs?

As a closing spring, air has no internal inertia, and doesn't suffer from harmonic resonant tension loss. As an opening media, it is infinitely variable. Timing is whatever you want at any given moment.

[slothspeed]

Where did you come up with the idea they have no cams? I believe all the current F1 engines have camshafts and are limited to 18k per the rules. The air spring is for closing the valve, not opening it. I think a system without cams is a ways off in the future.

[grayracer513]

Honda at least had an engine that is now illegal since it was a V12 at the older displacement limit that operated the valve train entirely with air, the distribution and timing of which was managed by a system of pumps and valving controlled by a computer, along with the rest of the engine. At the current limit of 18K, or even the '06 limit of 20K, or even higher, really, such a system isn't necessary, but it does offer the advantage of a completely manageable lift profile.

The point is that the technology exists at a feasible, if not practical, level.

[1987CR250R]

The big engines that redline at 90 rpm run hyraulically operated valves. The only advantage there is ease of maintenance as the valve assembly can be removed from the head without having to mess around with timing or heavy springs. The aspect of us handling the springs on our engines isn't really an issue, though.

[grayracer513]

The aspect of us handling the springs on our engines isn't really an issue, though.

You missed the point of pneumatic valve closing altogether.

[1987CR250R]

I didn't miss it, I just like being contrary.

I wasn't talking about using compressed air to open and close valves I was talking about using pressures generated in the engine to open and close valves. Sound travels a lot faster at the whatever000 psi F1 engines used for their valves than the 3 inHg vacuum seen in a normal engine's cylinder at full throttle.

[grayracer513]

The operating pressures are nor supplied by the engine. High pressure pump. Ducati has already used this in Moto GP, but I'm not aware that they currently do.

The speed of sound is a non-issue.

[cwtoyota]

The speed of sound is a non-issue.

You guys are talking about two entirely different issues:

The speed of sound is a HUGE issue in the design of an intake tract and matching valve train.

If at any point in the intake tract the inlet air/fuel mix reaches the speed of sound, a "choked flow" condition can result. This is detrimental to inlet airflow. The engine will feel like the power curve just hit a wall and stopped until those conditions change.

Increasing port velocity is hugely beneficial at any given engine RPM, however if your port velocity is optimized at too low an RPM, your engine will hit that sonic wall unless you take measures to correct this.

The speed of sound is a non-issue in the air or gas controlling a pneumatic valve actuation system because the likelyhood of that air or gas reaching the speed of sound is extremely low given the nature of such a system and associated design criteria.

[1987CR250R]

My point is that with the mentioned valve system, it would rely on positive and negative pressure pulses within the cylinder in order to open and close valves. Well the rate those pressure pulses can travel at are limited. There isn't a lot of time within an engine at 12,000 for any delays to happen.

[grayracer513]

My point is that with the mentioned valve system, it would rely on positive and negative pressure pulses within the cylinder in order to open and close valves.

I don't know what "above mentioned system" you are talking about, but the pneumatic valves in F1 engines and the old Ducati Moto GP bikes relied on no such thing. The air pressure was supplied by a pump external to, and independent of, the rest of the engine.

This is also the case with the much more exotic Honda V12 that had the valves opened by air pressure. The pressure to open and close the valves was supplied by an external pump, and entirely managed by a microprocessor based on crank position, engine speed and load, and other sensor readings. The engine idled smoothly at 1000 RPM, ran smoothly at any speed and load level, and had a ridiculously wide power curve. The speed of sound had not one thing to do with the operation of the system, nor did the compression pressures nor manifold vacuum levels.

[cwtoyota]

I think the "above mentioned system" in 1987CR250R's post is referring to the OP's system that started this discussion.

I agree with 1987CR250R. That "above mentioned system" would run, but would never reach the 12000 RPM range or yeld performance competitive with a contemporary mechanical valve train system.

You pretty much need a mechanical intake and exhaust valve control system of some kind to take full advantage of pressure pulses and the huge performance benefits they provide. A computer controlled system weather electrical, pneumatic or hydraulic is the obvious next step, but the technology just isn't in the mainstream phase yet. A system that reacts to those pulses using their energy to open the valves just cannot give the same performance.

Rotary valves are another interesting area that has been researched, but reliable methods for sealing them seems to be the big pitfall.

[grayracer513]

I think the "above mentioned system" in 1987CR250R's post is referring to the OP's system that started this discussion.

See post #5