Electric Valves

[legion]

So I was thinking...

A camshaft is essentially an analog computer. It controls when a valve opens, how far, and for how long. Some fancy systems like V-tech and Variocam are designed to allow "the program" to be altered on the fly, but they are really just fancier analog computers.

In theory, it is possible to eliminate the camshaft and have the engine computer directly control the valves. This would create an engine where valve timing could be continuously tuned to either peak power or peak efficiency, and move between both seemlessly.

So, why is this not happening?

I understand that a cylinder head is a brutal environment. It is hot, it is full of oil, it vibrates. Is there some sort of electric (or hydraulic) control system that could be used to actuate valves on demand?

[singpilot]

It's my understanding that the engine in my Prius has valves controlled by the computer. Atkinson cycle, I think. Was told the starting process involved spinning the engine to 1000?RPM, valves open, and as soon as oil pressure was above min, the valves were closed (operated) and fuel introduced for the start.

Like that? I suspect it is a system that is still a camshaft, but with a way of holding all the valves open without pistons hitting valves.

[MFAFF]

Try F1... air pressure used to activate the valves....at 18K rpm cams not happy...

[Joeaksa]

Agree with Mfaff, Formula One has used them for years with speeds up to 20,000 rpm. Course everything is hand built there and cost is no object in many cases...

Joe A

[oldE]

Also, I think it was Ford which put a head on a 4 cylinder Ranger a few years ago, in which the valves were actuated by electric solenoids. That gives you infinitely variable valve timing, but the problems with the prototype centered around accelerating the valves fast enough to get the cylinders filled and emptied on time. With big enough magnets/colis, you could do it.
Variable valve timing has developed pretty well with mechanical means, so there aren't too many applications for the electro-route, but...
The best spin off from this technology is the ability to eliminate the starter motor. The computer just checks which cylinder has passed TDC, squirts in some gas (with its high pressure direct injection), closes the valves on that one and gives it a spark. Voila! Who needs a starter?
Les

[Jared at Pelican Parts]

It has been done in the past with mixed results

Some aircraft piston engines are even using oil pressure activated valves.

[Rondinone]

It will likely be a part of the next generation, homogeneous charge combustion engines (HCCI). They will dispense with the throttle plate and instead throttle using intake valve timing for high efficiency over a low rpm range. Perfect for driving a generator for a gas-electric drivetrain.

[Joeaksa]

Originally posted by Jared Fenton
It has been done in the past with mixed results

Some aircraft piston engines are even using oil pressure activated valves.

Which ones? Assume its an experimental engine?

The FAA and aircraft engines are still in the dark ages for the most part. We are still using magneto's for ignition (old pre-war tractor tech) and compression ratio's in the 7-1 range.

High performance does not exist in 80% of the piston engined airplanes today.

JoeA

[Jared at Pelican Parts]

Some of the older helicopter engines, like Franklins. I'm no expert on piston driven planes, though.

More interested in jet engines

I dont see how a piston driven airplane could be high performance. Correct me if im wrong, but dont they usually only spin up to 3-4000 RPM?

[snowman]

THe first "hot rod" engines were for airplanes. Nitrous and whatever it takes for the ultimate power. With reliability so the airplane dosen't crash. Fighter aircraft are the ultimate "hot rods" either piston or jet.

[Joeaksa]

Originally posted by Jared Fenton
Some of the older helicopter engines, like Franklins. I'm no expert on piston driven planes, though.

More interested in jet engines

I dont see how a piston driven airplane could be high performance. Correct me if im wrong, but dont they usually only spin up to 3-4000 RPM?

Do not believe that Franklins had hyd valves...

Typical aircraft piston engine turns max 2600-2700. Problem is that the prop is bolted directly to the crankshaft and any faster than that and the tips of the propeller go supersonic. This is not good and causes them to lose lift (thrust) and also it vibrates, causing pieces to eventually fall off, like tips of the prop. This results in an imbalance and then bigger pieces fall off, like the engine, then the plane goes down.

There are a few gear driven engines, with a gear box that allows the engine to run at a higher rpm (more power) while the gearbox allows the prop to remain at slower speeds, but these are few and far between. The Continental GTSIO-520 on the Cessna C-421 is one version of this type of engine.

Joe A

[Joeaksa]

Originally posted by snowman
THe first "hot rod" engines were for airplanes. Nitrous and whatever it takes for the ultimate power. With reliability so the airplane dosen't crash. Fighter aircraft are the ultimate "hot rods" either piston or jet.

This is possible but the majority that you are referring to are in the experimental catagory.

NOS may be used in some race planes but have seen it only at the Reno Air Races and used only on a 15 minute race. The tanks needed for longer operation are far too large and heavy. By in large they make their power these days by running huge amounts of boost (120 inches) with very special fuels on the old WW2 transport engines.

The FAA mandates that any engine that is used in a certified airplane has to comply with a "Type certificate data sheet" and the limits on this are very strict. Lower compressions and turning low speed (prop limits) as well as magnetos for ignition in 99% of the cases so we are back to tractor era equipment.

Joe A

[snowman]

I think that you will find that the fighter planes used nos extensively. They were the ultimate, price is no object, and your life did depend on them, hot rods. Every hot rod or dragster out there did not preceed the airplane engines, the airplane engines preceeded the dragsters and all others.

[rick-l]

Originally posted by MFAFF
Try F1... air pressure used to activate the valves....at 18K rpm cams not happy...

Are you sure the compressed air isn't just the return spring? I think they still have cams

Electric valves? That would be a big piece of metal to move like a solenoid.

[Jared at Pelican Parts]

Originally posted by Joeaksa
Do not believe that Franklins had hyd valves...

Typical aircraft piston engine turns max 2600-2700. Problem is that the prop is bolted directly to the crankshaft and any faster than that and the tips of the propeller go supersonic. This is not good and causes them to lose lift (thrust) and also it vibrates, causing pieces to eventually fall off, like tips of the prop. This results in an imbalance and then bigger pieces fall off, like the engine, then the plane goes down.

There are a few gear driven engines, with a gear box that allows the engine to run at a higher rpm (more power) while the gearbox allows the prop to remain at slower speeds, but these are few and far between. The Continental GTSIO-520 on the Cessna C-421 is one version of this type of engine.

Joe A

Was actually talking about jet engine imbalance the other day with my family's Tom Hagen (no other way to explain it) He's an engineer for Qantas, over here from Australia, coordinating setup of newly leased LAX hangars. Day he got here, we went to see Mojave airport. "yea, worked on that one.. that one too.." reading the serial numbers. Top bloke.

Trying to visualize mutiple transonic shockwaves affecting airflow over the wing. Thank you for the new perspective. You owe me ten minutes of life

Would higher performance aircraft, say something like a P-38 or maybe a modern aerobatic plane have to run at even less RPM because of dives, banks and such? or is that where a variable pitch prop comes in? Obviously not on the P-38.

What sort of engine mounting, dampers? solid? would say a DC-3 have in comparison to a high performance prop? wondering just to what level of tolerance is aceptable and what is available?

[2.7RACER]

The present camshaft is a simple, reliable device to control intake and exhaust valves.
Why would you want to replace a hunk of metal with more parts?
A camshaft doesn't need electric power. It works at temperatures below zero to temps well above boiling water.
My '76 911 camshafts have worked for almost thirty years without failure and could go longer.
It accurately opens all six valves on one side at rpms up to 6,500 RPM on my engine. A lot higher RPM's with better springs and lighter valve trains.
The valves work under conditions that would make hell look like a resort. High temps, over fifty cycles per second, then seal and withstand several thousand pounds of pressure and fire.
This highly developed system just doesn't get the respect it deserves.

[Joeaksa]

Originally posted by snowman
I think that you will find that the fighter planes used nos extensively. They were the ultimate, price is no object, and your life did depend on them, hot rods. Every hot rod or dragster out there did not preceed the airplane engines, the airplane engines preceeded the dragsters and all others.

Out of the factory and in the military, none of the fighters used NOS. In the air races, yes this may be the case.

JA

[Joeaksa]

Originally posted by Jared Fenton
Trying to visualize mutiple transonic shockwaves affecting airflow over the wing. Thank you for the new perspective. You owe me ten minutes of life

Would higher performance aircraft, say something like a P-38 or maybe a modern aerobatic plane have to run at even less RPM because of dives, banks and such? or is that where a variable pitch prop comes in? Obviously not on the P-38.

What sort of engine mounting, dampers? solid? would say a DC-3 have in comparison to a high performance prop? wondering just to what level of tolerance is aceptable and what is available?

The P-51 was the first allied airplane to get near supersonic in flight and did that only in a dive. It would get near the transonic area and the flight controls would usually lock up, usually resulting in loss of the airplane.

The fighters (lumping them in because they almost all were about the same in this area) would get near supersonic on their prop tips, especially in a dive where the engine would be able to run as fast as possible. Even todays airplanes, like a Cessna C-206/7 are very loud because the prop tips are nearing supersonic on takeoff. In a dive most prop airplanes have to reduce power to keep the RPM's in the "green" range.

Regarding the engine mounts. Their were two types in the piston type of airplane. The Spit, P-51, P-38 and later FW-190's on used a "bed" type of mount as their engine was a watercooled inline V-12 that sat in a frame.

Two versions of a inline water cooled engine, the P-51 and P-38:



Notice how thin the engine nacelle is? Smaller size of the front of the engine made it thinner, which made the plane faster.

Why not all planes like that you say? One bullet from a rifle into the radiator and the plane is down. Radial engines have been known to have an entire cylinder and head shot off, blowing oil out everywhere and still return to base, plane and pilot in one piece. Any airplane used in ground support for the troops that was watercooled always was worried about the "golden bullet" that would bring them down, while the radial engined planes did not have this worry.

The P-47, F-4U, FW-190 (early radial versions) had radial engines that had conical mounts.



A better view of a aircraft radial engine on a ford Trimotor:



Finally, regarding shock waves over airplanes and props, look here:

[1967 R50/2]

Actaully, there are lots of engine designs which don't use poppet/reed valves OR a camshaft.

Here is one: http://www.coatesengine.com/technology.html

Kinda makes solenoid controlled valves look over complicated and un-necessary.

[Wrecked944]

Originally posted by legion
In theory, it is possible to eliminate the camshaft and have the engine computer directly control the valves. This would create an engine where valve timing could be continuously tuned to either peak power or peak efficiency, and move between both seemlessly.

I've sometimes wondered the same thing. I knew about the F1 hydraulic system. But an electromagnetic system would seem simpler IMO. In theory, if you could control the valves with the ECU, would it also be possible to eliminate the throttle and control the RPM's using valve timing and spark?

1967 R50/2: That's a very cool link!