Electromagnetic engine valves

[Jerboy]

Someone brought this up on the off-topic forums. If it works, it can provide greate control over valve timing and give all the crankshaft power to wheels, but I personally think this is a very technically demanding project. According to my math, a valve needs to be completely opened like you would with a valve compressor within 350µS.


To summarize it, each solenoid must be:

Small enough to be able to include one for every valve.

Not cost $1,200 a piece

Able to withstand temp and mechanical extreme found by engine for many years

Able to fully actuate the valve within 750µS

Have low enough inductance to allow fast response to 1,350Hz pulse

Able to take this at least 133 operations a second for hours and should not require maintenance for years.


Anybody have technical comments to add to this?


I'm pretty sure I calculated anything right, but if you see anything wrong please correct it.


So far this is what I came up with:

First of all, let's take a look at the four cycles

E=exhaust, I=Intake
TDC=Top dead center, LDC=Lower Dead center

Intake cycle: piston starts at TDC, intake valve open as soon as possible and closes before or at the moment piston reaches BDC

Compression: I and E closed, piston reaches TDC

Power: I and E closed, piston rolls off TDC slightly and ignited at certain timing

Exhaust: immediately before or right when piston reaches BDC exhaust valve opens, then immediately switch over to intake cycle.

The engine has exactly half a revolution to complete each intake and exhaust cycle. In order to effectively complete each cycle, the valve must be opened as soon as possible at the beginning of each cycle.

Valve only operates on the first and the fourth cycle.

Let's say within 20% of the cycle time, which is 1/10 of a revolution(36°).


First of all, the valve springs needs to be very strong to give reasonable closing response time. To open the valve you have to counter the resistance of spring and the momentum of the valve. According to F=m * a, greater the acceleration greater the force you need. I'd rule pneumatic valve out at this point since air is too cushiony in it's piping and drags the response time too long.

At 8,000RPM, crank shaft turns 133 times(532 individual cycles) a second. In order to completely open the valve within 1/5 the cycle time, valves needs to be capable of completely opening within 1/10 the revolution.

With those values, valves can take no grater than 752µS to go from completely closed to completely open position. Give it a little headroom and make that 750µS. The driving solenoid will be powered with approximately 1,350Hz pulse.

The solenoid must be capable of generating a force great enough to operate a valve within 750µS, have good enough inductive response to 1,350Hz pulse is capably mechanically and thermally to repeat this cycle 133 times every second.

Those solenoids will use alot of inrush power and each one might even need a farad capacitor.


Additions:

The energy required to open each valve can be calculated by 1/2kx^2 +thermal loss within the spring and acceleration applied upon each valves.

Required mechanical power is total energy per stroke/750µS. I wouldn't be surprised it's in orders of multi kilowatts.

Required electrical power is total mechanical power x solenoid efficiency.

Obcourse the device for such high current, high speed swithing brings another difficulty.

 

[Eli]

Hmm.. Is that accounting for lift and drop time, though? Perhaps you could have the valve pop open instantly.. but it would at least need to be let down somewhat gently... lol

 

[Eli]

Another thing to take into account is that 8,000rpm is realitivly low for some engines...

What would you figure for say, 12,000rpm? 200cycles/second... :Q

And if you really wanted to get extreme.. 16,000rpm .. 266cycles/second .. lol..

 

[puffpio]

16000 rpm isn't too extreme because the first applications of these things would be in motorsports. Then once the technology is proven will the cost reduction effort kick in and a consumer version should come about

 

[dnoyeb]

I think it can be done and not too hard either. Remember that lifters are on a pole. You have a long pole in which you can wrap a winding around. That gives you a long stroke for your electro magnet. That means you can get lots of power and quick response times. Further, you can reduce significantly the spring force since the electromagnet can simple reverse polarity to bring the valve back down. Its just a simple solenoid and I think you said as much.

Also lifters use lots of friction. Thats eliminated. Less heat because I believe the electromagnet will be more efficient that the sliding lifters, since there is no contact. Lifters are a main source of oil requirement too. Less oil burn. Easy to tune, ease to adjust timing. Its excellent.

Man, that will be the first automotive improvement in 20years that didnt make maintainance harder.

Also, I suppose the generator belt will have to be a generator chain..The Generator itself will have to gain size again. You can shoot cold starting down another notch. More than likely this will be integrated only in light of the new 42V technology.

Seems similar to what ABS valves are doing.

But not you have EMF going strong in the engine, and I imagine AM radio will be a thing of the past

 

[Jerboy]

I forgot to include some mean of preventing the valves from hammering shut. The valve follows along cam lobes and alot of valve related modification is done by alterning the lobe shapes. I'm not sure if it is important to imitate the mechanical valve train motion such as having the valve open to x% at x° crankshaft angle.

Using floating solenoid over a longer valve stemp as someone else mentioned means close to no spring assistance. To freely control, including stopping, slowing, reversing, and alter the velocity without mechanical contact, it will necessate a very sophisticated solenoid control algorithm. The solenoid must have low enough inductance to allow rapid current rise time, yet remain high enough to create magnetic field required to modulate the valves.

 

[Evadman]

Getting a valve open as quick as possable is what would be best. The problem with current engines /and spring baised valves is that the lifters can only go up so steep an angle. Lifters used to ( and some still are ) solid or hydralic. In high RPM or for radical cam profiles, the lifters have rollers on the bottom so they can "ramp up" faster and get that valve to full open.

The problem with solonid baised valves is the speed at which they hit on the seat. ( when closing ) The pressure is so strong, that it shatters valves. as soon as they figure out the "landing" we will be all set. Controlling the exact time the valves open would have a huge impact on MPG and power. Look at what honda could do with very minimal valve timing ( VTEC ) A solinoid would be perfect.

The problems don't quite end there tho. With a mechanical valve train, a valve's normal position would be closed. It is kept that way by the spring pressure. The solonoid would have to be "on" all the time, pulling towards the head. Even with the engine off. They sould probably use a light spring, but that woud defeat the purpose Also, the timing has to be PERFECT. If a spark plug misfires, you lose power. If a solonid valve misfires, the valve colides with the piston = engine death.

 

[KokomoGST]

Well, seems like the solenoid system would work best as a simple replacement for the cams
but Evadman brings up some good points... however, I think with todays materials, you can use stronger valve springs to reduce the possiblity of valve float (piston slapping against the valves). Usually, it's the "weak" valve springs that are the culprit for valve float. Most valves are OK with the return pressure. Rather than trying to vary the height of the valve opening/duration completely through the solenoid, you could try a mechanical hybrid system similar to BMW's Valvetronic system. You can ditch that throttle plate while you're at it to reduce pumping losses. The solenoid wouldn't have to change it's timing, but the height&consequently duration of the secondary control arm it sits on could it that instead. Thus you don't have to worry about valves cracking as much.

Valvetronic

My idea is purely a ripoff, but hey... BMW's got an ingenious idea... the solenoid system would improve upon it, creating even more tunability for valve control.

 

[highwire]

Jerboy -"At 8,000RPM, crank shaft turns 133 times(532 individual cycles) a second. In order to completely open the valve within 1/5 the cycle time, valves needs to be capable of completely opening within 1/20 the revolution"

Probably a factor of 2 error here. A 1/5 cycle time would be 1/10 of a rev. - or 36 degrees.

Never-the-less, when I heard of the electromagnetic valve, I cringed at the challenges it would present. It is obvious that others here appreciate the problem as well.

A very basic cam profile would be a sine squared function where Tclosed - Topen = pi radian, that is, 1/2 a sine^2 wave from 0 to 180 degrees of the wave. This is then fitted to the opening and closing points of the valve cycle. To increase the opening and closing rates, the 3rd harmonic is added. This will usually give good area with the lowest forces on the mechanism. Adding the 5th or higher frequencies will increase the area but with much higher forces required.

Using this approach and a small valve opening duration of 180 deg means the mechanism must produce motions with frequencies components of 6 times the crank frequency or 133 X 6 = 800 hertz at 8000 RPM. Still a very big challenge.

As evadman said, a soft landing for the valve is a must - or the valve breaks in a few hours.

Dunno, I'll watch with interest to see if/how they do it.

 

[Jerboy]

<< "How so? Intake=90, compression=90, power=90 and exhaust=90"

A 4 cycle engine takes 2 revs to get it done - 720 degrees or 180 per cycle. >>



Oh duh!
I'm such an idiot

 

[highwire]

"How so? Intake=90, compression=90, power=90 and exhaust=90"

A 4 cycle engine takes 2 revs to get it done - 720 degrees or 180 per cycle.

Edit to jerboy edit: Idiot? Hardly. Just typical of genius. Keep it up.

 

[bizmark]

Hmm just a random thought from a guy who likes cars but doesn't know as much as you guys obviously do

The new electro-dampened shocks that I think Cadillac has developed might be applicable to this, in particular to slow down the valve on its return to the closed position. These shocks are supposedly able to calibrate at ultra-high frequencies, and I imagine that on the scale of the relatively tiny valves (rather than big shocks) they could get the timing pretty perfect. Maybe they could use something like this to hold the valves closed too while the engine is off, if they could have enough dampening to halt motion completely.

Of course, this is adding a whole layer of complexity, and you'd have to have the damping adjustable from absolute 0 (so that the solenoid can do its work as quickly as it needs to) to very firm, but hey, this was just wild conjecture on my part.... seem like it might be possible?

Also, is it that great of a problem to adjust the current through the solenoid in order to bring the valve to a nice, smooth stop rather than to an immediate jerking halt? Or are solenoids more binary than analog, and I just have no idea what I'm talking about?

 

[Evadman]

KokomoGST:

There are a few problems with regular springs.

#1 off is easy. The pressure required to push them open enough ( and the friction back through the valve train ) is taxing to the engine. ( see #2 ) That is HP we want at the wheels.

#2 is only for high revving engines, and for racers. ( So I doubt you know ) is that metal springs have a certain frequency that can cause them to "vibrate" off the seats ( another kind of valve float ) what happens is that for a normal steel spring will go into this excited state at somewhere between 7 and 9k RPM. That is WELL within what engines can do today. That is one of the reasons ( besides weight ) most racing engines use Titanium valves. Titanium will not "excite" untill over 20k RPM ( I have never seen a production motor that cound reach this, but It is not out fo reach for a small stroke, large bore ( over square )engine such as a F1 car or motorcycle ) They have come out with dual and triple springs ( where more springs with a different LB/IN rating are used on the same valve ) to attempt to minimise this specific kind of float. Also, if your cam has to push 6 or 7 hundred lb's to open the valve, it is going to need some serious lube protection. ( 500 or so is about max that you would go on a street engine, with 320 or so being closer to normal )

#3 ( and this is the big reason why this is being worked on ) If you can control When a valve opens, you can totaly change the HP / Torque / Emissions of an engine. If you are just crusing down the EXPY, why do you need the valve to open all the way? Or even at all? ( GM is working on a few engines that can "turn off" one side of an engine for better economy ) Look at honda. There VTEC system uses 2 cams. basicly under WOT ( wide open throttle ) at a certain RPM, the cams switch ( Actually, the lobes / lifters switch, but who am I to argue ) form the normal "economy" to the High Performance. If you could control the valves like you do the fuel injectors, and have the vales set on some kind of map ( again like A/F delivery ) you could make huge HP and Torque as you cound change the whole way the engine works. ( one of the reasons a 350 chevy can make 130 HP with a crappy cam, then make 300 with a better cam )

Wbwither:

The shocks on the Caddy are made to work with a long throw shock, and shocks move at a snails crawl compaired to a valve ( A valve is probably over 1000 MPH, but Jerboy would have to get out the slide rule on that one ) Also, if I remember correctly, those shocks are fully mechanical ( I will have to look into that, not 100% sure ) they use a floating Inertia disk that opens and closes the holes that are in the piston, so more or less oil ca flow though for various damping effects baised on the speed at which the shock is expanding or contracting. Unfortunately, unless the valve covers were full of oil, I dont see how that could work. On the power to the soloniod, I am not actually sure on the on/off nature. I would assume there could be some dampning possable, but for how the solonid is moving, to deceleratie, it would have to turn back on and apply force as if the valve bere being pushed open. I am not sure how the latent magnetic fields would interact with the newly forming ones. Anyone know how long the magnetic field takes to break down and reform?

A valve stem with some elasticity might work tho. If the valve stem streached as the face hit the head, it may be enough to absorb the shock. But I do not know on the durability of such a valve. Might fatigue real fast.

 

[Jerboy]

<< A valve stem with some elasticity might work tho. If the valve stem streached as the face hit the head, it may be enough to absorb the shock. But I do not know on the durability of such a valve. Might fatigue real fast. >>



I don't think valve stem can prevent much damage. The valve head itself has a mass. The valve must be decelerated magnetically immediately before touching the valve seat. No matter how flexible/stretchable/elastic the stem is, valve head itself posseses kinetic energy when it is moving. All the kinetic energy will be dissipated as the valve head collide into the valve seat. One possibility I have not thought about until now is valve seat/head won't absorb all the kinetic energy and will simply bounce off after a hard collision. The collision energy increase in square with the engine speed. Valve system on 16,000RPM system is only given half the time allowed in a 8,000RPM system. The magnetics have to be able to manipulate four times as much kinetic energy.

 

[Evadman]

Good point jerboy, didn't think of that.

 

[dnoyeb]

GM is not working on such an engine. It was released several years ago in their Cadillacs. I have forgotten what they called it, but it left some valves closed so the car would run on fewer cylinders. I don't remember how well it did, but evidently not well enough or im sure I woudl still hear GM tooting their horn.


Since the valve opens and closes in a rythm, spring assist would be excellent. Think bumble bee and not birds. Bumble bees dont use their muscles for each flap of their wings. Their chest cavity is elastic. They draw their wings back, and let them snap free, and their wings bounce several flaps from 1 muscle pull. So their strumming their wings like a guitar string. Saves them tons of energy, and yes, the must have a sophisticated strumming algorithm. Somebody tell me this crap all started by accident and their is no God! Bah


This principle could be applied to the valves. they could esentially be given a bouncing drive by one set of coils, and a cushining fource to prevent valve slap and enhance opening distance could be applied by a 2nd coil. So the 1 coil is the strummer, and the 2nd coil is the nudger.

 

[PullMyFinger]

Evadman,
Actually, Honda built a motorcycle in the '80's with a redline of 22,000 rpm, I believe it was called the NS-500. Technically it was a V-4 but it had oval pistons, two connecting rods per piston, 8 valves per cylinder, and a stroke of right around an inch. Honda originally wanted a V-8 but the rules didn't allow it. The bike was built to prove that a 4 stroke could compete against the 2 strokes in Formula One, thus the reason for spinning twice as fast as a 2 stroke (same number of power pulses per unit time). One rider actually stated that it didn't really start making power until 17,000 rpm.

Regarding poppet valves, I've always felt that there has to be a better way of controlling the flow into and out of an engine. Just think of all the inefficiencies of the 4 stroke engine; axially actuate a valve from rest and open it as fast as possible, take a mass of air/fuel from rest and try to accelerate it as fast as possible past a valve head and into a closed volume, stop that air/fuel charge, do some work on it, then axially actuate another valve from rest, take the exhaust charge from rest and try to shove it out of the combustion chamber as fast as possible. Start-stop-start-stop-..... And at each start and stop point, there are significant amounts of energy being transferred with no real contribution to power production.

I've always thought that a rotating spherical or cylindrical "valve" with a large opening through the center would allow much better cylinder filling and eliminate many of the problems with reciprocating valves. Of course the rotating valve would create more frictional drag than the valve seals on poppet valves. However, this could be offset because there would be fewer frictional losses due to the elimination of rockers, followers, springs, etc. A major obstacle would be sealing the spherical or cylindrical surface against combustion pressure, this is where a poppet valve has an advantage.

Just a thought.

 

[highwire]

dnoyeb -

A friend has a really nice old Cad with the 4-6-8 V8 engine that you refer to. That engine simply disables 2 or 4 of the 8 cylinders depending on load to keep the BMEP and therefor the efficiency high at light loads. The added complexity/cost may not have been worthwhile or they may have simply moved on to smaller engines. But, you are right, they dropped that idea. The idea discussed here is a much more demanding one, to actuate the valves under complete computer control by means of an electromagnetic mechanism, a far more ambitious goal.

Your idea of an elastic mechanism - a la the bumble bee - to store the required energy to move the valve is interesting. But, how to do it is not obvious. For MOST of the valve cycle, the valve just sits there hopefully motionless. In present designs, any extra flexibility/elasticity is VERY VERY detrimental to valve train performance. God's bee just vibrates at a fundamental frequency. That is easy. Also, the African super runners are designed with elastic muscle to a greater extent than others which is an obvious advantage. But, again, a motion more like that of a bee wing than a valve.

However, if the electromechanical system was very efficient, it would also recover energy as it stops the valve's motion - dynamic braking - no resonance required. Now we have valve energy storage as well as control.

We will just have to see how it evolves.

 

[zephyrprime]

<< GM is not working on such an engine. It was released several years ago in their Cadillacs. I have forgotten what they called it, but it left some valves closed so the car would run on fewer cylinders. I don't remember how well it did, but evidently not well enough or im sure I woudl still hear GM tooting their horn. >>


They dropped the idea many years ago but now they're bringing it back! This time around, they have the benefit of computers to control the system.

Also, aren't car companies already working on some sort of electronic valve system? I'm sure that I read about it in popular mechanics or something.

 

[dkozloski]

Why not forget all about poppet valves. The penultimate aircraft piston engine was the Napier Sabre sleeve valve engine. This powerplant used sleeves that rotated and reciprocated as the result of a crank mechanism to make ports in the sleeves and cylinder walls match up to provide valve action similar to a two stroke engine but operating on the four stroke cycle principle. This engine was so intense that the cylinder heads were made from solid copper to carry away the heat. One variant was 2200cu.in. displacement, turned 5500RPM, and developed 4500HP for 75 hours straight without shutting it off. The engine layout was two flat twelve-cylinder crankshafts parallel with each other in one cylinder block and geared together on one end. In comparison the American Pratt & Whitney R2800 operated at a peak BMEP of about 180PSI to developed 2000HP. The Napier Sabre didn't exhibit distress until 450-500PSI BMEP was approached. This engine was used to power the fastest piston engine fighter of WWll, the Hawker Tempest. This aircraft could easily catch a V-1 buzz bomb in a tail chase while all other allied aircraft required a diving advantage to intercept. Another feature of this engine was that it had a "one lever control" for throttle, mixture, and propeller; only recently reinvented and incorporated in modern aircraft as FADEC. Because this powerplant was so complicated and expensive to operate it went out of service immediately at the close of hostilities, was rapidly forgotten, and replaced by gas turbines. There is only one sound recording of this engine known to exist but it will make the hair stand up on the back of your neck if you love the beautiful sound of an engineering masterpiece. Go to tempest page

 

[Evadman]

dkozloski:

It sounds like you are saying that engine uses a round cyl type of valve with a hole through the center. The spinning valve would let in air/fuel when it lined up between the intake manifold and the engine cyl? Kind of like a gas ball valve?

That would be much more efficient, as the spinning motion does not have to be halted and spun in the other direction. ( like a poppet valve ) Do you have another link besides the one you posted where we could find more out about that engine setup?

 

[highwire]

zephyrprime -
" This time around, they have the benefit of computers to control the system.

GM began using computers in production cars very early, an amazingly short time after the micro p was available. They were in their 2nd or 3rd generation or so when they introduced the controlled valve Cadillac 4-6-8 engine. So, if they are going to try again, it will just be a bigger, better computer.

dkozloski -

Being a pilot and aviation fan, I have to pick up a couple of points. The captured FW-190 early in WW II caused a commotion in the design of subsequent aircraft. The 190 did have a combined single power lever and many other features that were incorporated by others. The FW-190 was seen by many as a revoutionary design and dominated the Tempest developement. The Grumman Bearcat - similar to the Tempest and also influenced by the 190 came too late for WW II. Both are awesome piston aircraft.

The other , I think better Tempest engine, the Bristol Centaurus, a radial aircooled design, is also a sleeve valve engine. What the sleeve valve's downside is I don't know exactly, but it sure sounded good, too,
when I saw a demo a few years ago.

Which piston aircraft was the fastest of WW II is muddied by the altitude thing. The Hawker design just may have been the fastest on the deck. The brute force of 3000+ hp could get it done. But a Dornier twin engined push- puller design was conceded to be the fastest at altitude - near 500 MPH. Oh, its engines used poppet valves. It's hard to get away from those old things.

 

[dkozloski]

The cylinder block had ports in the side like a two stroke motorcycle but instead of the piston passing by doing the opening and closing, the sleeve with similar holes in the side was rotated back and forth and up and down by a crank and rod ball-joint arrangement. In fact some of the holes in the sleeve acted as both intake and exhaust ports which facilitated cooling. The porting was extremely efficient because there was no valve stem or head in the way like a poppet valve. Throughout the life span of the design the biggest limitations in performance were fuel of a sufficiently high anti-knock rating and propellers that could couple all that power to the air. I was told two years ago at the Reno unlimited air races that someone is working trying to get one of these monsters flying. I just did a Google search on "Napier Sabre" and there is a wealth of material out there.

 

[dkozloski]

Highwire, the Centaurus, because of its air cooling quickly reached thermal limits when abused. I noticed at the Reno air races that all the Sea Furies had been re-engined with C-W R3350's or P & W R4360's. One guy I talked to said that someone was trying to get a Tempest V with a Sabre engine flying. The FW 190 like the ME 109 was a tiny little airplane about half the size of a Typhoon or Tempest. The FW I saw up close at the Garber Restoration Facility seemed hardly bigger than a Beech Bonanza and the engine looked like a license built P & W R1830. The later long-nose TA-152 variant was water cooled with a Daimler-Benz engine. The Centaurus was used in commercial flying and had good durability but was in no way the performance equal of a liquid cooled Sabre. There were a lot of stories about the pusher-puller Dornier but I never heard of one going through the traps with a stop watch present. Most of the references I have seen on the Tempest have the top speed above 460MPH measured at WEP "throttle through the gate".

 

[highwire]

dkozloski-
You are right about the Sabre being one awesome piece of machinery. And I take your point about it maybe being THE ultimate for Reno work. These engines are pulling way over their normal ratings there and the Centaurus being heat limited makes sense.
I did see a Centaurus powered Sea fury a while ago and it was impressive - a leg up on a P-51, I thought. But if a Sabre engine could hang together and somebody gets the radiator and prop right, it might be hard to beat at Reno. Can you imagine doing a major on that 24 cylinder monster though?