Posted on 10/19/2005 10:59:55 AM PDT by Jack of all Trades
The REVETEC Engine design consists of two counter-rotating “trilobate” (three lobed) cams geared together, so both cams contribute to forward motion. Two bearings run along the profile of both cams (four bearings in all) and stay in contact with the cams at all times. The bearings are mounted on the underside of the two inter-connected pistons, which maintain the desired clearance throughout the stroke.
The two cams rotate and raise the piston with a scissor-like action to the bearings. Once at the top of the stroke the air/fuel mixture is fired. The expanded gas then forces the bearings down the ramps of the cams spreading them apart ending the stroke. The point of maximum mechanical advantage or transfer is around 10deg ATDC (the piston moving approximately 5% of its travel) making the most of the high cylinder pressure.
This compares to a conventional engine that reaches maximum mechanical advantage around 60deg ATDC. (after the piston has moved through 40% of its travel, losing valuable cylinder pressure). The effective cranking distance is determined by the length from the point of bearing contact to the centre of the output shaft (NOT the stroke). A conventional engine's turning distance is half of the piston stroke. The piston acceleration throughout the stroke is controlled by the cam “grind” which can be altered to give acceleration to suit a certain fuel and/or torque application. This also allows different port timing on opposite strokes, increasing efficiency on 2-Stroke engines.
The piston assembly slides rigidly through the block eliminating piston to cylinder-bore contact. This reduces wear and lubrication requirements. This also reduces piston shock to a negligible amount making ceramic technology suitable. One module which comprises of a minimum of five moving components, produces six power strokes per revolution. Increasing the number of lobes on each cam to five produces ten power strokes without increasing the number of components. The CCE integrates well with existing power plants and can utilise almost all existing engine technology with increased efficiency.
Summaries of CCE advantages are as follows;
i had an Arctic Cat with a 303cc in it that was a real screamer off the line but no top end. i could kick ass if the straights weren't too long. talked to a guy at an SCCA event once running an RX7 and when ask what his shift point was, he simply said, and i quote... "Whenever the high rev warning buzzer quits buzzing, I DOWN SHIFT." he won his event too.
a few years ago i saw a prototype F-1 engine with a notched cylinder running along the top of the head that acted in place of the valve train with the notches opening and closing over the input and exhaust ports. it was crank powered turning over ten grand too before running into problems. i wonder how it would work on an engine like this that doesn't turn high revs???
Id say you'd need some very hard surfacing to keep it going for any length of time, and that's the slower moving parts. What about the valve train? On a 3 lobed engine, that cam has to turn 3 times for each one revolution. At 2000 rpm, that cam is doing the work of a regular engine running at 6, which floats the valves on a conventional engine.
I haven't looked at what cam system they use, either 1, 2 or 4, but that's a lot of cam to turn. Even if say, that engine maxed out at 3,000 rpm shaft speed, that valve train would run at a punishing 9,000 rpm. If you've ever built a weekend race engine, it takes some doing to keep the valve train together at those speeds, plus expense, and it doesn't last long. The lobe problem may be overcome with some good metallurgy, but I doubt that the valve train issues can be. Not for a commuter car application at least. With 4 overhead cams, it would run pretty good for a while no doubt. It would be a train wreck if something let go through.
I don't know what the limits are for fuel injectors either, but I can't see them being of any practical use at the potential high rates needed. At say 12,000 firings per min, You may as well use a blower and carb and try to burn as much fuel as you can as it flows through the cylinder, LoL
I think they are counting on this engines torque and lower crank speeds than what I'm thinking of. Maybe in the 1000-1500 speed range max.
Yeah - I had that wrong - I was thinking the angles between cylinder banks... but that wouldn't make an x, either (that would have just 4 cylinders)... a 6 would be more like a an asterisk (not the * that I see on the screen when I type, but the six-armed one I have on my keyboard)...
an X-4 would still have some terrible vibrational modes - either the pistons all move to the top half of the x together and then to the bottom half, or they move left-right together (if any of that makes any sense). In any case, you have a lot of reciprocating mass moving in the same direction without a counterbalance. Now maybe you can counterbalance the shaft the cam lobes are on and fix it..... But I doubt an X-4 would be any better than a flat-4...
Thought you might be interested ping
Piston ported engines (2 strokes) have been around for a long long time.
I'd say this engine would work good as a 2 stroke. Lower rpm and more torque, which 2 stroke lack. Most good 2 strokes today run around 9,000 rpm. This engine would run about 1/3 of that as a 2 stroke but produce much more torque.
yeah, now combine it with the elimination of all the parts in the valve train and you're talking about an engine with very few moving parts and the piston assembly being the only start/stop moving parts...
The only thing that you have to do to keep them running is regularly changing the oil and maintaining the oil level between changes. Because of the unusual layout of the engine, as compaired to a piston engine, a metering pump injects oil into the intake to lubricate the apex seals. There are also three combustion cycles per engine revolution per rotor. The Mazda RX8 has a rotary engine with the exhaust ports moved to the sides of the rotor housings, so the apex seals never go over the ports. Unboosted they now make about 240HP. Also, Mazda is supposed to be introducing an direct-injection rotary (posibly part of a hybid engine system)at the Tokyo Motor Show at the end of this month. Long live the Wankel!
A few things to note here:
1) Mercedes worked on the Wankel for a while in the 60's...
( one of it's prototypes appeared regularly in the series UFO)
2) John Deere built a number of Wankels in the 80's in the SCORE series of engines (Stratified Charge Omniverous Rotory Engine)
3) My worry about this new engine would be lubrication. I don't see how the Piston Bearings or Rings can be force lubricated in this configuration. In most conventional engines, pressurized oil is fed through the crank to the big end bearings. Some is forced out into the pan, but some goes through the connecting rod to the small end bearing. This then is forced out and sprays the cylindar walls. The Rings in his engine may have a direct spray from somewhere in the block, but those bearings might find themselves on too lean a diet.
Just a few thoughts.
A few things to note here:
1) Mercedes worked on the Wankel for a while in the 60's...
( one of it's prototypes appeared regularly in the series UFO)
2) John Deere built a number of Wankels in the 80's in the SCORE series of engines (Stratified Charge Omniverous Rotory Engine)
3) My worry about this new engine would be lubrication. I don't see how the Piston Bearings or Rings can be force lubricated in this configuration. In most conventional engines, pressurized oil is fed through the crank to the big end bearings. Some is forced out into the pan, but some goes through the connecting rod to the small end bearing. This then is forced out and sprays the cylindar walls. The Rings in his engine may have a direct spray from somewhere in the block, but those bearings might find themselves on too lean a diet.
Just a few thoughts.
Imagine the load on the starter as well. It would have to turn the lobes somehow, not the output shaft. Even then...
They never show it being started on the video, nor do they let it idle down. With extra stiff valve springs (I see they use 4 cams on their test engine) It must be a bear to turn over.
Good point. The piston pairs would have to be run in sets of twos.
Your post reminded me of a friend of mine who lost both buttocks in a shark attack.
He still dives, and doesn't bother to get out of the water when there are sharks around.
He figures he doesn't have an asterisk...
No No, you've got to gut em, strip everything out cept the block and head, use a later 1500 cc motor and shave 60 thou off the head, dual webers, 40-80 cam, headers, 50 series tires in front, 60 series in rear, and you got a pocket rocket that sticks like a go-cart. But ya gotta get rid of all the emissions and safety crap. Its easier now that they can be registered historic, avoid all the inspections etc. and parts is way cheaper now than when they were new.
marker
There was nothing simple about the design of the Wankel engine. The rotor and chamber contour were very precise surfaces which require tighter tolerance control than a piston engine.
It's down fall was two fold. The apex seals required to separate the combustion zones were problematical due to the high surface running speeds of the tips of the rotor and the difficulty of getting any lubricant to them because combustion pressures alternated from one side to the other as the engine turned over. The second problem related to the surface geometry of the combustion space. For it's displacement any Wankel will have a greater surface area in it's combustion chamber then any equivalent piston engine. The larger surface area tends to quench the combustion process. The result of this is lower combustion flame temperatures with a corresponding increase in emissions of unburnt hydrocarbons. That also means that gasoline is going through the engine without burning which means mileage is less than optimal.
Versions of the engine have been used as rotary air compressors with good result, though as an engine it's more of a technical novelty.
Regards,
GtG
Felix Wankel controlled the licensing process for his patent and demanded that the engine be used in a production car within a set period (I recall something like 5 years). You had to commit to building under that schedule before he would sign a license. Mazda signed on and modified one of their existing small cars to meet the requirement while they continued development for several years. Curtis Wright in the US got a license for large, multi rotor aircraft engines. They never left the ground (snicker). I think Mercedes had a license. They were interested in the technology but not production so they stuck a triple rotor engine in a sport/racing car and called it production. Sticker was around $200,000 (OXYGEN PLEASE). Please note they didn't sell many of the fifty they built to fulfill the license. I saw a silver gull wing coupe at Concourse Motors on Silver Spring in Milwaukee that they had just rolled off the truck, I was ogling it before they got the ropes up. I would have given some body parts to take it out for a spin, like that's gonna happen.
That's about all the history I recall.
Regards,
GtG
That's really cool. Heaven forbid that American auto makers engage in any inovation. They'll probably thumb their noses at this.
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