The Revetec Controlled Combustion Engine

Revetec Website ^ | 10/19/05

[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;

• approximately one quarter the size and weight of a conventional engine (for similar applications) combined with improved output substantially increases power/weight and torque/weight ratio.
• fewer moving and total components. As a result of fewer components, more easily manufactured than conventional engines.

• identical cylinder head assembly (“top end”) to conventional engines. Most existing head technology can be either adapted or utilised.
• Flexible design - can be four-stroke, two-stroke, petrol, diesel or gas, natural of forced aspiration.
• Eliminated irregularly reciprocating components such as connecting rods.
• Output shaft can be run in either direction if multilobed cams with symmetrical lobes are employed.
• All rotational forces are counteracted via the counter rotating cam – eliminates the need for a heavy flywheel.
• Torque and power output can be varied using a fixed capacity and piston stroke.
• The CCE can be designed to operate at greatly reduced operating speeds while delivering high torque output.

• Substantial reduction in stroke reduces heat loss through cylinder wall.
• Extended piston dwell is possible because engine design allows a lower than normal compression ratio to be used reducing power loss from compression cycle.
• Maximum mechanical advantage can be applied to output shaft at only 10 degrees ATDC utilising high cylinder pressure early in the stroke, compared to around 60 degrees ATDC for conventional engines.
• Lower emissions can be achieved due to increased control over combustion.
• Extremely low idle speed due to increase in mechanical efficiency at the top of the stroke.
• Little or no bore contact/piston side thrust, which reduces wear on cylinder bore.
• Can have different port timing on compression stroke than power stroke allowing better control two-stroke).
• Lower centre of gravity.
• Due to controlled piston acceleration rates the CCE reduces engine vibration.

• A hollow output shaft can be utilised for specialty applications, such as peristaltic pumps.

[Yardstick]

Good point. Each piston stroke only turns the crankshaft 1/3 of a revolution, so it'd take three times as many strokes to produce a given rpm. It's like it has a built in gear reduction. But couldn't you get around this by gearing it back up through the transmission?

[wildcatf4f3]

maybe i'll put one in my X1/9

[mdefranc]

NSU was the first company to use the Wankel. Subsequent to Mazda's implementation, General Motors bought - but never used - rights.

The original Wankel problem was seal wear. Later, problems centered on emissions - but, this was, again, seal-related. Looking at rated reliability and service costs, I suspect that seals are still a problem. It's a very pleasing engine to drive, but, so far, just not practical; a Mazda salesman recently cautioned me that the latest model should be allowed a few minutes to warm up - get real!

[Nathan Zachary]

Download the video of the thing running. it sounds ok, meaning it "sounds" like it's revving at about 5 grand, but in reality it's barely hitting 1000 rpm. Looks like an 8 (4 sets of opposed piston assemblies) cylinder model they are testing. I think upper end wear is it's main problem, as well as too low of real rpm. Also the load on those "lobes" has to be tremendous.

[elbucko]

At any rate, the amount of hardening on high load surfaces, expensive metallurgy on a valve train, probably make it very expensive.

I agree. It seems to be a reinvention of the wheel.

It would be interesting to see and hear one running though.

Yes it would.

[CATravelAgent]

"What's wrong with the Wankle? Why did only Mazda use it?"

The dying gasp of Norton motorcycles was a wankel powered bike.

[midwestmidnight]

I have an '84 RX7 with 147,000 miles on it. I've never rebuilt it and I drive it regularly. When it was new in '84 it was quicker to 60 mph than the '84 Corvette. I'll stick with my 1.3 liter Rotary. Hummmmmmmmmmmmmmmmm!

[Jack of all Trades]

You probably just hit a couple of nails squarely on the head. I work with very high pressure fuel pumps that look stikingly similar to this concept. Most of the working internals are superfinished tool steels or ceramic. Big bucks.

As RPM increases, the demands on the injectors, valvetrain and ignition system will increase at 3X the rate of a standard engine. Keeping everything moving, timed and controlled at high RPM is probably going top be difficult (read: expensive).

[Rebelbase]

bump for later. Looks cool.

[JamminJAY]

Thanks.
Good post.

[Question_Assumptions]

Depending on how the valves and timing works, while each firing turns it only 1/3rd of a turn, you would get a piston firing once or twice for every turn because each piston get's six strokes per turn rather than two. If you apply the appropriate gearing, it shouldn't have to rev all that high any more than an old high displacement V8 had to.

[Joe Beerman]

have an '84 RX7 with 147,000 miles on it. I've never rebuilt it and I drive it regularly. When it was new in '84 it was quicker to 60 mph than the '84 Corvette. I'll stick with my 1.3 liter Rotary.

I suspect you're not the average driver. I haven't played with a rotary since the seventies, but was amazed at the power they pushed out of a 982cc engine!

The R100 was an awesome sleeper that would leave most vettes in the dust. Add a holley 650 carb and you had a true racing machine that ate fiberglass for lunch.

Happy to see you guys are getting more mileage out of them now.
.

[null and void]

More like an X-6, I think...

[-YYZ-]

Another way to achieve zero side loading on pistons is with dual counter-rotating crankshafts and two con rods to each piston, which isn't as bad as it sounds as they can be made half as big.

There's hundreds of ideas out there for improving the internal combustion piston engine, some of which might work, but they all require massive amounts of R&D money to ever be competitive with the current designs, in which we already have billions of dollars in tooling to produce.

[Nathan Zachary]

No, you are wrong about high compression ratios. True, you can develop more power with good fuel and high ratios, but we just don't have good fuel. With unleaded gas, compressions had to be reduced, and high cylinder temps also created nasty hydrocarbons which have been banned.

So we use lower compression ratios so we can burn crappy unleaded fuel which has a much lower flash point than fuels of the past. Notice how gas seems to go bad after sitting for a month or two? I swear, it's half water. (which helps control detonation)
You could raise compression a bit more, and get better power if you use alcohol blended gas, but you would have to use high percentage blends, 25% or more, re-jet carbs or recalibrate fuel injectors. You would loose fuel efficiency because you need more alcohol in the fuel air mixture to prevent meltdowns. So the option is low compression engines to burn todays crappy gas.

[-YYZ-]

Yep, the usual achille's heel of unconvential IC engine designs: parts, materials and manufacturing techniques that are either non-existent or extremely expensive. Too much so to overcome the inertia of conventional designs.

[Jack of all Trades]

Would stress really go up? Sure you have a large lever arm when the piston rolls over the nose of the cam and starts pushing it down, but it seems that there is a large bearing area available. In a standard IC engine all that force is transmitted through a half inch wrist pin and a two inch rod journal.

I just spoke with another engineer here and apparently Revetec has been hawking this engine for a couple of years without any real bites. Cool tech, high power density, but expensive.

On another note, I'll bet things could get interesting in a hurry if one of these engines develops a misfire.

[null and void]

But couldn't you get around this by gearing it back up through the transmission?

I suppose, But I don't think I've ever turned my tires at greater than 2000 RPM.

Hmmm. Tires, say, 24" diameter. 75 inches per rotation. 63360 inches per mile. About 840 rotations per mile. Two miles per minute at 120 MPH. 1700 RPM.

Maybe one could skip the transmission entirely if the low end torque is high enough?

[Fierce Allegiance]

cool stuff ping

[Red Badger]

I had a 75 X1/9. Worst engineered car I've ever owned! The pistons were in backwards!.........