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.

[babygene]

"fewer parts"

Does it have two counter rotating shafts? And won't you need gears to combine the two output shafts?

[Dan Evans]

Hard to believe that a 75% weight reduction could be achieved from replacing the crankshaft with cams.

[Yardstick]

I think what he means is that the piston is never side-loaded against the cylinder wall. Unlike a conventional engine, all the forces stay in-line with the stroke of the piston.

The problem with the Wankel engine IIRC is in maintaining a good seal between the tips of the triangular piston and the cylinder wall. It tends to get sloppy as the engine ages.

[IronJack]

The Wankel delivered on most of its promises. The seals were its Achilles' heel.

I have an RX8 with the new generation of rotary, the Renesis, and it appears to have all the strengths of the Wankel with none of the drawbacks. It's an incredibly strong powerplant for its diminiuitive size. Super-wide power band and only a handful of moving parts. Mileage could be better, but it's still not bad for a sports car.

The engine in this article looks interesting to me too. I love new motor technology.

[eraser2005]

Have you seen Pempek's FP3 engine? FP3 stands for Free Piston Power Pack. It seems like a somewhat similar compact, simple solution. No crankshaft, no connecting rods, passive and electronically controlled valves (no valve train), no starter needed, perfect compatibility with hybrid systems....

Pempek is a company with only 3 employees, but they've managed to get 24hp per pack (2 cylinder), with an expectation of 34hp achievable. Their estimates say that if they get 34hp, they can double the mileage of a Prius without losing power or requiring a plugin (its a very compact, small, and light engine).

They're also working on a diesel design (diesel being simpler to implement) that is projected to produce 400HP, and a 600HP version that should be 1/7th the size of a conventional diesel of similar output. Their director says "If we're successful, it could basically sit in the crankcase of a diesel V8 with the same output"...

Lots of potential, but until recently, not much incentive in terms of $$$ to go out and nail fuel efficiency....

[axxmann]

I think they meant piston to cylinder side loading as stated further down in the article.
The problem with the wankel was the seals on the cam lobes. They wore out way too soon and were a critical part due to combustion taking place directly on the cam lobe. Wankels are still awesome even though you have to rebuild them often.

[Cliff Dweller]

If you go (not Yugo) to the link, there are WMV files with sound as the engine is running. I like the approach, just curious on the torque transfer mechanism, a traditional flywheel? Like to see one in person.

[Safetgiver]

Mazda fixed the problems with it's rotary by replacing the rubber crown seals. My '82 (300,000 mis), 85, (450,000 mis) and the 92 (100,000 still running)and my soon to be RX8 never had anything but oil changes in them.

[OKSooner]

Looks like a lot of friction heat generated on those bearings to me too.

I'm not an engineer, though, I'm just some dude...

[OKSooner]

Looks like a lot of friction heat generated on those bearings to me too.

I'm not an engineer, though, I'm just some dude...

[Red Badger]

I don't get this comment at all "The piston assembly slides rigidly through the block eliminating piston to cylinder-bore contact."

I think what they meant was that the opposing pistons being ridgidly connected on one shaft are supported on the ends by the rings and the main weight of the whole assembly is supported by the bearings. The cylinder bore wear would be more "perfect circle" (pun) than normal horizontally opposed engines like BMW, VW, Porsche, Subaru, Corvair etc.........

[Red Badger]

I'm not an engineer, though, I'm just some dude...

Better ping Jesse Jackass.......

[Nathan Zachary]

Looks interesting, but I'm sure it has it's development curses. Durability is probably it's curse. Those lobes probably don't stand up to the high loads over the test of time. It probably has an upper limit as far as real drive shaft speed goes as well, about 2000 rpm, which is why they emphasize it's torque. At 2000 rpm the piston "pairs" have to fire 12,000 times with a tri lobed "cam". To build a valve train tough enough to maintain those operating speeds and be durable would be very expensive. It probably would make a better 2 stroke than a 4 stroke.
At any rate, the amount of hardening on high load surfaces, expensive metallurgy on a valve train, probably make it very expensive.
It would be interesting to see and hear one running though.

[bigsigh]

thanx

[JoeSixPack1]

This a nice innovative idea using a soon to be outdated principle of harnessing combusted fuel oil.

When I can feed my vehicle the garbage/refuse/effluent I put out on the street for collection or flush down my toilet I'll be ready to invest.

I will add that Dr. Felix Wankel would be properly impressed with this one. :-)

[Joe Beerman]

What's wrong with the Wankle?

There's nothing wrong with the Wankle. CAFE restrictions make it difficult to produce an economical rotary engine. They have a high power to weight ratio, but use more fuel than a reciprocating engine of the same power. The seals wear fast and rebuilds at 30,000 are not unusual. Great performance engine, but high maintenance. If you take good care of your rotary you can make them last, but most people won't do that.
.

[19th LA Inf]

The basic mechanism does the same job as the old "Scotch Yoke" used in countless millions of home refrigerator compressors. They were simpler and had far fewer moving parts, just a crank and some type of roller contact to push the yoke back and forth. I don't know of any IC engines that used that mechanism but I don't see why one couldn't.

I don't understand the "advantage" of being able to use a lower compression ratio unless it would be allowing the use of poor quality fuel. All other things being equal, engine efficiency and specific power output relies on use of highest possible compression ratio with clever combustion chamber design to suppress pinging.

[Blackmagic]

The Wankel was way ahead of its time when it first came out. Mazada was the only company to give intrest to it which is a shame as its a very good engine and getting better.

Although nothing sounds like 502c.i. of American Muscle

[Jack of all Trades]

I just took a look. What is it with Aussies and cool engine designs? The concept looks like some Stirling engine designs I've seen. The website is down so I only looked at one cached page.

[elbucko]

How can you eliminate piston to bore contact.

The reference is to the connecting rod forces acting upon the piston when the crankshaft rotation is at 90 degrees to the axis of the bore. The rod tends to push the piston, sideways, against the cylinder wall. It is a particular problem in short stroke engines, such as racing engines that have a high degree of "rod angularity". The longer the rod, the less the connecting rod forces act upon the piston. In this engines case, there is no connecting rod. There is also nothing new.