Revetec Technology Overview
The REVETEC Engine design consists of two counter-rotating “Trilobate” cams (1&2) geared together, so both cams contribute to forward motion. Two bearings (3&4) 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 (5a&5b), which maintain the desired bearing to Trilobe clearance throughout the stroke.
The two cams rotate and raise the piston with a scissor-like action to the bearings. Before the top of the stroke the air/fuel mixture is fired, just like a conventional engine. The expanded gas then forces the bearings down the ramps of the cams spreading them apart ending the stroke.
The piston assembly slides rigidly through the block via an oil pressure fed guiding system (6a&6b) eliminating piston to cylinder-bore contact. This reduces wear and lubrication requirements in the cylinder, and also reduces piston side shock making ceramic technology suitable.
The counter rotation is performed by a reverse gear set (7a&7b - Other gears not shown) at a 1:3 ratio shaft providing two strokes of the piston, to 360 degrees of output shaft (8) rotation. This is the same as a conventional engine.
The mechanical advantage or torque lever is increased around 20-80deg ATDC making the most of the high cylinder pressure. This compares to a conventional engine that reaches maximum mechanical advantage around 40-90deg ATDC.
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 trilobe cam “grind” which can be altered to suit a wide variety of fuels, torque requirements and/or rev range. One module can either comprise of two trilobate cams and either two, or four pistons in an “X” configuration.
Reducing Mechanical Losses
A Conventional engine produces a side thrust on the piston which is controlled by the piston skirt (Refer 1 below).
This side thrust is a result of the piston applying pressure on the crank via a connecting rod which is applying that force at an angle to the crankshaft. The resulting angle also produces a great down-ward loading on the crankshaft (Refer 2 below).
This downward force is a great mechanical loss which reduces engine efficiency. The total mechanical losses in this area of a conventional engine are approximately 36%.
The mechanical losses are reduced in the CCE design by deflecting the side thrust that is produced from the bearing to Trilobe cam angle of attack (Refer 3 below) into the counter-rotating cam.
This deflected force increases the torque lever, further increasing overall torque application. Downward thrust on the output shaft is reduced to a minimum resulting in total mechanical losses of approximately 12% compared to 36% of a conventional engine.
Main Features of Revetec's Technology
Increased Torque Lever
Below is just one example of the increase in torque lever. The Revetec design allows the easy customisation of this torque lever. Trilobe shape is almost infinitely variable, so customisation of engine characteristics are also as variable.
Rather than waste deflected forces which create friction and mechanical losses, the Revetec engine deflects these forces into usable torque. (1) Wasted force from piston side thrust. (2) Wasted down force on crankshaft main bearing. (3) Deflected side thrust into usable torque (shown in blue). (4) Reduced waste down force.
Increased Piston Dwell
By using Asymmetrical Trilobe's, extended piston dwell can be achieved. It is well known that piston dwell creates better combustion efficiency. Normally a downside is poor early mechanical transfer, so this is normally associated with high RPM engines. Revetec engines extend the dwell on the compression side of the stroke (Not the power side) which increases dwell, maintains good torque lever and raises the piston position at ignition.
This provides an increase in fuel particle density allowing leaner mixtures to be used and lowering the chance of detonation. By decreasing the chance of detonation, a higher compression ratio can also be used.
With a higher piston position at ignition and burn, less heat energy is absorbed into the cylinder due to decreased cylinder wall exposure. This also increases engine total efficiency.
Full List of Revetec's Engine Features
World Leading Fuel Efficiency
The Revetec X4v2 engine was independently tested at Orbital Australia where it achieved a top efficiency in BSFC of 207g/kWh and an average of 212g/kWh. Orbital test for many of the top automotive companies in the world including: Toyota, GM, Ford, Nissan and Renault. The results have been confirmed in a further independent test at Peus Testing in Germany.
Better Thermal Efficiency
Due to the piston dwell previously discussed, the engine is more thermal efficient.
Higher Mechanical Transfer
The Revetec Trilobes transfer torque at a higher level than a conventional engine. Not only is the torque higher, it is earlier in the stroke, which utilises the higher cylinder pressure.
Higher Torque at Low RPM
Because we reach higher mechanical advantage earlier in the stroke, engine torque is dramatically increased at lower RPM as well as low to part throttle responses.
Operates at Leaner Mixtures
Due to the higher piston position at ignition point, the fuel is denser in the chamber. This allows the mixture to be leaned off further than a conventional engine and lowering the risk of detonation.
Leaner Cold Starting and Running
Due to the longer piston dwell, the air in the cylinder has more time to absorb latent heat from the previous combustion cycle. This has reduced fuel enrichment normally used on conventional engines to under half. The engine then uses less fuel and emissions are lowered under cold start and run.
Leaner can reduce NOx
Another advantage of piston dwell has been the measurement of NOx under leaner mixtures. Normally NOx rises as the fuel mixture is enriched, although during tests we have found they slightly reduce.
Driving Style Efficiency
Due to the higher torque produced at lower RPM ranges, we have noticed that less throttle response is required to provide good acceleration. Producing higher torque at lower RPM also allows the driver to short shift the transmission without the engine labouring. This driving style greatly increases fuel efficiency with our engines.
The engine can be designed to provide an almost flat torque curve. This characteristic provides good torque through the whole normal rev range consistently. The driver experiences instantaneous torque and acceleration in a wider range of RPM. This characteristic is enjoyable to drive.
Increased piston Dwell
Increased piston dwell aids combustion, increases thermal efficiency, lowers NOx, reduces pumping losses, increases engine smoothness, decreases fuel enrichment under cold conditions, reduces friction etc.
More efficient Combustion
Increased piston dwell increases combustion efficiency.
Less Wasted Down Force
By deflecting side thrust we reduce wasted down force, normally transferred to main journal bearings.
Less Friction and Wear
The Trilobes and bearings provide a central position for the piston in the bore during most of the power stroke. The piston is rigidly guided via oil pressure fed guides as well. This allows us to give the piston clearance to the cylinder bore. At no time does the piston touch the bore. Only the rings on the piston which seal to the bore are the cylinder wearing component. This drastically reduces friction and wear.
Stroke Doesn't Create the Torque Lever
The torque lever isn't created by the stroke like in a conventional engine. This allows us to use reduced bore/stroke ratios (an oversquare engine) without sacrificing torque. This is a great feature that allows an independent relationship between the combustion process and torque application. It also allows us to tailor make an engine characteristic and/or a series of engines for different uses with more common parts.
Easily Customised to Varied Engine Applications
We have two engines that are identical in every aspect. One engine then has its trilobes and piston bearings changed to an alternative design we can drastically change the characteristics of the modified engine. Bore and Stroke can remain the same, although torque can be increased.
Customisable to Different Fuel Types Easily
By changing the shape of the trilobe, we can change the piston acceleration rate to match the combustion of a different type of fuel.
Very Compact in Design
The engine in the X4 configuration is very compact in design. The 2.4 litre fully dressed engine outside volume is approximately 50% of a comparable conventional engine.
Higher Power to Weight Ratio
BMW proudly say they have the lightest 2.5 litre on the market. Our 2.4 litre (heavy billet prototype) has 30% less weight.
The Revetec engine is simplistic in design. There are only six major mechanical components in our four cylinder engine.
None of the components in a Revetec engine pose any difficulties to manufacture. To prove this, the X4v2 engine prototype was almost totally manufactured by two people in 3.5 months, using a manual lathe, manual turret mill, a surface grinder, a 3 axis CNC mill and other general workshop equipment.
The Trilobes in small volumes can be CNC machined or wire cut. In larger volumes they can be drop forged or manufactured using powder metallurgy.
Economical to Manufacture
Many of the components are smaller and in duplicate form, reducing cost.
Lower Bill of Materials
The components that make up the Revetec engine are smaller in comparison to a conventional engine. We estimate that the bill of materials will be approximately 30% less.
Simple Engine Assembly
The engine assembly is fast and easy.
The engine design has little limitations on scalability.
The Revetec engine is a bottom end enhancement in essence. Almost all existing engine technology can be utilised with increased efficiency.
Longer Service Intervals
Due to the reduced wear by guiding the piston in the bore, the rings are the only wearing part in the cylinder. The rings are held at 90deg to the bore at all times, and the piston does not rock like a conventional engine when cold. For this reason the rings seal better and less contaminants are transferred to the oil system, extending service intervals.