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Revetecs 1800SV will start coming off the assembly line later this year
via a joint venture agreement with Osman. Its slated for use in Chinas
indigenous car production. However, a very major automaker reportedly
has expressed interest, signing a two-way confidentiality agreement with Revetec.
As the photo above shows, the 1800 SVwhich is 11-in. long, 25.6-in. wide
and 19.7-in. highis significantly more compact than the companys
2001 prototype. |
Crankshafts are inefficient devices for efficiently transferring power from the
pistons to the driveline, with losses that can approach 36%. At the top of the
piston stroke, where gas pressure is highest, force transfer efficiency is at
its lowest, though it rises as the piston descends and the connecting rods
leverage increases. Peak efficiency happens about 40% through the piston stroke,
then drops at an exponential rate that mirrors its rise. In addition, the piston
doesnt travel a path that is strictly parallel to the bore, so an angular
force equal to the pressure on the top of the piston is transferred to the cylinder
wall. This increases friction, wear, and fuel consumption.
Bradley Howell-Smith, managing director of Revetec Limited (Sydney, Australia)
and inventor of the Revetec engine, arrived at a solution to the problem in
1996, when he replaced the crank with counter-rotating cams driving an output
shaft, and made the connecting rods rigid. (See: How It Works)
Within six months, he says, I had a twin-cylinder, 500 cc
two-stroke demonstration engine no bigger than a loaf of bread running in my
garage. It put out more power and torque than an equivalent conventional
design, and used less fuel. Convinced he was on to something, Howell-Smith suspended
development, and spent the next few years raising capital and filing international
patents (29 so far, including the U.S.). Development resumed in 1999, and included
research into four-stroke, diesel, and alternate-fuel variants.
The latest version of the Revetec engine is the horizontally opposed 1800 SV;
its swept volume is 1.8-liters (hence the name). It measures 280-mm long, 650-mm
wide, 500-mm high, weighs 45 kg, and is scheduled to enter production in China
later this year. Asked about his growing list of joint ventures with Chinese
firms, Howell-Smith answers: This is such a new and different concept
that we thought it best to prove the technology in an emerging market.
In other words, hed rather show established automakers a proven product
than a proof-of-concept. Life is too short to waste time battling the
Not-Invented-Here Syndrome, he notes wryly.
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Inner cams attached to sleeve |
One reason for the interest from China is the superior emissions performance
Revetec claims for its design. Though the head design is totally conventional,
the engines greater mechanical efficiency means 60% less fuel is needed
to produce an equivalent output at wide-open throttle. That number rises to
75% in idle/no-load conditions, a big plus in crowded cities like Beijing. And
less fuel means lower emissions.
Airplane manufacturers have expressed interest in the Revetecs ability
to drive counter-rotating propellers in a high-torque/low-rpm situation without
the need for a separate drive unit or gear-reduction transmission. And ship
builders are interested in the engines potential to maintain a near-constant
piston speed. This increases control over propeller speed, and reduces the shocks
conventional engine designs place on a ships drive system.
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Piston and
carrier assemblies |
Howell-Smith sees automotive as the biggest prize, and touts the engines
modularity and simplicity alongside its mechanical efficiency to emphasize his
case. Development has shown us that we can have a generic block covering
certain capacities, and tailor it to the clients needs through the cam
design, he says. One example he uses shows how a car, tractor and truck
would use the same basic engineeverything would look the same on
the outside, he saysbut different cam designs to produce horsepower
and torque tailored to the application. We can change the cam to apply
far more leverage to the output shaft for the truck, or go to a five-lobe cam
and low rev limit to get the most torque for the tractor. Couple this
with his claim that the Revetec bottom end carries a 20% savings compared to
a conventional engine, and you can understand why he thinks his company has
a realistic chance getting its foot in the door at cost-conscious automakers.
How It Works
In the Revetec engine, pistons are attached to their horizontal opposites via
a rigid connecting rod. Just below the lower edge of the skirtless pistons sit
two roller bearings mounted on a common shaft, one on each side of the connecting
rod. The pre-loaded bearings ride along the outer edge of the cams (also found
on either side of the connecting rod), and drive them in opposite directions.
The outer cams are splined to the output shaft, while the inner set ride on
a sleeve fitted over the output shaft. The inner cams transfer their force to
a gear situated in the sump that drives a counter-rotating balance shaft. This
planetary gear arrangement reverses the direction of the force so it can be
transferred to a drive gear splined to the end of the output shaft. (An animation
of the engine is available at: www.Revetec.com.)
Each cam rotates three times per revolution, making the swept volume of the
Revetec three times its static volume. Accordingly, an 1,800-cc swept volume
four-cylinder engine measures 600 cc, or just 150 cc per cylinder. Maximum force
is applied to each cam within 10% of top-dead center and throughout the majority
of the piston stroke. Which means the free-revving engine reaches its torque
and horsepower peaks quickly, a potential problem in terms of drivability.
Electronic controls and variable valve timing will help, says Howell-Smith,
but theres still a lot we can do with the cam shape, including profile
changes, matching the dwell to the expansion rate of the fuel, etc. The
current engine idles at just 300 rpm, and Revetecs analysis suggests this
can be lowered to 120 rpm with a switch to variable valve timing. Howell-Smith
expects the rev limit to remain at 6,000 rpm.