Note: Descriptions are shown in the official language in which they were submitted.
CA 02368595 2002-O1-18
TRANSMISSION FOR DRIVING COUNTER-ROTATING PROPELLERS,
LUBRICATION SYSTEM, AND ASSOCIATED METHODS
BACKGROUND OF THE INVENTION
Field of the Invention
The present invention relates to propulsion mechanisms for vessels driven by
propellers, and, more particularly, to transmissions for aircraft and
airboats, and to
lubrication systems therefor.
Description of Related Art
Transmissions for driving a pair of counter-rotating propellers are known in
the art
for both airplanes and airboats. Such transmissions are known to be driven by
belts and
by gears, with input typically provided by a shaft driven by an aircraft
engine operating at
approximately 2500-3000 revolutions per minute (rpm). Aircraft engines are
extremely
expensive, noisy, and fuel inefficient.
Airboat systems that utilize belt-driven transmissions are inefficient owing
to power
losses caused by belt friction, especially at higher rotational velocities.
Belt breakage in
these systems is a source of failure. Another disadvantage of belt-driven
systems is their
inability to permit reduction of engine speed, since the shaft used to effect
such a reduction
would have to be too small to be practicable. Thus it has been deemed
advantageous to
utilize a different transmission method in an airboat to enable engine speed
reduction
without loss of efficiency.
A belt-driven, two-engine counter-rotating system has been disclosed by
Stewart
(U.S. Pat. No. 4,426,049). It has been taught by Becker et al. {U. S. Pat: No.
4;932,280)
to use coaxial drive shaft systems for driving multiple outputs from a single
input in an
aircraft. Gearing means are disclosed far driving two outputs at different
speeds.
A double-sprocket and wheel transmission fordriving multiple propellers in the
same
direction is described by Fay (U.S. Pat. No. 1,329,387).
The use of a gear-based transmission for airboats has been taught by Kaye
(U.S.
Pat. No. 5,807,149), including a transmission for driving a pair of counter-
rotating coaxial
shafts, to each of which is affixed a propeller. Such an arrangement can be
used with an
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automobile engine, which is far more economical than an aircraft engine. This
transmission
has been shown to reduce noise and torque, to permit varying gear ratios, to
increase fuel
efficiency and engine life, and to be less expensive to operate.
Improved gear-based transmissions for airboats have also been disclosed by
Jordan
(U.S. Pat. Nos. 5,724,867 6,053,782 and 6,299,495 the entire contents of both
of which are
incorporated herein by reference). In the 'xxx patent a lubrication system is
also taught that
includes a gear for driving lubricant from a well to the interior of the inner
output shaft, out
of that space to a pair of stiffener bearings, and into the space between the
output shafts.
Another source of failure in transmissions is failure of the oil pump that
heretofore
has been considered an essential element.
SUMII~ARY OF THE INVENTION
It is an object of the present invention to provide a transmission that has
improved
strength and stability characteristics for driving a pair of counter-rotating
propellers.
It is a further object to provide such a transmission having a single input
shaft for
driving means for driving the two output driven shafts.
It is another object to provide a transmission for driving coaxial counter-
rotating
propellers that is drivable at variable or equal speeds as desired.
It is an additional object to provide such a transmission with which it is
possible to
drive the counter-rotating propellers at different speeds to provide
additional thrust, reduce
noise output, and improve fuel efficiency.
It is also an object to provide such a transmission that is considerably
lighter than
previously known devices.
A further object is to provide a system and method for lubricating the output
driven
shafts that reduces weight and complexity.
Another object is to provide a system and method for achieving a simplified
lubrication of a transmission and propulsion for an airboat.
An additional object is to provide such a system and method that eliminates
the need
for an oil pump to circulate lubricant.
These and other objects are achieved by the transmission of the present
invention,
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which is for driving a pair of coaxial, counter-rotating propellers for, for
example, an airboat
or an aircraft, although these are not intended as limiting usages. The
transmission is
housed in a case that has an interior space.
A drive shaft extends from the outside of the case into the interior space and
is
rotatable in a frrst direction. When the transmission is in use on an aircraft
or airboat, the
drive shaft is mated at one end to a motor crank extending from and rotated by
an engine.
As mentioned above, previously known aircraft and airboats have utilized
aircraft-type
engines; however, with the transmission of the present invention, it has been
found that an
automobile engine can be used. This has a benefit of reducing cost, as well as
other
benefits to be discussed below.
A first driven shaft also extends into the interior space of the case,
typically from a
side opposite that of the drive shaft. The first driven shaft is for rotating
an outer propeller,
that is, the propeller farther from the airboat body.
A second driven shaft, which is hollow, likewise extends into the interior
space of the
case and is further positioned in surrounding, generally coaxial arrangement
to the first
driven shaft. The second driven shaft is shorter than the first, and both ends
protrude
beyond the ends of the first driven shaft. This second driven shaft is for
rotating an inner
propeller, that is, the propeller closer to the airboat body.
A gear train for driving the first shaft is housed in the interior space of
the case. In
its simplest configuration, the gear train comprises two gears: a drive gear
and a driven
gear. The drive gear is coaxially affixed to the drive shaft. The driven gear
is coaxially
affixed to the first shaft in such a position and configured so as to be
~otatable by the drive
gear. Thus, when the drive shaft rotates in the first direction, the drive
gearis rotated in the
first direction. This causes the first driven gear to be rotated in a second
direction opposite
in sense to the first direction, which consequently drives the first shaft in
the second
direction.
In an alternate embodiment, additional intermediate driven gears may be
interposed
between the drive gear and the first driven gear, so long as the total number
of intermediate
gears is an even number.
A sprocket train is also housed in the interior space of the case. This
sprocket train
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includes a first and a second sprocket and a chain. The first sprocket is
coaxially affixed
to the drive shaft. The second sprocket is eoaxially affixed to the first
shaft. The chain is
in engagement with both sprockets and is in such a position and configured so
as to rotate
the second sprocket upon the first sprocket turning. Thus, when the drive
shaft rotates in
the first direction, the first sprocket is rotated in the first direction.
This causes the second
sprocket also to be rotated in the first direction, which consequently drnres
the first shaft in
the first direction.
Thus it can be seen that the rotation of the drive shaft in one direction
achieves,
through the action of the hybrid transmission comprising the gear train and
the sprocket
train, a counter-rotation of the two coaxial driven shafts and thus imparts
counter-rotation
to propellers attached thereto. There is no known system that uses fewer
components than
that of the present invention, which permits lower weight, improved
efficiency, and
enhanced reliability.
Using the present hybrid gear/sprocket transmission permits driving an
automobile
engine at the point of maximum horsepower, which generally implies a motor
crank
rotational speed approximately in the range of 5000-5200 rpm, and then gearing
down the
rotational speed to roughly 1200-2800, possibly even lower; a quieter speed at
which to run
the propellers.
The invention is not, of course, limited to the use of an automobile engine;
in fact,
the presence of the gear and sprocket trains enables the user to optimize for
efficiency and
noise characteristics by altering gear ratios as desired. An aircraft engine
may also be
used.
Yet another feature of the present invention is an improved lubrication
system, in
which an oil pump is no longer necessary, owing to the presence of the two
coaxial driven
shafts, between which lubricant may pass and be moved by the counter-rotation
thereof.
This feature of the system comprises means for injecting a lubricant into a
space between
the driven shafts and means for blocking the entry hole during use to retain
the lubricant
therein.
Among the benefits of the present invention are a minimization of components,
which
is believed to increase reliability and dependability, and a decrease in the
weight, which
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increases performance and fuel efficiency. Present counter-rotator
transmissions known
in the art have a weight of 140-200 Ibs, whereas the hybrid transmission of
the present
invention has a weight in the range of 90-110 lbs.
The features that characterize the invention, both as to organization and
method of
operation, together with further objects and advantages thereof, will be
better understood
from the following description used in conjunction with the accompanying
drawing. It is to
be expressly understood that the drawing is for the purpose of illustration
and description
and is not intended as a definition of the limits of the invention. These and
other objects
attained, and advantages offered, by the present invention will become more
fully apparent
as the description that now follows is read in conjunction with the
accompanying drawing.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a side cross-sectional view of a first embodiment of a transmission
for
driving counter-rotating propellers, also showing the shaft lubrication
system.
FIG. 2 is a side cross-sectional view of a second embodiment of a transmission
for
driving counter-rotating propellers.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
A description of the preferred embodiments of the present invention will now
be
presented with reference to FIGS. 1 and 2.
The hybrid transmission 10 of the present invention, shown from the side in
FIG. 1,
which is designed to drive a pair of coaxial, counter-rotating propellers 20
and 30,
comprises a case 50 that has an interior space 502, a fore side 504, and an
aft side 506.
It is preferred that the case exterior be aerodynamically shaped in order to
confer good
airflow characteristics to the transmission 10 during use at high speeds.
A drive shaft 12 extends into the interior space 502 of the case 50 through
the case's
fore side 504. The drive shaft 12 is rotatable in a first direction, shown
here as
counterclockwise when viewed from the front. Typically the drive shaft's fore
portion 122,
which extends outside the case 50, contains a coupler 124 for mating with a
crank shaft 62
from an engine 60, which generates the rotational motion. The drive shaft 12
is preferably
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configured as a through shaft with respect to the case 50, and is thus
supportable via
brackets 508,509 affixed on the inside of both the fore 504 and the aft 506
sides,
respectively, of the case's interior space 502. This dual support confers
exceptional stability
to the drive shaft 12.
The outer propeller 20 is mounted via propeller mount 202 adjacent the aft end
224
of, and is rotated by, a first driven shaft 22 that extends from the back side
506 into the
interior space 502 of the case 50. The fore end 222 of the outer propeller 20
is supported
via bracketing 510 on the inside of the case's fore side 504. Preferably the
first driven shaft
22 comprises a hollow shaft, having a lumen 221 therethrough. A removable cap
223 at
the aft end 224 leads to the lumen 221, as does a hole 225 adjacent the fore
end 222.
The inner propeller 30 is mounted via propeller mount 302 to the aft portion
324 of,
and is rotated by, a second hollow driven shaft 32 that extends from the aft
side 506 into
the interior space 502 of the case 50. The second hollow shaft 32 is
positioned in
surrounding, generally coaxial arrangement to the first hollow driven shaft 20
and is shorter
than the first driven shaft 22. These relative lengths permit the fare end 222
and the aft
portion 224 of the first driven shaft 22 to protrude, respectively, beyond the
fore end 322
and the aft portion 324 of the second driven shaft 32. The second driven shaft
32 is
supported on the interior of the case's aft side 506 by bracketing 511.
In a preferred embodiment the longitudinal axes of the drive shaft 12 and the
first 22
and second 32 hollow driven shafts are positioned generally in vertical
alignment. This
positioning confers improved stability during use, as the gyroscopicforces
balance optimally
in this configuration.
The transmission 10 of the present invention further comprises two drive
trains
housed within the case 50, one for driving each of the hollow driven shafts
22,32. The first
train 40 comprises a gear train comprising an even number of gears for
changing the
incoming rotational direction. The embodiment shown in FIG.1 contains two
gears: a drive
gear 402 coaxially affixed to the drive shaft 12 and a driven gear 404
coaxially affixed to the
first hollow shaft 22. The driven gear 404 is positioned and configured so as
to be rotatable
by the drive gear 402. Thus, when the drive shaft 12 rotates in the first
direction, here
shown as counterclockwise, the drive gear 402 is rotated in the same
direction, and the
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driven gear 404 is rotated in a second direction opposite in sense to the
first direction, that
is, clockwise. Thus the first hollow shaft 22 is driven in a clockwise
direction also, as would
be an attached propeller 20.
The second drive train 42 comprises a sprocket train for maintaining the
incoming
rotational direction. The sprocket train 42 comprises a drive sprocket 422, a
driven sprocket
424, and a chain 426. The drive sprocket 422 is coaxially affixed to the drive
shaft 12, and
the driven sprocket 424 is coaxially affixed to the second hollow shaft 32.
The chain 426
is positioned in encompassing relation to the teeth of the sprockets 422;424
and is
configured so as to rotate the driven sprocket 424 upon a rotation of the
drive sprocket 422.
Therefore, in use, when the drive shaft 12 rotates in the first direction, the
drive sprocket
422 is rotated in the first direction, the driven sprocket 424 is also rotated
in the first
direction, and the second hollow shaft 32 is rotated in the first direction,
conferring counter-
rotational movement to the inner propeller 30 with respect to the outer
propeller 20.
In an alternate embodiment 10' (FIG. 2), the gear train 40 and the sprocket
train 50
are interchanged in axial position, with the gear train 40 driving the second
hollow driven
shaft 22 and the sprocket train 50 driving the first hollow driven shaft 32.
Particular benefits of the hybrid propulsion system of the present invention
include
the possibility of using an even number of gears, since a planetary,
intermediate, sense-
changing gear is no longer necessary to achieve counter-rotation. In addition
to the weight
and commensurate efficiency advantage conferred thereby, stability is also
improved, with
balancing force vectors conferring added reliability and durability. For
example, failures are
known to have been caused by oufinra~d-pointing forces imposed upon the
planetary gear
by the driving and driven gears. Further, all the gears in the present
invention are mounted
on through shafts, which are also stronger and more stable.
In either of the above-detailed embodiments it may be seen that the first and
the
second drive trains can be adapted to drive the propellers at different
speeds, if desired
which can provide improved thrust characteristics, increased fuel efficiency,
and reduced
noise.
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Shaft Lubrication System
An additional aspect of the present invention comprises a lubrication system
for
delivering lubricant to elements of the propulsion system. A particular
embodiment of the
lubrication system, illustrated in FIG. 1, comprises means for injecting,
sealing, and
circulating a lubricant within an enclosed space including the hollow shafts
22,32 without
the use of a mechanical pump. Upon removal of the cap 223; lubricant may be
injected into
the inner shaft's lumen 221. The rotational motion of the shaft 22 drives
lubricant via
"centrifugal force" from the inner shaft's lumen 221 out through a plurality
of holes 228 in
the aft portion of the shaft 22 to enter the space between the shafts 22,32,
where there are
positioned a plurality of floating cylindrical bearings 66, which maintain the
distance
between the shafts 22,32 and also assist to distribute lubricant. In a
preferred embodiment
there are between two and four of these bearings 66 positioned in spaced
relation from
each other between the shafts 22,32; and the material comprises brass.
Although brass
is disclosed herein, it will be understood by one of skill in the art that
another material may
be used, preferably a metal dissimilar from the material of which the shafts
22,32 are
composed.
In order to provide a path for the escape of trapped air in the space to be
lubricated,
a toroidal collar 44 is provided that is positioned around the inner shaft 22
between the gear
404 and the bearing 510. To an upper end of the collar 44 is affixed a line 45
that leads at
a top end from the case's 50 top side 512, and is sealable with a removable
cap 46. The
line 45 leads at a top end to a void 441 in the collar 44 that surrounds the
inner shaft 22.
Two O-rings 47 are positioned in surrounding relation to the collar 44 around
the inner shaft
22 to prevent lubricant from leaking out from the void 441 to the exterior of
the inner shaft
22. Thus, in use, lubricant that has been injected into the inner shaft's
lumen 221 also
proceeds forward through the lumen 221 and reaches the collar's void 441. Any
air bubbles
that have been trapped along the way can then escape through the uncapped line
45, and
then the cap 46 can be replaced. The collar 44 does not turn with the shaft
22, but rather
floats thereon, being held substantially in place by the line 45.
The bearings 66 themselves represent a novel lubrication element, being
designed
to maximize lubricant return in the fore direction. In a preferred embodiment
each bearing
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66 has a series of generally helical grooves 662 cut in the outer surface,
through which the
lubricant may move to be distributed within the outer shaft 32.
This lubrication system eliminates the oil pump and associated gear previously
known and used in the art, and thus also improves fuel efficiency by reducing
weight by 15-
201bs.
It may be appreciated by one skilled in the art that additional embodiments
may be
contemplated, including variable numbers and sizes of gears, which may be
positioned and
configured to permit variable relative speeds of the two counter-rotating
propellers.
In the foregoing description, certain terms have been used for brevity;
clarity, and
understanding, but no unnecessary limitations are to be implied therefrom
beyond the
requirements of the prior art, because such words are used for description
purposes herein
and are intended to be broadly construed. Moreover, the embodiments of the
apparatus
illustrated and described herein are by way of example, and the scope of the
invention is
not limited to the exact details of construction.
Having now described the invention, the construction, the operation and use of
preferred embodiment thereof, and the advantageous new and useful results
obtained
thereby, the new and useful constructions, and reasonable mechanical
equivalents thereof
obvious to those skilled in the art, are set forth in the appended claims.
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