Note: Descriptions are shown in the official language in which they were submitted.
CA 02390818 2002-O1-16
WO 00/03915 PCT/CA98/00698
MARINE PROPULSION SYSTEM
Technical Field
The invention relates to the field of marine propulsion systems. More
particularly, the invention relates to stern mounted drives or outboard marine
propul-
sion systems in which the inboard engine drives some form of transmission and
an
intermediate drive shaft mounted outboard of the transom, which in turn drives
a
propeller shaft.
Back~,round Art
Stern mounted, or outboard marine propulsion systems have a number
of advantages over conventional systems like the fixed propeller systems in
which an
onboard engine drives a fixed propeller shaft through a marine transmission
and
steering is provided by a rudder, and over purely outboard systems in which
the
entire engine, drivetrain and propeller are located aft of the transom. Stern
mounted
drives combined with inboard engines offer more mobility than fixed propeller
systems, and greater horsepower than purely outboard units. The term "outboard
drive" refers to the fact that the entire drive unit apart from the engine and
trans-
mission are located overboard, on the transom of the boat. This feature is
critical to
the vessel's trim, tilt and steering operations. With this type of system
propulsion is
achieved when rotation is transmitted from an inboard mounted engine through
some
form of drive train to a propeller located below the water line. Instead of a
rudder
setup, steering is executed by changing the angle of the entire unit in a
plane parallel
to the water surface. By varying this angle, propeller thrust is redirected
and the
vessel's course altered. The ability to direct propeller thrust makes the
vessel respon-
sive and extremely maneuverable, a feature that appeals to both commercial and
pleasure boat owners.
In existing stern drive propulsion systems, rotation from the inboard
power plant is reduced by the transmission and then directly coupled to the
outboard
leg using a universal joint. Power is then transmitted through an arrangement
of
clutches, bevel gears and shafts to the propeller located below the water
surface.
CA 02390818 2002-O1-16
WO 00/03915 PCT/CA98/00698
-2-
Such fixed gear ratio arrangements tend not to use fuel to the utmost
efficiency. For
example, accelerating a boat from a standstill requires more horsepower than
any
other time during operation, and this occurs when the engine is running at low
rpm
and producing very little horsepower. At that time engines are overfuelled in
order
to create more horsepower. However most of this excess fuel that is delivered
to the
engine is exhausted and not used. Also, particular engines, and particularly
diesel
engines, have a peak performance within a narrow rpm range, so in fixed ratio
systems, the engine will be operating efficiently in a limited number of boat
speeds
and so most often will be operating with reduced fuel efficiency, causing
increased
costs and pollution.
Currently the largest outboard drives on the market are made of cast
aluminum and do not adequately withstand the magnitude or the duration of the
torque
required by larger commercial boats (greater than 400 ft.-lb. of torque). In
existing
designs, an increase in torque would mean that the running gear would have to
be
made substantially more robust, and so could no longer be contained within a
streamlined lightweight casing. Instead, the case would have to be made larger
and
more bulky in an attempt to withstand the inherent side thrust associated with
bevel
gears. In higher speed applications where this unit is desirable, such a
massive leg
would compromise fuel efficiency with its increased mass and multiplied drag.
As
a result, current manufacturers have designed outboard drives that are more
suited to
high speed (3000-5000 rpm), gasoline-fuelled engines with relatively low
torque.
These restrictions have shaped their trim, lightweight drives to be suitable
for
pleasure boats and light duty commercial vessels with low operating hours.
However,
the maneuverability of these drives still appeals to customers operating
heavier boats
under more abusive conditions. With such operating benefits, larger commercial
operators still choose to purchase these lightweight units which results in
the need for
costly repairs after very low hours.
Using thrust vectoring to steer the boat, rather than the traditional fixed
propeller and rudder setup has considerable advantages in maneuverability.
However
CA 02390818 2002-O1-16
WO 00/03915 PCT/CA98/00698
-3-
there are some disadvantages. The universal joint which must penetrate the
transom
of the boat is both a weak link in the drive train, as well as a difficult
area to seal.
Consequently various designs have been proposed wherein the inboard
engine is used to drive a hydraulic pump, and the hydraulic pump provides
hydraulic
fluid under pressure to an outboard reversible hydraulic motor which drives
the
propeller shaft. For example, in United States Patent no. 3,139,062 Keefe
issued
June 30, 1964; 3,587,595 Buddrus issued June 28, 1971; 3,599,595 James issued
August 17, 1971; and 3,847,107, propulsion units are disclosed in which a
hydraulic
motor is mounted on the propeller shaft, below the water line. Such designs
result
in large drag factors due to the volume of the housing which is below the
water line.
Other designs such as shown in U.S. patents 2,486,049 Miller, issued October
25,
1949; 3,673,978 Jeffrey et al. issued July 4, 1972, all provide the hydraulic
motor
above the water line, and connect the motor to the propeller shaft through
bevel
gears. The disadvantage of such designs however is that again for such bevel
gear
connections, the running gear would have to be made substantially more robust
for
high torque applications, and so could no longer be contained within a
streamlined
lightweight casing. The case would have to be made larger and more bulky in an
attempt to withstand the inherent side thrust associated with bevel gears. In
higher
speed applications where this unit is desirable, such a massive leg would
compromise
fuel efficiency with its increased mass and multiplied drag.
There is therefore a need for an outboard drive system which will
satisfy the higher horsepower/torque requirements of larger commercial
vessels, as
well as compete with existing outboard drives.
Disclosure of Invention
The present invention therefore provides an outdrive designed to
surpass the horsepower and torque limitations set by current state-of the-art
units.
In order to meet these objectives the outdrive was designed to incorporate a
multi-
CA 02390818 2002-O1-16
WO 00/03915 PCT/CA98/00698
-4-
strand roller chain drive, replacing the conventional bevel gear arrangement.
Using
a chain drive in this application serves to increase the horsepower rating of
this type
of drive and increase the durability of the outdrive, while keeping the outer
casing
very streamlined.
The invention therefore provides a marine propulsion system, compris-
ing: i) a transom; ii) an engine inboard of the transom; iii) a steerable
screw
propulsion unit outboard of the transom, and comprising a propeller shaft
mounted
for rotation in the propulsion unit and having a propeller mounted thereon;
iv) a drive
shaft mounted for rotation in the propulsion unit parallel to the propeller
shaft; v)
means for transferring power from the engine to rotate the drive shaft; and
vi)
flexible belt means for coupling the drive shaft to the propeller shaft and
thereby
transferring rotational energy from the drive shaft to the propeller shaft.
Preferably
the means for transferring power from the engine to rotate the drive shaft
comprises
a hydraulic pump inboard of the transom and coupled to be driven by the
engine, a
reversible hydraulic motor mounted on the propulsion unit and coupled to drive
the
drive shaft, and fluid conduits communicating between the hydraulic pump and
the
hydraulic motor to transfer pressurized fluid from the hydraulic pump to the
hydraulic
motor.
Brief Description of Drawings
In drawings illustrating a preferred embodiment of the invention:
Figure 1 is a schematic illustration of a prior art stern drive system;
Figure 2 is a schematic illustration of the marine propulsion system according
to the present invention;
Figure 3 is a side elevation, partially cut-away, of the drive unit for the
marine propulsion system according to the present invention; and
Figure 4 is a rear view of the drive unit shown in Figure 3.
Figure 5 is a side elevation, partially cut-away, of a second embodiment of
the
drive unit for the marine propulsion system according to the present
invention;
CA 02390818 2002-O1-16
WO 00/03915 PCT/CA98/00698
-5-
Figure 6 is a side elevation, partially cut-away, of the second embodi-
ment of the drive unit for the marine propulsion system shown in
Figure 5, in a normally tilted-up position;
Figure 7 is a side elevation, partially cut-away, of the second embodiment of
the drive unit for the marine propulsion system shown in Figure 5, in an
emergency tilted-up position; and
Figure 8 is an end view, in cross-section, showing the drive chain arrange-
ment of the second embodiment of the drive unit for the marine propulsion
system shown in Figure 5.
Best Models) For Carr~;g Out the Invention
In the prior art propulsion system shown in Fig. 1, an internal
combustion engine 10, mounted inboard, has a fixed ratio transmission 12
mounted
directly in line with it. The outboard drive unit 14 is connected through the
transom
16 to the transmission 12 via a universal joint 18.
In the marine propulsion system of the present invention shown in Fig.
2, internal combustion engine 20, mounted inboard, drives a variable
displacement
pump 22. Pump 22 provides hydraulic fluid under pressure, through hydraulic
conductors 24, to a reversible hydraulic motor 26 mounted on the outboard
drive 28,
outboard of the transom 29. A suitable hydraulic pump and motor system for use
with a 250 horsepower engine producing 500 foot-pounds of torque is the EATON
Hydrostatic Transmission Model 76 pump and Model 54 motor.
The drive unit of the invention is shown in more detail in Figures 3 and
4. While in the preferred embodiment of this system, rotation is transmitted
from the
inboard engine 20 to the top shaft 30 of the outdrive by a variable hydraulic
transmission including a reversible hydraulic motor 26 as described above,
other
sources of rotation from the source, either inboard or outboard, can be used
to couple
the rotation to the top shaft of the outdrive, such as by a conventional
CA 02390818 2002-O1-16
WO 00/03915 PCT/CA98/00698
-6-
engine/gear-type system. The top shaft 30 comprises a multi-strand sprocket 31
supported by an arrangement of bearings 32. The propeller shaft 34, located in
the
lower portion of the drive 28, comprises another mufti-strand sprocket 35 and
is
supported by an arrangement of bearings 36. Propeller 38 is mounted on shaft
34.
Linking the two parallel shafts 30, 34 is a fixed ratio chain reduction that
may vary
depending on the application, whether conventional or hydraulic. This
reduction is
achieved using a durable, mufti-strand roller chain 40 such as a
DIAMOND~° multi-
strand chain. The chain is lubricated by an oil bath (not shown) or
pressurized
stream lubrication, and kept taut using a standard form of idler arrangement
as in Fig.
8. Typically, mufti-strand chains consist of two more lengths of roller chain
that are
joined side by side to form a wide belt. By adding more strands of chain or
changing
the pitch (link size) of the chain, the amount of torque transmitted can be
greatly
increased without making the outer dimensions of the chain case any wider.
Also by
replacing the prior art bevel gear drive with a chain, the loads in the drive
train
become pure radial loads as opposed to combined radial and thrust loads. These
pure
radial loads require only radial-type bearings which are much smaller in
diameter than
a similar combined radial and thrust bearing used with bevel gear system. The
advantages over the prior art systems are greater torque capacity, longer
bearing life
and improved durability, without compromising the streamlined casing profile.
The outer casing 43 may be fabricated or cast to include all appropriate
hydrodynamic features, such as steering and planing fms. The drive unit 28 is
mounted on the transom 29 by mounting bracket 42. Steering and trim are accom-
plished using standard hydraulic steering cylinders 44 and trim cylinders 46.
By combining the aforesaid chain drive unit design with the hydraulic
coupling from the engine to the drive unit, further benefits are obtained.
Increasing
or lowering the speed of the boat can be achieved through adjustment of the
pump's
flow control rather than varying the engine speed. The bi-directional
hydraulic motor
permits immediate shifting into reverse, and unlimited propeller speed is
possible in
both forward and reverse. This arrangement allows the engine to be operated
CA 02390818 2002-O1-16
WO 00/03915 PCT/CA98/00698
_7_
constantly in its most efficient range of engine speeds from the standpoint of
greatest
torque and fuel efficiency. This is generally a relatively low rpm, which
prolongs
engine life and reduces unburned fuel emissions. Also the universal joint
connection
is eliminated and the pump and outboard-located motor are connected only by
hydraulic lines, which improves the design flexibility for location of the
engine and
pump within the boat and reduces the area of openings through the transom. Two
outboard drives can be powered by a single inboard engine.
A second embodiment of the drive unit 150 of the invention, which
provides an emergency tilt-up feature and a reduction gear on the chain drive,
is
shown in Figures 5 through 8. Drive unit 150 has upper casing 115, lower
casing
128, propeller torque stop 126 and cavitation plate 134. The primary drive
shaft 116
is driven by hydraulic motor 112 and comprises a multi-strand sprocket 101
supported
by upper sprocket bearing 133. The propeller shaft 100 comprises mufti-strand
final
drive sprocket 103, propeller shaft forward and reverse thrust bearing 121 and
propeller shaft retaining nut 122 and is supported by propeller shaft load
carrying
roller 129. Seal carrier 127 holds the propeller shaft seal. Intermediate
shaft 106
comprises primary reduction sprocket 104 and reduction sprocket 105 and is
mounted
on bearings 107 held in bearing carriers 124. Linking the two parallel shafts
116,
106 is the primary drive chain 119. Final drive chain 109 links parallel
shafts 106,
100. Lubricating oil collects in Tube oil sump 130 through Tube oil drain
holes 81.
Figure 8 illustrates that the primary reduction sprocket 104 is larger
than reduction sprocket 105 and primary sprocket 101 and final drive sprocket
103.
A chain tensioner 102 bears against the return side of the chain, and can be
switched
from one side to the other depending on the direction of propeller rotation.
This
chain drive construction thereby permits a gear reduction of the engine speed
to
permit higher torque to be applied to the propeller.
Steering of the drive unit is accomplished in the usual way by steering
cylinder 131, steering tiller arm 110 and kingpin 141, mounted in kingpin
upper
CA 02390818 2002-O1-16
WO 00/03915 PCT/CA98/00698
_$_
bearing 113 and kingpin lower bearing 114. Activation of trim cylinder 171
causes
tilting of the drive unit, as shown in Fig. 6. This embodiment also has an
emergency
tilt-up system 140 which permits the drive unit to pivot upwardly about pivot
joint
220 when a submerged obstacle is struck, as shown in Fig. 7. When the drive
unit
is in forward drive, end 172 of trim cylinder 171 sits in open forward thrust
socket
107. If a submerged obstacle is hit, end 172 of trim cylinder 171 is forced
out of
forward thrust socket 107, and drive unit 151 pivots upwardly on emergency
tilt-up
arm 132 which is attached at one end to end 172 of trim cylinder 171 and
rotates at
its other end in pivot joint 220. When the drive unit is in reverse, reverse
lockup
cylinder 118 is activated to close hook 160 and thereby lock end 172 of trim
cylinder
171 in forward thrust socket 107.
Also according to the invention, an electrically-powered system can be
substituted for the hydraulically powered system. In this case, an electric
generator,
driven by the internal combustion engine 20, is substituted for the pump 22.
Electrical conductors are substituted for the hydraulic conductors 24. A small
DC
electric motor, preferably reversible, of the type manufactured by General
Electric
or Siemens, is substituted for the hydraulic motor 26. Otherwise the operation
of the
electrical version of the invention is the same.
As will be apparent to those skilled in the art in the light of the
foregoing disclosure, many alterations and modifications are possible in the
practice
of this invention without departing from the spirit or scope thereof.
Accordingly, the
scope of the invention is to be construed in accordance with the substance
defined by
the following claims.
