Note: Descriptions are shown in the official language in which they were submitted.
s~o
Title: GEAR CASE FOR MARINE PROPULSION DE~-ICE
Inventor: Philip J. McGowan
~ACKGROUND OF THE INVENTION
This invention relates to marine propulsion
devices, such as outboard motors and stern drive units
and, more particularly, to marine propulsion devices
includiny through-the-hub exhaust and means for
increasing propeller thrust. In another aspect, the
invention relates to such marine propulsion devices
including means for controlling hydrodynamic stall.
Outboard motors and stern drive units may
employ a so-called through-the-hub exhaust system
including an engine exhaust gas passageway extending
through the drive shaft housing, the gear case, and an
annular passage inside the propeller hub. Means for
increasing th~ thrust delivered by the propeller of
such marine propulsion devices is a continuing
objective.
~ t higher speeds, cavitation and flow
separation can occur along the outer surface of the
gear case, causing air to reach the low pressure side
of the propeller. When large quantities of air are
pxesent, there can be a sudden loss in the thrust and
load carrying capabilities of the propeller~ a
condition commonly referred to as hydrodynamic stall.
Attention is directed to the following
United States patents:
9S3~)
-2 -
Patentee Patent No. Issue Date
Linthwaite 2,111,3Z5 March 15, 1938
Irgens 2,564,903 August Zl, 1951
Strang 2,791,196 May 7, 1957
Shimanckas 3,310,021 March 21, 1967
Shimanckas 3,467,051 Sept. 16, 1969
Kiekhaefer 3,492,966 Feb~ 3, 1970
Granholm 3,799,103 March 26, 1974
Mapes et al 4,295,835 Oct. 20, 1981
Attention is also directed to copending
Canadian application entitled "Anti-Ventilation Means
for Marine Gear Case", Serial No. 415,526, filed
November 15, 1982.
SUMMARY OF THE INVENTION
The invention provides a marine
propulsion device comprising a lower unit inaluding
an exhaust gas passageway which terminates in a
discharge port, a rotatable propeller shaft extending
through the discharge port, a propeller which is
normally submerged in water and which is mounted on
the propeller shaft for common rotation therewith,
which propeller includes a hub which has a generally
. ~, .~
"i. :.
~:19~5~
circular outse surface and an exhaust gas passageway
which has an inlet in communication with the
discharge port and an outlet in communication with
the water, and a gear case rotatably supporting the
eropeller shaft. which gear case includes a leading
end which has a tapered nose, a trailing end which
has a generally circular cross section with an outer
diameter substantially larger than the outer diameter
of the propeller hub and which terminates in a
generally vertical trailing edge located forwardly of
the propeller hu~, and an outer surface which
substantially continuously radially outwardly expands
from the nose to the trailing edge and intersects the
trailing edge.
In one embodiment, the tapered nose of
the gear case e~tends some distance forwardly beyond
the leadlng edge of the drive shaft housing so as to
make the outer surface of the gear case more
pointed, thareby reducing cavitation and the flow
separation along the outer surface of the gear case
at higher speeds.
Other features, aspects, and advantages
of the invention will become apparent to those
skilled in the
11~395~0
art upon reviewing the following detailed description
the drawing, and the appended claims.
BF~IEF DESCRIPTION OF THE DRAWING
Fig. 1 is a fragmentary, partially broken away
and partially sectioned, view of the lower unit of a
marine propulsion device incorporating various of the
features of the invention.
Fig. 2 is a fragmentary view of the lower unit
of a marine propulsion device including a gear case of
an alternate construction.
Before explaining at least one of the
embodiments of the invention in detail, it is to be
understood that the invention is not limited in its
application to the details of construction and the
arrangements of components set forth in the following
description or illustrated in the drawing. The
invention is capable of other embodiments and of being
practiced and carried out in various ways. Also, it is
to be understood that the phraseology and the
terminology employed herein is for the purpose of
description and should not be regarded as limiting.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Illustrated fragmentarily in Fig. 1 is a
marine propulsion device 10, which can be either a
stern drive unit or an outboard motor, includiny a
propulsion or lower unit 12 having a drive shaft
housing 14 and a gear case 16 which is normally
:~ q 99~3~
submerged in water. The drive shaft housing 14 has a
leading e~ge 17. The gear case 16 has a leading end in
the form of a tapered nose 18, a streamlined or
torpedo-shaped outer surface 19 and an aft or trailing
end portion 20 having a generally circular
cross-section.
Rotatably mounted in the gear case 16 is a
propeller shaft 22 carrying a propeller 23 rearwardly
of the gear case 16. Extending throuqh the drive shaft
housing 14 transversely to the propeller shaft 22 is a
rotatably mounted drive shaft 24 which at the upper end
is operably connected to an internal combustion en~ine
(not shown) and at the lower end is drivingly connected
to the propeller shaft ~ through a conventional
reversing clutch or transmission 26. Extending
downwardly from the gear case 16 is a vertical fin or
skeg 28.
Extending through the drive shaft housing 14
is an exhaust gas passageway 30 which terminates an
exhaust gas discharge port 32 at the trailing end 20
of the gear case 16.
The propeller shaft 22 includes an aft or rear
portion 36 extending rearwardly of the gear case 16 and
a forward portion 38 extending through the discharge
port 32 and rotatably supported inside the gear case 16
by a bearing retainer 40 suitably affixed to the
interior the gear case 16. The bearing retainer 40
includes a central hub portion 42 carrying a roller
bearing 44 and a lubricant seal 46. The bearing
retainer 40 also includes an annular outer sleeve 48
engaging the interior of the gear case 16 and a
plurality of circumferentially-spaced, radially
S~30
extending spokes or ribs 50 interconnecting the hub
portion 42 and the sleeve 48. The openings 52 defined
between the ribs 50 form part of the engine exhaust gas
passageway 30.
The propeller 23 includes a hollow hub 54
having a generally circular outer surface 55 and
carrying a series of blades 56. The propeller 23 also
includes an inner sleeve 58 which is connected to the
hub 54 by a plurality of circumferentially-spaced,
radially extending ribs 60. The sleeve 58 is mounted
on the rear portion 36 of the propeller shaft 20 for
common rotation therewith, such as by splines 62. The
openings 64 between the ribs 60, together with the
interior of the hub 541 define an axially extending
exhaust gas passageway or duct 66 extending through the
hub 54. The duct 66 has an inlet communication with
the discharge port 32 and an outlet rearwardly of the
propeller blades 56 through which the exhaust gases are
discharged into the water. Such an engine exhaust gas
arrangement is commonly called a "through-the-hub"
exhaust system.
The forward thrust produced by the propeller
23 is increased by dimensioning the outer diameter of
the circular trailing end portion 20 of the gear case
16 so that it is substantially làrger than the outer
diameter of the propeller hub 54, by arranging the
, , .
trailing edge 21~of the gear case 16 generally vertical
so there is a sharp stepdown from the trailing end
portion 20 of the gear case 16 to the propeller hub 54,
and by configuring the outer surface 19 of the gear
case 16 so that it substantially continuously radially
outwardly expands from the nose 18 to the trailing edge
9530
21. This specific arrangement produces pressure
conditions in the vicinity of the propeller blades 56
which are favorable for enhancing the power
transimitting characteristics of the propeller 23.
In the alternate construction illustrated in
Fig. 2, the tapered nose 70 of the gear case 72 extends
forwardly some distance beyond the leading edge 17 of
the drive shaft housing 14 to make the outer surface 74
of the gear case 72 more pointed. As in the embodiment
illustrated in Fig. 1, the outer diameter of the
circlar trailing end portion 76 of the gear case 72 is
substantially larger than the outer diameter of the
propeller hub 54, the trailing edge 78 of the gear case
72 is generally vertical to provide a sharp stepdown
from the trailing end 76 of the gear case 72 to the
propeller hub 54, and the outer surface 74 of the gear
case 72 substantially continuously radially outwardly
expands from the nose 70 to the trailing edge 78. This
arrangement, in addition to increasing propeller
thrust, reduces the tendency for cavitation and flow
separation along the outer surface 74 of the gear case
72 at higher speeds, thereby minimizing the amount of
air present in the vicinity of the low pressure side of
the propeller blades 56 which can cause hydrodynamic
stall.
Various of the features of the invention are
set forth in the following claims:
