Marine propulsion – Means for accomodating or moving engine fluids – Means for handling exhaust gas
Utility Patent
1999-10-15
2001-01-02
Sotelo, Jesus D. (Department: 3617)
Marine propulsion
Means for accomodating or moving engine fluids
Means for handling exhaust gas
C416S09300R
Utility Patent
active
06168485
ABSTRACT:
FIELD OF THE INVENTION
This invention generally relates to pump jets used with outboard motors or in inboard/outboard or stern drive units of boats and other vehicles. In particular, the invention relates to pump jets in which exhaust gas from the motor is discharged into the water stream surrounding the pump jet.
BACKGROUND OF THE INVENTION
In conventional outboard motors, a propeller is driven by a powerhead to propel a boat through the water. Essentially all modern motors inject the exhaust gas stream under water in order to reduce noise of the engine. However, the injected stream of exhaust gas can occupy a space, causing drag.
Prior to the 1970s most outboard motors injected the exhaust gas from a powerhead through a downstream channel to an exhaust gas outlet
14
. The exhaust is injected from the exhaust gas outlet into the water at a location downstream from the propeller. This type of motor will be referred to herein as a downstream exhaust motor.
During the 1970s, many outboard motors were changed over to a configuration in which gas from the powerhead was exhausted through a hollow hub in the propellor (provided for that purpose). The reason for the change over to an “exhaust through hub” (ETH) motor was the drag caused by the exhaust. It is known that the gear case causes drag. By locating the exhaust stream concentrically behind the gear case, the drag of the exhaust can be canceled out by the drag of the gear case. Manufacturers received an added benefit when the ETH configuration was used, namely, they were able to increase efficiency by using a larger-diameter gear case, larger crown gears, and thus slower-turning, more efficient propellers without increasing drag.
Another type of conventional outboard motor has an axial-flow pump jet system driven by the powerhead. In a pump jet system, an impeller or rotor is mounted (e.g., spline fitted) directly on the propeller output shaft in place of the propeller. There are typically no modifications to the drive train, cooling or sealing components. A ducted housing surrounds the rotor. Such a system has the advantages of reducing hazards to swimmers in the vicinity of the motor, protecting the rotating elements from interference with and damage by foreign objects in the water, and improving the efficiency and performance of the propulsion system. Another benefit inherent with the pump jet is a directed jet of water that results in greater steering response.
An example of this kind of pump jet installed on a downstream exhaust motor is shown in
FIG. 1. A
bladed rotary impeller or rotor is positioned below an anti-ventilation plate
12
and rearward of a lower unit housing
10
. The rotor comprises a plurality of blades
18
extending radially outward from an outer rotor hub
19
, the latter being is attached to a rearwardly projecting propeller shaft
16
for rotation therewith. A housing or shroud
21
having a front section or rotor housing
20
and a rear section or stator housing
22
houses the bladed rotary impeller. The rotor housing
20
is part of a one-piece rotor housing assembly, which also comprises a plurality of inlet vanes
63
and an inlet vane hub
70
. Each inlet vane
63
is joined at one end to the inlet vane hub
70
and at the other end to the rotor housing
20
. The inlet vanes direct water flow into the blades
18
of the rotor. The inlet vanes also block debris, sea creatures or human limbs from contacting the rotating blades of the rotor. A bearing support
26
engages the rear end of the propeller shaft
16
. The stator vanes
30
, which are present to neutralize the swirl from the impeller, also serve to attach the bearing support
26
to the stator housing
22
. At the rear end of the anti-ventilation plate
12
is a downwardly projecting exhaust gas outlet
14
which directs the exhaust gas into a channel
24
formed in the upper surface of the stator housing
22
.
Referring to
FIG. 2
, a pump jet
44
is mounted on an outboard motor
32
. The outboard motor
32
comprises a powerhead
34
and a leg
36
. The outboard motor
32
also includes conventional anti-ventilation plate
12
and lower unit housing
10
. The outboard motor
32
is preferably attached to a boat
40
or other marine vehicle or watercraft by an appropriate mounting bracket
38
, which attaches to the transom of the boat hull.
During operation of the motor
32
, an exhaust gas stream
110
flows downwardly from the powerhead
34
through an exhaust duct
50
positioned in the central portion of the outboard motor. The exhaust gas stream is injected in a rearward direction from the exhaust gas outlet into the water at a location downstream of the squeeze point P and above the stator housing
22
.
In normal operation of a downstream exhaust motor having an attached pump jet as shown in
FIG. 2
, flow streamlines
102
follow the shape of the lower unit housing
10
. Streamlines
104
behind the lower unit housing
10
follow the surface of the rotor housing
20
and stator housing
22
. At the maximum diameter of the pump jet between the top of the pump jet surface and the bottom surface of the anti-ventilation plate
12
is a so-called “squeeze point” P. Streamlines
106
down-stream of the squeeze point P and near the surface of the pump jet try to follow the conical surface of the pump housing and streamlines
108
near the anti-ventilation plate
12
try to remain parallel thereto. During the operation of this downstream exhaust motor, drag is created downstream of the squeeze point P.
FIG. 3
diagrammatically illustrates a prior art pump jet apparatus in which an exhaust gas stream
110
flows downwardly from the powerhead
34
through an exhaust duct
62
positioned in the central portion of the outboard motor. The exhaust gas is channelled in a rearward direction from the exhaust duct
62
to an exhaust channel
42
. The exhaust gas flows from the exhaust channel
42
above the stator housing
22
to exit the outboard motor
32
. An exhaust extension duct
46
is positioned above the stator housing
22
and is coupled to the exhaust channel
42
for discharging the exhaust gas rearwardly of the squeeze point P. The rear end of the exhaust extension duct
46
flares outwardly for controlling the size of the exhaust gas stream. The angle of the flare of the exhaust extension duct
46
can be increased or decreased to control the expansion of the exhaust gas stream. A trough
48
is formed in the upper surface of the stator housing
22
below the exhaust extension duct
46
to receive the exhaust gas. The trough
48
allows a portion of the exhaust stream to be concealed behind the pump jet housing, whereby an improved flow of the exhaust gas stream is achieved and drag is reduced.
Since the exhaust streams of the prior art propulsion systems shown in FIGS.
1
-
3
are released near the water surface, the level of exhaust noise is relatively high. For pump jets to be viable on recreational watercraft, the level of exhaust noise needs to be reduced.
One current approach to this problem is to distribute the exhaust flow among several hollow stator vanes, which discharge the gas at relatively high velocity through several openings distributed circumferentially around the stator housing. The procedure is effective in reducing exhaust noise, but requires the use of rotating gas seals and hollow stator vanes. Such an “exhaust through vane” (ETV) configuration is depicted in FIG.
4
. The stator housing
52
is part of a one-piece stator housing assembly, which also comprises a plurality of stator vanes
54
and a stator hub
56
. Each stator vane
54
is joined at one end to the stator hub
56
and at the other end to the stator housing
52
. The stator vanes
54
convert rotational energy imparted to the water flow by the rotor blades into axial flow energy at the outlet of the stator housing
52
. One or more of the stator vanes
54
is hollow. Similarly, an internal cavity in the stator hub
56
forms a plenum cavity
58
, which is in flow communication with each hollow stator vane. The exhaust gas from the powerhea
Hall Kimball P.
Martino John D.
Varney A. Michael
Flaherty Dennis M.
Outboard Marine Corporation
Pilarski John H.
Sotelo Jesus D.
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