Pump jet with redirected exhaust gas through stator vane for...

Marine propulsion – Screw propeller – Having means to control flow around propeller

Reexamination Certificate

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Details

C440S08900C

Reexamination Certificate

active

06190218

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 directed through the pump jet and discharged into the water stream surrounding the pump jet.
BACKGROUND OF THE INVENTION
In one type of conventional outboard motor, a propeller is driven by a powerhead to propel a boat through water. Most large outboard motors of this type inject the exhaust gas stream under water in order to reduce engine noise and increase propulsive thrust.
In a typical configuration shown in
FIG. 1
, the gas exhausted from the powerhead
10
flows downwardly through an exhaust channel
12
and exits the motor rearwardly through the propeller
14
. This type of motor is referred to as an exhaust-through-hub (ETH) motor.
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.
U.S. Pat. No. 5,325,662 discloses a pump jet in which the exhaust gas discharged from the outboard motor is ducted downwardly through the central body of the motor and around a rotor shaft. An annular exhaust channel is formed in the rotor hub for receiving the exhaust gas and projecting it rearwardly of the motor. A cavity in the stator hub provides a plenum chamber for receiving the exhaust gas. Exhaust gas flows from the cavity of the stator hub to at least one hollow stator vane which serves as an exhaust pipe. In the case of multiple hollow stator vanes, the flow in the stator hub is split into multiple streams. Each stream of exhaust gas passes through a respective hollow stator vane. Discharge ports are formed in the stator housing for discharging exhaust gas into the water stream surrounding the stator housing. This arrangement will be referred to herein as an exhaust-through-vane (ETV) configuration.
The ETV configuration works well in practice. But the cross-sectional area of the hollow passages in the assemblage of hollow stator vanes is limited by practical considerations, with the result that the velocity of the gas streams exiting from the vanes must be several times greater than the velocity of the boat and pump jet through the water. There is a mismatch between boat velocity and exhaust gas velocity, so the exhaust gas stream must slow down, and in doing so, the exhaust gas stream “bushes out” and presents a significant added frontal area to the water stream, producing added drag. There is also a mismatch in the direction of the exhaust gas flow, which further adds to the frontal area of the gas stream, producing more drag.
Thus, there is a need for an improvement to an ETV-type pump jet which will minimize the mismatch in velocity and the mismatch in direction, thereby enhancing motor performance.
SUMMARY OF THE INVENTION
The present invention is an ETV-type pump jet having means for minimizing the mismatches between the velocity and direction of the exhaust gas flow and the velocity and direction of boat and pump jet motion. As used herein, the term “ETV-type” includes both “exhaust-through-vane” and “exhaust-through-strut” types of pump jet.
In accordance with one preferred embodiment of the invention, exhaust ducts are attached to the external surface of the stator housing. Each exhaust duct is positioned to be in flow communication with the exhaust gas outlet of a respective hollow stator vane. The exhaust ducts may be attached by welding or brazing, by fastening (e.g., using bolts or screws), or by any other conventional attachment means. As used herein, the term “exhaust duct” is not a tubular channel, which is the normal sense in which the term a “duct” is used, but rather is a portion of a duct which acts as a shield to allow the exhaust gases to discharge from the exhaust outlets free of interaction with the water stream external to the stator housing. The outlet of each exhaust duct is defined by the trailing edge of the duct and the opposing external surface of the stator housing.
Preferably, each exhaust duct comprises a curved piece of sheet material, e.g., metal, having a three-dimensional curved edge which abuts the external surface of the stator housing along a contour which partly surrounds the exhaust outlet of a corresponding hollow stator vane, and having an arc-shaped or eyebrow-shaped trailing edge which preferably lies in a plane perpendicular to the axis of the rotor shaft. Preferably, the duct material is a portion of a circular cylindrical surface and lies substantially parallel to the rotor shaft axis (i.e., the pump jet central axis). However, the ducts need not be sections of a circular cylinder. Other shapes may be used to decrease the cross-sectional area of the outlet formed by the stator housing and the trailing edge of each duct.
In the case where the ducts are circular cylindrical, exhaust gases exiting the exhaust outlets are redirected by the inner surfaces of the ducts to flow in parallel with the rotor shaft axis, i.e., in parallel with the direction of pump jet motion. In addition, the ducts provide a cross-sectional area for the exhaust gas stream which increases from adjacent the exhaust outlet to the duct outlet formed by the stator housing and the trailing edge of the exhaust duct. The result will be an exhaust gas stream which exits the exhaust duct parallel to and at a velocity equal to or less than that of the water stream flowing along the outer surface of the exhaust duct during forward motion of the pump jet (provided that the eyebrow-shaped ducts are properly sized). It is expected that the exhaust ducts in accordance with the preferred embodiment will achieve improved performance over the entire pump jet speed range.
In accordance with another preferred embodiment of the invention, an exhaust skirt is attached to the external surface of the stator housing. The exhaust skirt surrounds the stator housing, and is preferably coaxial with the stator housing. The skirt may be either circular cylindrical or conical with radius decreasing in the rearward direction. Exhaust gases exiting the exhaust outlets at the outer surface of the stator housing are redirected by the inner surface of the skirt to flow in parallel with the water flow at the trailing edge of the skirt. The exhaust skirt may be attached to the stator housing by welding or brazing, by fastening (e.g., using bolts or screws), or by any other conventional attachment means.


REFERENCES:
patent: 3658028 (1972-04-01), Koons
patent: 3943876 (1976-03-01), Kiekhaefer
patent: 4304558 (1981-12-01), Holtermann
patent: 4600394 (1986-07-01), dritz
patent: 4643685 (1987-02-01), Nishida
patent: 4832570 (1989-05-01), Solia
patent: 4931026 (1990-06-01), Woodland
patent: 5273467 (1993-12-01), Hall
patent: 5325662 (1994-07-01), Varney et al.
patent: 5482482 (1996-01-01), Davis
patent: 722842 (1942-07-01), None
patent: 748218 (1944-10-01), None
patent: 0298053 (1989-04-01), None
patent: 20843 (1907-09-01), None
patent: 1-273788 (1989-11-01), None

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