Pump jet with axial directional flow control device for...

Marine propulsion – Jet drive

Reexamination Certificate

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Details

C440S08900C

Reexamination Certificate

active

06224434

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 outboard 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 volumetric flow through an axial-flow pump jet device produces the propulsive thrust forces necessary to propel a boat or other watercraft. Generally, as the motor rpm approaches full throttle, the thrust forces are also reaching maximum values, provided that the boat velocity is low, as is typically encountered in work boats and pontoon boats. Often it is desirable to modulate the thrust of a pump jet while maintaining the rpm at near wide-open throttle, particularly if a quicker response is possible. In order to achieve this modulation effect at full rpm, it is necessary to control the axial flow through the pump jet device.
SUMMARY OF THE INVENTION
The present invention is a pump jet in which the axial flow of water through the device is controlled by bleeding exhaust gas into the pump jet water stream, thereby producing a thrust loss. In accordance with the preferred embodiment of the invention, an ETV-type pump jet is provided with means for bleeding exhaust gas from the plenum cavity in the stator hub directly into the exit flow stream. This addition of gas into the primary pump jet water flow stream reduces the effective flow density of the exit media, thereby reducing the exit momentum (and thrust) produced by the pump jet. The thrust modulation device can be actuated using any conventional electrical or mechanical actuation subsystem via a knob or lever positioned near the throttle control.
The invention also encompasses a method for operating an ETV pump jet comprising the steps of: activating a motor of an ETV pump jet to cause a rotor to impel a stream of water through the volume between a stator hub and a stator housing, and to cause exhaust gas to pass through a cavity in the stator hub and a hollow stator vane; and bleeding exhaust gas from said cavity inside the stator hub into said water stream.


REFERENCES:
patent: 2213610 (1940-09-01), Ronning
patent: 3754837 (1973-08-01), Shimanckas
patent: 3763817 (1973-10-01), Francis
patent: 4023353 (1977-05-01), Hall
patent: 4240251 (1980-12-01), Fuller
patent: 4274254 (1981-06-01), Jansen et al.
patent: 4631032 (1986-12-01), Nishida
patent: 4902254 (1990-02-01), Chas
patent: 4929200 (1990-05-01), Guezou et al.
patent: 5251436 (1993-10-01), Brogan
patent: 2-144293 (1990-04-01), None
patent: 1279-910 (1986-12-01), None
patent: 1497-109 (1989-07-01), None

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