Marine propulsion – Jet drive
Reexamination Certificate
1999-09-07
2001-08-07
Swinehart, Ed (Department: 3617)
Marine propulsion
Jet drive
C440S047000
Reexamination Certificate
active
06270385
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 means and methods for reducing noise produced by an operating 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.
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.
A boat powered by an outboard motor equipped with a conventional open propellor generates a unique noise signature which is characterized by a three-dimensional noise field similar in shape to an ice cream cone lying on its side. The size of the noise field is determined by the propeller size, the number of propellor blades, the rotational speed of the engine. etc.
For many applications, the capability to restrict the size of the emitted noise field, as well as change its spectral intensity over the field of interest (e.g., audible near-field alteration), is desirable. A shroud or propeller guard can be used to achieve part of the noise field reduction, but installation of a shroud or propeller guard is accompanied by a loss in performance of the propulsion system.
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. More pertinent to the present invention, the pump jet propulsor, with its high-efficiency shrouded design, alters the radial noise field and provides an opportunity to also alter the noise spectrum.
SUMMARY OF THE INVENTION
The present invention has application in pump jets of the type having a rotor assembly surrounded by a housing. In one conventional type of jet pump apparatus, the housing comprises a rotor housing connected to a stator housing, the former surrounding the rotor and the latter being downstream of the rotor. The rotor is driven by the powerhead via a drive train. Rotation of the rotor impels ambient water from the housing inlet to the housing outlet.
Due to manufacturing tolerances, during rotation the rotor can wobble on the propeller shaft, causing the tips of the rotor blades to contact the opposing surrounding surface, thereby causing that surface to wear. If the inner circumferential surface of the rotor housing were placed in close surrounding relationship to the rotor, without an intervening member, then that rotor housing surface would experience wear. If that wear were allowed to continue indefinitely, replacement of the worn rotor housing could become necessary.
A conventional solution to this problem is to make a circumferential recess in the rotor housing at a position opposing the rotor blade tips and then to install a replaceable, i.e., sacrificial, circular cylindrical wear liner in that recess. Consequently, wear caused by the wobbling rotor will occur on the inner circumferential surface of the wear liner. When the damage to the wear liner reaches an unacceptable level, the wear liner can then be replaced without the necessity of replacing the rotor housing.
In accordance with the present invention the wear liner inside the rotor housing is modified in order to alter the spectrum of noise produced by the pump jet. In the preferred embodiment, a replaceable wear liner in the form of a perforated sleeve is inserted in a circumferential recess formed on the inner surface of the rotor housing. The perforated wear liner surrounds the rotor tip region and has a multiplicity of small, preferably circular throughholes.
In accordance with the preferred embodiment of the invention, the throughholes or perforations are constant in size and regularly spaced. The holes may be drilled, punched or otherwise formed. Preferably, the perforated wear liner is a circular cylindrical continuous ring or rolled strip. In surrounding relationship to the tips of the rotor blades, the perforated wear liner acts as a Helmholtz resonator liner which alters the spectrum of noise emitted from the pump jet during operation. Proper selection of the size, number and spacing of the holes permits the designer to control the specific noise spectrum range that is emitted from the front and rear lobes of the pump jet, thereby altering the hydrodynamic noise field.
REFERENCES:
patent: 3034467 (1962-05-01), Pestronk
patent: 3346174 (1967-10-01), Lievens et al.
patent: 3398932 (1968-08-01), Koeller et al.
patent: 3821999 (1974-07-01), Guess et al.
patent: 4453887 (1984-06-01), Schucker
patent: 4637801 (1987-01-01), Schultz
patent: 4692091 (1987-09-01), Ritenour
patent: 4720239 (1988-01-01), Owczarek
patent: 4828175 (1989-05-01), Heufler et al.
patent: 5060471 (1991-10-01), Torkelson
patent: 5099566 (1992-03-01), Barrett
patent: 5160248 (1992-11-01), Clarke
patent: 5215433 (1993-06-01), Weiland et al.
patent: 5256031 (1993-10-01), Bothien et al.
Martino John D.
Varney A. Michael
Bombardier Motor Corporation of America
Flaherty Dennis M.
Swinehart Ed
LandOfFree
Pump jet rotor housing modification for noise signature... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Pump jet rotor housing modification for noise signature..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Pump jet rotor housing modification for noise signature... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2478436