Water jet propulsion unit with counter-rotating impellers

Details Water jet propulsion unit with counter-rotating impellers Water jet propulsion unit with counter-rotating impellers

2000-04-07

2001-08-14

Sotelo, Jesus D. (Department: 3617)

Marine propulsion

Jet drive

C440S038000, C440S075000, C440S079000

Reexamination Certificate

active

06273768

ABSTRACT:

FIELD OF THE INVENTION
This invention generally relates to water jet apparatus for propelling boats and other watercraft. In particular, the invention relates to mechanisms for impelling water through a flow-through housing of a water jet propulsion unit.
BACKGROUND OF THE INVENTION
It is known to propel a boat or other watercraft using a water jet apparatus mounted to the hull, with the powerhead being placed inside (inboard) or outside (outboard) the hull. The drive shaft of the water jet apparatus is coupled to the output shaft of the motor. The impeller is mounted on the drive shaft and installed in a housing, the interior surface of which defines a water tunnel having a convergent nozzle. The impeller is designed such that during motor operation, the rotating impeller impels water rearward through the water tunnel and out the convergent nozzle. The reaction force propels the boat forward.
In many water jet apparatus designs, the flow-through housing comprises an outer tubular section and a central hub, the outer tubular section and central hub being generally concentrically arranged to define a generally annular passageway downstream of the impeller. This passageway forms part of the water tunnel. The outer tubular section is sometimes referred to as the “stator housing” while the central hub is called the “stator hub”. The stator hub typically rotatably supports the impeller shaft. The stator hub is supported inside the stator housing by a plurality of stator vanes or ribs which are curved to straighten the swirling water flowing downstream from the impeller. This straightening of the impelled water absorbs energy, resulting in a loss of efficiency of the water jet propulsion unit or pump. There is a need for a mechanism which would decrease the amount of energy lost due to flow straightening by the stator vanes.
SUMMARY OF THE INVENTION
The present invention is directed to a water jet apparatus having means for decreasing the amount of energy lost due to flow straightening by the stator vanes. In accordance with the preferred embodiments of the invention, this is accomplished by installing counter-rotating impellers in sufficiently proximal relationship such that the swirling effect produced by the upstream impeller is at least partially countered by the downstream impeller. In other words, the water flow exiting the downstream impeller has a smaller rotational component than the water flow exiting the upstream impeller. This impeller arrangement requires a less severe curvature of the straightening vanes, resulting in an increase in efficiency. In accordance with the preferred embodiment of the invention, the vanes have no curvature, i.e., are straight.
In accordance with the preferred embodiments, the counter-rotating impellers are coupled by an assembly comprising an impeller shaft secured to one of the impellers and a gear train coupling the impeller shaft to the other impeller for counter-rotation. Preferably the gear train comprises one beveled gear secured to the impeller shaft, another beveled gear secured to the second impeller, and a beveled pinion meshed with the first and second beveled gears. The counter-rotating impellers can be driven by a drive shaft coupled to the first impeller for boats having an inboard motor or by a drive shaft coupled to the pinion for boats having an outboard motor.
In accordance with an alternative preferred embodiment, the drive shaft and impeller shaft can be combined in a single shaft having the first impeller and the first beveled gear attached thereto, with the second impeller being attached to a sleeve of the second gear which is rotatable relative to the shaft and to a hub which encircles the gear train and defines the inner boundary surface of a water tunnel through which impelled water flows rearward.
In accordance with one preferred embodiment, the water jet propulsion unit comprises the following: a flow-through housing; a central hub supported inside the housing by a plurality of vanes; first and second gears rotatably mounted in the central hub; a pinion rotatably mounted in the central hub and meshed with the first and second gears such that rotation of the first gear causes rotation of the second gear; an impeller shaft coaxial with the first and second gears and having one portion connected to the first gear and another portion rotatable relative to the second gear.
The preferred embodiment of the invention will be disclosed in the context of water jet propulsion system which is driven by an inboard motor. However, the person skilled in the art will readily appreciate that the counter-rotating impellers disclosed herein have application beyond water jet propulsion systems driven by an inboard motor. For example, the counter-rotating impellers disclosed herein have application in a water jet propulsion system driven by an outboard motor.


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Abstract of New Zealand Patent No. 123228, “Hydraulic Jet Propulsion Apparatus for Boats,” C.W.F. Hamilton, Mar. 24, 1960, tyaken from Patent office Journal, Oct. 1960, p. 547.

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