Marine propulsion – Jet drive
Reexamination Certificate
2003-04-14
2004-09-28
Morano, S. Joseph (Department: 3617)
Marine propulsion
Jet drive
C440S083000, C415S199400
Reexamination Certificate
active
06796858
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to jet powered watercraft, especially personal watercraft (“PWC”). More specifically, the invention relates to a jet power assembly, in particular to an impeller and its associated components.
2. Description of Related Art
Jet powered watercraft have become very popular in recent years for recreational use and for use as transportation in coastal communities. The jet power offers high performance and allows the watercraft to be more compact and fast. Accordingly, PWCs, which typically employ jet propulsion, have become common place, especially in resort areas.
A typical jet propulsion system for a PWC includes a jet pump. The jet pump pulls water in through an inlet, pressurizes it, and forces it through a venturi resulting in a high pressure water jet. The result is a reaction force called thrust that propels the PWC in the direction opposite to the water jet. Typically, a steering nozzle, located at the discharge end of the pump, is controlled by a steering mechanism to redirect the water jet so as to effect steering of the PWC. The jet pump utilizes an impeller, rotated by an engine via a drive shaft (and/or impeller shaft) to circulate and pressurize the water. However, the typical impeller utilizes impeller blades that have a relatively large pitch. Accordingly, as the impeller is rotated, the water stream exiting the impeller is directed into a relatively tight spiraling flow. In order to rectify or straighten the spiraling water stream, the typical jet pump includes a non-rotating stator having blades to attenuate or eliminate the rotation of the flow.
FIG. 14
shows a conventional jet pump, which can be used in a jet-propelled watercraft, indicated at
800
. The jet pump
800
includes a rigid housing
802
within which a stator
804
is fixedly mounted. An impeller
806
is rotatably mounted to the stator
804
via an impeller shaft
808
. As shown, the impeller
806
includes a plurality of impeller blades
810
. The stator
804
includes a plurality of stator vanes
812
. A pump cover
814
is fastened to a rearward end of the stator
804
with, e.g., fasteners
816
. A venturi
818
is connected to the housing
802
rearward of the stator
804
. The connecting element
808
is fixedly connected to the impeller
806
and rotates with the impeller
806
relative to the stator
804
on bearings
820
. The bearings
820
are disposed within a cavity
822
within the stator
804
, which is typically filled with a lubricant. A seal
824
prevents debris and water from entering the cavity
822
. The pump cover
814
protects the impeller shaft
808
and bearings
820
and encloses the cavity
822
to prevent lubricant leakage. The pump cover
814
is conically configured to facilitate the flow of water through the venturi
818
. The venturi
818
sometimes includes a plurality of fins
826
therein that extend radially inwardly therefrom.
In operation, an engine is coupled to the impeller
806
via a drive shaft (not show) to thereby rotate the impeller
806
. The impeller
806
thus pulls water from the body of water and pressurizes the water as the impeller
806
is rotated. Due to the rotational speed of the impeller
806
and to the pitch of the blades
810
, water being pressurized by the impeller
806
assumes a spiraling flow as it exits the impeller
806
. The stator vanes
812
extend relatively co-extensively to the axial direction of the jet pump
800
and serve to straighten or rectify the spiraling flow of water as it passes therethrough. The flow of water is accelerated in a progressive manner as the flow travels axially past the impeller
806
due to the progressive increase in diameter of the impeller hub
811
. The flow of water exits the stator
804
and enters the venturi
818
. A gradual reduction in diameter of the venturi
818
serves to converge the flow of water and also accelerates the flow. The venturi
818
includes an outlet opening
828
through which the flow of water exits the jet pump
800
to propel the watercraft.
FIG. 15
shows the stator
804
in relatively greater detail. As shown, each of the stator vanes
812
is curved to facilitate rectification of the flow of water from the impeller
806
. Additionally, each of the vanes
812
has a cross-sectional configuration similar to that of an airfoil with a trailing edge that is slightly tapered. The airfoil-like configuration serves to facilitate flow of water past the stator vanes
812
. However, the stator vanes
812
have a relatively constant thickness, typically about 2-5 mm. Since the stator vanes
812
are angled at their leading edge and progressively straighten out toward their trailing edge, and a flow area between the blades at the trailing edge portions is greater than a flow area between the blades at the leading edge portions, the flow of water decelerates as it moves past the vanes
812
. The venturi
818
and pump cover
814
are tapered in their cross-sectional configurations so as to converge and pressurize the water stream and, therefore, the water stream is accelerated as it flows past. However, the deceleration of the water flow through the stator
804
represents an energy loss that decreases the efficiency of the jet pump
800
.
FIG. 16
shows an improved type of jet pump
850
, which is referred to as a converging type jet pump. As shown, the jet pump
850
has a housing
852
that incorporates an integral venturi
854
. The jet pump
850
includes a stator
856
that has a plurality of stator vanes
858
. A hub
860
of the stator
856
has a conical configuration corresponding to that of the venturi
854
. The stator vanes
858
have an airfoil-like configuration similar to those shown in
FIG. 15
, but may be arranged with a greater degree of curvature. Additionally, the stator vanes
858
are also tapered (radially with respect to the stator hub
860
) to conform to the venturi
854
. Contrary to the stator
804
shown in
FIG. 15
, head loss through the stator
856
is reduced, since the cross-sectional area of the flow path between the stator vanes
858
is decreased due to the tapered configuration of the venturi
854
along the length of the vanes
858
, even though trailing edge portions of the vanes
858
are narrower than the leading edge portions thereof. This design effectively eliminates the degrading head loss within the stator
856
. However, typical manufacturing processes for producing stators, i.e., casting, may not be used or is highly costly due to the conical shape of the hub
860
and configuration of the vanes
858
. Therefore, other more costly and inefficient methods of manufacture must be used to create the stator
856
.
For at least these reasons, a need has developed for a jet pump that is highly efficient and is easily manufactured.
Another consideration with operation of PWCs is the creation of noise pollution during the operation thereof. The use of internal combustion engines operating at high RPMs make conventional watercraft typically quite noisy to operate. Technological advances in engine noise attenuation systems have dramatically decreased the operating volume of the engine in typical PWCs. Accordingly, now, noise from the jet pump of the jet propulsion system is a greater concern. In particular, an impeller of the jet pump is rotated at a relatively high RPM to generate sufficient power for the PWC. The interaction of the spatially non-uniform velocity distribution at the impeller discharge with the stator vanes of the stator causes lift and drag fluctuations on the stator vanes and flow fluctuations within the stator vane passages. In addition, the periodic blockage of the flow in the impeller blade passages by the stator vanes will result in similar force fluctuations on the impeller blades and also in flow pulsations within the blade passages. Fluctuating forces may be transmitted directly through the fluid or through the vibrational response of the structure (lift fluctuations causing a net axial force component exciting the hub at the pump atta
Dusablon Patrice
Pesant Gilles
Bombardier Recreational Products Inc.
BRP -Legal Services
Morano S. Joseph
Olson Lars
LandOfFree
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