Marine propulsion – Jet drive
Reexamination Certificate
1999-10-14
2001-05-15
Avila, Stephen (Department: 3617)
Marine propulsion
Jet drive
Reexamination Certificate
active
06231409
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a mixed-flow type water jet pump to be used as a propulsion unit of a watercraft.
2. Description of the Related Art
A watercraft which is propelled by a water jet pump, for example, a personal watercraft (which is also referred to as a “PWC”) is configured so as to suck water (including sea water) through a water intake port provided on a bottom of a hull of the watercraft, to pressurize and to accelerate the water by the water jet pump and to eject the water rearward from the hull through an outlet port of the water jet pump, thereby advancing the watercraft.
The water jet pump is configured so that an impeller is rotatably provided in a casing of which inner periphery is a circular cylinder-shaped.
Water jet pumps are broadly divided into so-called “mixed-flow type” water jet pumps and a so-called “axial-flow type” water jet pumps. In a “mixed-flow type” water jet pump, the outside diameter (outer edge) of a blade of an impeller thereof, and the outer diameter of a base portion thereof having a circular section to which the blade is attached, and the inner diameter of a inner wall of a pump casing thereof for covering the impeller, are gradually increased from the intake side toward the pressurization side. In an “axial-flow type” water jet pump, the outside diameter (outer edge) of an impeller, the outer diameter of a base portion having a circular section to which the blade is attached, and the inner diameter of a inner wall of a pump casing for covering the impeller, are straight (constant) from the intake side to the pressurization side.
In the water jet pump, pump performance is affected very greatly by the size of a tip clearance between the inner wall of the pump casing and the outer edge of the blade of the impeller. More specifically, the pump performance is degraded if the tip clearance is too great, and there is a possibility that a tip (an outer peripheral end) of the blade might temporarily come in contact with an inner wall of the pump casing if the clearance is too small. For this reason, generally, the tip clearance between the inner wall of the pump casing and the outer edge of the blade of the impeller is set to about 0.20 mm to about 0.30 mm.
In a mixed-flow type water jet pump, if the axial position of an impeller in a casing of the water jet pump is changed in a longitudinal (axial) direction, the tip clearance between the inner wall of the pump casing and the outer edge of the blade of the impeller is varied.
When assembly is performed, adjustment of the axial position of the impeller with respect to the pump casing is performed in the following way, such that the tip clearance between the inner wall of the casing and the outer edge of the blade of the impeller can be kept within the above-mentioned predetermined value.
As shown in
FIG. 8
, the pump casing
1
C of the mixed-flow type water jet pump P is divided into two portions, that is, a “front casing
1
Cf” and a “rear casing
1
Cr” in a portion in which the pump casing
1
C has the greatest diameter. A pump shaft
1
S is rotatably provided in the rear casing
1
Cr through a bearing
1
H such that a front end thereof is protruded forward. An impeller
1
Z to be rotated integrally with the pump shaft
1
S is attached on the front end of the pump shaft
1
S.
The impeller
1
Z is installed as follows. A suitable number of sheet-shaped shims
35
for adjusting the clearance are provided between the bearing support side of the pump shaft
1
S and the impeller
1
Z, such that a clearance between the inner wall of the pump casing
1
C (front casing
1
Cf) which is a slanted face and the outer peripheral edge of the impeller
1
Z is set within a predetermined range. Then, a female screw hole on the rear end of the impeller
1
Z is screwed and fixed to a male screw on the front end of the pump shaft
1
S.
When the impeller
1
Z is completely arranged as described above, the front casing
1
Cf is attached to the rear casing
1
Cr having the pump shaft
1
S and the impeller
1
Z provided therein, and both of them are fixed to each other with attaching bolts (not shown).
When the assembly of the water jet pump is thus completed, a clearance gauge is inserted from the outside (the outside of the pump intake side) into the tip clearance between the inner wall of the front casing
1
Cf and the outer peripheral edge of the impeller
1
Z, thereby ascertaining whether the tip clearance is within a predetermined range. After an inspection of the clearance, the water jet pump is mounted on a personal watercraft, at the same time inserting and fixing a spline shaft of a propeller shaft (not shown) coupled to the engine at an opposite side, into a spline hole
1
b
formed on the front end of the impeller.
However, if the clearance is not obtained within the predetermined range during the inspection performed by using the clearance gauge, the front casing
1
Cf is removed from the rear casing
1
Cr by loosening the attaching bolts. The impeller is, further, removed from the pump shaft. The number of the shims is increased or decreased, and the water jet pump is assembled again, followed by checking and confirming the clearance again.
Typically, assembly and disassembly of the water jet pump is performed many times to adjust the clearance. Moreover, a curved clearance is measured by means of the clearance gauge plate. Therefore, the clearance cannot be accurately measured due to a rigidity of a plate (tongue) shaped “clearance gauge” which is generally used. Consequently, the assembly and disassembly could be performed many more times.
U.S. Pat. No. 4,541,808 (Japanese Patent Publication No. Sho 60-30599) describe a mixed-flow type water jet pump according to the prior art, and Japanese Patent Publication No. Hei 3-11955 and Japanese Laid-open Patent Publication No. Hei 9-207885 describe an axial-flow type water jet pump according to the prior art.
SUMMARY OF THE INVENTION
In consideration of such circumstances, it is a first objective of the present invention to provide a mixed-flow type water jet pump having such a structure adapted to easily adjust a clearance between an inner wall of a pump casing and an outer peripheral edge of an impeller.
It is a second objective of the invention to provide an attaching structure of the mixed-flow type water jet pump which can easily be mounted on a watercraft.
A first aspect of the invention is directed to a mixed-flow type water jet pump to be used as a propulsion unit of a watercraft,
wherein a pump casing is divided into a front casing and a rear casing in a longitudinal direction. The front casing houses an impeller provided at a predetermined position in a longitudinal direction with respect to the rear casing and is attached to the rear casing through an intermediary of an adjusting shim such that a predetermined tip clearance is formed between an inner wall of the front casing and an outer peripheral edge of the impeller.
According to the mixed-flow type water jet pump having the above-mentioned structure, the impeller is provided in a predetermined relative position with respect to the rear casing during assembly. Then the front casing is joined with the rear casing up to a position where the outer peripheral edge of the impeller abuts against the inner wall of the front casing. In this state, a clearance between the rear casing and the front casing in the longitudinal direction is measured. According to the measured value, a shim having a predetermined thickness (the thickness exceeding the measured value, wherein a tip clearance between the inner wall of the casing and the outer edge of the blade of the impeller formed by the shim is previously confirmed) is provided between the rear casing and the front casing. Thus, the predetermined tip clearance can easily be formed. The above-mentioned “shim having a predetermined thickness” may be obtained by a plural number of shims or a shim having various thicknesses. Shims having various thicknesses may be previously prepared, and a shim having a de
LandOfFree
Mixed-flow type water jet pump of watercraft and attaching... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Mixed-flow type water jet pump of watercraft and attaching..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Mixed-flow type water jet pump of watercraft and attaching... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2501809