The present application claims priority under 35 U.S.C. §119 to Japanese Patent Application No. 2007-284746, filed Nov. 1, 2007. The contents of this application are incorporated herein by reference in their entirety.
1. Field of the Invention
The present invention relates to a water-jet pump (hereafter, also referred to simply as a jet pump), an impeller for the water-jet pump, and a boat including the water-jet pump.
2. Discussion of the Background
In a jet pump of this kind, a water jet is produced by driving the impeller 3 to revolve, propelling the boat.
The impeller 3 shown in
In the conventional jet pump shown in
Now, suppose a case where an either stopped or slowly-travelling boat starts to advance at full speed and another case where a boat goes circling. In these cases, the pressure at the forward side of the impeller 3 decreases while the impeller 3 revolves a high speed. Here, the above-described blades 2 of the impeller 3 brings about a problem of vibrations of impeller 3 caused by the cavitation. The vibrations of the impeller 3 are transmitted by the jet pump, and generate vibrations of the boat body and annoying sounds.
To be more specific, in each overlap region OL formed by the front portion 2f of each one of the blades 2 and the rear portion 2r of the adjacent one of the blades 2, a high-pressure region in the front portion 2f of that one of the blades 2 interferes with a low-pressure region in the rear portion 2r of the adjacent one of the blades 2. The interference causes an abrupt pressure fluctuation, and the water flow is disturbed to a great degree. Accordingly, vibrations and annoying sounds are generated, and are then passed on to the boat body via the impeller 3 and the jet pump.
According to one aspect of the present invention, a water-jet pump includes a cylindrical housing and an impeller. The impeller is disposed in the cylindrical housing and is configured to be rotated in a rotating direction. The impeller includes a shaft body and plural blades. The shaft body has an outer circumference and an axial direction. The plural blades are provided on the outer circumference of the shaft body. Each of the plural blades has a front portion and a rear portion along the axial direction. The front portion of one of the plural blades overlaps the rear portion of another of the plural blades adjacent to one of the plural blades when viewed in the axial direction. When viewed in the axial direction, at least a part of a rear edge of the rear portion is formed obliquely with respect to a radial direction of the impeller towards the rotating direction. A cutaway portion is formed in each of the plural blades between said at least a part of the rear edge and the outer circumference of the shaft body.
According to another aspect of the present invention, an impeller for a water-jet pump configured to be rotated in a rotating direction includes a shaft body and plural blades. The shaft body has an outer circumference and an axial direction. The plural blades are provided on the outer circumference of the shaft body. Each of the plural blades has a front portion and a rear portion along the axial direction. The front portion of one of the plural blades overlaps the rear portion of another of the plural blades adjacent to one of the plural blades when viewed in the axial direction. When viewed in the axial direction, at least a part of a rear edge of the rear portion is formed obliquely with respect to a radial direction of the impeller towards the rotating direction. A cutaway portion is formed in each of the plural blades between said at least a part of the rear edge and the outer circumference of the shaft body.
According to further aspect of the present invention, a boat includes a water-jet pump which includes a cylindrical housing and an impeller. The impeller is disposed in the cylindrical housing and is configured to be rotated in a rotating direction. The impeller includes a shaft body and plural blades. The shaft body has an outer circumference and an axial direction. The plural blades are provided on the outer circumference of the shaft body. Each of the plural blades has a front portion and a rear portion along the axial direction. The front portion of one of the plural blades overlaps the rear portion of another of the plural blades adjacent to one of the plural blades when viewed in the axial direction. When viewed in the axial direction, at least a part of a rear edge of the rear portion is formed obliquely with respect to a radial direction of the impeller towards the rotating direction. A cutaway portion is formed in each of the plural blades between said at least a part of the rear edge and the outer circumference of the shaft body.
A more complete appreciation of the invention and many of the attendant advantages thereof will be readily obtained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein:
The embodiments will now be described with reference to the accompanying drawings, wherein like reference numerals designate corresponding or identical elements throughout the various drawings.
As these drawings show (mainly
The boat body 11 is formed by joining a hull 14 and a deck 15 together. A space 16 is thus formed inside the boat body 11, so that the boat body 11 has a floating-body structure. An engine 20 is installed on the hull 14, inside the space 16. A water-jet pump 30, which serves as propelling means driven by the engine 20, is disposed in the rear portion of the hull 14.
The jet pump 30 includes an impeller 40 disposed inside a flow passage 18. The flow passage 18 is formed from a water-inlet port 17 being an opening formed in the bottom of the boat, to a jet-out port 32 being an opening formed around the stern, and extending to a nozzle 32a. A shaft 22 to drive the impeller 40 (a drive shaft 22) is coupled to an output shaft 21 of the engine 20 via a coupler 23. When the engine 20 drives to rotate the impeller 40 via the coupler 23 and the drive shaft 22, the water that has been taken in from the water-inlet port 17 is jet out through the jet-out port 32 and the nozzle 32a. Thus, the boat body 11 is propelled by the water jet. The rotation of the engine 20, that is, the propulsion of the jet pump 30, is controlled by a turning operation of a throttle lever 13a (see
As
The jet pump 30 is detachably attached to the hull 14 by fixing a flange portion 31d formed in the front portion of the housing 31 to the hull 14 by an unillustrated bolt.
The housing 31 includes an impeller-housing portion 31a, a bearing-housing portion 31b, and the jet-out port 32 (see
As
In each of
With respect to the radial direction r to the shaft center O, each of the obliquely-formed portions 41e, 42e, and 43e has an oblique angle θ that is desirably in a range from about 10° to about 60°, inclusive. The oblique angle θ is more preferably in a range from about 20° to about 40°, inclusive. The oblique angle θ is set at approximately 35° in this embodiment.
When the oblique angle θ is smaller than 10°, the cutaway portions 41a, 42a, and 43a become too small to sufficiently reduce the change in the pressure in the overlap region OL. Consequently, neither the vibrations nor the annoying sounds can be reduced. By contrast, when the oblique angle θ is larger than 60°, the cutaway portions 41a, 42a, and 43a become so large as to impair the pumping efficiency.
Accordingly, as described above, the oblique angle θ is desirably in a range from about 10° to about 60°, inclusive, and is more preferable in a range from about 20° to about 40°, inclusive.
As
On the other hand, an impeller shaft 35 that supports a rear boss portion 53 of the shaft body 50 is rotatably (capable of revolving on it axis) supported by the bearing portion 33 via shaft-bearing members 61 and 62 (ball bearings in the example shown in
As has been described above, the impeller 40 has its front boss portion 52 coupled to the shaft 22, and has its rear boss portion 53 coupled to the impeller shaft 35. Accordingly, the impeller 40 revolves together with the shaft 22 and the impeller shaft 35.
An impeller 40′ differs from the above-mentioned impeller 40 only in the following point. Of the rear edges of the blades 41, 42, and 43, the parts contiguous from the shaft center O are denoted by 41e1, 42e1, and 43e1, respectively. Each of the parts 41e1, 42e1, and 43e1 is directed obliquely towards the upstream side with respect to a radial direction r to the shaft center O. Thus, a cutaway portion 41a of the blade 41, a cutaway portion 42a of the blade 42, and a cutaway portion 43a of the blade 43 are formed respectively between an outer circumference 51 of the shaft body 50 and the obliquely-formed portions (i.e., the parts 41e1, 42e1, and 43e1). The rest of the configuration of the impeller 40′ is the same as that of the impeller 40.
Each of the obliquely-formed portions 41e1, 42e1, and 43e1 has an oblique angle θ that is set at approximately 45° with respect to the corresponding radial direction r to the shaft center O.
Each of the outer-side parts 41e2, 42e2, and 43e2 being other parts of the rear edges is directed in the same direction as the corresponding radial direction r towards the shaft center O.
According to the water-jet pump described above, the following advantageous effects can be obtained.
(a) When viewed in the axial direction, at least a part of each of the rear edges 41e, 42e, and 43e of the blades 41, 42, and 43 (each of the substantially entire parts of the rear edges 41e, 42e, and 43e in the case of
For this reason, in the cutaway portions 41a, 42a, and 43a, the pressure fluctuation is significantly reduced, and the disturbances in the water flow are reduced as well. Accordingly the vibrations and the annoying sounds caused by the disturbances in the water flow are reduced. As a consequence, the vibrations of the boat body 11 are reduced as well.
Moreover, while at least a part of a rear edge of each blade is directed obliquely toward the upstream side in the rotating direction with respect to the radial direction to the shaft center, each of the cut-away portion 41a, 42a and 43a is formed between each obliquely-formed portion and the outer circumference of the shaft body, in other words, in a portion closer to the center of the impeller 40. The water jet-pump with such cutaway portion has increased pumping efficiency (an achievement of higher pumping efficiency) compared to the water jet-pump, as shown in
(b) The oblique angle of each of the obliquely-formed portions is set in a range from about 10° to about 60°, inclusive with respect to the corresponding radial direction r to the shaft center O. This setting of the oblique angle guarantees the achieving of the above-described advantageous effects.
In the water-jet pump according to the embodiment of the present invention, an impeller is disposed in a cylindrical housing and is driven to rotate. The impeller includes a shaft body and plural blades formed on the outer circumference of the shaft body. A front portion of each one of the blades overlaps a rear portion of the adjacent one of the blades when viewed in the axial direction of the impeller. In addition, when viewed in the axial direction of the impeller, at least a part of a rear edge of each of the blades is formed obliquely, with respect to a radial direction to a shaft center, towards the upstream side in the rotating direction of the impeller. In addition, a cutaway portion of the blade is formed between each of the obliquely-formed portions and the outer circumference of the shaft body. With this configuration, the following advantageous effects are obtained.
Specifically, in the water-jet pump, when viewed in the axial direction of the impeller, at least a part of a rear edge of each of the blades is formed obliquely, with respect to a radial direction to a shaft center, towards the upstream side in the rotating direction of the impeller. In addition, a cutaway portion of the blade is formed between each of the obliquely-formed portions and the outer circumference of the shaft body. For these reasons, no interference between a high-pressure region in the front portion of each one of the blades and a low-pressure region of the rear portion of the adjacent one of the blades takes place in the corresponding one of the cutaway portions.
Accordingly, in the cutaway portions, the pressure fluctuation is significantly reduced, and the disturbances of the water flow are reduced as well. For these reasons, vibrations and annoying sounds that are caused by the disturbances of the water flow are reduced as well. As a consequence, the vibrations of the boat body are reduced as well.
As described above, according to the embodiment of the present invention, the pressure fluctuation in the overlap region can be reduced. Accordingly, the vibrations and the annoying sounds can be reduced as well.
Besides, the cutaway portions are formed between the outer circumference of the shaft body and their respective obliquely-formed portions each of which is formed by directing at least a part of a rear edge of the blade obliquely towards the upstream side with respect to the corresponding radial direction to the shaft center. The cutaway portions are thus formed in portions located closer to the center of the impeller. The above-described water-jet pump is compared with a second water-jet pump with the following configuration. The second water-jet pump has an impeller which with at least a part of the rear edge of each of its blades formed obliquely towards the downstream side with respect to the corresponding radial direction to the shaft center. In addition, in the impeller of the second water-jet pump, the cutaway portions are formed on the outer side of their respective obliquely-formed portions, that is, on the outer side of the impeller. The comparison reveals an improvement in the pumping efficiency (an achievement of higher pumping efficiency) that is obtained by use of the water-jet pump according to the embodiment of the present invention.
Moreover, while at least a part of a rear edge of each blade is directed obliquely toward the upstream side in the rotating direction with respect to the radial direction to the shaft center, the cut-away portion is formed between each obliquely-formed portion and the outer circumference of the shaft body, in other words, in a portion closer to the center of the impeller. The water jet-pump with such cutaway portion has increased pumping efficiency (an achievement of higher pumping efficiency) compared to the water jet-pump in which, by directing at least a part of a rear edge of each blade obliquely toward the downstream side in the rotating direction with respect to the radial direction to the shaft center, a cut-away portion is formed on the outer side of the obliquely-formed portion, that is, in a portion on the outer side of the impeller.
In addition, the oblique angle of each of the obliquely-formed portions is set in a range from about 10° to about 60°, inclusive, with respect to the corresponding radial direction. This setting of the oblique angle guarantees the achieving of the above-described advantageous effects.
Obviously, numerous modifications and variations of the present invention are possible in light of the above teachings. It is therefore to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described herein.
Number | Date | Country | Kind |
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2007-284746 | Nov 2007 | JP | national |
Number | Name | Date | Kind |
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6699016 | Dean | Mar 2004 | B1 |
Number | Date | Country |
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9-99895 | Apr 1997 | JP |
Number | Date | Country | |
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20090117790 A1 | May 2009 | US |