Patent Application
20050048852
This nonprovisional application claims priority under 35 U.S.C. ยง 119(a) on patent application No. 2003-305775, filed in Japan on Aug. 29, 2003, the entirety of which is incorporated herein by reference.
1. Field of the Invention
The present invention relates to water jet pumps (hereinafter also simply referred to as jet pumps). More specifically, the present invention relates to a jet pump used as a propelling device for a ship and, in particular, to anti-cavitation technology.
2. Description of Background Art
In the background art, a jet pump is known to include an impeller, which is driven for rotation and is provided in a cylindrical housing (see, e.g., Japanese Laid-Open Patent Publication No. 2003-89394 (Abstract, FIG. 3) and Japanese Laid-Open Patent Publication No. 2002-87385 (Abstract, FIGS. 1 to 4)). With the impeller being driven for rotation, a jet stream of water occurs to propel a ship.
In a jet pump of this type, it is desired to improve the pumping efficiency. Accordingly, in a jet pump according to the background art, as shown in
In the jet pump according to the background art, the outer circumferential surface 1a of the impeller 1 that opposes the inner surface 2a of the housing 2 has been sharpened by a cutting process to be entirely parallel to the inner surface 2a of the housing 2, as shown in
In the jet pump described in the above-mentioned Japanese Laid-Open Patent Publication No. 2002-87385, a connecting portion, which connects the rear surface side of the impeller to the front surface side thereof is provided in the outer circumferential surface of the impeller in order to reduce cavitation. However, the provision of such a connecting portion has a drawback in that it lowers the pump efficiency accordingly.
It is therefore an object of the present invention to solve the above-described problems and provide a water jet pump which reduces cavitation and thereby allows an improvement in pump efficiency.
To attain the foregoing object, a water jet pump according to the present invention includes an impeller that is driven for rotation and is provided in a cylindrical housing. An edge portion of the outer circumferential surface of the foregoing impeller which opposes the inner surface of the housing has a radius of curvature.
Preferably, the bearing of an impeller shaft for supporting the foregoing impeller in the foregoing housing is composed of an angular bearing.
Preferably, a size of the foregoing radius of curvature is adjusted to 0.5 mm or less.
In the water jet pump according to the present invention, the edge portion of the outer circumferential surface of the impeller which opposes the inner surface of the housing is formed with a radius of curvature. Therefore, a pressure variation is reduced when the impeller is driven for rotation and water under a high pressure on the rear surface side of the impeller enters a narrow cavity between the outer circumferential surface of the impeller and the inner surface of the housing to be pushed out of the narrow cavity toward the front surface side of the impeller under a lower pressure.
This reduces the occurrence of cavitation and resultantly improves the pump efficiency.
In addition, erosion (corrosion), which occurs in the vicinity of the outer circumference of the impeller is also suppressed as a result of the reduced occurrence of cavitation.
In the case where the bearing of the impeller shaft for supporting the foregoing impeller in the foregoing housing is composed of an angular bearing, the outer diameter of the bearing portion can be reduced.
By reducing the outer diameter of the impeller, while retaining a pump capacitance (pump performance), the circumferential speed of the outer circumferential surface of the impeller can be reduced. As a result, it becomes possible to further reduce the occurrence of cavitation and further improve the pump efficiency through the combined effect of the edge portion of the outer circumferential surface of the impeller being formed with a radius of curvature.
By adjusting the size of the foregoing radius of curvature to 0.5 mm or less, it becomes possible to reduce the occurrence of cavitation, while preventing pressure leakage, and more positively improve the pump efficiency.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.
The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus are not limitative of the present invention, and wherein:
The present invention will now we described with reference to the accompanying drawings, wherein the same or similar elements have been identified by the same reference numeral throughout the several views.
As shown in these drawings (primarily in
The body 11 has a floating structure composed of a hull 14 and a deck 15 joined to each other with a space 16 formed inside. In the space 16, an engine 20 is mounted on the hull 14 and a water jet pump 30 is provided as propelling means driven by the engine 20. The jet pump 30 is provided in the rear portion of the hull 14.
The jet pump 30 has an impeller 32 disposed in a flow path 18 extending from a water intake hole 17 opened to the bottom of the ship to reach a stream ejection hole 31c2 opened to the rear end of the body and a deflector 38. A shaft (drive shaft) 22 for driving the impeller 32 is coupled to the output shaft 21 of the engine 20 via a coupler 23. When the impeller 32 is driven to rotate by the engine 20 via the coupler 23 and the drive shaft 22, water taken in from the water intake hole 17 is ejected from the stream ejection hole 31c2 through the deflector 38, whereby the body 11 is propelled. The number of driving rotations of the engine 20, i.e., a propelling force exerted by the jet pump 30 is operated through a rotating operation of the throttle lever 13a (see
The jet pump 30 is removably attached to the hull 14 by fastening a flange portion 31d formed on the front portion of the housing 31 to the hull 14 by using a bolt (not shown).
The housing 31 has an impeller accommodating portion 31a, a bearing accommodating portion 31b, and a nozzle portion 31c (see
The boss portion 32a of the impeller 32 has a front portion engaged with a spline 22b formed in the rear end of the drive shaft 22 so that the impeller 32 rotates with the drive shaft 22. The drive shaft 22 has a tip portion thereof coupled to the output shaft 21 of the engine 20 mounted on the body 11 via the coupler 23 (
On the other hand, an impeller shaft 35 for supporting the rear portion 32b of the boss portion 32a of the impeller 32 is rotatably (free to self-rotate) supported by the bearing portion 33 via front and rear bearing members (ball bearings are depicted) 61 and 62. The impeller shaft 35 has a tip formed with a male screw 35a. With the male screw 35a being screwed into a female screw formed in the rear portion 32b of the boss portion of the impeller 32. The impeller 32 and the impeller shaft 35 are coupled to each other.
Consequently, the front portion of the boss portion 32a of the impeller 32 is coupled to the shaft 22, while the rear portion 32b of the boss portion is coupled to the impeller shaft 35, so that the impeller 32 rotates together with the shaft 22 and the impeller shaft 35.
As described above, the impeller 32 is driven to rotate with the drive shaft 22 being driven by the engine 20 so that a water stream is ejected rearward R and the body 11 is thereby propelled forward F. Consequently, a thrust force that pulls the impeller shaft 35 forward F is exerted thereon.
In the present embodiment, the rear-side bearing member 62 of the front and rear bearing members 61 and 62 is constituted by a bearing member larger in size than the front bearing member 61. This is because of the fact that the rear bearing member 62 receives the thrust force that is exerted on the impeller shaft 35.
A collar 40 has been attached to the outer circumference of the impeller shaft 35 and a water-resistant seal 37 is provided between the collar 40 and the bearing portion 33 of the housing. Accordingly, the water does not encroach in the bearing portion 33 from between the bearing portion 33 and the collar 40.
The collar 40 is also coupled to the rear portion 32b of the boss portion of the impeller 32 via a water-resistant seal 42 so that the water does not encroach toward the outer circumferential surface of the impeller shaft 35 from a cavity C1 between the collar 40 and the rear portion 32b of the boss portion of the impeller 32.
The water-resistant seal 42 is composed of an O-ring attached to a ring-shaped groove 41 formed in the outer circumferential surface of the collar 40.
In the boss portion 32a of the impeller, a cushioning member 50 for the rear end 22c of the drive shaft is provided between the front end 35b of the impeller shaft 35 and the rear end 22c of the drive shaft 22. The outer circumferential portion of the cushioning member 50 is configured to allow air to escape from the impeller shaft 35 toward the drive shaft 22 when the impeller shaft 35 is screwed into the boss portion 32a of the impeller.
Specifically, the cushioning member 50 is made of rubber. The cushioning member 50 has an engagement portion 51 with a screw hole 32c in the boss portion 32a of the impeller and a large diameter portion 53 which comes in close contact with the inner circumferential surface of the boss portion 32a of the impeller. The cushioning member 50 is formed with an air escape groove 54 extending from the outer circumferential surface of the engagement portion 51 to reach a midpoint of the large diameter portion 53.
With such an air escape groove 54 being formed, air (or grease) lying between the front end 35b of the impeller shaft and the cushioning member 50 when the impeller shaft 35 is screwed into the boss portion 32a of the impeller is guided to the air escape groove 54 with the screwing of the impeller shaft 35. The air then escapes from the tip portion of the air escape groove 54 toward the drive shaft 22, while slightly deforming the large diameter portion 53. Since the drive shaft 22 is engaged with the impeller shaft 35 with a spline, the air (or grease) is allowed to escape along the spline.
After screwing the impeller shaft 35 into the boss portion 32a of the impeller, the cushioning member 50 also functions to shut off water attempting to intrude from the side of the drive shaft 22 to the side of the impeller shaft 35 because the large diameter portion 53 comes in close contact with the inner circumferential surface of the boss portion 32a of the impeller.
The front portion of the cap 34 is formed with an insertion portion (cylindrical portion) 34b into the rear portion of the bearing portion 33 and with three (of which only one is shown) insertion holes 34c for screws 36. The cylindrical insertion portion 34b is formed with an attachment groove 34b1 for the O-ring 34e.
Accordingly, the O-ring 34e is attached to the cylindrical insertion portion 34b and the insertion portion 34b is inserted (press-fitted) in the rear portion of the bearing portion 33, whereby the cap 34 is attached to the rear portion of the bearing portion 33 with the screws 36.
In the state in which the cap has been attached, the encroachment of water into the bearing portion 33 is shut off by the O-ring 34e. The surface of the cap 34 abutting on the bearing portion 33 is formed with three partial cutaways 34d (of which only one is shown) so that, during maintenance, the cap 34 is easily removable by unscrewing the screw 36 and thrusting the tip of a tool (e.g., a driver) into the cutaway 34d.
In the state in which the cap 34 has been detached, the impeller shaft 35, front and rear bearing members 61 and 62, and collar 40 described above are integrally incorporated into the bearing portion 33 from behind.
More specifically, the bearing portion 33 is formed with a cylindrical bearing space 33a for accommodating the bearing members 61 and 62. The front portion of the bearing space 33a is formed with a first stepped portion 33b, while the rear portion thereof is formed with a second stepped portion 33c larger in diameter than the first stepped portion 33b.
On the other hand, the collar 40 and the front-side bearing member 61 are attached to the front portion of the impeller shaft 35, while the rear-side bearing member 62 is attached to the rear portion of the impeller shaft 35. Reference numeral 63 denotes a snap ring for the front-side bearing member 61 and reference numeral 64 denotes a snap ring for the rear-side bearing member 62.
Since the rear portion of the impeller shaft 35 has been formed integrally with a flange 35c, the rear-side bearing member 62, the snap ring 64 therefor, the snap ring 63 for the front-side bearing member 61, the front-side bearing member 61, and the collar 40 have been attached preliminarily (before the impeller shaft 35 and the like are incorporated in the bearing portion 33) to the impeller shaft 35 in this order from the front side of the impeller shaft 35 and the resultant assembly is attached to the bearing portion 33 from behind.
Since the rear end of the impeller shaft 35 has been formed with a planar portion 35d for a tool, the assembly composed of the impeller shaft 35 and the like is attached to the bearing portion 33 by rotating the impeller shaft 35 by using the planar portion 35d (by engaging the tool with the planar portion 35d), screwing the male screw 35a of the front portion thereof into the female screw formed in the rear portion 32b of the boss portion of the impeller 32, and tightening it.
Although the front-side bearing member 61 in the attached state is positioned between the first stepped portion 33b and the snap ring 63 in the bearing portion 33, a cavity C2 is designed to be formed between the inner race 61a of the front-side bearing member 61 and the snap ring 63. Therefore, a pulling force (thrust force) exerted by the impeller 32 on the impeller shaft 35 does not basically operate on the front-side bearing member 61.
On the other hand, the rear portion of the inner race 62a of the rear-side bearing member 62 comes to abut on the flange 35c of the impeller shaft 35 and the front portion of the outer race 62b thereof comes to abut on the second stepped portion 33c so that the rear-side bearing member 62 is brought into a state pressed between the flange 35c and the second stepped portion 33c. Consequently, the pulling force (thrust force) exerted by the impeller 32 on the impeller shaft 35 operates on the rear-side bearing member 62 and is received by the rear-side bearing member 62 (i.e., by the second stepped portion 33c).
Accordingly, the rear-side bearing member 62 of the front and rear bearing members 61 and 62, which receives the thrust force of the impeller shaft 35, is composed of a bearing member larger in size than the front-side bearing member 61, as has been described above in this embodiment.
As is also shown in
In such a water jet pump 30, the radius of curvature 32r has been formed on the edge portion of the outer circumferential surface 32d of the impeller 32, which opposes the inner surface 31a1 of the housing 31 so that a pressure variation is reduced when the impeller 32 is driven to rotate. Water W at a high pressure on the rear surface side 32b of the impeller 32 enters the narrow cavity C between the outer circumferential surface 32d of the impeller 32 and the inner surface 31a1 of the housing, and is further pushed out of the narrow cavity C to the front surface side 32f at a lower pressure.
This reduces the occurrence of cavitation and resultantly improves the pump efficiency. In addition, erosion (corrosion) occurring in the vicinity of the outer circumference of the impeller 32 is also suppressed as a result of the reduced occurrence of cavitation.
Preferably, the size of the radius of curvature 32r is adjusted to 0.5 mm or less. If the radius of curvature 32r is 0.5 mm or more, pressure escape from the rear surface side 32b of the impeller 32 to the front surface side 32f thereof is more likely to occur. If the radius of curvature 32r is not provided, on the other hand, cavitation occurs as described above.
Accordingly, the size of the radius of curvature 32r is preferably adjusted to be not less than a level, which eliminates an edge (a value which removes a burr occurring at the edge portion by a cutting process or the like) and not more than 0.5 mm. More preferably, the size of the radius of curvature 32r is adjusted to about 0.3 mm.
In this embodiment, the size of the radius of curvature 32r has been adjusted to a level which satisfies R=0.3 mm.
As stated previously, the drive shaft 22 is driven by the engine 20 to drive the impeller 32 to rotate. The water stream is ejected rearward R to propel the body 11 forward F so that the thrust force that pulls the impeller shaft 35 forward F is exerted thereon.
In view of the foregoing, each of these embodiments includes bearing members for the impeller shaft 35 that are angular bearings.
A structure shown in
A structure shown in
By supporting the impeller shaft 35 with angular bearings as in each of these embodiments, the outer diameter of the bearing portion 33 can be reduced.
By reducing the outer diameter of the impeller 32, while retaining the pump capacitance (pump performance), the circumferential speed of the outer circumferential surface 32d (see
The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2003-305775 | Aug 2003 | JP | national |
