Jet pump

Abstract

To provide a jet pump capable of fully exerting forward propulsive force by preventing air bubbles from entering the outer peripheral surface of an impeller from the rear surface of the main blade of the impeller. [Solution] In the present invention, a bubble inflow prevention vane is provided on the outer periphery of the main blade, which is formed on the front side including the front approximate end of the overlapping portion in the front-to-back direction between the front part of the main blade and the rear part of the main blade ahead of the main blade in the clockwise rotation direction, extending diagonally forward in the clockwise rotation from the approximate rear end of the boss part, and has a height that is 50% of the maximum height from the outer periphery of the boss part of the front side main blade.This makes it possible to create a high-speed, rectified flow with strong pumping force, prevents the impeller 3 from spinning freely, and enables the jet pump 1 to fully exert its propulsive force.

Description

[Technical Field]

[0001] The present invention relates to a jet pump for use in watercraft, including personal watercraft, hydroplanes, motorboats, and pleasure boats. [Background technology]

[0002] Jet pumps used in watercraft, including personal watercraft, planing watercraft, motorboats, and pleasure boats, have been known for some time. In this type of jet pump A, the boss portion 101a of the impeller 101 is roughly bullet-shaped, with a short rear portion of the same outer diameter. Blades 101b are provided on the outer periphery. A shaft mounting portion 101c is formed at the rear radial center of the boss portion 101a, to which the front end of a shaft 102 is threadably connected (see FIG. 10 ). The shaft 102 is rotatably supported by bearings 103, 103 within an inner cylindrical portion 107b. Rotational power is transmitted to the impeller 101 by a transmission shaft 104 at the front of the boss portion 101a, enabling it to rotate. FIG. 10 is a cross-sectional view of a conventional jet pump.

[0003] The outer peripheral surface of a cylindrical body 105 of jet pump A is formed by joining an impeller housing 106, a vane guide 107, and a nozzle 108 from the front side. The impeller housing 106 is cylindrical, and an impeller 101 is disposed inside the cylindrical body. The vane guide 107 is cylindrical and has the same diameter as the impeller housing 106, and is formed by, from the outside, an outer cylindrical portion 107a, a flow rectifying plate 107c, and an inner cylindrical portion 107b. The nozzle 108 has a front end with the same diameter as the vane guide 107 and a rear end with a reduced diameter. The nozzle 108 is provided with a conical guide cone 109 that is joined to the rear end of the inner cylindrical portion 107b. An inner space 110 between the outer inner peripheral surface behind the boss portion 101a and the outer peripheral surface of the rotary shaft mounting portion 101c is filled with resin 111 (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2005-138620 Summary of the Invention [Problem to be solved by the invention]

[0005] In the conventional jet pump A, the inner space 110 between the outer inner peripheral surface of the rear of the boss portion 101a and the outer peripheral surface of the rotary shaft mounting portion 101c is filled with resin 111, and most of the inner space 110 behind the boss portion 101a is blocked by the resin. However, the inner space 110 is still left in the inner peripheral surface of the rear side of the boss portion 101a behind the rear end of the rotary shaft mounting portion 101c, so that the air bubbles generated by the rotation of the impeller 101 are blocked by the resin. The liquid containing air bubbles 115 that flows inside vane guide 107 directly enters internal space 110 behind impeller 101 and flows inside vane guide 107. However, because the flow of the liquid on the radially outer side inside vane guide 107 is fast and the diameter of the flow path of nozzle 108 is narrow, the liquid containing air bubbles flows backward on the radially inner side inside vane guide 107, and the air bubbles contained in the liquid that flows backward inside vane guide 107 also enter internal space 110 of boss portion 101a. When internal space 110 behind impeller 101 is filled with air bubbles, the air bubbles are released from internal space 110. In this way, when air bubbles released from internal space 110 behind impeller 101 or air bubbles contained in the liquid flowing backward radially inside the flow path in vane guide 107 enter the outer peripheral surface of boss portion 101a from the rear of impeller 101, the air bubbles that have entered the outer peripheral surface of boss portion 101a may enter the rear surface of blade 101b, which has lower pressure than the surrounding area, into the gap between the outer peripheral surface of blade 101b and the inner peripheral surface of impeller housing 106. When air bubbles enter the gap between the outer peripheral surface of blade 101b and the inner peripheral surface of impeller housing 106, impeller 101 starts to spin freely, and the rotational driving force of impeller 101 cannot be sufficiently transmitted to the fluid. As a result, the pushing force with which impeller 101 pushes the fluid backward is weakened, resulting in a problem of a decrease in the thrust of jet pump A.

[0006] The present invention has been made in consideration of the above problems, and aims to provide a jet pump that can fully exert forward propulsive force by preventing air bubbles from entering the outer peripheral surface of the impeller from the rear surface of the main impeller blade. [Means for solving the problem]

[0007] In order to solve the above problems and achieve the above objects, a first aspect of the present invention provides a jet pump for use in watercraft including personal watercraft, hydroplanes, motorboats, and pleasure boats, the jet pump comprising: a hollow cylindrical body having a nozzle portion with a reduced diameter at the rear; an impeller disposed within the cylindrical body and rotationally driven to pump fluid taken in from a front opening of the cylindrical body to move it rearward; an inner cylindrical portion disposed within the cylindrical body and connected to the rear surface of the impeller, with a rotating shaft rotatably supported therein by a bearing; the impeller having a boss portion with a substantially circular cross section, an outer diameter at the rear end portion being larger than that at the front end portion, and having an inner space formed within its inner circumferential surface on the rear side; a plurality of main blades disposed on the outer periphery of the boss portion and extending diagonally forward and in a clockwise direction from the substantially rear end portion of the boss portion; and a rotating shaft mounting portion formed at the radial center rearward of the boss portion so as to protrude rearward in a concave shape, with the rotating shaft inserted into and coupled to the boss portion; From the rear end of the boss The overlapping portion in the front-to-back direction of the leading edge of the main blades and the rear edge of the leading edge of the main blades in the clockwise rotation direction Rotate right and diagonally forward until at least the tip of the front and main blade outer peripheral surface bubble inflow prevention vanes which are formed to extend from the outer peripheral surface of the boss portion of the front main blade and have a height which is 20% to 80% of the maximum height from the outer peripheral surface of the boss portion of the front main blade. Since the main blade outer peripheral surface bubble inflow prevention vanes have a height which is 20% to 80% of the maximum height from the outer peripheral surface of the boss portion of the front main blade, the fluid flow on the rear surface side of the front main blade and the front surface side of the rear main blade between the front main blade and the rear main blade which have an overlapping portion can be made into a high-speed, rectified flow with strong pumping force, and air bubbles released from the inner space behind the impeller can be prevented from flowing from the rear surface of the main blade to the outer surface of the main blade.

[0008] According to the present invention, the overlapping portion in the front-to-rear direction from the approximate rear end of the boss portion to the leading end of the main blade and the rear part of the leading main blade in the clockwise rotation direction of the main blade At least the front end in the diagonal direction of the right rotationThe main blade outer peripheral surface bubble inflow prevention vanes, which extend to the rear of the impeller and have a height that is 20% to 80% of the height of the front main blade, abruptly divide the highly turbulent fluid flow, creating a high-velocity, rectified flow with strong pumping force over almost the entire overlapping area of ​​the main blades in the front-to-rear direction. This high-velocity, rectified flow with strong pumping force can flush out air bubbles released from the internal space behind the impeller and air bubbles contained in the liquid flowing backward inside the vane guide flow path to the rear of the impeller, preventing the air bubbles from moving around to the outer peripheral surface of the boss. This significantly reduces the amount of air bubbles flowing from the rear surface of the main blade to the outer peripheral surface of the main blade, preventing the impeller from spinning freely and enabling the jet pump to fully exert its thrust.

[0009] A second aspect of the present invention relates to a jet pump for use in watercraft including personal watercraft, hydroplanes, motorboats, and pleasure boats, the jet pump comprising: a hollow cylindrical body having a nozzle portion with a reduced diameter at the rear; an impeller disposed within the cylindrical body and driven to rotate, thereby pressurizing and moving a fluid taken in from a front opening of the cylindrical body to the rear; an inner cylindrical portion disposed within the cylindrical body and connected to the rear surface of the impeller, within which a rotating shaft is rotatably supported by a bearing; the impeller having a boss portion having a substantially circular cross section, an outer diameter at the rear end portion being larger than that at the front end portion, and having an inner space formed within its rearward inner circumferential surface; a plurality of main blades disposed on the outer periphery of the boss portion and extending obliquely forward and in a counterclockwise direction from the substantially rear end portion of the boss portion; and a rotating shaft mounting portion formed at the radial center rearward of the boss portion and concavely projecting rearward, into which the rotating shaft is inserted and coupled. From the rear end of the boss The overlapping portion in the front-to-back direction of the leading edge of the main blades and the rear edge of the leading edge of the main blades in the left rotation direction Left rotation forward diagonally to at least the front endand main blade outer peripheral surface bubble inflow prevention vanes that are formed to extend from the outer peripheral surface of the boss portion of the front main blade and have a height that is 20% to 80% of the maximum height from the outer peripheral surface of the boss portion of the front main blade. Since the main blade outer peripheral surface bubble inflow prevention vanes have a height that is 20% to 80% of the maximum height from the outer peripheral surface of the boss portion of the front main blade, the fluid flow on the rear surface side of the front main blade and the front surface side of the rear main blade between the front main blade and the rear main blade that have an overlapping portion can be made into a high-speed, rectified flow with strong pumping force, and air bubbles released from the inner space behind the impeller can be prevented from flowing from the rear surface of the main blade to the outer surface of the main blade.

[0010] According to the present invention, the overlapping portion in the front-to-rear direction from the approximate rear end of the boss portion to the leading end of the main blade and the rear part of the leading main blade in the left rotation direction of the main blade Left rotation forward diagonally at least to the front end The main blade outer peripheral surface bubble inflow prevention vanes, which extend to the rear of the impeller and have a height that is 20% to 80% of the height of the front main blade, abruptly divide the highly turbulent fluid flow, creating a high-velocity, rectified flow with strong pumping force over almost the entire overlapping area of ​​the main blades in the front-to-rear direction. This high-velocity, rectified flow with strong pumping force can flush out air bubbles released from the internal space behind the impeller and air bubbles contained in the liquid flowing backward inside the vane guide flow path to the rear of the impeller, preventing the air bubbles from moving around to the outer peripheral surface of the boss. This significantly reduces the amount of air bubbles flowing from the rear surface of the main blade to the outer peripheral surface of the main blade, preventing the impeller from spinning freely and enabling the jet pump to fully exert its thrust.

[0011] A third aspect of the present invention is a jet pump according to the first aspect, characterized in that the main blade outer peripheral surface bubble inflow prevention vane extends from the approximate rear end of the boss portion beyond the approximate front end, in the diagonal direction forward in the clockwise direction, of the overlapping portion between the front end of the main blade and the rear end of the main blade forward in the clockwise direction of the main blade provided in the front-to-rear direction, and has a height that is 20% to 80% of the maximum height from the outer peripheral surface of the boss portion of the front main blade. .

[0012] According to the present invention, the overlapping portion in the front-to-rear direction from the approximate rear end of the boss portion to the leading end of the main blade and the rear part of the leading main blade in the clockwise rotation direction of the main blade The right-rotating forward oblique direction of the overlapping portion is reached beyond the front approximate end of the right-rotating forward oblique direction.The main blade outer peripheral surface bubble inflow prevention vanes, which extend to the forward side and have a height that is 20% to 80% of the height of the forward main blade, abruptly divide the highly turbulent fluid flow, creating a high-velocity, rectified flow with strong pumping force throughout almost the entire overlapping area of ​​the main blades in the fore-and-aft direction. This high-velocity, rectified flow with strong pumping force can flush out, behind the impeller, air bubbles released from the internal space behind the impeller and air bubbles contained in the liquid flowing backward inside the vane guide flow path, preventing the air bubbles from moving around to the outer peripheral surface of the boss. This significantly reduces the amount of air bubbles flowing from the rear surface of the main blade to the outer peripheral surface of the main blade, preventing the impeller from spinning freely and enabling the jet pump to fully exert its thrust.

[0013] A fourth aspect of the present invention is a jet pump according to the second aspect, wherein the bubble inflow prevention vane on the outer peripheral surface of the main blade extends from approximately the rear end of the boss portion beyond the approximate front end, in the diagonal direction forward of the left rotation, of the overlapping portion in the front-to-back direction between the front portions of the main blades provided in the plurality of main blades and the rear portion of the main blade forward of the left rotation direction of the main blades, and is characterized in that it has a height that is 20% to 80% of the maximum height from the outer peripheral surface of the boss portion of the front-side main blade.

[0014] According to the present invention, the overlapping portion in the front-to-rear direction from the approximate rear end of the boss portion to the leading end of the main blade and the rear part of the main blade leading in the left rotation direction of the main blade The left-rotating forward oblique direction of the overlapping portion is passed over the front approximate end portion of the left-rotating forward oblique direction. The main blade outer peripheral surface bubble inflow prevention vanes, which extend to the forward side and have a height that is 20% to 80% of the height of the forward main blade, abruptly divide the highly turbulent fluid flow, creating a high-velocity, rectified flow with strong pumping force throughout almost the entire overlapping area of ​​the main blades in the fore-and-aft direction. This high-velocity, rectified flow with strong pumping force can flush out, behind the impeller, air bubbles released from the internal space behind the impeller and air bubbles contained in the liquid flowing backward inside the vane guide flow path, preventing the air bubbles from moving around to the outer peripheral surface of the boss. This significantly reduces the amount of air bubbles flowing from the rear surface of the main blade to the outer peripheral surface of the main blade, preventing the impeller from spinning freely and enabling the jet pump to fully exert its thrust.

[0015] Of the present invention Fifth AspectIn the device relating to the above, the air bubble inflow prevention vanes on the outer peripheral surface of the main blade have a height that is 50% to 80% of the maximum height from the outer peripheral surface of the boss portion of the front main blade, and the air bubble inflow prevention vanes on the outer peripheral surface of the main blade can make it difficult for air bubbles released from the inner space behind the impeller to flow over the air bubble inflow prevention vanes on the outer peripheral surface of the main blade toward the rear surface of the front main blade, and can make the fluid flow on the rear surface of the front main blade and the front surface of the rear main blade between the front main blade and the rear main blade which have an overlapping portion into a high-speed, rectified flow with strong pumping force, and can prevent air bubbles released from the inner space behind the impeller from flowing from the rear surface of the main blade to the outer surface of the main blade.

[0016] According to the present invention, the main blade outer peripheral surface bubble inflow prevention vanes, which have a height that is 50% to 80% of the maximum height from the outer peripheral surface of the boss portion of the front main blade, make it difficult for bubbles and other particles released from the inner space behind the impeller to flow from the rear surface of the main blade outer peripheral surface bubble inflow prevention vanes to the rear surface of the front main blade, overcoming the main blade outer peripheral surface bubble inflow prevention vanes.In addition, the main blade outer peripheral surface bubble inflow prevention vanes, which have a height that is 50% to 80% of the maximum height from the outer peripheral surface of the boss portion of the front main blade, can abruptly divide the flow of fluid in which severe turbulence is occurring, and turn it into a high-speed, rectified flow with strong pumping force over almost the entire overlapping portion of the main blades in the fore-and-aft direction. This high-speed, rectified flow with strong pumping force allows air bubbles released from the internal space behind the impeller and air bubbles contained in the liquid flowing backward inside the flow path of the vane guide to be forced out behind the impeller, preventing the air bubbles from moving around to the outer circumferential surface of the boss. This extremely reduces the amount of air bubbles flowing from the rear surface of the main blade to the outer circumferential surface of the main blade, preventing the impeller from spinning freely and allowing the jet pump to fully exert its thrust.

[0017] Of the present invention Sixth Aspect The first aspect relates to Any one of the above-fourth aspectsThe jet pump according to the present invention is characterized in that the tip end of the bubble inflow prevention vane on the outer circumferential surface of the main vane is formed to rise at an inclination angle of approximately 70 degrees to approximately 110 degrees in the longitudinal direction relative to the outer circumferential surface of the boss portion.

[0018] According to the present invention, the leading ends of the air bubble inflow prevention vanes on the outer peripheral surface of the main blades are formed to rise at an inclination angle of approximately 70 to 110 degrees in the longitudinal direction relative to the outer peripheral surface of the boss portion, so that the inclined surfaces at the leading ends of the air bubble inflow prevention vanes on the outer peripheral surface of the main blades abruptly divide the flow of fluid in which severe turbulence is occurring, and rectify the fluid flow at a high flow rate on the rear surface side of the front main blade and the front surface side of the rear main blade between the front and rear main blades where the overlapping portions are located, thereby producing a fluid with a strong pumping force. This allows air bubbles to be more strongly forced out the rear of the impeller, and extremely reduces the amount of air bubbles that flow into the outer peripheral surface of the main blades.

[0019] Of the present invention Seventh aspect The first aspect relates to Any one of the above-fourth aspects In the jet pump according to the present invention, the impeller has three or four main blades arranged at approximately equal intervals in the circumferential direction of the outer periphery of the boss portion.

[0020] Of the present invention Eighth aspect The first aspect relates to Any one of the above-fourth aspects In this jet pump, the rear end of the outer inner peripheral surface behind the boss portion is formed to extend rearward from the rear end of the rotary shaft mounting portion, and an inner space between the outer inner peripheral surface behind the boss portion and the outer peripheral surface of the rotary shaft mounting portion is filled with resin, and the inner space is left rearward from the surface of the resin filled in the inner space.

[0021] Of the present invention Ninth aspect The first aspect relates to Any one of the above-fourth aspects The jet pump according to the present invention is characterized in that the main blade outer peripheral surface bubble inflow prevention vane is provided at a position close to the rear surface of the main blade on the front side of the overlapping portion in the front-to-rear direction.

[0022] According to the present invention, the main blade outer peripheral surface bubble inflow prevention vane is provided near the rear surface of the main blade on the front side in the longitudinal direction of the overlapping portion, and therefore the distance between the main blade outer peripheral surface bubble inflow prevention vane and the rear surface of the front side main blade is short. Therefore, the main blade outer peripheral surface bubble inflow prevention vane rectifies the fluid flow on the rear surface side of the front side main blade at an even higher flow rate, thereby making it possible to produce a fluid with a strong pumping force. Even if bubbles accumulate on the rear surface of the front side main blade 11a, the bubbles that accumulate on the outer peripheral surface of the boss portion on the rear surface of the front side main blade can be more efficiently and intensively discharged rearward. This extremely reduces the amount of bubbles that flow from the rear surface of the main blade to the outer peripheral surface of the main blade, preventing the impeller from spinning freely and enabling the jet pump to fully exert its thrust. [Effects of the Invention]

[0023] According to the jet pump of the present invention, by preventing air bubbles from entering the outer peripheral surface of the impeller from the rear surface of the main blade of the impeller, it is possible to fully exert forward propulsive force. [Brief explanation of the drawings]

[0024] [Figure 1] 1 is a cross-sectional view of a jet pump according to an embodiment of the present invention. [Figure 2] FIG. 2 is a perspective view of an impeller used in the jet pump. [Figure 3] FIG. [Figure 4] 1 is a side view of the impeller. [Figure 5] FIG. 1 is a front perspective view of an impeller provided with four main blades and air bubble inflow prevention blades on the outer circumferential surface of the main blades. [Figure 6] FIG. 10 is a front perspective view of an impeller having a main blade outer peripheral surface bubble inflow prevention vane whose front portion is provided at a position approximately at the front end of the overlapping portion in the front-to-rear direction between the front portion of the main blade and the rear portion of the main blade 11a that is forward of the main blade in the clockwise rotation direction. [Figure 7] 1 is a diagram showing the flow of liquid and bubbles in a jet pump according to an embodiment of the present invention. FIG. [Figure 8] FIG. 4 is a side view of an impeller used in a jet pump according to a first modified example of the present invention. [Figure 9] FIG. 10 is a cross-sectional view of a jet pump according to a second modified example of the present invention. [Figure 10] FIG. 1 is a cross-sectional view of a conventional jet pump. DETAILED DESCRIPTION OF THE INVENTION

[0025] An embodiment of a jet pump of the present invention will be described below with reference to the drawings. Fig. 1 is a cross-sectional view of a jet pump according to an embodiment of the present invention, and the cross section of the impeller 3 in Fig. 1 is taken along the line AA in Fig. 3. The jet pump 1 is used in watercraft including personal watercraft, hydroplanes, motorboats, and pleasure boats.

[0026] The jet pump 1 has a cylindrical body 2, an impeller 3, and an inner cylindrical portion 4 (see FIG. 1).

[0027] The cylindrical body 2 is hollow and has a nozzle portion 2a with a reduced diameter formed at the rear, and is formed by connecting, in order from the front side, an impeller housing 5, a vane guide 6, and a nozzle 7. A front opening 5a that opens forward is formed at the front end (tip) of the cylindrical body 2 (impeller housing 5).

[0028] The impeller housing 5 is formed in a cylindrical shape, and the impeller 3 is disposed inside the impeller housing 5.

[0029] The vane guide 6 is formed in a cylindrical shape with an outer diameter the same as that of the impeller housing 5, and an outer cylinder portion 6a is formed on the radially outer side. Inside the vane guide 6, there are provided a straightening plate 8 arranged in contact with the inner surface of the outer cylinder portion 6a, and an inner cylinder portion 4 arranged in contact with the inner surface of the straightening plate 8.

[0030] The nozzle 7 has a tip with the same diameter as the vane guide 6, and the diameter decreases from there toward the rear end, where the nozzle section 2a with a reduced diameter is formed. Inside the nozzle 7, a conical guide cone 9 connected to the rear end of the inner cylindrical section 4 is disposed.

[0031] Next, the impeller 3 disposed inside the impeller housing 5 will be described with reference to Figures 2 to 4. Here, Figure 2 is a perspective view of the impeller used in a jet pump according to one embodiment of the present invention, Figure 3 is a front view of the same impeller, and Figure 4 is a side view of the same impeller. The dotted line in Figure 3 indicates the configuration behind the configuration shown by the solid line.

[0032] The impeller 3 is provided inside the cylindrical body 2 and, when rotated, pressurizes and moves rearward the water (fluid) taken in from the front opening 5a of the cylindrical body 2, and has a boss 10 and blades 11 (see FIG. 2). Note that, although water is used in this embodiment, the impeller is not limited to this and other liquids (fluids) including water may also be used.

[0033] The boss portion 10 has a generally circular cross section, the outer diameter of the rear end being larger than the outer diameter of the front end, and an inner space 12 formed within the inner peripheral surface on the rear side. Specifically, the boss portion 10 is generally bullet-shaped with a short, uniformly sized portion of the rear outer peripheral surface. The boss portion 10 has a transmission shaft mounting portion 14 (see FIG. 1) at its front radial center, to which the rear end of a transmission shaft 13 (see FIG. 1) is splined and connected. The rear radial center portion has a rotating shaft mounting portion 16, to which the front end of a rotating shaft 15 (see FIG. 1) is threadedly connected. The rotating shaft mounting portion 16 is formed in a concave shape protruding rearward from the rear radial center of the boss portion 10, and is configured so that the rotating shaft 15 is inserted and connected within the concave shape. The impeller 3 can be rotated by rotation of the transmission shaft 13 at the front of the boss portion 10. The rear end of the boss portion 10 has an inner space 12 formed outside the rotating shaft mounting portion 16 to reduce the weight of the impeller 3. The rear end of the outer inner peripheral surface of the rear of boss portion 10 extends rearward beyond the rear end of rotary shaft mounting portion 16. In this embodiment, boss portion 10 is formed in a generally bullet shape with a short uniform diameter portion on the rear outer peripheral surface, but is not limited to this, and may be formed in a generally bullet shape with a long uniform diameter portion on the rear outer peripheral surface, or in a generally conical shape.

[0034] Next, a description will be given of the blade 11. The blade 11 has a main blade 11a and a bubble inflow prevention blade 11b on the outer peripheral surface of the main blade.

[0035] The main blades 11a are formed on the outer periphery of the boss portion 10, extending obliquely forward in a clockwise rotation direction from approximately the rear end of the boss portion 10, and three of them are provided at equal intervals in the circumferential direction of the outer periphery of the boss portion 10. In this way, each of the three main blades 11a is formed on the outer periphery of the boss portion 10, extending obliquely forward in a clockwise rotation direction from approximately the rear end of the boss portion 10, so that the front portion of each of the three main blades 11a and the rear portion 11a of the main blade ahead of the main blade 11a in the clockwise rotation direction overlap in the front-to-rear direction (see FIG. 3). Here, in the present embodiment, the direction of the front opening 5a of the cylindrical body 2 is described as the forward direction, and the direction of the nozzle portion 2a of the cylindrical body 2 is described as the rearward direction, so that the direction of the smaller outer diameter of the boss portion 10 is the forward direction of the main blade 11a, and the direction of the larger outer diameter of the boss portion 10 is the rearward direction of the main blade 11a. In addition, the direction of the tip of the main blade 11a extending diagonally forward in clockwise rotation will be referred to as the forward direction, and the direction of the rear end of the main blade 11a extending diagonally forward in clockwise rotation will be referred to as the rearward direction. In this embodiment, the main blade 11a extends diagonally forward in clockwise rotation from approximately the rear end of the boss portion 10 to the outer periphery of the boss portion 10. However, "extending diagonally forward in clockwise rotation from approximately the rear end of the boss portion 10" means that the main blade 11a may extend diagonally forward in clockwise rotation from near the rear end of the boss portion 10, as in this embodiment, or may extend diagonally forward in clockwise rotation from the rear end of the boss portion 10. In this embodiment, three main blades 11a are provided on the outer periphery of the boss portion 10. However, this is not limited to this, and four main blades may be provided on the outer periphery of the boss portion 10 (see FIG. 5). Alternatively, a plurality of main blades, including three or four main blades, may be provided. Here, FIG. 5 is a front perspective view of an impeller provided with four main blades and four bubble inflow prevention vanes on the outer periphery of the main blades. This impeller, which has four main blades and four main blade outer peripheral surface bubble inflow prevention vanes, differs only in the number of main blades 11a and main blade outer peripheral surface bubble inflow prevention vanes 11b of this embodiment, and is otherwise the same, so it is only shown in the drawing (without reference numerals) and detailed explanations are omitted.Furthermore, in this embodiment (including the notes), the main blades 11a are arranged at equal intervals in the circumferential direction of the outer periphery of the boss portion 10, but this is not limited thereto, and they may be arranged at approximately equal intervals in the circumferential direction of the outer periphery of the boss portion 10, or may be arranged at positions that are not equally spaced in the circumferential direction of the outer periphery of the boss portion 10.

[0036] The main blade outer peripheral surface bubble inflow prevention vane 11b is formed to extend obliquely forward in clockwise rotation from approximately the rear end of the boss portion 10 on the forward side including the approximate front end of the overlapping portion in the front-to-rear direction between the leading portions of the three main blades 11a and the rear portion of the main blade 11a that is forward of the main blade 11a in the clockwise rotation direction, and has a height that is 50% of the maximum height of the front-side main blade 11a from the outer peripheral surface of the boss portion 10. In this embodiment, the main blade outer peripheral surface bubble inflow prevention vane 11b extends to an approximate position on the outer peripheral surface perpendicular to the front-to-rear direction of the boss portion 10 at the position of approximately the tip of the front-side main blade 11a, which is forward of the overlapping portion in the front-to-rear direction between the leading portions of the three main blades 11a and the rear portion of the main blade 11a that is forward of the main blade 11a in the clockwise rotation direction. In this embodiment, the height of the main blade outer peripheral surface air bubble inflow prevention vane 11b from the outer peripheral surface of the boss portion 10 is 50% of the maximum height of the front main blade 11a from the outer peripheral surface of the boss portion 10, but this is not limited thereto, and the height may be 20% (preferably 30% (more preferably 40% (still more preferably 50%))) to 80% (preferably 75% (more preferably 70%)) of the maximum height of the front main blade 11a from the outer peripheral surface of the boss portion 10, and the height of the main blade outer peripheral surface air bubble inflow prevention vane 11b may be formed to be shorter by approximately 1.0 centimeter (preferably approximately 1.5 centimeters (more preferably approximately 2.0 centimeters) to approximately 3.0 centimeters (preferably approximately 2.5 centimeters (more preferably approximately 2.0 centimeters)) than the maximum height of the front main blade 11a from the outer peripheral surface of the boss portion 10.Here, the height of "20% (preferably 30% (more preferably 40% (even more preferably 50%))) to 80% (preferably 75% (more preferably 70%))" includes a height that is a combination of "any one of 20% (preferably 30% (more preferably 40% (even more preferably 50%)))" and "80% (preferably any one of 75% (more preferably 70%))", and also, with regard to "approximately 1.0 centimeter (preferably approximately 1.5 centimeters (more preferably approximately 2.0 centimeters) to approximately 3.0 centimeters (preferably approximately 2.5 centimeters (more preferably approximately 2.0 centimeters))", it is possible to combine "any one of approximately 1.0 centimeters (preferably approximately 1.5 centimeters (more preferably approximately 2.0 centimeters))" and "approximately 3.0 centimeters (preferably approximately 2.5 centimeters (more preferably approximately 2.0 centimeters ... Preferably, the height includes a shorter combined length of approximately 2.5 centimeters (more preferably approximately 2.0 centimeters). In this embodiment, the main blade outer peripheral surface air bubble inflow prevention vanes 11b are formed to extend obliquely forward in a clockwise direction from approximately the rear end of the boss portion 10. However, "extending obliquely forward in a clockwise direction from approximately the rear end of the boss portion 10" means that they may extend obliquely forward in a clockwise direction from near the rear end of the boss portion 10, as in this embodiment, or they may extend obliquely forward in a clockwise direction from the rear end of the boss portion 10. In this embodiment, three main blade outer peripheral surface air bubble inflow prevention vanes 11b are provided on the outer periphery of the boss portion 10. However, this is not limited to this, and four vanes may be provided on the outer periphery of the boss portion 10 (see FIG. 5). Alternatively, a plurality of vanes, including three or four vanes, may be provided.Furthermore, in this embodiment, the main blade outer peripheral surface bubble inflow prevention vane 11b is formed to extend to approximately a position on the outer peripheral surface perpendicular to the front-to-rear direction of the boss portion 10, which is approximately the tip of the front main blade 11a, which is on the front side of the overlapping portion in the front-to-rear direction between the front portions of the three main blades 11a and the rear portion of the main blade 11a that is forward of the main blade 11a in the clockwise rotation direction. However, without being limited to this, the bubble inflow prevention vane 11b may be provided at a position near the front end of the overlapping portion in the front-to-rear direction between the front portions of the three main blades 11a and the rear portion of the main blade 11a that is forward of the main blade 11a in the clockwise rotation direction (see FIG. 6), or the like. This "approximate leading end of the overlapping portion" refers to the approximate leading end of the overlapping portion on the leading direction side of the main blade 11a. Here, Fig. 6 is a front perspective view of an impeller with a main blade outer peripheral surface bubble inflow prevention vane whose leading portion is provided at the approximate leading end of the overlapping portion in the front-to-rear direction between the leading portion of the main blade and the rear portion of the main blade 11a that is forward of that main blade in the clockwise rotation direction. This main blade outer peripheral surface bubble inflow prevention vane differs from the main blade outer peripheral surface bubble inflow prevention vane 11b of this embodiment only in the position of its leading portion, and is otherwise the same, so it is shown only in the drawing (without reference numerals) and a detailed description will be omitted.

[0037] In this way, the main blade outer peripheral surface bubble inflow prevention vane 11b, which has a height that is 50% of the maximum height 11a of the front main blade 11a from the outer peripheral surface of the boss portion 10, makes it difficult for bubbles and the like released from the inner space 12 behind the impeller 3 to flow from the rear surface of the main blade outer peripheral surface bubble inflow prevention vane 11b to the rear surface of the front main blade 11a, overcoming the main blade outer peripheral surface bubble inflow prevention vane 11b. At least the same effect can be achieved as long as the main blade outer peripheral surface bubble inflow prevention vane 11b has a height that is 50% or more of the maximum height of the front main blade 11a from the outer peripheral surface of the boss portion 10.

[0038] The leading end of the air bubble inflow prevention vane 11b on the outer peripheral surface of the main blade is formed to rise at an inclination angle of approximately 80 degrees in the longitudinal direction relative to the outer peripheral surface of the boss portion 10. In this way, the leading end of the air bubble inflow prevention vane 11b on the outer peripheral surface of the main blade is formed to rise at an inclination angle of approximately 80 degrees in the longitudinal direction relative to the outer peripheral surface of the boss portion 10. Therefore, the inclined surface of the leading end of the air bubble inflow prevention vane 11b on the outer peripheral surface of the main blade abruptly divides the flow of fluid in which severe turbulence is occurring, and rectifies the flow of fluid at a high flow rate on the rear surface side of the front-side main blade 11a and the front surface side of the rear-side main blade 11a between the front-side main blade 11a and the rear-side main blade 11a, which have an overlapping portion in the front-rear direction between the front part of the main blade 11a and the rear part of the main blade 11a ahead of the main blade 11a in the clockwise rotation direction, thereby making it possible to produce a fluid with a strong pumping force. In this embodiment, the front end of the main blade outer peripheral surface bubble inflow prevention blade 11b is formed to rise at an inclination angle of approximately 80 degrees in the longitudinal direction relative to the outer peripheral surface of the boss portion 10, but this is not limited to this, and the blade may be formed to rise at an inclination angle of "approximately 70 degrees (preferably approximately 75 degrees (more preferably approximately 80 degrees (even more preferably approximately 85 degrees))" to approximately 110 degrees (preferably approximately 105 degrees (more preferably approximately 100 degrees (even more preferably approximately 95 degrees)))" in the longitudinal direction relative to the outer peripheral surface of the boss portion 10. Here, the inclination angle of "approximately 70 degrees (preferably approximately 75 degrees (more preferably approximately 80 degrees (even more preferably approximately 85 degrees))) to approximately 110 degrees (preferably approximately 105 degrees (more preferably approximately 100 degrees (even more preferably approximately 95 degrees)))" includes inclination angles that are a combination of "any one of approximately 70 degrees (preferably approximately 75 degrees (more preferably approximately 80 degrees (even more preferably approximately 85 degrees)))" and "any one of approximately 110 degrees (preferably any one of approximately 105 degrees (more preferably approximately 100 degrees (even more preferably approximately 95 degrees))))," just like the height of the main blade outer surface air bubble inflow prevention blade 11b from the outer surface of the boss portion 10 described above.Furthermore, with regard to the inclination angle of "approximately 70 degrees to approximately 110 degrees" or the like, even if a part of the inclination angle of the leading end of the main blade outer peripheral surface air bubble inflow prevention blade 11b has an angle other than 70 degrees to 110 degrees, it is sufficient as long as the inclination of the line connecting the "start point" and "end point" of the inclination angle of the leading end of the main blade outer peripheral surface air bubble inflow prevention blade 11b is an inclination angle of "approximately 70 degrees to approximately 110 degrees", etc. The scope of the present invention includes those that have the effect of abruptly dividing a violently turbulent fluid flow by the inclined surface at the leading end of the main blade 11a and rectifying at a high flow rate the fluid flow on the rear surface side of the front-side main blade 11a and the front surface side of the rear-side main blade 11a between the front-side main blade 11a and the rear-side main blade 11a, which have an overlapping portion in the front-rear direction between the leading portion of the main blade 11a and the rear portion of the main blade 11a ahead of the main blade 11a in the clockwise rotation direction. Also, with regard to the inclination angle of the leading end of the bubble inflow prevention blade 11b on the outer circumferential surface of the main blade, if the vicinity of the "starting point" and the "ending point" of the line connecting the "starting point" and the "ending point" are formed with a smooth or steep inclination angle, the inclination angle can be found by excluding the smooth or steep inclination portion as the "starting point" and the "ending point". Furthermore, the inclination angle may be calculated by combining the above-mentioned "when part of the rise has an angle other than 70 degrees to 110 degrees" and "when the area near the "starting point" and the area near the "ending point" are formed with a smooth or steep inclination angle," and in this case too, the configuration will essentially achieve the above-mentioned effects.

[0039] The main blade outer peripheral surface bubble inflow prevention vane 11b may be provided at a position close to the rear surface of the main blade 11a on the front side in the front-to-rear direction of the overlapping portion between the front portion of the main blade 11a and the rear portion of the main blade 11a ahead of the main blade 11a in the clockwise rotation direction. Specifically, the main blade 11a may be provided at a position close to 25% (preferably 20% (more preferably 15%)) to 40% (preferably 35% (more preferably 30%)) of the length between the front-side main blade 11a and the rear-side main blade 11a from the rear surface of the front-side main blade 11a in the front-to-rear direction of the overlapping portion between the front portion of the main blade 11a and the rear portion of the main blade 11a ahead of the main blade 11a in the clockwise rotation direction. Here, this "25% (preferably 20% (more preferably 15%)) to 40% (preferably 35% (more preferably 30%))" includes a combination of "any one of 25% (preferably 20% (more preferably 15%))" and "any one of 40% (preferably any one of 35% (more preferably 30%))," similar to the height of the main blade outer surface bubble inflow prevention blade 11b from the outer surface of the boss portion 10 described above. In this way, by providing the main blade outer peripheral surface air bubble inflow prevention vane 11b near the rear surface of the front main blade 11a in the longitudinal direction of the overlapping portion, the distance between the main blade outer peripheral surface air bubble inflow prevention vane 11b and the rear surface of the front main blade 11a becomes short, and the main blade outer peripheral surface air bubble inflow prevention vane 11b rectifies the fluid flow on the rear surface of the front main blade 11a at an even higher flow rate, thereby making it possible to produce a fluid with strong pumping power, and even if air bubbles accumulate on the rear surface of the front main blade 11a, the accumulated air bubbles can be more efficiently and intensively discharged rearward. As a result, the amount of air bubbles flowing from the rear surface of the main blade 11a to the outer peripheral surface of the main blade 11a is extremely reduced, preventing idling of the impeller 3 and allowing the jet pump 1 to fully exert its thrust.

[0040] Next, the inner cylindrical portion 4 will be described. The inner cylindrical portion 4 is connected to the rear surface of the impeller 3 inside the cylindrical body 2, and a rotary shaft 15 is rotatably supported inside the inner cylindrical portion 4 by a bearing 17 (see FIG. 1). In this way, the rotary shaft 15 can freely rotate inside the inner cylindrical portion 4 via the bearing 17. In addition, a seal 18 (see FIG. 1) is arranged around the rotary shaft 15 between the inner circumferential surface at the tip of the inner cylindrical portion 4 and the rotary shaft 15. In this way, the seal 18 between the inner circumferential surface at the tip of the inner cylindrical portion 4 and the rotary shaft 15 can prevent water from entering the inner cylindrical portion 4.

[0041] With the above-described configuration, when rotational power is applied to the transmission shaft 13 (see Figure 1) from the outside, the rotational power is transmitted to the impeller 3 connected to the transmission shaft 13, thereby driving the impeller 3 to rotate.

[0042] Next, the flow of water (liquid) inside the jet pump 1 and the bubbles generated by the rotation of the impeller 3 will be described with reference to Fig. 7. Here, Fig. 7 is a diagram showing the flow of liquid and bubbles inside a jet pump in one embodiment of the present invention.

[0043] When rotational power is applied to the transmission shaft 13 (see Figure 1) from the outside, the rotation of the transmission shaft 13 rotates the impeller 3, which in turn rotates the impeller 3. Then, the rotation of the impeller 3 causes water (liquid) on the front side to be sucked into the jet pump 1 from the front opening 5a at the front end (tip) of the cylindrical body 2, and the water (liquid) sucked into the jet pump 1 becomes water (liquid) containing air bubbles generated by the rotation of the impeller 3, and the water containing the air bubbles becomes a violent turbulent flow and is forced to be sent rearward of the impeller 3.

[0044] When the water is pumped rearward of the impeller 3, air bubbles generated by the rotation of the impeller 3 enter the inner space 12 between the outer inner peripheral surface behind the boss portion 10 and the outer peripheral surface of the rotary shaft mounting portion 19, and when the air bubbles that have entered the inner space 12 behind the impeller 3 are filled up, the air bubbles are released from the inner space 12 (see FIG. 7). Furthermore, the flowing water (liquid) containing air bubbles flowing inside the vane guide 6 flows faster on the radially outer side of the vane guide 6 and the diameter of the flow path toward the nozzle portion 2a is narrow, so that the water (liquid) containing air bubbles flows back on the radially inner side of the vane guide 6 (on the outer peripheral surface side of the inner cylindrical portion 4). Then, some of the air bubbles contained in the flowing water (liquid) that flows backward radially inside vane guide 107 (toward the outer peripheral surface of inner cylindrical portion 4) enter inner space 12 of boss portion 101a, and the flowing water (liquid) containing the air bubbles flows backward toward the rear of impeller 3. In this way, the air bubbles released from inner space 12 behind impeller 3 and the air bubbles contained in the fluid (liquid) that flows backward radially inside the flow passage in vane guide 6 (toward the outer peripheral surface of inner cylindrical portion 4) flow from the rear end side of boss portion 10 onto the outer peripheral surface of boss portion 10, and are drawn from there toward the rear surface of front main blade 11a, where the water pressure is lower than in other parts of the outer peripheral surface of boss portion 10.

[0045] In this embodiment, the main blade outer peripheral surface air bubble inflow prevention vane 11b is provided on the front side, including the front approximate end of the overlapping portion in the front-to-rear direction between the front portion of the main blade 11a and the rear portion of the main blade 11a ahead of the main blade 11a in the clockwise rotation direction, and extends obliquely forward in the clockwise rotation direction from the approximate rear end of the boss portion 10, and has a height that is 50% of the maximum height of the front-side main blade 11a from the outer peripheral surface of the boss portion 10. Therefore, the main blade outer peripheral surface air bubble inflow prevention vane 11b, which has a height that is 50% of the height 11a of the front-side main blade, makes it difficult for air bubbles and the like released from the inner space 12 behind the impeller 3 to flow from the rear surface side of the main blade outer peripheral surface air bubble inflow prevention vane 11b to the rear surface side of the front-side main blade 11a. Furthermore, the main-blade outer peripheral surface air bubble inflow prevention vanes 11b, which extend from approximately the rear end of the boss portion 10 to the front side including the approximate front end of the overlapping portion in the front-rear direction between the front portion of the main blade 11a and the rear portion of the main blade 11a forward in the clockwise rotation direction, and which are 50% of the maximum height of the front-side main blade 11a from the outer peripheral surface of the boss portion 10, can abruptly divide the intensely turbulent fluid flow and turn it into a high-speed, rectified flow with strong pumping force over almost the entire overlapping portion of the main blades 11a in the front-rear direction. This high-speed, rectified flow with strong pumping force can flush out, to the rear of the impeller 3, air bubbles released from the internal space 12 behind the impeller 3 and air bubbles contained in water (liquid) flowing backward inside the flow path of the vane guide 6, thereby preventing air bubbles from moving around from the rear surface of the front-side main blade 11a to the outer peripheral surface of the main blade 11a. This significantly reduces the amount of air bubbles that flow from the rear surface of the main blade 11a to the outer circumferential surface of the main blade 11a, preventing the impeller 3 from spinning freely and allowing the jet pump 1 to exert its propulsive force to the fullest.

[0046] Furthermore, by providing the main blade outer peripheral surface air bubble inflow prevention vane 11b near the rear surface of the front main blade 11a in the longitudinal direction of the overlapping portion, the distance between the main blade outer peripheral surface air bubble inflow prevention vane 11b and the rear surface of the front main blade 11a becomes short, and the main blade outer peripheral surface air bubble inflow prevention vane 11b rectifies the fluid flow on the rear surface of the front main blade 11a at an even higher flow rate, thereby making it possible to produce a fluid with strong pumping power, and even if air bubbles accumulate on the rear surface of the front main blade 11a, the accumulated air bubbles can be more efficiently and intensively discharged rearward. As a result, the amount of air bubbles flowing from the rear surface of the main blade 11a to the outer peripheral surface of the main blade 11a is extremely reduced, preventing idling of the impeller 3 and allowing the jet pump 1 to fully exert its thrust.

[0047] The embodiments disclosed herein should be considered to be illustrative in all respects and not restrictive. Furthermore, the scope of the present invention is defined by the claims rather than the above description, and it is intended to include all modifications within the meaning and scope of the claims.

[0048] Next, a modified example of the jet pump of the present invention will be described.

[0049] (Variation 1) First, a first modified example of the jet pump of the present invention will be described with reference to Fig. 8. Fig. 8 is a side view of an impeller used in the jet pump of the first modified example of the present invention. In the first modified example, the same components as those in the above embodiment are designated by the same reference numerals and are assumed to have the same functions and effects, and therefore description thereof will be omitted.

[0050] The difference between the first modified example and the above embodiment is that in the above embodiment, the impeller 3 has three main blades 11a that extend obliquely forward in clockwise rotation from approximately the rear end of the boss portion 10 on the outer periphery of the boss portion 10, and the bubble inflow prevention blades 11b on the outer periphery of the main blades of the impeller 3 are formed to extend obliquely forward in clockwise rotation from approximately the rear end of the boss portion 10 on the front side including the front approximate end of the overlapping portion in the front-to-rear direction between the front portion of the three main blades 11a and the rear portion of the main blade 11a forward in the clockwise rotation direction of the main blade 11a. In contrast, in Modification 1, three main blades 21a of the impeller 23 are provided on the outer periphery of the boss portion 10, extending obliquely forward in a counterclockwise direction from approximately the rear end of the boss portion 10, and the main blade outer peripheral surface air bubble inflow prevention vane 21b of the impeller 23 is formed to extend obliquely forward in a counterclockwise direction from approximately the rear end of the boss portion 10 on the forward side, including the approximate leading end of the overlapping portion in the front-to-rear direction between the leading portion of each of the three main blades 21a and the rear portion of the main blade 21a forward in the counterclockwise direction (see FIG. 8). That is, while in the above embodiment the main blades 11a and the main blade outer peripheral surface air bubble inflow prevention vane 11b of the impeller 3 are formed obliquely forward in a clockwise direction, in Modification 1, the main blades 21a and the main blade outer peripheral surface air bubble inflow prevention vane 21b of the impeller 23 are formed obliquely forward in a counterclockwise direction. In the first modified example, other than the above-mentioned configuration, the same operations and effects are achieved as in the above-mentioned embodiment (including the "notes"), and therefore a description thereof will be omitted.

[0051] (Variation 2) Next, a second modified example of the jet pump of the present invention will be described with reference to Fig. 9. Fig. 9 is a cross-sectional view of the jet pump in the second modified example of the present invention. In the second modified example, the same components as those in the above embodiment are designated by the same reference numerals, and the same functions and effects are achieved, so the description thereof will be omitted.

[0052] The difference between variant example 2 and the above embodiment is that in the above embodiment, nothing is filled in the inner space 12 between the outer inner surface at the rear of the boss portion 10 and the outer surface of the rotating shaft mounting portion 16, whereas in variant example 2, resin 19 is filled in the inner space 12 between the outer inner surface at the rear of the boss portion 10 and the outer surface of the rotating shaft mounting portion 16, and an inner space 20 is left behind and formed behind the surface of the resin 19 filled in the inner space 12. That is, in the above embodiment, nothing is filled in the internal space 12 behind the boss portion, whereas in Modification 2, the internal space 12 of the present embodiment behind the boss portion 10 is filled with resin 19, and the area behind the surface of the resin 19 becomes the internal space 20. Other than the above configuration, Modification 2 is the same as the above embodiment (including the "notes"), and the effects are also the same, so a description thereof will be omitted. [Explanation of symbols]

[0053] 1 Jet pump 2 Cylindrical body 2a Nozzle part 3 impeller 4 Inner cylinder 5 Impeller housing 5a Front opening 6 Vane Guide 6a Outer cylinder 7 nozzles 8 Rectifier plate 9 Guide Cone 10 Boss section 11 Feather 11a Main feather 11b Main blade outer surface air bubble inflow prevention blade 12 Inner space 13 Transmission shaft 14 Transmission shaft mounting part 15 Rotation axis 16 Rotating shaft mounting part 17 Bearings 18 Seal body 19 Resin 20 Inner space 21a Main feather 21b Main blade outer surface air bubble inflow prevention blade 23 Impeller

Claims

1. A jet pump for use in watercraft including personal watercraft, hydroplanes, motorboats, and pleasure boats, a hollow cylindrical body having a nozzle portion with a reduced diameter formed at the rear; an impeller provided within the cylindrical body and rotating to pump and move the fluid taken in from a front opening of the cylindrical body rearward; an inner cylindrical portion provided inside the cylindrical body and connected to a rear surface of the impeller, the inner cylindrical portion having a rotary shaft rotatably supported by a bearing; The impeller is a boss portion having a substantially circular cross section, an outer diameter of a rear end portion being larger than an outer diameter of a front end portion, and an inner space portion being formed within an inner peripheral surface on the rear side; a plurality of main blades provided on an outer periphery of the boss portion and extending obliquely forward in a clockwise rotation direction from a substantially rear end portion of the boss portion; a rotary shaft attachment portion formed in a radial center portion behind the boss portion and protruding rearward in a concave shape, the rotary shaft being inserted into and coupled to the interior of the concave shape; a main blade outer peripheral surface bubble inflow prevention vane formed to extend from the approximate rear end of the boss portion to at least the approximate front end in a diagonal direction forward of clockwise rotation of an overlapping portion in the front-to-rear direction between the leading portion of the main blade and the rear portion of the main blade forward of the clockwise rotation direction, the main blade having a height of 20% to 80% of the maximum height from the outer peripheral surface of the boss portion of the forward main blade, The main blade outer peripheral surface bubble inflow prevention vanes have a height that is 20% to 80% of the maximum height from the outer peripheral surface of the boss portion of the front main blade, and therefore can make the fluid flow between the front main blade having the overlapping portion and the rear main blade on the rear surface side of the front main blade and the front surface side of the rear main blade into a high-speed, rectified flow with strong pumping force, and can prevent bubbles released from the inner space behind the impeller from flowing from the rear surface of the main blade to the outer surface of the main blade.

2. A jet pump for use in watercraft including personal watercraft, hydroplanes, motorboats, and pleasure boats, a hollow cylindrical body having a nozzle portion with a reduced diameter formed at the rear; an impeller provided within the cylindrical body and rotating to pump and move the fluid taken in from a front opening of the cylindrical body rearward; an inner cylindrical portion provided inside the cylindrical body and connected to a rear surface of the impeller, the inner cylindrical portion having a rotary shaft rotatably supported by a bearing; The impeller is a boss portion having a substantially circular cross section, an outer diameter of a rear end portion being larger than an outer diameter of a front end portion, and an inner space portion being formed within an inner peripheral surface on the rear side; a plurality of main blades provided on an outer periphery of the boss portion and extending obliquely forward in a counterclockwise direction from a substantially rear end portion of the boss portion; a rotary shaft attachment portion formed in a radial center portion behind the boss portion and protruding rearward in a concave shape, the rotary shaft being inserted into and coupled to the interior of the concave shape; a main-blade outer peripheral surface bubble inflow prevention vane formed to extend from the approximate rear end of the boss portion to at least the approximate front end in a left-rotation forward diagonal direction of an overlapping portion in the front-to-rear direction between the leading portion of the main blade and the rear portion of the main blade forward of the left rotation direction of the main blade, and having a height of 20% to 80% of the maximum height from the outer peripheral surface of the boss portion of the front-side main blade, The main blade outer peripheral surface bubble inflow prevention vanes have a height that is 20% to 80% of the maximum height from the outer peripheral surface of the boss portion of the front main blade, and therefore can make the fluid flow between the front main blade having the overlapping portion and the rear main blade on the rear surface side of the front main blade and the front surface side of the rear main blade into a high-speed, rectified flow with strong pumping force, and can prevent bubbles released from the inner space behind the impeller from flowing from the rear surface of the main blade to the outer surface of the main blade.

3. The jet pump described in claim 1, characterized in that the bubble inflow prevention vanes on the outer peripheral surface of the main blades are formed to extend beyond the approximate front end, in the forward diagonal direction of the right rotation, of the overlapping portion in the front-to-back direction between the front portions of the main blades, which are provided in multiple pieces from the approximate rear end of the boss portion, and the rear portions of the main blades ahead of the main blades in the forward direction of the right rotation, to the forward side, in the forward diagonal direction of the overlapping portion, and have a height that is 20% to 80% of the maximum height from the outer peripheral surface of the boss portion of the main blade on the forward side.

4. The jet pump described in Claim 2, characterized in that the bubble inflow prevention vanes on the outer peripheral surface of the main blades are formed to extend beyond the approximate front end, in the forward diagonal direction of the left rotation, of the overlapping portion in the front-to-back direction between the front portions of the main blades, which are provided in multiple pieces from the approximate rear end of the boss portion, and the rear portions of the main blades ahead of the left rotation direction of the main blades, to the forward side, in the forward diagonal direction of the left rotation, of the overlapping portion, and have a height that is 20% to 80% of the maximum height from the outer peripheral surface of the boss portion of the main blade on the forward side.

5. the main blade outer peripheral surface bubble inflow prevention blade has a height that is 50% to 80% of the maximum height from the outer peripheral surface of the boss portion of the main blade on the front side, The jet pump according to any one of claims 1 to 4, wherein the main blade outer peripheral surface bubble inflow prevention vanes have a height that is 50% to 80% of the maximum height from the outer peripheral surface of the boss portion of the front main blade, thereby making it difficult for bubbles released from the inner space behind the impeller to flow over the main blade outer peripheral surface bubble inflow prevention vanes toward the rear surface of the front main blade, and making the fluid flow between the front main blade and the rear main blade having the overlapping portion on the rear surface of the front main blade and on the front surface of the rear main blade into a high-speed, rectified flow with strong pumping force, and preventing bubbles released from the inner space behind the impeller from flowing from the rear surface of the main blade to the outer surface of the main blade.

6. A jet pump according to any one of claims 1 to 4, characterized in that the tip end of the bubble inflow prevention vane on the outer peripheral surface of the main vane is formed to rise at an inclination angle of approximately 70 degrees to approximately 110 degrees in the longitudinal direction relative to the outer peripheral surface of the boss portion.

7. 5. The jet pump according to claim 1, wherein the impeller has three or four main blades arranged at approximately equal intervals in the circumferential direction of the outer periphery of the boss portion.

8. a rear end of the outer inner circumferential surface at the rear of the boss portion extends rearward beyond the rear end of the rotary shaft mounting portion, the inner space between the outer inner peripheral surface of the rear of the boss portion and the outer peripheral surface of the rotary shaft mounting portion is filled with resin, 5. The jet pump according to claim 1, wherein the inner space is left behind behind a surface of the resin filled in the inner space.

9. The jet pump according to any one of claims 1 to 4, characterized in that the main blade outer peripheral surface bubble inflow prevention vane is provided at a position close to the rear surface of the main blade on the front side of the overlapping portion in the front-to-rear direction.

Images