Abstract:
Disclosed is an exhaust structure of a jet-propulsion personal watercraft adapted to eject water pressurized and accelerated by a water jet pump from an outlet port so as to be propelled as the resulting reaction, which is configured to cause an exhaust gas from an engine for driving the water jet pump to be discharged to outside of the watercraft through an exhaust passage constituted by a water muffler, and the like. The exhaust structure is configured to cause the exhaust gas from the engine to flow into a pump room through a hollow portion partially or entirely formed in a pump cover covering a pump room that contains the water jet pump from a bottom side of the watercraft and to be discharged to outside of the watercraft through the pump room. The exhaust structure is advantageously capable of producing a high muffling effect and preventing water ingress into the exhaust passage even when the watercraft is inverted.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1 Field of the Invention  
           [0002]    The present invention relates to a jet-propulsion personal watercraft (PWC) which ejects water rearward and planes on a water surface as the resulting reaction. More particularly, the present invention relates to an exhaust structure of the personal watercraft capable of preventing water ingress into an exhaust system when the watercraft is inverted, and of producing a high muffling effect.  
           [0003]    2. Description of the Related Art  
           [0004]    In recent years, so-called jet-propulsion personal watercraft have been widely used in leisure, sport, rescue activities, and the like. The personal watercraft is configured to have a water jet pump that pressurizes and accelerates water sucked from a water intake generally provided on a hull bottom surface and ejects it rearward from an outlet port. Thereby, the personal watercraft is propelled.  
           [0005]    In general, in the personal watercraft, an exhaust gas from an engine for driving the water jet pump is introduced through an exhaust passage including a water muffler and discharged outside the watercraft through an exhaust outlet provided in a transom board.  
           [0006]    The water muffler has an internal structure called “labyrinth structure,” capable of preventing water entering through the exhaust outlet from reaching the engine, even when the watercraft is inverted. Such a structure is especially advantageous because waves following behind the watercraft sometimes enter the exhaust outlet when the watercraft is inverted. In particular, in the personal watercraft in which a four-cycle engine is equipped, the water ingress into the engine sometimes affects an engine power characteristic, and, therefore, it is essential that the water ingress into the engine be prevented.  
           [0007]    While the water muffler has a muffling function because of its labyrinth structure, a relatively loud exhaust sound is sometimes generated depending on the driving condition of the watercraft, since the exhaust gas is discharged rearwardly through the exhaust outlet located above the planing surface in the above constitution.  
           [0008]    In light of environmental problems, such an exhaust sound is needed to be reduced.  
           [0009]    As a solution to the above-mentioned problem, U.S. Pat. No. 6,066,014 discloses that a high muffling effect is produced by discharging the exhaust gas into water along a pump cover covering a lower surface of a pump room. However, this constitution is undesirable, because the shape of the pump cover significantly affects a planing performance of the watercraft, and the discharge of the exhaust gas along a planing surface of the pump cover might cause cavitations to occur in the planing surface.  
         SUMMARY OF THE INVENTION  
         [0010]    The present invention addresses the above-described condition, and an object of the present invention is to provide an exhaust structure of a jet-propulsion personal watercraft capable of producing a high muffling effect and preventing water ingress into an exhaust system even when the watercraft is inverted.  
           [0011]    The above-described object can be achieved by the jet-propulsion personal watercraft constituted as described below.  
           [0012]    An exhaust structure of a personal watercraft of the present invention, adapted to eject water pressurized and accelerated by a water jet pump from an outlet port so as to be propelled as the resulting reaction, is adapted to cause an exhaust gas from an engine for driving the water jet pump to be discharged to outside of the watercraft through an exhaust passage. The personal watercraft includes a pump cover covering a pump room, which contains the water jet pump, from the bottom side of the watercraft. The exhaust passage is configured to cause the exhaust gas from the engine to be discharged to outside of the watercraft through a space in a hollow portion partially or entirely formed in the pump cover and a space in the pump room.  
           [0013]    In accordance with the above invention, the exhaust gas from the engine is discharged into the pump room through the hollow portion formed by, for example, double-wall structuring of the pump cover, and then is muffled in the pump room. Therefore, a high muffling effect is produced. In addition, since the exhaust gas is discharged from inside of the pump cover to be located at the highest position and above the water surface to outside of the watercraft without being significantly affected by waves following when the watercraft is inverted, the water ingress into the exhaust system can be prevented. In particular, while the watercraft is planing, the pump room can be maintained in a hollow state without water ingress therein, and, therefore, the water ingress into the exhaust system through the hollow portion hardly occurs.  
           [0014]    In the above invention, an exhaust outlet of the hollow portion into the pump room is located in a space surrounded by walls of the pump room and the pump cover. This makes it possible that the water ingress into the exhaust system during planing of the watercraft can be effectively prevented. In addition, the hollow portion may be provided to the pump cover or integrally provided with the pump cover, for example by casting.  
           [0015]    In the above invention, the exhaust outlet of the hollow portion into the pump room may be opened upwardly or laterally. Therefore, the watercraft can be designed more freely in view of layout of the hull, the water jet pump, the exhaust system, and the like.  
           [0016]    In the above invention, the exhaust outlet of the hollow portion into the pump room may be provided at one spot, or otherwise the exhaust gas may be discharged into the pump room through a plurality of branched exhaust passages from the water muffler to the hollow portion.  
           [0017]    Furthermore, an exhaust structure of a personal watercraft of the present invention adapted to eject water pressurized and accelerated by a water jet pump from an outlet port so as to be propelled as the resulting reaction, is adapted to discharge an exhaust gas from an engine for driving the water jet pump outside the watercraft through an exhaust passage. The personal watercraft includes a pump room formed by recessing a rear end portion of the hull, for containing the water jet pump, and a pump cover over the pump room and a part of the hull bottom surface extending forward from the pump room from the bottom side of the watercraft. The exhaust passage has a gap, provided between the hull bottom surface and the pump cover, and for communicating the engine with the pump room. The exhaust passage is configured to cause the exhaust gas from the engine to flow into the pump room through the gap and to be discharged outside the watercraft through the pump room.  
           [0018]    In the above invention, without the above identified hollow portion, the exhaust gas from the engine is discharged into the pump room through the gap provided between the hull bottom surface and the pump cover, and for communicating the engine with the pump room. The gap allows the exhaust gas from the engine into the pump room therethrough. Therefore, the above mentioned muffling function and water-ingress-proof function can be achieved with a simple constitution.  
           [0019]    As a matter of course, in the above invention, the engine may be a two-cycle engine or a four-cycle engine.  
           [0020]    The above and further objects and features of the invention will more fully be apparent from the following detailed description with accompanying drawings. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0021]    [0021]FIG. 1 is a side view showing an entire personal watercraft according to a first embodiment of the present invention;  
         [0022]    [0022]FIG. 2 is a plan view showing the entire personal watercraft of FIG. 1;  
         [0023]    [0023]FIG. 3 is a bottom view showing the entire personal watercraft of FIG. 1;  
         [0024]    [0024]FIG. 4 is a partially cross-sectional view of the personal watercraft of FIG. 1, showing a pump room that contains a water jet pump and its vicinity;  
         [0025]    [0025]FIG. 5A is a perspective view showing a structure of a hollow portion, and an exhaust inlet thereof and an exhaust outlet thereof, as seen from a front-left side of the pump cover of FIG. 3;  
         [0026]    [0026]FIG. 5B is a perspective view showing another structure of the hollow portion, and the exhaust inlet thereof and the exhaust outlet thereof, as seen from the front-left side of the pump cover of FIG. 3;  
         [0027]    [0027]FIG. 6 is a partially cross-sectional view of the personal watercraft, showing a further structure of the hollow portion, and the exhaust inlet thereof and the exhaust outlet thereof; and  
         [0028]    [0028]FIG. 7 is a partially cross-sectional view of the personal watercraft, showing a still further structure of an exhaust passage to the pump room. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0029]    Hereinafter, a jet-propulsion personal watercraft according to embodiments of the present invention will be described with reference to the drawings.  
         [0030]    (Embodiment 1)  
         [0031]    [0031]FIG. 1 is a side view showing an entire personal watercraft according to a first embodiment of the present invention, and FIG. 2 is a plan view thereof. In FIGS.  1 ,  2 , reference numeral A denotes a body of the personal watercraft. The body A comprises a hull H and a deck D covering the hull H from above. A line at which the hull H and the deck D are connected over the entire perimeter thereof is called a gunnel line G. In this embodiment, the gunnel line G is located above a waterline L of the personal watercraft.  
         [0032]    As shown in FIG. 2, an opening  16 , which has a substantially rectangular shape seen from above, is formed at a relatively rear section of the deck D such that it extends in the longitudinal direction of the body A, and a riding seat S is provided above the opening  16  such that it covers the opening  16 . An engine E is provided in a chamber (engine room)  20  surrounded by the hull H and the deck D below the seat S.  
         [0033]    The engine E has multiple cylinders (e.g., three-cylinders). As shown in FIG. 1, a crankshaft  10   b  of the engine E is mounted along the longitudinal direction of the body A. An output end of the crankshaft  10   b  is rotatably coupled integrally with a pump shaft of a water jet pump P through a propeller shaft  15 . An impeller  21  is attached on the pump shaft of the water jet pump P. The impeller  21  is covered with a pump casing  21  C on the outer periphery thereof.  
         [0034]    A water intake  17  is provided on the bottom of the hull H. The water is sucked from the water intake  17  and fed to the water jet pump P through a water intake passage  14 . The water jet pump P pressurizes and accelerates the water by rotation of the impeller  21 . The pressurized and accelerated water is discharged through a pump nozzle  21 R having a cross-sectional area of flow gradually reduced rearward, and from an outlet port  21 K provided on the rear end of the pump nozzle  21  R, thereby obtaining a propulsion force. In FIG. 1, reference numeral  21 V denotes fairing vanes for fairing water flow behind the impeller  21 .  
         [0035]    As shown in FIGS. 1, 2, reference numeral  10  denotes a bar-type steering handle. The handle  10  operates in association with a steering nozzle  18  swingable around a swing shaft (not shown) to the right or to the left behind the pump nozzle  21 R. When the rider rotates the handle  10  clockwise or counterclockwise, the steering nozzle  18  is swung toward the opposite direction so that the watercraft can be correspondingly turned to any desired direction while the water jet pump P is generating the propulsion force.  
         [0036]    As shown in FIG. 1, a bowl-shaped reverse deflector  19  is provided above the rear side of the steering nozzle  18  such that it can swing downward around a horizontally mounted swinging shaft  19   a . The deflector  19  is swung downward to a lower position behind the steering nozzle  18  to deflect the ejected water from the steering nozzle  18  forward, and as the resulting reaction, the personal watercraft moves rearward.  
         [0037]    In FIGS. 1, 2, reference numeral  12  denotes a rear deck. The rear deck  12  is provided with an openable rear hatch cover  29 . A rear compartment (not shown) with a small capacity is provided under the rear hatch cover  29 . In FIGS. 1, 2, reference numeral  23  denotes a front hatch cover. A front compartment (not shown) is provided under the front hatch cover  23  for storing equipments and the like. Another hatch cover  25  is provided over the front hatch cover  23 , thereby forming a two-layer hatch cover. Life jackets or the like can be stored under the upper hatch cover  25  through an opening (not shown) provided in the rear end thereof.  
         [0038]    [0038]FIG. 3 is a bottom view showing the entire personal watercraft according to the embodiment of the present invention. FIG. 4 is a partially cross-sectional view of the personal watercraft of FIG. 1, showing a pump room that contains the water jet pump and its vicinity. As shown in FIGS. 3, 4, the water jet pump P is contained and fixed in a pump room  27  formed by recessing a rear-end central portion of the hull H in the form of a box. A plate-shaped pump cover  26  manufactured by e.g., aluminum die casting is secured to cover a lower side opening of the pump room  27  by screws via a seal member (not shown).  
         [0039]    The aforementioned water intake  17  is provided in front of the pump cover  26 . The propeller shaft  15  penetrates through the intake passage  14  for guiding the water sucked through the water intake  17  into the water jet pump P. As clearly shown in FIG. 4, the pump room  27  has an adequate space around the pump casing  21 C and this space is almost entirely occupied by only air while the watercraft is planing.  
         [0040]    The pump cover  26  partially has a double-wall structure, and therefore has a hollow portion  26   a  between the walls. The hollow portion  26   a  has two openings, i.e., an exhaust inlet  26   in  and an exhaust outlet  26   out . The exhaust inlet  26   in  is provided outside of the pump room  27 . One end of the water muffler  31  is connected to an exhaust side of the engine E and the other end thereof is connected to the exhaust inlet  26   in  through a U-shaped pipe  32 . More specifically, a lower end of the U-shaped pipe  32  is extended downwardly to the vicinity of a bottom surface of the hull H. The exhaust inlet  26   in  is opened upwardly to receive the lower end of the U-shaped pipe  32 . The exhaust outlet  26   out  is positioned so as to face the pump room  27 .  
         [0041]    As should be appreciated from the foregoing, the exhaust passage of the personal watercraft is comprised of the water muffler  31 , the U-shaped pipe  32 , the hollow portion  26   a , the pump room  27 , and the like in this order, from the side of the engine E. The exhaust gas from the engine E is muffled by the water muffler  31  and introduced from the exhaust inlet  26   in  into the hollow portion  26   a  through the U-shaped pipe  32 . Then, the exhaust gas is discharged from the exhaust outlet  26   out  into the pump room  27  through the hollow portion  26   a  and further muffled in the pump room  27 .  
         [0042]    The hollow portion  26   a  provided in the pump cover  26  for discharging the exhaust gas into the pump room  27  may be integrally formed by casting with the pump cover  26 . Therefore, the above-mentioned function can be attained merely by slightly altering the existing pump cover  26  without the necessity of an additional member for discharging the exhaust gas from the water muffler  31  into the pump room  27 .  
         [0043]    [0043]FIGS. 5A, 5B are perspective views showing detailed structures of the hollow portion, the exhaust inlet thereof, and the exhaust outlet thereof, as seen from the front-left side of the pump cover. In FIGS. 5A, 5B, “F” represents a front side of the pump cover  26 . As shown in FIG. 5A, the pump cover  26  is provided with a plurality of reinforcement ribs on an upper surface thereof. The hollow portion  26   a  extending in the front-and-rear direction in a left portion of the pump cover  26  can be formed by upwardly protruding the upper wall of the pump cover  26 . In the hollow portion  26   a  having such a structure, the exhaust inlet  26   in  may be opened upwardly at a front end of the hollow portion  26   a  and the exhaust outlet  26   out  is opened upwardly at a rear end portion of the hollow portion  26   a.    
         [0044]    The positions of the exhaust inlet  26   in  and the exhaust outlet  26   out  are not intended to be limited to the above. Nonetheless, it is required that the exhaust inlet  26   in  be provided outside of the pump room  27  and covered by the pump cover  26 , and the exhaust outlet  26   out  be provided inside of the pump room  27 . The position and shape of the hollow portion  26   a  may be determined according to the positions of the exhaust inlet  26   in  and the exhaust outlet  26   out.    
         [0045]    As an alternative, as shown in FIG. 5B, the hollow portion  26   a  may be extended in the front-and-rear direction in a right portion of the pump cover  26  and provided with the exhaust inlet  26   in  opened upwardly in an upper portion thereof and the exhaust outlet  26   out  opened laterally, e.g., to the left side, in a side portion thereof. In this manner, the exhaust inlet  26   in  and the exhaust outlet  26   out  may be opened in various directions.  
         [0046]    (Embodiment 2)  
         [0047]    [0047]FIG. 6 is a partially cross-sectional view of the pump room that contains the water jet pump and its vicinity, showing another embodiment of the hollow portion, and the exhaust inlet thereof and the exhaust outlet thereof. As shown in FIG. 6, the hollow portion  26   a  of this embodiment is extended over the entire pump cover  26  in the front-and-rear direction. The exhaust inlet  26   in  is substantially the same as that of the first embodiment. On the other hand, the exhaust outlet  26   out  is opened rearwardly, and the lower wall of the pump cover  26  is extended rearwardly so as to be somewhat longer than the upper wall. As a result, the exhaust gas from the exhaust outlet  26   out  is discharged into the pump room  27  and immediately released to atmosphere.  
         [0048]    Since other constitutions and functions of this embodiment are similar to those of the first embodiment, the same reference numerals are used to identify the same or corresponding parts, which will not be further described.  
         [0049]    (Embodiment 3)  
         [0050]    [0050]FIG. 7 is a partially cross-sectional view of the pump room that contains the water jet pump and its vicinity, showing a further embodiment of the exhaust passage to the pump room. As shown in FIG. 7, in this embodiment, instead of providing the hollow portion  26   a  in the pump cover  26 , there is provided a gap  26   b  between the hull bottom surface and the pump cover  26 , for discharging the exhaust gas from the engine E through the U-shaped pipe  32  into the pump room  27  therethrough.  
         [0051]    Since the other constitution and functions of this embodiment are similar to those of the first embodiment, the same reference numerals are used to identify the same or the corresponding parts, which will not be further described.  
         [0052]    As this invention may be embodied in several forms without departing from the spirit of essential characteristics thereof, the present embodiments are therefore illustrative and not restrictive, since the scope of the invention is defined by the appended claims rather than by the description preceding them, and all changes that fall within metes and bounds of the claims, or equivalents of such metes and bounds thereof, are therefore intended to be embraced by the claims.