Abstract:
Disclosed is an exhaust structure of a silent jet-propulsion personal watercraft capable of preventing water ingress into an exhaust system even when the watercraft is inverted. An exhaust structure of the watercraft is configured to cause an exhaust gas from an engine for driving a water jet pump to be discharged outside the watercraft through an exhaust passage, the exhaust passage includes a vertically extending water catcher having a substantially closed space in an upper portion thereof; an upstream exhaust passage having one end connected to an exhaust port of the engine and the other end connected to the water catcher at a position below the closed space; and a downstream exhaust passage having one end connected to the water catcher at a position below the closed space and the other end opened to outside of the watercraft.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    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 engine when the watercraft is inverted, and of producing a high muffling effect.  
           [0002]    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.  
           [0003]    In general, in the personal watercraft, an exhaust gas from an engine for driving the water jet pump is lead to an exhaust outlet provided in a transom board through an exhaust passage including a water muffler and discharged outside the watercraft from the exhaust outlet.  
           [0004]    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 the watercraft sometimes enter the exhaust outlet when the watercraft is inverted. In particular, in the personal watercraft with a four-cycle engine, 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.  
           [0005]    Under the circumstances, Japanese Laid-Open Patent Application Publication No. 2000-282840 discloses an exhaust structure, in which a water catcher constituted by an inverted-U shaped pipe is connected to downstream of the water muffler and an exhaust gas is discharged outside the watercraft through the water catcher, thereby allowing water flowing back from the exhaust outlet to be reserved in the water catcher when the watercraft is inverted. Thus, water ingress into the engine can be effectively subdued.  
           [0006]    However, the water catcher used in the above-mentioned exhaust structure is constituted by the U-shaped pipe manufactured from rubber exclusively for the water catcher. This is unfavorable because the manufacture of the water catcher is time-consuming which would lead to an increased manufacturing cost.  
         SUMMARY OF THE INVENTION  
         [0007]    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 subduing water ingress into an engine even when the watercraft is inverted, and of producing a high muffling effect, the exhaust structure being capable of suppressing manufacturing time and cost.  
           [0008]    In accordance with the present invention, there is provided an exhaust structure of a 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, the exhaust structure being configured to cause an exhaust gas from an engine for driving the water jet pump to be discharged outside the watercraft through an exhaust passage, wherein the exhaust passage includes: a vertically extending water catcher having a substantially closed space in an upper portion thereof; an upstream exhaust passage having one end connected to an exhaust port of the engine and the other end connected to the water catcher at a position below the closed space; and a downstream exhaust passage having one end connected to the water catcher at a position below the closed space and the other end being opened to outside of the watercraft.  
           [0009]    With this structure, when the watercraft is inverted, the vertically extending water catcher allows the water flowing in from the exhaust outlet opened to outside of the watercraft to be reserved in the upper portion thereof, thereby subduing the water ingress into the upper exhaust passage of the exhaust passage and the engine. In addition, since the water catcher has a relatively large capacity so as to function as a so-called “expansion chamber,” a greater muffling effect can be produced.  
           [0010]    In the invention, the downstream exhaust passage is connected to the lower end of the water catcher and the upstream exhaust passage is connected to the water catcher at a position higher than the connected position of the downstream exhaust passage. Such constitution makes it difficult that the water flowing in from the outside of the watercraft through the downstream exhaust passage enters into the upstream exhaust passage, while the watercraft is at its normal posture other than when it is inverted.  
           [0011]    The exhaust gas from the water catcher may be discharged from the transom board at the stern of the watercraft by suitably bending the lower end of the water catcher to the rearward, or otherwise discharged outside the watercraft by connecting a suitable passage to the lower end of the water catcher.  
           [0012]    Preferably, the upstream exhaust passage may include a water muffler, and an exhaust outlet of the water muffler may be positioned higher than the waterline of the watercraft. Such constitution also advantageously makes it difficult for the water to enter an upstream portion of the water muffler from the outside of the watercraft. Further, in the case of the water muffler having a labyrinth structure, the water entering the water muffler in the upstream exhaust passage is prevented from further entering the engine because of the structure, and the water reserved in the water muffler can be discharged outside the watercraft later, together with the exhaust gas from the engine.  
           [0013]    Preferably, the water muffler may be placed at a downstream end section of the upstream exhaust passage which is located apart from the engine and subsequently connected to the water catcher.  
           [0014]    Preferably, the water catcher may be adapted to discharge cooling water inside thereof at a position higher than the position where the water catcher is connected to the upstream exhaust passage, thus achieving so-called “wet exhaust” in which the exhaust gas inside of the water catcher is directly cooled by the cooling water.  
           [0015]    In the invention, the water catcher may be constituted such that it includes a vertically extending outer member having a substantially closed space and an inner member provided in the closed space of the outer member so as to be apart from the outer member, and the outer member is connected to the downstream exhaust passage and the inner member is connected to the upstream exhaust passage.  
           [0016]    It should be appreciated that the outer member and the inner member need not be completely separated as mentioned above. The outer member and the inner member should at least be constituted so as to provide a flowing space of the exhaust gas between the members. Therefore, the outer member and the inner member may be partially in contact with each other, or otherwise may be integrally formed.  
           [0017]    Preferably, the upper end of the outer member may be sealed by a separate cap which is independently constructed from the main part of the outer member.  
           [0018]    Preferably, the upper end face of the outer member, such as the cap, may be outwardly protruded. With this structure, the water dripping from the upper end face into the top opening of the inner pipe can be inhibited when the inverted watercraft is raised back up and the water reserved in the outer member is effectively discharged outside the watercraft.  
           [0019]    Preferably, the upper end face of the outer member, such as the cap, may have a double-walled structure. With this structure, the vibration noise of the end face caused by the oscillating exhaust gas can be inhibited.  
           [0020]    In the present invention, as a matter of course, the engine may be a two-cycle engine or a four-cycle engine.  
           [0021]    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  
       [0022]    [0022]FIG. 1 is a side view showing an entire personal watercraft according to embodiments of the present invention;  
         [0023]    [0023]FIG. 2 is a plan view showing the entire personal watercraft of FIG. 1;  
         [0024]    [0024]FIG. 3 is a perspective side view showing main components of an exhaust structure of the personal watercraft according to a first embodiment of the present invention;  
         [0025]    [0025]FIG. 4 is a perspective view from front-left side of the watercraft, showing arrangement of a water muffler and a water catcher of the personal watercraft according to a second embodiment of the present invention;  
         [0026]    [0026]FIG. 5 is a partly schematic, longitudinal sectional view of the water muffler and the water catcher shown in FIG. 4,  
         [0027]    [0027]FIG. 6 is a perspective view showing a structure of bend pipes constituting a water catcher according to the second embodiment; and  
         [0028]    [0028]FIGS. 7A and 7B are longitudinal sectional views of main components of the water catcher according to the second embodiment, showing configurations of caps for sealing an upper end of an outer pipe of the water catcher.  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0029]    The present invention will now be described in detail referring to the accompanying drawings illustrating embodiments thereof.  
       EMBODIMENT 1  
       [0030]    [0030]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 and 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.  
         [0031]    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 over 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.  
         [0032]    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.  
         [0033]    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 .  
         [0034]    As shown in FIGS. 1 and 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 a steered direction while the water jet pump P is generating the propulsion force.  
         [0035]    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.  
         [0036]    In FIGS. 1 and 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 and 2, reference numeral  23  denotes a front hatch cover. A front compartment (not shown) is provided under the front hatch cover  23  for storing equipment and the like. Another hatch cover  25  is provided over the front hatch cover  23  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.  
         [0037]    [0037]FIG. 3 is a perspective side view showing main components of an exhaust structure of the personal watercraft according to the embodiments of the present invention. As indicated by arrows in FIG. 3, the exhaust gas from the engine E is discharged outside the watercraft through an exhaust passage including a water muffler  31 , a water catcher  34 , and so on.  
         [0038]    For detail, the exhaust passage is comprised of the water catcher  34 , an upstream exhaust passage for connecting an exhaust port (not shown) of the engine E to the water catcher  34  at an upperstream position of the water catcher  34  in an exhaust gas flow path, and a downstream exhaust passage for connecting the water catcher  34  to an exhaust outlet  38  through which the exhaust gas is discharged outside, at a downstream position of the water catcher  34 .  
         [0039]    The exhaust gas from the engine E is introduced into the water muffler  31  through an exhaust manifold (not shown) constituting the upstream exhaust passage and muffled in the water muffler  31  having an internal labyrinth structure. Then, the muffled exhaust gas is introduced into the water catcher  34  through a connecting port  31   a  projected from a rear end face of the water muffler  31 .  
         [0040]    The water catcher  34  is manufactured mainly from a stainless-steel straight pipe and its longitudinal direction corresponds with the vertical direction of the watercraft. The upper end of the water catcher  34  is sealed by a cap  34   b,  thereby forming a substantially closed space S. The water catcher  34  is provided with a connecting port  34   a  at a predetermined position in the longitudinal (vertical) direction. The connecting port  34   a  has a diameter substantially equal to that of the connecting port  31   a  of the water muffler  31 . The connecting port  34   a  is fitted and fastened to the connecting port  31   a  of the water muffler  31  by means of a connecting band  45 .  
         [0041]    While the exhaust gas is introduced to the water catcher  34  by what is referred to as “dry exhaust” herein, it will also be appreciated that so-called “wet exhaust” shown in FIG. 3 may be employed, in which the outer wall of the water muffler  31  has a double-walled structure for allowing cooling water to flow inside thereof, thereby forming a water jacket in the water muffler  31 , and the cooling water in this water jacket is discharged from the upper end of the water catcher  34  to the inside of the water catcher  34  through a suitable cooling water passage  44 . Preferably, the cooling water is discharged at a position higher than the connecting port  31   a  of the water muffler  31 . More preferably, as shown in FIG. 3, the cooling water is discharged inside of the water catcher  34  from the upper end of the water catcher  34 .  
         [0042]    In this embodiment, the lower end of the water catcher  34  is bent at a right angle toward the rear side of the watercraft to form a connecting passage  37  leading to an exhaust outlet  38  provided in an outer face of the transom board. In order to use an inexpensive pipe as the water catcher  34 , the lower end of the water catcher  34  may be connected to the connecting passage  37  by any suitable connecting means.  
         [0043]    In general, the exhaust outlet  38  is located immediately above the waterline L indicated by a dashed line in FIG. 3. In this embodiment, the water muffler  31  is connected to the water catcher  34  at a position slightly higher than the exhaust outlet  38 . This constitution is capable of preventing the water from entering into the water muffler  31  and further into the engine E through the exhaust outlet  38  while the watercraft is at its normal posture (in stopping or cruising state).  
         [0044]    On the other hand, when the watercraft is inverted, the water entering through the exhaust outlet  38  is reserved in the closed space S in an upper portion of the water catcher  34  and does not flow into the water muffler  31  until the reserved water reaches the connecting port  31   a.  When the inverted watercraft is raised up, the water reserved in the closed space S in the upper portion of the water catcher  34  flows back to the exhaust outlet  38  and is discharged outside the watercraft.  
       EMBODIMENT 2  
       [0045]    [0045]FIG. 4 is a perspective view from the front left side of the watercraft, showing arrangement of a water muffler and a water catcher according to the second embodiment of the present invention. In FIG. 4, “F” indicates the front side of the watercraft. FIG. 5 is a longitudinal sectional view showing main components of the water of FIG. 4.  
         [0046]    As indicated by an arrow in FIG. 4, the exhaust gas from the engine E flows through the water muffler  31  constituting the upstream exhaust passage and then flows into the water catcher  34  through the connecting port  31  a provided on the side (left side in FIG. 4) of the water muffler  31 . Then, the exhaust gas flows into the connecting passage  37  constituting the downstream exhaust passage through the water catcher  34  and is discharged outside the watercraft through the exhaust outlet  38  on the rear side of the watercraft. While in this embodiment, the connecting port 31 a  is provided in the side face of the water muffler  31 , this may be alternatively provided on the rear side similarly to the first embodiment.  
         [0047]    Referring to FIG. 5, the water catcher  34  of this embodiment has a double-pipe structure in which an inner pipe  340   in  as an inner member is inserted into an inner space of an outer pipe  340   out  as an outer member (outer shell) so as to be spaced apart from each other. The outer pipe  340   out  vertically extends and its upper end is sealed, thereby forming the substantially closed space S in the upper portion of the water catcher  34 .  
         [0048]    The outer pipe  340   out  is comprised of a straight pipe  343   out  located on the upper side and a bend pipe (elbow pipe)  342   out  located on the lower side. The inner pipe  340   in  is comprised of a straight pipe  343   in  located on the upper side and a bend pipe (elbow pipe)  342   in  located on the lower side. The straight pipes  343   out ,  343   in  are made of rubber and the bend pipes (elbow pipes)  342   out ,  342   in  are made of metal. The water catcher  34  is configured such that the inner straight pipe  343   in  is connected to the connecting port  31   a  of the water muffler  31  at a connecting port  34   a  of the bend pipe  342   in  through the bend pipe  342   in  and the outer straight pipe  343   out  is connected to a connecting port  37   a  of the connecting passage  37  constituting the downstream exhaust passage at a connecting port  34   b  of the bend pipe  342   out  through the bend pipe  342   out  and further connected to the exhaust outlet  38  at the rear side of the watercraft through the connecting passage  37 .  
         [0049]    As shown in FIG. 6, commercially available pipes are used as the bend pipes  342   out ,  342   in  and are combined in the following manner. A hole is formed in an outer curved face of the outer bend pipe  342   out  which has a diameter equal to an outer diameter of the inner bend pipe  342   in , and the inner bend pipe  342   in  is inserted through the hole. The bend pipe  342   in  is fixed to the bend pipe  342   out  from outside by welding. The bend pipes  342   out ,  342   in  are not limited to the elbow pipes as described above, but bend pipes having a larger radius of curvature may be used.  
         [0050]    Referring to FIG. 5 again, the upper end of the inner bend pipe  342   in  projects upwardly so as to be higher than the upper end of the outer bend pipe  342   out . The inner straight pipe  343   in  is fitted to the upper end of the inner bend pipe  342   in , and then the outer straight pipe  343   out  is fitted to the upper end of the outer bend pipe  342   out . Commercially available pipes may be used as the straight pipes  343   out ,  343   in , but specially designed ones may be used for the sake of optimized shape.  
         [0051]    In FIG. 5, the upper portions of the straight pipes  343   out ,  343   in  are rearwardly curved. This is due to the fact that the commercially available pipes made of rubber are originally curved. The functions and effects of the present invention can be obtained regardless of such curves.  
         [0052]    The straight pipes  343   out ,  343   in  are sized so that the upper end of the outer straight pipe  343   out  extends upwardly so as to be higher by predetermined length d than the upper end of the inner straight pipe  343   in . A metal cap  341  is externally attached to the upper end of the outer straight pipe  343   out  and fixed thereto by means of a suitable fastening band. While the upper end of the outer straight pipe  343   out  is sealed by the metal cap  341  separable from the outer straight pipe  343   out  in this embodiment, the straight pipe  343   out  and the cap  341  may be integrally formed.  
         [0053]    In the water catcher  34  so constituted, as indicated by arrows in FIG. 5, the exhaust gas from the water muffler  31  first flows into the inner bend pipe  342   in  and is discharged from the upper end of the inner straight pipe  343   in  into the outer straight pipe  343   out . In this case, since the exhaust gas is discharged from the small-diameter inner straight pipe  343   in  into the large-diameter outer straight pipe  343   out , its exhaust pressure and exhaust noise are reduced. The exhaust gas discharged into the outer straight pipe  343   out  out flows downwardly inside of the outer straight pipe  343   out , and is led to the outer bend pipe  342   out  and the connecting passage  37  connected to the outer bend pipe  342   out  by the connecting band  46 , and then is discharged from the exhaust outlet  38  (see FIG. 4).  
         [0054]    While the watercraft is at its normal posture (in stopping or cruising state), the water flowing into exhaust outlet  38  from outside flows into the outer straight pipe  343   out  through the connecting passage  37  and the outer bend pipe  342   out , but such water does not flow into the inner straight pipe  343   in  until the water reaches the upper opening end of the inner straight pipe  343   in . Therefore, the water ingress into the water muffler  31 , and hence into the engine E, is prevented.  
         [0055]    On the other hand, when the watercraft is inverted, the water entering through the exhaust outlet  38  flows into the outer straight pipe  343   out  through the connecting passage  37  and the outer bend pipe  342   out , but such water is reserved in the closed space S in the upper portion of the water catcher  34  and does not flow into the water muffler  31  until the water reach the connecting port  31   a  of the water muffler  31 . Thereafter, when the watercraft is raised back up, the water reserved in the outer straight pipe  343   out  flows back to the exhaust outlet  38  through the outer bend pipe  342   out  and the connecting passage  37  and is discharged outside the watercraft. In this case, the water in the inner straight pipe  342   in  and a part of the water in the outer straight pipe  343   out  might flow into the water muffler  31 , but such amount of water is small and can be captured in the water muffler  31  and prevented from flowing into the engine E. Upon re-starting of the engine E, the captured water is discharged outside the watercraft, together with the exhaust gas.  
         [0056]    The muffling effect of the water catcher  34  of this embodiment is adjustable depending on various conditions, including material of the water catcher  34 , and the diameter and thicknesses of the outer straight pipe  343   out  and inner straight pipe  343   in . For example, these conditions may be set based on the water inflow, and the above-identified predetermined length d, equal to the difference in upper ends between the outer straight pipe  343   out  and the inner straight pipe  343   in , is adjustable based on observation of actual muffling effect. In this embodiment, such adjustment is easily achieved because the outer straight pipe  343   out  and the inner straight pipe  343   in  are made of rubber.  
         [0057]    [0057]FIG. 7A shows an alternative embodiment of the cap, in which a center part of a cap  341   a  is protruded outwardly in the shape of bowl. Such a shape is helpful in subduing the dripping of the water reserved in the outer straight pipe  343   out  into the inner straight pipe  343   in  when the inverted watercraft is raised back up.  
         [0058]    [0058]FIG. 7B shows a cap  341   b  having an end face portion with a double-walled structure. Such a shape can subdue a noise generated by the vibration of the end face portion of the cap  341   b,  which is caused by the exhaust gas.  
         [0059]    The cap  341   a  in FIG. 7A may have the double-walled structure similar to that shown in FIG. 7B. In this case, an inner side wall of the cap  341   a  may be formed in the shape of punching metal, woven metal wires, and the like. With such configuration, since a space between the outer and inner walls functions as a so-called “resonance chamber” of the exhaust gas, a greater muffling effect is attained.  
         [0060]    Moreover, while in this embodiment, the upper portion of the outer pipe  340   out  (straight pipe  343   out ) as the outer member of the water catcher  34  and the upper portion of the inner pipe  340   in  (straight pipe  343   in ) as the inner member are straight pipes, combination of various shapes, e.g., a spherical outer pipe  340   out  and a straight inner pipe  340   in , may be employed.  
         [0061]    The other constitutions and functions of this embodiment are similar to those of the first embodiment, and similar or corresponding parts are identified by the same reference numerals and will not be further described.  
         [0062]    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 the metes and bounds of the claims, or equivalents of such metes and bounds thereof are therefore intended to be embraced by the claims.