Abstract:
Disclosed is a personal watercraft capable of preventing an exhaust gas from contaminating a transom board in the vicinity of an exhaust outlet and of reducing an exhaust noise of the exhaust gas within a wide speed range. The personal watercraft having an engine disposed in a body thereof for driving a water jet pump comprises, an exhaust outlet  2 D formed at a rear end of an exhaust passage Ep extending from an exhaust port of the engine E to a transom board Tm of the watercraft so as to open rearwardly; a flexible sheet member  3  disposed at the exhaust outlet and having a closing portion  3 A capable of opening/closing the exhaust outlet by an exhaust pressure of the exhaust gas; and a short pipe  5 P mounted to the outside of the transom board and extending rearwardly from the transom board Tm so as to surround the closing portion  3 A of the sheet member  3 , for introducing the exhaust gas rearwardly.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a personal watercraft (PWC) which ejects water rearward and planes on a water surface as the resulting reaction. More particularly, the present invention relates to a structure of an exhaust outlet portion of an exhaust passage extending from an exhaust port of an engine to a transom board. 
     2. Description of the Related Art 
     In recent years, so-called jet-propulsion personal watercraft have been widely used in leisure, sport, rescue activities, and the like. The jet-propulsion personal watercraft is configured to have a water jet pump that pressurizes and accelerates water sucked from a water intake generally provided on a bottom of a hull and ejects it rearward from an outlet port. Thereby, the personal watercraft is propelled. 
     In the jet-propulsion personal watercraft, a steering nozzle provided behind the outlet port of the water jet pump is swung either to the right or to the left by operating a bar-type steering handle to the right or to the left, to change the ejection direction of the water to the right or to the left, thereby turning the watercraft to the right or to the left. 
     In the jet-propulsion personal watercraft, an engine is disposed in an engine room such that a crankshaft extends along the longitudinal direction of the watercraft. The crankshaft projects rearwardly and its rear end is coupled to a pump shaft of the water jet pump, thereby driving the water jet pump. 
     An exhaust gas from the engine is introduced into a muffler and muffled therein, and the resulting exhaust gas is discharged outside the watercraft from an exhaust outlet that opens in a transom board at the rear end of the watercraft. 
     In the personal watercraft having the above configured exhaust outlet, the transom board or the like in the vicinity of the exhaust outlet is susceptible to contamination by the exhaust gas. Accordingly, the applicant disclosed an invention relating to an exhaust outlet of the watercraft, in which, by attaching an extending pipe bent obliquely downwardly at the rear end thereof to the rear end of the exhaust outlet, the contamination of the transom board by the exhaust gas is prevented and the exhaust noise is caused to contact the water surface to be reduced (see U.S. Pat. No. 6,206,741). 
     Although, in this structure, the exhaust noise is reduced while the watercraft is cruising at a high speed, the watercraft sometimes resonates with the water surface while cruising at a medium or low speed. With this structure, the exhaust noise is difficult to effectively reduce within a wide speed range. 
     SUMMARY OF THE INVENTION 
     The present invention addresses the above described conditions, and an object of the present invention is to provide a personal watercraft capable of preventing an exhaust gas discharged from an exhaust outlet that opens in a transom board from contaminating the transom board in the vicinity of the exhaust outlet and of reducing an exhaust noise of the exhaust gas within a wide speed range. 
     According to the present invention, there is provided a personal watercraft having an internal combustion engine disposed in a body thereof, for driving a water jet pump, comprising: a transom board; an exhaust outlet formed in the transom board at a rear end of an exhaust passage extending from an exhaust port of the engine to the transom board so as to open rearwardly; a flexible sheet member disposed at the exhaust outlet and having a closing portion capable of opening/closing the exhaust outlet by an exhaust pressure of an exhaust gas of the engine; and a short pipe mounted to an outside of the transom board and extending rearwardly from the transom board so as to surround the closing portion of the sheet member, for introducing the exhaust gas rearwardly. 
     With such a structure, the exhaust gas being discharged from the exhaust outlet formed in the transom board at the rear end of the exhaust passage extending to the transom board so as to open rearwardly is discharged outside the watercraft from a passage formed between the exhaust outlet and the sheet member by opening the closing portion of the sheet member provided in the exhaust outlet by deforming the closing portion of the flexible sheet member due to the pressure of the exhaust gas. In addition, the short pipe extending rearwardly from the transom board so as to surround the periphery of the closing portion, i.e., the short pipe surrounding the portion of the sheet member through which the exhaust gas flows and introduces the exhaust gas rearwardly, extends rearwardly from the transom board. Thereby, the exhaust gas is discharged outside the watercraft from the rear end of the short pipe located behind and apart from the transom board. As a result, the transom board is prevented from being contaminated by the exhaust gas. In addition, the exhaust noise is caused to contact the flexible sheet member and to be absorbed therein, so that the noise is reduced while the watercraft is cruising at a wide range of speeds, or is at rest on the water surface. Further, in the case where water from behind the watercraft splashes toward the exhaust outlet, the closing portion of the sheet member protects the exhaust outlet by closing the same, thus preventing water ingress from the exhaust outlet into the engine. 
     Preferably, the personal watercraft may further comprise a press member for mounting the sheet member and the short pipe to the transom board, and the press member has a mounting portion for mounting the sheet member and the short pipe to the transom board from behind the body. 
     Preferably, the short pipe may be formed integrally with the press member. In this structure, the number of parts is reduced, and the seal between the short pipe and the press member and rigidity of these members are improved. 
     Preferably, the sheet member may have a closing portion larger than the exhaust outlet and capable of closing the exhaust outlet, a peripheral portion provided around the closing portion so as to be separated from the closing portion, and a connecting portion partially connecting the closing portion to the peripheral portion, and the short pipe may have a vent passage sized to permit the closing portion to swing rearwardly around the connecting portion. 
     Preferably, the mounting portion of the press member may be mounted to the transom board to mount the peripheral portion of the flexible sheet member. 
     Preferably, the connecting portion of the sheet member may be located at an upper portion of the closing portion. In this structure, when the exhaust gas is discharged, the closing portion is deformed around the upper portion by its exhaust pressure so as to swing around the upper portion away from the exhaust outlet, so that an exhaust passage is created. In this structure, since the closing portion of the sheet member is suspended from the upper portion, a reliable structure is achieved. 
     Preferably, the closing portion may be separated in an incomplete-circle shape by a slit from the peripheral portion of the sheet member except the connecting portion. 
     Preferably, the closing portion may be separated by a slit in a U-shape from the peripheral portion of the sheet member, except the connecting portion, the closing portion being substantially U-shaped with a lower portion formed by a semi-circular line and an upper portion formed by straight lines extending from the semi-circular line. In this structure, the length of the connecting portion can be set larger and durability can be thereby increased. 
     Preferably, the sheet member may be made of rubber. The sheet made of rubber has flexibility and durability. 
     The above and further objects and features of the invention will be more fully be apparent from the following detailed description with accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF DRAWINGS 
     FIG. 1 is an enlarged rear view showing an exhaust outlet portion of a personal watercraft according to an embodiment of the present invention; 
     FIG. 2A is a view taken in the direction of arrows along line IIa—IIa in FIG. 1, showing a structure of the exhaust outlet portion in FIG. 1; 
     FIG. 2B is a partial cross-sectional view taken in the direction of arrows along line IIb—IIb in FIG. 1, showing a structure of a mounting portion of the exhaust outlet portion in FIG. 1; 
     FIG. 3 is an exploded perspective view showing placement of an exhaust passage in a hull portion at a rear portion of the personal watercraft provided with the exhaust outlet portion in FIGS. 1 and 2, and the structure of the exhaust outlet portion; 
     FIG. 4 is a front view of a base member in FIGS. 1-3; 
     FIG. 5 is a front view of a sheet member in FIGS. 1-3; 
     FIG. 6 is a front view of a press member in FIGS. 1-3; 
     FIG. 7 is a front view showing a structure of a sheet member according to another embodiment; 
     FIG. 8 is a front view showing a structure of a press member according to another embodiment, which is used in the sheet member in FIG. 7; 
     FIG. 9 is a side view showing the personal watercraft according to the embodiment of the present invention; and 
     FIG. 10 is a plan view showing the personal watercraft in FIG.  9 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Hereinafter, a personal watercraft according to an embodiment of the present invention will be described with reference to the accompanying drawings. 
     Referring now to FIGS. 9 and 10, 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. 
     As shown in FIG. 10, 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 its extends in the longitudinal direction of the body A, and a riding seat S is mounted above the opening  16  such that it covers the opening  16  from above as shown in FIGS. 9 and 10. 
     An engine E is contained in a chamber  20  surrounded by the hull H and the deck D below the seat S and having a convex-shape in a cross-section of the body. The engine E includes multiple cylinders (e.g., four cylinders) and is a fuel-injection type. As shown in FIG. 9, a crankshaft  26  of the engine E is mounted along the longitudinal direction of the body A. An output end of the crankshaft  26  is rotatably coupled integrally with a pump shaft  21 S of a water jet pump P through a propeller shaft  27 . An impeller  21  is mounted on the output shaft  21 S of the water jet pump P. The impeller  21  is covered with a pump casing  21 C on the outer periphery thereof. 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  28 . The water jet pump P pressurizes and accelerates the water. 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 portion  21 K provided on the rear end of the pump nozzle  21 R, thereby obtaining the propulsion force. 
     In FIG. 9, reference numeral  21 V denotes fairing vanes for fairing water flow behind the impeller  21 . As shown in FIGS. 9 and 10, reference numeral  24  denotes a bar-type steering handle as a steering operation handle. By operating the steering handle  24  to the right or to the left, the steering nozzle  28  provided behind the pump nozzle  21 R swings to the right or to the left through a wire cable  25 . The watercraft can be turned to any desired direction while the water jet pump P is generating the propulsion force. A throttle lever Lt is mounted on the right end portion of the handle  24 . 
     As shown in FIG. 9, 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 toward a lower position behind the steering nozzle  18  to deflect the water ejected from the steering nozzle  18  forward and, as the resulting reaction, the personal watercraft moves rearward. 
     In FIGS. 9 and 10, reference numeral  22  denotes a rear deck. The rear deck  22  is provided with an operable hatch cover  29 . A rear compartment (not shown) with a small capacity is provided under the hatch cover  29 . 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. 
     In the personal watercraft according to an embodiment of the present invention, as shown in FIG. 10, an exhaust pipe (exhaust passage) Ep having a muffler Mf extends from exhaust ports of the engine E to a transom board Tm (see FIG.  9 ). As shown in FIG. 3, a rear end Ep 1  of the exhaust pipe Ep opens outside through an opening To formed in the transom board Tm. 
     As shown in FIG. 3, a base member  2  is attached to the rear end Ep 1  of the exhaust pipe Ep in such a manner that the base member  2  is inserted into the opening To from outside the watercraft. As shown in an enlarged cross-sectional view in FIG.  2 A and in a front view of the base member in FIG. 3, the base member  2  has a cylindrical pipe portion  2   p  having an opening as an exhaust outlet  2 D at the center thereof and extending inside the body. The pipe portion  2   p  of the base member  2  is inserted into the inside of the watercraft. The outer diameter of the pipe portion  2 P substantially conforms to the diameter of the opening To. To be precise, the outer diameter of the pipe portion  2   p  is slightly smaller than the diameter of the opening To. In a portion of the base member  2 , which is on the outer side of the pipe portion  2   p , a flange  2   f  having an outer diameter larger than the diameter of the opening To is provided. 
     As shown in FIG. 2A, an enlarged portion  2   a  having a diameter larger than that of the exhaust outlet  2 D is formed on an inner periphery of a tip end (an end on the inner side of the body) of the pipe portion  2   p  of the base member  2 . The rear end Ep 1  of the exhaust pipe Ep (indicated by a dashed line in FIG. 2) is connected to the enlarged portion  2   a.    
     As shown in FIG. 2B, the base member  2  is mounted to the transom board Tm through mounting holes  2   g  formed on the periphery of the base member  2  by means of hexagon socket head cap screws  10 . In this embodiment, the base member  2  is configured such that the pipe portion  2   p  to be inserted into the opening To protrudes from one side of the circular flange portion  2   f  provided with an opening  2   d  as the exhaust outlet  2 D at the center thereof. 
     As shown in FIGS. 2A and 4, a circular groove  2 E is formed on an outer face of the flange portion  2   f  of the base member  2  so as to surround the exhaust outlet  2 D from its outer periphery and be concentric with the exhaust outlet  2 D. However, the groove  2 E is not necessarily concentric with the exhaust outlet  2 D. Between the circular groove  2 E and the exhaust outlet  2 D, a support portion  2 F which is lip-shaped in cross-section and ring-shaped in rear view is provided for supporting the periphery of a closing portion  3 A of a seat member  3  from its rear surface side (inner side). As shown in FIG. 4, the base member  2  is provided with mounting holes  2   j  through which a press member  5  is mounted to the base member  2  between adjacent mounting holes  2   g  in the circumferential direction thereof. The mounting hole  2   j  is provided with a female screw on its inner periphery. 
     Then, to the outer face of the flange portion  2   f  of the base member  2 , the sheet member  3  which is made of a flexible sheet in a circular shape is attached (see FIG.  3 ). The flexible sheet member  3  has a slit  3   a  of an incomplete-circle shape except a connecting portion  3 B (in this embodiment, an upper end portion). The slit  3   a  forms a closing portion  3 A separated from a peripheral portion  3 C except a connecting portion  3 B. By the connecting portion  3 B located on the upper side in FIG. 5, the closing portion  3 A is connected to the peripheral portion  3 C provided on the outer periphery of the flexible sheet member  3 . 
     As shown in FIG. 1, the closing portion  3 A is sized to be larger than the exhaust outlet  2 D to close the exhaust outlet  2 D. In other words, the outer periphery of the closing portion  3 A is located radially outward of the outer periphery of the exhaust outlet  2 D. In this embodiment, further, the outer periphery of the closing portion  3 A is located radially outward of the outer diameter of the support portion  2 F annularly formed on an outer peripheral region of the exhaust outlet  2 D and, as described above, the closing portion  3 A is in contact with and supported by the support portion  2 F of the base member  2  from its rear face (inner side). At both ends of the slit  3   a  of the sheet member  3 , stop holes  3   b  are formed to prevent the slit  3   a  from being broken along its extended line. Four penetrating holes  3   j  through which bolts  12  are inserted are formed at upper, lower, right and left positions on the peripheral portion  3 C to coincide with the mounting holes  2   j  of the base member  2 . And, the sheet member  3  is mounted to the base member  2  side with the press member  5  shown in FIG.  6 . 
     As shown in FIG. 6, the press member  5  has outwardly protruding mounting portions  5 A at plural positions (upper, lower, right, and left positions) on its outer peripheral portion. A short pipe  5 P is formed integrally with the press member  5  to be located on near side in the depth direction in FIG. 6 (rear side in the state in which the press member  5  is mounted to the transom board Tm). Instead, the short pipe  5 P may be independent of the press member  5 . In this embodiment, as shown in FIG. 2A, the lower end portion of the short pipe  5   p  extends rearwardly to be longer than the upper portion thereof so as to be adapted to an operation region of the closing portion  3 A of the sheet member  3 . The press member  5  is mounted to the base member  2  by means of the mounting bolts  12  inserted through the mounting holes  5   j  formed in the mounting portion  5 A with the seat member  3  retained between them (see FIGS.  2  and  3 ). Such mounting is accomplished by screwing the mounting bolts  12  into the mounting holes  2   j  of the base member  2 . The short pipe  5 P has an inner space as a vent hole  5 R to permit the closing portion  3 A of the sheet member  3  to swing rearwardly around the connecting portion  3 B. Therefore, the vent hole  5 R is larger than the exhaust outlet  2 D of the base member  2 . 
     Instead of the sheet member  3  in FIG. 3, a sheet member  103  having a U-shaped slit  103   a  shown in FIG. 7 may be used. A closing portion  103 A of the sheet member  103  is substantially U-shaped such that the closing portion  103 A is comprised of a lower portion formed by a semi-circular line and an upper portion formed by straight lines extending upwardly from the semi-circular line. In this structure, a connecting portion  103 B connecting the closing portion  103 A to its outer peripheral portion  103 C is made longer. That is, the length of portion without the slit  103   a  between stop holes  103   b  formed at both ends of the slit  103   a  can be increased. In the sheet member  103  so structured, since the length of the connecting portion  103 B can be increased, the sheet member  103  becomes durable against fatigue break caused by the swing of the closing portion  103 A due to flow of the exhaust gas. 
     A press member  105  for mounting the sheet member  103  is configured such that an upper portion  105 U thereof has a mounting portion  105 A protruding greatly in the vertical and horizontal directions so as to conform in shape to the slit  103   a . With this structure, the stop holes  103   b  of the slit  103   a  are pressed toward the base member  2  by the mounting portions  105 A of the upper portion  105 U. The other structure is identical to that of the press member  5  (see FIG.  6 ), and the corresponding components in FIG. 8 are identified by the corresponding reference numerals plus  100 . 
     The personal watercraft provided with the exhaust outlet having the above structure functions as follows. As shown in FIG. 2A, when the exhaust gas is discharged from the exhaust pipe Ep outside the watercraft, the flexible sheet member  3  in contact with the support portion  2 F of the base member  2  (or  102 ) comes off the support portion  2 F by the exhaust pressure of the exhaust gas as indicated by a two-dot chain line in FIG. 2A, thereby causing the exhaust gas to be discharged to the ambient side as indicated by a broken line Y in FIG.  2 A. In this case, according to the exhaust pressure, i.e., the engine speed of the engine E, the swing degree of the sheet member  3  to the left in FIG. 2A varies. 
     The exhaust gas so discharged is smoothly introduced rearwardly from the transom board Tm through the short pipe  5 P of the press member  5  (or  105 ) extending rearwardly. Therefore, the exhaust gas is discharged rearwardly (outside the watercraft) without contaminating the transom board Tm of the personal watercraft. 
     The exhaust noise of the exhaust gas contacts the flexible sheet member  3  and is absorbed therein. Also, the exhaust noise is not emitted directly from the exhaust outlet outside the watercraft and is not diffused around the watercraft because the exhaust outlet is surrounded by the press member  5 P. As a result, the exhaust noise is reduced. 
     To obtain desirable functions and effects with the above structure, the flexibility of the sheet member  3  (or  103 ) is suitably selected according to the output of the engine. The flexibility can be varied by varying the thickness of the sheet member  3  or the material of the sheet member  3 . Also, the flexibility can be varied by providing a groove with a bottom or a hole with a bottom in the connecting portion  3 B of the sheet member  3 . The provision of the groove with a bottom or the hole with a bottom in the sheet member  3  produces a higher noise-absorbing effect in addition to the variation in the flexibility. The sheet members  3 ,  103  have similar function and effects, but the sheet member  103  is superior in durability to the sheet member  3 . 
     Preferably, the sheet members  3 ,  103  are made of waterproof rubber. For example, NBR sheet may be used. Alternatively, the sheet members  3 ,  103  may be made of soft plastic, or any other materials having flexibility and durability. 
     The base member  2  may be made of hard plastic, metal such as stainless steel or aluminum, or hard rubber. 
     The press member  5  may be made of hard plastic, metal such as stainless steel or aluminum, or hard rubber. 
     Numerous modifications and alternative embodiments of the invention will be apparent to those skilled in the art in view of the foregoing description. Accordingly, the description is to be construed as illustrative only, and is provided for the purpose of teaching those skilled in the art the best mode of carrying out the invention. The details of the structure and/or function may be varied substantially without departing from the spirit of the invention and all modifications which come within the scope of the appended claims are reserved.