Abstract:
An exhaust system for a jet propulsion boat and a jet propulsion boat including the exhaust system. The exhaust system includes a muffler connected to the boat&#39;s engine by an exhaust pipe, and an auxiliary muffler connected to the muffler by a first connecting portion of a connecting pipe, A second connecting portion of the connecting pipe connects the auxiliary muffler to a tail pipe, through which exhaust gases travel to be exhausted into the water through a nozzle of a jet propulsion device. The auxiliary muffler is elevated with respect to the connecting pipe, which prevents the entry of water into the auxiliary muffler and a corresponding degradation of its sound reduction capability.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an exhaust system for a jet propulsion boat that exhausts engine exhaust gas into water. 
     2. Background Art 
     A jet propulsion boat is known in which a rider rides a saddle-type seat, and controls the vehicle by a steering handlebar having an accelerator lever on a right end portion of the steering handlebar, and a decelerator lever on a left end portion of the steering handlebar. An exhaust system for a conventional jet propulsion boat, an “Engine Exhaust system of Small-Sized Ship,” is described in Japanese Unexamined Patent Publication No. 8-119196. This type of exhaust system will be described with reference to FIGS. 8 and 9 of this application. 
     FIG. 8 is a plan view of a conventional exhaust system for a jet propulsion boat. An engine  101  is mounted below a steering handlebar  100 , an impeller (not illustrated) of a jet propulsion device is attached to a drive shaft  102  extending rearwardly from engine  101 , and an exhaust system  105  is provided at the engine  101 . 
     An exhaust pipe  106  extends rearwardly from a left side portion of the engine  101 , and a muffler is connected to an outlet of the exhaust pipe  106  arranged on the left side of the jet propulsion device  103 . A connecting pipe  108  having an inverse U shape is connected to an outlet of the muffler  107  and extends to the right side by passing over the jet propulsion device  103 . An auxiliary muffler  109  is connected to an outlet of the connecting pipe  108  and is arranged on the left side of the jet propulsion device  103 . An exhaust pipe  110  is connected to an outlet of the auxiliary muffler  109 . 
     The jet propulsion boat is propelled by jetting water sucked from a hull bottom rearwardly from a nozzle  112  by rotating the impeller of the jet propulsion device  103  by the engine  101 . Exhaust gas from the engine  101  is exhausted from the exhaust pipe  110  into a casing of the jet propulsion device  103  by flowing through the exhaust pipe  106  to the muffler  107 . The gas then flows from the muffler  107  through the connecting pipe  108  to the auxiliary muffler  109 , then out the exhaust pipe  110 . 
     FIG. 9 is a sectional view taken along a  9 — 9  line of FIG.  8 . FIG. 9 shows the muffler  107  and the auxiliary muffler  109  respectively arranged at portions  113  and  114  of the hull bottom on the left side and the right side of the jet propulsion device. The muffler  107  and the auxiliary muffler  109  are connected by the connecting pipe  108  having an inverse U shape. 
     The height H of a top portion  108   a  of the connecting pipe  108  can be made sufficiently high to prevent water from accidentally entering the muffler  109  from crossing over the connecting pipe  108  and entering the engine  101 . Accordingly, the connecting pipe  108  is generally referred to as a water lock pipe. 
     However, since the auxiliary muffler  109  is attached between the connecting pipe  108  and the exhaust pipe  110 , when water enters the exhaust pipe  110  and an exhaust port of the exhaust pipe  110 , there is the concern that water which has entered the exhaust pipe  110  may also enter the auxiliary muffler  109 . 
     When water enters the auxiliary muffler  109  and the volume of the auxiliary muffler  109  is reduced, the noise reduction capacity of the auxiliary muffler is deteriorated, and exhaust noise increases. 
     It therefore is an object of the present invention to provide an exhaust system capable of sufficiently reducing exhaust noise. 
     SUMMARY OF THE INVENTION 
     In order to resolve the above-described problem and to achieve other advantages not present in conventional exhaust systems, there is provided an exhaust system in a jet propulsion boat. The jet propulsion boat has a jet propulsion device for jetting water sucked from a hull bottom rearward, and an engine for driving the jet propulsion device. A muffler is connected to the engine by an exhaust pipe. A connecting pipe having an inverse U shape extends from either side of an auxiliary muffler, with the auxiliary muffler located at the highest point along the connecting pipe. 
     In this configuration, when water enters the exhaust pipe, the water is blocked by the connecting pipe and does not enter the auxiliary muffler attached to the top portion of the connecting pipe. Water is therefore not stored in the auxiliary muffler and the noise reduction capacity of the auxiliary muffler is not reduced. 
     The auxiliary muffler is a horizontal cylinder type muffler, both ends of a cylindrical body of which being closed by lid plates. A pair of the lid plates are provided with an exhaust inlet and an exhaust outlet, and levels of a bottom of the exhaust inlet and a bottom of the exhaust outlet are substantially coincident with a level of a bottom of the cylindrical body. 
     Accordingly, when water accidentally enters the auxiliary muffler, water is not stored in the cylindrical member because water exits the cylindrical member via the exhaust inlet and the exhaust outlet. The noise reduction capacity of the auxiliary muffler is therefore unaffected. 
     Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING FIGURES 
     The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus are not limitative of the present invention, and wherein: 
     FIG. 1 is a side elevational view of a jet propulsion boat having an exhaust system according to the present invention; 
     FIG. 2 is a perspective view of the exhaust system according to the present invention; 
     FIG. 3 is a sectional view taken along line  3 — 3  in FIG. 2; 
     FIG. 4 is a sectional view taken along line  4 — 4  in FIG. 2; 
     FIG. 5 is a sectional view taken along line  5 — 5  in FIG. 2; 
     FIGS.  6 ( a ) and  6 ( b ) are views of an operational feature of the exhaust system according to the present invention; 
     FIG.  6 ( c ) is a comparative example of the operation of an exhaust system; 
     FIG. 7 is a view of an operational feature of the exhaust system according to the present invention; 
     FIG. 8 is a plan view of a conventional exhaust system; and 
     FIG. 9 is a sectional view taken along line  9 — 9  in FIG.  8 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In order to facilitate description of the present invention, the terms “uppermost,” “higher,” “above” and variations thereof are used with reference to the water surface when the jet propulsion boat is generally upright on a level water surface. The terms “front,” “rear,” “left” and “right” are determined from the perspective of a rider of the jet propulsion boat. 
     FIG. 1 shows a jet propulsion boat  10  having an engine  15  attached roughly at the center of a hull  11 . The engine  15  drives a jet propulsion device  20  which jets water sucked from an opening  13  of a hull bottom  12  rearwardly from the hull  11 . A steering handlebar  25  controls a turning direction of the hull  11 , and an exhaust system  30  exhausts engine exhaust gas into the water. Numeral  17  designates a fuel tank and numeral  18  designates a seat. 
     The jet propulsion device  20  includes the following elements: a housing  21  extending rearwardly from the opening  13  of the hull bottom; impellers  22  rotatably attached inside the housing  11  and connected to a drive shaft  16  of the engine  15 , and, a nozzle  23  attached to a rear end of the housing  21 . The nozzle  23  is pivotable in the turning direction of the hull. The jet propulsion device sucks water from the opening  13  by rotating the impellers  22  and generates propulsion force by jetting the water out of the nozzle  23 . 
     FIG. 2 shows the exhaust system  30  of the jet propulsion boat. An exhaust pipe  32  is connected to an exhaust manifold  31  of the engine  15 . The exhaust pipe  32  connects the engine  15  to a muffler  40 . A connecting pipe  60  having an inverse U shape connects one side of an auxiliary muffler  70  to the muffler  40 , and another side of the auxiliary muffler  70  to a tail pipe  35 . The auxiliary muffler  70  is at a position higher than the exhaust pipe  32 . 
     The exhaust pipe  32  includes an exhaust pipe  33  extending from the exhaust manifold  31  to the muffler  40 , and a tail pipe  35  extending rearwardly from an exhaust outlet of the connecting pipe  60 . 
     Connecting pipe  60  includes a left side connecting pipe  62  and a right side connecting pipe  66 . The horizontal auxiliary muffler  70  is connected to respective upper end portions  63  and  67  of the left side connecting pipe  62  and the right side connecting pipe  66 . When water enters the tail pipe  35 , the water is prevented from entering the side of the engine by the connecting pipe  60 , and the connecting pipe  60  is generally referred to as water lock pipe. 
     A detailed explanation of the muffler  40  and the auxiliary muffler  70  follows. 
     FIG. 3 is a sectional view taken along a  3 — 3  line of FIG.  2 . The muffler  40  has a cylindrical member  41  which extends along the length of the muffler  40 . A front end of the cylindrical member  41  is closed by a front lid  41   a , and the front lid  41   a  is attached to an exhaust outlet  33   a  of the exhaust pipe  33 . A rear end of the cylindrical member  41  is closed by a rear lid  41   b . A front side expansion chamber  45 , an intermediary expansion chamber  46 , and a rear side expansion chamber  47  are formed by partitioning the interior of the cylindrical member  41  by a front side partition wall  43  and a rear side partition  44 . Punching plates  48 ,  49  and  50  are respectively attached to inner peripheral walls  45   a ,  46   a  and  47   a  of the respective chambers. 
     A pair of first inner pipes  51  for guiding exhaust gas from the front side expansion chamber  45  to the rear side expansion chamber  47  are attached to the front and partition walls  43  and  44 . A second inner pipe  52  for guiding exhaust gas from the rear side expansion chamber  47  to the intermediary expansion chamber  46  is attached to the side partition wall  44 , and an exhaust inlet (not illustrated) of the left side connecting pipe  62  is inserted into the intermediary expansion chamber  46 . 
     The punching plates  48 ,  49  and  50  of the front side expansion chamber  45 , the intermediary expansion chamber  46 , and the rear side expansion chamber  47 , respectively, include a plurality of holes  53 . The punching plates  48 ,  49  and  50  have a lattice-like shape and are attached to be remote from the inner peripheral walls  45   a ,  46   a  and  47   a  by a constant interval D. The holes  53  in the punching plates  48 ,  49  and  50  have a diameter “d” at a pitch P. 
     The following values may be used in the muffler  40 . The constant interval D may be 6 mm, the diameter d may be 3 mm, and the pitch may be 5 mm. These values may be varied to achieve differing sound inhibiting capacities. 
     An explanation of exhaust gas flow in the muffler  40  follows. 
     The exhaust gas flows from the exhaust pipe  33  to the front side expansion chamber  45 , and follows the following path (shown by an arrow  1 ): the front side expansion chamber  45 → the pair of first inner pipes  51 → the rear side expansion chamber  47 → the second inner pipe  52 → the intermediary expansion chamber (arrow  2 ). Thereafter, the gas flows to the left side connecting pipe. Exhaust noise is reduced by expanding the exhaust gas in the respective expansion chambers  45 ,  46  and  47 . 
     Further, the exhaust gas which has flowed into the expansion chambers  45 ,  46  and  47  first passes through the holes  53  of the punching plates  48 ,  49  and  50 , and flows into spaces  54 ,  55  and  56  between the punching plates  48 ,  49  and  50  and the inner peripheral walls  45   a ,  46   a  and  47   a . Therefore, frequencies provided to the respective spaces interfere with each other at insides of the respective spaces  54 ,  55  and  56 , and the exhaust noise can be reduced. This increases the noise reduction function of the muffler  40 . 
     FIG. 4 is a sectional view taken along a  4 — 4  line of FIG. 3 FIG. 4 shows the left side connecting pipe  62  connected to the intermediary expansion chamber  46  of the muffler  40 . 
     An opening  65  of a front end portion  64  of the left side connecting pipe is opened in a skewed transverse direction by obliquely cutting the front end portion  64  at an angle θ. Therefore, if the front end portion  64  of the left side connecting pipe  62  is proximate to a bottom portion  46   b  of the inner peripheral wall  46   a  of the intermediary expansion chamber  46  (or, contacting the bottom portion  46   b ), the opening  65  remains separate from the bottom portion  46   b.    
     Therefore, the exhaust gas in the intermediary expansion chamber  46  of the muffler  40  smoothly flows from the opening  65  into the left side connecting pipe  62 . 
     FIG. 5 is a sectional view taken along a  5 — 5  line of FIG.  2 . The auxiliary muffler  70  is a horizontal elliptical cylinder type. The auxiliary muffler  70  has a cylindrical member  71  extending transversely to the longitudinal axis of the jet propulsion boat  10 . The cylindrical member has an elliptical transverse cross section. 
     The ends  71   a  and  71   b  of the cylindrical member  71  are respectively closed by lid plates  72 . The upper end portion  63  of the left side connecting pipe  62  is connected to the left side lid plate  72 , and the upper end portion  67  of the right side connecting pipe  66  is connected to the right side lid plate  73 . 
     By attaching the tail pipe  35  to a lower portion  68  of the right side connecting pipe  66  (corresponding to an exhaust outlet of the connecting pipe  60  shown in FIG. 2) the auxiliary muffler  70  can be arranged at a position higher than the tail pipe  35 . The difference in height is shown as a predetermined height H 1 . Therefore, when water enters the tail pipe  35 , it does not enter the auxiliary muffler  35 . 
     An opening of the upper end portion  63  of the left side connecting pipe  62  forms an exhaust inlet  63   a  of the auxiliary muffler  70 , and an opening of the upper end portion  67  of the right side connecting pipe  66  forms an exhaust outlet  67   a  of the auxiliary muffler  70 . The levels of a bottom  63   b  of the exhaust inlet  63   a  and a bottom  67   b  of the exhaust outlet  67   a  are substantially coincident with a level of a bottom  71   a  of the elliptical type cylindrical member  71 . The height difference between the levels of the bottoms  63   b  of the exhaust inlet  63   a  and the bottom  67   b  of the exhaust outlet  67   a , and the bottom  71   a  of the elliptical type cylindrical member  71  can be made as small as H 2 . 
     A description of the operation of the exhaust system  30  of the jet propulsion boat  10  follows. 
     FIGS.  6 ( a ) and  6 ( b ) are explanatory views of the operation of the exhaust system  30 . FIG.  6 ( c ) is a comparative example of the operation of an exhaust system. According to FIG.  6 ( a ), exhaust gas within the intermediary expansion chamber  46  of the muffler  40  is exhausted via the left side connecting pipe  62 , as shown by an arrow  3 . At the same time, water  75  stored in the intermediary expansion chambers  46  is sucked from the opening  65  of the left side connecting pipe  62  and exhausted along with the exhaust. 
     According to FIG.  6 ( b ), by sucking the water  75  until a water level of the water  75  is lowered to a lower end height hl of the opening  65 , only a very small portion of the water  75  remains in the intermediary expansion chamber  46 . Therefore, the water  75  in the intermediary expansion chamber  46  can be exhausted while operating the jet propulsion boat. 
     As a result, time and labor for draining the water is saved after completing operation of the jet propulsion boat  10 . Also, handling of the boat  10  is improved. Further, the noise reduction capacity is not deteriorated by storing the water  75  in the muffler  40  while operating the jet propulsion boat  10 . 
     According to FIG. 6 ( c ), exhaust gas inside a muffler  120  is exhausted into a left side connecting pipe  121  via an opening  122 , as shown by an arrow  4 . At the same time, water  124  stored inside an intermediary expansion chamber is exhausted from the opening  122  into the left side connecting pipe  121 , along with exhaust gas. 
     However, the opening  122  opens downwardly, and accordingly, when a level of the water  124  is lowered to a height h 2  of the opening  122 , the water  75  cannot be exhausted. Therefore, a comparatively large amount of the water  75  remains inside of the muffler  120 . 
     As a result, it is necessary to drain the water after operation of the jet propulsion boat, requiring time and labor. Further, the noise reduction capacity is reduced by storing a comparatively large amount of water in the muffler  120 . 
     FIG. 7 is an explanatory view of second operational feature of the exhaust system  30 . By flowing exhaust gas from the muffler  40  to the left side connecting pipe  62 , as shown by an arrow  5 , and by flowing the exhaust gas from the left side connecting pipe  62  into the auxiliary muffler  70 , the exhaust gas is expanded within the auxiliary muffler  70 , and exhaust noise of the exhaust gas is reduced. 
     By adding the auxiliary muffler  70  to function with the muffler  40 , the noise reduction capacity of exhaust noise can further be increased. In addition, the exhaust gas within the auxiliary muffler  70  is flowed to the right side connecting pipe  66  and is flowed out from the tail pipe  35  into water. 
     The auxiliary muffler  70  is arranged at a position higher than the tail pipe  35  by the predetermined height H 1 , and accordingly, even when water enters the tail pipe  35 , water is prevented from entering the auxiliary muffler  70 . 
     Even when water is stored in the auxiliary muffler  70 , the distance H 2  from the levels of the bottom  63   b  of the exhaust outlet  63   a  and the bottom  67   b  of the exhaust outlet  67   a  of the auxiliary muffler  70 , to the level of the bottom  71   a  of the elliptical type cylindrical member  71  is reduced. Accordingly, water is flowed out via the left and right connecting pipes  62  and  66  and water stored at the bottom  71   a  of the elliptical type cylindrical member is reduced. As a result, the noise reduction function of the auxiliary muffler  70  is not affected by stored water. 
     Further, as shown by FIG. 2, two mufflers of the muffler  40  and the auxiliary muffler  70  are attached to the exhaust pipe  32 . By making respective attenuating characteristics of the muffler  40  and auxiliary muffler  70  differ from one another, a wide operating region of noise reduction capacity can be achieved. 
     Although an explanation has been given of an auxiliary muffler having cylindrical member with an elliptical shape cross-section, a circular shape or the like may also be used. Further, although the tail pipe  35  is attached at the outlet side of the connecting pipe  60 , the connecting pipe  60  and the tail pipe  35  may be integrally formed. 
     The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims.