Patent Publication Number: US-6659089-B2

Title: Turbocharger arrangement structure for personal watercraft

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application claims priority under 35 USC 119 to Japanese Patent Application No. 2001-219321 filed on Jul. 19, 2001 the entire contents thereof is hereby incorporated by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to a turbocharger arrangement structure for a personal watercraft. 
     2. Description of Background Art 
     While the power source in widespread personal watercrafts conventionally is a 2-cycle engine, it has been considered to use a 4-cycle engine for the power source in order to cope with a reduction in pollution in recent years. 
     However, since the output power of the 4-cycle engine is lower than that of the 2-cycle engine of the same total stroke volume, it is examined to incorporate an engine with a turbocharger in order to make up the power. The assignee of the present invention has proposed a personal watercraft in which an engine with a turbocharger is incorporated as disclosed in Japanese Patent Laid-Open No. 2001-140641. 
     In this personal watercraft, a 4-cycle engine  2  with a turbocharger  3  is incorporated inside of a body  1  as shown in FIGS. 11 and 12. 
     As shown also in FIGS. 13 and 14, an exhaust manifold  4  is provided on the left side of the 4-cycle engine  2  in an advancing direction F of the body  1 . An intake chamber  5  is provided on the right side of the 4-cycle engine  2 . 
     Exhaust gas from an exhaust gas exit  4   a  of the exhaust manifold  4  is introduced into a turbine portion  3 T of the turbocharger  3 , and compressed air from a compressor portion  3 C of the turbocharger  3  is supplied into the intake chamber  5  described above through an intercooler  6 . 
     In such a personal watercraft as described above, in order to make it difficult for water to enter a body  1 , it is necessary to form a hull  1   a  (refer to FIG. 11) and a deck  1   b  to be watertight and to close an opening in the deck with a lid member (for example, a seat  7 ) to form an internal body space  1   c.    
     Meanwhile, in order to ensure intake of air into an engine  2 , it is necessary to introduce atmospheric air from outside the body into the body internal space  1   c . In a personal watercraft wherein a turbocharger is provided for an engine, when the atmospheric air outside the body is introduced into the body internal space  1   c  during operation of the personal watercraft, air is sometimes introduced together with water (for example, in the form of droplets) into the body. If the turbocharger is exposed to the water, then a casing and so forth of the turbocharger whose temperature is high is cooled suddenly and partially, which gives rise to disadvantages such as thermal fatigue that is liable to occur with the turbocharger. 
     SUMMARY AND OBJECTS OF THE INVENTION 
     The object of the present invention resides in a solution of such a problem as described above to provide a turbocharger arrangement structure for a personal watercraft which makes the turbocharger less liable to be exposed to water. 
     In order to attain the object described above, according to the present invention, a turbocharger arrangement structure for a personal watercraft includes a hull and a deck of the personal watercraft that are formed to be watertight and an opening of the deck that is closed up with a lid member to form a body internal space. An intake duct for introducing the atmospheric air outside the body is provided in the space while an engine and a turbocharger connected to an exhaust manifold of the engine are provided in the space and the turbocharger is disposed to be higher than a body internal opening of the intake duct. 
     According to the present invention, the turbocharger arrangement structure for a personal watercraft according to the present invention provides a water jacket that is formed in a casing of a turbine portion of the turbocharger and an oil jacket that is formed in a bearing casing of the turbocharger, and cooling water is supplied to the water jacket and cooling oil is supplied to the oil jacket. 
     According to the present invention, the turbocharger arrangement structure for a personal watercraft according to the present invention provides the cooling water to the water jacket that is supplied by a different turbocharger cooling water passage independent of any other cooling water passage. 
     With the turbocharger arrangement structure for a personal watercraft according to the present invention, the hull and the deck of the personal watercraft are formed to be watertight and the opening of the deck is closed up with the lid member to form the body internal space. The intake ducts for introducing the atmospheric air outside the body are provided in the space and the engine and the turbocharger are connected to the exhaust manifold of the engine and are provided in the space. The turbocharger is disposed to be higher than the body internal openings of the intake ducts. Therefore, when the atmospheric air outside the body is introduced into the body internal space through the intake ducts during operation of the personal watercraft, even if air is introduced together with water (for example, in the form of droplets), such a situation wherein the turbocharger becomes wet directly with the water becomes less likely to occur. 
     Accordingly, a situation wherein the casing and so forth of the turbocharger, whose temperature is high, are cooled suddenly and partially becomes less likely to occur. Thus thermal fatigue becomes less likely to occur with the turbocharger. As a result, the durability of the turbocharger is augmented. 
     The turbocharger arrangement structure for a personal watercraft according to the present invention provides a water jacket that is formed in the casing of the turbine portion of the turbocharge and the oil jacket is formed in the bearing casing for the turbocharger. Cooling water is supplied to the water jacket and cooling oil is supplied to the oil jacket. Consequently, such a situation wherein the temperature of the turbocharger becomes excessively high is eliminated. 
     Accordingly, when the atmospheric air outside the body is introduced into the body internal space through the intake ducts during operation of the personal watercraft, even if air is introduced together with water (for example, in the form of droplets) and the turbocharger becomes exposed to the water, the temperature variation of the casing of the turbocharger by the water is suppressed to be small. 
     As a result, thermal fatigue becomes less likely to occur with the turbocharger, and the durability of the turbocharger is augmented with certainty. 
     With the turbocharger arrangement structure for a personal watercraft according to the present invention, cooling water for the water jacket is supplied through the different turbocharger cooling water passages independent of the other cooling water passages. Thus, the turbocharger is cooled efficiently. 
     Accordingly, when the atmospheric air outside the body is introduced into the body internal space through the intake ducts during operation of the personal watercraft, even if air is introduced together with water (for example, in the form of droplets) and the turbocharger is exposed to the water, the temperature variation of the casing of the turbocharger by the water is suppressed smaller. 
     As a result, thermal fatigue becomes further less likely to occur with the turbocharger, and the durability of the turbocharger is augmented with a higher degree of certainty. 
     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 DRAWINGS 
     The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by illustration only, and thus are not limitative of the present invention, and wherein: 
     FIG. 1 is a schematic side elevational view showing an example of a watercraft which uses an embodiment of the turbocharger arrangement for a personal watercraft according to the present invention; 
     FIG. 2 is a plan view of the personal watercraft in FIG. 1; 
     FIG. 3 is a partial enlarged sectional view (partly omitted sectional view) taken along line III—III of FIG. 1; 
     FIG. 4 is a view principally showing an engine  20  and is a partial enlarged sectional view (partly omitted sectional view) taken along line IV—IV of FIG. 1; 
     FIG. 5 is a right side elevational view of the engine  20 ; 
     FIG. 6 is a left side elevational view of the engine  20 ; 
     FIG. 7 is a schematic perspective view of the engine  20  as viewed from obliquely rearwardly; 
     FIG. 8 is a partial enlarged view of FIG. 5; 
     FIG. 9 is a view of a circulation route of oil; 
     FIG. 10 is a sectional view of a turbocharger  140 ; 
     FIG. 11 is an explanatory view of the prior art; 
     FIG. 12 is an explanatory view of the prior art; 
     FIG. 13 is an explanatory view of the prior art; and 
     FIG. 14 is an explanatory view of the prior art. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In the following, an embodiment of the present invention is described with reference to the drawings. 
     As shown in FIG. 1, a personal watercraft  10  is a personal watercraft of the type, wherein a driver can sit on a seat  12  on a body  11  and grip a steering  13  with a throttle lever to steer the personal watercraft  10 . 
     The body  11  has a floating body structure wherein a hull  14  and a deck  15  are joined together such that a space  16  is formed inside thereof. An opening  15   a  (refer to FIG. 4) of the deck  15  is closed up with the seat  12  serving as a lid member removably mounted on the deck  15 . In the space  16 , an engine  20  is mounted on the hull  14 , and a jet pump (jet propulsion pump)  30  as propulsion means which is driven by the engine  20  is provided at a rear portion of the hull  14 . 
     The jet pump  30  has a passage  33  extending from an intake  17  open to the bottom to a jet outlet  31  and a nozzle  32  open to the rear end of the body and an impeller  34  disposed in the passage  33 . A shaft  35  of the impeller  34  is connected to an output power shaft  21   a  of the engine  20 . Accordingly, if the impeller  34  is driven to rotate by the engine  20 , then water taken in from the intake  17  is jetted from the nozzle  32  through the jet outlet  31  so that the body  11  is propelled. The driving speed of the engine  20 , that is, the propelling force by the jet pump  30 , is operated by a pivoting operation of a throttle lever  13   a  (refer to FIG. 2) of the steering handle  13  described above. The nozzle  32  is operatively associated with the steering handle  13  by an operation wire not shown such that it is pivoted by an operation of the steering handle  13 , and the advancing direction can be changed thereby. 
     A fuel tank  40  and an accommodation chamber  41  are operatively connected to the body  11 . 
     As illustrated in FIG. 4, the engine  20  is a DOHC in-line four-cylinder dry sump type 4-cycle engine and is disposed such that the crankshaft  21   a  thereof extends in the forward and backward direction of the body  11  as shown in FIG.  1 . 
     As shown in FIGS. 4 and 7, a surge tank (intake chamber)  22  and an intercooler  23  communicated with an intake port are connected and disposed on the left side of the engine  20  with respect to the advancing direction of the body  11 , and an exhaust manifold  24  is in communication with an exhaust port  200  and is connected and disposed on the right side of the engine  20 . 
     As shown in FIGS. 6 and 7, a turbocharger (turbocharger)  140  is disposed rearwardly of the engine  20 , and an exhaust gas exit  24   o  of the exhaust manifold  24  is connected to a turbine portion  140 T of the turbocharger  140  while the intercooler  23  is connected to a compressor portion  140 C of the turbocharger  140  by a pipe  26  (refer to FIG.  7 ). In FIG. 7, a cooling water hoses  23   a ,  23   b  are connected to the intercooler  23 . 
     It is to be noted that exhaust gas which has rotated a turbine in the turbine portion  140 T of the turbocharger  140  passes, as shown in FIGS. 1 and 2, through an exhaust pipe  27   a , a backflow preventing chamber  27   b  for preventing a backflow of water (admission of water into the turbocharger  140  and so forth). Upon capsize, a water muffler  27   c  and an drain pipe  27   d  and is exhausted into a water stream produced by the jet pump  30 . 
     Referring to FIG. 1, intake ducts  18 ,  19  are provided for introducing the atmospheric air outside the body  11  into the space  16  in the body  11 . Lower ends  18   a ,  19   a  of the intake ducts  18 ,  19  are provided to be lower than the turbocharger  140  described above in the body  11 . In other words, the turbocharger  140  is provided to be higher than the openings  18   a ,  19   a  of the intake ducts  18 ,  19  in the body. The turbocharger  140  is provided substantially in the center in the vertical direction in the space  16  of the body. 
     As shown in FIGS. 4 to  7 , an oil tank  50  and an oil pump  80  are provided integrally on an extension line of a crankshaft  21  at a front portion of the engine  20  (in the advancing direction of the body  11 , and at a left portion in FIGS.  1  and  5 ). The oil pump  80  is provided in the oil tank  50 . 
     The oil tank  50  is formed from a tank body (one divided case)  60  joined to a front face of the engine  20  and a cover (the other divided case)  70  joined to a front face of the tank body  60 . 
     As shown in FIGS. 4 and 6, a water cooling type oil cooler  90  is provided on the front face of the tank body  60  in the oil tank  50 , and an oil filter  100  is provided at an upper portion of the oil tank  50 . 
     As shown in FIGS. 4,  5  and  8 , the tank body  60  has a joining face  61  to the front face of the engine  20 , a joining face  62  to the cover  70 , a mounting portion  63  for the oil pump  80 , a mounting portion  64  for the water cooling type oil cooler  90 , a generally vertically elongated oil accommodation portion  65  defined by partition walls and outer walls which form the mounting surfaces of them, an ACG  110 , balancer shafts  114 L,  114 R, and a cover portion  66  for a drive chamber of a starter motor  120 . Further, as shown in FIG. 6, the tank body  60  has a mounting portion  68  for the oil filter  100 . 
     The tank body  60  is joined at the joining face  61  thereof described above to the front face of the engine  20  and integrally secured to the front face of the engine  20  by bolts not shown in such a manner that it covers the elements described above. It is to be noted that the tank body  60  is attached to the front face of the engine  20  after the oil pump  80  and the type oil cooler  90  are attached thereto. 
     The cover  70  has a joining face  71  to the tank body  60 , a refilling opening  72  for oil, a holding portion  73  for a relief valve  130 , an accommodation portion  74  (refer to FIG. 6) for the oil cooler  90 , and an oil accommodation portion  75  defined by outer walls and a partition wall. 
     The oil pump  80  includes a first case  81  joined to the tank body  60  described above, a second case  82  joined to the first case  81 , a pump shaft  83  provided such that it extends through the first and second cases, inner and outer rotors  84  coupled to the pump shaft  83  in the first case  81  described above for recovering oil, and inner and outer rotors  85  coupled to the pump shaft  83  in the second case  82  described above for supplying oil. 
     The inner and outer rotors  84  for recovering oil cooperates with the first case  81  to form an oil recovery pump, and the inner and outer rotors  85  for supplying oil cooperates with the first and second cases  81 ,  82  to form an oil supply pump. 
     The oil pump  80  is attached to the front face of the tank body  60  by means of bolts  88  after the joining face of the first case  81  to the tank body  60  is jointed to the mounting portion  63  on the front face of the tank body  60  formed in the same shape as that of the joining face. 
     After the oil pump  80  is attached to the tank body  60  in this manner, a coupling  89  is secured to the rear end of the pump shaft  83  from the rear face side of the tank body  60  by means of bolts. 
     Accordingly, the tank body  60  is attached to the front face of the engine  20  such that the coupling  89  is coupled to a coupling  111  provided at an end of an ACG shaft after the oil pump  80  and the coupling  89  are attached and further the oil cooler  90  is attached. 
     The water cooling type oil cooler  90  is attached to the front face side of the mounting portion  64  of the tank body  60  for the oil cooler  90 . 
     As shown in FIGS. 4 and 6, an upper hole  64   a  and a lower hole  64   b  which are in communication with an oil passage which is hereinafter described are formed in the mounting portion  64  of the tank body  60 . 
     The oil cooler  90  has a plurality of heat exchanging plates  91  through the inside of which oil passes, an entrance pipe  92  for oil in communication with an upper portion thereof with the inside of the plates  91 . An exit pipe  93  is provided for oil in communication with a lower portion thereof with the inside of the plates  91 . 
     Accordingly, the oil cooler  90  is attached to the mounting portion  64  of the tank body  60  such that the entrance pipe  92  thereof is connected to the upper hole  64   a  of the tank body  60  and the exit pipe  93  thereof is connected to the lower hole  64   b  of the tank body  60 . 
     As shown in FIGS. 4 and 6, a cooling water introduction pipe  97  is in communication with a hole  64   c  open to the mounting portion  64  and introduces cooling water into the accommodation portion  74  of the oil cooler in the mounting portion  64  and the cover  70  is provided on the tank body  60 . A discharge pipe  78  is provided for water in the cover  70 . A cooling water hole  97   a  from a cooling water output port  30   a  (refer to FIG. 7) of the jet pump  30  is connected directly to the introduction pipe  97  without intervention of any other cooling device. An drain pipe  23   c  is connected to the discharge pipe  78  as shown in FIG.  6 . Water from the discharge pipe  78  is supplied into the water jacket of the exhaust manifold  24  through the drain pipe  23   c.    
     The cover  70  is joined to the front face of the tank body  60  and secured by means of bolts not shown such that a front end  132  of the relief valve  130  is held down by the holding portion  73  described hereinabove after the tank body  60 , oil pump  80  and oil cooler  90  are attached to the front face of the engine  20  in such a manner as described above. Thereafter, a rear end  131  of the relief valve  130  is fitted into a hole  82   a  formed in the front face of the second case  82  of the oil pump  80  as shown in FIGS. 5 and 8. The relief valve  130  is disposed horizontally in this manner. 
     In the state wherein the tank body  60  and the cover  70  are joined together, a single oil accommodation section is formed from the oil accommodation portions  65 ,  75 . 
     Further, the oil filter  100  is attached to the mounting portion  68  of the tank body  60  for the oil filter  100 . 
     It is to be noted that, in a state wherein the engine  20  is incorporated in the body  11 , the engine  20  and the oil filter  100  are opposed to the opening  15   a  of the deck  15  as shown in FIGS. 2 and 4. The opening  15   a  of the deck  15  is opened by removing the seat  12 , which is removably mounted on the body  11 . 
     Such oil passages as described below are formed in a state wherein the oil tank  50  (that is, the tank body  60 , the cover  70 , and the oil pump  80 , oil cooler  90 , and relief valve  130  built in them) is mounted on the front face of the engine  20  and the oil filter  100  is mounted therein. 
     As shown in FIGS. 5 and 8, an oil recovery passage  51  is formed by the front face of the tank body  60  and the rear face of the first case  81  of the oil pump  80 . The recovery passage  51  is formed from an oil passage  51   a  formed on the tank body  60  side and an oil passage  51   b  formed on the first case  81  side of the oil pump  80  in an opposing relationship to the oil passage  51   a.    
     A lower end  51   c  of the oil recovery passage  51  is in communication with an oil pan  28  of the engine  20  through a pipe  52 . An upper end  51   d  of the oil recovery passage  51  is in communication with a recovered oil inlet port  81   i  formed in the first case  81  of the oil pump  80 . 
     Similarly, a discharge passage  53  for recovered oil is formed by the front face of the tank body  60  and the rear face of the first case  81  of the oil pump  80 . The discharge passage  53  is formed from an oil passage  53   a  formed on the tank body  60  side and a recovered oil discharge port  81   o  formed on the first case  81  side of the oil pump  80  in an opposing relationship to the oil passage  53   a.    
     An upper end  53   b  of the discharge path  53  is open to the inside of the oil tank  50  (that is, to the inside of the oil accommodation section). 
     Meanwhile, an intake passage  54  and a discharge passage  55  for supply oil are formed by the front face of the first case  81  and the rear face of the second case  82  of the oil pump  80 . 
     A lower end  54   a  of the intake passage  54  is open to the inside of the oil tank  50  (that is, to the inside of the oil accommodation section), and an upper end  54   b  of the intake passage  54  is in communication with a supply oil inlet port  82   i  of the oil supply pump. A screen oil filter  54   c  is provided in the intake passage  54 . 
     A lower end  55   a  of the discharge passage  55  is in communication with a supply oil discharge port  82   o  of the oil supply pump, and an upper end  55   b  of the discharge passage  55  extends horizontally through an upper portion of the first case  81  and is in communication with a horizontal hole  60   a  formed in the tank body  60 . The horizontal hole  60   a  is communicated with a vertical hole  60   b  similarly formed in the tank body  60 . An upper end  60   c  of the vertical hole  60   b  is open in the form of a ring as viewed in plan to the mounting portion  68  of the oil filter  100 . An oil inlet passage  101  of the oil filter  100  is in communication with the opening  60   c.    
     The mounting hole  82   a  for the relief valve  130  described hereinabove is open to the discharge passage  55 , and the relief valve  130  is attached in such a manner as described above to the mounting hole  82   a.    
     A male thread is provided on an oil exit pipe  102  in the oil filter  100 . The oil filter  100  is attached to the mounting portion  68  of the tank body  60  by screwing the oil exit pipe  102  into a female threaded hole  60   d  formed in the mounting portion  68  of the tank body  60 . 
     As shown in FIG. 6, a vertical hole  60   e  and a horizontal hole  60   f  are in communication with a lower end of the vertical hole  60   e  and are formed at a lower portion of the female threaded hole  60   d  in the tank body  60 . The horizontal hole  60   f  is in communication with the entrance pipe  92  of the oil cooler  90  through the upper hole  64   a  of the mounting portion  64  of the oil cooler  90  described hereinabove. 
     Meanwhile, an oil passage  60   g  communicating with the lower hole  64   b  and an oil distributing passage  60   h  communicating with the passage  60   g  are formed in the lower hole  64   b  of the tank body  60  described hereinabove to which the exit pipe  93  of the oil cooler  90  is connected. Further, a main gallery supply passage  60   i  for supplying oil to a main gallery  20   a  (refer to FIG. 5) of the engine  20 , a left balancer supply passage  60   j  for supplying oil to bearing portions of the left balancer  114 L described hereinabove and a right balancer supply passage  60   k  for supplying oil to bearing portions of the right balancer  114 R are in communication with the oil distributing passage  60   h.    
     It is to be noted that one end of the oil distributing passage  60   h  is closed up with a plug  60   n  (refer to FIG.  6 ). 
     The route of oil supplied to the main gallery  20   a  of the engine  20  is such as shown in FIG. 9 (oil circulation route diagram). 
     The route from the main gallery  20   a  is generally divided into two. 
     The first route is a route along which oil is supplied to bearing portions of the crankshaft  21  through a route  20   b  (refer to FIG.  5 ), and the second route is a route along which oil is supplied from a rear end  20   a   1  of the main gallery  20   a  through a pipe  25   a  (refer to FIG. 7) to cool and lubricate turbine bearings of the turbocharger  140 . The oil which has cooled and lubricated the turbine bearings of the turbocharger  140  is recovered into the oil pan  28  through pipes  25   b ,  25   c  (refer to FIG.  6 ). 
     The oil supplied to the bearing portions of the crankshaft  21  further lubricates cam journal  20   d  portions and lifter portions of a cylinder head through a route  20   c  and then returns to the oil pan  28  through a chain chamber  20   i.    
     Meanwhile, the oil supplied to the bearing portions of the crankshaft  21  is further supplied to the ACG, piston rear jet nozzles, connecting rod, cam chain and starter needle and is recovered into the oil pan  28  through respective recovery passages. In FIG. 5, a jet nozzle  20   e  is provided for jetting oil to the rear side of the piston to cool the piston. A passage  20   f  is provided to the connecting rod portion. A cam chain  20   g  is operatively connected to the engine. Further, a return passage  20   h  provides a returning passage for oil from an ACG chamber  110   c.    
     The oil in the ACG chamber returns to the oil pan  28  through a return passage  20   h  therefor, and the oil jetted to the rears of the pistons from jet nozzles  20   e , the oil supplied to the connecting rod and the oil supplied to the starter needle return to the oil pan  28  individually through a crank chamber  20   j.    
     As is apparent from the foregoing description, a general flow of oil is described below with reference principally to FIG.  9 . 
     Oil flows from the oil tank  50  to the intake passage  54  to the screen oil filter  54   c  to the oil pump (supply pump)  80  to the discharge passage  55  (and relief valve  130 , horizontal hole  60   a , vertical hole  60   b , ring-form opening  60   c ) to the oil filter  100  to the vertical hole  60   e , horizontal hole  60   f  to the oil cooler  90  to the oil passage  60   g , oil distributing passage  60   h  to the main gallery supply passage  60   i , left balancer supply passage  60   j , right balancer supply passage  60   k  and to the main gallery  20   a , left balancer  114 L, right balancer  114 R. 
     Relief oil RO from the relief valve  130  returns directly into the oil tank  50 . 
     Oil supplied to the left balancer  114 L, right balancer  114 R returns to the oil pan  28  through the crank chamber  20   j.    
     Meanwhile, oil supplied to the various portions described above from the main gallery  20   a  returns to the oil pan  28  in such a manner as described above. 
     Then, the oil returned to the oil pan  28  is recovered into the oil tank  50  through the pipe  52 , recovery passage  51 , oil pump  80  (recovery pump) and recovered oil discharge path  53 , and is circulated by the route described above from the intake passage  54 . 
     FIG. 10 is a sectional view of the turbocharger  140 . 
     As described above, the turbocharger  140  includes the turbine portion  140 T and the compressor portion  140 C. The turbocharger  140  further includes a bearing casing  141  which interconnects the turbine portion  140 T and the compressor portion  140 C. 
     A bearing portion (accommodation chamber for a bearing member)  142  is provided in the bearing casing  141 , and a turbine shaft  143  is supported for rotation by bearing members (ceramic ball bearings)  142   a  of the bearing portion  142 . 
     Turbine blades  143 T are secured to the turbine shaft  143  adjacent the turbine portion  140 T, and compressor blades  143 C are secured to the turbine shaft  143  adjacent the compressor portion  140 C. 
     Accordingly, within a process wherein exhaust gas from the exhaust manifold  24  described hereinabove is exhausted from an exhaust gas exit T 2  to the exhaust pipe  27   a  (refer to FIGS. 1 and 2) described hereinabove through an exhaust passage T 1  in the turbine portion  140 T, the turbine shaft  143  is driven to rotate, and the compressor blades  143 C are driven to rotate so that air from an intake air inlet port C 1  communicating with an intake box not shown is fed under pressure from the pipe  26  (refer to FIG. 7) to the intercooler  23  through an intake passage C 2  in the compressor portion  140 C. 
     An oil entrance  144  is provided at an upper portion of the bearing casing  141 . The oil entrance  144  is in communication with the rear end portion  20   a   1  of the main gallery  20   a  by the pipe  25   a  (refer to FIG. 7) described hereinabove which services as an oil supply passage. The pipe  25   a  is connected to the oil entrance  144  by an orifice bolt  145 . 
     An oil jacket  146  is formed inside of the bearing casing  141 , and the oil entrance  144  described above is in communication with the oil jacket  146  by an oil passage  144   a . The bearing portion  142  is in communication with the oil entrance  144  by a thin oil passage  144   b.    
     Accordingly, oil entering from the oil entrance  144  is supplied from the oil passage  144   a  to the oil jacket  146  to cool the bearing casing  141 , bearing portion  142 , turbine shaft  143  and members around them, and is supplied from the oil passage  144   b  to the bearing portion  142  to lubricate the bearing portion  142 . 
     The oil of the oil jacket  146  is recovered into the oil pan  28  from oil exits  146   a  and  146   b  of the oil jacket  146  through the pipes  25   b ,  25   c  (refer to FIG. 6) described hereinabove. Meanwhile, the oil of the bearing portion  142  once enters the oil jacket  146  from an exit  142   b  of the bearing portion  142  and then is recovered into the oil pan  28  from the oil exits  146   a  and  146   b  of the oil jacket  146  described above through the pipes  25   b ,  25   c  (refer to FIG. 6) described hereinabove. 
     The pipe  25   b  is connected to the oil exit  146   a , and the pipe  25   c  is connected to the oil exit  146   b.    
     The oil exits  146   a ,  146   b  are disposed higher than an oil surface O 1  (refer to FIG. 6) when the engine stops. 
     Further, a one-way valve  147  is interposed in each of the pipes  25   b ,  25   c  which serve as an oil returning path. 
     As shown in FIG. 10, a water jacket T 3  is formed in the casing of the turbine portion  140 T. An entrance T 4  for cooling water of the water jacket T 3  is connected to the cooling water output port  30   a  (refer to FIG. 7) of the jet pump  30  described hereinabove by a pipe  148   a  which forms a different turbocharger cooling water passage independent of the other cooling water passages. Further, an exit (not shown) of the water jacket T 3  for cooling water is connected to a water jacket of the exhaust pipe  27   a  (refer to FIGS. 1,  2 ) by a pipe  148   b  shown in FIG.  7 . 
     Accordingly, cooling water from the jet pump  30  is supplied to the water jacket T 3  of the turbocharger  140  directly without intervention of any other cooling device and cools the turbocharger  140 . Whereafter, the water cools the exhaust pipe  27   a . It is to be noted that the water having cooled the exhaust pipe  27   a  further flows into a water jacket of the backflow preventing chamber  27   b  to cool the backflow preventing chamber  27   b  and is then jetted into the water muffler  27   c , whereafter it is discharged together with exhaust gas into water current produced by the jet pump  30  through the exhaust and drain pipe  27   d.    
     According to such a turbocharger arrangement structure for a personal watercraft as described above, the following operation and effects are obtained. 
     The hull  14  and the deck  15  of the personal watercraft are formed watertight and the opening  15   a  of the deck  15  is closed up with the lid member  12  to form the body internal space  16 . The intake ducts  18 ,  19  for introducing the atmospheric air from outside the body are provided in the space  16  and the engine  20  and the turbocharger  140  are connected to the exhaust manifold  24  of the engine  20  and are provided in the space  16 . In addition, the turbocharger  140  is disposed higher than the body internal openings  18   a ,  19   a  of the intake ducts  18 ,  19 . Therefore, when the atmospheric air outside the body is introduced into the body internal space  16  through the intake ducts  18 ,  19  during operation of the personal watercraft, even if it is introduced together with water (for example, in the form of droplets), such a situation that the turbocharger  140  becomes wet directly with the water becomes less likely to occur. 
     Accordingly, such a situation wherein the casing and so forth of the turbocharger  140  whose temperature is high are cooled suddenly becomes partially less likely to occur. In addition, and thermal fatigue becomes less likely to occur with the turbocharger  140 . As a result, the durability of the turbocharger  140  is augmented. 
     The water jacket T 3  is formed in the casing of the turbine portion  140 T of the turbocharger  140  and the oil jacket  146  is formed in the bearing casing  141  for the turbocharger  140 . Cooling water is supplied to the water jacket T 3  and cooling oil is supplied to the oil jacket  146 . Consequently, such a situation wherein the temperature of the turbocharger  140  becomes excessively high is eliminated. 
     Accordingly, when the atmospheric air outside the body is introduced into the body internal space  16  through the intake ducts  18 ,  19  during operation of the personal watercraft, even if the air is introduced together with water (for example, in the form of droplets) and the turbocharger  140  becomes exposed to the water, the temperature variation of the casing of the turbocharger  140  by the water is suppressed small. 
     As a result, thermal fatigue becomes less likely to occur with the turbocharger  140 , and the durability of the turbocharger  140  is augmented with certainty. 
     Since cooling water for the water jacket T 3  is supplied through the different turbocharger cooling water passage  148   a  independent of the other cooling water passages, the turbocharger  140  is cooled efficiently. 
     Accordingly, when the atmospheric air outside the body is introduced into the body internal space  16  through the intake ducts  18 ,  19  during operation of the personal watercraft, even if it is introduced together with water (for example, in the form of droplets) and the turbocharger  140  becomes exposed to the water, the temperature variation of the casing of the turbocharger  140  by the water is suppressed smaller. 
     As a result, thermal fatigue becomes further less likely to occur with the turbocharger  140 , and the durability of the turbocharger  140  is augmented with a higher degree of certainty. 
     Since the cooling water from the turbocharger cooling water passage  148   a  is first supplied to the turbocharger  140  to cool the turbocharger  140  and is then supplied to the exhaust system (exhaust pipe  27   a , backflow preventing chamber  27   b , water muffler  27   c , exhaust and drain pipe  27   d ) provided on the downstream with respect to the turbocharger  140  in the exhaust system for the engine  20 , the turbocharger  140  can be cooled with cooling water in a state wherein the temperature is the lowest. 
     Accordingly, the turbocharger  140  can be cooled further efficiently and sufficiently. 
     Further, also the exhaust system provided downstream with respect to the turbocharger  140  can be cooled. 
     Since the cooling water having cooled the turbocharger  140  is discharged to the outside of the vessel  10  together with exhaust gas after it is supplied to the exhaust pipe  27   a  provided downstream with respect to the turbocharger  140  in the exhaust system, the exhaust gas which has driven the turbocharger  140  is further cooled in the exhaust pipe  27   a.    
     In other words, the exhaust gas is cooled in the turbocharger  140  and the exhaust pipe  27   a . Thus, the exhaust gas energy can be reduced synergetically, and as a result, the exhaust noise can be reduced. 
     Oil is supplied to the turbocharger  140  and the supplied oil is used to lubricate the bearing portion  142  of the turbocharger  140  and is supplied to the oil jacket  146  formed in the bearing casing  141  to cool the bearing casing  141 . Thus, the turbocharger  140  is cooled even better. 
     The engine  20  is provided in the body  11  formed from the hull  14  and the deck  15  and the turbocharger  140  is provided for the engine  20  and the oil exits  146   a ,  146   b  of the turbocharger  140  are disposed higher than the oil surface O 1  when the engine stops. If the engine  20  is stopped (accordingly if the operation of the oil pump  80  is stopped), then the oil in the turbocharger  140  is discharged quickly from the oil exits  146   a ,  146   b.    
     If oil resides in the turbocharger  140  which has a high temperature immediately after the engine stops, then the resident oil is liable to be carbonized, and as a result, there is a problem that the entire oil which circulates in the engine  20  is liable to be degraded. However, with the personal watercraft  10  in which the engine with a turbocharger of the present embodiment is incorporated, if the engine  20  stops, then oil in the turbocharger  140  is discharged rapidly from the oil exits  146   a ,  146   b , the oil which may reside in the turbocharger  140  after the engine stops can be minimized to reduce the degradation of all of the oil. 
     Since the engine  20  is a dry sump type engine and the oil tank  50  is provided on an extension line of the crankshaft thereof, the oil surface O 1  when the engine stops can be set to be low. 
     Accordingly, oil in the turbocharger  140  is discharged quickly from the oil exits  146   a ,  146   b , and as a result, the deterioration of the entire oil is further reduced. 
     Since the one-way valve  147  is interposed in each of the oil returning passages  25   b ,  25   c  is in communication with the oil exits  146   a ,  146   b  of the turbocharger  140 , when the personal watercraft  10  capsizes, a situation wherein oil reversely flows from the oil pan  28  to the turbocharger  140  which is in a high temperature state and resides in the turbocharger  140  is eliminated. 
     Accordingly, carbonization of oil can be prevented with a higher degree of certainty, and degradation of all of the oil can be reduced with a higher degree of certainty. 
     Since the turbocharger  140  and an end portion of the main gallery  20   a  for oil is provided in parallel to the crankshaft  21  of the engine  20  that are in communication with each other by the oil supply passage  25   a , oil to the turbocharger  140  is supplied from the end portion of the main gallery  20   a  to the turbocharger  140  directly through the oil supply passage  25   a.    
     Accordingly, the time until oil is supplied to the turbocharger  140  after the engine is started is reduced. Thus, a quick and reliable operation of the turbocharger  140  can be achieved. 
     Since the oil pump  80  is provided on the front side of the body  11  with respect to the engine  20  while the turbocharger  140  is provided on the rear side of the body  11  and the turbocharger  140  and the rear end portion of the main gallery  20   a  are in communication with each other by the oil supply passage  25   a , oil can be supplied rapidly to the turbocharger  140  rearwardly of the engine. 
     Since oil supplied to the turbocharger  140  is used to lubricate the bearing portion  142  of the turbocharger  140  and is supplied to the oil jacket  146  formed in the bearing casing  141  to cool the bearing casing  141 , not only can the bearing portion  142  of the turbocharger  140  be lubricated but also the bearing casing  141  can be cooled. 
     Further, where lubrication of the bearing portion  142  of the turbocharger  140  and cooling of the bearing casing  141  are performed with oil supplied to the turbocharger  140  in this manner, it is necessary to quickly supply a greater amount of oil than ever to the turbocharger  140 . However, with the turbocharger cooling structure  10  for a personal watercraft of the present embodiment, since the oil to the turbocharger  140  is supplied from the end portion of the main gallery  20   a  directly to the turbocharger  140  through the oil supply passage  25   a , a greater amount of oil can be supplied rapidly. 
     While an embodiment of the present invention is described above, the present invention is not limited to the embodiment described above but can be carried out suitably in various forms within the scope of the subject matter of the present invention. 
     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.