Abstract:
A personal watercraft typically comprises an engine having a plurality of fuel injectors arranged along a longitudinal direction of the watercraft, a fuel tank configured to store fuel and to have an outlet port from which the fuel outflows out and a return port through which the fuel is returned to the fuel tank, and a fuel distribution pipe provided between the outlet port and the return port of the fuel tank and configured to distribute the fuel outflowing from the fuel tank to a plurality of fuel injectors connected to the fuel distribution pipe at positions thereof and to return remaining fuel to the fuel tank, wherein the fuel distribution pipe is configured to extend such that an upstream portion is located lower than a downstream portion in a flow passage of the fuel flowing within the fuel distribution pipe.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a personal watercraft. More particularly, the present invention relates to a construction of a fuel supply passage configured to supply a fuel to an engine of the personal watercraft. 
     2. Description of the Related Art 
     In recent years, jet-propulsion personal watercraft have been widely used in leisure, sport, rescue activities, and the like. A typical personal watercraft includes an engine mounted substantially at a center position in a longitudinal direction within a body surrounded by a hull and a deck. The personal watercraft is equipped with a water jet pump behind the engine and a fuel tank forward of the engine. The engine drives the water jet pump, which pressurizes and accelerates water sucked from a water intake generally provided on a bottom surface of the hull and ejects it rearward from an outlet port. Thereby, the personal watercraft is propelled. 
     The engine mounted in the personal watercraft typically includes multiple cylinders that are arranged along the longitudinal direction of the watercraft (e.g., in-line multi-cylinder engine, and a V-type multi-cylinder engine). The engine is provided with fuel injectors such as electronically controlled fuel injectors respectively provided for the cylinders to inject a predetermined amount of fuel into air-intake passages or into a combustion chamber. The fuel tank has an outlet from which a fuel outflows and a return port through which some of the fuel is returned. The fuel stored within the fuel tank is delivered from the outlet to a fuel distribution pipe. The fuel distribution pipe extends along the longitudinal direction of the watercraft, and the fuel injectors are connected to a side portion of the fuel distribution pipe. Therefore, some of the fuel flowing within the fuel distribution pipe is distributed to the fuel injectors and the remaining fuel is returned to the fuel tank through the return port. 
     As described above, the fuel tank is placed forward of the engine. The outlet of the fuel tank is typically connected to a front portion of the fuel distribution pipe which is close to the outlet, and the return port is connected to a rear portion of the fuel distribution pipe. Therefore, the fuel outflowing from the fuel tank flows from the front portion (upstream portion) to the rear portion (downstream portion) within the fuel distribution pipe, and is distributed to the fuel injectors at positions of the fuel distribution pipe. 
     The engine tends to heat up to a high temperature during operation, and it takes some time for the engine to sufficiently decrease the temperature after the engine stops. Therefore, after the engine stops, some of the fuel remaining within the fuel distribution pipe is vaporized. Since the personal watercraft is constructed such that its center of gravity is located slightly rearward of the center position in the longitudinal direction, a fore part of the body is located higher than an aft part of the body when the watercraft is at rest on the water without a rider. When the rider rides on the watercraft and starts up the engine, the fore part is located higher than the fore part of the watercraft without the rider. In this construction, the vaporized fuel within the fuel distribution pipe tends to remain within the front portion of the fuel distribution pipe (on the upstream portion in a flow passage of the fuel) due to a buoyant force, when the watercraft is at rest on the water and the engine is starting up. 
     However, the vaporized fuel remaining within the front portion of the fuel distribution pipe while the watercraft is at rest on the water is guided from the front portion to the rear portion within the fuel distribution pipe, together with a liquefied fuel (hereinafter referred to as liquid fuel), when the engine starts up next. As a result, the vaporized fuel is mixed with the liquid fuel being distributed from the fuel distribution pipe to the fuel injectors. Under this condition, the fuel injectors cannot inject the liquid fuel in appropriate amount, thereby making it difficult for the engine to operate stably during start-up. 
     SUMMARY OF THE INVENTION 
     The present invention addresses the above described condition, and an object of the present invention is to provide a personal watercraft capable of inhibiting an unstable operation of the engine due to a vaporized fuel during start-up of an engine. 
     According to the present invention, there is provided a personal watercraft comprising an engine having a plurality of fuel injectors arranged along a longitudinal direction of the watercraft, a fuel tank configured to store a fuel supplied to the engine and to have an outlet from which the fuel outflows and a return port through which the fuel is returned to the fuel tank, and a fuel distribution pipe provided between the outlet and the return port of the fuel tank and configured to distribute the fuel outflowing from the outlet of the fuel tank to a plurality of fuel injectors connected to the fuel distribution pipe at positions thereof and to return a remaining fuel to the fuel tank through the return port, wherein the fuel distribution pipe is configured to extend such that an upstream portion thereof is located lower than a downstream portion thereof in a flow passage of the fuel flowing within the fuel distribution pipe. 
     In such a construction, while the engine is in a stopped state, the vaporized fuel remains within the downstream portion of the fuel distribution pipe. Upon start-up of the engine, the vaporized fuel is not supplied to the fuel injectors, but directly returned to the fuel tank together with a liquid fuel. As s result, the engine can start up stably. 
     The fuel distribution pipe may be configured to extend such that the downstream portion is located forward of the upstream portion in the longitudinal direction of the watercraft. 
     In such a construction, while the engine is in a stopped state, the fuel distribution pipe provided substantially horizontally is inclined such that a front end portion thereof is located higher than a rear end portion thereof as in a body of the watercraft. Therefore, the vaporized fuel remains within the front portion of the fuel distribution pipe, i.e., the downstream portion in the flow passage of the fuel. Upon start-up of the engine, the vaporized fuel remaining within the front portion of the fuel distribution pipe is not supplied to the fuel injectors but returned to the fuel tank together with the liquid fuel. As a result, the engine can start up stably. 
     The fuel tank may be placed forward of the engine in the longitudinal direction of the watercraft. In this case, the length of a pipe through which the fuel is returned to the fuel tank can be reduced, which makes it easy for the vaporized fuel to be returned to the fuel tank. 
     The personal watercraft may further comprise an open-looped cooling system configured to cool the engine using water outside the watercraft as cooling water. The cooling system is configured to draw some of the water pressurized by the water jet pump for use as cooling water to cool engine components and supply the cooling water to the engine through a cooling water pipe. The open-looped cooling system is typically employed in the personal watercraft. 
     In the personal watercraft equipped with the open-looped cooling system so constructed, when the engine stops, the water jet pump stops supplying the water, and the cooling water within the cooling water pipe is discharged outside the watercraft. Under this condition, it takes a relatively long time for the engine to sufficiently cool down to a low temperature after the engine stops, thereby causing the fuel within the fuel distribution pipe to be vaporized. Therefore, in the above described construction of the fuel distribution pipe, the fuel tank, and the like is suitable for use in the personal watercraft which is equipped with the open-looped cooling system and requires a relatively long time to cool down after the engine stops. With this construction, the engine can operate stably during start-up. 
     The fuel distribution pipe may be located higher than an upper end of the fuel tank. In a construction in which the fuel distribution pipe is located lower than the fuel tank, the vaporized fuel within the fuel distribution pipe flows into the fuel tank by a buoyant force. On the other hand, in the construction in which the fuel distribution pipe is located higher than the upper end of the fuel tank, the vaporized fuel tends to remain within the fuel distribution pipe without moving toward the fuel tank. Therefore, the construction in which the outlet of the fuel tank is connected to the rear portion of the fuel distribution pipe and the return port of the fuel tank is connected to the front portion of the fuel distribution pipe, is suitable for use in the personal watercraft in which the fuel distribution pipe is located higher than the upper end of the fuel tank. With this construction, the vaporized fuel within the fuel distribution pipe is inhibited from being supplied to the fuel injectors during start-up of the engine. 
     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 
         FIG. 1  is a side view of a personal watercraft according to an embodiment of the present invention; 
         FIG. 2  is a plan view of the personal watercraft in  FIG. 1 ; and 
         FIG. 3  is a partial plan view showing a construction of an engine, a fuel tank and a fuel distribution pipe in the personal watercraft in FIG.  1 . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Hereinafter, an embodiment of a personal watercraft of the present invention will be described with reference to the accompanying drawings. The personal watercraft in  FIG. 1  is a straddle-type personal watercraft provided with a seat  7  straddled by a rider. A body  1  of the watercraft comprises a hull  2  and a deck  3  covering the hull  2  from above. A line at which the hull  2  and the deck  3  are connected over the entire perimeter thereof is called a gunnel line  4 . The gunnel line  4  is located above a waterline  5  when the watercraft is at rest on water. 
     The personal watercraft in  FIG. 1  is constructed such that the gunnel line  4  is substantially parallel to the waterline  5  when the watercraft is at rest on the water without a rider. Some watercraft rest on the water with a body  1  inclined such that a fore part of the gunnel line  4  is located higher than an aft part of the gunnel line  4 . The embodiment described below is applicable to such a personal watercraft. In the personal watercraft in  FIG. 1 , the body  1  is inclined such that the fore part is located higher than the aft part when the rider rides on the watercraft. 
     As shown in  FIG. 2 , an opening  6 , which has a substantially rectangular shape as seen from above is formed at a substantially center section of the deck  3  in the upper portion of the body  1  such that its longitudinal direction corresponds with the longitudinal direction of the body  1 . The seat  7  is removably mounted over the opening  6 . 
     An engine room  8  is provided in a space defined by the hull  2  and the deck  3  below the opening  6 . An engine E is mounted within the engine room  8  and configured to drive a water jet pump P that propels the watercraft. The engine room  8  has a convex-shaped transverse cross-section and is configured such that its upper portion is smaller than its lower portion. In this embodiment, the engine E is an in-line four-cylinder four-cycle engine. 
     As shown in  FIG. 1 , the engine E is mounted such that a crankshaft  10  extends along the longitudinal direction of the body  1 . An output end of the crankshaft  10  is rotatably coupled integrally with a pump shaft  13  of the water jet pump P provided on the rear side of the body  1  through a propeller shaft  11 . An impeller  14  is attached to the pump shaft  13  of the water jet pump P. Fairing vanes  15  are provided behind the impeller  14 . The impeller  14  is covered with a pump casing  16  on the outer periphery thereof. 
     A water intake  17  is provided on the bottom of the body  1 . The water intake  17  is connected to the pump casing  16  through a water passage. The pump casing  16  is connected to a pump nozzle  18  provided on the rear side of the body  1 . The pump nozzle  18  has a cross-sectional area that gradually reduces rearward, and an outlet port  19  is provided on the rear end of the pump nozzle  18 . 
     The water outside the watercraft is sucked from the water intake  17  and fed to the water jet pump P. The water jet pump P pressurizes and accelerates the water and the fairing vanes  15  guide water flow behind the impeller  14 . The water is ejected through the pump nozzle  18  and from the outlet port  19  and, as the resulting reaction, the watercraft obtains a propulsion force. 
     The personal watercraft according to this embodiment comprises an open-looped cooling system  20 . As shown in  FIG. 1 , the cooling system  20  is provided with a water-drawing port  21  provided on an upper portion of the pump casing  16  and a cooling water pipe  22  extending from the water-drawing port  21  to the engine E. And, the cooling system  20  is configured to draw some of the water pressurized by the water jet pump P through the water-drawing port  21  for use as cooling water to cool engine components and supply the cooling water to the engine E through the cooling water pipe  22 . The cooling water cools the components of the engine E. 
     A bar-type steering handle  23  is provided on a front portion of the deck  3 . The handle  23  is connected to a steering nozzle  24  provided behind the pump nozzle  18  through a cable  25  in FIG.  2 . When the rider rotates the handle  23  clockwise or counterclockwise, the steering nozzle  24  is swung toward the opposite direction so that the ejection direction of the water being ejected through the pump nozzle  18  can be changed, and the watercraft can be correspondingly turned to any desired direction while the water jet pump P is generating the propulsion force. 
     As shown in  FIG. 1 , a bowl-shaped reverse deflector  26  is provided on the rear side of the body  1  and on an upper portion of the steering nozzle  24  such that it can vertically swing around a horizontally mounted swinging shaft  27 . When the deflector  26  is swung downward to a lower position around the swinging shaft  27  so as to be located behind the steering nozzle  24 , the water being ejected rearward from the steering nozzle  24  is ejected substantially forward. As the resulting reaction, the personal watercraft moves rearward. 
     As shown in  FIG. 1 , a fuel tank  30  is mounted within the body  1  to be located forward of the engine E. Within the fuel tank  30 , a fuel  29  to be combusted in the engine E is stored. The fuel  29  stored within the fuel tank  30  is supplied to the engine E through a supply pipe  31 , and some of the fuel is combusted in the engine E. The remaining fuel is returned to the fuel tank  30  through a return pipe  32 . How the fuel is delivered from the fuel tank  30  to the engine E through the supply pipe  31  will be described in detail later. 
     As shown in  FIG. 3 , air-intake pipes  34  are connected to a side portion of the cylinder head  33  in an upper portion of the engine E so as to correspond to four cylinders arranged in the longitudinal direction of the body  1 . The air-intake pipes  34  are respectively provided with fuel injectors  35 , each configured to inject a fuel to taken-in air flowing within a corresponding one of the air-intake pipes  34 . The fuel injectors  35  are attached at substantially the same positions of the air-intake pipes  34  and arranged to be spaced apart from one another in the longitudinal direction of the body  1 . 
     The fuel injectors  35  are connected to a fuel distribution pipe  36  of a straight-pipe shape. The fuel distribution pipe  36  extends along the longitudinal direction of the body  1  so as to conform to the arrangement of the fuel injectors  35 . The fuel injectors  35  are connected to a side portion of the fuel distributor  36 . As shown in  FIG. 1 , the fuel distribution pipe  36  is inclined such that a front end portion  36 B is located higher than a rear end portion  36 A with respect to the waterline  5 . And, the fuel distribution pipe  36  is located higher than an upper end of the fuel tank  30 . 
     Alternatively, the fuel distribution pipe  36  may be inclined such that the front end portion  36 B is located higher than the rear end portion  36 A with respect to the waterline  5  by mounting the engine E such that a front portion thereof is located higher than a rear portion thereof with respect to the waterline  5 . As a further alternative, by constituting the body  1  such that a fore part is located higher than an aft part, the fuel distribution pipe  36  may be inclined such that the front end portion  36 B is located higher than the rear end portion  36 A with respect to the waterline  5 . 
     Even in a case where the fuel distribution pipe  36  is inclined such that the front end portion  36 B is located lower than the rear end portion  36 A while the watercraft is at rest on the water without the rider, the fuel distribution pipe  36  may be inclined such that the front end portion  36 B is located higher than the rear end portion  36 A by inclining the body  1  such that the fore part is located higher than the aft part, when the rider rides on the watercraft and starts up the engine E. 
     As shown in  FIG. 3 , the fuel tank  30  is provided with a fuel pump  37 . The fuel pump  37  is provided with an outlet port  38  from which the fuel  29  outflows. The fuel tank  30  is provided with a return port  39  through which the fuel  29  is returned to the fuel tank  30 . The fuel pump  37  is driven by an operation of the engine E and stops when the engine E stops. 
     The outlet port  38  of the fuel pump  37  and the rear end portion  36 A of the fuel distribution pipe  36  are connected to each other through the supply pipe  31  with a filter  40  provided between the outlet port  38  and the rear end portion  36 A to remove substances contained in the fuel  29 . The supply pipe  31  is comprised of a first supply pipe  31 A configured to connect the outlet port  38  of the fuel pump  37  to the filter  40  and a second supply pipe  31 B configured to connect the filter  40  to the rear end portion  36 A of the fuel distribution pipe  36 . The front end portion  36 B of the fuel distribution pipe  36  is connected to the return port  39  of the fuel tank  30  through the return pipe  32 . 
     In the personal watercraft constructed as described above, while the engine E is operating, the fuel  29  stored in the fuel tank  30  is pumped by the fuel pump  37  to outflow from the outlet port  38  to the supply pipe  31  (see arrow  50  in FIG.  3 ). The fuel  29  is guided through the filter  40  and then guided into the fuel distribution pipe  36  through the rear end portion  36 A (see arrow  51  in FIG.  3 ). Within the fuel distribution pipe  52 , the fuel  29  flows from the rear end portion  36 A toward the front end portion  36 B (see arrow  52  in FIG.  3 ). 
     Some of the fuel  29  flowing within the fuel distribution pipe  36  is distributed to the fuel injectors  35  at positions thereof. Each of the fuel injectors  35  injects the fuel  29  into the taken-in air flowing within a corresponding one of the air-intake pipes  34 . As a result, the fuel is mixed with the taken-in air and an air-fuel mixture is drawn into the combustion chamber and combusted therein, thereby allowing the engine E to be driven. The remaining fuel is returned from the front end portion  36 B to the fuel tank  30  through the return pipe  32  and the return port  39  (see arrow  53 ) and collected into the fuel  29  reserved within the fuel tank  29 . 
     In the open-looped cooling system  20 , the cooling water is discharged outside the body  1  as soon as the engine E stops. The engine E maintains a relatively high-temperature condition for some time after the engine E has stopped, and the heat causes some of the fuel within the fuel distribution pipe  36  to be vaporized. In this case, since the fuel distribution pipe  36  is inclined such that the front end portion  36 B is higher than the rear end portion  36 A, the vaporized fuel tends to remain in the vicinity of the front end portion  36 B. It should be appreciated that, since the fuel distribution pipe  36  is located higher than the upper end of the fuel tank  30 , the vaporized fuel is inhibited from flowing toward the fuel tank  30  through the return pipe  32  while the engine E is in a stopped state. 
     However, when the engine E starts up next, the fuel  29  is pumped by the fuel pump  37  to outflow from the outlet port  38  and then is guided from the rear end portion  36 A toward the front end portion  36 B within the fuel distribution pipe  36 . As a result, the vaporized fuel remaining in the vicinity of the front end portion  36 B while the engine E is in the stopped state is pushed out by the fuel flowing within the fuel distribution pipe  36  and is guided from the front end portion  36 B to the fuel tank  30  through the return pipe  32 . As a matter of course, when the fuel distribution pipe  36  is located lower then the upper end of the fuel tank  30 , the vaporized fuel within the fuel distribution pipe  36  is smoothly guided to the fuel tank  30 . 
     Thus, in the personal watercraft constructed as described above, the vaporized fuel remaining within the fuel distribution pipe  36  while the engine E is the stopped state is guided from the front end portion  36 B of the fuel distribution pipe  36  to the fuel tank  30  as soon as the engine E starts up, and is not delivered to the fuel injectors  35 . Therefore, the fuel injectors  35  can inject the liquid fuel to the taken-in air within the air-intake pipes  34  in predetermined amount, thereby allowing the engine E to stably start up. 
     The fuel distribution pipe  36  may be formed integrally with the supply pipe  31  and/or the return pipe  32 . 
     As this invention may be embodied in several forms without departing from the spirit of essential characteristics thereof, the above embodiment is therefore illustrative and not restrictive, since the scope of the invention is defined by the appended claims rather than by the description preceding them, and all changes that fall within metes and bounds of the claims, or equivalence of such metes and bounds thereof are therefore intended to be embraced by the claims.