This nonprovisional application claims priority under 35 U.S.C. xc2xa7 119(a) on Patent Application No.  2001-216519 filed in Japan on Jul. 17, 2001, the entirety of which is hereby incorporated by reference. 
1.  Field of the Invention
The present invention relates to a system for lubricating an engine for a personal watercraft. 
2.  Description of Background Art
Systems for lubricating an engine for a personal watercraft, as shown in FIGS.  20 and 21 of the present invention, have been known, for example, from Japanese Patent Laid-open No.  2001-140613.  In this system, an engine 3 for driving a jet propelling pump 2 is provided in a watercraft body 1 surrounded by a hull 1a and deck 1b in such a manner as to extend in a length direction of the watercraft body 1.  An oil pump 4 driven by a crankshaft 3a of the engine 3 is provided on an extension of the crankshaft 3a of the engine 3.  The oil tank 5 is provided over the oil pump 4 and an oil filter 7 is provided on the oil tank 5. 
As shown in FIG.  21, the oil pump 4 is connected to an oil pan 3b of the engine 3 by way of piping 6a.  The oil pump 4 is connected to the oil tank 5 by way of piping 6b and 6c.  The oil pump 4 is connected to the oil filter 7 by way of piping 6d.  Furthermore, the oil filter 7 is connected to a main gallery 3c of the engine 3 by way of piping 6e.  
In FIG.  21, reference numeral 8 denotes a relief valve provided in such a manner as to be in communication with the main gallery 3c of the engine 3. 
According to the above-described background art system, the oil tank 5 is provided over the oil pump 4.  Accordingly, it becomes difficult to lay the oil piping 6a to 6e in the narrow watercraft body. 
An object of the present invention is to solve the above-described problem, and to provide a system for lubricating an engine for a personal watercraft, which is capable of simplifying an oil piping structure thereof. 
To achieve the above object, according to a first aspect of the present invention, a system for lubricating an engine for a personal watercraft includes an engine for driving a jet propelling pump provided in a watercraft body surrounded by a hull and a deck in such a manner as to extend in a length direction of the watercraft body.  An oil tank is provided on an extension of a crankshaft of the engine and an oil pump driven by the crankshaft is provided in the oil tank. 
According to a second aspect of the present invention, in addition to the configuration of the first aspect of the present invention, a relief valve for controlling a discharge pressure of the oil pump is provided in the oil tank. 
According to a third aspect of the present invention, in addition to the configuration of the second aspect of the present invention, the oil tank is composed of a tank main body and a cover.  The relief valve is accommodated in the oil tank in such a manner as to be in communication with a discharge passage of the oil pump and is brought into contact with the cover. 
According to a fourth aspect of the present invention, in addition to the configuration of the third aspect of the present invention, the tank main body and the cover are joined to each other with their contact planes extending substantially in the vertical direction.  The relief valve is accommodated in the oil tank in such a manner as to extend in the horizontal direction. 
According to a fifth aspect of the present invention, in addition to the configuration of the third and fourth aspects of the present invention, the oil pump is accommodated in a portion, on the tank main body side, of the oil tank.  Suction/discharge passages of the oil pump are formed integrally with the tank main body. 
According to a sixth aspect of the present invention, in addition to the configuration of the third through fifth aspects of the present invention, the tank main body covers drive chambers for accessories such as an AC generator, a balancer shaft, and a starter motor of the engine. 
According to a seventh aspect of the present invention, in addition to the configuration of the first through sixth aspects of the present invention, an oil filter in communication with the oil pump of the oil tank is provided in an upper portion of the oil tank.  A communication passage for communicating the oil tank to the oil filter is formed integrally with the oil tank. 
According to an eighth aspect of the present invention, in addition to the configuration of the seventh aspect of the present invention, the engine and the oil filter are aligned with an opening of the deck. 
According to a ninth aspect of the present invention, in addition to the configuration of seventh and eighth aspects of the present invention, a mounting portion for mounting the oil filter is provided on an upper portion of the oil tank.  An oil receiving portion is formed in the mounting portion and is in communication with the communication passage. 
According to the system for lubricating an engine for a personal watercraft according to the first aspect of the present invention, the engine for driving a jet propelling pump is provided in the watercraft body surrounded by the hull and the deck in such a manner as to extend in the length direction of the watercraft body.  The oil tank is provided on an extension of the crankshaft of the engine.  In addition, the oil pump is driven by the crankshaft and is provided in the oil tank.  Accordingly, it is possible to simplify the oil piping structure.  Specifically, at least the piping (6b and 6c) in the background art for connecting the oil pump to the oil tank can be omitted. 
According to the system for lubricating an engine for a personal watercraft according to the second aspect of the present invention, the relief valve for controlling a discharge pressure of the oil pump is provided in the oil tank.  Accordingly, it is possible to discharge relief oil from the relief valve 130 in the oil tank 50.  In addition, it is possible to reduce the volume of the oil pump as compared with a configuration where relief oil is discharged in the engine (for example, in the oil pan (3b) as in the above-described background art). 
According to the system for lubricating an engine for a personal watercraft according to the third aspect of the present invention, the oil tank is composed of the oil main body and the cover.  The relief valve is accommodated in the oil tank in such a manner as to be in communication with the discharge passage of the oil pump and is brought into contact with the cover.  Accordingly, it is possible to simplify the accommodation and fixture of the relief valve. 
According to the system for lubricating an engine for a personal watercraft according to the fourth aspect of the present invention, the tank main body and the cover are joined to each other with their contact planes extending substantially in the vertical direction.  The relief valve is accommodated in the oil tank in such a manner as to extend in the horizontal direction.  Accordingly, it is possible to easily assemble the relief valve. 
According to the system for lubricating an engine for a personal watercraft according to a fifth aspect of the present invention, the oil pump is accommodated in a portion, on the tank main body side, of the oil tank and the suction/discharge passages of the oil pump are formed integrally with the tank main body.  Accordingly, it is possible to further simplify the oil piping structure. 
According to the system for lubricating an engine for a personal watercraft according to the sixth aspect of the present invention, the tank main body covers drive chambers for accessories such as the ACG the balancer shaft, and the starter motor of the engine.  Accordingly, it is possible to eliminate the need for covers specialized for covering the drive chambers for the accessories.  Therefore, the engine can be made more compact. 
According to the system for lubricating an engine for a personal watercraft according to the seventh aspect of the present invention, the oil filter in communication with the oil pump in the oil tank is provided in the upper portion of the oil tank.  Passages for communicating the oil tank to the oil filter are formed integrally with the oil tank.  Accordingly, it is possible to further simplify the oil piping structure. 
According to the system for lubricating an engine for a personal watercraft according to the eighth aspect of the present invention, the oil filter is aligned with the opening of the deck.  Accordingly, it is possible to easily perform the necessary work to change the oil filter. 
According to the system for lubricating an engine for a personal watercraft according to the ninth aspect of the present invention, the mounting portion for mounting the oil filter is provided on an upper portion of the oil tank.  Furthermore, the oil receiving portion is formed in the mounting portion and is in communication with the communication passage.  As a result, oil, which may be dropped at the time of mounting/dismounting the oil filter to or from the mounting portion, is received in the oil receiving portion and is then returned into the oil tank.  Accordingly, the inside of the watercraft body will be less contaminated with oil. 
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.