Fuel feed system of engine

A fuel feed system of an engine is provided with a gas-fuel separating unit for separating oil mist generated in an engine case from air with a labyrinth, and an auto fuel cock is operated by pressure pulsation of the air from which the oil mist is separated by the gas-liquid separating unit. Thus, infiltration of the oil mist into the auto fuel cock is suppressed to the minimum, and a malfunction of the auto fuel cock caused by accumulation of the oil can be prevented. Additionally, a breather passage for feeding the air, from which the oil mist is separated by the gas-liquid separating unit, to a breathing unit is connected the auto fuel cock via a negative pressure tube. Thus, it is unnecessary to provide a specific passage for transmitting the pressure pulsation of the air in the engine case to the auto fuel cock.

TECHNICAL FIELD

The present invention relates to a fuel feed system of an engine in which an auto fuel cock for controlling fuel feed from a fuel tank to the engine is operated by pressure pulsation of air in an engine case.

Additionally, the present invention relates to a fuel feed system of an engine in which an auto fuel cock is arranged between an engine case and a fuel tank fixed above the engine case, and in which an inside of the engine case is connected to the auto fuel cock via a negative pressure tube.

BACKGROUND ART

Disclosed in JP-A-2003-171910 is an apparatus in which an auto fuel cock for controlling fuel feed from a fuel tank to an engine is connected to a crank case of the engine via a feed tube, and the auto fuel cock is operated by pressure pulsation generated in the crank case.

Disclosed in JP-U-61-097577 is an apparatus in which a tip of a communicating tube extended from an auto fuel cock for controlling fuel feed from a fuel tank to an engine is opened in oil accumulating at a bottom part of a crank case, and the auto fuel cock is operated by pressure pulsation generated in the crank case.

Additionally, disclosed in JP-Y-59-013336 is a apparatus in which an suction part of a fuel cock is inserted into a discharge cylinder provided on a fuel tank via an oil seal constituted by an elastic material so that the fuel cock is attached to the bottom part of the fuel tank, and in which a cylindrical lock body constituted by an elastic body fitted onto the outer circumferences of the discharge cylinder and the suction part is tightened and fixed with a fixing instrument.

In an apparatus of JP-A-2003-171910, there is a possibility that a malfunction of an auto fuel cock is caused by accumulation of oil generated by condensation of oil mist which is generated in the crank case of the engine and infiltrates into the auto fuel cock through a feed tube.

Additionally, in an apparatus of JP-U-61-097577, since a tip of a communicating tube is opened in oil accumulating at the bottom part of a crank case, there is no possibility that oil mist infiltrates into the auto fuel cock through the communicating tube. However, there is a possibility that the oil in the crank case directly infiltrates into the auto fuel cock through the communicating tube when the engine is tilted.

On the other hand, when an auto fuel cock is arranged between an engine case and a fuel tank fixed above the engine case and the inside of the engine case is connected to the auto fuel cock via a negative pressure tube, there is a problem that work for connecting a lower end of the negative pressure tube to the inside of the engine case and for connecting an upper end of the negative pressure tube to the auto fuel cock is necessary and therefore much labor and time are required for the work. In particular, the above work becomes more difficult in a case where a working space between the fuel tank and the engine case is small. The distance between the engine case and the fuel tank increases when sufficient space is ensured, and thus there exists a problem the whole engine enlarges.

Additionally, it is conceived that a negative pressure introduction joint of the auto fuel cock fixed to a lower surface of the fuel tank to a negative pressure introduction joint of the engine case via an approximate crank-shaped is a bent negative pressure tube so that the whole engine is miniaturized by shortening the distance between the engine case and the fuel tank fixed above the engine case. However, this causes a possibility that oil which infiltrates from the engine case accumulates at a bent part of the negative pressure tube when the engine is tilted. When a tip of the negative pressure introduction joint of the auto fuel cock is soaked into the oil, there is a possibility that the operation of the auto fuel cock, of which the communication with the inside of the engine case is cut off, becomes impossible.

DISCLOSURE OF THE INVENTION

A first object of the present invention is to provide a fuel feed system of an engine for preventing a malfunction of an auto fuel cock caused by an infiltration of oil from an engine case.

A second object of the present invention is to provide a fuel feed system of an engine in which work for connecting an inside of an engine case to an auto fuel cock via an negative pressure tube is easy without increasing a distance between the engine case and a fuel tank.

A third object of the present invention is to provide a fuel feed system of an engine in which a negative pressure tube for connecting a negative pressure introduction joint of an auto fuel cock fixed to a lower surface of a fuel tank to the negative pressure introduction joint of an engine case is not blocked due to the oil.

In accordance with one or more embodiments of the present invention, a fuel feed system of an engine in which an auto fuel cock for controlling fuel feed from a fuel tank to the engine is operated by pressure pulsation of air in an engine case is provided with a gas-liquid separating unit for separating oil mist generated in the engine case from air. The auto fuel cock is operated by the pressure pulsation of the air from which the oil mist is separated by the gas-liquid separating unit.

The fuel feed system may include a breather passage for feeding the air from which the oil mist is separated by the gas-liquid separating unit to a breathing unit and makes the breather passage communicate with the auto fuel cock.

In the above fuel feed system, the breather passage may be arranged at an upper part of the engine case.

In the above fuel feed system, a first negative pressure introduction joint provided on the auto fuel cock may be connected to a second negative pressure introduction joint provided on the breather passage via the negative pressure tube.

In the above fuel feed system, the negative pressure tube may be monotonously tilted downward from the first negative pressure introduction joint to the second negative pressure introduction joint.

In accordance with one or more embodiments of the present invention, a fuel feed system of an engine is provided with: an engine case; a fuel tank fixed above an engine case; an auto fuel cock which is arranged between the engine case and the fuel tank and fixed to a lower surface of the fuel tank; and a negative pressure tube connecting an inside of the engine case to the auto fuel cock. The auto fuel cock has a first negative pressure introduction joint projected downward, the engine case has a second negative pressure introduction joint projected upward from an upper surface of the engine case. The negative pressure tube has a first connection part fitted onto the first negative pressure introduction joint and a second connection part fitted onto the second negative pressure introduction joint. The negative pressure tube is positioned so that the first connection part of the negative pressure tube, of which the second connection part is fitted onto the second negative pressure introduction joint, is located on a movement route of the first negative pressure introduction joint of the auto fuel cock when the fuel tank, to which the auto fuel cock is fixed, is moved downward to be fixed above the engine case.

In the fuel feed system, a positioning part for regulating an attachment posture of the negative pressure tube to the engine case may be provided between the negative pressure tube and the engine case.

In the above fuel feed system, the positioning part may have a recessed part provided on the negative pressure tube and a projection provided on the engine case. Alternatively, the positioning part may have a projection provided on the negative pressure tube and a recessed part provided on the engine case.

In the above fuel feed system, a taper part of which the outer diameter is reduced downward may be formed at a lower end of the first negative pressure introduction joint of the auto fuel cock.

In the above fuel feed system, the negative pressure tube may be monotonously tilted downward from the first negative pressure introduction joint to the second negative pressure introduction joint.

Further, a projection and a recessed part of the exemplary embodiment described below correspond to the positioning part of the present invention.

In the above fuel feed system, the negative pressure tube may have a middle part between the first connection part and the second connection part and be formed in an approximate crank shape, and the first negative pressure introduction joint may have a notch at the lower end thereof.

In the above fuel feed system, the notch of the first negative pressure introduction joint may be opened toward the middle part side of the negative pressure tube.

The above fuel feed system may include the gas-liquid separating unit for separating the oil mist generated in the engine case from the air and make the auto fuel cock operate by the pressure pulsation of the air from which the oil mist is separated by the gas-liquid separating unit.

The above fuel feed system may include the breather passage for feeding the air from which the oil mist is separated by the gas-liquid separating unit to the breathing unit and makes the breather passage communicate with the auto fuel cock.

In the above fuel feed system, the breather passage may be arranged at the upper part of the engine case.

According to one or more embodiments of the present invention, a fuel feed system is provided with the gas-liquid separating unit for separating oil mist generated in the engine case from air and the auto fuel cock is operated by pressure pulsation of the air from which the oil mist is separated by the gas-liquid separating unit. Thereby, infiltration of the oil mist into the auto fuel cock can be suppressed to the minimum and a malfunction of the auto fuel cock caused by accumulation of the oil can be prevented.

Additionally, a breather passage for feeding the air from which the oil mist is separated by the gas-liquid separating unit to a breathing unit is connected to the auto fuel cock. Thus, it is unnecessary to provide a specific passage for transmitting the pressure pulsation of the air in the engine case to the auto fuel cock.

Additionally, the breather passage is arranged at an upper part of the engine case. Thus, the oil mist, which has not been completely removed and infiltrates into the breather passage, can be suppressed to the minimum.

Additionally, a first negative pressure introduction joint provided on the auto fuel cock is connected to a second negative pressure introduction joint provided on the breather passage via the negative pressure tube. Thus, the degree of freedom of an attachment position of the auto fuel cock can be raised.

Additionally, the negative pressure tube is monotonously tilted downward from the first negative pressure introduction joint to the second negative pressure introduction joint. Thus, the oil in the negative pressure tube is discharged to the breather passage by gravity and can be more reliably prevented from infiltrating into the auto fuel cock.

According to one or more embodiments of the present invention, when the fuel tank, to which the auto fuel cock is fixed, is moved downward so as to be fixed above the engine case, the first negative pressure introduction joint of the auto fuel cock is automatically fitted into a first connection part of the negative pressure tube, of which a second connection part is previously fitted onto the second negative pressure introduction joint of the engine case. Thus, it becomes possible to simultaneously complete attachment of the fuel tank and attachment of the negative pressure tube, and work efficiency is greatly improved. Further, since it is unnecessary to provide a working space, where the first and second connection parts of the negative pressure tube are respectively fitted onto the first and second negative pressure introduction joints, between a lower surface of the fuel tank and an upper surface of the engine case, the fuel tank is made to approach the engine case as much as possible so that the whole engine can be miniaturized.

Additionally, the positioning part for regulating an attachment posture of the negative pressure tube to the engine case is provided between the negative pressure tube and the engine case. Thus, the first negative pressure introduction joint of the auto fuel cock can be easily fitted into the first connection part of the negative pressure tube.

Additionally, the positioning part is constituted by a recessed part provided on the negative pressure tube and a projection provided on the engine case. Alternatively, the positioning part is constituted by a projection provided on the negative pressure tube and a recessed part provided on the engine case. Thus, the attachment posture of the negative pressure tube to the engine case can be easily and reliably regulated by engaging the projection with the recessed part.

Additionally, a taper part, of which the outer diameter is reduced downward, is provided at a lower end of the first negative pressure introduction joint of the auto fuel cock. Thus, the first negative pressure introduction joint of the auto fuel cock can be easily fitted into the first connection part of the negative pressure tube when the fuel tank is moved downward so as to be fixed above the engine case.

Additionally, the negative pressure tube is monotonously tilted downward from the first negative pressure introduction joint to the second negative pressure introduction joint. Thus, the oil infiltrating into the negative pressure tube is discharged by gravity, and can be reliably prevented from infiltrating into the auto fuel cock.

Additionally, the negative pressure tube has a middle part between the first connection part and the second connection part and is formed in an approximate crank shape, and the first negative pressure introduction joint has a notch at the lower end thereof. Thus, even if the engine is tilted so that the first connection part side of the middle part of the negative pressure tube is lowered and even if the oil is accumulated at the corners of the middle part and the first connection part, the auto fuel cock can be made to operate without any trouble so long as the notch formed at the lower end of the first negative pressure introduction joint is not soaked into the oil. That is why communication of the inside of the engine case and the auto fuel cock is not cut off.

Additionally, the notch of the first negative pressure introduction joint is opened toward the middle part side of the negative pressure tube. Thus, the notch can be hardly soaked into the oil even if the oil is accumulated at the corners of the middle part and the first connection part of the negative pressure tube.

Additionally, the gas-liquid separating unit for separating the oil mist generated in the engine case from the air is provided, and the auto fuel cock is made to operate by the pressure pulsation of the air from which the oil mist is separated by the gas-liquid separating unit. Thus, the infiltration of the oil mist into the auto fuel cock is suppressed to the minimum, and the malfunction of the auto fuel cock caused by the accumulation of the oil can be prevented.

Additionally, the breather passage for feeding the air from which the oil mist is separated by the gas-liquid separating unit to the breathing unit is made to communicate with the auto fuel cock. Thus, it is unnecessary to provide the specific passage for transmitting the pressure pulsation of the air in the engine case to the auto fuel cock.

Additionally, the breather passage is arranged at the upper part of the engine case. Thus, the oil mist, which has not been completely removed and infiltrates into the breather passage, can be suppressed to the minimum.

DESCRIPTION OF REFERENCE NUMERALS AND CHARACTERS

BEST MODE FOR CARRYING OUT THE INVENTION

Exemplary embodiments of the present invention will be described hereinafter with reference to the accompanying drawings.

FIGS. 1 to 12show an exemplary embodiment of the present invention.FIG. 1is a front view of a general purpose engine.FIG. 2is a view when being viewed from the arrow2inFIG. 1.FIG. 3is an enlarged cross sectional view taken along line3-3inFIG. 1.FIG. 4is a view when being viewed from the arrow4inFIG. 3.FIG. 5is an enlarged cross sectional view taken along line5-5inFIG. 4.FIG. 6is an enlarged cross sectional view taken along line6-6inFIG. 2.FIG. 7is an enlarged cross sectional view taken along line7-7inFIG. 6.FIG. 8is an enlarged cross sectional view taken along line8-8inFIG. 7.FIG. 9is an enlarged cross sectional view taken along line9-9inFIG. 6andFIG. 10.FIG. 10is an enlarged cross sectional view taken along line10-10inFIG. 2.FIG. 11is a partial view ofFIG. 10.FIG. 12is a cross sectional view taken along line12-12inFIG. 10.

As shown inFIG. 1andFIG. 2, in a single cylinder four cycle engine E, a cylinder head12and a head cover13are arranged so as to be raised in relation to an engine case11having a crank case and a cylinder block as one unit with a cylinder axis line L slightly tilted. The crank shaft14is projected from an end surface of the engine case11, and a recoil starter16for cranking and starting the crank shaft14is provided on an outer surface of a cover15which covers another end surface of the engine case11. A carburetor17is provided at the side of the cylinder head12, and an intake passage18extending upward from the carburetor17is connected to an air cleaner19. A muffler20is attached so as to align with the air cleaner19above the cylinder head12and the head cover13, and a fuel tank21is attached nearer the crank case than the air cleaner19and the muffler20.

The fuel tank21is constituted in such a way that a lower edge of a tank upper21a, an upper edge of a tank lower21band an upper edge of a tank holder22are combined as one unit by a caulking part23. A tank stay24is fixed to four attachment bosses11aprojected on the engine case11with bolts25, and outer circumference parts of four rubber bushes26are supported by an upper surface of the tank stay24. A bolt27penetrating from below to above of the center of each rubber bush26penetrates the tank holder22and a reinforcing plate28to be engaged with a nut29, and thus the fuel tank21is supported above the engine case11without vibration.

As shown inFIG. 3andFIGS. 6 to 8, an auto fuel cock30for automatically feeding fuel in the fuel tank21to the carburetor17during the operation of the engine E is attached to a lower surface of the fuel tank21. The auto fuel cock30includes a first housing31and a second housing32combined as one unit, and a stay31a(seeFIG. 6) projected from the first housing31is fixed to a lower surface of the tank holder22with a bolt33and a nut34. Here, an upper part of the auto fuel cock30is projected upward through an opening22a(seeFIG. 7) of the tank holder22, and a lower part of the auto fuel cock30is projected downward through an opening24a(seeFIGS. 3 and 6) of the tank stay24.

As most clearly shown inFIG. 8, the first housing31of the auto fuel cock30includes: a fuel entrance joint31b; a fuel exit joint31c; a valve seat31dformed between the fuel entrance joint31band the fuel exit joint31c; and a disc-shaped diaphragm supporting part31e. Additionally, the second housing32includes: a first negative pressure introduction joint32a; a negative pressure chamber32bcommunicating with the first negative pressure introduction joint32a; and a disc-shaped diaphragm supporting part32c. The fuel entrance joint31bis connected to a joint36provided on the lower surface of the fuel tank21via a first fuel hose35, the fuel exit joint31cis connected to the carburetor17via a second fuel hose37, and the first negative pressure introduction joint32ais connected to a second negative pressure introduction joint11bof the engine case11via a negative pressure tube38made of rubber. Since the negative pressure tube38made of rubber is employed, the degree of freedom of lay-out of the fuel tank21to the engine case11can be raised.

A ring-shaped diaphragm supporting member39is held between the diaphragm supporting part31eof the first housing31and the diaphragm supporting part32cof the second housing32. An outer circumference part of a first diaphragm40is fixed between the diaphragm supporting part31eof the first housing31and the diaphragm supporting member39via a sealing member41. The outer circumference part of a second diaphragm42is fixed between the diaphragm supporting part32cof the second housing32and the diaphragm supporting member39via a sealing member43. The first and second diaphragms40and42, a spacer block44held between the center parts of the first and second diaphragms40and42and a disc-shaped spring sheet45brought into contact with a rear surface of the second diaphragm42are fixed as one unit with a rivet46penetrating them.

A valve seat forming member48is fitted between the first negative pressure introduction joint32aof the second housing32and the negative pressure chamber32bvia a spacer plate47. A valve body40aformed on the center part of the first diaphragm40is energized in a direction to which the valve body40aformed at the center of the first diaphragm40is seated on the valve seat31dof the first housing31seat31dof the first housing31with a valve spring49arranged between the valve seat forming member48and the spring sheet45. An end of a reed valve50capable of sitting down on a valve seat48bfacing a through hole48apenetrating the center part of the valve seat forming member48and an end of a stopper51for regulating the movable range of the reed valve50by covering the outer side thereof are fixed to the valve seat forming member48with a bolt (not shown). A fine through hole50afor making the first negative pressure introduction joint32acommunicate with the negative pressure chamber32bis formed in the reed valve50.

As clearly shown inFIG. 7andFIG. 8, a taper part32dis formed at a lower end of the first negative pressure introduction joint32aso that the negative pressure tube38can be easily inserted into the introduction joint32a, and a reverse U-shaped notch32eis formed on the taper part32d. The negative pressure tube38includes: a first connection part38awhich vertically extends and is inserted into the first negative pressure introduction joint32a; a second connection part38bwhich vertically extends and is inserted into the second negative pressure introduction joint11b; and a middle part38cwhich obliquely extends downward from a lower end of the first connection part38ato an upper end of the second connection part38b, and is formed in an approximate crank shape. A linear recessed part38dis formed on a bottom surface of the first connection part38a. On the other hand, a linear projection11cwhich fits into the linear recessed part38dis formed on an upper surface of the engine case11facing the bottom surface of the first connection part38aof the negative pressure tube38, and the negative pressure tube38is positioned in a rotational direction around a vertical axis by engagement of the recessed part38dand the projection11c.

As clearly shown inFIG. 6andFIG. 9, a breathing unit52provided on the side of the engine case11includes a breather chamber54surrounded by a ring-shaped circumference wall lid and a cover53, and a breather passage11eis opened at an end of the breather chamber54. An end of a reed valve55capable of being seated down on a valve seat11fformed at an opening part of the breather passage11eand an end of a stopper56for regulating the movable range of the reed valve55are fixed to an inner wall of the breather chamber54with a bolt57. A joint53ais formed on the cover53so as to face another end of the breather chamber54far from the breather passage11e, and is connected to an intake system of the engine E via a breather pipe58. Two ribs11g,11hare projected in the breather chamber54in order to constitute a labyrinth59between the breather passage11eand the joint53a. A bottom part of the breather chamber54communicates with an inner space of the engine case11via an oil return hole11i. Additionally, a communication hole11jpenetrating the inside of the second negative pressure introduction joint11b, onto which the second connection part38bof the negative pressure tube38is fitted, communicates with the breather passage11e.

Next, the construction of a gas-liquid separating unit61of the engine E will be described with reference toFIGS. 9 to 12.

A pin part14aof the crank shaft14of the engine E is connected to a piston63via a connecting rod62. A journal part14bof the crank shaft14is supported by the engine case11via a ball bearing64. Another journal part14cof the crank shaft14is supported by a bearing holder66, which is fixed in the engine case11with six bolts65, via a ball bearing67. A covering member68is fixed to an opening11kof the engine case11so as to cover a front surface of the bearing holder66with nine bolts69, and an oil agitating chamber70is formed between the covering member68and the bearing holder66.

Moreover, both ends of a first balancer shaft73(seeFIG. 12) are supported between the engine case11and the bearing holder66via a pair of ball bearings71and72. A driving gear74provided on the crank shaft14is engaged with a driven gear75provided on the first balancer shaft73so that the first balancer shaft73rotates at the same number of rotations as that of the crank shaft14.

A rotor77is rotatably supported by a bottom part of the oil agitating chamber70via a rotor shaft76. A driven gear78provided on the rotor shaft76is engaged with a driving gear79provided on the crank shaft14so that the rotor77is rotationally driven by the crank shaft14. Additionally, a timing belt81wound around a driving sprocket80provided on the crank shaft14is connected to a driven sprocket (not shown) provided on the cylinder head12.

As clearly shown inFIG. 10andFIG. 11, a first rib66asurrounding a part of the outer circumference of the rotor77, a second rib66bsurrounding a part of the outer circumferences of the driving gear79and the driving sprocket80, a third rib66clying to an end of the first rib66aand is parallel with a lower surface of a lower bowstring of the timing belt81, a fourth rib66dlying to an end of the second rib66band is parallel with an upper surface of an upper bowstring of the timing belt81, and an independent fifth rib66eobliquely extending in a direction opposite to an oblique direction of the fourth rib66dfrom the vicinity of a connection part of the second rib66band the fourth rib66dare projected on the side of the bearing holder66. Additionally, a first rib68aand a second rib68b, which are approximately parallel with the fourth rib66dand the fifth rib66eof the bearing holder66respectively, are projected on the side of the cover member68.

The oil agitating chamber70is a region surrounded by the first to fourth ribs66ato66dof the bearing holder66. A gas-liquid separating chamber83having a labyrinth82constituted by the fourth and fifth ribs66dand66eof the bearing holder66and the first and second ribs68aand68bof the cover member68is formed outside of the first to fourth ribs66ato66d. An upper part of the gas-liquid separating chamber83is made to communicate with the breathing unit52via the breather passage11e(seeFIG. 9).

Next, action the fuel feed system of the exemplary embodiment of the present invention including the above constitution will be described.

InFIG. 10, when the engine E is operated, the rotor77connected to the crank shaft14via the driving gear79and the driven gear78rotates in the oil agitating chamber70, and the oil accumulated on the bottom part of the oil agitating chamber70is scrapped up and scattered. The scattered oil is guided between the third rib66cand the fourth rib66d, which are parallel with the timing belt81by the first and second ribs66aand66bof the bearing holder66, adhere to the timing belt81and is fed to a valve chamber (not shown) of the cylinder head12, thereby lubricating a valve mechanism. Air including oil mist generated in the oil agitating chamber70pass through the labyrinth82constituted by the fourth and fifth ribs66dand66eof the bearing holder66and the first and second ribs68aand68bof the cover member68in the gas-liquid separating chamber83, and the oil separated during the passage falls along the first and second ribs66aand66bto be returned to the bottom part of the oil agitating chamber70.

Since the bearing holder66which includes the ball bearing67for supporting the crank shaft14is fixed so as to face the opening ilk of the engine case11, and the gas-liquid separating chamber83is formed between the cover member68combined with the opening ilk and the bearing holder66, the bearing holder66can be used as a part of a wall surface of the gas-liquid separating chamber83. Therefore, the number of parts can be increased compared with a case where a part of the wall surface of the gas-liquid separating chamber83is constituted by a specific member, and miniaturization, lightening, simplification of the shape of the engine case11can be realized compared with a case where a part of the side wall of the gas-liquid separating chamber83is constituted by a partition wall integrally formed with the engine case11.

In addition, since the labyrinth82is provided in the gas-liquid separating chamber83, the oil mist included in the air in the engine case11can be effectively separated. In particular, the labyrinth82is constituted in such a way that the fourth and fifth ribs66dand66eprojecting from the bearing holder66side are mutually overlapped with the first and second ribs68aand68bprojected from the cover member68by the distance α (seeFIG. 9), and therefore the complicated labyrinth82is constituted with a simple structure and a gas-liquid separation effect can be further raised.

InFIG. 9, the air from which the oil caulking removed in the labyrinth82of the gas-liquid separating chamber83passes through the reed valve55of the breather passage11eand the breathing unit52, and is fed to the breather chamber54. That is, the pressure pulsation generated in accordance with reciprocation of the piston63is transmitted to the breather passage11e, and the reed valve55is opened when the pressure in the breather passage11ebecomes positive pressure, or is shut when the pressure therein becomes negative pressure, by which, the air in the breather passage11eis fed to the breather chamber54.

InFIG. 6, the oil, which is included in the air fed to the breather chamber54, has not been completely separated from the air by the gas-liquid separating unit61, is further separated while the air passes through the labyrinth59constituted by the ribs11gand11h, and is returned to a bottom part of the engine case11through the oil return hole11iprovided on the bottom part of the breather chamber54. The air, from which the oil mist is separated by the gas-liquid separating unit61, is introduced to the breathing unit52via the breather passage11eand further subjected to the gas-liquid separation. Therefore, the consumption amount of oil can be further reduced. Although the air, from which the oil caulking thus separated, still includes fuel vapor which blows from a combustion room to the inside of the engine case11, the air including the fuel vapor is returned to the intake system of the engine E through the joint53aof the cover53and the breather pipe58, and prevented from diffusing into the atmosphere by combustion of the fuel vapor and air-fuel mixture.

InFIG. 9, the pressure pulsation in the engine case11is transmitted to the first negative pressure introduction joint32aof the auto fuel cock30through the breather passage11e, the communication hole11jand the negative pressure tube38. InFIG. 8, when the pressure transmitted to the first negative pressure introduction joint32aof the auto fuel cock30becomes negative pressure, the reed valve50goes away from the valve seat48band the pressure in the negative pressure chamber32bbecomes negative pressure. Inversely, when the pressure transmitted to the first negative pressure introduction joint32aof the auto fuel cock30becomes positive pressure, the reed valve50sits down on the valve seat48band the negative pressure in the negative pressure chamber32bis maintained. Since the negative pressure in the negative pressure chamber32bis thus always maintained during the operation of the engine E, the first and second diaphragms40and42move left (inFIG. 8) against elastic force of the valve spring49and the valve body40aformed on the first diaphragm40goes away from the valve seat31d. As a result, the fuel in the fuel tank21is fed to the carburetor17via the first fuel hose35, the fuel entrance joint31b, a gap between the valve seat31dand the valve body40a, the fuel exit joint31cand the second fuel hose37.

Moreover, the first and second diaphragms40and42are energized in a right direction (inFIG. 8) by the elastic force of the valve spring49when the engine E stops and the pressure pulsation in the breather passage11edisappears, and therefore the reed valve50suctioned in the right direction sits down on the valve seat48bso that the negative pressure chamber32bis sealed. However, since the air flows into the negative pressure chamber32bfrom the first negative pressure introduction joint32avia the fine through hole50aprovided in the valve seat50, the valve body40asits down on the valve seat31dby the elastic force of the valve spring49and the auto fuel cock is shut. Therefore, the fuel feed from the fuel tank21to the carburetor17can be automatically stopped with the stopping of the engine E.

The combinations of the negative pressure tube38and the first and second negative pressure introduction joints32aand11bare performed in accordance with the following steps. That is, the tank stay24is previously assembled to the tank holder22of the fuel tank21via the rubber bushes26, and the first fuel hose35is previously assembled to the auto fuel cock30. On the other hand, the second connection part38bof the negative pressure tube38is previously fitted onto the second negative pressure introduction joint11bof the engine case11. Here, the recessed part38don the bottom surface of the first connection part38aof the negative pressure tube38is engaged with the projection11cof the engine case11(seeFIG. 7) so that the negative pressure tube38can be positioned in the rotation direction. The fuel tank21is made to approach the engine case11from above in this state, the first negative pressure introduction joint32aof the auto fuel cock30is fitted into the first connection part38aof the negative pressure tube38, and thereafter the tank stay24is fitted to the engine case11with the bolts25. Then, the second fuel hose37communicating with the carburetor17is fitted onto the fuel exit joint31cand the attachment is completed.

Thus, it is possible to fit the negative pressure tube38onto the first and second negative pressure introduction joints32aand11bonly by making the fuel tank21approach the engine case11from above, and assembly work of the negative pressure tube38is simplified. Additionally, since the recessed part38dof the negative pressure tube38is engaged with the projection11cof the engine case11and the negative pressure tube38is positioned, work for fitting the first negative pressure introduction joint32aof the auto fuel cock30into the first connection part38aof the negative pressure tube38becomes easy. In addition, the vertical movement of the negative pressure tube38once equipped is regulated, and the tube cannot be removed unless the fuel tank21is removed. Therefore, it is unnecessary to prevent pulling-off of the negative pressure tube38with a clip, etc.

If the assembly work of the negative pressure tube38is performed after the fuel tank21is fixed to the engine case11, not only a working space, where the negative pressure tube38is bent to fit onto the first and second negative pressure introduction joints32aand11b, is needed, but also the negative pressure tube38itself is enlarged. Therefore, the fuel tank21cannot be arranged in the vicinity of the engine case11, and the whole engine E is enlarged.

If the oil mist in the engine case11is accumulated inside of the negative pressure tube38or inside of the first negative pressure introduction joint32a, the pressure pulsation in the breather passage11ecannot be transmitted to the negative pressure chamber32bof the auto fuel cock30and there is a possibility that a malfunction of the auto fuel cock30occurs. However, according to the present exemplary embodiment, the air, from which almost the oil caulking removed by the gas-liquid separating unit61, is fed to the breather passage11e, and the pressure pulsation in the breather passage11eis introduced into the auto fuel cock30. Therefore, the malfunction of the auto fuel cock30caused by the oil mist can be previously prevented.

In particular, since the breather passage11efor feeding the air passed through the gas-liquid separating unit61to the breathing unit52is provided at an upper part of the engine case11, infiltration of the oil mist into the breather passage11ecan be further effectively prevented. In addition, since the auto fuel cock30is made to operate with use of the pressure pulsation in the breather passage11e, it is unnecessary to form the specific passage for transmitting the pressure pulsation to the auto fuel cock30.

Additionally, the negative pressure tube38includes the first connection part38awhich vertically extends and is inserted into the first negative pressure introduction joint32a, the second connection part38bwhich vertically extends and is inserted into the second negative pressure introduction joint11b, and the middle part38cwhich obliquely extends downward from the lower end of the first connection part38ato the upper end of the second connection part38b. Therefore, even if the oil mist infiltrates into the negative pressure tube38, the oil caulking discharged to the breather passage11eby gravity without accumulating in the negative pressure tube38, and a situation where the pressure pulsation is not transmitted to the auto fuel cock30can be previously avoided.

Further, since the taper part32dis formed at the lower end of the first negative pressure introduction joint32aof the auto fuel cock30, insertion work of the first negative pressure introduction joint32ainto the first connection part38aof the negative pressure tube38becomes easy. In addition, since the notch32eis formed on the taper part32d, the action of the notch32ecan prevent the first negative pressure introduction joint32afrom being closed even if the oil is accumulated on the lower end of the first connection part38aas shown being circled by the chain line inFIG. 7when the engine E is tilted. In particular, since the notch32eis opened toward the middle part38cside of the negative pressure tube38, the notch32ecan be further reliably prevented from sinking beneath the oil.

Even if the negative pressure introduction joint32ais cut off at an upper end of the taper part32d(upper end of the notch32e), the same effect as a case where the notch32eis provided can be obtained. However, since the taper part32dis eliminated, such cut-off makes the insertion of the negative pressure tube38difficult.

Additionally, since the auto fuel cock30operates by the negative pressure of the engine case11which is stronger than intake negative pressure of the engine E, the sufficient negative pressure is generated only by cranking by the recoil starter16and the fuel can be fed to the carburetor17. In particular, the auto fuel cock30can be reliably made to operate by employment of the first and second diaphragms40and42even if the negative pressure is small.

The exemplary embodiment of the present invention has been described above, various design modifications can be performed without departing from the substance of the present invention.

Although the exemplary embodiment regarding a general purpose engine E has been described, for example, the present invention can be applied to engines for arbitrary uses.

Additionally, although the recessed part38dprovided on the negative pressure tube38and the projection11cprovided on the engine case11have been exemplified as a positioning part in the exemplary embodiment, the positional relationship between the recessed part and the projection may be reversible, and any shapes of the recessed part and the projection are applicable.

The present application claims priority based on Japanese Patent Application No. P2005-183601 filed on Jul. 23, 2005, Japanese Patent Application No. P2005-183602 filed on Jul. 23, 2005, and Japanese Patent Application No. P2005-183603, the contents of them are incorporated herein by reference.

INDUSTRIAL APPLICABILITY

The present invention is applicable to a fuel feed system of an engine in which an auto fuel cock for controlling fuel feed from a fuel tank to the engine is operated by pressure pulsation of air in an engine case.

Additionally, the present invention is applicable to a fuel feed system of an engine in which an auto fuel cock is arranged between an engine case and a fuel tank fixed above the engine case, and in which an inside of the engine case is connected to the auto fuel cock via a negative pressure tube.