Patent Publication Number: US-8539937-B2

Title: Fuel supplying apparatus for internal combustion engine

Description:
FIELD OF THE INVENTION 
     The present invention relates generally to an apparatus for supplying fuel to an internal combustion engine and, more particularly, to a technique of opening a fuel supply path by using a negative pressure in a crankcase. 
     BACKGROUND OF THE INVENTION 
     Schemes of supplying fuel from a fuel tank to an intake system of an internal combustion engine includes a scheme of supplying fuel by using a fuel pump and a scheme of supplying fuel by using the gravity. According to the scheme of supplying fuel by using the gravity, a fuel tank is disposed above a carburetor and the fuel is supplied from the fuel tank to the carburetor. This scheme employs a relatively simple configuration and is often used. 
     According to the scheme of supplying fuel by using the gravity, an automatic cock is disposed in a fuel supply path to introduce the fuel from the fuel tank to the carburetor. The automatic cock is a valve that opens the fuel supply path by using a negative pressure in a crankcase. During the driving of the internal combustion engine, a negative pressure is generated in the crankcase associated with the reciprocating motion of a piston (more specifically, a large negative pressure and a micro positive pressure are alternately and repeatedly generated). The automatic cock is opened by this negative pressure and, thereby, the fuel in the fuel tank flows into the carburetor through the fuel supply path. 
     A common internal combustion engine rakes up a lubricating oil stored in the crankcase upward to splash the lubricating oil and, thereby, generates oil mist to lubricate a portion to be slid that is accommodated in the crankcase. This is not preferable because the oil mist adheres to parts in the automatic cock when the oil mist intrudes into the automatic cock. 
     In contrast, a fuel supplying apparatus that suppresses intrusion of the oil mist into a negative pressure introducing inlet of the automatic cock is known from, for example, Japanese Patent No. 4310294. In the known fuel supplying apparatus: a crankcase is connected to an intake system through a gas/liquid separating apparatus, a breather path, and a reed valve; and a branch outlet that branches from the breather path is connected to the negative pressure introducing inlet of the automatic cock. 
     When a positive pressure is generated in the crankcase, the reed valve is opened by the positive pressure. Oil mist and blowby gas produced in the crankcase are caused to circulate from the crankcase to the intake system and, thereby, are combusted in a combustion chamber. On the other hand, when a negative pressure is generated in the crankcase, the automatic cock is opened by this negative pressure. The fuel in the fuel tank is supplied to the carburetor through the fuel supply path. 
     The gas/liquid separating apparatus is positioned between the crankcase and the breather path, and separates from the air the oil mist produced in the crankcase. Therefore, the intrusion is suppressed of the oil mist into the negative pressure introducing inlet of the automatic cock through the breather path. In addition, the automatic cock is positioned immediately and exactly above the crankcase. Therefore, even if the oil mist intrudes into the negative pressure introducing inlet of the automatic cock, the oil mist tends to flow out to the breather path thereunder due to the gravity. 
     When the automatic cock is disposed immediately and exactly above the crankcase adjacent thereto, the thermal influence needs to be fully taken into consideration that is caused by the heat dissipation of the internal combustion engine. When the automatic cock is disposed above the crankcase far away therefrom to avoid receiving the thermal influence, the degree of freedom of disposing the fuel supplying apparatus is reduced and, therefore, this is not preferable. In addition, the fuel supplying apparatus employs the scheme of supplying the fuel by using the gravity and, therefore, the fuel tank is positioned above the automatic cock. Especially, for a configuration that has an internal combustion engine and a fuel supplying apparatus incorporated as one unit such as, for example, a small sound-proof engine-driven generator, the height of the unit as a whole is often limited. To suppress the total height, it is considered to make the fuel tank thin. However, this result in reducing the capacity of the fuel tank and, therefore, this is not an advisable solution. 
     SUMMARY OF THE INVENTION 
     It is therefore an object of the present invention to provide an apparatus that is capable of suppressing intrusion of oil mist into a negative pressure introducing inlet of an automatic cock, increasing the degree of freedom of disposition of a fuel supplying apparatus, and sufficiently securing the capacity of a fuel tank. 
     According to an aspect of the present invention, there is provided a fuel supplying apparatus for an internal combustion engine, which comprises: a crankcase of the internal combustion engine; a negative pressure introducing inlet of an automatic cock connected to the crankcase through a negative pressure communication path; and a fuel supplying path that is opened for supplying fuel from a fuel tank to the internal combustion engine, by opening the automatic cock through a negative pressure generated in the crankcase, wherein the negative pressure communication path communicates with an air cleaner through a purge path that branches from the negative pressure communication path at a halfway point of the negative pressure communication path, and a point at which the purge path branches from the negative pressure communication path is set to be at a lowest position of the negative pressure communication path so that oil mist that intrudes from the crankcase can be collected. 
     The apparatus uses a property that, during driving of the internal combustion engine, a pressure in the crankcase is usually lower than a pressure in the air cleaner. The pressure in the air cleaner is higher than the pressure in the crankcase. 
     The purge path branches from the negative pressure communication path at a halfway point of the negative pressure communication path. The negative pressure communication path communicates with the air cleaner through the purge path. Therefore, the air in the air cleaner flows from the purge path into the crankcase passing through the negative pressure communication path. The intrusion of the oil mist into the negative pressure communication path is able to be excluded by the air in the air cleaner. As a result, the intrusion is suppressed of the oil mist in the crankcase, into the negative pressure introducing inlet of the automatic cock passing through the negative pressure communication path. 
     In addition, according to the present invention, the point at which the purge path branches from the negative pressure communication path is set to be at the lowest position of the negative pressure communication path such that the point is able to collect the oil mist that intrudes from the crankcase. Even if the oil mist intrudes from the crankcase into the negative pressure communication path, the oil mist intruding gathers at the lowest position of the negative pressure communication path. Therefore, even when the automatic cock is not disposed above the crankcase, the intrusion is able to be suppressed of the oil mist into the negative pressure introducing inlet of the automatic cock. As above, the automatic cock does not need to be disposed above the crankcase and, therefore, the positions of the automatic cock and the fuel tank are able to arbitrarily be set at positions at which no thermal influence is received that is caused by the heat dissipation from the internal combustion engine. Therefore, the degree of freedom of disposition of the fuel tank and the fuel supplying apparatus is able to be increased. 
     Even when the height is limited for disposing the fuel tank, the capacity of the fuel tank is able to sufficiently be secured by disposing the fuel tank at a suitable position. For example, even when the internal combustion engine and the fuel supplying apparatus are incorporated as one unit and the height of the unit as a whole is limited, the capacity of the fuel tank is able to sufficiently be secured by suitably setting the position of the fuel tank. 
     Preferably, a point at which the purge path is connected to the air cleaner is positioned at a position that is lower than the point at which the purge path branches. Therefore, the oil mist gathering at the lowest position of the negative pressure communication path enters the air cleaner passing through the purge path due to the gravity. The oil mist entering the air cleaner is combusted in the combustion chamber. As a result, the intrusion of the oil mist into the negative pressure introducing inlet of the automatic cock can further be suppressed. 
     Desirably, the purge path has an air flow resistance increasing unit in the vicinity of the point at which the purge path branches, and the air flow resistance increasing unit is adapted to set air flow resistance of the purge path to be higher than air flow resistance of the negative pressure communication path. The pressure loss of the purge path as a whole is increased by increasing the air flow resistance of the purge path by the air flow resistance increasing unit as above. As a result, at the branching point, the pressure difference is able to be set to be an optimal value between the internal pressure of the negative pressure communication path and the internal pressure of the purge path. Because the pressure difference is suitable, the negative pressure state in the negative pressure communication path is not offset by the pressure of the air that flows from the purge path to the negative pressure communication path. The negative pressure in the negative pressure communication path is able to sufficiently be secured that acts to open the automatic cock and, therefore, the automatic cock is able to suitably be operated to open and close. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A preferred embodiment of the present invention will be described in detail below, by way of example only, with reference to the accompanying drawings in which: 
         FIG. 1  is a schematic diagrammatical view showing an internal combustion engine that includes a fuel supplying apparatus according to an embodiment of the present invention; 
         FIG. 2  is a side view of the internal combustion engine including the fuel supplying apparatus, shown in  FIG. 1 ; 
         FIG. 3  is a perspective view showing a relation between the fuel supplying apparatus and the internal combustion engine of  FIG. 2 ; 
         FIG. 4  is a side view showing a relation between an intake system and the fuel supplying apparatus of  FIG. 2 ; 
         FIG. 5  is a diagrammatical view showing a relation among the internal combustion engine, a carburetor, and an automatic cock, as seen in the direction of arrow  5  of  FIG. 4 ; and 
         FIG. 6  is a side view showing, partially in section, a portion with a point at which a purge path branches from a negative pressure communication path of  FIG. 4 . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     An internal combustion engine  10  depicted in  FIG. 1  includes, for example, a transverse single-cylinder four-cycle engine. The internal combustion engine  10  includes: a crankcase  12  that integrally has a cylinder  11 , a crank shaft  13 , a piston  14 , a combustion chamber  15 , an intake valve  16 , and an exhaust valve  17 . The crank shaft  13  is horizontally disposed. The cylinder  11  is inclined upward. 
     An intake system  30  for the internal combustion engine  10  includes an air cleaner  31 , a throttle valve  32 , a carburetor  33 , and an intake pipe  34 . The carburetor  33  has a float chamber  33   a  that temporarily retains fuel. The intake pipe  34  is connected to an intake inlet  21  of the internal combustion engine  10 . 
     In the internal combustion engine  10 , a portion of combustion gas produced in the combustion chamber  15  leaks from a point between the cylinder  11  and the piston  14  into the crankcase  12 . The combustion gas leaking is referred to as “blowby gas”. The blowby gas includes a large amount of oil mist and carbon hydrides (HC). To lubricate a sliding part that is accommodated in the crankcase  12 , lubricating oil in the crankcase  12  is raked up upward to be splashed around and, thereby, oil mist can be produced in the crankcase  12 . The blowby gas and the oil mist can not be released as they are into the atmosphere. 
     The internal combustion engine  10  of the embodiment includes a blowby gas reduction system  40  to circulate the blowby gas and the oil mist to the combustion chamber  15  through the intake system  30 . The blowby gas reduction system  40  is configured by connecting the crankcase  12  to the air cleaner  31  through a breather chamber  41 , a reed valve  42 , and a breather path  43 . The breather chamber  41  is formed in the top portion of the crankcase  12 . The reed valve  42  is a one-way valve to open and close the breather path  43 , is usually closed, and is opened only when a positive pressure is generated in the crankcase  12 . The breather path  43  includes a hose and connects between the breather chamber  41  and the air cleaner  31 . 
     During driving of the internal combustion engine  10 , a large negative pressure and a micro positive pressure are alternately generated repeatedly in the crankcase  12  associated with the reciprocating motion of the piston  14 . When the positive pressure is generated in the crankcase  12 , the blowby gas and the oil mist produced in the crankcase  12  are returned to the air cleaner  31  and, thereby, are circulated to the intake system  30 . Therefore, the blowby gas and the oil mist together with combustion air are supplied from the intake system  30  to the combustion chamber  15  and are again combusted. 
     As depicted in  FIGS. 1 and 2 , a fuel supplying apparatus  50  for the internal combustion engine  10  employs a scheme of supplying fuel by using the gravity. The fuel supplying apparatus  50  includes a fuel tank  51 , an automatic cock  52 , a fuel supply path  53 , and a negative pressure communication path  54 . More specifically, the fuel supplying apparatus  50  has the fuel tank  51  that is disposed above the carburetor  33  and the fuel is supplied from the fuel tank  51  to the carburetor  33  (more specifically, the float chamber  33   a  of the carburetor  33 ). 
     As depicted in  FIG. 1 , the automatic cock  52  is a valve that automatically opens the fuel supply path  53  by using the negative pressure in the crankcase  12 . The automatic cock  52  includes an oil filter  52   a , a case  52   b , a diaphragm  52   c , a return spring  52   d , and a valve body  52   e . The oil filter  52   a  filters the fuel supplied from the fuel tank  51  and introduces the fuel into the case  52   b . The case  52   b  accommodates the diaphragm  52   c , the return spring  52   d , and the valve body  52   e . The diaphragm  52   c  is a valve driving body that, in a valve chamber  52   f  in the case  52   b , drives the valve body  52   e . In the ordinary state where no negative pressure acts on a negative pressure introducing inlet  52   g , the return spring  52   d  biases the diaphragm  52   c  in a direction for the valve body  52   e  to be closed. 
     The case  52   b  includes the negative pressure introducing inlet  52   g , a fuel inlet  52   h , and a fuel outlet  52   i . The negative pressure introducing inlet  52   g  is connected to a communication opening  22  of the crankcase  12  by the negative pressure communication path  54 . This communication opening  22  is formed in the top portion of the crankcase  12 . The fuel inlet  52   h  is connected to the fuel tank  51 . The fuel outlet  52   i  is connected to the float chamber  33   a  by the fuel supply path  53 . The fuel supply path  53  and the negative pressure communication path  54  are each configured by a hose. As depicted in  FIGS. 2 to 5 , the fuel supply path  53  is inclined downward from the fuel outlet  52   i  toward the float chamber  33   a.    
     As depicted in  FIG. 1 , during the driving of the internal combustion engine  10 , a large negative pressure and a micro positive pressure are alternately generated repeatedly in the crankcase  12  associated with the reciprocating motion of the piston  14 . When a predetermined negative pressure set in advance acts from the crankcase  12  to the negative pressure introducing inlet  52   g , the diaphragm  52   c  resists a biasing force of the return spring  52   d  and opens the valve body  52   e . When the negative pressure is generated in the crankcase  12 , the automatic cock  52  automatically opens due to the negative pressure. As a result, due to the gravity, the fuel in the fuel tank  51  passes through the oil filter  52   a , the fuel inlet  52   h , the valve chamber  52   f , the fuel outlet  52   i , and the fuel supply path  53  and is supplied to the float chamber  33   a . The fuel supplied to the float chamber  33   a  is sprayed into the carburetor  33 , is mixed with the combustion air, and, thereafter, is supplied to the intake inlet  21  of the internal combustion engine  10 . 
     As depicted in  FIGS. 2 and 3 , the internal combustion engine  10  is incorporated in a frame  62  together with an electric generator  61 , the fuel tank  51 , and a muffler not depicted. A unit incorporated to be one in this manner is referred to as “electric generator unit  63 ”. The internal combustion engine  10  has the electric generator  61  and a recoil starter  64  that are integrally incorporated in a side portion thereof. The electric generator  61  is directly coupled to the crank shaft  13  ( FIG. 1 ) and, thereby, is driven by the internal combustion engine  10 . The periphery of the internal combustion engine  10  is covered with a shielding cover  65 . 
     As depicted in  FIGS. 2 and 3 , beside the internal combustion engine  10 , the intake system  30  is positioned being placed beside the electric generator  61  and the recoil starter  64 . The fuel tank  51  is positioned exactly above the intake system  30 , that is, exactly above the air cleaner  31  and the carburetor  33 . The automatic cock  52  is positioned exactly under the fuel tank  51  and is placed beside the top portion of the air cleaner  31 . The automatic cock  52  is positioned in the vicinity of the air cleaner  31  and the recoil starter  64 . 
     As depicted in  FIGS. 2 to 5 , the negative pressure communication path  54  including hoses is connected to the negative pressure introducing inlet  52   g  and the communication opening  22  in the state where the negative pressure communication path  54  is loose to take a substantially V-shape. Of the negative pressure communication path  54 , a portion (connecting portion)  54   a  at the bottom thereof having a substantially V-shape, that is, the halfway point of the negative pressure communication path  54  is the lowest position of the negative pressure communication path  54 . The portion  54   a  at the bottom having the V-shape is hereinafter referred to as “the lowest position  54   a  of the negative pressure communication path  54 ”. 
     Describing with reference also to  FIG. 1 , the negative pressure communication path  54  communicates with a connection opening  31   a  of the air cleaner  31  through a purge path  55  that branches from the halfway point of the path (the lowest position  54   a  of the negative pressure communication path  54 ). The purge path  55  includes a hose. The point at which the purge path  55  branches from the negative pressure communication path  54  is positioned at the lowest position  54   a  of the negative pressure communication path  54 . Therefore, the oil mist can be collected that intrudes from the crankcase  12 . Hereinafter, the lowest position  54   a  of the negative pressure communication path  54  is referred to as “point  54   a  at which the purge path  55  branches from the negative pressure communication path  54 ” when suitable. 
     The point  31   a  at which the purge path  55  is connected to the air cleaner  31 , that is, the connection opening  31   a  is located at a position that is lower than the branching point  54   a . The shape presents a substantially Y-shape, that is formed by connecting the purge path  55  to the bottom of the negative pressure communication path  54  having the V-shape. 
     The configuration around the branching point  54   a  will be described in more detail. As depicted in  FIGS. 1 and 6 , the negative pressure communication path  54  is divided into two along the longitudinal direction of the hose at the lowest position  54   a  and these divided portions are connected to each other by a hose joint  70  having a T shape or a Y shape. The negative pressure communication path  54  includes a first communication path  56  that is connected to the negative pressure introducing inlet  52   g  of the automatic cock  52 , and a second communication path  57  that is connected to the communication opening  22  of the crankcase  12 . 
     As depicted in  FIG. 6 , the hose joint  70  is a kind of pipe joint to connect three hoses to each other in a substantially T shape or a substantially Y shape and integrally has a first, a second, and a third joint units  71 ,  72 , and  73 . Preferably, the internal angle formed by the first and the second joint units  71  and  72  is in a range of 100° to 120°. The third joint unit  73  extends in a direction therefor to be aligned on a substantially straight line with the first joint unit  71 . The joint units  71  to  73  each are a male joint to be inserted into a hose. 
     The first joint unit  71  is inserted into an end of the first communication path  56  (first hose) and these components are clamped by a hose band  74 . The second joint unit  72  is inserted into an end of the second communication path  57  (second hose) and these components are clamped by a hose band  75 . The third joint unit  73  is inserted into an end of the purge path  55  (third hose) and these components are clamped by a hose band  76 . 
     When the purge path  55  and the first and the second communication paths  56  and  57  are fitted to the hose joint  70 , the third joint unit  73  is located at a position that is lower than those of the first and the second joint units  71  and  72 . The branching point  54   a  of the first, the second, and the third joint units  71 ,  72 , and  73  corresponds to the point  54   a  at which the purge path  55  branches from the negative pressure communication path  54 . 
     The purge path  55  has an air flow resistance increasing unit  77  in the vicinity of the branching point  54   a . The air flow resistance increasing unit  77  sets air flow resistance of the purge path  55  to be higher than that of the negative pressure communication path  54 . More specifically, the air flow resistance increasing unit  77  includes, for example, an orifice plate that is positioned in the third joint unit  73  and in the vicinity of the branching point  54   a . The orifice plate  77  (air flow resistance increasing unit  77 ) is a flat plate that intervenes in the piping path of the third joint unit  73 , and has one small hole (orifice)  77   a  in the center thereof such that a differential pressure is generated between its upstream side and its downstream side. The diameter d 1  of the small hole  77   a  is set to be smaller than the hole diameter d 2  of each of the first, the second, and the third joint units  71  to  73 . 
     An operation of the fuel supplying apparatus according to the embodiment will be described. 
     As depicted in  FIG. 1 , the embodiment uses a property that, during the driving of the internal combustion engine  10 , a pressure P 1  in the crankcase  12  is generally lower than a pressure P 2  in the air cleaner  31 . The pressure in the air cleaner  31  is higher than the pressure in the crankcase  12 . 
     According to the embodiment, the purge path  55  branches from the negative pressure communication path  54  at the halfway point thereof and the purge path  55  communicates between the negative pressure communication path  54  and the air cleaner  31 . Therefore, the air in the air cleaner  31  flows from the purge path  55  into the crankcase  12  passing through the negative pressure communication path  54 . The intrusion of the oil mist into the negative pressure communication path  54  can be excluded by the air in the air cleaner  31 . As a result, it is suppressed for the oil mist in the crankcase  12  to pass through the negative pressure communication path  54  and intrude into the negative pressure introducing inlet  52   g  of the automatic cock  52 . 
     In addition, the point  54   a  at which the purge path  55  branches from the negative pressure communication path  54  is set to be at the lowest position of the negative pressure communication path  54  to be able to collect the oil mist that intrudes from the crankcase  12 . Even when the oil mist intrudes from the crankcase  12  into the negative pressure communication path  54 , the oil mist intruding gathers at the lowest position  54   a  of the negative pressure communication path  54 . Therefore, even when the automatic cock  52  is not disposed above the crankcase  12 , the intrusion can be suppressed of the oil mist into the negative pressure introducing inlet  52   g . The automatic cock  52  does not need to be disposed above the crankcase  12  and, therefore, the positions of the automatic cock  52  and the fuel tank  51  can arbitrarily be set to be at positions at which no thermal influence is received that is caused by the heat dissipation from the internal combustion engine  10 . Therefore, the degree of freedom of the disposition of the fuel supplying apparatus  50  can be increased. 
     Even when the height is limited for disposing the fuel tank  51 , the capacity of the fuel tank  51  can sufficiently be secured by disposing the fuel tank  51  at a suitable position. For example, even when the internal combustion engine  10  and the fuel supplying apparatus  50  are incorporated as one unit and the height of the unit as a whole is limited, the capacity of the fuel tank  51  can sufficiently be secured by suitably setting the position of the fuel tank  51 . 
     According to the embodiment, the point  31   a  at which the purge path  55  is connected to the air cleaner  31 , that is, the connection opening  31   a  of the air cleaner  31  is located at the position that is lower than the branching point  54   a . Therefore, the oil mist gathering at the lowest position  54   a  of the negative pressure communication path  54  enters the air cleaner  31  passing through the purge path  55  due to the gravity. The oil mist entering the air cleaner  31  is combusted in the combustion chamber  15 . As a result, the intrusion of the oil mist into the negative pressure introducing inlet  52   g  can further be suppressed. 
     Furthermore, according to the embodiment, the purge path  55  has the air flow resistance increasing unit  77  and, therefore, the air flow resistance of the purge path  55  is larger than the air flow resistance of the negative pressure communication path  54 . Therefore, the pressure difference does not become excessive between the internal pressure Pa of the negative pressure communication path  54  and the internal pressure Pb of the purge path  55 . Because the pressure difference is proper, the negative pressure state in the negative pressure communication path  54  is not cancelled due to the pressure of the air that flows from the purge path  55  to the negative pressure communication path  54 . Therefore, the negative pressure can be secured in the negative pressure communication path  54  to cause the automatic cock  52  to open and, therefore, the automatic cock  52  can suitably be caused to operate to open and close. 
     Yet furthermore, the purge path  55  is provided, in the vicinity of the point  54   a  at which the purge path  55  branches from the negative pressure communication path  54 , with the air flow resistance increasing unit  77  to set the air flow resistance of the purge path  55  to be higher than the air flow resistance of the negative pressure communication path  54 . The pressure loss of the purge path  55  as a whole is increased by increasing the air flow resistance of the purge path  55  by the air flow resistance increasing unit  77 . As a result, at the branching point  54   a , the pressure difference can be set to be an optimal value between the internal pressure Pa of the negative pressure communication path  54  and the internal pressure Pb of the purge path  55 . Because the pressure difference is proper, the negative pressure state in the negative pressure communication path  54  is not offset by the pressure of the air that flows from the purge path  55  to the negative pressure communication path  54 . The negative pressure in the negative pressure communication path  54  can sufficiently be secured that acts to open the automatic cock  52  and, therefore, the automatic cock  52  can suitably be operated to open and close. 
     The fuel supplying apparatus  50  of the present invention is suitable to be used in a configured article having the internal combustion engine  10  and the fuel tank  51  incorporated therein as one unit, for example, a small generator that is driven by an internal combustion engine. 
     Obviously, various minor changes and modifications of the present invention are possible in light of the above teaching It is therefore to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described.