Abstract:
In this multipurpose engine, a fuel gas evaporated within a fuel tank of the engine is drawn out of the fuel tank and is adsorbed by an adsorbing material, the fuel gas is separated from the adsorbing material, and then the fuel gas separated from the adsorbing material is suctioned into an intake system of the engine by using negative pressure inside the intake system. The adsorbing material is accommodated in a canister, and two connection ports used for connection with the canister are respectively provided at a heat-insulating intake pipe between a carburetor and the engine and at a clear section of an air cleaner.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    Priority is claimed on Japanese Patent Application No. 2008-20930, filed Jan. 31, 2008, the content of which is incorporated herein by reference. 
       BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to a multipurpose engine in which a fuel gas evaporated within a fuel tank is adsorbed by an adsorbing material and the fuel gas separated from the adsorbing material is sucked into an intake system of the engine. 
         [0004]    2. Description of Related Art 
         [0005]    A conventional multipurpose engine with a canister disclosed in Japanese Unexamined Patent Application, First Publication No. 2005-163690 accommodates an adsorbing material which adsorbs the fuel gas evaporated within a fuel tank. The multipurpose engine with a canister includes a canister which adsorbs the fuel gas which leaks out from around a cap of the fuel tank, and returns the fuel gas to an intake system, and piping which takes the fuel gas into the canister is opened near an oil supply port of the fuel tank. This piping is coupled to the canister through the bottom of the tank from the inside of the fuel tank, and the fuel gas is charged and guided into the intake system through this piping. It is an aim of the prior art to shorten the piping for recovered fuel gas and to simplify attachment thereof to the intake system. 
         [0006]    A conventional multipurpose engine disclosed in Japanese Unexamined Patent Application, First Publication No. H07-34985 includes an adsorption means which adsorbs the fuel gas evaporated within a fuel tank. As the multipurpose engine, a structure in which an adsorbing material is accommodated in a chamber (equivalent to a canister) formed in a lid for a fuel filling port of a fuel tank, the fuel gas separated through a gas-liquid separation chamber is made to be adsorbed by an adsorbing material within an adsorbing material chamber, and the degassed fuel gas is sucked into an intake system pipe by using the intake negative pressure of the engine is suggested. In addition, a structure in which a block of an adsorbing material is adjacent to the downstream section of a filter element of an air cleaner, and the fuel gas separated through a gas-liquid separation chamber from a fuel tank is directly delivered to the adsorbing material block, and the fuel gas is adsorbed by the adsorbing material, thereby performing degassing of the fuel gas is suggested. 
         [0007]    When the fuel within the fuel tank is consumed by the operation of the engine, the pressure inside the fuel tank becomes negative, and thereby the fuel supply to the intake system is not smoothly performed. In the conventional multipurpose engine with a canister disclosed in the above 2005-163690, a liquid check valve which is adapted to keep a liquid fuel from leaking even if ambient air can be introduced into a fuel supplying cap of the tank, and through which gas can pass is provided. Further, the tip of the piping which feeds the fuel gas into, for example, the intake system is opened to an attachment portion of the cap, and this piping passes through a tank wall via the inside of the tank. Thus, a leak-preventing sealing means is provided between the piping and the wall. As a result, the structure is complicated, the cost is high, and the maintenance is not easy, either. 
         [0008]    In the conventional multipurpose engine disclosed in the above 07-34985 having the adsorption devices, a valve body of a float valve through which liquid is checked, and gas can pass is fixed to an attachment opening of the cap. Further, the cap with which the canister is integrated is large. Therefore, the layout of parts in an engine is not simple, and the fuel supply operation can not be smoothly performed. On the other hand, in a case where the adsorbing material is provided adjacent to the filter element of the air cleaner, the introduction resistance of sucked air may become large, and may have influence on engine output. 
         [0009]    The object of the invention is to solve these problems, and provide a multipurpose engine including a fuel gas adsorption device, which is simple and inexpensive in construction, and is easy to maintain. 
       SUMMARY OF THE INVENTION 
       [0010]    A first aspect of the present invention is a multipurpose engine in which a fuel gas evaporated within a fuel tank of the engine is drawn out of the fuel tank and is adsorbed by an adsorbing material, the fuel gas is separated from the adsorbing material, and then the fuel gas separated from the adsorbing material is suctioned into an intake system of the engine by using negative pressure inside the intake system. The adsorbing material is accommodated in a canister, and two connection ports used for connection with the canister are respectively provided at a heat-insulating intake pipe between a carburetor and the engine and at a clear section of an air cleaner. 
         [0011]    In the first aspect of the multipurpose engine of the present invention, a side face of the canister may be provided with a charge piping connection port to which charge piping of the fuel gas fed from the fuel tank is connected, and a purge piping connection port connected to the connection port provided in the heat-insulating intake pipe. Further, a side face of the canister opposite to where the charge piping is connected may be provided with a suction port for a suction pipe connected to the clear section of the air cleaner having a negative pressure smaller than the negative pressure inside the heat-insulating intake pipe. 
         [0012]    In the first aspect of the multipurpose engine of the present invention, a filter element may be provided at an upstream section of an adsorbing material block of the canister so as to be adjacent to the adsorbing material block. Further, a side face of the canister may be provided with a charge piping connection port to which charge piping of the fuel gas is connected, and a purge piping connection port connected to a clear section in which the negative pressure of the air cleaner is generated. Furthermore, a suction port which is opened to ambient air may be provided at an upstream section of the filter element and. In addition, the connection port provided at the heat-insulating intake pipe may be blocked. 
         [0013]    A second aspect of the present invention is a multipurpose engine in which a fuel gas is drawn out of a fuel tank and is adsorbed by an adsorbing material, the fuel gas is separated from the adsorbing material, and then the fuel gas separated from the adsorbing material is suctioned into an intake system of the engine. The multipurpose engine includes an adsorbing material block which is provided at an downstream section of a filter element inside an air cleaner so as to be adjacent to the filter element and which is opened to the inside of the air cleaner, and a charging pipe for drawing the fuel gas evaporated within the fuel tank out from the fuel tank. The adsorbing material block includes the adsorbing material therein and is formed so as not to narrow an air passage of the air cleaner. The charging pipe is opened to the adsorbing material block. In the multipurpose engine, the fuel gas is drawn out of the fuel tank and is adsorbed by the adsorbing material, the fuel gas is separated from the adsorbing material, and then the fuel gas separated from the adsorbing material is suctioned into an intake system of the engine. 
         [0014]    A third aspect of the present invention is a multipurpose engine in which a fuel gas is drawn out of a fuel tank and is adsorbed by an adsorbing material, the fuel gas is separated from the adsorbing material, and then the fuel gas separated from the adsorbing material is auctioned into an intake system of the engine. The multipurpose engine includes an air passage which is provided between an air cleaner and a carburetor and a connecting intake pipe for holding an adsorbing material block including the adsorbing material therein and which is opened to the air passage. A charging pipe for drawing the fuel gas evaporated within the fuel tank out from the fuel tank is connected to the connecting intake pipe. In the multipurpose engine, the fuel gas is drawn out of the fuel tank and is adsorbed by the adsorbing material, the fuel gas is separated from the adsorbing material, and then the fuel gas separated from the adsorbing material is auctioned into an intake system of the engine. 
         [0015]    According to the first aspect of the multipurpose engine of the invention, it is possible to cope with a canister in which a filter element is built or a canister in which a filter element is not built, without adding parts by properly using two ports on the side of an engine. Accordingly, a canister which recovers a fuel gas leaked from a fuel tank can be attached, without considerably remodeling a standard multipurpose engine. As a result, a multipurpose engine which is easy to maintain can be provided at a low cost. 
         [0016]    According to the second and third aspects of the multipurpose engine of the invention, the adsorbing material block can be provided and accommodated in an air passage between an air cleaner and a carburetor so as not to narrow the air passage. Thus, the number of gas pipes decreases, and the layout of parts is simplified. Moreover, since the flow resistance of an intake system passage does not increase, a fuel gas leaked from a fuel tank can be recovered without reducing engine power. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0017]      FIG. 1  is a side view of a multipurpose engine with a canister related to embodiments of the invention. 
           [0018]      FIG. 2  is a schematic view showing a fuel gas piping system around a canister to be attached to the engine of  FIG. 1  related to a first embodiment of the invention. 
           [0019]      FIG. 3  is a schematic view showing a fuel gas piping system around a canister to be attached to the engine of  FIG. 1  related to a second embodiment of the invention. 
           [0020]      FIG. 4  is a schematic view showing an adsorbing material block to be attached to the engine of  FIG. 1  related to a third embodiment of the invention, and its surroundings. 
           [0021]      FIG. 5  is a schematic view showing an adsorbing material block to be attached to the engine of  FIG. 1  related to a fourth embodiment of the invention, and its surroundings. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     First Embodiment 
       [0022]      FIG. 1  is a side view of a multipurpose engine with a canister related to the present embodiment, and  FIG. 2  is a schematic view showing a fuel gas piping system around a canister to be attached to the engine of  FIG. 1  related to the first embodiment of the invention. 
         [0023]    The multipurpose engine  10  shown in  FIG. 1  is an engine of a general-purpose air-cooling four-cycle single cylinder which is loaded on, for example, a fieldwork machine and in which the cylinder is inclined. An intake system of the multipurpose engine  10  includes a heat-insulating intake pipe  23  connected to a combustion chamber  15  of a cylinder head  14 , a carburetor  22  connected to the heat-insulating intake pipe  23 , and a connecting suction pipe  21  and an air cleaner  24  which are attached to the upstream of the carburetor  22 . The intake system is located at a side face of the inclined cylinder. 
         [0024]    A fuel tank  40  is disposed on the upside of the multipurpose engine  10 , and a detachable cap  50  is tightly screwed onto an oil hole of an upper face of the fuel tank  40 . Further, a rollover valve  60  is set on the upper face of the fuel tank  40 . Thereby, it is possible to pass the fuel gas which evaporates in the fuel-tank  40  to a canister  65  via a charge tube  61 . Also, it is possible to pass ambient air from the charge tube  61  to the fuel tank  40 . Even when the multipurpose engine  10  is inclined, and accordingly the fuel tank  40  inclines and the liquid fuel reaches a vent hole of the rollover valve  60 , the valve is closed by the operation of a float provided in the rollover valve  60 , thereby adding the function in which the liquid fuel is not leaked to the charge tube  61 . A fuel pipe which feeds fuel to the carburetor  22  is attached to a lower portion of the fuel tank  40 . 
         [0025]    While the multipurpose engine  10  is operated, fuel is continuously fed to the carburetor  22  through the fuel pipe by an oil-level head difference between the fuel level inside the fuel-tank  40  and the carburetor  22 , and the inside of the fuel tank  40  has slightly negative pressure. Thus, fuel gas does not leak to the outside. When the multipurpose engine  10  stops, supply of the fuel to the carburetor  22  stops, the fuel gas within the fuel tank  40  continues evaporating by the remaining heat of the multipurpose engine  10 , and the steam pressure becomes positive pressure. As a result, the fuel gas may leak out from a slight gap of pipes. 
         [0026]    In the multipurpose engine  10  including the canister  65 , the fuel gas leaks out of the fuel tank  40  through the rollover valve  60  and the charge tube  61 . Then, the fuel gas enters the canister  65 , and is adsorbed by an adsorbing material, such as activated carbons built in the canister  65 . Therefore, even when the multipurpose engine  10  is being operated and is being stopped, the fuel gas does not leak out to the surroundings. 
         [0027]    There is a limit to the amount of fuel gas adsorption of the adsorbing material built in the canister  65 . Then, a purge pipe  64  is piped from the canister  65  to the intake system. While the multipurpose engine  10  operates, the fuel gas is degassed using the negative pressure of the intake system, discharged from the canister  65 , and recovered to the intake system. Thereby, recycling of the canister  65  is performed. After the multipurpose engine  10  has stopped, the fuel tank  40  is warmed by the remaining heat for a while. Thus, the fuel evaporates to generate fuel gas, the internal pressure of the fuel tank  40  rises, and leakage of the fuel gas occurs. Although the leaked fuel gas is adsorbed by the adsorbing material of the canister  65 , generation of the fuel gas decreases when the multipurpose engine  10  gets cold. The amount of the adsorbing material within the canister  65  is determined to be more than the amount of adsorption calculated on the basis of the stopping time of the multipurpose engine  10 . 
         [0028]    With reference to the schematic view of  FIG. 2 , the layout of fuel gas piping which leads to the intake system from the canister  65 , and the adsorption process of fuel gas will be described. 
         [0029]    An inlet port  65   b  of the canister  65  is connected with the inside of the fuel tank  40  via the rollover valve  60  and the charge tube  61 . An outlet port  65   a  of the canister  65  is connected with a suction port  23   a  of the heat-insulating intake pipe  23  via the purge pipe  64 . A port  65   c  at the air section of the canister  65  is connected with a port  24   a  communicating with a clear section of an air cleaner  24  via a suction pipe  63 . A adsorbing material block  66  to which a porous adsorbing material is attached is built inside the canister  65 . 
         [0030]    After the multipurpose engine  10  has stopped, the fuel tank  40  is warmed by the remaining heat for a while. Thus, the fuel evaporates to generate fuel gas, the internal pressure of the fuel tank  40  rises, and leakage of the fuel gas occurs. The leaked fuel gas enters the canister  65  through the charge tube  61  (see an arrow A in the drawing), and is adsorbed by the adsorbing material of the adsorbing material block  66 . 
         [0031]    When the multipurpose engine  10  operates, negative pressure is generated in the intake system. The negative pressure increases toward the suction port of the multipurpose engine  10 . By the negative pressure inside the heat-insulating intake pipe  23  where the largest negative pressure is generated, the air at the clear section of the air cleaner  24  is sucked into the canister  65  through the suction pipe  63  (refer to an arrow B in the drawing). The fuel gas adsorbed by the adsorbing material block  66  is degassed by the sucked air (see the arrow C in a drawing). The degassed fuel is sucked into the heat-insulating intake pipe  23  through the purge pipe  64 . Thereby, the fuel gas is recovered, and the canister  65  is recycled. In addition, although negative pressure is also applied to the fuel tank  40  by the negative pressure of the heat-insulating intake pipe  23 , evaporation of the fuel by the negative pressure is slight, scarcely has an effect on an adsorption action of the adsorbing material block  66 , and is effective in eliminating fuel gas leakage. 
       Second Embodiment 
       [0032]      FIG. 3  is a schematic view showing a fuel gas piping system around a canister to be attached to the engine of  FIG. 1  related to the present embodiment. Since all portions other than the fuel gas piping system around the canister shown in  FIG. 3  are the same as those of the first embodiment, duplicate description is omitted. In the following, with reference to the schematic view of  FIG. 3 , the layout of fuel gas piping which leads to the intake system from a canister  70 , and the adsorption process of fuel gas will be described. 
         [0033]    An inlet port  70   b  of the canister  70  is connected with the inside of the fuel tank  40  via the rollover valve  60  and the charge tube  61 . An outlet port  70   a  of the canister  70  is connected with a port  24   a  communicating with a clear section of the air cleaner  24  via a purge pipe  71 . The suction port  23   a  of the heat-insulating intake pipe  23  is tightly blocked by a plug  28 . A port  67  at the air section of the canister  70  is opened to the ambient air. A adsorbing material block  66  to which a porous adsorbing material is attached is built inside the canister  70 . In addition, a filter element  68  is built at the intake section of the adsorbing material block  66 . 
         [0034]    After the multipurpose engine  10  has stopped, the fuel tank  40  is warmed by the remaining heat for a while. Thus, the fuel evaporates to generate fuel gas, the internal pressure of the fuel tank  40  rises, and leakage of the fuel gas occurs. The leaked fuel gas enters the canister  70  through the charge tube  61 , and is adsorbed by the adsorbing material of the adsorbing material block  66 . 
         [0035]    When the multipurpose engine  10  operates, negative pressure is generated in the intake system. Ambient air is sucked into the canister  70  through the port  67  by the negative pressure at the clear section of the air cleaner  24 . The ambient air sucked into the canister  70  is purified while passing through the filter element  68 . The fuel gas adsorbed by the adsorbing material block  66  is degassed by the purified ambient air. The degassed fuel gas is sucked into the air cleaner  24  through the purge pipe  71 . Thereby, the fuel gas is recovered, and the canister  70  is recycled. In addition, although slight negative pressure is also applied to the fuel tank  40  by the negative pressure of the air cleaner  24 , evaporation of the fuel by the negative pressure is slight, scarcely has an effect on an adsorption action of the adsorbing material block  66 , and is effective in eliminating fuel gas leakage. 
       Third Embodiment 
       [0036]    The present embodiment does not have a cylindrical adsorbing material block structure called a canister. Unlike the first and second embodiments, the adsorbing material block is directly housed in the intake system of an engine to perform adsorption, storage, or recovery of a fuel gas. Since all structures other than the above structure are the same as that of the first embodiment, the description of portions excluding different portions is omitted. In the following, with reference to  FIG. 4 , the adsorbing material block of the present embodiment to be attached to an engine and its surrounding structure will be described. 
         [0037]    As shown in  FIG. 4 , an adsorbing material block  126  is housed in a space at a clear section of the air cleaner  124 . The adsorbing material block  126  is arranged so as to avoid a passage for the clean air which has passed through a filter element  125  of the air cleaner  124  such that the passage does not become narrow. A charge tube  61  which leads to the fuel tank  40  from the outside is directly connected with the adsorbing material block  126 . 
         [0038]    After the multipurpose engine  10  has stopped, the fuel tank  40  is warmed by remaining heat for a while. Thus, the fuel evaporates to generate fuel gas, the internal pressure of the fuel tank  40  rises, and leakage of the fuel gas occurs. The leaked fuel gas passes through the charge tube  61 , and is adsorbed by the adsorbing material of the adsorbing material block  126  built in the air cleaner  124 . 
         [0039]    When the multipurpose engine  10  operates, negative pressure is generated in the intake system. The fuel gas adsorbed by the adsorbing material block  126  is degassed by the negative pressure at the clear section of the air cleaner  124 . Thereby, the fuel gas is recovered, and the adsorbing material block  126  is recycled. In addition, although slight negative pressure is also applied to the fuel tank  40  by the negative pressure of the air cleaner  124 , evaporation of the fuel by the negative pressure is slight, and an adsorption action of the adsorbing material block  126  is effective in eliminating fuel gas leakage. 
       Fourth Embodiment 
       [0040]    The present embodiment does not have a cylindrical adsorbing material block structure called a canister similarly to the above third embodiment, and the adsorbing material block is directly housed in the intake system of an engine to perform adsorption, storage, or recovery of fuel gas. Since all structures other than the above structure are the same as that of the first embodiment, the description of portions excluding different portions is omitted. In the following, with reference to  FIG. 5 , the adsorbing material block of the present embodiment to be attached to an engine and its surrounding structure will be described. 
         [0041]    As shown in  FIG. 5 , an overhang chamber is provided at a side of the connecting suction pipe  72  which connects the air cleaner  124  with the carburetor  22 . This overhang chamber is arranged so as to avoid a passage for the clean air which has passed through the filter element  125  of the air cleaner  124  such that the passage does not become narrow. An adsorbing material block  127  is housed in this overhang chamber. A charge tube  61  which leads to the fuel tank  40  from the outside is directly connected with the adsorbing material block  127 . 
         [0042]    After the multipurpose engine  10  has stopped, the fuel tank  40  is warmed by the remaining heat for a while. Thus, the fuel evaporates to generate fuel gas, the internal pressure of the fuel tank  40  rises, and leakage of the fuel gas occurs. The leaked fuel gas passes through the charge tube  61 , and is adsorbed by the adsorbing material of the adsorbing material block  127  built in the connecting suction pipe  72 . 
         [0043]    When the multipurpose engine  10  operates, negative pressure is generated in the intake system. The fuel gas adsorbed by the adsorbing material block  127  of the connecting suction pipe  72  is degassed by the negative pressure. Thereby, the fuel gas is recovered, and the adsorbing material block  127  is recycled. In addition, although slight negative pressure is also applied to the fuel tank  40  by the negative pressure of the intake system, evaporation of the fuel by the negative pressure is slight, and an adsorption action of the adsorbing material block  127  is effective in eliminating fuel gas leakage. 
         [0044]    While preferred embodiments of the invention have been described and illustrated above, it should be understood that these are exemplary of the invention and are not to be considered as limiting. Additions, omissions, substitutions, and other modifications can be made without departing from the spirit or scope of the present invention. Accordingly, the invention is not to be considered as being limited by the foregoing description, and is only limited by the scope of the appended claims.