Patent Publication Number: US-9416718-B2

Title: Engine equipped with secondary air supply device

Description:
FIELD OF THE INVENTION 
     The present invention relates to engines equipped with a secondary air supply device that connects an exhaust port of the engine to an exhaust muffler via an exhaust pipe and supplies air (secondary air) to the exhaust pipe. 
     BACKGROUND OF THE INVENTION 
     Among examples of the conventionally-known engines equipped with a secondary air supply device are ones in which an exhaust pipe is provided for directing exhaust gas to an exhaust muffler and in which a secondary air introduction pipe is provided in communication with the exhaust pipe so that air (secondary air) is introduced into the exhaust muffler via the secondary air introduction pipe using exhaust pulsation of the engine. By air being introduced into the exhaust muffler via the secondary air introduction pipe like this, an oxidation-reduction reaction (detoxifying reaction) can be caused in exhaust gas by means of a catalyst (catalytic) converter provided within the exhaust muffler. 
     Further, as a means for efficiently directing air into the exhaust muffler via the secondary air introduction pipe in such engines, it is required that a tailpipe connected to the exhaust muffler be set to a suitable length. By the tailpipe being set to a suitable length like this, it is possible to achieve a sufficient pulsation effect of the engine and thereby efficiently direct air into the exhaust muffler via the secondary air introduction pipe. Exhaust gas within the exhaust muffler is discharged to the outside through the tailpipe. 
     Further, one example of such engines equipped with a secondary air supply device is disclosed in Japanese Patent No. 2604659 (hereinafter referred to as “JP &#39;659”), in which respective upper portions of a crankcase and a cylinder are positioned at generally the same height, a fuel tank is provided over a crankcase and an exhaust muffler is provided over a cylinder. With the exhaust muffler provided over the cylinder, the exhaust muffler is located at a high position so that a sufficient space is secured beneath the exhaust muffler. The tailpipe is provided to extend downward using the space, so that a suitable length of the tailpipe can be secured. 
     The engine equipped with a secondary air supply device disclosed in JP &#39;659 is used, for example, in a power generator. In the case where such an engine is used in a power generator, the engine tends to be driven for a long time, and thus, it is necessary to secure a large storage capacity of the fuel tank. Therefore, in the case where the engine of a small size is used in a power generator, it is conceivable to secure a large storage capacity of the fuel tank by providing the fuel tank over both of the crankcase and the cylinder. 
     With the fuel tank provided over both of the crankcase and the cylinder as noted above, however, it is difficult to provide the exhaust muffler over the cylinder. To avoid such a difficulty, it is conceivable to provide the exhaust muffler laterally of the cylinder. In the case where the exhaust muffler is disposed laterally of the cylinder, the exhaust muffler is located at a low position. Therefore, it is difficult to secure a space sufficient to allow the tailpipe to extend beneath the exhaust muffler, so that the tailpipe cannot extend downward so as to have a sufficient length. 
     SUMMARY OF THE INVENTION 
     In view of the foregoing problems, it is an object of the present invention to provide an improved engine equipped with a secondary air supply device which can secure a sufficient length of the tailpipe without extending the tailpipe in a downward direction. 
     In order to accomplish the above-mentioned object, the present invention provides an improved engine equipped with a secondary air supply device where an exhaust port for discharging exhaust gas of the engine to outside is formed in a cylinder head, which comprises: a fuel tank disposed over the cylinder head for storing fuel of the engine; an exhaust muffler disposed beneath the fuel tank and below the exhaust port in a region lateral of the cylinder head; an exhaust pipe connecting the exhaust port to the exhaust muffler; a secondary air introduction pipe connected to the exhaust pipe for introducing air into the exhaust muffler; and a tailpipe for discharging exhaust gas of the exhaust muffler to the outside, the exhaust muffler and the fuel tank defining therebetween a space, the tailpipe being disposed to meander in the space. 
     According to the present invention, the exhaust muffler is disposed beneath the fuel tank, and the space is defined between the exhaust muffler and the fuel tank. Further, the tailpipe, through which exhaust gas of the exhaust muffler is discharged to the outside, is disposed in a meandering configuration in the space. The tailpipe disposed in such a meandering configuration in the space can have a suitable length in the limited space without extending downward. 
     In a preferred implementation, the exhaust pipe is connected to the exhaust port by means of a fastener member, and the tailpipe meanders in the space in such a manner as to avoid an imaginary extension line of the fastener member. 
     In the case where the exhaust muffler is disposed beneath the fuel tank and below the exhaust port in a region lateral of the cylinder head and where the exhaust pipe is connected to the exhaust port by means of the fastener member as noted above, the fastener member is located in the space between the exhaust muffler and the fuel tank. Thus, sometimes, it is likely that the tailpipe disposed in the space is located on the imaginary extension line of the fastener member. If the tailpipe is located on the imaginary extension line of the fastener member, operations for attaching and detaching the fastener member might be undesirably disturbed by the existence of the tailpipe, and the tailpipe might interfere with the fastener member. To avoid such an inconvenience, the tailpipe in the preferred implementation of the present invention is meandered in such a manner as to avoid the imaginary extension line of the fastener member. Thus, the operations for attaching and detaching the fastener member can be performed without being disturbed by the existence of the tailpipe. Further, the tailpipe disposed in such a manner as to avoid the imaginary extension line of the fastener member can be prevented from interfering with (hitting) the fastener member, which can secure an enhanced durability of the tailpipe. 
     The following will describe embodiments of the present invention, but it should be appreciated that the present invention is not limited to the described embodiments and various modifications of the invention are possible without departing from the basic principles. The scope of the present invention is therefore to be determined solely by the appended claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Certain preferred embodiments 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 front view showing a power generator employing an embodiment of an engine equipped with a secondary air supply device of the present invention; 
         FIG. 2  is a view taken in the direction of arrow  2  of  FIG. 1 ; 
         FIG. 3  is a perspective view showing an exhaust means provided in the engine and the secondary air supply device of  FIG. 1 ; 
         FIG. 4  is an exploded perspective view corresponding to  FIG. 3 ; 
         FIG. 5  is an enlarged view of a section surrounded at  5  in  FIG. 1 ; 
         FIG. 6  is a perspective view showing the secondary air supply device of  FIG. 3 ; 
         FIG. 7  is an exploded perspective view of the secondary air supply device of  FIG. 6 ; 
         FIG. 8  is a perspective view of the secondary air supply device of  FIG. 6  taken from the side of a filter cover; 
         FIG. 9  is an exploded perspective view of the filter cover and an intake nozzle of  FIG. 7 ; and 
         FIGS. 10A and 10B  are views illustrative of how exhaust gas is oxidized or reduced by the embodiment of the engine equipped with the secondary air supply device, dust, dirt etc. are prevented from entering the intake nozzle and fuel is prevented from adhering to the intake nozzle. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  is a front view showing a power generator  10  employing an embodiment of an engine  12  equipped with a secondary air supply device  26  of the present invention. For ease of understanding of a construction of the embodiment, let it be assumed that, in  FIG. 1 , directions toward and away from a reader of the figure are “forward” and “rearward”, respectively, and left and right sides of the figure are “one side” and “other side”, respectively. 
     As shown in  FIG. 1 , the power generator  10  includes the engine  12  equipped with the secondary air supply device  26 , a power generation section  14  provided integrally on the engine  12 , a fuel tank  16  for storing fuel to be supplied to the engine  12 , and a frame  18  supporting the power generator  10 . 
     The power generation section  14  is provided on one side portion (left side portion in  FIG. 1 )  31   a  of the engine  12  (more specifically, one side portion  31   a  of a crankcase  31 ), and the fuel tank  16  is provided over respective upper portions  12   a  and  14   a  of the engine  12  and the power generator  10 . With the fuel tank  16  provided over the engine  12  and the power generator  10  like this, a large storage capacity of the fuel tank  16  can be secured. 
     The engine  12  is a power-generating general-purpose internal combustion engine which includes: an engine body  21 ; a cooling fan  22  provided integrally on the engine body  21 ; a carburetor  23  provided in communication with an intake port of the engine body  21 ; an air cleaner  24  provided in communication with the carburetor  23 ; an exhaust means  25  provided in an exhaust port  42  ( FIG. 2 ) of the engine body  21 ; and the secondary air supply device (AI: Air Injection)  26  provided in communication with the exhaust means  25 . 
     The engine body  21  includes the crankcase  31 , a cylinder block  32  formed integrally with the crankcase  31 , a cylinder head  33  provided on the cylinder block  32 , and a head cover  34  covering the cylinder head  33 . The cylinder block  32  will hereinafter be referred to also as “cylinder”, for convenience of description. The cylinder  32  extends obliquely from the crankcase  31  so that a lower space  36  is defined beneath the cylinder  32 , and the fuel tank  16  is disposed over the cylinder head  33 . 
     The cooling fan  22  is located adjacent to respective side portions of the crankcase  31  and the cylinder head  33  by being provided on the other side portion  31   b  of the crankcase  31 . A recoil starter is connected to the cooling fan  22 , so that impellers of the cooling fan  22  rotate by a human operator pulling a handle  38  of the recoil starter and rotation of the impellers is transmitted to a crankshaft. Thus, the crankshaft rotates, so that the engine  12  is driven. By the engine  12  being driven like this, the power generation section  14  is driven. 
     The carburetor  23  is located closer to the lower space  36  than the cooling fan  22  and communicates with the intake port of the cylinder head  33 . The air cleaner  24  is provided in communication with the carburetor  23 . An inlet  24   a  of the air cleaner  24  is located beneath the carburetor  23 . 
     Air is directed through the intake  24   a  of the air cleaner  24  into the air cleaner  24 , so that fuel is vaporized by the carburetor  23  and the thus-vaporized fuel is directed to the cylinder head  33  via the intake port. 
     A discharge pipe  39  is provided in communication with a lower portion  23   a  of the carburetor  23 . Thus, the fuel directed to the carburetor  23  is discharged to the outside  61  via the discharge pipe  39  as it drops from the lower portion  23   a  of the carburetor  23 . 
     The exhaust means  25  includes an exhaust muffler  41  disposed adjacent to the one side (left side in  FIG. 1 ), an exhaust pipe  43  connecting the exhaust port  42  ( FIG. 2 ) to the exhaust muffler  41 , and a tailpipe  44  that discharges exhaust gas of the exhaust muffler  41  to the outside  61 . The exhaust port  42  is formed in the one side portion (left side portion in  FIG. 1 )  33   a  of the cylinder head  33 , so that exhaust gas within the cylinder  32  is discharged to outside of the cylinder head  33  via the exhaust port  42 . 
     Further, the power generation section  14  and the exhaust muffler  41  are disposed opposite from the carburetor  23  with the cylinder  32  and the cylinder head  33  interposed therebetween. The exhaust muffler  41  is disposed forward (in front) of the power generation section  14 . 
     Further, a partition member  46  is fixed to the engine  12  and the power generation section  14  by means of a bolt  47 . The exhaust muffler  41  is partitioned off from the fuel tank  16  via an upper wall portion  46   a  of the partition member  46 . Further, the exhaust muffler  41  is partitioned off from the engine  12  via a side wall portion  46   b  of the partition member  46 . 
     Further, as shown in  FIGS. 2 and 3 , the exhaust muffler  41  is disposed beneath the fuel tank  16  and below the exhaust port  42 . The exhaust muffler  41  has a retaining cylinder  53  accommodated in the interior  52  of the muffler box  51 , and a catalyst converter  54  retained on the inner wall of the retaining cylinder  53 . 
     A muffler box  51  is in the form of a hollow box of a rectangular parallelepiped shape. The muffler box  51  is disposed beneath the fuel tank  16  by being fixed, for example, to a boss  15  of the power generation section  14  by means of a bolt  55 . Thus, the fuel tank  16  is located above an upper muffler surface portion  51   a  of the muffler box  51 , so that an upper space  56  is defined between the upper muffler surface portion  51   a  and a lower portion  16   a  of the fuel tank  16 . 
     The retaining cylinder  53  has a front end portion  53   a  communicating with the interior of the cylinder head  33  (more specifically, a combustion chamber) via the exhaust pipe  43  and the exhaust port  42 . Further, a rear end portion  53   b  of the retaining cylinder  53  has a rear opening portion (not shown) that opens to the interior  52  of the muffler box  51 . 
     Further, as shown in  FIG. 4 , the exhaust pipe  43  has a flange  57  formed on its front end portion  43   a  and connected to the one side portion (left side portion)  33   a  of the cylinder head  33  by means of a bolt  58  and a nut  59  (see also  FIG. 2 ). Thus, the front end portion  53   a  of the exhaust pipe  43  communicates with the exhaust port  42  of the cylinder head  33 . Also, the exhaust pipe  43  has a rear end portion  43   b  communicating with the front end portion  53   a  of the retaining cylinder  53 . 
     Thus, exhaust gas within the cylinder  32  is directed to the exhaust port  42 , the exhaust pipe  43  and to the retaining cylinder  53 . The exhaust gas thus directed to the retaining cylinder  53  is subjected to oxidation-reduction (detoxification) by the catalyst converter  54  within the retaining cylinder  53 . The exhaust gas having been thus subjected to oxidation-reduction by the catalyst converter  54  is directed through the rear opening portion of the retaining cylinder  53  to the interior  52  of the muffler box  51 . 
     The tailpipe  44  has a proximal end portion  44   a  connected to a front wall  51   b  of the muffler box  51  so that it communicates with the interior  52  of the muffler box  51 . Further, the tailpipe  44  has a distal end portion  44   b  opening to the outside  61  of the muffler box  51 . Although the tailpipe  44  comprises a plurality of interconnected pipes as shown in the figures, it will hereinafter be described as comprising a single bent pipe, for convenience of description. 
     In the illustrated example, the tailpipe  44  comprises a first pipe section  63 , a second pipe section  64 , a third pipe section  65 , a fourth pipe section  66  and a fifth pipe section  67 . The tailpipe  44  is bent so that the first to fifth pipe sections  63  to  67  are interconnected in a meandering configuration. 
     Referring back to  FIG. 2 , the first pipe section  63  is connected at the proximal end portion  44   a  to the front wall  51   b  of the muffler box  51  and extends obliquely forward and upward away from the front wall  51   b . The first pipe section  63  has a front end portion  63   a  located near the upper muffler surface portion  51   a  of the muffler box  51 . 
     The second pipe section  64  extends upward from the front end portion  63   a  of the first pipe section  63  in an arcuately curved shape. Because the front end portion  63   a  of the first pipe section  63  is located near the upper muffler surface portion  51   a  of the muffler box  51 , the second pipe section  64  is located in the upper space  56  higher than the upper muffler surface portion  51   a.    
     The third pipe section  65  extends substantially horizontally from an upper end portion  64   a  of the second pipe section  64 , toward the power generator  14  (i.e., rearward), to a rear end portion  51   c  of the upper muffler surface portion  51   a . Thus, the third pipe section  65  is located in the upper space  56  higher than the upper muffler surface portion  51   a.    
     Further, as shown in  FIG. 4 , the fourth pipe section  66  extends substantially horizontally from a rear end portion  65   a  of the third pipe section  65 , toward the cylinder head  33  (i.e., toward the one side portion), to near an end portion  51   d  of the upper muffler surface portion  51   a  (see also  FIG. 1 ). Thus, the fourth pipe section  66  is located in the upper space  56  higher than the upper muffler surface portion  51   a . Further, the fourth pipe section  66  has an end portion  66   a  located above the end portion  51   d  of the upper muffler surface portion  51   a . A first horizontally curved portion  68  is formed in an intersecting portion between the rear end portion  65   a  of the third pipe section  65  and another end portion  66   b  of the fourth pipe section  66 . 
     Further, the fifth pipe section  67  extends substantially horizontally forward from the end portion  66   a  of the fourth pipe section  66 . Thus, the fifth pipe section  67  is located in the upper space  56  higher than the upper muffler surface portion  51   a  and the exhaust pipe  43 . An outer cylinder  71  is provided around the outer periphery of the fifth pipe section  67 , and the outer cylinder  71  is supported on an upper end portion  72   a  of a support member  72 . The support member  72  is fixed at its lower end portion  72   b  to the front wall  51   b  of the muffler box  51 . 
     A distal end portion  44   b  of the fifth pipe section  67  (i.e., distal end portion of the tailpipe  44 ) projects forward beyond a front end portion  51   e  of the upper muffler surface portion  51   a . A second horizontally curved portion  69  is formed in an intersecting portion between the end portion  66   a  of the fourth pipe section  66  and a rear end portion  67   a  of the fifth pipe section  67 . 
     Here, the fifth pipe section  67  is spaced apart from the bolt  58  and the nut  59  fastening the flange  57  to the cylinder head  33 ; more specifically, the fifth pipe section  67  is located closer to the one side portion  31   a  than the bolt  58  and the nut  59 . Further, with the second to fifth pipe sections  64  to  67  located above the upper muffler surface portion  51   a , these pipe sections  64  to  67  are disposed in the upper space  56  (see  FIG. 2 ). 
     Further, as shown in  FIGS. 2 and 4 , the tailpipe  44  is formed in such a manner that the first to third pipe sections  63  to  65  meander in a generally V shape as viewed laterally from one side of the muffler  41  (i.e., as viewed in a horizontal direction). Further, the tailpipe  44  is disposed in such a manner that the third to fifth pipe sections  65  to  67  meander in the upper space  56  in a generally U shape as viewed in the vertical direction. 
     Namely, the whole of the tailpipe  44  (more specifically, the second to fifth pipe sections  64  to  67  of the tailpipe  44 ) is formed in the upper space  56  so as to meander in the horizontal and vertical direction. By meandering in the upper space  56 , the tailpipe  44  can have a suitable length in the limited upper space  56  without extending downward. 
     Further, the third to fifth pipe sections  65 ,  66  and  67  are located above and forward of an imaginary horizontal extension line  74  extending from the axis of the bolt  58  and the nut  59  while avoiding the imaginary extension line  74 . Namely, the entire tailpipe  44  is provided to meander in the space  56  while avoiding the imaginary extension line  74 . 
     The following explains in detail why the entire tailpipe  44  is provided to meander in such a manner as to avoid the imaginary extension line  74 . Namely, the exhaust muffler  41  is disposed beneath the fuel tank  16  and below the exhaust port  42  in a region lateral of the one side of the cylinder head  33 . Further, the exhaust pipe  43  is fixedly connected to the one side portion  33   a  of the cylinder head  33  by means of the bolt  58  and the nut  59 , and the exhaust pipe  43  communicates with the exhaust port  42 . Thus, the bolt  58  and the nut  59  are located in the upper space  56  between the exhaust muffler  41  and the fuel tank  16 . 
     Therefore, in some cases, it is conceivable that the tailpipe  44  disposed in the upper space  56  is located on the imaginary extension line  74  of the bolt  58  and the nut  59 , in which cases operations for attaching and detaching the bolt  58  and the nut  59  might be undesirably disturbed by the existence of the tailpipe  44 . 
     Thus, in the instant embodiment, the third to fifth pipe sections  65  to  67  of the tailpipe  44  are disposed above and forward of the imaginary extension line  74  so as to avoid the imaginary extension line  74 . In this way, the entire tailpipe  44  can be meandered in such a manner as to avoid the imaginary extension line  74 , and thus, the bolt  58  and the nut  59  can be attached and detached without being disturbed by the existence of the tailpipe  44 . 
     In addition, the tailpipe  44  (more specifically, the fifth pipe section  67 ) is spaced apart from, i.e. disposed closer to the one side portion than, the bolt  58  and the nut  59 . In this way, the tailpipe  44  can be prevented from interfering with (hitting) the bolt  58  and the nut  59  and thus can have a sufficient durability. 
     Further, the proximal end portion  44   a  of the tailpipe  44  is in communication with the interior  52  of the muffler box  51 , and the distal end portion  44   b  of the tailpipe  44  opens to the outside  61 . Thus, exhaust gas directed to the interior  52  of the muffler box  51  through the rear opening portion of the retaining cylinder  53  is discharged to the outside  61  of the muffler box  51  via the tailpipe  44 . The secondary air supply device  26  is in communication with the exhaust pipe  43  of the exhaust means  25 . 
     Further, as shown in  FIG. 5 , the secondary air supply device  26  includes: a secondary air introduction pipe  81  connected to the exhaust pipe  43  (see  FIG. 1 ); a one-directional valve  82  provided on the secondary air introduction pipe  81 ; an air filter  83  connected to the one-directional valve  82 ; an intake nozzle  84  connected to the air filter  83 ; and a partition wall  85  supporting the intake nozzle  84 . 
     Further, as shown in  FIG. 3 , the secondary air introduction pipe  81  has an outlet end portion  81   a  connected to a portion of the exhaust pipe  43  adjacent to the flange  57 . The secondary air introduction pipe  81  is meandered in the upper space  56  and extends in a downward slope from the upper space  56  to the lower space  36  (see also  FIG. 1 ), so that an inlet end portion  81   b  of the secondary air introduction pipe  81  is located in the lower space  36 . With the secondary air introduction pipe  81  meandered in the upper space  56  and extending in a downward slope from the upper space  56  to the lower space  36  as noted above, a suitable length of the secondary air introduction pipe  81  can be secured. 
     Further, as shown in  FIG. 6 , an outlet pipe  86  of the one-directional valve  82  is connected via a connection pipe  87  to the inlet end portion  81   b  of the secondary air introduction pipe  81 . The one-directional valve  82  is opened in response to pressure in the interior  52  (see  FIG. 3 ) of the muffler box  51  becoming negative due to exhaust pulsation of the engine  12 , and the one-directional valve  82  is closed in response to the pressure in the interior  52  of the muffler box  51  becoming positive due to the exhaust pulsation of the engine  12 . Thus, once the pressure in the interior  52  of the muffler box  51  becoming negative, air (secondary air) can be introduced into the secondary air introduction pipe  81  via the one-directional valve  82 . The air filter  83  is provided upstream of the one-directional valve  82 . 
     Further, as shown in  FIG. 7 , the air filter  83  includes: a filter case  93  fixed to a boss  13  of the engine  12  by means of a bolt  91 ; a filter (not shown) accommodated in the filter case  93 ; and a filter cover  95  fixed to an opening portion  93   a  of the filter case  93  by means of a bolt  94 . Air is sucked into the air filter  83  from the intake nozzle  84 . The air thus sucked into the air filter  83  is filtered through the filter and then introduced into the secondary air introduction pipe  81  via the one-directional valve  82 . 
     Further, as shown in  FIG. 8 , a filter inlet pipe  96  extends in a curved shape from a front wall  95   a  of the filter cover  95  toward an upper inlet, and an inlet port  96   a  of the filter inlet pipe  96  projects vertically upward. An outlet port  96   b  (see  FIG. 7 ) of the filter inlet pipe  96  is located within the air filter  83  opens toward the upstream end of the filter. A fitting nozzle section  84   a  of the intake nozzle  84  is fittingly connected to the inlet port  96   a  of the filter inlet pipe  96 . 
     Further, as shown in  FIG. 9 , the intake nozzle  84  includes the fitting nozzle section  84   a  extending vertically to be fitted over the inlet port  96   a  of the filter inlet pipe  96 , and an extension nozzle section  84   c  extending from an upper end portion  84   b  of the fitting nozzle section  84   a  in a direction opposite from (i.e., away from) the cooling fan  22  (see  FIG. 1 ). With the fitting nozzle section  84   a  and the extension nozzle section  84   c , the intake nozzle  84  is formed in a generally inverted-J shape. 
     The extension nozzle section  84   c  has its distal end portion  84   d  inserted in a through-hole  88  of the partition wall  85 . With the fitting nozzle section  84   a  fitted over the inlet port  96   a  of the filter inlet pipe  96  and the distal end portion  84   d  inserted in the through-hole  88  as noted above, the intake nozzle  84  is fixed to the inlet port  96   a  and the partition wall  85 . 
     Referring now back to  FIG. 5 , with the intake nozzle  84  fixed in the aforementioned manner, an opening portion  84   e  of the intake nozzle  84  opens in the opposite direction from the cooling fan  22  (see  FIG. 1 ). Further, the opening portion  84   e  of the intake nozzle  84  is located beneath the carburetor  23  and closer to the one side portion (i.e., closer to the lower space  36 ) than the carburetor  23 . 
     Further, as shown in  FIG. 3 , the intake nozzle  84  is in communication with the secondary air introduction pipe  81  via the air filter  83  and the one-directional valve  82 . Thus, air sucked in through the opening portion  84   e  of the intake nozzle  84  by the exhaust pulsation of the engine  12  is directed to the secondary air introduction pipe  81  via the intake nozzle  84 , the filter inlet pipe  96 , the air filter  83  and the one-directional valve  82 . 
     Further, the air directed to the secondary air introduction pipe  81  as noted above is directed into the retaining cylinder  53  of the exhaust muffler  41  via the secondary air introduction pipe  81  and the exhaust valve  43 . Thus, the air sucked in through the opening portion  84   e  of the intake nozzle  84  is directed to the catalyst converter  54  of the retaining cylinder  53 . 
     Further, as shown in  FIGS. 5 and 9 , the partition wall  85  projects upward from an upper portion  95   b  of the filter cover  95 , and the through-hole  88  is formed through the thickness of the partition wall  85 . Thus, the through-hole  88  is located above the filter cover  95  and an outlet  39   a  of the discharge pipe  39 . The partition wall  85  is located beneath the carburetor  23  and closer to the one side (i.e., closer to the lower space  36 ) than the carburetor  23 . With the extension nozzle section  84   c  inserted through the through-hole  88  of the partition wall  85 , the opening portion  84   e  of the intake nozzle  83  is located adjacent to a side of the partition wall  85  opposite from the carburetor  23 , i.e. the partition wall  85  is located between the opening portion  84   e  of the intake nozzle  84  and the carburetor  23 . 
     Further, with the extension nozzle section  84   c  inserted through the through-hole  88  of the partition wall  85 , the opening portion  84   e  of the intake nozzle  84  is located adjacent to a side of the partition wall  85  opposite from the carburetor  23 . Namely, the opening portion  84   e  of the intake nozzle  84  is partitioned off from the carburetor  23  by the partition wall  85 . 
     The carburetor  23  is located closer to the lower space  36  than the cooling fan  22  ( FIG. 1 ). Thus, the partition wall  85  is located between the opening portion  84   e  of the intake nozzle  84  and the cooling fan  22  with the opening portion  84   e  partitioned off from the carburetor  23  by the partition wall  85 . 
     Thus, the partition wall  85  can not only prevent cooling air of the cooling fan  22  from reaching the opening portion  84   e  but also prevent dust, dirt, rain water, etc. from entering through the opening portion  84   eel  . Further, the opening portion  84   e  opens in the opposite direction from the cooling fan  22 , so that it is possible to further reliably prevent dust, dirt, rain water, etc. from entering the intake nozzle  84  through the opening portion  84   e  due to cooling air blown from the cooling fan  22 . 
     In some cases, it is conceivable to form, in a wall portion of the air filter  83  closer to the cooling fan  22 , an intake inlet for sucking secondary air into the air filter  83 . It is also likely for fuel within the carburetor  23  to be dropped (discharged) to the outside  61  via the discharge pipe  39  of the carburetor  23 . The discharge pipe  39  is located closer to the lower space  36  than the cooling fan  22 , and the intake inlet of the air filter  83  is located closer to the lower space  36  than the discharge pipe  39 . Thus, the fuel discharged to the outside  61  via the discharge pipe  39  may undesirably adhere to the intake inlet of the air filter  83  due to cooling air blown from the cooling fan  22 . 
     To avoid such an inconvenience, the extension nozzle section  84   c  in the instant embodiment is inserted through the through-hole  88  formed above the filter cover  95  so that the opening portion  84   e  of the intake nozzle  84  is located at a position H 1  higher than the outlet  39   a  of the discharge pipe  39 . Further, the partition wall  85  is located between the opening portion  84   e  of the intake nozzle  84  and the carburetor  23 , and thus, the opening portion  84   e  of the intake nozzle  84  is partitioned off from the carburetor  23  by the partition wall  85 . 
     Thus, the partition wall  85  in the instant embodiment can prevent fuel, having been dropped or discharged from the outlet  39   a  of the discharge pipe  39 , from being directed to the opening portion  84   e  and adhering to the opening portion  84   e  due to the cooling air from the cooling fan  2 . 
     In addition, the opening portion  84   e  of the intake nozzle  84  opens in the opposite direction from the carburetor  23  (outlet  39   a  of the discharge pipe  39 ). Thus, fuel discharged from the outlet  39   a  of the discharge pipe  39  can be more reliably prevented from adhering to the opening portion  84   e  due to cooling air sent from the cooling fan  22 . 
     Further, because the opening portion  84   e  of the intake nozzle  84  is located at the high position H 1  above the filter cover  95 , it is located higher than the intake  24   a  of the air cleaner  24  communicating with the carburetor  23 . Thus, in a rainstorm, for example, a water surface will reach the intake  24   a  of the air cleaner  24  before reaching the opening portion  84   e  of the intake nozzle  84 . The engine  12  can be deactivated by the water being sucked in through the intake  24   a  of the air cleaner  24 , so that the water can be prevented from sucking in through the opening portion  84   e  of the intake nozzle  84 . 
     Further, with the intake nozzle  84  connected to the air filter  83 , the interior space of the air filter  83  can be used as a resonator, so that a silencing effect can be achieved. In addition, because the opening portion  84   e  of the intake nozzle  84  is oriented toward the lower space  36 , it is oriented toward the interior of the power generator  10 . Thus, sound noise can be effectively prevented from being leaked to the outside, so that a further silencing effect can be achieved. 
     The following describes, with reference to  FIG. 10 , an example manner in which exhaust gas is oxidized and reduced by the catalyst converter  54  and entry of dust, dirt, rainwater, etc. into the intake nozzle  84  and adherence of fuel to the intake nozzle  84  is prevented in the instant embodiment. 
     During driving of the engine  12 , as shown in  FIG. 10A , exhaust gas is discharged from the distal end portion  44   b  of the tailpipe  44  to the outside  61  through the exhaust muffler  41  and the tailpipe  44 . At the same time, air (secondary air) is sucked in through the intake nozzle  84  of the secondary air supply device  26  by use of exhaust pulsation of the engine  12 , as indicated by arrow A. The air sucked into the intake nozzle  84  is directed to the exhaust pipe  43  via the air filter  83 , the one-directional valve  82  and the secondary air introduction pipe  81 , as indicated by arrow B. 
     Further, as shown in  FIG. 10B , the air directed to the exhaust pipe  43  is directed through the exhaust pipe  43  to the retaining cylinder  53  together with exhaust gas directed to the exhaust pipe  43 , as indicated by arrow C. 
     Further, in the instant embodiment, it is possible to secure suitable lengths of the tailpipe  44  of the exhaust muffler  41  and the secondary air introduction pipe  81 . Thus, by the negative pressure produced by the exhaust pulsation of the engine  12 , the air (secondary air) can be reliably supplied to the retaining cylinder  53  (i.e., to the catalyst converter  54 ). 
     Thus, the catalyst converter  54  is activated so that exhaust gas directed to the retaining cylinder  53  can be effectively oxidized or reduced (i.e., detoxified). The exhaust gas oxidized or reduced by the catalyst converter  54  is directed from the rear opening portion of the retaining cylinder  53  to the interior  52  of the muffler box  51  as indicated by arrow D. The exhaust gas thus directed to the interior  52  of the muffler box  51  is directed through the tailpipe  44  and discharged from the distal end portion  44   b  to the outside  61  as indicated by arrow E. 
     Referring now back to  FIG. 10A , the cooling fan  22  rotates during driving of the engine  12 , so that cooling air is sent or blown from the cooling fan  22  toward the engine body  21  as indicated by arrow F. The cooling air thus blown from cooling fan  22  is directed toward the exhaust muffler  41  by way of the lower space  36  as indicated by arrow G. 
     Because the opening portion  84   a  of the intake nozzle  84  is oriented in the opposite direction from the cooling fan  22  and is partitioned off from the carburetor  23  by the partition wall  85 , cooling air from the cooling fan  22  can be prevented from reaching the opening portion  84   a . Thus, it is possible to reliably prevent dust, dirt, rain water, etc. from entering through the opening portion  84   e  due to cooling air of the cooling fan  22 . 
     Further, the opening portion  84   a  of the intake nozzle  84  is located above the outlet  39   a  of the discharge pipe  39 . In addition, the opening portion  84   a  of the intake nozzle  84  is oriented in the opposite direction from the carburetor  23  and partitioned off from the carburetor  23  by the partition wall  85 . Thus, fuel having dropped from the outlet  39   a  of the discharge pipe  39  can be prevented by the partition wall  85  from being directed to the opening portion  84   e  due to cooling air from the cooling fan  22 . Thus, the fuel having dropped from the carburetor  23  can be prevented from adhering to the opening portion  84   e  of the intake nozzle  84 . 
     It should be appreciated that the engine  12  equipped with secondary air supply device  26  of the present invention is not limited to the above-described embodiment and may be modified variously. For example, whereas the embodiment has been described above in relation to the case where the bolt  58  and the nut  59  are used as fastener members, the bolt  58  and the nut  59  may be replaced with a rivet or any other suitable fastener member. 
     Further, the shapes and constructions of the power generator  10 , engine  12 , fuel tank  16 , secondary air supply device  26 , cylinder  32 , cylinder head  33 , exhaust muffler  41 , exhaust port  42 , exhaust pipe  43 , tailpipe  44 , bolt  58 , nut  59 , secondary air introduction pipe  81 , etc. are not limited to the ones illustratively shown and described above and may be modified as necessary. 
     The basic principles of the present invention are well suited for application to engines equipped with a secondary air supply device that connects an exhaust port of the engine to an exhaust muffler via an exhaust pipe and supplies air (secondary air) to the exhaust pipe.