Abstract:
An air intake muffler has an enclosure having a longitudinal axis, a first portion, and a second portion defining with the first portion an interior space of the enclosure. An air intake connecting duct is formed unitarily with the first portion of the enclosure and extends outwardly from the interior space of the enclosure. A pair of outside air intake ducts for introducting outside air into the interior space of the enclosure diverge in a V-shaped configuration from the longitudinal axis of the enclosure. Each of the outside air intake ducts has a pair of mating concave portions each formed unitarily with a respective one of the first and second portions of the enclosure and extending outwardly from the interior space of the enclosure.

Description:
FIELD OF THE INVENTION 
     The present invention relates generally to an air intake muffler (silencer) for an engine and, more particularly, to an air intake muffler for a vertical multi-cylinder engine for use in an outboard engine assembly. 
     BACKGROUND OF THE INVENTION 
     An air intake muffler (silencer) of this kind is disclosed in, for example, Japanese Patent Laid-Open Publication No. HEI-8-93433. The air intake muffler has an overall box shape which is composed of a flat base plate, a plurality of air horns mounted on the base plate so as to protrude toward the inside of the box, and a case covering the base plate. The base plate and the case are joined to one another in a unitary structure to form the box shape. The air horns form air intake connecting passages which communicate with a throttle of the engine. Since outermost surfaces of the air horns are flat, a difficulty is encountered in connecting a terminal end portion of the air intake passage or path of the throttle valve unit to the air horns and in sealing the joint portions, with a resultant difficulty in ensuring a sealing property in high precision. 
     Further, since the air horns are so arranged as to protrude in an internal space of the air intake muffler to allow the same to be connected to the air intake passage of the throttle valve unit in an easy and reliable manner, although it is thinkable to provide fitting-type joint portions to the outermost surfaces of the air horns, the base plate of the air intake muffler becomes complicated in structure causing intricate and troublesome manufacturing processes. 
     Furthermore, although there is a need for locating an outside air intake opening, in addition to the air intake connecting passage, in the air intake muffler and the prior art practice contemplates the provision of apertures in the box-shaped air intake muffler, the use of the apertures encounter a problem in view of an air intake efficiency. As a consequence, it is preferable for a cylindrical member to be incorporated in order to obtain a tube-length effect (wherein induction noise, generated by vibration of air caused during air sucking, is substantially determined by the dimension of the intake pipe), with a resultant increase in the number of component parts causing the need for providing a sealing structure between the cylindrical member and the air intake muffler, resulting in an additional increase in the number of component parts, a complicated structure and an increased cost. 
     In the outboard engine assembly, further, since the air intake muffler is mounted to one of areas in fore and aft directions of the vertical type engine with a vertical crankshaft, the outboard engine assembly involving the engine is largely sized in structure in fore and aft directions. 
     SUMMARY OF THE INVENTION 
     It is therefore an object of the present invention to provide an air intake muffler which is unitarily formed with a cylindrical outside air intake opening having a cylindrical joint opening, to be connected to a throttle valve unit, and a tube-length effect without requiring additional component parts in manufacturing stages of a box-shaped muffler body. 
     According to a first aspect of the present invention, there is provided an air intake muffler for introducing outside air to feed the same to an air intake passage of a throttle valve unit of an engine, which muffler comprises a box body, an air intake connecting duct adapted to be connected to the air intake passage, and at least one outside air intake duct for introducing the outside air into the box body, wherein the box body includes two halves by one of which the air intake connecting duct is unitarily formed so as to protrude outwardly, and the outside air intake duct is formed by mating concave portions to one another which are unitarily formed with both of the two halves so as to protrude outwardly. 
     The box-shaped air intake muffler body is able to be unitarily formed with the air intake connecting duct, to be connected to the throttle valve unit, and the outside air intake duct without the need for additional component parts except for the upper and lower halves in stages of manufacture of the air intake muffler body by allowing dish-shaped two halves to be mated to and jointed to one another. As a consequence, manufacture can be easily performed without need for additional component parts, with a resultant decrease in the number of component parts while cutting costs. 
     Further, the body of the air intake muffler is formed into dish-shaped two halves, one of which is unitarily formed with the air intake connecting duct and the other one of which is unitarily formed with the concave portion which forms a remaining half of the outside air intake duct. Accordingly, during manufacture of the air intake muffler, merely jointing the halves to one another by means of adhesion or screw tightening, etc, enables the air intake muffler, having the air intake connecting duct and the outside air intake duct, to be easily manufactured. 
     Furthermore, since the air intake connecting duct and the outside air intake duct are unitarily formed with the body of the air intake muffler, there is no need for the muffler body, and the air intake connecting duct and the outside air intake duct to be sealed off. 
     The outside air intake duct of the air intake muffler includes, for example according to examples of the preferred embodiments, two components, with these two outside air intake duct components being formed in a V-shaped configuration so as to diverge rearwardly. Thus, the presence of two outside air intake ducts whereas a single air intake connecting duct to be connected to the throttle valve unit is provided improves air intake efficiency with favorable reduction in induction noises. 
     The two halves are composed of upper and lower half components, and the air intake connecting duct and the outside air intake duct are located in a horizontal direction. Thus, the presence of the air intake connecting duct and the outside air intake duct extending in the horizontal direction enables the height of the air intake muffler to be limited to a minimum value to allow, for example, the use of the air intake muffler for the outboard engine assembly for thereby making it possible to miniaturize the outboard engine assembly. 
     One of the two halves of the air intake muffler is formed with a retaining frame at a position wherein the air intake connecting duct is formed to allow a peripheral edge of a flame arrester, which is composed of a mesh member, to be inserted in the retaining frame such that the flame arrester is mounted in the retaining frame. During the course of mating and jointing the two halves to one another, it is possible for the air intake muffler to be easily manufactured under a condition wherein the mesh member, which forms the flame arrester mounted to the retaining frame formed in one of the halves, is internally incorporated. The flame arrester is mounted in the retaining frame in a plane perpendicular to an axis of the air intake connecting duct. 
     According to a second aspect of the present invention, there is provided an outboard engine assembly which comprises an engine, and an air intake muffler located above the engine and including an air intake connecting duct connected to an air intake passage of a throttle valve unit of the engine, and at least one outside air intake duct for introducing outside air. 
     In the thus arranged outboard engine assembly, presence of the air intake muffler located above the engine allows an upper surface of the engine to be effectively utilized. According to the preferred embodiments, for example, the engine comprises a V-type multi-cylinder vertical engine wherein the air intake muffler having a substantially flat bottom wall is placed above a drive pulley, driven by a crankshaft of the engine, and a belt engaging the drive pulley. That is, since the air intake muffler is located above the belt, etc. which is positioned above the engine, the belt and the engine are opened at their side areas to provide an improved heat dissipating property of the belt and the engine. 
    
    
     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 perspective view of an air intake muffler according to a first embodiment of the present invention; 
     FIG. 2 is an exploded perspective view of the air intake muffler shown in FIG. 1; 
     FIG. 3 is a plan view of a lower half of the air intake muffler shown in FIG. 2; 
     FIG. 4 is a plan view of the air intake muffler shown in FIG. 1; 
     FIG. 5 is a front view of the air intake muffler shown in FIG. 1; 
     FIG. 6 is a cross sectional view taken on line  6 — 6  of FIG. 4; 
     FIG. 7 is an enlarged cross sectional view illustrating a retaining structure of a mesh member shown in FIG. 6 in detail; 
     FIG. 8 is a cross sectional view taken long a line  7 — 7  of FIG. 7; 
     FIG. 9 is a plan view illustrating a modified form of the air intake muffler; 
     FIG. 10 is a front view of the air intake muffler shown in FIG. 9; 
     FIG. 11 is a front view illustrating another example of the mesh member shown in FIG. 9; 
     FIG. 12 is a cross sectional view taken on line  12 — 12  of FIG. 11; 
     FIG. 13 is a side view of an outboard engine assembly; 
     FIG. 14 is an enlarged view of the outboard engine assembly shown in FIG. 13 with an upper part thereof cut away; 
     FIG. 15 is a plan view of an engine with an upper part of an engine cover of the outboard engine assembly cut away; 
     FIG. 16 illustrates an upper area of the engine with the air intake muffler and an intake system of FIG. 15 removed; 
     FIG. 17 is an enlarged longitudinal cross sectional view illustrating a relationship among the air intake muffler, a throttle valve unit and the engine; 
     FIG. 18 is a rear view of an essential part of the engine involving an intake manifold; 
     FIG. 19 is a perspective view of an air intake muffler according to a second embodiment of the present invention; and 
     FIG. 20 is a front view of the air intake muffler shown in FIG.  19 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     An air intake muffler  1  shown in FIG. 1 is used as an air intake muffler of an engine of an outboard engine assembly as shown in FIG.  14  and is located above a V-type multi-cylinder vertical engine with its crankshaft extending in a vertical direction. A body  2  of the air intake muffler  1  has a flat thin type box-shaped configuration and includes upper and lower halves  3 ,  4 . 
     The muffler body  2  has two outside air intake ducts  5 ,  5  for introducing outside air, and an air intake connecting duct  6  for delivering outside air, which is introduced, into the engine. The two outside air intake ducts  5 ,  5  extend rearward from both rear portions of the body  2  in a V-shape spreading direction. The air intake connecting duct  6  is formed at an intermediate portion of a lengthwise rear area of the body  2  so as to open rearwardly (in a direction opposed to a direction in which the outboard engine assembly is propelled). 
     The lower half  4  has a cover section  7  which protrudes forward from a front area of the upper half  3 . The lower half  4  has four mount stays  8  as shown in FIG.  3 . Each of the stays  8  has a mount bore. 
     FIG. 2 shows the intake air muffler in an exploded state of the upper and lower halves  3 ,  4 . 
     The lower half  4  has an outer periphery surrounded with an upright wall  4   a  to form a dish-shaped configuration. An intermediate area of a rear wall  4   b  which forms a part of the upright wall  4   a  is formed with the air intake connecting duct  6  which has a cylindrical structure formed in an oblong configuration with a lateral longitudinal axis lying in a horizontal plane. An intake air passage of the air intake connecting duct  6  communicates with the inside of the lower half . As shown in FIG. 6, the air intake connecting duct  6  has an upstream opening  6   b  formed in the rear wall  4   b,  and a downstream opening  6   c  whose rear distal end is opened. 
     Further, the rear wall  4   b  of the lower half  4  is formed with two gutter-shaped concave portions  4   c,    4   c.  The concave portions  4   c,    4   c  form gutter portions. The concave portions  4   c,    4   c  are formed at boundary areas between both sides of the rear wall  4   b  and right and left side walls  4   f,    4   f  to allow the inside and the outside of the dish-shaped lower half  4  to communicates with one another. 
     A front half of a bottom portion  4   d  of the lower half  4  is formed with an embossed portion  9  which is embossed upward in a semicircular configuration, as viewed in a plane, with a front area of the embossed portion  9  facing a laterally extending front wall  4   e  which is contiguous with the right and left side walls  4   f,    4   f.    
     The upper half  3  has a symmetrical shape with the lower half  4  to have a suspended wall  3   a  which suspends from a periphery of a ceiling portion  3   d  to surround the same and is formed in a reversed dish-shaped configuration. Both sides of a rear wall  3   b  the suspended wall  3   a  are formed with concave portions  3   c,    3   c  composed of downwardly facing gutter-shaped portions, which are reversed in structure, so as to meet with the associated concave portions  4   c,    4   c  of the lower half  4 . The concave portions  3   c ,  3   c  are formed at boundary areas between right and left ends of the rear wall  3   b  and right and left ends of the side walls  3   f  so as to protrude rearward. The bottom portion  4   d  of the lower half  4  is formed with four drain ports  4   h  as shown in the drawing. The drain ports  4   h  serve to drain water entering with outside air through the outside air intake ducts  5 ,  5 . Further, as shown in FIG. 3, a water entry block plate  16  is formed at an upstream side of the air intake connecting duct  6  to preclude water, which has entered from the outside air intake ducts  5 ,  5 , from being delivered to the air intake connecting duct  6 . The water entry block plate  16  functions as a dam. 
     The upper and lower halves  3 ,  4  are mated to and joined to one another to form a unitary structure. For example, a lower edge portion  3   g  of the suspended wall  3   a  of the upper half  3  is brought into abutting engagement with an upper edge portion  4   g  of the upright wall  4   a  of the lower half  4  via a seal member  2   a  and is adhered thereto by an adhesive. In place of the adhesive, the mated portions may be deposited to one another by vibrating deposition or may be fixed to one another by bolts if desired. The lower half  4  has a strut  17 . The presence of the strut  17  allows the upper and lower halves  3 ,  4  to resist the pressure exerted in a vertical direction and has a structure which prevents deformation while reducing vibrations and noises caused during air intake. Mating and jointing the upper and lower halves  3 ,  4  to one another allows the concave portions  3   c,    3   c  formed in the upper half  3  and the concave portions  4   c,    4   c  formed in the lower half  4  to be overlapped with one another, forming the air intake ducts  5 ,  5  as shown in FIG.  1 . 
     When mating and jointing the upper and lower halves  3 ,  4  with each another, a mesh member  10  serving as a frame arrestor is interposed. 
     As shown in FIGS. 2 and 3, a retaining frame  11 , which has a concave type structure, as viewed in a plane, composed of three frame components such as lower frame component and both sidewise frame components, is located at an area inside the rear wall  4   b  of the lower half  4  and upstream of the air intake connecting duct  5 . A continuous engaging recess  11   a  is formed inside the three frame components of the retaining frame  11 . The mesh member  10  is formed of metal, for example, stainless steel wires, and has a rectangular plate configuration with a lateral longitudinal axis lying in the horizontal plane in the illustrated preferred embodiment. The mesh member  10  is inserted downward from the above in the engaging recess  11   a  of the retaining frame  11  along with the right and left side edge portions  10   a,    10   a  and a lower edge portion  10   b.  And, an oblong cap-shaped press member  12  is put on an upper edge  10   c  of the mesh member  10  to fixedly secure the mesh member  10  to the retaining frame  11  in place. 
     As shown in FIGS. 4 to  6 , a front half portion of an intermediate section, in width wise direction, of the bottom portion of the lower half of the muffler body  2  is formed with the embossed portion  9  shaped in a semicircular configuration, as viewed in a plane, which upwardly extends from the bottom portion  4   d  as previously described above. The front portion of the lower half  4  has a cover portion  7  which extends forward in a unitary structure. 
     The ceiling  9   a  of the embossed portion  9  and a ceiling  7   a  of the cover portion  7  are contiguous in the same plane. A central portion of the ceiling  9   a  of the embossed portion  9  is formed with a protruding portion  9   b  which extends upward. A front portion of the ceiling  7   a  of the cover portion  7  is formed with a ventilation opening  7   b.    
     When mounting the air intake muffler  1  to the upper area of the engine, the embossed portion  9  and the cover portion  7  serve to avoid interference with the belt with respect to a height thereof. Thus, a need for miniaturization of an overall structure of an engine room is satisfied. Further, the presence of the air intake muffler  1  located above the belt allows a belt cover to be dispensed with. 
     The muffler body  2  internally defines an air intake muffler chamber  13 . The air intake muffler chamber  13  communicates with the air intake passage of a throttle valve unit via the air intake connecting duct  6  and also communicates with the outside via the outside air intake ducts  5 ,  5 . 
     Referring now to FIGS. 7 and 8 which illustrate the mount structure of the mesh member  10  in detail, the retaining fame  11  of the mesh member  10  is located in the vicinity of the upstream opening  6   b  so as to surround the right and left and lower areas of the upstream opening  6   b  formed at the rear wall  4   b  of the lower half  4 , with the upper area being open to form the concave configuration as viewed in FIG.  7 . The engaging recess  11   a,  through which the mesh member  10  is inserted, is formed inside the retaining frame  11 . The both side frame components of the retaining frame  11  of the concave configuration are slanted so as to spread in an upward direction. Thus, if the spread area of the upper side is wider than that of the bottom side, it becomes easy for the mesh member  10  to be inserted in the retaining frame  11 . 
     After the mesh member  10  is inserted such that the right and left side edge portions  10   a,    10   a  of the mesh member  10  engage the engaging recess  11   a  of the retaining frame  11 , the press member  12  is put on the upper edge portion  10   c  of the mesh member to retain the mesh member  10  in place. The right and left slide edge portions  10   a,    10   a  of the mesh member  10  are shaped in a downwardly narrowed profile so as to cope with the shape of the retaining frame  11 . This results in a protection of looseness, along with the inclination of the retaining frame  11 , that would occur after the mesh member  10  has been mounted. 
     Thus the mesh member  10 , which forms the flame arrester is assembled in the course of overlapping the upper and lower halves  3 ,  4  to one another. 
     FIGS. 9 and 10 show a modified form of the air intake muffler of the first preferred embodiment according to the present invention. 
     In the modified form, when jointing the upper and lower halves  3 ,  4  to one another to form the unitary structure, the edge portions  3   g,    4   g,  which form the joint portions of the upper and lower halves  3 ,  4 , are formed at pluralities of locations formed with boss portions  14  through which screws  15  are inserted and are tightened to allow the edge portion  3   g  of the upper half  3  and the edge portion  4   g  of the lower half  4  to be joined to one another. Thus, in addition to the adhesion and deposition technologies, or in place thereof, the upper and lower halves  3 ,  4  may be joined together by screws into the unitary structure. During such operation, the presence of the screws  15  arranged to be tightened in the same direction provides an improved workability and the presence of an arbitrary one of the screws  15  arranged to be tightened in a direction different from those of the other screws enables an assembling sequence to be standardized. 
     FIGS. 11 and 12 show a mesh member of another preferred embodiment. The mesh member  110  of this preferred embodiment includes a mesh body  110   a  which is made of stainless steel wires which are woven to expand at a central area. A peripheral portion of the mesh body  110   a  is retained with a frame member  110   b.  The mesh member  110  of this preferred embodiment also has a shape wherein right and left side edge portions are downwardly narrowed as that of the preferred embodiment described above, thereby precluding looseness, along with the inclination of the retaining frame  11 , that would occur after the mesh member  110  has been mounted. 
     Now, an outboard engine assembly, which is mounted with the air intake muffler according to the present invention, is described below with reference to FIGS. 13 to  18 . The outboard engine assembly shown in the drawings includes a vertical engine of the V-type multi-cylinder. 
     In FIG. 13, the outboard engine assembly  20  includes an upper engine cover  21 , an under cover  22  located below the engine cover  21 , an extension case  23  located below the under cover  22 , and a gear case  24  located below the extension case  23 . 
     A screw  25  is mounted at a rear end of the gear case  24 . At a front portion between the under cover  22  and the extension case  23 , a stern bracket  26  is mounted to be rotatable about a swivel axis  27 . 
     As shown in FIG. 14, the engine cover  21  covers the engine  30  and accessories and defines an engine room S. 
     The engine  30  includes a cylinder block  31 , a cylinder head  32 , a cylinder head cover  33 , a crankcase  34 , a piston  36  and a crankshaft  37 , and is mounted on a mount case  35 . 
     The cylinder block  31  has a plurality of cylinders  31   a  which are arrayed in a vertical direction. The cylinder head  32  is located rearward of the cylinder block  31 . The cylinder head cover  33  is located rearward of the cylinder head  32 . The crankcase  34  is located at a front of the cylinder block  31 . 
     The mount case  35  is supported with the extension case  38  which is covered with the under cover  22 . An oil pan  39  is located inside the extension case  38 . 
     An exhaust port of the cylinder head  32  is connected to an exhaust manifold  40 . The exhaust manifold  40  is connected to an exhaust pipe  41 . The exhaust pipe  41  extends downward and expels exhaust gases downward of the extension case  23  shown in FIG.  13 . 
     An alternating current electric power generator (ACG)  42  is mounted at an upper area of the front portion of the crankcase  42 . A pulley  43 , which is driven with the crankshaft  37 , and a drive pulley  47  for driving the electric power generator are located at an upper area of the cylinder block  31 . A camshaft drive pulley  44  is located at the upper area of the cylinder head  32 . The drive pulley  43  and the camshaft drive pulley  44  are drivably coupled to one another via an intermediate tension pulley  45  for driving the camshaft. An upper side of the camshaft drive pulley  44  is covered with a pulley cover  44   a . The air intake muffler  1  according to the present invention is located above the tension pulley  45 , the drive pulley  43 , the drive pulley for the electric power generator and the electric power generator pulley  48 . 
     The timing belt  46  is located so as to have a narrow width (in a lateral width) in a right and left direction in the engine room S by means of the plurality of tension pulleys  45 ,  45 ,  55 , thereby ensuring a space between the both sides of the lower area of the air intake muffler  1  and the upper area of the engine  30 . Accordingly, air is discharged from the side areas between the upper area of the engine and the air intake muffler, contributing to a heat dissipating property of the belt/pulley mechanism. Further, the presence of the intake air muffler allows covers for the pulleys  43 ,  45 ,  47  except for the camshaft drive pulley  44  to be dispensed with. 
     The crankshaft  37  is mounted with an electric power generator drive pulley  47  of a larger diameter than the drive pulley  43 . A timing belt  49  extends between the electric power generator drive pulley  47  and an electric power generator driven pulley  48  for driving the electric power generator  42 . 
     An intake manifold  50  is mounted at a rear area of the cylinder head cover  33 . A throttle valve unit  51  is mounted at an upper area of the intake manifold such that an air intake passage has an upstream portion orientated forward. 
     The air intake muffler  1  is located above the cylinder block  31  and the crankcase  34 . The body  2  of the air intake muffler  1  is mounted to the engine side by means of the plurality of mount stays  8 . The electric power generator drive pulley  47  of the larger diameter is located below the embossed portion  9  formed in the bottom portion of the body  2  of the air intake muffler  1 . The driven pulley  48  of the electric power generator  42  is located below the ventilation opening  7   b.  The embossed portion  9  and the cover portion  7  form a cover member for the electric power generator drive pulley  47  and the driven pulley  48 . 
     The air intake connecting duct  6  formed at the rear area of the box-shaped air intake muffler  2  is connected to the throttle body which forms the air intake passage of the throttle valve unit  51 . 
     Connection between the air intake passage of the throttle unit  51  and the air intake connecting duct  6  is performed by means of a grommet  52  by compelling a cylindrical portion of the air intake connecting duct  6  to be mated with the air intake passage. Thus, the connecting portion is easily and reliably sealed. 
     A front portion of the engine cover  21  is formed with a coolant air intake port  21   a.  An upper and rear portion of the engine cover  21  is formed with an outside air intake port  21   b  to allow an internal intake opening  21   c  to introduce outside air through a duct  53  into the engine room S defined with the engine cover  21 . 
     The engine  30  of the presently filed preferred embodiment shown in FIG. 14 has three cylinders  31   a  arrayed in a vertical direction, with the engine  30  being arranged in a V-type configuration, as viewed in a plane in FIG. 15, to form the four-stroke V-type six-cylinder vertical engine. 
     As shown in FIG. 15, a V-bank  30   a  of the cylinder block  31  is spread rearward. The air intake connecting duct  6  of the air intake muffler  1  is located inside the V-bank  30   a.  Also, the throttle valve unit  51  is located inside the V-bank  30   a.  The intake manifold  50  is located rearward of the spreading area of the V-bank  30   a.  An intake pipe  50   a  of each cylinder head  32  is located inside the V-bank  30   a.    
     In the drawings, reference numeral  54  designates a seal member which partitions off the engine room S defined with the engine cover  21  to preclude heat generated by the cylinder heads  32 ,  32  from being transferred toward the electric power generator  42 . 
     The exhaust manifold  40 , which is connected to the exhaust ports  32   a,    32   a  of the cylinder heads  32 ,  32  as shown in FIG. 16, extends downward in the engine room S as shown in FIG.  14  and is connected to the exhaust pipe  41 . The exhaust pipe  41  is orientated downward and extends toward an area below the under cover  22  while passing through the under cover  22  and the extension case  23  to expel exhaust gases. 
     As shown in FIG. 17, respective cylinders  31   a  arrayed in three rows in a vertical direction laterally accommodates therein pistons  31   b,  respectively. Transverse con-rods  31   c  are connected to the crankshaft  37 . 
     The cylinders  31   a  have respective combustion chambers  32   b.  Each of the combustion chambers  32   b  is mounted with an ignition plug  56 , two intake valves  57  and two exhaust valves  58 . 
     The camshafts  59  are positioned rearward of the respective cylinder heads  32 . The camshafts  59  are driven with the camshaft drive pulleys  44 , respectively. A rocker arm shaft  60  is located at right and left sides of the camshafts  59  for supporting valve rocker arms for opening and closing the intake and exhaust ports  57 ,  58 . The cylinder head cover  33  covers the camshaft  59  and the rocker arm shaft  60 . 
     As shown in FIG. 18, the intake manifold  50  has a large volume and is positioned at the area rearward of the V-bank  30   a  which expands rearward of the engine  30 . 
     The intake manifold  50  is connected to the intake valves  57  of the respective cylinders  30   a  of the engine  30  via the right and left two rows each with three in the vertical direction, i.e. the sum of six exhaust pipes  50   a.  The intake manifold  50  is connected at its upstream to the throttle valve unit  51 . The throttle valve unit  51  is connected to the air intake connecting duct  6  of the air intake muffler  1  via the grommet as previously noted. The air intake connecting duct  6  is mounted with the mesh member  11  which forms the flame arrester as described above. 
     FIGS. 19 and 20 show the air intake muffler of a second preferred embodiment according to the present invention, with like parts bearing the same reference numerals as those of the first preferred embodiment to omit a description of the same. 
     As shown in FIG. 20, rear end walls  205   a,    205   a  of outside air intake ducts  205 ,  205  are closed. The outside air intake ports  205   b,    205   b  are formed to open downward at positions in the vicinities of rear distal ends of the outside air intake ducts  205 ,  205 . 
     According to the present invention, as described in relation to the second preferred embodiment, the outside air intake ports  205   b,    205   b  may be opened downwardly, sidewardly or upwardly, though not shown. 
     The present disclosure relates to the subject matters of Japanese Patent Application No. 2001-031904, filed Feb. 8, 2001, and Japanese Patent Application No. 2001-030826, filed Feb. 7, 2001, the disclosures of which are expressly incorporated herein by reference in their entireties.