Abstract:
An exhaust muffler for an internal combustion engine included in a motorcycle includes a perforated inner pipe ( 32 ), an outer pipe ( 31 ) coaxially surrounding the inner pipe ( 32 ), and a glass wool mat ( 33 ) packed in a space between the inner pipe ( 32 ) and the outer pipe ( 31 ). A three-layer protective structure is formed by winding an inner stainless steel wire mesh ( 34 ) wound around the inner pipe ( 32 ), winding a stainless steel wool mat ( 35 ) around the inner stainless steel wire mesh ( 934 ), and winding an outer stainless steel wire mesh ( 36 ) around the stainless steel wool mat ( 35 ). The glass wool mat ( 33 ) is wound around the three-layer structure. The three-layer structure extends the life of the glass wool mat ( 33 ) even if the temperature and pressure of the exhaust gas discharged by the internal combustion engine increase.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention relates to an exhaust muffler for a vehicle, such as a motorcycle.  
           [0003]    2. Description of the Related Art  
           [0004]    A prior art exhaust muffler for a motorcycle, disclosed in Japanese Utility Model Registration No. 2513707 has a perforated inner pipe, an outer pipe, a glass wool mat, as a sound-absorbing element, packed in an annular space between the perforated inner and the outer pipe, and a steel wool mat interposed between the glass wool mat and the inner pipe to protect the glass wool mat from the damaging effect of the high-temperature, high-pressure exhaust gas.  
           [0005]    A steel wool mat is formed by subjecting superposed bundles of ferrous metal filaments to needle punching to make the ferrous metal filaments entangled. A steel wool mat is wound around the perforated inner pipe to protect the glass wool mat wound around the steel wool mat from the damaging effect of the high-temperature, high-pressure exhaust gas.  
           [0006]    The combustion efficiency and output of automotive internal combustion engines have been progressively increased in recent years, raising the temperature and pressure of the exhaust gas in the muffler. Consequently, ferrous metal filaments forming the steel wool mat for protecting the glass wool mat exert detrimental effects on the glass wool mat under a high-temperature, high-pressure condition, adversely affecting the durability of the glass wool mat.  
           [0007]    The present invention has been made in view of the foregoing problem and it is therefore an object of the present invention to provide an exhaust muffler provided with a glass wool mat effectively protected from the damaging effect of the high-temperature, high-pressure exhaust gas on the glass wool mat.  
         SUMMARY OF THE INVENTION  
         [0008]    With the foregoing object in view, according to one aspect of the present invention, an exhaust muffler includes: a perforated inner pipe; an outer pipe coaxially surrounding the inner pipe; and a glass wool mat formed by packing glass wool in a space between the inner and the outer pipe; wherein a three-layer protective structure consisting of an inner stainless steel wire mesh wound around the inner pipe, a stainless steel wool mat wound around the inner stainless steel wire mesh, and an outer stainless steel wire mesh wound around the stainless steel wool mat is interposed between the inner pipe and the glass wool mat.  
           [0009]    The three-layer protective structure is formed by holding the stainless steel wool mat between the inner and the outer stainless steel wire mesh, and the glass wool mat is protected from the high-temperature, high-pressure exhaust gas by the three-layer protective structure.  
           [0010]    Since the outer stainless steel wire mesh prevents the stainless steel wool mat from acting directly on the glass wool mat, the life of the glass wool layer can be extended even if the temperature and pressure of the exhaust gas increase.  
           [0011]    Desirably, the three-layer protective structure consisting of the inner and the outer stainless steel wire mesh and the stainless steel wool mat is tightened by rolling the same between rollers under pressure applied thereto by the rollers.  
           [0012]    Since the protective structure consisting of the inner and the outer stainless steel wire mesh and the stainless steel wool mat is thus formed by tightly winding the stainless steel wire meshes and the stainless steel wool mat around the inner pipe under pressure applied thereto by the rollers, the stainless steel wool mat has a uniform density, the protective structure retains its designed shape and has stable quality, and the exhaust muffler can be easily fabricated.  
           [0013]    Preferably, the three-layer protective structure consisting of the inner and the outer stainless steel wire mesh and the stainless steel wool mat and surrounding the inner pipe is wrapped in a knitted, cylindrical stainless steel wire net to retain the same in its designed shape.  
           [0014]    The knitted, cylindrical stainless steel wire net formed by knitting stainless steel cords and covering the outer stainless steel wire mesh wound around the stainless steel wool mat holds the trailing edge of the outer stainless steel wire mesh in place to retain the designed shape of the three-layer protective structure, which facilitates the fabrication of the exhaust muffler and work for carrying component parts.  
           [0015]    Preferably, glass cloth is wound around the cylindrical stainless steel wire net, and the glass wool mat is wound on the glass cloth.  
           [0016]    When the three-layer protective structure consisting of the inner and the outer stainless steel wire mesh and the stainless steel wool mat is wrapped in the cylindrical stainless steel wire net, and the glass cloth is wound around the cylindrical stainless steel wire net, the glass wool layer can be surely protected from the high-temperature, high-pressure exhaust gas and the action of the stainless steel wool mat, which extends the life of the glass wool mat.  
           [0017]    The inner pipe may be a round pipe, the outer pipe may be an elliptic pipe, and the glass wool mat may have a uniform thickness and may be wound in layers around the outer pipe, glass wool strips may be held between the layers of the glass wool mat at positions respectively corresponding to the opposite ends of a major diameter of the elliptic outer pipe.  
           [0018]    The glass wool mat can be formed in a substantially uniform density by winding the glass wool mat around the outer pipe with the glass wool strips extended on parts of the outer pipe respectively corresponding to the opposite ends of the major diameter of the outer pipe so as to be held between the outer pipe and the glass wool mat, so that the quality including sound-absorbing effect of the exhaust muffler can be improved and the life of the glass wool mat can be extended.  
           [0019]    According to another aspect of the present invention, an exhaust muffler includes: a perforated inner pipe; an outer pipe coaxially surrounding the inner pipe; and a glass wool mat formed by packing glass wool in a space between the inner and the outer pipe; wherein a two-layer protective structure is formed by winding a stainless steel wire mesh around the inner pipe, and winding a stainless steel wool mat around the stainless steel wire mesh, the two-layer protective structure is wrapped in a knitted, cylindrical stainless steel wire net to retain the two-layer structure in a designed shape, and the glass wool mat is wound around the knitted, cylindrical stainless steel wire net.  
           [0020]    The glass wool mat wound around the two-layer protective structure consisting of the stainless steel wire mesh and the stainless steel wool mat wound around the stainless steel wire mesh, and wrapped in the knitted, cylindrical stainless steel wire net can be protected from the high-temperature, high-pressure exhaust gas.  
           [0021]    The knitted, cylindrical stainless steel wire net covering the two-layer protective structure holds the trailing edge of the stainless steel wool mat wound around the stainless steel wire mesh in place to retain the two-layer protective structure in its designed shape. Thus, the exhaust muffler needs a small number of parts and can be easily fabricated, and the two-layer protective structure wrapped in the knitted, cylindrical stainless steel wire net facilitates the work for carrying the same.  
           [0022]    In the exhaust muffler provided with the two-layer protective structure, the two-layer protective structure may be formed by tightly winding the stainless steel wool mat around the stainless steel wire mesh with pressure applied thereto by rollers, the two-layer protective structure may be wrapped in the knitted, cylindrical stainless steel wire net to retain the two-layer protective structure in its designed shape, and the glass wool mat may be formed on the knitted, cylindrical stainless steel wire net.  
           [0023]    The two-layer protective structure formed by tightly winding the stainless steel wool mat around the stainless steel wire mesh with pressure applied thereto by rollers can be easily wrapped in the knitted, cylindrical stainless steel wire net, can retain its designed shape, and facilitates the work for fabricating the exhaust muffler and the work for carrying parts. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0024]    The above and other objects, features and advantages of the present invention will become more apparent form the following description taken in connection with the accompanying drawings, in which:  
         [0025]    [0025]FIG. 1 is a side elevation of a motorcycle provided with an exhaust muffler in a preferred embodiment of the present invention;  
         [0026]    [0026]FIG. 2 is a partly sectional side elevation of the exhaust muffler shown in FIG. 1;  
         [0027]    [0027]FIG. 3 is a sectional view taken on line III-III in FIG. 2;  
         [0028]    [0028]FIG. 4 is a perspective view of assistance in explaining a process of forming a three-layer protective structure by using three rollers;  
         [0029]    [0029]FIG. 5 is a perspective view of assistance in explaining a process of wrapping the three-layer protective structure in a knitted, cylindrical stainless steel wire net; and  
         [0030]    [0030]FIG. 6 is an enlarged, fragmentary view of the knitted, cylindrical stainless steel wire net. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0031]    Referring to FIG. 1, an off-road motorcycle  1  provided with an exhaust muffler  30  in a preferred embodiment of the present invention has a head pipe, a pair of bifurcate main frames  3  extending rearward from the head pipe  2 , a down tube  4  extending downward from the head pipe  2 , a lower pipe  4   b  extending rearward from the lower end of the down tube  4 , and a pivot plate  5  joined to the rear ends of the pair of main frames  3  and the rear end of the lower pipe  4   b.  An upper bracket  6  interconnects the rear ends of the pair of main frames  3 . A seat rail  7  extends rearward from the upper bracket  6 . A rear frame lower pipe  8  has one end connected to the rear end of the seat rail  7  and the other end connected to the pivot plate  5 . A front fork  10  has an upper part supported for turning on the head pipe  2 , and a pair of bifurcate arms having lower ends supporting a front wheel  11  for rotation. A handlebar  9  is attached to the upper end of the front fork  10  to turn the front fork  10 . A rear fork  12  has a front end pivotally supported on a lower part of the pivot plate  5 , and a pair of bifurcate arms having rear ends supporting a rear wheel  13  for rotation. A rear shock absorber  14  is extended between the upper bracket  6  and the rear fork  12 .  
         [0032]    A single-cylinder four-stroke cycle internal combustion engine  15  is suspended from the main frames  3  and the pivot plate  5  in a space behind the down tube  4 . A fuel tank  16  is disposed above the internal combustion engine  15  and is mounted on the main frame  3 . A seat  17  is disposed behind the fuel tank  16  and is supported on the seat rail  17 . The internal combustion engine  15  has a crankcase, a cylinder head  15 a joined to a cylinder held on the crankcase in a substantially upright position, an intake pipe  18  extended rearward from the cylinder head  15   a,  a carburetor  19  connected to the intake pipe  18 , an air cleaner  20  connected to the carburetor  19 , and an exhaust pipe  21  connected to a front part of the cylinder head  15   a  and extending rearward on the right side of the cylinder. The exhaust muffler  30  is connected to the rear end of the exhaust pipe  21  so as to extend obliquely upward toward the rear. A rear end part of the exhaust pipe  21  connected to the exhaust muffler  30  is fixed to a bracket  25  attached to a middle part of the rear frame lower pipe  8 . The exhaust muffler  30  connected to the rear end part of the exhaust pipe  21  is fixed to a bracket  26  attached to the rear end of the seat rail  7 .  
         [0033]    The construction of the exhaust muffler  30  will be described with reference to FIGS. 2 and 3. The exhaust muffler  30  has an elliptic outer pipe  31 , and a round inner pipe  32  extended through the outer pipe  31  and connected to the exhaust pipe  21 . The inner pipe  32  is provided with many small holes  32   a.  An annular space between the outer pipe  31  and the inner pipe  32  is packed with a glass wool mat  33  serving as a sound-absorbing member. An inner stainless steel wire mesh  34  of stainless steel wires is wound around the inner pipe  32  provided with the small holes  32   a,  a stainless steel wool mat  35  of intertwining stainless steel filaments is wound around the inner stainless steel wire mesh  34 , and an outer stainless steel wire mesh  36  is wound around the stainless steel wool mat  35  to form a three-layer structure. The three-layer structure is wrapped in a flexible, diametrically expandable, cylindrical stainless steel wire net  37  formed by knitting stainless steel cords, and a glass cloth  38  is wound around the stainless steel wire net  37 . The glass wool mat  33  is packed in a space between the glass cloth  38  and the outer pipe  31 . Thus, the three-layer structure formed by holding the stainless steel wool mat  35  between the stainless steel wire meshes  34  and  36 , the stainless steel wire net  37  and the glass cloth  38  are interposed between the inner pipe  32  and the glass wool mat  33  to protect the glass wool mat  33  from the high-temperature, high-pressure exhaust gas.  
         [0034]    When fabricating the exhaust muffler  30 , the inner stainless steel wire mesh  34 , the stainless steel wool mat  35  and the outer stainless steel wire mesh  36  are wound in that order around the inner pipe  32  to form the three-layer structure. Then, three rollers  51 ,  52  and  53  are pressed against the three-layer structure as shown in FIG. 4, and the three rollers  51 ,  52  and  53  are rotated to tighten the three-layer structure. The tightened three-layer structure formed on the inner pipe  32  is inserted in the radially expandable stainless steel wire net  37  as shown in FIG. 5 to ensure that the three-layer structure is retained in its designed shape. As the glass wool forming the glass wool mat, SUS 434(Japanese Industrial Standards) can be used, while as the wire glass wool forming the wire meshes, SUS 304 (Japanese Industrial Standards) can be used.  
         [0035]    As shown in FIG. 6, the stainless steel wire net  37  is formed in a cylindrical shape by knitting stainless steel cords. The stainless steel wire net  37  is expandable particularly diametrically. Therefore, the three-layer structure consisting of the inner stainless steel wire mesh  34 , the stainless steel wool mat  35  and the outer stainless steel wire mesh  36  and wrapped in the stainless steel wire net  37  is compressed radially and hence the three-layer structure can be surely retained in its designed shape. Thus, the three-layer structure can be readily retained in its designed shape by the stainless steel wire net  37  without welding the trailing edge of the outer stainless steel wire mesh  36  of the three-layer structure, which facilitates the fabrication of the exhaust muffler.  
         [0036]    The retention of the three-layer structure in its designed shape facilitates work for carrying parts, suppresses the variation of the density of the stainless steel wool mat  35 , and stabilizes quality.  
         [0037]    Then, as shown in FIG. 3, the glass cloth  38  is wound around a structure formed by wrapping the three-layer structure in the stainless steel wire net  37 , and the glass wool mat  33  is wound in three or four layers on the glass cloth  38 . When winding the glass wool mat  33 , glass wool mat strips  39  are placed between the layers of the glass wool mat  33  at positions diametrically opposite to each other to form the layers of the glass wool mat  33  in an elliptic cross section. An assembly of the inner pipe  32 , the three-layer structure, the stainless steel wire net  37 , the glass cloth  38  and the glass wool mat  33  and the glass wool strips  39  is fitted in the elliptic outer pipe  31  to assemble the exhaust muffler  30 .  
         [0038]    The glass wool mat  33  is coated partly or entirely with an inorganic silica binder. The glass wool strips  39  can be formed by cutting such a glass wool mat in strips.  
         [0039]    When the glass wool mat  33  is wound in layers in an elliptic cross section by holding the glass wool strips  39  between the layers of the glass wool mat  33 , a desired quantity of glass wool can be uniformly packed in the elliptic outer pipe  31  to improve the quality including sound-absorbing effect can be improved.  
         [0040]    The stainless steel wool mat  35  interposed between the inner pipe  32  and the glass wool mat  33  protects the glass wool mat  33  from high-temperature, high-pressure exhaust gas. However, since the stainless steel wool mat  35  is formed by subjecting superposed bundles of stainless steel filaments to needle-punching to make the stainless steel filaments entangled, the surface of the stainless steel wool mat  35  is nappy with free ends of many stainless steel fibers. It is possible that such a nappy surface of the stainless steel wool mat  35  damages the glass wool mat  33 . However, since the stainless steel wool mat  35  is sandwiched between the stainless steel wire meshes  34  and  36  to form the three-layer structure, and the three-layer structure is wrapped in the stainless steel wire net  36 , the stainless steel wool mat  35  is unable to act directly on the glass wool mat  33 . Therefore, even if the temperature and pressure of the exhaust gas increases, the glass wool mat  33  is not deteriorated by the stainless steel wool mat  35 , and hence the glass wool mat  33  has an extended life.  
         [0041]    In some cases, a two-layer structure consisting of the stainless steel wire mesh  34  and the stainless steel wool mat  35 , and wrapped in the stainless steel wire net  36  can be effectively employed instead of the three-layer structure consisting of the stainless steel wool mat  35  and the stainless steel wire meshes  34  and  36 , and wrapped in the stainless steel wire net  36 . The trailing edge of the stainless steel wool mat  35  is held in place by the stainless steel wire net  36  to retain the two-layer structure in its designed shape. When the two-layer structure is employed, the number of parts can be reduced, the work for assembling the exhaust muffler can be facilitated and the work for carrying parts can also be facilitated.  
         [0042]    Since the stainless steel wire net  36  is interposed between the stainless steel wool mat  35  and the glass wool mat  33 , the glass wool mat  35  is not deteriorated and has an extended life.  
         [0043]    The glass cloth  38  is used to ensure the protection of the glass wool mat  35  from the high-temperature, high-pressure exhaust gas and the damaging effect of the stainless steel wool mat  35 . However, in some cases, only the stainless steel wire mesh  36  or the stainless steel wire net  37  is sufficiently effective in protecting the glass wool mat  33 , and the glass cloth  38  may be omitted.  
         [0044]    Although the invention has been described in its preferred embodiment with a certain degree of particularity, obviously many changes and variations are possible therein. It is therefore to be understood that the present invention may be practiced otherwise than as specifically described herein without departing from the scope and spirit thereof.