Abstract:
An exhaust muffler system for use on a motorcycle or four-wheeled vehicle provides for operation in either of two modes, a regular configuration that provides a high degree of noise reduction, or a racing specification that provides for a freer-flowing exhaust. Without changing the main body of the muffler, an operator can choose between a quieter, public road setting or a louder, high performance setting. The muffler is provided with two interchangeable spark arresters, and a main body having multiple expansion chambers therein, defined by bulkheads. When a regular spark arrester is installed, exhaust gas passes through one bulkhead three times, greatly reducing the noise produced. With the spark arrester removed, the exhaust gas passes straight through to the open air, enhancing performance. A seal is provided between the bulkheads and the spark arrester, which provides for extension or retraction in the lengthwise direction of the tail pipe.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
         [0001]    The present application claims priority under 35 USC 119 based on Japanese patent application No. 2002-354612, filed Dec. 6, 2002.  
         BACKGROUND OF THE INVENTION  
         [0002]    1. Field of the Invention  
           [0003]    The present invention relates to an exhaust muffler and to a muffler system for connecting to an exhaust pipe of an internal combustion engine, used on a motorcycle or four-wheeled vehicle. More particularly, the present invention relates to an exhaust muffler and related muffler system, for connecting to an exhaust pipe of an internal combustion engine used on a motorcycle or four-wheeled vehicle, in which an exhaust muffler is convertible between a first configuration, for use on public roads where low noise is required, and a second configuration for use in racing competition, where enhanced performance is required.  
           [0004]    2. Description of the Background Art  
           [0005]    Vehicular exhaust mufflers have been known that define a plurality of expansion chambers using a plurality of bulkheads, and that are provided with a removable spark arrester equipped with a tail pipe at a rear part thereof.  
           [0006]    A spark arrester is a device for catching and trapping sparks and soot included in exhaust gas of an internal combustion engine, and for preventing the sparks and soot from being released to the atmosphere. When the spark arrester is detachable, exhaust back pressure in the expansion chambers is usually set to be highest at the expansion chamber closest to the front near the exhaust pipe, and becomes sequentially lower as it moves rearwardly within the exhaust muffler. The object of providing a detachable spark arrester is to enable maintenance of the muffler and the spark arrester, and to enable changing of the spark arrester in order to economically provide exhaust devices for differing performance requirements.  
           [0007]    An exhaust muffler including a removable and replaceable spark arrester is described in Japanese Patent Laid-open Publication No. Hei. 10-266828 (refer, for example, to effects of the invention, FIG. 2, and FIG. 5 of the reference).  
           [0008]    Although the known devices have some utility for their intended purposes, a need still exists in the art for an improved exhaust muffler for an internal combustion engine. In particular, there is a need for an improved exhaust muffler for an internal combustion engine.  
         SUMMARY OF THE INVENTION  
         [0009]    The present invention therefore provides an improved exhaust muffler with a detachable spark arrester, equipped with a tail pipe at a rear part thereof. An exhaust muffler according to a first illustrative embodiment hereof is equipped with a plurality of expansion chambers defined by a plurality of bulkheads. In the exhaust muffler according to the first embodiment hereof, the muffler can be adapted for use on public roads or for use in racing by changing the spark arrester without changing the main body. By using the muffler according to the present invention, either quietness of the exhaust muffler or output performance of the internal combustion engine can be maximized, depending on which spark arrester is used.  
           [0010]    In a first aspect of the present invention, an exhaust muffler, provided for use with an internal combustion engine, is provided with a plurality of expansion chambers defined by a plurality of bulkheads within a main body of the exhaust muffler. The muffler is adapted to be connected to an exhaust pipe of an internal combustion engine, and includes a removable spark arrester equipped with a tail pipe provided in a detachable manner at a rear part of the main body.  
           [0011]    The muffler according to the first embodiment is structured, constructed and arranged such that when a regular, non-racing spark arrester is installed, exhaust flow is made to pass through at least one bulkhead three times. This occurs because the tailpipe of the regular spark arrester is configured to connect the expansion chambers, and a plurality of communicating pipes are fixed so as to also connect the expansion chambers.  
           [0012]    When the regular spark arrester is removed, exhaust flow passes through the communicating pipes, and may bypass one of the expansion chambers so as to be released to the outside.  
           [0013]    As a result of the present invention having the above configuration, when the regular non-racing spark arrester is installed, a so-called “three-pass” structure is adopted, where exhaust gas passes through a bulkhead three times. Silencing of the exhaust muffler is therefore improved when traveling on public roads, and when the regular spark arrester is removed, this can be used as a racing exhaust muffler for which high-output is demanded. It is therefore possible to divide use of this exhaust muffler between traveling on public roads and racing use, without changing the main portion of the exhaust muffler.  
           [0014]    In a second aspect of the present invention, an exhaust muffler for an internal combustion engine is provided with a plurality of expansion chambers, defined by a plurality of bulk heads within a main body of the exhaust muffler. The muffler is adapted to be connected to an exhaust pipe of an internal combustion engine, and includes a removable spark arrester equipped with a tail pipe provided in a detachable manner at a rear part of the main body.  
           [0015]    The muffler is configured such that when the regular non-racing spark arrester is installed, exhaust flow is made to pass through at least one bulkhead three times by the tail pipe installed so as to connect the expansion chambers and plurality of communicating pipes fixed so as to connect the expansion chambers. When the regular spark arrester is removed, exhaust flow passes straight through a through-hole opening at the bulkheads, so as to be released to the open air.  
           [0016]    In this second aspect of the invention also, when the spark arrester is installed, a so-called “three-pass” structure is adopted where exhaust gas passes through a bulkhead three times. Silencing of the exhaust muffler is therefore improved when traveling on public roads, and when the regular spark arrester is removed, this can be used as a racing exhaust muffler for which high output is demanded, without changing portions of the body of the exhaust muffler.  
           [0017]    In a third aspect of the present invention, a seal is provided between the bulkheads and the spark arrester when the spark arrester is installed, and the seal is provided via a sliding part or elastic part, permitting extension and retraction in the lengthwise direction of the tail pipe while still maintaining a seal.  
           [0018]    As the present invention is configured in this manner, gas and sound do not leak into neighboring expansion chambers and silencing is improved. Further, the tail pipe has a slide structure that permits extension and retraction. Thermal expansion is therefore relieved, there is little fatigue even with repeated expansion and retraction, and durability is improved. Further, it is therefore possible to provide a minimum pressure expansion chamber next to a maximum pressure expansion chamber, a three-pass structure can be realized, and silencing on public roads can be improved.  
           [0019]    For a more complete understanding of the present invention, the reader is referred to the following detailed description section, which should be read in conjunction with the accompanying drawings. Throughout the following detailed description and in the drawings, like numbers refer to like parts. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0020]    [0020]FIG. 1 is a longitudinal cross-sectional view of a main body  2  of an exhaust muffler system  100 , according to a first embodiment of the present invention.  
         [0021]    [0021]FIG. 2 is a longitudinal cross-sectional view of the exhaust muffler  1  according to the first embodiment hereof, with a regular spark arrester installed therein to form a regular configuration  1 A of the muffler system for public road travel.  
         [0022]    [0022]FIG. 3( a ) is a longitudinal cross-sectional view of the regular spark arrester  18  for use in the exhaust muffler system  100  of the first embodiment during public road travel.  
         [0023]    [0023]FIG. 3( b ) is a rear plan view of the regular spark arrester  18 .  
         [0024]    [0024]FIG. 4 is a longitudinal cross-sectional view of the exhaust muffler  1  according to the first embodiment hereof, with a racing spark arrester  31  installed therein for a high-performance configuration  1 B thereof.  
         [0025]    [0025]FIG. 5( a ) is a longitudinal cross-sectional view of a racing spark arrester  31  which is used in both the first embodiment and the second embodiment.  
         [0026]    [0026]FIG. 5( b ) is a rear plan view of the racing spark arrester  31 .  
         [0027]    [0027]FIG. 6 is a longitudinal cross-sectional view of an exhaust muffler for illustrating a first example of a proposed seal structure that can be applied between the first expansion chamber and the third expansion chamber in the regular configuration  1 A thereof.  
         [0028]    [0028]FIG. 7 is a longitudinal cross-sectional view of an exhaust muffler for illustrating a second example of a proposed seal structure that can be applied between the first expansion chamber and the third expansion chamber in the regular configuration  1 A thereof.  
         [0029]    [0029]FIG. 8 is a longitudinal cross-sectional view of an exhaust muffler for illustrating a third example of a proposed seal structure that can be applied between the first expansion chamber and the third expansion chamber in the regular configuration  1 A thereof.  
         [0030]    [0030]FIG. 9 is a longitudinal cross-sectional view of the main body  42  of the exhaust muffler  41  of a second embodiment of the present invention.  
         [0031]    [0031]FIG. 10 is a longitudinal cross-sectional view of the exhaust muffler  41  of the second embodiment, with a regular spark arrester installed therein for a regular configuration  41 A thereof.  
         [0032]    [0032]FIG. 11( a ) is a longitudinal cross-sectional view of the regular spark arrester  53  for use in the exhaust muffler  41  of the second embodiment during public road travel.  
         [0033]    [0033]FIG. 11( b ) is a rear plan view of the regular spark arrester  53  of FIG. 11( a ).  
         [0034]    [0034]FIG. 12 is a longitudinal cross-sectional view of the exhaust muffler  41  of the second embodiment, with the racing spark arrester  31  installed therein for a high-performance configuration  41 B thereof.  
         [0035]    [0035]FIG. 13 is a side view of a motorcycle equipped with an exhaust muffler system according to the present invention.  
         [0036]    [0036]FIG. 14 is a side view of a four-wheeled vehicle equipped with an exhaust muffler system according to the present invention; and  
         [0037]    [0037]FIG. 15 is a top plan view, partially in cross-section, showing the three major components of an exhaust muffler system according to the first embodiment of the invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0038]    Herein, only structures considered necessary for clarifying the present invention are described. Other conventional structures, and those of ancillary and auxiliary components of the system, are assumed to be known and understood by those skilled in the art.  
         [0039]    [0039]FIG. 13 is a side view of a motorcycle  60  equipped with an exhaust muffler  1  according to a first embodiment of the present invention. A powertrain  65 , integrating an internal combustion engine  63  and a transmission  64 , is suspended at the center of a vehicle frame  62  spanning to the head pipe  61  of the motorcycle. The vehicle frame  62  is configured by connecting a plurality of members.  
         [0040]    The front fork  66  is rotatably supported at the head pipe  61 , a handlebar  67  is mounted at an upper end of the head pipe  61 , and a front wheel  68  is attached to the front fork in conventional fashion.  
         [0041]    A rear fork is pivotally attached to a rear part of the vehicle frame  62  at a pivot  72 , so as to be capable of swinging up and down. A rear shock absorber  70  is installed between the rear fork  69  and the vehicle frame  62 . A rear wheel  71  is axially supported at a rear end of the rear fork  69 . The rear wheel  71  is driven by a chain  74  wrapped around a driven sprocket  72  installed at the end of an output shaft of the power unit  65  and a driven sprocket  73  fitted to a shaft of the rear wheel  71 . The output shaft is parallel with the crankshaft, etc, in a direction from left to right of the vehicle body.  
         [0042]    An exhaust pipe  75 , spanning to an exhaust port provided at the front side of the internal combustion engine  63 , goes around the right side of the vehicle body so as to reach the rear part of the vehicle body. The rear end of the exhaust pipe  75  is connected to the front end of the exhaust muffler  1 . The front end of the exhaust muffler  1  is supportively connected to the vehicle frame  62 , and is suspended from a seat rail  76  extending to the rear.  
         [0043]    A fuel tank  77  is installed at an upper part of the vehicle frame  62 , and a seat  78  is provided at an upper part of the vehicle frame  62 . The seat  78  is situated at an upper part of the seat rail  76 . Numeral  79  denotes a side cover.  
         [0044]    An exhaust muffler of a second embodiment (to be described later) is installed at a position that is the same as the depicted position of the exhaust muffler  1 .  
         [0045]    [0045]FIG. 14 is a side view of a four-wheeled all-terrain vehicle (off-road saddled vehicle)  80  equipped with an exhaust muffler  1  according to a first embodiment of the present invention. This vehicle  80  is provided with a pair of left and right front wheels  82  and a pair of left and right rear wheels  83  to the front and rear of the vehicle frame  81 . A powertrain  86 , integrating an internal combustion engine  84  and a transmission  85 , is supported in the center of the vehicle frame  81 . The powertrain  86  has a structure where the crankshaft  87  runs in the longitudinal direction of the vehicle. Rotation of the crankshaft  87  is transmitted to an output shaft  88  via each shaft of the transmission  85 . Each of these shafts is parallel with the crankshaft  87  and is arranged in a direction running from the front to the rear of the vehicle body.  
         [0046]    The front wheel  82  is driven by a front drive shaft  89 , coupled to a front end of the output shaft  88 , and the rear wheel  83  is driven by a rear wheel drive shaft  90 , coupled to a rear end of the output shaft  88 .  
         [0047]    An exhaust pipe  91 , spanning to an exhaust port provided at the front side of the internal combustion engine  84 , goes around the side of the internal combustion engine  84  so as to reach the rear part of the vehicle body. The rear end of the exhaust pipe  91  is connected to the front end of the exhaust muffler  1 . The exhaust muffler  1  is suspended, at a vehicle frame  81 , between the vehicle frame  81  and the rear wheel  83 .  
         [0048]    A handlebar  92 , a fuel tank  93 , and a seat  94  are also installed on an upper part of the vehicle, in order from the front towards the back.  
         [0049]    An exhaust muffler according to a second embodiment hereof (to be described later) is installed at a position that is the same as the exhaust muffler  1 .  
         [0050]    Overview of the Exhaust Muffler System  
         [0051]    The exhaust muffler system  1  according to the first embodiment of the present invention will now described, with reference to the drawing figures.  
         [0052]    The exhaust muffler system  100  of the first embodiment includes a set of three component members, including an exhaust muffler main body  2 , and two interchangeable spark arresters  18 ,  32  that can be selectively attached to and detached from the main body  2 . The three components of the system  100  can be seen together in FIG. 15. The muffler system  100  includes both a regular, non-racing spark arrester  18  for use in public road travel, and a racing spark arrester  31 . The two types of spark arrester can be interchanged on the exhaust muffler body  2 , according to the contemplated use of the vehicle.  
         [0053]    A state in which the regular spark arrester  18  is installed at the exhaust muffler body  2  is referred to herein as a regular configuration  1 A of the first embodiment. A state in which the racing spark arrester  31  is installed at the exhaust muffler body  2  is referred to herein as a racing configuration  1 B of the first embodiment.  
         [0054]    Main Body Portion  
         [0055]    [0055]FIG. 1 is a longitudinal cross-section of a main body portion  2  of the exhaust muffler system  100 , according to the first embodiment hereof. In FIG. 1, the outer shell of the main body  2  of the exhaust muffler system  100  includes a cylindrical central body part  3 , a conical front cover  4 , and a rear plate  5  having a large opening at a central part thereof. The central body part  3  also includes an outer body plate  6 , an inner body plate  7  disposed inside the outer body plate, and heat-tolerant noise-absorbing material  8 , such as glass wool, etc., filling in between the respective inner and outer body plates  6 ,  7 .  
         [0056]    An introduction pipe  9 , connected to the exhaust pipe of the internal combustion engine, passes through the top part of the front cover  4 , and extends into the central body part  3 , as shown. An exhaust gas nozzle  10 , at the end of the introduction pipe  9 , opens out within the main body  2 . The exhaust gas nozzle  10  defines an end opening  111  of the introduction pipe  9 , and has a multiplicity of small holes  12  made in the side surface of the top part thereof, to create a gush of gas spread out about the interior of the main body  2 .  
         [0057]    In order from the front, a perforated metal partition plate  13 , a first bulkhead  14 , and a second bulkhead  15  are provided inside the inner body plate  7 . A portion behind the partition plate  13 , and in front of the first bulkhead  14 , is a first (front) expansion chamber C 1 . A portion spaced away from the first expansion chamber C 1  and in back of the second bulkhead  15  is a second (rear) expansion chamber C 2 , and a portion sandwiched between the first bulkhead  14  and the second bulkhead  15  is a third (intermediate) expansion chamber C 3 . The numbers of the expansion chambers follow the order in which the exhaust gas passes through the muffler in a regular configuration  1 A (described later). The perforated metal partition plate  13  is a sheet metal partition plate punched with a multiplicity of small holes allowing gas to pass freely. The partition plate  13  makes the speed of the exhaust gas uniform, and substantially prevents gas from building up within the first expansion chamber C 1 .  
         [0058]    On the inside of the main body  2 , a first communicating pipe  16  passing through the first bulkhead  14  and the second bulkhead  15  is fixed to these bulkheads. A second communicating pipe  17  passing through the second bulkhead  15  is fixed to the second bulkhead  15 . It is also possible to provide two first communicating pipes  16  with the same positional relationship with respect to a central line of the body.  
         [0059]    Regular Configuration of Muffler System  
         [0060]    [0060]FIG. 2 is a longitudinal cross-sectional view of the exhaust muffler  1  according to the first embodiment of the present invention, in the regular configuration  1 A thereof for public road travel. In this regular configuration  1 A, as shown in FIG. 2, the regular spark arrester  18  for public road travel is installed on the main body  2 . In the installed configuration thereof, the regular spark arrester  18  passes through the first bulkhead  14 , second bulkhead  15 , and the rear plate  5 .  
         [0061]    In the regular configuration of the exhaust system  100 , as depicted in FIG. 2, the bulkheads  14 ,  15 , the communicating pipes  16 ,  17 , and the regular spark arrester  18  cooperate to define an exhaust flow path FP through the main body. The flow path FP is illustrated by a number of arrows in FIG. 2, and passes through the second bulkhead  15  three times before exiting from the tail pipe  19 , as will be further detailed herein.  
         [0062]    The regular spark arrester  18  for public road travel is installed by attaching a flange  20  to the rear plate  5 , using a bolt  21 . The flange  20  is welded to the rear part of the tail pipe  19  of the spark arrester. A cylindrical gasket  22  is installed between the tail pipe  19  and the first bulkhead  14 , to prevent gas from flowing through the area of connection therebetween.  
         [0063]    [0063]FIG. 3( a ) is a longitudinal cross-sectional view of the regular spark arrester  18  for use in the regular configuration  1 A for the exhaust muffler system  100 . FIG. 3( b ) is a rear plan view of the regular spark arrester.  
         [0064]    The regular spark arrester  18  includes a tail pipe  19  with holes  26  formed through a portion thereof. Other components of the regular spark arrester  18  are welded to the tail pipe  19 , including, in order from the front end, a tail pipe front cover  23 , a first support ring  24 , a second support ring  25 , and the flange  20 .  
         [0065]    The cylindrical gasket  22  is installed at the outer periphery of the tail pipe  19 , between the tail pipe front cover  23  and the first support ring  24 . A multiplicity of gas-introducing small holes  26  are provided at a portion of the side surface of the tail pipe  19  sandwiched between the first support ring  24  and the second support ring  25 .  
         [0066]    Further, stainless steel wire mesh  27  surrounds the tail pipe  19  between the first and second support rings  24 ,  25 , and is spot-welded to the outer periphery of the first support ring  24  and the second support ring  25 . The wire mesh  27  is provided for filtering sparks and soot out of the exhaust stream, and preventing them from flowing out of the tail pipe  19 . A fitting bolt through-hole  20   a  is provided at the flange  20 .  
         [0067]    With reference to FIG. 2, in the regular configuration  1 A of the exhaust muffler system  100 , exhaust gas from the internal combustion engine (not shown) gushing into the main body  2  of the exhaust muffler  1 , via the introduction pipe  9 , is exhausted to the open air by the following route. After exiting the introduction pipe  9 , the exhaust gas flows through the perforated partition plate  13 , and then passes through the first expansion chamber C 1 , first communicating pipe  16 , second expansion chamber C 2 , reverses direction and flows through the second communicating pipe  17 , third expansion chamber C 3 , stainless steel wire mesh  27 , gas-introducing small holes  26  and outwardly through the tail pipe  19 .  
         [0068]    The exhaust gas alternately passes through large volume expansion chambers and long communicating pipes, so that gas pressure is reduced by the extent of repeated expansion and compression, and noise is muffled. The exhaust gas is then filtered by the stainless steel wire mesh  27 , before being exhausted from the rear end of the tail pipe  19 .  
         [0069]    In the regular configuration  1 A of this exhaust muffler system  100  for public road travel, the gas flow has a so-called “three-pass” structure, where the gas flow passes through the second bulkhead  15  three times via the first communicating pipe  16 , second communicating pipe  17 , and the tail pipe  19 . This structure improves sound-abating effects by elongating the gas flow path.  
         [0070]    Racing Configuration  
         [0071]    [0071]FIG. 4 is a longitudinal cross-sectional view of the exhaust muffler  1  in the racing configuration  1 B thereof, according to the first embodiment of the system  100 .  
         [0072]    It is possible to improve output of the internal combustion engine, during use of the exhaust muffler system  100  in racing, simply by detaching the regular spark arrester  18 . However, when there is no spark arrester, sparks and soot are simply discharged into the open air, and this is disfavored from an environmental point of view.  
         [0073]    In the racing configuration  1 B of the exhaust muffler system  100  of this embodiment, the regular spark arrester  18  is disconnected and removed from the main body  2 , and the racing spark arrester  31  is installed in its place. The dimensions of the racing spark arrester  31  are short in the axial direction. Therefore, in the racing configuration  18 , a central through-hole  14   a  for the first bulkhead  14  and a central through-hole  15   a  for the second bulkhead  15  are opened up.  
         [0074]    [0074]FIG. 5( a ) is a longitudinal cross-sectional view of a racing spark arrester  31  which is used in both the first embodiment and the second embodiment. FIG. 5( b ) is a rear plan view of the racing spark arrester  31 .  
         [0075]    The racing spark arrester  31  includes a tail pipe  32  that is short in the axial direction but has a large diameter, an annular collar member  33 , stainless steel mesh  34  stretched at the front surface and side surface of the annular collar member, and a flange  35  welded to the tail pipe  32 . The other end of the stainless steel mesh  34 , stretched at the side surface of the annular collar member  33 , is spot-welded to the tail pipe  32 .  
         [0076]    As shown in FIG. 4, the racing spark arrester  31  is installed by fixing the flange  35  of the racing spark arrester  31  to the rear plate  5 , using a bolt  21  inserted through a fitting bolt insertion hole  35   a.    
         [0077]    In the racing configuration  1 B of the exhaust muffler system  100  according to the first embodiment, shown in FIG. 4, exhaust gas from the internal combustion engine, (not shown) gushing into the main body  2  of the exhaust muffler  1  via the introduction pipe  9 , is exhausted to the open air by passing linearly through the muffler  1  from front to back.  
         [0078]    In detail, the exhaust gas passes through the perforated partition plate  13  into the first expansion chamber C 1 , passes through the first bulkhead  14  via the central through-hole  14   a , moves through the centrally located third expansion chamber C 3 , passes through the second bulkhead  15  via the central through-hole  15   a , enters the second expansion chamber C 2 , and passes through the stainless steel mesh  34 , and exits from the tail pipe  32 .  
         [0079]    The central through-holes  14   a ,  15   a  have large diameters and permit the gas to advance in a straight line and therefore present little resistance to the gas flowing out. Further, the tail pipe  32  is also short with a large diameter and therefore also presents little resistance to the gas flowing out. For these reasons, it will be understood that back pressure exerted by the muffler  1  in the racing configuration  1 B is less than the back pressure in the regular configuration  1 A, and accordingly, the power output of the internal combustion engine is improved by the racing configuration  1 B of the exhaust muffler system  100 , equipped with the racing spark arrester  31 , and a condition appropriate for racing is attained.  
         [0080]    Sealing Considerations  
         [0081]    When the exhaust muffler system  100  of the first embodiment is assembled for the regular configuration  1 A (FIG. 2), of the first to third expansion chambers, the first expansion chamber C 1 , at maximum pressure, and the third expansion chamber C 3  at minimum pressure are located next to each other. Sound-abating effects decrease sharply if gas leaks between the chambers.  
         [0082]    It is therefore necessary to provide a gas leakage prevention seal between the first bulkhead  14  and the regular spark arrester  18 . The tail pipe  19  of the regular spark arrester  18  extends when the internal combustion engine is running and retracts when the internal combustion engine is halted, due to normal expansion and contraction of the materials. The seal therefore has to maintain its function, even in the case of the extension and retraction movement of the tail pipe  19  relative to the bulkhead  14 .  
         [0083]    [0083]FIG. 6 to FIG. 8 are longitudinal cross-sectional views of the muffler  1 , for illustrating various proposed seal structures that can be applied between the first expansion chamber C 1  and the third expansion chamber C 3  in the regular configuration  1 A of the exhaust muffler system  100  of the first embodiment. Portions in FIGS. 6-8 corresponding to portions shown in FIG. 2 are given the same numerals. The drawings are slightly simplified. The perforated metal partition plate  13  is not the object of discussion and is therefore omitted from these drawings.  
         [0084]    [0084]FIG. 6 is an example where the cylindrical gasket  22 , of the type shown in FIG. 2, is installed between the first bulkhead  14  and the tail pipe  19  of the regular spark arrester  18 . This seals in the diameter direction. A stainless steel wool gasket, a glass wool gasket, a steel gasket, or a cladding material of these can be used as the gasket  22 . Mutual sliding takes place with a member making contact at the outer periphery or the inner periphery of the gasket  22 , in order to permit extension and retraction of the tail pipe  19 , the rear end of which is fixed in place.  
         [0085]    [0085]FIG. 7 is an example where a resilient ring-shaped gasket  36  is installed between the first bulkhead  14  and a first support ring  24  (FIG. 3) of the regular spark arrester  18 . This seals in an axial direction. This gasket  36  is made of a fibrous aluminum material. This may be SUS material or SK material, etc. These are extendable and retractable gasket materials. Further, the inner periphery of the ring-shaped resilient gasket  36  and the tail pipe  19  are capable of sliding over each other. It is therefore possible to permit extension and retraction of the tail pipe  19 , the rear end of which is fixed in place.  
         [0086]    [0086]FIG. 8 is an example where a ring-shaped metal member  37  fitted to a tail pipe  19  of the regular spark arrester  18  is thrust in an axial direction from the rear end side of the tail pipe  19  towards the first bulkhead  14 . The tail pipe  19  is urged forward by a coil spring  39  fitted between a bolt screwed into the rear plate  5  and the flange  20  welded to the rear end of the tail pipe  19 . This causes the tail pipe  19  to push the ring-shaped metal member  37  in the direction of the first bulkhead  14 .  
         [0087]    In order to ensure reliable contact with the first bulkhead  14  of the ring-shaped metal member  37 , it is necessary to provide a gap between the rear plate  5  and the flange  20  even under initial conditions. In order to prevent gas leaking from between the rear plate  5  and the flange  20 , a gasket  40  having resilience is fitted to this part. When the tail pipe  19  expands due to heating, the tail pipe  19  extends to the rear while pushing in the coil spring so as to permit extension and retraction of the tail pipe  19 .  
         [0088]    With regards to increasing the gap between the rear plate  5  and the flange  20 , gas leakage is prevented by using a resilient gasket  40 . In the above example, a separate ring-shaped metal member  37  is provided to the front of the first support ring  24 , but it is also possible for the first support ring  24  to make contact with the first bulkhead  14 .  
         [0089]    Second Embodiment  
         [0090]    Next, a description is given of a configuration for an exhaust muffler system  41  according to a second embodiment of the present invention. The exhaust muffler system  41  of the second embodiment includes a set of three members, an exhaust muffler body  42 , and two interchangeable spark arresters  53 ,  31  that can be selectively and interchangeably attached to or detached from the main body  42 .  
         [0091]    The spark arresters include a regular spark arrester  53  and a racing spark arrester  31 . The two types of spark arrester can be changed according to the purpose of the vehicle use.  
         [0092]    A state in which the regular spark arrester  53  is installed at the exhaust muffler body  42  is referred to as a regular configuration  41 A of the exhaust muffler  41  of the second embodiment. A state where the racing spark arrester  31  is installed at the exhaust muffler body  42  is referred to as a racing configuration  41 B of the exhaust muffler  41  of the second embodiment. The racing spark arrester  31  is the same as that (of FIG. 5) used in the first embodiment. This exhaust muffler  41  is also adapted to be connected to an exhaust pipe of an internal combustion engine of a motorcycle or four-wheeled vehicle as shown in FIG. 13 and FIG. 14.  
         [0093]    [0093]FIG. 9 is a vertical cross-section of a main body  42  of the exhaust muffler  41 . In FIG. 9, the outward appearance of the main body  42  of the exhaust muffler  41  includes a cylindrical central body part  43 , a conical front cover  44 , and a rear plate  45  having a large opening at a central part thereof.  
         [0094]    An introduction pipe  46 , for connecting to the exhaust pipe of the internal combustion engine, passes through the top part of the front cover  44  and is integrally connected to an exhaust gas nozzle  47 , which opens out within the main body  42 . This configuration is the same as for the first embodiment.  
         [0095]    In order from the front, a perforated metal partition plate  48 , a first bulkhead  49 , and a second bulkhead  50  are provided within the main body  42  at the inside of an inner body plate. A portion behind the partition plate  48  and in front of the first bulkhead  49  is a first (front) expansion chamber C 1 . A portion in back of the second bulkhead  50  is a second (rear) expansion chamber C 2 , and a portion sandwiched between the first bulkhead  49  and the second bulkhead  50  is a third (intermediate) expansion chamber C 3 .  
         [0096]    The numbers of the expansion chambers follow the order with which the exhaust gas passes through in a regular configuration  41 A of the exhaust system  41  (described later). A perforated metal partition plate  48  is a sheet metal partition plate punched with a multiplicity of small holes. The speed of the exhausted gas is therefore made uniform and gas is prevented from building up in the first expansion chamber C 1 . A first communicating pipe  51  passing through the first bulkhead  49  and the second bulkhead  50  is fixed to these bulkheads. A second communicating pipe  52  passing through the second bulkhead  50  is fixed to the second bulkhead  50 .  
         [0097]    The point where the exhaust muffler body  42  differs from the exhaust muffler body  2  of the first embodiment is that there is no central through-hole formed in the first bulkhead  42 . The first communicating pipe  51  is made slightly thicker to take performance into consideration when converting to a race configuration  42 B (described later). It is also possible to provide two first communicating pipes  51  of slightly smaller diameters with the same positional relationship with respect to a central line of the body.  
         [0098]    [0098]FIG. 10 is a longitudinal cross-sectional view of regular configuration  41 A of the exhaust muffler  41  of the second embodiment of the present invention. In this configuration  41 A, the regular spark arrester  53  is installed so as to pass through the second bulkhead  50 , and the rear plate  45 .  
         [0099]    The regular spark arrester  53  is installed by fixing a flange  57  welded to the rear end part of the tail pipe  54  of the central part to the rear plate  45  using a bolt  21 . The overall length of the regular spark arrester  53  is made short to provide compatibility with the fact that the first bulkhead  49  has no central through-hole.  
         [0100]    [0100]FIG. 11( a ) is a longitudinal cross-sectional view of the regular spark arrester  53  for use in the exhaust muffler  41  of the second embodiment during public road travel.  
         [0101]    [0101]FIG. 11( b ) is a rear plan view of the regular spark arrester  53  of FIG. 11( a ).  
         [0102]    Referring now to FIG. 11( a ), in order from the front, a tail pipe front cover  55 , a support ring  56 , and a flange  57  are welded to a center tail pipe  54 . A multiplicity of gas-introducing small holes  58  are made in the side surface of the front end part of the tail pipe  46 . A stainless steel mesh  59  is made to span the side surface of the tail pipe front cover  55  and the support ring  56  and is spot-welded. The regular spark arrester  53  is fitted to the rear plate  45  using a bolt  21  inserted through a fitting bolt through-hole  57   a  of a flange  57  that is welded to the tail pipe  54 .  
         [0103]    In the regular configuration  41 A of the exhaust muffler  41  shown in FIG. 10, exhaust gas exhausted from the internal combustion engine (not shown) gushing into the main body  42  of the exhaust muffler  41  via the introduction pipe  46  is exhausted by passing through the first expansion chamber C 1 , first communicating pipe  51 , second expansion chamber C 2 , second communicating pipe  52 , third expansion chamber C 3 , stainless steel wire mesh  59 , gas-introducing small holes  58  and tail pipe  54 .  
         [0104]    The gas flow for this exhaust muffler  41  is also a so-called three-pass structure where the gas flow passes through the second bulkhead  50  three times. The exhaust gas alternately passes through large volume expansion chambers and long communicating pipes so that gas pressure is reduced by the extent of repeated expansion and retraction, noise is muffled, and the exhaust gas is then purified by the stainless steel wire mesh  59  before being exhausted to the open air from the rear end of the tail pipe  54 .  
         [0105]    There is no central through-hole at the first bulkhead at the exhaust muffler  41  of this embodiment. The gas leakage seal structure (FIG. 6 to FIG. 8) provided in order to prevent gas from leaking between the first expansion chamber C 1  and the third expansion chamber C 3  in the regular configuration  1 A of the exhaust muffler system  100  of the first embodiment can therefore be omitted and the structure is simplified accordingly.  
         [0106]    [0106]FIG. 12 is a longitudinal cross-sectional view of racing configuration  41 B of the exhaust muffler  41  of the second embodiment. It is possible to improve output of the internal combustion engine during use of the exhaust muffler  41  in racing simply by detaching the regular spark arrester  53 .  
         [0107]    However, when there is no spark arrester, sparks and soot are simply discharged into the open air and this is disfavored from an environmental point of view. Because of this, when the regular spark arrester  53  is removed, and the racing spark arrester  31  short in overall length shown in FIG. 5 is installed. The racing spark arrester  31  is the same as that used in the first embodiment.  
         [0108]    In the racing configuration  41 B (FIG. 12) of the exhaust muffler  41  of the second embodiment, exhaust gas exhausted from the internal combustion engine (not shown) gushing into the main body  42  of the exhaust muffler  41  via the introduction pipe  46  is exhausted to the open air by passing through the first expansion chamber C 1 , first communicating pipe  51 , second expansion chamber C 2 , stainless steel mesh  34  and tail pipe  32 .  
         [0109]    In the race configuration  41 B of this embodiment, exhaust gas passes through the first communicating pipe  51  so as to be exhausted to the open air without necessarily passing through the third expansion chamber C 3 . Namely, compared to the regular configuration  41 A (FIG. 10), the path by which gas flows out is made shorter. There is therefore little resistance to the gas flowing out, the output of the internal combustion engine is improved, and a state appropriate for racing is attained.  
         [0110]    With the race configuration  41 B of the exhaust muffler  41  of the second embodiment, the exhaust gas cannot go through the center of the first bulkhead in a straight line, and makes a detour so as to flow via the first communicating pipe  51 . The increase in output of the internal combustion engine is therefore insufficient. Because of this, the first communicating pipe  51  of this embodiment is of a diameter that is made large compared to the first communicating pipe  16  of the exhaust muffler  1  of the first embodiment in order to reduce resistance to the gas flowing out. Instead of this, it would also be possible to provide two first communicating pipes  51  of smaller diameters.  
         [0111]    As described in detail above, in each of the above embodiments, a spark arrester equipped with a tail pipe is detachably provided at a rear part of an exhaust muffler body equipped with a plurality of expansion chambers defined by a plurality of bulkheads. It is therefore possible to provide quick-change compatibility with use either on public roads or in racing, without changing the main body, simply by removing a regular spark arrester and replacing this spark arrester with a racing spark arrester.  
         [0112]    A three-pass structure is adopted for use when traveling on public roads, and the silencing of the exhaust muffler is therefore improved. When the spark arrester is then removed or is replaced with a racing spark arrester, the output of the internal combustion engine is improved. It is therefore possible to divide use of this exhaust muffler between traveling on public roads and racing use, without removing the main body of the exhaust muffler.  
         [0113]    Further, in the regular configuration  1 A of the exhaust muffler system  100  of the first embodiment, leakage of gas or sound into a neighboring expansion chamber does not occur due to the seal structure shown in FIG. 6 to FIG. 8 and silencing is therefore improved. Further, the tail pipe has a slide structure that permits extension and retraction thereof. Thermal expansion is therefore accommodated, there is little fatigue even with repeated expansion and retraction, and durability is improved.  
         [0114]    Further, it is therefore possible to provide a minimum pressure third expansion chamber next to a maximum pressure first expansion chamber within the main body  2  of the exhaust muffler  1 , a three-pass structure can be realized, and silencing on public roads can be improved. With the exhaust muffler  41  of the second embodiment, a central through-hole for passing the tail pipe through the first bulkhead is omitted. Sound muffling occurring in the regular configuration  41 A is therefore improved, the seal structure between the first expansion chamber and the third expansion chamber is not necessary, and the structure is simplified.  
         [0115]    Although the present invention has been described herein with respect to a limited number of presently preferred embodiments, the foregoing description is intended to be illustrative, and not restrictive. Those skilled in the art will realize that many modifications of the preferred embodiment could be made which would be operable. All such modifications, which are within the scope of the claims, are intended to be within the scope and spirit of the present invention.