Patent Publication Number: US-2005115764-A1

Title: Muffler

Description:
BACKGROUND OF THE INVENTION  
      The present invention relates to mufflers for suppressing a noise caused by exhaust gas of a vehicle engine.  
      For example, Japanese Laid-Open Patent Publication No. 57-113919 describes this type of muffler, as illustrated in  FIG. 7 . With reference to the drawing, a generally used, conventional muffler, such as the one described in the aforementioned publication, will hereafter be explained.  
      As shown in  FIG. 7 , a muffler  50  is deployed at a bottom side of a vehicle body and between exhaust pipes EX 1 , EX 2 . More specifically, the muffler  50  includes an outer shell  53  and a pair of outer plates  51 ,  52 , which are securely supported by the outer shell  53 . The muffler  50  is connected to the exhaust pipes EX 1  through the outer plate  51  and to the exhaust pipe EX 2  through the outer plate  52 . Exhaust gas is introduced to the interior of the muffler  50  through the exhaust pipes EX 1  (the inlet pipes) and discharged to the exterior through the exhaust pipe EX 2  (the outlet pipe). While flowing through the muffler  50 , the energy of the exhaust gas is reduced such that a noise caused by the exhaust gas is suppressed.  
      Since the muffler  50  is normally installed along a portion of the bottom side of the vehicle body, the installing position of the muffler  50  is limited. The exhaust pipes EX 1 , EX 2  of the engine thus must be curved at a plurality of positions as connected to the muffler  50 . Normally, curved portions R of the exhaust pipes EX 1 , EX 2  are formed in the immediate vicinity of the muffler  50 .  
      The rigidity of each of the curved portions R is relatively low as compared to the remainder of the corresponding exhaust pipes EX 1 , EX 2 . Thus, when the engine or vehicle body vibrates, the external force acting on the exhaust pipes EX 1 , EX 2  causes relatively great deformation (vibration) in the curved portions R, as compared to the remainder of the corresponding exhaust pipes EX 1 , EX 2 . As aforementioned, the curved portions R are located in the immediate vicinity of the muffler  50 . Accordingly, for example, the vibration of the curved portion R of each exhaust pipe EX 1  acts directly on a connecting portion P of the exhaust pipe EX 1  with the outer plate  51  of the muffler  50  as moment E, as illustrated in  FIG. 8 , which is an enlarged view showing the section D of  FIG. 7 . As is clear from  FIG. 8 , the moment E acts to deform the connecting portion P, thus lowering the durability of the connecting portion P of the exhaust pipe EX 1 , as well as that of the muffler  50 . A connecting portion of the exhaust pipe EX 2  with the outer plate  52  of the muffler  50  ( FIG. 7 ) is also affected in a similar manner by the vibration of the vehicle engine or body.  
      In order to avoid the disadvantage, various solutions have been proposed. For example, the outer plates  51 ,  52  of the muffler  50  may be formed of a relatively thick material. Alternatively, a reinforcing member or damper may be added for suppressing the deformation (the vibration) of each curved portion R. However, the solutions may increase the weight of the muffler  50  or complicate the exhaust system configuration and thus are not significantly efficient.  
     SUMMARY OF THE INVENTION  
      Accordingly, it is an objective of the present invention to provide a simply configured muffler capable of preferably suppressing lowering of durability, which is otherwise caused by vibration of a curved portion of an exhaust pipe.  
      To achieve the foregoing and other objectives and in accordance with the purpose of the present invention, the invention provides a muffler for suppressing a noise caused by exhaust gas of an internal combustion engine of a vehicle. The muffler is disposed in an exhaust pipe extending from the engine along a bottom side of the vehicle. The muffler includes a cylindrical outer shell having a pair of openings defined at opposing axial ends of the outer shell, and a pair of outer plates each secured to the corresponding one of the opposing ends of the outer shell. The exhaust pipe is connected to the outer plates and has a curved portion in the vicinity of at least one of the connecting portions of the exhaust pipe with the outer plates. The curved portion is accommodated in the interior of the muffler defined by the outer plates and the outer shell.  
      Other aspects and advantages of the invention will become apparent from the following description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      The invention, together with objects and advantages thereof, may best be understood by reference to the following description of the presently preferred embodiments together with the accompanying drawings in which:  
       FIG. 1  is a plan view showing an exhaust system of a vehicle to which an embodiment of the present invention is applied;  
       FIG. 2  is a partially cross-sectional, plan view showing the interior of a muffler of the illustrated embodiment;  
       FIG. 3  is a front view showing the muffler of  FIG. 2  as viewed from the direction indicated by arrow A;  
       FIG. 4  is a front view showing the muffler of  FIG. 2  as viewed from the direction indicated by arrow B;  
       FIG. 5  is an enlarged cross-sectional view showing the section C of  FIG. 2 ;  
       FIG. 6  is a plan view showing arrangement of exhaust pipes in the vicinity of the muffler;  
       FIG. 7  is a plan view showing a conventional exhaust system configuration of a vehicle; and  
       FIG. 8  is a view schematically showing moment acting on a connecting portion of an exhaust pipe with a conventional muffler. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
      An embodiment of the present invention will now be described.  
      First, an exhaust system configuration of a vehicle to which a muffler  20  of the present invention is applied will be explained with reference to  FIG. 1 .  
      As shown in the drawing, the muffler  20  is disposed in an exhaust pipe extending from an internal combustion engine along a bottom side of a vehicle body, like the conventional muffler  50  of  FIG. 7 . The exhaust pipe includes a pair of exhaust pipes (first pipe sections)  12  extending from the engine to the muffler  20  and an exhaust pipe (a second pipe section)  14  extending from the muffler  20  to the exterior.  
      The structure of the muffler  20  will hereafter be explained in detail referring to  FIG. 2 .  
      As illustrated in the drawing, the muffler  20  includes inlet pipes  22 , an outlet pipe  24 , a pair of outer plates  26 ,  28 , and an outer shell  30 . Each of the inlet pipes  22  is connected to the corresponding one of the exhaust pipes  12 . The outlet pipe  24  is connected to the exhaust pipe  14 . The outer plate  26  is connected to the inlet pipes  22  and the outer plate  28  is connected to the outlet pipe  24 . The outer shell  33  supports the outer plates  26 ,  28 .  
      In other words, each inlet pipe  22  is connected to the corresponding exhaust pipe  12  ( FIG. 1 ) and thus forms a section of the exhaust pipe  12 . More specifically, each exhaust pipe  12  includes the corresponding inlet pipe  22 , which is an inner pipe section disposed in the interior of the muffler  20 , and an outer pipe section arranged in the exterior of the muffler  20  and connected to the inner pipe section. Like the inlet pipes  22 , the outlet pipe  24  is connected to the exhaust pipe  14  ( FIG. 1 ) and thus forms a section of the exhaust pipe  14 . More specifically, the exhaust pipe  14  includes the outlet pipe  24 , which is an inner pipe section disposed in the interior of the muffler  20 , and an outer pipe section arranged in the exterior of the muffler  20  and connected to the inner pipe section. The outer plate  26  is connected to a portion of each of the inlet pipes  22  and the outer plate  28  is connected to a portion of the outlet pipe  24 . The outer shell  30  is formed like a cylinder having a substantially oval cross-sectional shape. Each of the outer plates  26 ,  28  and the outer shell  30  is formed by piling a pair of metal thin plates together.  
      In the illustrated embodiment, a plurality of separators  32  are formed in the interior of the muffler  20 , the space defined by the outer plates  26 ,  28  and the outer shell  30 . The separators  32  thus define a plurality of resonance chambers in the interior of the muffler  20  along the axial direction of the muffler  20 .  
      Each of the outer plates  26 ,  28  is formed in a manner expanded in the axial direction of the muffler  20 , as shaped like a substantially spherical, or, more specifically, oval surface as a whole. As compared to the case in which each outer plate  26 ,  28  is formed as a flat surface, the outer plate  26 ,  28  of the illustrated embodiment has a relatively large heat dissipating surface area, thus improving the noise suppressing performance of the muffler  20 . Further, as compared to the case in which each outer plate  26 ,  28  forms a flat surface, the wind received by the outer plates  26 ,  28  when the vehicle is moving is deflected more smoothly along the outer wall of the muffler  20 , thus decreasing the aerodynamic drag acting on the muffler  20 . In addition, since the inlet and outlet pipes  22 ,  24  are supported by the corresponding outer plates  26 ,  28  having improved surface rigidity, the rigidity of the muffler  20  as a whole is increased, thus enhancing the durability of the muffler  20 .  
      The outer plate  26  has a plurality of projections  34  each projected outward from the muffler  20 . Similarly, the outer plate  28  has a plurality of projections  36  each projected outward from the muffler  20 . As illustrated in the front views of  FIGS. 3 and 4 , each of the projections  34 ,  36  is formed in an elongated shape and functions as a reinforcing rib. This structure further improves the surface rigidity of each outer plate  26 ,  28 . Further, in addition to the outer plates  26 ,  28  that are shaped in the expanded manner, the projections  34 ,  36  increase the surface area, or the heat dissipating surface area, of the corresponding outer plates  26 ,  28 . This enhances the exhaust gas cooling performance of the muffler  20 , as well as the noise suppressing performance of the muffler  20 .  
      With reference to  FIG. 2 , each of the inlet pipes  22  is connected to the outer plate  26  as passed through the outer plate  26 . Likewise, the outlet pipe  24  is connected to the outer plate  28  as passed through the outer plate  28 . More specifically, a connecting portion of each inlet pipe  22  with the outer plate  26  (the section C of  FIG. 2 ) is shown in the enlarged view of  FIG. 5 , by way of example. That is, a through hole  38  extends through each of the outer plates  26 ,  28 . A burring portion  40  is formed through burring along the periphery of each of the through holes  38 . Each of the inlet and outlet pipes  22 ,  24  is thus passed through the corresponding one of the through holes  38  of the outer plate  26 ,  28  and welded to the burring portion  40 . The inlet and outlet pipes  22 ,  24  are thus secured to the corresponding outer plates  26 ,  28 . In the interior of the muffler  20 , the inlet pipes  22  and the outlet pipes  24  are secured to the corresponding separators  32  as passed through the separators  32 .  
      Further referring to  FIG. 2 , each of the inlet pipes  22  includes a curved portion R in the vicinity of the connecting portion with the outer plate  26 . The extending direction of each inlet pipe  22  is changed at the corresponding curved portion R. Similarly, the outlet pipe  24  includes a curved portion R in the vicinity of the connecting portion with the outer plate  28 . The extending direction of the outlet pipe  24  is changed at the curved portion R. In the illustrated embodiment, each of the curved portions R is formed in the muffler  20  as received in the space defined by the expanded portion of the corresponding outer plate  26 ,  28 .  
      With reference to  FIG. 1  or  FIG. 6 , an enlarged view showing a section of  FIG. 1 , this structure makes it unnecessary to form a curved portion in either of the exhaust pipes  12 ,  14  corresponding to the exterior of the muffler  20 , in the vicinity of the corresponding outer plate  26 ,  28 . Further, the configuration of the illustrated embodiment saves the space defined in the muffler  20  efficiently. Also, in the muffler  20 , the sections of the inlet pipes  22  (the exhaust pipes  12 ) and the section of the outlet pipe  24  (the exhaust pipe  14 ), each including the corresponding curved portion R (see  FIG. 2 ), are supported by a plurality of portions of the muffler  20  corresponding to the separators  32 . This structure suppresses deformation and vibration occurring in the curved portions R, which are received in the interior of the muffler  20 . Accordingly, simply by accommodating the curved portions R in the interior of the muffler  20 , the durability of the muffler  20  of the illustrated embodiment is improved. Further, among a plurality of curved portions formed in each of the exhaust pipes  12 ,  14 , some of the curved portions, the curved portions R, are received in the interior of the muffler  20  This suppresses deformation of the exhaust pipes  12 ,  14 , as well as vibration of the exhaust system as a whole.  
      In addition, as is often the case with a conventional muffler, it may be possible to bond an outer shell and outer plates together through “caulking”. More specifically, the outer plates are fitted in the outer shell, which is originally shaped as a cylinder. Each of the outer plates is then securely pressed by a mold at the entire circumference for preventing the outer plates from separating from the outer shall. The outer shell and the outer plates are thus subjected to the caulking. Accordingly, the portion of each outer plate pressed by the mold must be shaped as a flat surface.  
      However, if the caulking is employed for forming the muffler  20  of the illustrated embodiment, the inlet pipes  22  and the outlet pipe  24  may interfere with the mold, making it difficult to bond the outer shell  30  and the outer plates  26 ,  28  together. Also, since each outer plate  26 ,  28  is shaped as a substantially spherical, oval surface, it may be difficult to provide a flat surface portion for being pressed by the mold. In this case, the pressing may not be accomplished appropriately. Further, if each of the outer plates  26 ,  28  includes the flat surface portion, vibration of the outer plate  26 ,  28  as a whole, or that of the muffler  20 , may be caused by vibration of the flat portion. The rigidity of the muffler  20  is thus lowered.  
      To avoid this, the illustrated embodiment employs laser welding for bonding the outer shell  30  and the outer plates  26 ,  28  together. The laser welding is accomplished easily and appropriately simply by securely holding the outer plates  26 ,  28  with respect to the outer shell  30  using a mold such that the outer plates  26 ,  28  are positioned accurately. It is thus unnecessary to press the entire circumference of each outer plate  26 ,  28  against the outer shell  30 . Further, the position for applying the mold in each outer plate  26 ,  28  can be selected such that the mold is not interfered by the inlet pipes  22  or the outlet pipes  24 .  
      It is thus possible to form the muffler  20  relatively easily while maintaining the bonding strength between the outer shell  30  and the outer plates  26 ,  28  at a relatively high level. Further, the extending direction of each of the inlet pipes  22  (the exhaust pipes  12 ) and the outlet pipe  24  (the exhaust pipe  14 ) outside the muffler  20  may be selected with less restrictions. Also, it is unnecessary to form a flat surface portion in each outer plate  26 ,  28  for bonding the outer plates  26 ,  28  and the outer shell  30  together. The outer plates  26 ,  28  are thus assembled with the outer shell  30  relatively easily.  
      In the following, a procedure for assembling the muffler  20  will be explained by way of example. The muffler  20  of the illustrated embodiment is assembled in accordance with the following steps 1 to 3.  
      &lt;Step 1&gt; The inlet pipes  22  and the outlet pipe  24  are secured to the separators  32 . More specifically, each of the inlet pipes  22  is configured by a bent portion  22   a  and a straight portion  22   b . The bent portion  22   a  includes the corresponding curved portion R and is located closer to the outer plate  26 . The straight portion  22   b  is located inward in the muffler  20 . In Step  1 , only the straight portions  22   b  of the inlet pipes  22  are secured to the separators  32 .  
      &lt;Step 2&gt; Two metal sheets that are piled together are wound around the separators  32  to which the inlet and outlet pipes  22 ,  24  are secured. The ends of the metal sheets are then joined together through welding, such that the outer shell  30  is completed.  
      &lt;Step 3&gt; An end of the bent portion  22   a  of each inlet pipe  22  is fitted in the corresponding end of the straight portion  22   b , such that the bent portion  22   a  and the straight portion  22   b  form a single pipe. The bent portion  22   a  of each inlet pipe  22  is then connected to the outer plate  26 . In this state, the outer plates  26 ,  28  are fitted in a pair of opposing ends of the outer shell  30 . The outer plates  26 ,  28  and the outer shell  30  are then bonded together through welding.  
      The illustrated embodiment has the following advantages.  
      (1) The connecting portion of each inlet pipe  22  with the outer plate  26  and the connecting portion of the outlet pipe  24  with the outer plate  28  are each prevented from being affected directly by the vibration of the corresponding curved portion R, which is applied to the connecting portion as the moment acting to deform the connecting portion. Accordingly, the durability of the muffler  20  of the illustrated embodiment is improved simply by receiving the curved portions R in the interior of the muffler  20 .  
      (2) In the illustrated embodiment, the strength of each outer plate  26 ,  28  is increased by shaping the outer plate  26 ,  28  in an expanding manner. The volume and heat dissipating surface area of the muffler  20  is also increased, and the noise caused by exhaust gas is suppressed further effectively. Further, the curved portion R of each of the inlet and outlet pipes  22 ,  24  is accommodated in the space defined by the expanded portion of the corresponding outer plate  26 ,  28 , such that the space in the muffler  20  is saved efficiently. Also, when the vehicle is moving, the wind received by the muffler  20  is easily deflected along the outer wall of the muffler  20  by following the expanded shape of each outer plate  26 ,  28 . This structure reduces the aerodynamic drag acting on the muffler  20 , thus lowering the air flow resistance when the vehicle is moving.  
      (3) Since each of the outer plates  26 ,  28  is shaped as a substantially oval surface in the illustrated embodiment, the surface rigidity of each outer plate  26 ,  28  supporting the inlet or outlet pipes  26 ,  28  is relatively large. The rigidity of the muffler  20  is thus enhanced as a whole, such that the durability of the muffler  20  is improved further preferably.  
      (4) Each outer plate  26 ,  28  is provided with the burring portion(s)  40  for supporting the corresponding inlet or outlet pipes  22 ,  24 . This structure makes it possible to support the inlet and outlet pipes  22 ,  24  by the corresponding outer plates  26 ,  28  without providing a flat surface portion in the outer plates  26 ,  28 . The vibration of the muffler  20  is thus suppressed in a preferable manner.  
      (5) In the illustrated embodiment, the projections (the reinforcing ribs)  34 ,  36  are formed respectively in the outer plates  26 ,  28 . This structure further improves the surface rigidity of each outer plate  26 ,  28  and increases the heat dissipating surface area of the outer plate  26 ,  28 .  
      (6) In the illustrated embodiment, the outer plates  26 ,  28  and the outer shell  30  are bonded together through laser welding. This makes it easy to position the outer plates  26 ,  28  with respect to the outer shell  30  and maintain the bonding strength between the outer plates  26 ,  28  and the outer shell  30  at a relatively high level. Particularly, since the muffler  20  of the illustrated embodiment accommodates the curved portions R in the interior, the outer plates  26 ,  28  are relatively difficult to securely assemble with the outer shell  30 . However, as long as the laser welding is employed, the problem is solved preferably. Further, as compared to the case in which the outer plates  26 ,  28  and the outer shell  30  are bonded together through, for example, caulking, the weight of the muffler  20  of the illustrated embodiment is relatively light.  
      The present invention may be embodied in the following modified forms.  
      Although each of the projections  34 ,  36  is formed in an elongated shape in the illustrated embodiment, the shape of each projection  34 ,  36  may be modified as needed.  
      Instead of, or in addition to, the projections  34 ,  36 , a plurality of recesses recessed inward with respect to the muffler  20  may be formed in the outer plates  26 ,  28 . Since the recesses each function as a reinforcing rib, this structure also increases the surface rigidity of each outer plate  26 ,  28 . Further, the recesses increase the heat dissipating surface area of each outer plate  26 ,  28 .  
      Alternatively, the projections  34 ,  36  or the recesses may be eliminated from the outer plates  26 ,  28 , as long as the required surface rigidity and heat dissipating surface area are reliably obtained in the outer plates  26 ,  28 .  
      In the illustrated embodiment, the burring portions  40  may be omitted or replaced by other types of flanges, as long as the inlet and outlet pipes  22 ,  24  are held in a secure state appropriately.  
      If the space in the muffler  20  is saved sufficiently in the illustrated embodiment, each curved portion R does not necessarily have to be accommodated in the space defined by the expanded portion of the corresponding outer plate  26 ,  28 . As long as the curved portions R are located in the interior of the muffler  20 , similar advantages to those of the illustrated embodiment may be obtained.  
      Alternatively, only some of the curved portions R may be accommodated in the interior of the muffler  20 . This structure also prevents the connecting portion of each inlet pipe  22  with the outer plate  26  and the connecting portion of the outlet pipe  24  with the outer plate  28  from being affected directly by the vibration of the corresponding curved portion R, which is applied to such connecting portion as the moment acting to deform the connecting portion.  
      In the illustrated embodiment, only one of the outer plates  26 ,  28  may be formed in an expanded shape along the axial direction of the muffler  20 .  
      In the illustrated embodiment, each of the outer plates  26 ,  28  is shaped as a substantially oval surface. However, a portion or the entire part of each outer plate  26 ,  28  may be shaped as a cone-like surface or a substantially cone-like surface. In other words, as long as the outer plates  26 ,  28  are each shaped as a substantially spherical surface, the surface rigidity of each outer plate  26 ,  28  is enhanced as compared to the case in which the outer plates  26 ,  28  are formed as flat surfaces.  
      In the illustrated embodiment, the outer shell  30  and the outer plates  26 ,  28  are bonded together through laser welding. However, bonding of the outer shell  30  and the outer plates  26 ,  28  may be accomplished through a similar but different type of welding, other than the laser type.  
      The present invention may be applied to a muffler having a single inlet pipe  22  or a muffler having a plurality of outlet pipes  24 .  
      The present examples and embodiments are to be considered as illustrative and not restrictive and the invention is not to be limited to the details given herein, but may be modified within the scope and equivalence of the appended claims.