Patent Publication Number: US-7591345-B1

Title: Angled muffler seam construction and method

Description:
BACKGROUND AND SUMMARY 
   The invention relates to mufflers for noise-silencing. 
   The invention arose during continuing development efforts directed toward mufflers such as shown in U.S. Pat. Nos. 6,076,632, 6,250,422, 6,457,553, all incorporated herein by reference. The invention also arose during continuing development efforts directed toward cost reduction. 
   Mufflers for internal combustion engines, particularly small engines, e.g. for lawnmowers, tractors, and the like, are typically made with two shells or stampings that together comprise the outer shell of the muffler. The shells are joined together in a crimping operation. This process has been reliable and efficient, resulting in a low cost muffler. One problem which may be encountered is that many small engines exhibit an afterfire condition upon engine shutdown. This happens when unburned fuel is ignited by hot internal muffler surfaces causing an explosion in the muffler. This afterfire explosive force in the muffler can rupture the muffler at the seam of the two shells. Countermeasures for afterfire survival typically include making the muffler shells thicker or adding tack welds to the seam joint to keep the joint from separating during an afterfire. Both of these solutions may add objectionable cost. 
   The present invention provides a simple and effective solution to the noted afterfire problem, in a cost-effective manner. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is an isometric elevational view of a muffler known in the prior art. 
       FIG. 2  is a view of a portion of  FIG. 1  partially cutaway. 
       FIG. 3  is a sectional view taken along line  3 - 3  of  FIG. 1 . 
       FIG. 4  is like  FIG. 3  and illustrates the present invention. 
       FIG. 5  is like  FIG. 4  and shows a further embodiment. 
   

   DETAILED DESCRIPTION 
     FIGS. 1-3  show a muffler  10  known in the prior art. The muffler has an inlet  12  receiving exhaust as shown at arrow  14  from internal combustion engine  16 , and has an outlet  18  discharging the exhaust as shown at arrow  20 . The muffler is formed by first and second shells or stampings  22  and  24  defining an enclosure  26 . Incoming exhaust at  14  is routed as shown at arrow  28  into the enclosure which may include various expansion chambers, baffling chambers, etc. for noise reduction, and then the exhaust is directed as shown at arrow  30  to outlet  18 . The muffler may have one or more dividing walls such as  32  in the enclosure and defining sub-chambers therein, e.g. at  34 ,  36 , etc. 
   The enclosure has respective first and second sidewalls  38  and  40  along the perimeter thereof, which sidewalls have respective first and second facing lips  42  and  44 ,  FIG. 3 . Sidewall  38  extends axially in a first axial direction  46  from first lip  42 . Second sidewall  40  extends axially in a second axial direction  48  from second lip  44 . Second axial direction  48  is opposite to first axial direction  46 . First lip  42  extends away from first sidewall  38 . Second lip  44  extends away from second sidewall  40  then around first lip  42  and then toward first sidewall  38 . First and second sidewalls  38  and  40  are subject to a lateral force  50  thereon due to afterfire explosive force in the muffler. The lateral force at  50  acts to push sidewalls  38  and  40  laterally outwardly (rightwardly in  FIG. 3 ) along a first lateral direction  52 . It is known in the prior art to provide improved seam strength between the muffler shells by tack welding sidewall  38  to the turned back end of lip  44  of sidewall  40 , as shown at tack weld  54 . In various embodiments, there may be multiple dividing walls  32 , or no dividing wall  32 . 
     FIGS. 4 and 5  illustrate the present invention and use like reference numerals from above where appropriate to facilitate understanding. 
   In  FIG. 4 , sidewalls  38  and  40  have respective first and second facing lips  56  and  58 . First sidewall  38  extends axially in the noted first axial direction  46  from first lip  56 . Second sidewall  40  extends axially in the noted second axial direction  48  from second lip  58 . First lip  56  extends away from first sidewall  38 . Second lip  58  extends away from second sidewall  40  then around first lip  56  then toward first sidewall  38 . First and second sidewalls  38  and  40  are subject to the noted lateral force  50  thereon due to afterfire explosive force in the muffler. The lateral force acts to push the sidewalls laterally outwardly along the noted first lateral direction  52 . In  FIG. 4 , lips  56  and  58  extend at an angle  60  along an angled direction  62  relative to the noted lateral direction  52  such that outward lateral movement of first sidewall  38  is blocked by second lip  58  in the path of lateral movement of first lip  56  and such that outward lateral movement of second sidewall  40  is blocked by first lip  56  in the path of lateral movement of second lip  58 . 
   First lip  56  has an inner portion  64  extending laterally outwardly along the noted first lateral direction  52  from first sidewall  38 , and an outer portion  66  extending from inner portion  64  to an outer end  68 . The noted first lateral direction  52  is perpendicular to the noted first and second axial directions  46  and  48 . Second lip  58  has an inner portion  70  adjacent and extending laterally outwardly along the noted first lateral direction  52  from second sidewall  40 , and an outer portion  72  having a U-shape including a bight  74  and first and second legs  76  and  78 . First leg  76  extends from inner portion  70  of second lip  58  to bight  74 . Bight  74  extends along outer end  68  of outer portion  66  of first lip  56 . Second leg  78  extends from bight  74  to an outer end  80 . Outer portion  66  of first lip  56  is between first and second legs  76  and  78  and extends at an oblique angle relative to each of the noted first lateral direction  52  and first and second axial directions  46  and  48 . First and second legs  76  and  78  and outer portion  66  of first lip  56  extend parallel to each other along the noted oblique angle along direction  62 . Bight  74  extends along a direction  82  which is along a second oblique angle relative to each of the first lateral direction  52  and first and second axial directions  46  and  48 . The noted first and second oblique angles are perpendicular to each other. In  FIG. 4 , the outer portions  66  and  72  of the first and second lips  56  and  58  extend rectilinearly, e.g. along direction  62 . In  FIG. 5 , the outer portions  66  and  72  of first and second lips  56  and  58  extend curvilinearly. 
   A dividing wall  32  may be present in the enclosure and defines sub-chambers such as  34  and  36  therein. In other embodiments, plural dividing walls may be provided, for example FIG. 3 of incorporated U.S. Pat. No. 6,250,422. In other embodiments, no dividing wall is present. When a dividing is present, it is preferred that the dividing wall such as  32  have a third lip  90  disposed in sandwich relation between first and second lips  56  and  58 . Dividing wall  32  extends in a second lateral direction  92  from third lip  90 . Second lateral direction  92  is opposite to first lateral direction  52 . Third lip  90  has an inner portion  94  adjacent and extending laterally outwardly along first lateral direction  52  from dividing wall  32 , and an outer portion  96  extending from inner portion  94  of third lip  90  to an outer end  98  and extending at oblique angle  60  relative to each of the first and second lateral directions  52  and  92 . Bight  74  of outer portion  72  of second lip  58  extends along outer end  98  of third lip  90  and outer end  68  of first lip  56 . Outer portion  66  of first lip  56  and outer portion  96  of third lip  90  are between first and second legs  76  and  78  and extend at an oblique angle relative to each of first and second lateral directions  52  and  92  and first and second axial directions  46  and  48 . 
   The present system provides a method for enhancing seam strength of a muffler, the method comprising bending lips  56  and  58  at an angle  60  along an angled direction  62  relative to lateral direction  52  such that outward lateral movement of first sidewall  38  is blocked by second lip  58  in the path of lateral movement (rightwardly in  FIGS. 4 ,  5 ) of first lip  56 , and such that outward lateral movement (rightwardly in  FIGS. 4 ,  5 ) of second sidewall  40  is blocked by first lip  56  in the path of lateral movement of second lip  58 . The method includes bending the first and second legs  76  and  78  of the U-shaped outer portion  72  of lip  58  at an oblique angle relative to each of first lateral direction  52  and first and second axial directions  46  and  48 . Legs  76  and  78  and outer portion  66  of first lip  56  are bent to extend parallel to each other along the noted oblique angle along direction  62 . In one embodiment, legs  76  and  78  and outer portion  66  of first lip  56  are bent to extend rectilinearly,  FIG. 4 . In another embodiment, first and second legs  76  and  78  and outer portion  66  of first lip  56  are bent to extend curvilinearly,  FIG. 5 . The method further includes, when one or more dividing walls  32  are present, bending the outer portion  96  of third lip  90  at an oblique angle relative to each of the first and second lateral directions  52  and  92  and the first and second axial directions  46  and  48 . The method includes bending first and second legs  76  and  78 , with lips  56  and  90  therebetween, at the noted oblique angle relative to each of first and second lateral directions  52  and  92  and first and second axial directions  46  and  48 . The system further enables a method of assembling the first and second shells  22  and  24  at the noted first and second lips  56  and  58  of the first and second sidewalls  38  and  40  without tack welding to otherwise withstand the lateral force  50  due to afterfire explosive force in the muffler, whereby to eliminate a welding step. 
   In the foregoing description, certain terms have been used for brevity, clearness, and understanding. No unnecessary limitations are to be implied therefrom beyond the requirement of the prior art because such terms are used for descriptive purposes and are intended to be broadly construed. The different configurations, systems, and method steps described herein may be used alone or in combination with other configurations, systems and method steps. It is to be expected that various equivalents, alternatives and modifications are possible within the scope of the appended claims.