Abstract:
A muffler assembly includes an outer shell defining an internal cavity that extends between first and second ends. A first end cap is attached to the first end and a second end cap is attached to the second end. The first and second end caps provide a substantially enclosed internal cavity within the outer shell. A heat shield extends along a length of the outer shell and has a first shield end attached to the first end cap and a second shield end attached to the second end cap. The first and second shield ends are deformed around an outer perimeter of the first and second ends caps, or separate retaining members are used to secure the first and second shield ends to the first and second end caps.

Description:
TECHNICAL FIELD  
       [0001]     The subject invention relates to a method and apparatus for attaching a heat shield to a muffler.  
       BACKGROUND OF THE INVENTION  
       [0002]     A vehicle exhaust system includes a plurality of exhaust components that handle exhaust gases generated by an internal combustion engine. A typical exhaust system includes an exhaust pipe that guides exhaust gases from the internal combustion engine to a muffler. A tailpipe transfers exhaust gases from the muffler to external atmosphere. In addition to guiding exhaust gases, the muffler reduces operational noise levels generated by the internal combustion engine and exhaust system. The exhaust system can include other exhaust components for processing exhaust gases or for reducing noise, such as additional silencers, a catalytic converter, or a resonator.  
         [0003]     The exhaust components are typically routed from the internal combustion engine, located near a front portion of a vehicle, underneath a passenger compartment to a rear portion of the vehicle where the tailpipe is traditionally located. The muffler is typically positioned directly underneath the passenger compartment. As known, the exhaust gases generated by the exhaust system have high temperatures. Due to the proximity of the muffler to the passenger component, there is a concern that this heat could be transferred to the passenger compartment.  
         [0004]     One solution to reduce effects of the heat generated by exhaust system components has been to install a heat shield between the muffler and a vehicle structure such as a vehicle floor. Many different methods have been used to attach the heat shield to the muffler. One known method involves using bands to secure the heat shield to the muffler. A banding machine typically secures a band around the heat shield at each end of the muffler. This method has some disadvantages. One disadvantage is that the bands may not be secured tightly enough to the muffler. Loose bands can generate an annoying rattle sound. Another disadvantage involves the size, maintenance, and overall cost of the banding machine.  
         [0005]     Another known attachment method uses a weld to attach the heat shield to the muffler. Typically in this method, the heat shield is welded directly to an outer shell of the muffler. This weld interface does not accommodate thermal expansion that occurs as the muffler heats up and cools down. This can adversely affect the welds and can even result in weld failures.  
         [0006]     Another known attachment method involves capturing ends of the heat shield under a spun end of a muffler end cap. A muffler includes an outer shell with a muffler end cap mounted to each end of the outer shell. In a spin process, ends of the outer shell and circumferential edges of the muffler end caps are spun or folded over each other to provide a secure and permanent attachment between the muffler end caps and the outer shell. Attempting to capture another layer of material, i.e. a heat shield end portion, in the muffler end cap spun end can be disruptive to the assembly process. Further, muffler leak rate properties can be degraded due to the additional layer of material at the spun joint.  
         [0007]     Thus, there is a need for an improved attachment interface between a heat shield and a muffler assembly that can accommodate thermal expansion without degrading the attachment interfaces, and which is more reliable than prior attachment interfaces.  
       SUMMARY OF THE INVENTION  
       [0008]     A muffler assembly includes an outer shell having a first end cap at one shell end and a second end cap at an opposite shell end. The first and second end caps are attached to the outer shell via a spin attachment process. A heat shield extends along a length of the outer shell and includes a first shield end attached over the first end cap at a first attachment interface and a second shield end attached over the second end cap at a second attachment interface.  
         [0009]     In one example, the first and second attachment interfaces are provided by deforming the first and second shield ends around at least a portion of a perimeter of the first and second end caps. In another example, at least one retaining member is used to provide the first and second attachment interfaces. The retaining member could be a single clip, multiple clips, or a retaining ring that directly secures the first and second heat shield ends to the first and second end caps.  
         [0010]     In one embodiment, the heat shield includes a plurality of convolutes that are spaced apart from each other along a length of the heat shield. Each convolute is formed as an accordion-like protrusion extending outwardly from an upper surface of the heat shield. The plurality of convolutes dissipates stress that would be generated at the first and second attachment interfaces as the muffler assembly heats up and cools down.  
         [0011]     In another embodiment, the heat shield is made from a first component and a second component attached to the first component via an adjustable attachment interface. The adjustable attachment interface allows an overall length of the heat shield to be adjusted to any one of a plurality of overall lengths within a predetermined range of overall lengths. The adjustable attachment interface includes at least one longitudinal slot formed in at least one of the first or second components and at least one fastener received within the longitudinal slot to secure the first and second components together.  
         [0012]     The subject invention provides an improved method and apparatus for attaching a heat shield to a muffler assembly. The improved method and apparatus can accommodate thermal expansion without degrading attachment interfaces, is more reliable than prior attachment interfaces, and has improved acoustics over prior designs. These and other features of the present invention can be best understood from the following specification and drawings, the following of which is a brief description. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0013]      FIG. 1  is a perspective view of a muffler and heat shield assembly incorporating the subject invention.  
         [0014]      FIG. 2A  is a partial cross-sectional view of one example of an attachment interface between a heat shield and a muffler.  
         [0015]      FIG. 2B  is an end view of another example of an attachment interface between a heat shield and a muffler.  
         [0016]      FIG. 3  is a partial cross-sectional view of another example of an attachment interface between a heat shield and a muffler.  
         [0017]      FIG. 4A  is a partial cross-sectional view of another example of an attachment interface between a heat shield and a muffler.  
         [0018]      FIG. 4B  is an enlarged partial cross-section showing a portion of the attachment interface of  FIG. 4A .  
         [0019]      FIG. 4C  is an end view of the attachment interface of  FIG. 4A .  
         [0020]      FIG. 5  is a side view of an example of a heat shield including convolutes.  
         [0021]      FIG. 6  is a side view of an example of an adjustable length heat shield assembly.  
         [0022]      FIG. 7  is an enlarged detail view of circled portion  7  shown in  FIG. 6 .  
         [0023]      FIG. 8  is a top view of the detail of  FIG. 7 .  
         [0024]      FIG. 9  is a side view of a washer used in the attachment shown in  FIG. 6 . 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0025]     A muffler  10 , shown in  FIG. 1 , includes an outer shell  12 , a first end cap  14  mounted to one end of the outer shell  12 , and a second end cap  16  mounted to an opposite end of the outer shell  12 . The first  14  and second  16  end caps are attached to the outer shell  12  by using a spin process. This spin process is well-known in the art and will not be discussed in detail.  
         [0026]     A heat shield  18  is mounted to the muffler  10  to reduce adverse effects of heat generated by the muffler  10 . The heat shield  18  has a first shield end  20  mounted to the first end cap  14  at a first attachment interface and a second shield end  22  mounted to the second end cap  16  at a second attachment interface. The heat shield  18  extends along an upper length of the outer shell  12  and is to be positioned between the muffler  10  and a vehicle structure, such as a floor (not shown).  
         [0027]     The heat shield  18  can be attached to the first  14  and second  16  end caps in many different manners to define the first and second attachment interfaces. In one example, at least one retaining clip  24  is used to secure each of the first  20  and second  22  shield ends to the respective first  14  and second  16  end caps. A detail of the retaining clip  24  is shown in  FIG. 2A  for attaching the first shield end  20  to the first end cap  14 . It should be understood that the second shield end  22  would be attached to the second end cap  16  in a similar manner.  
         [0028]     As shown in  FIG. 2A , the outer shell  12  includes an outer end  28  and the first end cap  14  includes an outer peripheral edge  30 . The spin process aligns the outer end  28  and outer peripheral edge  30  and spins or folds the outer peripheral edge  30  over the outer end  28  to form a muffler end cap spin attachment, shown generally at  32 . The first shield end  20  is positioned over the muffler end cap spin attachment  32  and the retaining clip  24  is used to secure the heat shield  18  to the first end cap  14 .  
         [0029]     In this attachment configuration, the first shield end  20  directly engages an end cap portion adjacent the outer peripheral edge  30 . The retaining clip  24  has a first portion  36  that directly engages the first shield end  20  and a second portion  38  that directly engages an external surface  40  of the first end cap  14 .  
         [0030]     A single retaining clip can be used to secure the heat shield  18  to the muffler  10  or a plurality of retaining clips  24 , as shown in  FIG. 2B , can be used to secure the heat shield  18  to the muffler  10 . The first shield end  20  is attached to the first end cap  14  preferably only along an upper portion of the first end cap  14 . The single retaining clip  24  can be positioned anywhere along the upper portion. Optionally, the single retaining clip  24  could be configured to extend continuously along the upper portion.  
         [0031]     In the attachment configuration shown in  FIG. 2B , each retaining clip  24  is spaced apart from an adjacent retaining clip  24  along the upper portion. The number of retaining clips  24  needed may vary depending upon muffler size, vehicle application, or other known characteristics.  
         [0032]     As shown in  FIG. 2A , the heat shield includes a body portion  42  that is spaced apart from an external surface  44  of the outer shell  12  to define a gap  46 . The gap  46  allows the body portion  42  to flex or move to accommodate thermal expansion as the muffler  10  heats up and cools down. The heat shield  18  is shown in a thermally expanded position in  FIG. 2A . An example of a heat shield position at a cooler temperature is shown by dashed lines at  48 . During thermal expansion, a small amount of relative movement occurs between the first shield end  20  and the first end cap  14 . The retaining clip  24  allows sufficient movement to accommodate thermal expansion but prohibits separation of the heat shield  18  from the muffler. The invention also prohibits any rattling noise.  
         [0033]     The retaining clip  24  can be formed from a resilient spring material that is snapped over the first end cap  14 . The retaining clip  24  could also be deformed over the muffler end cap spin attachment  32  with tack welds being used if needed. An example of a tack weld location is shown at  50 . The retaining clip  24  could also be staked in place using a manual or automated process. Optionally, the first end cap  14  could include a retention feature  52  that cooperates with the retaining clip  24  to provide a more secure attachment interface as needed.  
         [0034]     Another attachment interface  54  for attaching the first shield end  20  to the first end cap  14  is shown in  FIG. 3 . It should be understood that the second shield end  22  would be attached to the second end cap  16  in a similar manner. This attachment interface  54  includes deforming the first shield end  20  around the muffler end cap spin attachment  32 . The first shield end  20  is thus mechanically locked in place by forming or crimping the first shield end  20  over the muffler end cap spin attachment  32 . Staking operations could also be performed after attachment to provide a more secure attachment as needed. One benefit with this configuration is that additional hardware, such as clips, is eliminated.  
         [0035]     Another attachment interface  60  for attaching the first shield end  20  to the first end cap  14  is shown in  FIGS. 4A-4C . It should be understood that the second shield end  22  would be attached to the second end cap  16  in a similar manner. This attachment interface  60  includes the use of a retaining ring  62  that is snapped over, formed over, or crimped over the first shield end  20  and the muffler end cap spin attachment  32 .  
         [0036]     As shown in  FIG. 4A , the heat shield  18  only covers an upper portion of the outer shell  12 . In this attachment configuration, the retaining ring  62  is installed over the entire perimeter of the first end cap  14 . As shown in  FIG. 4B , the retaining ring  62  includes a first portion  64  that directly engages the first shield end  20  and a second portion  66  that directly engages the external surface  40  of the first end cap  14 . Crimping or staking, as indicated at  68  in  FIG. 4C , could also be used as needed. The retaining ring  62  can be formed from resilient spring steel or other similar material.  
         [0037]     As discussed above, the heat shield  18  can be attached to the first  14  and second  16  end caps in many different manners to define the first and second attachment interfaces.  FIGS. 2A-2B ,  3 , and  4 A- 4 C show different examples of these attachment interfaces. It should be understood that similar attachments could be used for both the first and second attachment interfaces, or different attachments could be used for each of the first and second attachment interfaces. Further, each attachment interface could be used with different types of heat shields.  
         [0038]     One example of a heat shield is shown generally at  70  in  FIG. 5 . In this configuration, the heat shield includes a longitudinally extending body  72  that is attached to the first  14  and second  16  end caps by any of the attachment methods described above. The longitudinally extending body includes a plurality of convolutes  76  that extend outwardly, away from the outer shell  12 . The convolutes  76  are positioned transverse to a longitudinal axis L defined by the longitudinally extending body  72 . The convolutes  76  allow the heat shield  70  to flex in a manner similar to movement of an accordion. This flexing movement occurs as the muffler  10  heats up and cools down. This movement dissipates stress that would otherwise attempt to degrade heat shield/end cap attachment interfaces.  
         [0039]     Another example of a heat shield  80  is shown in  FIG. 6 . In this example, the heat shield  80  includes a first portion  82  and a second portion  84  that is attached to the first portion  82  via an adjustable attachment interface  100 . The adjustable attachment interface  100  allows the overall length of the heat shield  80  to be adjusted between a plurality of overall lengths within a predetermined range of overall lengths.  
         [0040]     In the example shown, the first  82  and second  84  portions overlap and are connected with a series of Belleville washers  86  and fasteners, such as rivets  88 . At least one of the first  82  and second  84  portions includes a series of slots  90  that receive the rivets  88 . Strengthening ribs  92  are formed on the first  82  and second  84  portions. The strengthening ribs  92  extend generally parallel to a longitudinal axis L defined by the heat shield  80 .  
         [0041]     An example of a rivet  88  being received within a slot  90  is shown in  FIG. 7 . The Belleville washer  86  is positioned on an external surface  94  of the first  82  or second  84  portion depending on which of the first  82  or second  84  portions is overlaid on top of the other of the first  82  or second  84  portions. The rivet  88  and Belleville washer  86  can be moved linearly back and forth within the slot  90  (see  FIG. 8 ) to adjust the overall length. The Belleville washer  86  includes turned up edges  96  (see  FIG. 9 ) to prevent the Belleville washer  86  from digging into the heat shield  80 .  
         [0042]     The linear movement allows adjustment of the heat shield  80  prior to attaching the heat shield  80  to the first  14  and second end caps  16  as described above. This allows a common heat shield assembly to be used for mufflers  10  of different lengths within a predetermined range. Also, mufflers of even greater or lesser lengths than the predetermined range could also benefit from this type of heat shield  80  as only one of the first  82  or second  84  portions would have to be changed to accommodate the variable length.  
         [0043]     Further, the linear movement of the rivet  88  within the slot  90  can occur during vehicle operation. This allows for the difference in thermal expansion between the muffler  10  and the heat shield  80  generated during normal thermal cycling. This helps to dissipate stress that would otherwise attempt to degrade heat shield/end cap attachment interfaces. The Belleville washers  86  keep tension on the adjustable attachment interface  100 , which allows this relative movement without having looseness or rattling.  
         [0044]     Although a preferred embodiment of this invention has been disclosed, a worker of ordinary skill in this art would recognize that certain modifications would come within the scope of this invention. For that reason, the following claims should be studied to determine the true scope and content of this invention.