Abstract:
A lightweight exhaust component cover having a small number of components is disclosed. In the exhaust component cover, an internal plate is formed by bending part of a single plate at both ends, and the internal plate is joined to the inside surface of an external plate.

Description:
FIELD OF THE INVENTION 
     The present invention relates to an exhaust component cover for covering an exhaust component. 
     BACKGROUND OF THE INVENTION 
     Mufflers, for example, and other exhaust components extending from an engine include exhaust component covers referred to as noise and heat insulation covers installed particularly in regions prone to sound and heat, such as is disclosed in Japanese Patent Application Laid-Open Publication No. 2002-87078 (JP 2002-087078 A), for example. The exhaust component cover disclosed in JP 2002-87078 A is shown in  FIG. 14  hereof. 
     Referring to  FIG. 14 , an exhaust component cover  100  is manufactured by joining an internal plate  103  to an external plate  101  via aluminum foil  102 , bending one end of the external plate  101  in the direction of the internal plate  103 , and then integrally press-forming the external plate  101 , the aluminum foil  102 , and the internal plate  103  together. 
     The exhaust component cover  100  manufactured in this manner covers regions of the exhaust component prone to sounds, and muffles noise produced by the exhaust component. 
     While the engine is operating, the vibration of the engine is transmitted to the exhaust component, and the vibration is further transmitted to the exhaust component cover. This vibration causes self-excited vibration in the exhaust component cover, and also causes so-called radiant noise. 
     The natural frequency fn of the exhaust component cover  100  is expressed by the equation fn=1/(2π)×(k/m) 0.5 . The letter k denotes a spring constant whose numerical value differs depending on the material, and the letter m denotes mass. 
     When the external plate  101  and the internal plate  103  have different thicknesses, the external plate  101  and the internal plate  103  also have different masses in; therefore, the external plate  101  and the internal plate  103  will have different natural frequencies fn, and the vibration can be damped. 
     However, in order to damp the vibration of the exhaust component cover  100  described above, an external plate  101  and an internal plate  103  of different thicknesses must be prepared, increasing both the weight and number of components. 
     SUMMARY OF THE INVENTION 
     It is therefore an object of the present invention to provide a lightweight exhaust component cover that can be manufactured with a small number of components. 
     According to one aspect of the present invention, there is provided an exhaust component cover comprising an external plate designed so as to cover an exhaust component, and an internal plate formed by bending part of the external plate, the internal plate being joined to the inside surface of the external plate. 
     Thus, in the present invention, only a single plate need be prepared because the internal plate is formed by bending part of the external plate. Specifically, the number of components can be reduced and material costs can be curtailed because there is no need to prepare two plates of different thicknesses. Furthermore, since the internal plate is formed by bending the two ends of the external plate, a space can be created between two halves of the internal plate. In other words, there is no need to join the internal plate to the entire inside surface of the external plate. Therefore, the weight of the exhaust component cover can be reduced. Furthermore, forming the internal plate by bending part of the external plate causes only the external plate to be visible from the outside. The outward appearance of the exhaust component cover is improved by forming the external plate from a single plate. 
     It is preferred that a plurality of punched holes be formed in the internal plate. Therefore, the weight of the internal plate can be reduced, and the exhaust component cover can be further reduced in weight. 
     It is preferred that the external plate have a plurality of louvers formed so as to allow air to flow from the outside of the external plate to the inside, and that each of the louvers have a semicircular shape when the exhaust component cover is viewed from the outside, the semicircles each being one fourth of a spherical shell extending outward from the exhaust component cover. Radiant heat that extends in a straight line from the exhaust component to the exhaust component cover is blocked by the exhaust component cover. However, communicating the outside of the exhaust component cover with the inside via the louvers allows convection current to be created from the outside of the exhaust component cover to the inside. Heat can be radiated to the outside by this convection current. Therefore, heat is not readily confined between the exhaust component and the exhaust component cover, and the temperature of the exhaust component cover can be reduced. 
     It is preferred that the external plate have a plurality of louvers formed so as to allow air to flow from the outside of the external plate to the inside, and that each of the louvers have a circular shape obtained by combining two semicircles when the exhaust component cover is viewed from the outside, one semicircle being one fourth of a spherical shell extending outward from the exhaust component cover, and the other semicircle being one fourth of a spherical shell recessed toward the exhaust component. Therefore, the amount of air taken in from the exterior of the exhaust component cover can be increased, and the cooling performance of the exhaust component can be further improved. 
     According to another aspect of the present invention, there is provided an exhaust component cover comprising an internal plate designed so as to cover an exhaust component, and an external plate formed by bending part of the internal plate, the external plate being joined to the outside surface of the internal plate. 
     Thus, in the exhaust component cover according to the other aspect, only a single plate need be prepared because the external plate is formed by bending part of the internal plate. Specifically, the number of components can be reduced and material costs can be curtailed because there is no need to prepare two plates of different thicknesses. Furthermore, since the external plate is formed by bending the two ends of the internal plate, a space can be created between two halves of the external plate. In other words, there is no need to join the external plate to the entire outside surface of the internal plate. Therefore, the weight of the exhaust component cover can be reduced. Furthermore, forming the external plate by bending the two ends of the internal plate causes the internal peripheral surface of the internal plate to lie within a single plane. Therefore, the size of the exhaust component cover can be made closer to the size of the exhaust component, and the exhaust component cover can be made more compact. 
     It is preferred that a plurality of punched holes be formed in the external plate. Therefore, the external plate can be made more lightweight, and the weight of the exhaust component cover can be further reduced. 
     In a preferred form, the internal plate has a plurality of louvers formed to allow air to flow from outside of the internal plate to inside of the latter. Each of the louvers may have a semicircular shape when the exhaust component cover is viewed from the outside. The semicircles each may be one fourth of a spherical shell extending outwardly from the exhaust component cover. 
     In a desired form, the internal plate has a plurality of louvers formed to allow air to flow from outside of the internal plate to inside of the latter. Each of the louvers may have a circular shape obtained by combining two semicircles when the exhaust component cover is viewed from the outside. One semicircle may be one fourth of a spherical shell extending outwardly from the exhaust component cover while the other semicircle may be one fourth of a spherical shell recessed toward the exhaust component. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Certain preferred embodiments of the present invention will be described in detail below, by way of example only, with reference to the accompanying drawings, in which: 
         FIG. 1  is a perspective view showing an exhaust component cover according to a first embodiment of the present invention; 
         FIG. 2  is a view of the exhaust component as seen in the direction of arrow  2  of  FIG. 1 ; 
         FIG. 3  is a cross-sectional view taken along line  3 - 3  of  FIG. 1 ; 
         FIG. 4  is a cross-sectional view taken along line  4 - 4  of  FIG. 1 ; 
         FIGS. 5A through 5C  are schematic views illustrating a method for manufacturing the exhaust component cover of  FIG. 1 ; 
         FIGS. 6A through 6C  are schematic views illustrating a method for manufacturing an exhaust component cover according to a second embodiment of the present invention; 
         FIG. 7  is a perspective view showing an exhaust component cover according to a third embodiment of the present invention; 
         FIG. 8  is a cross-sectional view showing the exhaust component cover according to the third embodiment shown in  FIG. 7 ; 
         FIG. 9  is a view showing a louver as seen in the direction of arrow  9  of  FIG. 8 ; 
         FIG. 10  is a cross-sectional view taken along line  10 - 10  of  FIG. 8 ; 
         FIGS. 11A through 11D  are schematic views showing the exhaust component cover according to the third embodiment of the present invention, as compared to conventional exhaust component covers; 
         FIGS. 12A and 12B  are views showing a modification of the exhaust component cover according to the third embodiment shown in  FIGS. 11C and 11D ; 
         FIG. 13  is a cross-sectional view showing an exhaust component cover according to a fourth embodiment of the present invention; and 
         FIG. 14  is a cross-sectional view showing a conventional exhaust component cover. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Reference is now made to  FIGS. 1 through 4  showing an exhaust component cover according to the first embodiment of the present invention. 
     As shown in  FIG. 1 , an exhaust component cover  10  is comprised of an external plate  12  for covering an exhaust component  11  shown by imaginary lines, an internal plate  13  formed by bending part of the external plate  12 , and a plurality of bolt holes  14 ,  14  formed through the external plate  12  and the internal plate  13  in order to attach the exhaust component cover  10  to the exhaust component  11 . In addition to an automotive muffler or catalyzer, another possible example of the exhaust component  11  is a common exhaust tube. 
     The reference numerals  15 ,  15  denote weld marks formed when the internal plate  13  is spot welded to the external plate  12 . 
     Welding, crimping, riveting, bolting, screwing, or any other desired method can be used to join the internal plate  13  to the external plate  12 , and the joining method is not limited to spot welding. 
     Forming the internal plate  13  by bending part of the external plate  12  allows only the external plate  12  to be outwardly visible. Forming the external plate  12  from a single plate allows the exhaust component cover  10  to have a satisfactory outward appearance. 
     Two halves of the internal plate  13 ,  13  are formed by bending part of the external plate  12  so that the two halves are joined to the inside surface of the external plate  12 , as shown in  FIG. 2 . Since the internal plate  13  is formed by bending part of the external plate  12  in this manner, the exhaust component cover  10  can be manufactured from a single plate. The portions where the external plate  12  is bent constitute end parts  17 ,  17  of the exhaust component cover  10 . Specifically, high strength can be obtained because the end parts  17 ,  17  are formed by bending. 
     Forming the two halves of the internal plate  13 ,  13  by bending part of the external plate  12  allows the edge portions  18 ,  18  of the external plate  12  to be folded inward. Since the edge portions  18 ,  18 , which are textured by trimming, are folded inward, the portions exposed to the exterior (i.e., the end parts  17  and the external plate  12 ) can be made flat. Flattening the exposed portions and folding the textured portions inward increases the safety of the operation for attaching the exhaust component cover  10 . 
     A plurality of punched holes  16  is formed in the internal plate  13 , and tapered parts  12   a ,  12   a  formed by drawing are provided to the front and rear ends, as shown in  FIG. 3 . Since the punched holes  16  are formed in the internal plate  13 , the mass of the internal plate can be reduced. The weight of the exhaust component cover  10  can be reduced by reducing the mass of the internal plate  13 . 
     The bolt holes  14 ,  14  are formed through the external plate  12  and the internal plate  13 . Specifically, the bolt holes  14 ,  14  are formed in the portions where the internal plate  13  is positioned. The accumulation of stress from forming the bolt holes  14  can be minimized and strength can be ensured to a greater degree than in a case of opening holes in portions of the external plate  12  alone. The joining strength between the external plate  12  and the internal plate  13  can be increased by providing the bolt holes  14  to the portions where the internal plate  13  is positioned. 
     Moreover, the internal plate  13  is folded onto the external plate  12  to provide a two-ply construction and fastened to the exhaust component  11 . Owing to this arrangement, engine vibrations transmitted to the exhaust component  11 , even inputted into the two-ply part forming the internal plate  13 , can hardly be transmitted to the single-ply external plate  12  because there is produced a large difference in rigidity between the two-ply part and the single-ply part of the external plate  12 . 
     Since the bolt holes  14  are formed through the external plate  12  and the internal plate  13 , there is no need to provide separate flanges or the like when attaching the exhaust component cover  10  to the exhaust component  11  ( FIG. 1 ). Since there is no need to provide flanges or the like, the exhaust component cover  10  can be made more compact. 
     The natural frequency fn related to the vibration of the exhaust component cover  10  is expressed by the equation fn=1/(2π)×(k/m) 0.5 , as shown in  FIG. 4 . The letter k denotes a spring constant, whose numerical value differs depending on the material, and the letter m denotes mass. 
     Since the punched holes  16  are formed in the two halves of the internal plate  13 ,  13 , the internal plate  13  is lighter than the external plate  12  by an amount proportionate to the punched holes  16 . Since the internal plate  13  is formed by bending part of the external plate  12 , the spring constant k is the same value for both the internal plate  13  and the external plate  12 . Since the mass m differs between the external plate  12  and the internal plate  13  as described above, the natural frequency fn differs between the external plate and the internal plate, and the vibration characteristics can be improved. 
     Since the internal plate  13  is formed by bending the two ends of the external plate  12 , a space between two halves of the internal plate  13 ,  13  can be formed. Specifically, there is no need to join the internal plate  13  to the entire inside surface of the external plate  12 . The weight of the exhaust component cover  10  can be reduced by not joining the internal plate  13  to the entire inside surface of the external plate  12 . This type of method for manufacturing an exhaust component cover is described based on  FIGS. 5A through 5C . 
     In the external plate  12 , the punched holes  16  are formed by punching the portions that will be bent and become the internal plate, as shown in  FIG. 5A . 
     Next, the portions where the punched holes  16  are formed are bent inward as shown by the arrows ( 1 ) in  FIG. 5B , and the internal plate  13  is formed. The plate in which the internal plate  13  is formed is press-formed as shown in  FIG. 5C , manufacturing the exhaust component cover  10 . 
     Any desired shape can be obtained by the subsequent application of drawing as necessary. Forming the bolt holes  14  ( FIG. 1 ) and joining the internal plate  13  and the external plate  12  together can be performed with the desired timing after the internal plate  13  is formed. 
     In the exhaust component cover  10  according to the first embodiment, an example was described in which a plurality of punched holes was formed, but the present invention is not limited to this option alone, and another option is an exhaust component cover in which a plurality of punched holes  16  has not been formed.  FIGS. 6A through 6C  show a method for manufacturing an exhaust component cover according to a second embodiment. 
     First, a plate that will become an internal plate  24  is prepared as shown in  FIG. 6A . 
     Next, the two ends of the internal plate  24  are bent as shown by the arrows ( 2 ) in  FIG. 6B , and an external plate  25  is formed. 
     The plate in which the external plate  25  is formed is press-formed into a cross-sectional arcuate shape as shown in  FIG. 6C , and an exhaust component cover  20  is manufactured. 
     Thus, the internal peripheral surface of the internal plate  24  becomes what is referred to as flush by bending the two ends of the internal plate  24  to form the external plate  25 . A flush internal peripheral surface of the internal plate  24  makes it possible for the size of the exhaust component cover  20  to be nearer to the size of the exhaust component. The exhaust component cover  20  can thereby be made more compact. 
     In the second embodiment, an example of an exhaust component cover was described in which a plurality of punched holes was not formed, but the present invention is not limited to this option alone, and the external plate may be formed by bending the two ends of the internal plate in addition to forming a plurality of punched holes. 
       FIGS. 7 and 8  show an exhaust component cover  30  according to the third embodiment. In the description of the exhaust component cover  30  according to the third embodiment, members similar to those of the exhaust component cover  10  presented in the first embodiment are described using the same numerical symbols. 
     Referring to  FIGS. 7 and 8 , the exhaust component cover  30  according to the third embodiment is disposed so as to cover the exhaust component  11  shown by the imaginary lines. Specific examples of the exhaust component  11  would be the same as the components suggested in the description of the first embodiment. 
     The exhaust component cover  30  is attached to the exhaust component  11  by fitting bolts through the bolt holes  14 ,  14  formed in the exhaust component cover  30  via stays or the like (not shown) mounted on the exhaust component  11 . 
     The exhaust component cover  30  has an external plate  12 , two halves of the internal plate  13 ,  13  formed by bending part of the external plate  12  so as to join the halves to the internal sides of the external plate  12 , and a plurality of louvers  31  formed on the top surface of the external plate  12 , as shown in  FIG. 8 . The exhaust component  11  is exposed to the exterior via the louvers  31 . 
     The two halves of the internal plate  13 ,  13  have a plurality of punched holes  16 . These punched holes  16  are formed in advance in the portions of the external plate  12  that will be bent to form the two halves of the internal plate  13 ,  13 . 
     When the pulsation of exhaust gas is transmitted to the exhaust component  11  in the form of vibration, the vibration is further transmitted to the exhaust component cover  30 . At this time, the natural frequency fn of vibration of the exhaust component cover  30  is expressed by the equation fn=1/(2π)×(k/m) 0.5 . The letter k denotes a spring constant whose numerical value differs depending on the material, and the letter m denotes mass. 
     Since the two halves of the internal plate  13 ,  13  are the same material as the external plate  12 , the spring constant k is the same value as in the external plate  12 . Since the mass m differs between the external plate  12  and the two halves of the internal plate  13 ,  13  by an amount proportionate to the punched holes  16  formed in the two halves of the internal plate  13 ,  13 , the natural frequency fn differs between the external plate  12  and the two halves of the internal plate  13 ,  13 , and the vibration characteristics can be improved. 
     Furthermore, the rigidity of the exhaust component cover  30  is increased by forming the louvers  31  into semicircular shapes. 
     The louvers  31  have top and bottom semicircular portions whose border is the external plate  12 , and the louvers are circular as a whole, as shown in  FIGS. 9 and 10 . The top semicircular portions are convex parts  32  extending upward, and the bottom semicircular portions are concave parts  33  recessed downward. Each convex part  32  is a fourth of a spherical shell extending outward from the exhaust the external plate  12  (upward), and each concave part  33  is a fourth of a spherical shell recessed toward the exhaust component  11  ( FIG. 8 ) disposed on the inside of the external plate  12  (downward). Distal ends  34  of the convex parts  32  and distal ends  35  of the concave parts  33  lie along vertical straight lines. 
     Next, the operation of the exhaust component cover  30  according to the third embodiment will be described based on  FIGS. 11A through 11D , using conventional examples for the sake of comparison.  FIGS. 11A and 11B  show conventional examples, and  FIGS. 11C and 11D  show the exhaust component cover according to the third embodiment. 
     In Conventional Example 1, an exhaust component cover  110  does not have holes for radiation; therefore, radiant heat from an exhaust component  111  is blocked as shown by the arrows ( 2 ), and heat is confined between the exhaust component  111  and the exhaust component cover  110 . 
     In Conventional Example 2, in which a plurality of holes  113  is formed in an exhaust component cover  112  as shown in  FIG. 11B , radiant heat from the exhaust component  111  is radiated to the exterior through the holes  113 , as shown by the arrows ( 3 ). In other words, heat is not confined, but the radiant heat cannot be blocked. 
     In  FIG. 11C , when the exhaust component cover  30  according to the third embodiment is used, radiant heat can be blocked by the exhaust component cover  30  as shown by the arrows ( 4 ), cooling air can be taken into the exhaust component cover  30  from the exterior as shown by the arrow ( 5 ) in  FIG. 11D , and the exhaust component  11  can be cooled. 
     In other words, radiant heat shown by arrows ( 4 ) extending directly toward the exterior comes up against and is blocked by the exhaust component cover  30  as shown in  FIGS. 11C and 11D . Communicating the inside of the exhaust component cover  30  with the outside through the louvers  31  allows a convection current to be created from the exterior of the exhaust component cover  30  to the interior. Heat can be radiated to the exterior by this convection current, and the temperature of the exhaust component  11  can be reduced. Furthermore, the exhaust component cover  30  is also capable of blocking sound that expands directly outward in the same manner as the radiant heat. 
       FIGS. 12A and 12B  show a modification of the exhaust component cover according to the third embodiment shown in  FIGS. 7 through 10 . The louvers  31  in this modification are composed only of top convex parts  32 . 
     In  FIG. 12A , the exhaust component cover  30  according to the modification blocks radiant heat as shown by the arrows ( 6 ), and the exhaust component  11  can be cooled by cooling air being taken in from the exterior as shown in  FIG. 12B . 
     Reference is now made to  FIG. 13  showing an exhaust component cover  40  according to a fourth embodiment of the present invention. Opposite ends of an internal plate  42  is bent outwardly to thereby provide an external plate  43 . Then, the external plate  43  press-formed into an arc shaped in cross section to thereby provide the exhaust component cover  40 . The internal plate  42  has a flush internal peripheral surface, like the arrangement according to the second embodiment shown in  FIG. 2 . The external plate  43  has a plurality of punched holes. 
     The exhaust component cover  40  according to the fourth embodiment of the present invention has a plurality of louvers  44  constructed similarly to the louvers formed in the external plate of the exhaust component cover according to the third embodiment discussed in relation to  FIG. 8 . 
     Namely, the internal plate  42  has the louvers  44  that allow air to flow from outside the internal plate into inside the latter. The exhaust component  11  is thus placed in air communication with outside through the louvers  44 . Each louver  44  has a circular shape formed by upper (top) and lower (bottom) semicircular portions separated by the internal plate  42 , like the louver according to the third embodiment discussed in relation to  FIGS. 9 and 10 . 
     Upper semicircular portion comprises a convex part protruding upwardly while the lower semicircular portion comprises a concave part recessed downwardly. The convex part is a one fourth of a spherical shell extending outwardly (upwardly) of the internal plate  42 . The concave part is a one fourth of a spherical shell extending internally (downwardly) of the internal plate  42  toward the exhaust component  11 . 
     The exhaust component cover  40  according to the fourth embodiment operates similarly to the exhaust component cover  30  according to the third embodiment and produces results similar to those produced by the latter. 
     Obviously, various minor changes and modifications of the present invention are possible in light of the above teaching. It is therefore to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described.