Patent Abstract:
Disclosed is an exhaust purification device in which an entire length of an outer cylinder of a catalyst can be used effectively for exhaust purification and it is possible to prevent heat in fixing of the catalyst to an exhaust pipe from affecting a connection portion between the outer cylinder and catalyst main bodies. A catalyst includes an outer cylinder and a plurality of catalyst main bodies provided in the outer cylinder in a state of being spaced each other in a direction of an axial center of the outer cylinder. An outer face of the outer cylinder positioned between the catalyst main bodies is a fixed face to be fixed to an inside of the exhaust pipe.

Full Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an exhaust purification device structured by providing a catalyst in an exhaust pipe of a vehicle or the like. 
     2. Description of the Related Art 
     In a vehicle such as a two-wheeled motor vehicle and a four-wheeled automobile, a catalyst is provided in an exhaust pipe in order to remove hydrocarbon (HC), nitrogen oxides (NOx), and the like included in exhaust gas. In Japanese Patent Application Laid-open No. 60-17220, there is disclosed a technique in which a catalyst is provided in a muffler of the exhaust pipe of the two-wheeled motor vehicle. 
       FIG. 8  is a sectional view showing an example of the exhaust pipe provided with the catalyst. The catalyst  100  includes an outer cylinder  102  and a catalyst main body  103  provided in the outer cylinder  102 . The outer cylinder  102  is made of metal such as stainless steel. The catalyst main body  103  is formed by depositing catalyst metal on a surface of a honeycomb structure made of stainless steel or the like. The catalyst main body  103  is secured to an inner face of the outer cylinder  102  by brazing. 
     In fixing the catalyst  100  to the exhaust pipe  101 , if an outer face of the outer cylinder  102  positioned on an outer periphery side of the catalyst main body  103  is subjected to welding, the brazed portion between the outer cylinder  102  and the catalyst main body  103  is susceptible to heat. Therefore, an end portion  102 A of the outer cylinder  102  is caused to protrude from the catalyst main body  103  along a direction of an axial center O 1  of the catalyst  100  and welding W 5  is applied to this protruding portion, thereby preventing heat from affecting the brazed portion between the outer cylinder  102  and the catalyst main body  103 . 
     However, if the end portion  102 A of the outer cylinder  102  is caused to protrude from the catalyst main body  103 , there is a useless area that does not contribute to purification of the exhaust gas in the outer cylinder  102 . Therefore, this catalyst is inferior in purification performance to a catalyst in which a catalyst main body is provided throughout an inside of the outer cylinder  102  by an amount corresponding to the useless area. 
     SUMMARY OF THE INVENTION 
     The present invention addresses the above described condition, and an object of the present invention is to provide an exhaust purification device in which an entire length of an outer cylinder of a catalyst can be used effectively for exhaust purification and it is possible to prevent heat in fixing of the catalyst to an exhaust pipe from affecting the catalyst. 
     According to the invention, there is provided an exhaust purification device structured by providing a catalyst in an exhaust pipe, wherein the catalyst includes an outer cylinder and a plurality of catalyst main bodies provided in the outer cylinder in a state of being spaced from each other in an axial direction of the outer cylinder, and an outer face of the outer cylinder positioned between the plurality of catalyst main bodies is a fixed face to be fixed to an inside of the exhaust pipe. 
     As described above, if the plurality of catalyst main bodies are disposed spaced apart from each other in the outer cylinder, the exhaust gas which has passed through one of the catalyst main bodies is first mixed in the space between the catalyst main bodies and then passes through the other catalyst. Therefore, it is possible to uniformly purify the exhaust gas with the entire length of the catalyst main bodies. Therefore, the catalyst formed by providing the plurality of catalyst main bodies at intervals in the outer cylinder can exert substantially the same performance in spite of smaller amounts of catalyst main bodies as compared with a catalyst formed by providing one catalyst main body throughout an outer cylinder of the same length. 
     Therefore, in the present invention, the entire length of the outer cylinder can be utilized for purifying the exhaust gas and can exert substantially the same performance as the catalyst formed by providing one catalyst main body throughout the outer cylinder. Moreover, because the catalyst is fixed to the exhaust pipe through the fixed face positioned on the outer periphery side of the space between the plurality of catalyst main bodies, it is possible to prevent heat in fixing of the catalyst to the exhaust pipe from affecting a connection portion between the outer cylinder and the catalyst main bodies. 
     Preferably, a mounting bracket may be fixed to an inner face of the exhaust pipe and the fixed face may be fixed to the mounting bracket. 
     In accordance with this structure, a difference between a shape of the inner face of the exhaust pipe and a shape of the outer face of the catalyst can be accommodated by the mounting bracket, thereby properly fixing the catalyst irrespective of an inside shape of the exhaust pipe. 
     Preferably, the plurality of catalyst main bodies may have different axial lengths and the catalyst main body of the shorter axial length may be disposed at an upstream side of the longer catalyst main body in an exhaust gas flowing direction. 
     In accordance with this structure, because the exhaust gas of higher temperature circulates through the shorter catalyst main body, it is possible to further promote increase in temperature of the catalyst main body to activate the catalyst main body, thereby enhancing purification efficiency. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and other objects and features of the present invention will become more clear from the following description taken in conjunction with a preferred embodiment thereof with reference to the accompanying drawings. 
         FIG. 1  is a plan view of exhaust pipes according to a first embodiment of the present invention. 
         FIG. 2  is an enlarged sectional view of the exhaust pipe of  FIG. 1 . 
         FIG. 3  is an enlarged sectional view of a fixed portion of a catalyst in the exhaust pipe (an enlarged sectional view of a part III in  FIG. 2 ). 
         FIG. 4  is a plan view of an exhaust pipe according to a second embodiment of the present invention. 
         FIG. 5  is an enlarged sectional view of a fixed portion of a catalyst in the exhaust pipe (an enlarged sectional view of a part V in  FIG. 4 ). 
         FIG. 6  is a sectional view of an exhaust pipe according to a third embodiment of the present invention. 
         FIG. 7  is an enlarged sectional view of a fixed portion of a catalyst in the exhaust pipe (an enlarged sectional view of a part VII in  FIG. 6 ). 
         FIG. 8  is a sectional view of a prior-art exhaust pipe. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       FIG. 1  is a plan view of an exhaust purification device according to a first embodiment of the present invention. The exhaust purification device includes two exhaust pipes  11  and the exhaust pipes  11  are connected to respective cylinders of a V-type two-cylinder engine  10 . Each of the exhaust pipes  11  includes a first pipe portion  13  with its front end connected to each of the cylinders of the engine and a second pipe portion  14  connected to a rear end of the first pipe portion  13 . The second pipe portion  14  forms a muffler in which expansion chambers are formed. 
       FIG. 2  is an enlarged sectional view of a muffler (second pipe portion)  14 . An outer shell of the second pipe portion (the muffler)  14  is formed of an outer cylinder body  16  and an inner cylinder body  17  (i.e. an exhaust pipe  17 ) disposed inside the outer cylinder body  16 . Inside the inner cylinder body  17 , a first expansion chamber  18 , a second expansion chamber  19 , and a third expansion chamber  20  are formed. The muffler  14  is disposed in a front-rear direction and exhaust gas flows front to rear in a direction X in the muffler  14 . 
     A coupling pipe body  21  is attached to the first expansion chamber  18 . A front portion of the coupling pipe body  21  protrudes forward from the first expansion chamber  18  and is connected to the first pipe portion  13  ( FIG. 1 ). A rear portion of the coupling pipe body  21  is supported on the inner cylinder body  17  through a support plate  23  and a large number of first circulation holes  21 A are formed to penetrate an outer peripheral face of the rear portion. A plurality of openings  23 A are formed in the support plate  23  in a circumferential direction. Therefore, the exhaust gas flowing from the first pipe portion  13  passes through the coupling pipe body  21 , flows into the first expansion chamber  18  through the first circulation holes  21 A, and flows behind the support plate  23  through the openings  23 A in the support plate  23 . 
     Between the first expansion chamber  18  and the second expansion chamber  19 , a first partition  35  is provided. A catalyst  30  is provided in such a manner as to penetrate the first partition  35 . The exhaust gas flows from the first expansion chamber  18  through the catalyst  30  into the second expansion chamber  19 . The catalyst  30  will be described later. 
     Between the second expansion chamber  19  and the third expansion chamber  20 , a second partition  24  is provided. A rear end portion of the third expansion chamber  20  is closed with a rear end wall  25 . An intermediate pipe body  26  extending in the front-rear direction is provided to penetrate the second partition  24  and the rear end wall  25 . In the third expansion chamber  20 , the intermediate pipe body  26  is closed with a third partition  27 . A plurality of second circulation holes  26 A are formed in an outer peripheral face of the intermediate pipe body  26  positioned in front of the third partition  27  and in the second expansion chamber  19 . A plurality of third circulation holes  26 B are formed in the outer peripheral face of the intermediate pipe body  26  positioned in front of the third partition  27  and in the third expansion chamber  20 . A plurality of fourth circulation holes  26 C are formed in the outer peripheral face of the intermediate pipe body positioned behind the third partition  27  and in the third expansion chamber  20 . 
     The exhaust gas that has flowed into the second expansion chamber  19  flows into the intermediate pipe body  26  through the second circulation holes  26 A and flows into the third expansion chamber  20  through the third circulation holes  26 B. Then, the exhaust gas flows into the intermediate pipe body  26  through the fourth circulation holes  26 C and is emitted outside through a rear end opening of the intermediate pipe body  26 . 
     As shown in  FIG. 1 , the two exhaust pipes  11  are connected to each other through a connecting pipe  28 . Respective end portions of the connecting pipe  28  are connected to the first expansion chambers  18  in the mufflers  14  of the respective exhaust pipes  11  as shown in  FIG. 2 . In this way, the exhaust gas substantially uniformly flows into the two exhaust pipes  11 . 
     As shown in  FIG. 2 , the catalyst  30  is formed of a cylindrical outer cylinder  31  and catalyst main bodies  32 ,  33  disposed in the outer cylinder  31 . The outer cylinder  31  is made of metal such as stainless steel and is disposed with its-axial center O 1  oriented in the front-rear direction (exhaust flowing direction X). The catalyst main bodies  32 ,  33  are formed by depositing catalyst metal on surfaces of honeycomb structures made of stainless steel or the like. The catalyst main bodies  32 ,  33  are secured to the outer cylinder  31  by brazing. 
     The two catalyst main bodies  32 ,  33  are arranged side by side along the direction of the axial center O 1  (axial direction) of the outer cylinder  31  and a space S is formed between them. The catalyst main body  32  on the front side (upstream side of the exhaust flowing direction X) is formed to be shorter than the catalyst main body  33  on the rear side (downstream side). A front end of the front catalyst main body  32  is substantially aligned with a front end of the outer cylinder  31  and a rear end of the rear catalyst main body  33  is substantially aligned with a rear end of the outer cylinder  31 . 
     The catalyst  30  is fixed inside the muffler  14  through the first partition  35 . In other words, the first partition  35  also functions as a mounting bracket for fixing the catalyst  30  to the muffler  14 .  FIG. 3  is an enlarged sectional view of a fixed portion of the catalyst  30 . The first partition bracket (the mounting bracket)  35  is formed of an outer cylinder portion  35 A disposed along an inner face of the inner cylinder body  17  of the muffler  14 , an inner cylinder portion  35 B disposed along an outer face of the outer cylinder  31  of the catalyst  30  and displaced at a position apart from the outer cylinder portion  35 A in the direction of the axial center O 1  and in a radial direction, and a connecting cylinder portion  35 C inclined to connect adjacent end portions of the outer cylinder portion  35 A and the inner cylinder portion  35 B. The outer cylinder portion  35 A, the inner cylinder portion  35 B, and the connecting cylinder portion  35 C are formed integrally. 
     A plurality of through holes  17 A are formed in a portion of the inner cylinder body  17  which the outer cylinder portion  35 A of the mounting bracket  35  overlaps. By applying plug welding W 1  into the through holes  17 A, the outer cylinder portion  35 A is fixed to the inner face of the inner cylinder body  17 . 
     The outer face of the outer cylinder  31  of the catalyst  30  is fixed to the rear end of the inner cylinder portion  35 B of the mounting bracket  35  by fillet welding W 2  in a plurality of positions in the circumferential direction. A portion (fixed face)  31 A of the outer face of the outer cylinder  31  where the welding W 2  is applied is positioned on an outer periphery side of the space S between the front and rear catalyst main bodies  32 ,  33 . 
     Therefore, the present embodiment performs and exerts the following functions and effects. 
     (1) The space S is formed between the two catalyst main bodies  32 ,  33  and the portion (fixed face)  31 A of the outer face of the outer cylinder  31  positioned on the outer periphery side of the space S is fixed to the inner face of the muffler  14  through the mounting bracket  35 . Therefore, heat of welding W 2  is less likely to be transferred to the brazed portion between the outer cylinder  31  and the catalyst main bodies  32 ,  33  and it is possible to reduce the influence of the heat on the brazed portion. 
     (2) Because the catalyst  30  is fixed to the muffler  14  through the mounting bracket  35 , a shape of the catalyst  30  does not necessarily require to be adapted to an inside shape of the muffler  14  and the mounting bracket  35  is adaptable to the inside shape of the muffler  14 . Therefore, the catalyst  30  can be fixed properly irrespective of the inside shape of the muffler  14 . 
     (3) If one catalyst main body is provided in the outer cylinder as in the prior art, the exhaust gas flows through the same cell of the honeycomb from start to finish. Therefore, depending on temperature distribution, gas distribution, and the like in the catalyst main body, unevenness may develop in such a manner that purification is finished in one cell of the honeycomb while little progress has been made with purification in another cell of the honeycomb. In the catalyst  30  of the present embodiment, because the two catalyst main bodies  32 ,  33  are disposed with a clearance (space S) between them, the exhaust gas which has passed through the front catalyst main body  32  and has been purified is once mixed in the space S and then flows into the rear catalyst main body  33  and is purified again. Therefore, it is possible to purify the exhaust gas without causing unevenness by using the two catalyst main bodies  32 ,  33 , thereby enhancing purification efficiency. 
     In general, in the outer cylinders of the same length, one of which is provided with one catalyst main body throughout the length of the outer cylinder and the other of which is provided with two catalyst main bodies  32 ,  33  with the space S between them will have substantially the same performance. Therefore, in the catalyst  30  of the present embodiment, it is possible to reduce amounts of the catalyst main bodies  32 ,  33  by an amount corresponding to the space S, thereby reducing the cost. 
     (4) Because the catalyst  30  is disposed in the front portion of the muffler  14 , it is possible to circulate the exhaust gas of relatively high temperature, thereby promoting increase in temperature of the catalyst  30  so as to activate the catalyst  30 . 
     (5) In the catalyst  30 , because the front catalyst main body  32  is formed to be shorter than the rear catalyst main body  33 , it is possible to further promote increase in temperature of the front catalyst main body  32  through which the exhaust gas of the higher temperature circulates to activate the catalyst main body  32 , thereby enhancing the purification efficiency. 
       FIG. 4  is a plan view of a second embodiment of the present invention. Although the example in which the catalyst  30  is provided in the expansion chamber  19  of the muffler  14  has been shown in the first embodiment, an example in which the catalyst  30  is disposed in the exhaust pipe  11  before the muffler is shown in the present embodiment. An exhaust pipe  11  of the present embodiment is used for a parallel four-cylinder engine  10  and includes four first pipe portions  41  connected to exhaust ports of respective cylinders of the engine  10 , two first collecting pipes  42  for collecting four of the first pipe portions  41  into two, two catalyst pipes  43  connected to the respective first collecting pipes  42 , a second collecting pipe  44  for collecting the two catalyst pipes  43  into one, and a second pipe portion  45  connected to the second collecting pipe  44 . A branch pipe, a muffler, and the like (not shown) are connected to the second pipe portion  45 . 
     A catalyst  30  is disposed in each of the catalyst pipes  43 . The catalyst  30  of the present embodiment is also formed of an outer cylinder  31  and two catalyst main bodies  32 ,  33  provided in the outer cylinder  31 . However, two catalyst main bodies  32 ,  33  have substantially the same length and a space S is formed in a central portion in an axial direction of the outer cylinder  31 . The respective catalyst main bodies  32 ,  33  are brazed to the outer cylinder  31  through brazing foils  77  disposed at substantially central portions of outer peripheral faces of the catalyst main bodies  32 ,  33  in the direction of the axial center O 1 . 
       FIG. 5  is an enlarged sectional view of a fixed portion of the catalyst  30 . The mounting bracket  35  as used in the first embodiment ( FIG. 2 ) is not used in the present embodiment and the catalyst  30  is directly mounted to the exhaust pipe (catalyst pipe  43 ). A portion  31 A of an outer face of the outer cylinder  31  positioned on the outer periphery side of the space portion S of the catalyst  30  is used as a fixed face of the outer cylinder  31  as in the first embodiment and a plurality of through holes  43 A are formed in a plurality of positions in a circumferential direction of the catalyst pipe  43  in contact with the fixed face. The catalyst  30  is fixed to the catalyst pipe  43  by applying plug welding W 3  into the through holes  43 A. Therefore, the present embodiment also performs and exerts the same functions and effects as the first embodiment. 
       FIG. 6  is a sectional view of an exhaust pipe  11  according to a third embodiment of the present invention. The exhaust pipe  11  of the present embodiment is a muffler having expansion chambers and a catalyst  30  is provided in this muffler  11 . An outer shell of the exhaust pipe (the muffler)  11  is formed of an outer cylinder body  51  and an inner cylinder body  52  and opposite ends of the outer cylinder body  51  in a direction of an axial center are closed with a front end wall  53  and a rear end wall  54 . Inside the inner cylinder body  52 , a first expansion chamber  56 , a fourth expansion chamber  57 , a third expansion chamber  58 , and a second expansion chamber  59  are disposed in this order from front and the respective expansion chambers  56 ,  57 ,  58 , and  59  are separated by first, second, and third partitions  60 ,  61 , and  62 . 
     A first communicating pipe  63  for communicating with the first expansion chamber  56  and the second expansion chamber  59  penetrates the first, second, and third partitions  60 ,  61 , and  62 . A second communicating pipe  64  for communicating with the third expansion chamber  58  and the fourth expansion chamber  57  penetrates the second partition  61 . Moreover, a discharge pipe  65  penetrates the second and third partitions  61 ,  62 , and the rear end wall  54 . An end portion of the discharge pipe  65  opens in the fourth expansion chamber  57  and the other end portion opens in the rear end wall  54 . The third partition  62  is formed with a communicating hole (not shown) for communicating with the second expansion chamber  59  and the third expansion chamber  58 . 
     A catalyst  30  is provided in the inner cylinder body  52 . The catalyst  30  is provided in such a manner as to penetrate the first, second, and third partitions  60 ,  61 , and  62  and is directly supported by the partitions  61 ,  62 , and  63 . One end portion of the catalyst  30  is disposed in the first expansion chamber  56 . A delivery pipe  70  having a large number of circulation holes  70 A on an outer peripheral face thereof is mounted to the one end portion of the catalyst  30 . The other end portion of the catalyst  30  is disposed in the second expansion chamber  59  and one end of a curved pipe  71  curved into a U shape is connected to the other end portion. The other end of the curved pipe  71  is connected to an inflow pipe  72 . The inflow pipe  72  is provided in such a manner as to penetrate the front end wall  53 , the first, second, and third partitions  60 ,  61 , and  62 . 
     Into the muffler  11  of the present embodiment, the exhaust gas flows from the one end of the inflow pipe  72 . Then, the exhaust gas passes from the curved pipe  71  through the catalyst  30  and flows into the first expansion chamber  56  through the circulation holes  70 A in the delivery pipe  70 . Then, the exhaust gas flows from the first expansion chamber  56  into the second expansion chamber  59  through the first communicating pipe  63 , flows from the second expansion chamber  59  into the third expansion chamber  58  through the communicating hole (not shown), flows from the third expansion chamber  58  into the fourth expansion chamber  57  through the second communicating pipe  64 , and is discharged outside from the fourth expansion chamber  57  through the discharge pipe  65 . 
     The catalyst  30  is formed of an outer cylinder  31  and two catalyst main bodies  32 ,  33 . Between the two catalyst main bodies  32 ,  33 , a space S is formed. In this point, the embodiment is similar to the above-described first and second embodiments. The catalyst main body  32  on an upstream side of an exhaust flowing direction X is formed to be shorter than the catalyst main body  33  on the downstream side. A portion  31 A of an outer face of the outer cylinder  31  positioned on an outer peripheral side of the space S between the two catalyst main bodies  32 ,  33  is used as a fixed face of the outer cylinder  31  and fixed to the second partition  61  by welding. 
       FIG. 7  is an enlarged sectional view of a fixed portion of the catalyst  30 . The outer cylinder  31  of the catalyst  30  penetrates a hole  61 A formed in the second partition  61 . A peripheral edge portion of the hole  61 A is bent in the exhaust flowing direction X. The peripheral edge portion of the hole  61 A and the portion (the fixed face)  31 A of the outer face of the outer cylinder  31  are fixed to each other in a plurality of positions in a circumferential direction by welding W 4 . 
     The present embodiment also performs and exerts the same functions and effects as the first embodiment. By providing the catalyst  30  in such a manner that the catalyst  30  penetrates the partition  61  separating the plurality of expansion chambers in the muffler  11  as in the present embodiment, it is possible to fix the catalyst  30  by using the partition  61  as a mounting bracket. 
     (1) Although the two catalyst main bodies  32 ,  33  are provided in the outer cylinder  31  in the catalyst  30  in the above embodiments, three or more catalyst main bodies may be provided. 
     (2) The plurality of catalyst main bodies  32 ,  33  may have the same or different purification performance (such as size of cells of the honeycomb). 
     (3) The present invention can be utilized effectively as an exhaust purification device of vehicles such as a two-wheeled motor vehicle and a four-wheeled automobile, a working machine, industrial machine, or the like. 
     Although the invention has been described in its preferred embodiments with a certain degree of particularity, obviously many changes and variations are possible therein. It is therefore to be understood that the present invention may be practical otherwise than as specifically described herein with out departing from the scope and spirit thereof.

Technology Classification (CPC): 5