Patent Publication Number: US-8535611-B2

Title: Exhaust gas purifying device

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to Application No. PCT/JP2009/063018 filed on Jul. 21, 2009, which application claims priority to Application No. JP 2008-206129 filed on Aug. 8, 2008. The entire contents of both applications are incorporated herein by reference in their entireties. This application is also related to concurrently filed application Ser. No. 13/058,164, entitled “Exhaust Gas Purifying Device” by Hiroshi Yamamoto that claims priority to Application No. PCT/JP2009/063024 filed Jul. 21, 2009, which application claims priority to Application No. JP 2008-206130 filed on Aug. 8, 2008, having the same assignee as this application, both applications are hereby incorporated by reference in their entireties. 
     TECHNICAL FIELD 
     The present invention relates to an exhaust gas purifying device. 
     BACKGROUND ART 
     It has typically been known that an exhaust gas purifying device provided is in an exhaust pipe of an engine so that particulate matters (PM), i.e., particulate substances contained in exhaust gas that causes black exhaust, thereby preventing discharge of the PM into the atmosphere. The exhaust gas purifying device is generally provided with a soot filter for capturing PM and an oxidizing catalyst for oxidizing dosing fuel (e.g., diesel oil) to generate heat, the soot filter and the oxidizing catalyst each being covered by a cylindrical case (Patent Literature 1). 
     CITATION LIST 
     Patent Literature 
     Patent Literature 1: JP-A-2004-263593 
     SUMMARY OF THE INVENTION 
     Problems to Be Solved by the Invention 
     According to Patent Literature 1, when the case in which the oxidizing catalyst is provided and the case in which the soot filter is provided are coupled to each other to assemble the exhaust gas purifying device, a space is formed between the oxidizing catalyst and the soot filter. 
     Inner surfaces of parts of the cases defining this space are directly exposed to exhaust gas having a high temperature, so that the heat of the exhaust gas is transferred from the inner surfaces to outer surfaces of the cases, and, consequently, the surface temperature of the cases becomes high. 
     An object of the invention is to provide an exhaust gas purifying device capable of preventing surface temperature of a case from becoming high. 
     Means for Solving the Problems 
     According to an aspect of the invention, an exhaust gas purifying device includes: a case body that includes a plurality of cases, and a heat insulating unit that covers the is provided to an inner surface of body over a substantially-entire area from an upstream side to a downstream side in an exhaust gas flowing direction; in which the heat insulating unit includes: first heat insulating units and second heat insulating units provided in the plurality of cases, the first heat insulating units being placed in the cases in such a manner as not to protrude from openings of the cases, and the second heat insulating units being placed in such a manner as to bridge over joint portions between the cases. 
     The term “substantially-entire area” includes an area having a slight gap that happens to be formed in assembling the case body because such a gap does not have a substantial influence on heat insulation ability. 
     The expression “placed inward” means that the first heat insulating units are housed within the cases in a manner not to protrude from openings of the cases. 
     With the above arrangement, the heat insulating unit is continuously formed over the substantially-entire area from the upstream side to the downstream side of the case body, thereby reliably preventing the surface temperature of the case body of the exhaust gas purifying device from becoming high. 
     With the above arrangement, the second heat insulating units are placed in such a manner as to bridge over the joint portions between the cases. Thus, when each of the second heat insulating units is beforehand attached to an end of one of the cases to be coupled, the other case can be guided by the second heat insulating unit so that these cases are fit-coupled to each other, thereby improving assembly efficiency. 
     In the exhaust gas purifying device, it is preferable that each of the second heat insulting units include: an inner ring member placed on inner sides of the cases; and a heat insulator placed between the inner ring member and inner surfaces of the cases. 
     With the above arrangement, the inner surface of each of the second heat insulating units is provided with the inner ring member, so that exhaust gas passing through the second heat insulating unit is prevented from easily contacting the heat insulator placed between the inner ring member and the inner surfaces of the cases, thereby preventing deterioration of the heat insulator and improving the durability of the heat insulator. 
     In the exhaust gas purifying device, it is preferable that each of the second heat insulating units include an outer ring member placed between the inner surfaces of the cases and the heat insulator. 
     With the above arrangement, the outer ring member is provided between the heat insulator and the inner surfaces of the cases. Thus, when the cases are fit-coupled to each other, the inner surface of one of the cases is in contact with an outer surface of the outer ring member of the other case, thereby favorably preventing the heat insulator from, for instance, getting caught between the cases. 
     In the exhaust gas purifying device, it is preferable that the inner ring member and the outer ring member be spaced apart from each other. 
     The expression “being spaced apart from” means being spaced apart in a direction perpendicular to the exhaust gas flowing direction. 
     With the above arrangement, the inner ring member and the outer ring member are spaced apart from each other. Since the inner ring member and the outer ring member are not in contact with each other, the heat of the inner ring member can be prevented from being transferred to the outer ring member. 
     In the exhaust gas purifying device, it is preferable that the inner ring member be provided with outer flanges to have a concave cross section. 
     With the above arrangement, the inner ring member is provided with the outer flanges to have the concave cross section. The outer flanges of the inner ring member serve to prevent the heat insulator from protruding outward. Moreover, exhaust gas passing through the second heat insulating unit is more reliably prevented from easily contacting the heat insulator, thereby more reliably preventing deterioration of the heat insulator and improving the durability of the heat insulator. 
     According to another aspect of the invention, an exhaust gas purifying device includes: a case body that includes a plurality of cases, and a heat insulating unit that is provided to an inner surface of the case body over a substantially-entire area from an upstream side to a downstream side in an exhaust gas flowing direction, in which the heat insulating unit includes: first heat insulating units and second heat insulating units provided in the plurality of cases, the first heat insulating units being placed in the cases in such a manner as not to protrude from openings of the cases, and the second heat insulating units being placed in such a manner as to bridge over joint portions between the cases, among the plurality of cases, a case placed on an upstream end in the exhaust gas flowing direction is provided with an inflow section into which exhaust gas flows in a radial direction of the case and a case placed on a downstream end in the exhaust gas flowing direction is provided with an outflow section from which the exhaust gas flows in a radial direction of the case, each of the cases provided with the inflow section and the outflow section has a double- wall structure of an inner wall plate and an outer wall plate, and the first heat insulating unit is interposed between the inner wall plate and the outer wall plate. 
     With the above arrangement, the case body is covered by the heat insulating unit over the substantially-entire area from the upstream side to the downstream side of the exhaust gas flowing direction, and the first heat insulating units are interposed between the inner wall plates and the outer wall plates placed on both end surfaces of the case body. Thus, the case body is entirely covered by the heat insulating unit. Even when exhaust gas having a high temperature passes through the inflow section and the outflow section radially provided to the cases placed on both ends of the case body, the surface temperature of the case body can be reliably prevented from becoming high. 
     The inflow section and the outflow section are placed in such a manner as to allow exhaust gas to flow into and from the cases in the radial direction, so that an exhaust pipe or the like can be collectively placed, thereby reducing a space for the exhaust pipe. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a perspective view showing an entire exhaust gas purifying device according to a first exemplary embodiment of the invention. 
         FIG. 2  is an illustration viewed in a direction of arrows A-A in  FIG. 1 . 
         FIG. 3  is a cross sectional view showing a primary part according to the first exemplary embodiment 
         FIG. 4  is a cross sectional view showing a case as a part of the exhaust gas purifying device. 
         FIG. 5  is a cross sectional view showing a primary part of an exhaust gas purifying device according to a second exemplary embodiment of the invention. 
         FIG. 6  is a cross sectional view showing a primary part according to a third exemplary embodiment of the invention. 
         FIG. 7  is a cross sectional view showing a primary part according to a fourth exemplary embodiment of the invention. 
         FIG. 8  is a cross sectional view showing a primary part according to a fifth exemplary embodiment of the invention. 
         FIG. 9  is a cross sectional view showing a primary part according to a sixth exemplary embodiment of the invention. 
     
    
    
     DESCRIPTION OF EXEMPLARY EMBODIMENTS 
     Exemplary embodiments of the invention will be described below with reference to the attached drawings. In a below-described second exemplary embodiment and subsequent exemplary embodiments, the same reference numerals are attached to components identical to or functionally similar to those in a below-described first exemplary embodiment so as to simplify or omit the explanation thereof. 
     First Exemplary Embodiment 
     A first exemplary embodiment of the invention will be described below with reference to the attached drawings. 
     Hereinafter, an upstream side of an exhaust gas flow direction is referred to as an “upstream side” and a downstream side of the exhaust gas flow direction is a “downstream side” for convenience. 
       FIG. 1  is a perspective view showing an entire exhaust gas purifying device  1  according to this exemplary embodiment.  FIG. 2  is an illustration viewed in a direction of arrows A-A in  FIG. 1 . In  FIG. 1 , the exhaust gas purifying device  1  is provided between exhaust pipes of a diesel engine (not shown) (hereinafter, simply referred to as an “engine”) for capturing PM contained in exhaust gas and is provided with a case body  1 A. The case body  1 A includes: a cylindrical case  2  connected to the exhaust pipe of the engine; a cylindrical case  3  placed on a downstream side of the case  2 ; a cylindrical case  4  placed on a downstream side of the case  3 ; and a case  5  placed on the most downstream side and connected to an outlet pipe (not shown). 
     The cases  2  and  5  are placed on both ends of the case body  1 A and each includes a cylindrical outer periphery provided with a side wall  8 . The inner spaces of the cases  2  and  5  respectively function as an inlet chamber  11  and an outlet chamber  12 . The case  2  placed on the upstream end is provided with an inflow section  21  into which exhaust gas flows in the radial direction of the case  2 . The case  5  placed on the downstream end is provided with an outflow section  51  from which the exhaust gas flows in the radial direction of the case  5 . On both end surfaces of the case body  1 A, the side wall  8  of each of the cases  2  and  5  has a double-wall structure having an inner wall plate  13  and an outer wall plate  14 . A heat insulator  15  made of glass fiber as a first heat insulating unit is interposed between the inner wall plate  13  and the outer wall plate  14 . Likewise, the cylindrical portion of each of the cases  2  and  5  has a double-wall structure having an inner cylinder  16  and an outer cylinder  17 . The heat insulator  15  is interposed also between the inner cylinder  16  and the outer cylinder  17 . With this arrangement, even when exhaust gas passes through the inlet chamber  11  and the outlet chamber  12 , heat from the exhaust gas is blocked by the heat insulator  15  to restrain heat transmission to outer surfaces of the cases  2  and  5 . A flange joint  6  integrally formed with an exposed portion of the inner cylinder  16  is formed on an opening end of each of the cases  2  and  5 . 
     In the cylindrical case  3 , an oxidizing catalyst  31  is placed to oxidize dosing fuel to obtain heat therefrom, and ringed stainless-steel wire meshes  81  and stoppers  82  are provided on both sides of the oxidizing catalyst  31 . The stoppers  82  press the oxidizing catalyst  31  via the wire meshes  81  so as to prevent the protrusion of the oxidizing catalyst  31  from the ends of the case  3 . 
     Likewise, in the cylindrical case  4 , a soot filter  41  for capturing PM in exhaust gas is housed, and the ringed stainless-steel wire meshes  81  and the stoppers  82  are provided on both sides of the soot filter  41 . 
     The cases  3  and  4  each have a single-wall structure. Heat insulators  19  made of ceramic fiber as the first heat insulating units are interposed between the inner surface of the case  3  and the oxidizing catalyst  31  housed in the case  3 , and between an inner surface of the case  4  and the soot filter  41 . With this arrangement, heat from exhaust gas passing through the oxidizing catalyst  31  and the soot filter  41  is restrained from being transferred to outer surfaces of the cases  3  and  4 . Likewise, in each of the cases  3  and  4 , the flange joints  6  are integrally formed on open ends of both sides. 
     In the cases  2  to  5  described above, the flange joints  6  facing each other are brought into contact with each other through a sealing material  65  and connected to each other by a bolt  61  penetrating the flanges  6  and a nut  62  screwed onto the bolt  61 . The sealing material  65 , which is made of exfoliated graphite exhibiting high heat resistance, is placed so as to prevent exhaust gas passing through the exhaust gas purifying device  1  from leaking into to the atmosphere. When the cases  2  to  5  are coupled, heat insulating rings  9  as second heat insulating units are housed so as to respectively bridge interiors of the cases  2  to  5  as shown in  FIGS. 2 and 3 . Specifically, a heat insulating ring  9 A is placed between the cases  2  and  3  in a manner to protrude beyond the flange joint  6  of the case  2  so as to approach an inflow end of the oxidizing catalyst  31 . A heat insulating ring  9 B is placed between the cases  3  and  4  in a manner to protrude beyond the flange joint  6  of the case  4  so as to approach an outflow end of the oxidizing catalyst  31  and an inflow end of the soot filter  41 . A heat insulating ring  9 C is placed between the cases  4  and  5  in a manner to protrude beyond the flange joint  6  of the case  5  so as to approach an outflow end of the soot filter  41 . 
     The heat insulating rings  9  ( 9 A,  9 B,  9 C) each have the same overall structure except for different lengths in the exhaust gas flow direction. Specifically, as shown in an enlarged manner in  FIG. 3  (in the figure, the heat insulating ring  9 B is shown as a representative example), the heat insulating rings  9  each include: a stainless-steel outer ring member  91  abutting on an inner surface of each of the cases  2  to  5 ; a stainless-steel inner ring member  92  formed to have a concave cross section and having a pair of outer flanges  93 ; and a heat insulator  94  made of ceramic fibers and interposed between the outer ring member  91  and the inner ring member  92 . The heat insulator  94  is also formed in a cylindrical shape and has an inner diameter substantially equal to an outer diameter of a cylindrical portion of the inner ring member  92 . 
     In each of the heat insulating rings  9 , the inner ring member  92  is housed in the outer ring member  91  while the heat insulator  94  having a predetermined thickness is fitted on the outer periphery of the cylindrical portion of the inner ring member  92 . As a result, the heat insulator  94  is pressed toward the outer ring member  91  by the inner ring member  92  to be interposed between the respective members  91  and  92  while being compressed. A reaction force at this time prevents positional shift of the inner ring member  92  relative to the outer ring member  91 . The heat insulating rings  9  can be assembled in advance for easy handling. Moreover, interposing the heat insulator  94  between the outer flanges  93  prevents the heat insulator  94  from being shifted. 
     The heat insulating rings  9  are respectively housed in the cases  2  to  5  after the members  91 ,  92  and  94  are assembled. At this time, the outer ring member  91  is welded to an inner circumference of each of the cases  2  to  5 . Welded parts will be described in detail below. In assembled heat insulating rings  9 , the inner ring member  92  and the outer ring member  91  are not in contact with each other. Specifically, a thickness of the heat insulator  94  and a height of the outer flanges  93  of the inner ring member  92  are set such that the inner ring member  92  and the outer ring member  91  are not in contact with each other in view of an estimated compressed amount of the heat insulator  94 . Accordingly, although the exhaust gas passing the heat insulating rings  9  is directly in contact with the inner ring member  92 , heat at this time is restrained from transmitting from the inner ring member  92  to the outer ring member  91  and is favorably blocked by the heat insulator  94 . 
     In each of the heat insulating rings  9 , the heat insulating ring  9 A radially overlaps with the heat insulator  15  of the case  2  on the upstream side and is adjacent to the heat insulator  19  of the case  3  through the wire mesh  81  and the stopper  82  on the downstream side. The heat insulating ring  9 B is adjacent to the heat insulator  19  of the case  3  through the wire mesh  81  and the stopper  82  on the upstream side and is adjacent to the heat insulator  19  of the case  4  through the wire mesh  81  and the stopper  82  on the downstream side. The heat insulating ring  9 C is adjacent to the heat insulator  19  of the case  4  through the wire mesh  81  and the stopper  82  on the upstream side and overlaps radially with the heat insulator  15  of the case  5  on the downstream side. Regarding the term “adjacent”, the heat insulating rings  9  may be in contact with the heat insulators  19  or may not be in contact with the heat insulators  19 . 
     With this arrangement, the substantially-entire case body  1 A of the exhaust gas purifying device  1  from the upstream side to the downstream side is substantially covered by the heat insulators  15 ,  19  and  94 . Even the cases  3  and  4  having no double-wall structure can practically realize a double-wall structure excellent in heat insulating property by using the heat insulating rings  9 . Consequently, the outer surfaces of all the cases  2  to  5  are prevented from being easily heated to a high temperature. 
     The heat insulating ring  9 A among the heat insulating rings  9  has a larger engagement margin with the inner cylinder  16  of the case  2  than that with the case  3 . The heat insulating ring  9 A is housed in the inner cylinder  16  in advance. The heat insulating ring  9 B has a larger engagement margin with the case  4  than that with the case  3 . The heat insulating ring  9 B is housed in the case  4  in advance. The heat insulating ring  9 C has a larger engagement margin with the case  5  than that with the case  4 . The heat insulating ring  9 C is housed in the case  5  in advance. The outer ring members  91  of the heat insulating rings  9  are respectively welded to the cases  2  to  5  at the larger engagement margin between the heat insulating rings  9  and each of the cases  2  to  5 . Specifically, the outer ring member  91  of the heat insulating ring  9 A is welded to four weld holes (not shown) formed on the outer surface of the case  2 . The outer ring member  91  of the heat insulating ring  9 B is welded to weld holes of the case  4 . The outer ring member  91  of the heat insulating ring  9 C is welded to weld holes of the case  5 . 
     Accordingly, in assembling the case body  1 A by coupling the cases  2  to  5 , a part of the heat insulating ring  9 A protrudes from an opening of the case  2 . An outer periphery of the protruding heat insulating ring  9 A is fitted to an inflow end of the case  3 . In other words, an outflow end of the case  2  and the inflow end of the case  3  are fit-coupled to each other while being guided by the heat insulating ring  9 A. 
     Similarly, as shown in  FIG. 4 , a part of the heat insulating ring  9 B protrudes from an opening of an inflow end of the case  4 . An outer periphery of the protruding heat insulating ring  9 B is fitted to an outflow end of the case  3 , thereby coupling the cases  3  and  4 . In other words, the outflow end of the case  3  and the inflow end of the case  4  are also fit-coupled to each other while being guided by the heat insulating ring  9 B. 
     Moreover, a part of the heat insulating ring  9 C protrudes from an opening of an inflow end of the case  5 . An outer periphery of the protruding heat insulating ring  9 C is fitted to an outflow end of the case  4 , thereby fit-coupling the cases  5  and  4  to each other. 
     Specifically, for the above fit-coupling, the heat insulating rings  9 A and  9 C are set in advance respectively in the cases  2  and  5  (i.e., the both sides of the case body  1 A) in such a manner as to protrude from the cases  2  and  5  to face each other. No heat insulating rings  9  is provided in the case  3  housing the oxidizing catalyst  31 . In the case  4  housing the soot filter  41 , the heat insulating ring  9 B is provided in advance only on the upstream side in such a manner as to protrude from the case  4 . Accordingly, when the cases  2  to  5  are arranged in a right order, the case  4  in which the soot filter  41  is housed is prevented from being connected at a reverse position (i.e., the inflow end and the outflow end of the soot filter  41  are reversed), so that an orientation of the case  4  for connection can be constantly fixed. 
     A sensor boss  101  is provided to each of the cases  2  and  5  of the case body  1  for attaching a temperature sensor (not shown) to measure temperature inside the inlet chamber  11  and the outlet chamber  12 . The sensor boss  101  is attached to the inner cylinder  16 . On the outer cylinder  17 , an opening  18  is formed at a position corresponding to the sensor boss  101 . A sensor boss  102  is similarly provided to the case  5  at a position adjacent to the sensor boss  101 . A rigid pipe  71  such as a steel pipe into which the exhaust gas flows is attached to the sensor boss  102 . 
     Thick disc sensor bosses  103  and  104  are provided on the outer surface near the exhaust gas inflow end of the case  4 . The sensor boss  103  is attached with a temperature sensor (not shown) that measures an exhaust gas temperature at the inflow end of the soot filter  41 . The sensor boss  104  is attached with a rigid pipe  72  such as a steel pipe into which exhaust gas flows from the inflow end of the soot filter  41 . The pipe  72  and the above-described pipe  71  are connected to a differential pressure sensor  7 . In this exemplary embodiment, the differential pressure sensor  7  is located close to the exhaust gas outflow end of the case  4  and is attached to the flange joint  6  near the outflow end of the case  4  by the bolt  61  and the nut  62  through a bracket  63 . 
     The differential pressure sensor  7  detects a pressure difference between the inflow end and outflow end of the soot filter  41 . In the differential pressure sensor  7 , a diaphragm provided with a strain gauge is placed. The diaphragm is displaced by the exhaust gas flowing into the pipes  71  and  72 , and the electrical resistance of the strain gauge is changed in response to the displacement of the diaphragm. The differential pressure can thus be detected based on the changed electrical resistance. Within the case  4 , the soot filter  41  causes a pressure loss of exhaust gas: a pressure at the inflow end of the soot filter  41  (i.e., a pressure in the soot filter  41  close to the sensor boss  104 ) is larger than a pressure at the outflow end of the soot filter  41  (i.e., a pressure in the soot filter  41  close to the sensor boss  102 ). As PM begins to clog in the soot filter  41 , the pressure loss, i.e., the differential pressure between the inflow end and the outflow end of the soot filter  41 , becomes larger. A clogging degree of the soot filter  41  can be judged based on the differential pressure. 
     The connected differential sensor  7  and pipes  71  and  72  are placed in such a manner as to bridge over a joint portion between the cases  4  and  5 . A dimension of the pipe  72  is larger than that of the pipe  71 . Accordingly, in this exemplary embodiment with the different dimensions of the pipes  71  and  72 , the orientation of the case  4  for connection, to which the pipe  72  is attached, is fixed relative to the case  5  to which the pipe  71  is attached. 
     In other words, when the case  4  is coupled to the case  5  in a manner such that the upstream and the downstream are reversed, the sensor bosses  102  and  104  become too close to each other, whereby the rigid pipes  71  and  72  cannot be connected to the sensor bosses  102  and  104  and the differential pressure sensor  7  cannot be attached to the case  4 . In view of the above, similarly to the advantage of the above fit-coupling, the case  4  housing the soot filter  41  can be constantly coupled in the fixed orientation and prevented from being attached in a manner such that the upstream and the downstream are reversed. 
     In an engine room in which an engine is housed, the exhaust gas purifying device  1  of the invention may be attached to a frame and a bonnet constituting an engine room, or may be attached to an upper side of an engine and the like. An attachment position or the like may be appropriately determined at the time of attaching the exhaust gas purifying device  1 . 
     According to this exemplary embodiment, the case body  1 A of the exhaust gas purifying device  1  is covered by the heat insulators  15 ,  19  and  94 , so that the surface temperature of the case body  1 A is reliably prevented from becoming high due to the exhaust gas passing through the exhaust gas purifying device  1 . 
     Second Exemplary Embodiment 
       FIG. 5  shows a heat insulating ring  9  according to a second exemplary embodiment. In  FIG. 5 , the joint portion between the cases  3  and  4  is shown as a representative of example, so that the same heat insulating ring  9  is used for any other joint portion. The same is applied to the below-described third to sixth exemplary embodiments. 
     The heat insulating ring  9  according to this exemplary embodiment includes the stainless-steel inner ring member  92  having a concave cross section, and the heat insulator  94  made of ceramic fiber set in the inner ring member  92 . The outer ring member  91  according to the first exemplary embodiment is not provided to the inner ring member  92 . 
     The heat insulator  94 , also having a predetermined thickness, is pressed against the inner surfaces of ones of the cases  2  to  5  by the inner ring member  92  to be compressively housed between the inner surface of the case  4  and the inner ring member  92 . Since the inner ring member  92  receives the pressure of the heat insulator  94 , the inner ring member  92  can be beforehand attached to the case  4  along with the heat insulator  94  without positional shift relative to the case  4 . The inner ring member  92  and the inner surfaces of the ones of the cases  2  to  5  are not in contact in the same manner as in the first exemplary embodiment. Thus, the heat of the inner ring member  92  is prevented from being transferred to the ones of the cases  2  to  5 . 
     In this exemplary embodiment, as well as in the above first exemplary embodiment, the entire exhaust gas purifying device  1  is continuously covered by the heat insulators  15 ,  19  and  94 , thereby reliably preventing the surface temperature of the entire exhaust gas purifying device  1  from becoming high. 
     Third Exemplary Embodiment 
       FIG. 6  shows a heat insulating ring  9  according to a third exemplary embodiment. 
     The heat insulating ring  9  includes a stainless-steel inner ring member  95  and a heat insulator  94  interposed between the inner ring member  95  and the cases  3  and  4 . The inner ring member  95  does not have a concave cross section but is formed in a cylindrical shape without the outer flanges  93  ( FIG. 3 ). The other arrangement is the same as in the second exemplary embodiment. 
     Likewise, in this exemplary embodiment, the surface temperature of the entire exhaust gas purifying device  1  can be reliably prevented from becoming high. 
     Fourth Exemplary Embodiment 
       FIG. 7  shows a heat insulating ring  9  according to a fourth exemplary embodiment. 
     The heat insulating ring  9  according to this exemplary embodiment includes the cylindrical outer ring member  91  described in the first exemplary embodiment and the cylindrical inner ring member  95  described in the third exemplary embodiment. 
     Likewise, in this exemplary embodiment, the surface temperature of the entire exhaust gas purifying device  1  can be reliably prevented from becoming high, so that the same advantages as those of the above first exemplary embodiment can be obtained. 
     Fifth Exemplary Embodiment 
       FIG. 8  shows a heat insulating ring  9  according to a fifth exemplary embodiment. 
     Unlike in the first exemplary embodiment, the heat insulating ring  9  according to this exemplary embodiment employs an inner ring member  97  that contacts the outer ring member  91 , thereby completely enclosing the heat insulator  94  within a space between the outer ring member  91  and the inner ring member  97 . 
     In this exemplary embodiment, since the heat insulator  94  is completely housed, there is no possibility that the heat insulator  94  is exposed to the exhaust gas. Thus, the deterioration of the heat insulator  94  can be suppressed, thereby improving the durability. 
     Sixth Exemplary Embodiment 
       FIG. 9  shows a sixth exemplary embodiment. 
     In the cases  2  to  5  according this exemplary embodiment, the sealing material  65  is interposed between the flange joints  6  and the flange joints  6  are connected by being fastened by a V-shaped clamp  64 . With the above arrangement, the cases  2  to  5  can be favorably coupled in the same manner as in the above exemplary embodiments. 
     Although the best arrangements, methods and the like for carrying out the invention are disclosed above, the invention is not limited thereto. In other words, while the invention has been particularly explained and illustrated mainly in relation to specific embodiments, a person skilled in the art could make various modifications in terms of shape, quantity or other particulars to the above described embodiment without deviating from the technical idea or any object of the invention. 
     Accordingly, any descriptions of shape or quantity or the like disclosed above are given as examples to enable easy understanding of the invention, and do not limit the invention, so that descriptions using names of components, with any such limitations of shape or quantity or the like removed in part or whole, are included in the invention. 
     Though the cases  2  and  3  are separately formed in the above exemplary embodiments, the cases  2  and  3  may be integrally formed. 
     Though the exhaust gas purifying device  1  according to the above exemplary embodiments is provided with the oxidizing catalyst  31 , the oxidizing catalyst  31  may be omitted depending on a different regeneration method of the soot filter  41 . 
     Though the heat insulator  94  is made of ceramic fibers in the above respective exemplary embodiments, the heat insulator  94  may be made of glass fibers or any appropriate material.