AU2008207497B2

AU2008207497B2 - Exhaust purification device

Info

Publication number: AU2008207497B2
Application number: AU2008207497A
Authority: AU
Inventors: Ken Hara; Shuichi Kizawa
Original assignee: Toyota Motor Corp
Current assignee: Toyota Motor Corp
Priority date: 2007-08-24
Filing date: 2008-08-25
Publication date: 2010-06-03
Anticipated expiration: 2028-08-25
Also published as: AU2008207497A1; JP4501971B2; JP2009052441A

Description

S&F Ref: 865681 AUSTRALIA PATENTS ACT 1990 COMPLETE SPECIFICATION FOR A STANDARD PATENT Name and Address Toyota Jidosha Kabushiki Kaisha, of 1, Toyota-cho, of Applicant: Toyota-shi, Aichi-ken, 471-8571, Japan Actual Inventor(s): Shuichi Kizawa Ken Hara Address for Service: Spruson & Ferguson St Martins Tower Level 35 31 Market Street Sydney NSW 2000 (CCN 3710000177) Invention Title: Exhaust purification device The following statement is a full description of this invention, including the best method of performing it known to me/us: 5845c(1375648_1) EXHAUST PURIFICATION DEVICE BACKGROUND OF THE INVENTION 1. Field of the Invention 5 [0001] The invention relates to an exhaust purification device in which a protective cover is mounted over a shell of an exhaust purification unit with a space layer provided therebetween, and in particular to the exhaust purification device suitably employed when it is difficult to clamp end portions of the protective cover. 10 2. Description of the Related Art [00021 In vehicles, such as automobiles, on which internal combustion engines are installed, exhaust purification devices are provided so as to meet the recent requirement for high exhaust purification performance. In one type of the 15 exhaust purification devices, a catalyst that converts pollutants in exhaust gas into harmless substances in an exhaust passage of the engine or a filter that captures particulate matter in the exhaust gas is housed in a cylindrical shell. Since the exhaust purifying catalyst exhibits insufficient exhaust purification performance until it reaches an activation temperature region, the temperature of 20 the catalyst needs to be raised to the activation temperature region at an early stage during starting of the engine. To this end, the following measures are often employed: (1) the exhaust purification device is placed immediately behind an exhaust manifold close to exhaust ports of the engine, so as to provide an enhanced warm-up effect, and (2) a shell of an exhaust purification unit containing the 25 catalyst or filter is covered with a protective cover, so that the exhaust purification unit is insulated from heat or reserves heat, namely, to provide an enhanced heat insulating effect. [0003] As one example of the above type of exhaust purification devices, there is known an exhaust purification device (as disclosed in, for example, 1 Japanese Patent Application Publication No. 11-36851 (JP-A-11-36851)) which has a shell of a catalyst unit and a protective cover in the form of inner and outer cylindrical shells, and a heat insulating space formed between the inner and outer cylindrical shells. 5 [0004] In another known example of exhaust purification device, the inner cylindrical shell, as one of the inner and outer cylindrical shells, is formed with an increased thickness, to act as a heat shield against heat radiated from the catalyst, and the diameter of an end portion(s) of the outer cylindrical shell is reduced by spinning, thereby to eliminate a need to superimpose shell halves of the outer LO cylindrical shell on each other and assemble the shell halves together, as disclosed in Japanese Patent Application Publication No. 2002-227640 (JP-A-2002-227640). In this case, a straight portion at one end of the outer cylindrical shell is supported by a straight portion at one end of the inner cylindrical shell, via a cylindrical metal mesh, L5 [0005] In the known exhaust purification device as described above, unless the opposite end portions of the protective cover are reliably clamped onto the opposite end portions of the shell of the catalyst unit or the exhaust pipes such that a difference in the amount of contraction due to heat between the shell of the catalyst unit and the outer cylindrical shell that provides the protective cover is 20 absorbed, abnormal noises are likely to occur due to contact between the protective cover and the shell during running of the vehicle. Therefore, the end portions of the protective cover and the end portions of the catalyst unit are normally provided with straight portions so that each end portion of the exhaust purification device has a double-pipe structure in which the straight portions are 25 clamped by clamping means. [0006] In some cases, however, the protective cover may not be provided with a straight portion or portions since the exhaust purification device needs to be located close to the exhaust ports of the engine, so as to meet the growing demand for high exhaust purification performance in recent years. In this case, an end 2 3 portion(s) of the protective cover may terminate at a tapered portion of the shell, and a clearance may be created between the end portion of the protective cover and the shell, causing a problem that foreign matters, such as dead leaves, tend to enter the interior of the protective cover. 5 While it may be proposed to reduce the clearance between the protective cover and the shell only at the outermost end portions thereof, high dimensional accuracy of the components and high assembling accuracy are required, resulting in an increased manufacturing cost, and the abnormal noises as described above may occur if the protective cover contacts the tapered portions of the shell of the catalyst unit. 10 If the end portions of the outer cylindrical shell are secured or fixed to the inner cylindrical shell, the above-mentioned difference in the amount of contraction due to heat between the inner and outer cylindrical shells cannot be absorbed, and the catalyst unit is likely to degrade early because of poor heat dissipation when the catalyst unit is overheated. is SUMMARY OF THE INVENTION An exhaust purification device according to one aspect of the present invention is an exhaust purification device, including an exhaust purification unit located in an exhaust passage of an internal combustion engine, a shell having a cylindrical shape in which the exhaust purification unit is housed and having a tapered portion formed at at 20 least one end portion thereof, and a protective cover mounted on an outer peripheral side of the shell with a space layer provided therebetween, wherein: at least one end portion of the protective cover is opposed to the tapered portion of the shell with the space layer provided therebetween, and a porous member having air permeability and flexibility is provided between said at least one end portion of the 25 protective cover and the tapered portion of the shell, so as to define the inside and outside of the protective cover. The porous member may be formed in the shape of a string that extends in a circumferential direction of the tapered portion of the shell, and fills a clearance between the protective cover and the tapered portion of the shell at the above-indicated at least one 30 end portion of the protective cover. With the above arrangement, the porous member need not be formed in a special or particular shape so that it extends along the circumference of the tapered portion of the shell, and the clearance between the end portion of the protective cover and the tapered portion of the shell of the exhaust purification unit can be filled with the porous member.

4 Also, the porous member is easily mounted on the tapered portion of the shell. The shape of a string mentioned herein means that the thickness of the porous member as measured in the radial direction of the shell is close in dimension to the width of the porous member as measured in the longitudinal direction of the shell, and the porous member has an 5 elongate shape of a circular cross-section, or a polygonal cross-section, or a cross-section of some other shape. When the porous member is placed between the end portion of the protective cover and the tapered portion of the shell of the exhaust purification unit, the porous member may be in line contact or surface contact, with a width equal to or smaller than the thickness of the heat insulating space layer, with the protective cover and the to shell, over the entire circumference thereof. The string-shaped porous member may be a solid or hollow component. The porous member may consist of a cylindrically woven metal mesh. In this case, the metal mesh woven in a cylindrical shape is only required to be laid along the circumference of the tapered portion of the shell of the exhaust purification is unit, thus assuring very easy mounting and improved adhesion to the shell. Furthermore, the metal mesh, which has excellent heat resistance, assures heat dissipation at the time of overheating. In the exhaust purification device as described above, the porous member disposed between said at least one end portion of the protective cover and the tapered 20 portion of the shell may be in line contact or surface contact with the protective cover and the shell over the entire circumference thereof, such that widths of a contact region of the porous member and the protective cover and a contact region of the porous member and the shell are equal to or smaller than the thickness of the porous member as measured across a space between the protective cover and the shell. 25 In the exhaust purification device as described above, a retaining portion that inhibits the porous member from coming out of the protective cover may be provided in the above-indicated at least one end portion of the protective cover, and the porous member may be held between the retaining portion and the tapered portion of the shell. In this case, the position of the porous member relative to the protective cover is 30 appropriately held by the retaining portion at the optimum position as viewed in the longitudinal direction of the exhaust purification device, and the inside diameter of the retaining portion may be suitably set so that a clearance suitable for heat dissipation at the time of overheating can be easily established between the end portion of the protective cover and the shell of the exhaust purification unit.

5 The protective cover may consist of a pair of cover members having concave inner surfaces that are opposed to the shell, and the porous member may be secured to at least one of the pair of cover members. With the above arrangement, the porous member and the cover members can be 5 handled as an integral structure, and can be thus easily assembled with the shell of the exhaust purification unit, with the porous member being stably positioned during mounting thereof. In another embodiment, a part of an arch-shaped porous member may be secured to each of a pair of cover members, so that the porous member is mounted between the cover member and the shell of the exhaust purification unit at the same time 10 that the pair of cover members are mounted over the shell of the exhaust purification unit. According to the above aspect of the invention, the flexible porous member is placed between at least one end portion of the protective cover and the tapered portion of the shell such that the porous member is in intimate contact with these portions. It is thus possible to provide an exhaust purification device having excellent exhaust purification is performance at low cost, which device is less likely or unlikely to suffer from abnormal noises due to interference between the protective cover and the shell of the catalyst unit, and wherein the porous member ensures heat dissipation when the exhaust purification unit is overheated. According to an embodiment of the present invention the flexible porous 20 member can be placed between at least one end portion of the protective cover and the tapered portion of the shell such that the porous member is in intimate contact with these portions. Accordingly, abnormal noises due to interference between the protective cover and the shell of the catalyst unit are suppressed or avoided, and the porous member ensures heat dissipation when the exhaust purification unit is overheated, while restricting 25 or preventing entry of foreign matters into the space layer. Brief Description of the Drawings The foregoing and further objects, features and advantages of the invention will become apparent from the following description of example embodiments with reference to the accompanying drawings, wherein like numerals are used to represent like elements, 30 and wherein: FIG. I is perspective view showing the outer appearance of an exhaust purification device according to one embodiment of the invention; FIG. 2 is perspective view showing a condition of the exhaust purification device of this embodiment from which the upper half of a protective cover is removed; 6 FIG. 3 is cross-sectional view showing the arrangement of a part of the exhaust purification device according to this embodiment, which part includes one end of the protective cover; and FIG. 4A and FIG. 4B are cross-sectional views each showing a porous member 5 mounted to the protective cover in the exhaust purification device of this embodiment, wherein FIG. 4A shows one example in which the porous member consists of a single component formed in an annular shape, and FIG. 4B shows another example in which the porous member is divided into two arc-shaped components. 5 DETAILED DESCRIPTION OF EMBODIMENTS [0022] One embodiment of the invention will be described with reference to the drawings. [0023] FIG. 1 is a perspective view showing the outer appearance of an exhaust purification device according to one embodiment of the invention. FIG. 2 10 is a perspective view showing a condition of the exhaust purification device of this embodiment from which the upper half of a protective cover is removed. FIG. 3 is a cross-sectional view showing the arrangement of a part of the exhaust purification device according to this embodiment, which part includes one end of the protective cover. FIG. 4A and FIG. 4B are cross-sectional views each showing 15 a porous member mounted to the protective cover in the exhaust purification device of this embodiment. More specifically, FIG. 4A shows one example in which the porous member consists of a single component formed in an annular shape, and FIG. 4B shows another example in which the porous member is divided into two arc-shaped components. 20 [0024] As shown in FIG. 1 and FIG. 2, the exhaust purification device of this embodiment has a known exhaust purification unit 11 inserted in an exhaust passage 10 that extends from the internal combustion engine (not shown), a shell 12 in which the exhaust purification unit 11 is housed, and a protective cover 14 that is mounted around the shell 12 with a heat insulating space layer 13 (space 25 layer) provided between the cover 14 and the shell 12. [0025] The exhaust purification unit 11 is a known unit that incorporates a catalyst that converts pollutants in exhaust gas into harmless substances in the exhaust passage of the engine, or a filter that captures particulate matter in the exhaust gas, or the like, in the shell 12. For example, the exhaust purification 7 unit 11 incorporates a three-way catalyst generally used in gasoline-driven vehicles, or an oxidation catalyst, reduction catalyst, or DPF (diesel particulate filter) generally used in diesel vehicles. The shell 12 is a heatproof container made of, for example, stainless steel, which includes a longitudinally middle 5 portion having a cylindrical shape, and longitudinally opposite end portions at least one of which is tapered from the middle portion. In this embodiment, the shell 12 includes tapered portions 12a, 12b connected to exhaust pipes 10a, 10b located ahead of and behind the device, at the opposite end portions thereof. [00261 At least one end portion of the protective cover 14, for example, the 10 opposite end portions 14a, 14b, are opposed to the tapered portions 12a, 12b of the shell 12 in the radial directions of the shell 12, with the heat insulating space layer 13 provided between the cover 14 and the shell 12. Also, string-shaped, annular porous members 21 having flexibility and heat resistance are respectively provided between the opposite end portions 14a, 14b of the protective cover 14 and 15 the corresponding tapered portions 12a, 12b of the shell 12, such that the porous members 21 serving as partitions define the inside and outside of the protective cover 14. The flexibility of the porous members 21 is of such a degree that permits elastic deformation of the porous members 21 (compressibility) when they are compressed between the tapered portions 12a, 12b of the shell 12 and the 20 opposite end portions 14a, 14b of the protective cover 14, or of such a degree that permits bending of the porous members 21 during mounting thereof, in addition to the elastic deformation. The heat resistance of the porous members 21 is equivalent to or higher than that of the protective cover 14. [0027] The porous members 21 are formed in the shape of strings that 25 extend in the circumferential directions of the tapered portions 12a, 12b of the shell 12. In the opposite end portions 14a, 14b of the protective cover 14, the porous members 21 fill spaces between the protective cover 14 and the tapered portions 12a, 12b of the shell 12 so as to hold the spaces substantially constant. The porous member 21 formed in the shape of a string has an elongate shape, and 8 has a thickness as measured in the radial direction of the shell 12 and a width as measured in the longitudinal direction of the shell 12, which are close to each other. For example, the ratio t/w of the thickness "t" to the width "w" as indicated in FIG. 3 is set to be larger than 1/2 and smaller than 2. The porous member, which has a 5 circular cross-section in this embodiment, may have a polygonal cross-section or a cross-section of some other shape, and may be a solid or hollow component. [0028] The length and flexibility of the string-shaped porous member 21 are determined such that the porous member 21 is in line contact or surface contact, with a width equal to or smaller than the thickness of the heat insulating 10 space layer 13, with each end portion 14a, 14b of the protective cover 14 and the tapered portion 12a, 12b of the shell 12 of the exhaust purification unit 11, over the entire circumference thereof, when the porous member 21 is placed between each end portion 14a, 14b of the protective cover 14 and the corresponding tapered portion 12a, 12b of the shell 12. 15 [0029] More specifically, the porous member 21 of this embodiment consists of a metal mesh formed from a stainless steel wire that is woven into a cylindrical shape. The metal mesh has a density (g/cm3) of stainless steel that is about a fraction of the normal density of stainless steel, and the diameter of the stainless steel wire is equal to or smaller than a fraction of the thickness of the 20 protective cover. The porous member 21 has sufficiently high heat resistance and corrosion resistance, and flexibility high enough to ensure intimate contact between the porous member 21 and each end portion 14a, 14b of the protective cover 14 and between the porous member 21 and each tapered portion 12a, 12b of the shell 12 when the protective cover 14 is mounted over the shell 12 of the 25 exhaust purification unit 11. The porous member 21 also has gas permeability, and a filtering characteristic that prevents entry of foreign matters into the heat insulating space layer 13. [0030] It is to be understood that the porous member 21 is not limited to the metal mesh provided that it possesses the above-described properties. For 9 example, the porous member 21 may be produced by twining thin metal wires into a low-density rope, or winding a thin metal wire or wires in a spiral fashion, or forming metal fibers into an unwoven fabric or a low-density string, or rolling a thin metal plate having a multiplicity of small-diameter punch holes or 5 small-width slits. In sum, the porous member 21 may be in any form provided that it can be formed with a multiplicity of air passages (pores) through which air passes between the inside and the outside of the protective cover 14, with the size of each air passage or pore being small enough to inhibit entry of foreign matters, such as dead leaves. 10 [0031] In the meantime, each of the opposite end portions 14a, 14b of the protective cover 14 includes a retaining portion 14c that inhibits the porous member 21 from coming out of the protective cover 14 or moving outwards from the inside of the protective cover 14. The retaining portion 14c has an inside diameter that is smaller than the outside diameter of the porous member 21 15 measured when the porous member 21, which consists of a cylindrical metal mesh, is wound around and extends over the periphery of an end portion of the tapered portion 12a, 12b of the shell 12 of the exhaust purification unit 11. [0032] More specifically, each retaining portion 14c provided at each of the opposite end portions 14a, 14b of the protective cover 14 extends continuously from 20 a coned portion 14f (of the end portion 14a, 14b) that faces the tapered portion 12a, 12b of the shell 12 of the exhaust purification unit 11 with a constant clearance therebetween, and includes a diameter reducing portion 14s whose diameter reduces from an end portion of the coned portion 14f along the outer periphery of the porous member 21, to provide a curved profile. In this embodiment, each of 25 the end portions 14a, 14b of the protective cover 14 further includes an annular opening edge 14t that extends continuously from the diameter reducing portion 14s, and has an inside diameter that is reduced to such an extent as to form a clearance "g" suitable for heat dissipation when the exhaust purification unit 11 is overheated, between the opening edge 14t and the exhaust pipe 10. Here, the 10 clearance "g" on the left-hand side of the porous member 21 in FIG. 3 is defined by the porous member 21, as a region outside the protective cover 14, and the space, i.e., heat insulating space layer 13, on the right-hand side of the porous member 21 in FIG. 3, is defined by the porous member 21 as a region inside the protective 5 cover 14. [0033] The porous member 21 is sandwiched and retained between the retaining portion 14c of the protective cover 14 and the tapered portion 12a, 12b of the shell 12 of the exhaust purification unit 11, such that the leftward movement of the porous member 21 as viewed in FIG. 3 is restricted by the retaining portion 10 14c, and such that the rightward movement thereof as viewed in FIG. 3 is restricted by the tapered portion 12a, 12b of the shell 12. [0034] As shown in FIG. 1 and FIGS. 4A and 4B, the protective cover 14 consists of a pair of cover members 31, 32 each having a concave inner surface that faces the shell 12, and the porous member 21 is secured to at least one of the pair 15 of the cover members 31, 32 by, for example, spot welding. The protective cover 14 is formed by stamping with protrusions and recesses, so that the cover 14 has a plurality of ribs R1, R2 that are spaced from each other in the circumferential direction and the longitudinal direction. The retaining portions 14c of the protective cover 14 provide annular grooves or recesses, which also function as 20 part of the annular ribs R2 that are spaced from each other in the longitudinal direction. [0035] While the porous member 21 may be formed in a ring shape as a single component, as shown in FIG. 4A by way of example, the porous member 21 may consist of a pair of arc-shaped components 21a, 21b, as shown in FIG. 4B, and 25 the pair of the arc-shaped components 21a, 21b may be spot-welded at two or more locations to the cover members 31, 32, respectively. In the latter case, when the pair of the cover members 31, 32 that constitute the protective cover 14 are mounted over the shell 12 of the exhaust purification unit 11, the opposite ends of the arc-shaped components 21a, 21b of the porous member 21 are brought into 11 close proximity to each other to be opposed to each other, or brought into abutment on each other, so that the porous member 21 is mounted in the form of a ring between the protective cover 14 and the shell 12 of the exhaust purification unit 12. Also, the cover members 31, 32 are fastened into an integral structure by means of 5 bolts (not shown), at a plurality of mounting holes 31c, 31d, ... formed in longitudinally middle portions of flanges 31a, 31b, 32a, 32b formed at the circumferentially opposite ends of the cover members 31, 32. In FIG. 1, only the mounting holes 31c, 31d of the flange 31a are shown, and other holes are not illustrated. With this arrangement, the protective cover 14 may be attached to 10 and detached from the shell 12. The flanges 31a, 31b, 32a, 32b formed at the circumferentially opposite ends of the cover members 31, 32 have outer edges, of which one of a pair of mutually facing edges is bent toward the other outer edge. [0036] Next, the operation of the exhaust purification device will be explained. 15 [00371 In the exhaust purification device of this embodiment constructed as described above, when the engine is in an operating condition in which exhaust gas passes through the exhaust purification unit 11, heat is applied from the exhaust gas to the exhaust purification device, giving rise to a difference in the amount of contraction due to the heat between the shell 12 of the exhaust 20 purification unit 11 and the protective cover 14, but the difference in the amount of contraction is absorbed by the porous members 21 having flexibility and compressibility. [0038] In the exhaust purification device of this embodiment, the porous members 21 are placed between the opposite end portions 14a, 14b of the 25 protective cover 14 and the tapered portions 12a, 12b of the shell 12 while being in intimate contact with these portions 14a, 14b, 12a, 12b, so that the opposite end portions 14a, 14b of the protective cover 14 are adequately elastically supported by the opposite end portions 12a, 12b of the shell 12 via the porous members 21. Therefore, when vibrations arising from the operations of the engine and the 12 vehicle are applied to the exhaust purification device, the opposite end portions of the protective cover 14, which are elastically supported as described above, are prevented from contacting the exhaust pipes 10a, 10b and the shell 12. Accordingly, abnormal noises that would arise from contact or interference 5 between the protective cover 14 and the shell 12 of the exhaust purification unit 11 are suppressed or avoided. Furthermore, since the porous members 21 having sufficient air permeability are placed in end portions of the heat insulating space layer 13, the porous members 21 restrict or prevent entry of foreign matters into the heat insulating space layer 13, while ensuring dissipation of heat from the 10 exhaust purification unit 11 when it is overheated. [0039] Also, the porous members 21, which are flexible string-shaped components in this embodiment, need not be formed (molded) in a particular shape so as to be laid along the peripheries of the tapered portions 12a, 12b of the shell 12. Also, the porous members 21 fill the clearances between the end portions 14a, 15 14b of the protective cover 14 and the tapered portions 12a, 12b of the shell 12 so as to hold the clearance substantially constant. In this case, the retaining portions 14c of the protective cover 14 for holding the porous members 21 in position also function as ribs of the end portions 14a, 14b of the protective cover 14, so that the end portions 14a, 14b of the protective cover 14 are stably held in 20 position with improved reliability, without being clamped by clamping means. [0040] Furthermore, the porous members 21 formed from a cylindrically woven metal mesh having a circular cross-section are only required to be laid along the peripheries of the tapered portions 12a, 12b of the shell 12 of the exhaust purification unit 11, thus permitting very easy mounting of the porous members 21. 25 In addition, the porous members 21 having adequate flexibility have good adhesion to the shell 12 and the protective cover 14, and the porous members 21 formed from a metal mesh, which have sufficient air permeability and heat resistance, ensure sufficient heat dissipation during overheating. [00411 Owing to the retaining portions 14c of the protective cover 14, the 13 positions of the porous members 21. relative to the protective cover 14 are appropriately held at the optimum positions as viewed in the longitudinal direction of the exhaust purification device. Also, by suitably setting the inside diameters of the opening edges 14t of the retaining portions 14c, the clearances "g" 5 adequate for heat dissipation during overheating can be easily established between the end portions 14a, 14b of the protective cover 14 and the shell 12 of the exhaust purification unit 11. [0042] Where the arc-shaped components 21a, 21b of each of the porous members 21 are spot-welded to the cover members 31, 32 that constitute the 10 protective cover 14, the protective cover 14 and the porous members 21 can be handled as an integral structure, and can be thus easily assembled with the shell 12 of the exhaust purification unit 11, with the porous members 21 being stably positioned during mounting thereof. [0043] As described above, in the exhaust purification device of this 15 embodiment, the flexible porous member(s) 21 is/are placed between at least one end portion 14a, 14b of the protective cover 14 and the tapered portion(s) 12a, 12b of the shell 12, such that the porous member(s) 21 is/are in intimate contact with these portions 14a, 14b, 12a, 12b. It is thus possible to provide an exhaust purification device having excellent exhaust purification performance at low cost, 20 which is less likely or unlikely to suffer from abnormal noises due to contact or interference between the protective cover 14 and the shell 12 of the exhaust purification unit 11, and ensures heat dissipation through the porous members 21 when the exhaust purification unit 11 is overheated. [00441 While the porous member of the present invention is preferably 25 formed from a metal mesh having a cross-sectional shape in which the ratio of the thickness to the width is close to 1, the cross-section of the porous member is not limited to the circular cross-section as in the illustrated embodiment, but may be of a different cross-sectional shape, such as an ellipse, oval shape, or a rhombus. As described above, the porous member may be formed from a material other than 14 a metal mesh provided that the porous member has substantially the same degrees of flexibility, heat resistance, corrosion resistance, filtering characteristic for preventing entry of foreign matters and air permeability as those of the porous member formed from the metal mesh. Also, the porous member may be provided 5 at only one end of the exhaust purification unit 11, and the other end portion may have a conventional clamped structure having a straight portion. Furthermore, the sizes of the clearances at opposite end portions of the heat insulating space layer 13 may differ between one end of the exhaust purification unit 11 and the other end, and porous members that are different from each other in terms of the 10 shape and required properties may be provided at the opposite ends of the exhaust purification unit 11. While each of the tapered portions 12a, 12b at the opposite ends of the shell 12 has the shape of a truncated cone in the illustrated embodiment, the tapered portion of the present invention may have a transverse cross-section that is not circular in shape, or may have a vertical or longitudinal 15 cross-section having a generally trapezoidal shape with a curved profile (corresponding to a curved outer circumferential surface), provided that the end portion of the shell of the exhaust purification unit has a reduced diameter compared to an axially middle portion of the shell. [0045] As explained above, in the exhaust purification device of the 20 invention, the flexible porous member(s) is/are placed between at least one end portion of the protective cover and the tapered portion(s) of the shell, such that the porous member(s) is/are in intimate contact with these end portions and tapered portions. It is thus possible to provide an exhaust purification device having excellent exhaust purification performance at low cost, which is less likely or 25 unlikely to suffer from abnormal noises due to contact or interference between the protective cover and the shell of the exhaust purification unit, and ensures heat dissipation through the porous member(s) when the exhaust purification unit is overheated. Thus, the present invention is useful for vehicular exhaust purification devices in general, in which a protective cover is mounted over a shell 15 of an exhaust purification unit with a heat insulating space layer provided therebetween. 16

Claims

1. An exhaust purification device, including an exhaust purification unit located in an exhaust passage of an internal combustion engine, a shell having a cylindrical shape in which the exhaust purification unit is housed and having a tapered s portion formed at at least one end portion thereof, and a protective cover mounted on an outer peripheral side of the shell with a space layer provided therebetween, wherein: at least one end portion of the protective cover is opposed to the tapered portion of the shell with the space layer provided therebetween, and a porous member having air permeability and flexibility is provided between said at least one end portion of the 1o protective cover and the tapered portion of the shell, so as to define the inside and outside of the protective cover.

2. The exhaust purification device according to claim 1, wherein the porous member is formed in the shape of a string that extends in a circumferential 15 direction of the tapered portion of the shell, and fills a clearance between the protective cover and the tapered portion of the shell at said at least one end portion of the protective cover.

3. The exhaust purification device according to claim 2, wherein the 20 porous member comprises a cylindrically woven metal mesh.

4. The exhaust purification device according to claim 2 or 3, wherein the porous member disposed between said at least one end portion of the protective cover and the tapered portion of the shell is in line contact or surface contact with the protective 25 cover and the shell over the entire circumference thereof, such that widths of a contact region of the porous member and the protective cover and a contact region of the porous member and the shell are equal to or smaller than the thickness of the porous member as measured across a space between the protective cover and the shell.

5. The exhaust purification device according to any one of claims 2 to 4, wherein the ratio (tiw) of the thickness ( of the porous member as measured in a radial direction of the shell to the width (w) of the porous member as measured in a longitudinal direction of the shell is larger than 1/2, and is equal to or smaller than 2.

6. The exhaust purification device according to any one of claims 1 to 5, wherein a retaining portion that inhibits the porous member from coming out of the protective cover is provided in said at least one end portion of the protective cover, and the porous member is held between the retaining portion and the 0 tapered portion of the shell.

7. The exhaust purification device according to claim 6, wherein the retaining portion has an inside diameter that is smaller than an outside diameter of the porous member.

8. The exhaust purification device according to any one of claims 1 to 7, 5 wherein the protective cover consists of a pair of cover members having concave inner surfaces that are opposed to the shell, and the porous member is secured to at least one of said pair of cover members.

9. The exhaust purification device according to any one of claims 1 to 8, wherein the porous member is elastically deformed when compressed between the 20 tapered portion of the shell and one end portion of the protective cover.

10. The exhaust purification device according to any one of claims 1 to 9, wherein the porous member has heat resistance that is equal to or higher than that of the protective cover. 1.8

11. A exhaust purification device, substantially as hereinbefore described with reference to the accompanying drawings. Dated 25 August, 2008 Toyota Jidosha Kabushiki Kaisha Patent Attorneys for the Applicant/Nominated Person SPRUSON & FERGUSON 19