Title of Invention

EXHAUST EMISSION CONTROL DEVICE

Abstract

An exhaust emission control device for an engine, in which a cylindrical catalyst case (31) for holding a catalyst support (28) is disposed in a casing (24) including a taper portion (26) having a small-diameter end connected to a connection pipe (34) connected to an exhaust pipe (21) for introducing an exhaust gas from an engine (E) and a cylindrical portion (25) connected to a large-diameter end of said taper portion (26); said catalyst case (31) is supported by said cylindrical portion (25) via a supporting member (32) said catalyst support (28) has a circular outer surface having a diameter larger than the outside diameter of said connection pipe (34); and the upstream end of said catalyst support (28) is opposed to the downstream end of said connection pipe (34), said exhaust emission control device being characterized in that the downstream end of said connection pipe (34) enters from the small-diameter end of said taper portion (26) into said casing (24) up to a position at which the downstream end of said connection pipe (34) is opposed to the upstream end of said catalyst support (28) with a specific gap put therebetween.

Full Text

FORM 2 THE PATENTS ACT 1970 [39 OF 1970] PROVISIONAL/COMPLETE SPECIFICATION [See Section 10) AN EXHAUST EMISSION CONTROL DEVICE HONDA GIKEN KOGYO KABUSHIKI KAISHA, A Corporation of Japan., 1-1, Minamiaoyama 2-chome, Minato-ku, Tokyo, Japan The following specification particularly describes the nature of the invention and the manner in which it is to be performed :- [Detailed Description of the Invention] [Technical Field to Which the Invention Pertainsl The present invention relates to an exhaust emission control device for an engine, in which a catalyst support is disposed in a casing including a taper portion having a small-diameter end connected to a connection pipe connected to an exhaust pipe for introducing an exhaust gas from an engine and a cylindrical portion connected to a large-diameter end of the taper portion; the catalyst support has a circular outer surface having a diameter larger than the outside diameter of the connection pipe; and the upstream end of the catalyst support is opposed to the downstream end of the connection pipe, and in which a cylindrical catalyst case for holding the catalyst support is disposed in the cylindrical portion; and the catalyst case is supported by the cylindrical portion via a supporting member. [Prior Art] The exhaust emission control device of this type has been known, for example, from Japanese Utility Model Laid-open No. Sho 55-135118, in which the downstream end of a connection pipe connected to an exhaust pipe is connected to a small-diameter end of a taper portion of a casing. Further, the exhaust emission control device having a feature in a holding configuration of a catalyst case has been already known, for example, from Japanese utility Model Laid-open No. Hei 4-87323. [Problem to be Solved by the Invention) By the way, in an engine having a small displacement mounted on a motorcycle or the like, to speedily raise the temperature of a catalyst supported by a catalyst support up to its activation temperature, it is effective to make the distance between the engine and the catalyst support as short as possible. In the above-described exhaust emission control device, if the distance between the engine and the catalyst support is made as short as possible, the axial distances of the exhaust pipe and connection pipe become shorter. However, since the axial distances of the exhaust pipe and connection pipe become shorter, the output torque of the engine is reduced in a low speed rotational range of the engine, and accordingly, the axial distances of the exhaust pipe and connection pipes may be desirable to be set longer. To cope with such an inconvenience, it may be considered to make large the opening angle of the taper portion of the casing for shortening the distance between the engine and the catalyst support in place of extending the axial distances of the exhaust pipe and connection pipe; however, in this case, since the downstream end of the exhaust pipe comes near to the upstream end of the catalyst support and also the volume of the taper portion is reduced, the ventilation resistance of the catalyst support is deteriorated upon high load operation of the engine. In view of the foregoing, the present invention has been made, and a first object of the present invention is to provide an exhaust emission control device for an engine, which is capable of raising the temperature of a catalyst at an early stage while avoiding a reduction in output torque of the engine in a low speed rotational range of the engine, and also preventing deterioration of the ventilation resistance of a catalyst support upon high load operation of the engine. The prior art exhaust emission control device described in Japanese Utility Model No. Hei 4-87323, however, has problems. Since both ends in the longitudinal direction of a catalyst case are supported by a cylindrical portion of a casing by respective supporting members, two pieces of the supporting members for supporting the catalyst: case in the cylindrical portion are required to be provided and thereby the number of parts becomes large, and further the heat transfer area of a heat transfer path between the catalyst case and the cylindrical portion becomes relatively larger and thereby the catalyst is susceptible to an external temperature. In view of the foregoing, the present invention has been made, and a second object of the present invention is to provide an exhaust emission control device of an engine, which is capable of supporting a catalyst case by a cylindrical portion of a casing while preventing a catalyst from being affected by an external temperature. [Means for Solving the Problem] To achieve the above first object, according to an invention described in claim 1, there is provided an exhaust emission control device for an engine, in which a cylindrical catalyst case for holding a catalyst support is disposed in a casing including a taper portion having a small-diameter end connected to a connection pipe connected to an exhaust pipe for introducing an exhaust gas from an engine and a cylindrical portion connected to a large-diameter end of the taper portion; the catalyst case is supported by the cylindrical portion via a supporting member; the catalyst support has a circular outer surface having a diameter larger than the outside diameter of the connection pipe; and the upstream end of the catalyst support is opposed to the downstream end of the connection pipe, the exhaust emission control device being characterized in that the downstream end of the connection pipe enters from the small-diameter end of the taper portion into the casing up to a position at which the downstream end of the connection pipe is opposed to the upstream end of the catalyst support with a specific gap put therebetween. With this configuration, even if the distance between the engine and the catalyst support is made as short as possible for speedily raising the temperature of the catalyst up to its activation temperature, it is possible to eliminate the need of shortening the distances of the exhaust pipe and connection pipe in the axial direction without enlarging the opening angle of the taper portion and hence to prevent a reduction in output torque of the engine in a low speed rotational range of the engine, and also to prevent deterioration of the ventilation resistance of the catalyst support by making relatively large the volume of the taper portion and utilizing the taper portion as a buffer chamber upon high load operation of the engine. According to an invention described in claim 2, in addition to the configuration of the invention described in claim 1, the inside diameter of at least the downstream end of the connection pipe is set to be smaller than the inside diameter of the exhaust pipe. With this configuration, since the exhaust gas flows from the connection pipe to the central portion of the catalyst support, it is possible to speedily raise the temperature of the catalyst supported at the central portion of the catalyst support up to its activation temperature upon start-up of the engine. To achieve the above second object, according to an invention described in claim 3, there is provided an exhaust emission control device for an engine, in which a cylindrical catalyst case for holding a catalyst support is disposed in a casing including a taper portion having a small-diameter end connected to a connection pipe connected to an exhaust pipe for introducing an exhaust gas from ^n engine and a cylindrical portion connected to a large-diameter end of the taper portion; the catalyst case is supported by the cylindrical portion via a supporting member; the catalyst support has a circular outer surface having a diameter larger than the outside diameter of the connection pipe; and the upstream end of the catalyst support is opposed to the downstream end of the connection pipe, the exhaust emission control device being characterized in that the supporting member comprises a supporting cylinder relatively slidably fitted on a portion, extending from one end to an intermediate point in the longitudinal direction, of the catalyst case and having one end fixed to one end of the catalyst case; and a flange projecting radially outwardly from the other end of the supporting cylinder; and the outer peripheral edge of the flange is fixed to the inner surface of the cylindrical portion of the casing. with this configuration, since one end of the catalyst case is fixed to one end of the supporting cylinder of the supporting member fixed to the cylindrical portion and a portion, extending from one end to an intermediate point in the longitudinal direction, of the catalyst case is relatively slidably fitted in the supporting cylinder, it is possible to support the catalyst case in the cylindrical portion of the casing while allowing the deformation of the catalyst case due to thermal expansion thereof by means of a single supporting member. Since the supporting member is formed into a simple shape, it is possible to reduce the number of parts and hence to lower the manufacturing cost. Since the outer peripheral edge of the flange projects radially outwardly from the other end of the supporting cylinder at a position corresponding to an intermediate portion in the longitudinal direction of the catalyst case and is fixed to the cylindrical portion of the casing, the supporting member is fixed to the cylindrical portion at a position near the center of gravity of each of the catalyst support and the catalyst case, so that it is possible to suppress the effect of stress exerted on the supporting member due to vibration of the catalyst support and catalyst case at minimum. Further, since the heat transfer area of a heat transfer path between the cylindrical portion of the casing and the catalyst case is smaller than that in the prior art device using a plurality of supporting members, the catalyst can be prevented from being affected by an external temperature, and particularly, part of the catalyst supported by a portion, not fitted to the supporting cylinder of the supporting member, of the catalyst case can be more effectively prevented from being affected by an external temperature. As a result, it is possible to further stabilize the catalyst temperature. According to an invention described in claim 4, in addition to the configuration of the invention described in claim 3, the inside of the casing is partitioned into a plurality of expansion chambers in the axial direction, to form a muffler, and the expansion chamber to which the upstream end of the catalyst support faces is partitioned from the expansion chamber to which the downstream end of the catalyst support faces by means of the flange. With this configuration, since the casing is provided commonly to the exhaust emission control device and the muffler and further the exhaust emission control device constitutes part of the muffler, it is possible to reduce the number of parts of the muffler and to reduce the size and weight of the muffler. [Brief Description of the Drawings] [Fig. 1] A right side view of a motorcycle. [Fig. 2] A vertical sectional view of an exhaust emission control device and a muffler. [Fig. 3] An enlarged view of an essential portion of Fig. 2 [Fig. 4] A sectional view taken on line 4-4 of Fig. 3. [Fig. 5] A graph showing a change in temperature of a catalyst at the central portion of a catalyst support depending on a change in restriction ratio of a connection pipe [Mode for carrying Out the Invention] Hereinafter, one embodiment of the present invention will be described with reference to the accompanying drawings. Figs. 1 to 5 show one embodiment of the present invention, wherein Fig. 1 is a right side view of a motorcycle; Fig. 2 is a vertical sectional view of an exhaust emission control device and a muffler; Fig. 3 is an enlarged view of an essential portion of Fig. 2; Fig. 4 is a sectional view taken on line 4-4 of Fig. 3; and Fig. 5 is a graph showing a change in temperature of a catalyst at the central portion of a catalyst support depending on a change in restriction ratio of a connection pipe. Referring first to Fig. 1, a body frame F of a backborn type motorcycle includes a backborn 5 made from a steep pipe tilting backwardly, downwardly and a rear frame 6 made from a steel plate welded to the rear end of the backborn 5. A front fork 8 for rotatably supporting a front wheel WF is steerably, pivotably supported by a head pipe 7 provided at the front end of the backborn 5. A steering handlebar 9 is connected to the upper end of the front fork 8. A rear fork 10 for rotatably supporting a rear wheel WR is pivotably supported by the rear frame 6. A rear cushion 11 is provided between the rear fork 10 and the rear frame 6. A saddle 12 is mounted on the upper surface of the rear frame 6. A fuel tank 13 is contained in the rear frame 6 at a position directly under the saddle 12. A crank case 14 of an engine E is mounted to a front end portion of the rear frame 6 at a position under a connection portion between the front end of the rear frame 6 and the backborn 5. An air cleaner 15 is mounted to a front end portion of the backborn 5. The air cleaner 15 is connected to an intake port (not shown) provided in a cylinder head 16 of the engine E via a horn pipe 17, a throttle body 18 and an intake pipe 19. A fuel injection valve 20 for injecting a fuel to the intake port is mounted to an intermediate portion of the intake pipe 19. The upstream end of an exhaust pipe 21 for introducing an exhaust gas from the engine E is connected to an exhaust port (not shown) provided in a lower portion of the cylinder head 16. The downstream end of the exhaust pipe 21 is connected to a casing 24 provided commonly to an exhaust emission control device 22 and a muffler 23 disposed on the right side of a rear portion of the body frame F. Referring to Figs. 2 and 3, the casing 24 includes a cylindrical portion 25, a taper portion 26 having a large-diameter end to which one end of the cylindrical portion 25 is coaxially connected, and a terminal wall 27 fixed to the other end of the cylindrical portion 25. The exhaust emission control device 22 has a catalyst support 28 and is contained in the casing 24 at a portion near one end of the casing 24 with the catalyst support 28 disposed coaxially with the cylindrical portion 25. Referring particularly to Fig. 4, the catalyst support 28 is formed into 3 honeycomb cylinder having a circular outer surface and extending coaxially with the casing 24. To be more specific, the catalyst support 28 is obtained by overlapping a flat sheet 29 and a corrugated sheet 30, each of which is made from a stainless steel, to each other and spirally winding the sheets 29 and 30 thus overlapped. A catalyst (not shown) is supported by the catalyst support 28. The catalyst support 28 is contained in a catalyst case 31 made from the same material as that of the catalyst support 28, typically, a stainless steel. To be more specific, the catalyst case 31 is formed into a cylindrical shape longer than that of the catalyst support 28. The catalyst support 28 is fitted in the catalyst case 31 with their both ends positioned inwardly from both ends of the catalyst case 31. In such a fitted state, the catalyst support 28 is welded to the catalyst case 31. The catalyst case 31 is concentrically disposed in the cylindrical portion 25 with its longitudinal one end projecting in the taper portion 26, and is supported in the cylindrical portion 25 by means of a supporting member 32. The supporting member 32 includes a supporting cylinder 32a, a flange 32b, and a mounting cylinder 32c which are integrated to each other. The supporting cylinder 32a is relatively slidably fitted on a portion, extending from one end to an intermediate point in the longitudinal direction, of the catalyst case 31. The flange portion 32b projects radially outwardly from the other end of the supporting cylinder 32a. The mounting cylinder 32c is continuous to the outer peripheral edge of the flange 32b and is fitted in the inner surface of the cylindrical portion 25. The supporting member 32 is made from the same material as that of the catalyst support 28 and the catalyst case 31, typically, a stainless steel. One end of the supporting cylinder 32a is fixedly welded to one end of the catalyst case 31. In this case, by welding one end of the supporting cylinder 32a to one end of the catalyst case 31 projecting from one end of the catalyst support 28, the thermal effect upon welding exerted to the catalyst supported by the catalyst support 28 can be made avoided as much as possible. The mounting cylinder 32c, that is, the outer peripheral edge of the flange 32b is fixedly welded to the inner surface of the cylindrical portion 25 of the casing 24. By the way, if the temperature of an exhaust gas is relatively high, the fixedly welded portion between one end of the supporting cylinder 32a and one end of the catalyst case 31 may be desirable to be set on the upstream side as described in this embodiment; however, if the temperature of the exhaust gas is relatively low, typically, slightly more than the activation temperature of the catalyst, the fixedly welded portion may be desirable to be set on the downstream side. To be more specific, as an exhaust gas discharged from the engine E along with start-up of the engine E flows in the catalyst support 28 from the upstream side to the downstream side, the temperature of the catalyst support 28 rises sequentially from the upstream end side by the catalytic reaction generated when the temperature of the catalyst reaches the activation temperature, and thereby the temperature of the catalyst case 31 rises sequentially from the upstream end side. In this case, by fixedly welding one end of the supporting cylinder 32a of the supporting member 32 to the upstream end of the catalyst case 31, the fixedly welded portion can be prevented from being subjected to an excess stress due to a differential thermal expansion. Accordingly, in the case where the temperature of the exhaust gas is relatively high, one end of the supporting cylinder 32a is fixedly welded to the upstream end of the catalyst case 31. On the other hand, since heat transfer occurs from the catalyst case 31 to the casing 24 via the supporting member 32, if one end of the supporting cylinder 32a is fixedly welded to the upstream end of the catalyst case 31 in the case where the temperature of the exhaust gas is relatively low, typically, slightly more than the activation temperature of the catalyst, the temperature rise of the catalyst is retarded by the heat transfer from the catalyst case 31 to the casing 24 via the supporting member 32, to thereby retard the starting of the catalytic reaction. Accordingly, in the case where the temperature of the exhaust gas is relatively low, one end of the supporting cylinder 32a may be desirable to be fixedly welded to the downstream end of the catalyst case 31. A cap 33 is provided at a small-diameter end of the taper portion 26 of the casing 24. A connection pipe 34 is coaxially connected to the small-diameter end of the taper portion 26 via the cap 33. The downstream end of the exhaust pipe 21 is coaxially connected to the connection pipe 34. The cap 33 is formed into a stepped cylinder shape having a small-diameter cylinder 33a. The cap 33 is coaxially, fixedly welded to the small-diameter end of the taper portion 26 with the small - diameter cylinder 33a projecting outwardly from the taper portion 26. The connection pipe 34 includes an outer pipe 35, and an inner pipe 36. The inner pipe 36 is inserted in the outer pipe 35 with their both ends projecting outwardly from both ends of the outer pipe 35, and is fixedly welded to the outer pipe 35. The downstream end of the connection pipe 34, that is, the downstream end of the inner pipe 36 passes through the small - diameter cylinder 33a of the cap 33, and enters from the small-diameter end of the taper portion 26 into the casing 24 up to a position at which the downstream end of the connection pipe 34 is opposed to the upstream end of the catalyst support 28 with a gap L put therebetween. In such a state, an intermediate portion of the outer pipe 35 is fixedly welded to the cap 33. The outside diameter of the inner pipe 36 is set at a value fittable in the exhaust pipe 21. The upstream end of the inner pipe 36 is fitted in the downstream end of the exhaust pipe 21, and the downstream end of the exhaust pipe 21 is fixedly welded to the upstream end of the outer pipe 35. In this case, an inside diameter Dl of the inner pipe 36, that is, the connection pipe 34 at least on the downstream end side (over the entire length in this embodiment) is set to be smaller than an inside diameter D2 of the exhaust pipe 21. As a result, an exhaust gas from the exhaust pipe 21 is restricted in the connection pipe 34 before being introduced into the casing 24. Since at least the downstream end of the connection pipe 34 is restricted as described above, the exhaust gas flows from the connection pipe 34 to the central portion of the catalyst support 28. As a result, the temperature of the catalyst supported by the central portion of the catalyst support 28 can be speedily raised upon start-up of the engine E. Fig. 5 is a graph showing a change in temperature of the catalyst at the central portion of the catalyst support 28 depending on a change in ratio (D2-D1)/D2 when the ratio (D2-D1)/D2 iess than 0.05, the effect of concentratedly directing the flow of the exhaust gas to the central portion of the catalyst support 28 cannot be obtained, with a result that the temperature rise of the catalyst at the central portion of the catalyst support 28 is sufficient. Meanwhile, when the ratio (D2-D1)/D2 more than 0.40, the exhaust gas is excessively restricted and thereby the amount of the exhaust gas is reduce, with a result that the temperature rise of the catalyst at the central portion of the catalyst support 28 is also insufficient. Accordingly, the ration(D2-D1)/D2 may be desirable to be set in a range of 0.05 With respect to the above-described gap L between the downstream end of the connection pipe 34 and the upstream end of the catalyst support 28, if the gap L is excessively short, a local deterioration of the catalyst may occur, and if the gap L is excessively large, the effect of speedily raising the temperature of the catalyst supported at the central portion of the catalyst support 28 upon start-up of the engine E cannot be obtained. From the practical viewpoint, the gap L may be set in a range of 0.5 XDI to 5 XDl, preferably, in a range of 0. 5XDI to 3 XDl. Referring again to Fig. 2, the muffler 23 is configured by partitioning the inside of the casing 24 into a first expansion chamber 37, a second expansion chamber 38, a fourth expansion chamber 40 and a third expansion chamber 39, which chambers are axially arranged in this order from the upstream side. The first expansion chamber 37 is formed in the casing 24 at a position between the taper portion 26 and the flange 32b of the supporting member 32 in such a manner that the upstream end of the catalyst support 28 faces to the first expansion chamber 37. A cylindrical body 41 is inserted in the rear half on the downstream side of the cylindrical portion 25 of the casing 24 with a slight gap put between the cylindrical body 41 and the inner surface of the cylindrical portion 25. A plurality of projections 41a provided on the upstream end portion of the cylindrical body 41 and a plurality of projections 41b provided on the downstream end portion of the cylindrical portion 41 are fixedly welded to the inner surface of the cylindrical portion 25. The second expansion chamber 38 is formed in the casing 24 at a position between a partition wall 42 and the supporting member 32. The outer periphery of the partition wall 42 is fixed to the inner surface of an approximately central portion of the cylindrical body 41 in such a manner as to partition the inside of the cylindrical body 41 into an upstream half and a downstream half. The downstream end of the catalyst support 28 faces to the second expansion chamber 38. The flange 32b of the supporting member 32 serves as a partition wall for partitioning the first and second expansion chambers 37 and 28 from each other. The third expansion chamber 39 is formed in the casing 24 at a position between a partition wall 43 and the terminal wall 27. The outer periphery of the partition wall 43 is fixed to the inner surface of a portion, near the downstream end, of the cylindrical body 41. The fourth expansion chamber 40 is formed in the casing 41 at a position between the partition walls 42 and 43. The second and third expansion chambers 38 and 39 are communicated to each other by means of a pair of cpmmunication pipes 44 with their both ends supported by the partition walls 42 and 43. The third and fourth expansion chambers 39 and 40 are communicated to each other by means of a pair of communication pipes 45 supported by the partition wall 43. A single discharge pipe 46 with its upstream end opened to the fourth expansion chamber 40 and its downstream end opened to the outside is fixed on both the partition wall 43 and the terminal wall 27 while passing through central portions of the partition wall 43 and the terminal wall 27. The exhaust gas is finally discharged from the discharge pipe 46. The function of the embodiment will be described below. The downstream end of the connection pipe 34 connected to the exhaust pipe 21 for introducing an exhaust gas from the engine E projects from the small-diameter end of the taper portion 26 of the casing 24 into the casing 24 up to the position at which the downstream end of the connection pipe 34 is opposed to the upstream end of the catalyst support 28 with a specific gap put therebetween. Accordingly, even if the distance between the engine E and the catalyst support is made as short as possible for speedily raising the temperature of the catalyst up to the activation temperature, it is possible to eliminate the need of shortening the axial distances of the exhaust pipe 21 and the connection pipe 34 without enlarging the opening angle of the taper portion 26. As a result, it is possible to prevent a reduction in output torque in a low speed rotational range of the engine E, and also to prevent deterioration of the ventilation resistance of the catalyst support 28 by making relatively large the volume of the taper portion 26, that is, the volume of the first expansion chamber 37, and utilizing the first expansion chamber 37 as a buffer chamber upon high load operation of the engine E. Since the inside diameter Dl of at least the downstream end of the connection pipe 34 is set to be smaller than the inside diameter D2 of the exhaust pipe 21, the exhaust gas flows from the connection pipe 34 to the central portion of the catalyst support 28. As a result, the temperature of the catalyst supported at the central portion of the catalyst support 28 can be speedily raised up to the activation temperature upon start-up of the engine E. The cylindrical catalyst case 31 for holding the catalyst support 28 which supports the catalyst is coaxially disposed in the cylindrical portion 25 of the casing 24, and is supported in the cylindrical portion 25 by the supporting member 32, wherein the supporting member 32 includes the supporting cylinder 32a relatively slidably fitted on a portion, extending from one end to an intermediate point in the longitudinal direction, of the catalyst case 31 and is fixed at its one end to one end of the catalyst case 31, and the flange 32b projecting outwardly from the other end of the supporting cylinder 32a and having the outer periphery edge (mounting cylinder 32c in this embodiment) fixed to the inner surface of the cylindrical portion 25. As a result, the catalyst case 31 can be supported in the cylindrical portion 25 of the casing 24 by the single supporting member 32 while allowing the deformation of the catalyst case 31 due to the thermal expansion thereof. Further, since the supporting member 32 has a simple shape, it is possible to reduce the number of parts required for supporting the catalyst case 31, and hence to lower the manufacturing cost. Since the outer peripheral edge of the flange 32b projecting outwardly from the other end of the supporting cylinder 32a is fixed to the cylindrical portion 25 of the casing 24 at a position corresponding to an intermediate portion of the catalyst case 31 in the longitudinal direction, the supporting member 32 is fixed to the cylindrical portion 25 at the position near the centers of gravity of the catalyst support 28 and the catalyst case 31. As a result, it is possible to suppress the effect of stress exerted on the supporting member 32 due to vibration of the catalyst support 28 and the catalyst case 31 at minimum. Since the heat transfer area of the heat transfer path between the cylindrical portion 25 of the casing 24 and the catalyst case 31 that in the prior art device using a plurality of supporting members, the catalyst can be prevented from being affected by an external temperature, and particularly, part of the catalyst supported by a portion, not fitted to the supporting cylinder 32a of the supporting member 32, of the catalyst case 31 can be more effectively prevented from being affected by an external temperature. As a result, it is possible to further stabilize the catalyst temperature. Since the muffler 32 is configured by partitioning the inside of the casing 24 into the plurality of expansion chambers 37 to 40 in the axial direction and also the first expansion chamber 37 to which the upstream end of the catalyst support 28 faces is partitioned from the second expansion chamber 38 to which the downstream end of the catalyst support 28 faces by means of the flange 32b of the supporting member 32, the exhaust emission control device 22 constitutes part of the muffler 23 by using the casing 24 commonly to the exhaust emission control device 22 and the muffler 23. As a result, it is possible to reduce the number of parts of the muffler 23 and to reduce the size and weight of the muffler 23. While the embodiment of the present invention has been described in detail, the present invention is not limited thereto, and it is to be understood that various changes in design may be made without departing from the scope of the present invention described in claims. For example, while the exhaust emission control device 22 and the muffler 23 are integrated with each other in the common casing 24 in the above-described embodiment, the present invention can be applied to the exhaust emission control device provided independently from the muffler 23. For example, the mounting cylinder 32c of the supporting member 32 may be omitted and instead the outer periphery of the flange 32b be directly fixed to the inner surface of the cylindrical portion 25 of the casing 24; and while the catalyst support 28 is directly welded to the catalyst case 31 in the above embodiment, the catalyst support 28 may be held by the catalyst case 31 via a net portion. [Effect of the Invention] As described above, according to the invention described in claim 1, even if the distance between the engine and the catalyst support is made as short as possible for speedily raising the temperature of the catalyst up to its activation temperature, it is possible to eliminate the need of shortening the distances of the exhaust pipe and connection pipe in the axial direction without enlarging the opening angle of the taper portion, and hence to prevent a reduction in output torque of the engine in a low speed rotational range of the engine, and also to prevent deterioration of the ventilation resistance of the catalyst support by making relatively large the volume of the taper portion and utilizing the taper portion as a buffer chamber upon high load operation of the engine. According to the invention described in claim 2, it is possible to speedily raise the temperature of the catalyst supported at the central portion of the catalyst support up to its activation temperature upon start-up of the engine. As described above, according to the invention described in claim 3, it is possible to support the catalyst case in the cylindrical portion of the casing by the single supporting member while allowing the deformation of the catalyst case due to the thermal expansion thereof, and hence to reduce the number of parts and lower the manufacturing cost. Since the supporting member is fixed to the cylindrical portion at the position near the centers of gravity of the catalyst support and the catalyst case, it is possible to suppress the effect of stress exerted on the supporting member due to vibration of the catalyst support and the catalyst case at minimum. Further, the catalyst can be prevented from being affected by an external temperature, and particularly, part of the catalyst supported by a portion, not fitted to the supporting cylinder of the supporting member, of the catalyst case can be more effectively prevented from being affected by an external temperature. As a result, it is possible to further stabilize the catalyst temperature. According to the invention described in claim 4, it is possible to reduce the number of parts of the muffler and to reduce the size and weight of the muffler. [Explanation of Characters] 21: exhaust pipe, 22: exhaust emission control device, 24: casing, 25: cylindrical portion, 26: taper portion, 28: catalyst support, 34: connection pipe, E; engine, 23: muffler, 31: catalyst case, 32: supporting member, 32a: supporting cylinder, 32b: flange, 37-40: expansion chamber WE CLAIM:- 1. An exhaust emission control device for an engine, in which a cylindrical catalyst case (31) for holding a catalyst support (28) is disposed in a casing (24) including a taper portion (26) having a small-diameter end connected to a connection pipe (34) connected to an exhaust pipe (21) for introducing an exhaust gas from an engine (E) and a cylindrical portion (25) connected to a large-diameter end of said taper portion (26); said catalyst case (31) is supported by said cylindrical portion (25) via a supporting member (32) said catalyst support (28) has a circular outer surface having a diameter larger than the outside diameter of said connection pipe (34); and the upstream end of said catalyst support (28) is opposed to the downstream end of said connection pipe (34), said exhaust emission control device being characterized in that the downstream end of said connection pipe (34) enters from the small-diameter end of said taper portion (26) into said casing (24) up to a position at which the downstream end of said connection pipe (34) is opposed to the upstream end of said catalyst support (28) with a specific gap put therebetween. 2. An exhaust emission control device for an engine as claimed in claim 1, wherein the inside diameter of at least the downstream end of said connection pipe (34) is set to be smaller than the inside diameter of said exhaust pipe (21). 3. An exhaust emission control device for an engine as claimed in claim 1, wherein a cylindrical catalyst case (31) for holding a catalyst support (28) is disposed in a casing (24) including a taper portion (26) having a small-diameter end connected to a connection pipe (34) connected to an exhaust pipe (21) for introducing an exhaust gas from an engine (E) and a cylindrical portion (25) connected to a large-diameter end of said taper portion (26); said catalyst case (31) is supported by said cylindrical portion (25) via a supporting member (32); said catalyst support (28) has a circular outer surface having a diameter larger than the outside diameter of said connection pipe (34); and the upstream end of said catalyst support (28) is opposed to the downstream end of said connection pipe (34), said exhaust emission control device being characterized in that said supporting member (32) comprises a supporting cylinder (32a) relatively slidably fitted on a portion, extending from one end to an intermediate point in the longitudinal direction, of said catalyst case (31) and having one end fixed to one end of said catalyst case (31); and a flange (32b) projecting radially outwardly from the other end of said supporting cylinder (32a); and the outer peripheral edge of said flange (32b) is fixed to the inner surface of said cylindrical portion (25) of said casing (24). 4. An exhaust emission control device for an engine as claimed in claim 3, wherein the inside of said casing (24) is partitioned into a plurality of expansion chambers (37 to 40) in the axial direction, to form a muffler (23), and said expansion chamber (37) to which the upstream end of said catalyst support (28) faces is partitioned from said expansion chamber (38) to which the downstream end of said catalyst support (28) faces by means of said flange (32b). 5. An exhaust emission control device for an engine substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings. Dated this 15th day of June, 2000. [SANJAY KUMAR] OF REMFRY &.SAGAR ATTORNEY FOR THE APPLICANTS

Documents:

554-mum-2000-cancelled pages(14-10-2004).pdf

554-mum-2000-claims(granted)-(14-10-2004).doc

554-mum-2000-claims(granted)-(14-10-2004).pdf

554-mum-2000-correspondence(2-12-2005).pdf

554-mum-2000-correspondence(ipo)-(17-5-2004).pdf

554-mum-2000-drawing(16-6-2000).pdf

554-mum-2000-form 1(16-6-2000).pdf

554-mum-2000-form 19(15-4-2004).pdf

554-mum-2000-form 2(granted)-(14-10-2004).doc

554-mum-2000-form 2(granted)-(14-10-2004).pdf

554-mum-2000-form 3(12-3-2001).pdf

554-mum-2000-form 3(16-6-2000).pdf

554-mum-2000-form 5(16-6-2000).pdf

554-mum-2000-petition under rule 137(19-10-2004).pdf

554-mum-2000-power of authority(13-11-2000).pdf

554-mum-2000-power of authority(15-10-2004).pdf

abstract1.jpg