GB2383606A

GB2383606A - Exhaust system for internal combustion engines

Info

Publication number: GB2383606A
Application number: GB0217640A
Authority: GB
Inventors: Hiroyuki Murase
Original assignee: Honda Motor Co Ltd
Current assignee: Honda Motor Co Ltd
Priority date: 2000-10-11
Filing date: 2001-09-27
Publication date: 2003-07-02
Anticipated expiration: 2021-09-27
Also published as: WO2002031326A1; CN1233924C; BR0107306B1; CN1392920A; JPWO2002031326A1; TW550334B; DE10194626T1; MY129022A; GB2383606B; BR0107306A; JP4094423B2; GB0217640D0

Abstract

An exhaust system for internal combustion engines, which, in order to improve the durability of an exhaust system for internal combustion engines having an exhaust gas purifying device welded to an exhaust pipe, comprises a first exhaust pipe (3) and an exhaust gas purifying device (4) having a casing (20). The casing (20) is composed of first and second casing halves (21, 22) joined together by welding. The upstream end (3a) of the first exhaust pipe (3) is connected to an exhaust manifold through a spherical joint (6), while the downstream end (3b) of the first exhaust pipe (3) is welded to a first casing half (21), of two casing halves (21, 22), which forms the upper portion of he casing (20), in such a manner that the downstream end (3b) does not overlap a weld (W2) which joins the two casing halves (21, 22). Therefore. there is no possibility of overlap of a weld (W1) between the first exhaust pipe (3) and the first casing half (21), nor is the possibility of strength being decreased. Further, exhaust gases flow into the casing (20) only through the first exhaust pipe (3).

Description

-it 5 DESCRIPTION

EXHAUST SYSTEM OF AN ENGINE

This invention relates to an exhaust system of an engine, and more particularly, to an exhaust system including an exhaust gas with a casing to which an exhaust pipe is welded.

Background Art

Conventional exhaust systems used to make an exhaust passage for releasing to the atmospheric air an exhaust gas after combustion discharged from the combustion chamber of an engine are equipped with an exhaust gas purifier for purifying the exhaust gas, and an exhaust pipe communicating with the discharge port of the engine is connected to the exhaust gas purifier.

For example, Japanese Patent Laid-Open Publication No. hei 11-13461 discloses a technique connecting an exhaust gas outlet pipe from each cylinder of a three-cylinder engine to a catalyst case containing a catalyst (corresponding to a casing of an exhaust gas purifier. This catalyst case is made of two divisional case elements with flanges welded to each other. An exhaust gas outlet pipe from the first cylinder is welded at the Joint of both these case elements, and an exhaust gas outlet pipe extending from

the second cylinder while gathering an exhaust gas outlet pipe from the third cylinder is welded to one of the case elements. A mount seat of an O2 sensor is formed on the other of the case elements.

In the conventional technique reviewed above, since the exhaust gas outlet pipe from the first cylinder is welded to the welded joint of both case elements of the catalyst case, welded joints overlap, and they decrease in strength at the overlapping portion. On the other hand, vibrations of the engine are transmitted to the exhaust gas outlet pipe, and a load by the vibrations acts upon the welded Joint between the catalyst case and the exhaust gas outlet pipe and produces a stress. Thus, there is the problem that cracks are liable to be produced at the overlapping welded joint decreased in strength due to the load caused by the vibrations of the exhaust gas outlet pipe acting upon the welded joint. In addition, since the mount seat for the O2 sensor is restricted in position by the exhaust gas outlet pipe welded to the welded joint between both case elements, there is the problem that the O2 sensor is restricted in position on the other case element.

Disclosure of Invention

Under the circumstances it is a common object of the inventions recited in claims 1 through 4 to improve the durability of an exhaust system of an engine having

an exhaust gas purifier with a casing to which an exhaust pipe is welded. An object of the invention recited in claim 2 is to improve the efficiency of exhaustion. An object of the invention recited in claim 3 is to ensure a large freedom for disposition of an oxygen concentration sensor on to the casing. An object of the invention recited in claim 4 is to prevent thermal damage by the exhaust gas purifier and also improve the durability of the sensor and the catalyst. An object of the invention recited in claim 5 is to make it easier to connect exhaust pipes located downstream of the exhaust gas purifier.

According to the invention recited in claim 1, there is provided an exhaust system of an engine having an upstream exhaust pipe permitting exhaust gas to flow from the engine, an exhaust gas purifier having a casing made up of two casing halves welded to each other, and a downstream exhaust pipe having AL downstream end welded to the casing, characterized in: the upstream end being connected to the upstream exhaust pipe via a spherical joint, the downstream end being welded to one of the casing halves such that the welded joint thereof does not overlap the welded joint of the casing halves, and the exhaust gas flowing into the casing only through the downstream exhaust pipe.

According to the invention recited in claim 1, since part of vibrations of the engine transmitted to

the upstream exhaust pipe is absorbed by sliding relative movements along a sphericalmle acebe ween the upstream exhaust pipe and the downstream exhaust pipe by the spherical joint and prevented from reaching the downstream exhaust pipe as the sole exhaust pipe for introducing exhaust gas into the casing, no large load caused by such vibrations act on the welded joint between the downstream exhaust pipe and the casing, and generation of cracks in the welded Joint can be prevented. Even when vibrations that cannot be absorbed effectively by the spherical Joint are produced and transmitted to the downstream exhaust pipe, thereby to result in applying a load caused by the vibrations on the welded joint, not only because the vibrations themselves transmitted to the downstream exhaust pipe are attenuated by the spherical joint as compared with a configuration without such a spherical joint but also because the welded joint between the downstream end of the downstream exhaust pipe and one of the casing halves does not overlap the welded joint coupling both casing halves, the welded Joint is kept strong, and generation of cracks in the welded joint À can be alleviated significantly.

As a result! the following effects are provided.

That is, since vibrations of the engine transmitted to the upstream exhaust pipe are absorbed by the spherical joint, even when vibrations the spherical joint cannot

absorb are transmitted to the downstream exhaust pipe as the sole exhaust pipe for introducing exhaust gas to the casing, not only because the vibrations themselves transmitted to the downstream exhaust pipe are attenuated by the spherical joint to a certain extent but also because the welded joint between the downstream exhaust pipe and the casing has a high strength, generation of cracks in the welded joint can be alleviated significantly, and the exaust system having the assing with the upstream exhaust pipe welded thereto is improved in durability.

The invention recited in claim 2 is based on the exhaust system of an engine recited in claim 1, and it is characterized in that the casing in a lower level than the upstream end and one of the casing halves form the top part of the casing.

According to the invention recited in claim 2, since the downstream exhaust pipe extends downward from the upstream end and is connected to one of the casing halves forming the top part of the casing located in a lower level than the upstream end, the downstream exhaust pipe can be shortened and decreased in curves.

As a result, in addition to the effects of the invention recited in claim 1, the short and less-curved layout of the downstream exhaust pipe decreases the flow path resistance and contributes to smooth flow of the exhaust gas in the exhaust system, thereby to

improve the exhaustion efficiency and simplify the layout of the downstream exhaust pipe.

The invention recited in claim 3 is based on the exhaust system of an engine recited in claim 2, and it is characterized in that the exhaust gas purifier includes a catalyst contained in the casing, an exhaust inlet to the casing from the downstream exhaust pipe is located upstream of the catalyst, and an upstream part of the other of the casing halves located upstream of the catalyst has formed a mount seat for mounting an oxygen concentration sensor for detecting oxygen concentration in the exhaust gas.

According to the invention recited in claim 3, the oxygen concentration sensor detects oxygen concentration in the exhaust gas flowing into the casing from the exhaust inlet located upstream of the catalyst at a position upstream of the catalyst.

However, since the mount seat for mounting the oxygen concentration sensor is formed in a part of the casing half located upstream of the catalyst, which casing half is other than the casing half to which the downstream exhaust pipe is connected, restriction concerning the position of the mount seat is reduced in the part of the casing upstream of the catalyst.

As a result, in addition to the effects of the invention recited in claim 2, here is provided the effect that the mount seat provided in the casing half

not having the downstream exhaust pipe connected thereto reduces the constraint to the positioning of itself, ensures a larger freedom concerning the position of the oxygen concentration sensor, and enables selection of an optimum position of the oxygen concentration sensor from the view point of its detection accuracy and response.

The invention recited in claim 4 is based on the exhaust system of an engine recited in claim 3 and it is characterized in that the welded joint connecting the downstream end and that casing half is located upstream of the catalyst, and a heat-shield cover covering the outside of the casing is fixed to the casing at a plurality of fixture points upstream of the catalyst. According to the invention recited in claim 4, since the heat-shield cover is provided outside the casing, thermal damage to elements around the casing -; can be prevented. Moreover, since the position of the welded joint is upstream of the catalyst in the casing and the heat-shield cover is fixed to the casing at a plurality of fixture points upstream of the catalyst, the casing is enhanced in rigidity near the welded Joint between the downstream exhaust pipe and one of the casing halves, because of an additional rigidity of the heat- shield cover.

As a result, in addition to the effects of the

invention recited in claim 3, the following effects are provided. That is, thermal damage to elements around the casing can be prevented by the heat-shield cover.

In addition, in a part of the casing upstream of the-

cataly,st, since the heat-shield cover fixed at a plurality of fixture points upstream of the catalyst attenuates vibrations transmitted from the downstream exhaust pipe, thereby suppresses vibrations of the entire casing, and thereby enhances the durability of the catalyst contained in the casing.

The invention recited in claim 5 is based on the exhaust system of an engine recited in claim 1 and it is characterized in that a second exhaust pipe is connected to the downstream end of the easing, a . connection flange is provided at the downstream end of the second exhaust pipe to connect a third exhaust pipe to the second exhaust pipe with fastening members, and the second exhaust pipe is bent to direct a straight line normal to a connection surface of the connection flange toward a direction offset from an axial line of the easing.

According to the invention recited in claim 5, since the connection surface of the connection flange of the second exhaust pipe bent to be offset from the axial line of the casing of the exhaust gas purifier is directed toward a direction offset from the axial line of the easing, the connection surface can be oriented

not to face on an element disposed to face on the exhaust gas purifier in the axial line direction.

As a result, in addition to the effects of the invention recited in claim 1, the following effects are provided. that is, since the second exhaust pipe is bent to orient the connection surface of the connection flange toward a direction offset from the axial line of the casing such that the connection surface does not face on an element disposed to face on the exhaust gas purifier in the axial line direction, when the second exhaust pipe and the third exhaust pipe are connected together, even if that element is disposed to face on the exhaust gas purifier with a relatively short distance therefrom in the axial line direction, a tool for fixing the fastening members can be brought near the connection flange without interfering with that element, and this makes connection of the connection flange and the third exhaust pipe with the fastening members easier, and enhances the working efficiency for connection of the second and third exhaust pipes.

As far as used here, the terms up. and down" mean such directions and portions related to the exhaust system of the engine when fixed in position of a vehicle or other vehicle, or other equipment.

Similarly, the terms Upstream and Downstream are used in relation to the flowing direction of exhaust gas. AIL

Brief Description of Drawings

Fig. l is a plan view that schematically shows a part of an exhaust system of an engine to be mounted in a vehicle, to which the present invention is applied; Fig. 2 is a side elevational view that schematically shows a part of the exhaust system of the engine of Fig. 1; Fig. 3 is a cross-sectional view of a spherical joint; Fig. 4 is a partial view of an exhaust gas purifier, taken from a direction normal to a divisional plane of a casing: Fig. 5 is a cross-sectional view of a part of a heat-shield cover, taken along from the direction indicated by the arrow V in Fig. 4: Fig. 6 is a view of the casing of the exhaust gas purifier, taken from a direction normal to the divisional plane thereof; Fig. 7 is a cross-sectional view that shows a junction of an exhaust pipe with the casing; Fig. 8 is a perspective view that shows a positional relation between the exhaust system of Fig. 1 and a fuel tank: Fig. 9 is a plan view similar to Fig. 1,w ch shows a positional relation between the exhaust system of Fig l and the fuel tank; and

Fig. 10 is a side elevational view similar to Fig. 2, which shows a positional relation between the exhaust system of Fig. 1 and the fuel tank.

Best Mode for Carrying Out than Invention

Embodiments of the invention will now be explained below with reference to Figs. 1 through 10.

First referring to Fig. 1, which is a plan view schematically showing a part of an exhaust system of an in-line four-cylinder engine according to an embodiment of the invention to be mounted in a vehicle, and Fig. 2, which is a side-elevational view thereof, the exhaust system 1 configured to purify, an exhaust gas, which is combustion gas discharged from a combustion chamber of an engine (not shown) having reciprocal pistons, and to discharge it to the atmospheric air, includes, sequentially in the upstream-to-downstream direction, an exhaust manifold 2 to be connected to--a cylinder head E of the engine, first exhaust pipe 3, exhaust gas purifier 4, and second exhaust pipe 5, and includes a third exhaust pipe 40 and a supplemental muffler 41 disposed downstream of them, (all best shown in Figs. 8 through 10). The exhaust system also includes, downstream of them, a main muffler and a tail pipe (neither shown), and exhaust gas is guided through an exhaust path defined by these elements and discharged from the tail pipe to the atmospheric air.

The exhaust manifold 2 is made up of four branch pipes 21 through 24 connected to exhaust ports of respective cylinders aligned in the axial direction of the rotation axis of the crank shaft of the engine (in the direction indicated by the arrow A in Fig. 1) by a cylinder head E and a collecting duct 2a uniting these branch pipes 21 through 2 into a single duct. The downstream end 2a1 of the collecting pipe 2a is connected to the upstream end 3a of the first exhaust pipe 3 through a spherical joint 6, which will be explained later, whereas the downstream end of the first exhaust pipe 3 is connected to a casing 20 of the exhaust gas purifier 4. Therefore, the exhaust manifold 2, located upstream of the spherical Joint 6, forms an upstream exhaust pipe whereas the first exhaust pipe 3, located downstream of the spherical joint 6, forms a downstream exhaust pipe.

Referring to Fig. 3, the spherical joint 6 includes an upstream flange 7 welded to an outer circumferential surface of the collecting pipe 2a, and a downstream flange 8 welded to an outer circumferential surface of the upstream end 3a of the first exhaust pipe 3 having a double-pipe structure made of an inner pipe 31 and an outer pipe 32, both being cylindrical pipes. The downstream flange 8 has formed a spherical seat 8a defining a spherical seat surface bulging toward the downstream direction,

whereas the upstream flange 7 has formed a planar seat 7a defining a flat plane.

The spherical joint 6 includes a spherical gasket 9 located between the upstream and downstream flanges 7, 8 for engagement with the outer circumference of the downstream end 2al. The spherical gasket has a planar portion 9a disposed at an upstream position and defining a flat plane for contact with the planar seat 7a, and a spherical portion 9b disposed at a downstream position and defining a spherical plane for contact with the spherical seat 8a.

The upstream flange 7 has formed two bolt holes 12 which allows bolts 11 inserted through two through holes 10 formed in the downstream flange 8 to pass through, such that the bolt 11 is fastened and fixed to the upstream flange 7 with a nut 14 while compressing a coil-shaped spring 13 around the bolt 11 between the head of the bolt 11 and the downstream flange 8.

Diameters of. respective through holes 10 are larger than the outer diameter of the bolt 11 to provide a gap allowing relative sliding movements between the spherical seat 8a and the spherical portion 9b. When vibrations of the engine are transmitted to the manifold 2, these vibrations are absorbed by sliding movements along the sphericalinte ace, which occur between the spherical seat 8a and the spherical portion 9b at the spherical joint 6, and therefore,

transmission of the vibrations to the first exhaust pipe 3 is prevented or suppressed.

As shown in Fig. 2, when the exhaust system 1 is fixed to a vehicle, the exhaust gas purifier 4 connected to the first exhaust pipe 3 is located in a lower level than the upstream end 3a of the first exhaust pipe 3. The exhaust gas purifier 4 has a casing 20 containing a ternary catalyst 15 for purifying Nox (nitrogen oxide), HC (hydrocarbon) and CO (carbon monoxide) in the exhaust gas, and the downstream end 3b of the first exhaust pipe 3 extending downward from the upstream end 3a is welded to the casing 20 at the welded joint W1 formed thereby (see Figs. 4 through 7).

More specifically, referring to Figs. 4 and 5, the casing 20 made of a metal thin plate has an upstream portion 20a located upstream of the upstream end surface 15a of the substantially columnar catalyst 15, a downstream portion 20b having substantially frustum-shaped contour and located downstream, and a substantially cylindrical central portion 20c located between the upstream portion 20a and the downstream portion 20b in terms of the exhaust gas flowing direction, and this casing 20 is made up of substantially semi-cylindrical first and second casing halves 21, 22 which are two divisional parts along a divisional plane P passing the substantially horizontal

axial line L1 of the cylinder of the central potion 20c (see Fig. 7). In this embodiment, as shown in Figs. 1 and 2, since a most part of the casing 20 above the horizontal plane, including the top portion of the casing 20, is defined by the first casing half 21, the fist casing half 21 and the second casing half 22 form the upper casing half and the lower casing half, respectively. As shown in Fig. 6, the first and second casing halves 21, 22 have flanges 21a, 22a along their circumferential edges except for their downstream portions 20b forming a recess, which will be explained later, and these casing halves 21, 22 are Joined together by welding their flanges 21a, 22a along the entire circumference. Since the flange 21a of the first casing half 21 projects outwardly than the flange 22a of the second casing half 22, the second casing half 22 is welded along its outer circumferential edge i to the bottom surface of the flange 21a of the first casing half 21. The welded joint is shown in Fig. 6 by the reference numeral W2. Projections B1, B2 of the flange 21a belonging to the upstream portion 20a of the first casing half 21 and projections B3, B4 of the flange 21a belonging to the downstream portion 20b have formed four bolt holes C1 through C4 in total, every two of which are substantially symmetrically located relative to the plane including the axial line L1 and

orthogonally crossing the divisional plane P. These bolt holes C1 through C4 receive four bolts D1 through D4 (see Fig. 4) fixing a heat-shield cover 30, explained later, to the casing 20 to cover the outside of the casing 20 via a gap.

Referring to Figs. 4 through 6, the upstream portion of the first casing half 21 belonging to the upstream portion 20a includes a substantially planar slope 21b slanting upward from a portion near the upstream end of the flange 21a toward the downstream direction whereas the upstream portion of the second casing half 22 belonging to the upstream portion 20a includes a slope 22b slanting downward from a portion near the upstream end of the flange 22a toward the downstream direction and two side slopes 22c which are slopes slanting downward to approach one another from the flange 22a in the direction normal to the axial line L1 (hereinbelow called normal direction.) on the divisional plane P. Downstream end portions of the first and second casing halves 21, 22 have formed semi-circular recesses for forming engage holes for receiving the second exhaust pipe 5 connected to the downstream end portion of the downstream portion 20b of the casing 20.

Circumferential edges of the engage holes and the outer circumferential surface of the second exhaust pipe 5 are joined together by welding over their entire

circumference at welded joint W3. As shown in Figs. 8 through 10, a connection flange 16 provided at the downstream end of the second exhaust pipe 5 has formed an exhaust path downstream of the second exhaust pipe 5, and a connection flange 42 provided at the upstream end of the third exhaust pipe 40 connected to the supplemental muffler 41 is joined to the connection flange 16 with three bolts 45 and nuts 46 as fasteners to continuously connect the second exhaust pipe 5 and the third exhaust pipe 40.

Referring to Fig. 7, On the slope 21b of the first casing half 21, a cylindrical boss portion is formed to define an opening as an exhaust inlet through which an exhaust gas flows into the casing 20. The outer pipe 32 Of the first exhaust pipe 3 engages with the outer circumference of the boss portion 24, and they are welded over the entire circumferential length to form the welded joint W1. In this case, the welded: Joint W1 is chosen not to overlap the welded joint W2 of the casing 20.

Inside the casing 20, an upstream end surface 15a of the catalyst 15 having a number of fine air paths inside to permit exhaust gas to flow therethrough is located slightly downstream of the downstream end of the opening 23 in terms of the axial direction of the axis L1 of the casing 20, and the axial line L2 of the downstream end 3b of the first exhaust pipe 5

approximately directs the center of the upstream end surface 15a.

As shown in Fig. 5, in the upstream portion of the second casing half 22, one of the side slopes, 22c, has formed a mount seat 27 having an insertion hole 26 for receiving therein an oxygen concentration sensor 25 for detecting oxygen concentration in the exhaust gas, which is one of properties of the exhaust gas. The oxygen concentration sensor 25 is affixed to the mount seat 27 such that its detective portion occupies an adequate position in the exhaust gas immediately after entering the opening 23, from the viewpoint of detection accuracy and response.

With reference to Figs. 4 and 5, in the exhaust gas purifier 4, the heatshield cover 30 covering the outside of the casing 20 via a gap is made up of a first cover half 31 and a second cover half 32 associated with the fist casing half 21 and the second casing half 22, respectively. The first cover half 31 covers the first casing half 21, following its outer contour, and an upstream portion of the first cover half 31 covering the upstream portion 20a of the casing 20 has an surrounding portion 31a partly covering the upstream portion around the first exhaust pipe 3 welded to the casing 20. The surrounding portion 31a has extended side portions 3lb extending gradually longer in the upstream direction from the central portion of

the first cover half 31 in terms of the said normal direction toward the flange 21a of the first casing half 21. The first cover half 31 has formed a plurality of vent holes at positions of the catalyst 15 highest in temperature in the exhaust gas purifier 4 such that hot air in the gap between the casing 20 and the heat-shield cover 30 is replaced with relatively cool temperature around the exhaust gas purifier 4.

Thereby, the casing 20 is prevented from overheating.

The second cover half 32 covers the central portion and the downstream portion of the second casing half 22, following their outer contours, and its downstream end reaches near the connection flange 16 of the second exhaust pipe 5.

The first and second cover halves 31, 32 have four fixing portions F1 through F4 and G1 through G4, respectively, which have formed four bolt holes (not shown) corresponding to four bolt holes C1 through C4 of the flange 21a of the first casing half 21. Among them, two upstream fixing portions F1 and F2 of the first cover half 31 are formed in those two extended side portions 31b, whereas the downstream two fixing portions F3 and F4 are formed at the downstream end.

The upstream fixing portions G1 and G2 of the second cover half 32 are formed at positions corresponding to the fixing portions F1 and F2 in a part extending from the front end of the portion covering the central part

of the second cover half 32 toward the upstream direction along the flange 21a whereas the two downstream fixing portions G3 and G4 are formed at positions corresponding to the fixing portions F3 and F4. Then, under the condition where the projections B1 through B4 are sandwiched between the fixing portions F1 through F4 of the first cover half 31 and the fixing portions G1 through G4 of the second cover half 32, the bolts D1 through D4 are inserted and fastened by the nuts HI through H4 to join the casing 20 and the heat-

shield cover 30 together.

Among the bolts hole C1 through C4 that are fixture portions of the casing 20 for fixing the heat-

shield cover 30 with the bolts D1 through D4 and the nuts Hi through H4 as the fixture means, positions of the upstream bolt holes C1 and C2 lie upstream of the upstream end surface 15a of the catalyst 15 as shown in Fig. 7, and they are within the range S occupied by the welded joint.W1 in terms of the axial direction of the axis L1. Therefore, positions of the bolt holes C1 and C2 are located near the welded Joint W1 of the first exhaust pipe 3 and the casing 20.

Referring to Figs. 8 through 10, in a vehicle equipped with an engine, a fuel tank 43 is located with a relatively short distance from the exhaust gas purifier 4 at a position opposed to and behind the exhaust gas purifier 4 in the axial direction of the

axis L1 of the casing 20. Then the third exhaust pipe 40 is bent to bypass the fuel tank 43 and connected to the supplemental muffler 41 located beside the fuel tank 43. Reference numeral 44 denotes two brackets for fixing the third exhaust pipe 40 to the vehicle body.

The second exhaust pipe 5 is bent slightly downward from the upstream end connected to the exhaust gas purifier 4 toward a direction offset from the axial line L1 of the casing 20 toward the side of the position of the supplemental muffler 41 (see Figs. 9 and lo). As a result, the connection surface 16a of the connection flange 16 (see Fig. 4 as well) is oriented not to face on the fuel tank 43, with the line normal to the connection surface 16a directing the offset direction. Thus, in this embodiment, as shown in Figs. 9 and 10, the second exhaust pipe 5 is bent so that the connection surface 16a faces on an orthogonally lower position nearer to the supplemental muffler 41 of the fuel tank 43.

Therefore, when the third exhaust pipe 40 having the connection flange 42 to be coupled to the connection flange 16 with three bolts 45 inserted through the connection flange 16 and the nuts 46 for fastening the bolts 45 is connected to the second exhaust pipe 5, a tool for fastening the nuts 46 onto the bolts 45, such as an impact wrench, can be introducedfrom under the fuel tank 43 to the

connection flange 42 without interfering with the fuel tank 43.

Next explained are operations and effects of the embodiment having the above-explained configuration.

When the engine is driven, exhaust gas passing through the exhaust path is purified by the exhaust gas purifier 4, and thereafter discharged to the atmospheric air. Vibrations produced by the motion of the engine are transmitted to the exhaust system 1 as well. Part of vibrations of the engine transmitted to the exhaust manifold 2 is absorbed by sliding relative movements along the spherical interface between the spherical seat 8a and the spherical portion 9b of the spherical junction 6, and prevented from transmission to the first exhaust pipe 3 that is the sole exhaust pipe introducing exhaust gas to the casing 20.

Therefore, no large load caused by such vibrations acts on the welded joint between the first exhaust pipe 3 and the casing 20, and cracks in the welding joint W2 can be prevented. In addition, even when vibrations that cannot be absorbed effectively even by the spherical joint 6, such as large vibrations exceeding the slidable range between the exhaust manifold 2 and the first exhaust pipe 3 of the spherical joint 6 or vibrations in the flowing direction axial direction of the collecting duct 2a) produced at the downstream end 2a of the exhaust manifold 2, are transmitted to the

first exhaust pipe 3 and a load caused by the vibrations acts on the welded joins I those vibrations themselves will be attenuated by the spherical joint 6 as compared with a configuration without the spherical Joint 6, and the welding junction W1 between the downstream end 3b of the first exhaust pipe 3 and the first casing half 21 does not overlap the welded joint W2 joining the first and second casing halves 21, 22 of the casing 20. Therefore, the welded Joint Wl has a high strength, and greatly reduced in liability of generating cracks.

As a result, the following effects are ensured.

That is, since vibrations of the engine transmitted to the exhaust manifold 2 are absorbed by the spherical . joint 6, even when vibrations the spherical joint 6 cannot absorb are transmitted to the first exhaust pipe 3 as the sole exhaust pipe *or introducing exhaust gas into the casing 20, not only because the transmitted vibrations themselves are attenuated by the spherical joint 6 to a certain extent but also because the welded joint W1 between the first exhaust pipe 3 and the casing 20 has a high strength, cracks produced at the welded joint W1 by the vibrations transmitted to the first exhaust pipe 3 are largely reduced, and the exhaust system having the casing 20 with the first exhaust pipe 3 welded thereto is improved in durability.

Since the first exhaust pipe 3 extends downward from its upstream end 3a and is connected to the first casing half 21 forming the top part of the casing 20 located in a lower level than the upstream end 3a, the first exhaust pipe 3 can be shortened and arranged with less curves. The short and less-curved configuration o* the first exhaust pipe 3 results in reducing the flow path resistance and contributes to smooth discharge of the exhaust gas in the exhaust system and improvements of the efficiency of exhaustion, with the effect of simplifying the layout of the first exhaust pipe 3 being added.

The oxygen concentration sensor 25 detects oxygen concentration in the exhaust gas introduced into the ansing 20 from the opening 23 located. upstream of the catalyst 15 at a position upstream of the catalyst 15. However, since the mount seat 27 for mounting the oxygen concentration sensor 25 is formed in an upstream portion of the second casing half 22 than the catalyst 15, which second casing half 22 is the casing half different from the first casing half 21 to which the first exhaust pipe 3 is welded, positional limitation of the mount seat 27 is alleviated in the portion of the casing 20 upstream of the catalyst 15.

As a result, the mount seat 27 can be provided on the casing half to which the downstream exhaust pipe is not connected, restriction regarding the position of

the mount seat 27 is reduced to provide a larger freedom for the position of the oxygen concentration sensor 25. This is effective for appropriately placing the oxygen concentration sensor 25 for optimizing its detection accuracy and response.

Since the heat-shield cover 30 is provided to cover the outside of the casing 20, thermal damage to elements around the casing 20 can be prevented.

Further, since the welded joint is located upstream of the upstream end surface 15a of the catalyst 15 in the casing 20 and the heat-shield cover 30 is fixed to the casing 20 with the bolts D1, D2 and the nuts Hi, H2 through bolt holes C1, C2 that are two fixture points upstream of the catalyst 15, the casing 20 is increased in rigidity near the welded joint W1 between the first exhaust pipe 3 and the first casing half 21, with a rigidity if the heat-shielding cover 30 being added.

Moreover, since the bolt holes C1, C2 are located within the range S occupied by the welded joint W1 in the direction of the axial line L1 and are close to the welded joint W1 and the mount seat 27, vibrations transmitted from the first exhaust pipe 3 can be alleviated effectively, and the oxygen concentration sensor 26 mounted on the mount seat 27 can be also effectively prevented from vibrations.

- As a result, the following effects are provided.

That is, thermal damage to elements around the casing

20 can be prevented by the heat-shield cover 30, and in the part of the casing 20 upstream of the catalyst 15, since vibrations transmitted from the first exhaust pipe 3 can be suppressed by the heat-shield cover 30 fixed with bolts D1, D2 and the nuts Hi, H2 located upstream of the catalyst 15, the entirety of the casing 20 is prevented from vibrations, and the catalyst 15 contained in the casing 20 is improved in durability.

At the downstream end of the second exhaust pipe 5 connected to the casing 20, the connection flange 16 is provided for connecting the third exhaust pipe 40 to the second exhaust pipe 5 with the bolts 45, and the second exhaust pipe 5 is bent to direct the straight line normal to the connecting plane surface 16a of the connection flange 16 to the direction offset from the axial line L1 of the casing 20 such that the connection surface 16a of the connection flange of the second exhaust pipe 5 bent to be offset from the axial line L1 of the casing 20 of the exhaust gas purifier 4.

Therefore, the connection surface 16a can be oriented not to entirely face on the fuel tank 43 located to face on the exhaust gas purifier 4 in the axial direction L1.

As a result, the following effects are provided.

That is, since the second exhaust pipe 5 is bent to direct the connection surface 16a of the connection flange 16 toward a direction offset from the axial line

i L1 of the casing 20 such that the connection surface 16a is oriented not to face on the fuel tank 43 disposed to face on the exhaust gas purifier 4 in the axial direction L1, when the second exhaust pipe 5 and the third exhaust pipe 40 are connected, an impact wrench for fastening the nuts 46 onto the bolts 45 can be brought closely to the connection flange 42 without interfering with the fuel tank 43 even when the fuel tank 43 is disposed in confrontation with the exhaust gas purifier 4 via a relative short distance in the axial direction L1. Therefore, coupling of the connection flange 16 and the connection flange 42 of the third exhaust pipe 40 by the bolts 46 and the nuts 46 is made easier, and the second exhaust pipe 5 and the third exhaust pipe 40 can be connected under an improved efficiency.

Explained below are modified structures of embodiments partly modified from the above-explained embodiment.. Although the foregoing embodiment has been explained as orienting the axial line L1 of the exhaust gas purifier 4 substantially in the horizontal direction, the invention is applicable with an exhaust gas purifier 4 having the axial line extending vertically. Although the first exhaust pipe 3 has been explained as being welded directly to the first casing., the embodiment is modified to connect the first exhaust

pipe 3 to a flange welded to the first casing half 21.

It is also possible to use three or more upstream fixture points, instead of two, for fixing the heat-

shield cover 30 to the casing 20. Although the exhaust gas purifier 4 has been explained as containing a ternary catalyst 15, the catalyst is not limited to ternary one but may be a catalyst for purifying Non alone, for example, or an exhaust gas purifier 4 containing no catalyst is also useable.

Although the engine in the foregoing embodiment has been explained as being mounted in a vehicle, the exhaust system according to the invention is applicable to any mobiles or equipment equipped with an engine.

Moreover, although the forgoing embodiment has been explained as bending the second exhaust pipe such that the entire area of the connection surface of the connection flange does not face on the fuel tank, it is sufficient that at least a part of the connection surface does not face on the fuel tank to prevent interference of a tool for fixing the tightening members with the fuel tank.

Claims

1. An exhaust system of an engine having an upstream exhaust pipe permitting exhaust gas to flow from the engine, an exhaust gas purifier having a casing made up of two casing halves welded to each other, and a downstream exhaust pipe having a downstream end welded to the casing, characterized in that: said upstream end is connected to said upstream exhaust pipe via a spherical joint, said downstream end is welded to one of said casing halves such that the welded Joint thereof does not overlap the welded joint of said casing halves, and said exhaust gas flows into said casing only through said downstream exhaust pipe.

2. An exhaust system of an engine according to claim 1 wherein said casing is located in a lower level than said upstream end, and said one of the casing halves constitutes the top part of said casing.

3. An exhaust system of an engine according to claim 2 wherein said exhaust gas purifier includes a catalyst contained in said casing, an exhaust inlet to said casing from said downstream exhaust pipe is located upstream of said catalyst, and an upstream part of the other of said casing halves located upstream of

said catalyst has formed a mount seat for mounting an oxygen concentration sensor for detecting oxygen concentration in the exhaust gas.

4. An exhaust system of an engine according to claim 3 wherein the welded joint connecting said downstream end and said one of the casing- halves is located upstream of said catalyst, and a heat-shield cover covering the outside of said casing is fixed to said casing at a plurality of fixture points upstream of said catalyst.

5. An exhaust system of an engine according to claim 1 wherein a second exhaust pipe is connected to the downstream end of said casing, a connection flange provided at the downstream end of said second exhaust pipe to connect a third exhaust pipe to said second exhaust pipe with fastening members, and said second exhaust pipe is bent to direct a straight line normal to a connection surface of said connection flange. toward a direction offset from an axial line of said casing.

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