EXHAUST SYSTEM FOR INTERNAL COMBUSTION ENGINE

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

The present disclosure claims the benefit of Japanese Patent Application No. 2024-175059 filed on Oct. 4, 2024 with the Japanese Patent Office, the disclosures of which are incorporated herein by reference in its entirety.

BACKGROUND

Field of the Disclosure

The embodiment of the present disclosure relates to an exhaust system for purifying exhaust gas emitted from an internal combustion engine.

Discussion of the Related Art

An exhaust system of this kind comprises a catalytic converter and a filter. The catalytic converter detoxifies harmful substances resulting from combustion of fuel by oxidizing the harmful substances, and the filter captures particulate matter contained in the exhaust gas. The flow of the exhaust gas is hindered by a deposition of the particulate matter on the filter, and consequently the performance of the internal combustion engine is reduced and an amount of harmful substances in the exhaust gas is increased. In order to avoid such disadvantages, clogging of the filter is detected, and the particulate matter is removed when the deposition of the particulate matter on the filter increases to some extent.

JP-A-2007-023996 describes a device for detecting the clogging of filters of an exhaust purification device for capturing the particulate matter. The exhaust gas purifying device according to JP-A-2007-023996 comprises a differential pressure detecting device that detects a difference between an upstream pressure and a downstream pressure of the filter, a pipe that introduces the exhaust gas flowing upstream of the filter to the differential pressure detecting device, and a pipe that introduces the exhaust gas flowing downstream of the filter to the differential pressure detecting device.

Exhaust gas emitted from an internal combustion engine of a vehicle is delivered to a catalytic converter through an exhaust manifold, and a filter is connected to a downstream side of the catalytic converter. Since the catalytic converter and the filter are heated during propulsion, the catalytic converter and the filter are arranged e.g., under the floor of the vehicle to be exposed to the external air. Whereas, since the differential pressure detector includes an electronic component, the differential pressure detector is disposed in an engine compartment where the differential pressure detector is protected from the external air or dust. Thus, the differential pressure detector and the filter are disposed away from each other and hence a long pipe is necessary to connect those elements. Specifically, a long pipe is required to introduce the exhaust gas flowing downstream of the filter to the differential pressure detector. A long pipe of this kind is divided into two pipes, and one of the divided pipes is connected to the differential pressure detector and the other one of the divided pipes is connected to the downstream side of the filter. As a result, a length of each of the pipes is individually shortened, and hence the pipes may be handled easily to assemble the exhaust purification device.

However, those divided pipes have to be connected to each other to assemble the exhaust purification device, but it is difficult for workers to connect such flexible pipes underneath the floor of the vehicle.

SUMMARY

The embodiment of the present disclosure has been conceived noting the foregoing technical problems, and it is therefore an object of the present disclosure to make an assembling work of an exhaust system easy by simplifying a connecting work of a pipe for introducing an exhaust gas flowing downstream of a filter to a differential pressure detector.

According to the exemplary embodiment the present disclosure, there is provided an exhaust system for an internal combustion engine, comprising: a catalytic converter that performs an oxidation reaction or a reduction reaction to remove pollutants from an exhaust gas resulting from a combustion of the engine and flowing therethrough; a filter unit that is joined to a downstream side of the catalytic converter to capture particulate matter contained in the exhaust gas; and a differential pressure detector that detects a difference between a pressure of the exhaust gas flowing upstream of the filter unit and a pressure of the exhaust gas flowing downstream of the filter unit. In order to solve the above-explained problems, according to the exemplary embodiment of the present disclosure, the catalytic converter comprises a first flange as a connection member, the filter unit comprises a second flange that is joined to the first flange of the catalytic converter, and the catalytic converter further comprises a bracket in which a through hole is formed. In addition. the exhaust system further comprises a first downstream pipe in which one end thereof is connected to a downstream section of the filter unit, and a second downstream pipe in which one end thereof is connected to the differential pressure detector. The other end of the first downstream pipe and the other end of the second downstream pipe are held by the bracket and communicated with each other through the through hole of the bracket. In the exhaust system, a portion of the catalytic converter upstream of the first flange is connected to the differential pressure detector through an upstream pipe.

In a non-limiting embodiment, the through hole may comprise a first opening that opens toward the filter unit and a second opening that opens toward the catalytic converter. In addition, the other end of the first downstream pipe may be pushed onto the first opening to be communicated with the first opening, and the other end of the second downstream pipe may be fixed to the bracket while being communicated with the second opening.

In a non-limiting embodiment, the exhaust system may further comprise a plate member that pushes the other end of the first downstream pipe onto the first opening, and the plate member may be attached to the second flange in a detachable manner.

In a non-limiting embodiment, the plate member may be formed of flexible material, and the exhaust system may further comprise a protrusion formed on the first downstream pipe that is in contact with the plate member to be pushed by the plate member.

In a non-limiting embodiment, the first downstream pipe may penetrate through the plate member. In addition, the exhaust system may further comprise: a protrusion that is formed on the first downstream pipe to be opposed to the plate member; and an elastic member that is interposed between the protrusion and the plate member to push the first downstream pipe in a direction that the other end of the first downstream pipe is pushed onto the first opening.

In a non-limiting embodiment, the exhaust system may further comprise a cylindrical member that is attached to an outer circumference of the other end of the first downstream pipe. In addition, the plate member may be adapted to push the cylindrical member toward the bracket, and a sealing member is interposed between the cylindrical member and the bracket.

In a non-limiting embodiment, a circumferential edge of the first opening may be shaped into a concave spherical receiving surface, and the other end of the first downstream pipe may be shaped into a spherical convex curve.

In a non-limiting embodiment, a sealing member may be interposed between the concave spherical receiving surface and the spherical convex curve.

Thus, in the exhaust system according to the exemplary embodiment of the present disclosure, the downstream pipe for introducing the exhaust gas flowing downstream of the filter unit is divided into the first downstream pipe in which one end thereof is connected to the portion downstream of the filter unit and the second downstream pipe in which one end thereof is connected to the differential pressure detector. The other end of the first downstream pipe and the other end of the second downstream pipe are held by the bracket formed integrally with the first flange of the catalytic converter, and communicated with each other through the through hole of the bracket. Since the downstream pipe is divided into two pipes, a length of each of the downstream pipes is individually shortened, and hence the pipes may be handled easily to combine the filter unit with the catalytic converter even if a total length of the downstream pipe is long. In addition, the other end of the second downstream pipe is fixed to the bracket. Therefore, when combining the filter unit with the catalytic converter by fastening the flanges thereof to assemble the exhaust system, the downstream pipes may be connected to each other by pushing the other end of the first downstream pipe extending along the filter unit onto the through hole of the bracket. Further, since the bracket formed integrally with the first flange has a function of connecting the downstream pipes together, the downstream pipes may be connected together easily as compared with a case of directly connecting the downstream pipes together. Furthermore, since the bracket supports the intermediate portion of the long downstream pipe connecting the portion downstream of the filter unit to the differential pressure detector, the number of members supporting the downstream pipe may be reduced.

In addition, according to the exemplary embodiment of the present disclosure, the first downstream pipe may be elastically pushed onto the first opening of the bracket. Therefore, even if the first downstream pipe is subjected to an external force derived from vibration or the like, the connection between the first downstream pipe and the second downstream pipe may be maintained. For this reason, a leakage of the exhaust gas and a change in the pressure of the exhaust gas may be prevented.

Further, according to the exemplary embodiment of the present disclosure, the sealing material is interposed between the bracket and the first downstream pipe. Therefore, airtightness of the exhaust system may be enhanced so that a difference between a pressure of the exhaust gas flowing upstream of the filter unit and a pressure of the exhaust gas flowing downstream of the filter unit may be detected accurately.

Furthermore, according to the exemplary embodiment of the present disclosure, the first downstream pipe may be connected to the second downstream pipe by pushing the spherical convex curve formed on the other end of the first downstream pipe onto the concave spherical receiving surface formed on the bracket. Therefore, even if the first downstream pipe is displaced in the vertical direction or the horizontal direction, an airtight connection between the spherical convex curve and the concave spherical receiving surface may be maintained.

BRIEF DESCRIPTION OF THE DRAWINGS

Features, aspects, and advantages of exemplary embodiments of the present disclosure will become better understood with reference to the following description and accompanying drawings, which should not limit the disclosure in any way.

FIG. 1 is an overall view schematically showing a structure of the exhaust system according to the exemplary embodiment of the present disclosure;

FIG. 2 is a cross-sectional view showing one example of a joint mechanism for connecting the first downstream pipe to the second downstream pipe in a bracket;

FIG. 3 is a cross-sectional view showing another example of the joint mechanism for connecting the first downstream pipe to the second downstream pipe in the bracket; and

FIG. 4 is a cross-sectional view illustrating still another example of the joint mechanism for connecting the first downstream pipe to the second downstream pipe in the bracket.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

The exemplary embodiment of the present disclosure will now be explained with reference to the accompanying drawings. Note that the embodiment shown below is merely an example of the present disclosure, and do not limit the present disclosure.

Referring now to FIG. 1, there is shown a structure of the exhaust system according to the exemplary embodiment of the present disclosure. For example, a gasoline engine may be adopted as an internal combustion engine (hereinafter, simply referred to as an engine) 1. The engine 1 includes an exhaust manifold 2 for collecting and discharging exhaust gas 3 generated by burning fuel. The exhaust manifold 2 is connected to a catalytic converter 4, and an oxidation catalyst or a reduction catalyst (neither of which is shown) is held in a casing 5 of the catalytic converter 4. As illustrated in FIG. 1, the casing 5 comprises an inlet conducting pipe 5a and an outlet conducting pipe 5b. The inlet conducting pipe 5a is joined to the exhaust manifold 2, and a flange 5c as a connection member is formed around an outlet of the outlet conducting pipe 5b. That is, the flange 5c servs as a first flange of the exemplary embodiment of the present disclosure. In the flange 5c, a bracket 6 is formed on the periphery of the flange 5c. For example, the bracket 6 may be formed into a protrusion by partially expanding the flange 5c to protrude radially outwardly from the outlet conducting pipe 5b. Instead, another plate member may be attached to the flange 5c to serve as bracket 6. In addition, the bracket 6 may be arranged in the catalytic converter 4 instead of the flange 5c.

A filter unit 7 is connected to the downstream side of the catalytic converter 4, and e.g., a gasoline particulate filter (not shown) is arranged in a casing 8 of the filter unit 7. Likewise, the casing 8 also comprises an inlet conducting pipe 8a and an outlet conducting pipe 8b. For example, the outlet conducting pipe 8b may be formed integrally with a part of the exhaust pipe. A flange 8c as a connection member is formed around an inlet of the inlet conducting pipe 8a. That is, the flange 8c serves as a second flange of the exemplary embodiment of the present disclosure. A shape of the flange 8c is similar to a shape of the part of the flange 5c of the catalytic converter 4 excluding the bracket 6. The flange 5c and the flange 8c are coaxially opposed to each other, and fastened together by e.g. a bolt (not shown). That is, the catalytic converter 4 and the filter unit 7 are connected to each other through the flange 5c and the flange 8c. Optionally, a gasket (not shown) may be interposed between the flange 5c and the flange 8c to ensure airtightness.

In order to detect a clogging condition of the filter unit 7, the exhaust system is provided with a differential pressure sensor 9 serving as a differential pressure detector of the exemplary embodiment of the present disclosure. Specifically, the differential pressure sensor 9 detects a difference between a pressure of the exhaust gas flowing upstream of the filter unit 7 and a pressure of the exhaust gas flowing downstream of the filter unit 7, and transmits a detection signal in accordance with a detection value. For example, a differential pressure sensor described in JP-A-2007-023996 may be adopted as the differential pressure sensor 9. The differential pressure sensor 9 is disposed in the vicinity of the engine 1. Specifically, the differential pressure sensor 9 is arranged in an engine compartment (not shown) together with the engine 1. Whereas, the catalytic converter 4, the flange 5c, the filter unit 7, the flange 8c etc. are arranged underneath a floor panel (not shown) of the vehicle.

The exhaust system further comprises an upstream pipe 10 for introducing the exhaust gas flowing upstream of the filter unit 7 to the differential pressure sensor 9, and a downstream pipe 11 for introducing the exhaust gas flowing downstream of the filter unit 7 to the differential pressure sensor 9. In order to transmit a pressure of the exhaust gas to the differential pressure sensor 9, for example, a metal pipe or a heat-resistant synthetic resin pipe may be adopted as the upstream pipe 10 and the downstream pipe 11 respectively. One end of the upstream pipe 10 is joined to the outlet conducting pipe 5b of the catalytic converter 4, the other end of the upstream pipe 10 is joined to the differential pressure sensor 9, and an intermediate portion of the upstream pipe 10 is held by a stay 12 which is attached to the casing 5 of the catalytic converter 4.

The downstream pipe 11 comprises a first downstream pipe 11a connected to a downstream side of the filter unit 7 and a second downstream pipe 11b connected to the differential pressure sensor 9. Specifically, one end (hereinafter, referred to as the first end) of the first downstream pipe 11a is joined to the outlet conducting pipe 8b of the filter unit 7, and the other end (hereinafter, referred to as the second end) of the first downstream pipe 11a is communicated with the second downstream pipe 11b in the bracket 6. In order to easily adjust a position of the other end of the first downstream pipe 11a, a flexible joint hose 13 is arranged in an intermediate portion of the first downstream pipe 11a.

One end (hereinafter, referred to as the first end) of the second downstream pipe 11b is joined to the differential pressure sensor 9, and the other end (hereinafter, referred to as the second end) of the second downstream pipe 11b is communicated with the second end of the first downstream pipe 11a in the bracket 6. An intermediate portion of the second downstream pipe 11b is also held by the stay 12 attached to the casing 5 of the catalytic converter 4 together with the upstream pipe 10.

Thus, the first downstream pipe 11a and the second downstream pipe 11b are connected to each other in the bracket 6. For example, the first downstream pipe 11a and the second downstream pipe 11b may be connected directly to each other while being held by the bracket 6. Otherwise, the first downstream pipe 11a and the second downstream pipe 11b may also be connected to each other through a through hole formed in the bracket 6, and held by the bracket 6. Turning to FIG. 2, there is shown one example of a joint mechanism for connecting the first downstream pipe 11a and the second downstream pipe 11b. As illustrated in FIG. 2, the joint mechanism shown therein is adapted to connect the first downstream pipe 11a and the second downstream pipe 11b through the through hole.

In the joint mechanism shown in FIG. 2, the second end of the second downstream pipe 11b extending along the catalytic converter 4 is fixed to the flange 5c or bracket 6, and the second end of the first downstream pipe 11a extending along the filter unit 7 is brought into contact with the bracket 6. As illustrated in FIG. 2, a through hole 14 penetrates through the bracket 6 in a thickness direction. The through hole 14 comprises a first opening 14a opening toward the filter unit 7 and a second opening 14b opening toward the catalytic converter 4. The second end of the second downstream pipe 11b is fixed to one of lateral faces of the bracket 6 by welding or the like to be communicated with the second opening 14b. That is, the second downstream pipe 11b is unitized with the catalytic converter 4 joined to the exhaust manifold 2.

A circumferential edge of the first opening 14a is shaped into a concave sphere recessed in the axial direction of the through hole 14 to serve as a receiving surface (or sealing surface), and the second end of the first downstream pipe 11a is shaped into a spherical convex curve which is congruent with the concave sphere of the first opening 14a to be mated with the first opening 14a. The spherical convex curve formed on the second end of the first downstream pipe 11a is pushed tightly onto the concave spherical receiving surface of the first opening 14a directly or indirectly through a sealing member S interposed therebetween. In this way, the spherical convex curve formed on the second end of the first downstream pipe 11a is allowed to pivot freely on the concave spherical receiving surface of the first opening 14a. That is, the first downstream pipe 11a is allowed to pivot with respect to the bracket 6 within a predetermined angular range while maintaining the airtight condition.

According to the example shown in FIG. 2, the second end of the first downstream pipe 11a is pushed onto the receiving surface of the first opening 14a by a spring 15 as an elastic member. On the first downstream pipe 11a, a flange 16 serving as a protrusion of the exemplary embodiment of the present disclosure is arranged in the vicinity of the second end, and a holding plate 17 serving as a plate member of the exemplary embodiment of the present disclosure is arranged at a site closer to the filter unit 7 than the spring 15 (i.e., on the right side of the spring 15 in FIG. 2). As illustrated in FIG. 2, a through hole or a slit is formed in the holding plate 17. Specifically, an inner diameter or an inner width of the through hole is larger than an outer diameter of the first downstream pipe 11a so that the first downstream pipe 11a is allowed to penetrate through the through hole and to pivot within the through hole.

The holding plate 17 is fixed to the flange 5c or the flange 8c to be fastened together to connect the filter unit 7 to the catalytic converter 4. According to the example shown in FIG. 2, the holding plate 17 is fixed to the flange 8c formed around the inlet of the inlet conducting pipe 8a of the filter unit 7 by a bolt 18, and the spring 15 is interposed between the holding plate 17 and the flange 16 mounted on the first downstream pipe 11a while being compressed. Therefore, the first downstream pipe 11a is pushed by the spring 15 toward the bracket 6 so that the spherical convex curve formed on the second end of the first downstream pipe 11a is brought into airtight contact with the concave spherical receiving surface formed on the first opening 14a. As described, the first opening 14a is communicated with the through hole 14 formed in the bracket 6, and the second end of the second downstream pipe 11b is also communicated with the through hole 14. That is, the first downstream pipe 11a and the second downstream pipe 11b are communicated with each other through the through hole 14. Consequently, the first downstream pipe 11a and the second downstream pipe 11b are connected to each other in the bracket 6 to form a pipe line, and an intermediate portion of the pipe line is held by the bracket. Therefore, the first downstream pipe 11a and the second downstream pipe 11b are prevented from drooping, being shaken by vibrations, and colliding with other members. In addition, the first downstream pipe 11a may be warped with respect to the bracket 6 by vibrations of the catalytic converter 4 and the filter unit 7. Nonetheless, according to the example shown in FIG. 2, the circumferential edge of the first opening 14a of the bracket 6 is shaped into the concave spherical receiving surface, and the second end of the first downstream pipe 11a is shaped into the spherical convex curve. Therefore, the first downstream pipe 11a is allowed to pivot within a predetermined angular range with respect to the bracket 6 while maintaining the airtight condition, and hence the first downstream pipe 11a and the bracket 6 will not be subjected to a large stress. For this reason, deformations of the first downstream pipe 11a and the bracket 6 may be prevented, and damages of the first downstream pipe 11a and the bracket 6 may be limited. That is, the durability of the first downstream pipe 11a and the bracket 6 may be improved.

In the exhaust system having the above-described configuration, the exhaust gas 3 resulting from the combustion of the fuel in the engine 1 is delivered to the catalytic converter 4 through the exhaust manifold 2. In the catalytic converter 4, pollutants such as carbon monoxide (CO) and hydrocarbons (HC) contained in the exhaust gas 3 are removed by a chemical reaction such as an oxidation reaction or a reduction reaction. Thereafter, the exhaust gas 3 passes through the filter unit 7 so that the particulate matter is captured by the filter unit 7. After capturing the particulate matter from the exhaust gas 3, the exhaust gas 3 is discharged to the outside through an exhaust pipe (not shown) connected to the downstream side of the filter unit 7.

The exhaust gas 3 flowing upstream of the filter unit 7 is partially introduced to the differential pressure sensor 9 through the upstream pipe 10, and the exhaust gas 3 flowing downstream of the filter unit 7 is partially introduced to the differential pressure sensor 9 through the first downstream pipe 11a and the second downstream pipe 11b. The differential pressure sensor 9 detects a difference between a pressure of the exhaust gas 3 flowing upstream of the filter unit 7 and a pressure of the exhaust gas 3 flowing downstream of the filter unit 7, and transmits a detection value in the form of an electrical signal.

As a result of capturing the particulate matter by the filter unit 7, the filter unit 7 is clogged. In a situation where an amount of the particulate matter captured by the filter unit 7 is still small, a flow resistance of the exhaust gas 3 flowing through the filter unit 7 is small. In this situation, therefore, a detection value of the differential pressure detected by the differential pressure sensor 9 is still small. Whereas, in a situation where an amount of the particulate matter captured by the filter unit 7 increases, the flow resistance of the exhaust gas flowing through the filter unit 7 increases. In this situation, therefore, a detection value of the differential pressure detected by the differential pressure sensor 9 increases. When the differential pressure detected by the differential pressure sensor 9 increases to a predetermined value or greater, the particulate matter captured by the filter unit 7 is removed. For example, the particulate matter deposited on the filter unit 7 is combusted to be removed.

Next, an example of a procedure of combining the filter unit 7 with the catalytic converter 4 will be explained hereinafter. For example, the differential pressure sensor 9 is arranged in the engine compartment. Specifically, the differential pressure sensor 9 is connected to the engine 1 or a peripheral device (not shown) of the engine 1 through a bracket or the like, and the catalytic converter 4 is connected to the outlet side of the exhaust manifold 2 to be unitized with the engine 1.

As described, one end of the upstream pipe 10 is joined to the outlet conducting pipe 5b of the catalytic converter 4, and the other end of the upstream pipe 10 is joined to the differential pressure sensor 9 so that the differential pressure sensor 9 and the outlet conducting pipe 5b are connected to each other through the upstream pipe 10. In addition, the intermediate portion of the upstream pipe 10 is held by the stay 12. Consequently, the upstream pipe 10 is combined with the unit including the engine 1 and the catalytic converter 4.

Likewise, the first end of the second downstream pipe 11b is joined to the differential pressure sensor 9, and the second end of the second downstream pipe 11b is joined to the flange 5c formed around the outlet of the outlet conducting pipe 5b of the catalytic converter 4 or the bracket 6 formed integrally with the flange 5c. In addition, the intermediate portion of the second downstream pipe 11b is also held by the stay 12. Consequently, the second downstream pipe 11b is combined with the unit including the engine 1 and the catalytic converter 4.

On the other hand, the first downstream pipe 11a is attached to the filter unit 7 by joining the first end of the first downstream pipe 11a to the outlet conducting pipe 8b of the filter unit 7, and the holding plate 17, the spring 15, and the flange 16 are mounted on the first downstream pipe 11a in order in the vicinity of the second end. Thereafter, the filter unit 7 is placed downstream of the catalytic converter 4 in an extension of the outlet of the catalytic converter 4, and an orientation of the filter unit 7 is adjusted such that the second end of the first downstream pipe 11a is directed toward the bracket 6. In this situation, the flange 8c formed around the inlet of the inlet conducting pipe 8a of the filter unit 7 is brought into contact with the flange 5c of the catalytic converter 4, and fastened to the flange 5c by e.g., a bolt (not shown).

In this situation, since only the first end of the first downstream pipe 11a has been joined to the outlet conducting pipe 8b in the filter unit 7, the first downstream pipe 11a droops from the filter unit 7. At the same time as or after fastening the flange 8c to the flange 5c, the spherical convex curve formed on the second end of the first downstream pipe 11a is brought into contact with the concave spherical receiving surface formed on the first opening 14a of the bracket 6. In this situation, the bracket 6 has already been fixed to the catalytic converter 4. Therefore, the spherical convex curve formed on the second end the first downstream pipe 11a may be brought into contact easily with the concave spherical receiving surface of the first opening 14a of the bracket 6. If the flexible joint hose 13 is arranged in the intermediate portion of the first downstream pipe 11a, the second end of the first downstream pipe 11a may be moved easily in all directions. Therefore, the spherical convex curve formed on the second end of the first downstream pipe 11a may be fitted easily onto the concave spherical receiving surface of the first opening 14a of the bracket 6.

Thereafter, the holding plate 17 is fixed to the flange 8c of the filter unit 7 by e.g., a bolt. Consequently, the spring 15 is compressed between the holding plate 17 and the flange 16 mounted on the first downstream pipe 11a so that the first opening 14a is pushed toward the bracket 6 by the spring 15. As a result, the spherical convex curve formed on the second end of the first downstream pipe 11a is hermetically pushed onto the concave spherical receiving surface of the first opening 14a of the bracket 6. That is, the first downstream pipe 11a is connected to the second downstream pipe 11b.

As described above, in the exhaust system according to the exemplary embodiment of the present disclosure, the downstream pipe 11 for introducing the exhaust gas 3 flowing downstream of the filter unit 7 to the differential pressure sensor 9 is divided into two pipes 11a and 11b. Those downstream pipes 11a and 11b are joined together in the flange 5c and held by the flange 5c, and the flange 8c is fastened to the flange 5c thereby joining the filter unit 7 to the catalytic converter 4. According to the exemplary embodiment of the present disclosure, therefore, the filter unit 7 may be joined easily to the downstream side of the catalytic converter 4 so that the exhaust system may be assembled easily.

Here will be explained another example of the joint mechanism with reference to FIG. 3. According to the example shown in FIG. 3, a holding plate 17A formed of elastic material serves as the elastic member instead of the spring 15 so as to push the first downstream pipe 11a toward the bracket 6. For example, the holding plate 17A shown in FIG. 3 may be made of elastic material such as spring steel. In the holding plate 17A, the second end of the first downstream pipe 11a penetrates through a portion opposed to the bracket 6 which extends from a portion fixed to the flange 8c by the bolt 18, and the flange 16 as a protrusion mounted on the second end of the first downstream pipe 11a is brought into contact with one of lateral faces of the holding plate 17A. Thus, according to the example shown in FIG. 3, the flange 16 is elastically pushed toward the bracket 6 by the holding plate 17A serving as the elastic member.

According to the example shown in FIG. 3, since the spring 15 shown in FIG. 2 is omitted, the number of components of the exhaust system may be reduced, and hence the structure of the exhaust system may be simplified.

Next, still another example of the joint mechanism will be explained with reference to FIG. 4. According to the example shown in FIG. 4, an attachment 19 as a cylindrical member is attached to an outer circumference of the second end of the first downstream pipe 11a. Specifically, an outer diameter of the attachment 19 is larger than an outer diameter of the first downstream pipe 11a, and a bore or recess 19a whose diameter is slightly larger than the outer diameter of the first downstream pipe 11a is formed on a central portion of one of lateral faces of the attachment 19 opposed to the bracket 6. The second end of the first downstream pipe 11a is inserted into the attachment 19 from the side opposite to the bore 19a, and the second end of the first downstream pipe 11a opens toward the bore 19a.

An outer diameter of the other one of the lateral faces of the attachment 19 opposite to the bracket 6 is larger than the outer diameter of the first downstream pipe 11a, and hence the lateral face of the attachment 19 opposite to the bracket 6 serves as the protrusion of the exemplary embodiment of the present disclosure. In the example shown in FIG. 4, the holding plate 17A fixed to the flange 8c by the bolt 18 is warped by tightening the bolt 18 so that the attachment 19 and the first downstream pipe 11a integrated therewith are pushed toward the bracket 6 by the elastic force resulting from the warpage of the holding plate 17A. A center axis of the assembly of the attachment 19 and the first downstream pipe 11a substantially coincides with a center axis of the through hole 14 of the bracket 6 or the second downstream pipe 11b. According to the example shown in FIG. 4, the attachment 19 is pushed onto the lateral face of the bracket 6 through a gasket 20 as a sealing member for ensuring an airtight condition. Thus, the first downstream pipe 11a is communicated with the second downstream pipe 11b through the through hole 14.

The present disclosure should not be limited to the foregoing examples, and may be modified arbitrarily as necessary. For example, the bracket 6 may be arranged at appropriate sites on the outer surface of the catalytic converter 4 instead of the flange 5c. Moreover, the first downstream pipe 11a and the second downstream pipe 11b may be directly connected to each other inside the through hole 14 formed in the bracket 6. Further, the protrusion of the first downstream pipe engaged with the elastic member or the plate member is not limited to the flange 16 and the lateral face of the attachment 19. Furthermore, the stay 12 holding the upstream pipe 10 and the second downstream pipe 11b may be omitted. Otherwise, another stay for holding the first downstream pipe 11a may be attached to the casing 8 of the filter unit 7. In addition, the exhaust system according to the exemplary embodiment of the present disclosure may also be applied to a diesel engine instead of the gasoline engine.