Exhaust device for internal combustion engine

Abstract

To provide an exhaust device for an internal combustion engine that enables suppression of erosion.SOLUTION: An exhaust device for an internal combustion engine includes: an exhaust passage (11) in which exhaust gas discharged from the internal combustion engine (1) passes; and a catalyst carrier (15) provided in the exhaust passage (11) and held by a catalyst carrier holding material (16). A coating layer (18) formed of low-melting metal is provided on an inner wall surface on the upstream side of the catalyst carrier (15) in the exhaust passage (11). Due to this, since hard particles (19) included in the exhaust gas are captured by the coating layer (18), the amount of the hard particles (19) reaching an upstream end (15a) of the catalyst carrier (15) can be reduced, so as to enable suppression and reduction of erosion.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to an exhaust system for an internal combustion engine. [Background technology]

[0002] In an internal combustion engine, if the exhaust gas contains hard particles, the hard particles may reach and collide with the upstream end of the catalyst carrier, causing damage and wear to the partition at the upstream end. This phenomenon is called erosion. Hard particles are welding spatters or unburned components discharged from the inside of the engine cylinder. Patent Document 1 proposes a honeycomb structure used as a catalyst carrier in an exhaust gas purification device for an internal combustion engine such as an automobile engine. Patent Document 1 discloses a honeycomb structure having a plurality of axially penetrating through holes separated by partition walls, the surface of the honeycomb structure containing more glass phase than the axial center of the partition walls. It is said that the strength, particularly erosion resistance, is improved by vitrifying the surface of the honeycomb structure, particularly the ends of the partition walls. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2003-26488 A Summary of the Invention [Problem to be solved by the invention]

[0004] Although there are measures to strengthen the catalyst carrier as described in Patent Document 1, it would be useful to have measures to suppress erosion other than those for the catalyst carrier.

[0005] The present invention has been made in view of the above circumstances, and has an object to provide an exhaust system for an internal combustion engine that suppresses erosion. [Means for solving the problem]

[0006] The exhaust system for an internal combustion engine of the present invention comprises an exhaust path through which exhaust gas discharged from the internal combustion engine passes, and a catalyst carrier provided in the exhaust path and held by a catalyst carrier holding material, and is characterized in that a coating layer made of a low-melting point metal is provided on an inner wall surface of the exhaust path upstream of the catalyst carrier. Effect of the Invention

[0007] According to the present invention, it is possible to provide an exhaust system for an internal combustion engine that suppresses erosion. [Brief description of the drawings]

[0008] [Figure 1] 1 is a diagram showing a schematic configuration of an engine and its peripheral structure according to an embodiment; [Diagram 2] 1 is a diagram for explaining an exhaust device of an engine according to an embodiment and a comparative example; [Diagram 3] 4A to 4C are diagrams for explaining a catalyst carrier and a catalyst carrier holding material according to an example and a comparative example. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] An exhaust system for an internal combustion engine according to one embodiment of the present invention includes an exhaust path (11) through which exhaust gas discharged from an internal combustion engine (1) passes, and a catalyst carrier (15) provided in the exhaust path (11) and held by a catalyst carrier holding material (16), and a coating layer (18) made of a low-melting point metal is provided on an inner wall surface of the exhaust path (11) upstream of the catalyst carrier (15). As a result, the hard particles (19) contained in the exhaust gas are captured by the coating layer (18), thereby reducing the amount of hard particles (19) that reach the upstream end (15a) of the catalyst carrier (15), thereby making it possible to suppress or reduce erosion. EXAMPLES

[0010] Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings. 1 shows a schematic configuration of an engine 1, which is an internal combustion engine according to an embodiment, and its peripheral structure. A vehicle such as an automobile is equipped with the engine 1 as its drive source. Engine 1 has a combustion chamber 3 in which piston 2 is housed so as to be able to reciprocate, a crank chamber 4 in which a crankshaft (not shown) linked to piston 2 is rotatably housed, an intake port 5 which is an inlet for air to be used for combustion, and an exhaust port 6 which is an outlet for exhaust gas. Engine 1 also has an ignition plug (not shown) disposed so as to be located within combustion chamber 3, an intake valve 7 located between combustion chamber 3 and intake port 5, and an exhaust valve 8 located between combustion chamber 3 and exhaust port 6. Engine 1 thus configured burns fuel in combustion chamber 3, reciprocates piston 2, and rotates the crankshaft, thereby obtaining driving force for an automobile.

[0011] An intake path 9 that introduces intake air taken in from the outside into the combustion chamber 3 is connected to the engine 1. The intake path 9 includes an intake port 5 and an intake pipe 10 that is connected to the intake port 5. An injector 13 that injects fuel is installed in each cylinder on the intake side.

[0012] In addition, an exhaust path 11 through which exhaust gas discharged from the combustion chamber 3 passes is connected to the engine 1. In each drawing, the flow direction of the exhaust gas is indicated by an arrow F. The exhaust path 11 includes an exhaust port 6, an exhaust pipe 12 connected to the exhaust port 6, and a catalytic converter 14 connected to the exhaust pipe 12. The catalytic converter 14 is a three-way catalyst or the like that purifies harmful substances in the exhaust gas by oxidation and reduction.

[0013] The exhaust device of the engine 1 according to the embodiment will be described in detail below. In this embodiment, the exhaust device of the engine 1 is configured by an exhaust path 11 including a catalytic converter 14. Fig. 2(a) is a diagram for explaining the exhaust device of the engine 1 according to the embodiment. Fig. 3(a) is a diagram for explaining a catalyst carrier 15 and a catalyst carrier holding material 16 according to the embodiment.

[0014] The catalytic converter 14 comprises a cylindrical catalyst carrier 15, a catalyst carrier holding material 16 that holds the catalyst carrier 15, and a converter case 17 that houses the catalyst carrier 15 held by the catalyst carrier holding material 16. The catalyst carrier 15 is a honeycomb structure having partition walls and an outer peripheral wall, and is made of ceramics. The catalyst carrier holding material 16 is made of ceramic fibers, and is cylindrical or has multiple plate shapes combined to cover the outer peripheral surface of the catalyst carrier 15 and hold the catalyst carrier 15.

[0015] Here, a coating layer 18 made of a low melting point metal is provided on the inner wall surface of the exhaust port 6 and the exhaust pipe 12. The low melting point metal in this application refers to a metal with a melting point lower than that of the metal material constituting the exhaust port 6 and the exhaust pipe 12, and refers to a material that can capture hard particles contained in the exhaust gas in a semi-molten state or cover the outer periphery of the hard particles with a soft metal when the hard particles fly to the relevant location. This makes it possible to prevent or suppress erosion of the catalyst carrier 15. In addition, examples of the coating method include electroless plating and thermal spraying, and the coating material is preferably a single component such as antimony or tin, or an alloy component such as brass.

[0016] As shown in FIG. 3(a), on the upstream side of the exhaust gas flow direction F, the end of the catalyst carrier holding material 16 protrudes from the end face of the upstream end 15a of the catalyst carrier 15. Hereinafter, this protruding part 16a, i.e., the part upstream of the upstream end 15a of the catalyst carrier 15, is called the upstream part, and the rest is called the downstream part 16b. In FIG. 3(a), the upstream part 16a and the downstream part 16b are shown separated by a dotted line, which is an imaginary line. Note that, on the downstream side, the end of the catalyst carrier holding material 16 and the end face of the downstream end 15b of the catalyst carrier 15 may be substantially flush with each other. The length of the upstream part 16a is, for example, about 10% of the longitudinal length of the catalyst carrier 15 (the dimension between the upstream and downstream ends 15a, 15b).

[0017] In the catalyst carrier holding material 16, the upstream portion 16a has a lower density than the downstream portion 16b. The upstream portion 16a contains the same low-melting point metal as the coating layer 18. For example, when manufacturing the catalyst carrier holding material 16, an organic substance is added to the upstream portion 16a when forming the catalyst carrier holding material 16 into a predetermined shape, and then the organic substance is removed by firing to reduce the density of the upstream portion 16a. The low-melting point metal is then incorporated into the upstream portion 16a by weaving it into the voids formed by the reduction in density, by impregnation, spraying, deposition, or the like.

[0018] Hereinafter, the action and effect of suppressing erosion in the exhaust system of the engine 1 will be described with reference to Figs. 2(b) and 3(b) are diagrams for explaining a comparative example, and for convenience, the same components as those in the embodiment are given the same reference numerals. FIG. 2(b) is a diagram for explaining an exhaust device of an engine 1 according to the comparative example. In the comparative example, unlike the embodiment, a coating layer 18 is not provided. Also, FIG. 3(b) is a diagram for explaining a catalyst carrier 15 and a catalyst carrier holding material 16 according to the comparative example. In the comparative example, like the embodiment, the catalyst carrier holding material 16 has a protruding portion at the upstream end, but unlike the embodiment, the protruding portion is not made low density and does not contain a low melting point metal.

[0019] As shown in FIGS. 2(a) and (b), exhaust gas flowing through exhaust passage 11 is introduced into catalyst carrier 15 from upstream end 15a, and purified by the catalytic components carried on catalyst carrier 15. At that time, if the exhaust gas contains hard particles 19 (● in Figure 2, ◯ in Figure 3), in the comparative example, as shown in Figures 2(b) and 3(b), the hard particles 19 reach and collide with the upstream end 15a of the catalyst support 15, causing erosion.

[0020] In contrast, in this embodiment, as shown in Fig. 2(a), the hard particles 19 are captured by the adhesive coating layer 18 on the way downstream along with the flow of the exhaust gas. This makes it possible to reduce the amount of hard particles 19 that reach the upstream end 15a of the catalyst carrier 15, making it possible to suppress and reduce erosion. Even if the hard particles 19 come into contact with the coating layer 18 but cannot be captured, as shown in Fig. 3(a), the low-melting point metal is transferred to the outer peripheral surface of the hard particles 19 that come into contact with the coating layer 18, and the outer peripheral surface of the hard particles 19 is covered with the low-melting point metal 19a.

[0021] In the comparative example, as shown in Fig. 3(b), when hard particles 19 contained in the exhaust gas reach and collide with the upstream end 15a of the catalyst carrier 15, erosion occurs, and the collision of the hard particles 19 causes peeling of the catalyst carrier 15, generating catalyst carrier particles 20 (△ in Fig. 3). Secondary erosion progresses due to re-collision of the hard particles 19 and drag wear caused by friction between the catalyst carrier particles 20 and the wall surface of the catalyst carrier 15. Some of the hard particles 19 pass through the catalyst carrier 15 and are discharged from the downstream end 15b.

[0022] In contrast, in this embodiment, as shown in FIG. 3(a), the outer peripheral surface of the hard particles 19 that reach the upstream end 15a of the catalyst carrier 15 is coated with a low-melting point metal 19a, which exerts a buffering effect and can soften the collision with the upstream end 15a of the catalyst carrier 15. This makes it possible to suppress and reduce erosion, and also to suppress the peeling of the catalyst carrier 15 due to the collision of the hard particles 19. In addition, the low-melting point metal that coated the hard particles 19 is transferred to the catalyst carrier particles 20 that are peeled off due to the collision of the hard particles 19, and the outer peripheral surface of the catalyst carrier particles 20 is coated with the low-melting point metal 20a. In addition, since the low-melting point metal has adhesiveness, the hard particles 19 and catalyst carrier particles 20 coated with the low-melting point metal can be captured and collected in the upstream portion 16a of the catalyst carrier holding material 16, thereby suppressing the progress of secondary erosion.

[0023] Furthermore, in this embodiment, the upstream portion 16a of the catalyst carrier holding material 16 has a trap structure (mesh structure) due to low density, and contains the same metal as the low melting point metal that constitutes the coating layer 18. This physically and chemically changes the structure of the catalyst carrier holding material 16, increasing the probability of capturing the hard particles 19 and exfoliated catalyst carrier particles 20, and preventing them from falling off due to the chemical affinity with the ceramic fibers woven with the same metal species.

[0024] In addition, the low melting point metal that constitutes the coating layer 18 has a small surface energy, and the ceramic catalyst carrier 15 is also inactive, so even if the low melting point metal adheres to the catalyst carrier 15, it is unlikely to accumulate and is unlikely to clog the pores of the catalyst carrier 15. Therefore, there is almost no effect on the engine performance and purification performance, and it is possible to maintain the same engine performance and purification performance as before.

[0025] As described above, the coating layer 18 made of a low-melting point metal is provided on the inner wall surface of the exhaust path 11 upstream of the catalyst carrier 15. As a result, the hard particles 19 contained in the exhaust gas are captured by the coating layer 18, so that the amount of hard particles 19 reaching the upstream end 15a of the catalyst carrier 15 can be reduced, making it possible to suppress and reduce erosion. Even if the hard particles 19 cannot be captured by the coating layer 18, the outer peripheral surface of the hard particles 19 in contact with the coating layer 18 is covered with the low-melting point metal 19a, making it possible to suppress and reduce erosion and to suppress peeling of the catalyst carrier 15 due to collision of the hard particles 19.

[0026] In addition, the catalyst carrier holding material 16 is formed of ceramic fibers, and the upstream portion 16a of the catalyst carrier holding material 16 has a lower density than the downstream portion 16b. This allows the upstream portion 16a to have a porous structure by reducing the density, thereby capturing and recovering the hard particles 19 and the catalyst carrier particles 20, and suppressing the progress of secondary erosion. At that time, the outer peripheral surfaces of the hard particles 19 and the catalyst carrier particles 20 are covered with adhesive low-melting point metals 19a, 20a, which are difficult to detach even after being captured by the porous structure, and the occurrence and progress of erosion can be suppressed.

[0027] Furthermore, the upstream portion 16a of the catalyst carrier holding material 16 is a portion that is located upstream of the upstream end 15a of the catalyst carrier 15, and by reducing the density of this portion, it is possible to capture some of the hard particles 19 before they reach the upstream end 15a of the catalyst carrier 15, and hard particles 19 that have bounced off after colliding with the upstream end 15a, thereby suppressing the occurrence and progression of erosion. Furthermore, since reducing the density of the side surface of the catalyst carrier 15 or, for example, the downstream portion beyond the downstream end 15b by protruding it, does not have the effect of suppressing erosion, by not reducing the density of the catalyst carrier holding material 16 more than necessary, its durability can be ensured.

[0028] Furthermore, the upstream portion 16a of the catalyst carrier holding material 16 is made to contain the same low-melting point metal as the low-melting point metal constituting the coating layer 18. This improves the chemical affinity of the hard particles 19 that are in contact with the coating layer 18 and coated with the low-melting point metal when they are captured in the porous structure of the upstream portion 16a, thereby reducing the detachment of the hard particles 19 from the porous structure.

[0029] As described above, it is possible to provide an exhaust device for the engine 1 that suppresses erosion by measures other than those for the catalyst carrier 15.

[0030] Although the embodiments of the present invention have been described in detail above with reference to the drawings, each embodiment merely shows a specific example of the implementation of the present invention. The technical scope of the present invention is not limited to each embodiment. Various modifications of the present invention are possible without departing from the spirit of the present invention, and these modifications are also included in the technical scope of the present invention. In this embodiment, the coating layer 18 is provided on the inner wall surface of each of the exhaust port 6 and the exhaust pipe 12, but is not limited thereto. From the viewpoint of capturing as many hard particles 19 as possible, it is preferable that the coating layer 18 is provided over as wide an area as possible, but it is sufficient that the coating layer 18 is provided on the inner wall surface upstream of the catalyst carrier 15 in the exhaust path 11, and for example, the coating layer 18 may be provided on only the inner wall surface of either the exhaust port 6 or the exhaust pipe 12. Furthermore, in addition to the exhaust port 6 and the exhaust pipe 12, the coating layer 18 may also be provided on the inner wall surface upstream of the upstream end 15a of the catalyst carrier 15 of the converter case 17 of the catalytic converter 14. [Explanation of symbols]

[0031] 1: engine, 3: combustion chamber, 6: exhaust port, 11: exhaust path, 12: exhaust pipe, 14: catalytic converter, 15: catalyst carrier, 16: catalyst carrier holding material, 17: converter case, 18: coating layer, 19: hard particles, 20: catalyst carrier particles

Claims

1. An exhaust path through which exhaust gas discharged from the internal combustion engine passes; a catalyst carrier provided in the exhaust path and held by a catalyst carrier holding material; 13. An exhaust system for an internal combustion engine, comprising: a coating layer made of a low-melting point metal provided on an inner wall surface of said exhaust passage upstream of said catalyst carrier.

2. The catalyst carrier holding material is formed of ceramic fibers, 2. The exhaust system for an internal combustion engine according to claim 1, wherein an upstream portion of the catalyst carrier holding material has a lower density than a downstream portion.

3. 3. The exhaust system for an internal combustion engine according to claim 2, wherein the upstream portion of the catalyst carrier holding material is a portion located upstream of an upstream end of the catalyst carrier.

4. 4. The exhaust system for an internal combustion engine according to claim 2, wherein the upstream portion of the catalyst carrier holding material contains the same low melting point metal as that constituting the coating layer.

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