EXHAUST SYSTEM FOR INTERNAL COMBUSTION ENGINE

Description

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to Japanese Patent Application No. 2024-227385 filed on Dec. 24, 2024. The disclosure of the above-identified application, including the specification, drawings, and claims, is incorporated by reference herein in its entirety.

BACKGROUND

1. Technical Field

The present disclosure relates to an exhaust system for an internal combustion engine.

2. Description of Related Art

An exhaust manifold for an internal combustion engine is known in which a recess having an arc shape is provided at a collection pipe (see, for example, Japanese Unexamined Patent Application Publication No. 2018-150926 (JP 2018-150926 A)). Japanese Unexamined Patent Application Publication No. 2018-071353 (JP 2018-071353 A) discloses a configuration in which a bent portion that is bent is provided in an exhaust passage from an internal combustion engine to a catalyst such that a flow rate of exhaust gas entering an exhaust gas cleaning catalyst is uniform in a direction orthogonal to an axial direction of the catalyst. Japanese Unexamined Patent Application Publication No. 2006-283586 (JP 2006-283586 A) discloses a configuration in which, in an exhaust pipe structure in which an exhaust gas cleaning catalyst is connected to a collection pipe of an exhaust manifold, an axial line of a branch pipe of the exhaust manifold and an axial line of the exhaust gas cleaning catalyst are made to intersect with each other. In addition, a configuration in which a protrusion is provided in the collection pipe at a portion of the exhaust pipe structure where the axial lines intersect is disclosed. Japanese Unexamined Patent Application Publication No. 2020-002831 (JP 2020-002831 A) discloses a configuration in which an expansion portion is provided in an exhaust passage that connects an oxidation catalyst and a DPF, and a guide wall that causes exhaust gas to swirl is provided in the expansion portion. Japanese Unexamined Patent Application Publication No. 2007-303398 (JP 2007-303398 A) discloses a configuration in which an inlet side of a catalyst housing is provided to expand in diameter while being bent.

SUMMARY

An object of the present disclosure is to provide an effective technique for suppressing blow-through of exhaust gas in an exhaust gas cleaning catalyst.

One aspect of the present disclosure is an exhaust system for an internal combustion engine. The exhaust system for an internal combustion engine in that case includes, for example,

• • an exhaust manifold including multiple branch pipes connected to multiple cylinders of the internal combustion engine, respectively, and a collection portion provided by merging the branch pipes, and
  • a catalyst casing connected to a downstream side of the collection portion in the exhaust manifold, in which
  • each of the branch pipes may be configured such that a flow direction of exhaust gas flowing into the collection portion is acute with respect to an axial direction of the catalyst casing, and
  • the collection portion may be configured such that an internal space of the collection portion has a spherical shape.

According to the present disclosure, it is possible to provide an effective technique for suppressing blow-through of exhaust gas in an exhaust gas cleaning catalyst.

BRIEF DESCRIPTION OF THE DRAWINGS

Features, advantages, and technical and industrial significance of exemplary embodiments of the disclosure will be described below with reference to the accompanying drawings, in which like signs denote like elements, and wherein:

FIG. 1 is a sectional view schematically showing an example of a configuration of an exhaust system according to an embodiment;

FIG. 2 is a first diagram for describing a flow of exhaust gas in the exhaust system of the embodiment;

FIG. 3 is a second diagram for describing the flow of the exhaust gas in the exhaust system of the embodiment; and

FIG. 4 is a third diagram for describing the flow of the exhaust gas in the exhaust system of the embodiment.

DETAILED DESCRIPTION OF EMBODIMENTS

An exhaust system for an internal combustion engine in which an exhaust gas cleaning catalyst (catalyst casing) is disposed on a downstream side of an exhaust manifold connected to the internal combustion engine is known. In such an exhaust system, a phenomenon (so-called blow-through) may occur in which a cleaning target component in exhaust gas passes through the exhaust gas cleaning catalyst without being cleaned in an operating region (for example, a high rotation operating region) in which a flow rate of the exhaust gas is increased.

The present disclosure is suitable for suppressing the blow-through described above. In an example, an exhaust system for an internal combustion engine according to the present disclosure includes an exhaust manifold and a catalyst casing. The exhaust manifold according to the present disclosure includes a plurality of branch pipes connected to a plurality of cylinders of the internal combustion engine, respectively, and a collection portion provided by merging the branch pipes. The catalyst casing according to the present disclosure is connected to a downstream side of the collection portion in the exhaust manifold. Then, each of the branch pipes according to the present disclosure is configured such that a flow direction of exhaust gas flowing into the collection portion is acute with respect to an axial direction of the catalyst casing. As a result, the exhaust gas flowing into the collection portion from each of the branch pipes flows toward an inner wall surface of the collection portion and collides with the inner wall surface. In addition, the collection portion according to the present disclosure is configured such that an internal space of the collection portion has a spherical shape. As a result, the exhaust gas flowing into the collection portion from the branch pipes swirls along the inner wall surface after colliding with the inner wall surface of the collection portion. In this case, even when a collision position of the exhaust gas on the inner wall surface of the collection portion is changed by changing the flow rate of the exhaust gas according to the operating state of the internal combustion engine, the exhaust gas can be swirled. Therefore, the exhaust gas flowing into the collection portion from the branch pipes is decelerated by consuming the kinetic energy by the collision with the inner wall surface of the collection portion and the swirling along the inner wall surface of the collection portion. The exhaust gas decelerated in this way flows into the catalyst casing from the collection portion. Therefore, when the internal combustion engine is operated in the operating region where the flow rate of the exhaust gas is increased, the blow-through described above can be suppressed.

Here, in the exhaust system for an internal combustion engine according to the present disclosure, a protrusion protruding radially inward may be provided at an outlet portion of the collection portion. As a result, an amount of exhaust gas that flows into an inlet portion of the catalyst casing from the outlet portion of the collection portion can be reduced from the exhaust gas swirling in the internal space of the collection portion. In other words, the amount of exhaust gas that continues to swirl in the internal space of the collection portion can be increased from the exhaust gas swirling in the internal space of the collection portion. As a result, the flow rate of the exhaust gas discharged from the outlet portion of the collection portion can be more reliably decreased.

Embodiment

Hereinafter, specific embodiments of the present disclosure will be described with reference to the drawings. The dimensions, materials, shapes, relative arrangements, and the like of the components described in the present embodiment are not intended to limit the technical scope of the disclosure to the dimensions, materials, shapes, relative arrangements, and the like unless otherwise specified.

Overview of Exhaust System

FIG. 1 is a sectional view schematically showing an example of a configuration of an exhaust system Es1 of an internal combustion engine 1 according to the present embodiment. The internal combustion engine 1 is mounted on a vehicle for driving or generating power. The internal combustion engine 1 of the present embodiment includes a plurality of cylinders. The internal combustion engine 1 of the present embodiment may be a spark ignition type internal combustion engine or a compression ignition type internal combustion engine.

An exhaust manifold 2 is connected to the internal combustion engine 1. The exhaust manifold 2 according to the present embodiment is configured to include a plurality of branch pipes 20 through which burnt gas (exhaust gas) burned in each of a plurality of cylinders 10 of the internal combustion engine 1 flows. In addition, the exhaust manifold 2 according to the present embodiment is configured to include a collection portion (collector) 21 that merges the exhaust gas flowing through the branch pipes 20. In addition, in FIG. 1, although only one of the branch pipes 20 of the exhaust manifold 2 is shown, the exhaust manifold 2 includes the branch pipes 20. A detailed configuration of the exhaust manifold 2 according to the present embodiment will be described below.

The catalyst casing 3 is connected to an outlet (downstream side) of the collection portion 21 of the exhaust manifold 2. The catalyst casing 3 is configured to include a cylindrical portion that houses the exhaust gas cleaning catalyst 30 and a conical portion that is disposed in front and rear of the cylindrical portion. The exhaust gas cleaning catalyst 30 cleans a cleaning target component contained in the exhaust gas. In an example, the exhaust gas cleaning catalyst 30 may be configured to clean exhaust components, such as hydrocarbons (HC), carbon monoxides (CO), and nitrogen oxides (NO_x), contained in exhaust gas. The exhaust gas cleaning catalyst 30 is not limited to the three-way catalyst, and may be an oxidation catalyst, a NO_X storage reduction catalyst (NSR catalyst), or a selective catalytic reduction catalyst (SCR catalyst).

In the exhaust system Es1 configured as described above, the exhaust gas discharged from the cylinders of the internal combustion engine 1 merges with each other by flowing into the collection portion 21 of the exhaust manifold 2. At this time, the exhaust gas discharged from the cylinders of the internal combustion engine 1 passes through each of the branch pipes 20 of the exhaust manifold 2. The exhaust gas merged in the collection portion 21 flows into the catalyst casing 3 and is discharged to the downstream side through the exhaust gas cleaning catalyst 30 in the catalyst casing 3. At that time, the cleaning target component contained in the exhaust gas is cleaned by the exhaust gas cleaning catalyst 30.

Configuration of Exhaust Manifold

Here, a specific configuration of the exhaust manifold 2 according to the present embodiment will be described. As shown in FIG. 1, the collection portion 21 of the exhaust manifold 2 according to the present embodiment is configured to provide an internal space having a spherical shape. In the collection portion 21, an outlet 22 having a substantially cylindrical shape for discharging the exhaust gas from the inside of the collection portion 21 is provided at a portion of the exhaust gas cleaning catalyst 30 housed in the catalyst casing 3 on the axial direction. The axial direction of the exhaust gas cleaning catalyst 30 is a virtual straight line (one-dot chain line arrow CL1 in FIG. 1) obtained by extending the center axis of the exhaust gas cleaning catalyst 30 to the collection portion 21 side. In an example, the outlet 22 may be configured to be substantially coaxial with the center axis of the exhaust gas cleaning catalyst 30. On the inner wall surface of the collection portion 21, the protrusion 23 that protrudes radially inward of the outlet 22 (the center side of the outlet 22) is provided at a portion surrounding the outlet 22. The protrusion 23 may be provided over the entire periphery of the inner wall surface surrounding the outlet 22, or may be provided at a part of the inner wall surface surrounding the outlet 22. The installation location in a case where the protrusion 23 is provided at a part of the inner wall surface surrounding the outlet 22 may be decided according to the direction of the flow of the exhaust gas to be described later in the internal space of the collection portion 21.

In addition, the branch pipes 20 of the exhaust manifold 2 according to the present embodiment are configured such that an angle (angle A1 in FIG. 1) between a flow direction of exhaust gas when the exhaust gas flows into the collection portion 21 from the branch pipes 20 and an axial direction CL1 of the exhaust gas cleaning catalyst 30 housed in the catalyst casing 3 is acute. The flow direction of the exhaust gas when the exhaust gas flows into the collection portion 21 from the branch pipe 20 is indicated by a solid line arrow De1 in FIG. 1. An acute angle is an angle of less than 90 degrees. The connection positions of the branch pipes 20 and the angle A1 in the collection portion 21 are not particularly limited as long as the flow of the exhaust gas that will be described later in the internal space of the collection portion 21 can be generated.

Action and Effect of Present Embodiment

In the exhaust system Es1 of the present embodiment, the exhaust gas flowed into the collection portion 21 from each of the branch pipes 20 collides with the inner wall surface of the collection portion 21 before being discharged from the outlet 22. This is because the angle A1 between the flow direction De1 of the exhaust gas when the exhaust gas flows into the collection portion 21 from the branch pipes 20 and the axial direction CL1 of the exhaust gas cleaning catalyst 30 is acute. Then, since the collection portion 21 according to the present embodiment is configured to provide the internal space having the spherical shape, as shown in FIG. 2, the exhaust gas that collides with the collection portion 21 flows to swirl along the inner wall surface of the collection portion 21 (solid line arrow Ef1 in FIG. 2). In this case, even when the collision position of the exhaust gas on the inner wall surface of the collection portion 21 is changed by changing the flow rate of the exhaust gas according to the operating state of the internal combustion engine 1, the exhaust gas can be swirled. As a result, the exhaust gas flowed into the collection portion 21 from each of the branch pipes 20 is decelerated by consuming the kinetic energy by the collision with the inner wall surface of the collection portion 21 and the swirling in the internal space of the collection portion 21.

In addition, since at least a part of the exhaust gas swirling in the internal space of the collection portion 21 is blocked from flowing into the outlet 22 by the protrusion 23, as shown in FIG. 3, the exhaust gas continues to swirl in the internal space of the collection portion 21 (solid line arrow Ef2 in FIG. 3). As a result, the amount of exhaust gas that continues to swirl in the internal space of the collection portion 21 can be increased from the exhaust gas swirling in the internal space of the collection portion 21. As a result, the flow rate of the exhaust gas discharged from the outlet 22 of the collection portion 21 can be more reliably decreased.

The flow of the exhaust gas swirling in the internal space of the collection portion 21 may have a swirling direction that changes in the middle, as indicated by the solid line arrow Ef3 in FIG. 4. This is because the flow of the exhaust gas is affected by the pressure of the exhaust gas that newly flows into the internal space of the collection portion 21 from the branch pipes 20. Even in such a case, since at least a part of the exhaust gas swirling in the internal space of the collection portion 21 is blocked from flowing into the outlet 22 by the protrusion 23, the flow rate of the exhaust gas discharged from the outlet 22 of the collection portion 21 can be more reliably decreased.

Therefore, with the exhaust system Es1 of the present embodiment, even in a case where the flow rate of the exhaust gas discharged from the internal combustion engine 1 is increased as in a case where the internal combustion engine 1 is operated at a high rotation, the flow rate of the exhaust gas flowing into the catalyst casing 3 can be decreased. This is because the flow rate of the exhaust gas can be decelerated in the collection portion 21 of the exhaust manifold 2. As a result, the amount of the cleaning target component that blows through the exhaust gas cleaning catalyst 30 (the cleaning target component that passes through the exhaust gas cleaning catalyst 30 without being cleaned) can be reduced.

Modification

In the embodiment, the protrusion 23 is provided at the outlet 22 of the collection portion 21, but the protrusion 23 may not be provided. In particular, in the internal combustion engine having a relatively small exhaust amount (total of the cylinder content volumes) or in the internal combustion engine having a relatively low rev limit, the protrusion 23 may be omitted. This is because, even when the protrusion 23 is not provided, the flow rate of the exhaust gas flowing into the exhaust gas cleaning catalyst 30 can be sufficiently decelerated.