JP2019167831A - Exhaust passage structure of internal combustion engine - Google Patents

Abstract

To suppress the elongation of a warmup time of an exhaust emission purification catalyst at a cold time, in an exhaust passage structure of an internal combustion engine in which a rectification member is arranged in an exhaust passage at an upstream side rather than the exhaust emission purification catalyst.SOLUTION: In the exhaust passage structure of an internal combustion engine having a plurality of branch pipes, a collection pipe having an exhaust emission purification catalyst therein, and a rectification member arranged at the collection pipe at an upstream-side rather than the exhaust emission purification catalyst, the rectification member is formed of an annular porous plate material whose center portion is opened. Then, in each of the branch pipes, two curved parts are arranged which are formed so that most of the exhaust emission flowing out to the collection pipe from each branch part passes an opening part in the center portion of the rectification member when an exhaust emission flow rate is small, and on the other hand, when the exhaust emission flow rate is large, most of the exhaust emission flowing out to the collection pipe from the branch pipe collides with the porous plate material of the rectification member.SELECTED DRAWING: Figure 2

Description

  The present invention relates to an exhaust passage structure for an internal combustion engine.

  As an exhaust passage structure of an internal combustion engine, a structure is known in which a rectifying member for rectifying the flow of exhaust gas is provided in an exhaust passage upstream of an exhaust purification catalyst. For example, an exhaust passage having a plurality of slits provided with inclined plates for guiding the flow of exhaust gas in a desired direction, and a rectifying member arranged to cover the upstream end surface of the exhaust purification catalyst The structure is known (see, for example, Patent Document 1).

JP 2012-193719 A

  According to the above-described conventional exhaust passage structure, the exhaust flow is rectified by the rectifying member immediately before the exhaust flows into the exhaust purification catalyst, so that the exhaust gas is uniformly exhausted over a wide range on the upstream end face of the exhaust purification catalyst. Can be introduced. However, even when it is necessary to warm up the exhaust purification catalyst, such as immediately after the internal combustion engine is cold-started, the exhaust comes into contact with the rectifying member. By being deprived, the amount of heat transferred from the exhaust to the exhaust purification catalyst is reduced. As a result, the time required for warming up the exhaust purification catalyst may become longer.

  The present invention has been made in view of various circumstances as described above, and an object of the present invention is to provide an internal combustion engine exhaust passage structure in which a rectifying member is disposed in an exhaust passage upstream of an exhaust purification catalyst. It is an object of the present invention to provide a technology capable of suppressing an increase in warm-up time of an exhaust purification catalyst at the time.

  The present invention employs the following means in order to solve the above-described problems. That is, the present invention is a plurality of branch pipes for circulating the exhaust discharged from each cylinder of the internal combustion engine, and a pipe for circulating the exhaust discharged from the plurality of branch pipes, A collecting pipe in which an exhaust purification catalyst is arranged, and a rectifying member arranged in the collecting pipe upstream from the exhaust purification catalyst and for adjusting the flow direction of the exhaust gas flowing through the collecting pipe, 2 is an exhaust passage structure of an internal combustion engine. The rectifying member is formed of an annular porous plate having an open central portion. In addition, each branch pipe is formed in a substantially S shape in which a portion in front of the downstream end portion of each branch pipe has two curved portions having different bending directions. The two bent portions in each branch pipe are formed such that an extension line of the axis at the outlet portion of each branch pipe passes through the opening in the central portion of the rectifying member, and Each of the straight lines extending between the inner wall surfaces located on the inner side of the curved portion is formed so as to intersect with the porous plate member in the rectifying member.

  According to the present invention, in the exhaust passage structure of the internal combustion engine in which the rectifying member is disposed in the exhaust passage upstream of the exhaust purification catalyst, it is possible to suppress an increase in the warm-up time of the exhaust purification catalyst when it is cold.

It is a figure which shows schematic structure of the internal combustion engine to which this invention is applied, and its exhaust system. It is an expanded sectional view in the connection part of a branch pipe and a collecting pipe. It is a top view of a baffle member. It is a figure which shows the time-dependent change of the bed temperature of an exhaust gas purification catalyst when an internal combustion engine is cold-started.

  Hereinafter, specific embodiments of the present invention 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 invention to those unless otherwise specified.

FIG. 1 is a diagram showing a schematic configuration of an internal combustion engine and its exhaust system according to the present invention. An internal combustion engine 1 shown in FIG. 1 includes a plurality of cylinders 2. In the example shown in FIG. 1, the internal combustion engine 1 has four cylinders 2. However, the internal combustion engine 1 may have three or less cylinders, or may have five or more cylinders. Good. An exhaust manifold 3 is connected to the internal combustion engine 1. The exhaust manifold 3 includes a plurality of branch pipes 30 for circulating the exhaust discharged from each cylinder 2 and a collecting pipe 31 for combining and flowing the exhaust discharged from the branch pipes 30. An exhaust purification catalyst 4 for purifying harmful gas components contained in the exhaust is disposed in the middle of the collecting pipe 31. The exhaust purification catalyst 4 here is a general term for a catalyst carrier and a catalyst carried on the catalyst carrier. Examples of the catalyst carried on the catalyst carrier include an oxidation catalyst, a three-way catalyst, and NO _X storage reduction. A type catalyst (NSR (NO _X Storage Reduction) catalyst), a selective reduction type catalyst (SCR (Selective Catalytic Reduction) catalyst), or the like can be used.

  FIG. 2 is an enlarged cross-sectional view of a connection portion between the branch pipe 30 and the collecting pipe 31 in the exhaust manifold 3. In FIG. 2, only one branch pipe is illustrated for convenience, but other branch pipes (not shown) are configured in the same manner. As shown in FIG. 2, a rectifying member 310 is disposed in a portion of the collecting pipe 31 upstream of the exhaust purification catalyst 4. As shown in FIG. 3, the rectifying member 310 is formed by forming a porous plate having a plurality of pores 310 a into an annular shape having an open central portion. At this time, the outer diameter of the rectifying member 310 is formed to be substantially the same as the inner diameter of the collecting pipe 31. In the example shown in FIG. 2, the rectifying member 310 is formed in a tapered shape that is inclined so as to approach the exhaust purification catalyst 4 from the central portion toward the radially outer side, but the upstream end face of the exhaust purification catalyst 4 And may be formed in parallel. The rectifying member 310 configured as described above is disposed coaxially with the collecting pipe 31 and the exhaust purification catalyst 4 in the collecting pipe 31 upstream of the exhaust purification catalyst 4.

  Here, when the exhaust gas flowing into the collecting pipe 31 from each branch pipe 30 collides with the rectifying member 310, the exhaust gas is first guided radially outward on the surface of the rectifying member 310. Subsequently, when the exhaust gas guided radially outward on the surface of the rectifying member 310 reaches the inner wall surface of the collecting pipe 31, the flow direction of the exhaust gas is changed from the radially outward direction to the circumferential direction. That is, when the exhaust gas flowing into the collecting pipe 31 from each branch pipe 30 collides with the rectifying member 310, the exhaust gas is diffused in the radial direction and the circumferential direction. Further, in the process in which the exhaust flows as described above, a part of the exhaust flows into the upstream end face of the exhaust purification catalyst 4 through the pores 310a of the rectifying member 310, and therefore the upstream side of the exhaust purification catalyst 4 Exhaust gas can be allowed to flow into a wide range at the end face.

By the way, when the exhaust purification catalyst 4 needs to be warmed up immediately after the internal combustion engine 1 is cold-started, most of the exhaust gas flowing into the collecting pipe 31 from each branch pipe 30 collides with the rectifying member 310. Then, since the heat of the exhaust is lost to the wall of the rectifying plate and the collecting pipe 31, the amount of heat transferred from the exhaust to the exhaust purification catalyst 4 is reduced. As a result, the time required for the exhaust purification catalyst 4 to rise to the activation temperature or higher after the internal combustion engine 1 is cold started increases, so that the amount of harmful gas components that are not purified by the exhaust purification catalyst 4 increases. There is a fear.

  On the other hand, in the exhaust passage structure according to the present embodiment, most of the exhaust gas flowing into the collecting pipe 31 from each branch pipe 30 when the exhaust gas flow rate is large as in the case where the internal combustion engine 1 is operated at a high load. When the exhaust gas flow rate is small as in the case where the internal combustion engine 1 is operated in the first idle immediately after the cold start is completed, the exhaust gas flowing from the branch pipes 30 into the collecting pipe 31 is reduced. Most of them flow directly into the upstream end face of the exhaust purification catalyst 4 without contacting the flow regulating member 310.

  Specifically, as shown in FIG. 2, each branch pipe 30 is bent in a substantially S-shape before a connection portion (downstream end portion) with the collecting pipe 31. That is, two bending portions having different bending directions are formed at a site before the downstream end portion of each branch pipe 30. At that time, the two curved portions in each branch pipe 30 are arranged such that the extension line of the axis (the one-dot chain line L1 in FIG. It is formed. Further, the two curved portions in each branch pipe 30 are an inner wall surface 30a located inside the curved portion of the upstream curved portion (that is, the curved direction side (left side in FIG. 2)) and the downstream curved portion. A straight extension line (two-dot chain line L2 in FIG. 2) connecting the inner wall surface 30b located on the inner side of the curved portion (right side in FIG. 2) is formed so as to intersect the porous plate material of the rectifying member 310. .

  When the shape of each branch pipe 30 is determined as described above, when the exhaust flow rate is small as in the case where the internal combustion engine 1 is operated in a fast idle immediately after the cold start is completed, the flow rate of the exhaust gas is reduced. The exhaust gas flowing through each branch pipe 30 easily flows along the inner wall surface of the branch pipe 30. Therefore, most of the exhaust gas flowing from each branch pipe 30 into the collecting pipe 31 flows in the axial direction at the outlet portion 30 c of each branch pipe 30. That is, most of the exhaust gas flowing into the collecting pipe 31 from each branch pipe 30 flows along the one-dot chain line L1 in FIG. As a result, most of the exhaust gas flowing into the collecting pipe 31 from each branch pipe 30 passes through the opening in the central portion of the rectifying member 310 and directly flows into the upstream end face of the exhaust purification catalyst 4. As a result, the amount of heat taken from the exhaust gas to the flow regulating member 310 and the wall surface of the collecting pipe 31 is reduced, so that the amount of heat transferred from the exhaust gas to the exhaust purification catalyst 4 can be increased.

  Here, FIG. 4 shows a change with time of the bed temperature (catalyst bed temperature) of the exhaust purification catalyst 4 when the internal combustion engine 1 is cold-started. The solid line in FIG. 4 shows the change over time of the catalyst bed temperature in the exhaust passage structure according to the present embodiment, and the one-dot chain line in FIG. 4 shows that most of the exhaust gas flowing from the branch pipes into the collecting pipe is the rectifying member. The time-dependent change of the catalyst bed temperature in the comparative example comprised so that it may collide is shown. As shown in FIG. 4, the time required for the catalyst bed temperature to rise to the activation start temperature after the internal combustion engine 1 is started is shorter in the exhaust passage structure according to this embodiment than in the comparative example. Yes. Therefore, according to the exhaust passage structure according to the present embodiment, it is possible to suppress an increase in the time required for warming up the exhaust purification catalyst 4 due to the provision of the rectifying member 310. As a result, during the period from when the internal combustion engine 1 is cold started to when the catalyst bed temperature rises to the activation start temperature, the amount of harmful gas components discharged into the atmosphere can be reduced.

Further, when the exhaust gas flow rate is large as in the case where the internal combustion engine 1 is operated at a high load, the flow rate of the exhaust gas increases so that the exhaust gas flowing through each branch pipe 30 is separated from the inner wall surface of each branch pipe 30. And easy to flow. Therefore, after the exhaust gas passes through the inner wall surface 30a of the upstream curved portion in each branch pipe 30, most of the exhaust gas is peeled off from the inner wall surface of each branch pipe 30, and along the two-dot chain line L2 in FIG. Will begin to flow. The exhaust gas thus peeled off from the inner wall surface of each branch pipe 30 flows through the inner wall surface 30b of the downstream curved portion of each branch pipe 30 so that its directing direction is indicated by a two-dot chain line L2 in FIG. It flows into the collecting pipe 31 while keeping in the direction along. As a result, most of the exhaust gas flowing into the collecting pipe 31 from each branch pipe 30 collides with the rectifying member 310. As a result, the exhaust can be made to uniformly flow into a wide range on the upstream end face of the exhaust purification catalyst 4. As a result, local heat deterioration of the exhaust purification catalyst 4 due to high temperature exhaust gas concentrating on a part of the exhaust purification catalyst 4, reduction in the purification rate of harmful gas components by the exhaust purification catalyst 4, etc. Can be suppressed.

DESCRIPTION OF SYMBOLS 1 Internal combustion engine 2 Cylinder 3 Exhaust manifold 30 Branch pipe 30a Inner wall surface 30b Inner wall surface 30c Outlet part 31 Collecting pipe 310 Rectification member 4 Exhaust purification catalyst

Claims (1)

A plurality of branch pipes for circulating the exhaust discharged from each cylinder of the internal combustion engine;
A pipe for joining and circulating the exhaust discharged from the plurality of branch pipes, and a collecting pipe in which an exhaust purification catalyst is disposed,
A rectifying member that is disposed in the collecting pipe upstream of the exhaust purification catalyst and adjusts the flow direction of the exhaust gas flowing through the collecting pipe;
An exhaust passage structure for an internal combustion engine comprising:
The rectifying member is formed of an annular porous plate having an open central portion,
Each of the branch pipes is formed in a substantially S shape in which a portion in front of the downstream end portion of each branch pipe has two curved portions with different bending directions,
The two curved portions in each branch pipe are formed such that an extension of the axis at the outlet portion of each branch pipe passes through the opening in the central portion of the rectifying member, and in each of the two curved portions Formed so that the extension of the straight line connecting the inner wall surfaces located on the inner side of the curved portion intersects the porous plate material in the rectifying member,
An exhaust passage structure for an internal combustion engine.

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