JP2018076852A - Exhaust system structure for internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an exhaust system structure for an internal combustion engine for enabling exhaust gas to equally flow into an exhaust emission control part.SOLUTION: The exhaust system structure for the internal combustion engine includes an exhaust passage provided so that exhaust gas from the internal combustion engine flows along a linear direction, and the exhaust emission control part for purifying the exhaust gas passing through the exhaust passage. The axial line of the exhaust emission control part is inclined to the linear direction. The exhaust passage includes a straight part, and a diffusion part provided on the downstream side of the straight part for, when the cross-sectional shape of the straight part is projected along the linear direction, guiding the exhaust gas to the upstream side end face of the exhaust emission control part at its portion where the cross-sectional shape is not projected.SELECTED DRAWING: Figure 2

Description

  The present invention relates to an exhaust system structure of an internal combustion engine.

  2. Description of the Related Art Conventionally, there has been known an exhaust purification device that is provided in an exhaust system of an internal combustion engine and includes a catalyst (exhaust purification unit) that removes carbon monoxide, unburned hydrocarbons, and the like in exhaust gas discharged from the internal combustion engine. .

  Patent Document 1 discloses an exhaust purification device in which an axis of a catalyst is inclined with respect to an axis of an exhaust gas inflow pipe.

JP-A 64-60711

  By the way, in order to effectively use the exhaust gas purification unit of the exhaust gas purification device, it is desired that the exhaust gas flow evenly into the exhaust gas purification unit.

  However, the exhaust emission control device disclosed in Patent Document 1 has a problem that the amount of exhaust gas flowing into the catalyst is not uniform.

  An object of the present invention is to provide an exhaust system structure of an internal combustion engine that allows exhaust gas to uniformly flow into an exhaust purification section.

  An exhaust system structure for an internal combustion engine according to the present invention includes an exhaust passage provided so that exhaust gas from the internal combustion engine flows along a linear direction, and the exhaust passage structure provided on the downstream side of the exhaust passage and passed through the exhaust passage. An exhaust gas purification unit that purifies the exhaust gas, an axis of the exhaust gas purification unit is inclined with respect to the linear direction, and the exhaust passage is provided on the downstream side of the linear part and the linear part. A diffusion portion for guiding the exhaust gas to a portion where the cross-sectional shape is not projected on the upstream end surface of the exhaust purification portion when the cross-sectional shape of the straight portion is projected along the linear direction. ing.

  According to the exhaust system structure of the internal combustion engine of the present invention, the exhaust gas can be made to uniformly flow into the exhaust purification unit.

Schematic showing an exhaust system according to an embodiment of the present invention. Partial enlarged view of FIG. Sectional drawing which shows typically the flow volume distribution of the exhaust system which concerns on one Embodiment of this invention Sectional view schematically showing the flow distribution of the comparative example

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In addition, embodiment described below is an example and this invention is not limited by this embodiment.

  FIG. 1 is a schematic view showing an exhaust system according to the present invention. FIG. 2 is a partially enlarged view of FIG. 1 and 2, the X axis, the Y axis, and the Z axis are drawn. In the following description, the left-right direction in FIGS. 1 and 2 is referred to as the X direction or the vehicle front-rear direction, the right direction is “+ X direction” or “vehicle front side”, and the left direction is “−X direction” or “vehicle rear side”. That's it. 1 and 2 is referred to as a Y direction or a vehicle vertical direction, an upward direction is referred to as a “+ Y direction” or “vehicle upper side”, and a downward direction is referred to as a “−Y direction” or “vehicle lower side”. 1 and 2, the direction perpendicular to the paper surface is referred to as the Z direction or the vehicle width direction, the front direction is referred to as "+ Z direction" or "vehicle right side", and the back direction is referred to as "-Z direction" or "vehicle left side". . Further, the upstream side and the downstream side in the flow direction of the exhaust gas flowing through the exhaust passage are simply referred to as “upstream side” and “downstream side”.

  As shown in FIGS. 1 and 2, the exhaust system 1 includes an exhaust manifold 3 provided on the right side of the vehicle of the engine 2, a turbocharger 4 connected to a collecting portion of the exhaust manifold 3, and a turbocharger. 4, an upstream exhaust passage 5 extending from 4, an aftertreatment device 6, and a downstream exhaust passage 7. In the case of the present embodiment, the above-described members are arranged on the right side of the engine 2 in the vehicle. However, the arrangement of the above members with respect to the engine 2 in the vehicle width direction is not limited to the illustrated structure.

  The direction (opening direction), size, and shape of the exhaust gas outlet 4a of the turbocharger 4 are comprehensively determined based on the shape, size, installation location, and the like of the aftertreatment device 6. Here, the direction of the exhaust gas outlet 4a is the -X direction. The shape of the exhaust gas outlet 4a is a general circular shape. The installation location of the post-processing device 6 is set at a position in the −X direction of the turbocharger 4.

  The upstream exhaust passage 5 is configured by an internal space of a hollow tubular straight tube 8. The straight pipe 8 causes the exhaust gas flowing into the internal space from the upstream opening to flow linearly along the extending direction of the straight pipe 8 (that is, the direction of the axis 8a) and flows out from the downstream opening. It has a function as a flow path. In the case of this configuration example, the shaft 8 a corresponds to the central axis of the straight tube 8.

  The upstream end of the straight tube 8 is connected to the exhaust gas outlet 4a. On the other hand, the downstream end of the straight pipe 8 is fixed to the upstream end of a case 10 (described later) of the post-processing device 6. The extending direction (that is, the direction of the shaft 8a), the length, and the hollow cross-sectional shape of the straight tube 8 are comprehensive based on the direction of the exhaust gas outlet 4a, the position of the DOC 11 (described later) in the aftertreatment device 6, and the like. Determined.

  Note that the hollow cross-sectional shape of the straight tube 8 refers to a transverse cross-section of the internal space defined by the inner peripheral surface of the straight tube 8 (cross-sectional shape related to a virtual plane orthogonal to the axis 8a). In other words, the outer shape (the shape of the outer peripheral edge) of the hollow cross-sectional shape of the straight tube 8 matches the cross-sectional shape of the inner peripheral surface of the straight tube 8 with respect to a virtual plane orthogonal to the axis 8a.

  The extending direction of the straight tube 8 is tilted three-dimensionally based on, for example, the position of the DOC 11. Here, in order to make the explanation easy to understand, as shown in FIGS. 1 and 2, the straight tube 8 is extended linearly in the same −X direction as the exhaust gas outlet 4a. Moreover, the hollow cross-sectional shape of the straight tube 8 is the same circular shape as the shape of the exhaust gas outlet 4a.

  The reason why the extending direction and the hollow cross-sectional shape of the straight tube 8 are the same direction and shape as the exhaust gas outlet 4a is that the flow rate of the exhaust gas flowing into the straight tube 8 from the turbocharger 4 is reduced by the straight tube 8 as much as possible. It is for making it flow out to DOC11, maintaining it in a high state without doing. Further, the length of the straight pipe 8 is preferably as short as possible in order to prevent heat dissipation between the turbocharger 4 and the DOC 11 and to suppress a decrease in the flow rate of the exhaust gas.

  As described above, the upstream end of the post-processing device 6 is connected to the downstream end of the straight tube 8. The aftertreatment device 6 includes a cylindrical case 10, a DOC 11 for purifying exhaust gas (corresponding to the “exhaust purification unit” of the present invention), and a diesel particulate filter (DPF) 12 (“exhaust gas” of the present invention). Corresponding to the “purification section”). The details of the structure connecting the downstream end of the straight pipe 8 and the upstream end of the post-processing device 6 will be described later.

  The DOC 11 and the DPF 12 are held in the case 10 with an inorganic mat 13. The DOC 11 is formed in a column shape having an axis 11a. In the present embodiment, the shaft 11a corresponds to the central axis of the DOC 11. The shaft 11a extends in the direction perpendicular to the upstream end surface 11b of the DOC 11. That is, the cross-sectional shape of the DOC 11 (the cross-sectional shape related to the virtual plane orthogonal to the axis 11a) is the same shape as the upstream end surface 11b.

  Similarly, the DPF 12 is formed in a column shape having a shaft 12a. In this embodiment, the shaft 12a corresponds to the central axis of the DPF 12. The shaft 12a extends in the direction perpendicular to the upstream end surface 12b of the DPF 12. That is, the cross-sectional shape of the DPF 12 (the cross-sectional shape related to the virtual plane orthogonal to the axis 12a) is the same shape as the upstream end surface 12b.

  The installation place of the post-processing device 6 is set at the position in the −X direction of the turbocharger 4 as described above. Here, the DOC 11 and the DPF 12 are not arranged linearly in the −X direction in order to effectively use the installation location, but the axes 11a and 12a are arranged with respect to the X direction, the Y direction, and the Z direction. It is arranged so as to be tilted three-dimensionally. Details of the inclinations of the axes 11a and 12a will be described later.

  In DOC11, for example, platinum, iridium oxide or cobalt oxide as an oxidation catalyst is supported on alumina as a carrier. The DOC 11 has a function of oxidizing unburned gases such as hydrocarbons, carbon monoxide, and nitrogen oxides contained in the exhaust gas. Note that the basic structure and function of the DOC 11 are the same as those of conventionally known DOCs, and thus detailed description thereof is omitted.

  The DPF 12 arranges a number of cells forming a grid-like exhaust flow path partitioned by porous ceramic partition walls along the flow direction of the exhaust gas, and alternately seals the upstream and downstream sides of these cells. It is configured to stop. The DPF 12 has a function of collecting particulate matter (PM) contained in the exhaust gas. Note that the basic structure and function of the DPF 12 are the same as those of the conventional DPF, and thus detailed description thereof is omitted.

  A downstream exhaust passage 7 is connected to the downstream end of the post-processing device 6. The exhaust gas purified by the post-treatment device 6 is led out through the downstream exhaust passage 7. The downstream side of the downstream side exhaust passage 7 extends linearly in the −X direction, and the exhaust gas is led out from the rear end of the downstream side exhaust passage 7 toward the rear of the vehicle.

  Next, the detail of the structure which connects the downstream end part of the straight pipe 8 and the upstream end part of the post-processing apparatus 6 is demonstrated. FIG. 2 shows a circle P as the shape of the exhaust gas outlet 4a seen from the direction of the axis 8a (that is, the hollow cross-sectional shape of the straight tube 8), and an ellipse Q as the shape of the upstream end face 11b seen from the direction of the axis 11a. Indicates. Moreover, the flow of the exhaust gas which passes the straight tube 8 and DOC11 is shown in FIG. 2 with a broken line.

  The straight tube 8 includes a straight portion 8b and a diffusion portion 8c. The axis 8a of the straight tube 8 coincides with the axis of the straight portion 8b. Therefore, in the following description, the “axis 8a” means the axis of the straight tube 8 and the axis of the straight portion 8b. Further, the hollow cross-sectional shape of the straight portion 8b corresponds to the “cross-sectional shape of the straight portion” of the present invention. The direction of the axis 8a of the straight tube 8 (straight portion 8b) is the -X direction as described above.

  The axis 11a of the DOC 11 is tilted three-dimensionally with respect to the axis 8a in the -X direction. Here, in order to make the explanation easy to understand, the shaft 11a is inclined by a predetermined angle α around the Z axis (counterclockwise) with respect to the shaft 8a in the −X direction. That is, the upstream end surface 11b of the DOC 11 is inclined by a predetermined angle (π / 2−α) around the Z axis (clockwise) with respect to the shaft 8a.

  As shown in FIG. 2, the axis 8 a of the straight portion 8 b and the axis 11 a of the DOC 11 do not intersect at the upstream end surface 11 b of the DOC 11 but intersect inside the DOC 11. That is, the shaft 8a of the straight portion 8b is located below the center of the upstream end surface 11b of the DOC 11 in the vehicle vertical direction.

  When the hollow cross-sectional shape (here, a circle) of the straight portion 8b is projected in the linear direction (−X direction), the image of the hollow cross-sectional shape projected on the upstream end surface 11b of the DOC 11 is on the long axis of the ellipse Q. On the other hand, an ellipse R having a long axis located on the same straight line is obtained. Further, as shown in FIG. 2, the major axis end of the ellipse R near the exhaust gas outlet 4 a coincides with the major axis end of the ellipse Q near the exhaust gas outlet 4 a.

  That is, in this embodiment, the lower end in the vehicle up-down direction of the upstream end surface 11b is located at the same height as the lower end in the vehicle up-down direction of the inner periphery of the straight portion 8b. The inclination angle of the upstream end surface 11b with respect to the shaft 8a is set based on, for example, the size and shape of the DOC 11 and its arrangement location.

  The upstream end edge 10 a of the case 10 substantially coincides with the upstream end face 11 b of the DOC 11. The inner periphery of the downstream end portion of the straight pipe 8 is formed so as to follow the outer periphery of the upstream end edge 10a of the case 10 without a gap. In the present embodiment, the downstream end of the straight tube 8 is fitted to the upstream end edge 10a of the case 10 and welded, whereby the straight tube 8 and the case 10 are sealed.

  As shown in FIG. 2, a diffusion part 8c is provided on the downstream side of the straight part 8b. The diffusion portion 8c includes a peripheral wall portion 8d and a lid portion 8e that closes one end of the peripheral wall portion 8d. A surface of the lid portion 8e that faces the upstream end surface 11b forms a facing surface 8f. A gap through which exhaust gas passes is provided between the upstream end face 11b and the facing face 8f. In the present embodiment, the lid portion 8e is provided in parallel to the upstream end surface 11b, and the gap between the upstream end surface 11b and the facing surface 8f is constant. The lid portion 8e may be tapered, and the gap between the upstream end surface 11b and the facing surface 8f may be made smaller toward the outer diameter side.

<Effect of this embodiment>
The effect of this embodiment will be described with reference to a comparative example. FIG. 3 schematically shows the flow of exhaust gas in the present embodiment. FIG. 4 schematically shows the flow of the exhaust gas in the comparative example. The arrows in the figure conceptually show the flow of exhaust gas, and the thicker the arrows, the higher the flow rate.

  In the comparative example, the shaft 8b of the straight tube 8 and the shaft 11a of the DOC 11 intersect at the upstream end surface 11b of the DOC 11, and the upstream exhaust gas is directed from the exhaust gas outlet 4a of the turbocharger 4 toward the upstream end surface 11b. The case where the diameter of the passage 5 is gradually expanded in the vehicle vertical direction is shown.

  As shown in FIG. 4, when the upstream exhaust passage 5 is gradually expanded in the vehicle vertical direction from the exhaust gas outlet 4a toward the upstream end surface 11b, the flow a located at the lower side in the vehicle vertical direction is The flow b positioned and the flow c positioned above reach the upstream end face 11b while gradually spreading.

  A part of the flow a that has reached the upstream end face 11b of the DOC 11 is bent and flows into the DOC 11 (a flow f inside the bend), and a part thereof becomes a flow d along the upstream end face 11b of the DOC 11. Furthermore, the flow d merges with the flow b.

  A flow obtained by joining the flow b and the flow d is a flow g at the center of bending where part of the flow b is bent and flows into the DOC 11, and part of the flow is a flow e along the upstream end surface 11 b of the DOC 11. The inflow amount of the flow g to the DOC 11 is hindered by the influence of the flow d along the upstream end surface 11b, and is approximately the same as the inflow amount of the flow f. Further, the flow rate of the flow e is larger than the flow rate of the flow d.

  The flow e merges with the flow c, bends, and flows into the DOC 11 (flow h outside the bend). Therefore, the amount of the flow h flowing into the DOC 11 increases. In other words, only the flow h outside the bending increases in the amount of inflow into the DOC 11. Therefore, the amount of exhaust gas flowing into the DOC 11 is biased, and the DOC 11 cannot be used effectively.

  On the other hand, as shown in FIG. 3, according to the present embodiment, the flow A positioned on the lower side, the flow flow B positioned on the center, and the flow C positioned on the upper side in the vehicle vertical direction are It reaches the upstream end face 11b in a linear flow state along the direction 8a. A part of the flow A that has reached the upstream end face 11b is bent and flows into the DOC 11 (flow F inside the bend), and a part thereof becomes a flow D along the upstream end face 11b.

  Furthermore, stream D merges with stream B. A flow obtained by joining the flow B and the flow D is a flow that is partially bent and flows into the DOC 11, and a part of the flow is a flow E along the upstream end surface 11 b of the DOC 11.

  Further, stream E merges with stream C. A flow obtained by joining the flow C and the flow E becomes a flow G at the center of bending where a part of the flow is bent and flows into the DOC 11. Further, a part of the flow obtained by joining the flow C and the flow E becomes a flow J, which is diffused to a region where the cross-sectional shape of the straight portion 8b on the upstream end face 11b is not projected by the diffusion portion 8c, and then bent to be a DOC11. (Flow H outside the bend).

  For this reason, the inflow amount of the flow H outside the bending is smaller than that in the comparative example. Thereby, compared with the comparative example shown in FIG. 4, the amount of inflow into the DOC 11 can be made uniform in the flow F inside the bending, the flow G in the bending center, and the flow H outside the bending.

  As described above, according to the present embodiment, the diffusion portion 8c for guiding the exhaust gas to the portion where the cross-sectional shape of the straight portion 8b is not projected on the upstream end surface 11b of the DOC 11 is provided downstream of the straight tube 8. Since it was provided, the amount of exhaust gas flowing into the DOC 11 can be made uniform.

<Modification of the present embodiment>
In the above embodiment, the straight tube 8 is extended to the rear side of the vehicle. However, the present invention is not limited to this, and is extended to the front side of the vehicle, for example, depending on the installation location of the post-processing device 6. May be.

  In the above embodiment, the shaft 12a of the DPF 12 is tilted two-dimensionally at a predetermined angle β around the Z axis (counterclockwise) with respect to the shaft 11a of the DOC 11, as shown in FIG. The DPF 12 may be tilted three-dimensionally with respect to the shaft 11a according to the size and shape of the DPF 12 and the arrangement location thereof.

  Moreover, although the said embodiment demonstrated what provided DOC11 in the upstream of DPF12, it is not limited to this. Various catalysts for purifying exhaust gas such as a lean NOx trap catalyst (LNT) and a selective catalytic reduction catalyst (SCR) as other catalysts may be provided on the upstream side of the DPF 12, such as a lean NOx trap catalyst (LNT) or a selective catalytic reduction catalyst (SCR). In addition to the above, another catalyst may be provided. When the present invention is applied to this configuration, the upstream end face of the LNT is inclined at a predetermined angle with respect to the axis 8a of the straight tube 8.

  In the above embodiment, the shaft 11a of the DOC 11 extends in a direction perpendicular to the upstream end surface 11b of the DOC 11, and the cross-sectional shape of the DOC 11 is the same as the shape of the upstream end surface 11b. It is not limited to. You may make it incline the upstream end surface 11b with respect to the cross section of DOC11.

  The exhaust system structure of the internal combustion engine of the present disclosure is useful as an exhaust gas aftertreatment device that requires effective use of an exhaust purification unit.

DESCRIPTION OF SYMBOLS 1 Exhaust system 2 Engine 3 Exhaust manifold 4 Turbo supercharger 4a Exhaust gas outlet 5 Upstream exhaust passage 6 Post-processing device 7 Downstream exhaust passage 8 Straight pipe 8a, 11a, 12a Shaft 8b Straight portion 8c Diffusion portion 8d Circumferential wall portion 8e Lid 8f Opposing surface 10 Case 11 DOC
11b, 12b Upstream end face 12 DPF

Claims (4)

An exhaust passage provided so that exhaust gas from the internal combustion engine flows along a linear direction, and an exhaust purification unit provided on the downstream side of the exhaust passage and purifying the exhaust gas that has passed through the exhaust passage. ,
The axis of the exhaust purification unit is inclined with respect to the linear direction,
The exhaust passage is provided on the downstream side of the straight portion and the straight portion, and when the cross-sectional shape of the straight portion is projected along the straight direction, the cross-sectional shape on the upstream end surface of the exhaust purification portion A diffusion portion for guiding the exhaust gas to a portion where is not projected,
The exhaust system structure of an internal combustion engine. The edge of the image of the cross-sectional shape projected on the upstream end surface of the exhaust purification unit coincides with the edge of the upstream end surface of the exhaust purification unit at least at one point.
The exhaust system structure of the internal combustion engine according to claim 1. The distance between the surface facing the upstream end surface in the diffusion portion and the upstream end surface is constant.
The exhaust system structure of the internal combustion engine according to claim 1. The distance between the surface facing the upstream end face in the diffusing portion and the upstream end face decreases as the distance from the projected image decreases.
The exhaust system structure of the internal combustion engine according to claim 1.

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