Engine exhaust structure

Abstract

This invention provides an engine exhaust structure that allows the catalytic converter to heat up quickly, thereby improving its purification performance. [Solution] An upstream passage 50 extending from the exhaust port opening end 12A is provided in the exhaust passage 2, and a catalytic converter 6 is provided at a position lower than the exhaust port opening end. Multiple independent passages 51 are provided in the upstream passage 50, arranged in parallel in the cylinder arrangement direction and individually connected to each exhaust port opening end. The upstream passage 50 is shaped to curve so as to bulge downward toward the exhaust side from each exhaust port opening end, and the catalytic converter 6 is positioned such that its central axis extends along the cylinder arrangement direction, between the exhaust side surface 1H of the engine body 1 and the upstream passage 50, overlapping with each independent passage 51 when viewed in the vertical direction, and overlapping with the upstream passage 50 when viewed in the engine width direction.

Description

【Technical Field】 【0001】 The present invention relates to an exhaust structure of an engine. 【Background Art】 【0002】 Conventionally, in an engine provided in a vehicle or the like, it is known to provide a catalytic device in an exhaust passage to purify exhaust gas. Also, improving the purification performance of this catalytic device has been studied. 【0003】 For example, Patent Document 1 discloses an engine that diffuses exhaust gas in a portion upstream of a catalytic device so that it uniformly flows into the catalytic device, thereby enhancing the exhaust gas purification efficiency in the catalytic device. Specifically, in the engine of Patent Document 1, it has an exhaust pipe extending downward from a plurality of exhaust ports, a swirl flow generator provided at the lower end of the exhaust pipe for swirling the exhaust gas, and a catalytic device provided downstream of the swirl flow generator, and the catalytic device is arranged so as to extend downward from the swirl flow generator. 【Prior Art Documents】 【Patent Documents】 【0004】 【Patent Document 1】 Japanese Unexamined Patent Application Publication No. 2006 - 9793 【Summary of the Invention】 【Problems to be Solved by the Invention】 【0005】 When the temperature of the catalytic device is lower than the activation temperature, sufficient purification performance by the catalytic device cannot be obtained. Therefore, it is desirable to increase the temperature of the catalytic device at an early stage, such as at the start of the engine. In the structure of Patent Document 1, this point is not considered, and there is room for improvement. 【0006】 The present invention has been made in view of the above circumstances, and an object thereof is to provide an exhaust structure of an engine that can increase the temperature of a catalytic device at an early stage and enhance its purification performance. [Means for solving the problem] 【0007】 To solve the above problems, the engine exhaust structure of the present invention comprises an engine body having a plurality of cylinders arranged in a predetermined cylinder arrangement direction and a plurality of exhaust ports extending from each of the cylinders, and an exhaust passage through which exhaust gases discharged from the engine body flow, wherein when one side is the exhaust side and the opposite side is the intake side in the engine width direction perpendicular to the cylinder arrangement direction and the vertical direction, a plurality of exhaust port openings, which are the outlets of the exhaust ports, are opened along the cylinder arrangement direction on the exhaust side surface of the engine body, and the exhaust passage comprises an upstream passage extending from each of the exhaust port openings and each of the exhaust The engine has a cylindrical catalytic converter provided below the port opening end for purifying exhaust gas that has passed through the upstream passage, wherein the upstream passage includes a plurality of independent passages arranged in parallel in the cylinder arrangement direction and individually connected to each of the exhaust port opening ends, and has a curved shape that bulges downward toward the exhaust side from each of the exhaust port opening ends, and the catalytic converter is positioned such that its central axis extends along the cylinder arrangement direction, between the exhaust-side surface of the engine body and the upstream passage, overlapping with each of the independent passages when viewed in the vertical direction, and overlapping with the upstream passage when viewed in the engine width direction. 【0008】 In this configuration, the upstream passage has a curved shape that bulges downward toward the exhaust side from the exhaust port opening. The catalytic converter is positioned below each exhaust port opening and is located between the exhaust side of the engine body and the upstream passage, overlapping with each independent passage when viewed vertically and overlapping with the upstream passage when viewed horizontally. Thus, the catalytic converter is surrounded by the engine body and the upstream passage. Furthermore, the upstream passage includes multiple independent passages individually connected to the exhaust port openings, and these independent passages are arranged in parallel in the cylinder arrangement direction, so that the upper part of the catalytic converter is covered by the upstream passage over a wide area. Moreover, because the catalytic converter's central axis extends along the cylinder arrangement direction, it is not necessary to separate the catalytic converter from the engine body in the engine width direction to install the exhaust passages extending from the catalytic converter, allowing the catalytic converter to be placed close to the engine body. Therefore, this configuration promotes heat absorption by the catalytic converter from the engine body and the upstream passage. Therefore, this configuration allows the catalytic converter to heat up quickly and maintain its temperature, thereby improving the catalytic converter's purification performance and, consequently, the engine's exhaust performance. 【0009】 In the above configuration, preferably, each of the exhaust port opening ends is formed in the central portion of the exhaust-side surface of the engine body in the direction of cylinder arrangement (Claim 2). 【0010】 This configuration allows each independent passage to be placed close together, minimizing heat dissipation from these independent passages and increasing the temperature of the exhaust gas flowing into the catalytic converter. 【0011】 In the above configuration, preferably, the exhaust passage covers the upstream end of the catalytic converter in the exhaust flow direction from one side in the cylinder arrangement direction and has a connecting portion that connects the upstream end of the catalytic converter to the downstream end of the upstream passage, and the downstream end of the upstream passage is connected to the exhaust side surface of the connecting portion (Claim 3). 【0012】 This configuration allows for a shorter upstream passage length, suppressing heat dissipation from the exhaust in the upstream passage and enabling the introduction of high-temperature exhaust through the catalytic converter. 【0013】 In the above configuration, preferably, the connecting portion has an inner circumferential surface that is substantially circular when viewed along the cylinder arrangement direction (Claim 4). 【0014】 With this configuration, exhaust gas can be introduced into the connection point along the lower circumferential surface and swirled around an axis aligned with the cylinder arrangement direction within the connection point, thereby diffusing the exhaust gas. As a result, exhaust gas can be uniformly introduced into the catalytic converter, improving the exhaust gas purification efficiency of the catalytic converter. 【0015】 In the above configuration, preferably, the upstream passage has a collection passage connected to the downstream end of each of the independent passages, to which the exhaust gas that has passed through the independent passages is collected, and the connection part is connected to the downstream end of the collection passage (Claim 5). 【0016】 This configuration allows for the exhaust gas flowing into the connection point through each independent passage to be made equal, reducing variations in exhaust gas flow to the catalytic converter between each independent passage and even between cylinders. In other words, exhaust gas can be uniformly introduced to the catalytic converter for all cylinders, reliably improving the engine's purification performance. 【0017】 In the above configuration, preferably, the exhaust passage has a filter for collecting particulate matter contained in the exhaust gas that has passed through the catalytic converter, and the filter is positioned on the exhaust side of the catalytic converter, overlapping with the catalytic converter when viewed along the engine width direction, and overlapping with the upstream passage when viewed along the cylinder arrangement direction (Claim 6). 【0018】 In this configuration, the filter is positioned close to the catalyst and the upstream passage, allowing the filter to be warmed by the heat emitted from the catalyst and the upstream passage. 【0019】 In the above configuration, preferably, a cover is provided that integrally surrounds at least a part of the catalyst device and at least a part of the upstream passage (Claim 7). 【0020】 According to this configuration, heat dissipation to the outside of the upstream passage can be suppressed by the cover, and heat reception from the upstream passage of the catalyst device can be further promoted. 【Effect of the Invention】 【0021】 As described above, according to the exhaust structure of the engine of the present invention, the catalyst device can be heated up early and its purification performance can be enhanced. 【Brief Description of the Drawings】 【0022】 [Figure 1] It is a schematic plan view of an engine to which the exhaust structure of an engine according to an embodiment of the present invention is applied. [Figure 2] It is a schematic side view of the engine shown in FIG. 1 as viewed from the right side. [Figure 3] It is a schematic side view of the engine shown in FIG. 1 as viewed from the front side. [Figure 4] It is a schematic perspective view showing a part of the engine shown in FIG. 1 as viewed from the right front obliquely. [Figure 5] It is a cross-sectional view showing a part of the cross-section taken along the line V-V of FIG. 3 in an enlarged manner. [Figure 6] It is a cross-sectional view showing a part of the cross-section taken along the line VI-VI of FIG. 3 in an enlarged manner. [Figure 7] It is a cross-sectional view showing a part of the cross-section taken along the line VII-VII of FIG. 5 in an enlarged manner. [Figure 8] It is a cross-sectional view showing a part of the cross-section taken along the line VIII-VIII of FIG. 6 in an enlarged manner. [Figure 9] It is a schematic side view of the engine corresponding to FIG. 2 with the cover attached. [Figure 10] It is a schematic bottom view of the engine with the cover attached. [Figure 11]This is an enlarged view of a portion of the cross-section near line VII-VII in Figure 5, showing the engine with the cover attached. [Figure 12] This diagram corresponds to Figure 7 and is a cross-sectional view illustrating the flow of exhaust gas in the exhaust passage. [Modes for carrying out the invention] 【0023】 Figure 1 is a schematic plan view of an engine E to which the exhaust structure of an engine according to one embodiment of the present invention is applied. The engine E of this embodiment is a four-cylinder in-line reciprocating engine, and the engine body 1 has four cylinders 1A arranged in a predetermined direction. A piston (not shown) is fitted into each cylinder 1A, and when a mixture of fuel and air is burned in each cylinder 1A, the piston reciprocates in the vertical direction, thereby rotating the crankshaft (not shown), which is the output shaft of the engine E. The engine E of this embodiment is a gasoline engine, and fuel mainly composed of gasoline is supplied into each cylinder 1A. A crank pulley 1B is attached to one end of the crankshaft in the longitudinal direction. Hereinafter, the direction of arrangement of the cylinders 1A, i.e., the cylinder arrangement direction, will be referred to as the front-rear direction, the side where the crank pulley 1B is located (right side in Figure 1) will be referred to as the front side, and the opposite side as the rear side. Also, the left-right direction, which is perpendicular to the vertical direction and the cylinder arrangement direction (front-rear direction) and is facing the crank pulley 1B side (front side), will be referred to as the left-right direction. Here, the left-right direction corresponds to the "engine width direction" of the present invention, with the right side corresponding to the "exhaust side" and the left side to the "intake side". Also, as described above, the front-rear direction corresponds to the "cylinder arrangement direction" of the present invention, with the front side corresponding to "one" side of the cylinder arrangement direction of the present invention and the rear side corresponding to "the other" side. 【0024】 Figure 2 is a schematic side view of engine E viewed from the right side. Figure 3 is a schematic side view of engine E viewed from the front. Figure 4 is a schematic perspective view showing a part of engine E viewed from the front right. Figures 1 to 4 show the engine with the exhaust cover 22 and EGR cover 400, which will be described later, removed. In Figure 1, where the rear bracket 25 and lower bracket 26, which will be described later, are shown, these brackets 25 and 26 are colored for clarity. 【0025】 As shown in Figure 1, engine E comprises an engine body 1, an exhaust passage 2, an intake passage 3, and an EGR passage 4. Note that only a portion of the EGR passage 4 is shown in the drawing. 【0026】 As shown in Figure 2, the engine body 1 includes a cylinder block 1E, a cylinder head 1D covering the top of the cylinder block 1E, a head cover 1C covering the top of the cylinder head 1D, and a crankcase 1F covering the bottom of the cylinder block 1E. Cylinder 1A is formed in the cylinder block 1E. As shown in Figure 3, an oil pan 1G is attached to the bottom surface of the crankcase 1F. 【0027】 As shown in Figure 1, the engine body 1 has multiple exhaust ports 12 extending to the right from each cylinder 1A and multiple intake ports 11 extending to the left from each cylinder 1A. These ports 11 and 12 are formed in the cylinder head 1D. 【0028】 The exhaust port 12 opens onto the exhaust side surface 1H, which is the right side of the engine body 1. More specifically, the exhaust port 12 opens onto the portion of the exhaust side surface 1H that is formed by the cylinder head 1D, i.e., the right side surface 111H of the cylinder head 1D. There are three opening ends 12A of the exhaust port 12 formed on the exhaust side surface 1H, and the exhaust ports 12 extending from two cylinders 1A converge inside the engine body 1. The two cylinders 1A corresponding to the converged exhaust ports 12 are cylinders in which combustion is not continuous. Specifically, the engine E is controlled so that combustion occurs sequentially in the four cylinders 1A with timings shifted by 180° CA, and so that combustion does not occur continuously in two adjacent cylinders 1A. In this embodiment, the combustion of the second cylinder 1A and the third cylinder 1A from the front is not continuous, and the exhaust ports 12 of these two cylinders 1A converge inside the engine body 1 to form a single exhaust port 12 that opens onto the exhaust side surface 1H. Hereinafter, the open end 12A of the exhaust port 12 formed on the exhaust side surface 1H will be referred to as the exhaust port open end 12A. Each exhaust port 12 branches into two ports on the upstream side in the direction of exhaust flow, i.e., on the cylinder 1A side, and two open ends of the exhaust port 12 are formed on the cylinder side for each cylinder 1A. 【0029】 The three exhaust port openings 12A are arranged in the front-to-back direction. Hereafter, the frontmost exhaust port opening 12A will be referred to as the first opening 121A, the central exhaust port opening 12A will be referred to as the second opening 122A, and the rearmost exhaust port opening 12A will be referred to as the third opening 123A. 【0030】 The three exhaust port openings 12A are located in close proximity in the front-rear direction. In this embodiment, the three exhaust port openings 12A are formed within the range occupied by the two central cylinders 1A (the second and third cylinders 1A from the front) in the front-rear direction. Specifically, if we define the center line X1 as the line extending left and right through the front-rear center point of the region where the four cylinders 1A are formed, and passing through the front-rear center point of the two central cylinders 1A, then the second opening 122A is located on the center line X1. The first opening 121A is located slightly forward of the center line X1. The third opening 123A is located slightly behind the center line X1. Here, the center line X1 substantially coincides with a line extending left and right through the front-rear center of the engine body 1 (cylinder head 1D) and the exhaust side surface 1H, and the three exhaust port openings 12A are formed in the central portion of the exhaust side surface 1H in the front-rear direction. 【0031】 The first open end 121A is the open end of the exhaust port 12 that communicates with the foremost cylinder 1A, and this exhaust port 12 is greatly curved diagonally to the right and rear from cylinder 1A. The second open end 122A is the open end of the exhaust port 12 that communicates with the second and third cylinders 1A from the front, and the exhaust port 12 extending from the second cylinder 1A from the front extends diagonally to the right and rear from cylinder 1A toward the second open end 122A, and the exhaust port 12 extending from the third cylinder 1A from the front extends diagonally to the right and forward from cylinder 1A toward the second open end 122A. The third open end 123A is the open end of the exhaust port 12 that communicates with the rearmost cylinder 1A, and this exhaust port 12 is greatly curved diagonally to the right and forward from cylinder 1A. 【0032】 The exhaust passage 2 is attached to the exhaust side surface 1H in a manner that communicates with each exhaust port opening end 12A. The structure of the exhaust passage 2 will be described later. 【0033】 The intake port 11 opens on the left side of the engine body 1. The intake passage 3 includes an intake manifold 31 for distributing intake air to each cylinder 1A. The intake passage 3 is fixed to the right side of the engine body 1 such that the intake manifold 31 communicates with the opening ends of each intake port 11. Note that the portion of the intake passage 3 upstream of the intake manifold 31 in the direction of intake air flow is not shown in the illustration. 【0034】 The EGR passage 4 is a passage for recirculating EGR gas, which is a portion of the exhaust gas flowing through the exhaust passage 2, to the intake passage 3, and connects the exhaust passage 2 and the intake passage 3. A portion of the EGR passage 4 is formed inside the engine body 1. That is, the EGR passage 4 includes a second EGR passage 42 formed inside the engine body 1, a first EGR passage 41 connecting the second EGR passage 42 and the exhaust passage 2, and a third EGR passage 43 connecting the second EGR passage 42 and the intake passage 3. Hereafter, the flow direction of the EGR gas from the exhaust passage 2 to the intake passage 3 will be simply referred to as the flow direction of the EGR gas. 【0035】 The second EGR passage 42 is formed in the cylinder head 1D. As shown in Figure 1, the second EGR passage 42 is formed to extend from left to right at the rear end of the cylinder head 1D. The right end of the second EGR passage 42, which is the upstream end in the direction of EGR gas flow, opens to the rear end of the right side surface 111H of the cylinder head 1D, which is the portion of the exhaust side surface 1H that is made up of the cylinder head 1D. The left end of the second EGR passage 42, which is the downstream end in the direction of EGR gas flow, opens to the left end of the rear side surface of the cylinder head 1D. 【0036】 As shown in Figure 2, etc., the first EGR passage 41 is located to the right of the right side surface 111H of the cylinder head 1D and communicates with the upstream opening end in the EGR gas flow direction of the second EGR passage 42 formed on the right side surface 111H. The first EGR passage 41 connects the upstream opening end of the second EGR passage 42 to the second connecting passage 7 of the exhaust passage 2, which will be described later. The second connecting passage 7 is located lower than the upstream opening end of the second EGR passage 42, and the second EGR passage 42 communicates with the upstream opening end of the second EGR passage 42 at its upper end, and extends downward from that opening end and connects to the second connecting passage 7 at its lower end. In detail, as shown in Figures 1 and 4, etc., the first EGR passage 41 extends to the right from the opening end and then extends diagonally downward and forward. 【0037】 A block-shaped EGR mounting member 43A is attached to the rear side of the cylinder head 1D, with a passage formed on its inside that communicates with the second EGR passage 42. The third EGR passage 43 is connected to this EGR mounting member 43A in a manner that it communicates with the passage inside it. The third EGR passage 43 extends upward from the EGR mounting member 43A, then extends forward, and is connected to the portion of the intake passage 3 upstream of the intake manifold 31 in the direction of intake airflow (not shown). An EGR cooler 43B for cooling the EGR gas is provided in the middle of the third EGR passage 43. 【0038】 (Detailed structure of the exhaust passage) Next, the detailed structure of the exhaust passage 2 will be described. Figure 5 is an enlarged cross-sectional view of a portion of the cross-section along line VV in Figure 3. Figure 6 is an enlarged cross-sectional view of a portion of the cross-section along line VI-VI in Figure 3. Figure 7 is an enlarged cross-sectional view of a portion of the cross-section along line VII-VII in Figure 5. In the following description of the exhaust passage 2, the upstream and downstream sides in the direction of exhaust flow will be simply referred to as the upstream side and the downstream side, respectively. 【0039】 The exhaust passage 2 includes a catalytic converter 6 and a filter 8. The filter 8 is located downstream of the catalytic converter 6. The exhaust passage 2 includes a first connecting passage 5 connecting each exhaust port opening end 12A to the upstream end of the catalytic converter 6, a second connecting passage 7 connecting the downstream end of the catalytic converter 6 to the upstream end of the filter 8, and a third connecting passage 9 extending downstream from the downstream end of the filter 8. 【0040】 The catalytic converter 6 is a device that purifies exhaust gas through the action of a catalyst. As shown in Figure 6, the catalytic converter 6 has a substantially cylindrical shape. Specifically, the catalytic converter 6 includes a substantially cylindrical catalyst case 61 and a substantially cylindrical catalyst body 62 arranged inside the catalyst case 61. In this embodiment, the catalyst body 62 is a monolithic catalytic converter and supports a three-way catalyst. 【0041】 The catalytic converter 6 is positioned on the right side of the exhaust side 1H in an orientation that extends in the front-rear direction (more specifically, in an orientation where its central axis extends in the front-rear direction). As shown in Figure 2, etc., the catalytic converter 6 is positioned lower than the exhaust port opening end 12A, i.e., at a height below the exhaust port opening end 12A, and is located to the right of the right side of the cylinder block 1E on the exhaust side 1H. As shown in Figure 3, etc., in this embodiment, the catalytic converter 6 is positioned in close proximity to the exhaust side 1H. 【0042】 The first connection passage 5 communicates with the front end surface of the catalyst device 6 and connects the front end of the catalyst device 6 to each exhaust port opening end 12A. The second connection passage 7 communicates with the rear end surface of the catalyst device 6 and connects the rear end of the catalyst device 6 to the filter 8. The exhaust gas that has passed through the first connection passage 5 flows into the catalyst device 6 from the front end surface and is led out to the second connection passage 7 from the rear end surface. Thus, in this embodiment, the front end of the catalyst device 6 constitutes the upstream end of the catalyst device 6, and the rear end constitutes the downstream end. 【0043】 The filter 8 is a device that collects particulate matter in the exhaust gas and thereby purifies the exhaust gas. As described above, the engine E in this embodiment is a gasoline engine, and the filter 8 is a so-called GPF (Gasoline Particulate Filter). As shown in Figure 6, etc., the filter 8 has a substantially cylindrical shape. Specifically, the filter 8 includes a substantially cylindrical filter case 81 and a substantially cylindrical filter body 82 arranged inside the filter case 81. In this embodiment, the filter body 82 is made of a ceramic filter having a honeycomb structure. As shown in Figure 3, etc., the filter 8 is positioned in a orientation that extends in the left-right direction (more specifically, in an orientation where its central axis extends in the left-right direction), on the right side of the exhaust side surface 1H and diagonally to the right rear of the catalytic converter 6. The filter 8 is positioned at a lower height than the exhaust port opening end 12A. 【0044】 As shown in Figure 6, the filter 8 is positioned in the region from near the center of the catalyst device 6 in the front-to-back direction to a position behind the catalyst device 6. Also, as shown in Figure 7, the height positions of the filter 8 and the catalyst device 6 are approximately the same. Thus, the front part of the filter 8 and the rear part of the catalyst device 6 overlap in the left-to-right direction. In this embodiment, approximately the front half of the filter 8 and approximately the rear half of the catalyst device 6 overlap when viewed in the left-to-right direction, i.e., along the left-to-right direction. 【0045】 The second connection passage 7 communicates with the left end face of the filter 8, and the third connection passage 9 communicates with the right end face of the filter 8. Exhaust air that has passed through the second connection passage 7 flows into the filter 8 from the left end face and is led out to the third connection passage 9 from the right end face of the filter 8. Thus, in this embodiment, the left end of the filter 8 constitutes the upstream end of the filter 8, and the right end constitutes the downstream end. 【0046】 (First connecting passage) The first connecting passage 5 includes a plurality of independent passages 51, a collection passage 52, and a swirling section 53. As described above, the first connecting passage 5 is a passage that connects each exhaust port opening end 12A to the catalytic converter 6. The catalytic converter 6 is positioned lower than each exhaust port opening end 12A. Therefore, the first connecting passage 5 extends upward from the catalytic converter 6. As shown in Figure 3 and other figures, in this embodiment, a part of the downstream portion of the collection passage 52 and the swirling section 53 are integrally formed. The swirling section 53 corresponds to the "connecting section" of the present invention. 【0047】 Each independent passage 51 is a passage that extends individually from each exhaust port opening end 12A and is fixed to the exhaust side surface 1H in communication with each exhaust port opening end 12A. In this embodiment, three independent passages 51 are provided in the exhaust passage 2 corresponding to the three exhaust port opening ends 12A. That is, as shown in Figure 5, the exhaust passage 2 has, as independent passages 51, a first independent passage 511 connected to the first opening end 121A, a second independent passage 512 connected to the second opening end 122A, and a third independent passage 513 connected to the third opening end 123A. The cross-sectional shapes of the three independent passages 511 to 513 are substantially the same and exhibit a roughly rectangular shape extending in the vertical direction. 【0048】 The three independent passages 51 (511-513) extend to the right from their respective opening ends 12A (121A-123A), and these independent passages 51 (511-513) are aligned in the front-to-back direction. As described above, the three exhaust port opening ends 12A (121A-123A) are formed in the central part of the exhaust side surface 1H in the front-to-back direction. Accordingly, the three independent passages 51 (511-513) extending from each exhaust port opening end 12A (121A-123A) are positioned close to each other, facing the central part of the exhaust side surface 1H in the front-to-back direction. Specifically, in this embodiment, as shown in Figure 5, the front-to-back gap between each independent passage 51 (511-513) is set to be smaller than the front-to-back dimension of these independent passages 51 (511-513). 【0049】 In detail, as shown in Figure 5 and other figures of the embodiment, the first independent passage 511 extends almost straight to the right from the first opening end 121A in a plan view (i.e., when viewed along the vertical direction). The upstream portions, i.e., the left portions, of the second independent passage 512 and the third independent passage 513 are slightly inclined diagonally forward to the right from the corresponding opening ends 122A and 123A in a plan view, while their downstream portions, i.e., the right portions, extend almost straight in the left-right direction in a plan view. The inclination angle of the upstream portion of the second independent passage 512 with respect to the left-right direction is smaller than that of the upstream portion of the third independent passage 513. Thus, although the inclination angles of the upstream portions of the three independent passages 511 to 513 with respect to the left-right direction differ, the difference is small, and the three independent passages 511 to 513 are arranged side by side in a nearly parallel position close to each other. 【0050】 As shown in Figures 3 and 4, the three independent passages 51 (511-513) have almost the same shape when viewed in the front-to-back direction and are configured to pass through almost the same location. Therefore, when viewed in the front-to-back direction, the three independent passages 51 (511-513) almost completely overlap each other. 【0051】 As shown in Figures 3 and 4, the three independent passages 51 (511-513) are curved so as to bulge upwards and to the right from the exhaust port opening end 12A (121A-213A) diagonally downwards. In other words, these independent passages 51 (511-513) are curved along an arc centered at a point located below the exhaust port opening end 12A (121A-213A) when viewed in the front-to-back direction. 【0052】 The catalyst device 6 is located below the three independent passages 51 (511-513), and as shown in Figure 5, etc., in a plan view, the catalyst device 6 and the three independent passages 51 (511-513) overlap. In this embodiment, almost the entirety of the three independent passages 51 (511-513) overlaps with the catalyst device 6. Specifically, the front end position of the first independent passage 511 is slightly in front of the front end position of the catalyst device 6, and the rear end position of the third independent passage 513 is approximately 1 / 3 of the total length of the catalyst device 6 in front of the rear end of the catalyst device 6, so that the three independent passages 51 (511-513) overlap with the front of the catalyst device 6 for approximately 2 / 3 of its total length. Note that, as shown in Figure 5, etc., the front-to-back gap between each of the independent passages 51 (511-513) is smaller than the front-to-back dimensions of these independent passages 51 (511-513). 【0053】 As shown in Figure 3, the collection passage 52 connects the three independent passages 51 and the swivel section 53 located below them. The collection passage 52 is connected to the common downstream ends of the three independent passages 51 and extends downward from these downstream ends. As shown in Figure 5, there is only one passage within the collection passage 52, and the exhaust gases that have passed through the three independent passages 51 are collected in the collection passage 52. The cross-section of the upper end, or upstream end, of the collection passage 52 is approximately rectangular in shape, extending in the front-to-back direction. On the other hand, as shown in Figure 6, the cross-section of the downstream portion of the collection passage 52 is approximately circular, the dimensions of the collection passage 52 in the front-to-back direction gradually decrease toward the downstream side, and the dimensions of the collection passage 52 in the left-to-right direction gradually increase toward the downstream side. 【0054】 As shown in Figure 3, the upstream passage 50, which is composed of three independent passages 51 and a collective passage 52, curves downward and to the right when viewed in the front-to-back direction. Specifically, the collective passage 52 curves downward and to the right. The curvature of the collective passage 52 and the curvature of each independent passage 51 are approximately the same when viewed in the front-to-back direction. The downstream end of each independent passage 51 opens diagonally downward to the right, and the upstream end of the collective passage 52 opens diagonally upward to the left. Also, when viewed in the front-to-back direction, the tangent to the upstream end of the collective passage 52 and the tangent to the downstream end of each independent passage 511 to 513 are approximately coincident. Thus, when viewed in the front-to-back direction, the three independent passages 51 and the collective passage 52 are smoothly connected, and the entire upstream passage 50 curves smoothly downward and to the right from the exhaust port opening end 12A. 【0055】 The swivel section 53 connects the upstream end of the catalyst device 6 to the downstream end of the collection passage 52. As shown in Figure 6, the swivel section 53 is located in front of the catalyst device 6 and covers the front end surface of the catalyst device 6 from the front. As shown in Figure 3, etc., the swivel section 53 has a substantially circular shape when viewed in the front-rear direction (i.e., when viewed along the front-rear direction) and has an inner circumferential surface that is substantially circular when viewed in the front-rear direction. In this embodiment, the central axis X2 extending in the front-rear direction of the swivel section 53 and the central axis X2 extending in the front-rear direction of the catalyst device 6 are substantially the same, and the outer diameter of the swivel section 53 and the outer diameter of the catalyst device 6 are substantially the same, and the swivel section 53 has a substantially bowl shape that extends forward from the outer peripheral edge of the front end of the catalyst device 6. Specifically, the rotating portion 53 includes a front end surface portion 53A that forms its front end surface and exhibits a substantially circular shape when viewed in the front-rear direction, and an outer peripheral portion 53B that extends in the front-rear direction from the outer peripheral edge of the front end surface portion 53A to the outer peripheral edge of the front end of the catalyst device 6, with the outer peripheral portion 53B gradually increasing in diameter toward the rear. 【0056】 Figure 8 is a cross-sectional view of the swivel section 53 along the line VIII-VIII in Figure 6, and is a cross-sectional view of the swivel section 53 in a plane extending in the front-rear and up-down directions along the central axis X2 of the swivel section 53. In the cross-sectional view shown in Figure 8, the distance between the inner circumferential surface of the swivel section 53 (specifically the rear surface of the front end surface 53A) and the front end surface 6A of the catalyst device 6 in the front-rear direction is smaller above (d1) the central axis X2 than below (d2). Specifically, a bulge 53F that bulges slightly to the rear is formed near the center of the front end surface 53A, and the maximum value of the distance d1 of the portion 53C above the bulge 53F of the swivel section 53 is set to be smaller than the minimum value of the distance d1 of the portion 53D below the bulge 53F. 【0057】 The upper portion 53C and the lower portion 53D of the swivel section 53 are both inclined diagonally downward and forward, so the swivel section 53 as a whole is inclined diagonally downward and forward. Mounting portions 91, 91 for attaching sensors are provided on the upper portion 53C and the lower portion 53D of the swivel section 53, respectively. In this embodiment, an O2 sensor is attached to the upper mounting portion 91 and a temperature sensor is attached to the lower mounting portion 91. As described above, each portion 53C and 53D is inclined diagonally downward and forward, and each mounting portion 91 extends diagonally upward and forward from the front end surface portion 53A. 【0058】 The swivel section 53 is configured to swivel the exhaust gas around an axis extending in the front-rear direction within its interior. 【0059】 Specifically, the downstream end of the converging passage 52, that is, the downstream end of the upstream passage 50, is in communication with the lower part of the right side of the swivel section 53. In this embodiment, the area between the lower end of the right side of the swivel section 53 and a position approximately 1 / 4 of the diameter of the swivel section 53 below its upper end is in communication with the downstream end of the upstream passage 50. Thus, the upstream passage 50 extends to the right from the lower part of the right side of the swivel section 53 and curves to bulge to the right as described above. Therefore, in a view in the front-rear direction, the upstream passage 50 and the swivel section 53 are smoothly connected, and the upstream passage 50 extends in a substantially arc shape along the inner circumferential surface on the lower side of the swivel section 53, near the connection point between the swivel section 53 and the converging passage 52. 【0060】 As described above, the downstream end of the upstream passage 50 (the downstream end of the collection passage 52) is in communication with the lower part of the swirling section 53, so that the exhaust that has passed through the upstream passage 50 is introduced into the lower part of the swirling section 53. From there, as shown by arrow Y0 in Figure 7, the exhaust flows into the swirling section 53 along the lower inner circumferential surface of the swirling section 53 and swirls around the central axis X2 of the swirling section 53 along that inner circumferential surface. 【0061】 Here, as described above, the swirling section 53 is located in front of the catalytic converter 6, and the catalytic converter 6 extends rearward from the swirling section 53. Accordingly, as shown in Figure 3 and other figures, in a front-to-back view, the upstream passage 50 is arranged to extend from the right side of the catalytic converter 6 to the left, then pass over the catalytic converter 6 and extend to the right. Thus, the catalytic converter 6 is surrounded by the exhaust side 1H and the upstream passage 50. Specifically, the catalytic converter 6 is located below and to the left of the upstream passage 50, and the catalytic converter 6 and the upstream passage 50 overlap in a plan view as shown in Figure 5 and other figures, as well as in a left-to-right view as shown in Figure 2. 【0062】 (Second connecting passage) As shown in Figure 5, the second connecting passage 7 extends diagonally to the right and rearward from the downstream portion, i.e., the rear portion, of the catalyst device 6 toward the left end face of the filter 8, connecting the rear portion of the catalyst device 6 with the left end of the filter 8. As shown in Figure 6, the downstream portion of the catalyst device 6, specifically its downstream end and the portion upstream thereof, is inserted into the second connecting passage 7, and the second connecting passage 7 connects the downstream portion of the catalyst device 6 to the filter 8 while accommodating it. 【0063】 Specifically, as shown in Figures 5 and 6, the rear portion of the second connection passage 7 (hereinafter referred to as the second connection rear portion 71 as appropriate) extends from the rear portion of the outer peripheral edge of the upstream end (left end) of the filter 8 toward the downstream end (rear end) of the catalyst device 6, covering the rear portion of the filter 8 from the left and covering the catalyst device 6 from the rear. The second connection rear portion 71 is approximately 1 / 4 spherical (a shape obtained by further dividing a hemisphere into two equal parts by a plane passing through the center), and in a plan view, the rear edge of the second connection rear portion 71 is inclined diagonally to the rear right. The front portion of the second connection passage 7 (hereinafter referred to as the second connection front portion 72 as appropriate) extends to the right from the outer peripheral surface of the catalyst device 6 toward the front portion of the filter 8. As shown in Figure 6, the second connection front portion 72 connects the outer peripheral surface in front of (upstream of) the rear end (downstream end) of the catalyst device 6 to the upstream end (left end) of the filter 8. The overlapping portions of the filter 8 and the catalyst device 6 in a left-right view, specifically the front of the filter 8 and the rear of the catalyst device 6, are facing each other in the left-right direction inside the second connecting front portion 72. In the left-right direction, the extension of the second connecting passage 7 to the right from the catalyst device 6 is short, and the filter 8, located downstream of the second connecting passage 7, is in close proximity to the catalyst device 6. Consequently, as shown in Figure 7, the filter 8 and the collection passage 52 overlap in the front-to-back view. In this embodiment, the upper left portion of the filter 8 and the downstream portion of the upstream passage 50 overlap in the front-to-back view. 【0064】 The lower end of the first EGR passage 41 (the upstream end in the direction of EGR gas flow) is connected to the rear side of the second connecting passage 7, and the first EGR passage 41 extends upward from the rear side. In this embodiment, a portion of the exhaust gas introduced into the second connecting passage 7 after passing through the catalyst device 6 is recirculated as EGR gas to the intake passage 3 through the first EGR passage 41 and the EGR passage 4. 【0065】 As shown in Figure 6, in this embodiment, a shielding plate 78 is provided at a position inside the second connection passage 7 facing the lower end of the first EGR passage 41. The shielding plate 78 is intended to prevent metal powder and the like contained in the exhaust gas from flowing into the EGR passage 4, that is, to prevent so-called contamination from occurring in the EGR passage 4. The exhaust gas discharged from the catalyst device 6 is configured to flow around the shielding plate 78 into the first EGR passage 41. Specifically, the shielding plate 78 is plate-shaped and extends substantially parallel to the rear side surface of the second connection passage 7, and is fixed to the inner circumferential surface of the second connection passage 7 in contact with it at a position upstream (in the direction of exhaust gas flow) from the position facing the downstream end of the first EGR passage 41. The cylindrical member 79A provided in the second connection passage 7 as shown in Figure 5, etc., is a member to which a pipe for guiding the exhaust gas to a differential pressure sensor is attached. The opening formed in the second connection passage 7, denoted by reference numeral 79B, is an opening for attaching a sensor. 【0066】 (Third connecting passage) As shown in Figure 1, the third connection passage 9 extends to the right from the right end of the filter 8. In this embodiment, the third connection passage 9 extends slightly to the right from the right end of the filter 8, then diagonally forward to the right, and then extends to the right. As shown in Figure 5, the third connection passage 9 is also provided with a cylindrical member 99A for attaching a pipe to guide the exhaust gas to the differential pressure sensor, similar to the second connection passage 7. 【0067】 (Cover component) In this embodiment, the first connection passage 5, the catalyst device 6, the second connection passage 7, and the filter 8 are integrally enclosed by the exhaust cover 22. The first EGR passage 41 is enclosed by the EGR cover 400. These covers 22 and 400 will be described below. Figure 9 is a diagram corresponding to Figure 2 and is a schematic side view of the engine E with the exhaust cover 22 and EGR cover 400 installed. Figure 10 is an enlarged view of a portion of the bottom view of the engine E with the exhaust cover 22 and EGR cover 400 installed. Figure 11 is an enlarged view of a portion of the cross section near line VII-VII in Figure 5 and is a cross-sectional view of the engine with the exhaust cover 22 and EGR cover 400 installed. 【0068】 The exhaust cover 22 surrounds almost the entire upstream passage 50 (first connection passage 5 and swirl section 53), the catalytic converter 6, the second connection passage 7, and the filter 8, as well as the area near the upstream end of the third connection passage 9. Hereinafter, the upstream passage 50, the catalytic converter 6, the second connection passage 7, and the filter 8, and the area near the upstream end of the third connection passage 9 surrounded by the exhaust cover 22 will be referred to as the exhaust module 20. The exhaust cover 22 has a shape that is almost parallel to the outer surface of the exhaust module 20. Brackets for supporting the exhaust module 20 on the engine body 1 are attached to the exhaust module 20, as will be described later. The exhaust cover 22 surrounds almost the entire area of ​​the outer surface of the exhaust module 20, excluding the areas where sensors such as the O2 sensor are attached and where the brackets are attached. 【0069】 The exhaust cover 22 is composed of multiple cover members. In this embodiment, the exhaust cover 22 consists of six cover members (first cover 221, second cover 222, third cover 223, fourth cover 224, fifth cover 225, and sixth cover 226). 【0070】 As shown in Figures 9 and 10, the first cover 221 primarily covers the front of the first connection passage 5 from above, below, and in front. The second cover 222 is located behind the first cover 221 and primarily covers the left rear portion of the first connection passage 5 from above and in rear. The third cover 223 is located behind the first cover 221 and to the right of the second cover 222 and primarily covers the right rear portion of the first connection passage 5 from above and in rear. The fourth cover 224 is located to the right and behind the third cover 223 and covers the rear of the catalyst unit 6 and the second connection passage 7 from above, as well as the area near the upstream end of the filter 8 and the third connection passage 9 from above, to the right, and in front. The fifth cover 225, as shown in Figure 10, covers almost the entire exhaust module 20 from below. The sixth cover 226 is positioned between the fifth cover 225 and the second and third covers 222 and 223, and as shown in Figure 11, it mainly covers the catalyst device 6 from the left and the upstream portion of the first connection passage 5 from below. Adjacent covers 221 to 206 are connected to each other, and as described above, these first to sixth covers 221 to 206 cover almost the entire exhaust module 20. 【0071】 As shown in Figure 9, the EGR cover 400 has a cylindrical shape that houses the first EGR passage 41 inside. In this embodiment, the first EGR passage 41 is almost entirely surrounded by the EGR cover 400. 【0072】 (Support structure) The exhaust module 20 is supported by the cylinder head 1D by a first connection passage 5 and a first EGR passage 41 contained within it. The exhaust module 20 is also supported by the cylinder block 1E by a rear bracket 25 and a lower bracket 26. The support structure of the exhaust module 20 will be described below. 【0073】 As shown in Figure 5, the upstream ends of the three independent passages 51 are connected to each other by an independent passage mounting flange 24. The independent passage mounting flange 24 is plate-shaped. Each independent passage 51 is fixed to the independent passage mounting flange 24 in a position extending in the direction of its plate thickness. For example, the upstream end of each independent passage 51 is fixed to the independent passage mounting flange 24 by welding. The independent passage mounting flange 24 is fixed to the right side surface 111H of the cylinder head 1D by bolts, and the three independent passages 51 are fixed to the right side surface 111H of the cylinder head 1D via the independent passage mounting flange 24. Thus, in this embodiment, the exhaust module 20 is supported by the cylinder head 1D by fixing the three independent passages 51, i.e., the first connecting passage 5, to the right side surface 111H of the cylinder head 1D. The independent passage mounting flange 24 is fixed to the vicinity of the center in the front-rear direction of the right side surface 111H of the cylinder head 1D. 【0074】 As described above, the lower end of the first EGR passage 41 is connected to the rear side surface of the second connecting passage 7. For example, the lower end of the first EGR passage 41 is fixed to the rear side surface of the second connecting passage 7 by welding. As shown in Figure 4, a plate-shaped EGR mounting flange 41A is fixed to the upper end of the first EGR passage 41. The first EGR passage 41 is fixed to the EGR mounting flange 41A in a position extending from the EGR mounting flange 41A in the direction of its plate thickness. For example, the upper end of the first EGR passage 41 is fixed to the EGR mounting flange 41A by welding. The EGR mounting flange 41A is fixed to the right side surface 111H of the cylinder head 1D by bolts, thereby supporting the first EGR passage 41 and, consequently, the exhaust module 20, on the right side surface 111H of the cylinder head 1D. In this embodiment, the EGR mounting flange 41A is fixed to the rear end of the right side surface 111H of the cylinder head 1D. 【0075】 As shown in Figure 6, the rear bracket 25 is composed of two brackets (first rear bracket 25A and second rear bracket 25B). The first rear bracket 25A is roughly plate-shaped. The first rear bracket 25A is fixed to the rear side surface of the second connection passage 7 by welding or the like, in a position that extends rearward from the rear side surface of the second connection passage 7. As shown in Figure 2, the first rear bracket 25A extends rearward from near the vertical center of the rear side surface of the second connection passage 7. As shown in Figure 6, the first rear bracket 25A is positioned to the right of the exhaust side surface 1H. The second rear bracket 25B extends horizontally across the first rear bracket 25A and the exhaust side surface 1H. The right end of the second rear bracket 25B is fixed to the rear end of the first rear bracket 25A by a bolt. The left end of the second rear bracket 25B is fixed to the exhaust side surface 1H by a bolt. Specifically, a boss 115 protruding to the right is provided near the upper and lower center of the rear end of the portion of the exhaust side 1H that is formed by the cylinder block 1E, on the right side of the cylinder block 1E. The left end of the second rear bracket 25B is fixed to this boss 115 by bolts. In this way, the second connection passage 7 and thus the exhaust module 200 are supported on the right side of the cylinder block 1E via the rear bracket 25. 【0076】 As shown in Figure 3, the lower bracket 26 is composed of two brackets (first lower bracket 26A and second lower bracket 26B). The first lower bracket 26A is roughly plate-shaped. The first lower bracket 26A is fixed to the lower surface of the exhaust module 20 by welding or the like, in a position that extends rearward from the lower surface of the exhaust module 20. As shown in Figure 7, the first lower bracket 26A is fixed to the lower surface of the catalyst device 6, the lower surface of the second connection passage 7, and the lower surface of the filter 8, respectively, and extends downward from these lower surfaces. The first lower bracket 26A is positioned spaced to the right of the exhaust side surface 1H. As shown in Figure 3, the second lower bracket 26B extends in the left-right direction across the first lower bracket 26A and the exhaust side surface 1H. The right end of the second lower bracket 26B is fixed to the lower end of the first lower bracket 26A by bolt. The left end of the second lower bracket 26B is fixed to the exhaust side surface 1H by bolt. Specifically, a boss 116 protruding to the right is provided on the right side of the cylinder block 1E, near the center in the front-to-back and vertical directions of the portion of the exhaust side 1H that is formed by the cylinder block 1E. The left end of the second lower bracket 26B is fixed to this boss 116 by bolts. In this way, the exhaust module 200 is supported on the right side of the cylinder block 1E via the lower bracket 26. 【0077】 (effect, etc.) As described above, in the engine exhaust structure according to the above embodiment, the upstream passage 50, which constitutes the exhaust passage upstream of the catalytic converter 6, has a curved shape that bulges downward to the right from the exhaust port opening end 12A. Furthermore, the catalytic converter 6 is positioned below each exhaust port opening end 12A and is located between the exhaust side surface 1H and the upstream passage 50, in a position that overlaps with the upstream passage 50 in both a plan view and a left-right view. Therefore, early warm-up and heat retention of the catalytic converter 6 can be promoted. In other words, with the above structure, the catalytic converter 6 is surrounded by the engine body 1 and the upstream passage 50, so that heat absorption from the engine body 1 and the upstream passage 50 to the catalytic converter 6 can be promoted, and heat dissipation from the catalytic converter 6 can be suppressed, thereby keeping it warm. 【0078】 In particular, the upstream passage 50 includes three independent passages 51 (511-513) that are individually connected to the exhaust port opening end 12A and arranged front to back, and the catalytic converter 6 is positioned below these independent passages 51 (511-513) so as to overlap them in a plan view. As a result, the catalytic converter 6 can be covered from above over a wider area in the front-to-back direction by the three independent passages 51 (511-513). Consequently, heat transfer from the engine body 1 and the upstream passage 50 to the catalytic converter 6 and the heat retention of the catalytic converter 6 can be reliably promoted. 【0079】 Furthermore, because the catalytic converter 6 is positioned to extend in the front-rear direction, it is not necessary to space the catalytic converter 6 away from the exhaust side surface 1H in the left-right direction in order to install the exhaust passage extending from the catalytic converter 6, and the catalytic converter 6 can be brought closer to the engine body 1. Specifically, in the above embodiment, the second connecting passage 7 extends from the downstream end of the catalytic converter 6, which opens to the rear, diagonally to the rear right, that is, away from the engine body 1. Therefore, the catalytic converter 6 can be brought closer to the exhaust side surface 1H without being obstructed by the second connecting passage 7. Accordingly, according to the above embodiment, heat transfer from the engine body 1 to the catalytic converter 6 and heat retention of the catalytic converter 6 can be promoted more reliably. 【0080】 As described above, the exhaust structure of the engine according to the above embodiment promotes heat transfer from the engine body 1 and the upstream passage 60 to the catalytic converter 6 and maintains the temperature of the catalytic converter 6. This allows the catalytic converter 6 to heat up quickly during engine E startup, thereby improving its purification performance early on. It also prevents a decrease in the purification performance due to a drop in the temperature of the catalytic converter 6, thereby improving the exhaust performance of the engine E. 【0081】 Furthermore, in the above embodiment, the three exhaust port openings 12A are formed in the central part of the exhaust side surface 1H in the front-rear direction. That is, these exhaust port openings 12A are located close together. Therefore, the three independent passages 51 (511-513) connected to them can be placed close together, and the amount of heat dissipated from these independent passages 51 (511-513) can be kept to a minimum. Accordingly, according to the above embodiment, the temperature of the exhaust gas flowing into the catalyst device 6 can be increased, and the heating and heat retention of the catalyst device 6 can be further promoted. 【0082】 Furthermore, in the above embodiment, a swivel section 53 connecting the upstream end of the catalyst device 6 and the downstream end of the collection passage 52, i.e., the downstream end of the upstream passage 50, is provided in front of the catalyst device 6 so as to cover the catalyst device 6 from the front, and the downstream end of the upstream passage 50 is connected to the right side of the swivel section 53. 【0083】 If the downstream end of the upstream passage 50 were to be connected to the front or left side of the swivel section 53, the upstream passage 50 would need to be routed in front of or to the left of the swivel section 53, increasing its length. In contrast, the configuration described in the above embodiment allows for a shorter length of the upstream passage 50, thereby suppressing heat dissipation from the exhaust gas in the upstream passage 50. Therefore, according to the above embodiment, the catalytic converter 6 can reliably introduce high-temperature exhaust gas. 【0084】 Furthermore, in the above embodiment, the swirling section 53 has an inner circumferential surface that is substantially circular when viewed in the front-rear direction. Therefore, as described above, and as shown by arrow Y0 in Figure 7, the exhaust gas can be swirled around the central axis X2 of the swirling section 53. Consequently, the exhaust gas can be diffused within the swirling section 53 and uniformly introduced into the catalytic converter 6, thereby increasing the exhaust gas purification efficiency of the catalytic converter 6. 【0085】 In particular, in the above embodiment, the entire upstream passage 50 is smoothly curved so as to bulge downward to the right from the exhaust port opening end 12A, and the downstream end of the upstream passage 50 is connected to the lower part of the right side of the swirling section 53. As a result, a flow path is realized in which the entire flow path from each exhaust port opening end 12A to the swirling section 53 extends in an arc shape along the inner circumferential surface near the connection point between the swirling section 53 and the upstream passage 50. Therefore, as shown by arrows Y1 and Y2 in Figure 12, the exhaust gases discharged from each exhaust port opening end 12A can be allowed to flow into the swirling section 53 more smoothly and, consequently, more vigorously. Consequently, the swirling and diffusion of the exhaust gases in the swirling section 53 can be promoted, and the exhaust gases can be uniformly introduced by the catalyst device 6 to improve their purification performance. 【0086】 Furthermore, in the above embodiment, a collection passage 52 is provided in the upstream passage 50, which is connected to the downstream end of each independent passage 51 (511-513) and collects the exhaust gases that have passed through them. As a result, the inflow path of the exhaust gases that flow into the swirling section 53 through each independent passage 51 (511-513) can be made equal, and variations in the inflow of exhaust gases into the catalytic converter 6 among each independent passage 51 (511-513) and thus between cylinders 1A can be reduced. Consequently, exhaust gases can be uniformly introduced into the catalytic converter 6 for all cylinders 1A, and the purification performance of the engine E can be reliably improved. 【0087】 Furthermore, in the above embodiment, the filter 8 is positioned to the right of the catalyst device 6, overlapping with the catalyst device 6 in a left-right view and overlapping with the upstream passage 50 in a front-back view. In other words, the filter 8 is positioned in close proximity to the catalyst device 6 and the upstream passage 50. Therefore, the filter 8 can be warmed by the heat emitted from the catalyst device 6 and the upstream passage 50. 【0088】 Furthermore, in the above embodiment, the entire exhaust module 20, including the upstream passage 50 (first connection passage 5 and swirling section 53), the catalyst device 6, the second connection passage 7 and the filter 8, and the vicinity of the upstream end of the third connection passage 9, is enclosed by a common exhaust cover 22. As a result, heat exchange between these devices, and consequently heat reception from the upstream passage 50 of the catalyst device 6 and the filter 8, can be further promoted, thereby raising their temperature. 【0089】 (modified version) In the above embodiment, the case in which the exhaust ports 12 corresponding to the two cylinders 1A converge inside the cylinder head 1D was described. However, the exhaust ports extending from each cylinder 1A may be individually opened on the exhaust side surface 1H without converging the exhaust ports 12 at the cylinder head 1D. Furthermore, the exhaust port opening end 12A may be provided at a position off-center from the front-to-rear center of the exhaust side surface 1H. 【0090】 In the above embodiment, the upstream passage 50 and the swirling section 53 were described in such a way that the distance between their inner circumferential surface and the front end surface 6A of the catalyst device 6 in the front-rear direction is smaller above (d1) the central axis X2 than below (d2). However, the specific shape of the swirling section 53 is not limited to this. Also, in the above embodiment, the swirling section 53 connecting the upstream end of the catalyst device 6 and the downstream end of the upstream passage 50 was described in such a way that it has the function of swirling the exhaust gas. However, the swirling section 53 does not have to have this swirling function. Furthermore, the swirling section 53 does not have to have an inner circumferential surface that is substantially circular when viewed in the front-rear direction. Also, the position to which the downstream end of the upstream passage 50 is connected is not limited to the right side of the swirling section 53. 【0091】 In the above embodiment, a converging passage 52 is provided in the upstream passage 50, and the three independent passages 51 (511 to 513) converge at the converging passage 52, with the downstream end of the converging passage 52 connected to the swing section 53. However, the converging passage 52 may be omitted, and each independent passage 51 (511 to 513) may be connected individually to the swing section 53. 【0092】 In the above embodiment, the case where the engine E has four cylinders was described, but the number of cylinders is not limited to this. Also, the engine E is not limited to a gasoline engine. Furthermore, the catalytic converter 6 can be any device that purifies exhaust gases by the action of a catalyst, and is not limited to a monolithic catalytic converter. Furthermore, the catalyst supported by the catalytic converter body 62 is not limited to a three-way catalytic converter. Furthermore, the filter 8 can be any device that captures particulate matter in the exhaust gases, and is not limited to a ceramic filter having a honeycomb structure. [Explanation of Symbols] 【0093】 1. Engine body 1A cylinder 1H Exhaust side (the exhaust side of the engine block) 2 Exhaust passage 6. Catalytic converter 8 filters 12 exhaust ports 12A Exhaust port opening end 50 Upstream passage 51 Independent passage 52 Gathering aisle 53. Swivel section (connection section)

Claims

[Claim 1] In an engine exhaust structure comprising an engine body having a plurality of cylinders arranged in a predetermined cylinder arrangement direction and a plurality of exhaust ports extending from each of the cylinders, and an exhaust passage through which exhaust gases led out from the engine body flow, When one side is designated as the exhaust side and the other as the intake side in the engine width direction perpendicular to the cylinder arrangement direction and the vertical direction, the exhaust side surface of the engine body has multiple exhaust port openings, which are the outlets of the exhaust ports, opening along the cylinder arrangement direction. The exhaust passage comprises an upstream passage extending from each of the exhaust port opening ends, and a cylindrical catalytic device provided at a position lower than each of the exhaust port opening ends for purifying the exhaust gas that has passed through the upstream passage. The upstream passage includes a plurality of independent passages arranged in parallel in the cylinder arrangement direction and individually connected to each of the exhaust port opening ends, and has a curved shape that bulges downward toward the exhaust side from each of the exhaust port opening ends. The exhaust structure of an engine, characterized in that the catalytic converter is positioned such that its central axis extends along the cylinder arrangement direction, and is located between the exhaust-side surface of the engine body and the upstream passage, overlapping with each of the independent passages when viewed in the vertical direction, and overlapping with the upstream passage when viewed in the engine width direction. [Claim 2] In the exhaust structure of the engine according to claim 1, An engine exhaust structure characterized in that each of the aforementioned exhaust port opening ends is formed in the central portion of the exhaust-side surface of the engine body in the direction of cylinder arrangement. [Claim 3] In the exhaust structure of the engine according to claim 1, The exhaust passage covers the upstream end of the catalytic converter in the exhaust flow direction from one side in the cylinder arrangement direction and has a connecting portion that connects the upstream end of the catalytic converter to the downstream end of the upstream passage. An engine exhaust structure characterized in that the downstream end of the upstream passage is connected to the exhaust side of the connection portion. [Claim 4] In the exhaust structure of the engine according to claim 3, The exhaust structure of an engine is characterized in that the connecting portion has an inner circumferential surface that is substantially circular when viewed along the cylinder arrangement direction. [Claim 5] In the exhaust structure of the engine according to claim 4, The upstream passage has a collection passage connected to the downstream end of each of the independent passages, where the exhaust gas that has passed through the independent passages is collected. An engine exhaust structure characterized in that the connecting portion is connected to the downstream end of the collection passage. [Claim 6] In the exhaust structure of the engine according to claim 1, The exhaust passage has a filter that collects particulate matter contained in the exhaust gas that has passed through the catalytic converter. The engine exhaust structure is characterized in that the filter is positioned on the exhaust side of the catalytic converter, overlapping with the catalytic converter when viewed along the engine width direction, and overlapping with the upstream passage when viewed along the cylinder arrangement direction. [Claim 7] In the exhaust structure of an engine according to any one of claims 1 to 6, An engine exhaust structure characterized by comprising a cover that integrally encloses at least a portion of the catalytic converter and at least a portion of the upstream passage.

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