JP2009209878A - Exhaust system for internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve a valve housing of a flow passage switching valve in which a bypass catalytic converter that purifies exhaust immediately after cold starting can be arranged on further upstream side. <P>SOLUTION: The flow passage switching valve 4 is arranged at a gathering section where four upstream side main passages connected to respective cylinders gather as a downstream side main passage. A bypass passage diverges from each of the upstream side main passages and bypass catalytic converters are installed in midway. When the flow passage switching valve 4 is closed, the main flow passage is blocked and the upstream side main passage of each cylinder is disconnected from each other. The flow passage switching valve 4 is provided with the valve housing 21 and a valve body 26, and four valve ports 22 that gather with each other are integrally formed on the valve housing 21 by casting. A center hole 37 that extends in the port longitudinal direction of the valve ports 22 is formed on a center thick section 36 surrounded by four valve ports 22 in a way that it intersects a seal surface 25 in order to equalize the thickness D of the periphery of each valve port 22 in the circumferential direction. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention is directed to an exhaust system for an internal combustion engine that performs exhaust purification with a catalytic converter, and in particular, to guide exhaust to the bypass flow path side provided with another catalytic converter immediately after a cold start when the main catalytic converter is not activated. It relates to the improvement of the exhaust system of the type.

  As conventionally known, in a configuration in which the main catalytic converter is disposed relatively downstream of the exhaust system such as under the floor of a vehicle, the temperature of the catalytic converter rises and is activated after a cold start of the internal combustion engine. In the meantime, a sufficient exhaust purification action cannot be expected. On the other hand, the closer the catalytic converter is to the upstream side of the exhaust system, that is, the internal combustion engine side, the lower the durability due to thermal degradation of the catalyst.

  Therefore, the present applicant has previously proposed an exhaust device described in Patent Document 1. In this apparatus, a flow path switching valve is arranged at a junction where four upstream main passages connected to each cylinder gather as a downstream main passage. As bypass channels, an upstream bypass passage is branched from each of the upstream main passages, and a bypass catalytic converter is interposed in the middle of the downstream bypass passage. When the flow path switching valve is closed, the main flow path is shut off, and at the same time, the upstream main passages of the cylinders are in a non-communication state. The flow path switching valve has a valve base having four valve openings and a valve body. After processing the sealing surface and assembling the valve body, a metal pipe for the upstream main passage is welded to the partition wall of the valve base.

According to such an apparatus, it is possible to arrange the bypass catalytic converter more upstream, that is, at a position close to each cylinder, without being restricted by the position of the confluence of the main flow path generally configured as an exhaust manifold. Moreover, since the cooling action due to the heat capacity of the exhaust manifold or the like constituting the main flow path is reduced, the exhaust purification action can be obtained early after the cold start.
JP 2007-032414 A

  However, in the above-described conventional exhaust device, it is necessary to fix a separate metal pipe to the valve base by welding, and there is a problem that the number of parts and the number of manufacturing steps increase. Therefore, instead of the above metal pipe, it may be possible to integrally form a plurality of valve ports by casting or the like in the valve housing. In this case, for example, if four valve ports are assembled together, Among the partition walls, the central portion where the partition wall crosses in a cross shape inevitably becomes thicker than the other partition walls, and is likely to become high temperature. The thermal strain in the circumferential direction becomes non-uniform, and there is a concern that the sealing performance is lowered.

  The present invention has been made in view of such problems. That is, an exhaust system for an internal combustion engine according to the present invention includes an upstream main passage for each cylinder connected to each cylinder, a downstream main passage formed by joining the upstream main passages of a plurality of cylinders, and the upstream side And a flow path switching valve that opens and closes the main passage at the downstream end and blocks communication between the upstream main passages when the main passage is closed. More preferably, it has a main catalytic converter interposed in the downstream main passage or a downstream flow passage, and a bypass passage branched from the upstream main passage and having a bypass catalytic converter interposed therebetween. The flow path switching valve opens and closes the upstream main passage at the downstream end so that the exhaust discharged from each cylinder flows to the bypass passage. The flow path switching valve includes a valve housing integrally formed with a valve port for each cylinder to which an end of the upstream main passage of each cylinder is connected, and a valve seated on a seal surface surrounding the valve port The valve housing has a central thick wall portion surrounded by at least three valve ports that gather together so that the thickness around each valve port is uniform in the circumferential direction. A central hole extending in the longitudinal direction of the valve port is formed so as to cross the surface.

  According to the present invention, it is possible to dispose the bypass catalytic converter more upstream, that is, closer to each cylinder, without being restricted by the position of the confluence of the main flow path generally configured as an exhaust manifold. Since the cooling action due to the heat capacity of the exhaust manifold or the like constituting the flow path is reduced, the exhaust purification action can be obtained early after the cold start.

  And, by forming a plurality of valve ports in the valve housing, the number of parts and manufacturing man-hours can be greatly reduced compared to the case where separate metal pipes are fixed by welding as in the conventional example described above. And a central hole extending in the longitudinal direction of the port is formed so as to cross the sealing surface in the central thick part of at least three valve ports that can be assembled with each other. It is possible to increase the cooling effect of the central thick part while avoiding the deterioration of the sealing performance due to the distortion of the seal surface.

  Hereinafter, an embodiment in which the present invention is applied as an exhaust system for an in-line four-cylinder internal combustion engine will be described in detail with reference to the drawings. FIG. 1 is an explanatory view schematically showing the piping layout of the exhaust device. First, the configuration of the entire exhaust device will be described with reference to FIG.

  An upstream main passage 2 is connected to each cylinder 1 including # 1 cylinder to # 4 cylinder arranged in series. The four upstream main passages 2 individually connected to the four cylinders merge as one downstream main passage 3 at the downstream side, and in other words, the upstream main passage 2 A flow path switching valve 4 that opens and closes the four upstream main passages 2 at the same time is provided at a portion that becomes a boundary with the downstream main passage 3. The switching valve 4 is closed when it is cold, and when closed, the upper and lower communication between the upstream main passage 2 and the downstream main passage 3 is blocked and the four upstream main passages 2 are closed. It is the structure which is made into a mutually non-communication state between.

  A main catalytic converter 8 is interposed in the middle of the downstream main passage 3 extending downstream from the flow path switching valve 4. The main catalytic converter 8 has a large capacity arranged under the floor of the vehicle, and includes a three-way catalyst and an HC trap catalyst as the catalyst. The upstream main passage 2, the downstream main passage 3, and the main catalytic converter 8 constitute a main flow path through which exhaust flows during normal operation.

  As the main flow path, one downstream main passage 3 is provided for each of the pair of upstream main passages 2 so as to gather in a well-known “4-2-1” form in the in-line four-cylinder internal combustion engine. It is also possible to arrange the main catalytic converter 8 by merging the pair of downstream main passages 3 into one flow path. Also in this case, the flow path switching valve 4 is provided between the downstream main passage 3 so as to open and close the ends of the four upstream main passages 2.

  On the other hand, an upstream bypass passage 11 is branched from each of the upstream main passages 2 as bypass passages. The upstream bypass passage 11 has a sufficiently smaller passage cross-sectional area than the upstream main passage 2, and the branch point 12 serving as the upstream end of the upstream bypass passage 11 is set at a position as upstream as possible in the upstream main passage 2. Has been. The upstream bypass passage 11 of the # 1 cylinder and the upstream bypass passage 11 of the # 2 cylinder, which are adjacent to each other, merge with each other as a single intermediate bypass passage 14 at the merge point 13. The upstream bypass passage 11 of the # 3 cylinder and the upstream bypass passage 11 of the # 4 cylinder which are adjacent to each other join each other as a single intermediate bypass passage 14 at the junction 13. In FIG. 1 schematically showing each passage, each upstream bypass passage 11 is drawn relatively long, but in practice it is as short as possible. In other words, it merges as the intermediate bypass passage 14 with the shortest distance. The two intermediate bypass passages 14 join each other as one downstream bypass passage 16 at the junction 15. The downstream end of the downstream bypass passage 16 joins the downstream main passage 3 at a junction 17 upstream of the main catalytic converter 8 in the downstream main passage 3. In the middle of the downstream bypass passage 16, a bypass catalytic converter 18 using a three-way catalyst is interposed. The bypass catalytic converter 18 is disposed as upstream as possible in the bypass flow path. That is, the intermediate bypass passage 14 is as short as possible.

  In the above embodiment, four upstream bypass passages are used in order to shorten the passage length of the entire bypass passage (the sum of the bypass passages of each cylinder) and reduce the heat capacity of the pipe itself and the heat radiation area for the outside air. 11 are combined into two intermediate bypass passages 14 on the upstream side without being routed for a long time, but such a configuration is arbitrary, for example, when the bypass catalytic converter 18 is biased to one side of the cylinder row For example, the entire passage length can be shortened by connecting the upstream bypass passages of the remaining cylinders at substantially right angles to the upstream bypass passage extending linearly from the other end cylinder.

  The bypass catalytic converter 18 includes two monolith catalyst carriers, that is, a first catalyst 18a and a second catalyst 18b, which are divided in the front and rear directions. One end of the exhaust gas recirculation passage 20 is connected to the gap 19 between the first catalyst 18a and the second catalyst 18b. The other end of the exhaust gas recirculation passage 20 extends to the engine intake system via an exhaust gas recirculation control valve (not shown). That is, the gap 19 serves as a recirculation exhaust outlet. The bypass catalytic converter 18 has a small capacity as compared with the main catalytic converter 8, and a catalyst excellent in low temperature activity is desirably used.

  In the exhaust system configured as described above, at the stage where the engine temperature or the exhaust temperature after the cold start is low, the flow path switching valve 4 is closed via an appropriate actuator, and the main flow path is shut off. Therefore, the entire amount of exhaust discharged from each cylinder 1 flows from the branch point 12 to the bypass catalytic converter 18 through the upstream bypass passage 11 and the intermediate bypass passage 14. Since the bypass catalytic converter 18 is located upstream of the exhaust system, that is, close to the cylinder 1 and is small in size, the bypass catalytic converter 18 is activated quickly and exhaust purification is started at an early stage. At this time, the flow path switching valve 4 is closed, so that the upstream main passages 2 of the cylinders 1 are not in communication with each other. Therefore, a phenomenon in which the exhaust discharged from a certain cylinder wraps around the upstream main passage 2 of the other cylinder is prevented, and a decrease in the exhaust gas temperature due to this wraparound is surely avoided.

  On the other hand, when the engine warm-up proceeds and the engine temperature or the exhaust temperature becomes sufficiently high, the flow path switching valve 4 is opened. Thereby, the exhaust discharged from each cylinder 1 mainly passes through the main catalytic converter 8 through the upstream main passage 2 and the downstream main passage 3. At this time, the bypass flow path side is not particularly blocked, but the bypass flow path side has a smaller passage cross-sectional area than the main flow path side, and the bypass catalytic converter 18 is interposed. Most of the exhaust flow passes through the main flow path side and hardly flows into the bypass flow path side. Therefore, the thermal deterioration of the bypass catalytic converter 18 is sufficiently suppressed. In addition, since the bypass flow path side is not completely cut off, a part of the exhaust flow flows through the bypass flow path side at a high speed and high load where the exhaust flow rate becomes large, so that a reduction in charging efficiency due to back pressure can be avoided.

  Next, the structure of the flow-path switching valve 4 which is the principal part of this invention is demonstrated using FIGS. This example is provided with a pair of downstream main passages 3 so as to collect the exhaust system in the form of the well-known “4-2-1” in the in-line four-cylinder internal combustion engine described above. The pair of downstream main passages 3 merge into one passage further downstream.

  In this embodiment, the flow path switching valves 4 for four cylinders are integrated as one valve unit. The flow path switching valve 4 is mainly composed of a valve housing 21 formed integrally by casting. The valve housing 21 is formed with four valve ports 22 corresponding to the respective cylinders in two rows, that is, at the positions where the square apexes are formed, and these valve ports 22 are formed as valve bodies 26. Open and close from the upstream side. In the middle of the valve port 22, a sealing surface 25 that is in contact with the outer peripheral edge of the valve body 26 is machined. The sealing surface 25 has an inclined surface / tapered surface that gradually decreases in diameter from the upstream side toward the downstream side. A port upstream portion 23 on the upstream side of the seal surface 25 of each valve port 22 constitutes a downstream end portion of the main passage 3, and a valve at the open position is provided on the side wall of the port upstream portion 23. A recess 24 for accommodating the body 26 is formed. Further, the valve port 22 is provided with a tubular port downstream portion 29 that linearly extends from the lower end of the sealing surface 25 whose diameter is reduced to the downstream side.

  The valve body 26 is attached to the tip of an arm 28 that swings together with the rotary shaft 27, and the outer peripheral edge thereof has a tapered shape corresponding to the seal surface 25. As shown in FIG. 4, the rotating shaft 27 is common to two cylinders, and two valve bodies 26 are attached to one rotating shaft 27. Therefore, the flow path switching valve 4 as a whole is provided with two rotating shafts 27. The two rotary shafts 27 are driven by an actuator via an interlocking mechanism such as an appropriate link mechanism 27A (see FIGS. 2 and 3) and simultaneously open and close symmetrically. That is, the four valve bodies 26 open and close all at once. As shown in FIG. 5, in order to rotatably support the rotary shaft 27, bearing portions 31, 32, and 33 are integrally formed in the valve housing 21 at a total of three locations with respect to each rotary shaft 27. Yes.

  The four valve ports 22 are juxtaposed in parallel with each other while being gathered / closed to each other, and the partition wall portion 35 around the valve port 22 is substantially tented at a central thick portion 36 surrounded by the four valve ports 22. It is continuous and intersects with a letter shape. Therefore, the central thick portion 36 is partially thickened in the partition wall portion 35. Therefore, in the present embodiment, the longitudinal direction of the port of the valve port 22 extends across the central thick portion 36 so as to cross the seal surface 25 so that the thickness D of the partition wall portion 35 around the valve port 22 is made uniform in the circumferential direction. A central hole 37 is formed extending to the center. The central hole 37 is formed in a straight line in the longitudinal direction of the port of the valve housing 21 so that it can be easily formed during casting, and the cross-sectional shape thereof is set to be substantially circular. Furthermore, an appropriate recess 55 is formed in the valve housing 21 so that the wall thickness D of the partition wall 35 around the valve port 22 is made uniform in the circumferential direction.

  An upstream flange 43 having a predetermined thickness projecting in the radial direction is integrally cast on the valve housing 21, and the upstream flange 43 is fixed to a mounting flange 41 of the exhaust manifold 39 with bolts 42. The upstream end of the central hole 37 is opened in the upstream flange 43. Also, the exhaust manifold 39 is integrally formed with four exhaust branches 40 in which a part of the main upstream passage 2 is formed, and one end of these exhaust branches 40 is opened to the mounting flange 41. is doing. In this embodiment, the central hole 37 is closed by the mounting flange 41 of the exhaust manifold 39 as shown in FIG. However, a through hole 44 (see the broken line in FIG. 4) connected to the center hole 37 may be formed in the mounting flange 41 of the exhaust manifold 39. In this case, the center hole 37 is open both vertically and centrally. The cooling effect of the thick portion 36 can be further enhanced.

  The valve housing 21 is integrally cast with a passage joining portion 45 in which a part of the downstream main passage 3 where the plurality of port downstream portions 29 join together is formed. As shown in FIGS. 4 and 6, the center hole 37 is open to the space 46 between the plurality of tubular port downstream portions 29 such that the lower end thereof faces the upper surface 45 a of the passage merging portion 45. The passage joining portion 45 is provided with a downstream flange portion 50 fixed by a bolt 49 to a flange portion 48 of a bracket 47 in which a part of the downstream main passage 3 is formed. In order to shorten and simplify the piping, the bracket 47 is integrally cast with the downstream bypass passage 16 that joins the downstream main passage 3 at the junction 15 and is attached with the bypass catalytic converter 18. It has been.

  FIG. 7 shows the thickness of the periphery of the sealing surface 25 of the present embodiment in which the central hole 37 is formed in the central thick portion 36 and the comparative example in which such a central hole is not formed. As shown in the figure, in the comparative example without the central hole, the thickness is locally increased at the portion (d) of the central thick portion 36, whereas in the present embodiment in which the central hole 37 is formed, The thickness of the portion (d) of the central thick portion 36 is reduced to the same level as the other portions, and the thickness around the seal surface 25 is made substantially uniform.

  With reference to FIG. 8, the seal structure of the flange mating surface portion of the mounting flange 41 of the exhaust manifold 39 and the upstream flange 43 where the valve port 22 opens will be described. As shown in FIG. 8A, when the sealing performance at the flange mating surface portion is insufficient and communication / gas flow occurs between a plurality of valve ports (upstream main passages) 22 provided for each cylinder, The actual distance to the catalyst becomes longer, and the catalyst temperature rise performance decreases. Therefore, in order to improve the sealing performance of the flange mating surface portion, in the example of FIGS. 8B and 8C, the shape of the flange mating surface portion is a key type having a convex portion 51 and a concave portion 52 that are fitted to each other. It has a structure. In the example shown in FIG. 8D, a gasket 54 is put in a groove 53 formed in one of the flanges 41 and 43, and both the flanges 41 and 43 are fastened with bolts or the like so as to crush the gasket 54. Or joined.

  The characteristic configuration of the present embodiment as described above and the operation and effects thereof are listed below.

  (1) This exhaust system includes an upstream main passage 2 for each cylinder connected to each of the # 1 to # 4 cylinders, and a downstream main passage 3 formed by joining the upstream main passages 2 of a plurality of cylinders. A main catalytic converter 8 interposed in the downstream main passage 3 or a downstream flow passage, and bypass passages 11, 14, branched from the upstream main passage 2 and provided with a bypass catalytic converter 18. 16 and the upstream main passage 2 is opened and closed at the downstream end so that the exhaust discharged from each cylinder flows to the bypass passages 11, 14, and 16, and the upstream main passages 2 communicate with each other when closed. A flow path switching valve 4 that shuts off, and the flow path switching valve 4 has a valve housing 21 in which a valve port 22 for each cylinder to which an end of the upstream main passage 2 of each cylinder is connected is formed. Includes a valve body 26 seated on the seal surface 25 surrounding the valve port 22, a.

  In such an exhaust device, at least the upstream portion 11 of the bypass passage is the same number of passages as the number of cylinders, and at a position upstream of the main flow path, that is, the junction 13 of the upstream main path 2. , Branch from the upstream main passage 2. Therefore, the bypass catalytic converter 18 can be arranged on the upstream side without being restricted by the position of the junction of the main flow path 2. Further, since the point branching to the bypass flow path side is a position close to each cylinder, the exhaust flows into the bypass flow path side relatively without being cooled by the heat capacity of the main flow path immediately after cold start. That is, immediately after the cold start or the like, the flow path switching valve 4 is closed, and the upstream main passage 2 and the downstream main passage 3 are shut off. As a result, the exhaust discharged from each cylinder flows through the bypass passages 11, 14, and 16 provided with the bypass catalytic converter 18. At the same time, since the flow path switching valve 4 individually closes the valve ports 22 of the plurality of upstream main passages 2, the mutual communication of the upstream main passages 2 of each cylinder is blocked. If the upstream main passages 2 are in communication with each other when the flow path switching valve 4 is in the closed state, exhaust strokes sequentially arrive at each cylinder, and therefore, from the upstream main passage of one cylinder to another cylinder A phenomenon occurs in which the exhaust gas flows into the upstream main passage. Therefore, heat easily escapes to the outside, and the temperature rise of the bypass catalytic converter is hindered. By causing the upstream main passages 2 to be out of communication with each other when the flow path switching valve 4 is closed, this wraparound phenomenon can be avoided.

  In the valve housing 21, a plurality of valve ports 22 for each cylinder are integrally formed by casting or the like. Then, the central thick portion 36 surrounded by at least three valve ports 22 that are gathered and close to each other so as to cross the seal surface 25 so as to make the thickness D around each valve port 22 uniform in the circumferential direction. A central hole 37 extending in the longitudinal direction of the port of the valve port 22 is formed.

  In this way, by forming the plurality of valve ports 22 integrally in the valve housing 21 by casting or the like, the number of parts can be reduced compared to the case where a separate metal pipe is fixed by welding as in the above-described conventional example. And manufacturing man-hours can be greatly reduced. Since a central hole 37 extending in the longitudinal direction of the port is formed so as to cross the seal surface 25 in the central thick portion 36 where at least three valve ports 22 are gathered, as shown in FIG. It is possible to improve the cooling effect of the central thick portion 36 while making the circumferential thickness of the port 22, particularly the sealing surface 25 uniform, to avoid the deterioration of the sealing performance due to the thermal strain in the circumferential direction of the sealing surface 25. it can.

  (2) In a four-cylinder (or more) multi-cylinder internal combustion engine, typically, as shown in FIGS. 3 and 4, the valve housing 21 has four (or more) valve ports 22 corresponding to four cylinders. Are arranged in two rows, and the partition wall portion 35 around the valve port 22 continues and intersects in a substantially cross shape at the central thick portion 36 of the valve housing 21. For this reason, the central thick part 36 in which the two partition walls continue and intersect in a cross shape is inevitably thickened, and is easily heated to a high temperature by the exhaust gas. The performance improvement effect is remarkably obtained.

  (3) The valve body 26 is configured to swing around the rotary shaft 27 supported by the valve housing 21. When the valve is closed, the valve body 26 may be inadvertently opened by the pressure of the exhaust gas from the upstream side. In order to prevent this, the valve port 22 is opened and closed from the upstream side.

  (4) A plurality of valve ports 22 are provided side by side, and a plurality of valve bodies 26 that open and close each are attached to a common rotating shaft 27. Thus, the simplification of the configuration is achieved by sharing the rotating shaft 27.

  (5) The central hole 37 has a simple shape that is linearly penetrated in the longitudinal direction of the port of the valve housing 21 so that it can be easily formed when the valve housing 21 is cast.

  (6) As shown in FIG. 4, the sealing surface 25 has a tapered surface that gradually decreases in diameter from the upstream side to the downstream side. For this reason, the downstream portion of the port downstream of the seal surface 25 is set to a size (diameter direction dimension) comparable to that of the port upstream portion 23, and the portion of the seal surface 25 protrudes inward. If so, the smooth flow of the exhaust is hindered, the heat capacity around the seal surface 25 is reduced, the temperature tends to be high, and the heat distortion of the seal surface 25 is likely to occur.

  Therefore, the valve port 22 is provided with a tubular port downstream portion 29 that linearly extends from the lower end of the sealing surface 25 whose diameter is reduced to the downstream side. In other words, the protruding portion in which the periphery of the sealing surface 25 partially protrudes inward is eliminated, and the port downstream portion 29 is also formed into a thin linear shape corresponding to the reduced diameter due to the sealing surface 25. . For this reason, the flow of exhaust gas is smoother than that of the above-mentioned projection shape, and the periphery of the seal surface 25 is thickened, the heat capacity is increased, and the periphery of the seal surface 25 is increased. Can be further suppressed.

  (7) The valve housing 21 is integrally cast with an upstream flange 43 fixed to the exhaust manifold 39. The central hole 37 has an upstream end opened to the upstream flange 43, The downstream end is open to the space 46 (see FIG. 4) between the plurality of downstream ports 29. For this reason, the cooling effect of the central thick part 36 can be further enhanced.

  (8) For the purpose of reducing the number of parts and simplifying the piping structure, the passage merging portion 45 in which a part of the downstream main passage 3 into which the plurality of port downstream portions 29 merge is formed in the valve housing 21. Is integrally cast.

  As described above, the present invention has been described based on the specific embodiments. However, the present invention is not limited to the above-described embodiments, and includes various modifications and changes without departing from the spirit of the present invention. . For example, in the above-described embodiment, the description has been given by taking a four-cylinder internal combustion engine as an example. However, the present invention is not limited to this, and the present invention can be applied to a multi-cylinder internal combustion engine having three or more cylinders. In the above embodiment, the central hole 37 has a substantially circular cross-section that is easy to manufacture. However, in order to make the wall thickness more uniform, the central hole 37 has a substantially rectangular shape corresponding to the shape of the adjacent valve port. It is good also as a different cross-sectional shape.

BRIEF DESCRIPTION OF THE DRAWINGS Structure explanatory drawing which shows one Example of the exhaust apparatus which concerns on this invention. The assembly perspective view which shows the flow-path switching valve of a present Example. The disassembled perspective view of the said flow-path switching valve. Sectional drawing of the said flow-path switching valve. Sectional drawing in alignment with the AA of FIG. Sectional drawing which follows the BB line of FIG. Explanatory drawing which shows the thickness of the circumference | surroundings of a sealing surface. Explanatory drawing which shows the seal structure of the flange joint surface part of an exhaust manifold and a valve housing.

Explanation of symbols

2 ... Upstream main passage 3 ... Downstream main passage 4 ... Flow path switching valve 8 ... Main catalytic converter 11 ... Upstream bypass passage 16 ... Downstream bypass passage 18 ... Bypass catalytic converter 21 ... Valve housing 22 ... Valve port 25 ... Seal surface 26 ... Valve element 35 ... Partition part 36 ... Central thick part 37 ... Central hole

Claims (9)

An upstream main passage for each cylinder connected to each cylinder;
A downstream main passage formed by joining upstream main passages of a plurality of cylinders;
A flow path switching valve that opens and closes the upstream main passage at the downstream end and shuts off communication between the upstream main passages when closed, and
The flow path switching valve includes a valve housing integrally formed with a valve port for each cylinder to which an end of an upstream main passage of each cylinder is connected, and a valve body seated on a seal surface surrounding the valve port; With
In order to make the wall thickness around each valve port uniform in the circumferential direction, the valve housing has a central thick wall portion surrounded by at least three valve ports that gather together so as to cross the sealing surface. An exhaust device for an internal combustion engine, wherein a central hole extending in a longitudinal direction of the valve port is formed. The valve housing is provided with four valve ports corresponding to four cylinders arranged in two rows,
2. An exhaust system for an internal combustion engine according to claim 1, wherein the partition wall around the valve port intersects in a substantially cross shape at the central thick part of the valve housing.   3. The internal combustion engine according to claim 1, wherein the valve body is configured to swing around a rotation shaft supported by the valve housing, and opens and closes the valve port from the upstream side. Exhaust system.   The exhaust device for an internal combustion engine according to claim 3, wherein a plurality of valve ports are provided side by side, and a plurality of valve bodies for opening and closing each of the valve ports are attached to a common rotating shaft.   The exhaust device for an internal combustion engine according to any one of claims 1 to 4, wherein the central hole is formed in a straight line in the longitudinal direction of the port of the valve housing. The sealing surface has a tapered surface that gradually decreases in diameter from the upstream side to the downstream side,
6. The exhaust system for an internal combustion engine according to claim 5, wherein the valve port has a tubular port downstream portion extending linearly from the lower end of the sealing surface having a reduced diameter toward the downstream side. The valve housing is integrally casted with an upstream flange fixed to the exhaust manifold,
The center hole has an upstream end opened to the upstream flange, and a downstream end opened to a space between the plurality of downstream ports. An exhaust system for an internal combustion engine as described.     8. The internal combustion engine according to claim 6, wherein the valve housing is integrally cast with a passage merging portion in which a part of a downstream main passage where a plurality of downstream portions of the ports merge is formed. Engine exhaust system. A main catalytic converter interposed in the downstream main passage or a passage downstream thereof; and
A bypass passage branched from the upstream main passage and having a bypass catalytic converter interposed therebetween,
9. The flow path switching valve according to claim 1, wherein the flow path switching valve opens and closes the upstream main passage at a downstream end so that exhaust discharged from each cylinder flows to the bypass passage. An exhaust system for an internal combustion engine according to any one of the above.

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