JP4591251B2 - Exhaust device for internal combustion engine - Google Patents

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, as disclosed in Patent Document 1, a bypass flow path is provided in parallel with the upstream portion of the main flow path including the main catalytic converter, and another bypass catalytic converter is interposed in the bypass flow path. However, an exhaust device has been conventionally proposed in which exhaust gas is guided to the bypass flow path side immediately after the cold start by a switching valve for switching between the two. In this configuration, the bypass catalytic converter is positioned relatively upstream of the main catalytic converter in the exhaust system and is activated relatively early, so that exhaust purification can be started from an earlier stage. it can.
JP-A-5-321644

  In the conventional exhaust apparatus, the bypass flow path branches off from the main flow path on the downstream side of the junction of the exhaust manifold. That is, in the multi-cylinder internal combustion engine, the main flow path and the bypass flow path are arranged in parallel at the downstream side of the junction where the exhaust flow paths of the cylinders merge into one flow path. ing. Therefore, although the bypass catalytic converter interposed in the bypass flow path is located upstream from the main catalytic converter, the distance from the exhaust port of each cylinder is considerably large, and exhaust purification can be started immediately after starting. Can not.

  In addition, since it branches off to the bypass flow path downstream of the exhaust manifold, the temperature of the exhaust gas flowing into the bypass flow path decreases due to the heat capacity of the exhaust manifold, which is a large component, and the exhaust purification by the bypass catalytic converter starts accordingly. Will be delayed. In addition, even when the switching valve is closed on the main flow path side, exhaust strokes sequentially arrive at each cylinder, so that exhaust flows from the exhaust flow path of one cylinder to the exhaust flow path of another cylinder. Occurs. Therefore, heat easily escapes to the outside, and the temperature rise of the bypass catalytic converter is hindered.

  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 downstream main passage. A main catalytic converter interposed in a passage or a flow path downstream thereof, a bypass passage branched from the upstream main passage and provided with a bypass catalytic converter, and exhaust exhausted from each cylinder is bypassed by the bypass A flow path switching valve that opens and closes the upstream main passage so as to flow to the passage and shuts off communication between the upstream main passages when closed. The flow path switching valve has a plurality of valve openings arranged side by side, and a plurality of valve bodies for opening and closing each of the flow path switching valves are attached to a common rotating shaft, and a rotational force is applied by a drive mechanism. Depending on the axial distance of the rotary shaft from the driven point of the rotary shaft to each valve body, the support structure of each valve body with respect to the rotary shaft is varied.

  In the exhaust device of the present invention, at least the upstream portion of the bypass passage is the same number of passages as the number of cylinders, and the upstream side of the main passage, that is, the upstream side of the junction of the upstream main passage. Branch from the side main passage. Therefore, the bypass catalytic converter can be arranged on the upstream side without being restricted by the position of the confluence of the main flow path. 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 is closed, and the upstream main passage and the downstream main passage are shut off. Thereby, the exhaust discharged from each cylinder flows through the bypass passage provided with the bypass catalytic converter. At the same time, since the flow path switching valve individually closes the valve openings of the plurality of upstream main passages, the communication between the upstream main passages of the cylinders is blocked. If the upstream main passages are in communication with each other when the flow path switching valve is in the closed state, exhaust strokes sequentially arrive at each cylinder, so that the upstream main passage of one cylinder is upstream of the other cylinders. A phenomenon occurs in which the exhaust gas flows into the side 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 to be in a non-communication state when the flow path switching valve is closed, this wraparound phenomenon can be avoided.

  Thus, in order to open and close the upstream main passage of each cylinder, the flow path switching valve is provided with a plurality of valve openings, and a plurality of valve bodies for opening and closing each of them are attached to a common rotating shaft. However, in such a configuration in which the rotating shaft is common, for example, when the rotation mechanism is rotated by the driving mechanism with one end portion of the rotating shaft as a driven point, the valve body close to the driven point becomes the valve opening. When seated, it may occur that the valve body farther from the driven point cannot fully contact the valve opening due to errors or tolerances. Even if the valve bodies are in close contact with the valve opening at the same time, the seal surface pressure of the valve body farther from the driven point becomes relatively low due to the twist of the rotating shaft.

  Therefore, in the present invention, in particular, depending on the axial distance of the rotary shaft from the driven point of the rotary shaft to each valve body, the support structure of each valve body with respect to the rotary shaft is made different so that it is far from the driven point. This prevents the valve body from rising or the seal surface pressure from decreasing.

  In one specific aspect, at the time of closing operation, each valve body with respect to the rotation shaft is so seated that the valve body far from the driven point is seated relatively earlier than the valve body near the driven point. The mounting angle is different. That is, in the initial state, the valve body farther from the driven point is relatively closer to the valve opening. For this reason, the valve body farther from the driven point tends to press against the sealing surface of the valve opening relatively strongly, and the influence due to the difference in distance from the driven point is offset.

  In another aspect of the present invention, the elastic modulus of the arm supporting the valve body closer to the driven point is larger than the elastic coefficient of the arm supporting the valve body farther from the driven point. Is set. That is, in the seated state, the arm that supports the valve body closer to the driven point can be displaced relatively greatly, and as a result, each valve body is seated uniformly.

  In another aspect of the present invention, a part of a plurality of valve bodies attached to a common rotating shaft is supported via a spring. When the valve body is closed, the valve body that does not have a spring is seated on the seal surface of the valve opening, whereby the rotational position of the rotary shaft is defined. At this rotational position, the valve body that has the spring is a spring. The urging force ensures seating on the valve opening. Therefore, the valve body provided with the spring may be either far or near from the driven point.

In yet another aspect of the present invention, a plurality of valve bodies are mounted on a common axis of rotation, while supported by a spring respectively, are at different respective spring constants. Specifically, the spring constant of the valve body closer to the driven point is made larger than the spring constant of the valve body farther from the driven point so that the valve body can be displaced more greatly.

  According to the present invention, it is possible to dispose 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 that is 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. In addition, it is possible to avoid a decrease in the sealing performance of some of the valve bodies sharing the rotating shaft, and in the state where the flow path switching valve is closed to guide the exhaust to the bypass passage side, The flow path can be reliably shut off, and the exhaust gas can be prevented from flowing around between the upstream main passages of the respective cylinders, so that the temperature rise performance of the bypass catalytic converter is improved. Further, by sharing the rotating shaft with a plurality of cylinders, the flow path switching valve becomes relatively small.

  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 so as to open and close the four upstream main passages 2 individually.

  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. Thus, 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 based on FIG.

  In this embodiment, the flow switching valves 4 for four cylinders are integrated as one valve unit, and four circular cylinders are formed in a housing 21 having a substantially rectangular plate shape along a surface orthogonal to the flow. The valve openings 22 are formed in two rows, that is, at the positions of the apexes of the squares, and a pair of rotating shafts 23 are arranged in parallel to each other on both sides of the housing 21. . A pair of disc-shaped valve bodies 24 that open and close a pair of adjacent valve openings 22 are respectively attached to a common rotating shaft 23 via arms 25.

  Specifically, the arm 25 has a substantially rectangular plate shape, the base end is fixed to the rotary shaft 23, and has a circular mounting hole 27 at the tip as shown in FIG. A shaft portion 28 at the center of the valve body 24 is slidably inserted into the mounting hole 27 and is prevented from coming off by a holding ring 29. Therefore, the valve body 24 is not completely fixed to the arm 25 and is slightly swung (so-called so-called) so that it can come into close contact with a sealing surface (not shown) around the valve opening 22. Swinging) is possible.

  In addition, it is desirable that the valve body 24 is configured to open and close the valve opening 22 from the upstream side from the viewpoint of ensuring sealing performance due to a pressure difference. In this case, the end (not shown) of the exhaust pipe of each cylinder that becomes the upstream main passage 2 is configured to have a substantially U-shaped cross section so as to accommodate the oscillating valve body 24, and each valve opening. And welded along the partition wall 30 of the housing 21 surrounding the housing 22. Therefore, the upstream main passage 2 of each cylinder is completely separated and independent on the upstream side of the housing 21.

Each rotating shaft 23 is rotatably supported by three bearing portions 31, 32, 33 of the housing 21, and a link plate 34 is attached to one end protruding from the housing 21. It is driven in the rotational direction via Here, the link plates 34 of the two rotating shafts 23 are interlocked with each other via an interlocking mechanism (not shown) such as an appropriate link mechanism, and are simultaneously opened and closed symmetrically by one actuator (not shown). That is, four of the valve body 2 4 are opened and closed in unison.

  In this way, in the above embodiment, the position of the link plate 34 at one end of the rotating shaft 23 is the driven point, so one of the two valve bodies 24 opened and closed by the common rotating shaft 23 is driven. Near the point, the other is far from this driven point. That is, as shown in the explanatory diagram of FIG. 4, the distance L1 from the driven point to the one arm 25 and the distance L2 to the other arm 25 are different, and the relationship is L1 <L2. Therefore, if the configurations of the two valve bodies 24 with respect to the rotating shaft 23 are exactly the same, when a certain torque is applied in the closing direction at the driven point, the valve body 24 closer to the driven point (hereinafter, For convenience, the seal surface pressure of the valve body 24 (also referred to as the second valve body 24B) far from the driven point tends to be relatively lower than that of the first valve body 24A.

  Therefore, in the present invention, the support structures of the valve bodies 24A and 24B with respect to the rotating shaft 23 are made different so as to cancel the influence of the distances L1 and L2. Several specific examples will be described below.

  In the embodiment of FIG. 5, the mounting angles of the valve bodies 24 </ b> A and 24 </ b> B with respect to the rotating shaft 23, more specifically, the mounting angles of the two arms 25 with respect to the rotating shaft 23 are different from each other. That is, with respect to the rotation direction of the rotating shaft 23, the arm 25 of the second valve body 24B (hereinafter referred to as the second arm 25B for convenience) is the arm 25 of the first valve body 24A (similarly, the first arm 25A). A slight angle difference θ is provided between the first arm 25A and the second arm 25B so as to be relatively closer to the valve opening 22 than the first arm 25A. Therefore, when the rotary shaft 23 is driven in the closing direction, the second valve body 24B having a large distance L2 from the driven point is seated first, and then the first valve is associated with the torsional deformation of the rotary shaft 23. The body 24A is seated. Therefore, the seal surface pressure of the second valve body 24B is increased, and a seal surface pressure substantially equal to that of the first valve body 24A is obtained.

  In the embodiment of FIG. 6, the dimensions and materials are selected so that each arm 25 can be regarded as a kind of elastic body under the magnitude of torque applied from the link plate 34 to the rotating shaft 23. The elastic coefficient of the first arm 25A is larger than the elastic coefficient of the second arm 25B. This can be realized by, for example, a difference in the plate thickness or width of the arm 25.

  Accordingly, the reaction force that acts on the rotating shaft 23 from the first valve body 24A when the valve is closed is reduced, and a substantially equal sealing surface pressure is obtained between the first valve body 24A and the second valve body 24B.

  In the embodiment of FIG. 7, a compression spring 35 (for convenience, the first spring body 24A and the first arm 25A) and the second valve body 24B and the second arm 25B are each formed of a coil spring or the like. The one valve body 24A side is provided with a first spring 35A, and the second valve body 24B is referred to as a second spring 35B). The direction in which the compression spring 35 separates the valve body 24 from the arm 25 is provided. That is, it is biased in a direction approaching the valve opening 22. In particular, the spring constant of the first spring 35A is set larger than the spring constant of the second spring 35B.

  Accordingly, the reaction force that acts on the rotating shaft 23 from the first valve body 24A when the valve is closed is reduced, and a substantially equal sealing surface pressure is obtained between the first valve body 24A and the second valve body 24B.

  FIG. 8 shows a configuration in which a compression spring 36 is disposed between the arm 25 and the holding ring 29, and FIG. 9 shows both sides of the arm 25, that is, between the valve body 24 and between the holding ring 29. The structure which has arrange | positioned the compression springs 37 and 38 is shown. The arrangement of the compression spring 35 shown in FIG. 7 and those shown in FIGS. 8 and 9 can be used in appropriate combination on the first valve body 24A side and the second valve body 24B side.

  Further, for example, the compression spring 35 shown in FIG. 7 is disposed only in one of the first valve body 24A and the second valve body 24B, and the position of the valve body 24 in the free state is more than that of the other valve body 24. Alternatively, it may be configured to protrude slightly (that is, relatively close to the valve opening 22). In this case, the valve body 24 that does not include the compression spring 35 is pressed against the valve opening 22 directly by the rotating shaft 23, and the other valve body 24 is pressed against the valve opening 22 by the spring force of the compression spring 35. Therefore, it is possible to obtain a uniform seal surface pressure in both cases. The compression spring 35 may be provided on either the first valve body 24A or the second valve body 24B. Further, instead of the configuration of FIG. 7, an arrangement as shown in FIG. 9 is also possible.

  A metal pipe (not shown) serving as the downstream main passage 3 is welded to the downstream surface of the housing 21, and this metal pipe constitutes a Y-shaped flow path, for example. Exhaust gas from a pair of adjacent valve openings 22 having a common rotating shaft 23 merges immediately below. Desirably, among the four cylinders, the # 1 and # 4 cylinders share one rotating shaft 23, and the # 2 and # 3 cylinders share the other rotating shaft 23. Part 22 is arranged.

  The present invention is not limited to the four-cylinder internal combustion engine as in the above embodiment, or the configuration in which the two valve bodies 24 share one rotating shaft 23, but various configurations in which a plurality of valve bodies share the rotating shaft. It is applicable to.

BRIEF DESCRIPTION OF THE DRAWINGS Structure explanatory drawing which shows one Example of the exhaust apparatus which concerns on this invention. Sectional drawing of the whole flow-path switching valve. Sectional drawing of the valve body supported by the rotating shaft. Explanatory drawing which shows the positional relationship of a rotating shaft and two arms. Explanatory drawing of the Example which provided the angle difference in two arms. Explanatory drawing of the Example which varied the elastic coefficient of the arm. Explanatory drawing of the Example which varied the spring constant of the compression spring of two valve bodies. Explanatory drawing which shows the example of different arrangement | positioning of a compression spring. Explanatory drawing which shows the example of further different arrangement | positioning of a compression spring.

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 ... Housing 22 ... Valve opening 23 ... Rotating shaft 24 ... Valve body 25 ... Arm

Claims (7)

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 main catalytic converter interposed in the downstream main passage or a downstream passage, and
A bypass passage branched from the upstream main passage and having a bypass catalytic converter interposed therebetween;
A flow path switching valve that opens and closes the upstream main passage so that the exhaust discharged from each cylinder flows to the bypass passage, and shuts off communication between the upstream main passages when closed,
With
The flow path switching valve is provided with a plurality of valve openings arranged side by side, and a plurality of valve bodies for opening and closing each of the flow path switching valves are attached to a common rotating shaft, and a rotation force is applied by a driving mechanism. Depending on the axial distance of the rotating shaft from the driven point of the shaft to each valve body, the support structure of each valve body with respect to the rotating shaft is varied ,
In particular, an exhaust system for an internal combustion engine, wherein the support structure of each valve body is different so that the valve body has substantially the same seal surface pressure in consideration of the twist of the rotating shaft . 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 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;
A flow path switching valve that opens and closes the upstream main passage so that the exhaust discharged from each cylinder flows to the bypass passage, and shuts off communication between the upstream main passages when closed,
With
The flow path switching valve is provided with a plurality of valve openings arranged side by side, and a plurality of valve bodies for opening and closing each of the flow path switching valves are attached to a common rotating shaft, and a rotation force is applied by a driving mechanism. Depending on the axial distance of the rotating shaft from the driven point of the shaft to each valve body, the support structure of each valve body with respect to the rotating shaft is varied,
In particular, during the closing operation, the mounting angle of each valve body with respect to the rotating shaft is different so that the valve body far from the driven point is seated relatively earlier than the valve body near the driven point. exhaust system of the internal combustion engine characterized in that there. 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 main catalytic converter interposed in the downstream main passage or a downstream passage, and
A bypass passage branched from the upstream main passage and having a bypass catalytic converter interposed therebetween;
A flow path switching valve that opens and closes the upstream main passage so that the exhaust discharged from each cylinder flows to the bypass passage, and shuts off communication between the upstream main passages when closed,
With
The flow path switching valve is provided with a plurality of valve openings arranged side by side, and a plurality of valve bodies for opening and closing each of the flow path switching valves are attached to a common rotating shaft, and a rotation force is applied by a driving mechanism. Depending on the axial distance of the rotating shaft from the driven point of the shaft to each valve body, the support structure of each valve body with respect to the rotating shaft is varied,
In particular, the elastic coefficient of the arm supporting the valve body closer to the driven point is set larger than the elastic coefficient of the arm supporting the valve body farther from the driven point. exhaust system of the internal combustion engine that. 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 main catalytic converter interposed in the downstream main passage or a downstream passage, and
A bypass passage branched from the upstream main passage and having a bypass catalytic converter interposed therebetween;
A flow path switching valve that opens and closes the upstream main passage so that the exhaust discharged from each cylinder flows to the bypass passage, and shuts off communication between the upstream main passages when closed,
With
The flow path switching valve is provided with a plurality of valve openings arranged side by side, and a plurality of valve bodies for opening and closing each of the flow path switching valves are attached to a common rotating shaft, and a rotation force is applied by a driving mechanism. Depending on the axial distance of the rotating shaft from the driven point of the shaft to each valve body, the support structure of each valve body with respect to the rotating shaft is varied,
In particular, a plurality of valve bodies are mounted on a common axis of rotation, while supported by a spring respectively, the exhaust system of the internal combustion engine you characterized by having different respective spring constants. The exhaust device for an internal combustion engine according to any one of claims 1 to 4, wherein one end portion of a rotating shaft to which a plurality of valve bodies are attached serves as the driven point. The exhaust system for an internal combustion engine according to claim 1 , wherein a part of the plurality of valve bodies attached to the common rotating shaft is supported via a spring. 4. Four valve openings corresponding to four cylinders are provided in two rows, and a pair of valve bodies are respectively supported by two rotating shafts interlocking with each other at one end. The exhaust device for an internal combustion engine according to any one of 1 to 6 .

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