JP2007247437A - Exhaust system of internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent leakage of exhaust gas via a flow passage switching valve 4, by arranging a bypass catalytic converter on the further upstream side for performing exhaust emission control just after cold starting. <P>SOLUTION: The flow passage switching valve 4 is arranged in a confluent part of gathering four upstream side main passages connected with every cylinder as a downstream side main passage. An upstream side bypass passage branches off from the respective upstream side main passages as a bypass passage, and the bypass catalytic converter is interposed in the middle of the downstream side bypass passage. When closing the flow passage switching valve 4, the main flow passage is cut off, and at the same time, the mutual upstream side main passages of the respective cylinders become an uncommunicating state. The flow passage switching valve 4 is constituted so that a pair of rotary shafts 27 attached with a valve element symmetrically rotate, and is simultaneously driven by one actuator via a first link 31, a second link 35 and a third link 36. A connecting pin 37 is regulated so as to linearly move along the symmetrical center line L by a guide wall 41. <P>COPYRIGHT: (C)2007,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, 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 is provided with a pair of valve openings adjacent to each other, and a pair of valve bodies for opening and closing each of the flow path switching valves is attached to a pair of rotating shafts respectively disposed outside the valve opening. In addition, the two rotation shafts are linked to the actuator via a link mechanism so as to rotate symmetrically at the same time. The link mechanism is fixed to the rotating shaft, and a pair of first links that rotate together with the rotating shaft, a base end portion is connected to be swingable at a connecting point, and a distal end portion is connected to the first link. A pair of second links that are swingably connected to the ends of the first guide, a guide mechanism that guides the connecting point so as to move along a symmetrical centerline between the pair of rotating shafts, and the connecting point. And a third link connected and moved by the actuator.

  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.

  Here, in the present invention, a plurality of valve openings are simultaneously opened and closed by a pair of rotating shafts provided with valve bodies rotating symmetrically via a link mechanism. Since the movement of the connecting point that connects the pair of second links to each other is regulated by the guide mechanism so as to follow the center line of symmetry between the pair of rotating shafts, a pair (or a plurality of pairs) is driven by driving one actuator. The valve body surely moves symmetrically, and a state where both of them are seated at the same time is surely obtained.

  In one specific aspect, the guide mechanism includes a guide groove provided on a straight line in the housing of the flow path switching valve along the symmetry center line, and supports the connection point in the guide groove. For example, a connecting pin itself that becomes a connecting point can be used as the slider.

  In another aspect of the present invention, the guide mechanism includes a control link whose base end portion is rotatably supported so that the tip end portion moves along an arc approximate to the symmetry center line, and the control link tip end portion. A connecting portion that connects the control link tip portion and the connecting point through a long hole so as to allow a difference between the movement locus and the symmetrical center line.

  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. A plurality of valve openings can be reliably opened and closed with a single actuator, and exhaust leakage can be avoided.

  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. A bypass catalytic converter 18 using a three-way catalyst is interposed in the downstream bypass passage 16. 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 based on 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. FIG. 2 is a perspective view of the main part, FIG. 3 is a sectional view of the main part, and FIG. It is a perspective view which shows the state integrated in the actual exhaust system. As shown in the drawing, the flow path switching valve 4 mainly includes a valve base 21 having a substantially rectangular plate shape along a surface orthogonal to the flow, and the upstream side main passage metal pipe 22 is welded to one surface thereof. The downstream main passage metal pipes 23 are welded to the other surface.

  The valve base 21 is formed with four circular valve openings 25 arranged in two rows, that is, at the positions of the apexes of the squares. The valve openings 25 are formed as disc-shaped valves. The body 26 opens and closes from the upstream side. The upstream opening edge of the valve opening 25 is machined as a tapered sealing surface 25a with which the outer periphery of the valve body 26 contacts. 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 25a. As shown in the figure, a recess 29 for accommodating the valve element 26 when in the open position is formed on the side wall of the upstream-side main passage metal tube 22.

  As shown in FIGS. 2 and 4, the rotating shaft 27 is common to two cylinders, and two valve bodies 26 are attached to one rotating shaft 27. Accordingly, the flow path switching valve 4 as a whole includes two parallel rotating shafts 27 arranged outside the four valve openings 25. The two rotating shafts 27 are interlocked with each other via a link mechanism described later, and are simultaneously opened and closed symmetrically by a single actuator (not shown). That is, the four valve bodies 26 open and close all at once. A first link 31 that is a part of a link mechanism is attached to the end of the rotating shaft 27, and a fan-shaped guide plate 32 is integrated with the valve base 21 so as to follow the rotation locus of the tip. Is formed. The guide plate 32 includes an arcuate slit 33 for limiting the rotation angle of the first link 31 between the closed position and the open position of the valve body 26.

  FIG. 5 shows the structure of the link mechanism. The link mechanism is configured such that one end of the pair of first links 31 and the end of the first link 31 are oscillated through connecting pins 34 respectively. A pair of second links 35 that are connected to each other and a third link 36 that is linked to a single actuator (not shown) are provided, and the other ends of the pair of second links 35 are connected to each other. The pins 37 are swingably connected to each other, and are connected to the tip end portion of the third link 36 via the same connecting pin 37 so as to be swingable. The third link 36 that forms a straight line is disposed substantially along the symmetry center line L (see FIG. 6) between the pair of rotating shafts 27, and is moved back and forth substantially along the longitudinal direction by an actuator not shown. To be driven. That is, the pair of second links 35 and the center third link 36 are combined to form a Y-shape.

  Here, on the outer surface of the housing of the flow path switching valve 4 where the connection pin 37 is located, for example, the pair of adjacent downstream main passage metal tubes 23, the end of the connection pin 37 is placed on the symmetrical center line L. A pair of guide walls 41 for guiding along the guide wall 41 are integrally provided, and the end of the connecting pin 37 is fitted into the guide groove 42 between the pair of guide walls 41 so that the connection is achieved. The movement trajectory of the pin 37 is limited to that along the symmetry center line L.

  In the link mechanism having such a configuration, as shown in the explanatory view of FIG. 6, when the pair of second links 35 swings as the third link 36 advances and retracts, the position of the connecting pin 37 is always the center of symmetry. Since it is on the line L, the entire link mechanism does not tilt to one side, and a pair (more specifically, two pairs) of valve bodies 26 arranged symmetrically are opened and closed simultaneously and in a symmetrical relationship. Therefore, both seating states can be obtained reliably, and exhaust leakage due to poor seating can be avoided.

  Note that the connecting pin 34 at the tip of the first link 31 passes through the slit 33 of the guide plate 32 described above, so that the rotation angle of the first link 31 corresponds to the closed position and the open position of the valve body 26 as described above. Limited during.

  Next, FIG. 7 shows a different embodiment of the guide mechanism. In this embodiment, a control link 51 for supporting the connecting pin 37 from the side is provided instead of the guide wall 41 described above. As shown in FIG. 8, the length of the control link 51 and the rotation center position of the base end portion 51b are such that the tip end portion 51a draws an arcuate movement locus that approximates the symmetry center line L. It has been established. And the said connection pin 37 is supported by the front-end | tip part 51a. Here, as shown in FIG. 8, an elongated slot 52 is provided along the longitudinal direction of the tip 51a of the control link 51, and the connecting pin 37 passes through the slot 52. Yes. The long hole 52 is for absorbing a difference (shift amount) between the arc-shaped movement locus of the tip 51a of the control link 51 and the symmetrical center line L that is a complete straight line. When 37 is in the closed position of the valve body 26 (FIG. 8A) and when the connecting pin 37 is in the open position of the valve body 26 (FIG. 8C), one end of the long hole 52 When the connecting pin 37 is located at the end of the control link 51 near the base end 51b and is in the middle position between the two (FIG. 8B), the connecting pin is connected to the other end of the long hole 52. 37 is located.

  Conversely, a configuration in which a pin is fixedly provided at the distal end portion 51 a of the control link 51 and a long hole is provided in a slider that supports the connecting pin 37 is also possible. Further, a similar long hole structure may be provided on the side of the base end portion 51b that becomes the rotation center of the control link 51.

  Thus, in the configuration using the control link 51 as the guide mechanism, the degree of freedom of layout is higher than in the first embodiment using the guide wall 41, and the control link 51 does not directly contact the exhaust pipe. Therefore, there is an advantage that less heat is transmitted to the actuator.

BRIEF DESCRIPTION OF THE DRAWINGS The structure explanatory drawing which shows the piping layout of the exhaust apparatus which concerns on this invention. The perspective view of a flow-path switching valve. Sectional drawing of a flow-path switching valve. The perspective view of the flow-path switching valve shown in an assembly state. The top view of the flow-path switching valve principal part which shows 1st Example of a link mechanism. Explanatory drawing of this link mechanism. Structure explanatory drawing which shows 2nd Example of a link mechanism. Explanatory drawing which shows the positional relationship of a long hole and a connection pin.

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 base 26 ... Valve element 27 ... Rotating shaft 31 ... 1st link 35 ... 2nd link 36 ... 3rd link 41 ... Guide wall 42 ... Guide groove 51 ... Control link

Claims (6)

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 pair of valve openings adjacent to each other, and a pair of valve bodies for opening and closing each of the flow path switching valves are attached to a pair of rotating shafts respectively disposed outside the valve opening. At the same time, it is linked to the actuator via a link mechanism so that both rotation shafts rotate symmetrically at the same time,
The link mechanism is fixed to the rotating shaft, and a pair of first links that rotate together with the rotating shaft are connected to a base end portion so as to be swingable at a connecting point, and a distal end portion is connected to the first link. A pair of second links that are swingably connected to the ends of the two, a guide mechanism that guides the connecting point to move along a symmetrical centerline between the pair of rotating shafts, and a connecting point. An exhaust system for an internal combustion engine, further comprising a third link connected and moved by the actuator.   The guide mechanism includes a guide groove provided linearly along the symmetry center line in the flow path switching valve housing, and a slider that supports the connection point and slides in the guide groove. The exhaust system for an internal combustion engine according to claim 1, wherein   The exhaust device for an internal combustion engine according to claim 2, wherein the connecting pin itself serving as the connecting point is fitted into the guide groove as the slider.   The guide mechanism includes a control link whose base end portion is rotatably supported so that the distal end portion moves along an arc approximating the symmetry center line, a movement locus of the control link distal end portion, and the symmetry center line. The internal combustion engine according to claim 1, further comprising: a connecting portion that connects the control link tip portion and the connecting point through a long hole so as to allow a difference between the control link and the control link. Exhaust system.   The exhaust device for an internal combustion engine according to any one of claims 1 to 4, wherein a plurality of valve bodies are attached to one rotating shaft. Four valve openings corresponding to four cylinders are provided in two rows, and two valve bodies each attached to a pair of rotating shafts open and close each valve opening simultaneously. 6. An exhaust system for an internal combustion engine according to claim 5.

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