JP2007040112A - Exhaust system of internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To allow a bypass catalytic converter for performing exhaust emission control immediately after cold start to be disposed on a more upstream side and to prevent leakage of exhaust gas through a flow passage switching valve. <P>SOLUTION: The flow passage switching valve 4 is disposed in a junction where four upstream side main passages connected to respective cylinders gather together as a downstream side main passage. An upstream side bypass passage is branched from each of the upstream side main passages as a bypass flow passage and the bypass catalytic converter is interposed in the middle of a downstream side bypass passage. When the flow passage switching valve 4 is closed, the main flow passage is blocked off and concurrently the upstream side main passages of the respective cylinders are brought in a non-communication state with each other. The flow passage switching valve 4 has a housing 21 with four valve openings 22 opened and valve elements 24 and the two valve elements 24 commonly use a single rotation shaft 23. The rotation shaft 23 has a fitting shaft portion of an irregular cross-section in a width across flat shape where an arm 25 is attached by fitting. Deterioration of sealability due to welding distortion at a second bearing portion 32 is avoided. <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 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 via an arm. The cross section gradually expands and changes from the base end to the base end, and the connecting portion with the arm has a different cross sectional shape corresponding to a different shape fitting hole on the arm side, and the plurality of different cross sectional shape portions. The cross-sectional circular part in between passes through the partition between the two upstream main passages arranged adjacent to each other.

  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 with a common rotating shaft, the rotating shaft penetrates the partition wall between the adjacent upstream main passages in some form, and in order to avoid the above wraparound phenomenon Therefore, it is necessary to suppress leakage at the penetration portion. For example, if the arm of each valve element is to be attached to the rotating shaft by welding, the rotating shaft is likely to be bent due to welding distortion, and as a result, the sealing performance at the penetrating portion is lowered.

  Therefore, in the present invention, the connecting portion with the arm of the rotating shaft is formed in a deformed cross-sectional shape such as a so-called two-sided width, and basically the arm and the valve body by fitting with the arm-shaped deformed fitting hole Is supported on the rotating shaft. Thereby, the bending of the rotating shaft due to welding distortion is prevented, and the sealing performance at the fitting portion of the partition wall between the upstream main passages is enhanced. It should be noted that the fitting portion may be further welded so that the arm does not move in the axial direction. Even in this case, the welding length is very short, so that the bending of the rotating shaft can be sufficiently prevented.

  In order to attach a plurality of arms by fitting, the rotary shaft has a cross-sectionally enlarged enlargement from the distal end portion toward the base end portion, and is sequentially inserted into the fitting holes of the plurality of arms, Assembly is possible. In a specific embodiment, the position of each arm in the axial direction is regulated by abutting the side surface of each arm toward the tip side with a part of the housing of the flow path switching valve. In another embodiment, a cylindrical collar inserted through a rotating shaft is interposed between the side surface of the arm and a part of the housing, and the shaft of each arm is interposed through the collar. The position of the direction is regulated.

  Desirably, a minimum gap that allows the rotation of the rotating shaft is provided between the partition wall and the circular section in order to minimize the leakage of exhaust gas. Moreover, you may make it provide a cylindrical bush in the partition which this cross-section circular part penetrates.

  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. Further, by improving the sealing performance between the rotating shaft and the partition wall through which the rotating shaft passes, the upstream side main passage of each cylinder is closed in a state where the flow path switching valve is closed to guide the exhaust to the bypass passage side. Therefore, 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. 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 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, and as shown in FIG. 3, an odd-shaped fitting hole 26 provided in the shaft portion 25 a at the base end is fitted and fixed to the rotating shaft 23. In addition, a circular mounting hole 27 is provided at the tip, and 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 be configured to open and close the valve opening 22 from the upstream side from the viewpoint of ensuring the sealing performance due to the 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 rotary shaft 23 is rotatably supported by three bearing portions of the housing 21, that is, the first bearing portion 31, the second bearing portion 32, and the third bearing portion 33, and at one end protruding from the housing 21. A link plate 34 is attached and driven in the rotational direction via the link plate 34. 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, the four valve bodies 23 open and close all at once.

  Here, as shown in FIGS. 4 and 5, the rotating shaft 23 includes a first cylindrical portion 41 having a circular cross section supported by the first bearing portion 31 on the link plate 34 side, and an intermediate second bearing. A second cylindrical portion 42 having a circular cross section supported by the portion 32, and a third cylindrical portion 43 having a circular cross section supported by the third bearing portion 33 on the distal end side. The diameter is the largest, and the second cylindrical portion 42 and the third cylindrical portion 43 have a smaller diameter in order. And between the 1st cylindrical part 41 and the 2nd cylindrical part 42, and between the 2nd cylindrical part 42 and the 3rd cylindrical part 43, the irregular cross-sectional shape corresponding to the fitting hole 26 by the side of the arm 25 is made. A first fitting shaft portion 44 and a second fitting shaft portion 45 are provided. As shown in FIG. 5D, the first fitting shaft portion 44 has a cylindrical surface 44a having an intermediate diameter between the diameter of the first cylindrical portion 41 and the diameter of the second cylindrical portion 42 and a pair of parallel portions. It has a so-called two-sided cross-sectional shape composed of the flat surface 44b. Similarly, as shown in FIG. 5B, the second fitting shaft portion 45 has a cylindrical surface 45a having a diameter intermediate between the diameter of the second cylindrical portion 42 and the diameter of the third cylindrical portion 43 and a pair. The cross-sectional shape of the two-plane width which consists of the parallel plane 45b of no. That is, as for the rotating shaft 23 as a whole, the cross section gradually changes from the distal end portion toward the proximal end portion, and the first to third bearing portions 31, 32, 33 and the fitting holes of the pair of arms 25. 26 can be inserted sequentially. The fitting holes 26 of the pair of arms 25 have irregular cross-sectional shapes corresponding to the cross-sectional shapes of the first fitting shaft portion 44 and the second fitting shaft portion 45, respectively. The rotation direction is fixed securely.

  As described above, the attachment of the arm 25 to the rotating shaft 23 is basically performed by fitting the fitting hole 26 having the irregular cross-sectional shape and the first and second fitting shaft portions 44 and 45 to each other. Done. Therefore, it is possible to avoid the deterioration of the sealing performance in the second bearing portion 32 due to the distortion of the rotating shaft 23 due to the welding operation of the arm 25 and the bending of the rotating shaft 23. That is, the second bearing portion 32 forms a part of a partition wall that separates the upstream main passages 2 of two adjacent cylinders, and leakage at this portion causes the exhaust gas between the cylinders to wrap around. In the above embodiment, the leakage of exhaust gas between the adjacent cylinders can be sufficiently suppressed. In the illustrated example, another cylindrical bush 46 made of a material suitable for the bearing is attached to the second bearing portion 32, thereby further improving the sealing performance.

  Several methods are possible to position the arm 25 attached to the rotary shaft 23 by fitting in the axial direction. In one embodiment, as shown in the explanatory view of FIG. On one side surface of the inserted arm 25, as shown as a welded portion 51, the contact portion between the rotating shaft 23 and the fitting hole 26 is locally welded. Since welding in this case is local and auxiliary, welding distortion of the rotating shaft 23 can be sufficiently avoided.

  FIG. 7 is an explanatory diagram showing a different method of positioning in the axial direction, in which the second bearing portion 32 and the third bearing portion 33 are formed long in the axial direction, and the arm is fitted to the rotary shaft 23. The arm 25 is positioned in the axial direction by the one side surface of 25 abutting against the end surfaces of these bearing portions 32 and 33. The movement of each arm 25 in the opposite direction is caused by a step generated between the first cylindrical portion 41 and the first fitting shaft portion 44 and between the second cylindrical portion 42 and the second fitting shaft portion 45. It is regulated by the level difference that occurs in each. In this example, welding between the rotating shaft 23 and the arm 25 is completely unnecessary.

  FIG. 8 is an explanatory view showing a further different method of positioning in the axial direction. Instead of forming the second and third bearing portions 32 and 33 long as in the embodiment of FIG. Cylindrical collars 52 and 53 are inserted through the rotary shaft 23. That is, the movement of the arm 25 in the axial direction is restricted by the second and third bearing portions 32 and 33 through the collars 52 and 53. Also in this example, the welding between the rotating shaft 23 and the arm 25 is completely unnecessary.

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 a rotating shaft typically. Explanatory drawing which contrasts and shows each cross section of the rotating shaft of FIG. Explanatory drawing which shows the Example which welded the arm fitted to the rotating shaft partially. Explanatory drawing which shows the Example which positions an arm by a part of housing. Explanatory drawing which shows the Example provided with the cylindrical collar.

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 (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 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 side by side, and a plurality of valve bodies for opening and closing each are attached to a common rotating shaft via an arm,
The rotating shaft has a cross-sectionally enlarged change from the distal end portion toward the base end portion, and the connecting portion with the arm has a deformed cross-sectional shape corresponding to a deformed fitting hole on the arm side, and An exhaust system for an internal combustion engine, characterized in that a circular cross-section between the plurality of irregular cross-sectional shapes penetrates a partition wall between two adjacent upstream main passages.   2. The exhaust system for an internal combustion engine according to claim 1, wherein the connecting portion is formed in a two-sided width shape in which a plane is provided at two locations of a circular cross section.   The exhaust system for an internal combustion engine according to claim 1 or 2, wherein a fitting portion between the fitting hole of each arm and the deformed cross-sectional shape portion is further welded to fix each arm to a rotating shaft. .   The exhaust system for an internal combustion engine according to claim 1 or 2, wherein each arm is supported by the rotating shaft only by fitting the fitting hole of each arm and the deformed cross-sectional shape portion.   The axial position of the arm is regulated by a side surface of each arm of the rotating shaft toward the tip side contacting a part of a housing of a flow path switching valve. 5. An exhaust system for an internal combustion engine according to 4.   5. An exhaust system for an internal combustion engine according to claim 4, wherein a cylindrical collar inserted through a rotating shaft is interposed between the side surface and a part of the housing.   The exhaust device for an internal combustion engine according to any one of claims 1 to 6, wherein a minimum gap capable of allowing rotation of the rotary shaft is provided between the partition wall and the circular section. .   The exhaust device for an internal combustion engine according to any one of claims 1 to 7, wherein a cylindrical bush is provided in the partition wall through which the circular section is passed.   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. An exhaust device for an internal combustion engine according to any one of 1 to 8.

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