JP2018053905A - Exhaust system for engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an exhaust system for an engine capable of enhancing oxygen detection accuracy.SOLUTION: In an exhaust system for an engine including an exhaust pipe and a muffler connected to the downstream side of the exhaust pipe, the exhaust pipe has a catalyst, and the muffler has an expansion chamber in which exhaust gas is expanded. The exhaust pipe is extended to the expansion chamber, and the expansion chamber has a first expansion chamber and a second expansion chamber coupled to the downstream side of the first expansion chamber. The first expansion chamber and the second expansion chamber are coupled to each other by a first communication pipe, and a downstream side oxygen sensor for detecting an oxygen constituent in exhaust gas is provided downstream of the catalyst to face an opening of the first communication pipe. The exhaust pipe has a plurality of upstream side exhaust pipes and an exhaust collection section coupled to the downstream sides of the upstream side exhaust pipes. An upstream side oxygen sensor for detecting the oxygen constituent in exhaust gas is provided in the vicinity of a rear end of the exhaust collection section and on the upstream side of the catalyst.SELECTED DRAWING: Figure 2

Description

  The present invention relates to an improvement in an exhaust system for an engine provided with an oxygen sensor.

  An engine exhaust device having an oxygen sensor for detecting an oxygen component in exhaust gas is known (see, for example, Patent Document 1 (FIG. 2)).

  As shown in FIG. 2 of Patent Document 1, an engine exhaust device (6) (the numbers in parentheses indicate the reference numerals described in Patent Document 1. The same applies hereinafter) is an exhaust pipe (7) extending from the engine exhaust port. And a silencer (8) connected to the downstream end (7a) of the exhaust pipe (7), and the downstream end (7a) extends into the silencer (8). A three-way catalyst (10) is disposed in the exhaust pipe (7), and an O2 sensor (14) (hereinafter referred to as an “oxygen sensor (14)” is connected to the silencer (8) downstream of the three-way catalyst (10). ) ") Is placed. The oxygen sensor (14) is disposed so as to face the outlet of the exhaust pipe (7) in the first expansion chamber (8a) of the silencer (8). A secondary air introduction pipe (12) is connected to the exhaust pipe (7) on the upstream side of the three-way catalyst (10).

  In the technique of Patent Document 1, when the oxygen sensor (14) is arranged so as to face the outlet of the exhaust pipe (7), the temperature of the exhaust gas remaining in the silencer (8) decreases. In addition, the amount of moisture attached to the oxygen sensor (14) may increase due to condensation. When the amount of moisture adhering to the oxygen sensor (14) increases, the oxygen sensor (14) easily deteriorates, and there is a problem in the durability of the sensor.

Further, the exhaust gas after being mixed with the secondary air and combusted and treated with the three-way catalyst (10) is not sufficiently stirred in the exhaust pipe (7), and is detected by the oxygen sensor (14). Data to be local. As a result, there was room for improvement in terms of accurately determining the life of the catalyst .

International Publication No. WO2005 / 075805

The present invention aims to provide an exhaust apparatus capable of increasing the detection accuracy of the oxygen.

According to a first aspect of the present invention, there is provided an engine having an exhaust pipe for leading exhaust gas from the engine, and a silencer connected to a downstream side of the exhaust pipe to reduce exhaust noise and exhaust the exhaust gas to the outside. In the exhaust device, the exhaust pipe includes a catalyst for purifying the exhaust gas, the silencer includes an expansion chamber in which the exhaust gas expands, and the exhaust pipe extends to the expansion chamber, which is the first expansion chamber. And a second expansion chamber connected to the downstream side of the first expansion chamber, and the first expansion chamber and the second expansion chamber are connected by a first communication pipe, and are connected to the opening of the first communication pipe. As shown, a downstream oxygen sensor that detects an oxygen component in the exhaust gas is provided on the downstream side of the catalyst, and the exhaust pipe includes a plurality of upstream exhaust pipes and an exhaust collecting portion connected downstream thereof. Oxygen in the exhaust gas near the rear end of the exhaust assembly and upstream of the catalyst Wherein the upstream oxygen sensor for detecting the amount is provided.
The invention according to claim 2 is characterized in that the downstream oxygen sensor is disposed outside the downstream edge of the exhaust pipe when the exhaust pipe is viewed from the longitudinal axis direction .
In the invention according to claim 3, the downstream oxygen sensor is provided with an element portion as an oxygen detection portion, and this element portion overlaps the first communication pipe when the exhaust pipe is viewed from the longitudinal axis direction. And
In the invention according to claim 4, the downstream oxygen sensor is disposed at a position facing the exhaust pipe in either the up / down direction or the left / right direction across the first communication pipe when the exhaust pipe is viewed from the longitudinal axis direction. It is characterized by that .

The invention according to claim 5 is characterized in that the downstream oxygen sensor is disposed above the downstream edge of the exhaust pipe.

The invention according to claim 6 is characterized in that a recess is formed on the upper surface of the silencer, and a downstream oxygen sensor is disposed in the recess.

The invention according to claim 7 is characterized in that the downstream oxygen sensor is provided in a first expansion chamber located on the upstream side of the first communication pipe.

In the invention which concerns on Claim 8 , the drain hole for draining is provided in any expansion chamber in a silencer, and the drain hole for draining is formed in the lower end of the separator which partitions off an expansion chamber. Features.
In the invention which concerns on Claim 9, it has the inclination part which inclines upwards so that the height of a drain hole may become higher than the drain hole in the bottom part of a silencer .
The invention according to claim 10 is characterized in that a cap member that is formed of a perforated plate and diffuses and discharges exhaust gas that has been cleaned with the catalyst is provided at the downstream end of the catalyst .

In the invention according to claim 1, the exhaust pipe extends to the first expansion chamber of the silencer in which the exhaust gas expands. The exhaust gas touches an upstream oxygen sensor provided near the rear end of the exhaust collecting portion and upstream of the catalyst. The exhaust gas discharged from the exhaust pipe expands in the first expansion chamber, and expands in the second expansion chamber from the first expansion chamber through the first communication pipe. At that time, the exhaust gas stirred in the first expansion chamber touches the downstream oxygen sensor arranged so as to face the opening of the first communication pipe that connects the first expansion chamber and the second expansion chamber. The detection accuracy of oxygen can be enhanced by two oxygen sensors having different arrangements .

In the invention according to claim 2, since the downstream oxygen sensor is disposed outside the extension line of the downstream edge of the exhaust pipe, the exhaust gas in a state sufficiently stirred and homogenized in the first expansion chamber is Hits the downstream oxygen sensor. Therefore, the homogenized downstream exhaust gas can be applied to the oxygen sensor. As a result, exhaust gas in a sufficiently agitated state can be detected, and the life of the catalyst can be accurately determined.

Further, the downstream oxygen sensor is arranged outside the downstream edge of the exhaust pipe. Exhaust gas discharged from the exhaust pipe and having a high temperature hardly hits the downstream oxygen sensor directly. Thereby, when the temperature of the silencer decreases, moisture generated by thermal condensation becomes difficult to adhere to the downstream oxygen sensor. As a result, deterioration of the downstream oxygen sensor is suppressed, and durability of the downstream oxygen sensor can be enhanced.

In the invention which concerns on Claim 5 , a downstream oxygen sensor is arrange | positioned above the downstream edge of an exhaust pipe. When the engine is stopped and the temperature in the exhaust pipe decreases, the moisture contained in the gas in the exhaust pipe may condense in the exhaust pipe. The condensed moisture goes downward.

In this regard, in the present invention, the downstream oxygen sensor is disposed above the downstream edge of the exhaust pipe, so that it is possible to make a structure in which the condensed moisture hardly adheres directly to the oxygen sensor. As a result, the lifetime of the downstream oxygen sensor can be increased.

In the invention which concerns on Claim 6 , the downstream oxygen sensor is arrange | positioned at the recessed part formed in the upper surface of a silencer. If the downstream oxygen sensor can be disposed in the recess, the components disposed above the silencer can be disposed low. As a result, the vehicle can have a low center of gravity.

In the invention which concerns on Claim 7 , a downstream oxygen sensor is provided in the 1st expansion chamber located in the upstream of a 1st communicating pipe. If the first expansion chamber is farther from the silencer outlet than the second expansion chamber, the data detected by the downstream oxygen sensor will be used even when the outside air flows back into the silencer due to turbulence of exhaust gas. It is possible to suppress the influence. Therefore, the state of the catalyst can be judged more precisely.

In the invention which concerns on Claim 8 , the drain hole for draining water is provided in either expansion chamber. When the temperature of the muffler drops, condensable and moisture flows out through the de Len hole. Since moisture is prevented from staying in the first expansion chamber, deterioration of the downstream oxygen sensor is suppressed. As a result, the lifetime of the downstream oxygen sensor can be extended.

1 is a right side view of a motorcycle according to the present invention. It is a top view of the exhaust apparatus which concerns on this invention. FIG. 3 is a view taken in the direction of arrow 3 in FIG. 2. It is a 4 arrow line view of FIG. 3 explaining a silencer. It is the top view which fractured | ruptured a part explaining the internal structure of a silencer. FIG. 6 is a sectional view taken along line 6-6 of FIG. FIG. 7 is a cross-sectional view taken along line 7-7 of FIG. It is operation | movement explanatory drawing of the exhaust apparatus which concerns on this invention. It is a modification figure of FIG. It is a longitudinal cross-sectional view of the exhaust apparatus which concerns on 2nd Example. It is a cross-sectional view of the exhaust device according to the second embodiment. It is a 12-part enlarged view of FIG.

  Hereinafter, embodiments of the present invention will be described in detail. In the drawings and examples, “up”, “down”, “front”, “rear”, “left”, and “right” respectively indicate directions viewed from the driver who rides the motorcycle.

First, Embodiment 1 of the present invention will be described with reference to the drawings.
As shown in FIG. 1, a motorcycle 10 includes a body frame 11, a front wheel steering unit 13 that is steerable provided at the front end of the body frame 11, and a rear wheel suspension that is swingably provided on the body frame 11. A portion 14, an engine 17 suspended on the vehicle body frame 11 between the front wheel 15 and the rear wheel 16, a fuel tank 18 mounted on the vehicle body frame 11 above the engine 17, and the fuel tank 18. Thus, a seat 19 is provided on the vehicle body frame 11 on which a passenger sits. The front wheel steering section 13 includes a front wheel 15, a front fork 20 that supports the front wheel 15, and a steering handle 21 that is mounted on the front fork 20. The rear wheel suspension portion 14 includes a swing arm 23 that swings from the pivot portion 22 to the rear of the vehicle and a rear wheel 16 that is rotatably attached to a rear end portion of the swing arm 23.

  The engine 17 suspended from the vehicle body frame 11 includes a crankcase 25, a cylinder block 26 extending obliquely forward and upward from the crankcase 25, and a cylinder head 27 attached on the cylinder block 26. . In this embodiment, the engine 17 is an in-line four-cylinder engine.

  An intake device 28 is connected to the rear surface 27 b of the cylinder head 27, and an exhaust device 29 is connected to the front surface 27 a of the cylinder head 27. The exhaust device 29 of the engine 17 extends from the front surface 27a of the cylinder head 27, and is connected to an exhaust pipe 31 for deriving exhaust gas from the engine 17 and a downstream side of the exhaust pipe 31 to reduce exhaust noise and exhaust. And a silencer 32 for discharging gas to the outside. Under the engine 17, the side and lower side of the exhaust device 29 are covered with an under cover 33.

Next, the configuration of the exhaust device will be described.
As shown in FIG. 2, the exhaust device 29 includes a first upstream exhaust pipe 41, a second upstream exhaust pipe 42, a third upstream exhaust pipe 43, and a fourth upstream exhaust that are connected to the exhaust ports of the engine. A pipe 44 and an exhaust collecting portion 45 connected to the downstream ends of the first upstream exhaust pipe 41, the second upstream exhaust pipe 42, the third upstream exhaust pipe 43, and the fourth upstream exhaust pipe 44; A silencer 32 connected to the rear end of the exhaust collecting portion 45 and having a substantially rectangular shape is a main element. At each upstream end of the first upstream exhaust pipe 41, the second upstream exhaust pipe 42, the third upstream exhaust pipe 43, and the fourth upstream exhaust pipe 44, the first upstream exhaust pipe 41, the second upstream exhaust. Flange members 46, 47, 48, and 49 for fixing the pipe 42, the third upstream exhaust pipe 43, and the fourth upstream exhaust pipe 44 to the engine 17 are attached. Further, silencer stays 51, 51 for supporting the silencer 32 are provided on the vehicle body side on the upper surface 32 a of the silencer 32.

  As shown in FIG. 3, the first upstream exhaust pipe 41, the second upstream exhaust pipe 42, the third upstream exhaust pipe 43, the fourth upstream exhaust pipe 44, and the exhaust collecting portion 45 are jointed together. A gathering collar 52 is interposed. The exhaust collecting portion 45 is formed by abutting a half body 45A on one side and a half body 45B on the other side. An upstream oxygen sensor 53 that detects an oxygen component in the exhaust gas is provided in the vicinity of the rear end of the exhaust collecting portion 45.

  The silencer 32 is formed by abutting a lower half body 32A and an upper half body 32B placed on the lower half body 32A from above, and a recess 55 is provided in a part of the upper surface of the upper half body 32B. A downstream oxygen sensor 54 (hereinafter also referred to as “oxygen sensor 54”) that detects an oxygen component in the exhaust gas is provided.

Next, the internal structure of the silencer will be described.
As shown in FIGS. 4 and 5, the silencer 32 has a first separator 57 extending in the width direction of the silencer 32 on the inner side of the silencer 32, and behind the first separator 57. A second separator 58 extending to the left and right in the width direction of the silencer 32 is provided, and the first separator 57 and the second separator 58 form three expansion chambers in which the exhaust gas expands in the silencer 32.

The exhaust pipe 31 includes a catalyst 50 that purifies the exhaust gas, and extends to the expansion chamber 60 located inside the silencer 32. The front wall 32aa of the silencer 32 is provided with a front catalyst holder 64 that supports the front end of the catalyst 50, and the first separator 57 is provided with a rear catalyst holder 65 that supports the rear end of the catalyst 50. The catalyst 50 is supported by the holder 64 and the rear catalyst holder 65. At the downstream end of the catalyst 50, a cap member 66 having a substantially truncated cone shape in a side view and formed of a perforated plate and diffusing and discharging exhaust gas cleaned by the catalyst 50 is attached.
The upstream oxygen sensor 53 (see FIG. 3) is provided on the upstream side of the catalyst 50, and the downstream oxygen sensor 54 is provided on the downstream side of the catalyst 50.

  The three expansion chambers 60 include a first expansion chamber 61, a second expansion chamber 62 provided on the downstream side of the first expansion chamber 61, and a third expansion chamber provided on the downstream side of the second expansion chamber 62. 63. Each expansion chamber is provided in order of the third expansion chamber 63, the first expansion chamber 61, and the second expansion chamber 62 from the front to the rear of the silencer 32. The third expansion chamber 63 and the first expansion chamber 61 are provided in this order. Is partitioned by a first separator 57, and a space between the first expansion chamber 61 and the second expansion chamber 62 is partitioned by a second separator 58.

  The first expansion chamber 61 and the second expansion chamber 62 are connected by a first communication pipe 71 supported by the second separator 58, and the second expansion chamber 62 and the third expansion chamber 63 are the first separator 57 and The third expansion chamber 63 and the outside are connected by the second communication pipe 72 supported by the second separator 58, and the third communication pipe 73 and the third communication are supported by the first separator 57 and the second separator 58. It extends from the downstream end of the pipe 73 and is connected by a second pipe 58 and a tail pipe 74 supported by the upper half 32B of the silencer 32.

  The exhaust gas that has passed through the downstream end of the catalyst 50 passes through the cap member 66, expands in the first expansion chamber 61, passes through the first communication pipe 71 provided in the first expansion chamber 61, and passes through the second expansion chamber 61. The expansion chamber 62 is reached. The exhaust gas expands in the second expansion chamber 62, and the exhaust gas expanded in the second expansion chamber 62 passes through the second communication pipe 72 and reaches the third expansion chamber 63. The exhaust gas expands in the third expansion chamber 63, passes through the third communication pipe 73, passes through the tail pipe 74 connected to the rear end of the third communication pipe 73, and is discharged to the outside.

Next, the point where the downstream oxygen sensor 54 is disposed in the vicinity of the first communication pipe will be described. As shown in FIG. 6, the first expansion chamber 61 and the second expansion chamber 62 are provided inside the silencer 32. A second separator 58 is disposed between the first separator 58 and the second separator 58. A support hole 76 is provided in an upper portion of the second separator 58, and the first communication pipe 71 is disposed in the support hole 76 so that its axial direction extends horizontally. Is done. A flare portion 77 having an enlarged diameter is formed at the upstream end of the first communication pipe 71, and the exhaust gas stirred in the first expansion chamber 61 is smoothly guided to the first communication pipe 71.

A concave portion 55 is formed in the upper surface 32a of the silencer 32 at a position corresponding to the first expansion chamber 61. The concave portion 55 is formed in the concave portion 55, and the oxygen sensor 54 is disposed in the concave portion 55. A second boss 82 having a female screw 78 into which the oxygen sensor 54 is screwed is welded to the recess 55. Since the oxygen sensor 54 is attached to the silencer 32 via the second boss 82, the support strength of the oxygen sensor 54 can be ensured. The oxygen sensor 54 includes an element portion 83 as an oxygen detection portion at the lower end, and the element portion 83 is disposed at a height such that the element portion 83 faces the inner diameter portion 71u (opening 71k) of the first communication pipe 71. . In the example of FIG. 6, the element portion 83 overlaps the first communication pipe 71, particularly the flare portion 77 when the exhaust pipe 31 is viewed from the longitudinal axis direction .

  That is, an oxygen sensor 54 that detects an oxygen component in the exhaust gas is provided on the downstream side of the catalyst 50 so as to face the opening 71k of the first communication pipe 71. The oxygen sensor 54 is provided in the first expansion chamber 61 located on the upstream side of the first communication pipe 71.

As shown in FIG. 7, the oxygen sensor 54 is disposed outside the downstream edge 31 b of the exhaust pipe 31 when the exhaust pipe 31 is viewed from the longitudinal axis direction. That is, the oxygen sensor 54 is disposed above the downstream edge 31 b of the exhaust pipe 31. The recess 55 is disposed at a position facing the exhaust pipe 31 in either the up / down direction or the left / right direction across the first communication pipe 71 when viewed from the longitudinal axis direction of the exhaust pipe 31. For this reason, the oxygen sensor 54 provided in the recess 55 is opposed to the exhaust pipe 31 in either the vertical or horizontal direction with the first communication pipe 71 interposed therebetween when viewed from the longitudinal axis direction of the exhaust pipe 31. Is arranged .

  As shown in FIG. 8, a first drain hole 86 for draining water is formed at the lower end of the first separator 57, and a second drain hole 87 for draining water is formed at the lower end of the second separator 58. ing. Further, the third expansion chamber 63 is provided with a drain hole 88 for draining water.

  The bottom 32 s of the silencer 32 is rearward so that the height of the first drain hole 86 is higher than the height of the drain hole 88 and the height of the second drain hole 87 is higher than the height of the first drain hole 86. And an inclined portion 89 inclined upward. When the temperature of the silencer 32 decreases, the moisture condensed in the second expansion chamber 62 by the inclined portion 89 falls to the inclined portion 89, and the moisture that has fallen on the inclined portion 89 travels through the inclined portion 89, It flows into the first expansion chamber 61 through the second drain hole 87. Then, the moisture flowing from the second expansion chamber 62 to the first expansion chamber 61 and the moisture condensed in the first expansion chamber 61 flow downward through the inclined portion 89 and pass through the first drain hole 86 to form the third. The water that flows into the expansion chamber 63, travels along the inclined portion 89 and flows from the first expansion chamber 61 to the third expansion chamber 63 and the water condensed in the third expansion chamber 63 is discharged from the drain hole 88 to the outside. . Combined with the inclined portion 89 that inclines toward the rear, the moisture accumulated in the bottom portion 32s of the silencer 32 can be easily released to the outside by the acceleration when the vehicle starts.

Next, the operation of the engine exhaust system provided with the oxygen sensor described above will be described.
5 and 6 together, the exhaust pipe 31 includes a front catalyst holder 64 and a catalyst 50, and extends to the first expansion chamber 61 of the silencer 32 where the exhaust gas expands.

  The exhaust gas discharged from the exhaust pipe 31 expands in the first expansion chamber 61, passes through the first communication pipe 71 from the first expansion chamber 61, and expands in the second expansion chamber 62. At that time, the exhaust gas stirred in the first expansion chamber 61 touches the oxygen sensor 54 disposed so as to face the opening 71 k of the first communication pipe 71.

  In this regard, in the present invention, since the oxygen sensor 54 is disposed outside the extension line of the downstream edge 31b (see FIG. 7) of the exhaust pipe 31, it passes through the cap member 66 and is stirred in the first expansion chamber 61. The exhaust gas in the state hits the oxygen sensor 54. Accordingly, the state of the catalyst 50 can be determined more precisely by hitting the oxygen sensor 54 with exhaust gas that has been sufficiently stirred and homogenized.

  If the state of the catalyst 50 can be determined more precisely, the life of the catalyst 50 can be accurately determined.

  As shown in FIG. 7, the oxygen sensor 54 is disposed outside the downstream edge 31 b of the exhaust pipe 31 when the exhaust pipe 31 is viewed from the longitudinal axis 31 </ b> X direction of the exhaust pipe 31. The exhaust gas having a high temperature discharged from the exhaust pipe 31 can be prevented from directly hitting the oxygen sensor 54. Thereby, when the temperature of the silencer 32 is lowered, it is possible to make it difficult for moisture generated by thermal condensation to adhere to the oxygen sensor 54. As a result, the deterioration of the oxygen sensor 54 can be suppressed, and the durability of the oxygen sensor 54 can be improved.

  The oxygen sensor 54 is disposed above the downstream edge 31 b of the exhaust pipe 31. When the engine 17 is stopped and the temperature in the exhaust pipe 31 decreases, the moisture contained in the gas in the exhaust pipe 31 may condense in the exhaust pipe 31. The condensed moisture goes downward. In this regard, in the present invention, since the oxygen sensor 54 is disposed above the downstream edge 31b of the exhaust pipe 31, a structure in which condensed moisture is difficult to adhere directly to the oxygen sensor 54 can be achieved. As a result, the lifetime of the oxygen sensor 54 can be increased.

  Returning to FIG. 6, the oxygen sensor 54 is disposed in a recess 55 formed in the upper surface 32 a of the silencer 32. If the oxygen sensor 54 can be disposed in the recess 55, the components disposed above the silencer 32 can be disposed low. As a result, the vehicle can have a low center of gravity.

  The oxygen sensor 54 is provided in the first expansion chamber 61 located on the upstream side of the first communication pipe 71. If the first expansion chamber 61 is farther from the outlet 32d (see FIG. 5) of the silencer 32 than the second expansion chamber 62, even when the outside air flows back into the silencer 32 due to the turbulent flow of exhaust gas. The influence on the data detected by the oxygen sensor 54 can be suppressed. Therefore, the state of the catalyst 50 (see FIG. 5) can be determined more precisely.

  Returning to FIG. 8, the silencer 32 includes a first expansion chamber 61 provided with the oxygen sensor 54 and a third expansion chamber 63 that is partitioned, and a drain hole 88 is provided in the third expansion chamber 63. When the temperature of the silencer 32 decreases, the moisture condensed in the first expansion chamber 61 flows out through the drain hole 88 of the third expansion chamber 63. Since moisture hardly stays in the first expansion chamber 61, the deterioration of the oxygen sensor 54 is suppressed. As a result, the life of the oxygen sensor 54 can be extended.

Next, a modification of FIG. 6 will be described.
As shown in FIG. 9, a second separator 58 that partitions the first expansion chamber 61 and the second expansion chamber 62 is disposed inside the silencer 32, and a support hole is formed above the second separator 58. 76 is provided, and the first communication pipe 71 is disposed in the support hole 76 so that the axial direction extends horizontally.

  The difference from the first embodiment is that a concave portion 55 that is recessed downward is formed in the upper surface 32a of the silencer 32 at a position corresponding to the second expansion chamber 62, and the oxygen sensor 54 is disposed in the concave portion 55. There is in point. That is, the oxygen sensor 54 is disposed on the downstream side of the first communication pipe 71 where the exhaust gas flows. There are no other significant changes and the description is omitted.

The operation of the above modification will be described.
The exhaust gas discharged from the exhaust pipe 31 expands in the first expansion chamber 61, and expands in the second expansion chamber 62 from the first expansion chamber 61 through the first communication pipe 71. At that time, the exhaust gas stirred in the first expansion chamber 61 touches the oxygen sensor 54 disposed so as to face the opening 71 k of the first communication pipe 71. Since the oxygen sensor 54 is disposed outside the extension line of the downstream edge 31b (see FIG. 7) of the exhaust pipe 31, the exhaust gas that has been sufficiently stirred and homogenized in the first expansion chamber 61 is converted into oxygen. It hits the sensor 54. Therefore, the exhaust gas in a sufficiently agitated and homogenized state hits the oxygen sensor 54, so that the state of the catalyst 50 (see FIG. 5) can be determined more precisely.

  Since the oxygen sensor 54 is disposed outside the extension line of the downstream edge 31 b of the exhaust pipe 31, exhaust gas that has been sufficiently stirred and homogenized in the first expansion chamber 61 hits the oxygen sensor 54. Therefore, the life of the catalyst 50 can be accurately determined by the homogenized exhaust gas hitting the oxygen sensor 54.

  The oxygen sensor 54 is disposed outside the downstream edge 31b of the exhaust pipe 31 when the exhaust pipe 31 is viewed from the longitudinal axis 31X (see FIG. 7) direction of the exhaust pipe 31. The exhaust gas having a high temperature discharged from the exhaust pipe 31 is difficult to directly hit the oxygen sensor 54. Thereby, when the temperature of the silencer 32 is lowered, it is possible to make it difficult for moisture generated by thermal condensation to adhere to the oxygen sensor 54. As a result, the deterioration of the oxygen sensor 54 can be suppressed, and the durability of the oxygen sensor 54 can be improved.

  Further, the oxygen sensor 54 is provided in the second expansion chamber 62 located on the downstream side of the first communication pipe 71. If the second expansion chamber 62 is farther from the outlet 32d (see FIG. 5) of the silencer 32 than the third expansion chamber 63 (see FIG. 5) in the length of the exhaust path starting from the outlet 32d of the silencer 32. Even when the outside air flows back into the silencer 32 due to the turbulent flow of the exhaust gas, the influence on the data detected by the oxygen sensor 54 can be suppressed. Therefore, the state of the catalyst 50 (see FIG. 5) can be determined more precisely. Other operations are the same as those in the first embodiment, and the description thereof is omitted.

Next, a second embodiment of the present invention will be described with reference to the drawings.
As shown in FIGS. 10 and 11, the exhaust device 29 includes an exhaust pipe 31 and a silencer 32 connected to the downstream side of the exhaust pipe 31. The exhaust pipe 31 includes a catalyst 50 that purifies the exhaust gas.

  The silencer 32 includes an enlarged diameter portion 91, an outer cylinder portion 92 that is connected to the rear end of the enlarged diameter portion 91 and extends rearward, and an inner portion provided coaxially with the outer cylinder portion 92 inside the outer cylinder portion 92. A cylindrical portion 93, an inner lid 94 that closes the rear end of the inner cylindrical portion 93, and an outer lid 95 that is fitted to the outer cylindrical portion 92 from the outer rear side of the inner lid 94 are provided. The inner cylinder portion 93 includes a first separator 57, a second separator, and a third separator 59. The first separator 57, the second separator, and the third separator 59 extend at right angles to the longitudinal axis direction of the inner cylinder portion 93, are provided intermittently, are formed in the silencer 32, and the exhaust gas expands. The expansion chamber 60 is partitioned. The first separator 57, the second separator, and the third separator 59 extend in a direction perpendicular to the longitudinal axis of the silencer. The expansion chamber 60 is divided into four expansion chambers by the first separator 57, the second separator, and the third separator 59.

  The expansion chamber 60 includes a first expansion chamber 61, a second expansion chamber 62 provided on the downstream side of the first expansion chamber 61, a third expansion chamber 63 provided on the downstream side of the second expansion chamber 62, The fourth expansion chamber 64 is provided on the downstream side of the third expansion chamber 63. From the front to the rear of the silencer 32, a first expansion chamber 61, a fourth expansion chamber 64, a third expansion chamber 63, and a second expansion chamber 62 are provided in this order, and the first expansion chamber 61 and the second expansion chamber 62 are provided in this order. The expansion chamber 62 is communicated by a first communication pipe 71 that passes through the first separator 57, the second separator, and the third separator 59 and is supported by the first separator 57, the second separator, and the third separator 59, and The second expansion chamber 62 and the third expansion chamber 63 are communicated by a second communication pipe 72 that penetrates the third separator 59 and is supported by the third separator 59, and the third expansion chamber 63 and the fourth expansion chamber 64 Passes through the second separator 58 and is communicated by a third communication pipe 73 supported by the second separator 58, and the fourth expansion chamber 64 and the outside penetrate through the second and third separators 58 and 59. Two fourth communication pipe 97A which is supported by the second and third separators 58 and 59 together, are communicated by 97B. In addition, a porous plate 98 is erected between the first separator 57 and the enlarged diameter portion 91.

  The exhaust gas that has passed through the downstream end of the catalyst 50 expands in the first expansion chamber 61 in which the perforated plate 98 is erected, passes through the first communication pipe 71 provided in the first expansion chamber 61, and passes through the first expansion chamber 61. 2 The expansion chamber 62 is reached. The exhaust gas expands in the second expansion chamber 62, and the exhaust gas expanded in the second expansion chamber 62 passes through the second communication pipe 72 and reaches the third expansion chamber 63. The exhaust gas expands in the third expansion chamber 63, passes through the third communication pipe 73, passes through the two fourth communication pipes 97 </ b> A and 97 </ b> B connected to the rear end of the third communication pipe 73, and goes to the outside. Discharged.

  The exhaust pipe 31 includes a catalyst 50 at the rear end of the exhaust pipe 31, and extends to the enlarged diameter portion 91 that forms the first expansion chamber 61. An oxygen sensor 54 that detects an oxygen component in the exhaust gas is provided in the enlarged diameter portion 91 of the silencer 32 on the downstream side of the catalyst 50, and this oxygen sensor 54 is obtained when the exhaust pipe 31 is viewed from the longitudinal axis direction. The exhaust pipe 31 is disposed outside the downstream edge 31b. The oxygen sensor 54 is provided in the first expansion chamber 61, and the oxygen sensor 54 is disposed above the downstream edge 31 b of the exhaust pipe 31.

  As shown in FIG. 12, a boss (second boss 82) having a female screw 78 into which the oxygen sensor 54 is screwed is welded to the enlarged diameter portion 91 at a portion corresponding to the first expansion chamber 61. Since the oxygen sensor 54 is attached to the silencer 32 via the second boss 82, the support strength of the oxygen sensor 54 can be ensured. The oxygen sensor 54 includes an element portion 83 as an oxygen detection portion at the lower end, and the element portion 83 is disposed outside the downstream edge 31b (see FIG. 10) of the exhaust pipe 31.

Next, the operation of the second embodiment will be described.
Returning to FIG. 10, the exhaust pipe 31 extends to the first expansion chamber 61 of the silencer 32 where the exhaust gas expands. The exhaust gas discharged from the exhaust pipe 31 is expanded in the first expansion chamber 61. At this time, the exhaust gas stirred in the first expansion chamber 61 is an oxygen sensor disposed outside the downstream edge 31b of the exhaust pipe 31 when the exhaust pipe 31 is viewed from the longitudinal axis 31X direction of the exhaust pipe 31. Touch 54.

  Since the oxygen sensor 54 is disposed outside the extension line of the downstream edge 31 b of the exhaust pipe 31, exhaust gas that has been sufficiently stirred and homogenized in the first expansion chamber 61 hits the oxygen sensor 54. Accordingly, the state of the catalyst 50 can be determined more precisely by hitting the oxygen sensor 54 with exhaust gas that has been sufficiently stirred and homogenized.

  The oxygen sensor 54 is disposed outside the downstream edge 31b of the exhaust pipe 31 when the exhaust pipe 31 is viewed from the longitudinal axis direction. The exhaust gas having a high temperature discharged from the exhaust pipe 31 can be made difficult to directly hit the oxygen sensor 54. Thereby, when the temperature of the silencer 32 is lowered, moisture generated by thermal condensation is less likely to adhere to the oxygen sensor 54. As a result, deterioration of the oxygen sensor 54 can be suppressed, and the durability of the oxygen sensor can be enhanced.

  Further, the oxygen sensor 54 is disposed above the downstream edge 31 b of the exhaust pipe 31. When the engine 17 is stopped and the temperature in the exhaust pipe 31 decreases, the moisture contained in the gas in the exhaust pipe 31 may condense in the exhaust pipe 31. The condensed moisture goes downward. In this regard, in the present invention, the oxygen sensor 54 is disposed above the downstream edge 31 b of the exhaust pipe 31, so that the condensed moisture hardly adheres directly to the oxygen sensor 54. As a result, the lifetime of the oxygen sensor 54 can be increased.

  The oxygen sensor 54 is provided in the first expansion chamber 61. If the first expansion chamber 61 is farther from the outlet 32d of the silencer 32 than the second expansion chamber 62, the oxygen sensor 54 detects even when the outside air flows back into the silencer due to the turbulent flow of the exhaust gas. The influence on the data to be performed can be suppressed. Therefore, the state of the catalyst 50 can be determined more precisely.

  Although the structure of the exhaust device has been described above, this exhaust device is the left exhaust device among the left and right exhaust devices provided in a pair. The structure of the right exhaust device is a structure that is bilaterally symmetric with respect to the center line in the vehicle width direction when mounted on a vehicle and has the same operational effects, and therefore the description of the right exhaust device is omitted.

  Although the present invention is applied to a motorcycle in the embodiment, it can also be applied to a tricycle and can be applied to a general vehicle.

  The present invention is suitable for a motorcycle including an oxygen sensor in an engine exhaust device.

  DESCRIPTION OF SYMBOLS 17 ... Engine, 29 ... Exhaust device, 31 ... Exhaust pipe, 31b ... Downstream edge of exhaust pipe, 32 ... Silencer, 50 ... Catalyst, 54 ... Oxygen sensor, 55 ... Recess, 60 ... Expansion chamber, 61 ... First expansion Chamber 62, second expansion chamber 63, third expansion chamber 71, first communication pipe 88, drain hole.

Claims (10)

An exhaust pipe (31) for deriving exhaust gas from the engine (17), and a silencer (32) connected to the downstream side of the exhaust pipe (31) for reducing exhaust noise and exhausting the exhaust gas to the outside In an exhaust system for an engine equipped with
The exhaust pipe (31) includes a catalyst (50) for purifying the exhaust gas,
The silencer (32) includes an expansion chamber (60) in which the exhaust gas expands,
The exhaust pipe (31) extends to the expansion chamber (60),
The expansion chamber (60) includes a first expansion chamber (61) and a second expansion chamber (62) connected to the downstream side of the first expansion chamber (61).
The first expansion chamber (61) and the second expansion chamber (62) are connected by a first communication pipe (71),
A downstream oxygen sensor (54) for detecting an oxygen component in the exhaust gas is provided on the downstream side of the catalyst (50) so as to face the opening of the first communication pipe (71),
The exhaust pipe (31) includes a plurality of upstream exhaust pipes (41, 42, 43, 44) and an exhaust collecting portion (45) connected downstream thereof.
Exhaust gas from the engine, characterized in that an upstream oxygen sensor (53) for detecting an oxygen component in the exhaust gas is provided in the vicinity of the rear end of the exhaust collecting portion (45) and upstream of the catalyst (50). apparatus. The downstream oxygen sensor (54) is disposed outside a downstream edge of the exhaust pipe (31) when the exhaust pipe (31) is viewed from the longitudinal axis direction. The engine exhaust system described . The downstream oxygen sensor (54) is provided with an element part (83) as an oxygen detection part. When the exhaust pipe (31) is viewed from the longitudinal axis direction, the element part (83) is the first oxygen sensor. The engine exhaust device according to claim 1 or 2, wherein the exhaust device overlaps the communication pipe (71) . When the exhaust pipe (31) is viewed from the longitudinal axis direction, the downstream oxygen sensor (54) is connected to the exhaust pipe (31) in either the vertical or horizontal direction with the first communication pipe (71) interposed therebetween. The engine exhaust device according to any one of claims 1 to 3, wherein the engine exhaust device is disposed at a position facing each other . The exhaust system for an engine according to any one of claims 1 to 4, wherein the downstream oxygen sensor (54) is disposed above a downstream edge of the exhaust pipe (31). A recess (55) is formed on the upper surface of the silencer (32),
The engine exhaust system according to any one of claims 1 to 5 , wherein the downstream oxygen sensor (54) is disposed in the recess (55). The said downstream oxygen sensor (54) is provided in the said 1st expansion chamber (61) located in the upstream of the said 1st communicating pipe (71), The any one of Claims 1-6 characterized by the above-mentioned. The engine exhaust system described. A drain hole (88) for draining water is provided in any expansion chamber (61, 62, 63) in the silencer (32),
The drainage hole (86, 87) for draining water is formed in the lower end of the separator (57, 58) partitioning the expansion chamber (60). The engine exhaust system according to the item . The bottom part (32s) of the silencer has an inclined part (89) inclined upward so that the drain holes (86, 87) are higher than the drain hole (88). 9. The exhaust system for an engine according to claim 8, wherein The cap member (66), which is formed of a perforated plate and diffuses and discharges exhaust gas purified by the catalyst (50), is provided at the downstream end of the catalyst (50). The engine exhaust device according to any one of claims 9 to 9 .

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