EXHAUST DEVICE FOR ENGINE

Abstract

 An exhaust device 29 for an engine includes a silencer 32 connected to a downstream side of an exhaust pipe 31. The exhaust pipe 31 includes a catalyst 50 and the silencer 32 includes an expansion chamber 60. The expansion chamber 60 includes a first expansion chamber 61 and a second expansion chamber 62, which are connected to each other by a first fluid communication pipe 71. The exhaust device includes an oxygen sensor 54 for detecting an oxygen component in the exhaust gas, the oxygen sensor being disposed downstream of the catalyst 50 and facing an opening 71k of the first fluid communication pipe 71. The oxygen sensor 54 is disposed outwardly of a downstream edge 31 b of the exhaust pipe 31 when the exhaust pipe 31 is viewed along a longitudinal axis thereof.

Description

[0001] The present invention relates to an exhaust device for an engine which is provided with an oxygen sensor.

[0002] There is known an exhaust device for an engine which is provided with an oxygen sensor for detecting an oxygen component in an exhaust gas (see, for example, WO 2005/075805 (FIG. 2))

[0003] As shown in FIG. 2 of WO 2005/075805, an exhaust device (6) for an engine (the number in parentheses denotes a reference character as used in WO 2005/075805, and the same holds true for other numbers below) includes an exhaust pipe (7) extending from the exhaust port of an engine and a silencer (8) connected to the downstream end (7a) of the exhaust pipe (7), the downstream end (7a) extending 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 "oxygen sensor (14)") is disposed in the silencer (8) downstream of the three-way catalyst (10). The oxygen sensor (14) is disposed in a first expansion chamber (8a) of the silencer (8) in facing relation to the outlet of the exhaust pipe (7). A secondary air inlet pipe (12) is connected to the exhaust pipe (7) upstream of the three-way catalyst (10).

[0004] According to the technology of WO 2005/075805, with the oxygen sensor (14) being disposed in facing relation to the outlet of the exhaust pipe (7), when the temperature of an exhaust gas that remains in the silencer (8) drops, the amount of water deposited on the oxygen sensor (14) may possibly increase due to condensation. If the amount of water deposited on the oxygen sensor (14) increases, then the oxygen sensor (14) can deteriorate, which leads to a durability problem.

[0005] Further, the exhaust gas that has been mixed with secondary air, burned, and treated by the three-way catalyst (10) is not sufficiently stirred in the exhaust pipe (7), so that data from the oxygen sensor (14) may only relate to local conditions. As a result, the known exhaust device is not ideal with regard to the accuracy with which the service life of the catalyst can be ascertained.

[0006] Accordingly, there is a desire for an exhaust device for an engine which is provided with an oxygen sensor whose durability is increased, and which is capable of detecting an oxygen component while an exhaust gas is being sufficiently stirred, so that the detected data relates to the exhaust gas as a whole and not merely local conditions.

[0007] It is an object of at least the preferred embodiments of the present invention to provide an exhaust device for an engine which is capable of increasing the durability of an oxygen sensor and increasing the accuracy with which the oxygen sensor detects oxygen.

[0008] According to a first aspect of the invention, there is provided an exhaust device for an engine, including an exhaust pipe for guiding exhaust gas from an engine and a silencer connected to a downstream side of the exhaust pipe, for reducing exhaust sounds and discharging the exhaust gas out of the exhaust device, wherein the exhaust pipe includes a catalyst for purifying the exhaust gas, the silencer includes an expansion chamber in which the exhaust gas expands, the exhaust pipe extends into the expansion chamber, the expansion chamber includes a first expansion chamber and a second expansion chamber downstream of the first expansion chamber, the first expansion chamber and the second expansion chamber are connected to each other by a first fluid communication pipe, the exhaust device includes an oxygen sensor for detecting an oxygen component in the exhaust gas, the oxygen sensor is disposed downstream of the catalyst in facing relation to an opening of the first fluid communication pipe, and the oxygen sensor is disposed outwardly of a downstream edge of the exhaust pipe when the exhaust pipe is viewed along a longitudinal axis thereof.

[0009] With this arrangement, the exhaust pipe extends into the first expansion chamber of the silencer in which the exhaust gas expands. The exhaust gas discharged from the exhaust pipe expands in the first expansion chamber, passes from the first expansion chamber through the first fluid communication pipe, and then expands in the second expansion chamber. At this time, the exhaust gas stirred in the first expansion chamber is brought into contact with the oxygen sensor that is disposed in facing relation to the opening of the first fluid communication pipe that interconnects the first expansion chamber and the second expansion chamber.

[0010] Since the oxygen sensor is disposed outwardly of the extension of the downstream edge of the exhaust pipe, the exhaust gas that has been sufficiently stirred and uniformized in the first expansion chamber is brought into contact with the oxygen sensor. Therefore, the exhaust gas that has been uniformized is brought into contact with the oxygen sensor. As a result, the oxygen sensor can detect the exhaust gas that has been sufficiently stirred, and the service life of the catalyst can be ascertained accurately.

[0011] The oxygen sensor is disposed outwardly of the downstream edge of the exhaust pipe. The exhaust gas discharged from the exhaust pipe and having its temperature increased is less likely to be brought into direct contact with the oxygen sensor. Therefore, when the temperature of the silencer drops, water produced by thermal condensation is less liable to be deposited on the oxygen sensor. As a result, deterioration of the oxygen sensor is reduced, and durability of the oxygen sensor can be increased.

[0012] Preferably, the oxygen sensor is disposed upwardly of the downstream edge of the exhaust pipe.

[0013] When the engine is shut down and the temperature in the exhaust pipe drops, water contained in a gas in the exhaust pipe may condense in the exhaust pipe. The condensed water is directed downwardly. Since the oxygen sensor is disposed upwardly of the downstream edge of the exhaust pipe, it is less likely that the condensed water will be deposited directly on the oxygen sensor. As a consequence, the oxygen sensor has its service life increased.

[0014] Preferably, the silencer has a recess defined in an upper surface thereof, and the oxygen sensor is disposed in the recess.

[0015] With the oxygen sensor disposed in the recess, components that are disposed above the silencer can be lowered. As a result, the vehicle may have its centre of gravity lowered.

[0016] Preferably, the oxygen sensor is provided in the first expansion chamber which is upstream of the first fluid communication pipe.

[0017] As the first expansion chamber is farther from the outlet of the silencer than the second expansion chamber, even if ambient air flows back into the silencer, the adverse effect that the ambient air can have on data detected by the oxygen sensor is reduced. Therefore, the state of the catalyst can be ascertained more accurately.

[0018] Preferably, the expansion chamber included in the silencer further includes a third expansion chamber disposed downstream of the second expansion chamber, and the third expansion chamber has a drain hole for draining water.

[0019] With this arrangement, the silencer includes the first expansion chamber that is provided with the oxygen sensor, the second expansion chamber, and the third expansion chamber, and the drain hole is provided in the third expansion chamber. When the temperature of the silencer drops, water condensed in the first expansion chamber flows out through the drain hole in the third expansion chamber. As water is less likely to remain in the first expansion chamber, deterioration of the oxygen sensor can be reduced. As a result, the service life of the oxygen sensor can be extended.

[0020] Preferred embodiments of the invention will now be described by way of example only and with reference to the accompanying drawings, in which:

FIG. 1 is a right side elevational view of a motorcycle with an exhaust device according to a first embodiment of the present invention;

FIG. 2 is a plan view of an exhaust device according to a first embodiment of the present invention;

FIG. 3 is a view taken along arrow 3 in FIG. 2;

FIG. 4 is a view taken along arrow 4 in FIG. 3, illustrating a silencer;

FIG. 5 is a plan view, partly cut away, showing an internal structure of the silencer;

FIG. 6 is a cross-sectional view taken along line 6-6 of FIG. 4;

FIG. 7 is a cross-sectional view taken along line 7-7 of FIG. 4;

FIG. 8 is a view illustrating the manner in which the exhaust device according to a first embodiment of the present invention operates;

FIG. 9 is a view showing a modification of the structure shown in FIG. 6;

FIG. 10 is a vertical cross-sectional view of an exhaust device according to a second embodiment;

FIG. 11 is a horizontal cross-sectional view of the exhaust device according to the second embodiment; and

FIG. 12 is an enlarged view of region 12 shown in FIG. 10.

[0021] Preferred embodiments of the present invention will be described in detail below. In the drawings and embodiments, terms such as "upward", "downward", "forward", "rearward", "leftward", and "rightward" represent directions as viewed from the rider of a motorcycle.

[0022] A first embodiment of the present invention will now be described with reference to the drawings.

[0023] As shown in FIG. 1, a motorcycle 10 has a vehicle body frame 11, a front wheel steering assembly 13 steerably mounted at the front of the vehicle body frame 11, a rear suspension assembly 14 swingably mounted on the vehicle body frame 11, an engine 17 suspended from the vehicle body frame 11 between a front wheel 15 and a rear wheel 16, a fuel tank 18 placed on the vehicle body frame 11 upwardly of the engine 17, and a seat 19, for the rider to sit thereon, mounted on the vehicle body frame 11 behind the fuel tank 18. The front wheel steering assembly 13 has the front wheel 15, a front fork 20 supporting the front wheel 15 thereon, and a steering handle 21 mounted on the front fork 20. The rear suspension assembly 14 has a swing arm 23 swingably extending rearwardly from a pivot member 22 and the rear wheel 16 rotatably mounted on a rear end portion of the swing arm 23.

[0024] The engine 17 that is suspended from the vehicle body frame 11 includes a crankcase 25, a cylinder block 26 extending obliquely forwardly and upwardly from the crankcase 25, and a cylinder head 27 mounted on the cylinder block 26. In the present embodiment, the engine 17 is an in-line four-cylinder engine.

[0025] An intake device 28 is connected to a rear surface 27b of the cylinder head 27, and an exhaust device 29 is connected to a front surface 27a of the cylinder head 27. The exhaust device 29 of the engine 17 includes an exhaust pipe 31 extending from the front surface 27a of the cylinder head 27, for guiding exhaust gas from the engine 17, and a silencer 32 connected to a downstream side of the exhaust pipe 31, for reducing exhaust sounds and discharging the exhaust gas out of the exhaust device 29. The exhaust device 29 has lateral and lower sides covered with an under cover 33 below the engine 17.

[0026] The structure of the exhaust device will now be described.

[0027] As shown in FIG. 2, the exhaust device 29 has as its main components a first upstream exhaust pipe 41, a second upstream exhaust pipe 42, a third upstream exhaust pipe 43, and a fourth upstream exhaust pipe 44 which are each connected to the exhaust ports of the engine, an exhaust manifold 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, and the silencer 32, which is of a substantially rectangular shape, connected to the rear end of the exhaust manifold 45. Flanges 46, 47, 48, and 49 for respectively fixing 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 to the engine 17 are mounted to the upstream 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. Two silencer stays 51 for supporting the silencer 32 on the vehicle body frame are mounted on an upper surface 32a of the silencer 32.

[0028] As shown in FIG. 3, a manifold collar 52 is interposed between 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, and the exhaust manifold 45, and joins them together. The exhaust manifold 45 includes two halves 45A and 45B held in abutment against each other. An upstream oxygen sensor 53 for detecting an oxygen component in the exhaust gas is mounted on the exhaust manifold 45 at a position near its rear end.

[0029] The silencer 32 includes a lower half 32A and an upper half 32B covering the lower half 32A from above. The upper half 32B has a recess 55 defined in an upper surface thereof. A downstream oxygen sensor 54 (hereinafter also referred to as "oxygen sensor 54") for detecting an oxygen component in the exhaust gas is mounted in the recess 55.

[0030] The internal structure, etc. of the silencer 32 will be described below.

[0031] As shown in FIGS. 4 and 5, the silencer 32 houses therein a first separator 57 extending transversely therein and a second separator 58 extending transversely therein behind the first separator 57. The first separator 57 and the second separator 58 define three expansion chambers in the silencer 32 wherein the exhaust gas expands.

[0032] The exhaust pipe 31, which has a catalyst 50 disposed therein for purifying the exhaust gas, extends into the expansion chambers 60 positioned within the silencer 32. The silencer 32 has a front wall 32aa, on which is mounted a front catalyst holder 67 that supports the front end of the catalyst 50. A rear catalyst holder 65 that supports the rear end of the catalyst 50 is mounted on the first separator 57. The front catalyst holder 67 and the rear catalyst holder 65 support the catalyst 50. A cap 66, which is of a substantially frustoconical shape as viewed in side elevation and which is formed from a perforated plate for diffusing and discharging the exhaust gas purified by the catalyst 50, is mounted on the downstream end of the catalyst 50.

[0033] The upstream oxygen sensor 53 (see FIG. 3) is positioned upstream of the catalyst 50, whereas the downstream oxygen sensor 54 is positioned downstream of the catalyst 50.

[0034] The three expansion chambers 60 include a first expansion chamber 61, a second expansion chamber 62 disposed downstream of the first expansion chamber 61, and a third expansion chamber 63 disposed downstream of the second expansion chamber 62. These expansion chambers are arranged successively in the order from the third expansion chamber 63 to the first expansion chamber 61 to the second expansion chamber 62 in the longitudinal direction of the silencer 32, from front to back. The third expansion chamber 63 and the first expansion chamber 61 are separated from one another by the first separator 57, and the first expansion chamber 61 and the second expansion chamber 62 are separated from one another by the second separator 58.

[0035] The first expansion chamber 61 and the second expansion chamber 62 are connected to each other by a first fluid communication pipe 71 that is supported by the second separator 58. The second expansion chamber 62 and the third expansion chamber 63 are connected to each other by a second fluid communication pipe 72 that is supported by the first separator 57 and the second separator 58. The third expansion chamber 63 is vented to the outside by a third fluid communication pipe 73 that is supported by the first separator 57 and the second separator 58 and a tail pipe 74 that extends from the downstream end of the third fluid communication pipe 73 and that is supported by the second separator 58 and the upper half 32B of the silencer 32.

[0036] The exhaust gas that has passed through the downstream end of the catalyst 50 passes through the cap 66, expands in the first expansion chamber 61, passes through the first fluid communication pipe 71 that is disposed in the first expansion chamber 61, and reaches the second expansion chamber 62. The exhaust gas then expands in the second expansion chamber 62, passes through the second fluid communication pipe 72, and reaches the third expansion chamber 63. The exhaust gas then expands in the third expansion chamber 63, passes through the third fluid communication pipe 73, then passes through the tail pipe 74 that is connected to the rear end of the third fluid communication pipe 73 and is discharged out of the silencer 32.

[0037] As shown in FIG. 6, the second separator 58 that separates the first expansion chamber 61 and the second expansion chamber 62 is disposed in the silencer 32. The second separator 58 has a support hole 76 defined in an upper portion thereof, and the first fluid communication pipe 71 is disposed in the support hole 76 such that the axis of the first fluid communication pipe 71 extends generally horizontally. The first fluid communication pipe 71 has an upstream end with a lip 77 that flares radially outwardly for guiding the exhaust gas stirred in the first expansion chamber 61 smoothly into the first fluid communication pipe 71.

[0038] The recess 55 which is downwardly depressed is defined in the upper surface 32a of the silencer 32 at a position corresponding to the first expansion chamber 61. The oxygen sensor 54 is disposed in the recess 55. A boss 82 having an internally threaded surface 78 with which the oxygen sensor 54 is held in threaded engagement is welded in the recess 55. Since the oxygen sensor 54 is mounted on the silencer 32 by the boss 82, the strength with which the oxygen sensor 54 is supported is ensured. The oxygen sensor 54 has on its lower end an element 83 serving as an oxygen detector which is disposed at such a height that the element 83 faces an inside-diameter region 71 u (opening 71 k) of the first fluid communication pipe 71.

[0039] Specifically, the oxygen sensor 54 for detecting an oxygen component in the exhaust gas is disposed downstream of the catalyst 50 and faces the opening 71 k of the first fluid communication pipe 71. The oxygen sensor 54 is provided in the first expansion chamber 61 that is positioned upstream of the first fluid communication pipe 71.

[0040] As shown in FIG. 7, the oxygen sensor 54 is disposed outwardly of a downstream edge 31 b of the exhaust pipe 31 when the exhaust pipe 31 is viewed along the longitudinal axis thereof. In particular, the oxygen sensor 54 is disposed upwardly of the downstream edge 31 b of the exhaust pipe 31.

[0041] As shown in FIG. 8, the first separator 57 has a first drain hole 86 defined in the lower end thereof for draining water, and the second separator 58 has a second drain hole 87 defined in the lower end thereof for draining water. The third expansion chamber 63 has a drain hole 88 for draining water.

[0042] The silencer 32 includes a bottom 32s having a slanted portion 89 which is slanted rearwardly and upwardly such that the height of the first drain hole 86 is greater than the height of the drain hole 88 and the height of the second drain hole 87 is greater than the height of the first drain hole 86. When the temperature of the silencer 32 drops, water which condenses in the second expansion chamber 62 falls onto the slanted portion 89 and flows along the slanted portion 89 through the second drain hole 87 into the first expansion chamber 61. The water that has flowed from the second expansion chamber 62 into the first expansion chamber 61 and water condensed in the first expansion chamber 61 flow downwardly along the slanted portion 89 through the first drain hole 86 into the third expansion chamber 63. The water that has flowed from the first expansion chamber 61 into the third expansion chamber 63 along the slanted portion 89 and water condensed in the third expansion chamber 63 is discharged out of the silencer 32 through the drain hole 88. The water that is collected on the bottom 32s of the silencer 32 can easily be drained out of the silencer 32 by the acceleration of the vehicle when it starts to move as well as the slanted portion 89 that is slanted rearwardly.

[0043] Operation of the exhaust device of the engine which is provided with the oxygen sensors described above will be described below.

[0044] As shown in FIGS. 5 and 6, the exhaust pipe 31 includes the front catalyst holder 67 and the catalyst 50, and extends into the first expansion chamber 61 of the silencer 32 in which the exhaust gas expands.

[0045] The exhaust gas discharged from the exhaust pipe 31 expands in the first expansion chamber 61, passes from the first expansion chamber 61 through the first fluid communication pipe 71, and then expands in the second expansion chamber 62. At this time, the exhaust gas stirred in the first expansion chamber 61 is brought into contact with the oxygen sensor 54 that is disposed in facing relation to the opening 71 k of the first fluid communication pipe 71.

[0046] Since the oxygen sensor 54 is disposed outwardly of the extension of the downstream edge 31 b (see FIG. 7) of the exhaust pipe 31, the exhaust gas that has passed through the cap 66 and has been stirred in the first expansion chamber 61 is brought into contact with the oxygen sensor 54. Therefore, as the exhaust gas that is brought into contact with the oxygen sensor 54 has been sufficiently stirred and uniformized, it is possible to ascertain the state of the catalyst 50 more accurately.

[0047] Given that the state of the catalyst 50 can be ascertained more accurately, the service life of the catalyst 50 can be determined to a nicety.

[0048] As shown in FIG. 7, the oxygen sensor 54 is disposed outwardly of the downstream edge 31 b of the exhaust pipe 31 when the exhaust pipe 31 is viewed along a longitudinal axis 31X thereof. Thus, exhaust gas discharged from the exhaust pipe 31 and having its temperature increased is less likely to be brought into direct contact with the oxygen sensor 54. Therefore, when the temperature of the silencer 32 drops, water produced by thermal condensation is less liable to be deposited on the oxygen sensor 54. As a result, deterioration of the oxygen sensor 54 is reduced, and durability of the oxygen sensor 54 is increased.

[0049] The oxygen sensor 54 is disposed upwardly of the downstream edge 31 b of the exhaust pipe 31. When the engine 17 is shut down and the temperature in the exhaust pipe 31 drops, water contained in a gas in the exhaust pipe 31 may condense in the exhaust pipe 31. The condensed water is directed downwardly. Since the oxygen sensor 54 is disposed upwardly of the downstream edge 31 b of the exhaust pipe 31, it is less likely that the condensed water will be deposited directly on the oxygen sensor 54. As a consequence, the oxygen sensor 54 has its service life increased.

[0050] Referring back to FIG. 6, the oxygen sensor 54 is disposed in the recess 55 defined in the upper surface 32a of the silencer 32. With the oxygen sensor 54 disposed in the recess 55, components that are disposed above the silencer 32 can be lowered. As a result, the vehicle may have its centre of gravity lowered.

[0051] The oxygen sensor 54 is provided in the first expansion chamber 61 that is positioned upstream of the first fluid communication pipe 71. As the first expansion chamber 61 is farther from an outlet 32d (see FIG. 5) of the silencer 32 than the second expansion chamber 62, even if ambient air flows back into the silencer 32, any adverse effect that the ambient air has on data detected by the oxygen sensor 54 can be reduced. Therefore, the state of the catalyst 50 (see FIG. 5) can be ascertained more accurately.

[0052] Referring back to FIG. 8, the silencer 32 has the third expansion chamber 63 that is separate from the first expansion chamber 61 that is provided with the oxygen sensor 54, and the drain hole 88 is provided in the third expansion chamber 63. When the temperature of the silencer 32 drops, water condensed in the first expansion chamber 61 flows out through the drain hole 88 in the third expansion chamber 63. As water is less likely to remain in the first expansion chamber 61, therefore, deterioration of the oxygen sensor 54 is reduced. As a result, the service life of the oxygen sensor 54 can be extended.

[0053] A modification of the structure shown in FIG. 6 will be described below.

[0054] As shown in FIG. 9, the second separator 58 that separates the first expansion chamber 61 and the second expansion chamber 62 is disposed in the silencer 32, and has the support hole 76 defined in the upper portion thereof. The first fluid communication pipe 71 is disposed in the support hole 76 such that the axis of the first fluid communication pipe 71 extends generally horizontally.

[0055] The modification differs from the first embodiment in that the downwardly depressed recess 55 is defined 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 recess 55. In other words, the oxygen sensor 54 is disposed downstream of the first fluid communication pipe 71 through which the exhaust gas flows. Other details of the modification are not different from those of the first embodiment, and will not be described in detail below.

[0056] Operation of the modification will be described below.

[0057] The exhaust gas discharged from the exhaust pipe 31 expands in the first expansion chamber 61, passes from the first expansion chamber 61 through the first fluid communication pipe 71, and is then expanded in the second expansion chamber 62. At this time, the exhaust gas stirred in the first expansion chamber 61 is brought into contact with the oxygen sensor 54 that is disposed in facing relation to the opening 71k of the first fluid communication pipe 71. Since the oxygen sensor 54 is disposed outwardly of the extension of the downstream edge 31 b (see FIG. 7) of the exhaust pipe 31, the exhaust gas that is brought into contact with the oxygen sensor 54 has been sufficiently stirred and uniformized in the first expansion chamber 61. Therefore, as the exhaust gas that has been sufficiently stirred and uniformized is brought into contact with the oxygen sensor 54, it is possible to ascertain the state of the catalyst 50 (see FIG. 5) more accurately.

[0058] Since the oxygen sensor 54 is disposed outwardly of the extension of the downstream edge 31 b of the exhaust pipe 31, the exhaust gas that has been sufficiently stirred and uniformized in the first expansion chamber 61 is brought into contact with the oxygen sensor 54. Therefore, as the exhaust gas that has been sufficiently stirred and uniformized is brought into contact with the oxygen sensor 54, the service life of the catalyst 50 can be determined to a nicety.

[0059] The oxygen sensor 54 is disposed outwardly of the downstream edge 31 b of the exhaust pipe 31 when the exhaust pipe 31 is viewed along the longitudinal axis 31X (see FIG. 7) thereof. The exhaust gas discharged from the exhaust pipe 31 and having its temperature increased is less likely to be brought into direct contact with the oxygen sensor 54. Therefore, when the temperature of the silencer 32 drops, water produced by thermal condensation is less liable to be deposited on the oxygen sensor 54. As a result, deterioration of the oxygen sensor 54 can be reduced, and durability of the oxygen sensor 54 can be increased.

[0060] Furthermore, the oxygen sensor 54 is provided in the second expansion chamber 62 that is positioned downstream of the first fluid communication pipe 71. As 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) along the length of the exhaust route starting from the outlet 32d of the silencer 32, even if ambient air flows back into the silencer 32 due to a turbulent flow of the exhaust gas, any adverse effect that the ambient air has on data detected by the oxygen sensor 54 is reduced. Therefore, the state of the catalyst 50 (see FIG. 5) can be ascertained more accurately. Other operational details are the same as those of the first embodiment and will not be described below.

[0061] A second embodiment of the present invention will be described below with reference to the drawings.

[0062] As shown in FIGS. 10 and 11, an 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 for purifying an exhaust gas.

[0063] The silencer 32 has an increasing-diameter portion 91, an outer tube 92 connected to the rear end of the increasing-diameter portion 91 and extending rearwardly, an inner tube 93 disposed coaxially within the outer tube 92, an inner lid 94 closing off the rear end of the inner tube 93, and an outer lid 95 fitted in the outer tube 92 from behind the outer side of the inner lid 94. The inner tube 93 has a first separator 57, a second separator 58, and a third separator 59 housed therein. The first separator 57, the second separator 58, and the third separator 59 extend perpendicularly to the longitudinal axis of the inner tube 93 at spaced intervals, and divide an expansion chamber 60 defined in the silencer 32, wherein the exhaust gas expands, into compartments. The first separator 57, the second separator 58, and the third separator 59 extend generally perpendicularly to the longitudinal axis of the silencer 32. The expansion chamber 60 is divided into four expansion chambers by the first separator 57, the second separator 58, and the third separator 59.

[0064] The expansion chamber 60 includes a first expansion chamber 61, a second expansion chamber 62 disposed downstream of the first expansion chamber 61, a third expansion chamber 63 disposed downstream of the second expansion chamber 62, and a fourth expansion chamber 64 disposed downstream of the third expansion chamber 63. The first expansion chamber 61, the fourth expansion chamber 64, the third expansion chamber 63, and the second expansion chamber 62 are arranged longitudinally successively in that order in the silencer 32 from front to back. The first expansion chamber 61 and the second expansion chamber 62 are held in fluid communication with each other by a first fluid communication pipe 71 extending through the first separator 57, the second separator 58, and the third separator 59 and supported by the first separator 57, the second separator 58, and the third separator 59. The second expansion chamber 62 and the third expansion chamber 63 are held in fluid communication with each other by a second fluid communication pipe 72 extending through the third separator 59 and supported by the third separator 59. The third expansion chamber 63 and the fourth expansion chamber 64 are held in fluid communication with each other by a third fluid communication pipe 73 extending through the second separator 58 and supported by the second separator 58. The fourth expansion chamber 64 is vented to the outside by two fourth fluid communication pipes 97A and 97B extending through the second and third separators 58 and 59 and supported by the second and third separators 58 and 59. A perforated plate 98 is located between the first separator 57 and the increasing-diameter portion 91.

[0065] The exhaust gas that has passed through the downstream end of the catalyst 50 expands in the first expansion chamber 61 wherein the perforated plate 98 is located, passes through the first fluid communication pipe 71 provided in the first expansion chamber 61, and reaches the second expansion chamber 62. The exhaust gas expands in the second expansion chamber 62, and the exhaust gas that has expanded in the second expansion chamber 62 passes through the second fluid communication pipe 72, and reaches the third expansion chamber 63. The exhaust gas expands in the third expansion chamber 63, and thereafter passes through the third fluid communication pipe 73, then passes through the two fourth fluid communication pipes 97A and 97B that are connected to the rear end of the third fluid communication pipe 73, and is discharged out of the silencer 32.

[0066] The exhaust pipe 31, which houses a catalyst 50 disposed in the rear end thereof, extends into the increasing-diameter portion 91 that defines the first expansion chamber 61. An oxygen sensor 54 for detecting an oxygen component in the exhaust gas is mounted on the increasing-diameter portion 91 of the silencer 32 downstream of the catalyst 50. The oxygen sensor 54 is disposed outwardly of the downstream edge 31b of the exhaust pipe 31 when the exhaust pipe 31 is viewed along the longitudinal axis thereof. The oxygen sensor 54 is provided in the first expansion chamber 61 and disposed upwardly of the downstream edge 31 b of the exhaust pipe 31.

[0067] As shown in FIG. 12, a boss 82 having an internally threaded surface 78 with which the oxygen sensor 54 is held in threaded engagement is welded to a portion of the increasing-diameter portion 91 which corresponds to the first expansion chamber 61. Since the oxygen sensor 54 is mounted on the silencer 32 by the boss 82, the strength with which the oxygen sensor 54 is supported can be ensured. The oxygen sensor 54 has on its lower end an element 83 serving as an oxygen detector. The element 83 is disposed outwardly of the downstream edge 31 b (see FIG. 10) of the exhaust pipe 31.

[0068] The operation of the second embodiment will be described below.

[0069] Referring back to FIG. 10, the exhaust pipe 31 extends into the first expansion chamber 61 of the silencer 32 in which the exhaust gas expands. The exhaust gas discharged from the exhaust pipe 31 expands in the first expansion chamber 61. At this time, the exhaust gas that has been stirred in the first expansion chamber 61 is brought into contact with the oxygen sensor 54 that is disposed outwardly of the downstream edge 31 b of the exhaust pipe 31 when the exhaust pipe 31 is viewed along the longitudinal axis 31X thereof.

[0070] Since the oxygen sensor 54 is disposed outwardly of the extension of the downstream edge 31 b of the exhaust pipe 31, exhaust gas that has been sufficiently stirred and uniformized in the first expansion chamber 61 is brought into contact with the oxygen sensor 54. Therefore, as the exhaust gas that has been sufficiently stirred and uniformized is brought into contact with the oxygen sensor 54, it is possible to ascertain the state of the catalyst 50 more accurately.

[0071] The oxygen sensor 54 is disposed outwardly of the downstream edge 31 b of the exhaust pipe 31 when the exhaust pipe 31 is viewed along the longitudinal axis thereof. The exhaust gas discharged from the exhaust pipe 31 and having its temperature increased is thus less likely to be brought into direct contact with the oxygen sensor 54. Therefore, when the temperature of the silencer 32 drops, water produced by thermal condensation is less liable to be deposited on the oxygen sensor 54. As a result, deterioration of the oxygen sensor 54 can be reduced, and durability of the oxygen sensor 54 can be increased.

[0072] The oxygen sensor 54 is disposed upwardly of the downstream edge 31 b of the exhaust pipe 31. When the engine 17 is shut down and the temperature in the exhaust pipe 31 drops, water contained in a gas in the exhaust pipe 31 may condense in the exhaust pipe 31. The condensed water is directed downwardly. Since the oxygen sensor 54 is disposed upwardly of the downstream edge 31 b of the exhaust pipe 31, the condensed water is less likely to be deposited directly on the oxygen sensor 54. As a consequence, the oxygen sensor 54 can have its service life increased.

[0073] The oxygen sensor 54 is provided in the first expansion chamber 61. As the first expansion chamber 61 is farther from the outlet 32d of the silencer 32 than the second expansion chamber 62, even if ambient air flows back into the silencer 32 due to a turbulent flow of the exhaust gas, any adverse effect that the ambient air has on data detected by the oxygen sensor 54 can be reduced. Therefore, the state of the catalyst 50 can be ascertained more accurately.

[0074] The structure of the exhaust device has been described above. The exhaust device that has been described is a left one of a pair of left and right exhaust devices. The right exhaust device has a structure which is bilaterally symmetric with respect to the lateral centreline of the vehicle across the transverse directions thereof, and operates in the same manner and offers the same advantages as the left exhaust device Therefore, the right exhaust device will not be described herein.

[0075] The present invention has been described as applied to a motorcycle. However, the present invention is also applicable to a three-wheeled vehicle and may also be applied to vehicles in general.

[0076] The present invention is preferably applicable to a motorcycle wherein an exhaust device for an engine is provided with an oxygen sensor.

Claims

1. An exhaust device for an engine, comprising an exhaust pipe (31) for guiding an exhaust gas from the engine (17) and a silencer (32) connected to a downstream side of the exhaust pipe (31), for reducing exhaust sounds and discharging the exhaust gas out of the exhaust device, wherein
said exhaust pipe (31) includes a catalyst (50) for purifying the exhaust gas; said silencer (32) includes an expansion chamber (60) in which the exhaust gas expands;
said exhaust pipe (31) extends into said expansion chamber (60);
said expansion chamber (60) includes a first expansion chamber (61) and a second expansion chamber (62) downstream of said first expansion chamber (61);
said first expansion chamber (61) and said second expansion chamber (62) are connected to each other by a first fluid communication pipe (71);
said exhaust device includes an oxygen sensor (54) for detecting an oxygen component in the exhaust gas, said oxygen sensor (54) being disposed downstream of said catalyst (50) in facing relation to an opening of said first fluid communication pipe (71); and
said oxygen sensor (54) is disposed outwardly of a downstream edge of said exhaust pipe (31) when said exhaust pipe (31) is viewed along a longitudinal axis thereof.

2. The exhaust device for an engine according to claim 1, wherein said oxygen sensor (54) is disposed upwardly of the downstream edge of said exhaust pipe (31).

3. The exhaust device for an engine according to claim 1 or 2, wherein said silencer (32) has a recess (55) defined in an upper surface thereof; and
said oxygen sensor (54) is disposed in said recess (55).

4. The exhaust device for an engine according to any preceding claim, wherein said oxygen sensor (54) is provided in said first expansion chamber (61) which is upstream of said first fluid communication pipe (71).

5. The exhaust device for an engine according to any preceding claim, wherein said expansion chamber (60) included in said silencer (32) further includes a third expansion chamber (63) disposed downstream of said second expansion chamber (62); and
said third expansion chamber (63) has a drain hole (88) for draining water.

Drawing