JP5285505B2 - Engine exhaust system - Google Patents

Description

  The present invention relates to an improvement in an exhaust system for an engine provided with a catalyst for purifying exhaust gas in the middle of an exhaust passage.

  An exhaust system for an engine in which an exhaust passage through which exhaust gas passes is connected to the engine and a catalyst for purifying exhaust gas is provided in the middle of the exhaust passage is known as a prior art (for example, Patent Document 1 (FIG. 1 See 1).).

  In FIG. 1 of Patent Document 1, an exhaust gas purification apparatus for an automobile is connected to an engine 41 (the reference sign is the same as that of the same publication; the same applies hereinafter), and an exhaust pipe 47 is connected to the middle of the exhaust pipe 47. The sub-catalytic converter 45 having a function of heating the metal catalyst carrier 61 is provided, and a bypass line 49 is provided between the upstream and downstream of the exhaust line 47, and the bypass line is provided downstream of the bypass line 49. 49 and an exhaust pipe 47 are provided, and a first butterfly valve 57 is disposed on the exhaust pipe 47 upstream of the connection 51 and similarly upstream of the connection 51. The second butterfly valve 59 is disposed on the side of the bypass line 49, the main exhaust line 55 is provided downstream of the connecting portion 51, and the main catalytic converter 53 is provided downstream of the main exhaust line 55. It is provided. Then, during warm-up operation, the first butterfly valve 57 is opened, the second butterfly valve 59 is closed, and the metal catalyst carrier 61 is energized and heated to activate the catalyst early.

  However, in the engine exhaust apparatus of Patent Document 1, the metal catalyst carrier 61 capable of energizing the sub-catalytic converter 45 is provided, which causes a problem that the entire apparatus is complicated and easily increases the cost of the apparatus.

JP-A-8-14032

  An object of the present invention is to provide an engine exhaust device that can activate a catalyst at an early stage while suppressing an increase in cost of the device.

The invention according to claim 1 is an engine exhaust system comprising an engine, an exhaust passage through which exhaust gas of the engine passes, and a catalyst disposed in the exhaust passage to purify exhaust gas. A part of the exhaust passage is a substantially U-shaped curved portion, the catalyst is disposed downstream of the curved portion, and the curved portion passage is disposed between the upstream of the curved portion and the downstream of the curved portion and upstream of the catalyst. A bypass passage connected at a distance shorter than the length is provided, and the catalyst includes a first catalyst and a second catalyst provided downstream of the first catalyst. The first catalyst has a volume larger than that of the two catalysts. It is small, and is arranged downstream of a branch portion where the exhaust passage and the bypass passage branch, and upstream of a junction portion where the exhaust passage and the bypass passage merge .

  The invention according to claim 2 is characterized in that the bending portion is disposed below the engine.

In the invention according to claim 3 , the first catalyst and the second catalyst are arranged in the same axial direction and close to each other, and store the first catalyst storage portion for storing the first catalyst and the second catalyst. An enlarged-diameter portion that expands in the downstream direction is provided between the second catalyst housing portion and a bypass passage is connected to the enlarged-diameter portion.

The invention according to claim 4 is characterized in that the diameter of the bypass passage is smaller than the diameter of the curved portion of the exhaust passage.

In the invention according to claim 5 , the engine includes a front bank and a rear bank disposed behind the front bank, and an exhaust passage extending from the cylinders is connected to a common catalyst, and has a curved portion. The bypass passage is provided in the exhaust passage of the rear bank.

In the invention according to claim 1, a bypass passage is provided between the upstream side of the bending portion and the downstream side of the bending portion and upstream of the catalyst so as to be connected at a distance shorter than the passage length of the bending portion.
When the engine is started, the exhaust gas discharged from the engine passes through a bypass passage shorter than the length of the curved portion and reaches the catalyst.

  Conventionally, in order to activate the catalyst at an early stage, a separate catalytic converter having a catalyst metal catalyst carrier is provided, and the metal catalyst carrier is energized and heated. According to such means, there is a problem that it is easy to increase the cost of the exhaust device.

  In this regard, in the present invention, it is only necessary to provide a bypass passage shorter than the passage length of the bending portion between the upstream side of the bending portion and the downstream side of the bending portion and upstream of the catalyst. Cost increase can be suppressed. In this case, since the exhaust gas passes through the bypass passage and can reach the catalyst at a short distance, the high-temperature gas can be applied to the catalyst. Since the high-temperature gas can hit the catalyst, the catalyst can be activated early.

Therefore, the engine exhaust device of the present invention can activate the catalyst at an early stage while suppressing an increase in the cost of the device.
In addition, since the exhaust passage includes a curved portion and has a sufficient length, there is an advantage that it is easy to obtain the optimum output characteristics of the engine.
Furthermore, since the catalyst is composed of the first catalyst and the second catalyst, and the exhaust gas is purified by both the first catalyst and the second catalyst, the purification performance can be improved.
In addition, since the volume of the first catalyst is made smaller than the volume of the second catalyst, the heat capacity of the first catalyst can be reduced, and the activation of the first catalyst can be promoted.

  In the invention which concerns on Claim 2, the curved part is arrange | positioned under the engine. For example, the engine and the exhaust passage can be arranged compactly as compared with the case where the curved portion is arranged behind the engine.

In the invention which concerns on Claim 3 , the enlarged diameter part is provided between the 1st catalyst accommodating part and the 2nd catalyst accommodating part, and the bypass channel is connected to this enlarged diameter part. The outlet of the bypass passage can be directed to the upstream end of the second catalyst, and the exhaust gas that has exited from the outlet of the bypass passage can be smoothly flowed toward the second catalyst.

In the invention according to claim 4 , by setting the diameter of the bypass passage to be smaller than the diameter of the curved portion of the exhaust passage, the surface area of the bypass passage can be reduced, and as a result, radiation that escapes from the bypass passage into the air. The amount of heat can be reduced and the heat capacity of the bypass passage itself can be reduced. As a result, the temperature of the exhaust gas passing through the bypass passage can be kept high.

In the invention according to claim 5 , the exhaust passage extending from the cylinder provided in the front bank and the cylinder provided in the rear bank is connected to a common catalyst, and the curved portion and the bypass passage are connected to the exhaust passage of the rear bank. Is provided. The exhaust passage extending from the rear bank is less susceptible to traveling wind and easily maintained by the front bank disposed at the front, so that the catalyst is more easily activated by providing a curved portion and a bypass passage.

1 is a left side view of a motorcycle according to the present invention. 1 is a rear left side view of a motorcycle according to the present invention. 1 is a rear right side view of a motorcycle according to the present invention. 1 is a bottom view for explaining an exhaust device for a motorcycle according to the present invention. 1 is a plan view illustrating an exhaust device for a motorcycle according to the present invention. 1 is a perspective view illustrating an exhaust device for a motorcycle according to the present invention. It is a top view of the chamber storage part with which the motorcycle concerning the present invention is equipped. FIG. 8 is a cross-sectional view taken along line 8-8 in FIG. 7. FIG. 9 is a sectional view taken along line 9-9 in FIG. 8. FIG. 10 is a sectional view taken along line 10-10 in FIG. 8. It is the 11-11 line sectional view of FIG. It is another Example figure of FIG. It is another Example figure 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. The drawings are viewed in the direction of the reference numerals.

First, Embodiment 1 of the present invention will be described with reference to the drawings.
In FIG. 1, a motorcycle 10 has a front fork 12 attached to a head pipe 11 so as to be steerable, and main frames 13 and 14 (only the reference numeral 13 on the front side is shown) extend from the head pipe 11 to the left and right. The engine 15 is attached to the main frames 13 and 14, and a pivot shaft 18 is provided on the rear portion 16 of the engine so as to penetrate left and right. A swing arm 21 is attached to the pivot shaft 18 so as to freely swing up and down. This is a vehicle in which the rear frame 22 is extended from the rear. A body frame 20 is constituted by the main frames 13 and 14 and the rear frame 22 extending from the rear of the main frames 13 and 14.

The front fork 12 has a front wheel 26 rotatably attached to the lower end and a steering handle 27 attached to the upper end. The front fender 28 covers the front wheel 26 with a front fender 28.
The engine 15 includes a crankcase 31, a front bank 33 extending obliquely upward and forward from the crankcase 31, and a rear bank extending obliquely upward and rearward from the crankcase 31 and at an angle of 90 ° with respect to the front bank 33. , A front bank 33 is a two-cylinder, and a rear bank 34 is a two-cylinder V-type V-type engine.

  The front bank 33 includes a front cylinder block 35, a front cylinder head 36 attached above the front cylinder block 35, and a front head cover 37 that covers the front cylinder head 36. Similarly, the rear bank 34 includes a rear cylinder block 45, a rear cylinder head 46 attached above the rear cylinder block 45, and a rear head cover 47 that covers the rear cylinder head 46. An oil pan 48 covers the lower part of the crankcase 31.

The swing arm 21 has a rear wheel 25 rotatably attached to the rear end via an axle 19, and a lower end of the rear cushion unit 26 is attached to a front portion of the swing arm 21 via a link mechanism 55. The upper end of the rear cushion unit 26 is attached to the main frames 13 and 14 side. The link mechanism 55 is also attached to an underframe 56 provided at the rear portion of the engine 15.
In the figure, 57 is a main seat supported by the rear frame 22, 58 is a pillion seat supported by the rear frame 22, 61 is a front cowl, 62 is a center cowl, 63 is a lower cowl, 64 is a rear cowl, 65 is a fuel tank, 66, Reference numeral 66 (only the reference numeral 66 on the front side of the figure is shown) is a pillion step holder, 67 is a chain cover, 68 is a rear fender, 69 is a chain, and 70 is a sprocket.

2 and 3, first and third suspension parts 71 to 73 to which the engine 15 is attached are provided on the left and right main frames 13 and 14 as constituent members of the vehicle body frame 20.
A pivot shaft support portion 74 that supports the above-described pivot shaft 18 is formed in the rear portion 16 of the engine, and an underframe 56 that supports an exhaust pipe 77 including an exhaust passage 76 described later near the pivot shaft support portion 74. Underframe support portions 78, 78 to which are attached are provided. The underframe 56 is supported not only by the underframe support portion 78 but also by the pivot shaft support portion 74.

  Rear frames 22 extend rearward and obliquely upward from the rear portions of the left and right main frames 13, 14, and these rear frames 22 are upper rear frames 23, 23 (only the reference numeral 23 on the front side in the figure is shown) and a lower portion. The rear frames 24 and 24 (only the reference numeral 24 on the front side of the figure is shown), and the rear end portions 23a and 23a of the upper rear frame and the rear end portions 24a and 24a of the lower rear frame are connected to each other. Reference numerals 79 and 79 (only the reference numeral 79 on the front side of the drawing) are reinforcing members. 51 is a dynamo cover, 52 is a clutch cover.

Hereinafter, the configuration of the engine exhaust device will be described.
2 to 4, left and right front exhaust pipes 81 and 82 as components of the exhaust passage 76 are extended from the front cylinder head 36, and the left and right two front exhaust pipes 81 and 82 are moved rearward. After extending, the front collecting portion 83 is connected to the rear ends of the two left and right front exhaust pipes 81 and 82 and joined together, and the first catalyst 85 and the second catalyst 86 are connected to the rear end portion 84 of the front collecting portion. It connected to the chamber storage part 87 to be stored. The left and right front exhaust pipes 81 and 82 pass below the engine 15.

Further, left and right two rear exhaust pipes 91 and 92 as components of the exhaust passage 76 are extended from the rear cylinder head (reference numeral 46 in FIG. 1), and the left and right two rear exhaust pipes 91 and 92 are temporarily connected. After extending to the right side of the vehicle, it extends downward, connects the rear collecting portion 93 to the rear ends of the two left and right rear exhaust pipes 91, 92 and joins them, and is downstream of the rear collecting portion 93. The rear end portion 94 was connected to a chamber housing portion 87 in which the first catalyst 85 and the second catalyst 86 were housed. The left and right rear exhaust pipes 91 and 92 pass behind the engine 15.
The rear assembly portion 93 includes a rear extending portion 97 extending from the rear upper portion to the front lower portion, and a curved portion 98 connected to the downstream side of the rear extending portion 97 and having a substantially U shape.

  A bypass pipe 102 through which exhaust gas passes between a rear extending portion 97 constituting the rear collecting portion 93 and a diameter expanding portion 101 provided on the upstream side of the second catalyst 86 in the chamber storage portion 87. Has been passed. A bypass passage 103 is formed in the bypass pipe 102, and a valve unit 104 is interposed in the bypass passage 103.

  The first catalyst 85 is disposed downstream of the branch portion 106 where the bypass passage 103 branches, and upstream of the junction portion 107 where the bypass passage 103 joins and is disposed in the chamber housing portion 87 constituting the exhaust passage.

  The chamber storage portion 87 to which the front collection portion 83 and the rear collection portion 93 are connected is continuous with the first catalyst storage portion 111 in which the first catalyst 85 is stored, and behind the first catalyst storage portion 111. And a second catalyst storage portion 112 in which the second catalyst 86 is stored, and an outlet portion 113 through which the purified exhaust gas passes is provided on the downstream side of the chamber storage portion 87. A connecting pipe 114 extends from the connecting pipe 114, and a silencer 115 is connected to the connecting pipe 114.

The exhaust gas passes through the front exhaust pipes 81 and 82, the front collecting portion 83, the rear exhaust pipes 91 and 92, the rear collecting portion 93, and the chamber housing portion 87 extending from the engine 15 described above. These members are collectively referred to as an exhaust passage 76.
The connecting pipe 114 extending rearward from the rear part 117 of the chamber housing part and the silencer 115 connected to the connecting pipe 114 are collectively referred to as a rear exhaust passage 76R. The rear exhaust passage 76R is attached to a muffler stay 118 that extends downward from the right lower rear frame 24 that constitutes the body frame 20 side.

  A chamber housing portion 87 is provided with a chamber mounting portion 121 at an upper portion of the first catalyst housing portion 111, and this chamber mounting portion 121 is provided on the side of the vehicle body frame (reference numeral 20 in FIG. 2). 56 is attached.

  That is, the motorcycle 10 includes a front exhaust pipe 81 and 82 as an exhaust passage that extends rearward and passes through the lower side of the engine 15 and through which the exhaust gas passes, and a body frame in the middle of the front exhaust pipe 81 and 82. 20 is provided with a chamber accommodating portion 87 in which a first catalyst 85 disposed below 20 and a second catalyst 86 disposed adjacent to the downstream side of the first catalyst 85 are accommodated.

  The height (H10) of the upper surface 123 of the first catalyst from the ground is set lower than the height (H20) of the upper surface 124 of the second catalyst from the ground, and the upper surface 125 of the first catalyst storage unit from the ground. The height (H1) is set lower than the height (H2) from the ground of the upper surface 126 of the second catalyst storage unit.

  A curved portion 98 provided in the rear collecting portion 93 through which the exhaust gas of the rear cylinder head 46 merges and passes is disposed below the engine 15. Since the curved portion 98 is disposed below the engine 15, the rear collecting portion 93 that forms the exhaust passage with the engine 15 can be compactly disposed.

  The engine 15 is mounted on a vehicle, and the left and right rear exhaust pipes 91 and 92 as components of the exhaust passage extend from the rear surface of the engine (reference numeral 17 in FIG. 1). That is, the exhaust passage 76 extending from the cylinder provided in the front bank 33 and the cylinder provided in the rear bank 34 is connected to the common catalyst 131, and the curved portion 98 and the bypass passage 103 are connected to the exhaust passage of the rear bank 34. And the rear exhaust pipes 91 and 92 are provided in a rear collecting portion 93. The rear exhaust pipes 91 and 92 serving as exhaust passages extending from the rear bank 34 are less likely to be hit by traveling wind and easily maintained by the front bank 33 and the like disposed at the front. By providing 98 and the bypass passage 103, the catalyst is more easily activated. That is, since the traveling wind hardly hits the rear exhaust pipes 91 and 92, the cooling of the rear exhaust pipes 91 and 92 by the traveling wind can be suppressed, and the activation of the catalyst can be further promoted.

5 and 6, the engine exhaust device 130 exhausts into the exhaust passage 76 through which the exhaust gas of the engine (reference numeral 15 in FIG. 1) passes and the chamber housing portion 87 arranged in the middle of the exhaust passage 76. And a catalyst 131 for purifying the gas. A part of the rear collecting portion 93 provided in the exhaust passage 76 is a substantially U-shaped curved portion 98, and the catalyst is disposed downstream of the curved portion 98. A first catalyst 85 that constitutes one of 131 is disposed and is connected between the upstream of the curved portion 98 and the downstream of the curved portion 98 and upstream of the second catalyst 86 at a distance shorter than the passage length of the curved portion 98. A bypass passage 103 is provided. That is, the bypass passage 103 is connected to the enlarged-diameter portion 101 that is the chamber housing portion 87 and is provided between the first catalyst 85 and the second catalyst 86.
In this embodiment, the merging portion of the bypass passage is connected between the first catalyst and the second catalyst, but may be connected to the chamber storage portion and upstream of the first catalyst. Absent.

Hereinafter, the detailed structure of the chamber storage portion 87 in which the first catalyst 85 and the second catalyst 86 are stored will be described.
7 and 8, the catalyst unit 132 includes a first catalyst storage unit 111 that stores the first catalyst 85, a second catalyst storage unit 112 that stores the second catalyst 86, a first catalyst storage unit 111, and a first catalyst storage unit 111. A diameter-expanding portion 101 that expands in the downstream direction is provided between the two catalyst storage portions 112.

A spacer 136 that is formed in a ring shape on the rear outer peripheral portion 135 of the first catalyst and that holds the first catalyst 85 is provided. The spacer 136 is fixed to the first catalyst storage portion 111, and is attached to the front outer peripheral portion 137 of the first catalyst. A first mesh spacer 141 for holding is provided.
A plurality of first welding holes for attaching the first catalyst 85 fixed to the spacer 136 to the first catalyst housing portion 111 at a position corresponding to the spacer 136 serving as a holding portion of the first catalyst 85 in the first catalyst housing portion 111. 143... (... indicates a plurality. The same applies hereinafter) is formed, and the first catalyst 85 is fixed using these first welding holes 143.

A holding guide portion 146 is provided on the front outer peripheral portion 147 of the second catalyst, the guide portion 146 is fixed to the second catalyst storage portion 112, and a second mesh spacer for holding is provided on the rear outer peripheral portion 145 of the second catalyst. 142 is provided.
In the second catalyst storage portion 112, a plurality of second catalysts that stop the second catalyst 86 including the guide portion 146 in the second catalyst storage portion 112 at a position corresponding to the guide portion 146 serving as a holding portion of the second catalyst 86. Weld holes 144 are formed, and the second catalyst 86 is fixed using these second weld holes 144.

In FIG. 9, a holding first mesh spacer 141 is provided between the front outer peripheral portion 137 of the first catalyst and the first catalyst storage portion 111, and the first catalyst 85 has a major axis along the vehicle width direction. It has an elongated oval cross section.
The first catalyst storage unit 111 has an oval cross section, and is formed by abutting the first upper half 151 and the first lower half 152 and welding them together.

  In FIG. 10, the spacer 136 is fixed to the outer peripheral portion 138 of the first catalyst. A chamber attachment portion 121 is attached to the upper surface 125 of the first catalyst storage portion. In the figure, reference numeral 154 denotes a welded portion for fixing the space between the spacer 136 and the first catalyst housing portion 111.

  In FIG. 11, the guide part 146 attached to the outer peripheral part of the second catalyst 86 is fixed to the outer peripheral part 148 of the second catalyst. In the figure, 155... Are welded portions that adhere between the guide portion 146 and the second catalyst housing portion 112.

  Referring also to FIGS. 5 to 7, the catalyst 131 includes a first catalyst 85 and a second catalyst 86 provided downstream of the first catalyst 85, and the first catalyst 85 is a second catalyst. 86, the rear extension portion 97 constituting the rear connecting portion 157 as the exhaust passage and the branching portion 106 where the bypass passage 103 branches, and the enlarged diameter portion 101 constituting the exhaust passage and the bypass. It arrange | positions upstream of the confluence | merging part 107 where the channel | path 103 merges.

The catalyst 131 includes the first catalyst 85 and the second catalyst 86, and the exhaust gas is purified by both the first catalyst 85 and the second catalyst 86, so that the purification performance can be improved.
In addition, since the volume of the first catalyst 85 is smaller than the volume of the second catalyst 86, the heat capacity of the first catalyst 85 can be reduced, and the activation of the first catalyst 85 can be promoted.

  Since the diameter of the bypass passage 103 is smaller than the diameter of the curved portion 98 of the exhaust passage, the surface area of the bypass passage 103 can be reduced, and as a result, the amount of radiant heat that escapes from the bypass passage 103 into the air is reduced. At the same time, the heat capacity of the bypass passage itself can be lowered, and as a result, the temperature of the exhaust gas passing through the bypass passage 103 can be kept high.

The operation of the above-described motorcycle and its exhaust device will be described next.
A bypass passage 103 connected between the upstream side of the bending portion 98 and the downstream side of the bending portion 98 and upstream of the catalyst 131 is connected at a distance shorter than the passage length of the bending portion 98.

  Conventionally, in order to activate the catalyst at an early stage, there are cases where a corresponding means is separately utilized by energizing or heating the metal catalyst carrier of the catalyst. However, such means has a problem that it tends to increase the cost of the exhaust device.

In this regard, in the present invention, it is only necessary to provide a bypass passage 103 shorter than the passage length of the bending portion 98 between the upstream side of the bending portion 98 and the downstream side of the bending portion 98 and upstream of the catalyst 131. Therefore, the cost increase of the exhaust device 130 can be suppressed. In addition, since the exhaust gas can pass through the bypass passage 103 and reach the second catalyst 86 constituting the catalyst at a short distance, the high-temperature gas can be applied to the catalyst. Since the high-temperature gas can be applied to the catalyst, the second catalyst 86 can be activated early. Therefore, it is possible to activate the second catalyst 86 at an early stage while suppressing an increase in the cost of the exhaust device 130.
Furthermore, since the exhaust passage 76 includes the curved portion 98 and has a sufficient length, there is an advantage that the optimum output characteristics of the engine 15 can be easily obtained.

  Referring to FIGS. 2, 4, and 9, first catalyst 85 has an oval cross section in which the long axis extends along the vehicle width direction, so that the cross sectional area of first catalyst 85 is sufficient. The height of the first catalyst 85 can be suppressed while ensuring a large capacity of the first catalyst 85. In addition, the chamber attachment portion 121 is attached to the upper portion of the first catalyst storage portion 111, and the height (H1) of the upper surface 125 of the first catalyst storage portion is disposed adjacent to the downstream side of the first catalyst. It is set lower than the height (H2) of the upper surface 126 of the second catalyst storage portion. And the chamber attachment part 121 is attached to the upper surface 125 of the 1st catalyst storage part by which height is set lower than the height (H2) of the upper surface 126 of a 2nd catalyst storage part. Since the chamber mounting portion 121 is disposed in a region where there is a difference between the height of the upper surface 125 of the first catalyst and the height of the upper surface 126 of the second catalyst housing portion, the height of the first catalyst housing portion 111 from the ground ( The chamber accommodating portion 87 can be supported while keeping H10) high.

Therefore, even when the size of the first catalyst 85 is increased, the height (H10) of the first catalyst 85 can be suppressed, and the ground height (H1) of the first catalyst storage unit 111 can be increased. Therefore, the minimum ground clearance (HL) of the vehicle can be easily increased.
A rear exhaust passage 76 extending to the rear portion 117 of the chamber housing portion is attached to the vehicle body frame 20 side. The chamber storage portion 87 includes a chamber mounting portion 121 provided at the upper part of the first catalyst storage portion 111 that constitutes the front portion 116 of the chamber storage portion, and a muffler that constitutes a rear exhaust passage 76 disposed behind the chamber storage portion 87. It is supported by a muffler stay 118 to which the container 115 is attached. That is, the chamber storage portion 87 is attached to the body frame 20 at the front and rear portions. For this reason, it becomes possible to attach the chamber accommodating part 87 more reliably to the vehicle body side.

Furthermore, the height (H10) of the upper surface 125 of the first catalyst from the ground (H10) is the height (H0) of the upper surface 161 of the front collecting pipe as an exhaust passage connected immediately before the first catalyst housing 111 from the ground. ), It is possible to suppress the downward bulging of the first catalyst storage unit 111. In addition, since the first catalyst 85 is disposed behind the oil pan 48 swelled below the engine 15, the capacity of the oil pan 48 can be sufficiently secured.
As a result, it is possible to ensure a sufficient cross-sectional area of the catalyst 131 while ensuring a sufficient capacity of the oil pan 48 and to secure a minimum ground clearance (HL) of the vehicle to a sufficient height.

  Further, as described above, the engine 15 includes four cylinders, and the exhaust passages 76... Extend from these cylinders, and a plurality of exhaust passages 76.・ Are connected side by side in the vehicle width direction. Since the exhaust passages 76 are arranged in the vehicle width direction, the height direction dimension of the exhaust passages 76 can be suppressed, and the minimum ground clearance (HL) is easily secured.

Next, a second embodiment of the present invention will be described with reference to the drawings.
12 to 13, the main difference from the first embodiment is that the height (H11) from the ground surface of the lower surface 163 of the first catalyst storage unit in which the first catalyst 85 is stored and the second catalyst 86 are stored. The height (H21) from the ground surface of the lower surface 164 of the second catalyst storage portion is set to the same height (H11 = H21), and there is no other significant difference.

The chamber attachment portion 121 is attached to the upper surface 125 of the first catalyst storage portion, and the height (H1) of the upper surface 125 of the first catalyst storage portion is disposed adjacent to the downstream side of the first catalyst storage portion 111. It is set lower than the height (H2) of the upper surface 126 of the second catalyst storage portion.
The height (H11) of the lower surface 163 of the first catalyst storage unit is the same as the height (H21) of the lower surface 164 of the second catalyst storage unit disposed adjacent to the downstream side of the first catalyst storage unit 111. Since it is set, the minimum ground height (HL) of the vehicle can be increased while increasing the capacity of the catalyst.

  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 straddle-type vehicle.

  The engine exhaust device according to the present invention is preferably used in a motorcycle equipped with a V-type engine.

  DESCRIPTION OF SYMBOLS 15 ... Engine, 17 ... Engine rear surface, 20 ... Body frame, 48 ... Oil pan, 76 ... Exhaust passage, 76R ... Rear exhaust passage, 85 ... 1st catalyst, 86 ... 2nd catalyst, 87 ... Chamber accommodating part, 98 DESCRIPTION OF SYMBOLS ... Curve part, 101 ... Expanded diameter part, 103 ... Bypass passage, 111 ... 1st catalyst storage part, 112 ... 2nd catalyst storage part, 121 ... Chamber attachment part, 106 ... Branching part, 107 ... Merging part, 130 ... Engine Exhaust device, 131 ... catalyst.

Claims (5)

An engine (15) , an exhaust passage (76) through which the exhaust gas of the engine (15) passes, and a catalyst (131) disposed in the middle of the exhaust passage (76) to purify the exhaust gas are provided. In the exhaust system of the engine
A part of the exhaust passage (76) is a substantially U-shaped curved portion (98) ,
The catalyst (131) is disposed downstream of the curved portion (98) ,
Upstream of downstream between a and the catalyst (131) of the upstream and the curved portion of the curved portion (98) (98), a bypass passage (103 for connecting a short distance than the passage length of the curved portion (98) ) it is provided,
The catalyst (131) includes a first catalyst (85) and a second catalyst (86) provided downstream of the first catalyst (85).
The first catalyst (85) has a volume smaller than that of the second catalyst (86), is downstream of a branching portion (106) where the exhaust passage (76) and the bypass passage (103) branch, and the An exhaust system for an engine, characterized in that the exhaust path (76) and the bypass path (103) are arranged upstream of a joining portion (107) where they join . The exhaust system for an engine according to claim 1, wherein the curved portion (98) is disposed below the engine (15) . The first catalyst (85) and the second catalyst (86) are disposed in the same axial direction and close to each other,
The diameter of the first catalyst storage portion (111 ) that stores the first catalyst (85) and the second catalyst storage portion (112) that stores the second catalyst (86) are increased in diameter toward the downstream. Part (101) is provided,
The exhaust system for an engine according to claim 1 or 2 , wherein the bypass passage (103) is connected to the enlarged diameter portion (101) . The diameter of the bypass passage path (103), according to claim 1, characterized in that it has a smaller diameter than the diameter of the curved portion (98) of the exhaust passage (76), according to claim 2 or claim 3, wherein the engine Exhaust system. The engine (15) includes a front bank (33) and a rear bank (34) disposed behind the front bank (33) , and an exhaust passage (76) extending from the cylinders has a common catalyst (131). ) to be one that is connected to any one of claims 1-4 wherein the curved portion (98) and the bypass passage (103), characterized in that provided in the exhaust passage (76) of said rear bank (34) The engine exhaust device according to claim 1.

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