JPH06330739A - Exhaust device provided with catalyst for motorcycle - Google Patents

Abstract

PURPOSE:To stabilize the temperature of exhaust gas after confluence, and to improve the cleaning efficiency of a primary catalyst by providing each secondary catalyst on each exhaust tube of a multicylinder engine, by providing the primary catalyst on a confluent exhaust tube, and by reducing the difference in the temperature of each exhaust gas running in each exhaust tube. CONSTITUTION:Exhaust tubes 7, 8 are connected to the exhaust outlets of cylinders 6a, 6b in a multicylinder engine of an exhauster. The exhaust tubes 7, 8 are extended backwards, and after they are confluent downstream, they are connected to a muffler 16. In this structure, a primary catalyst 22 is provided straddling over the confluence part of the exhaust tubes 7, 8. Secondary catalysts 19, 20 are provided on the exhaust tubes 7, 8 before confluence. The difference in the temperature of the exhaust gas running in the exhaust tubes 7, 8 is reduced and the temperature of the confluent exhaust gas is thus stabilized. Namely, the front side exhaust tube 7, which is exposed to running wind, has long tube path, and the temperature of which is ready to be reduced, is formed into a dual tube 17, 18 structure, to reduce the difference in the temperature compared with the rear side exhaust tube 8.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improved exhaust system with catalyst for motorcycles, and more particularly to an exhaust system provided with a plurality of catalysts.

[0002]

2. Description of the Related Art Conventionally, in view of environmental problems and the like, it has been practiced to interpose a catalyst in an exhaust system in order to purify exhaust gas. Exhaust pipes are provided respectively in front and rear cylinders of a V-type engine in which cylinders are arranged in front of and behind the vehicle (hereinafter, in the present specification, an exhaust pipe connected to a front cylinder is referred to as a front exhaust pipe and a rear exhaust pipe). The exhaust pipe connected to the cylinder is referred to as a rear exhaust pipe.), And the exhaust pipes of the type in which these exhaust pipes are joined together on the downstream side and connected to a muffler have been conventionally used. In a multi-cylinder engine such as the V-type engine as described above, since each cylinder does not explode at the same time, high-temperature exhaust gas flows in each exhaust pipe at a shifted timing.

[0003]

When a catalyst is provided in the exhaust system of a V-type engine of the type described above, the catalyst system is provided in the exhaust pipe after joining because of manufacturing cost and arrangement space. However, in this case, the following problems occur. That is, in the engine of the type described above, the lengths of the front exhaust pipe and the rear exhaust pipe are different (specifically, the front exhaust pipe is longer than the rear exhaust pipe),
In addition, since the front exhaust pipe is easily hit by traveling wind, the exhaust gas passing through the front exhaust pipe has a lower temperature than the exhaust gas passing through the rear exhaust pipe, and as a result, is provided downstream from the point where the coalescence has occurred. The temperature of the catalyst becomes unstable because the hot exhaust gas from the rear exhaust pipe and the exhaust gas at a temperature lower than that of the rear exhaust pipe from the front exhaust pipe will flow to the generated catalyst at different timings. Therefore, the purification efficiency is not stable. Therefore, the present invention solves the above-mentioned conventional problems, and the lengths of a plurality of exhaust pipes such as a V-type engine are different,
Further, it is an object of the present invention to provide an exhaust device with a catalyst, in which the purification efficiency of the catalyst is stable even when it is adopted in a multi-cylinder engine having different cooling conditions due to the arrangement of the exhaust pipe.

[0004]

In order to achieve the above-mentioned object, a catalyst-equipped exhaust system for a motorcycle according to the present invention is provided with a plurality of cylinders arranged in a front-rear direction with respect to a traveling direction of the vehicle. Connecting exhaust pipes to the exhaust holes of each cylinder of the engine, extending each exhaust pipe toward the rear of the vehicle, merging these exhaust pipes on the downstream side, and connecting the combined exhaust pipes to the muffler. In the configured exhaust device, a main catalyst is provided at a position where the plurality of exhaust pipes join together so as to straddle each exhaust pipe, while a plurality of exhaust pipes before joining are provided with auxiliary catalysts, respectively. The temperature difference of the exhaust gas flowing through the exhaust pipe is eliminated as much as possible, and the temperature of the exhaust gas at the merged position is stabilized.

[0005]

In the exhaust system with catalyst of the present invention configured as described above, when the engine is started, the exhaust gas from each cylinder flows to each exhaust pipe at a different timing. Then, these exhaust gases flow to the downstream main catalyst while being kept at a temperature that is almost constant with the temperature of the exhaust gas of the other exhaust pipes due to the reaction heat of the auxiliary catalysts provided in each exhaust pipe. , Then exhausted through the muffler.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the exhaust system with catalyst of the present invention will be described below with reference to the accompanying drawings. FIG. 1 is a schematic side view of a motorcycle 2 that adopts the exhaust system with catalyst 1 of the present invention, FIG. 2 is a schematic side view showing the details of the engine 6, the air cleaner 9, and the exhaust device 1 with catalyst of the present invention, and FIG. FIG. 2 is a schematic top view showing the positional relationship of each constituent element of the exhaust device with catalyst 1 of the present invention.

Reference numeral 3 in the drawing denotes a frame. The frame 3 includes a head pipe 3a having a front fork 4 rotatably mounted thereon, a pair of left and right main frames 3b fixed to the head pipe 3a, and a down tube. It is composed of 3c and. Cross pipes 3d, 3e and a pivot shaft 15 are installed between the pair of left and right main frames 3b,
A rear shock absorber 13 is provided between a bracket (no reference sign) extending from the cross pipe 3e and an arm (no reference sign) provided on the cross pipe 3d, and a pair of left and right swing arms 15a is provided on the pivot shaft 15. It is provided (see FIG. 2). A fuel tank 5 and an air cleaner 9 are fixedly installed on the upper portion of the main frame 3b.

Reference numeral 6 in the figure shows a V-type two-cylinder engine in which a front cylinder 6a and a rear cylinder 6b are arranged in a V-shape in a crankcase 6c. This engine 6 is located below the main frame 3b. In the space surrounded by 3b and the down tube 3c, the cylinders 6a, 6b are suspended by pipes 6d, 6e, 6f so that the cylinders 6a, 6b are located at the front and rear, and the engine-equipped exhaust device 1 (hereinafter , Simply referred to as an exhaust device). Further, the engine 6 has a shape in which a rear wall 6g is partially cut off, and forms a recess through which a rear exhaust pipe 8 described later can pass, together with a sprocket cover 6h provided on the side wall ( (See FIG. 3). In the figure, 11 is a motorcycle 2.
It shows a cowl that covers the front from the side to the side. This cowl 11 is a front wheel such as a front fork 4 at the lower front side.
A large opening 11a through which a member relating to 12 can be inserted is provided. Incidentally, 14 in the figure indicates a rear wheel. The exhaust device 1 controls the exhaust pipes 7 and 8 connected to the exhaust holes of the engine 6, the muffler device 16 provided downstream of these exhaust pipes 7 and 8, and the introduction of secondary air into the exhaust pipes 7 and 8. Control unit 10
It consists of and.

The structure of the exhaust device 1 will be described in detail below. An exhaust pipe 7 (hereinafter referred to as a front exhaust pipe 7) is connected to an exhaust hole of a front cylinder 6a of the engine 6, and the front exhaust pipe 7 passes below the engine 6 from the exhaust hole of the engine 6. It extends toward the rear of the vehicle. The front exhaust pipe 7 has a double pipe structure in which a pipe 17 in which a honeycomb-type auxiliary oxidation catalyst 19 (hereinafter, simply referred to as the auxiliary catalyst 19) is interposed is covered with a pipe 18. An exhaust pipe 8 (hereinafter referred to as a rear exhaust pipe 8) is connected to an exhaust hole of the rear cylinder 6b of the engine 6, and the cross pipe 3 is connected to the rear exhaust pipe 8.
d, a honeycomb type secondary oxidation catalyst 20 (hereinafter, simply referred to as secondary catalyst 20) at a position avoiding the suspension pipe 6d and the pivot shaft 15.
Is installed. The above-mentioned two exhaust pipes 7 and 8 are connected to an apparently united exhaust pipe 21 whose interior is partitioned into passages 7 ′ and 8 ′ by a partition wall 21a, and the combined exhaust pipe 21 is directed toward the rear of the vehicle. Extends the honeycomb type main oxidation catalyst 22
(Hereinafter, simply referred to as main catalyst 22).

FIG. 4 (a) is a sectional view showing the details of the connecting portion between the combined exhaust pipe 21 and the main catalyst 22, and FIG. 4 (b) is an AA sectional view in FIG. 4 (a). As shown in the drawing, the inside of the combined exhaust pipe 21 is partitioned by a partition wall 21a, the upper passage is connected to the front exhaust pipe 7, and the lower exhaust passage 7'is connected to the rear exhaust pipe 8. ', And as mentioned above, it is apparently a single exhaust pipe. A connecting pipe 24, which has a diameter smaller than the diameter of the downstream end of the combined exhaust pipe 21 and is tapered in the downstream direction, is fitted to the combined exhaust pipe 21 in an airtight manner. Connection pipe 24
The downstream end of the main catalyst 22 having a diameter substantially the same as that of the main catalyst 22 is connected by a pipe 25, and the main catalyst 2 is divided by the partition wall 21a.
Up to 2, it is divided into upper and lower passages 7 ', 8'. Further, a connecting pipe 26 connecting the main catalyst 22 and the muffler device 16 is connected to the downstream side of the main catalyst 22 by a pipe 27. The connecting pipe 26 has a one-hole structure without a partition plate therein, and the connecting pipe 26 joins the front exhaust pipe 7 and the rear exhaust pipe 8. The main catalyst 22 is the two auxiliary catalysts 1 described above.
The exhaust gas discharged from each cylinder 6a, 6b is purified when passing through the main catalyst 22, and is a muffler device through the connecting pipe 26.
It flows to 16, is muffled by the muffler device 16, and is then exhausted to the atmosphere.

On the other hand, an air cleaner 9 is provided on the upper part of the engine 6, and the air cleaner 9 introduces outside air from an intake duct 9a provided on the upper part and is provided with an element (not shown) provided inside thereof. After purifying the outside air, the air-fuel mixture is supplied from below to the engine 6 via the carburetor. A control unit 10 is provided between the air cleaner 9 and the exhaust pipes 7, 8. The control unit 10 includes a valve device 32 connected to the air cleaner 9 via a connecting pipe 39, a valve device 32 having one end connected to the valve device 32, and the other end connected via a rubber joint (no reference numeral) to the front side exhaust. The exhaust pipes 7 and 8 which are composed of the pipe 7 and the secondary air introduction pipes 28 and 29 which are respectively connected to the upstream portions of the rear exhaust pipes 8 and which control the amount of secondary air and the supply timing. Supply secondary air to.

In order to show the detailed structure of the valve device 32, FIG. 5 (a) is a schematic front view of the valve device 32, and FIG.
The BB sectional drawing in (a) is each shown. As shown in the drawing, the valve device 32 is configured by connecting the outlet case 30 and the inlet case 31 so as to airtightly partition the inside into an outlet side and an inlet side with a valve mechanism 43, and a main frame 3b with a bracket 33. It is fixed to a bracket (not shown) provided on the. Outlet case 30
Has a pair of left and right independent outlet chambers 35 and 36 formed inside by a partition wall 34, and the secondary air introduction pipes 28 and 29 described above are each made of a rubber joint (no reference numeral) at the lower end of each chamber. The connecting pipes 37 and 38 are provided to be connected via. In the figure, 37 is a connecting pipe connected to the secondary air introducing pipe 28 of the front exhaust pipe 7, and 38 is an exhaust pipe connecting to the secondary air introducing pipe 29 of the rear exhaust pipe 8. Further, the inlet case 31 is provided with a connecting pipe 39 connected to the air cleaner 9 on the back surface thereof, and clean air is supplied from the connecting pipe 39 to the inlet chamber.
Introduced in 40. The valve mechanism 43 has outlet chambers 35, 3
In order to communicate 6 with the inlet chamber 40, a pair of left and right vent holes 41,42 are provided at positions corresponding to the pair of left and right outlet chambers 35,36, and the wall on the outlet chamber 35,36 side is formed. A flexible one-way valve plate 43a having a size that closes the vent holes 41, 42 and a stopper 44 for limiting the deformation of the valve plate 43a are provided. This valve mechanism
Outlet room 35,36 and inlet room always by 43
40 is separated, but the secondary air introduction pipes 28,29
When the exhaust pipes 7 and 8 connected to each other become negative in pressure, the valve plate 43a of the valve mechanism 43 is opened to open the outlet chamber 3 from the inlet chamber 40 side.
The secondary air is configured to flow to the secondary air introduction pipes 28,29 via 5,36.

The operation of the embodiment of the exhaust system 1 of the present invention constructed as described above will be described. When the engine 6 is started, explosions occur alternately in the cylinders 6a and 6b, and exhaust is emitted from the corresponding exhaust holes. The exhaust gas exhausted from the exhaust holes flows through the exhaust pipes 7 and 8 corresponding to the cylinders 6a and 6b, that is, the front exhaust pipe 7 and the rear exhaust pipe 8, respectively. Since the exhaust pipes 7 and 8 have a negative pressure when the exhaust gas flows, at the same time as the exhaust gas flows, the secondary air introducing pipes 28 and 29 provided upstream of the exhaust pipes 7 and 8 are connected via the valve device 32. Secondary air is introduced into the exhaust pipes 7, 8. The exhaust gas into which the secondary air is introduced flows into the auxiliary catalysts 19,20 together with the secondary air,
The heat of reaction keeps the temperature high. This secondary air allows the auxiliary catalyst 1 to operate regardless of the degree of combustion in each cylinder 6a, 6b.
At 9,20, stable reaction heat is always obtained, and the exhaust gas temperature becomes stable. On the other hand, the normal temperature conditions of the front exhaust pipe 7 and the rear exhaust pipe 8 are different due to the running wind hit and the difference of the exhaust pipe length, but the front exhaust pipe 7 has a double structure to enhance the heat retention capacity. Therefore, the temperature of the exhaust gas passing therethrough can be kept substantially equal to the temperature of the exhaust gas flowing through the rear exhaust pipe 8.

These exhaust pipes 7, 8 are connected downstream to the apparently one combined exhaust pipe 21, and are connected to the main catalyst 22 connected to the downstream end of the exhaust pipe 21. Therefore, the exhaust gas flowing through these exhaust pipes 7 and 8 flows to the main catalyst 22 while maintaining the pipe lengths of the exhaust pipes 7 and 8, and since the main catalyst 22 is of a honeycomb type, the main catalyst 22 is effectively Even in the interior, the front exhaust pipe 7 and the rear exhaust pipe 8 are in the same state as being separated, and the pipe length of each exhaust pipe 7, 8 is maintained up to the downstream end of the main catalyst 22. As described above, in the case of the multi-cylinder engine 6, the cylinders 6a and 6b are ignited and explode at different timings. Therefore, the exhaust gas flowing into the main catalyst 22 also has the same timing between the front exhaust pipe 7 and the rear exhaust pipe 8. Although they are deviated, the temperature of the exhaust gas flowing through the front exhaust pipe 7 and the rear exhaust pipe 8 is kept substantially constant because the front exhaust pipe 7 has a double pipe structure, so that the temperature of the main catalyst 22 is also almost constant. Becomes constant,
Stable purification action is performed. Then, the exhaust gas that has passed through the main catalyst 22 is mixed in the connecting pipe 26, and the muffler device
Exhaust to the outside through 16

FIGS. 6 (a) and 6 (b) show another embodiment of the connecting portion between the main catalyst 22 and the combined exhaust pipe 21, respectively. In FIG. 6 (a),
21 'is a combined exhaust pipe, 22' is a honeycomb type main oxidation catalyst, 2
6'is a connecting pipe that connects the main oxidation catalyst 22 'and a muffler device (not shown). The combined exhaust pipe 21' and the main oxidation catalyst 22 ', the main oxidation catalyst 22' and the connection pipe 26 ' Are fixed by annular connecting members 25 'and 27', respectively. Further, the inflow surface 22a of the connecting members 25 ', 27' and the main oxidation catalyst 22 'described above.
An appropriate gap is provided between each of them and the outflow surface 22b, so that the main oxidation catalyst 22 'effectively operates. With such a configuration, the connecting pipe 24 used in the embodiment of FIG. 4 can be omitted, and the exhaust pipe length can be shortened. In addition, FIG.
An embodiment is shown in which the configuration of the annular connecting members 25 ″ and 27 ″ is different from the configuration shown in (a). In the figure, 21 '' is a combined exhaust pipe, and this combined exhaust pipe 21 '' is connected to the main oxidation catalyst 22 '' by an annular connecting member 25 ''. This annular connecting member 25 '' is formed in a corrugated shape so that air layers 45 and 46 are formed around the main oxidation catalyst 22 '' and is welded to the main oxidation catalyst 22 '' at the valley portion. There is. Further, a connecting pipe 26 ″ is connected downstream of the main oxidation catalyst 22 ″ by an annular connecting member 27 ″. The connecting member 27 ″ is fixed to the connecting member 25 ″ so as to form the air layer 46 together with the connecting member 25 ″. With this configuration, the air layers 45 and 46 are formed around the main oxidation catalyst 22 ″, and the effect of improving the heat retention of the main oxidation catalyst 22 ″ is exerted.

The structure of the connecting portion between the main oxidation catalyst 22 and the combined exhaust pipe 21 is not limited to these embodiments, and the main oxidation catalyst 22 and the combined exhaust pipe 21 can be connected downstream of the combined exhaust pipe 21. Any configuration may be used as long as it has such a configuration. Further, in the present embodiment, the air cleaner 9 for engine intake is shared as the air cleaner 9 for supplying the secondary air, but this is not limited to this embodiment, and an air cleaner is separately provided for supplying the secondary air. Of course, it may be provided.
Further, in the present embodiment, the front exhaust pipe 7 has a double pipe structure in order to improve the heat retention performance of the front exhaust pipe 7, but this is not limited to this embodiment, and the front exhaust pipe and the rear exhaust pipe are not limited to this. As long as the temperature of the exhaust gas passing through the pipe and the temperature can be balanced, any configuration may be used. The front exhaust pipe and the rear exhaust pipe may be balanced by activating the reaction of the auxiliary oxidation catalyst on the front exhaust pipe side, or the front exhaust pipe may have a triple pipe structure or more. Of course good things. Further, in the present embodiment, the front exhaust pipe 7 and the rear exhaust pipe 8 are respectively provided with one auxiliary oxidation catalysts 19 and 20, respectively, but this is not limited to this embodiment, and Any configuration may be used as long as the temperature of the exhaust gas passing therethrough can be maintained at a high temperature when reaching the main oxidation catalyst, and for example, each exhaust pipe may be provided with a plurality of auxiliary oxidation catalysts, or Of course, the auxiliary oxidation catalyst may be changed from the honeycomb type to the supported type.

As described above, in the catalyst-equipped exhaust system 1 of the present embodiment, the front exhaust pipe 7 of the V-type two-cylinder engine 6 has a double pipe structure to enhance the heat retaining effect, and the rear exhaust pipe 8 is provided. Since the temperature of the exhaust gas flowing and the temperature of the exhaust gas flowing to the front exhaust pipe 7 are made substantially the same, the temperature of the exhaust gas flowing into the main oxidation catalyst 22 after uniting is stable and the main oxidation catalyst 22 is stably purified. An effect is obtained that an action is obtained. Further, in the exhaust system with catalyst 1 of the present embodiment, the auxiliary oxidation catalyst 1 provided in each of the exhaust pipes 7 and 8 is
Since the secondary air cleaned by the air cleaner 9 is introduced through the control unit 10 to a position upstream of 9,20, the secondary oxidation is always performed regardless of the degree of combustion in each cylinder 6a, 6b. The catalysts 19 and 20 have an effect of obtaining stable reaction heat. Furthermore, the exhaust device with a catalyst 1 of the present embodiment
In the above, since the front exhaust pipe 7 and the rear exhaust pipe 8 are apparently connected to one combined exhaust pipe 21 downstream and the combined exhaust pipe 21 is connected to the main oxidation catalyst 22, the purification effect is maintained. Therefore, there is an effect that it is sufficient to provide only one main oxidation catalyst 22 which tends to be relatively large. Further, in the exhaust system with catalyst 1 of the present embodiment, the front exhaust pipe 7 and the rear exhaust pipe 8 are connected to the combined exhaust pipe 21, but the inside of the combined exhaust pipe 21 is partitioned by a partition wall. Since the exhaust pipe length is maintained up to the oxidation catalyst 22 and the honeycomb type catalyst is adopted for the main oxidation catalyst 22, there is an effect that each exhaust pipe length can be maintained up to the downstream end of the main oxidation catalyst 22 in practice. Also, with this,
As a result, it is possible to easily attach the catalyst to the exhaust device which has a narrow degree of design freedom.

[0018]

According to the exhaust system with catalyst of the present invention, since a plurality of cylinders are arranged in the front-rear direction with respect to the traveling direction of the vehicle like the V-type engine, the exhaust pipe connected to each cylinder is Even if the temperature conditions are different due to the arrangement of the exhaust pipes, such as the length being different, the temperature of the exhaust gas flowing through each exhaust pipe will be different depending on the auxiliary catalyst installed in each exhaust pipe. The temperature of the exhaust gas passing through the main catalyst provided at the confluence is stable and the purification efficiency of the main catalyst is improved because the temperature of the exhaust gas is maintained to be almost the same as the temperature of the exhaust gas flowing through the exhaust pipe. Play.

[Brief description of drawings]

FIG. 1 is a schematic side view of a motorcycle that employs an exhaust device with a catalyst according to the present invention.

FIG. 2 is a schematic side view showing details of the vicinity of the engine of the motorcycle shown in FIG.

FIG. 3 is a schematic top view showing a positional relationship between respective constituent elements of the exhaust device with catalyst.

FIG. 4A is a schematic cross-sectional view showing details of a connecting portion between a combined exhaust pipe and a main oxidation catalyst. (b) is A- in (a)
FIG.

FIG. 5 (a) is a schematic front view of a reed valve device.
(b) is a BB sectional view in (a).

FIG. 6 (a) is a schematic cross-sectional view showing another embodiment of the connecting portion between the combined exhaust pipe and the main oxidation catalyst. (b) is a schematic cross-sectional view showing still another embodiment of the connecting portion between the combined exhaust pipe and the main oxidation catalyst.

[Explanation of symbols]

 1 exhaust system with catalyst 2 motorcycle 3 frame 3a head pipe 3b main frame 3c down tube 3d cross pipe 4 front fork 5 fuel tank 6 engine 6a front cylinder 6b rear cylinder 6c crankcase 6d engine suspension pipe 6e engine suspension pipe 6f engine Suspended pipe 7 Front exhaust pipe 8 Rear exhaust pipe 9 Air cleaner 9a Intake pipe 10 Control unit 11 Cowl 11a Opening 12 Front wheel 13 Rear shock absorber 14 Rear wheel 15 Swing arm 16 Muffler device 17 Pipe 18 Pipe 19 Sub-oxidation catalyst 20 Sub-oxidation catalyst 21 Combined exhaust pipe 21a Partition wall 22 Main oxidation catalyst 23 Partition wall 24 Connecting pipe 25 Pipe 26 Connecting pipe 27 Pipe 28 Secondary air introducing pipe 29 Secondary air introducing pipe 30 Outlet case 31 Inlet case 32 Valve device 33 Bracket 34 Partition wall 35 Outlet chamber 36 Outlet chamber 37 Connection pipe 38 Connection pipe 39 Connection pipe 40 Inlet chamber 41 Vent hole 42 Vent hole 43 Valve mechanism 43a One-way valve plate 44 Stopper

Claims (3)

[Claims] 1. An exhaust pipe is connected to an exhaust hole of each cylinder of a V-type engine provided such that a plurality of cylinders are located in front of and behind the traveling direction of the vehicle, and each exhaust pipe is directed toward the rear of the vehicle. In the exhaust device configured to extend and join those exhaust pipes on the downstream side, and connect the joined exhaust pipes to the muffler so that the exhaust pipes straddle each exhaust pipe at a position where the exhaust pipes join. While the main catalyst is provided in the exhaust gas, the auxiliary catalyst is provided in each of the plurality of exhaust pipes before the merging, and the temperature difference of the exhaust gas flowing through the plurality of exhaust pipes is eliminated as much as possible. An exhaust system with a catalyst for a motorcycle, characterized in that it is made stable. 2. An exhaust gas of an engine, wherein a sub-catalyst provided in an exhaust pipe connected to an exhaust hole of a front cylinder is at least exhausted from an auxiliary catalyst provided in an exhaust pipe connected to an exhaust hole of a rear cylinder. The exhaust device with a catalyst for a motorcycle according to claim 1, wherein the exhaust device is equipped with a catalyst. 3. The exhaust pipe connected to the exhaust hole of the front cylinder is structured to have a higher heat insulation effect than at least the exhaust pipe connected to the exhaust hole of the rear cylinder. The exhaust system with catalyst for a motorcycle according to 1.