Title of Invention

CATALYST ARRANGEMENT STRUCTURE OF MOTORCYCLE

Abstract

To enhance an output of an engine while enhancing the purification efficiency of a metal honeycomb catalyst and, at the same time, to realize the reduction of cost. [Means for Resolution] In a catalyst arrangement structure of a motorcycle in which a vehicle body frame includes a main frame extending in the rearward direction from a head pipe and a down frame 3 6 extending in the oblique rearward and downward direction from the head pipe, an engine 18 is arranged behind the down frame 36, and a metal honeycomb catalyst 57 is arranged in an exhaust pipe 5 6 extending in the downward and rearward direction from the engine 18, the exhaust pipe 56 forms a first tapered portion 71 and a second tapered portion 72 which have diameters thereof gradually enlarged toward the metal honeycomb catalyst 57 on portions thereof in front of and behind the metal honeycomb catalyst 57, and the metal honeycomb catalyst 57 is arranged along the down frame 36. [Selected Drawing] Fig. 3

Full Text

[Designation of Document] Specification [Title of the Invention] CATALYST ARRANGEMENT STRUCTURE OF MOTORCYCLE [Technical Field] [0001] The present invention relates to an improvement of a catalyst arrangement structure 'of a motorcycle. [Background Art] [0002] As a conventional catalyst arrangement structure of ; motorcycle, there has been known a catalyst arrangement structure of a motorcycle in which a honeycomb-type catalysis arranged in a plurality of exhaust pipes which extends fro;? a V-type engine (see patent document 1, for example). [Patent document 1] Japanese Patent No. 3242488 [0003] The catalyst arrangement structure shown in Fig. 2 : patent document 1 is explained hereinafter. To a front cylinder 6a and a rear cylinder 6b of a V-tyo 2-cylinder engine, a front exhaust pipe 7 and a rear exhauo' pipe 8 are respectively connected. Respective end portioo of the front exhaust pipe 7 and the rear exhaust pipe 8 ai connected to a merged exhaust pipe 21. A honeycomb-type :.: .: catalyst 19 is arranged in the front exhaust pipe 7 an: honeycomb-type sub catalyst 20 is arranged in the rear exhoo. pipe 8. A honeycomb-type main catalyst 22 is arranged betweer. the merged exhaust pipe 21 and a muffler device 16. [0004] Due to such an arrangement of the sub catalysts 19, 2!> and the main catalyst 22, the lowering of temperatures of exhaust gases which flow in the respective exhaust'pipes 7, 8 can be suppressed due to heat generated by reactions in the sub catalysts 19, 20. Accordingly, a temperature of the merged exhaust gas when the merged exhaust gas flows in the man catalyst 22 after the exhaust gases in the exhaust pipes 7, 8 are merged is held at a high temperature and hence, the purification efficiency of the main catalyst 22 arranged a position remote from the front cylinder 6a and the rear cylinder 6b can be enhanced. [Disclosure of the Invention] [Problems that the Invention is to Solve] [0005] However, in an attempt to use a catalyst arrangeirie:. ■ structure in which only the main catalyst 22 is activated, wher the main catalyst 22 is arranged directly behind the fr exhaust pipe 7 and the rear exhaust pipe 8 respectively in pla of the sub catalysts 19, 20, the large main catalysts 22 exhir. _: large exhaust resistances and hence, there may be a case t;. v an output of the engine cannot be ensured. Further, when the plurality of catalysts consisting the main catalyst 22 and the sub catalysts 19, 20 is provide:], such an arrangement pushes up a cost. Accordingly, it is an object of the present invention to enhance an output of an engine while enhancing the purification efficiency of a metal honeycomb catalyst and, a; the same time, to realize a reduction of cost. [Means for Solving the Problem] [0006] The invention according to claim 1 is characterized ia that, in a catalyst arrangement structure of a motorcycle la which a vehicle body frame includes a main frame extending aa the rearward direction from a head pipe and a down frans;-extending in the oblique rearward and downward direction f a : ::. the head pipe, an engine is arranged behind the down frame and a metal honeycomb catalyst is arranged in an exhaust pi::-extending in the downward and rearward direction from ea . engine, the exhaust pipe forms tapered portions which hav diameters thereof gradually enlarged toward the meta honeycomb catalyst on portions thereof in front of and behin the metal honeycomb catalyst, and the metal honeycomb catalysis arranged along the down frame. [0007] To explain the manner of operation of the inventi... according to claim 1, an exhaust gas discharged from the engaa-is expanded by the tapered portion formed upstream of the met a honeycomb catalyst and flows in the metal honeycomb catalyst. The metal honeycomb catalyst is arranged in the vicinity of the engine behind the down frame. Accordingly, althoiKjh a temperature of the exhaust gas which flows in the tapered portion arranged upstream of the metal honeycomb catalyst i x high, the exhaust gas is expanded by the tapered portion and impinges on a catalyst surface of the metal honeycomb catalyst smoothly and in a uniformly-dispersed manner and hence, it impossible to reduce an exhaust-air resistance as much a possible. Accordingly, even when the catalyst is arranged it the vicinity of the engine, an output of the engine can !>• ensured. Further, discharge heat is also dispersed on ttt respective catalyst surfaces and hence, temperatures of tt catalyst surfaces are not overheated and the catalysts at maintained at favorable activation temperatures. Further, the metal honeycomb catalyst is mounted on only the exhaust pipe arranged behind the down frame and hence, :.t increase in cost can be suppressed. [0008] The invention according to claim 2 is characterized it that the exhaust pipe includes a horizontal portion there;: arranged in a horizontal posture or in a substantial.: horizontal posture below the engine, and the tapered porti.:: arranged downstream of the metal honeycomb catalyst is arran :t in front of the horizontal portion. f To explain the manner of operation of the invention according to claim 2, the horizontal portion of the exhaust pipe assumes a ground clearance and hence, even when a diameto* of the exhaust pipe is enlarged on both sides of the metal honeycomb catalyst, the ground clearance of the motorcycle in not decreased. [0009] The invention according to claim 3 is characterized in that the metal honeycomb catalyst is arranged on a side of tho down frame and more inside a vehicle body than an outermost surface of a crankcase of the engine as viewed in a plan view. 'To explain the manner of operation of the inventicn according to claim 3, the metal honeycomb catalyst is arrange:; more inside the vehicle body and hence, there is no possibility that pebbles or the like impinge on the catalyst from a sici:. of the vehicle body. [0010] The invention according to claim 4 is characterized in that a connection portion is formed on the cylinder head of the engine for connecting the exhaust pipe to the cylinder head, an insertion hole to which a secondary air supply pipe for supplying air into the inside of the exhaust pipe is connected by insertion is formed in the vicinity of the connection porinn. and the secondary air supply pipe extends downwardly towar.i the connection portion from an upper portion of the cylinder head. [0011] To explain the manner of operation of the invention according to claim 4, the secondary air supply pipe is connected to the insertion hole of the cylinder head, and secondary ai; is supplied into the inside of the exhaust pipe to burn an unburnt gas in the inside of the exhaust pipe. Further, the secondary air supply pipe is protected by the down frame which is arranged in front.of the secondary ai.:: supply pipe. Further, the secondary air supply pipe extend.: downwardly and hence, the secondary air supply pipe does no-. bulge in the vehicle width direction. [0012] The invention according to claim 5 is characterized : . that a plurality of metal honeycomb catalysts is arranged in parallel in the exhaust pipe. By making use of the tapered portion which is arrange.: upstream of the metal honeycomb catalyst, the exhaust gas f lew into each one of the plurality of respective metal honeycon: catalysts arranged in parallel in a dispersed manner and nh-. exhaust gas is purified by the respective metal honeycon., catalysts. [Advantage of the Invention] [0013] According to the invention described in claim 1, 4:n - tapered portions which have diameters thereof gradual". enlarged toward 'the metal honeycomb catalyst are formed .: portions of the exhaust pipe in front of and behind the met,: i honeycomb catalyst, and the metal honeycomb catalyst i .-arranged along the down frame. Accordingly, even when H. Further, the metal honeycomb catalyst is arranged on1 on the exhaust pipe behind the down frame and hence, an increa. in cost can be suppressed. [0014] According to the invention described in claim 2, i: exhaust pipe includes the horizontal portion thereof arran :(■••■ in a horizontal posture or in a substantially horizon":; posture below the engine, and the tapered portion arrange"; downstream of the metal honeycomb catalyst is arranged in froh ; of the horizontal portion and hence, even when the diamete: of the exhaust pipe is enlarged by forming the tapered portioo on the exhaust pipe, it is possible to maintain the grouoj clearance of the motorcycle. [0015] According to the invention described in claim 3, tho metal honeycomb catalyst is arranged on the side of the dow\ frame and more inside the vehicle body than the outermo.:; surface of the crankcase of the engine as viewed in a plan view. . Accordingly, the metal honeycomb catalyst is arranged m: :; inside the vehicle body than the outermost surface of oro. crankcase and hence, it is possible to prevent the pebbles or the like from impinging on the catalyst from a side of oh vehicle body. [0016] According to the invention described in claim 4, to-connection portion is formed on the cylinder head of the eogio for connecting the exhaust pipe to the cylinder head of to engine, the insertion hole to which the secondary air supp.i :, pipe for supplying air into the inside of the exhaust pipe : connected by insertion is formed in the vicinity of oo connection portion, and the secondary air supply pipe exteroo f downwardly toward the connection portion from the upper port io:. of the cylinder head. Accordingly, it is possible to further purify the exhaust gas by supplying the secondary air to th exhaust pipe in addition to the purification performed by th. ■ metal honeycomb catalyst. Further, the secondary air supply pipe can be protected by the down frame and, at the same time, it is possible to prevent the secondary air supply pipe free bulging in the vehicle width direction. [0017] According to the invention described in claim 5, th -plurality of metal honeycomb catalysts is arranged inparall-.: in the exhaust pipe and hence, it is possible to increase catalyst area of the metal honeycomb catalyst thus enhance: • purification ability. [Best Mode for Carrying Out the Invention] [0018] The best mode for carrying out the present invention L :• explained hereinafter in conjunction with attached drawings. Here, the drawings are observed in the direction of symbole. Fig. 1 is a side view of a motorcycle which includes , catalyst arrangement structure according to the presere: invention. In Fig. 1, a motorcycle 10 is constituted of : vehicle body frame 11 which constitutes a skeleton of ee motorcycle 10, a front fork 13 which is steerablly mounted oe a head pipe 12 arranged on a front end of the vehicle body freiu- 11/ a bar handle 14 which is mounted on an upper portion :: the front fork 13, a front wheel 17 which is mounted on a lowe: end portion of the front fork 13 by way of an axle 16, an engin. 18 which is supported on the vehicle body frame 11, a rear for.*: 23 which is mounted on center frames 21 which constitute : center portion of the vehicle body frame 11 by way of a piv ; : shaft 22 in a vertically swingable manner, a rear wheel 2 6 whins is mounted on a rear end portion of the rear fork 23 by way of an axle 24, a rear cushion unit 27 which extends between a rear portion of the vehicle body frame 11 and a rear portion of the rear fork 23, and a fuel tank 31 and a seat 32 whine are mounted on an upper portion of the vehicle body frame 11 . [0019] The vehicle body frame 11 is constituted of the head pip-.-12, a main frame 35 which extends rearwardly from the head pip: 12, a down frame 36 which has an upper portion thereof mount- i on the main frame 35 and extends in the oblique rearward an ; downward direction from the head pipe 12, the above-mentions ! pair of left and right center frames 21, 21 which has uppn: ends thereof connected to the main frame 35 and is formed inn: a Y-shape (only symbol 21 indicative of the center frame :,.n one side being shown in the drawing) , and a pair of left e.n 1 right reinforcing members 37, 37 which is mounted on a ren: lower portion of the main frame 35 and rear upper portions . : the center frames 21 (only symbol 37 indicative of th reinforcing member on one side being shown in the drawing.! . [0020] The down frame 36 supports a front portion of the engin 18 by way of a bracket 38. The center frames 21 support the engine 18 on front lowo;. portions thereof and, at the same time, support a front en,: of the rear fork 23 by way of the pivot shaft 22. [0021] The engine 18 is configured such that a transmission 4 "i is integrally mounted on a rear portion of the engine 18, -\ cylinder portion 42 is mounted on a front upper portion of th-.: engine 18, and an intake device 44, an exhaust device 4 6 writhe secondary air supply device 47 are mounted on the cylin:;-::: head 43 which constitutes a cylinder portion 42. [0022] The intake device 44 is constituted of an air clean?r 51 which is arranged between the left and right center fraia-.' 21, 21, a carburetor 53 which is connected to the air cleans ■. 51 by way of a connecting tube 52, and an intake pipe 54 wh: The exhaust device 46 is constituted of an exhaust pir 56 which extends along the down frame 36 from a front portion of the cylinder head 43 and extends rearwardly while passi:. : below the engine 18, a metal honeycomb catalyst 57 which is arranged on a midst portion of the exhaust pipe 56, and a muffler 58 which is connected to a rear end of the exhaust pipe 56. The metal honeycomb catalyst 57 is formed by adhering active components in a dispersed manner on a surface of a metal carrier which is integrally formed in a honeycomb shape. [0024] Here, numeral 61 indicates a head lamp, numeral 62 indicates a meter, numeral 63 indicates a front fender, numeral 64 indicates a main stand, and numeral 66 indicates a rear fender. [0025] Fig. 2 is a perspective view showing a catalyst . arrangement structure of a motorcycle according to the present invention (an arrow (FRONT) in the drawing indicating a front side of the vehicle) . In Fig. 2, a first tapered portion 71 which has a diameter thereof gradually enlarged toward the metal honeycomb catalyst 57 is formed on the exhaust pipe 56 upstream of the metal honeycomb catalyst 57, that is, on a cylinder-head-43-side, and a second tapered portion 72 which has a diameter thereof gradually enlarged toward the metal honeycomb catalyst 57 is formed on the exhaust pipe 56 downstream of the metal honeycomb catalyst 57, that is, on a muffler-58-side. For example, an opening diameter dl of the first tapered portion 71 is set to 26 mm, and an outer diameter r d2 of the metal honeycomb catalyst 57 is set to 60 mm. [0026] The metal honeycomb catalyst 57 is arranged in the vicinity of the cylinder head 43 and hence, the metal honeycomb catalyst 57 is exposed to a high exhaust air temperature. However, the exhaust gas which flows in the exhaust pipe 56 is expanded in the first tapered portion 71 and flows in respective portions of the metal honeycomb catalysts 57 in a dispersed manner and hence, exhaust air heat is also dispersed in the respective portions of the metal honeycomb catalyst 57 • Accordingly, a temperature of the metal honeycomb catalyst 57 is not excessively elevated thus preventing the metal honeycomb catalyst 57 from being melted. Further, the temperature of the metal honeycomb catalyst 57 is maintained at a high temperature necessary for activating the metal honeycomb catalyst 57 and hence, it is possible to effectively purify the exhaust gas. [0027] Further, the temperature of the metal honeycomb catalyst 57 also tends to elevate immediately after the engine is started and hence, the metal honeycomb catalyst 57 can be quickly activated. Accordingly, it is possible to start the purification of the exhaust gas at an early stage after starting the engine. [0028] Fig. 3 is a side view showing an essential part of the motorcycle according to the present invention. In Fig. 3, the exhaust pipe 56 is constituted of a connection portion 75 which is connected to the cylinder head 43, the first tapered portion 71 which is arranged downstream of the connection portion 75, a large-diameter portion 76 in which the metal honeycomb catalyst 57 is accommodated, the second tapered portion 72 which is arranged downstream of the large-diameter portion 76, and a horizontal portion 77 which extends rearwardly from a rear end of the second tapered portion 72 in a horizontal posture and is connected to the muffler 58 (see Fig. 1) . The large-diameter portion 76 and the metal honeycomb catalyst 57 are arranged in parallel to the down frame 36. [0029] The secondary air supply device 47 is constituted of an intake hose 81 which has one end thereof opened in the vicinity of the air cleaner 51 (see Fig. 1), an air filter 82 to which another end of the intake hose 81 is connected, a secondary air control valve 84 which is connected to the air filter 82 for controlling a quantity of secondary air which is supplied to the exhaust device 46 corresponding to an operation state of the engine 18 by way of a relay hose 83, a relay hose 86 which has one end thereof connected to the secondary air control valve 84, a metal tube 87 which has one end thereof connected to the relay hose 86 and has another end thereof inserted into a tube insertion hole 43a formed in the cylinder head 43, and a negative pressure supply pipe 88 which has one end thereof connected to the secondary air control valve 84 for supplying a secondary-air-controlling negative pressure to the secondary air control valve 84 and has another end thereof connected to the intake pipe 54. Here, numeral 91 indicates a bracket for mounting the secondary air control valve 84 on the vehicle body frame 11. The metal tube 87 mounts a flange 87a on an end portion thereof, and the flange 87a is mounted on the cylinder head 43 by two bolts 93, 93. [0030] Fig. 4 is a plan view showing an essential part of the motorcycle according to the present invention. In Fig. 4, the metal honeycomb catalyst 57 is arranged more outside the vehicle body than the down frame 36 and, at the same time, is arranged more inside the vehicle body than an outermost surface 95a of a crankcase 95 of the engine 18. Here, numeral 90 indicates a straight line which passes the outermost surface 95a and extends in the longitudinal direction of the vehicle body. [0031] As described above, the metal honeycomb catalyst 57 is arranged more inside the vehicle body than the outermost surface 9 5a of the crankcase 95 and hence, there is no possibility that pebbles or the like impinge on the metal honeycomb catalyst 57 from a side of the vehicle body. [0032] Fig. 5 (a) and Fig. 5 (b) are cross-sectional views of the secondary air control valve according to the present invention. In Fig. 5(a), the secondary air control valve 84 is constituted of a valve body 101, an intake port 102, an exhaust port 103 and a negative pressure introducing port 104 which are formed in the valve body 101, and a lead valve assembly 105 which is arranged between the valve body 101 and the exhaust port 103. The relay hose 83 is connected to the intake port 102, the relay hose 86 is connected to the exhaust port 103, and the negative pressure supply pipe 88 is connected to the negative pressure introducing port 104. [0033] The valve body 101 is constituted of a base portion 106, a rod 107 which is movably inserted into a rod supporting portion 106a formed on the base portion 106, a diaphragm 108 which is mounted on one end of the rod 107, a valve element 111 which is mounted on another end of the rod 107, and a compression coil spring 112 which is arranged between the valve element 111 and the base portion 106 for biasing the valve element 111 toward the intake port 102. Here, numeral 113 indicates a bushing which is arranged between the rod supporting portion 106a and the rod 107. [0034] The base portion 106 includes a first recessed portion 106b which is formed in a diaphragm-108-side portion of the base portion 106, a second recessed portion 106c which is formed in a valve-element-lll-side portion of the base portion 106, a main passage 106d which is communicated'with the second recessed portion 10 6c, and a side passage 10 6e which is communicated with the main passage 106d. Here, numeral 106f indicates a connection passage which connects the first recessed portion 106b and the main passage 106d. [0035] The intake port 102 is constituted of a plate-like annular portion 102a which is mounted on the base portion 106 using a plurality of screws 115, a bulging portion 102b which bulges from the annular portion 102a in a substantially tapered manner, and a cylindrical hose connection portion 102c which extends from the bulging portion 102b. [0036] The bulging portion 102b forms a valve chamber 117 together with the second recessed portion 106c of the base portion 106, and the valve element 111 is pushed to the bulging portion 102b using the compression coil spring 112 so as to bring the secondary air control valve 84 into a closed state. That is, the bulging portion 102b functions as a valve seat. [0037] The exhaust port 103 is constituted of an exhaust port mounting portion 103a which is mounted on the base portion 106 using a plurality of screws 121, and a cylindrical hose connection portion 103b which extends from the exhaust port mounting portion 103a, and the exhaust port mounting portion 103a forms an accommodating chamber 10 3c therein for accommodating a portion of the lead valve assembly 105. [0038] The negative pressure introducing port 104 is constituted of an introducing port mounting portion 104a which is mounted on the base portion 106 using a plurality of screws 123, a bulging portion 104b which bulges from the introducing port mounting portion 104a, and a cylindrical pipe connection portion 104c which extends from the bulging portion 104b. The bulging portion 104b forms a diaphragm chamber 125 together with the first recessed portion 106b of the base portion 106. The diaphragm chamber 125 is divided into a first chamber 127 and a second chamber 128 by the diaphragm 108 which functions as a partition. [0039] Fig. 5(b) is a cross-sectional view taken along a line b-b in Fig. 5(a). In Fig. 5(b), the lead valve assembly 105 is constituted of a base plate 131 which is fitted in a third recessed portion 106h of the base portion 106, a lead valve 132 formed of a thin leaf spring which is arranged to close a penetration hole 131a formed in the base plate 131, and a plate-like stopper member 134 which is mounted on the base portion 106 together with the lead valve 132 using a screw 133. The lead valve 132 and the stopper member 134 are accommodated in the accommodating chamber 103c. [0040] The manner of operation of the above-mentioned secondary-air control valve 84 is explained hereinafter. In Fig. 5(a) and Fig. 5(b), when a negative pressure is supplied to the first chamber 127 of the diaphragm chamber 125 through the negative pressure introducing port 104 from an intake-device side, the diaphragm 108 is moved to a f irst;-chamber-127 side and hence, the valve element 111 which is mounted on the diaphragm 108 by way of the rod 107 is separated from the bulging portion 102b of the intake port 102 whereby the secondary air control valve 84 assumes an open state. [0041] In this open state, at timing that the exhaust port 43b which is formed in the exhaust-device side, that is, in the cylinder head 43 (see Fig. 3) to which the metal tube 87 (see Fig. 3) is connected and is communicated with the exhaust pipe 56 assumes a negative pressure, air is sucked from an opening formed in a distal end of the intake hose 81 shown in Fig. 1, the sucked air passes through the intake hose 81 as well as > the air filter 82 and the relay hose 83 shown in Fig. 3 and, thereafter, arrives at the penetration hole 131a through the inside of the hose connection portion 192c of the intake port 102, the valve chamber 117, the main'passage 106d, and the side passage 106e which are shown in Fig. 5(a) and Fig. 5(b) so as to open the lead valve 132. Then, the air passes through the inside of the accommodating chamber 103c and the hose connection portion 103b. Further, the air passes through the relay hose 86, the metal tube 87, and the tube insertion hole 43a of the cylinder head 43 which are shown in Fig. 3 and, thereafter, flows into the inside of the exhaust port 43b of the cylinder head 43 to burn the unburnt gas in the inside of the exhaust gas. At timing that the exhaust port 43b assumes a positive pressure, the lead valve 132 is closed and the exhaust gas does not flow backward to the secondary air control valve 84 side. [0042] As has been explained heretofore in conjunction with Fig. 1 and Fig. 3, the present invention is firstly characterized in that, in the catalyst arrangement structure of the motorcycle 10 in which the vehicle body frame 11 includes the main frame 35 extending in the rearward direction from the head pipe 12 and the down frame 36 extending in the oblique rearward and downward direction from the head pipe 12, the engine 18 is arranged behind the down frame 36, and the metal honeycomb catalyst 57 is arranged in the exhaust pipe 56 extending in the downward and rearward direction from the engine 18, the exhaust pipe 56 forms the first tapered portion 71 and the second tapered portion 72 which have diameters thereof gradually enlarged toward the metal honeycomb catalyst 57 on portions thereof in front of and behind the metal honeycomb catalyst 57, and the metal honeycomb catalyst 57 is arranged along the down frame 3 6. [0043] Due to such a constitution, even when the metal honeycomb catalyst 57 is arranged upstream of the exhaust pipe 56 in the vicinity of the engine 18 along the down frame 36, it is possible to allow the exhaust gas to smoothly flow into the metal honeycomb catalyst 57 after expanding the exhaust gas by the first tapered portion 71 arranged upstream of the metal honeycomb catalyst 57 thus reducing the exhaust-air resistance as much as possible. Accordingly, even when the catalyst is arranged in the vicinity of the engine 18, it is possible to ensure the output of the engine 18. Further, the metal honeycomb catalyst 57 can be maintained at favorable activation temperature thereof while lowering the temperature of the exhaust gas by dispersing the exhaust gas and hence, it is possible to prevent the metal honeycomb catalyst 57 from being melted. It is also possible to effectively purify the exhaust gas . Further, the metal honeycomb catalyst 57 is arranged only on the exhaust pipe 56 behind the down frame 36 and hence, an increase in cost can be suppressed. [0044] The present invention is secondary characterized in that the exhaust pipe 56 includes the horizontal portion 77 thereof arranged in a horizontal posture or in a substantially horizontal posture below the engine 18, and the second tapered portion 72 arranged downstream of the metal honeycomb catalyst 57 is arranged in front of the horizontal portion 77. Due to such a constitution, even when the diameter of the exhaust pipe 56 is enlarged by forming the second tapered portion 72 on the exhaust pipe 56, it is possible to maintain the ground clearance of the motorcycle. [0045] As shown in Fig. 4, the present invention is thirdly characterized in that the metal honeycomb catalyst 57 is arranged on a side of the down frame 36 and more inside the vehicle body than the outermost surface 95a of the crankcase 95 of the engine 18 as viewed in a plan view. [0046] Due to such a constitution, the metal honeycomb catalyst 57 and the large-diameter portion 76 are arranged more inside the vehicle body than the outermost surface 95a of the crankcase 95 and hence, it is possible to prevent the pebbles or the like from impinging on the large-diameter portion 76 which covers the metal honeycomb catalyst 57 from a side of the vehicle body. As shown in Fig. 3, the present invention is fourthly characterized in that the connection portion 75 is formed on the cylinder head 43 of the engine 18 for connecting the exhaust pipe 56 to the cylinder head 43 of the engine 18, the tube insertion hole 43a to which the metal tube 87 as the secondary air supply pipe for supplying air into the inside of the exhaust pipe 56 is connected by insertion is formed in the vicinity of the connection portion 75, and the metal tube 87 extends downwardly toward the connection portion 75 from an upper portion of the cylinder head 43. [0048] Due to such a constitution, it is possible to further purify the exhaust gas by supplying the secondary air to the exhaust pipe 56 in addition to the purification performed by the metal honeycomb catalyst 57. Further, the metal tube 87 can be protected by the down frame 36 and, at the same time, it is possible to prevent the metal tube 87 from bulging in the vehicle width direction, [0049] Fig. 6 is a side view showing another embodiment of the catalyst arrangement structure according to the present invention. In Fig. 6, an exhaust pipe 140 is constituted of a connection portion 75 which is connected to a cylinder head 43 (see Fig. 2) , a first tapered portion 141 which is arranged downstream of the connection portion 75, a catalyst accommodating portion 147 which accommodates two columnar metal honeycomb catalysts 146, 146 arranged in parallel therein, a second tapered portion 142 which is arranged downstream of the catalyst accommodating portion 147, and a horizontal portion 77 which extends rearwardly from a rear end of the second tapered portion 142 in a horizontal posture and is connected to a muffler 58 (see Fig. 1) . [0050] Fig. 7 is a plan view showing another embodiment of the catalyst arrangement structure according to the present invention. In Fig. 7, two metal honeycomb catalysts 146, 146 are arranged in the vehicle width direction and hence, it is possible to increase an area of a catalyst surface compared to a case that one metal honeycomb catalyst is arranged. Further, for example, it is possible to decrease an occupied space of the catalysts 146, 146 in the longitudinal direction of the vehicle compared to a case that one columnar metal honeycomb catalyst having a cross-sectional area equal to a total cross-sectional area of two combined metal honeycomb catalysts 146, 146 is adopted and hence, it is unnecessary to change a distance between the front wheel and the engine. [0051] As shown in Fig. 6 and Fig. 7, the present invention is fifthly characterized in that the plurality of metal honeycomb catalysts 146 is arranged in parallel in the exhaust pipe 140. Due to such a constitution, it is possible to increase a catalyst area of the metal honeycomb catalyst 14 6 thus enhancing the purification property. [0052] Here, as shown in Fig. 7, in this embodiments, although two metal honeycomb catalysts 14 6 having a circular 'cross section are arranged in parallel in the inside of the catalyst accommodating portion 147 of the exhaust pipe 140, the present invention is not limited to such a constitution, and one metal honeycomb catalyst having an oblong or elliptical cross section may be accommodated in the inside of the catalyst accommodating portion 147. [Industrial Applicability] [0053] The catalyst arrangement structure of the present invention is favorably applicable to a motorcycle. [Brief Description of the Drawings] [0054] [Fig. 1] A side view of a motorcycle which includes a catalyst arrangement structure according to the present invention. [Fig. 2] A perspective view showing the catalyst arrangement structure of the motorcycle according to the present invention. [Fig.' 3] A side view showing an essential part of the motorcycle according to the present invention. [Fig. 4] A plan view showing an essential part of the motorcycle according to the present invention. [Fig. 5] A cross-sectional view of a secondary air control valve according to the present invention. [Fig. 6] A side view showing another embodiment of the catalyst arrangement structure according to the present invention. [Fig. 7] A plan view showing another embodiment of the catalyst arrangement structure according to the present invention. [Description of Reference Numerals and Signs] [0055] 10: motorcycle 11: vehicle body frame 12: head pipe 18: engine 35: main frame 36: down frame 43: cylinder head 43a: insertion hole (tube insertion hole) 56, 140: exhaust pipe 57, 146: metal honeycomb catalyst 71, 72, 141, 142: tapered portion (first taped portion, second tapered portion, first' tapered portion, second tapered portion) 75: connection portion 77: horizontal portion 87: secondary air supply pipe (metal tube) 95: crankcase 95a: outermost surface of crankcase [Designation of Document] Claims [Claim 1] A catalyst arrangement structure of a motorcycle in which a vehicle body frame includes a main frame extending in the rearward direction from a head pipe and a down frame extending in the oblique rearward and downward direction from the head pipe, an engine is arranged behind the down frame, and a metal honeycomb catalyst is arranged in an exhaust pipe extending in the downward and rearward direction from the engine, wherein the exhaust pipe forms tapered portions which have diameters thereof gradually enlarged toward the metal honeycomb catalyst on portions thereof in front of and behind the metal honeycomb catalyst, and the metal honeycomb catalyst is arranged along the down frame * [Claim 2] A catalyst arrangement structure of a motorcycle according to claim 1, wherein the exhaust pipe includes a horizontal portion thereof arranged in a horizontal posture or in a substantially horizontal posture below the engine, and the tapered portion arranged downstream of the metal honeycomb catalyst is arranged in front of the horizontal portion. [Claim 3] A catalyst arrangement structure of a motorcycle according to claim 1 or claim 2, wherein the metal honeycomb catalyst is arranged on a side of the down frame and more inside a vehicle body than an outermost surface of a crankcase of the engine as viewed in a plan view. [Claim 4] A catalyst arrangement structure of a motorcycle according to any one of claims 1 to 3, wherein a connection portion is formed on the cylinder head of the engine for connecting the exhaust pipe to the cylinder head, an insertion hole to which a secondary air supply pipe for supplying air into the inside of the exhaust pipe is connected by insertion is formed in the vicinity of the connection portion, and the secondary air supply pipe extends downwardly toward the connection portion from an upper portion of the cylinder head. [Claim 5] A catalyst arrangement structure of a motorcycle according to any one of claims 1 to 4, wherein a plurality of metal honeycomb catalysts is arranged in parallel in the exhaust pipe.

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306-CHE-2008 AMENDED CLAIMS 30-04-2012.pdf

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