JP2007187004A - Internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To arrange a catalyst near a cylinder part with the influence on cooling performance of the cylinder part suppressed in the internal combustion engine having a cylinder part including a cooling fin arranged with an axial line thereof kept roughly horizontal. <P>SOLUTION: In the engine 20 having the cylinder part 22 including the cooling fins 61a, 61b arranged with the axis C thereof kept roughly horizontal, the catalyst 28 for exhaust emission control is provided roughly in parallel with the axis C of the cylinder part 22, and is arranged offset to a lower side and outward to the side of the cylinder part 22. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an internal combustion engine in which a cylinder portion is arranged with its axis substantially horizontal.

2. Description of the Related Art Conventionally, motorcycles equipped with the internal combustion engine are widely known (for example, see Patent Document 1).
JP 2002-47939 A

By the way, many vehicles such as motorcycles equipped with the internal combustion engine include a catalyst for purifying exhaust gas from the internal combustion engine. It is desirable to arrange this catalyst near the exhaust valve to obtain a predetermined reaction acceleration temperature. However, particularly in the case of an air-cooled engine equipped with cooling fins, an arrangement that does not affect the cooling performance of the cylinder portion is considered. There is a need.
The present invention has been made in view of the above circumstances, and in an internal combustion engine in which a cylinder portion having a cooling fin is arranged with its axis substantially horizontal, the influence on the cooling performance of the cylinder portion is suppressed, and the vicinity of the cylinder portion The purpose is to arrange the catalyst in

  As a means for solving the above problems, the invention described in claim 1 is characterized in that a cylinder portion (for example, the cylinder portion 22 of the embodiment) having cooling fins (for example, the cooling fins 61a and 61b of the embodiment) has its axis (for example, of the embodiment). In an internal combustion engine (for example, the engine 20 of the embodiment) arranged with the axis C) substantially horizontal, an exhaust gas purifying catalyst (for example, the catalyst 28 of the embodiment) is provided substantially parallel to the axis of the cylinder portion. Further, the cylinder portion is arranged to be offset downward and outward from the cylinder portion.

  The invention described in claim 2 is characterized in that the catalyst is disposed below a cam chain chamber (for example, the cam chain chamber 62 of the embodiment) of the cylinder portion.

  According to the third aspect of the present invention, an air jacket (for example, implementation) is provided in the cylinder head of the cylinder portion (for example, the cylinder head 24 of the embodiment) for cooling around a plug hole (for example, each of the plug holes 66 and 67 of the embodiment). An air jacket 69) of the example is provided, and the catalyst is arranged offset from a traveling wind inlet (for example, the traveling wind inlet 75 of the embodiment) of the air jacket.

  According to the first aspect of the present invention, since the traveling wind hits the cooling fins of the cylinder portion without being hindered by the catalyst, the cooling performance of the cylinder portion can be maintained well. Further, since the activation of the catalyst is accelerated by the catalyst being located near the cylinder portion, it is possible to improve the exhaust gas purification performance especially during the warm-up operation.

  According to the second aspect of the present invention, since the running wind strikes the periphery of the combustion chamber in the cylinder portion well and the heat of the heated catalyst is difficult to be transmitted to the periphery of the combustion chamber, the cooling performance of the cylinder portion is further improved. Can do.

  According to the third aspect of the present invention, the heat of the catalyst is less likely to enter the air jacket from the traveling wind inlet, so that the engine cooling effect by the air jacket can be enhanced.

  Embodiments of the present invention will be described below with reference to the drawings. In the following description, the directions such as front, rear, left and right are the same as those in the vehicle unless otherwise specified. In the figure, the arrow FR indicates the front of the vehicle, the arrow LH indicates the left side of the vehicle, and the arrow UP indicates the upper side of the vehicle.

  In the motorcycle (vehicle) 1 shown in FIG. 1, left and right front forks 5 that pivotally support the front wheels 4 are pivoted to a head pipe 3 positioned at the front end portion of the vehicle body frame 2 via a steering stem 6. Be supported. A steering bar handle 7 is attached to the upper portion of the steering stem 6.

  The vehicle body frame 2 is a so-called backbone type in which one main tube 8 is extended obliquely downward and rearward from the head pipe 3 and the stride between the head pipe 3 and the occupant seat 9 is lowered to improve the ease of straddling. The The left and right pivot plates 10 are joined to the rear end portion of the main tube 8, and the front end portion of the swing arm 12 that pivotally supports the rear wheel 11 is pivotally supported on the left and right pivot plates 10.

  The front ends of the left and right seat frames 13 extending obliquely upward and rearward are joined to the rear portion of the main tube 8, and between the front and rear intermediate portions of the left and right seat frames 13 and the left and right arm rear ends of the swing arm 12, Left and right rear cushions 14 are respectively disposed. Above the left and right seat frames 13, the seat 9 having front and rear seat surfaces for a driver and a rear passenger is disposed. In the figure, reference numeral 15 denotes a driver step, and reference numeral 16 denotes a rear passenger step.

  An engine (internal combustion engine) 20, which is a prime mover of the motorcycle 1, is disposed inside the center lower part of the body frame 2 (inside the lower part). The engine 20 is an air-cooled single-cylinder engine having a crank rotation axis along the vehicle width direction (left-right direction), and has a basic configuration in which a cylinder portion 22 is erected from the front end portion of the crankcase 21 toward the front of the vehicle. . The engine 20 is supported by the left and right pivot plates 10 at the rear upper and lower portions of the crankcase 21, and the upper portion of the crankcase 21 is supported by the front and rear intermediate portions of the main tube 8 via the engine hanger 8a. Mounted on.

  The cylinder head on the front end side (front end side) of the cylinder portion 22 is connected to the downstream side of the throttle body 26 from above and to the base end side of the exhaust pipe 27 from below. An air cleaner case 26 a supported on the lower front side of the main tube 8 is connected to the upstream side of the throttle body 26.

  Referring also to FIG. 2, the exhaust pipe 27 is bent and extended forward at one end below the cylinder head, and is folded back leftward and slightly forward from the front end of the cylinder portion 22, so that the diagonally lower left side of the cylinder portion 22 And extends rearward substantially parallel to the rear side of the crankcase 21 and then changes to substantially the center in the vehicle width direction and is connected to the front end (base end) of the silencer 27a located behind the engine 20. A catalytic converter (hereinafter sometimes simply referred to as a catalyst) 28 for purifying exhaust gas is provided in a portion of the exhaust pipe 27 located obliquely below and to the left of the cylinder portion 22 (see FIG. 5). Silencer 27a extends from the base end located between the rear end of engine 20 and the front end of rear wheel 11 to the right of rear wheel 11, and overlaps with the front of rear wheel 11 from the extended portion in a side view. Is formed in a substantially L shape when viewed from above.

  Rotational power from the engine 20 is output to a drive sprocket 32 on the rear left side of the crankcase 21 via clutches and transmissions 31 (see FIG. 4), which will be described later, housed in the crankcase 21, and the drive sprocket 32 To the driven sprocket 34 on the left side of the rear wheel 11 through the drive chain 33.

  The front part of the body frame 2, the cylinder part 22 of the engine 20, the throttle body 26, the air cleaner case 26a, and the like are covered with a front body cover 35 made of synthetic resin. The front body cover 35 also serves as a leg shield that protects the driver's legs from wind pressure and the like from the front. The rear portion of the vehicle body frame 2 is covered with a rear vehicle body cover 36 that is also made of synthetic resin. The rear body cover 36 supports the seat 9 together with the left and right seat frames 13. An article storage box 37 located under the seat 9 is disposed in the rear body frame 2, and a fuel tank 38 supported by the front part of the left and right seat frames 13 is disposed below the front part of the article storage box 37. Is placed.

  As shown in FIG. 3, the cylinder portion 22 of the engine 20 protrudes forward (vehicle traveling direction) from the front end portion of the crankcase 21 with the axis C thereof being substantially horizontal (in detail, slightly upward). Therefore, the cylinder main body 23 attached to the front end portion of the crankcase 21, the cylinder head 24 attached to the front end portion of the cylinder main body 23, and the head cover 25 attached to the front end portion of the cylinder head 24 are mainly used. Hereinafter, the front-rear direction parallel to the axis C (cylinder axis) in the cylinder portion 22 may be referred to as the cylinder front-rear direction, and the vertical direction orthogonal to the axis C may be referred to as the cylinder vertical direction.

  Referring also to FIG. 4, the cylinder body 23 is formed with a cylinder bore 39 along the axis C, and a piston 40 is fitted in the cylinder bore 39 so as to be able to reciprocate. A small end portion of a connecting rod 41 is slidably connected to the piston 40 via a piston pin extending in the left-right direction. The large end portion of the connecting rod 41 rotates to a crankshaft 42 via a crank pin extending in the left-right direction. Connected freely. The crankshaft 42 supports a crankpin between left and right shaft portions along the left-right direction via left and right crank webs.

  A centrifugal clutch 29 is coaxially arranged at the right end of the crankshaft 42, and the rotational power of the crankshaft 42 is transmitted to the primary drive gear 43 via the centrifugal clutch 29 according to the rotational speed. The primary drive gear 43 is coaxially arranged on the right shaft portion of the crankshaft 42, and the primary drive gear 43 meshes with a primary driven gear 44 coaxially arranged on the right side portion of the main shaft 45 behind the crankshaft 42. The main shaft 45 is disposed behind the crankshaft 42 in parallel with the left and right shaft portions, and a multi-plate clutch 30 capable of intermittently transmitting power by a driver's operation is coaxially disposed at the right end thereof. The rotational power input to the primary driven gear 44 via the plate clutch 30 is transmitted to the main shaft 45.

  The main shaft 45 supports a transmission gear group (only one set of transmission gear pairs fitted to each other is shown in FIG. 4) 47 together with a counter shaft 46 arranged in parallel behind the main shaft 45. The main shaft 45, the counter shaft 46, and the transmission gear group 47 mainly constitute the transmission 31, and the reduction ratio of the transmission gear group 47 is changed in multiple stages through a change mechanism (not shown) by the operation of the driver. Let The left end portion of the counter shaft 46 projects out of the crankcase 21, and the drive sprocket 32 is attached to the left end portion.

  The cylinder head 24 closes the front end opening of the cylinder bore 39 and forms a so-called pent roof type combustion chamber together with the piston 40 at the top dead center. The engine 20 in this embodiment is an OHC two valve, and a single combustion chamber side opening in the intake port 49 or the exhaust port 50 is formed on two inclined upper surfaces in the roof forming portion 48 of the combustion chamber, respectively. The combustion chamber side opening is opened and closed by an intake valve 51 or an exhaust valve 52, respectively.

  Each port 49, 50 is a flow passage that communicates the combustion chamber with a throttle body attachment portion 53 at the upper part of the cylinder head 24 or an exhaust pipe attachment portion 54 at the lower part of the cylinder head 24. After extending obliquely forward so as to be substantially orthogonal, it curves upward or downward to reach the throttle body attachment portion 53 or the exhaust pipe attachment portion 54. The throttle body attaching portion 53 and the exhaust pipe attaching portion 54 form a plane that is substantially orthogonal to the cylinder vertical direction, and the insulator of the throttle body 26 or the coupling flange of the exhaust pipe 27 is brought into contact with each plane to be fastened. .

  The stems of the valves 51 and 52 extend obliquely forward so as to be substantially orthogonal to the inclined upper surface and pass through the inner walls of the intake and exhaust ports 49 and 50, respectively, and then the intake side or exhaust side rocker arm 55 and 56 tips are engaged. The other ends of the rocker arms 55 and 56 are in sliding contact with two cam peaks formed on a single camshaft 57, and the valves 51 and 52 reciprocate along the stem by driving the camshaft 57. It moves and opens and closes the combustion chamber side opening of each port 49,50. The stems of the valves 51 and 52, the rocker arms 55 and 56, the camshaft 57 and the like are supported inside the front portion of the cylinder head 24. These are the front portion of the cylinder head 24 and the cup-shaped head cover 25 that closes the cylinder head 24. It is accommodated in the valve train chamber to be formed.

  A driven sprocket 58 is coaxially fixed to the left end portion of the camshaft 57, and an endless cam chain 60 is wound around the driven sprocket 58 and a drive sprocket 59 coaxially fixed to the left end portion of the crankshaft 42. As a result, the camshaft 57 is linked to the crankshaft 42 to open and close the valves 51 and 52. A generator (not shown) is coaxially arranged at the left end of the crankshaft 42.

  Referring also to FIG. 5, a large number of cooling fins 61 a and 61 b are integrally formed on the outer periphery of the cylinder portion 22. Specifically, a plurality of side cooling fins 61 a are formed on the right side of the cylinder body 23 and the cylinder head 24 so as to be substantially orthogonal to the cylinder axis C, and above and below the cylinder body 23, approximately the cylinder axis C. A plurality of upper and lower cooling fins 61b are formed in parallel.

  A cam chain chamber 62 for accommodating the cam chain 60 is formed in the left side portion of the cylinder portion 22. The cam chain chamber 62 also functions as a return path for the engine oil fed into the cylinder head 24 into the crankcase 21, and the engine oil temperature is adjusted so that the detection unit faces the cam chain chamber 62. An oil temperature sensor 63 for detection is provided. The oil temperature sensor 63 is located on the lower left side of the cylinder body 23 and in the vicinity of the crankcase 21 (see FIG. 8), and is attached to the cylinder body 23 so as to be inserted from the left side. Reference numeral 60a in the figure denotes a cam chain tensioner that applies a predetermined tension to the cam chain 60. Further, the catalyst 28 is located below the cam chain chamber 62 (slightly lower left of the cylinder portion 22).

  Referring also to FIG. 6, the cam chain chamber 62 forms a flat space with reduced left and right widths in the left side portions of the cylinder body 23 and the cylinder head 24, and includes an inner wall portion 62 a integrated with the cylinder inner wall and its The outer side of the upper inner wall portion 73 that continues upward is surrounded by an outer wall portion 62b having a U-shaped cross section. That is, heat due to combustion in the cylinder bore 39 is not directly transmitted to the outer wall portion 62b of the cam chain chamber 62, and therefore no cooling fin is formed on the outer wall portion 62b (the left side portion of the cylinder portion 22).

  Here, as shown in FIGS. 6 and 7, the engine 20 is twin-plugged in order to improve the combustion performance to improve the output and to reduce fuel consumption. A first spark plug 64 is attached, and a second spark plug 65 is attached to the left side of the cylinder head 24 from the diagonally right front side. First and second plug holes 66 and 67 for allowing the plugs 64 and 65 to reach the roof forming portion 48 inside the cylinder head 24 are formed on the lower and left sides of the cylinder head 24, respectively. Each plug 64, 65 is screwed into a female screw hole formed in the roof forming portion 48 through the corresponding plug hole 66, 67, and is fixed to the cylinder head 24 with its tip electrode portion facing the combustion chamber. Ru

  The first plug 64 is inclined with respect to the cylinder vertical direction in a plane substantially perpendicular to the left-right direction, and the central axis of the first plug 64 is the position of the intake / exhaust ports 49 and 50 when viewed from the cylinder axis direction (arrow view along the cylinder axis C). It arrange | positions so that it may be substantially parallel to the extension direction (it is substantially parallel to the up-down direction). On the other hand, the second plug 65 is inclined with respect to the left-right direction in a plane substantially perpendicular to the cylinder vertical direction, and the central axis thereof is substantially orthogonal to the extending direction of the intake / exhaust ports 49, 50 as viewed in the cylinder axial direction. (So as to be substantially parallel to the left-right direction). In other words, the plugs 64 and 65 are arranged so as to be substantially L-shaped when viewed in the cylinder axial direction. The first plug 64 is provided with an offset so that the center axis thereof is located on the left side of the cylinder axis C, and the second plug 65 is provided so that the center axis thereof is located above the cylinder axis C. Is provided offset.

  The intake port 49 has a combustion chamber side opening located above the roof forming portion 48 and on the left side of the cylinder axis C, and extends generally upward (incline slightly to the right) from the opening. The throttle body mounting portion 53 is located almost immediately above the axis C. On the other hand, the exhaust port 50 has an opening on the combustion chamber side located below the roof forming portion 48 and on the right side of the cylinder axis C, and extends substantially downward (incline slightly to the right). As a result, the exhaust pipe mounting portion 54 is located on the right side of the cylinder axis C. Since the exhaust pipe attaching portion 54 is offset to the right side, a work space for attaching and detaching the first plug 64 is secured.

  The exhaust port 50 is provided with an exhaust gas sensor (oxygen concentration sensor) 68 so that the target air-fuel ratio of intake air can be set based on the oxygen concentration of the exhaust gas. The exhaust gas sensor 68 uses a gate (catalyst) such as platinum. The exhaust gas sensor 68 is arranged so that the detection portion of the exhaust gas sensor 68 faces the exhaust port 50 of the cylinder head 24, so that the gate has a predetermined operating temperature. The detection sensitivity during warm-up operation (during cold operation) increases.

  The exhaust gas sensor 68 is attached so as to be inserted from the right into the lower right side of the cylinder head 24 (the right side of the exhaust port 50). The first plug 64 is located on the opposite side (left side) of the exhaust gas sensor 68 across the exhaust port 50 in the cylinder head 24, and the second plug 65 is located on the same side (right side) as the exhaust gas sensor 68. Further, the exhaust gas sensor 68 is disposed so as to be spaced below the cylinder axis C and the center axis thereof is substantially parallel to the left-right direction. That is, the exhaust gas sensor 68 is disposed so as to be substantially orthogonal to the first plug 64 and substantially parallel to the second plug 65 when viewed in the cylinder axial direction.

  Here, the engine 20 has cooling air (running air) in the rear part of the cylinder head 24 so that the cylinder head 24 (especially around the plug holes 66 and 67) having a particularly large thermal load can be effectively cooled. An air jacket (cooling airflow passage) 69 is provided. The air jacket 69 is a space formed between the roof forming portion 48 at the rear of the cylinder head 24 and the bottom portion 70 of the valve operating chamber so as to allow the plug holes 66 and 67 to communicate with each other. 72, the upper inner wall portion 73 of the cam chain chamber 62, the insertion portion 74 of the fastening bolt between the cylinder body 23 and the crankcase 21, and the like. The air jacket 69 allows the cooling air (running air) to flow well around the plug holes 66 and 67 and introduce the cooling air (running air) to the inside of the cylinder head 24. Coolability is improved.

  The air jacket 69 has a traveling air inlet 75 around the first plug hole 66 that opens downward in the lower part of the cylinder head 24 by the action of two air guide plates 78 and 79, which will be described in detail later. The second plug hole 67 opening to the right in FIG. 6 is configured as a traveling wind exhaust port (exhaust port) 76. In other words, the air jacket 69 is formed so as to be bent in a substantially L shape when viewed from the cylinder axial direction from the traveling wind introduction port 75 to the exhaust port 76.

  The traveling wind introduction port 75 (first plug hole 66) is formed between the exhaust port forming portion 72 and the lower left fastening bolt insertion portion 74, and the air discharge port 76 (second plug hole 67) is formed at the upper right and lower right. The fastening bolt insertion part 74 is formed. The traveling wind introduction port 75 has a narrower width in the cylinder axial direction view than the exhaust port 76, and the first plug 64 is disposed so as to be sandwiched between the exhaust port forming portion 72 and the fastening bolt insertion portion 74. The exhaust port forming portion 72 (exhaust port 50), the traveling wind introduction port 75, and the first plug 64 are arranged so as to be lined up substantially on the left and right. Further, the exhaust gas sensor 68 is disposed on the opposite side of the cylinder head 24 from the first plug 64 and the traveling air inlet 75 with the exhaust port forming portion 72 (exhaust port 50) interposed therebetween.

  A center fin 77 is provided in the air jacket 69 so as to cross the vicinity of the cylinder axis C to the left and right as viewed in the cylinder axis direction. The center fin 77 is a plate-like shape extending over the upper and lower walls of the air jacket 69, and is positioned between the intake / exhaust port forming portions 71 and 72, and the left end thereof is inclined downward (toward the traveling air inlet 75). Provided. The center fin 77 smoothly guides the traveling wind introduced into the air jacket 69 from the traveling wind introduction port 75 toward the exhaust port 76 and increases the contact area of the traveling wind to cool the cylinder head 24. Improves.

  As shown in FIGS. 8 and 9, the traveling wind (indicated by a chain line arrow in FIG. 8) is directed toward the traveling wind inlet 75 (first plug hole 66) of the air jacket 69 at the lower part (road surface side) of the cylinder head 24. ) Is provided. The first air guide plate 78 has a flat plate-like air guide plate main body 78a that is substantially parallel to the left-right direction spaced downward from the traveling air introduction port 75, and a pair of legs that support both left and right ends of the air guide plate main body 78a. And a traveling airflow passage penetrating in the front-rear direction is formed in a substantially U-shape that opens upward when viewed in the cylinder axial direction. The wind guide plate main body 78a is inclined rearward and guides a part of the traveling wind flowing through the traveling wind flow path toward the traveling wind introduction port 75 above. Such a first air guide plate 78 is integrally formed under the cylinder head 24 by aluminum die casting or the like.

  The oil temperature sensor 63 is located behind (on the downstream side) the first air guide plate 78, and immediately before the oil temperature sensor 63, a stopper wall 80 is provided to suppress the air contact with the oil temperature sensor 63. Is erected downward. The stopper wall 80 has a plate-like shape substantially orthogonal to the axis C, and is integrally formed at the lower part of the cylinder head 24 by aluminum die casting or the like to reduce the contact of obstacles from the road surface to the oil temperature sensor 63.

  Further, a second air guide plate 79 that guides the traveling wind toward the inside of the first air guide plate 78 is provided below the head cover 25 (on the road surface side). The second air guide plate 79 includes a flat air guide plate body 79a that is substantially parallel to the left-right direction spaced downward from the lower portion of the head cover 25, and a pair of leg portions 79b that support both left and right ends of the air guide plate body 79a. And a traveling airflow passage penetrating in the front-rear direction is formed in a substantially U-shape that opens upward when viewed in the cylinder axial direction. The front end of the second air guide plate 79 is located in the vicinity of the front end of the head cover 25, takes in the traveling air just after hitting the front end of the head cover 25, flows this rearward, and guides it into the first air guide plate 78. Such a second air guide plate 79 is integrally formed under the head cover 25 by aluminum die casting or the like.

  Here, as shown in FIGS. 3 and 5, the catalytic converter 28 accommodates, for example, a honeycomb structure (monolith) to which a catalyst such as platinum is attached in a cylindrical case having a diameter larger than that of the exhaust pipe 27. Thus, the cylinder portion 22 is provided in the middle of the exhaust pipe 27 at a position offset obliquely to the lower left and obliquely. The catalyst 28 is heated to a predetermined reaction promoting temperature. Exhaust gas from the passing engine 20 is appropriately purified. The catalyst 28 is located obliquely below and to the left of the cylinder portion 22, that is, below the cam chain chamber 62, so that the heat of the heated catalyst 28 is not directly transmitted to the cylinder inner wall. Further, the catalyst 28 is arranged to be offset to the left from the traveling wind inlet 75 of the air jacket 69, so that the heat of the catalyst 28 hardly enters the air jacket 69.

  As described above, the engine 20 in the above embodiment has the cylinder portion 22 having the cooling fins 61a and 61b arranged with the axis C substantially horizontal, and the exhaust gas-purifying catalyst 28 has the above-described configuration. While being provided substantially parallel to the axis C of the cylinder part 22, the cylinder part 22 is arranged to be offset downward and outward from the cylinder part 22.

  According to this configuration, since the traveling wind hits the cooling fins 61a and 61b of the cylinder portion 22 without being hindered by the catalyst 28, the cooling performance of the cylinder portion 22 can be maintained well. Further, since the activation of the catalyst 28 is accelerated because the catalyst 28 is positioned near the cylinder portion 22, it is possible to improve the exhaust gas purification performance particularly during the warm-up operation.

  Further, in the engine 20, the catalyst 28 is disposed below the cam chain chamber 62 of the cylinder portion 22, so that the running air strikes well around the combustion chamber in the cylinder portion 22 and the heated catalyst 28. This makes it difficult to transfer the heat to the periphery of the combustion chamber, so that the cooling performance of the cylinder portion 22 can be further improved.

  Further, in the engine 20, the cylinder head 24 of the cylinder portion 22 is provided with an air jacket 69 that cools around the plug holes 66 and 67, and is offset from the traveling wind inlet 75 of the air jacket 69. By disposing the catalyst 28, it becomes difficult for heat of the catalyst 28 to enter the air jacket 69 from the traveling wind inlet 75, so that the cooling effect of the cylinder head 24 by the air jacket 69 can be enhanced.

The present invention is not limited to the above-described embodiment. For example, an engine having a single spark plug instead of a twin plug, a DOHC engine having two camshafts for intake and exhaust in a cylinder head, and a rocker arm The present invention can also be applied to a direct-pressing engine in which a valve is directly driven by a camshaft without using an engine, an engine having a plurality of intake and exhaust valves, and a multi-cylinder engine.
And the structure in the said Example is an example of this invention, Of course, various changes are possible in the range which does not deviate from the summary of this invention not only being applicable to various vehicles, such as a low floor type vehicle, such as a scooter. Needless to say.

1 is a left side view of a motorcycle according to an embodiment of the present invention. It is a top view which shows arrangement | positioning of the engine, exhaust pipe, etc. of the said motorcycle. It is a right view of the said engine and an exhaust pipe. It is an expanded sectional view of the above-mentioned engine. It is sectional drawing orthogonal to the axis line of the cylinder main body of the said engine. It is sectional drawing orthogonal to the axis line of the cylinder head of the said engine. It is a right view equivalent to FIG. 3 which shows arrangement | positioning of the ignition plug of the said engine. It is explanatory drawing which looked at the cylinder part of the said engine from the left side. It is an arrow line view which follows the axis line which looked at the cylinder head of the above-mentioned engine from the front side.

Explanation of symbols

1 Motorcycle (vehicle)
20 engine (internal combustion engine)
22 Cylinder part 24 Cylinder head 28 Catalytic converter (catalyst)
61a Side cooling fin (cooling fin)
61b Vertical cooling fins (cooling fins)
62 Cam chain chamber 66 First plug hole (plug hole)
67 Second plug hole (plug hole)
69 Air jacket 75 Running air inlet C axis

Claims (3)

In an internal combustion engine in which a cylinder portion having cooling fins is arranged with its axis substantially horizontal, an exhaust gas purifying catalyst is provided substantially parallel to the axis of the cylinder portion, and below and outward of the cylinder portion. An internal combustion engine characterized by being arranged offset. The internal combustion engine according to claim 1, wherein the catalyst is disposed below a cam chain chamber of the cylinder portion. The cylinder head of the cylinder part is provided with an air jacket that cools the periphery of the plug hole, and the catalyst is arranged offset from a running air inlet of the air jacket. The internal combustion engine described.

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