JP6900418B2 - Internal combustion engine - Google Patents

Description

The present invention relates to an internal combustion engine in which a cylinder accommodating a piston for reciprocating motion is held in a cylinder block, and a cylinder head holding a valve operating mechanism for controlling the inflow and outflow of air to the cylinder is attached adjacent to the cylinder block. ..

For example, in Patent Document 1, a hole communicating with the outside is formed around the combustion chamber and the valve operating chamber in the cylinder head, and the hole is used as an air jacket for cooling the spark plug and the intake port. Is disclosed. In this case, the air jacket cools the inside of the cylinder head.

Japanese Unexamined Patent Publication No. 2013-15122

By the way, the cylinder head is attached adjacent to the cylinder block that holds the cylinder. Cooling fins for cooling the cylinder are provided on the outer peripheral surface of the cylinder block. Therefore, when the vehicle is running, it is difficult for the cooling air (running wind) to hit the cylinder head side portion of the cylinder block.

Therefore, an object of the present invention is to provide an internal combustion engine capable of effectively cooling a cylinder with a simple configuration.

Aspects of the present invention are powered by at least one cylinder (74) accommodating at least one piston (72) that performs reciprocating motion and a crank shaft (68) that converts the reciprocating motion of the piston (72) into rotary motion. A valve operating mechanism (90) that controls the inflow and outflow of air to and from the cylinder (74) by operating by power transmitted via the transmission mechanism (132), and a cylinder block (54) that holds the cylinder (74). ) and mounted adjacent to said cylinder block (54), have a cylinder head (56) for holding the valve operating mechanism (90), towards the axis of the cylinder (74) forward, horizontal inclined more upwardly about the vehicle (12) an internal combustion engine that will be mounted on the (10). In this case, a plurality of cooling fins (84) intersecting in the axial direction of the cylinder (74) are provided on the outer peripheral surface of the cylinder block (54). Further, on the cylinder block (54) side of the cylinder head (56), an opening (266) that opens from the outer peripheral surface of the cylinder head (56) toward the cooling fin (84) is formed. .. On the side of the cylinder head (56), a plug hole (94) to which a spark plug (96) is attached, an intake port (104) formed on the upper side of the cylinder head (56), and the cylinder head. An exhaust port (260) formed on the lower side of (56) is provided. The cylinder head (56) has an air jacket (268) that communicates the side portion of the spark plug (96), the side portion of the intake port (104), and the side portion of the exhaust port (260) with the outside. It is provided. The opening (266) is provided on the side of the exhaust port (260), and is more than the exhaust port (260) in the vertical direction of the vehicle (12) when viewed from the bottom of the cylinder head (56). It is below and above the lower end of the power transmission mechanism accommodating chamber (202) in which the power transmission mechanism (132) is accommodated. In this case, the opening (266) is formed from the air jacket (268) between the exhaust port (260) and the power transmission mechanism accommodating chamber (202) in the left-right direction of the vehicle (12). It is open toward the cooling fin (84). As a result, the traveling wind introduced from the plug hole (94) into the air jacket (268) passes through the side portion of the intake port (104) and the side portion of the exhaust port (260), and the opening ( As well as exiting rearward via 266), it also exits downward from the air jacket (268).

Further, the internal combustion engine (10) further includes a crank case (52) for accommodating the front Symbol crankshaft (68). Before Symbol cylinder (74) protrudes upwardly or forwardly from a front portion of the crankcase (52). It said opening (266) is above the lower surface of the exhaust port (260), and are formed before kidou force transmission mechanism housing chamber vertically in width (202).

The front Symbol opening (266) is formed in the longitudinal direction in the cylinder head (56).

The front Symbol opening (266) is formed in said cylinder head (56) inside so as to be positioned on the lower side of the cylinder (74).

According to the present invention, when the vehicle is traveling, the traveling wind from the front flows to the cylinder block through the opening. As a result, by attaching the cylinder head to the cylinder block adjacent to the cylinder block, it is possible to apply running air (cooling air) to the cooling fins on the cylinder head side that are hidden by the cylinder head. As a result, the cooling effect of the cylinder by the cooling fins can be improved with a simple configuration.

Further, by opening the opening from the air jacket toward the cooling fin, the opening is provided at a position where the running wind flows. As a result, the efficiency of air conduction from the cylinder head side to the cooling fins of the cylinder block is improved.

Further, since the cylinder block protrudes upward or forward from the front part of the crankcase and the axis of the cylinder block is inclined upward from the horizontal toward the front, the running wind hits the outer peripheral surface of the cylinder head and passes through the opening. Is guided to the cooling fins of the cylinder block. As a result, the air conduction efficiency can be further improved.

Further, by forming the opening in the front-rear direction in the cylinder head, the opening is provided in the same direction as the flow of the running wind. Thereby, the amount of air guided to the opening can be improved. As a result, the running wind can be easily applied to the cooling fins on the cylinder head side of the cylinder block, which are arranged behind the cylinder head so that the running wind is less likely to hit.

Further, by forming an opening in the cylinder head so as to be located on the lower side of the cylinder block, a negative pressure is generated between the lower surface side of the cylinder block facing the opening and the ground, and the running wind from the front Can be taken in more at the opening.

It is a left side view of a vehicle. It is a left side view of the internal combustion engine of FIG. It is a right side view of the internal combustion engine of FIG. It is a top view of the internal combustion engine of FIG. It is sectional drawing along the VV line of FIG. FIG. 5 is a cross-sectional view taken along the line VI-VI of FIG. It is a top view illustrated by breaking the crankcase. It is the perspective view which showed by breaking the crankcase. It is a top view of the gasket. It is sectional drawing along the X-ray line of FIG. It is sectional drawing along the XI-XI line of FIG. It is a bottom view of a cylinder head. It is sectional drawing along the XIII-XIII line of FIG. It is sectional drawing along the XIV-XIV line of FIG.

Hereinafter, the internal combustion engine according to the present invention will be described in detail below with reference to suitable embodiments and the accompanying drawings.

[1. Outline configuration of vehicle 12]
FIG. 1 is a left side view of a vehicle 12 equipped with the internal combustion engine 10 according to the present embodiment. In the present embodiment, the front-rear, left-right, and up-down directions of the vehicle 12 will be described with reference to the direction seen from the driver seated on the seat 14 of the vehicle 12. Further, the pair of left and right components may be described by adding a reference numeral of "L" to the reference number of the component on the left side and an "R" to the reference number of the component on the right side.

This embodiment is applied to the turnip type motorcycle shown in FIG. The present embodiment is not limited to the motorcycle of FIG. 1, and can be applied to various saddle-type vehicles and motors (internal combustion engines).

The vehicle 12 has a body frame 16. The vehicle body frame 16 includes a head pipe 18, a single main frame 20 extending diagonally downward and rearward from the head pipe 18, and a seat frame 22 extending obliquely upward and rearward from the rear end portion of the main frame 20.

A steering handle 24 operated by the driver is pivotally supported at the upper end of the head pipe 18. A pair of left and right front forks 28L and 28R are pivotally supported at the lower end of the head pipe 18 via a steering stem 26. The lower ends of the front forks 28L and 28R pivotally support the front wheels 30.

An internal combustion engine 10 (power unit) is supported below the main frame 20. A pair of left and right pivot brackets 32L and 32R extend downward at the rear end of the main frame 20. The front end portion of the swing arm 34 is supported on the pivot bracket 32L so as to be swingable in the vertical direction. The rear end of the swing arm 34 pivotally supports the rear wheel 36 (rotated moving portion). A rear cushion 38 is connected between the seat frame 22 and the swing arm 34. A seat 14 is arranged above the seat frame 22.

The vehicle body frame 16 is covered with a vehicle body cover 40. The body cover 40 includes a front cover 42, a pair of left and right main frame covers 44L and 44R, a leg shield 46, an under cowl 48, a body cover 50, and the like. The front cover 42 covers the head pipe 18 from the front. The main frame covers 44L and 44R cover the main frame 20 and the like from the left and right. The leg shield 46 connects the front cover 42 and the main frame covers 44L and 44R, and covers the driver's feet from the front. The under cowl 48 connects the main frame covers 44L and 44R below. The body cover 50 covers the rear end portion of the main frame 20, the seat frame 22, and the like.

[2. Configuration of internal combustion engine 10]
Next, the configuration of the internal combustion engine 10 will be described with reference to FIGS. 2 to 14. Here, the external configuration, the internal configuration, and the configuration of each part of the internal combustion engine 10 will be described.

<2.1 External configuration of internal combustion engine 10>
First, the appearance configuration of the internal combustion engine 10 will be described with reference to FIGS. 2 to 4.

The internal combustion engine 10 is mounted on the vehicle 12 below the main frame 20 while being supported by the main frame 20 and the pivot brackets 32L and 32R. The internal combustion engine 10 includes a crankcase 52 (power unit case), a cylinder block 54 (cylinder) extending obliquely upward and forward from the front end of the crankcase 52, and a cylinder head 56 connected to the front end of the cylinder block 54. And have.

The crankcase 52 is a metal case. One coupling boss 58a that bulges toward the main frame 20 is provided on the upper portion (upper wall, upper surface) of the crankcase 52. Further, two coupling bosses 58b and 58c that bulge toward the pivot brackets 32L and 32R are provided on the rear portion (rear wall and rear surface) of the crankcase 52. On the other hand, a pair of left and right ribs 60L and 60R extending downward toward the upper part of the crankcase 52 are provided on the rear end side of the main frame 20.

A screw hole is formed in the coupling boss 58a on the upper portion of the crankcase 52 in the vehicle width direction. Two bolts 62a through which the holes formed in the pair of left and right ribs 60L and 60R are inserted are screwed into the screw holes. Further, screw holes are formed in the two coupling bosses 58b and 58c at the rear of the crankcase 52 in the vehicle width direction. Two bolts 62b for inserting holes formed in the pivot brackets 32L and 32R are screwed into the screw holes of the coupling boss 58b. Two bolts 62c for inserting holes formed in the pivot brackets 32L and 32R are screwed into the screw holes of the coupling boss 58c. As a result, the internal combustion engine 10 including the crankcase 52 is supported by the vehicle body frame 16 directly under the main frame 20.

Then, various components are connected to the internal combustion engine 10. In this case, there is a dead space between the vehicle body frame 16 (main frame 20) and the internal combustion engine 10. Therefore, in the present embodiment, various components are arranged in the dead space in order to avoid protrusion of these components from the internal combustion engine 10 in the vehicle width direction.

Specifically, in the upper part of the crankcase 52, a starting electric motor 66 is arranged in front of the coupling boss 58a. A crankshaft 68 (crankshaft, power generation unit) as a drive shaft (rotary shaft) of the internal combustion engine 10 extending in the vehicle width direction is housed in the crankcase 52 (FIGS. 2, 3, 5, and 5). (See FIG. 6). The electric motor 66 is arranged above the crankshaft 68 in the upper part of the crankcase 52.

Further, in the upper part of the crankcase 52, a rotation speed detecting unit 70 is attached in front of the starting electric motor 66. The rotation speed detection unit 70 is a sensor (vehicle speed sensor, pickup sensor) that detects the rotation speed of the crankshaft 68 according to the vehicle speed of the vehicle 12, and the crankcase 52 is directed to the axial center of the crankshaft 68. It is attached to the crankcase 52 in a state of extending diagonally upward and forward from the upper part of the crankcase 52.

The cylinder block 54 has a cylinder chamber 74 (cylinder) that houses a piston 72 that reciprocates (see FIGS. 5 and 6). A plurality of insertion holes 76 are formed in the cylinder block 54 along the axial direction of the cylinder chamber 74, that is, in the diagonally upward and forward direction in which the cylinder block 54 extends from the crankcase 52. The cylinder head 56 is also formed with a plurality of insertion holes 78 along the axial direction of the cylinder chamber 74. The plurality of insertion holes 76 of the cylinder block 54 and the plurality of insertion holes 78 of the cylinder head 56 communicate with each other, and a fastening member 80 such as a stud bolt is inserted into each of the insertion holes 76 and 78.

In this case, each of the plurality of fastening members 80 through which the plurality of insertion holes 76 are inserted is screwed into a screw hole (not shown) formed in the crankcase 52 at one end and a nut at the other end on the cylinder head 56 side. Screw with 82. As a result, the cylinder block 54 and the cylinder head 56 are sequentially attached to the crankcase 52.

A plurality of cooling fins 84 are formed on the outer peripheral surface of the cylinder block 54 in a direction (intersection direction) substantially orthogonal to the axial direction of the cylinder chamber 74. Further, a frame plate-shaped stay member 86 is fixed to the upper portion (upper surface) of the cylinder block 54. An ignition coil 88 is attached to the upper surface of the stay member 86 in a state of being separated from the cylinder block 54.

The cylinder head 56 has a structure in which a valve operating mechanism 90 (valve valve structure) shown in FIGS. 5 and 6 and a main body portion accommodating an intake / exhaust system and a portion corresponding to a head cover are integrated. On the cylinder block 54 side of the outer peripheral surface of the cylinder head 56, a plurality of cooling fins 92 are formed in a direction (intersection direction) substantially orthogonal to the axial direction of the cylinder chamber 74.

A plug hole 94 is formed in the central portion on the right side surface of the cylinder head 56 on the cylinder block 54 side. A spark plug 96 is attached to the plug hole 94. The spark plug 96 and the ignition coil 88 are connected via a high-voltage wiring 98. The ignition coil 88 generates a high voltage required to ignite the spark plug 96, and supplies the generated high voltage to the spark plug 96 via the high voltage wiring 98.

An intake member 100 is connected to the upper part of the cylinder head 56. The intake member 100 includes a throttle body 100a that controls the intake amount of the internal combustion engine 10, and an intake pipe 100b that connects the throttle body 100a and the intake port 104 (see FIG. 6) that communicates with the combustion chamber 102 described later. An injector 106 that injects fuel into the combustion chamber 102 is attached to the intake pipe 100b. Therefore, the intake member 100 and the injector 106 are arranged in front of the ignition coil 88.

As described above, the internal combustion engine 10 has various configurations supported by the vehicle body frame 16 directly under the main frame 20 and connected to the internal combustion engine 10 in the dead space between the main frame 20 and the internal combustion engine 10. The elements are arranged. Therefore, as shown in the plan view of FIG. 4, various components are arranged above the internal combustion engine 10 so as to overlap the internal combustion engine 10 and the main frame 20.

That is, the ignition coil 88 is arranged above the cylinder block 54 so as to overlap the cylinder block 54 in the plan view of FIG. Further, in the side view of FIGS. 2 and 3, the ignition coil 88 is located behind the cylinder head 56 and the intake member 100 (throttle body 100a, intake pipe 100b), three coupling bosses 58a to 58c, and a rotation speed detection unit. It is arranged in front of the 70 and the electric motor 66. Further, the ignition coil 88 is arranged so as to overlap the intake member 100 and the electric motor 66 in a front view when viewed from the front with reference to FIG. Moreover, in the side view of FIGS. 2 and 3, when the virtual line 108 of the two-dot chain line connecting the top (upper end) of the cylinder head 56 and the top (coupling boss 58a on the upper side) of the crankcase 52 is set, At least a part of the ignition coil 88 or the stay member 86 is arranged above the cylinder head 56 so as to be located in the space below the virtual line 108 (the space between the virtual line 108 and the internal combustion engine 10). ing.

<2.2 Internal configuration of internal combustion engine 10>
Next, the internal configuration of the internal combustion engine 10 will be described with reference to FIGS. 5 to 14. The internal combustion engine 10 is an air-cooled single-cylinder engine in which the axial direction (axis line) of the crankshaft 68 is along the vehicle width direction. The main components of the internal combustion engine 10 are disclosed in, for example, Japanese Patent Application Laid-Open No. 2016-160812 and Japanese Patent No. 60022269. Therefore, in the description of the internal configuration of the internal combustion engine 10, the same components as those disclosed in these publications will be described schematically, and the description thereof will be simplified or omitted. ..

(2.2.1 Internal configuration on the crankcase 52 and cylinder block 54 side)
First, the internal configuration of the internal combustion engine 10 on the crankcase 52 side and the cylinder block 54 side will be described with reference to FIGS. 5 to 8.

The crankcase 52 is divided into a first case 112L on the left side and a second case 112R on the right side with a dividing surface (left and right center surfaces 110 shown in FIGS. 5, 7 and 8) substantially orthogonal to the vehicle width direction as a boundary. This is a possible case. A first case cover 114L (see FIGS. 1, 2, 4 and 5) is attached to the left side of the first case 112L. On the other hand, the second case cover 114R (see FIGS. 3 to 5) is attached to the right side of the second case 112R. Further, the crankcase 52 also serves as a transmission case for accommodating a transmission such as a manual transmission. Inside the internal combustion engine 10 including the crankcase 52, a lubricating liquid as engine oil is appropriately circulated and agitated.

The cylinder block 54 has a cylindrical cylinder sleeve 116. The cylinder sleeve 116 has an axis along the left and right central surfaces 110 and forms the cylinder chamber 74. A piston 72 is fitted in the cylinder chamber 74 so as to be reciprocating along the left and right center surfaces 110 (the axis of the cylinder chamber 74).

The piston 72 is connected to the crank pin 120 of the crankshaft 68 via a connecting rod 118. The crankshaft 68 has left and right crank webs 122L and 122R that support the crank pin 120, journal portions 124L and 124R that protrude left and right outward from the crank webs 122L and 122R, respectively, and further left and right outside from the journal portions 124L and 124R. It has extension shafts 126L and 126R extending to, respectively. Therefore, the power of the reciprocating motion of the piston 72 is converted into the power of the rotary motion by the crankshaft 68.

A cam drive sprocket 128 is provided on the base end side of the extension shaft 126L on the first case 112L side (left side). A power transmission mechanism accommodating chamber 130 along the axial direction of the cylinder chamber 74 is formed on the left side of the cylinder block 54. The power transmission mechanism accommodating chamber 130 accommodates a power transmission mechanism 132 as a chain type transmission mechanism including a cam drive sprocket 128. A camshaft 134 rotatably connected to the power transmission mechanism 132 is provided in the cylinder head 56. The power transmission mechanism 132 including the cam drive sprocket 128 transmits the power of the rotational movement of the crankshaft 68 to the cam shaft 134 to rotationally drive the cam shaft 134 in conjunction with the crankshaft 68.

Inside the crankcase 52, a plurality of rotation shafts extending in the vehicle width direction are arranged substantially parallel to each other. The plurality of rotating shafts are arranged behind the crank shaft 68, the first shift shaft 136 (first driven shaft) which is the main shaft arranged behind the crank shaft 68, and the first shift shaft 136. It is a second speed change shaft 138 (second driven shaft) which is a counter shaft.

The left side wall 140L of the first case 112L and the right side wall 140R of the second case 112R form a pair of side walls 140L and 140R facing each other. The pair of side walls 140L and 140R are formed with support holes 142L and 142R (see FIG. 8) that rotatably support both ends of the plurality of rotating shafts described above. Therefore, in the crankcase 52, the crankshaft 68, the first transmission shaft 136, and the second transmission shaft 138 are rotatably supported by the two support holes 142L and 142R formed in the pair of side walls 140L and 140R, respectively. And are arranged in the vehicle width direction.

In the crankcase 52, a first power transmission device 144 is provided between the crankshaft 68 and the first transmission shaft 136. Further, in the crankcase 52, a second power transmission device 146 is provided between the first shift shaft 136 and the second shift shaft 138. Further, in the crankcase 52, a kick spindle 148 is arranged behind the second transmission shaft 138.

The first power transmission device 144 is provided on the second case 112R side in the crankcase 52, and transmits the power of the rotational movement by the crankshaft 68 to the first transmission shaft 136. The second power transmission device 146 is provided in the crankcase 52 so as to straddle the left and right central surfaces 110, and transmits the power of the rotational movement by the first shift shaft 136 to the second shift shaft 138. The second transmission shaft 138 outputs the power transmitted from the second power transmission device 146 to the engine output unit 150 on the rear left side of the first case 112L, and the chain type transmission mechanism in the swing arm 34 from the engine output unit 150. It is transmitted to the rear wheel 36 (see FIG. 1) via 152.

The first power transmission device 144 includes a centrifugal clutch 154 connected to the right end portion (right extension shaft 126R) of the crankshaft 68 on the second case 112R side in the crankcase 52, and a second case 112R in the crankcase 52. It has a multi-plate clutch 156 connected to the right end of the first speed change shaft 136 on the side.

The centrifugal clutch 154 is coaxially supported by the extension shaft 126R on the right side, and has a clutch outer 154a, a clutch inner 154b, and a centrifugal weight 154c. The clutch outer 154a is a bottomed cylindrical member that opens to the right, and is supported by an extension shaft 126R on the right side so as to be relatively rotatable. The clutch inner 154b is rotatably supported by the extension shaft 126R on the right side on the inner peripheral side of the clutch outer 154a. The centrifugal weight 154c is supported by the clutch inner 154b on the inner peripheral side of the clutch outer 154a so as to be expandable. A centrifugal oil filter 158 is formed on the right side of the clutch inner 154b.

The centrifugal weight 154c is separated from the inner peripheral surface of the clutch outer 154a when the crankshaft 68 is stopped and when the crankshaft 68 is rotated at a low speed, so that the centrifugal clutch 154 is in a disengaged state in which power cannot be transmitted. Further, the centrifugal weight 154c expands and operates as the rotation speed of the crankshaft 68 increases, frictionally engages with the inner peripheral surface of the clutch outer 154a at a predetermined rotation speed or higher, and is in a connected state capable of transmitting power to the centrifugal clutch 154. And.

A one-way clutch 160 is fitted in the center of the clutch outer 154a. When the clutch inner 154b and the crankshaft 68 rotate in the normal direction prior to the clutch outer 154a, the one-way clutch 160 is in a free state and does not transmit torque. As a result, the clutch inner 154b and the crankshaft 68 idle with respect to the clutch outer 154a. The forward rotation of the crankshaft 68 corresponds to the rotation of the internal combustion engine 10 during operation.

Further, in the one-way clutch 160, when the clutch inner 154b and the crankshaft 68 rotate in the normal direction prior to the clutch inner 154b and the crankshaft 68, or when the clutch inner 154b and the crankshaft 68 reverse with respect to the clutch outer 154a, the clutch inner 154b If the rotation speed is less than the predetermined speed, the clutch is not transmitted while maintaining the free state. As a result, the clutch outer 154a idles with respect to the clutch inner 154b and the crankshaft 68.

On the other hand, the one-way clutch 160 goes into a one-way operating state when the rotation speed of the clutch inner 154b becomes equal to or higher than a predetermined speed. When the clutch outer 154a rotates in the normal direction prior to the clutch inner 154b and the crankshaft 68 in this state, torque transmission becomes possible, and the clutch outer 154a, the clutch inner 154b and the crankshaft 68 can rotate in the normal direction integrally.

A cylindrical transmission cylinder 154d extending to the left is provided on the left side of the central portion of the clutch outer 154a. A primary drive gear 162 is rotatably provided on the left end side of the transmission cylinder 154d. The primary drive gear 162 meshes with the primary driven gear 164 rotatably supported on the right side of the first transmission shaft 136. The primary drive gear 162 and the primary driven gear 164 form a primary reduction mechanism of the internal combustion engine 10.

The right end of the first transmission shaft 136 is terminated to the left of the right end of the centrifugal clutch 154, and the multi-plate clutch 156 is coaxially supported. The multi-plate clutch 156 is a shifting clutch, and has a clutch outer 156a, a clutch inner 156b, and a plurality of clutch plates 156c.

The clutch outer 156a is a bottomed cylindrical member that opens to the right, and is supported by a right end portion of the first transmission shaft 136 so as to be relatively rotatable. A primary driven gear 164 is integrally rotatably supported on the left side of the clutch outer 156a. The clutch inner 156b is arranged on the inner peripheral side of the clutch outer 156a and is integrally rotatably supported by the right end portion of the first transmission shaft 136. Each clutch plate 156c is laminated in the vehicle width direction between the clutch outer 156a and the clutch inner 156b.

The multi-plate clutch 156 press-contacts and frictionally engages the clutch plate 156c with the urging force of a diaphragm spring (not shown). The multi-plate clutch 156 temporarily releases the pressure welding of the clutch plate 156c in conjunction with the shift operation of the shift pedal (not shown), and smoothly shifts the shift in the second power transmission device 146, which is the transmission of the vehicle 12. To do.

The second power transmission device 146 is a transmission provided between the first transmission shaft 136 and the second transmission shaft 138, and includes a plurality of gear trains 166a to 166d that enable alternative establishment. The power generated by the rotational movement of the crankshaft 68 is transmitted from the first shift shaft 136 to the second shift shaft 138 via any gears constituting the gear trains 166a to 166d. The left end portion of the second transmission shaft 138 projects to the rear left side of the crankcase 52 and becomes the engine output portion 150.

The gear trains 166a to 166d are composed of gears corresponding to the number of gears supported by the first shift shaft 136 and the second shift shaft 138, respectively. The second power transmission device 146 is of a constant meshing type in which the corresponding gears of the gear trains 166a to 166d are always meshed between the first transmission shaft 136 and the second transmission shaft 138. Each gear has a free gear that can rotate relative to the transmission shaft that supports itself, a fixed gear that can rotate integrally with the transmission shaft that supports itself, and a slide that spline fits to the transmission shaft that supports itself. It is classified as a gear.

The second power transmission device 146 moves the slide gear by operating a change mechanism (not shown), and selects gear trains 166a to 166d according to the shift stage. In FIG. 5, from the left side to the right side, the fourth gear train 166d, the second gear train 166b, the third gear train 166c, and the first gear train 166a are arranged side by side.

An ACG (alternator) starter 168 is coaxially supported at the left end of the extension shaft 126L on the left side of the crankshaft 68. The ACG starter 168 is a three-phase AC type generator motor, and functions as a starter motor (starter motor) for starting the internal combustion engine 10 and also as an AC generator for generating power when the internal combustion engine 10 is operated.

The ACG starter 168 is an outer rotor type rotary electric machine, and has an outer rotor 168a and an inner stator 168b. The outer rotor 168a is a bottomed cylindrical member that opens to the left, and is integrally rotatably supported by the left end portion of the left extension shaft 126L. The inner stator 168b is arranged on the inner peripheral side of the outer rotor 168a and is fixedly supported by the first case cover 114L. A plurality of magnets 168c arranged in the circumferential direction are fixed to the inner peripheral side of the outer rotor 168a. A plurality of coils 168d arranged in the circumferential direction are formed on the outer peripheral side of the inner stator 168b.

A detection gear 170 containing a magnetic material is attached to a portion of the extension shaft 126L on the left side on the ACG starter 168 side. The rotation speed detection unit 70 is attached to the crankcase 52 so as to face the tooth surface of the detection gear 170 so as to face the axial center of the crankshaft 68. Therefore, when the detection gear 170 rotates with the rotation of the crankshaft 68, the rotation speed detection unit 70 detects the number of teeth of the detection gear 170, so that the crankshaft 68 corresponds to the detected number of teeth. Detect the number of revolutions.

The right end of the kick spindle 148 projects to the rear right of the second case 112R and is connected to a kick arm (not shown). A kick drive gear 172 is coaxially supported at the left end of the kick spindle 148. The kick drive gear 172 rotates integrally with the kick spindle 148 via a meshing mechanism (not shown) only when the kick spindle 148 rotates in one direction by stepping down on the kick arm.

The kick drive gear 172 meshes with the driven gear of the first gear train 166a. The rotational power of the kick drive gear 172 is input as forward rotation to the clutch outer 154a of the centrifugal clutch 154 via the first speed gear train 166a, the first transmission shaft 136, the multi-plate clutch 156, the primary driven gear 164 and the primary drive gear 162. Will be done. If the forward rotation torque is equal to or higher than a predetermined torque, the one-way clutch 160 is in the one-way operating state. When the one-way clutch 160 is locked by the further forward rotation, the forward rotation torque can be transmitted from the clutch outer 154a to the clutch inner 154b and the crankshaft 68. That is, the internal combustion engine 10 can be cranked by the kick starter.

Then, in the present embodiment, as shown in FIGS. 6 and 8, the crankcase 52 is provided with a lubricating liquid holding portion 174 for holding the lubricating liquid for lubricating the inside of the crankcase 52 below the inside of the crankcase 52. There is. Note that FIG. 6 schematically shows a portion of the internal combustion engine 10 with a crankcase 52.

As shown in FIGS. 6 to 8, a first wall portion 176 is provided above the lubricating liquid holding portion 174 in the crankcase 52 and below the first shift shaft 136 or the second shift shaft 138. There is. A second wall portion 178 is provided above the lubricating liquid holding portion 174 and below the crankshaft 68 in the crankcase 52.

In the crankcase 52, the crankshaft 68, the first shift shaft 136, and the second shift shaft 138 are arranged in this order from the front to the rear. Therefore, in the crankcase 52, a second wall portion 178 is provided forward between the crankshaft 68, the first shift shaft 136, the second shift shaft 138, and the lubricating liquid holding portion 174, and the first wall portion is provided. The 176 is provided rearward so as to be connected to the second wall portion 178.

In this case, at least a part of the first wall portion 176 is formed in a downwardly convex arc shape centered on the first shift shaft 136 or the second shift shaft 138. Further, at least a part of the second wall portion 178 is formed in a downwardly convex arc shape centered on the crankshaft 68. As shown in FIGS. 6 to 8, the first wall portion 176 is formed so that the arc of the first wall portion 176 deviates from the cylinder chamber 74. Further, the second wall portion 178 is formed in an arc shape so as to extend to the cylinder block 54.

As described above, the crankcase 52 can be divided into a first case 112L and a second case 112R. Therefore, the first wall portion 176 is in the vehicle width direction (crank shaft 68, first shift shaft 136) from the first shift shaft 136 and the second shift shaft 138 side of the side wall 140L of the first case 112L toward the left and right center surface 110. And the first wall portion 176L on the first case side as an arc-shaped rib extending in each axial direction of the second transmission shaft 138, and the first transmission shaft 136 and the second transmission shaft 138 side of the side wall 140R of the second case 112R. It is composed of a first wall portion 176R on the second case side as an arc-shaped rib extending from the left and right central surfaces 110 in the vehicle width direction.

A first gap 180 is formed between the first wall portion 176L on the first case side and the first wall portion 176R on the second case side. That is, the gap formed in the front-rear direction between the right end portion of the first wall portion 176L on the first case side and the left end portion of the first wall portion 176R on the second case side is the first gap 180. The first gap 180 is composed of a first narrow gap 180a that is narrow in the vehicle width direction and a first wide gap 180b that is wide in the vehicle width direction. Here, of the first narrow gap portion 180a and the first wide gap portion 180b, one gap portion is formed in the front and the other gap portion is formed in the rear. 7 and 8 show a case where the first wide gap portion 180b is formed in the front and the first narrow gap portion 180a is formed in the rear.

Similarly, the second wall portion 178 is a second wall portion 178L on the first case side as an arcuate rib extending in the vehicle width direction from the crankshaft 68 side of the side wall 140L of the first case 112L toward the left and right central surfaces 110. And the second wall portion 178R on the second case side as an arcuate rib extending in the vehicle width direction from the crankshaft 68 side of the side wall 140R of the second case 112R toward the left and right central surfaces 110.

A second gap 182 is formed between the second wall portion 178L on the first case side and the second wall portion 178R on the second case side. Also in this case, the gap formed in the front-rear direction between the right end portion of the second wall portion 178L on the first case side and the left end portion of the second wall portion 178R on the second case side is the second gap 182. The second gap 182 is composed of a second narrow gap portion 182a that is narrow in the vehicle width direction and a second wide gap portion 182b that is wide in the vehicle width direction. Of the second narrow gap portion 182a and the second wide gap portion 182b, one gap portion is formed in the front and the other gap portion is formed in the rear. 7 and 8 show a case where the second narrow gap portion 182a is formed in the front and the second wide gap portion 182b is formed in the rear.

Then, in the internal combustion engine 10, when the internal combustion engine 10 starts and the crankshaft 68 rotates, a pump (not shown) is driven. The pump pumps out the lubricating liquid held in the lubricating liquid holding portion 174. The pumped lubricating liquid passes through the supply passage 184 provided in the crankcase 52, and is injected into the cylinder chamber 74 from the injection hole 185 toward the bottom surface of the piston 72 (see FIG. 5). As a result, the cylinder chamber 74 and the piston 72 are lubricated.

Further, the crankcase 52 is formed with a branch passage 186 that branches from the supply passage 184 to the second case 112R side and reaches the extension shaft 126R on the right side of the crankshaft 68. A crankshaft passage 188 communicating with the branch passage 186 is formed in the vehicle width direction at the axial center portion of the extension shaft 126R on the right side. Further, in the extension shaft 126R on the right side, a plurality of communication holes 190 that open radially from the crankshaft passage 188 are formed. Therefore, the lubricating liquid supplied from the supply passage 184 to the crankshaft passage 188 via the branch passage 186 is in the crankcase 52 in the radial direction of the crankshaft 68 from the plurality of communication holes 190 as the crankshaft 68 rotates. Scatter to. Thereby, each part in the crankcase 52 can be lubricated.

Further, the crank pin 120 is formed with a crank pin passage 192 that communicates with the crank shaft passage 188. A part of the lubricating liquid supplied to the crankshaft passage 188 is also supplied to the crankpin passage 192. As a result, the crank pin 120 can be lubricated.

The lubricating liquid that lubricates the internal space above the first wall portion 176 and the second wall portion 178 in the crankcase 52 falls on the lower first wall portion 176 and the second wall portion 178. A first gap 180 is formed in the first wall portion 176, and a second gap 182 is formed in the second wall portion 178. Therefore, the lubricating liquid that has fallen on the first wall portion 176 falls on the lubricating liquid holding portion 174 through the first gap 180. Further, the lubricating liquid that has fallen on the second wall portion 178 falls on the lubricating liquid holding portion 174 through the second gap 182.

(2.2.2 Gasket 194 configuration)
Further, as shown in FIGS. 5, 6 and 9, a gasket 194 is inserted between the cylinder block 54 and the crankcase 52. Gasket 194 is a non-metal sealing member such as paper. The gasket 194 is formed in a substantially annular shape so as to surround the cylinder chamber 74 or the power transmission mechanism accommodating chamber 130 when viewed from the axial direction of the cylinder chamber 74. That is, as shown in FIG. 9, the gasket 194 has an annular portion 194a surrounding the cylinder chamber 74 and a recess 194b formed on the power transmission mechanism accommodating chamber 130 side from the annular portion 194a so as to be separated from the cylinder chamber 74. Have. That is, the annular portion 194a of the gasket 194 surrounds the cylinder chamber 74, and the recess 194b connected to the annular portion 194a encloses the power transmission mechanism accommodating chamber 130.

Further, in the cylinder block 54, a plurality of chambers including the cylinder chamber 74 and the power transmission mechanism accommodating chamber 130 are provided with the wall 196 interposed therebetween. In this case, the annular portion 194a and the recess 194b of the gasket 194 are formed as a communication portion 194c which is a gap portion for communicating at least two of the plurality of adjacent chambers in the cylinder block 54. FIG. 9 illustrates a case where the cylinder chamber 74 and the power transmission mechanism accommodating chamber 130 are communicated with each other by the communication portion 194c. Therefore, the recess 194b is formed by providing the communication portion 194c.

Further, the gasket 194 is formed with a plurality of insertion holes 198 for inserting the fastening member 80 (see FIGS. 2 and 3) screwed into the screw holes of the crankcase 52. That is, the gasket 194 is formed with a plurality of insertion holes 198 corresponding to the plurality of insertion holes 76 and 78 of the cylinder block 54 and the cylinder head 56 and the plurality of screw holes. The communication portion 194c is provided between the plurality of insertion holes 198 so as to avoid the plurality of insertion holes 198. The annular portion 194a and the concave portion 194b are connected by a curved connecting portion 200.

(2.2.3 Internal configuration on the cylinder head 56 side)
Next, the internal configuration of the internal combustion engine 10 on the cylinder head 56 side will be described with reference to FIGS. 10 to 14.

In the cylinder head 56, a power transmission mechanism accommodating chamber 202 communicating with the power transmission mechanism accommodating chamber 130 (see FIGS. 5 and 9) of the cylinder block 54 is formed on the left end side of the cylinder head 56. Further, in the cylinder head 56, a valve mechanism accommodating chamber 204 for accommodating the valve mechanism 90, which will be described later, is formed on the right end side of the cylinder head 56. The valve operating mechanism accommodating chamber 204 and the power transmission mechanism accommodating chamber 202 are separated by a wall 206.

The power transmission mechanism accommodating chamber 202 can be accessed from the outside by removing the cover member 208 on the left side of the cylinder head 56. Further, the valve operating mechanism accommodating chamber 204 can be accessed from the outside by removing the cover members 210 and 212 on the upper and lower sides of the cylinder head 56. In this case, the valve mechanism accommodating chamber 204 has one adjusting hole 214 that opens upward and the other adjusting hole 216 that opens downward. One of the adjusting holes 214 is closed by the upper cover member 210. Further, the other adjusting hole 216 is closed by the lower cover member 212. Therefore, with the cover members 210 and 212 removed from the cylinder head 56, the valve operating mechanism 90 is accessed through the adjusting holes 214 and 216.

The valve operating mechanism accommodating chamber 204 holds a valve operating mechanism 90 for controlling the inflow and outflow of air to and from the cylinder chamber 74 (combustion chamber 102). The valve operating mechanism 90 includes the above-mentioned camshaft 134, two rocker arm shafts 218 and 220, two rocker arms 222 and 224, an intake valve 226 (valve, valve) and an exhaust valve 228 (valve, valve).

The cam shaft 134 extends in the vehicle width direction in the valve operating mechanism accommodating chamber 204. The left end of the camshaft 134 penetrates the wall 206, is inserted into the power transmission mechanism accommodating chamber 202 , and is connected to the power transmission mechanism 132. The right end of the cam shaft 134 is rotatably supported by the inner wall 230 on the right side of the cylinder head 56. Therefore, the cam shaft 134 can rotate by receiving a driving force (power of rotational movement) from the crank shaft 68 via the power transmission mechanism 132.

The two rocker arm shafts 218 and 220 are arranged above and below the cam shaft 134 in the valve drive mechanism accommodating chamber 204, and extend in the vehicle width direction.

In this case, the inner wall 230 on the right side of the cylinder head 56 is formed with a head boss 232 protruding to the left side corresponding to the rocker arm shaft 218 on the upper side. One end (right end) of the rocker arm shaft 218 is fitted into a hole 234 formed in the head boss 232. The other end of the Lock car arm shaft 218 (left end) is fitted in a hole formed in the wall 206. As a result, the rocker arm shaft 218 is supported in the vehicle width direction in the valve operating mechanism accommodating chamber 204.

On the other hand, one end (right end) of the lower rocker arm shaft 220 is fitted into a hole formed in the inner wall 230. A head boss 236 projecting to the right is formed on the wall 206 corresponding to the lower rocker arm shaft 220. The other end (left end) of the rocker arm shaft 220 is fitted into a hole 238 formed in the head boss 236. As a result, the rocker arm shaft 220 is supported in the vehicle width direction in the valve operating mechanism accommodating chamber 204.

The two head bosses 232 and 236 are formed with two holes 234 and 238, that is, insertion holes 240 and 242 directed to the central axes (axis centers) of the two rocker arm shafts 218 and 220, respectively. Each insertion hole 240, 242 is a substantially cylindrical through hole having a central axis. In this case, in the valve operating mechanism accommodating chamber 204, the insertion hole 240 provided in the upper head boss 232 (the insertion hole 240 on the intake valve 226 side) is formed so as to face the upper adjustment hole 214. Further, the insertion hole 242 (the insertion hole 242 on the exhaust valve 228 side) provided in the lower head boss 236 is formed so as to be directed to the lower adjustment hole 216. Further, the central axes of the insertion holes 240 and 242 provided in the head bosses 232 and 236 are substantially orthogonal to the adjustment holes 214 and 216 facing the insertion holes 240 and 242, respectively.

On the other hand, insertion holes 244 and 246 penetrating in the radial direction of the rocker arm shafts 218 and 220 are also formed at one end of the rocker arm shaft 218 and the other end of the rocker arm shaft 220. In the present embodiment, the insertion holes 240 and 242 of the head bosses 232 and 236 and the insertion holes 244 and 246 of the rocker arm shafts 218 and 220 fitted into the holes 234 and 238 of the head bosses 232 and 236 are the rocker arm shaft 218. By rotating 220 in an arbitrary phase around the axis, a pair of insertion holes 240 to 246 that communicate with each other are formed.

Then, a rod-shaped member 248 for restricting the relative rotation of the rocker arm shaft 218 is inserted into the pair of insertion holes 240 and 244. Further, a rod-shaped member 250 for restricting the relative rotation of the rocker arm shaft 220 is inserted into the pair of insertion holes 242 and 246.

The two rod-shaped members 248 and 250 have rod-shaped insertion portions 248a and 250a that are inserted into the pair of insertion holes 240 to 246, and head bosses 232 and 236 sides (adjustment holes 214 and 216 sides) of the insertion portions 248a and 250a, respectively. It has heads 248b and 250b having a diameter larger than that of the insertion portions 248a and 250a.

The insertion portions 248a and 250a sides of the heads 248b and 250b are formed in a flat shape. Further, on the adjustment holes 214 and 216 sides of the head bosses 232 and 236, when the insertion portions 248a and 250a are inserted into the pair of insertion holes 240 to 246, the flat surface portions 252 that come into surface contact with the flat surface portions of the head 248b and 250b. It is formed as 254. In this case, it is desirable that the flat surface portions 252 and 254 are flat surfaces substantially parallel to the adjusting holes 214 and 216.

Specifically, the rod-shaped members 248 and 250 are screw members on which a spiral male screw portion is formed. Further, a spiral female screw portion is formed on the inner peripheral surface of the pair of insertion holes 240 to 246 corresponding to the rod-shaped members 248 and 250. In this case, by substantially matching the shapes of the male screw portion and the female screw portion, the rod-shaped members 248 and 250 as the screw members can be screwed into the female screw portions of the pair of insertion holes 240 to 246. Thereby, the rotation of the rocker arm shafts 218 and 220 can be easily regulated.

The rod-shaped members 248 and 250 are not limited to the screw members, and any member can be used as long as the rotation of the rocker arm shafts 218 and 220 can be regulated. For example, if at least one end (right end) of the rocker arm shafts 218 and 220 is made of a magnetic material and the rod-shaped members 248 and 250 are made of permanent magnets, the insertion portions 248a and 250a of the rod-shaped members 248 and 250 are made into a pair of insertion holes 240. The rotation of the rocker arm shafts 218 and 220 can be easily regulated by inserting the rocker arm shafts 218 and 220.

The two rocker arms 222 and 224 are rotatably supported by the rocker arm shafts 218 and 220, respectively. One end of each rocker arm 222, 224 is connected to the cam shaft 134 via rollers 256, 258. The rocker arms 222 and 224 swing around the rocker arm shafts 218 and 220 by the driving force transmitted from the cam shaft 134 via the rollers 256 and 258.

Further, in the internal combustion engine 10, the combustion chamber 102 is formed by the cylinder head 56 and the piston 72 of the cylinder chamber 74. On the cylinder block 54 side of the cylinder head 56, an intake port 104 having one end communicating with the intake pipe 100b and the other end communicating with the combustion chamber 102 is formed in the upper portion. Further, on the cylinder block 54 side in the cylinder head 56, an exhaust port 260 is formed in a lower portion in which one end communicates with the combustion chamber 102 and the other end communicates with an exhaust device (not shown). ..

Further, in the cylinder head 56, the intake valve 226 opens and closes the combustion chamber 102 by the driving force transmitted from the other end of the rocker arm 222 on the intake port 104 side (upper side), thereby opening and closing the combustion chamber 102 from the intake port 104 to the combustion chamber 102. Supply air to. Further, the exhaust valve 228 opens and closes the combustion chamber 102 with a driving force transmitted from the other end of the rocker arm 224 on the exhaust port 260 side (lower side), so that the exhaust valve 228 is exhausted from the combustion chamber 102 via the exhaust port 260. To do. Further, a spark plug 96 is attached to the plug hole 94 of the cylinder head 56 so that the tip portion faces the combustion chamber 102.

Further, in the valve operating mechanism accommodating chamber 204, an intake side adjusting mechanism 262 for adjusting the tappet clearance is provided between the intake valve 226 and the other end of the upper rocker arm 222. Therefore, the upper adjusting hole 214 also serves as an adjusting hole for accessing the intake side adjusting mechanism 262. Similarly, in the valve operating mechanism accommodating chamber 204, an exhaust side adjusting mechanism 264 for adjusting the tappet clearance is provided between the exhaust valve 228 and the other end of the lower rocker arm 224. Therefore, the lower adjustment hole 216 is an adjustment hole for accessing the exhaust side adjustment mechanism 264.

Further, as shown in FIGS. 12 to 14, the cylinder head 56 is opened on the cylinder block 54 side (bottom side of the cylinder head 56) from the outer peripheral surface of the cylinder head 56 toward the cooling fin 84 of the cylinder block 54. An opening 266 is formed.

Specifically, inside the cylinder head 56, an air jacket 268 that communicates the side portion of the spark plug 96 (plug hole 94), the side portion of the intake port 104, and the side portion of the exhaust port 260 with the outside is provided. There is. The opening 266 opens from the air jacket 268 toward the cooling fins 84. In this case, the opening 266 is formed so as to be located on the lower side of the cylinder block 54 in the cylinder head 56. The air jacket 268 and the intake port 104 and the exhaust port 260 are separated by a wall 270.

As a result, as shown by the arrows in FIGS. 13 and 14, when the vehicle 12 is traveling, the traveling wind is introduced into the air jacket 268 from the side portion (plug hole 94) of the spark plug 96. The introduced running wind passes through the side portion of the intake port 104 and the side portion of the exhaust port 260, and exits (guides) rearward through the opening 266. Since there is a cooling fin 84 on the cylinder head 56 side of the cylinder block 54 behind the opening 266, the running wind that has passed backward from the opening 266 can suitably cool the cooling fin 84. A part of the running wind passing through the air jacket 268 also escapes downward.

[3. Modification example]
In the above description, the case where the internal combustion engine 10 is a single cylinder has been described. The present embodiment is not limited to a single-cylinder internal combustion engine, and can be applied to a multi-cylinder internal combustion engine. Therefore, in the present embodiment, an internal combustion engine in which one piston 72 is provided in each of the plurality of cylinder chambers 74, an internal combustion engine in which a plurality of pistons 72 are provided in one cylinder chamber 74, and a plurality of cylinder chambers 74. It is also applicable to an internal combustion engine provided with a piston 72 of the above.

Further, in the above description, a case where a plurality of rotating shafts (crankshaft 68, first shifting shaft 136, second shifting shaft 138) are arranged in the vehicle width direction has been described. In the present embodiment, it is also applicable to the internal combustion engine 10 in which a plurality of rotation axes are arranged in a direction different from the vehicle width direction (for example, a front-rear direction and a vertical direction). In this case, in the crankcase 52, support holes 142L and 142R for axially supporting both ends of the plurality of rotation shafts are formed on the two side walls 140L and 140R orthogonal to each other in the different directions and facing each other.

Further, in the above description, the rod-shaped members 248 and 250 described above may be used as screw members, and may also serve as screw members for fixing the cover members 210 and 212 that close the adjusting holes 214 and 216. As a result, the insertion portions 248a and 250a of the rod-shaped members 248 and 250 are screwed into the pair of insertion holes 240 to 246 to prevent the rocker arm shafts 218 and 220 from rotating and to close the adjustment holes 214 and 216. be able to.

Furthermore, in the above description, the case where the insides of the crankcase 52 and the cylinder chamber 74 are lubricated with a lubricating liquid has been described. In the present embodiment, the lubricating liquid may be supplied into the cylinder head 56, and the valve operating mechanism 90 may be lubricated with the supplied lubricating liquid. In this case, the insertion holes 76 and 78 may be used as a lubricating liquid supply passage, or a lubricating liquid supply passage from the crankcase 52 to the cylinder head 56 via the cylinder block 54 may be separately provided. .. As a result, in the cylinder head 56, each part in the cylinder head 56 can be suitably lubricated by scattering the lubricating liquid in the radial direction of the cam shaft 134 as the cam shaft 134 rotates.

[4. Effect of this embodiment]
The effects of the configuration of the present embodiment described above will be described below.

<4.1 Effect of the first configuration>
The first embodiment is an internal combustion engine 10 (power unit) including a crankshaft 68 (power generation unit) that generates power by rotational movement, and performs rotational movement on the rear wheels 36 (rotated movement unit). (Crankshaft 68, 1st speed change shaft 136, 2nd speed change shaft 138), 1st power transmission device 144 and 2nd power transmission device 146, and a plurality of rotation shafts. A crank case 52 (power unit case) for holding the first power transmission device 144 and the second power transmission device 146 inside is further provided.

The plurality of rotating shafts include a crank shaft 68 (drive shaft) as a power generating unit and a first speed change shaft 136 (first driven shaft) in which power is transmitted from the crank shaft 68 via the first power transmission device 144. , The second shift shaft 138 (second driven shaft), in which power is transmitted from the first shift shaft 136 via the second power transmission device 146 and the transmitted power is transmitted to the rear wheels 36.

The crankcase 52 includes a cylinder block 54 and a lubricating liquid holding portion 174 that holds the lubricating liquid that lubricates the inside of the crankcase 52 below the inside of the crankcase 52. A first wall portion 176 is provided above the lubricating liquid holding portion 174 and below the first shift shaft 136 or the second shift shaft 138 in the crankcase 52.

According to this configuration, the first wall portion 176 is provided between the lubricating liquid holding portion 174 and the first shift shaft 136 or the second shift shaft 138. As a result, even if the lubricating liquid held in the lubricating liquid holding portion 174 flutters during sudden acceleration of the vehicle 12 or wheelie traveling, the lubricating liquid is applied to the first shift shaft 136 or the second shift shaft 138. Can be avoided. As a result, it is possible to prevent unnecessary application of lubricating liquid and prevent friction and false positives from occurring.

In this case, if at least a part of the first wall portion 176 is formed in an arc shape centered on the first transmission shaft 136 or the second transmission shaft 138, a large acceleration is generated in the vehicle 12 including the crankcase 52. Even so, it is possible to effectively prevent the lubricating liquid from fluttering greatly and unnecessarily applying the lubricating liquid to the first transmission shaft 136, the second transmission shaft 138, and the like.

The internal combustion engine 10 is mounted on the vehicle 12. The crankcase 52 is a case that can be divided into a first case 112L and a second case 112R along the vehicle width direction (axial direction of the crankshaft 68). The first wall portion 176 is composed of a first case-side first wall portion 176L extending in the vehicle width direction from the first case 112L and a second case-side first wall portion 176R extending in the vehicle width direction from the second case 112R. Will be done. By extending the wall portion from both cases in this way, the assembling property of the crankcase 52 can be improved.

Further, a first gap 180 is formed between the first wall portion 176L on the first case side and the first wall portion 176R on the second case side. By allowing a small amount of lubricating liquid to flow in and out in this way, the lubricating oil applied to the first speed change shaft 136 and the second speed change shaft 138 can be efficiently discharged to the lubricating liquid holding portion 174.

Further, a second wall portion 178 is provided above the lubricating liquid holding portion 174 and below the crankshaft 68 in the crankcase 52. As a result, even if a large acceleration is generated in the vehicle 12 including the internal combustion engine 10, it is possible to prevent the lubricating liquid from fluttering greatly and unnecessarily applying the lubricating liquid to the crankshaft 68 and the like.

In this case, if at least a part of the second wall portion 178 is formed in an arc shape centered on the crankshaft 68, it is possible to effectively suppress the unnecessary application of lubricating liquid to the crankshaft 68 and the like. it can.

The crankcase 52 has a pair of side walls 140L and 140R facing each other along at least the vehicle width direction of the vehicle 12. The first wall portion 176 and the second wall portion 178 extend from the pair of side walls 140L and 140R in the vehicle width direction, and the crankshaft 68, the first transmission shaft 136 and the second transmission shaft 138 have the pair of side walls 140L and 140L, respectively. It is rotatably supported by the support holes 142L and 142R provided in 140R. As described above, since the first wall portion 176 or the second wall portion 178 and the support holes 142L and 142R are formed in the same direction on the same side wall 140L and 140R, the crankcase 52 can be easily processed.

The second wall portion 178 is composed of a second wall portion 178L on the first case side extending in the vehicle width direction from the first case 112L and a second wall portion 178R on the second case side extending in the vehicle width direction from the second case 112R. Will be done. Thereby, the assembling property of the crankcase 52 can be further improved.

In this case, a second gap 182 is formed between the second wall portion 178L on the first case side and the second wall portion 178R on the second case side. By allowing a small amount of lubricating liquid to flow in and out in this way, the lubricating oil applied to the crankshaft 68 can be efficiently discharged to the lubricating liquid holding portion 174.

The first gap 180 and the second gap 182 are a narrow gap portion (first narrow gap portion 180a, second narrow gap portion 182a) and a wide wide gap portion (first gap portion 182a) along the front-rear direction of the vehicle 12, respectively. It is composed of one wide gap portion 180b and a second wide gap portion 182b). As a result, the efficiency of discharging the lubricating liquid from the crankshaft 68, the first speed change shaft 136, and the second speed change shaft 138 side to the lubricating liquid holding portion 174 side can be improved.

In this case, of the narrow gap and the wide gap, one of the gaps is formed in the front and the other gap is formed in the rear. As a result, the efficiency of discharging the lubricating liquid can be further improved by providing the wide gap portion in the direction in which the acceleration of the vehicle 12 is likely to be applied. For example, when the vehicle 12 accelerates or brakes, the lubricating fluid moves forward. Therefore, if the wide gap portion is provided in the front, the lubricating liquid can be efficiently discharged to the lubricating liquid holding portion 174.

The internal combustion engine 10 generates a rotary motion by a piston 72 that reciprocates in the cylinder chamber 74 (cylinder), and the first shift shaft 136 and the second shift shaft 138 are a plurality of gears capable of selectively transmitting power. Power is transmitted by rows 166a-166d. As a result, the internal combustion engine 10 can be suitably mounted on the vehicle 12.

<4.2 Effect of the second configuration>
Further, in the second embodiment, as a second configuration, the cam shaft 134 that receives the driving force from the crank shaft 68 (crankshaft), the rocker arm shafts 218 and 220, and the rocker arm shafts 218 and 220 are supported so as to be relatively rotatable. At least, the rocker arms 222 and 224 swinging around the rocker arm shafts 218 and 220 by the driving force transmitted from the cam shaft 134 and the combustion chamber 102 by the driving force transmitted from the rocker arms 222 and 224 are opened and closed. The present invention relates to a valve operating mechanism 90 (valve valve structure) of an internal combustion engine 10 including one valve (intake valve 226, exhaust valve 228).

The valve operating mechanism 90 further includes head bosses 232 and 236 that support the rocker arm shafts 218 and 220 on the cylinder head 56 of the internal combustion engine 10, and rod-shaped members 248 and 250. The head bosses 232 and 236 and the rocker arm shafts 218 and 220 are formed with a pair of insertion holes 240 to 246 that communicate with each other by rotating the rocker arm shafts 218 and 220 in an arbitrary phase around the axis. The rod-shaped members 248 and 250 are inserted into the pair of insertion holes 240 to 246 to regulate the relative rotation of the rocker arm shafts 218 and 220.

According to this configuration, the rocker arm shafts 218 and 220 are relatively rotated by inserting the rod-shaped members 248 and 250 into the pair of insertion holes 240 to 246 formed in the rocker arm shafts 218 and 220 and the head bosses 232 and 236. regulate. As a result, the relative rotation of the rocker arm shafts 218 and 220 is regulated by a simple configuration, so that the component cost and the manufacturing cost can be reduced.

In this case, the cam shaft 134, the rocker arm shafts 218 and 220, the rocker arms 222 and 224, the intake valve 226 and the exhaust valve 228 have an integral structure housed in the cylinder head 56. An adjustment mechanism (intake side adjustment mechanism 262, exhaust side adjustment mechanism 264) for adjusting the tappet clearance is provided between the intake valve 226 and the exhaust valve 228 and the rocker arm 222 and 224 in the cylinder head 56. There is. Further, the cylinder head 56 is formed with adjustment holes 214 and 216 for accessing the intake side adjustment mechanism 262 and the exhaust side adjustment mechanism 264 from the outside. The pair of insertion holes 240 to 246 have a substantially cylindrical shape having a central axis, and the central axes of the insertion holes 240 and 242 on the head boss 232 and 236 sides are directed to the adjustment holes 214 and 216.

This makes it possible to easily access the rod-shaped members 248 and 250 via the adjusting holes 214 and 216. As a result, the maintainability and assembling property of the valve operating mechanism 90 including the detents of the rocker arm shafts 218 and 220 can be improved.

Further, the central axes of the pair of insertion holes 240 to 246 are oriented substantially at the centers of the rocker arm shafts 218 and 220. That is, insertion holes 240 to 246 are formed in the radial direction of the rocker arm shafts 218 and 220. As a result, the total length of the insertion holes 240 to 246 can be secured to the maximum. As a result, the effect of detenting the rocker arm shafts 218 and 220 by the rod-shaped members 248 and 250 can be further improved.

Further, the rod-shaped members 248 and 250 are provided on the head bosses 232 and 236 of the insertion portions 248a and 250a and the rod-shaped insertion portions 248a and 250a that are inserted into the pair of insertion holes 240 to 246, and are more than the insertion portions 248a and 250a. It has large diameter heads 248b and 250b. The head bosses 232 and 236 have flat surfaces 252 and 254 that come into surface contact with the heads 248b and 250b when the insertion portions 248a and 250a are inserted into the pair of insertion holes 240 to 246. The flat surface portions 252 and 254 are flat surfaces substantially parallel to the adjusting holes 214 and 216. This makes it possible to easily form the flat surface portions 252 and 254 by machining from a single direction (for example, the directions of the adjusting holes 214 and 216). As a result, the processing cost and processing man-hours of the cylinder head 56 can be reduced.

Furthermore, the central axis of the insertion holes 240 and 242 on the head boss 232 and 236 sides and the adjustment holes 214 and 216 are substantially orthogonal to each other. This makes it easier to access the rod-shaped members 248 and 250 via the adjusting holes 214 and 216.

Further, a spiral female screw portion is formed on the inner peripheral surface of the pair of insertion holes 240 to 246, and a spiral male screw portion is formed on the outer peripheral surfaces of the rod-shaped members 248 and 250. In this case, the female screw portion and the male screw portion have substantially the same shape. As a result, the valve operating mechanism 90 including the rod-shaped members 248 and 250 can be easily assembled and disassembled.

<4.3 Effect of the third configuration>
Further, as a third configuration, the present embodiment is attached to at least one cylinder chamber 74 (cylinder) accommodating at least one piston 72 that performs reciprocating motion and a cylinder block 54 having the cylinder chamber 74, and the cylinder. The present invention relates to an internal combustion engine 10 having a cylinder head 56 forming a combustion chamber 102 together with a chamber 74, and an ignition plug 96 attached to the cylinder head 56 so as to face the combustion chamber 102.

In this case, the internal combustion engine 10 further has an ignition coil 88 that generates a voltage required to ignite the spark plug 96, and is mounted on the vehicle 12 in a state of being supported by the vehicle body frame 16 of the vehicle 12. .. The ignition coil 88 is arranged on the upper portion (upper surface) of the cylinder block 54 so as to overlap the cylinder block 54 including the cylinder chamber 74 in a plan view.

According to this configuration, since the ignition coil 88 is arranged on the upper part of the cylinder block 54, the ignition coil 88 can be arranged close to the spark plug 96. As a result, the expensive high-voltage wiring 98 can be made as short as possible. Further, it is possible to prevent the ignition coil 88 and the high-voltage wiring 98 from protruding from the internal combustion engine 10 in the vehicle width direction of the vehicle 12. As a result, the appearance of the vehicle 12 on which the internal combustion engine 10 is mounted is improved. Further, it is possible to suppress the failure of the ignition coil 88 and the disconnection of the high-voltage wiring 98 due to a side collision or a stepping stone during traveling of the vehicle 12.

Further, the internal combustion engine 10 further includes an intake member 100 connected to the cylinder head 56. The ignition coil 88 is arranged behind the cylinder head 56 or the intake member 100 in a side view. By arranging the ignition coil 88 near the intake member 100 that easily protrudes in the vertical direction in this way, the dead space between the vehicle body frame 16 and the internal combustion engine 10 can be effectively utilized.

The intake member 100 includes a throttle body 100a that controls the intake amount of the internal combustion engine 10, and an intake pipe 100b that connects the throttle body 100a and the intake port 104 that communicates with the combustion chamber 102. The ignition coil 88 is arranged behind the throttle body 100a in a side view. Among the members of the intake system, the throttle body 100a takes up a lot of space, so that a dead space is likely to occur. Therefore, by arranging the ignition coil 88 behind the throttle body 100a, the dead space can be effectively utilized. Further, the wirings connected to the throttle body 100a and the wirings connected to the ignition coil 88 can be efficiently combined.

The internal combustion engine 10 further includes an electric motor 66 for starting. The ignition coil 88 is arranged in front of the motor 66 in a side view. In the internal combustion engine 10, the most protruding component on the crankcase 52 side is often the starter motor. In particular, in the vehicle 12, the front portion where the distance between the vehicle body frame 16 and the internal combustion engine 10 is wide is likely to be a dead space. Therefore, by arranging the ignition coil 88 in front of the electric motor 66, the dead space can be utilized more effectively. Further, the wiring of the electric motor 66 and the wiring of the ignition coil 88 can be efficiently combined.

Further, the internal combustion engine 10 further includes a crankshaft 68 (rotational shaft) that rotates due to the reciprocating motion of the piston 72, and a rotation speed detection unit 70 that detects the rotation speed of the crankshaft 68. The ignition coil 88 is arranged in front of the rotation speed detection unit 70 in a side view.

In the internal combustion engine 10, a pickup sensor such as the rotation speed detection unit 70 is often provided in the front portion of the upper surface of the crankcase 52. As a result, the circumference of the rotation speed detection unit 70 tends to become a dead space. Therefore, by arranging the ignition coil 88 in front of the rotation speed detection unit 70, the dead space can be effectively utilized. Further, the wiring of the rotation speed detection unit 70 and the wiring of the ignition coil 88 can be efficiently combined.

The internal combustion engine 10 further includes a crankcase 52 that accommodates a plurality of shaft members (crankshaft 68, first shift shaft 136, second shift shaft 138). A coupling boss 58a for coupling to the vehicle body frame 16 is provided on the upper portion of the crankcase 52. The ignition coil 88 is arranged in front of the coupling boss 58a in a side view. In the vehicle 12 of a Cub-type motorcycle, it is often coupled to the vehicle body frame 16 on the upper surface of the crankcase 52. As a result, the circumference of the coupling boss 58a tends to become a dead space. Therefore, by arranging the ignition coil 88 in front of the coupling boss 58a, the dead space can be effectively utilized.

In this case, it is desirable that the ignition coil 88 is arranged so as to overlap the vehicle body frame 16 in a plan view. The ignition coil 88, like the cylinder block 54, tends to have a high temperature. Therefore, with the above configuration, it is possible to prevent the member having a high temperature from protruding in the vehicle width direction and to make the arrangement difficult to touch.

The internal combustion engine 10 further includes an intake member 100 connected to the combustion chamber 102 and an electric motor 66 for starting. The ignition coil 88 is arranged so as to overlap the intake member 100 and the electric motor 66 when viewed from the front. As a result, it is possible to save space in the internal combustion engine 10 while preventing the ignition coil 88 from protruding in the vertical direction.

In this case, the ignition coil 88 is attached to the cylinder block 54 via the stay member 86. As a result, it is possible to prevent the ignition coil 88 from becoming hot due to the heat from the cylinder block 54.

The internal combustion engine 10 further includes a crankcase 52 that is connected to the cylinder head 56 via a cylinder block 54. In this case, at least a part of the ignition coil 88 or the stay member 86 is located below the virtual line 108 connecting the top of the cylinder head 56 and the top of the crankcase 52 in a side view. The area formed by connecting the virtual line 108 with the upper portions of the crankcase 52, the cylinder block 54, and the cylinder head 56 tends to be a dead space. Therefore, by arranging the ignition coil 88 or the stay member 86 in such a region, the dead space can be effectively utilized.

If the vehicle 12 is a saddle-mounted vehicle, the above-mentioned effects can be easily achieved.

<4.4 Effect of the fourth configuration>
Furthermore, in the fourth embodiment, as a fourth configuration, at least one cylinder chamber 74 (cylinder) accommodating at least one piston 72 that performs reciprocating motion, and a valve operating mechanism that controls the inflow and outflow of air into and out of the cylinder chamber 74. The present invention relates to an internal combustion engine 10 having a 90, a cylinder block 54 for holding a cylinder chamber 74, and a cylinder head 56 which is attached adjacent to the cylinder block 54 and holds a valve operating mechanism 90.

A plurality of cooling fins 84 that intersect in the axial direction of the cylinder chamber 74 are provided on the outer peripheral surface of the cylinder block 54. Further, on the cylinder block 54 side of the cylinder head 56, an opening 266 that opens from the outer peripheral surface of the cylinder head 56 toward the cooling fins 84 is formed.

According to this configuration, when the vehicle 12 is traveling, the traveling wind from the front flows to the cylinder block 54 through the opening 266. As a result, when the cylinder head 56 is attached adjacent to the cylinder block 54, running air (cooling air) can be applied to the cooling fins 84 on the cylinder head 56 side, which are hidden by the cylinder head 56. As a result, the cooling effect of the cylinder chamber 74 (cylinder head 56) by the cooling fins 84 can be improved with a simple configuration.

The internal combustion engine 10 further includes a spark plug 96 attached to the cylinder head 56 so as to face the combustion chamber 102 formed by the cylinder chamber 74 and the cylinder head 56. The cylinder head 56 has an intake port 104 for supplying air to the combustion chamber 102 from the outside, an exhaust port 260 for exhausting air from the combustion chamber 102 to the outside, a side portion of the spark plug 96, and a side of the intake port 104. An air jacket 268 that communicates the side portion of the portion and the exhaust port 260 with the outside is provided. The opening 266 opens from the air jacket 268 toward the cooling fins 84. In this way, since the opening 266 is provided at the position where the traveling wind flows, the efficiency of guiding the air from the cylinder head 56 side to the cooling fin 84 of the cylinder block 54 is improved.

The internal combustion engine 10 further includes a crankshaft 68 that converts the reciprocating motion of the piston 72 into a rotary motion, and a crankcase 52 that houses the crankshaft 68. The internal combustion engine 10 is mounted on the vehicle 12, and the cylinder block 54 projects upward or forward from the front portion of the crankcase 52. The axis of the cylinder chamber 74 (cylinder block 54) is inclined upward from the horizontal toward the front. As a result, the running wind hits the outer peripheral surface of the cylinder head 56 and is guided to the cooling fins 84 of the cylinder block 54 through the opening 266. As a result, the air conduction efficiency can be further improved.

Further, the opening 266 is formed in the cylinder head 56 in the front-rear direction. By providing the opening 266 in the same direction as the flow of the running wind, the amount of air guided to the opening 266 can be improved. As a result, the running wind can be easily applied to the cooling fins 84 on the cylinder head 56 side of the cylinder block 54, which is arranged behind the cylinder head 56 so that the running wind is less likely to hit.

Further, the opening 266 is formed in the cylinder head 56 so as to be located on the lower side of the cylinder block 54. As a result, a negative pressure is generated between the lower surface side of the cylinder block 54 facing the opening 266 and the ground, and more running wind from the front can be taken into the opening 266.

<4.5 Effect of 5th configuration>
Further, in the fifth embodiment, as a fifth configuration, an internal combustion engine 10 having at least one cylinder chamber 74 accommodating at least one piston 72 that performs reciprocating motion and a crankshaft 68 that converts reciprocating motion into rotary motion. Regarding.

The internal combustion engine 10 includes a crankcase 52 that houses a crankshaft 68, a cylinder sleeve 116 that forms a cylinder chamber 74, a cylinder block 54 that covers the cylinder sleeve 116, and an intake valve 226 and an exhaust valve 228 (in response to rotational movement). The valve mechanism 90 that controls the inflow and outflow of air to and from the cylinder chamber 74 by operating the valve), the power transmission mechanism 132 that transmits the power of rotational movement from the crankshaft 68 to the valve mechanism 90, and the inside of the cylinder block 54. It further has a power transmission mechanism accommodating chamber 130 formed in the cylinder block 54 and accommodating the power transmission mechanism 132, and a gasket 194 interposed between the cylinder block 54 and the crankcase 52.

In this case, the gasket 194 is formed in a substantially annular shape so as to surround the cylinder chamber 74 or the power transmission mechanism accommodating chamber 130 when viewed from the axial direction of the cylinder chamber 74. At least a part of the annular portion 194a surrounding the cylinder chamber 74 in the gasket 194 forms a recess 194b away from the cylinder chamber 74 with respect to the other portion of the annular portion 194a. The recess 194b is provided on the side of the power transmission mechanism accommodating chamber 130.

According to this configuration, the recess 194b of the gasket 194 is provided from the cylinder chamber 74 toward the power transmission mechanism accommodating chamber 130. As a result, the cylinder chamber 74 and the power transmission mechanism accommodating chamber 130 communicate with each other between the cylinder block 54 and the crankcase 52 via a gap portion formed by the recess 194b. As a result, even if thermal expansion of the cylinder sleeve 116 occurs, the stress (strain) of the gasket 194 is suppressed, and the strain of the cylinder chamber 74 is reduced. Further, by providing the recess 194b of the gasket 194 on the power transmission mechanism accommodating chamber 130 side, the rigidity of the gasket 194 is lowered, and the effect of suppressing distortion of the cylinder chamber 74 is further improved.

Here, in the cylinder block 54, a plurality of chambers including at least one cylinder chamber 74 and a power transmission mechanism accommodating chamber 130 are provided with a wall 196 (wall portion) separated from the cylinder block 54. The gasket 194 is formed with a communication portion 194c that communicates at least two of the plurality of adjacent chambers in the cylinder block 54, and the communication portion 194c forms a recess 194b. This facilitates the processing of the gasket 194.

Further, the cylinder block 54 and the gasket 194 are formed with a plurality of insertion holes 76 and 198 through which the fastening member 80 to be fastened to the crankcase 52 is inserted. The communication portion 194c is provided between the plurality of insertion holes 76 and 198. By securing the insertion holes 76 and 198 in this way, the positioning of the gasket 194 with respect to the crankcase 52 and the cylinder block 54 becomes easy. Further, by providing the communication portion 194c between the insertion holes 76 and 198, the communication portion 194c can be secured to the maximum.

Further, the connecting portion (connecting portion 200) between the annular portion 194a and the concave portion 194b is formed in a curved shape. As a result, the stress applied to the gasket 194 can be efficiently released.

If the gasket 194 is a non-metal member, the processing of the gasket 194 becomes easier.

Although the present invention has been described above using suitable embodiments, the technical scope of the present invention is not limited to the scope described in the above embodiments. It will be apparent to those skilled in the art that various changes or improvements can be made to the above embodiments. It is clear from the description of the claims that such modified or improved forms may also be included in the technical scope of the present invention. Further, the reference numerals in parentheses described in the claims are attached following the reference numerals in the accompanying drawings for the sake of facilitation of understanding of the present invention, and the elements to which the present invention has the reference numerals are attached. It is not limited and interpreted.

10 ... Internal combustion engine (power unit) 12 ... Vehicle 16 ... Body frame 36 ... Rear wheel (rotated moving part)
52 ... Crankcase (power unit case)
54 ... Cylinder block (cylinder, power unit case)
56 ... Cylinder head 68 ... Crankshaft (crankshaft, drive shaft, rotating shaft)
72 ... Piston (power generator) 74 ... Cylinder chamber (cylinder)
76, 198 ... Insertion hole 84 ... Cooling fin 88 ... Ignition coil 90 ... Valve mechanism (valve structure)
96 ... Spark plug 102 ... Combustion chamber 116 ... Cylinder sleeve 130 ... Power transmission mechanism accommodation chamber 132 ... Power transmission mechanism 134 ... Camshaft 136 ... First speed change shaft (first driven shaft, rotation shaft)
138 ... 2nd transmission shaft (2nd driven shaft, rotating shaft)
144 ... 1st power transmission device 146 ... 2nd power transmission device 174 ... Lubricant holding part 176 ... 1st wall part 194 ... Valve 194a ... Circular part 194b ... Recessed 218, 220 ... Rocker arm shaft 222, 224 ... Rocker arm 226 … Intake valve (valve, valve) 228… Exhaust valve (valve, valve)
232, 236 ... Head boss 248, 250 ... Rod-shaped member 266 ... Opening

Claims (4)

A power transmission mechanism (132) is provided from at least one cylinder (74) accommodating at least one piston (72) that performs reciprocating motion, and a crank shaft (68) that converts the reciprocating motion of the piston (72) into rotary motion. A valve operating mechanism (90) that controls the inflow and outflow of air to and from the cylinder (74) by operating by power transmitted through the cylinder, a cylinder block (54) that holds the cylinder (74), and the cylinder block. mounted adjacent to (54), said to have a cylinder head (56) for holding the valve mechanism (90), towards the axis of the cylinder (74) forward, the vehicle upwardly inclined from the horizontal (12) in mounted on Ru internal combustion engine (10), the
A plurality of cooling fins (84) intersecting in the axial direction of the cylinder (74) are provided on the outer peripheral surface of the cylinder block (54).
An opening (266) that opens from the outer peripheral surface of the cylinder head (56) toward the cooling fin (84) is formed on the cylinder block (54) side of the cylinder head (56).
On the side of the cylinder head (56), a plug hole (94) to which a spark plug (96) is attached, an intake port (104) formed on the upper side of the cylinder head (56), and the cylinder head. An exhaust port (260) formed on the lower side of (56) is provided.
The cylinder head (56) has an air jacket (268) that communicates the side portion of the spark plug (96), the side portion of the intake port (104), and the side portion of the exhaust port (260) with the outside. Provided,
The opening (266) is
Provided on the side of the exhaust port (260)
A power transmission mechanism accommodating chamber (132) in which the power transmission mechanism (132) is housed, below the exhaust port (260) in the vertical direction of the vehicle (12) when viewed from the bottom of the cylinder head (56). 202) above the bottom edge
In the left-right direction of the vehicle (12), an opening is made between the exhaust port (260) and the power transmission mechanism accommodating chamber (202 ) from the air jacket (268) toward the cooling fins (84) .
The traveling wind introduced from the plug hole (94) into the air jacket (268) passes through the side portion of the intake port (104) and the side portion of the exhaust port (260), and passes through the opening (266). with exits rearward through, that omission also downward from the air jacket (268), the internal combustion engine (10). In the internal combustion engine (10) according to claim 1 .
Before Symbol further comprising a crankcase (52) for accommodating the crankshaft (68),
Before Symbol cylinder (74), said projecting upward or forward from a front portion of the crankcase (52),
Before Symbol opening (266), the above lower surface of the exhaust port (260), and, before kidou force transmission mechanism housing chamber (202) in the vertical direction are formed within the width, the internal combustion engine ( 10). In the internal combustion engine (10) according to claim 1 or 2 .
Before Symbol opening (266), it said formed in the longitudinal direction in the cylinder head (56), the internal combustion engine (10). In the internal combustion engine (10) according to any one of claims 1 to 3 .
Before Symbol opening (266), said cylinder (74) of the to be positioned on the lower side is formed in the cylinder head (56) in an internal combustion engine (10).

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