阅读说明：本技术 动力单元 (Power unit ) 是由 原田诚 上村拓真 于 2020-03-27 设计创作，主要内容包括：本发明提供一种动力单元。在内燃机(10)的曲轴箱(52)内设置有：第一变速轴(136),其从曲轴(68)经由第一动力传递装置(144)被传递动力；第二变速轴(138),其将从第一变速轴(136)经由第二动力传递装置(146)传递过来的动力传递给后轮(36)；和润滑液保持部(174),其保持对曲轴箱(52)内进行润滑的润滑液。在曲轴箱(52)内的润滑液保持部(174)的上方且在第一变速轴(136)或第二变速轴(138)的下方设置有第一壁部(176)。据此,能够避免不必要地施加润滑液。(The invention provides a power unit. A crankcase (52) of an internal combustion engine (10) is provided with: a first transmission shaft (136) to which power is transmitted from a crankshaft (68) via a first power transmission device (144); a second transmission shaft (138) that transmits power transmitted from the first transmission shaft (136) via a second power transmission device (146) to the rear wheels (36); and a lubricating fluid holding unit (174) that holds a lubricating fluid for lubricating the inside of the crankcase (52). A first wall section (176) is provided above a lubricating fluid holding section (174) in the crankcase (52) and below the first transmission shaft (136) or the second transmission shaft (138). This can avoid unnecessary application of the lubricating liquid.)

1. A power unit (10) having a power generation portion (68) that generates power based on rotational motion, characterized in that,

and a plurality of rotary shafts (68, 136, 138), a first power transmission device (144), a second power transmission device (146), and a power unit case (52), wherein,

a plurality of said rotary shafts (68, 136, 138) transmitting said rotary motion to a driven rotary motion portion (36);

the first power transmission device (144) and the second power transmission device (146) transmit the power;

the power unit case (52) holds the power generation unit (68), the plurality of rotating shafts (68, 136, 138), the first power transmission device (144), and the second power transmission device (146) inside,

the plurality of rotary shafts (68, 136, 138) are a drive shaft (68), a first driven shaft (136), and a second driven shaft (138), wherein the drive shaft (68) is coupled to the power generation section (68); the power is transmitted from the drive shaft (68) to the first driven shaft (136) via the first power transmission device (144); the power is transmitted from the first driven shaft (136) to the second driven shaft (138) via the second power transmission device (146), the second driven shaft (138) transmits the transmitted power to the driven rotational movement portion (36),

the power unit case (52) has a lubricating liquid holding section (174) at the lower part of the interior thereof, the lubricating liquid holding section (174) holding lubricating liquid for lubricating the interior of the power unit case (52),

a first wall portion (176) is provided in the power unit case (52) above the lubricating fluid retaining portion (174) and below the first driven shaft (136) or the second driven shaft (138).

2. The power unit (10) of claim 1,

at least a part of the first wall portion (176) is formed in an arc shape with the first driven shaft (136) or the second driven shaft (138) as a center.

3. The power unit (10) of claim 1 or 2,

the power unit (10) is mounted on a vehicle (12),

the power unit case (52) is a case body that can be divided into a first case body (112L) and a second case body (112R) in the axial direction of the drive shaft (68),

the first wall portion (176) is constituted by a first case-side first wall portion (176L) and a second case-side first wall portion (176R), wherein the first case-side first wall portion (176L) extends in the axial direction from the first case (112L); the second case-side first wall portion (176R) extends in the axial direction from the second case (112R).

4. The power unit (10) of claim 3,

a first gap (180) is formed between the first case-side first wall portion (176L) and the second case-side first wall portion (176R).

5. The power unit (10) of claim 4,

a second wall (178) is provided in the power unit case (52) above the lubricating fluid retaining section (174) and below the drive shaft (68).

6. The power unit (10) of claim 5,

at least a part of the second wall portion (178) is formed in an arc shape with the drive shaft (68) as a center.

7. The power unit (10) of claim 5,

the power unit case (52) has a pair of side walls (140L, 140R) that face each other at least in the vehicle width direction of the vehicle (12),

the first wall portion (176) and the second wall portion (178) extend in the vehicle width direction from the pair of side walls (140L, 140R),

the drive shaft (68), the first driven shaft (136), and the second driven shaft (138) are rotatably supported by support holes (142L, 142R) provided in the pair of side walls (140L, 140R), respectively.

8. The power unit (10) of claim 5,

the second wall portion (178) is configured by a first case-side second wall portion (178L) extending in the axial direction from the first case (112L) and a second case-side second wall portion (178R) extending in the axial direction from the second case (112R).

9. The power unit (10) of claim 8,

a second gap (182) is formed between the first case-side second wall portion (178L) and the second case-side second wall portion (178R).

10. The power unit (10) of claim 9,

the first gap (180) and the second gap (182) are respectively configured by narrow gap portions (180a, 182a) having a narrow width in the front-rear direction of the vehicle (12) and wide gap portions (180b, 182b) having a wide width in the front-rear direction of the vehicle (12).

11. The power unit (10) of claim 10,

one of the narrow gap portions (180a, 182a) and the wide gap portions (180b, 182b) is formed in the front, and the other is formed in the rear.

12. The power unit (10) of claim 1 or 2,

the power unit (10) is an internal combustion engine that produces the rotary motion by a piston (72) reciprocating within a cylinder (74),

the drive shaft (68) is a crankshaft,

the first driven shaft (136) and the second driven shaft (138) are transmission shafts that transmit power through a plurality of gear trains (166a to 166d) that can selectively transmit the power.

Technical Field

The present invention relates to a power unit that generates power based on rotational motion.

Background

For example, japanese patent application laid-open No. 4391914 discloses that, in a crankcase (power unit case) of an internal combustion engine (power unit), an arc-shaped partition wall is provided between a lubricating liquid holding portion that holds lubricating liquid below the crankcase and a crankshaft (drive shaft) above the lubricating liquid holding portion.

Disclosure of Invention

However, a transmission shaft (driven shaft) that transmits power generated by rotational motion from a drive shaft to wheels (driven rotational motion portion), a rotational speed sensor (vehicle speed sensor), and the like are disposed in the power unit case; the rotation speed sensor detects the rotation speed of the drive shaft or the driven shaft corresponding to the vehicle speed. However, in the structure of japanese patent application laid-open No. 4391914, when the vehicle is accelerated rapidly or when the vehicle is running with the front wheels lifted (Wheelie), the lubricating fluid may be unnecessarily applied to the driven shaft, the vehicle speed sensor, and the like, which may cause friction or erroneous detection.

Accordingly, an object of the present invention is to provide a power unit capable of avoiding unnecessary application of a lubricating liquid.

The present invention relates to a power unit having a power generation unit that generates power based on rotational motion. The power unit further has a plurality of rotating shafts that transmit the rotational motion to a driven rotational motion section, a first power transmission device, a second power transmission device, and a power unit case; the first power transmission device and the second power transmission device transmit the power; the power unit case holds the power generation unit, the plurality of rotary shafts, the first power transmission device, and the second power transmission device inside.

In this case, the plurality of rotating shafts are a drive shaft coupled to the power generation unit, a first driven shaft, and a second driven shaft; the power is transmitted from the drive shaft to the first driven shaft via the first power transmission device; the power is transmitted from the first driven shaft to the second driven shaft via the second power transmission device, and the second driven shaft transmits the transmitted power to the driven rotational motion section. The power unit case has a lubricant retaining portion at a lower portion inside thereof, and the lubricant retaining portion retains a lubricant for lubricating the inside of the power unit case. In the power unit case, a first wall portion is provided above the lubricating liquid holding portion and below the first driven shaft or the second driven shaft.

In this case, at least a part of the first wall portion is formed in an arc shape with the first driven shaft or the second driven shaft as a center.

In addition, when the power unit is mounted on a vehicle, the power unit case is a case that can be divided into a first case and a second case in the axial direction of the drive shaft. The first wall portion is constituted by a first case-side first wall portion extending from the first case in the axial direction and a second case-side first wall portion; the second case-side first wall portion extends in the axial direction from the second case.

In this case, a first gap is formed between the first case-side first wall portion and the second case-side first wall portion.

Further, a second wall portion is provided in the power unit case above the lubricating liquid holding portion and below the drive shaft.

At least a part of the second wall portion is formed in an arc shape around the drive shaft.

In this case, the power unit case has a pair of side walls that face each other at least in the vehicle width direction of the vehicle. The first wall portion and the second wall portion extend in the vehicle width direction from the pair of side walls, and the drive shaft, the first driven shaft, and the second driven shaft are rotatably supported by support holes provided in the pair of side walls, respectively.

The second wall portion is configured by a first case-side second wall portion extending in the axial direction from the first case and a second case-side second wall portion extending in the axial direction from the second case.

In this case, a second gap is formed between the first case-side second wall portion and the second case-side second wall portion.

The first gap and the second gap are each configured by a narrow gap portion having a narrow width in the front-rear direction of the vehicle and a wide gap portion having a wide width in the front-rear direction of the vehicle.

In this case, one of the narrow gap portion and the wide gap portion is formed in the front, and the other is formed in the rear.

Further, the power unit is an internal combustion engine that generates the rotational motion by a piston reciprocating in a cylinder, the drive shaft is a crankshaft, and the first and second driven shafts are transmission shafts that transmit power through a plurality of gear trains that can selectively transmit the power.

According to the present invention, the first wall portion is provided between the lubricating liquid holding portion and the first driven shaft or the second driven shaft. Accordingly, even if the lubricating liquid held in the lubricating liquid holding portion is shaken when the vehicle is suddenly accelerated or is in slip running, the lubricating liquid can be prevented from being applied to the first driven shaft or the second driven shaft. As a result, unnecessary application of the lubricating liquid can be avoided, and occurrence of friction or erroneous detection can be prevented.

Further, since at least a part of the first wall portion is formed in an arc shape, even when a vehicle including the power unit case generates a large acceleration, it is possible to effectively suppress the lubricating liquid from being applied to the first transmission shaft, the second transmission shaft, and the like unnecessarily due to a large vibration of the lubricating liquid.

Further, the wall portion extends from the first case and the second case of the crankcase, so that the ease of assembly of the crankcase can be improved.

Further, by forming the first gap to allow a slight amount of lubricant to enter and exit, the lubricant applied to the first transmission shaft and the second transmission shaft can be efficiently discharged to the lubricant retaining portion.

By providing the second wall portion, even when a large acceleration is generated in a vehicle including an internal combustion engine, the lubricating liquid can be prevented from being applied to a crankshaft and the like unnecessarily due to a large sloshing of the lubricating liquid.

Further, by forming at least a part of the second wall portion in an arc shape, unnecessary application of the lubricating liquid to the crankshaft and the like can be effectively suppressed.

Further, the first wall portion or the second wall portion and the support hole are formed in the same side wall in the same direction, whereby the crankcase can be easily processed.

Further, the second wall portion is formed by the first case-side second wall portion and the second case-side second wall portion, whereby the ease of assembly of the crankcase can be further improved.

By forming the second gap to allow the entry and exit of some lubricating fluid, the lubricating fluid applied to the crankshaft can be efficiently discharged to the lubricating fluid holding portion.

Further, by providing the narrow gap portion and the wide gap portion in the first gap and the second gap, the discharge efficiency of the lubricating liquid from the crankshaft, the first transmission shaft, and the second transmission shaft side to the lubricating liquid retaining portion side can be improved.

Further, by forming one of the narrow gap portion and the wide gap portion in the front direction and the other in the rear direction, the discharge efficiency of the lubricating liquid can be further improved by providing the wide gap portion in a direction in which the acceleration of the vehicle is likely to be applied.

Further, the internal combustion engine can be mounted on a vehicle as appropriate.

The above objects, features and advantages will be readily understood from the following description of the embodiments with reference to the accompanying drawings.

Drawings

Fig. 1 is a left side view of the vehicle.

Fig. 2 is a left side view of the internal combustion engine of fig. 1.

Fig. 3 is a right side view of the internal combustion engine of fig. 1.

Fig. 4 is a top view of the internal combustion engine of fig. 1.

Fig. 5 is a sectional view taken along line V-V of fig. 2.

Fig. 6 is a sectional view taken along line VI-VI of fig. 5.

Fig. 7 is a plan view of the crankcase in section.

Fig. 8 is a perspective view of the crankcase in section.

Fig. 9 is a top view of the gasket.

Fig. 10 is a sectional view taken along line X-X of fig. 4.

Fig. 11 is a sectional view taken along line XI-XI of fig. 2.

Fig. 12 is a bottom view of the cylinder head.

Fig. 13 is a sectional view taken along line XIII-XIII in fig. 3.

Fig. 14 is a sectional view taken along the line XIV-XIV of fig. 3.

Detailed Description

Hereinafter, the power unit according to the present invention will be described in detail with reference to the drawings, taking preferred embodiments as examples.

[1. schematic Structure of vehicle 12 ]

Fig. 1 is a left side view of a vehicle 12 equipped with an internal combustion engine 10 as a power unit according to the present embodiment. In the present embodiment, the front-rear, left-right, and up-down directions of the vehicle 12 are described with reference to directions viewed from a driver seated on the seat 14 of the vehicle 12. In addition, with respect to the pair of left and right components, the reference numeral of the left component may be denoted by "L", and the reference numeral of the right component may be denoted by "R".

This embodiment is applied to a "Cub (trade name)" type motorcycle shown in fig. 1. The present embodiment is not limited to the motorcycle shown in fig. 1, and can be applied to various straddle-type vehicles and prime movers (internal combustion engines).

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

A steering handle 24 operated by the driver is pivotally supported on the upper end of the head pipe 18. A pair of left and right front forks 28L, 28R are pivotally supported at the lower end of the head pipe 18 via a steering rod 26 so as to be steerable. The lower ends of the front forks 28L, 28R pivotally support a front wheel 30.

An internal combustion engine 10 (power unit) is supported below the main frame 20. At the rear end of the main frame 20, a pair of left and right pivot brackets 32L, 32R extend downward. The front end of the rocker arm 34 is supported by the pivot bracket 32L so as to be swingable in the vertical direction. The rear end of the rocker arm 34 pivots a rear wheel 36 (driven rotary motion portion). A rear cushion 38 is coupled between the seat frame 22 and the swing arm 34. A seat 14 is disposed above the seat frame 22.

The body frame 16 is covered with a body cover 40. The body cover 40 includes a front cover 42, a pair of right and left main frame covers 44L, 44R, a leg shield 46, a floor cover (under hood) 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 legs of the driver from the front. The bottom cover 48 connects the main frame covers 44L and 44R at the lower side. The body cover 50 covers the rear end portion of the main frame 20, the seat frame 22, and the like.

[2. Structure of internal Combustion Engine 10 ]

Next, the structure of the internal combustion engine 10 will be described with reference to fig. 2 to 14. Here, the external structure, the internal structure, and the structure of each part of the internal combustion engine 10 will be described.

<2.1 external appearance Structure of internal Combustion Engine 10 >

First, an external appearance structure of the internal combustion engine 10 will be described with reference to fig. 2 to 4.

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

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

A screw hole is formed in the vehicle width direction in the coupling boss 58a at the upper portion of the crankcase 52. Two bolts 62a are screwed into the screw holes, and the two bolts 62a are inserted into holes formed in the pair of left and right ribs 60L, 60R, respectively. Screw holes are formed in the vehicle width direction in the two coupling bosses 58b, 58c at the rear portion of the crankcase 52. Two bolts 62b are screwed into the screw holes of the coupling boss 58b, and the two bolts 62b are inserted into holes formed in the pivot holders 32L and 32R, respectively. Two bolts 62c are screwed into the screw holes of the coupling boss 58c, and the two bolts 62c are inserted into holes formed in the pivot holders 32L and 32R, respectively. Accordingly, the internal combustion engine 10 including the crankcase 52 is supported by the vehicle body frame 16 directly below the main frame 20.

Various components are connected to the internal combustion engine 10. In this case, a dead space (space) is formed between the body frame 16 (main frame 20) and the internal combustion engine 10. Therefore, in the present embodiment, various components are disposed in the dead space in order to avoid the components from protruding in the vehicle width direction from the internal combustion engine 10.

Specifically, a starting motor 66 is disposed in front of the coupling boss 58a at the upper portion of the crankcase 52. A Crankshaft 68(crank shaft, power generation unit) as a drive shaft (rotation shaft) of the internal combustion engine 10 extending in the vehicle width direction is housed in the crankcase 52 (see fig. 2, 3, 5, and 6). The motor 66 is disposed above the crankshaft 68 in the upper portion of the crankcase 52.

A rotation speed detecting unit 70 is attached to an upper portion of the crankcase 52 in front of the electric motor 66 for starting. The rotation speed detecting unit 70 is a sensor (vehicle speed sensor, pickup) for detecting the rotation speed of the crankshaft 68 corresponding to the vehicle speed of the vehicle 12, and is attached to the crankcase 52 so as to extend obliquely upward and forward from the upper portion of the crankcase 52 toward the axis of the crankshaft 68.

The cylinder block 54 has a cylinder chamber 74 (cylinder) that houses the reciprocating piston 72 (see fig. 5 and 6). The cylinder block 54 is formed with a plurality of insertion holes 76 in the axial direction of the cylinder chamber 74, i.e., in the direction diagonally upward and forward of the cylinder block 54 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 fastening members 80 such as stud bolts are inserted through the respective insertion holes 76, 78.

In this case, one end portions of the fastening members 80 inserted into the insertion holes 76 are screwed into screw holes, not shown, formed in the crankcase 52, and the other end portions are screwed to nuts 82 on the cylinder head 56 side. Accordingly, the cylinder block 54 and the cylinder head 56 are sequentially mounted to the crankcase 52.

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

The cylinder head 56 has a structure in which a main body portion housing an air distribution (Valve train) mechanism 90 (air distribution structure) and an intake/exhaust system shown in fig. 5 and 6 are integrated with a portion corresponding to a cylinder head cover. A plurality of fins 92 are formed on the outer peripheral surface of the cylinder head 56 on the cylinder block 54 side in a direction (intersecting direction) substantially orthogonal to the axial direction of the cylinder chamber 74.

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

An intake member 100 is connected to an upper portion of the cylinder head 56. The intake member 100 has an intake pipe 100b connecting a throttle body 100a and an intake port 104 (see fig. 6), wherein the throttle body 100a controls the intake air amount of the internal combustion engine 10; the intake port 104 communicates with the throttle body 100a and a combustion chamber 102 described later. An injector 106 for injecting fuel into the combustion chamber 102 is attached to the intake pipe 100 b. 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 is supported by the vehicle body frame 16 directly below the main frame 20, and various components connected to the internal combustion engine 10 are arranged in the dead space between the main frame 20 and the internal combustion engine 10. Therefore, as shown in the plan view of fig. 4, various components are disposed on the upper portion of 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 disposed on the upper portion of the cylinder block 54 so as to overlap the cylinder block 54 in a plan view of fig. 4. In the side views of fig. 2 and 3, the ignition coil 88 is disposed behind the cylinder head 56 and the intake member 100 (throttle body 100a and intake pipe 100b), and is disposed in front of the three coupling bosses 58a to 58c, the rotation speed detection unit 70, and the motor 66. Referring to fig. 4, the ignition coil 88 is disposed so as to overlap the intake member 100 and the electric motor 66 when viewed from the front. In the side view of fig. 2 and 3, when a virtual line 108 of a two-dot chain line connecting the top (upper end) of the cylinder head 56 and the top (upper-side coupling boss 58a) of the crankcase 52 is set, at least a part of the ignition coil 88 or the support member 86 is disposed above the cylinder head 56 so as to be located in a space below the virtual line 108 (a space between the virtual line 108 and the internal combustion engine 10).

<2.2 internal Structure of internal Combustion Engine 10 >

Next, the internal structure of the internal combustion engine 10 will be described with reference to fig. 5 to 14. The internal combustion engine 10 is an air-cooled single cylinder engine in which the axial direction (axis) of the crankshaft 68 is arranged along the vehicle width direction. Further, the main structural elements of the internal combustion engine 10 are disclosed in, for example, japanese patent laid-open publication No. 2016-160812 and japanese patent laid-open publication No. 6002269. Therefore, in the description of the internal structure of the internal combustion engine 10, the same components as those disclosed in these publications are briefly described, and the description of the operation thereof is simplified or omitted.

(2.2.1 inner structure of crankcase 52 and cylinder block 54 side)

First, the internal structure of the internal combustion engine 10 on the crankcase 52 and cylinder block 54 side will be described with reference to fig. 5 to 8.

The crankcase 52 is a case that is divided into a left first case 112L and a right second case 112R by a dividing surface (a left-right center surface 110 shown in fig. 5, 7, and 8) substantially perpendicular to the vehicle width direction. A first casing cover 114L (see fig. 1, 2, 4, and 5) is attached to the left side of the first casing 112L. On the other hand, a second casing cover 114R (see fig. 3 to 5) is attached to the right side of the second casing 112R. The crankcase 52 also serves as a transmission case for accommodating a transmission such as a manual transmission. The lubricating fluid as the engine oil is appropriately circulated and stirred in the internal combustion engine 10 including the crankcase 52.

The cylinder block 54 has a cylindrical cylinder liner 116. The cylinder liner 116 has an axis along the left and right center planes 110 and forms the cylinder chamber 74. The piston 72 is fitted into the cylinder chamber 74 so as to be capable of reciprocating along the left and right center planes 110 (the axis of the cylinder chamber 74).

Piston 72 is coupled to a crankpin 120 of crankshaft 68 by a connecting rod 118. The crankshaft 68 includes left and right crank arms 122L and 122R that support the crank pin 120, journal portions 124L and 124R that project laterally outward from the crank arms 122L and 122R, respectively, and extension shafts 126L and 126R that extend laterally outward from the journal portions 124L and 124R, respectively. Therefore, the power of the reciprocating motion of the piston 72 is converted into the power of the rotational motion by the crankshaft 68.

A cam drive sprocket 128 is provided on the proximal end side of the extension shaft 126L on the first casing 112L side (left side). A power transmission mechanism housing chamber 130 is formed on the left side in the cylinder block 54 along the axial direction of the cylinder chamber 74. A power transmission mechanism 132 as a chain transmission mechanism including the cam drive sprocket 128 is housed in the power transmission mechanism housing chamber 130. A camshaft 134 is provided in the cylinder head 56, and the camshaft 134 is rotatably coupled to the power transmission mechanism 132. The power transmission mechanism 132 including the cam drive sprocket 128 transmits the power of the rotational motion of the crankshaft 68 to the camshaft 134, thereby driving the camshaft 134 to rotate in conjunction with the crankshaft 68.

A plurality of rotating shafts extending substantially parallel to each other in the vehicle width direction are disposed inside the crankcase 52. The plurality of rotation shafts are the crankshaft 68, the first shift shaft 136 (first driven shaft) as a main shaft disposed rearward of the crankshaft 68, and the second shift shaft 138 (second driven shaft) as an intermediate shaft disposed rearward of the first shift shaft 136.

The left side wall 140L of the first casing 112L and the right side wall 140R of the second casing 112R constitute a pair of side walls 140L, 140R facing each other. Support holes 142L, 142R (see fig. 8) are formed in the pair of side walls 140L, 140R, and the support holes 142L, 142R pivotally support both end portions of the plurality of rotation shafts so as to be rotatable. Therefore, in the crankcase 52, the crankshaft 68, the first transmission shaft 136, and the second transmission shaft 138 are rotatably pivoted to two support holes 142L, 142R formed in a pair of side walls 140L, 140R, respectively, and are disposed along the vehicle width direction.

A first power transmission device 144 is provided between the crankshaft 68 and the first transmission shaft 136 in the crankcase 52. Further, a second power transmission device 146 is provided between first transmission shaft 136 and second transmission shaft 138 in crankcase 52. Further, a kick spindle (kick spindle)148 is disposed rearward of the second transmission shaft 138 in the crankcase 52.

The first power transmission device 144 is provided on the second case 112R side in the crankcase 52, and transmits power based on the rotational motion of 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 center planes 110, and transmits power based on the rotational motion of the first transmission shaft 136 to the second transmission shaft 138. The second transmission shaft 138 outputs the power transmitted from the second power transmission device 146 to an engine output portion 150 on the rear left side of the first case 112L, and transmits the power from the engine output portion 150 to the rear wheels 36 via a chain transmission mechanism 152 in the rocker arm 34 (see fig. 1).

The first power transmission device 144 includes a centrifugal clutch 154 and a multiple disc clutch 156, wherein the centrifugal clutch 154 is coupled to the right end portion (the right extension shaft 126R) of the crankshaft 68 on the second case 112R side in the crankcase 52; the multiple disc clutch 156 is coupled to a right end portion of the first transmission shaft 136 on the second case 112R side in the crankcase 52.

The centrifugal clutch 154 is coaxially supported by the right extension shaft 126R, and includes a clutch outer 154a, a clutch inner 154b, and a centrifugal weight 154 c. The clutch outer 154a is a bottomed cylindrical member that is open to the right, and is relatively rotatably supported by the right extension shaft 126R. The clutch inner 154b is integrally rotatably supported on the right extension shaft 126R on the inner peripheral side of the clutch outer 154 a. The centrifugal weight 154c is supported by the clutch inner 154b so as to be capable of expanding on the inner circumferential side of the clutch outer 154 a. A centrifugal oil filter 158 is formed on the right side of the clutch inner 154 b.

The centrifugal weight 154c is separated from the inner circumferential surface of the clutch outer 154a when the crankshaft 68 is stopped and rotating at a low speed, and the centrifugal clutch 154 is brought into a disengaged state in which power cannot be transmitted. The centrifugal weight 154c expands as the rotational speed of the crankshaft 68 increases, and frictionally engages with the inner circumferential surface of the clutch outer 154a at a predetermined rotational speed or higher, thereby bringing the centrifugal clutch 154 into a connected state in which power can be transmitted.

A one-way clutch 160 is fitted to a central portion of the clutch outer 154 a. When the clutch inner 154b and the crankshaft 68 rotate forward prior to the clutch outer 154a, the one-way clutch 160 is in a free state and torque transmission is not performed. Accordingly, the clutch inner 154b and the crankshaft 68 idle relative to the clutch outer 154 a. Further, the normal rotation of the crankshaft 68 corresponds to the rotation during the operation of the internal combustion engine 10.

Further, when the clutch outer 154a rotates forward prior to the clutch inner 154b and the crankshaft 68, or when the clutch inner 154b and the crankshaft 68 rotate backward relative to the clutch outer 154a, if the rotation speed of the clutch inner 154b is lower than a predetermined speed, the one-way clutch 160 is kept in a free state and torque transmission is not performed. Accordingly, the clutch outer 154a idles against the clutch inner 154b and the crankshaft 68.

On the other hand, when the rotational speed of the clutch inner 154b becomes equal to or higher than the predetermined speed, the one-way clutch 160 is set to the one-way operation state. In this state, when the clutch outer 154a rotates forward before the clutch inner 154b and the crankshaft 68, torque can be transmitted, and the clutch outer 154a, the clutch inner 154b, and the crankshaft 68 can rotate forward integrally.

A cylindrical transmission cylinder 154d extending leftward is provided on the left side of the center portion of the clutch outer 154 a. The primary drive gear 162 is provided on the left end side of the transmission cylinder 154d so as to be integrally rotatable. The primary drive gear 162 meshes with a primary driven gear 164, and the primary driven gear 164 is relatively rotatably supported on the right side portion of the first transmission shaft 136. The primary drive gear 162 and the primary driven gear 164 constitute a primary speed reduction mechanism of the internal combustion engine 10.

The right end of the first transmission shaft 136 terminates leftward from the right end of the centrifugal clutch 154, and a multiple disc clutch 156 is coaxially supported. The multiple disc clutch 156 is a speed change clutch, and includes a clutch outer 156a, a clutch inner 156b, and a plurality of clutch discs 156 c.

The clutch outer 156a is a bottomed cylindrical member that is open to the right, and is relatively rotatably supported by the right end portion of the first shift shaft 136. A primary driven gear (primary drive gear)164 is supported on the left side of the clutch outer 156a so as to be integrally rotatable. The clutch inner 156b is disposed 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. The clutch plates 156c are stacked in the vehicle width direction between the clutch outer 156a and the clutch inner 156 b.

The multiple disc clutch 156 is frictionally engaged by pressing the clutch disc 156c with an urging force of a diaphragm spring (not shown). The multiple disc clutch 156 is temporarily released from pressure contact with the clutch disc 156c in conjunction with a shift operation of a shift pedal, not shown, so that a shift through the transmission of the vehicle 12, that is, the second power transmission device 146 is smoothly performed.

The second power transmission device 146 is a transmission provided between the first transmission shaft 136 and the second transmission shaft 138 and having a plurality of gear trains 166a to 166d that can be selectively established. The power generated by the rotational motion of the crankshaft 68 is transmitted from the first transmission shaft 136 to the second transmission shaft 138 via any of the gears constituting the gear trains 166a to 166 d. The left end portion of the second transmission shaft 138 protrudes to the left of the rear portion of the crankcase 52 to become an engine output portion 150.

The gear trains 166a to 166d are constituted by gears corresponding to the number of gear stages supported by the first transmission shaft 136 and the second transmission shaft 138, respectively. The second power transmission device 146 is of a constant mesh type in which gears corresponding to the gear trains 166a to 166d are constantly meshed with each other between the first transmission shaft 136 and the second transmission shaft 138. The gears are classified into a free gear, a fixed gear, and a sliding gear, wherein the free gear is relatively rotatable with respect to a transmission shaft supporting itself; the fixed gear can rotate integrally relative to the speed change shaft supporting the fixed gear; the slide gear is spline-fitted to a shift shaft supporting itself.

The second power transmission device 146 moves the slide gear by the operation of a not-shown switching mechanism, and selects the gear trains 166a to 166d corresponding to the gear positions (shift positions). In fig. 5, a four-speed (second-speed) gear train 166d, a second-speed gear train 166b, a third-speed gear train 166c, and a first-speed gear train 166a are arranged in this order from the left side to the right side.

An ACG (alternator) starter 168 is coaxially supported on a left end portion of the left extension shaft 126L of the crankshaft 68. The ACG starter 168 is a three-phase ac generator motor, and functions as a starter motor (cell motor) for starting the internal combustion engine 10 and also functions as an alternator for generating electric power in accordance with the operation of the internal combustion engine 10.

The ACG starter 168 is an outer rotor type rotating electric machine having an outer rotor 168a and an inner stator 168 b. The outer rotor 168a is a bottomed cylindrical member that is open to the left, and is supported integrally rotatably at the left end portion of the left extension shaft 126L. The inner stator 168b is disposed on the inner circumferential 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 circumferential side of the outer rotor 168 a. A plurality of coils 168d arranged in the circumferential direction are formed on the outer circumferential side of the inner stator 168 b.

A detection gear 170 including a magnetic material is attached to a portion of the left extension shaft 126L on the ACG starter 168 side. The rotation speed detecting unit 70 is attached to the crankcase 52 so as to face the tooth surface of the detection gear 170 toward 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, and detects the rotation speed of the crankshaft 68 corresponding to the detected number of teeth.

The right end of the kick spindle 148 protrudes to the rear right side of the second casing 112R, and is connected to a kick lever, not shown. A kick start drive gear 172 is coaxially supported on the left end portion of the kick start main shaft 148. The kick start drive gear 172 rotates integrally with the kick start spindle 148 by a meshing mechanism not shown only when the kick start spindle 148 rotates in one direction due to depression of the kick arm.

The kick start drive gear 172 meshes with a driven gear of the first speed gear train 166 a. The rotational power of the kick start drive gear 172 is input to the clutch outer 154a of the centrifugal clutch 154 as normal rotation 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. When the rotational torque of the normal rotation is equal to or greater than a predetermined torque, the one-way clutch 160 is in a one-way operation state. When the one-way clutch 160 is locked by 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, cranking of the internal combustion engine 10 by the pedal starter can be performed.

In the present embodiment, as shown in fig. 6 and 8, the crankcase 52 has a lubricating liquid holding portion 174 at the lower portion of the inside thereof, and the lubricating liquid holding portion 174 holds lubricating liquid for lubricating the inside of the crankcase 52. In fig. 6, a part of the crankcase 52 in the internal combustion engine 10 is schematically illustrated.

As shown in fig. 6 to 8, a first wall portion 176 is provided in the crankcase 52 above the lubricating fluid retaining portion 174 and below the first transmission shaft 136 or the second transmission shaft 138. Further, a second wall portion 178 is provided in the crankcase 52 above the lubricating fluid retaining portion 174 and below the crankshaft 68.

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

In this case, at least a part of the first wall portion 176 is formed in an arc shape that protrudes downward around the first shift shaft 136 or the second shift shaft 138. At least a part of the second wall portion 178 is formed in an arc shape protruding downward around the crankshaft 68. As shown in fig. 6 to 8, the first wall portion 176 is formed such that the arc of the first wall portion 176 deviates from the cylinder chamber 74. 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 the first case 112L and the second case 112R. Therefore, first wall portion 176 is constituted by first case-side first wall portion 176L and second case-side first wall portion 176R, first case-side first wall portion 176L extending in the vehicle width direction (each axial direction of crankshaft 68, first transmission shaft 136, and second transmission shaft 138) from first transmission shaft 136 and second transmission shaft 138 sides of side wall 140L of first case 112L to left and right center plane 110 as arc-shaped ribs; second case side first wall portion 176R is an arc-shaped rib extending in the vehicle width direction from first shift shaft 136 and second shift shaft 138 sides of side wall 140R of second case 112R to left and right center plane 110.

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

Similarly, second wall portion 178 is constituted by a first case-side second wall portion 178L and a second case-side second wall portion 178R, wherein first case-side second wall portion 178L is an arc-shaped rib extending in the vehicle width direction from crankshaft 68 side of side wall 140L of first case 112L toward left and right center plane 110; the second case-side second wall portion 178R is an arc-shaped rib extending in the vehicle width direction from the crankshaft 68 side of the side wall 140R of the second case 112R to the left and right center planes 110.

A second gap 182 is formed between first case-side second wall portion 178L and second case-side second wall portion 178R. In this case, a gap formed in the front-rear direction between the right end portion of the first case-side second wall portion 178L and the left end portion of the second case-side second wall portion 178R also becomes the second gap 182. The second gap 182 includes a second narrow gap portion 182a having a narrow width in the vehicle width direction and a second wide gap portion 182b having a wide width in the vehicle width direction. One of the second narrow gap portion 182a and the second wide gap portion 182b is formed forward, and the other is formed rearward. Fig. 7 and 8 illustrate a case where the second narrow gap portion 182a is formed at the front and the second wide gap portion 182b is formed at the rear.

In the internal combustion engine 10, when the internal combustion engine 10 is started and the crankshaft 68 is rotated, a pump, not shown, is driven. The pump sucks the lubricating liquid held in the lubricating liquid holding portion 174. The pumped lubricating liquid passes through a supply passage 184 provided in the crankcase 52, and is injected from an injection hole 185 toward the bottom surface of the piston 72 into the cylinder chamber 74 (see fig. 5). Accordingly, the cylinder chamber 74 and the piston 72 are lubricated.

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

A crank pin passage 192 communicating with the crank passage 188 is formed in the crank pin 120. A portion of the lubricating liquid supplied to crankshaft passage 188 is also supplied to crankpin passage 192. Accordingly, 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 down to the first wall portion 176 and the second wall portion 178 below. First wall 176 has a first gap 180 formed therein, and second wall 178 has a second gap 182 formed therein. Therefore, the lubricating liquid that has fallen to the first wall portion 176 falls to the lubricating liquid retaining portion 174 through the first gap 180. Further, the lubricating liquid that has fallen onto the second wall portion 178 falls onto the lubricating liquid holding portion 174 through the second gap 182.

(2.2.2 Structure of spacer 194)

As shown in fig. 5, 6, and 9, a gasket 194 is interposed between the cylinder block 54 and the crankcase 52. The gasket 194 is a nonmetallic seal 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 housing chamber 130 when viewed in the axial direction of the cylinder chamber 74. That is, as shown in fig. 9, the gasket 194 includes an annular portion 194a surrounding the cylinder chamber 74, and a recessed portion 194b formed from the annular portion 194a to the power transmission mechanism accommodating chamber 130 side so as to be spaced apart from the cylinder chamber 74. That is, the annular portion 194a of the spacer 194 surrounds the cylinder chamber 74, and the recess 194b continuous with the annular portion 194a surrounds 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 housing chamber 130 are provided with a wall 196 therebetween. In this case, a communicating portion 194c is formed between the annular portion 194a and the recessed portion 194b of the gasket 194, and the communicating portion 194c is a gap portion for communicating at least two of the adjacent chambers in the cylinder block 54. Fig. 9 illustrates a case where the cylinder chamber 74 and the power transmission mechanism housing chamber 130 are communicated with each other through the communication portion 194 c. Therefore, the communication portion 194c is provided, so that the concave portion 194b is formed.

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

(2.2.3 inner structure of cylinder head 56 side)

Next, the internal structure of the internal combustion engine 10 on the cylinder head 56 side will be described with reference to fig. 10 to 14.

A power transmission mechanism housing chamber 202 that communicates with the power transmission mechanism housing chamber 130 (see fig. 5 and 9) of the cylinder block 54 is formed in the cylinder head 56 on the left end side of the cylinder head 56. Further, a valve gear housing chamber 204 for housing a valve gear 90, which will be described later, is formed in the cylinder head 56 on the right end side of the cylinder head 56. The valve train housing chamber 204 and the power transmission mechanism housing chamber 202 are separated by a wall 206.

By removing the cover member 208 on the left side of the cylinder head 56, the power transmission mechanism housing chamber 202 can be inspected (accessed) from the outside. Further, by removing the cover members 210, 212 on the upper and lower sides of the cylinder head 56, the valve train housing chamber 204 can be inspected from the outside. In this case, the valve train housing chamber 204 has one adjustment hole 214 that opens upward and the other adjustment hole 216 that opens downward. One of the adjustment holes 214 is closed by the upper cover member 210. The other adjustment hole 216 is closed by the lower cover member 212. Therefore, the valve train 90 is inspected through the adjustment holes 214 and 216 in a state where the cover members 210 and 212 are removed from the cylinder head 56.

The valve train 90 for controlling the intake and exhaust of air to and from the cylinder chamber 74 (combustion chamber 102) is held in the valve train accommodating chamber 204. The valve train 90 includes the camshaft 134, two rocker shafts 218, 220, two rocker arms 222, 224, an intake valve 226 (valve), and an exhaust valve 228 (valve).

The camshaft 134 extends in the vehicle width direction in the valve train housing chamber 204. The left end of the cam shaft 134 is inserted into the power transmission mechanism housing chamber 202 through the wall 206 and is coupled to the power transmission mechanism 132. The right end of the camshaft 134 is rotatably pivoted to the right inner wall 230 of the cylinder head 56. Therefore, the camshaft 134 is rotatable by receiving a driving force (power of rotational motion) from the crankshaft 68 via the power transmission mechanism 132.

The two rocker shafts 218, 220 are disposed vertically in the valve train housing chamber 204 with the camshaft 134 interposed therebetween, and extend in the vehicle width direction.

In this case, a cylinder head boss 232 protruding to the left side is formed on the inner wall 230 on the right side of the cylinder head 56 corresponding to the upper rocker arm shaft 218. One end portion (right end portion) of the rocker shaft 218 is fitted into a hole 234 formed in the top cylinder head boss 232. Further, the other end portion (left end portion) of the rocker arm shaft 218 is fitted into a hole formed in the wall 206. Accordingly, the rocker arm shaft 218 is disposed and supported in the vehicle width direction in the valve train housing chamber 204.

On the other hand, one end portion (right end portion) of the lower rocker shaft 220 is fitted into a hole formed in the inner wall 230. A cylinder head boss 236 protruding to the right side is formed on the wall 206 corresponding to the lower rocker arm shaft 220. The other end portion (left end portion) of the rocker shaft 220 is fitted into a hole 238 formed in the cylinder head boss 236. Accordingly, the rocker arm shaft 220 is disposed and supported in the vehicle width direction in the valve train housing chamber 204.

Two holes 234, 238, i.e., insertion holes 240, 242 facing the center axes (axial centers) of the two rocker arms 218, 220, are formed in the two cylinder head bosses 232, 236, respectively. Each of the through holes 240 and 242 is a substantially cylindrical through hole having a central axis. In this case, in the valve train housing chamber 204, the insertion hole 240 of the cylinder head boss 232 provided on the upper side (the insertion hole 240 on the intake valve 226 side) is formed so as to face the adjustment hole 214 on the upper side. Further, the through hole 242 of the cylinder head boss 236 provided on the lower side (the through hole 242 on the exhaust valve 228 side) is formed so as to face the lower adjustment hole 216. The center axes of the insertion holes 240 and 242 provided in the cylinder head bosses 232 and 236 are substantially perpendicular 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 shafts 218 and 220 are also formed in one end of the rocker shaft 218 and the other end of the rocker shaft 220. In the present embodiment, the through holes 240 and 242 of the cylinder head bosses 232 and 236 and the through holes 244 and 246 of the rocker arms 218 and 220 fitted into the holes 234 and 238 of the cylinder head bosses 232 and 236 are formed as pairs of through holes 240 to 246 that communicate with each other by rotating the rocker arms 218 and 220 to an arbitrary phase around the shaft.

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

The two rod members 248, 250 each have a rod-shaped insertion portion 248a, 250a inserted through the pair of insertion holes 240 to 246, and a head portion 248b, 250b provided on the cylinder head boss 232, 236 side ( adjustment hole 214, 216 side) of the insertion portion 248a, 250a and having a larger diameter than the insertion portion 248a, 250 a.

The insertion portions 248a and 250a of the head portions 248b and 250b are formed in a planar shape. The adjustment holes 214 and 216 of the cylinder head bosses 232 and 236 are formed with flat portions 252 and 254, and when the insertion portions 248a and 250a are inserted into the pair of insertion holes 240 to 246, the flat portions 252 and 254 are in surface contact with the flat portions of the head portions 248b and 250 b. In this case, the flat portions 252 and 254 are preferably flat surfaces substantially parallel to the adjustment holes 214 and 216.

Specifically, the rod- like members 248 and 250 are threaded members formed with helical male threads. 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- like members 248 and 250. In this case, the rod- like 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 by making the shapes of the male screw portion and the female screw portion substantially identical. Accordingly, the rotation of the rocker shafts 218, 220 can be easily restricted.

Further, the rod- like members 248, 250 are not limited to threaded members, and any member may be used as long as the rotation of the rocker arms 218, 220 can be restricted. For example, if at least one end (right end) of the rocker shafts 218 and 220 is made of a magnetic material and the rod- like members 248 and 250 are made of permanent magnets, the rotation of the rocker shafts 218 and 220 can be easily restricted by inserting the insertion portions 248a and 250a of the rod- like members 248 and 250 into the pair of insertion holes 240 to 246.

The two rocker arms 222, 224 are supported by the rocker shafts 218, 220 so as to be relatively rotatable. One end of each rocker arm 222, 224 is coupled to the camshaft 134 via a roller 256, 258. The rocker arms 222 and 224 are rocked about the rocker shafts 218 and 220 by a driving force transmitted from the camshaft 134 via the rollers 256 and 258.

In addition, in the internal combustion engine 10, the cylinder head 56 and the piston 72 of the cylinder chamber 74 form a combustion chamber 102. An intake port 104, one end of which communicates with the intake pipe 100b and the other end of which can communicate with the combustion chamber 102, is formed in an upper portion of the cylinder block 54 side in the cylinder head 56. Further, an exhaust port 260 having one end portion communicable with the combustion chamber 102 and the other end portion communicable with an exhaust device, not shown, is formed in a lower portion of the cylinder block 54 side in the cylinder head 56.

In the cylinder head 56, the intake valve 226 opens and closes the combustion chamber 102 by a driving force transmitted from the other end portion of the rocker arm 222 on the intake port 104 side (upper side), thereby supplying air from the intake port 104 to the combustion chamber 102. The exhaust valve 228 opens and closes the combustion chamber 102 by a driving force transmitted from the other end portion of the rocker arm 224 on the side (lower side) of the exhaust port 260, and exhausts gas from the combustion chamber 102 through the exhaust port 260. Further, the spark plug 96 is attached to the spark plug hole 94 in the cylinder head 56 such that the tip end portion faces the combustion chamber 102.

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

As shown in fig. 12 to 14, an opening 266 that opens from the outer peripheral surface of the cylinder head 56 to the fins 84 of the cylinder block 54 is formed on the cylinder block 54 side of the cylinder head 56 (the bottom surface side of the cylinder head 56).

Specifically, an air tank (air socket) 268 is provided inside the cylinder head 56 to communicate the side portion of the spark plug 96 (spark plug hole 94), the side portion of the intake port 104, and the side portion of the exhaust port 260 with the outside. The opening 266 opens from the air tank 268 to the heat sink 84. In this case, the opening portion 266 is formed to be located on the lower side of the cylinder block 54 in the cylinder head 56. The air box 268 is separated from the intake 104 and exhaust 260 by a wall 270.

Accordingly, as shown by arrows in fig. 13 and 14, when the vehicle 12 travels, traveling wind is introduced into the air tank 268 from a portion of the side portion (the plug hole 94) of the ignition plug 96. The introduced traveling wind passes through the side portion of intake port 104 and the side portion of exhaust port 260, and is discharged (guided) rearward through opening 266. Since the fin 84 on the cylinder head 56 side of the cylinder block 54 is provided behind the opening 266, the fin 84 can be appropriately cooled by the traveling wind discharged rearward from the opening 266. Further, a part of the traveling wind passing through the air tank 268 is also discharged downward.

[3. modification ]

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, but may be applied to a multi-cylinder internal combustion engine. Therefore, the present embodiment can be applied to 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 an internal combustion engine in which a plurality of pistons 72 are provided in a plurality of cylinder chambers 74.

In the above description, a case where the plurality of rotary shafts (the crankshaft 68, the first transmission shaft 136, and the second transmission shaft 138) are arranged in the vehicle width direction has been described. In the present embodiment, the present invention can also be applied to the internal combustion engine 10 in which a plurality of rotation shafts are arranged in a direction different from the vehicle width direction (for example, the front-rear direction, the vertical direction). In this case, in the crankcase 52, support holes 142L, 142R for pivotally supporting both end portions of the plurality of rotary shafts are formed in two side walls 140L, 140R that are orthogonal to the different directions and face each other.

In the above description, the rod- like members 248 and 250 may be screw members serving as screw members for fixing the cover members 210 and 212 for closing the adjustment holes 214 and 216. Accordingly, the rotation of the rocker shafts 218 and 220 and the closing of the adjustment holes 214 and 216 can be performed by screwing the insertion portions 248a and 250a of the rod- like members 248 and 250 to the pair of insertion holes 240 to 246.

In the above description, the case where the inside of the crankcase 52 and the cylinder chamber 74 is lubricated with the lubricating liquid is also described. In the present embodiment, the lubricating liquid may be supplied into the cylinder head 56, and the valve train 90 may be lubricated by the supplied lubricating liquid. In this case, the through holes 76, 78 may be used as supply passages of the lubricating liquid, or a supply passage of the lubricating liquid that reaches the cylinder head 56 from the crankcase 52 via the cylinder block 54 may be separately provided. Accordingly, in the cylinder head 56, the lubricating liquid is scattered in the radial direction of the camshaft 134 as the camshaft 134 rotates, and thus each part in the cylinder head 56 can be appropriately lubricated.

[4. effect of the present embodiment ]

Next, the effects of the structure of the present embodiment described above will be described.

< 4.1 Effect of the first Structure >

As a first configuration, the internal combustion engine 10 of the present embodiment is an internal combustion engine 10 (power unit) having a crankshaft 68 (power generating portion) that generates power by rotational motion, and further having a plurality of rotating shafts (the crankshaft 68, the first transmission shaft 136, the second transmission shaft 138) that transmit rotational motion to the rear wheels 36 (driven rotational motion portion), a first power transmission device 144, a second power transmission device 146, and a crankcase 52 (power unit case); the first power transmission device 144 and the second power transmission device 146 transmit power; the crankcase 52 holds a plurality of rotating shafts, a first power transmission device 144, and a second power transmission device 146 inside.

The plurality of rotation shafts are a crankshaft 68 (drive shaft), a first transmission shaft 136 (first driven shaft), and a second transmission shaft 138 (second driven shaft) as power generating portions, wherein the first transmission shaft 136 transmits power from the crankshaft 68 via a first power transmission device 144; the second transmission shaft 138 transmits power from the first transmission shaft 136 via the second power transmission device 146, and transmits the transmitted power to the rear wheels 36.

The crankcase 52 has a lubricating liquid holding portion 174 at a lower portion inside thereof, and the lubricating liquid holding portion 174 holds lubricating liquid for lubricating the cylinder block 54 and the crankcase 52. First wall portion 176 is provided above lubricating fluid retaining portion 174 in crankcase 52 and below first transmission shaft 136 or second transmission shaft 138.

With this configuration, first wall portion 176 is provided between lubricating fluid retaining portion 174 and first transmission shaft 136 or second transmission shaft 138. Accordingly, even if the lubricating fluid held in the lubricating fluid holding portion 174 is shaken when the vehicle 12 is suddenly accelerated or is in slip running, the lubricating fluid can be prevented from being applied to the first transmission shaft 136 or the second transmission shaft 138. As a result, unnecessary application of the lubricating liquid can be avoided, and occurrence of friction or erroneous detection can be prevented.

In this case, if at least a portion 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, even if a large acceleration is generated in the vehicle 12 including the crankcase 52, it is possible to effectively prevent the lubricating liquid from greatly shaking 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 a vehicle 12. The crankcase 52 is a case body that can be divided into a first case body 112L and a second case body 112R in the vehicle width direction (axial direction of the crankshaft 68). The first wall portion 176 is constituted by a first case-side first wall portion 176L and a second case-side first wall portion 176R, wherein the first case-side first wall portion 176L extends in the vehicle width direction from the first case 112L; the second case-side first wall portion 176R extends in the vehicle width direction from the second case 112R. In this way, since the wall portions extend from the two cases, the ease of assembly of the crankcase 52 can be improved.

Further, a first gap 180 is formed between first case-side first wall portion 176L and second case-side first wall portion 176R. By allowing a small amount of lubricant to enter and exit in this way, the lubricant applied to first transmission shaft 136 and second transmission shaft 138 can be efficiently discharged to lubricant retaining portion 174.

A second wall portion 178 is provided above the lubricating liquid holding portion 174 and below the crankshaft 68 in the crankcase 52. Accordingly, even when the vehicle 12 including the internal combustion engine 10 generates a large acceleration, the lubricating liquid can be prevented from greatly shaking and being unnecessarily applied to the crankshaft 68 and the like.

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

The crankcase 52 has a pair of side walls 140L, 140R that face each other at least in the vehicle width direction of the vehicle 12. First wall portion 176 and second wall portion 178 extend in the vehicle width direction from the pair of side walls 140L and 140R, and crankshaft 68, first transmission shaft 136, and second transmission shaft 138 are rotatably supported by support holes 142L and 142R provided in the pair of side walls 140L and 140R, respectively. In this way, 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 walls 140L and 140R, the crankcase 52 can be easily processed.

Second wall portion 178 is constituted by a first case-side second wall portion 178L extending in the vehicle width direction from first case 112L and a second case-side second wall portion 178R extending in the vehicle width direction from second case 112R. This can further improve the assemblability of the crankcase 52.

In this case, a second gap 182 is formed between first case-side second wall portion 178L and second case-side second wall portion 178R. By allowing some lubricant to enter and exit in this way, the lubricant applied to crankshaft 68 can be efficiently discharged to lubricant retaining portion 174.

The first gap 180 and the second gap 182 are each constituted by a narrow gap portion (a first narrow gap portion 180a, a second narrow gap portion 182a) having a narrow width in the front-rear direction of the vehicle 12 and a wide gap portion (a first wide gap portion 180b, a second wide gap portion 182b) having a wide width in the front-rear direction of the vehicle 12. This improves the efficiency of discharging the lubricating liquid from the crankshaft 68, the first transmission shaft 136, and the second transmission shaft 138 to the lubricating liquid retaining portion 174.

In this case, one of the narrow gap portion and the wide gap portion is formed in the front, and the other is formed in the rear. Accordingly, by providing the wide gap portion in the direction in which the vehicle 12 is likely to be accelerated, the discharge efficiency of the lubricating liquid can be further improved. For example, when the vehicle 12 decelerates or brakes, the lubricating fluid moves forward. Therefore, if the wide gap portion is provided at the front, the lubricating liquid can be efficiently discharged to the lubricating liquid holding portion 174.

Further, the internal combustion engine 10 generates a rotational motion by the piston 72 reciprocating in the cylinder chamber 74 (cylinder), and the first transmission shaft 136 and the second transmission shaft 138 transmit power through a plurality of gear trains 166a to 166d capable of selectively transmitting power. Accordingly, the internal combustion engine 10 can be appropriately mounted on the vehicle 12.

<4.2 Effect of the second Structure >

Further, as a second configuration, the present embodiment relates to a valve gear 90 (valve gear) of an internal combustion engine 10, which has a camshaft 134, rocker shafts 218, 220, rocker arms 222, 224, and at least one valve (intake valve 226, exhaust valve 228), wherein the camshaft 134 receives a driving force from a Crankshaft 68 (Crankshaft); rocker arms 222 and 224 are relatively rotatably supported by the rocker shafts 218 and 220, and are rocked about the rocker shafts 218 and 220 by a driving force transmitted from the camshaft 134; at least one valve (intake valve 226, exhaust valve 228) opens and closes the combustion chamber 102 by the driving force transmitted from the rocker arms 222, 224.

The valve train 90 also has cylinder head bosses 232, 236 and rod- like members 248, 250, wherein the cylinder head bosses 232, 236 support the rocker arms 218, 220 on the cylinder head 56 of the internal combustion engine 10. A pair of through-holes 240-246 are formed in the cylinder head bosses 232, 236 and the rocker arms 218, 220, and the pair of through-holes 240-246 communicate with each other by pivoting the rocker arms 218, 220 to an arbitrary phase. The rod- like members 248, 250 are inserted into the pair of insertion holes 240 to 246 to restrict the relative rotation of the rocker shafts 218, 220.

According to this structure, the rod- like members 248, 250 are inserted through a pair of insertion holes 240 to 246 formed in the rocker arms 218, 220 and the head bosses 232, 236, thereby restricting the relative rotation of the rocker arms 218, 220. Accordingly, since the relative rotation of the rocker arms 218 and 220 can be restricted with a simple structure, the component cost and the manufacturing cost can be reduced.

In this case, the camshaft 134, rocker shafts 218, 220, rocker arms 222, 224, intake valve 226, and exhaust valve 228 are an integral structure housed within the cylinder head 56. Adjustment mechanisms (an intake side adjustment mechanism 262 and an exhaust side adjustment mechanism 264) for adjusting the tappet clearance are provided between the intake valve 226 and the exhaust valve 228 and the rocker arms 222 and 224 in the cylinder head 56. Further, the cylinder head 56 is formed with adjustment holes 214, 216 for externally inspecting the intake-side adjustment mechanism 262 and the exhaust-side adjustment mechanism 264. The pair of insertion holes 240 to 246 have a substantially cylindrical shape with a central axis, and the central axes of the insertion holes 240 and 242 on the cylinder head bosses 232 and 236 side face the adjustment holes 214 and 216.

Accordingly, the rod- like members 248 and 250 can be easily inspected through the adjustment holes 214 and 216. As a result, the maintenance and assembly of the valve train 90 including the rotation prevention of the rocker shafts 218 and 220 can be improved.

The center axes of the pair of insertion holes 240 to 246 face the substantial centers of the rocker shafts 218 and 220. That is, the through holes 240 to 246 are formed in the radial direction of the rocker shafts 218 and 220. Thus, the entire length of the insertion holes 240 to 246 can be secured to the maximum. As a result, the effect of the lever members 248 and 250 to stop the rocker shafts 218 and 220 can be further improved.

The rod- like members 248, 250 have rod- like insertion portions 248a, 250a and head portions 248b, 250b, wherein the insertion portions 248a, 250a are inserted through the pair of insertion holes 240-246; the head portions 248b, 250b are provided on the cylinder head bosses 232, 236 side of the through- insertion portions 248a, 250a and have a larger diameter than the through- insertion portions 248a, 250 a. The cylinder head bosses 232, 236 have flat portions 252, 254, and when the through insertion portions 248a, 250a are inserted through the pair of through insertion holes 240-246, the flat portions 252, 254 are in surface contact with the head portions 248b, 250 b. The flat portions 252 and 254 are flat surfaces substantially parallel to the adjustment holes 214 and 216. Accordingly, the flat portions 252 and 254 can be easily formed by machining from a single direction (e.g., the direction of the adjustment holes 214 and 216). As a result, the machining cost and the machining man-hours of the cylinder head 56 can be reduced.

Further, the center axes of the insertion holes 240 and 242 on the cylinder head bosses 232 and 236 side are substantially orthogonal to the adjustment holes 214 and 216. Accordingly, the rod- like members 248, 250 can be more easily inspected through the adjustment holes 214, 216.

Further, a spiral female screw portion is formed on the inner peripheral surface of each of the pair of through holes 240 to 246, and a spiral male screw portion is formed on the outer peripheral surface of the rod- like members 248 and 250. In this case, the shape of the female screw portion substantially matches the shape of the male screw portion. Accordingly, the valve train 90 including the rod- like members 248 and 250 can be easily assembled and disassembled.

<4.3 effects of the third Structure >

Further, as a third configuration, the present embodiment relates to an internal combustion engine 10 having at least one cylinder chamber 74 (cylinder) accommodating at least one reciprocating piston 72, a cylinder head 56, and an ignition plug 96; the cylinder head 56 is mounted on the cylinder block 54 having a cylinder chamber 74, and forms a combustion chamber 102 together with the cylinder chamber 74; the ignition plug 96 is mounted on the cylinder head 56 so as to face the combustion chamber 102.

In this case, the internal combustion engine 10 further includes an ignition coil 88 for generating a voltage necessary for igniting the ignition plug 96, and is mounted on the vehicle 12 in a state of being supported by the body frame 16 of the vehicle 12. The ignition coil 88 is disposed on an 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 disposed at the upper portion of the cylinder block 54, the ignition coil 88 can be disposed close to the ignition plug 96. This makes it possible to shorten the expensive high-voltage wiring 98 as much as possible. Further, the ignition coil 88 and the high-voltage wiring 98 can be prevented from protruding from the internal combustion engine 10 in the vehicle width direction of the vehicle 12. This improves the appearance of the vehicle 12 on which the internal combustion engine 10 is mounted. Further, it is possible to suppress the occurrence of a failure of the ignition coil 88 and a disconnection of the high-voltage wiring 98 due to a side collision, flying stones, or the like while the vehicle 12 is traveling.

In addition, the internal combustion engine 10 also has an intake member 100 connected to the cylinder head 56. The ignition coil 88 is disposed rearward of the cylinder head 56 or the intake member 100 in a side view. By disposing the ignition coil 88 in the vicinity of the intake member 100, which easily protrudes in the vertical direction, the dead space between the vehicle body frame 16 and the internal combustion engine 10 can be effectively utilized.

The intake part 100 includes: a throttle body 100a that controls the intake air amount of the internal combustion engine 10; and an intake pipe 100b connecting the throttle body 100a and an intake port 104 communicating with the combustion chamber 102. The ignition coil 88 is disposed rearward of the throttle body 100a in a side view. Among the components of the intake system, the throttle body 100a in particular is liable to generate a dead zone due to occupying space. Therefore, by disposing the ignition coil 88 behind the throttle body 100a, the dead zone can be effectively utilized. Further, the wiring connected to the throttle body 100a and the wiring connected to the ignition coil 88 can be efficiently collected.

The internal combustion engine 10 also has an electric motor 66 for starting. The ignition coil 88 is disposed forward of the motor 66 in a side view. In the internal combustion engine 10, a starter motor (cell motor) is often the most protruding component on the crankcase 52 side. In particular, in the vehicle 12, a front portion where the distance between the vehicle body frame 16 and the internal combustion engine 10 is extended tends to become a dead space. Therefore, by disposing the ignition coil 88 in front of the motor 66, the dead zone can be utilized more effectively. Further, the wiring of the motor 66 and the wiring of the ignition coil 88 can be efficiently collected.

Further, the internal combustion engine 10 further includes a crankshaft 68 (rotating shaft) and a rotational speed detection portion 70, wherein the crankshaft 68 (rotating shaft) is rotated by the reciprocating motion of the piston 72; the rotation speed detecting portion 70 detects the rotation speed of the crankshaft 68. The ignition coil 88 is disposed forward of the rotation speed detecting unit 70 in a side view.

In the internal combustion engine 10, a pickup such as the rotation speed detection unit 70 is often provided in a front portion of the upper surface of the crankcase 52. As a result, the periphery of the rotation speed detection unit 70 is likely to become a dead zone. Therefore, the dead zone can be effectively utilized by disposing the ignition coil 88 in front of the rotation speed detecting unit 70. Further, the wiring of the rotation speed detection unit 70 and the wiring of the ignition coil 88 can be efficiently integrated.

The internal combustion engine 10 further includes a crankcase 52 housing a plurality of shaft members (a crankshaft 68, a first transmission shaft 136, and a second transmission shaft 138). A coupling boss 58a for coupling with the vehicle body frame 16 is provided at an upper portion of the crankcase 52. The ignition coil 88 is disposed forward of the coupling projection 58a in side view. In the "Cub" type motorcycle vehicle 12, the upper surface of the crankcase 52 is often coupled to the body frame 16. As a result, the periphery of the coupling projection 58a is likely to become a dead space. Therefore, the dead space can be effectively utilized by disposing the ignition coil 88 in front of the coupling projection 58 a.

In this case, the ignition coil 88 is preferably disposed so as to overlap the vehicle body frame 16 in plan view. The ignition coil 88 is likely to be high in temperature, as in the cylinder block 54. Therefore, by adopting the above configuration, it is possible to prevent the member that becomes high in temperature from protruding in the vehicle width direction and to arrange the member so as to be less likely to contact.

The internal combustion engine 10 also has an intake member 100 connected to a combustion chamber 102 and an electric motor 66 for starting. The ignition coil 88 is disposed so as to overlap the intake member 100 and the motor 66 in a front view. Accordingly, the ignition coil 88 can be prevented from protruding in the vertical direction, and the internal combustion engine 10 can be made more space-saving.

In this case, the ignition coil 88 is mounted on the cylinder block 54 via the support member 86. Accordingly, the temperature of the ignition coil 88 can be prevented from becoming high due to the heat from the cylinder block 54.

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

Further, if the vehicle 12 is a straddle-type vehicle, the above-described effects can be easily achieved.

<4.4 effects of the fourth Structure >

As a fourth configuration, the present embodiment relates to an internal combustion engine 10 having at least one cylinder chamber 74 (cylinder), a valve train 90, a cylinder block 54, and a cylinder head 56, wherein at least one reciprocating piston 72 is housed in at least one cylinder chamber 74; the air distribution mechanism 90 controls the ingress and egress of air with respect to the cylinder chamber 74; the cylinder block 54 holds a cylinder chamber 74; the cylinder head 56 is attached to the cylinder block 54 adjacent to the cylinder block 54, and holds the valve train 90.

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

According to this configuration, when the vehicle 12 travels, the traveling wind from the front flows into the cylinder block 54 through the opening 266. Accordingly, by attaching the cylinder head 56 to the cylinder block 54 adjacent to the cylinder block 54, the traveling wind (cooling wind) can be brought into contact with the fins 84 on the side of the cylinder head 56 shielded by the cylinder head 56. As a result, the cooling effect of the fins 84 on the cylinder chamber 74 (cylinder head 56) can be improved with a simple configuration.

The internal combustion engine 10 also has an ignition plug 96, and the ignition plug 96 is mounted to the cylinder head 56 so as to face a combustion chamber 102 formed by the cylinder chamber 74 and the cylinder head 56. An intake port 104 for supplying air from the outside to the combustion chamber 102, an exhaust port 260, and an air tank 268 are provided in the cylinder head 56; an exhaust port 260 for exhausting gas from the combustion chamber 102 to the outside; the air tank 268 communicates the side of the spark plug 96, the side of the intake port 104, and the side of the exhaust port 260 with the outside. The opening 266 opens from the air tank 268 to the heat sink 84. Since the opening 266 is provided at the position where the traveling wind flows in this way, the wind guiding efficiency from the cylinder head 56 side to the fins 84 of the cylinder block 54 is improved.

The internal combustion engine 10 also has a crankshaft 68 and a crankcase 52, wherein the crankshaft 68 converts reciprocating motion of the piston 72 into rotational motion; the crankcase 52 houses a crankshaft 68. The internal combustion engine 10 is mounted on the vehicle 12, and the cylinder block 54 protrudes upward or forward from the front portion of the crankcase 52. The axis of the cylinder chamber 74 (cylinder block 54) is oriented forward, being inclined upward with respect to the horizontal. Accordingly, the traveling wind can be directed to the outer peripheral surface of the cylinder head 56 and guided to the fins 84 of the cylinder block 54 through the opening 266. As a result, the air guiding efficiency can be further improved.

Further, an opening 266 is formed in the front-rear direction in the cylinder head 56. By providing the opening 266 in the same direction as the flowing direction of the traveling wind, the amount of wind guided to the opening 266 can be increased. As a result, the traveling wind can be easily blown to the fins 84 on the cylinder head 56 side of the cylinder block 54, which are disposed behind the cylinder head 56 and thus are less likely to be blown by the traveling wind.

The opening 266 is formed in the cylinder head 56 so as to be located on the lower side of the cylinder block 54. Accordingly, negative pressure is generated between the lower surface side of the cylinder block 54 facing the opening 266 and the ground, and more traveling wind from the front can be introduced through the opening 266.

<4.5 Effect of the fifth configuration >

In addition, as a fifth configuration, the present embodiment relates to an internal combustion engine 10 having at least one cylinder chamber 74 and a crankshaft 68, wherein the at least one cylinder chamber 74 houses at least one piston 72 that reciprocates; the crankshaft 68 converts reciprocating motion into rotary motion.

The internal combustion engine 10 further has a crankcase 52, a cylinder liner 116, a cylinder block 54, a valve train 90, a power transmission mechanism 132, a power transmission mechanism accommodating chamber 130, and a gasket 194, wherein the crankcase 52 accommodates the crankshaft 68; cylinder liner 116 forms cylinder chamber 74; the cylinder block 54 covers the cylinder liner 116; the valve train 90 controls the ingress and egress of air with respect to the cylinder chamber 74 by actuating the intake and exhaust valves 226, 228 (valves) in response to rotational motion; the power transmission mechanism 132 transmits the power of the rotational motion from the crankshaft 68 to the valve gear 90; a power transmission mechanism housing chamber 130 formed in the cylinder block 54 and housing a power transmission mechanism 132; the gasket 194 is sandwiched 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 housing chamber 130 when viewed in the axial direction of the cylinder chamber 74. At least a part of the annular portion 194a of the gasket 194 surrounding the cylinder chamber 74 forms a recess 194b distant from the cylinder chamber 74 with respect to the other part of the annular portion 194 a. The recess 194b is provided on the power transmission mechanism accommodating chamber 130 side.

With this configuration, the recess 194b of the spacer 194 is provided from the cylinder chamber 74 toward the power transmission mechanism housing chamber 130. Accordingly, the cylinder chamber 74 and the power transmission mechanism housing chamber 130 communicate between the cylinder block 54 and the crankcase 52 via the gap portion formed by the recess 194 b. As a result, even if the cylinder liner 116 thermally expands, the stress (strain) of the gasket 194 is suppressed, and the strain of the cylinder chamber 74 can be reduced. Further, by providing the recess 194b of the spacer 194 on the power transmission mechanism housing chamber 130 side, the rigidity of the spacer 194 is reduced, and the effect of suppressing the strain of the cylinder chamber 74 is further improved.

Here, a plurality of chambers including at least one cylinder chamber 74 and the power transmission mechanism housing chamber 130 are provided in the cylinder block 54 via a wall 196 (wall portion). The gasket 194 is provided with a communicating portion 194c, the communicating portion 194c communicating at least two of the adjacent chambers in the cylinder block 54, and the communicating portion 194c forming a recessed portion 194 b. This facilitates processing of the spacer 194.

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

The connecting portion (connecting portion 200) between the annular portion 194a and the recessed portion 194b is formed in a curved shape. Accordingly, the stress applied to the spacer 194 can be efficiently released.

If the spacer 194 is a non-metal member, the spacer 194 can be more easily processed.

The present invention has been described above with reference to preferred embodiments, but the technical scope of the present invention is not limited to the description of the above embodiments. It is apparent to those skilled in the art that various alterations and modifications can be added to the above embodiments. As is clear from the description of the claims, the embodiments to which such changes and improvements are added can be included in the technical scope of the present invention. In the claims, the numerals in parentheses are added to the numerals in the drawings for easy understanding of the present invention, and the present invention is not to be construed as being limited to the elements denoted by the numerals.