WO2009122825A1

WO2009122825A1 - Internal combustion engine for small-sized vehicle

Info

Publication number: WO2009122825A1
Application number: PCT/JP2009/053418
Authority: WO
Inventors: 直樹河野; 文則水谷
Original assignee: 本田技研工業株式会社
Priority date: 2008-03-31
Filing date: 2009-02-25
Publication date: 2009-10-08
Also published as: CN101981291B; PE20100342A1; BRPI0909473A2; AR070536A1; JP2009243421A; CN101981291A; JP4994285B2; BRPI0909473B1

Abstract

An internal combustion engine for a small-sized vehicle, in which a tension sprocket at one end of a tensioner arm is engaged with a cam chain of a timing and power transmitting mechanism mounted between a crankshaft and a camshaft and in which a gear transmission mechanism having a main shaft and a countershaft which are parallel to the crankshaft is housed in a crankcase. When viewed in the direction of the axis of the crankshaft (53), the countershaft (72) is located rearward of the crankshaft (53), the axis of the main shaft (71) is located at a position which is between the crankshaft (53) and the countershaft (72) and above a line interconnecting the crankshaft (53) and the countershaft (72), and a support shaft (96) for pivotably supporting the tensioner arm (95) is located between the axes of the crankshaft (53) and the main shaft (71). The construction reduces the length in the front-rear direction of the internal combustion engine.

Description

Internal combustion engine for small vehicles

According to the present invention, there is provided a crankshaft having an axis extending in the width direction of a vehicle body frame and rotatably supported on a crankcase, and a cam having an axis parallel to the crankshaft and rotatably supported on a cylinder head. A timing transmission mechanism having a shaft, an endless cam chain and provided between the crankshaft and the camshaft, and a tension sprocket engaged with the cam chain in a direction to tension the cam chain are provided at one end. A tensioner arm rotatably supported by the crankcase, a guide cylinder fixed to the crankcase, and slidably supported by the guide cylinder and abutted against the other end of the tensioner arm Lock cam chain lifter with push rod, and parallel to the crankshaft A main shaft and a counter shaft about a small vehicle internal combustion engine and a gear transmission mechanism housed within the crankcase.

The contact part between the push rod of the oil lock cam chain lifter and the tensioner arm is disposed rearward of the crankshaft in a side view, and further rearward than the contact part, the main shaft and counter of the gear transmission mechanism An internal combustion engine for a motorcycle in which a shaft is arranged is known from Patent Document 1.
Japanese Patent Application Laid-Open No. 2002-309960

In the case disclosed in the above-mentioned Patent Document 1, the tip end of the tensioner arm is often disposed between the crankshaft and the main shaft, and the crankshaft and the main shaft are disposed apart to secure the swing allowance. As a result, the distance from the crankshaft to the countershaft is increased, and as a result, the longitudinal length of the internal combustion engine is relatively large.

The present invention has been made in view of such circumstances, and an object of the present invention is to provide an internal combustion engine for a small vehicle in which the length in the front-rear direction can be shortened.

In order to achieve the above object, the present invention provides a crankshaft rotatably supported on a crankcase with an axis extending in the width direction of a vehicle body frame, and a cylinder head having an axis parallel to the crankshaft. And a timing transmission mechanism provided between the crankshaft and the camshaft with an endless cam chain and meshed with the cam chain in a direction to tension the cam chain Tensioner arm having a tension sprocket at one end and rotatably supported by the crankcase, a guide cylinder fixed to the crankcase and slidably supported by the guide cylinder and the tensioner arm Lock-type cam chain lifter having a push rod abutted to the other end of the An internal combustion engine for a small vehicle having a main shaft and a countershaft parallel to the crankshaft and having a gear shift mechanism accommodated in the crankcase, wherein the internal combustion engine is viewed from the axial direction of the crankshaft more than the crankshaft; The countershaft is disposed rearward, the axis of the main shaft is disposed between the crankshaft and the countershaft above the straight line connecting the axes of the crankshaft and the countershaft, and the tensioner arm is rotated. According to a first feature of the present invention, a support shaft rotatably supported is disposed between the axes of the crankshaft and the main shaft.

Further, according to the present invention, in addition to the first feature, a cylinder block having a cylinder bore for slidably fitting a piston to be connected to the crank shaft is configured to rise upward from the crank case. The second feature is that it is coupled to the top.

Further, in the present invention, in addition to the first or second feature, an engine hanger boss supported by an engine hanger of a vehicle body frame is provided at a lower front portion of the crankcase, and the guide cylinder has a lower end portion thereof. According to a third feature of the present invention, it is fixed to the crankcase at a position close to the engine hanger boss.

The second engine hanger boss 45 of the embodiment corresponds to the engine hanger boss of the present invention, and the bolt 96 of the embodiment corresponds to the support shaft of the present invention.

According to the first aspect of the present invention, the countershaft is disposed rearward of the crankshaft as viewed in the axial direction of the crankshaft, and the main shaft is between the crankshaft and the countershaft, the crankshaft and the countershaft The crankshaft, the main shaft, and the countershaft are arranged on a triangle with the axis of the mainshaft at the top, since the crankshaft, the mainshaft, and the countershaft are arranged above the straight line connecting the axes of the Can be shortened. In addition, since the support shaft for rotatably supporting the tensioner arm is disposed between the axes of the crankshaft and the main shaft, a portion that requires less area for swinging the tensioner arm can be the crankshaft and the main shaft. As a result, the distance between the crankshaft and the main shaft can be shortened, and the length between front and rear of the internal combustion engine can be reduced in combination with the fact that the distance between the crankshaft and the countershaft can be shortened.

Further, according to the second aspect of the present invention, since the cylinder block is coupled to the upper portion of the crankcase so as to rise upward from the crankcase, the longitudinal length of the internal combustion engine can be further reduced.

Furthermore, according to the third feature of the present invention, the guide cylinder of the oil lock cam chain lifter is fixed to the crankcase at a position close to the engine hanger boss provided on the lower front side of the crankcase. By arranging the cam chain lifter using the overhang of the engine hanger boss from the crankcase, the internal combustion engine can be made compact by the arrangement that effectively utilizes the dead space.

FIG. 1 is a left side view of a motorcycle. (First embodiment) FIG. 2 is a longitudinal sectional view of an essential part of the internal combustion engine, which is a sectional view taken along line 2-2 of FIG. (First embodiment) FIG. 3 is a sectional view taken along line 3--3 of FIG. (First embodiment) FIG. 4 is a cross-sectional view taken along line 4-4 of FIG. (First embodiment) FIG. 5 is a cross-sectional view taken along line 5-5 of FIG. (First embodiment) FIG. 6 is a vertical sectional side view of the crankcase and the cylinder block as viewed from the right, and is a sectional view taken along line 6-6 in FIG. (First embodiment) 7 is a cross-sectional view taken along line 7-7 of FIG. (First embodiment)

Explanation of sign

17 ... engine hanger 22 ... crank case 24 ... cylinder head 45 ... second engine hanger boss 53 ... crankshaft 54 ... cylinder bore 55 ... piston 70 ... gear shift mechanism 71 · · · Main shaft 72 · · · Counter shaft 85 · · · Cam shaft 86 · · · Time adjustment transmission mechanism 89 · · · Cam chain 94 · · · · · · · · · · · · · · · Tension sprocket 95 · · · Tensioner arm 96 · · · Bolt 97 which is the cam chain lifter 98 guide tube 99 push rod F body frame

Hereinafter, an embodiment of the present invention will be described based on one embodiment of the present invention shown in the attached drawings.

1 to 7 show an embodiment of the present invention.

First, in FIG. 1, a body frame F of a motorcycle, which is a small-sized vehicle, has a head pipe 13 for supporting the front fork 11 and the steering handle 12 pivotally supported by the front wheel WF. Of the left and right main frames 14 extending to the right, pivot plates 15 connected to the rear ends of the main frames 14 connected to the head pipe 13 below the main frames 14. And a pair of left and right down frames 16 extending backward at a steeper angle than main frames 14, engine hangers 17 provided at lower ends of the down frames 16, and a rear portion of the main frames 14 Seat pipes 19 extending upward and downward, the pivot plates 15 and the sheet pipes 1 ... comprises a rear frame 20 ... and connecting between.

The engine main body 21 of the internal combustion engine E is mounted on the engine hangers 17 and the pivot plates 15. The engine main body 21 is coupled to a crankcase 22 and a front upper portion of the crankcase 22. A cylinder block 23 rising upward and a cylinder head 24 coupled to an upper end of the cylinder block 23 are provided.

A fuel tank 27 is mounted on the main frames 14 above the engine body 21. A passenger seat 28 disposed behind the fuel tank 27 is supported by the seat pipes 19. The upstream end of an intake pipe 29 whose downstream end is connected to the rear side surface of the cylinder head 24 in the engine body 21 is connected to a carburetor 30, and the carburetor 30 is disposed below the front of the passenger seat 28 31 connected to the air cleaner. Furthermore, an exhaust pipe 32 connected to the front side surface of the cylinder head 24 extends rearward through the lower part of the engine body 21 and is connected to an exhaust muffler 33 disposed on the right side of the rear wheel WR.

A front end portion of a swing arm 34 pivotally supporting the rear wheel WR at a rear end portion is pivotally supported by the pivot plates 15 through the shaft 35, and the seat pipe 19 and the rear in the vehicle body frame F A rear cushion 36 is provided telescopically between the connection portion of the frame 20 and the rear end of the swing arm 34. Further, the rotational power output from the internal combustion engine E is transmitted to the rear wheel WR by a transmission means 38 having an endless chain 37.

2 to 4, in the crankcase 22, a first case member 41 disposed on the right side in the traveling direction of the motorcycle and a second case member 42 disposed on the left side in the traveling direction of the motorcycle are coupled. The first and

second case members

41 and 42 are molded by casting, and the die removal direction 40 of the case members 41 and 42 (the left and right direction in FIGS. 2 and 4 The first and

second case members

41 and 42 are coupled to each other at a mating surface 43 orthogonal to the

In such a crankcase 22, a first engine hanger boss 44 for fastening with a bolt 48 to an upper portion of the engine hanger 17 projects forward on the front upper portion of the first and

second case members

41 and 42. Thus, a second engine hanger boss 45, which is integrally provided and is fastened to the lower part of the first and

second case members

41 and 42 with a bolt 49 at the lower part of the engine hanger 17, projects forward. In this manner, a third engine hanger boss 46 for fastening with a bolt 50 to the upper portion of the pivot plate 15... Is provided at the rear upper portion of the first and

second case members

41 and 42 integrally provided. It is integrally provided in a protruding manner, and bolts 51 are provided at lower portions of the pivot plates 15 at the lower rear sides of the first and

second case members

41, 42. Fourth engine hanger boss 47 for being fastened is provided integrally.

A crankshaft 53 having an axis orthogonal to the mating surface 43 is rotatably supported on the crankcase 22, and a piston 55 slidably fitted in a cylinder bore 54 provided in the cylinder block 23 is connected. It is connected to the crankshaft 53 via a rod 56 and a crank pin 57.

A generator cover 59 forming a generator chamber 58 between the second case member 42 and the second case member 42 in the crankcase 22 is coupled to the end portion of the crankshaft 53 in the generator chamber 58. A generator 62 is configured by the fixed outer rotor 60 and the stator 61 fixed to the generator cover 59 so as to be disposed in the outer rotor 60.

Moreover, a gear 64 having a one-way clutch 63 interposed between the generator 62 and the outer rotor 60 is supported by the crankshaft 53 in the generator chamber 58 so as to be relatively rotatable. The starting power is transmitted from the starting motor 65 attached to the second case member 42, and the one-way clutch 63 transmits the power from the starting motor 65 to the outer rotor 60, that is, the crankshaft 53 side. The rotational power from the crankshaft 53 side is not transmitted to the starting motor 65 side.

A clutch cover 67 forming a clutch chamber 66 between the first case member 41 and the first case member 41 in the crankcase 22 is coupled, and a drive gear 68 is connected to the crankshaft 53 in the clutch chamber 66. The key is coupled and fixed together with the flywheel 69.

The crankcase 22 accommodates a normally meshed gear transmission mechanism 70 for shifting power from the crankshaft 53 in a plurality of steps. The gear transmission mechanism 70 has an axis parallel to the crankshaft 53. Between the main shaft 71 and the counter shaft 72 rotatably coupled to the crankcase 22 and having, for example, a first gear train G1, a second gear train G2, a third gear train G3 and a third gear train G3. A gear train G4 for fourth gear is provided to be able to be established alternatively.

A drive sprocket 73 constituting a part of the transmission means 38 is fixed to the projecting portion of the counter shaft 72 from the second case member 42 of the crankcase 22, and the chain 37 is wound around the drive sprocket 73. It is hung.

Moreover, as clearly shown in FIG. 3, the counter shaft 72 is disposed rearward of the crankshaft 53 as viewed in the axial direction of the crankshaft 53, between the crankshaft 53 and the counter shaft 72, and the axis of the crankshaft 53. The axis C2 of the main shaft 71 is disposed above the straight line L connecting the axis C3 of the countershaft 72 with C1.

Between the crankshaft 53 and the main shaft 71, a primary reduction gear 74 disposed within the clutch chamber 66, a damper rubber 75 and a start clutch 76 are interposed, and the start clutch 76 is disposed on the main shaft 71. A clutch outer 77 rotatably supported relatively, a plurality of drive friction plates 78 engaged with the clutch outer 77, a clutch inner 79 non-rotatably coupled to the main shaft 71, and the drive This is a conventional multi-plate clutch having a plurality of driven friction plates 80... Engaged with the clutch inner 79 so as to alternately overlap the friction plates 78. A coil spring may be used instead of the damper rubber 75.

The primary reduction gear 74 includes the drive gear 68 and a driven gear 81 which is rotatably supported by the main shaft 71 in mesh with the drive gear 68, and the driven gear 81 is interposed with a damper rubber 75. The clutch outer 77 is connected.

Focusing on FIG. 2, an ignition plug 83 is attached to the cylinder head 24 so that the top of the piston 55 faces the combustion chamber 82 formed between the cylinder block 23 and the cylinder head 24. . In the cylinder head 24, a cam constituting a part of a valve gear 84 for opening and closing an intake valve (not shown) and an exhaust valve (not shown) disposed so as to be able to open and close the cylinder head 24. A shaft 85 is rotatably supported, and the camshaft 85 has an axis parallel to the crankshaft 53.

Between the crankshaft 53 and the camshaft 85, there is provided a timing transmission mechanism 86 for transmitting rotational power of the crankshaft 53 while decelerating it by half, and this timing transmission mechanism 86 is provided in the generator chamber 58 includes a drive sprocket 87 fixed to the crankshaft 53 in 58, a driven sprocket 88 provided on the camshaft 85, and an endless cam chain 89 wound around the drive sprocket 87 and the driven sprocket 88, A cam chain passage 90 for causing the cam chain 89 to travel is formed in the cylinder block 23 and the cylinder head 24 so as to communicate with the generator chamber 58. An idle sprocket 91 is rotatably supported on the cylinder block 23 between the drive sprocket 87 and the driven sprocket 88 so as to mesh with the cam chains 89 on both sides.

On the second case member 42 of the crankcase 22, a tensioner arm 95 having a tension sprocket 94 at one end which meshes with the cam chain 89 in a direction to tension the cam chain 89 is rotatably supported. The tensioner arm 95 is disposed diagonally above the rear of the crankshaft 53 such that the cam chain 89 is pressed from above by the tension sprocket 94. A bolt 96, which is a support shaft for pivotally supporting the tensioner arm 95, is screwed to the second case member 42. This bolt 96 is an axis of the crankshaft 53 as clearly shown in FIG. It is disposed between the axis C1 of the crankshaft 53 and the axis C2 of the main shaft 71 when viewed from the direction.

The tensioner arm 95 is urged by an oil lock type cam chain lifter 97 in a direction to press the tension sprocket 94 against the cam chain 89. The cam chain lifter 97 is a second case of the crankcase 22. It has a guide cylinder 98 fixed to the member 42, and a push rod 99 slidably supported by the guide cylinder 98 and in contact with the other end of the tensioner arm 95.

Of the second engine hanger bosses 45 provided on the lower front side of the crankcase 22, the guide cylinder 98 raises its rear end while bringing its lower end close to the second engine hanger boss 45 provided on the second case member 42 of the second engine hanger bosses. The sealing bolt 100 is screwed to the lower end portion of the guide cylinder 98. As shown in FIG.

A push rod 99 is slidably fitted in the guide cylinder 98 so that the rod head 101 provided at the upper end is brought into contact with the other end of the tensioner arm 95. Further, a communication hole 102 is provided in the upper portion of the push rod 99, and an oil pressure chamber 103 is formed in the guide cylinder 98 between the push rod 99 and the sealing bolt 100.

A cap-shaped ball seat 125 having a valve hole 104 is fixed to the lower end of the push rod 99, and the ball seat 125 and the ball 126 housed in the ball seat 125 so as to close the valve hole 104. And a spring 127 provided between the sealing bolt 100 and the ball 126 so as to bias the ball 126 to the side closing the valve hole 104, the oil entering the push rod 99 from the communication hole 102 is hydraulically operated. A check valve 128 for introducing into the chamber 103 side is configured.

6 and 7, the oil pump 105 is attached to the first case member 41 of the crankcase 22 so as to be accommodated in the clutch chamber 66. The pump housing 106 of the oil pump 105 It consists of a plate-like housing main body 107 opened to the first case member 41 side, and a cover plate 108 for closing the open end of the housing main body 107, and is on the side opposite to the mating surface 43 of the first case member 41. It is concluded.

A pump shaft 109 of the oil pump 105 is rotatably supported by the pump housing 106, and an inner rotor 110 fixed to the pump shaft 109 in the pump housing 106 and an outer meshed with the inner rotor 110 are provided. The rotor 111 is accommodated.

A driven gear 112 is fixed to an end of the pump shaft 109 protruding from the pump housing 106, and the driven gear 112 is engaged with a drive gear 68 fixed to the crankshaft 53. Thus, the gear train 113 configured by the drive gear 68 and the driven gear 112 is disposed outside the pump housing 106 and inside the clutch cover 67.

Oil is drawn into the oil pump 105 from the lower portion in the crankcase 22 and the lower portion of the clutch chamber 66 via an oil strainer 114 disposed in the lower portion of the first case member 41.

A suction passage 115 communicating with the oil strainer 114 is formed at a lower portion between the housing main body 107 and the cover plate 108, and a discharge path 116 is formed between an upper portion between the housing main body 107 and the cover plate 108.

By the way, an oil passage 117 is formed in the upper portion on the cylinder block 23 side among the coupling surfaces of the clutch cover 67 and the first case member 41, and the discharge passage 116 and the oil passage 117 are formed in the crankcase 22. It communicates by way of the communication passage 118.

The first case member 41 includes first and second communication holes 119 and 120 extending in the mold removal direction 40 so as to allow the discharge passage 116 and the oil passage 117 to communicate with one end, and first and second communication holes. The second case member 42 is provided with a common communication hole 121 extending in the mold removal direction 40 and communicating with the other end of each of the other ends 119 and 120 while extending in the mold removal direction 40. The communication passage 118 is formed by the first communication hole 119, the second communication hole 120, and the common communication hole 121, and the other end side opening of the common communication hole 121 is formed at the time of coupling with the first case member 41. A closing part 122 is provided which closes the part.

The first and second communication holes 119 and 120 are formed by die-cut to the side of the mating surface 43 in the same manner as the common communication hole 121, and the closed portion 122 is flush with the mating surface 43. The other end side opening portion of the common communication hole 121 is closed by being in contact with the first case member 41. The first case member 41 is provided with a first engine hanger boss 44 fastened to an engine hanger 17 provided on the vehicle body frame F, but the communication passage 118 is in the vicinity of the first engine hanger boss 44 Be placed.

An oil passage 117 formed between the clutch cover 67 and the first case member 41 is connected via an orifice 124 to an oil passage 123 provided in the cylinder block 23 to guide the oil to the valve gear 84 side. An oil passage 125 for guiding the oil to the transmission mechanism 70 side is provided in the first case member 41.

Further, as shown in FIG. 2, the clutch cover 67 is formed with an oil passage 127 communicating with the oil passage 117, and the oil passage 127 is provided in an oil passage 128 coaxially provided in the crankshaft 53, It is connected via a centrifugal filter 126 formed in the flywheel 69.

Next, the operation of this embodiment will be described. The countershaft 72 is disposed rearward of the crankshaft 53 as viewed in the axial direction of the crankshaft 53, and the main shaft 71 is between the crankshaft 53 and the countershaft 72. Is disposed above the straight line L connecting the axes C1 and C3 of the crankshaft 53 and the countershaft 72, the axes C1, C2 and C3 of the crankshaft 53, the main shaft 71 and the countershaft 72 It will be arrange | positioned on the triangle which made the axis line C2 the vertex, and between the crankshaft 53 and the countershaft 72 can be shortened. Further, since the bolt 96 for pivotally supporting the tensioner arm 95 is disposed between the crankshafts 53 and the axes C1 and C2 of the main shaft 71, the area required for swinging the tensioner arm 95 can be reduced. The part is to be disposed between the crankshaft 53 and the main shaft 71, the distance between the crankshaft 53 and the main shaft 71 can be shortened, and the distance between the crankshaft 53 and the countershaft 72 can be shortened. The front and back length of the engine E can be reduced.

Further, since the cylinder block 23 is coupled to the upper portion of the crankcase 22 so as to rise upward from the crankcase 22, the longitudinal length of the internal combustion engine E can be further reduced.

Further, the guide cylinder 98 of the oil lock cam chain lifter 97 is fixed to the crankcase 22 at a position close to the second engine hanger boss 45 provided on the lower front side of the crankcase 22. By arranging the cam chain lifter 97 utilizing the protrusion of the boss 45 from the crankcase 22, the internal combustion engine E can be made compact by the arrangement that effectively utilizes the dead space.

Further, a discharge passage 116 is formed between the cover main body 108 and the cover plate 108 which is in contact with the first case member 41 and fastened to the first case member 41, and between the first case member 41 and the clutch cover 67. An oil passage 117 is formed, and the first and second communication holes 119 and 120 extending in the demolding direction so as to cause the discharge passage 116 and the oil passage 117 to communicate with one end, and the first and second communication holes 119 and 120 The first case member 41 is provided with a common communication hole 121 extending in the mold removal direction by bringing one end into common communication with the other end portion of the first case member 41 and the common communication hole 121 The communication passage 118 communicating between the discharge passage 116 and the oil passage 117 is closed by closing the other end side opening, and the first communication hole 119, the second communication hole 120 and the front Since it is formed by the common communication hole 121, the discharge passage 116 and the oil passage 117 correspond to the complication of the oil passage, thereby avoiding the enlargement of the cover and the complication of the shape of the cover to lay out the oil passage. Can increase the degree of freedom.

Moreover, the communication passage 118 can be formed by molding of the first and

second case members

41 and 42, and the communication passage 118 can be formed with a simple structure that does not require machining. In addition, a closing member such as a sealing plug for closing the opening at the other end of the common communication hole 121 is unnecessary, so that an increase in the number of parts can be avoided and processing costs can be reduced.

Further, since the housing main body 107, which is a part of the pump housing 106 of the oil pump 105, is covered by the clutch cover 67, the pump housing 106 can be protected by the clutch cover 67 and the appearance can be enhanced.

Further, since the gear train 113 for driving the oil pump 105 is disposed in the clutch cover 67, the gear train 113 can be protected from dust and dirt.

In addition, the communication passage 118 is disposed in the vicinity of the first engine hanger boss 44 projecting laterally from the crankcase 22. Therefore, the crankcase 22 does not become large due to the formation of the communication passage 118.

In addition, since the first and second communication holes 119 and 120 are formed by die-cut to the same mating surface 43 side as the common communication hole 121, the parting line can be disposed on the opposite side to the mating surface 43, In the first case member 41, burrs can be removed when machining the seal portion between the pump housing 106 and the clutch cover 67.

Furthermore, since the closed portion 122 of the second case member 42 abuts on the first case member 41 on the same plane as the mating surface 43, it is possible to contribute to shortening of the number of machining steps when machining the second case member 42.

As mentioned above, although the Example of this invention was described, this invention is not limited to the said Example, It is possible to perform various design changes, without deviating from the summary.

Claims

A crankshaft (53) rotatably supported on the crankcase (22) with an axis extending in the width direction of the vehicle body frame (F), and a cylinder head having an axis parallel to the crankshaft (53) (24) A timing transmission mechanism provided between the crankshaft (53) and the camshaft (85), having a camshaft (85) rotatably supported on the (24), and an endless cam chain (89) (86) and a tension sprocket (94) meshing with the cam chain (89) in a direction to tension the cam chain (89) at one end and supported rotatably by the crankcase (22) Supported by the tensioner arm (95), the guide cylinder (98) fixed to the crankcase (22), and the guide cylinder (98). Also, an oil lock type cam chain lifter (97) having a push rod (99) abutted to the other end of the tensioner arm (95), and a main shaft (71) parallel to the crankshaft (53) And a countershaft (72) having a gear shift mechanism (70) housed in the crankcase (22), as viewed from the axial direction of the crankshaft (53). The countershaft (72) is disposed rearward of the crankshaft (53), and between the crankshaft (53) and the countershaft (72), the crankshaft (53) and the countershaft (72). The axis of the main shaft (71) is disposed above the straight line connecting the axes, and the tension Support shaft for supporting the arm (95) rotatably (96) is small vehicle internal combustion engine, characterized in that disposed between the axis of the crankshaft (53) and said main shaft (71).
A cylinder block (23) having a cylinder bore (54) slidably fitted with a piston (55) to be connected to the crankshaft (53) stands up from the crankcase (22) and the crankcase The internal combustion engine for a small vehicle according to claim 1, wherein the internal combustion engine is coupled to an upper portion of (22).
An engine hanger boss (45) supported by an engine hanger (17) of a vehicle body frame (F) is provided at a lower front portion of the crankcase (22), and a lower end portion of the guide cylinder (98) is the engine The internal combustion engine for a small vehicle according to claim 1 or 2, wherein the internal combustion engine is fixed to the crankcase (22) at a position close to a hanger boss (45).