JP2003193854A - Internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an internal combustion engine provided with a crankshaft, a main shaft of a transmission holding a transmission gear train, a clutch arranged on an extension line of the main shaft, and a countershaft of the transmission holding a gear train meshing with the transmission gear train to transmit power to the crankshaft, the clutch, the main shaft, and the counter shaft in this order and capable of reducing a width of the internal combustion engine and shortening a length in the axial direction to improve the knee grip property when loaded on a vehicle and enhance the loading property on the vehicle. <P>SOLUTION: The main shaft is arranged substantially just below the crankshaft, and at least a part of the main shaft is provided at a position in the axial direction equal to the crankshaft. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an internal combustion engine suitable as a vehicle power unit.

[0002]

2. Description of the Related Art Japanese Patent No. 2858017 shows a conventional internal combustion engine used in a motorcycle. In a conventional internal combustion engine, the crankshaft center line is arranged in the center plane of the vehicle body in the front-rear direction, the clutch and the transmission are arranged on one of the left and right sides of the lower side of the crank shaft, and the starting motor and the power generator are arranged on the other side. Auxiliary machine drive system including machines is arranged. Further, the main shaft and the counter shaft of the transmission equipped with the gear group for speed change are parallel to the crank shaft, but the axial position is arranged rearward of the crank shaft, and the mission case that houses them is
It is connected to the rear of the crankcase.

[0003]

In the conventional internal combustion engine,
Since the large-diameter clutch is arranged on either the left or right side of the center surface of the vehicle body and the generator is arranged on the other side, the width of the internal combustion engine becomes large and the knee grip performance is deteriorated. Further, since a transmission case for accommodating the transmission is provided behind the crankcase, the length of the internal combustion engine in the front-rear direction is large, and the mountability on the vehicle is not good.

The present invention is intended to reduce the width of an internal combustion engine and shorten the axial length thereof to improve the knee grip when mounted on a vehicle and to enhance the mountability on the vehicle. Furthermore, other improvements will be made to improve assembly workability and the like.

[0005]

SUMMARY OF THE INVENTION The present invention is to solve the above-mentioned problems, and the invention according to claim 1 is to provide a crankshaft, a main shaft of a transmission for holding a transmission gear train, and a main shaft. A clutch arranged on an extension line of the transmission, and a counter shaft of a transmission that holds a gear train that meshes with the transmission gear train, a crank shaft, a clutch, a main shaft,
In the internal combustion engine in which power is transmitted in the order of the counter shaft, the main shaft is arranged substantially directly below the crank shaft.

In this structure, the main shaft is arranged substantially directly below the crank shaft, and the clutch having a large outer diameter is connected to the front extension line of the main shaft. That is, when viewed from the crankshaft direction, since it is located at the center in the left-right direction, the width of the internal combustion engine in the left-right direction can be reduced.

According to a second aspect of the invention, in the internal combustion engine according to the first aspect, at least a part of the main shaft is provided at an axial position equivalent to that of the crankshaft. That is, the main shaft and the crank shaft are in a position where they overlap each other when viewed from a position on the side of the shaft. Therefore, the axial length of the internal combustion engine can be shortened as compared with the internal combustion engine described in Japanese Patent No. 2858017. Further, there is an effect that the oil dropped by lubricating the piston and the crank can be used for lubricating the gear group of the main shaft.

According to a third aspect of the present invention, in the internal combustion engine according to the first or second aspect, the crank chamber is constituted by upper and lower case members, and the crankshaft is held between the upper and lower case members, The main shaft is mounted on the lower case member, and at least one of the crank bearing and the main bearing is provided so as to be displaced from each other so as to be at different axial positions. With such a configuration, the length of the bolt for tightening the crankshaft bearing portion can be shortened, and the workability can be improved.

According to a fourth aspect of the present invention, in the internal combustion engine according to the first to third aspects, the crankshaft is mounted on the motorcycle with the front-rear direction of the vehicle. . With such a mounting positional relationship between the vehicle and the internal combustion engine, the front projected area of the vehicle can be reduced and the knee grip can be easily performed. Furthermore, since the length of the internal combustion engine in the front-rear direction is short, the mountability on the vehicle is improved.

The invention according to claim 5 is characterized in that the internal combustion engine according to claim 4 is a V-type internal combustion engine. As a result, the vertical height of the central portion of the internal combustion engine can be reduced, and the mountability on the vehicle is improved.

[0011]

1 is a side view of a motorcycle 1 equipped with an internal combustion engine of the present invention. A front fork 2 is rotatably supported on a front portion of a frame of a vehicle body, a front wheel 3 is pivotally supported on a lower portion of the front fork 2, and a handle 4 is provided on an upper portion. A rear wheel 6 is pivotally supported on a swing arm 5 connected to the rear portion of the frame. A fuel tank 7 and a seat 8 are provided on the upper part of the frame. A stand 9 is provided below the frame. An internal combustion engine 10 is supported in the center of the frame and is covered with a fairing 11. The internal combustion engine 10 is a V-type four-cylinder four-stroke cycle internal combustion engine having a cylinder row that opens in a V shape to the left and right at an included angle of 90 degrees, and the crankshaft centerline L faces the front-rear direction of the vehicle. Internal combustion engine 10
The lower part is provided with a speed change mechanism part 12, an exhaust pipe 13 curving backward from the central part of the internal combustion engine, and a muffler 14 connected to the rear end thereof.

FIG. 2 is a front view of the internal combustion engine 10 with the crankcase front cover removed. A crankshaft 20 is provided at the center of the internal combustion engine 10.
Is supported by being sandwiched between the lower crankcase 21 and the upper cylinder block 23. The lower part of the crankcase 21 is closed by an oil pan 22. The cylinder block 23 is provided with a pair of front and rear cylinder holes facing left and right at an included angle of 90 degrees toward the center line of the crankshaft 20. Cylinder block 23
Cylinder heads 24 are connected to the upper left and right sides of the cylinder head 24, respectively. A cylinder head cover 25 is connected to the top of each cylinder head 24. An AC generator 28 is provided above the crankshaft 20. A cooling water pump 29 is provided slightly to the left of the drawing. It is driven from the crankshaft 20.

Crankcase 21 Crankshaft 20 in front of center
Directly underneath, there is a large-diameter multi-disc friction clutch 30,
Its input is driven by a gear from the crankshaft 20. The output shaft of the clutch 30 is provided rearward from the center of the clutch.

FIG. 3 is a rear view of the internal combustion engine 10 with the crankcase rear cover removed. The crankshaft 20 is located in the center, and the transmission main shaft 32 is located directly below it.
There is a counter shaft 33 next to it, and an output shaft 34 diagonally above it.
There is. A shift drum 35 is provided below the middle of the main shaft 32 and the counter shaft 33. A constant mesh type gear transmission is constituted by these.

An oil pump 36, which is chain-driven by the crankshaft 20, is provided at the lower left of the crankshaft 20. A starter 37 is provided on the upper right of the crankshaft 20.
An AC generator 28 is provided directly above the crankshaft 20,
It is driven from the crankshaft 20 via gears 40, 41, 42, 43.

FIG. 4 is a sectional view taken along the line IV-IV in FIG. 3, showing a longitudinal section of one of the cylinder rows and the crankcase of the internal combustion engine 10. The arrow F points to the front. The alternate long and short dash line L is the crankshaft center line. The main body of the internal combustion engine 10 is provided with a crankcase 21 having an oil pan 22 coupled to the lower end surface thereof, a cylinder row on the left and right, and a cylinder block 23 coupled to the upper end surface of the crankcase 21, and to the left and right cylinder rows. A pair of left and right cylinder heads 24 that are respectively coupled, a pair of left and right cylinder head covers 25 that are respectively coupled to the cylinder heads 24, and a crankcase front cover 26 that is coupled to the front surfaces of the crankcase 21 and the cylinder block 23. It comprises a crankcase rear cover 27 joined to the rear surface of the crankcase 21 and the cylinder block 23.

In FIG. 4, the connecting surface between the crankcase 21 and the cylinder block 23 is located at the crankshaft center line L. In the cylinder block 23, four cylinder holes 23h are formed by alternately arranging the center lines thereof in the direction of the crankshaft center line L, and the pair of left and right cylinder rows are V-shaped. Two cylinder holes 23h are shown in the figure.
Is shown. In the following description of the present embodiment, up, down, left and right, and front and rear indicate directions with reference to the motorcycle.

The crankcase 21 and the lower portion of the cylinder block 23 form a crank chamber 45. Corresponding upper and lower portions of the crankcase 21 and the cylinder block 23 in the crank chamber 45 jointly form a crankshaft front holding portion 46, a crankshaft intermediate holding portion 47, and a crankshaft rear holding portion 48. The crankshaft 20 is rotatably supported via slide bearings held by these shaft holding portions. A piston 50 is connected to the crankshaft 20 via a connecting rod 49, and reciprocates in each cylinder hole 23h. Crankshaft 20 is this piston 50
It is rotationally driven by the reciprocating motion of.

A multi-plate friction clutch 30 is provided just below the crankshaft and in front of the crankshaft. This clutch 30 is a clutch output shaft
31 is held by a bearing holding member 52 via a ball bearing 51, and the holding member 52 is supported by the crankcase 21 by attaching it to the crankcase 21 with bolts 53. By the shaft holding structure with the bearing holding member 52 interposed,
The mounting hole of the large-diameter cam type torque damper 72, which will be described later, can be made large, which facilitates mounting.

The multi-plate friction clutch 30 is a device for disconnecting and connecting the power transmitted from the crankshaft 20 to the speed change mechanism.
The multi-disc friction clutch 30 meshes with a gear 60 fixed to the crankshaft 20, and an input gear 61 rotatably provided around an output shaft 31 of the clutch and a clutch to which the input gear 61 is connected. Outer 62, clutch inner 63 fixed to the output shaft 31 of the clutch, a plurality of friction plates 64 axially slidable inside the clutch outer 62, axially slidable outside the clutch inner 63 And a plurality of friction plates 65 alternately arranged with the sliding plates 64 of the clutch outer,
A pressing plate 6 that pushes the alternately arranged friction plates 64 and 65 in the axial direction so as to closely contact each other by the urging force of the coil spring 66.
7, a push rod 68 provided in the center holes of the output shaft 31 and the main shaft 32 to push the pressing plate 67 against the biasing force of the coil spring 66, and a hydraulic device 6 provided on the rear cover of the crankcase.
9, a hydraulic piston 70 provided in the hydraulic device 69 and connected to the end of the push rod 68, and a hydraulic connection port 71 for supplying pressure oil to the hydraulic device. Although this clutch is normally connected, the clutch lever provided on the steering wheel of the vehicle is operated to send pressure oil to the hydraulic device 69,
When the pressing plate 67 is moved via the pressing rod 68 and the contact state of the friction plates 64, 65 is released, the clutch is disengaged.

The clutch output shaft 31 is the main shaft of the transmission.
32 are connected via a cam type torque damper 72. The torque damper 72 is a pair of cams that mesh with each other on inclined surfaces.
73, 74 and the coil spring 75, the cam 73 retreats against the urging force of the coil spring 75 to provide a buffering action when the load torque suddenly increases.

The main shaft 32 of the transmission is supported at two front and rear positions. The front portion of the main shaft 32 is provided with a main shaft front holding portion 78 in a downward extension of a crank shaft intermediate holding portion 47 provided in the crank case, and is supported via a ball bearing 79. The rear portion of the main shaft 32 is held by a bearing holding member 81 via a ball bearing 80, and the holding member 81 is supported by the crankcase 21 by attaching it to the rear end of the crankcase 21 with a bolt 82.

FIG. 5 is a cross-sectional view of the vicinity of the crankshaft intermediate holding portion 47 and the main shaft front holding portion 78 described above. FIG. 5A is a view taken along the line A--A of FIG. FIG. 6B is a view taken along the line BB of FIG. The drawing shows a state in which the crankcase 21 and the cylinder block 23 are joined together by tightening bolts 54, except for the crankshaft 20 and the main shaft 32. The crankshaft intermediate holding portion 47 is a recess provided in the crankcase 21.
21a and a recess 23a provided in the cylinder block 23. Reference numerals 21b and 23b are oil grooves formed on each side. The main shaft front holding portion 78 is provided below the crankshaft intermediate holding portion 47. The main shaft front part holding part 78 is provided at a position shifted forward (arrow F) while avoiding the extension line of the tightening bolt 54 of the crankshaft intermediate holding part 47, as shown in FIG. Since the main shaft front part holding portion 78 is provided at a position avoiding the tightening bolt 54, the length of the tightening bolt 54 can be shortened and the workability of assembling can be improved.

FIG. 6 is a development view of the main shaft 32, the counter shaft 33, and the output shaft 34 which are connected to the output shaft 31 of the multi-disc friction clutch. The ball bearing 83 is located in front of the counter shaft 33.
It is supported by the crankcase 21 via. The rear portion of the counter shaft 33 and the front portion of the output shaft 34 are supported by the same bearing holding member 81 as that of the rear portion of the main shaft 32 via ball bearings 84 and 85, respectively, and the bearing holding member 81 is supported by bolts 82 in the crankcase. It is installed in 21. Output shaft
The rear portion of 34 is supported by the crankcase rear cover 27 via a ball bearing 86.

The main shaft 32 has a gear group consisting of m1 to m5.
88, a counter shaft 33 is provided with a gear group 89 consisting of c1 to c5 corresponding to each of the gear groups 88 and a drive gear 90. The output shaft 34 has a driven gear that meshes with the drive gear 90.
91 is provided. In the above gear group, m1, m2, m
3, m4, m5 are for 1st speed, 2nd speed, 3rd speed, 4th speed, 5th
It corresponds to speed. Similarly, the gear groups c1 to c5 also correspond to the first speed to the fifth speed.

Of the gear groups 88 and 89, gears m1 and m2 are fixed gears fixed to the shaft, and gears c1, c2, c3 and m.
Numerals 4 and m5 are gears that cannot freely move in the axial direction, but can freely rotate because they are not constrained in the circumferential direction. Hereinafter, this is called a floating gear. The gears m3, c4, and c5 are spline-fitted onto the shaft and are gears that are slidable in the axial direction while being constrained by the shaft in the circumferential direction. Hereinafter, this is referred to as a sliding gear. The sliding gear m3 includes a shift fork 92a and a sliding gear c.
4 is engaged with a shift fork 92b, and sliding gear c5 is engaged with a shift fork 92c. These shift forks are operated by a shift operation mechanism section described later.

FIG. 7 is a development view of the shift operation mechanism section.
The shift forks 92a, 92b, 92c are held by a support shaft 93 so as to be slidable in the axial direction. The support shaft 93 has a front portion fixed to the crankcase 21 and a rear portion fixed to the bearing holding member 81. Next to the support shaft 93, parallel to the support shaft 93, the shift drum 94
The front part to the crankcase 21 and the rear part to the bearing holding member 81.
It is rotatably held at. Groove 95 of the shift drum 94
A shift pin 96 protruding from each shift fork is engaged therewith. The shift drum 94 rotates in conjunction with a shift spindle 97 that is rotated by the operation of a speed change lever (not shown) attached to the steering wheel of the vehicle, and through a shift pin 96 fitted in the groove 95. Move any of the shift forks 92, and each shift fork moves any of the sliding gears that are engaged.

In FIG. 6, the sliding gear m3 that rotates integrally with the main shaft 32 is moved by the shift fork 92a.
It moves axially above and selectively engages with either the idle gear m4 or the idle gear m5, and the engaged idle gear rotates integrally with the main shaft. The idle gear m4 or m5 is
The counter gear 33 drives the corresponding sliding gear c4 or c5 in the neutral position, and the fourth speed or the fifth speed is changed.

Similarly, the sliding gear c4, which rotates integrally with the counter shaft 33, moves axially on the counter shaft 33 by the shift fork 92b, and selectively moves to either the floating gear c1 or the floating gear c3. The engaged idle gear rotates together with the counter shaft 33. The idle gear c1 or the idle gear c3 is driven by the corresponding fixed gear m1 of the main shaft 32 or the sliding gear m3 in the neutral position.
Gear shifting of the third speed or the third speed is performed.

Further, when the sliding gear c5 which rotates integrally with the counter shaft 33 moves axially on the counter shaft 33 by the shift fork 92b and engages with the floating gear c2, the floating gear c2 becomes the counter shaft. It rotates integrally and is driven by the fixed gear m2 of the main shaft 32 which meshes correspondingly, so that the second speed is changed.

The changed rotation of the counter shaft 33 is transmitted to the output shaft 34 by the drive gear 90 and the driven gear 91 meshing with the drive gear 90, and finally drives the rear wheels of the vehicle.

FIG. 8 is a sectional view taken along the line VIII-VIII in FIG. 3, and is a longitudinal sectional view showing the AC generator 28 located immediately above the crankcase 21 and the crankshaft 20. The AC generator 28 is shown in Fig. 3.
As shown in FIG. 4, the gear train is connected to the gears 41, 42, 43 from the gear 40 fixed to the crankshaft. The gear 41 is not shown in FIG. 8, and the other gears 40, 42, 43
Is shown. These gear trains are cylinder block 23
And the rear cover 27 of the crankcase. gear
43 rotations via alternator 98 with damper alternator
Electric power is generated by being transmitted to the rotating shaft 99 of 28.

A crank pulser 44 is mounted near the crankshaft center line L of the crankcase front cover 26.
The position on the front surface of the internal combustion engine is indicated by a chain double-dashed line in FIG. This device is a device that detects the position of the crank and the rotation speed of the crankshaft. Since it can be attached from the front of the front cover 26, it is easy to maintain.

Since this embodiment has the above-mentioned structure, it has the following operations and effects. (1) The main shaft is located almost directly under the crankshaft, and the clutch with a large outer diameter is connected to the extension line of the front of the main shaft. Since it is located at the central portion in the direction, the width of the internal combustion engine in the left-right direction can be narrowed. (2) The main shaft is arranged in parallel below the crankshaft,
At least a part of the main shaft is in the same axial position as the crank shaft. That is, the main shaft and the crank shaft are in a position where they overlap when viewed from a position on the side of the shaft,
Compared with the internal combustion engine described in Japanese Patent No. 2858017, the axial length of the internal combustion engine can be shortened, and the oil dropped by lubricating the piston and crank can be used for lubricating the gear group of the main shaft. (3) The crank chamber is configured by upper and lower case members, that is, the lower portion of the cylinder block and the crank case, the crank shaft is held between the upper and lower case members, and the main shaft is attached to the lower case member. Since the main shaft bearing and the crank shaft bearing at some locations are displaced so that their axial positions do not overlap, the length of the bolt for tightening the crank shaft bearing portion can be shortened and workability can be improved. (4) Since the internal combustion engine of the present embodiment is mounted on the motorcycle so that the crankshaft extends in the vehicle front-rear direction, the horizontal width of the internal combustion engine is narrow, so the front projected area of the vehicle can be made small and the knee grip can be reduced. Easy to peel. Further, since the length of the internal combustion engine in the front-rear direction is short, the mountability on the vehicle is good. (5) Since the internal combustion engine of the present embodiment is a V-type internal combustion engine, the vertical height of the central portion of the internal combustion engine can be reduced, and the mountability on a vehicle is good. (6) Since the large-diameter devices and members of the AC generator, the crankshaft, and the main shaft are arranged vertically on the center plane of the internal combustion engine, the width of the internal combustion engine can be narrowed. (7) Since the AC generator is driven by the gear train, the space of the transmission member is smaller than that of a chain or the like. Further, since the rotation direction of the AC generator is opposite to the rotation direction of the crankshaft, the AC generator mass can be used as an anti-torque balancer for the crank mass. (8) Since the internal combustion engine starter is arranged on the opposite side of the AC generator driving gear train with respect to the center plane of the internal combustion engine, the left and right weight balance of the internal combustion engine is good. (9) Since the oil pump is arranged on the opposite side of the counter shaft with respect to the center plane of the internal combustion engine, the left and right weight balance of the internal combustion engine is good. (10) The crank pulsar is mounted on the front cover of the crankcase, so maintenance is good.

[Brief description of drawings]

FIG. 1 is a side view of a motorcycle equipped with an internal combustion engine of the present invention.

FIG. 2 is a front view of the internal combustion engine with a crankcase front cover removed.

FIG. 3 is a rear view of the internal combustion engine with a crankcase rear cover removed.

FIG. 4 is a cross-sectional view taken along the line IV-IV in FIG. 3, showing a vertical cross section of one cylinder row and the crankcase of the internal combustion engine.

5A and 5B are cross-sectional views of the vicinity of a crankshaft intermediate holding portion and a main shaft front holding portion. FIG. 5A is a view taken along the line AA in FIG. 5B, and FIG. It is a BB arrow line view.

FIG. 6 is a development view of a main shaft, a counter shaft, and an output shaft that are connected to the output shaft of the multi-plate friction clutch.

FIG. 7 is a development view of a shift operation mechanism unit.

8 is a cross-sectional view taken along the line VIII-VIII of FIG. 3, which is a vertical cross-sectional view showing the crankcase and the AC generator immediately above the crankshaft.

[Explanation of symbols]

L ... Crankshaft center line, 1 ... Motorcycle, 2 ... Front fork, 3 ... Front wheel, 4 ... Steering wheel, 5 ... Swing arm, 6 ... Rear wheel, 7 ... Fuel tank, 8 ... Seat, 9 ... Stand, 10 ... Internal combustion engine, 11 ... Fairing, 12 ... Transmission mechanism section, 13 ... Exhaust pipe, 14 ... Muffler, 20 ... Crankshaft, 21 ... Crankcase, 21a ... Recess, 21b ... Oil groove, 22 ... Oil pan, 23 ... Cylinder Block, 23a ... Recess, 23b ... Oil groove,
23h ... Cylinder hole, 24 ... Cylinder head, 25 ... Cylinder head cover, 26 ... Crankcase front cover, 27 ... Crankcase rear cover, 28 ... Alternator, 29 ... Cooling water pump, 30 ... Multi-disc friction clutch, 31 ... Output shaft of multi-disc friction clutch, 32 ... Main shaft, 33 ... Counter shaft, 34 ... Output shaft, 35 ... Shift drum, 36 ... Oil pump, 37 ... Starter, 40 ... Gear, 41 ... Gear, 42 ... Gear , 43 ... Gears, 44 ... Crank pulser, 45 ... Crank chamber, 46 ... Crankshaft front holding section, 47 ... Crankshaft intermediate holding section, 48 ... Crankshaft rear holding section, 49 ... Connecting rod, 50 ... Piston, 51 ... Ball bearing, 52 ... Bearing holding member, 53 ... Bolt, 54 ... Tightening bolt, 60 ... Gear, 61 ... Input gear, 62 ... Clutch outer, 63 ... Clutch inner, 64 ... Clutch outer friction plate, 65 ... Clutch inner Friction plate, 66 ... coil Ne, 67
... Pressing plate, 68 ... Push rod, 69 ... Hydraulic device, 70 ... Hydraulic piston, 71 ... Hydraulic connection port, 72 ... Cam type torque damper, 73 ...
Cam, 74 ... Cam, 75 ... Coil spring, 78 ... Main shaft front holding part, 79 ... Ball bearing, 80 ... Ball bearing, 81 ... Bearing holding member, 82 ... Bolt, 83 ... Ball bearing, 84 ... Ball bearing, 85… ball bearings,
86 ... Ball bearing, 88 ... Gear group, 89 ... Gear group, 90 ...
Drive gear, 91 ... Followed gear, 92 ... Shift fork, 93 ... Shift fork support shaft, 94 ... Shift drum, 95 ... Groove, 96 ...
Shift pin, 97… Shift spindle, 98… Damper joint, 99… Alternating shaft of alternator.

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) B62M 7/02 B62M 7/02 D F02B 75/22 F02B 75/22 H F02F 7/00 301 F02F 7/00 301F F16H 3/091 F16H 3/091 57/02 302 57/02 302A (72) Inventor Isamu Takahashi 1-4-1 Chuo, Wako-shi, Saitama Honda R & D Co., Ltd. F-term (reference) 3D039 AA02 AA04 AB04 AC01 AC64 AC77 AC86 AD06 AD23 AD53 3G024 AA48 DA19 EA04 FA00 3J028 EA08 EA25 EB33 EB35 EB62 FA35 FA42 FB05 FC32 FC42 FC64 3J063 AA06 AB02 AC07 BA01 BA03 BA04 BB41 CA01 CB42 CB43 CB44 CD01 CD11 XA

Claims (5)

[Claims] 1. A crankshaft, a main shaft of a transmission that holds a transmission gear train, a clutch arranged on an extension of the main shaft, and a counter shaft of a transmission that holds a gear train that meshes with the transmission gear train. Equipped with a crankshaft, clutch,
An internal combustion engine in which power is transmitted in the order of a main shaft and a counter shaft, wherein the main shaft is arranged substantially directly below the crankshaft. 2. The internal combustion engine according to claim 1, wherein at least a part of the main shaft is provided at an axial position equivalent to that of the crank shaft. 3. A crank chamber is constituted by upper and lower case members, a crank shaft is held between the upper and lower case members, and a main shaft is attached to a lower case member. At least one crank bearing and a main shaft are provided. The internal combustion engine according to claim 1 or 2, wherein the bearing and the bearing are provided so as to be displaced from each other so as to have different axial positions. 4. The internal combustion engine according to claim 1, wherein the internal combustion engine is mounted on a motorcycle with a crankshaft oriented in the front-rear direction of the vehicle. 5. The internal combustion engine according to claim 4, which is a V-type internal combustion engine.