JP4625413B2 - Parallel two-cylinder internal combustion engine for vehicles - Google Patents

Description

  In the present invention, a combustion chamber that faces the top of a piston that is slidably fitted to a cylinder bore is formed between the cylinder block and the cylinder head, and opens to the combustion chamber on one side of a plane that includes the axis of the cylinder bore. An intake valve port and an exhaust valve port that opens to the combustion chamber on the other side of the plane are provided in the cylinder head, and an intake valve operating shaft disposed in the cylinder head so that the intake valve port can be opened and closed. A camshaft for opening and closing the intake valve is disposed on the line, and a rocker shaft is fixedly disposed between the exhaust valve disposed in the cylinder head and the camshaft so that the exhaust valve port can be opened and closed. The present invention relates to an internal combustion engine in which a rocker arm that swings in response to rotation and opens and closes an exhaust valve is supported so as to be swingable by the rocker shaft.

Such an internal combustion engine is already known from, for example, Patent Document 1, in which the operating axis of the pair of exhaust valves is set substantially parallel to the axis of the cylinder bore, and the operating axis of the pair of intake valves is the exhaust valve. Is set so as to cross the operation axis of the slant.
Japanese Patent No. 2537205

  However, in the device disclosed in Patent Document 1, the air-fuel mixture flows obliquely into the combustion chamber from the intake valve port when the intake valve is opened, and it can be said that the air-fuel mixture diffuses well in the combustion chamber. In addition, the combustion efficiency is not sufficient. Further, since the intake valve is inclined so that its stem end is separated from the axis of the cylinder bore, the side surface of the cylinder head on the side where the intake port is provided must be set at a position relatively away from the axis of the cylinder bore. Accordingly, the degree of freedom in arrangement of the intake system connected to the cylinder head is narrowed.

The present invention has been made in view of such circumstances, and improves the combustion efficiency by improving the inflow of the air-fuel mixture into the combustion chamber and suppresses the overhang of the cylinder head to the intake system side, and the degree of freedom in the arrangement of the intake system. It is an object of the present invention to provide a parallel two-cylinder internal combustion engine for a vehicle with an improved level.

In order to achieve the above object, a first aspect of the present invention is a vehicle parallel two-cylinder internal combustion engine mounted on a vehicle having left and right steps on which an occupant puts both feet, and is arranged between the left and right steps. A crankcase that houses the crankshaft and the transmission, a cylinder block that is erected on the top of the crankcase, and a cylinder head that is coupled to the top of the cylinder block. A combustion chamber facing the top of a piston slidably fitted into the cylinder bore is formed between the cylinder block and the cylinder head, and an intake valve port that opens into the combustion chamber on one side of the plane including the axis of the cylinder bore; An exhaust valve port that opens to the combustion chamber on the other side of the plane is provided in the cylinder head so that the intake valve port can be opened and closed. A camshaft for opening and closing the intake valve is disposed on the operating axis of the intake valve provided, and a rocker shaft is fixedly disposed between the exhaust valve and the camshaft disposed in the cylinder head so that the exhaust valve port can be opened and closed. The rocker arm that swings in response to the rotation of the camshaft and opens and closes the exhaust valve is supported by the rocker shaft so as to be swingable. The crankshaft and the camshaft are arranged along the vehicle longitudinal direction. And the cylinder bore axis extends upwardly inclining to the other side of the left and right direction from a position offset to the one side in the left and right direction from the center position in the left and right direction on the crankcase upper surface, and the camshaft passes through the center between the left and right steps located on the vertical plane which extends in the longitudinal direction of the vehicle, actuation axis of the intake valve is set substantially parallel to the cylinder bore axis With, the cylinder head for opening the intake port communicating with the intake valve ports, said one lateral side direction one side is formed substantially parallel to the cylinder bore axis, said one of the intake system member is a cylinder head connected to the intake port be arranged by substantially along the side, characterized in that extends to approach gradually to the vertical plane.

Incidentally, the throttle body 56 of the embodiment corresponds to the intake system member of the present invention. In the present invention, the “left-right direction” refers to the left-right direction of the vehicle.

According to the present invention, since the operation axis of the intake valve is set substantially parallel to the axis of the cylinder bore, the air-fuel mixture flows from the intake valve port into the combustion chamber substantially parallel to the axis of the cylinder bore when the intake valve is opened, Combustion efficiency can be increased by improving the diffusion of the air-fuel mixture in the combustion chamber. In addition, since one side surface of the cylinder head that opens the intake port is formed substantially parallel to the axis of the cylinder bore, the side surface of the cylinder head on the side where the intake port is provided is set to a position close to the axis of the cylinder bore. The overhang to the system side can be suppressed and the degree of freedom of the arrangement of the intake system can be increased.

Further, by air suction system member is disposed substantially along one side of the cylinder head, suppress the projecting amount from the axis of the cylinder bore of an internal combustion engine comprising an intake system, Ru can configure an internal combustion engine in a compact .

Embodiments of the present invention will be described below based on reference examples shown in the accompanying drawings and examples of the present invention.

1 to 3 show a first reference example, FIG. 1 is a side view of a motorcycle, FIG. 2 is a longitudinal side view of a main part of an internal combustion engine, and FIG. 3 is an enlarged view of a main part of FIG.

  First, in FIG. 1, a front fork 12 that pivotally supports the front wheel WF is supported on the head pipe 11 provided at the front end of the body frame F of the motorcycle so that the steering wheel 13 is connected to the front fork 12. The A power unit P composed of an internal combustion engine EA and a transmission (not shown) housed in a crankcase 14A provided in the internal combustion engine EA is mounted on the front portion of the vehicle body frame F. A fuel tank 15 is mounted on the front portion of the vehicle body frame F so as to cover the upper side of the internal combustion engine EA.

  The front ends of a pair of left and right swing arms 16 extending in the front-rear direction are supported on the body frame F behind the power unit P so as to swing up and down, and a rear wheel WR is pivoted between the rear ends of the swing arms 16. Be supported. Further, rear cushion units 17 are interposed between the body frame F and the rear portions of the swing arms 16. Moreover, the left swing arm 16 of both the swing arms 16 is formed in a cylindrical shape, and a drive shaft 18 for transmitting the power from the power unit P to the rear wheel WR is accommodated in the left swing arm 16. .

  A main seat 19 for seating a rider is attached to the vehicle body frame F behind the fuel tank 15, and a pillion seat 20 for passengers is attached to the vehicle body frame F behind the main seat 19. Is installed.

  In FIG. 2, the internal combustion engine EA is inclined so as to rise frontward in the traveling direction of the motorcycle, and the first bank BFA connected to the crankcase 14 </ b> A and the first bank BFA upward together with the first bank BFA. A V-type internal combustion engine having a second bank BRA connected to the crankcase 14A on the rear side of the first bank BFA so as to form an open V-shape. The crankcase 14A includes a left-right direction of the motorcycle. A crankshaft 21 having an axis extending in the direction is rotatably supported.

  Further, the first and second banks BFA, BRA include a cylinder block 22 coupled to the crankcase 14A, a cylinder head 23A coupled to the cylinder block 22 and a head cover coupled to the cylinder head 23A. 24, respectively, and pistons 26 are respectively slidably fitted in cylinder bores 25 provided in the cylinder blocks 22 of both banks BFA and BRA, respectively. The BRA pistons 26 are commonly connected to the crankshaft 21 via connecting rods 27. Further, combustion chambers 28 are formed between the cylinder blocks 22 and the cylinder heads 23A in the banks BFA and BRA so that the tops of the pistons 26 face each other.

  By the way, the first and second banks BFA, BRA are arranged at the center between the connecting rods 27 provided in the banks BFA, BRA, respectively, at the center between the axes of the cylinder bores 25, which are orthogonal to the crankshaft 21. In the following, the configuration of the first bank BFA will be described in detail, and for the second bank BRA, the same reference numerals are assigned to the main parts corresponding to the first bank BFA. Therefore, detailed description is omitted only for illustration.

  3, the cylinder head 23A of the first bank BFA is provided with a pair of intake valve ports 29 arranged on one side of the plane PL including the axis of the cylinder bore 25 so as to open to the combustion chamber 28. A pair of exhaust valve ports 30 arranged on the other side of the plane PL are provided so as to open to the combustion chamber 28, and the exhaust valve ports 30 are formed to have a smaller diameter than the intake valve ports 29. The In addition, the cylinder head 23A is provided with a plug mounting hole 32 for attaching the spark plug 31 with its tip facing substantially the center of the combustion chamber 28.

Thus, in the first reference example, the plane PL includes the axis of the cylinder bore 25 and is set parallel to the axis of the crankshaft 21. The intake valve ports 29 are arranged on the second bank BRA side with respect to the plane PL. The exhaust valve ports 30 are disposed on the side opposite to the second bank BRA with respect to the plane Pl.

  The intake valves 34 that can open and close both the intake valve ports 29 are slidably fitted to guide cylinders 35 provided in the cylinder head 23A, and are arranged to protrude from the guide cylinders 35. Between the retainers 36 fixed to the end portions and the cylinder head 23A, valve springs 37 for urging the intake valves 34 in the valve closing direction are contracted. The exhaust valves 38 that can open and close the exhaust valve ports 30 are slidably fitted into guide cylinders 39 provided in the cylinder head 23A, and the exhaust valves 38 that protrude from the guide cylinders 39 are provided. Between the retainer 40 fixed to the end of the cylinder and the cylinder head 23A, a valve spring 41 for biasing the exhaust valve 38 in the valve closing direction is contracted.

  A camshaft 42 to which rotational power is transmitted from the crankshaft 21 at a reduction ratio of 1/2 is arranged on the operating axis LI of the intake valves 34. The shaft is parallel to the crankshaft 21 and is rotatably supported between the cam holder 45 fastened to the cylinder head 23A and the cylinder head 23A. Thus, the cams 43 provided on the camshaft 42 come into contact with the closed ends of the bottomed cylindrical lifters 44 formed in a bottomed cylindrical shape, and the lifters 44. Are fitted to the cylinder head 23A so as to be able to slide along the operation axis LI of the intake valves 34. That is, the intake valves 34 are opened / closed according to the rotation of the camshaft 42.

  On the other hand, a rocker shaft 46 having an axis parallel to the camshaft 42 is fixedly disposed on the cylinder head 23A between the exhaust valve 38 and the camshaft 42. A rocker arm 47 is slidably contacted with a rocker shaft 46 so that the rocker arm 46 can swing and a tappet screw 48 is screwed to the other end of the rocker arm 47 so that the forward / backward position can be adjusted. It abuts on the valve 38. That is, the rocker arms 47 open and close the exhaust valves 38 according to the rotation of the camshaft 42.

  Moreover, the operation axis LI of the intake valves 34 is set substantially parallel to the axis of the cylinder bore 25, and the operation axis LE of the exhaust valves 38 includes the axis of the cylinder bore 25 and the axis of the crankshaft 21. Is set so as to cross at an angle with respect to the plane PL which is parallel to the plane PL.

  Incidentally, one side surface of the cylinder head 23A on the second bank BRA side is formed substantially parallel to the axis of the cylinder bore 25, and the both intake valve ports are connected to the connecting pipe portion 50A integrally projecting from the one side surface. 29... Are opened in common. Further, a connecting pipe portion 52 is integrally projected from the other side opposite to the first bank BRA of the cylinder head 23A, and the exhaust gas connected to the exhaust pipe ports 30 is connected to the connecting pipe portion 52 in common. Port 53 is opened.

  The spark plug 31 is disposed between the intake valves 34 and the exhaust valves 38. The piston 26 is disposed on the ceiling surface of the combustion chamber 28 between the spark plugs 31 and the intake valve ports 29. A partition wall 54 that protrudes to the side is projected, and the tip of the spark plug 31 is disposed at substantially the same position as the projecting end of the partition wall 54. Further, at least a part of the exhaust valve ports 30 is disposed above the partition wall 54.

  In FIG. 2 again, an intake pipe 55 connected to the intake port 51 is connected to the connection pipe portion 50A in the cylinder head 23A of the first bank BFA. The intake pipe 55 is connected to a throttle body 56 that is an intake system member. Connected. Thus, a fuel injection valve 57 that injects fuel toward the intake port 51 is attached to the throttle body 56.

  Moreover, the throttle body 56 is formed substantially parallel to the axis of the cylinder bore 25 and is arranged substantially parallel to one side of the cylinder head 23A where the intake port 51 is opened. Therefore, the intake pipe 55 is formed to be curved in an arc shape.

  In addition, intake valves 34 are respectively arranged on the first and second banks BFA, BRA on the sides close to the cylinder heads 23A, 23A, and the second bank BRA is also similar to the first bank BFA side. An intake pipe 55 is connected to the connecting pipe portion 50A of the cylinder head 23A, and a throttle body (not shown) is connected to the intake pipe 55. Moreover, the throttle body on the second bank BRA side is disposed so as to overlap the throttle body 56 on the first bank BFA side in the axial direction of the crankshaft 21.

Next, the operation of the first reference example will be described. The operation axis LI of the intake valves 34 disposed in the cylinder heads 23A of the first and second banks BFA and BRA so as to be opened and closed is Is set substantially parallel to the axis of the cylinder bores 25 included in the cylinder bores 25, so that the flow direction of the air-fuel mixture flowing into the combustion chambers 28 from the intake valve ports 29 when the intake valves 34 are opened is mainly the axis of the cylinder bores 25. The combustion efficiency can be improved by improving the diffusion of the air-fuel mixture in the combustion chambers 28, and the air-fuel mixture is prevented from flowing into the spark plugs 31 and the exhaust valve ports 30 in an unburned state. It is possible to suppress the blowout of the unburned air-fuel mixture and the spark plug 31.

  Moreover, since one side surface of the cylinder head 23A for opening the intake ports 51 connected to the intake valve ports 29 is formed substantially parallel to the axis of the cylinder bore 25, the cylinder head 23A on the side where the intake ports 51 are provided. Is set to a position close to the axis of the cylinder bores 25, so that the cylinder heads 23A are prevented from overhanging to the intake system side, and the degree of freedom of arrangement of the intake systems can be increased.

  Further, since the throttle bodies 56 connected to the intake ports 51 are arranged substantially along one side surface of the cylinder heads 23A, the amount of protrusion from the axis of the cylinder bore of the internal combustion engine EA including the intake system is suppressed. The internal combustion engine EA can be configured compactly.

  In addition, since the intake valves 34 are disposed on the sides close to each other of the pair of cylinder heads 23A and 23A that respectively constitute part of the pair of banks BFA and BRA that form a V shape, both banks BFA , BRA. BRA. It is possible to facilitate the arrangement of the intake system in the space formed between the BRAs and contribute to the compactness of the V-type internal combustion engine EA.

  Further, a partition wall 54 projecting toward the piston 26 is provided on the ceiling surface of the combustion chamber 28 between the spark plug 31 and the intake valve ports 29, so that the operation axis LI of the intake valve 34 is substantially the same as the axis of the cylinder bore 25. Combined with the parallelism, the air-fuel mixture flowing from the intake valve port 29 to the combustion chamber 28 when the intake valve 34 is opened flows more effectively into the ignition plug 31 and the exhaust valve port 30 in an unburned state. It is possible to suppress the blowout of the unburned mixture and the spark plug 31 more effectively.

  And since the front-end | tip of the spark plug 31 is arrange | positioned in the substantially same position as the protrusion end of the partition 54, favorable flame propagation can be achieved, suppressing the curl of the spark plug 31. FIG.

  Further, the operating axis LE of the exhaust valve 38 is set so as to obliquely intersect the plane PL including the axis of the cylinder bore 25, and at least a part of the exhaust valve port 30 is disposed above the partition wall 54. Therefore, the side close to the intake valve 34 in the exhaust valve port 30 is disposed at a position deeper from the partition wall 54, and the blowout of the unburned mixture can be further effectively suppressed.

FIG. 4 shows a second reference example, and parts corresponding to the first reference example are given the same reference numerals and are shown in the drawings, and detailed description thereof is omitted.

  The internal combustion engine EB includes a first bank BFB which is inclined so as to rise frontward in the forward direction of the motorcycle and is connected to the crankcase 14B, and a V opened upward together with the first bank BFB. This is a two-cylinder V-type internal combustion engine having a second bank BRB connected to the crankcase 14B on the rear side of the first bank BFB so as to form a mold.

Further, the first and second banks BFB and BRB include a cylinder block 22 coupled to the crankcase 14B, a cylinder head 23B coupled to the cylinder block 22 and a head cover coupled to the cylinder head 23B. .., And the angle formed by both banks BFB and BRB is set larger than the angle formed by the first and second banks BFA and BRA in the first reference example.

Thus, the intake valves 34 and the exhaust valves 38 disposed in the cylinder heads 23B so as to be openable and closable are supported so as to be swingable by the camshaft 42 and the rocker shaft 46, as in the first reference example. The operating axis LI of the intake valves 34 is set substantially parallel to the axis of the cylinder bore 25, and the operating axis LE of the exhaust valves 38 includes the axis of the cylinder bore 25 and the axis of the crankshaft 21. And the structure of the combustion chambers 28 is configured in the same manner as in the first reference example.

  Further, one side surface of the banks BFB and BRB, which are opposed to each other, of the cylinder heads 23B is formed substantially in parallel with the axis of the cylinder bores 25, and is connected to the connecting pipe projecting integrally from the one side surface. An intake port 51 that is connected in common to the intake valve ports 29 is opened in the portions 50B.

In this second reference example, the throttle bodies 56, 56 of both banks BFB, BRB are arranged so as not to overlap each other when viewed from the direction along the axis of the crankshaft 21, and extend vertically. Throttle bodies 56 are connected to connecting pipe portions 50B through insulators 58.

By arranging the throttle bodies 56 and 56 so as not to overlap each other when viewed from the direction along the axis of the crankshaft 21 as in the second reference example, the angle formed by the two banks BFB and BRB is relatively small. Even if it must be set large, one side surface of the cylinder head 23A for opening the intake ports 51 connected to the intake valve ports 29 is formed substantially parallel to the axis of the cylinder bore 25, so that the intake ports 51 ... Is set to a position close to the axis of the cylinder bores 25, so that the cylinder heads 23B can be prevented from overhanging to the intake system side. Therefore, the angle formed by both banks BFB and BRB Can be set relatively small, and the V-type internal combustion engine EB can be made compact.

FIG. 5 shows a third reference example, and portions corresponding to the first and second reference examples are given the same reference numerals, and detailed description thereof is omitted.

  The internal combustion engine EC includes a first bank BFC that is inclined so as to rise frontward in the traveling direction of the motorcycle and is connected to the crankcase 14C, and a V that opens upward together with the first bank BFC. This is a two-cylinder V-type internal combustion engine having a second bank BRC connected to the crankcase 14C on the rear side of the first bank BFC so as to form a mold.

Further, the first and second banks BFC, BRC include a cylinder block 22 coupled to the crankcase 14C, a cylinder head 23C coupled to the cylinder block 22 and a head cover coupled to the cylinder head 23C. .., And the angle formed by both banks BFC and BRC is set larger than the angle formed by the first and second banks BFB and BRB in the second reference example.

Thus, the intake valves 34 and the exhaust valves 38 disposed in the cylinder heads 23C so as to be openable and closable are swung by the camshaft 42 and the rocker shaft 46, as in the first and second reference examples. The operating axis LI of the intake valves 34 is set substantially parallel to the axis of the cylinder bore 25, and the operating axis LE of the exhaust valves 38 includes the axis of the cylinder bore 25 and the crankshaft. 21 is set so as to intersect obliquely to the plane PL is parallel to the axis of the structure of the combustion chamber 28 ... also configured similarly to the first and second reference examples.

  Further, one side surface, which is a side of the cylinder heads 23B in the banks BFC, BRC, facing each other is formed substantially parallel to the axis of the cylinder bore 25, and a connecting pipe integrally protruding from the one side surface. An intake port 51 that is connected in common to the intake valve ports 29 is opened in the portions 50C.

In this third reference example, an air cleaner 60 is disposed between both banks BFC, BRC, and throttle bodies 56, 56 disposed substantially horizontally below the air cleaner 60 are provided with insulators 61 in the connecting pipe portion 50C. The connecting pipes 59 extending upward from the throttle bodies 56 are connected to the air cleaner 60 in common.

Even when the air cleaner 60 is arranged between the banks BFC and BRC as in the third reference example, the angle between the banks BFC and BRC must be set relatively large. Since one side surface of the cylinder heads 23A for opening the intake ports 51 connected to the cylinder bores 25 is formed substantially in parallel with the axis of the cylinder bores 25, the side surfaces of the cylinder heads 23C on the side where the intake ports 51 are provided are connected to the cylinder bores 25 ... Since the cylinder heads 23C... Can be prevented from overhanging to the intake system side, the angle formed by both banks BFC and BRC can be set relatively small. A certain internal combustion engine EC can be made compact.

Figure 6 shows the actual施例of the present invention, a vertical sectional view as seen from the rear side of the internal combustion engine mounted on the wasteland traveling vehicle, a portion corresponding to the first to third reference example Detailed description is omitted only by attaching the same reference numerals to the drawings.

The internal combustion engine ED is disposed between a pair of left and right steps 62 and 62 on which a rider of a vehicle for traveling on rough terrain rides both feet, and is configured as a parallel 2-cylinder with the crankshaft 21 along the front-rear direction of the vehicle. A cylinder block 25 having an axis inclined to the left when viewed from the rear side of the vehicle and coupled to the crankcase 14C; a cylinder head 23A coupled to the cylinder block 22; The head covers 24 are coupled to the cylinder heads 23A.

Thus, the intake valves 34 and the exhaust valves 38 disposed in the cylinder heads 23A so as to be openable and closable are supported so as to be swingable by the camshaft 42 and the rocker shaft 46, as in the first reference example. The operating axis LI of the intake valves 34 is set substantially parallel to the axis of the cylinder bore 25, and the operating axis LE of the exhaust valves 38 includes the axis of the cylinder bore 25 and the axis of the crankshaft 21. And the structure of the combustion chambers 28 is configured in the same manner as in the first reference example.

  Further, one side surface (right side surface when the vehicle is viewed from the rear side) of the cylinder head 23A is formed substantially in parallel with the axis of the cylinder bores 25, and the connecting pipe portion 50A that projects integrally from one side surface thereof. In addition, an intake port 51 connected in common to the intake valve ports 29 is opened. An intake pipe 55 connected to the intake port 51 is connected to the connection pipe portion 50A. This intake pipe 55 is connected to a throttle body 56 provided with a fuel injection valve 57. The throttle body 56 is connected to the cylinder bore 25. And is arranged substantially parallel to one side surface of the cylinder head 23A in which the intake port 51 is opened.

  Further, a connecting pipe portion 52 is integrally projected from the other side of the cylinder head 23A, and an exhaust port 53 connected to the exhaust valve port 30 is opened in the connecting pipe portion 52, so that exhaust gas discharged from the exhaust port 53 is exhausted. Is led to the exhaust muffler 64 through the exhaust pipe 63.

According to the actual施例, among the effects obtained in the first to third reference example, it is possible to obtain the effect of excluding the unique effect that the internal combustion engine is type V.

  Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and various design changes can be made without departing from the present invention described in the claims. It is.

It is a side view of a motorcycle according to a first reference example. It is a principal part vertical side view of an internal combustion engine. It is a principal part enlarged view of FIG. It is a vertical side view corresponding to FIG. 2 of the 2nd reference example. It is a vertical side view corresponding to FIG. 2 of the 3rd reference example. BRIEF DESCRIPTION OF THE DRAWINGS It is the longitudinal cross-sectional view which looked at the Example of this invention, and was seen from the back side of the internal combustion engine mounted in the vehicle for rough terrain travel.

22 ... Cylinder block
2 3C · · · cylinder head 25 · · · cylinder bore 26 · · · piston 28 · · · combustion chamber 29 · · · intake valve port 30 · · · exhaust valve port 34 · · · intake valve 38 · · · exhaust valve 42 · · camshafts 46 ... rocker shaft 47 ... throttle Bode rocker arm 51 is ... intake port 56 ... intake pipe member
62 ... Step LI ... Intake valve operating axis PL ... Plane

Claims (1)

A parallel two-cylinder internal combustion engine for a vehicle mounted on a vehicle provided with left and right steps (62, 62) on which the occupant puts both feet,
A crankcase (14C) that is disposed between the left and right steps (62, 62) and accommodates the crankshaft (21) and the transmission therein, and a cylinder block (22) that stands on the crankcase (14C). ) And a cylinder head (23C) coupled to the upper portion of the cylinder block (22), and the piston (26) of the piston (26) slidably fitted to the cylinder bore (25) of the cylinder block (22 ). a combustion chamber for exposing the top portion (28) is formed between the cylinder block (22) and the cylinder head (2 3C), the cylinder bore a combustion chamber on one side of a plane (PL) containing the axis (25) (28) an opening to the intake valve port (29), an exhaust valve port opening into the combustion chamber (28) at the other side (30) is provided in the cylinder head (2 3C) of said plane (PL) Camshaft (42) for opening and closing the intake valve (34) on the actuating axis (LI) of the cylinder head as a possible opening and closing an intake valve port (29) an intake valve which is arranged in the (2 3C) (34) There are disposed, the rocker shaft (46) is fixedly arranged between the exhaust valves disposed in the cylinder head (2 3C) as a possible opening and closing the exhaust valve port (30) (38) and the camshaft (42), the cam A rocker arm (47) that swings according to the rotation of the shaft (42) and opens and closes the exhaust valve (38) is supported by the rocker shaft (46) so as to be swingable.
The crankshaft (21) and the camshaft (42) are arranged along the vehicle longitudinal direction,
The cylinder bore (25) axis is inclined upward from the position offset to the one side in the left-right direction from the center position in the left-right direction on the upper surface of the crankcase (14C) and extends upward, and the camshaft (42) is stepped left and right. (62, 62) is located on a vertical plane extending in the vehicle longitudinal direction through the center between,
Actuation axis of the intake valve (34) in (LI) is cylinder bore (25) Rutotomoni substantially parallel to set the axis, the cylinder head to open the intake port (51) communicating with the intake valve ports (29) (2 3C), One side surface in the left-right direction is formed substantially parallel to the cylinder bore (25) axis ,
The intake system member (56) connected to the intake port (51) is disposed substantially along the one side surface of the cylinder head (23C) and extends so as to gradually approach the vertical surface. A parallel two-cylinder internal combustion engine for vehicles .

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