JP6851409B2 - Internal combustion engine for saddle-type vehicles - Google Patents

Description

The present invention relates to an internal combustion engine for a saddle-type vehicle provided with a cooling air passage capable of effective cooling.

In the cylinder head of an internal combustion engine for a saddle-type vehicle, ribs are erected in the cooling air passage (air jacket) in the front-rear direction to deflect the cooling air, branch from the cooling air passage in the front-rear direction, and head toward the spark plug seat. The structure that guides air to the cooling air passage in the lateral direction is also shown in the patent application of the present applicant, for example, as in the following patent document.
However, it is required to guide the cooling air toward the spark plug seat more efficiently and cool the spark plug more preferably.

Japanese Unexamined Patent Publication No. 2004-13853 (FIGS. 2 to 4)

In view of the above prior art, the present invention provides an internal combustion engine for a saddle-type vehicle capable of more efficiently guiding cooling air toward a spark plug seat and efficiently cooling the spark plug in a cylinder head. Make it an issue.

In order to solve the above problems, according to the present invention,
It is provided with a crankcase that rotatably supports the crankshaft, and a cylinder portion that has a cylinder bore that slidably fits a piston connected to the crankshaft and forms a combustion chamber that faces the top of the piston.
The cylinder portion is an internal combustion engine for a saddle-type vehicle having a cylinder block forming the cylinder bore and a cylinder head coupled to the cylinder block and supporting a valve operating mechanism.
The cylinder head has a front-rear cooling air passage that passes between the perimeter of the intake port and the perimeter of the exhaust port arranged in the front-rear direction of the vehicle.
A lateral cooling air passage that branches from the front-rear cooling air passage toward the side surface of the vehicle extends around the spark plug seat.
The lateral cooling air passage includes a bottom wall on the combustion chamber side and an upper wall on the valve mechanism side.
The upper wall on the upstream side of the spark plug seat is provided with an upper wall rib projecting toward the bottom wall.
The upper wall rib is provided over both ends in the passage width direction of the spark plug side opening located on the upstream side in the vicinity of the spark plug seat in the lateral cooling air passage. Institutions are provided.

According to the internal combustion engine for saddle-type vehicles of the present invention.
The cooling air that has entered the front-rear cooling air passage in the cylinder head is diverted to the lateral cooling air passage and flows around the spark plug seat to cool the spark plug seat and the screw-mounted ignition plug. Since the cooling air that hits the upper wall rib in the passage is blown down toward the lower spark plug seat, the cooling air toward the spark plug seat and the spark plug mounted screwed in is strengthened, and effective cooling is performed. be able to.

Since the upper wall ribs are provided at both ends in the path width direction of the spark plug side opening at the upstream position near the spark plug seat, a downward cooling air flow is created over the entire width of the spark plug side opening. The spark plug seat and the spark plug screwed into the spark plug seat can be cooled more effectively.

According to a preferred embodiment of the present invention
The upper wall ribs are formed by a top portion formed by a top portion farthest from the top wall, an upstream slope from the top wall on the upstream side of the top wall toward the top portion, and from the top portion. It has a downstream slope toward the downstream side of the spark plug side opening.
The spark plug screwed into the spark plug seat is located on the virtual extension surface of the upstream slope.
Therefore, the direction of the cooling air guided by the upstream slope of the upper wall rib points to the spark plug, and the spark plug is effectively cooled.

According to a preferred embodiment of the present invention
The upper wall rib has a concave elliptical arc shape or a normal arc shape toward the spark plug seat in the direction of the plug screwing axis of the spark plug seat, and is inward in the center of the passage width direction of the upper wall rib. The normal is provided so that it faces the center of the plug.
Therefore, the distance between the entire upper wall rib and the spark plug seat can be kept within a certain range, and the cooling air passing through the opening on the spark plug side hits the screw-mounted ignition plug as a whole, and the spark plug is effective. It is cooled.

According to a preferred embodiment of the present invention
The front-rear cooling air passage and the lateral cooling air passage are provided with an air guide wall having an inclined surface that deflects the cooling air toward the upper wall rib and the spark plug seat.
Therefore, the flow rate of the cooling air from the front-rear cooling air passage to the upper wall rib, the spark plug seat, and the ignition plug screwed into the spark plug seat can be increased, and the spark plug can be cooled more effectively. To.

According to a preferred embodiment of the present invention
The wind guide wall is formed by connecting the upper wall and the bottom wall.
The wind guide wall is formed by connecting the upper wall and the bottom wall, and by not providing a gap between the wind guide wall and the upper wall and the bottom wall, the directivity of the airflow of the cooling air can be improved, and the cylinder head. The rigidity of the is also improved. Further, since the upper wall rib extends from the upper wall, the amount of air guided to the upper wall rib increases due to the wind guide wall.

According to the internal combustion engine for saddle-type vehicles of the present invention.
The cooling air that has entered the front-rear cooling air passage in the cylinder head is diverted to the lateral cooling air passage and flows around the spark plug seat to cool the spark plug seat and the screw-mounted ignition plug. Since the cooling air that hits the upper wall rib in the passage is blown down toward the lower spark plug seat, the cooling air toward the spark plug seat and the spark plug mounted screwed in is strengthened, and effective cooling is performed. be able to.

It is a right side schematic diagram of the motorcycle which concerns on one Embodiment of this invention. It is a right side view which shows the internal combustion engine in FIG. 1 taken out. It is sectional drawing of the cylinder part by the arrow III-III in FIG. FIG. 3 is a plan sectional view of the cylinder head viewed from the arrow IV-IV in FIG. FIG. 4 is a vertical cross-sectional view of the cylinder head as viewed by the arrow VV in FIG. FIG. 5 is a top view of a cross section of a front-rear cooling air passage and a lateral cooling air passage of a cylinder head as viewed from the arrow VI-VI in FIG. FIG. 5 is a perspective view of the cylinder head viewed from the arrow VII.

An internal combustion engine for a saddle-type vehicle according to an embodiment of the present invention will be described with reference to FIGS. 1 to 7.
The directions of the front, back, left, right, up and down, etc. within the scope of the description and claims of the present specification shall follow the orientation of the saddle-type vehicle equipped with the internal combustion engine for the saddle-type vehicle according to the present embodiment. In the present embodiment, the saddle-mounted vehicle is a motorcycle.
Further, the arrow FR in the figure indicates the front of the saddle-mounted vehicle according to the present embodiment, LH indicates the left side of the vehicle, RH indicates the right side of the vehicle, and UP indicates the upper part of the vehicle.
In addition, the small arrows drawn on each device and member schematically indicate the flow of cooling air.

FIG. 1 is a schematic view of the right side surface of a motorcycle (“saddle-type vehicle” in the present invention) 1 according to an embodiment of the present invention.
The body frame 2 of the motorcycle 1 of the present embodiment extends rearward from the head pipe 20 while the main frame 21 is covered by the fuel tank 16 from above, extends slightly downward, and then bends downward. The pivot frame 21a is formed. From the head pipe 20, the down frame 22 extends diagonally backward and downward in the center of the vehicle width direction.

The front part of the crankcase 30 in the internal combustion engine (“internal combustion engine for saddle-mounted vehicle” in the present invention) 3 is attached to the support bracket 22a at the lower part of the down frame 22 by hanger bolts 3a at two places above and below, and the crankcase. The rear portion of the 30 is attached to the support bracket of the pivot frame 21a by a hanger bolt 3b, and the internal combustion engine 3 is supported by the vehicle body frame 2.
A pair of left and right seat rails 23 extend rearward from the bent portion of the main frame 21, and a back stay 24 connecting the seat rail 23 and the central portion of the pivot frame 21a supports the seat rail 23.

A front fork 10 is pivotally supported by the head pipe 20, a front wheel 11 is pivotally supported at the lower end thereof, and a steering handle 12 is provided at the upper end of the pivot shaft of the front fork 10.
A swing arm 13 whose front end is pivotally supported by a pivot shaft 25 provided at the lower part of the pivot frame 21a extends rearward, and a rear wheel 14 is pivotally supported at the rear end, and the central portion of the swing arm 13 and the back stay 24 A rear cushion (not shown) is installed between the two.
The fuel tank 16 is erected on the main frame 21 so as to straddle the left and right sides, and the seat 17 is supported by the seat rail 23 behind the fuel tank 16.

The internal combustion engine 3 according to the present embodiment is integrally provided with a multi-speed transmission in the rear portion of the crankcase 30 as shown in FIG. 2 which is a right side view showing the internal combustion engine 3 in FIG. 1 taken out. , A so-called power unit, in which the crankshaft line X of the crankshaft 31 is oriented in the vehicle width direction of the motorcycle 1, that is, in the left-right direction, and the cylinder portion 32 is slightly tilted forward to stand upright. This is an air-cooled single-cylinder SOHC type 4-stroke cycle internal combustion engine mounted on a motorcycle 1.

In the internal combustion engine 3, the cylinder block 33 and the cylinder head 34 are sequentially stacked diagonally above the crankcase 30, and are integrally fastened by the stud bolt 40a inserted into the stud bolt insertion hole 40 (see FIG. 4), and the cylinder head is integrally fastened. A cylinder head cover 35 is placed on the 34, and the cylinder block 33, the cylinder head 34, and the cylinder head cover 35 are cranked by tilting the central axis of the cylinder bore 33a formed in the cylinder block 33, that is, the cylinder axis C forward. It constitutes a cylinder portion 32 that protrudes slightly forward from the case 30.
A throttle body 53, which is an intake system component 51, is connected to the rear side of the cylinder portion 32 via an intake pipe 52, a throttle valve 53b is internally provided in the throttle body 53, and a fuel injection valve 54 is provided in the intake pipe 52. It is provided. An exhaust pipe 57, which is an exhaust system component 56, is connected to the front side of the cylinder portion 32, and the exhaust pipe 57 extends rearward on the right side of the lower part of the vehicle and is connected to the muffler 58 (see FIG. 1).

As shown in FIG. 3, which is a cross-sectional view of the cylinder portion 32 viewed from the arrow III-III in FIG. 2, the cylinder portion 32 is mounted on the cylinder block 33 directly fastened to the crankcase 30 and on the cylinder block 33. It mainly comprises a cylinder head 34 and a cylinder head cover 35 mounted on the cylinder head 34. A piston 45 is slidably fitted in the cylinder bore 33a of the cylinder block 33, and a combustion chamber 36 is formed between the top of the piston 45 and the cylinder head 34.
A spark plug 39 is attached to the right side of the cylinder head 34 so as to face the combustion chamber 36.
Due to the combustion of the mixture of fuel and outside air in the combustion chamber 36, the piston 45 reciprocates in the cylinder bore 33a, and the reciprocating motion is converted into the rotational motion of the crankshaft 31 via the connecting rod 46.

As shown in FIG. 3, a valve chamber 60 is defined in the cylinder head 34, and a camshaft 61 having a camshaft axis Y parallel to the crank axis X is provided above the bottom wall portion 60b. A valve operating mechanism 6 mainly composed of a camshaft 61 for both intake and exhaust equipped with an intake cam 63 and an exhaust cam 64 is supported.
A cam chain chamber 65 that houses a transmission mechanism 62 that transmits the power of the crankshaft 31 to the valve operating mechanism 6 and communicates the inside of the crankcase 30 and the inside of the cylinder head 34 is provided on one side of the cylinder portion 32, and the cam is provided. The shaft 61 is driven in cooperation with the crankshaft 31 via a transmission mechanism 62 by a cam chain 62a.
The transmission mechanism 62 may be configured by other means such as a gear train.

Intake ports 37 and exhaust ports 38 are formed in the rear portion and the front portion of the cylinder head 34, respectively (see FIG. 4), and the combustion chamber side openings 37a and 38a of the ports 37 and 38 form the combustion chamber ceiling wall 36a. It is formed through and is opened and closed by an intake valve and an exhaust valve (not shown).
In FIG. 3, the combustion chamber side opening 38a of the exhaust port 38 is located on the other side of the drawing, and the combustion chamber side opening 37a of the intake port 37a is located on the front side of the drawing.
The camshaft 61 is rotated by the transmission mechanism 62 at a rotation speed of 1/2 of that of the crankshaft 31, and the valve mechanism 6 is an intake valve by the movement of the intake cam 63 and the exhaust cam 64 formed on the camshaft 61. , The exhaust valve can be opened and closed at a predetermined timing.

In the throttle body 53 shown in FIG. 2, an intake passage 53a connected to the intake port 37 is formed, and the intake passage 53a is opened and closed by a butterfly type throttle valve 53b. Further, a fuel injection valve 54 for injecting fuel into the intake pipe 52 is attached to the intake pipe 52 on the downstream side of the throttle body 53. The fuel injection valve 54 may be provided on the throttle body 53.

In the cylinder head 34 of the internal combustion engine 3 of the present embodiment, between the bottom wall portion (“upper wall” in the present invention) 60b and the combustion chamber ceiling wall (“bottom wall” in the present invention) 36a of the valve chamber 60. A front-rear cooling air passage 9 that passes between the perimeter of the exhaust port 38 and the perimeter of the intake port 37, which are arranged in the front-rear direction of the vehicle, is provided, and the exhaust port 38 side, which is the front part in the traveling direction of the motorcycle 1. To the intake port 37 side, which is the rear part in the direction of travel, the running air is taken in as cooling air to cool the cylinder head 34, especially around the exhaust port 38 and the combustion chamber ceiling wall 36a, and in addition, around the spark plug 39. It is intended to cool.

As shown in FIG. 4, which is a plan sectional view of the cylinder head 34 viewed from the IV-IV arrow in FIG. 3, the front-rear cooling air passage 9 of the present embodiment is the cylinder head 34 of the internal combustion engine 3 when mounted on a vehicle. In the front wall portion 34a, a wind guide opening 9a is provided on the left side of the cylinder head front opening 38b of the exhaust port 38.
Further, in the rear wall portion 34b of the cylinder head 34, an exhaust air opening portion 9b is provided on the left side portion of the cylinder head rear side opening 37b of the intake port 37.

That is, the front-rear cooling air passage 9 is provided at a position linearly rearward in the front-rear direction from the air-guide opening 9a provided on the left side of the exhaust port 38 in the top view, and the exhaust air opening provided on the left side of the intake port 37. A portion 9b is provided, and a lateral cooling air passage 9c that branches in the vehicle side surface direction is further provided from the middle of the front-rear cooling air passage 9.
The lateral cooling air passage 9c extends around the spark plug seat 39a through the plug side opening 91 and is open to the right outside.

As shown in FIG. 5, which is a vertical sectional view of the cylinder head 34 as viewed by VV in FIG. 4, the lateral cooling air passage 9c has the combustion chamber ceiling wall 36a of the combustion chamber 36 as the bottom wall 36a. The bottom wall portion 60b of the valve chamber 60 is provided as the upper wall 60b, and the upper wall 60b on the upstream side of the spark plug seat 39a is provided with the upper wall rib 92 protruding toward the bottom wall 36a.

The upper wall rib 92 is formed in the spark plug side opening 91 located on the upstream side near the spark plug seat 39a in the lateral cooling air passage 9c, in the front-rear direction cooling air of the cylinder head 34 according to the VI-VI arrow in FIG. As shown in FIG. 6, which is a top view of the cross section of the passage 9 and the lateral cooling air passage 9c, the lateral cooling air passage 9c intersects the lateral cooling air passage 9c over both ends in the passage width direction of the upper wall 60b surface of the lateral cooling air passage 9c. It is provided to do so.
Then, as shown in FIG. 5, the upper wall rib 92 protrudes from the upper wall 60b toward the bottom wall 36a, and the top portion 92a formed by the top portion farthest from the top wall 60b and the top side are continuously formed. It has an upstream slope 92b from the upper wall 60b on the upstream side of the portion 92a toward the top 92a, and a downstream slope 92c from the top 92a toward the downstream side of the spark plug side opening 91.
Therefore, the spark plug 39 screwed into the spark plug seat 39a is located on the virtual extension surface S of the upstream slope 92b.

Further, as shown in FIG. 7, which is a perspective view of the cylinder head 34 viewed from the arrow VII in FIG. 5, the upper wall rib 92 is attached to the spark plug seat 39a in the plug screwing axis Z direction of the spark plug seat 39a. It has a concave elliptical arc shape or a regular arc shape, and is provided so that the inward normal line N at the center O in the passage width direction of the upper wall rib 92 faces the plug screwing center Zo of the spark plug seat 39a.

As shown in FIG. 4, the front-rear cooling air passage 9 and the lateral cooling air passage 9c have a wind guide wall 96 having an inclined surface that deflects the cooling air toward the upper wall rib 92 and the spark plug seat 39a. The wind guide wall 96 is provided, and is formed by connecting the upper wall 60b and the bottom wall 36a.
That is, in the front-rear cooling air passage 9 and the lateral cooling air passage 9c, the cooling air is deflected toward the spark plug seat 39a and the upper wall rib 92 between the branch portion 95 and the spark plug side opening 92. A plurality of air guide walls 96 having a predetermined width are provided, and the air guide wall 96 serves as an upper wall 60b in the front-rear cooling air passage 9 and the lateral cooling air passage 9c. It is formed by connecting the bottom wall portion 60b of 60 and the combustion chamber ceiling wall 36a which is the bottom wall 36a.

As a modified example of the top view shown in FIG. 4, an exhaust air opening is located on the right side of the intake port 37 at a position symmetrical with respect to the air guide opening 9a provided on the left side of the exhaust port 38 and the cylinder axis C. Even when 9b is provided, the upper wall rib 92 of the present embodiment has the same effect.

As described above, in the internal combustion engine 3 for a saddle-mounted vehicle of the present embodiment, the crankcase 30 that rotatably supports the crankshaft 31 and the piston 45 connected to the crankshaft 31 are slidably fitted. A cylinder portion 32 having a cylinder bore 33a and forming a combustion chamber 36 facing the top of the piston 45 is provided, and the cylinder portion 32 is coupled to the cylinder block 33 forming the cylinder bore 33a and a valve operating valve. An internal combustion engine for a saddle-type vehicle having a cylinder head 34 that supports the mechanism 6 has the following features.
That is, the cylinder head 34 has a front-rear cooling air passage 9 that passes between the periphery of the intake port 37 and the periphery of the exhaust port 38 arranged in the front-rear direction of the vehicle, and the front-rear cooling air passage 9 is directed toward the side surface of the vehicle. A branching lateral cooling air passage 9c extends around the spark plug seat 39a.
The lateral cooling air passage 9c includes a bottom wall 36a on the combustion chamber 36 side and an upper wall 60b on the valve mechanism 6 side, and faces the bottom wall 36a on the upstream side upper wall 60b of the spark plug seat 39a. It has a protruding upper wall rib 92.

Therefore, the cooling air that has entered the front-rear cooling air passage 9 in the cylinder head 34 is diverted to the lateral cooling air passage 9c, flows around the spark plug seat 39a, and is screwed into the spark plug seat 39a. However, since the cooling air that hits the upper wall rib 92 in the lateral cooling passage 9c is blown down toward the lower spark plug seat 39a, it is screwed into and mounted on the spark plug seat 39a and the spark plug seat 39a. The cooling air toward the spark plug 39 is strengthened, and effective cooling can be performed.

Further, since the upper wall rib 92 is provided over both ends of the spark plug side opening 91 located on the upstream side near the spark plug seat 39a in the lateral cooling air passage 9c in the passage width direction, the spark plug side opening A downward cooling air flow can be created over the entire width of 91, and the spark plug 39a and the spark plug 39 screwed into the spark plug seat 39a can be cooled more effectively.

The upper wall rib 92 includes a top portion 92a formed by the top portion farthest from the top wall 60b, an upstream slope 92b extending from the top wall 60b on the upstream side of the top portion 92a to the top portion 92c, and a top portion. The spark plug 92 having a downstream slope 92c from 92a toward the downstream side of the spark plug side opening 91 and screwed into the spark plug seat 39a is located on the virtual extension surface S of the upstream slope 92b. There is.
Therefore, the direction of the cooling air guided by the upstream slope 92b of the upper wall rib 92 is directed toward the spark plug 39, and the spark plug 39 is effectively cooled.

Further, the upper wall rib 92 forms a concave elliptical arc shape or a regular arc shape toward the spark plug seat 39a in the plug screwing axis Z direction of the spark plug seat 39a, and the center O in the passage width direction of the upper wall rib 92. The normal line N in the above is provided so as to face the plug screwing center Zo of the spark plug seat 39a.
Therefore, the distance between the entire upper wall rib 92 and the spark plug seat 39a can be kept within a certain range, and the cooling air passing through the spark plug side opening 91 hits the screw-mounted ignition plug 39 as a whole, and the spark plug 39 is effectively cooled.

The front-rear cooling air passage 9 and the lateral cooling air passage 9c are provided with a wind guide wall 96 having an inclined surface that deflects the cooling air toward the spark plug seat 39a and the upper wall rib 92.
Therefore, the flow rate of the cooling air from the front-rear cooling air passage 9 toward the upper wall rib 92, the spark plug seat 39a, and the spark plug 39 screwed in can be increased, and the cooling of the spark plug 39 is more effective. Be done.

The wind guide wall 96 is formed by connecting the upper wall 60b and the bottom wall 36a.
As described above, the wind guide wall 96 is formed by connecting the upper wall 60b and the bottom wall 36a, and by not providing a gap between the wind guide wall 96 and the upper wall 60b and the bottom wall 36a, the air flow of the cooling air can be flowed. The directivity can be improved, and the rigidity of the cylinder head 34 is also improved.
Further, since the upper wall rib 92 extends from the upper wall 60b, the amount of air guided to the upper wall rib 92 is increased by the wind guide wall 96.

Although one embodiment of the present invention has been described above, the present invention is not limited to the above-described embodiment, and various other modifications can be made within the scope of the gist of the present invention.
In particular, in the above embodiment, it is shown that the cylinder head 34 and the cylinder block 33 forming the cylinder portion 32 are projected upward from the crankcase 30 with the cylinder axis C slightly tilted forward in the vehicle-mounted direction. However, the cylinder axis C is projected upward from the crankcase 30 with a slight backward tilt in the vehicle-mounted direction, and the cylinder axis C is located approximately horizontally in the vehicle-mounted direction from the crankcase 30 to the front. The present invention also includes a case where the cylinder is tilted forward until it is projected. In that case, "upper" in the cylinder head or cylinder block as the cylinder part is the direction away from the crankcase, "lower" is the direction toward the crankcase, and "front" and "rear" are when the cylinder axis C is mounted on the vehicle. It refers to the side facing at least forward and backward regardless of the inclination of the direction.
The "saddle-type vehicle" is not limited to the motorcycle of the present embodiment, and includes various saddle-type vehicles such as a motorcycle, a two-wheeled vehicle, and a multi-wheeled buggy.
For convenience of explanation, the left-right arrangement of the device has been described according to the illustrated embodiment, but the present invention is not limited to this, and the left-right arrangement may be reversed.

1 ... Motorcycle ("saddle-type vehicle" in the present invention), 2 ... Body frame, 3 ... Internal combustion engine ("Saddle-type vehicle internal combustion engine" in the present invention), 6 ... Valve mechanism, 9 ... Front-rear direction Cooling air passage, 9a ... Wind guide opening, 9b ... Exhaust air opening, 9c ... Lateral cooling air passage, 30 ... Crank case, 31 ... Crank shaft, 32 ... Cylinder part, 33 ... Cylinder block, 33a ... Cylinder bore, 34 ... Cylinder head, 34a ... Front wall, 34b ... Rear wall, 35 ... Cylinder head cover, 36 ... Combustion chamber, 36a ... Combustion chamber ceiling wall ("bottom wall" in the present invention), 37 ... Intake port, 37a ... Combustion chamber side opening, 37b ... Cylinder head rear opening, 38 ... Exhaust port, 38a ... Combustion chamber side opening, 38b ... Cylinder head front opening, 39 ... Spark plug, 39a ... Spark plug seat, 45 ... Piston, 51 ... Intake System parts, 52 ... Intake pipe, 54 ... Fuel injection valve, 60 ... Valve chamber, 60b ... Bottom wall ("upper wall" in the present invention), 61 ... Camshaft, 62 ... Transmission mechanism, 62a ... Cam chain, 63 ... Intake cam, 64 ... Exhaust cam, 65 ... Cam chain chamber, 91 ... Spark plug side opening, 92 ... Upper wall rib, 92a ... Top, 92b ... Upstream slope, 92c ... Downstream slope, 95 ... Branch part, 96 ... Wind guide wall, C ... Cylinder axis, X ... Crank axis, Y ... Camshaft axis, Z ... Spark plug seat 39a plug screwing axis, Zo ... Spark plug seat 39a plug screwing center, S ... Virtual extension surface of the upstream slope 92b, O ... Center in the passage width direction of the upper wall rib 92, N ... Normal line at the center O in the passage width direction of the upper wall rib 92.

Claims (5)

It has a crankcase (30) that rotatably supports the crankshaft (31), a cylinder bore (33a) that slidably fits the piston (45) connected to the crankshaft (31), and the piston (33a). It is equipped with a cylinder part (32) that forms a combustion chamber (36) that faces the top of 45).
The cylinder portion (32) includes a cylinder block (33) forming the cylinder bore (33a) and a cylinder head (34) that is coupled to the cylinder block (33) and supports a valve operating mechanism (6). In the internal combustion engine (3) for saddle-mounted vehicles
The cylinder head (34) has a front-rear cooling air passage (9) that passes between the perimeter of the intake port (37) and the perimeter of the exhaust port (38) arranged in the front-rear direction of the vehicle.
A lateral cooling air passage (9c) branching from the front-rear cooling air passage (9) toward the side surface of the vehicle extends around the spark plug seat (39a).
The lateral cooling air passage (9c) includes a bottom wall (36a) on the combustion chamber (36) side and an upper wall (60b) on the valve operating mechanism (6) side.
The upper wall (60b) on the upstream side of the spark plug seat (39a) is provided with an upper wall rib (92) protruding toward the bottom wall (36a) .
The upper wall rib (92) is provided over both ends in the passage width direction of the spark plug side opening (91) located on the upstream side near the spark plug seat (39a) in the lateral cooling air passage (9c). An internal combustion engine for saddle-type vehicles, which is characterized by being used. It has a crankcase (30) that rotatably supports the crankshaft (31), a cylinder bore (33a) that slidably fits the piston (45) connected to the crankshaft (31), and the piston (33a). It is equipped with a cylinder part (32) that forms a combustion chamber (36) that faces the top of 45).
The cylinder portion (32) includes a cylinder block (33) forming the cylinder bore (33a) and a cylinder head (34) that is coupled to the cylinder block (33) and supports a valve operating mechanism (6). In the internal combustion engine (3) for saddle-mounted vehicles
The cylinder head (34) has a front-rear cooling air passage (9) that passes between the perimeter of the intake port (37) and the perimeter of the exhaust port (38) arranged in the front-rear direction of the vehicle.
A lateral cooling air passage (9c) branching from the front-rear cooling air passage (9) toward the side surface of the vehicle extends around the spark plug seat (39a).
The lateral cooling air passage (9c) includes a bottom wall (36a) on the combustion chamber (36) side and an upper wall (60b) on the valve operating mechanism (6) side.
The upper wall (60b) on the upstream side of the spark plug seat (39a) is provided with an upper wall rib (92) protruding toward the bottom wall (36a) .
The upper wall rib (92) is formed by a top portion (92a) formed by a top portion farthest from the top wall (60b) and the top wall (60b) on the upstream side of the top wall portion (92a). It has an upstream slope (92b) toward the top (92a) and a downstream slope (92c) from the top (92a) toward the downstream of the spark plug side opening (91).
The spark plug (39) screwed into the spark plug seat (39a) is located on a virtual extension surface (S) of the upstream slope (92b). .. The upper wall rib (92) forms a concave elliptical arc or a regular arc toward the spark plug seat (39a) in the direction of the plug screwing axis (Z) of the spark plug seat (39a). Claim 1 or claim 2 characterized in that the inward normal line (N) at the center (O) in the passage width direction of the upper wall rib (92) is provided so as to face the plug screwing center (Zo). Internal combustion engine for saddle type vehicle described in. The front-rear cooling air passage (9) and the lateral cooling air passage (9c) have inclined surfaces that deflect the cooling air toward the upper wall rib (92) and the spark plug seat (39a). The internal combustion engine for a saddle-type vehicle according to any one of claims 1 to 3, wherein a wind wall (96) is provided. The internal combustion engine for a saddle-type vehicle according to claim 4 , wherein the wind guide wall (96) is formed by connecting the upper wall (60b) and the bottom wall (36a).

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