internal combustion engine

Abstract

To suppress influence of an auxiliary machine on blown air and to prevent an occurrence of an event in which the rotation resistance of the auxiliary machine increases due to influence of the blown air.SOLUTION: In a forced air-cooling type internal combustion engine in which a centrifugal fan (43) is provided at an end of a crank shaft (31), an auxiliary machine (51) is provided between a crank case (23) that supports the crank shaft (31) and the centrifugal fan (43), and a space which allows blown air by the centrifugal fan (43) to flow in a cylinder portion (24) is formed by a fan shroud (45), at least either one of the crank case (23) and the fan shroud (45) includes a step portion (73) that couples, with each other, a first partition wall (71) that gradually increases a distance to the centrifugal fan (43) toward the cylinder portion (24) and a second partition wall (72) that makes a distance to the auxiliary machine (51) constant. The step portion (73) is at the same height as that of a bottom surface (M1) of the centrifugal fan (43) in an axial direction of the crank shaft (31).SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present invention relates to an internal combustion engine. [Background technology]

[0002] In recent years, efforts to realize a low-carbon or carbon-free society have become more active, and research and development is being conducted on improving the efficiency of forced air-cooling fans in internal combustion engines in order to reduce CO2 emissions and improve energy efficiency in vehicles. As one example of this type of technology, an internal combustion engine is known in which cooling air generated by a centrifugal fan is sent to the cylinders and an exhaust port is provided below the fan cover to cool the oil pan (see, for example, Patent Document 1). This internal combustion engine has a centrifugal fan at the end of the crankshaft, and an auxiliary device consisting of an alternating current generator (ACG) between the crankcase that supports the crankshaft and the centrifugal fan. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2023-077107 Summary of the Invention [Problem to be solved by the invention]

[0004] In order to improve the efficiency of the forced-air cooling fan, it is desirable to reduce the influence of the auxiliary equipment on the air blown by the centrifugal fan and to prevent the rotational resistance of the auxiliary equipment from increasing due to the influence of the blown air. The present invention has been made in view of the above-mentioned circumstances, and aims to suppress the influence of the auxiliary equipment on the blown air and to prevent a situation in which the rotational resistance of the auxiliary equipment increases due to the influence of the blown air, thereby contributing to improvement of energy efficiency. [Means for solving the problem]

[0005] The present invention provides a forced-air-cooled internal combustion engine in which a centrifugal fan is provided at the end of a crankshaft, auxiliary equipment is provided between the centrifugal fan and a crankcase that supports the crankshaft, and a space is formed by a fan shroud through which the air blown by the centrifugal fan flows into a cylinder section, wherein at least one of the crankcase and the fan shroud is provided with a step portion that connects a first partition that gradually widens the distance to the centrifugal fan toward the cylinder section and a second partition that keeps the distance to the auxiliary equipment constant, and the step portion is at the same height as the bottom surface of the centrifugal fan in the axial direction of the crankshaft. [Effects of the Invention]

[0006] According to the present invention, it is possible to suppress the influence of the auxiliary equipment on the blown air, and to prevent a situation in which the rotational resistance of the auxiliary equipment increases due to the influence of the blown air. [Brief explanation of the drawings]

[0007] [Figure 1] 1 is a side view of a saddle-ride type vehicle according to an embodiment of the present invention. [Figure 2] FIG. [Figure 3] FIG. 3 is a cross-sectional view taken along the line III-III in FIG. 2. [Figure 4] FIG. 4 is a cross-sectional view taken along line IV-IV of FIG. [Figure 5] FIG. 2 is a perspective view showing the fan cover together with the surrounding configuration from diagonally below. [Figure 6] FIG. 5 is an enlarged view of the fan area of ​​FIG. 4. [Figure 7] FIG. 2 is a view showing the inside of the power unit on a plane horizontally intersecting the cylinder axis. DETAILED DESCRIPTION OF THE INVENTION

[0008] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. In the description, directions such as front, rear, left, right, up and down are the same as directions relative to the vehicle body unless otherwise specified. In addition, in each drawing, the symbol FR indicates the front of the vehicle body, the symbol UP indicates the upper side of the vehicle body, and the symbol LH indicates the left side of the vehicle body.

[0009] [Embodiment Mode] FIG. 1 is a side view of a saddle-ride type vehicle 10 according to an embodiment of the present invention. The saddle-ride type vehicle 10 is a vehicle that includes a body frame 11, a power unit 12 supported by the body frame 11, a front fork 14 that supports a front wheel 13 so as to be steerable, a swing arm 16 that supports a rear wheel 15, and a seat 17 for a passenger. The saddle-ride type vehicle 10 is a vehicle in which a passenger sits astride a seat 17. The seat 17 is provided above the rear part of the body frame 11.

[0010] The body frame 11 includes a head pipe 18 provided at the front end of the body frame 11, a front frame 19 located rearward of the head pipe 18, and a rear frame 20 located rearward of the front frame 19. The front end of the front frame 19 is connected to the head pipe 18. The seat 17 is supported by a rear frame 20 .

[0011] The front forks 14 are supported by a head pipe 18 so as to be steerable to the left and right. The front wheel 13 is supported by an axle 13a provided at the lower end of the front forks 14. A steering handle 21 that is held by the rider is attached to the upper end of the front forks 14.

[0012] The swing arm 16 is supported by a pivot shaft 22 that is supported by the body frame 11. The pivot shaft 22 is a shaft that extends horizontally in the vehicle width direction. The pivot shaft 22 is inserted into the front end of the swing arm 16. The swing arm 16 swings up and down around the pivot shaft 22. The rear wheel 15 is supported by an axle 15 a provided at the rear end of the swing arm 16 .

[0013] The power unit 12 is disposed between the front wheels 13 and the rear wheels 15 and is supported by the body frame 11. The power unit 12 is an internal combustion engine. The power unit 12 includes a crankcase 23 and a cylinder section 24 that houses a reciprocating piston. An exhaust device 25 is connected to an exhaust port of the cylinder section 24. The output of the power unit 12 is transmitted to the rear wheels 15 by a driving force transmission member that connects the power unit 12 and the rear wheels 15 .

[0014] The saddle-ride type vehicle 10 also includes a front fender 26 that covers the front wheel 13 from above, a rear fender 27 that covers the rear wheel 15 from above, a step 28 on which a rider places their feet, and a fuel tank 29 that stores fuel used by the power unit 12. The front fender 26 is attached to the front fork 14. The rear fender 27 and the step 28 are provided below the seat 17. The fuel tank 29 is supported by the body frame 11.

[0015] The saddle-ride type vehicle 10 is a motorcycle. The saddle-ride type vehicle 10 includes a body cover 30 that covers the body, such as the body frame 11. The power unit 12 is a unit swing engine in which the internal combustion engine and the swing arm 16 are integrally provided. The front frame 19 is located in front of the power unit 12. The rear frame 20 is located above the power unit 12. The front frame 19 includes a down frame 19a extending downward from the head pipe 18, and a lower frame 19b extending rearward from a lower portion of the down frame 19a. The rear frame 20 extends rearward and upward from the rear end of the lower frame 19b.

[0016] 2 is a right side view of the power unit 12. FIG. 3 is a cross-sectional view taken along line III-III in FIG. As shown in FIG. 2, the crankcase 23 rotatably supports the crankshaft 31, which extends horizontally in the vehicle width direction (left-right direction). An oil pan 23p is provided below the crankcase 23, functioning as an oil storage section that stores oil that lubricates various parts of the power unit 12. The oil pan 23p is located below the crankshaft 31, and the bottom surface of the oil pan 23p forms the bottom surface of the crankcase 23. The crankcase 23 is disposed in front of the rear wheel 15 and is connected to the rear end of the cylinder section 24. In this description, the direction relative to the vehicle body and the direction relative to the power unit 12 coincide with each other.

[0017] The cylinder section 24 extends forward from the front of the crankcase 23. A cylinder axis 24L of the cylinder section 24 extends forward at an angle close to horizontal. A drive pulley that constitutes part of a V-belt type continuously variable transmission is attached to the left portion of the crankshaft 31. The rotation of the crankshaft 31 is transmitted to the axle 15a of the rear wheel 15 via the V-belt type continuously variable transmission. The V-belt type continuously variable transmission is disposed inside the swing arm 16.

[0018] The right side of the crankcase 23 is covered by a fan cover 41 and a cap portion 42. The fan cover 41 is a cover that covers a fan 43 (see FIG. 3 ) provided at the right end of the crankshaft 31 from the outside in the vehicle width direction; in other words, it is a cover that covers the crankshaft 31 and its surroundings. The fan cover 41 has an air intake port 41a that opens to the outside in the vehicle width direction. The front edge of the fan cover 41 is connected to the rear edge of a shroud 44, and the space inside the fan cover 41 communicates with the internal space of the shroud 44. The fan cover 41 and the shroud 44 form a fan shroud 45 that forms a space through which air blown by the fan 43 flows to the cylinder portion 24.

[0019] 2, reference numeral 12x denotes a portion where the power unit 12 is suspended from the body frame 11, that is, an engine hanger portion. The body frame 11 is fixed to the engine hanger portion 12x by fastening bolts. In this embodiment, the fan cover 41 has a recessed avoidance portion 41b that avoids the portion that overlaps with the engine hanger portion 12x in a side view of the vehicle body, and the cap portion 42 is configured to be detachable and positioned to cover the avoidance portion 41b of the fan cover 41.

[0020] Therefore, even when the fan cover 41 is attached to the crankcase 23, by disengaging the cap portion 42, the engine hanger portion 12x can be accessed from the outside, enabling the work of attaching and detaching the power unit 12. As a result, when the power unit 12 is mounted on the vehicle body, the work of fixing the power unit 12 can be performed with the fan cover 41 attached to the power unit 12.

[0021] The fan cover 41 and the cap portion 42 are each provided with two through holes 41h, 42h, and the cap portion 42 can be fixed by inserting fastening bolts 47, 48 into the through holes 41h, 42h from the outer side of the cap portion 42 in the vehicle width direction and fastening them to the crankcase 23. In other words, the cap portion 42 can be easily attached and detached by attaching and detaching the two fastening bolts 47, 48. The position, shape, etc. of the cap portion 42 may be set appropriately depending on the position of the engine hanger portion 12x of the power unit 12.

[0022] As shown in Fig. 3, a flywheel 50 that rotates integrally with the crankshaft 31 is fixed to the right side of the crankshaft 31. Note that the reference symbol C1 in Fig. 3 and other figures described below indicates the center of the crankshaft 31, and will hereinafter be referred to as the crankshaft center C1. The flywheel 50 includes a disk portion 50a extending radially outward from the crankshaft 31, and a cylindrical portion 50b extending inward in the vehicle width direction from the outer periphery of the disk portion 50a. A generator 51 that generates electricity by the rotation of the crankshaft 31 is provided inside the flywheel 50. The generator 51 is an ACG (alternating current generator) and constitutes one of the auxiliaries of the power unit 12. A bottom surface M1 of the centrifugal fan 43 abuts against an end surface M2 of the generator 51 in the crankshaft direction.

[0023] FIG. 4 is a cross-sectional view taken along line IV-IV in FIG. As shown in FIGS. 3 and 4, the fan 43 is provided on the outer side (right side) of the flywheel 50 and the generator 51 in the vehicle width direction. The fan 43 is a centrifugal fan that rotates integrally with the crankshaft 31 to draw in outside air through an intake port 41a (FIG. 2) provided in the fan cover 41 and blow it out in the centrifugal direction of the fan 43. The fan 43 and the generator 51 are provided coaxially with the crankshaft 31 and are rotating bodies that rotate integrally with the crankshaft 31. More specifically, the generator 51 has a rotor that rotates integrally with the crankshaft 31.

[0024] The shroud 44 surrounds the cylinder portion 24 with a gap therebetween, thereby covering approximately the entire circumference of the cylinder portion 24. The space between the shroud 44 and the cylinder portion 24 forms a cylinder cooling air passage 44w that flows the air blown by the fan 43 around the cylinder portion 24. The air that has cooled the cylinder portion 24 is discharged from the gap around the connection port of the exhaust device 25, the gap around the oxygen sensor 24s1, and the like.

[0025] As a result, the power unit 12 is configured as a forced air-cooling type in which the cylinder portion 24 is forcibly air-cooled by air blown by the fan 43 driven by the crankshaft 31. Although FIG. 4 shows a case where the fan 43 is provided with 18 blades 43w, the number and shape of the blades 43w may be changed as appropriate.

[0026] FIG. 5 is a perspective view showing the fan cover 41 together with the surrounding structure from diagonally below. As shown in FIGS. 5, 2 and 4, the lower part of the fan cover 41 is provided with an air exhaust part 41w that exhausts part of the air blown by the fan 43 downwards in the crankcase 23. 4 and 5, the direction of air discharged from air exhaust section 41w is indicated by arrow We. Air exhaust section 41w forms an exhaust passage that extends downward along one of the left and right sides of crankcase 23 and extends inward in the vehicle width direction along the bottom surface of crankcase 23, thereby discharging a portion of the air blown by fan 43 downward and inward in the vehicle width direction to cool oil pan 23p.

[0027] In this configuration, as shown in Fig. 4, the air exhaust section 41w opens rearward and downward with respect to the crankshaft 31, thereby exhausting a portion of the air blown by the fan 43 in a rearward and downward direction. As a result, when the saddle-ride type vehicle 10 is traveling, air can be exhausted along the direction of the traveling wind from the front of the vehicle body, thereby reducing the effects of the traveling wind being drawn in. Note that the position, shape, etc. of the air exhaust section 41w may be changed as appropriate.

[0028] 3, the position of the bottom surface M1 of the fan 43 (corresponding to the height in the crankshaft direction) is indicated by the symbol P1. Since the flywheel 50 and the generator 51 are located inside the fan 43 in the vehicle width direction, the position P1 also indicates the boundary between the fan 43 and the flywheel 50 and the generator 51. In order to improve the efficiency of the fan 43, it is desirable to reduce the influence of the generator 51 (auxiliary equipment) on the air blown by the fan 43 and to prevent the rotational resistance of the generator 51 from increasing due to the influence of the air blown. Therefore, in this embodiment, as shown in Figures 3 and 4, a first partition 71 is provided on the outside in the vehicle width direction based on position P1, which gradually increases the distance to the fan 43 toward the cylinder section 24, and a step section 73 is provided on the inside in the vehicle width direction based on position P1, which connects to a second partition 72 that keeps the distance to the generator 51 constant. The step portion 73 is a portion that forms a step between the first partition 71 and the second partition 72, and is provided at the same height as position P1 of the bottom surface M1 of the fan 43 in the axial direction of the crankshaft 31 (which coincides with the left-right direction of the vehicle body).

[0029] FIG. 6 is an enlarged view of the fan 43 area of ​​FIG. The first partition 71 is formed as a wall that covers the radial outside of the fan 43 from a position Pa below and behind the fan, based on the crankshaft center C1, through to the rear of the fan, above and behind the fan, and above the fan, to a position Pe above and in front of the fan, when viewed from the side of the vehicle body. This first partition wall 71 is closest to the fan 43 at position Pa below and rear of the fan, and the separation distance d1 from the fan 43 gradually increases toward position Pe above and front of the fan, thereby forming an air passage between the outer peripheral surface of the fan 43 and the first partition wall 71 that gradually widens in the fan radial direction toward the cylinder portion 24. This allows air generated in the centrifugal direction from the fan 43 to flow efficiently in the direction indicated by symbol W1 in Figure 6, which means that a large amount of blown air can easily flow through the cylinder cooling air passage 44w inside the shroud 44.

[0030] In this embodiment, a position Pa below and rear of the fan relative to the crankshaft center C1 coincides with the position of the air discharge section 41w. As shown in Fig. 6, the first partition 71 in this embodiment extends from a position Pa below and rear of the fan relative to the crankshaft center C1 to a position Px below and front of the fan, which is opposite the rotation direction of the fan 43. This allows air generated in the centrifugal direction from the fan 43 to flow smoothly from position Px to position Pa, i.e., in the direction indicated by reference symbol W2 in Fig. 6. This allows the blown air to flow efficiently toward the air discharge section 41w and the cylinder cooling air passage 44w, and is also advantageous in reducing the rotational resistance of the fan 43.

[0031] A portion 71a of the first partition 71, extending from a position Pa below and rear of the fan to a position Pc above the fan 43, is formed by at least one of the crankcase 23 and the fan cover 41. A portion 71b of the first partition 71, extending from a position Pc above and front of the fan to a position Pd, is formed by the cap portion 42. A portion 71c of the first partition 71, extending from a position Pd to a position Pe, is formed by the fan shroud 45. Because a portion of the first partition 71 is formed by the cap portion 42 and the fan shroud 45, an increase in the size of the crankcase 23 can be suppressed.

[0032] The second partition 72 is formed as a wall that covers the radial outside of the fan 43 from a position Pb below and behind the fan relative to the crankshaft center C1, through to the rear of the fan, above and behind the fan, and above the fan, to a position Pd above and in front of the fan, when viewed from the side of the vehicle body. In the side view of the vehicle body shown in FIG. 6, this second partition 72 maintains a constant and narrow separation distance d2 from the fan 43. Furthermore, as shown in FIG. 3, the second partition 72 is disposed closer to the generator 51 than position P1 of the bottom surface M1 of the fan 43 in the vehicle width direction, thereby covering the outer peripheral surface of the generator 51 but not the fan 43. This allows the second partition 72 to narrow the gap around the outer periphery of the generator 51 without narrowing the airflow path around the outer periphery of the fan 43, thereby stabilizing the airflow around the generator 51. Therefore, it is possible to suppress the influence of the generator 51 on the air blown by the fan 43, indicated by reference numerals W1 (and W2) in FIG. 6, and to prevent the rotational resistance of the generator 51 from increasing due to the influence of the blown air.

[0033] 6, the second partition 72 of this embodiment includes an extension wall 72c that extends from a position Pd above and in front of the fan relative to the crankshaft center C1 to a position Pe above and in front of the fan. The extension wall 72c is formed as a wall that smoothly extends forward toward the cylinder portion 24. A portion 72a of the second partition 72, extending from a position Pb above and rear of the fan to a position Pc above the fan 43, is formed by at least one of the crankcase 23 and the fan cover 41. A portion 72b of the second partition 72, extending from a position Pc above and front of the fan to a position Pd, is formed by the cap portion 42. A portion (extension wall 72c) of the second partition 72 extending from position Pd to position Pe is formed by the fan shroud 45. Because a portion of the second partition 72 is formed by the cap portion 42 and the fan shroud 45, an increase in the size of the crankcase 23 can be suppressed.

[0034] Furthermore, with regard to step 73 connecting first partition 71 and second partition 72, a portion 73a extending from position Pb above and rear of the fan to near position Pc above the fan relative to crankshaft center C1 is formed by at least one of crankcase 23 and fan cover 41. Further, a portion 73b of step 73 extending from near position Pc to position Pd above and front of the fan is formed by cap portion 42. Furthermore, a portion 73c of step 73 extending from position Pd to position Pe is formed by fan shroud 45. Since a portion of the step portion 73 is formed by the cap portion 42 and the fan shroud 45, the crankcase 23 can be prevented from becoming large.

[0035] As shown in FIG. 6, a plate-shaped cord clamper 81 for fixing the cord of the generator 51 is provided inside the crankcase 23. FIG. 7 is a view showing the inside of the power unit 12 along a plane horizontally intersecting the cylinder axis 24L, and shows the cord clamper 81 together with the surrounding configuration. As shown in Fig. 7, the cord clamper 81 is formed in a plate shape extending in the front-to-rear direction on the vehicle widthwise inner side of the generator 51 in a bottom view. This cord clamper 81 is arranged more inward in the vehicle width direction than the fan 43, as shown in Fig. 7. Furthermore, the cord clamper 81 is arranged in a position that covers the space between the fan 43 and the second partition wall 72, as shown in Fig. 6, in a side view of the vehicle body. This makes it possible for the cord clamper 81 to prevent the air blown by the fan 43, indicated by the symbol W1 in Fig. 6, from leaking into the space between the fan 43 and the second partition wall 72, as seen in a side view of the vehicle body.

[0036] As described above, in the power unit 12 of this embodiment, the fan 43, which is a centrifugal fan, is provided at the end of the crankshaft 31, and the generator 51, which constitutes an accessory, is provided between the crankcase 23 that supports the crankshaft 31 and the fan 43. The power unit 12 is also configured as a forced-air-cooled type in which the fan shroud 45 forms a space through which the air blown by the fan 43 flows toward the cylinder portion 24. With this configuration, the power unit 12 is provided with a step portion 73 that connects the crankcase 23 and the fan shroud 45 to a first partition 71 that gradually increases the distance from the fan 43 toward the cylinder portion 24, and a second partition 72 that keeps the distance from the generator 51 constant.

[0037] With this configuration, the first partition 71 can effectively send the air blown by the fan 43 into the cylinder portion 24, and the second partition 72 can stabilize the airflow by maintaining a constant distance from the generator 51. This reduces the effect of the generator 51 on the blown air and prevents the rotational resistance of the generator 51 from increasing due to the effect of the blown air. Therefore, it is possible to improve the cooling performance of the power unit 12 and reduce the rotational resistance, contributing to improved energy efficiency. Moreover, since the step portion 73 is at the same height as the bottom surface M1 of the fan 43 in the axial direction of the crankshaft 31, the air blown by the fan 43 can be effectively used to cool the cylinder portion 24.

[0038] Furthermore, the cylinder section 24 is arranged horizontally, extending forward from the front of the crankcase 23 at an angle close to horizontal, and the step section 73 extends toward the back of the horizontally arranged cylinder section 24, so that the air blown by the fan 43 can effectively cool the horizontally arranged cylinder section 24.

[0039] Also, the crankcase 23 includes a cap portion 42 that is attached to the power unit 12, and the step portion 73 is composed of the crankcase 23, the cap portion 42, and the fan shroud 45. With this configuration, a portion of the step portion 73 is formed by the cap portion 42 and the fan shroud 45, so that the crankcase 23 can be prevented from becoming large.

[0040] Furthermore, the cap portion 42 is detachably attached to a position that overlaps with the engine hanger portion 12x of the power unit 12 in a side view of the vehicle body, and therefore the engine hanger portion 12x is accessible even with the fan shroud 45 attached to the power unit 12. Therefore, when mounting the power unit 12 on the vehicle body, the power unit 12 can be fixed with the fan shroud 45 attached to the power unit 12, improving workability.

[0041] The power unit 12 also has a plate-shaped cord clamper 81 that secures the cords of the generator 51. The cord clamper 81 is positioned to cover the space between the fan 43 and the second partition wall 72 in a side view of the vehicle body, and is disposed more inward in the crankshaft direction than the fan 43. With this configuration, the cord clamper 81 can prevent the air blown by the fan 43 from leaking into the space between the fan 43 and the second partition wall 72. This is advantageous for improving the cooling performance of the power unit 12. The cord clamper 81 is an example of the "plate-shaped cord clamper 81 for fixing a predetermined cord" of the present invention. The predetermined cord is not limited to the cord of the generator 51, and may be another cord. The shape and position of the cord clamper 81 may also be changed as appropriate.

[0042] Additionally, an exhaust section 41w is provided below fan shroud 45, which exhausts a portion of the air blown by fan 43 downward in crankcase 23. Exhaust section 41w opens downward and rearward with respect to crankshaft 31, and exhausts a portion of the air blown by fan 43 toward oil pan 23p, which is an oil reservoir below crankcase 23. With this configuration, the air blown by fan 43 can be exhausted along the airflow from the front, thereby cooling oil pan 23p while suppressing the effects of wind being drawn in by the airflow.

[0043] Furthermore, bottom surface M1 of fan 43, which is a centrifugal fan, abuts against end surface M2 of generator 51 in the crankshaft direction, and step portion 73 is at the same height as end surface M2 of generator 51 in the axial direction of crankshaft 31. With this configuration, centrifugal fan 43 can be compactly arranged as close as possible to generator 51, while suppressing the effect of generator 51 on the blown air and preventing a situation in which the rotational resistance of generator 51 is increased due to the effect of the blown air. The positional relationship between the bottom surface M1 of the fan 43, the end surface M2 of the generator 51, and the step portion 73 in the axial direction of the crankshaft 31 does not need to be perfectly consistent, and some deviation is allowed. This deviation is not limited to deviation due to dimensional tolerances.

[0044] For example, if the bottom of fan 43 is located inward in the axial direction of crankshaft 31 from step 73, a gap is created between bottom surface M1 of fan 43 and step 73, resulting in diffusion of the cooling air sent out from the outlet of fan 43. Also, if the bottom of fan 43 is located outward in the axial direction of crankshaft 31 from step 73, the cooling air sent out from the outlet of fan 43 hits second partition 72, resulting in a slight decrease in the efficiency of fan 43. However, this is within the scope of the present invention as long as the decrease in efficiency of fan 43 is kept within an appropriate range. Therefore, the description of the present invention that "the step portion 73 is at the same height as the bottom surface M1 of the fan 43 in the axial direction of the crankshaft 31" includes cases where the step portion 73 is not at the same height as the bottom surface M1 of the fan 43, as long as the efficiency of the fan 43 is kept within an appropriate range.

[0045] [Other embodiments] The above-described embodiment merely shows one aspect of the present invention, and any modifications and applications are possible without departing from the spirit of the present invention.

[0046] In the above embodiment, the auxiliary machine of the present invention is the generator 51, but the auxiliary machine may be an auxiliary machine other than the generator 51. Furthermore, in the above embodiment, the present invention has been described as being applied to the power unit (internal combustion engine) 12 of the saddle-ride type vehicle 10 shown in FIG. 1, but the present invention may also be applied to the engine of any saddle-ride type vehicle, the power unit of a vehicle other than a saddle-ride type vehicle, or a power unit (internal combustion engine) used for something other than a vehicle.

[0047] [Configuration supported by the above embodiment] The above embodiment supports the following configurations.

[0048] (Configuration 1) In a forced-air-cooled internal combustion engine in which a centrifugal fan is provided at the end of the crankshaft, an auxiliary device is provided between the centrifugal fan and a crankcase that supports the crankshaft, and a space is formed by a fan shroud to allow the air blown by the centrifugal fan to flow into a cylinder section, at least one of the crankcase and the fan shroud is provided with a step portion that connects a first partition that gradually widens the distance to the centrifugal fan toward the cylinder section and a second partition that keeps the distance to the auxiliary device constant, and the step portion is at the same height as the bottom surface of the centrifugal fan in the axial direction of the crankshaft. With this configuration, the first partition effectively directs the air blown by the centrifugal fan into the cylinder section, and the second partition maintains a constant distance from the auxiliary equipment, stabilizing the airflow. This reduces the effect of the auxiliary equipment on the blown air and prevents the rotational resistance of the auxiliary equipment from increasing due to the influence of the blown air, contributing to improved energy efficiency.

[0049] (Configuration 2) An internal combustion engine according to Configuration 1, wherein the cylinder portion is horizontally disposed so as to extend forward from the front portion of the crankcase at an angle close to horizontal, and the step portion extends toward the back surface of the horizontally disposed cylinder portion. With this configuration, the horizontally disposed cylinder portion can be effectively cooled by the air blown by the centrifugal fan.

[0050] (Configuration 3) The internal combustion engine according to configuration 1 or 2, further comprising a cap portion attached to the internal combustion engine, the step portion being composed of the crankcase, the cap portion, and the fan shroud. According to this configuration, a part of the step portion is formed by the cap portion and the fan shroud, so that an increase in the size of the crankcase can be suppressed.

[0051] (Configuration 4) The internal combustion engine according to any one of configurations 1 to 3, wherein the cap portion is detachably attached to a position that overlaps an engine hanger portion, which is a portion on which the internal combustion engine is suspended, in a side view of the vehicle body. According to this configuration, when mounting the power unit on a vehicle body or the like, the power unit can be fixed with the fan shroud attached to the power unit, improving workability.

[0052] (Configuration 5) An internal combustion engine according to any one of Configurations 1 to 4, wherein an exhaust section is provided at a lower part of the fan shroud to exhaust a portion of the blown air toward below the crankcase, the exhaust section opening rearward and downward with respect to the crankshaft, and the centrifugal fan exhausts a portion of the blown air toward an oil reservoir below the crankcase. According to this configuration, the air blown by the centrifugal fan can be discharged along the wind coming from the front, so that the oil reservoir can be cooled while suppressing the influence of wind being drawn in by the running wind.

[0053] (Configuration 6) An internal combustion engine according to any one of configurations 1 to 5, wherein the bottom surface of the centrifugal fan abuts against an end surface of the auxiliary device in the crankshaft direction, and the step portion is at the same height as the end surface of the auxiliary device in the axial direction of the crankshaft. With this configuration, the centrifugal fan can be positioned as close as possible to the auxiliary equipment in a compact manner, while suppressing the influence of the auxiliary equipment on the blown air and preventing the rotational resistance of the auxiliary equipment from increasing due to the influence of the blown air. [Explanation of symbols]

[0054] 10 Saddle-type vehicle 12 Power unit (internal combustion engine) 23 Crankcase 23p Oil pan (oil reservoir) 24 Cylinder section 24L Cylinder axis 31 Crankshaft 41 Fan cover 41w exhaust part 42 Cap part 43 Fan (Centrifugal Fan) 44 Shroud 45 Fan shroud 51 Generator 71 1st bulkhead 72 Second bulkhead 73 Step part 81 Cord clamper C1 Crankshaft center M1 Bottom of centrifugal fan 43 M2 End face of generator 51 (end face of auxiliary equipment)

Claims

1. A forced-air-cooled internal combustion engine in which a centrifugal fan (43) is provided at an end of a crankshaft (31), an auxiliary device (51) is provided between a crankcase (23) supporting the crankshaft (31) and the centrifugal fan (43), and a fan shroud (45) forms a space through which air blown by the centrifugal fan (43) flows into a cylinder section (24), a step portion (73) that connects a first partition wall (71) that gradually widens the distance from the centrifugal fan (43) toward the cylinder portion (24) to a second partition wall (72) that keeps the distance from the auxiliary machine (51) constant, in at least one of the crankcase (23) and the fan shroud (45); The step (73) is at the same height as the bottom surface (M1) of the centrifugal fan (43) in the axial direction of the crankshaft (31). Internal combustion engine.

2. The cylinder portion (24) is horizontally disposed and extends forward from the front portion of the crankcase (23) at an angle close to horizontal, The step portion (73) extends toward the top of the horizontally disposed cylinder portion (24).

2. The internal combustion engine according to claim 1.

3. a cap portion (42) to be attached to the internal combustion engine; The step portion (73) is composed of the crankcase (23), the cap portion (42), and the fan shroud (45).

3. An internal combustion engine according to claim 1 or 2.

4. The cap portion (42) is detachably attached to a position where it overlaps with an engine hanger portion (12x) on which the internal combustion engine is suspended in a side view.

4. The internal combustion engine according to claim 3.

5. an exhaust section (41w) that exhausts a portion of the blown air downward toward the crankcase (23) is provided at a lower portion of the fan shroud (45); The exhaust section (41w) opens downward and rearward with respect to the crankshaft (31), and exhausts a portion of the air blown by the centrifugal fan (43) toward an oil reservoir (23p) below the crankcase (23).

3. An internal combustion engine according to claim 1 or 2.

6. A bottom surface (M1) of the centrifugal fan (43) abuts against an end surface (M2) of the auxiliary machine (51) in the crankshaft direction, The step portion (73) is flush with the end face (M2) of the auxiliary device (51) in the axial direction of the crankshaft (31).

3. An internal combustion engine according to claim 1 or 2.

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