JPS6349556Y2 - - Google Patents

Description

[Detailed Description of the Invention] Industrial Application Field The present invention relates to an internal combustion engine that is mounted on a motorcycle or the like and has cooling fins exposed to the outside.

Prior Art As shown in Figs. 1 and 2, the cooling fin shape as seen from the cylinder centerline is formed into a square by casting, and the corner b where the linear sides a intersect is 1/4 It is formed into an arcuate surface, and only the straight side part a is buffed to give it a metallic luster, and the corner part b, which corresponds to the curved part, is not buffed and is colored in a plain color like the other parts. I left it there.

Problem to be Solved by the Invention However, when casting a cylinder, if the shapes of the cooling fins arranged in the vertical direction are not precisely matched, the boundary c between the straight side part a and the corner part b
cannot be aligned in a fixed positional relationship, and the boundary portion c tends to become irregular as shown in FIG.

In addition, in the device described in Japanese Utility Model Application Publication No. 52-66841, the cooling fins are sealed by the air guide duct and cannot be seen from the outside, so there is no need to make the side lengths of the cooling fins the same. If the cooling fins are exposed to the outside, it will be unsightly if both ends of the sides of the cooling fins are uneven.

Means and Effects for Solving the Problems The present invention relates to an improvement of the cooling fin structure of a cylinder for an internal combustion engine that overcomes the above-mentioned difficulties. In a cylinder for an internal combustion engine in which a polygonal corner curved portion is left and only the linear side portion connecting the curved portion is polished, the curved surface has a radius of curvature smaller than that of a circular arc that smoothly touches both ends of the adjacent linear side portion. and the corner curved portion is formed at a step closer to the center of the cylinder than the extension line of both ends of the linear side, and the end of the corner curve is curved outward to form a substantially right angle to both ends of the linear side. It is characterized by being connected to.

In the present invention, the fins of the cylinder are formed into a polygonal shape when viewed from the cylinder center line, and only the straight side parts connecting the curved parts are polished, leaving the curved corners of the polygon. The corner curved portion is formed at a step that is a curved surface with a smaller diameter than a circular arc that smoothly touches both ends of the linear side and is closer to the center of the cylinder than the extension line of both ends of the linear side, Since the ends of the curved portions are curved outward and connected at a substantially right angle to both ends of the linear sides, if only the positions of the ends of the step corner curved portions are set in a constant positional relationship, the cooling fins can be easily Even if the distance from the cylinder center to the linear side portion varies somewhat for each cooling fin, the positions of the boundaries between the stepped corner curved portion and the linear side portion can always be regularly aligned.

Embodiment An embodiment of the present invention illustrated in FIGS. 3 and 4 will be described below.

1 is an aluminum cylinder block of an air-cooled gasoline engine for a motorcycle, and approximately square cooling fins 2 are integrally provided on the outer periphery of the cylinder block 1 at predetermined intervals along the center line of the cylinder block 1. The cooling fins 2 are formed so as to become linearly narrower from the top to the bottom.

Further, a step 5 of approximately 0.5 to 1.0 mm toward the center of the cylinder is formed at both boundary portions 6 between each linear side portion 3 of the cooling fin 2 and the corner curved portions 4 adjacent to both ends thereof.

Further, the corner curved portion 4 is formed on a curved surface having a smaller diameter than the circular arc 7 that smoothly contacts the linear side portion 3 at both the boundary portions 6 .

Furthermore, the entire outer peripheral surface of the cylinder block 1 is painted black.

The embodiment shown in FIGS. 3 and 4 is constructed as described above, so that only the straight sides 3 of the cooling fins 2 are polished, in contrast to the other black areas. Only part 3 is given metallic luster.

Since the step 5 is formed at the boundary 6 between the straight side portion 3 and the corner curved portion 4, the buffing range is reliably defined.

As a result, buffing becomes easy, and the boundary 6 between the black background part and the silver metallic luster part of the cooling fin 2 is accurately positioned, and the boundary 6 is regular as shown in FIG. This creates a visually accurate and functional impression of the engine.

Effects of the invention As described above, according to the invention, if the cylinder is manufactured so that only the positions of the ends of the corner curved portions have a constant positional relationship, the cooling fin can be reached from the center of the cylinder to the straight side portion. Even if the distance varies somewhat from cooling fin to cooling fin, the boundary line between the edge of the stepped corner curved part and the straight side can be easily aligned, so machining can be carried out efficiently and machining costs can be reduced. can be reduced.

Further, in the present invention, the corner curved portion is formed on a curved surface having a smaller radius of curvature than a circular arc that smoothly touches both ends of the adjacent linear side portion, and is located at a step closer to the center of the cylinder than the extension line of both ends of the linear side portion. form,
The end of the corner curved part is curved outward and connected at a substantially right angle to both ends of the straight side part, and the straight side part is polished into a straight shape, thereby increasing the amount of heat dissipated from this polished part. Moreover, it is possible to increase the heat dissipation area at this wide corner, thereby improving the cooling performance, and also making the temperature gradient nearly uniform, thereby reducing internal distortion of the cylinder due to thermal expansion and contraction.

[Brief explanation of the drawing]

FIG. 1 is a plan view of a cylinder block of a conventional air-cooled internal combustion engine, FIG. 2 is a side view thereof, FIG. 3 is a plan view of a cylinder block showing an embodiment of an air-cooled internal combustion engine according to the present invention, and FIG. is its side view. 1...Cylinder block, 2...Cooling fin,
3...Straight side part, 4...Corner curved part, 5...Step, 6...Boundary part, 7...Circular arc.

Claims (1)

[Scope of utility model registration request] In an internal combustion engine cylinder in which the fins of the cylinder are formed into a polygonal shape when viewed from the cylinder center line, the polygonal corner curved portion is left, and only the linear side portions connecting the curved portions are polished. The corner curved portion is formed on a curved surface having a smaller diameter of curvature than a circular arc that smoothly touches both ends of the side portion, and is located at a step closer to the center of the cylinder than the extension line of both ends of the linear side portion, and the corner curved portion ends are A cooling fin structure for a cylinder for an internal combustion engine, characterized in that the cooling fin is curved outward and connected substantially at right angles to both ends of the linear side.