JPS6120251Y2 - - Google Patents

Description

[Detailed description of the invention] This invention relates to a forced air-cooled engine equipped with a centrifugal cooling fan.

Typically, this type of engine has a cut-off point around the cooling fan. However, when the cooling fan was covered with an air guide cover, it was observed that cooling air was blown out from a part of the air intake port that was shifted by approximately 45 degrees toward the lower side of rotation than the cut-off point.

This is because the wind sent out by the fan blade
The highest pressure is reached near the point where the cutoff point is shifted approximately 45 degrees toward the lower side of the rotation, and with the help of the relatively large ventilation resistance on the cylinder side, the high-pressure air flows between the rotating surface of the fan's front end and the air guide cover. It is assumed that the air flows out through the gap and blows out from the air intake port.

The main purpose of this invention is to prevent cooling air from blowing back and improve the air blowing efficiency of the cooling fan without significantly reducing the amount of air taken in from the air intake. A feature is that a blowback prevention wall for catching blowback cooling air is formed at a location that is shifted, for example, approximately 45 degrees toward the lower side of the rotation from the cutoff point.

Examples of this invention will be described below based on the drawings.

FIG. 1 is a front view with main parts of the forced air-cooled engine cut away, and FIG. 2 is a sectional view taken along the line shown in FIG. 1. This engine has a crankcase 1, a cylinder 2, and a fan case bracket 3 that are integrally cast to form an outer shell, and inside the outer shell there is a crankshaft 4 and a piston, camshaft, valve train, etc. (not shown) for operation. It is constructed in a known structure to house the members.

A crankshaft 4 protrudes from the front surface of the crankcase 2, and a centrifugal cooling fan 5, which also serves as a flywheel, is fixed to the crankshaft 4. In order to guide the cooling air sent out from the cooling fan 5 to the cylinder 2 and head cover 6 side,
The outer surface of the cooling fan 5 is covered with a wind guide cover 7.

This air guide cover 7 is attached to a circumferential side wall 7a that surrounds the front surface of the engine along the fan case bracket 3.
and a front wall 7b facing the cooling fan 5, cylinder 2, etc., forming a container shape, and the front wall 7b has a portion facing the inner edge of the fan blade 5a to form an air intake port 8. There is. This wind guide cover 7
In order to guide the cooling air to the cylinder 2 side when the cooling fan 5 rotates in either the left or right direction, the lower center of the circumferential wall 7a is brought closest to the rotating circumferential surface of the fan blade 5a, and the shutoff is made. It forms a point S.

A blowback prevention wall 9 is formed on the inner edge of the air suction port 8 at a position deviating from the cut-off point S by approximately 45 degrees on the downstream side of the rotation, projecting toward the rotation center of the cooling fan 5. As shown in FIG. 2, the blowback prevention wall 9 extends so as to completely cover the inner edge of the fan blade 5a on the blowing side.

Symbols 10 and 11 in the figure are cylinder side cooling air outlets,
12 is a head side cooling outlet, 13 is a non-contact ignition unit, and 14 is a recoil starter.

With the above configuration, the high-pressure cooling air sent out from the fan blade 5a on the rotationally downstream side of the cutoff point S is directed to the front end of the fan blade 5a and the front wall 7.
Even if it moves to the side of the air intake port 8 through the gap C with the air outlet b, the blowback prevention wall 9 catches it and prevents it from blowing out to the outside. After being caught by the above-mentioned prevention wall 9, the cooling air is guided toward the rotation center, merges with the main flow of intake air, and is sucked into the cooling fan 5 again. Therefore, not only can leakage of cooling air be prevented, but also the collision of the returned cooling air with the main flow of intake air and disturbance of the intake air flow can be prevented, and the air blowing efficiency of the cooling fan 5 can be increased accordingly. It is possible to improve the cooling effect of the engine. Moreover,
On the inside of the air intake port 8, a blowback prevention wall 9 is formed only at a portion slightly below the cut-off point S, and the air intake port 8 is made to have a wide opening, so that the air intake efficiency of the cooling fan is not very high. Does not decrease. In addition, dust blown back by the returned cooling air may adhere to the internal mechanism of the recoil starter 14 and obstruct its operation, but this can also be eliminated.

FIGS. 3A and 3B show different embodiments, and A
The one shown in FIG.
In the example shown in FIG.
Each differs from the above embodiments in that they are formed gradually closer to the center of rotation.

In the above embodiment, a vertical single-cylinder engine has been described, but the type of engine, number of cylinders, etc. are not particularly limited.

As explained above, in this invention, air is blown out through the air intake port of the air guide cover from a portion on the rotationally downstream side of the cut-off point. Since the cooling air is caught by the blowback prevention wall, it eliminates the leakage of cooling air, and also prevents interference between the blowback cooling air and the intake airflow, eliminating disturbance of the intake airflow. The cooling fan's air blowing efficiency can be improved by that amount, and the engine's cooling capacity can be increased. Moreover, since the air intake port is wide open in the portion other than the blowback prevention wall, the air intake efficiency of the cooling fan is hardly reduced, and the engine cooling effect can be maintained at a high level.

[Brief explanation of the drawing]

The drawings show an embodiment of this invention; FIG. 1 is a cutaway front view of the main parts of the engine, FIG. 2 is a sectional view taken along the line of FIG. 1, and FIGS. FIG. 3 is a cross-sectional view of the fan case and a front view of the fan case. 5... Cooling fan, 5a... Fan blade,
7... Air guide cover, 8... Air intake port of 7, 9... Back blow prevention wall, S... Closing point.

Claims (1)

[Scope of claim for utility model registration] 1. The outer surface of the centrifugal cooling fan 5 is covered with a wind guide cover 7.
A cut-off point S is formed facing the circumferential surface of the cooling fan 5, and a blow-back prevention wall 9 is disposed at a portion slightly downstream of the cut-off point S. is on the inner edge of the air intake port 8 of the air guide cover 7,
A forced air-cooled engine characterized by being formed in a shape to catch cooling air blown back from inside the air guide cover 7 to the outside. 2 Utility Model Registration Claims The forced air-cooled engine according to claim 1, in which a part of the peripheral wall of the air intake port 8 extends toward the rotation center of the cooling fan 5 to form a blowback prevention wall 9. 3 Utility Model Registration The forced air-cooled engine according to claim 1, in which a blowback prevention wall 9 is formed to face the edge of the fan blade 5a on the intake side of the cooling fan 5.