JP2001241326A - Cooling structure of forced-air-cooled four cycle engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a cooling structure of a forced-air-cooled four cycle engine capable of selectively cooling a specified position of the engine. SOLUTION: In this cooling structure of a forced-air-cooled four cycle engine wherein a plug attaching seat 18 is disposed between an exhaust port 16 and an intake port vertically opened to a cylinder head 9, the whole of the engine 1 is covered with an air shroud 24, and a part of the engine is forcibly cooled with cooling wind led into the air shroud 24 by a cooling fan 21 rotated coaxially with a crankshaft; an inclining surface 24A inclined toward a specified position (a diagonal line part) of the engine 1 is formed on the air shroud 24, and a flow passage cross section of the air shroud 24 is throttled toward the specified position. Cooling wind is concentrically supplied to the specified position (a region including an exhaust pipe attaching part to the exhaust port 16 and the plug attaching seat 18 having a high temperature) of the engine 1, and the specified position is selectively cooled with a good efficiency by cooling wind.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cooling structure for a forced air-cooled four-cycle engine in which each part of the engine is forcibly cooled by cooling air introduced into an air shroud by a cooling fan.

[0002]

2. Description of the Related Art FIG. 4 shows a conventional example of a cooling structure of such a forced air-cooled four-cycle engine. In the conventional cooling structure, an entire engine 101 including a cylinder body and a cylinder head is made of a resin air shroud. The cooling air introduced into the air shroud 124 by the cooling fan 121 that is covered by the cooling air 124 and rotates coaxially with the crankshaft of the engine 101 flows in the direction indicated by the arrow in FIG.
A configuration is adopted in which each part is forcibly cooled.

[0003]

However, in the above-described conventional cooling structure, since the air shroud 124 simply adopts a structure in which the cylinder body and the cylinder head of the engine 101 are simply wrapped, the cooling air flows through the cylinder body and the cylinder. Although the entirety of the engine 101 is substantially uniformly cooled by passing all around the head and the like, the cooling air is intensively sent to a specific portion of the engine 101 where the temperature is particularly high, and the portion is mainly cooled. That was impossible.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and has as its object to provide a cooling structure of a forced air-cooled four-stroke engine capable of mainly cooling a specific part of the engine. is there.

[0005]

In order to achieve the above object, according to the first aspect of the present invention, a plug mounting seat is provided between an intake port and an exhaust port which open up and down of a cylinder head, and the entire engine is air shroud. And a forced air-cooled four-cycle engine cooling structure for forcibly cooling each part of the engine with cooling air introduced into the air shroud by a cooling fan rotating coaxially with a crankshaft.
The air shroud is formed with an inclined surface inclined toward a specific location of the engine, and a flow path cross section of the air shroud is narrowed toward the specific location.

According to a second aspect of the present invention, in the first aspect of the invention, the specific portion is a region including the plug mounting seat and an exhaust pipe mounting portion for the exhaust port.

Therefore, according to the present invention, since the air shroud is formed with an inclined surface which is inclined toward a specific portion of the engine, the cooling air is supplied to the specific portion of the engine (for example, a high temperature between the plug mounting seat and the exhaust port). (The area including the exhaust pipe attachment area), and since the flow cross section of the air shroud is narrowed down to a specific location, the cooling air is accelerated and guided to the specific location, and the engine The specific location is efficiently and intensively cooled by the cooling air.

[0008]

Embodiments of the present invention will be described below with reference to the accompanying drawings.

FIG. 1 is a plan sectional view of a unit swing type engine, FIG. 2 is a plan sectional view of a four-cycle engine part of the unit swing type engine, and FIG. 3 is a cutaway side view of the four-cycle engine part.

A unit swing type engine 1 shown in FIG.
Numeral 0 is mounted on a scooter-type motorcycle (not shown), which is a forced air-cooled four-stroke engine equipped with a cooling structure according to the present invention (hereinafter simply referred to as engine).
1, a transmission mechanism including a V-belt type automatic transmission 2 is compactly incorporated in a crankcase 3 to constitute a unit.

Here, a schematic configuration of the engine 1 will be described.

The engine 1 is a single-cylinder engine, and a single cylinder 5 is formed in a cylinder body 4 which is disposed substantially horizontally toward the front of the body of the scooter type motorcycle. Are slidably fitted. The piston 6 is connected via a connecting rod 8 to a rotatable crankshaft 7 arranged in the vehicle width direction.

The cylinder head 9 attached to the cylinder body 4 is formed with an intake port and an exhaust port (not shown), respectively. The valve is opened and closed at an appropriate timing by an intake valve and an exhaust valve (not shown) driven by the actuator, thereby performing a required gas exchange in the cylinder 5. A chain sprocket 12 is attached to one end of the camshaft 11, and an endless cam chain 14 is wound between the chain sprocket 12 and a chain sprocket 13 attached to an intermediate portion of the crankshaft 7. The rotation of the crankshaft 7 is transmitted to the camshaft 11 through the chain sprocket 13, the cam chain 14, and the chain sprocket 12, and the camshaft 11 is rotated at a predetermined speed (1/2 of the crankshaft 7).
Speed).

As shown in FIGS. 2 and 3, an intake port 15 connected to the intake port and an exhaust port 16 connected to the exhaust port are opened above and below the cylinder head 9, respectively. An intake pipe 17 is attached to 15, and an exhaust pipe (not shown) is attached to the exhaust port 16. As shown in FIG. 3, a plug mounting seat 18 is formed obliquely on the right side (the right side toward the front of the vehicle body) between the intake port 15 and the exhaust port 16 of the cylinder head 9. The plug mounting seat 18 has a spark plug 1
9 is screwed (see FIG. 1). Although not shown,
A carburetor and an air cleaner are connected to the intake pipe 17 shown in FIG. 3, and an exhaust muffler is connected to the exhaust pipe.

On the other hand, as shown in detail in FIG. 2, the crankshaft 7 is rotatably supported by a pair of right and left bearings 20, and one end (right end) of the cooling fan 2 is provided.
1 is attached, and a generator 22 is provided inside thereof. A drive pulley 23 constituting the V-belt type automatic transmission 2 is attached to the other end (left end) of the crankshaft 7.

The entire engine 1 having the above structure is covered with an air shroud 24 made of resin, and a portion of the air shroud 24 facing the cooling fan 21 has a circular cooling air flow. The inlet 24 a is formed coaxially with the crankshaft 7. Also, air shroud 24
A plug hole 24b that opens diagonally to the side is formed at the front end, and a circular hole 24c for confirming the top dead center is formed behind the plug hole 24b. As shown in FIG. 1, the ignition plug 19 is passed through the plug hole 24b, and the ignition plug 19 is inserted into the plug hole 24b from outside.
5 and a circular hole 24 for confirming the top dead center.
A rubber cap 26 is detachably fitted in c.

Here, the air shroud 24 is attached to the crankcase 3 at a plurality of peripheral portions by screws 27. The upper surface of the air shroud 24 is connected to a plug mounting seat 18 which is a high temperature portion of the engine 1 as shown in FIG. An inclined surface 24A that is inclined downward toward a region including an exhaust pipe attachment portion to the exhaust port 16 (a region shaded in FIG. 3 and hereinafter referred to as a specific portion) is configured. The right side surface of the air shroud 24 forms an inclined surface 24B inclined toward the specific portion as shown in FIG. Therefore,
The cross section of the air shroud 24 is gradually narrowed toward a specific location by the inclined surfaces 24A and 24B.

Next, the structure of the transmission mechanism of the unit swing type engine 10 will be described.

As shown in FIG. 1, a driven shaft 28, an intermediate shaft (not shown) and an output shaft (axle) are provided at the rear of the crankcase 3.
A driven pulley 30 and a centrifugal clutch 31 are attached to a driven shaft 28, and an endless V-belt 32 is wound between the driven pulley 30 and the driving pulley 23. The V-belt type automatic transmission 2 is configured to be mounted. A small-diameter drive gear 33 is integrally formed at one end (right end) of the driven shaft 28.

A drive gear and a driven gear (not shown) of large and small diameters are attached to the intermediate shaft. The drive gear 33 meshes with the driven gear of the intermediate shaft. The drive gear meshes with a large-diameter driven gear 34 attached to the output shaft 29. A rear wheel 35 of a scooter-type motorcycle is attached to an end of the output shaft 29 protruding outward from the crankcase 3. In FIG. 1, reference numeral 36 denotes a kick lever for a kick starter.

Next, the operation of the unit swing type engine 10 having the above configuration will be described.

In the unit swing type engine 10, when the kick lever 36 is operated to start the engine 1 and rotate the crankshaft 7, the cooling fan 21 and the generator 22 coaxially mounted on the crankshaft 7 are driven. And the rotation of the crankshaft 7 is automatically shifted by the V-belt type automatic transmission 2 and transmitted to the centrifugal clutch 31. Here, when the rotation speed of the centrifugal clutch 31 reaches a certain value or more, the centrifugal clutch 31 is turned ON to transmit the rotation to the driven shaft 28, and the rotation of the driven shaft 28 is transmitted to the drive gear 33 and a driven gear (not shown) provided on the intermediate shaft. And is transmitted to the intermediate shaft. The rotation of the intermediate shaft is further reduced through a drive gear and a driven gear 34 (not shown) and transmitted to the output shaft 29. The output shaft 29 and the rear wheel 35 attached to the output shaft 29 are driven to rotate, and the scooter type is rotated. A motorcycle is driven.

On the other hand, in the engine 1, when the cooling fan 21 is driven to rotate as described above, the cooling air is introduced into the air shroud 24 from the cooling air inlet 24a opened on the side surface of the air shroud 24. The cooling air flows in the air shroud 24 in the direction of the arrow in FIG. 3 to cool the components including the cylinder body 4 and the cylinder head 9 of the engine 1.

In the present embodiment, as described above, the air shroud 24 is inclined toward a specific portion of the engine 1 (a region including a plug mounting seat 18 and an exhaust pipe mounting portion to the exhaust port 16). Since the inclined surfaces 24A and 24B are formed, the cooling air flows to a specific portion of the engine 1 (a hatched portion in FIG. 3).
The cooling air is accelerated and guided to a specific location because the flow path cross section of the air shroud 24 is narrowed down toward a specific location. As a result, the engine 1 is identified. The location is efficiently and intensively cooled by the cooling air, and its overheating is effectively prevented.

In this embodiment, the region including the plug mounting seat and the exhaust pipe mounting portion to the exhaust port is selected as the specific portion of the engine to be cooled mainly. However, other arbitrary portions may be used depending on the engine. It is needless to say that the specific portion may be used as a specific portion and the portion may be mainly cooled.

[0026]

As is apparent from the above description, according to the present invention, a plug mounting seat is provided between an intake port and an exhaust port which open up and down of a cylinder head, and the entire engine is covered with an air shroud. In a cooling structure of a forced air-cooled four-stroke engine in which each part of the engine is forcibly cooled by cooling air introduced into the air shroud by a cooling fan rotating coaxially with a crankshaft, the air shroud is directed toward a specific portion of the engine. Since the inclined surface is formed so as to narrow the flow path cross section of the air shroud toward the specific portion, the cooling air is intensively sent to the specific portion of the engine to cool the specific portion intensively. Is obtained.

[Brief description of the drawings]

FIG. 1 is a plan sectional view of a unit swing type engine.

FIG. 2 is a plan sectional view of a forced air-cooled four-stroke engine provided with a cooling structure according to the present invention.

FIG. 3 is a side sectional view of a forced air-cooled four-stroke engine provided with a cooling structure according to the present invention.

FIG. 4 is a side sectional view of a forced air-cooled four-cycle engine showing a conventional cooling structure.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Forced air-cooled 4-cycle engine 7 Crankshaft 9 Cylinder head 15 Intake port 16 Exhaust port 18 Plug mounting seat 21 Cooling fan 24 Air shroud 24A, 24B Inclined surface

Claims (2)

[Claims] 1. A plug mounting seat is provided between an intake port and an exhaust port which open up and down of a cylinder head. The entire engine is covered with an air shroud, and a cooling fan which rotates coaxially with a crankshaft is provided in the air shroud. In a cooling structure of a forced air-cooled four-stroke engine forcibly cooling each part of an engine with introduced cooling air, an inclined surface inclined toward a specific portion of the engine is formed in the air shroud, and a flow path cross section of the air shroud is formed. Characterized in that it is narrowed down toward the specific location. 2. The cooling structure for a forced air-cooled four-stroke engine according to claim 1, wherein the specific portion is a region including the plug mounting seat and an exhaust pipe mounting portion to the exhaust port.