JPH09242599A - Structure of two-cycle engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enhance air-tightness between a cylinder barrel and a cylinder head by integrally forming the inner circumferential. wall portion of the cylinder barrel on the cylinder head, and connecting the cylinder head to the outer peripheral wall portion in a state in which the inner circumferential wall portion is fitted to the outer peripheral wall portion of the cylinder barrel. SOLUTION: The outer peripheral wall portion 2 of a cylinder barrel is integrally formed above a crank case 1 with an aluminum die-cast or the like. Similarly, the inner circumferential wall portion 6 of the cylinder barrel is integrally formed under a cylinder head 5 with an aluminum die-cast or the like. The inner circumferential, wall portion 6 of the cylinder head 5 is press- fitted into the outer peripheral wall portion 2 formed above the crank case 1. The cylinder head 5 is integrally tightened to the outer peripheral wall portion 2 via a bolt 7. A window-shaped scavenging port 11 opened to a cylinder bore is formed on the inner circumferential wall portion 6 of the cylinder barrel. Furthermore, a grooved scavenging port 12 is formed on the inner circumferential side of the outer peripheral wall portion 2 of the cylinder barrel.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a crankcase,
The present invention relates to a structure of a two-cycle engine including a cylinder barrel and a cylinder head.

[0002]

2. Description of the Related Art Conventionally, as a structure of a two-cycle engine, for example, a structure as shown in FIG. 4A and a structure as shown in FIG. 4B are known.

FIG. 4A shows a cylinder liner in which a crankcase 101 integrally provided with a cylinder barrel 102, a cylinder liner 103 with which a piston 108 slides, and a cylinder head 105 are separately formed in advance. 103 is pressed into the cylinder barrel 102, and the upper edge of the cylinder liner 103 is sandwiched between the cylinder barrel 102 and the cylinder head 105.
And with the gasket 106 interposed in this portion,
The cylinder head 105 is fastened to the upper end of the cylinder barrel 102 with a bolt 107.

In the structure shown in FIG. 4B, a cylinder barrel 112 is integrally connected to a cylinder head 115, and a crankcase 111 is formed separately from the cylinder head 115. The lower end of the cylinder barrel 112 and the crankcase 111 are formed. The upper end is fastened with a bolt 117. The inner peripheral surface of the cylinder barrel 112 formed integrally with the cylinder head 115 is in sliding contact with the piston 108.
Further, a scavenging passage 120 for guiding the air-fuel mixture from the crankcase 111 into the cylinder is formed directly on the inner peripheral surface of the cylinder barrel 112.

[0005]

Among the conventional structures described above, according to the structure shown in FIG.
The cylinder liner is made of ferrous metal, while the cylinder barrel 102 is integrally provided with the crankcase 101.
Also, since the cylinder head 105 is formed of an aluminum-based metal and the thermal expansion coefficient of the aluminum-based metal is higher than that of the iron-based metal, the press-fitting margin between the cylinder barrel 102 and the cylinder liner 103 during engine operation is reduced. When the difference in thermal expansion due to the temperature increase becomes large, a gap may be formed between the two. In such a case, the cooling efficiency is reduced, and even if the cylinder head 105 is firmly fastened to the cylinder barrel 102, the cylinder liner 103 itself vibrates, and these factors reduce the engine performance. .. Furthermore, since the cylinder liner 103 and the cylinder head 105 are separate members, the gasket 106 is required, and it is also difficult to ensure complete airtightness with the gasket 106.

Further, according to the structure shown in FIG. 4 (b), a groove-shaped scavenging passage 120 is directly formed on the inner peripheral surface of the cylinder barrel 112 which is in sliding contact with the piston 108, and this scavenging passage forming portion is formed. Is separated from the piston 108, the guide surface of the piston 108 becomes extremely small,
The piston swings easily. Therefore, the durability of the piston, the piston ring, the piston ring groove, the cylinder port, etc. is adversely affected.

In view of these circumstances, the present invention can prevent vibration of a portion corresponding to a cylinder liner and a decrease in cooling efficiency to improve engine performance, ensure airtightness, and further, to prevent the piston neck. An object of the present invention is to provide a structure of a two-cycle engine that can suppress swinging and improve durability of a piston ring and the like.

[0008]

In order to achieve the above object, the present invention provides a two-cycle engine having a crankcase, a cylinder barrel and a cylinder head, in which the inner peripheral wall portion of the cylinder barrel is integrated with the cylinder head. A cylinder head is connected to the outer peripheral wall portion of the cylinder barrel in a coupled state with the inner peripheral wall portion fitted to the outer peripheral wall portion of the cylinder barrel.

According to this structure, since the inner peripheral wall portion of the cylinder barrel is integrated with the cylinder head, the airtightness between them is completely ensured, and the cylinder head is mounted on the outer peripheral wall portion of the cylinder barrel. By being fixed, the vibration of the inner peripheral wall portion of the cylinder barrel is reliably prevented. In addition, the cylinder barrel integrated with the cylinder head secures the guide surface of the piston and prevents the piston from swinging.

In the present invention, the outer peripheral wall portion of the cylinder barrel may be integrally formed with the crankcase.
Further, it is preferable that a member in which the inner peripheral wall portion of the cylinder barrel is integrally connected to the cylinder head and a member in which the outer peripheral wall portion of the cylinder barrel is integrally connected to the crankcase are formed of the same material. With this configuration, since the outer peripheral wall portion and the inner peripheral wall portion of the cylinder barrel have the same thermal expansion coefficient, the press-fitting margin does not change due to thermal expansion during engine operation.

In the present invention, as a method of disposing the scavenging port and the scavenging passage, for example, a window hole-shaped scavenging port opening to the cylinder bore is formed in the inner peripheral wall portion of the cylinder barrel, while the outer peripheral wall portion of the cylinder barrel is formed. A groove-shaped scavenging passage may be formed on the inner peripheral surface side of the.

Alternatively, a scavenging port opening to the cylinder bore may be provided in the inner peripheral wall portion of the cylinder barrel, and a scavenging passage communicating with the scavenging port may be formed on the outer peripheral surface side of the inner peripheral wall portion. This is advantageous in terms of molding and processing.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described with reference to FIGS.
It will be described based on. FIG. 1 shows the structure of the entire engine according to the first embodiment of the present invention. In this figure, 1 is a crankcase, and this crankcase 1
The outer peripheral wall portion 2 of the cylinder barrel is integrally formed on the upper part of the. That is, the crankcase 1 and the cylinder barrel outer peripheral wall portion 2 are integrally formed by aluminum die casting or the like. A crankshaft 3 is rotatably supported on the crankcase 1. Further, an intake port 4 for introducing an air-fuel mixture through a reed valve 4a is provided at a predetermined lower portion of the crankcase 1.

Reference numeral 5 denotes a cylinder head, and an inner peripheral wall portion 6 of the cylinder barrel is integrally connected to a lower portion of the cylinder head 5. That is, the inner peripheral wall portion 6
Corresponds to a conventional cylinder liner, but this portion 6 and the cylinder head 5 are integrally formed by aluminum die casting or the like. The inner peripheral wall portion 6 is press-fitted into the outer peripheral wall portion 2 connected to the crankcase 1, and the cylinder head 5 is fastened to the outer peripheral wall portion 2 with bolts 7.

A piston 8 is slidably arranged inside the inner peripheral wall portion 6, and the piston 8 is connected to the crankshaft 3 via a connecting rod 9.

Further, in the portion forming the cylinder barrel, scavenging and exhaust ports 11 opening in the cylinder,
13 and scavenging and exhaust passages 12 and 14 communicating therewith, and in the present embodiment, the ports 11 and 13 are formed in the inner peripheral wall portion 6, while the passages 12 and 14 are formed in the outer peripheral wall portion 2. 14 is formed.

That is, as shown in FIG. 2, the inner peripheral wall portion 6 is formed on a comparatively thin cylinder, and a scavenging port 11 is provided at a predetermined number of positions thereof, and an exhaust port 13 is provided at another predetermined position. Are provided, and the scavenging port 11 and the exhaust port 13 are formed in a window hole shape that penetrates the inner peripheral wall portion 6 inward and outward. On the other hand, the outer peripheral wall portion 2 is formed thicker than the inner peripheral wall portion 6, and a scavenging passage 12 is provided at a predetermined number of locations on the inner peripheral surface side of the outer peripheral wall portion 2 and corresponds to the exhaust port 13. An exhaust passage 14 is formed at the location.

The scavenging passage 12 is formed in a groove shape extending downward from a portion corresponding to the scavenging port 11 so that the scavenging port 11 communicates with the space inside the crankcase 1. The exhaust passage 14 is formed to penetrate the outer peripheral wall portion 2 inward and outward. The cylinder head 5 is provided with a plug hole 17 for mounting the spark plug 16.

The structure of the present embodiment as described above is superior to the conventional structure shown in FIG. 4A in terms of cooling efficiency, prevention of vibration of the inner peripheral wall of the cylinder barrel, and ensuring of airtightness. ing.

That is, since the cylinder barrel outer peripheral wall portion 2 integral with the crankcase 1 and the cylinder barrel inner peripheral wall portion 6 integral with the cylinder head 5 are made of the same aluminum-based material, the engine is in operation. It is possible to prevent the press-fitting margin from changing due to the thermal expansion, and to keep the cooling efficiency excellent. Further, since the cylinder barrel inner peripheral wall portion 6 is integrated with the cylinder head 5, the outer peripheral wall portion 2 is
Even if a slight gap occurs between the inner peripheral wall portion 5 and the inner peripheral wall portion 5, vibration of the inner peripheral wall portion 5 can be prevented as long as the cylinder head 5 is firmly fastened to the outer peripheral wall portion 2 of the cylinder barrel. It Further, no gasket is required between the cylinder head 5 and the cylinder barrel inner peripheral wall 6, and the airtightness is completely ensured.

Further, as compared with the conventional structure shown in FIG. 4B, it is advantageous in preventing the piston from swinging. That is, the cylinder barrel inner peripheral wall portion 6 integrated with the cylinder head 5 has a function equivalent to a cylinder liner, and forms a sliding contact surface with the piston 8 inside the scavenging passage 12, so that the piston 8 swings. The function of preventing the above is ensured, whereby the durability of the piston ring and the like is improved and the engine performance is also improved.

FIG. 3 shows a second embodiment of the present invention. Also in this embodiment, the outer peripheral wall portion 22 of the cylinder barrel is integrally connected to the crankcase 21, while the inner peripheral wall portion 26 of the cylinder barrel is integrally connected to the cylinder head 25, and the inner peripheral wall portion 26 is the outer periphery. With the cylinder head 25 being pressed into the wall portion 22, the cylinder head 25
The point of being fastened to No. 2 is the same as that of the first embodiment. In this embodiment, as a difference from the first embodiment, the scavenging passage 32 is formed on the outer peripheral side of the inner peripheral wall portion 26.

More specifically, the cylinder head 25
The inner peripheral wall portion 26 connected to the inner peripheral wall portion 26 is thicker than that of the first embodiment, and the scavenging port 31 opening to the cylinder bore is formed at a predetermined number of the inner peripheral wall portion 26. A groove-shaped scavenging passage 32 continuous with the scavenging port 31 is formed on the outer peripheral side of the scavenging port 31. The scavenging passage 32 is formed to extend to the lower end portion of the inner peripheral wall portion 26 and communicates with the inside of the crankcase 21. Has become. On the other hand, the outer peripheral wall portion 22 has a wall thickness reduced by an increase in the wall thickness of the inner peripheral wall portion 26, and the inner peripheral surface thereof is a substantially circumferential surface, and the scavenging passage 32 formed in the inner peripheral wall portion 26. Is formed so as to cover the. Exhaust port 3
3 and the exhaust passage 34 communicating therewith are formed so as to penetrate inward and outward at corresponding portions of the inner peripheral wall portion 26 and the outer peripheral wall portion 22.

Also according to the second embodiment, the same action and effects as those of the first embodiment can be obtained, such as improvement of cooling efficiency, prevention of vibration of the inner peripheral wall of the cylinder barrel, ensuring airtightness, and prevention of swinging of the piston. To be Furthermore, the second embodiment is more advantageous in terms of molding, processing, etc. than the first embodiment.

That is, when the scavenging passage 12 is formed on the inner peripheral side of the outer peripheral wall portion 2 of the cylinder barrel integral with the crankcase 1 as in the first embodiment, the shapes of the die casting mold and the core are complicated at the time of molding. In addition, since the scavenging passage 12 is formed by using the core, it is difficult to make the position of the scavenging passage 12 uniform. Further, in order to improve the intake efficiency, it is desired that the upper end of the scavenging passage 12 is smoothly connected to the scavenging port 11 to smooth the scavenging, but the scavenging port 11 and the scavenging passage 12 are formed as separate members. In addition, since the positions of the scavenging passages 12 are difficult to be uniform as described above, vertical and horizontal shift steps are likely to occur between the scavenging ports 11 and the upper ends of the scavenging passages 12.

On the other hand, according to the second embodiment, the scavenging passage 32 is formed on the outer peripheral side of the cylinder barrel inner peripheral wall portion 26, that is, the groove forming the passage is formed on the outer peripheral side of the cylindrical portion. Therefore, the structure of the die casting mold is simplified and the cost can be reduced.
The positions of 2 can be made uniform. Further, since both the scavenging port 31 and the scavenging passage 32 are continuously formed in the cylinder barrel inner peripheral portion 26, there is no shift step between the scavenging port 31 and the scavenging passage 32, and the intake efficiency is improved. Be advantageous.

[0027]

As described above, according to the present invention, in the two-cycle engine, the cylinder head is integrally coupled to the inner peripheral wall portion of the cylinder barrel, and the inner peripheral wall portion and the outer peripheral wall portion of the cylinder barrel are fitted to each other. Since the cylinder head is connected to the outer peripheral wall portion in this state, the airtightness between the cylinder barrel and the cylinder head is ensured, the vibration of the inner peripheral wall portion of the cylinder barrel is surely prevented, and the neck of the piston is prevented. Swing can be prevented. Therefore, the performance and durability of the engine can be improved.

Particularly, if a member in which the inner peripheral wall portion of the cylinder barrel is integrally connected to the cylinder head and a member in which the outer peripheral wall portion of the cylinder barrel is integrally connected to the crankcase are formed of the same material, The press-fitting margin between the outer peripheral wall portion and the inner peripheral wall portion is suppressed from changing due to thermal expansion during engine operation, which is advantageous for improving cooling efficiency and the like.

If a scavenging port opening to the cylinder bore is provided in the inner peripheral wall portion of the cylinder barrel, and a scavenging passage communicating with the scavenging port is formed on the outer peripheral surface side of the inner peripheral wall portion, the molding is performed. In addition, the processing is simplified, and there is no shift step between the scavenging port and the scavenging passage, which is advantageous in terms of intake efficiency.

[Brief description of drawings]

FIG. 1 is a sectional view showing an overall structure of a two-cycle engine according to a first embodiment of the present invention.

FIG. 2 is an enlarged sectional view showing a main part of the structure of a two-cycle engine.

FIG. 3 is an enlarged cross-sectional view showing a main part of a structure of a two-cycle engine according to a second embodiment.

FIG. 4A is a sectional view showing one type of conventional structure, and FIG. 4B is a sectional view showing another type of conventional structure.

[Explanation of symbols]

 1,21 Crankcase 2,22 Cylinder barrel outer peripheral wall part 5,25 Cylinder head 6,26 Cylinder barrel inner peripheral wall part 11,31 Scavenging port 12,32 Scavenging passage

Claims (5)

[Claims] 1. A two-cycle engine including a crankcase, a cylinder barrel and a cylinder head, wherein the cylinder head is integrally connected to an inner peripheral wall portion of the cylinder barrel, and the inner peripheral wall portion and the outer peripheral wall portion of the cylinder barrel are connected to each other. A structure of a two-cycle engine, characterized in that a cylinder head is connected to the outer peripheral wall portion in a fitted state. 2. The structure of a two-cycle engine according to claim 1, wherein an outer peripheral wall portion of the cylinder barrel is integrally connected to the crankcase. 3. A member in which an inner peripheral wall portion of a cylinder barrel is integrally connected to a cylinder head, and a member in which an outer peripheral wall portion of a cylinder barrel is integrally connected to a crankcase are formed of the same material. The structure of the two-cycle engine according to claim 2. 4. A window-shaped scavenging port opening to the cylinder bore is formed in the inner peripheral wall portion of the cylinder barrel, and a groove-shaped scavenging passage is formed on the inner peripheral surface side of the outer peripheral wall portion of the cylinder barrel. The structure of the two-stroke engine according to any one of claims 1 to 3. 5. The inner peripheral wall portion of the cylinder barrel is provided with a scavenging port opening to the cylinder bore, and a scavenging passage communicating with the scavenging port is formed on the outer peripheral surface side of the inner peripheral wall portion. The structure of the two-stroke engine according to any one of 1 to 3.