JP3301125B2 - 2 cycle engine - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention changes the exhaust timing according to the operating condition by forming a main exhaust port and a sub-exhaust port on the inner peripheral surface of a cylinder and conducting or blocking the sub-exhaust port. It relates to an enabled two-stroke engine.

[0002]

2. Description of the Related Art A scavenging port and an exhaust port, which are opened and closed by reciprocating sliding of a piston, are formed on the inner peripheral surface of a cylinder of a two-cycle engine, and when the piston descends to the bottom dead center during an explosion stroke, The scavenging port and the exhaust port are opened so that the exhaust gas in the cylinder is exhausted from the exhaust port, and at the same time, the air-fuel mixture primarily compressed from the scavenging port is charged into the cylinder.

In general, the more the exhaust port is provided near the top dead center in the cylinder, the earlier the exhaust timing can be made and the output at the time of high-speed rotation can be improved. If it is provided, the exhaust timing is too early at low speed rotation and the torque decreases,
There is a possibility that the air-fuel mixture will blow through and the fuel efficiency will deteriorate.

Therefore, the exhaust port is divided into a main exhaust port and a sub-exhaust port and opened on the inner peripheral surface of the cylinder, respectively.
The upper end of the opening of the auxiliary exhaust port is located closer to the top dead center than the upper end of the opening of the main exhaust port, and the auxiliary exhaust port is turned on or off by an opening / closing means such as an exhaust valve according to the operating condition. The two-cycle engine has been put to practical use.

The auxiliary exhaust port is shut off at the time of low-speed rotation of the two-cycle engine, and exhaust gas is exhausted only from the main exhaust port at a late timing. When the two-cycle engine is rotating at a high speed, the sub exhaust port is conducted, and the exhaust gas is discharged from the sub exhaust port at an early timing, and then from the main exhaust port.

As described above, the exhaust is performed at a low timing during low-speed rotation, and the exhaust is performed at an early timing during high-speed rotation, so that good output, torque characteristics and fuel consumption characteristics can be obtained from low-speed rotation to high-speed rotation. .
The timing at which the sub exhaust port opens and closes in the cylinder, that is, the difference between the height of the upper edge of the opening of the main exhaust port and the height of the upper edge of the opening of the sub exhaust port depends on the usage of the two-stroke engine and the like. Is set.

[0007]

However, in the case of such a two-stroke engine, when making minor changes such as changing the timing at which the auxiliary exhaust port opens and closes in the cylinder to change the engine characteristics, etc. It was necessary to newly design and remanufacture the cylinder block with the height of the upper edge of the opening changed.

For this reason, a new casting mold has to be manufactured, which leads to a great increase in cost, and a long time is required for designing the cylinder block and manufacturing the casting mold, which delays the development of the engine. Such a problem arises.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and it is possible to easily change the opening / closing timing of a sub-exhaust port without newly designing a cylinder block, thereby reducing costs and shortening an engine development period. It is an object of the present invention to provide a two-stroke engine that can be designed.

[0010]

In order to achieve the above object, a two-stroke engine according to the present invention comprises a main exhaust port which is opened and closed by reciprocating sliding of a piston on an inner peripheral surface of a cylinder formed in a cylinder block. And a sub-exhaust port are opened, and a two-stroke engine provided with an opening / closing means for conducting or blocking the sub-exhaust port according to the operating condition is provided with a recess at a peripheral portion corresponding to the sub-exhaust port on the top surface of the piston. The opening and closing timing of the auxiliary exhaust port is set according to the depth of the concave portion on the outer peripheral surface of the piston.

[0011]

When the two-stroke engine is constructed as described above, the opening / closing timing of the auxiliary exhaust port can be easily changed only by changing the depth of the concave portion, that is, by replacing the piston. For this reason,
When changing the opening / closing timing of the sub-exhaust port, it is not necessary to remanufacture the cylinder block as in the conventional case, and it is possible to realize a significant cost reduction and a shortened engine development period.

[0012]

An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a longitudinal sectional view of a two-stroke engine showing one embodiment of the present invention. The two-cycle engine 1 is, for example, a single-cylinder engine for a motorcycle, and has a crankcase 2 in which a cylinder block 3 and a cylinder head 4 are fixed in order.

A cylinder 5 is formed in the cylinder block 3, and a piston 6 slidably inserted into the cylinder 5 and a crankpin of a crankshaft 7 rotatably supported in the crankcase 2. 8 are connected by a connecting rod 9 so that the reciprocating sliding of the piston 6 is converted into a rotational movement of the crankshaft 7.

A combustion chamber 11 matching the cylinder 5 is formed in the cylinder head 4, and a spark plug 12 is screwed into the center of the combustion chamber 11 from the outside. In addition, cylinder 5
A water jacket 13 is formed around the combustion chamber 11.

A reed valve housing 14 is formed in the crankcase 2, and a reed valve 15 is installed therein. A carburetor (not shown) is connected to an outer opening of the reed valve housing 14, and an inner opening is connected to the inside of the crankcase 2 and a scavenging port 16 formed in the cylinder block 3. The scavenging port 16 is open on the inner peripheral surface of the cylinder 5.

On the inner peripheral surface of the cylinder 5, a main exhaust port 17 is provided at a position facing the scavenging port 16, and a pair of left and right positions located on both sides of the main exhaust port 17 as shown in FIGS. Sub exhaust ports 18L and 18R are opened. For example, the auxiliary exhaust ports 18L, 18R
The main exhaust port 17 is opened such that the height of the upper edge of the opening coincides with the height of the upper edge of the opening of the main exhaust port 17. The main exhaust port 17 and the sub exhaust ports 18L and 18R are opened and closed by the reciprocating sliding of the piston 6 together with the scavenging port 16. The main exhaust port 17 passes through the outside of the cylinder block 3, and an exhaust muffler (not shown) is connected to an outer opening thereof. The sub-exhaust ports 18L and 18R join the exhaust port 17 in the cylinder block 3, and exhaust valves 20L and 20R are provided at intermediate portions thereof. These exhaust valves 20L and 20R serve as opening / closing means for conducting or shutting off the auxiliary exhaust ports 18L and 18R according to the operating condition of the two-cycle engine 1.

The exhaust valves 20L and 20R are formed in a cylindrical shape having, for example, notches 21L and 21R and pinion gears 22L and 22R, and are arranged so as to extend longitudinally through the auxiliary exhaust ports 18L and 18R, and are rotatable. The exhaust valves 20L and 20R are rotationally displaced, and the notches 21L and 21R are moved to the auxiliary exhaust ports 18L and
The sub exhaust ports 18L and 18R are made conductive when they match with 18R.

A rack gear 23 meshes with the pinion gears 22L and 22R. The rack gear 23 is reciprocally movable along its longitudinal direction by an actuator (not shown). When the rack gear 23 moves, the pinion gears 22L and 22R are driven, and the exhaust valve 2 is moved.
0L and 20R are rotationally displaced, and the auxiliary exhaust ports 18L and 18R are displaced.
R is turned on or off. Although FIGS. 2 and 3 show the exhaust valve 20L side open and the exhaust valve 20R side closed in order to make the drawings easy to understand, actually, both exhaust valves 20L and 20R are simultaneously opened and closed. Operate. And both exhaust valves 20L, 20R
Is closed during low-speed rotation of the two-cycle engine 1,
It is controlled to open at high speed rotation.

As shown in FIG. 4, recesses 25L and 25R are formed on the top surface of the piston 6 at peripheral portions corresponding to the auxiliary exhaust ports 18L and 18R. These recesses 25L, 25R are formed in, for example, an inclined surface climbing toward the center of the top surface of the piston 6. The depth H of the recesses 25L, 25R on the outer peripheral surface of the piston 6
The opening / closing timing of the sub exhaust ports 18L, 18R is set according to this.

That is, as described above, the sub exhaust port 1
The height of the upper edge of the opening of each of the openings 8L and 18R is the same as the height of the upper edge of the opening of the main exhaust port 17, but since the recesses 25L and 25R are formed in the piston 6, its depth H is increased. The auxiliary exhaust ports 18L and 18R open earlier than the main exhaust port 17 by the amount of. The depth H is changed to freely set the time difference in which the auxiliary exhaust ports 18L and 18R open before the main exhaust port 17. be able to.

When the two-stroke engine 1 is rotating at high speed, the exhaust valves 20L, 20R
Is opened and the auxiliary exhaust ports 18L and 18R conduct, so that the exhaust gas in the cylinder 5 is opened first in the cylinder 5 as the piston 6 descends.
From the main exhaust port 17 which is subsequently opened. Therefore, the exhaust timing of the two-cycle engine 1 is advanced, and the engine characteristics are directed to high-speed rotation, so that a higher output can be exhibited.

When the two-cycle engine 1 is rotating at a low speed, the exhaust valves 20L and 20R are closed and the sub exhaust port 1 is closed.
Since 8L and 18R are shut off, the exhaust gas in the cylinder 5 is exhausted only from the main exhaust port 17 at a late timing, the engine characteristic becomes a low-speed rotation direction, the low-speed torque increases, and the air-fuel mixture blows through. It is prevented and fuel economy is kept good.

In the two-stroke engine 1 having the above-described structure, the secondary exhaust ports 18L, 18R are merely converted into the pistons 6 having the recesses 25L, 25R having the changed depth H.
Can be easily changed. Therefore, when the engine characteristics are changed by changing the opening / closing timing of the sub-exhaust ports 18L and 18R, it is not necessary to newly design and remanufacture the cylinder block 3 as in the conventional case. The period can be shortened. In order to change the depth H of the recesses 25L and 25R formed in the piston 6, only a slight modification needs to be made to the forging die of the piston 6,
There is almost no cost increase.

By the way, by applying the present invention,
Since the heights of the upper edges of the openings of the sub exhaust ports 18L and 18R can be made equal to the heights of the upper edges of the openings of the main exhaust port 17 as in the present embodiment, the chamfering process of each of the ports 18L, 18R and 17 is performed. Can be simplified, and the cost can be further reduced. However, it is not always necessary to make the opening upper edge heights of the sub exhaust ports 18L and 18R equal to the opening upper edge height of the main exhaust port 17.

In addition to the auxiliary exhaust ports 18L and 18R, other ports, for example, recesses corresponding to the scavenging port 16 are formed on the top surface of the piston 6, or a two-stroke engine or the like having no auxiliary exhaust port. In addition, it is possible to change the exhaust timing or the exhaust timing without recreating the cylinder block, for example, by forming a concave portion corresponding to the exhaust port on the top surface of the piston.

[0027]

As described above, in the two-stroke engine according to the present invention, the main exhaust port and the sub exhaust port which are opened and closed by the reciprocating sliding of the piston are provided on the inner peripheral surface of the cylinder formed in the cylinder block. In a two-stroke engine provided with an opening / closing means for conducting or blocking the sub-exhaust port according to the operating condition, a recess is formed in a peripheral portion corresponding to the sub-exhaust port on the top surface of the piston, The opening and closing timing of the sub exhaust port is set according to the depth of the concave portion on the outer peripheral surface.

Therefore, the opening / closing timing of the auxiliary exhaust port can be easily changed only by changing the depth of the concave portion, that is, by replacing the piston. Therefore, when changing the opening / closing timing of the sub exhaust port,
It is not necessary to remanufacture the cylinder block as in the related art, and it is possible to significantly reduce costs and shorten the engine development period.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view of a two-cycle engine showing one embodiment of the present invention.

FIG. 2 is a cross-sectional view of the two-stroke engine taken along the line II-II in FIG.

FIG. 3 is a longitudinal sectional view taken along the line III-III in FIG. 2;

FIG. 4 is a perspective view of a piston.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 2 cycle engine 2 Crankcase 3 Cylinder block 4 Cylinder head 5 Cylinder 6 Piston 7 Crankshaft 16 Scavenging port 17 Main exhaust port 18L, 18R Secondary exhaust port 20L, 20R Exhaust valve 25L, 25R as opening / closing means Depression H Depth of depression Sa

Claims (1)

(57) [Claims] 1. A main exhaust port and a sub exhaust port that are opened and closed by reciprocating sliding of a piston are opened on an inner peripheral surface of a cylinder formed in a cylinder block, and the sub exhaust port is connected according to an operation condition. Alternatively, in a two-cycle engine provided with opening / closing means for shutting off, a concave portion is formed in a peripheral portion corresponding to the sub-exhaust port on the piston top surface, and the opening / closing timing of the sub-exhaust port is determined by the depth of the concave portion on the outer peripheral surface of the piston. A two-stroke engine characterized by the following.