JP2726717B2 - Exhaust system for two-stroke internal combustion engine - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exhaust system for a two-stroke internal combustion engine, and more particularly to an exhaust system for a two-cylinder two-stroke internal combustion engine having an exhaust valve in an exhaust system.

[Prior Art] Generally, a two-stroke internal combustion engine is widely used for marine propulsion such as an outboard motor because of its characteristics such as good acceleration and light weight. There are problems such as an increase in the amount of HC in the exhaust gas due to irregular combustion. In order to solve such a problem, various types have been proposed in which an exhaust valve such as a so-called butterfly valve is provided in the middle of the exhaust passage, and its effect has been recognized (Japanese Patent Publication No. 56-15365, published No. 53-165922, U.S. Pat. No. 4,766,854).

[Problems to be Solved by the Invention] In a marine propulsion device, a plurality of cylinders are arranged adjacent to each other in a row, and each exhaust port is similarly opened adjacent to each other in a row. Many include an exhaust system configured to be substantially directly connected to a combined exhaust path extending along the row of exhaust ports.

Here, the structure of the exhaust device having the conventional exhaust valve has a structure in which an exhaust pipe having a certain length extends from an exhaust port, and an exhaust valve such as a butterfly valve is provided in the exhaust pipe. The exhaust pipes are then assembled and an exhaust valve is arranged at the assembly.

Therefore, such a conventional technique cannot be directly applied to the above-mentioned exhaust port that is substantially directly connected to the merged exhaust path, and therefore, the exhaust valve is disposed far away from the exhaust port. There is a problem that it is inevitable and its effectiveness is reduced.

The present invention has been made in view of such problems,
The purpose is to provide a structure in which the exhaust ports of a plurality of cylinders are directly connected to the combined exhaust path.
It is an object of the present invention to provide an exhaust system for a two-stroke internal combustion engine in which an exhaust valve can be disposed at an appropriate position with respect to an exhaust port, thereby preventing blow-by of fresh air and irregular combustion.

Means for Solving the Problems According to the present invention, in order to achieve such an object, the exhaust ports of a plurality of cylinders are arranged adjacent to each other in a row, and each exhaust port is arranged along the row of the exhaust ports. Exhaust device of a two-stroke internal combustion engine configured to be substantially directly connected to a converging exhaust passage extending in the converging exhaust passage, and an exhaust valve is disposed in the confluent exhaust passage at a position between adjacent exhaust ports. Are protruded through the engine outer wall and are interlocked with each other.

[Operation] As described above, one end of the valve shaft of the exhaust valve is supported using the position between the adjacent exhaust ports, and the other end of the valve shaft is projected through the engine outer wall and these are interlocked with each other. With such a configuration, the exhaust valves can be arranged at positions relatively close to the respective exhaust ports, the exhaust valves are operated to be closed during idling operation, and the exhaust valves are fully opened during output operation. It can function to prevent irregular combustion at low load.

EXAMPLES The present invention will be described below based on examples shown in the drawings.

FIGS. 1 to 3 show an embodiment in which the present invention is applied to a three-cylinder two-stroke internal combustion engine for an outboard motor.
First, in FIG. 2, the cylinder body 10 has a crankshaft.
The cylinders 12 are arranged vertically in the crank chamber 14, and each of the cylinders 18 arranged horizontally is connected to the crankshaft 12 via a connecting rod 16.
A piston 20 housed therein is connected. Reference numeral 22 denotes a spark plug facing the combustion chamber 21 of each cylinder 18.

Reference numeral 24 denotes an intake box. Air introduced from the intake box 24 is supplied to a carburetor 26 provided for each cylinder 18 and the carburetor 26.
The fresh air mixed with the fuel through a throttle valve 28 in 26 is introduced into the crank chamber 14 through an intake passage 30 and a reed valve 32 provided in the intake passage 30 (first, second). See figure). The fresh air introduced into the crankcase 14
The pressure is pre-pressurized in the crank chamber 14 and is introduced into the combustion chamber 21 via an exhaust passage 34 and a third scavenging passage 36 (see FIG. 3) which are opened and closed by the reciprocating motion of the piston 20.

In particular, as shown in FIG. 3, the three cylinders 18 are arranged vertically adjacent to each other in a row, so that the exhaust ports 40 of the cylinders 18 are also opened adjacent to each other in a row. Cylinder body 10
The portion existing between the respective cylinders 18, that is, the boundary portion 42 is formed so as to define a passage obliquely downward from the exhaust port 40. Reference numeral 44 denotes a cylinder body cover attached to the cylinder body 10 via bolts 45, and its inner surface 46 extends along the row of each exhaust port 40 and joins with the boundary portion 42 of the cylinder body 10 to form a combined exhaust passage. 48 are defined. Accordingly, each exhaust port 40 is substantially directly connected to the combined exhaust path 48.

Reference numeral 50 denotes an exhaust valve, which is disposed so as to cross the combined exhaust path 48 at a position between the exhaust ports 40.
In this embodiment, since there are three cylinders, two are provided. An exhaust valve 50 is provided downstream of the exhaust port 40 of the lowermost cylinder 18.
May be further provided. One end of a valve shaft 52 of each exhaust valve 50 is supported by the boundary portion 42, and the other end is a cylinder body cover 44.
And protrudes outward.

As shown in FIG. 1, the protruding portions of the two valve shafts 52 are operatively connected to each other by a link mechanism 56 forming a so-called parallel crank mechanism, whereby the exhaust valves 50 are operated synchronously. A cam follower 58 is mounted on an extension of one link of the link mechanism 56, and the cam follower 58 is driven by a cam 60. The cam 60 is linked to the throttle valve 28 in this embodiment. That is, the rotation of the throttle valve 28 is transmitted to the rotating shaft 64 supported on the cylinder body 10 via the links 61, 62, 63,
The rotation of the rotating shaft 64 is transmitted to the cam 60 via the links 65 and 66, and the cam 60 rotates around a pin 67 supported by the cylinder body cover 44. The operation of each exhaust valve 50 is not limited to this embodiment, and may be driven using, for example, an electric motor, a solenoid coil, or a hydraulic system.

These exhaust valves 50 are actuated by the above-described link mechanism 56 so as to close during idling or low-speed operation, thereby preventing fresh air from flowing out from the exhaust port 40 of each cylinder 18 and simultaneously discharging fresh air from the adjacent cylinder 18. The positive pressure pulse is transmitted to the other cylinders 18 at the optimal time, thereby preventing irregular combustion and fresh air blow-through. During a medium to high speed operation, each exhaust valve 50 is opened, and a positive pressure pulse from the adjacent cylinder 18 reaches another cylinder 18 immediately before its exhaust port 40 is closed, thereby preventing blow-by of fresh air.

[Effects] As described above, according to the present invention, even when each exhaust port is configured to be substantially directly connected to the combined exhaust path, the boundary of the cylinder body located between the cylinders is used. The exhaust valve is arranged in such a manner that the space can be effectively used and the exhaust valve can be arranged relatively close to each exhaust port, so that the desired effect of the exhaust valve can be sufficiently exhibited. As a result, there is an excellent effect that blow-by of fresh air and irregular combustion can be more reliably prevented.

[Brief description of the drawings]

FIG. 1 is a front view showing a three-cylinder two-stroke internal combustion engine for an outboard motor which is an embodiment of an exhaust system for a two-stroke internal combustion engine according to the present invention, and FIG. 2 is a main part of FIG. FIG. 3 is an enlarged sectional view taken along line III-III in FIG. 18 Cylinder 40 Exhaust port 48 Merging exhaust path 50 Exhaust valve 52 Valve stem 56 Link mechanism

Claims (1)

(57) [Claims] An exhaust port of a plurality of cylinders is arranged adjacent to each other in a row, and each exhaust port is configured to be substantially directly connected to a combined exhaust path extending along the row of the exhaust ports.
In an exhaust system for a cycle internal combustion engine, exhaust valves are respectively disposed at positions between adjacent exhaust ports in a combined exhaust passage, and valve shafts of the exhaust valves protrude through the engine outer wall and interlock with each other. An exhaust device for a two-stroke internal combustion engine configured to perform the following.