JPS599082Y2 - Intake system for 2-stroke internal combustion engine - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement in an intake system for a two-stroke internal combustion engine, particularly a two-stroke gasoline engine.

Figure 1 shows an example of a two-stroke gassonon engine used in brush cutters, etc. In the figure, 1 is the cylinder, 2 is the piston, 3 is the connecting rod, 4 is the crankshaft, 5 is the crankcase, and 6 is the cylinder. 7 is an intake pipe, 8 is a spark plug, 9 is a cooling fin fixed to the outer surface of the cylinder 1, and 10 is a combustion chamber formed within the cylinder 1.

The air-fuel mixture from the carburetor 6 passes through the intake pipe 7 to the intake port 1b.
The air enters the crankcase 5, is compressed by the downward movement of the piston 2, enters the combustion chamber 10 through the scavenging port 1d, is compressed by the upward movement of the piston 2, and is then ignited and combusted by the spark plug 8.

The cylinder 1 of this type of gasoline engine is a cylinder body 1a.
An intake port 1b, an exhaust port 1c, and a scavenging port 1d are integrally formed.

In such a two-stroke gasoline engine, the shape of the intake port 1b must generally be differentiated into a shape suitable for high-speed operation of the engine and a shape suitable for low-speed operation.
Two types of cylinders must be provided depending on the application of the engine: a high-speed cylinder having a high-speed type intake port, and a low-speed type cylinder having low-speed type intake ports 1 to 1.

That is, when using a high-speed cylinder, for example, the main objective is to improve the performance of the engine in the high-speed range, and the intake passage is designed to handle the flow of a large amount of air-fuel mixture from the carburetor 6 toward the cylinder 1 during high-speed operation. In order to reduce the resistance and slow down the flow velocity in the intake passage to lengthen the scavenging time, as shown in Fig. 2, the intake port Hb and the intake pipe 7 are made large in diameter, and the cross-sectional area of the intake passage is made large. ing.

However, in this case, when the rotation speed is low and the opening degree of the throttle valve of the carburetor is small, the cross-sectional area of the intake passage becomes excessive, so the flow rate of the mixture in the intake passage decreases, resulting in atomization of the mixture. The effect deteriorates and the scavenging efficiency decreases.

As mentioned above, in order to adapt the engine to both high and low speed operating conditions, one type of engine must be equipped with two types of cylinders, one for high speed and one for low speed, which makes cylinder production management complicated. Furthermore, there was a problem in that the production cost of the cylinder also increased.

Therefore, there has been a demand for a single type of cylinder that can be used for both high and low speed operation of the engine, but at present such a cylinder is not available.

The present invention was developed in view of the above, and aims to provide an intake system for a two-stroke internal combustion engine that can be adapted to both high and low speed engine operating conditions using one type of cylinder. .

For this reason, the present invention is characterized in that a throttle member is interposed in the intake path between the carburetor cylinder and the air-fuel mixture is jetted into the cylinder by the throttle member.

Hereinafter, with reference to FIGS. 1, 3 to 7, 1 of the present invention will be described.
An example will be explained.

The intake system for a two-stroke internal combustion engine according to the present invention is provided with a throttle member 20 in place of the intake pipe 7 shown in FIG. 1, and other aspects of the structure are the same as those shown in FIG.

That is, in the present invention, as shown in FIG. 3, a throttle member 20 is removably interposed in the intake path between the carburetor 6 and the intake port 1b of the cylinder 1 using bolts (not shown) or the like. .

As shown in FIGS. 4 and 5, the throttle member 20 is shaped into a tapered shape by cutting out a portion of its circular cross section with a basic diameter d so that the cross-sectional area of the flow path decreases as it approaches the cylinder 1. .

That is, the cross-sectional area of the flow path of the throttle member 20 is as shown in FIGS. 3 to 5.
As shown in the figure, the size is reduced from the carburetor 6 side end toward the cylinder 1 side end.

The shape of the flow path of the throttle member 20 is selected to be suitable for both high-speed operation and low-speed operation.

Further, as shown in FIG. 3, one end of the throttle member 20 is tapered so as to be continuously reduced from the carburetor outlet passage toward the intake port side end, and the intake port Hb
It is forced to protrude inward.

Further, it is desirable that the cross-sectional area of the distal end jetting portion 20a of the throttle member 20 be smaller than that of the cylinder-side opening end 1e of the intake port 1b.

In the intake system having the above structure, when the intake port 1b is opened by the piston 2 during low speed operation of the engine, the air-fuel mixture from the carburetor 6 is throttled within the throttle member 20 to increase the flow velocity and Intake port from a}lb
After being introduced into the crankcase 5, the air flows into the combustion chamber 10 of the cylinder 1 through the scavenging port 1d, cleaning the inside of the combustion chamber 10, and then part of the air flows into the combustion chamber 1 as fresh air.
0 remains in the interior, and the others are exhausted to the outside from the exhaust port 1C.

As described above, in this intake device, the flow velocity of the air-fuel mixture is increased by the throttle member 20, so atomization of the air-fuel mixture in the crankcase 5 is promoted, and the scavenging port H is increased.
The flow velocity of the air-fuel mixture flowing out into the combustion chamber 10 from d also increases.

Therefore, the scavenging efficiency and air supply ratio during low-speed operation increase, and the torque during low-speed operation increases.

FIGS. 6 and 7 show an example in which the performance test results of a conventional engine and an engine equipped with the intake device of the present invention are compared.

Figure 6 shows the torque measurement results when the engine rotational speed is varied with the throttle opening fully open, and Figure 7 shows the torque measurement results when the engine rotational speed is kept constant and the throttle opening is varied. These are the results, and in these figures, the solid line shows the conventional one, and the broken line shows the one of the present invention.

As is clear from both figures, the torque of the present invention increases in the low rotation and low throttle opening range compared to the conventional one, and also exhibits almost the same torque characteristics in the high rotation and high throttle opening range.

As described above, in the two-stroke internal combustion engine according to the present invention, a throttle member is interposed in the intake path between the carburetor and the cylinder, and the mixture is jetted into the cylinder by the throttle member. Therefore, with the extremely simple structure of interposing a throttle member in the intake passage, it is possible to increase the torque in the low rotation and low throttle opening range, and also increase the torque in the high speed and high throttle opening range. This is comparable to engines using conventional high-speed cylinders.

Therefore, one type of cylinder can be adapted to both high and low speed engine operating conditions, and in particular, by combining a high-speed cylinder and the above-mentioned throttle member, high torque characteristics can be obtained over the entire high and low speed range. be able to.

Furthermore, by selectively replacing the throttle members, the torque characteristics of the engine can be adjusted to some extent.

Furthermore, since there is no need to prepare two types of high-speed and low-speed cylinders for one type of engine depending on the application, cylinder production management is simplified, and cylinder production costs are also reduced.

Furthermore, in the present invention, since the end of the throttle member is made to protrude into the intake port, the length of the tapered throttle passage within the throttle member can be increased, which allows the air to be injected into the intake port. It is possible to prevent the flow rate of the air-fuel mixture from dropping suddenly.

[Brief explanation of the drawing]

FIG. 1 is a sectional view taken along the cylinder axis of a two-stroke gasoline engine, and FIG. 2 is a sectional view showing an example of a conventional intake device. 3 to 7 show one embodiment of the present invention, FIG. 3 is a view corresponding to FIG. 2, FIG. 4 is a sectional view taken along line A-A in FIG. 3, and FIG. Sectional view taken along line B-B in Figure 3, No. 6
Figures 7 and 7 are torque diagrams of the engine. 1... Cylinder, 1a... Cylinder body, 1b...
・Intake port, 1C... Exhaust port, 1d... Scavenging port, 5... Crank case, 6... Carburetor, 2
0... Aperture member.

Claims (1)

[Scope of utility model registration request] In a two-stroke internal combustion engine comprising a scavenging port communicated with or blocked off from a combustion chamber by a piston, and an intake port communicated with or blocked off from the inside of a crank chamber by the piston, a carburetor and the intake port are connected to each other. The air-fuel mixture in the intake path is tapered so that the cross-sectional area of the flow path continuously decreases from the outlet passage of the carburetor toward the intake port side end. An intake system for a two-stroke internal combustion engine, characterized in that a throttle member is provided that ejects air into the port, and an end of the throttle member projects into the intake port.