JPH03182620A - Two-cycle engine - Google Patents

Abstract

PURPOSE:To make it compatible to decrease in pumping loss and increase in charging efficiency by setting substantially, to 3, 5 a rate of volume of the side of a crank chamber at the time when a piston is at a bottom dead point with respect to a stroke volume. CONSTITUTION:In a two-cycle engine 1 which flows air compressed in a crank chamber 3 into a cylinder 2 via a scavenging port 4 by reciprocating a piston 8, a rate of volume of the side of a crank chamber 3 is substantially set to 3, 5 when the piston 8 is at a bottom dead point with respect to a stroke volume. Increase in a pumping loss is restrained without excessively increasing compression in the crank chamber 3 by the piston 8. Fresh air pressure-supplied from the crank chamber 3 at the beginning of the opening of a scavenging port 4 without being subjected to a combustion process is controlled to be blown to an exhaust port 5 whereby charging efficiency of the fresh air is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a two-stroke ennon that utilizes a new type of compressed air in the crankcase for cylinder scavenging.

(Prior art and its problems) A two-stroke engine that uses air compressed in the crank chamber as the piston descends to scavenge the cylinder basically eliminates the need for a supercharger or the like to forcefully feed the scavenging flow (for example, (Refer to Utility Model Application Publication No. 60-39731).

Conventionally, in two-stroke engines that generate compressed air in the crank chamber, there has been a tendency to reduce the volume of the crank chamber as much as possible to increase the flow velocity of air flowing into the cylinder from the scavenging port.

However, if the volume of the crank chamber is made too small, piston pumping loss due to compression of the crank chamber increases, resulting in a problem of deterioration of fuel efficiency and output.

The present invention focuses on these conventional problems and optimizes the volume of the crank chamber.

(Means for Solving Problems) In the present invention, a scavenging port is closed in the middle of the cylinder, this scavenging port is communicated with the crank chamber, and air compressed in the crank chamber by the reciprocating motion of the piston is passed through the scavenging port. In a two-stroke engine that allows air to flow into the cylinder, the ratio of the volume on the crank chamber side when the piston is at the bottom dead center relative to the stroke volume is set to approximately 3.5.

(Function) Based on the above configuration, the compression of the crank chamber by the piston is not increased excessively, and the increase in the pumping loss due to the compression of the crank chamber by the piston is suppressed. This suppresses the pressure-fed fresh air from blowing into the exhaust port without undergoing the combustion process, increasing the new type's charging efficiency.

Further, the compression of the crank chamber by the piston will not be insufficient, and the necessary amount of scavenging air can be secured and residual gas can be sufficiently reduced.

(Embodiments) Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.

As shown in FIG. 1, in a two-stroke engine 1, a scavenging port 4 communicating with a crank chamber 3 on a wall surface of a cylinder 2 is closed, and an exhaust port 5 is closed. The exhaust port 5 and the scavenging port 4 are opened and closed by the reciprocating movement of the piston 8, respectively, and open at a predetermined crank angle symmetrical to the bottom dead center (BDC), thereby exhausting the burned gas from the exhaust port 5. , fresh air is sent from the crank chamber 3 through the scavenging port 4.

A six-port intake 6 is closed in the crank chamber 3, and an air-fuel mixture created through an air cleaner, a throttle valve, a carburetor, etc. (not shown) flows into the crank chamber 3 via a reed valve 7.

In addition, in the figure, 9 is a fuel injection valve, 10 is a spark plug, and 11 is a crankshaft.

In the present invention, the volume of the crank chamber defined by the back surface of the piston 8 of the crank chamber 3, the reed valve 7, the crank case 13, etc. at the time of piston bottom dead center is 3, and the volume of the scavenging port 4 is 2. The stroke volume (cylinder side volume) defined by the bore and stroke of the piston 8 is V2.
Then, the value of the volume ratio C=(V s +V 4 )/V 2 on the crank chamber 3 side is limited.

Figure v & 2 shows the experimental results of measuring the average effective pressure corresponding to the torque generated by the engine 1 using the volume ratio C of the crank chamber 3 as a variable, but the average effective pressure decreases significantly in the region where the volume ratio C is 3 or less, Moreover, it gradually decreased even in the region where the volume ratio Cht was 4 or more, and the highest value was obtained when the volume ratio C was around 3.5.

Figure 3 shows the experimental results of measuring the fuel consumption rate under specified operating conditions of Ennon 1 using the volume ratio C of the crank chamber 3@ as a variable.The fuel consumption rate greatly increases in the region where the volume ratio C is 3 or less. , and also gradually increased in the region where the volume ratio C was 4 or more, and the lowest value was obtained when the volume ratio C was around 3.5.

In addition, in Figs. 2 and 3, the difference between the indicated value shown by the broken line and the net value shown by the solid line increases significantly in the region where the volume ratio C on the crank chamber 3 side is 3 or less, and in the region of 4:. It can be seen that losses such as bombing loss are increasing.

Fig. 4 shows the experimental results of measuring the air supply ratio, which is the dimensionless amount of air taken into the cylinder under predetermined operating conditions of the engine 1, using the volume ratio C on the side of the crank chamber 3 as a variable. increases as the fuel consumption rate decreases, but when the volume ratio C is 3
．． A sufficiently high value was obtained around 5.

Based on these experimental results, the present invention sets the volume ratio C=(V:l+V4)/V2 of the crank chamber 3 to approximately 3.
Set to 5.

FIG. 5 shows the volume ratio C of the crank chamber 311Il as 0.80.
3.02.6.00, and measured the pressure change in the crank chamber 3 under the specified operating conditions of the engine 1. As the volume ratio C becomes smaller, the width of the pressure change becomes larger. It can be seen that the grossness increases.

If the volume on the crank chamber 3 side is excessively large, for example, if the volume ratio C is 6.00, the pumping action of the crank chamber 3 becomes small, as shown in Fig. 6, and sufficient sweeping Xt cannot be obtained. , the residue caused the occurrence of sulfur.

If the effective volume of the crank chamber 3ga is excessively small, for example, if the volume ratio C is 0.80, as shown in FIG.
The pumping effect of the crank chamber 3 increases, and the pressure in the crank chamber 3 increases immediately after the scavenging port 4 opens.
Since the new type that is pressure-fed from the crank chamber 3 at the beginning of the opening of the scavenging port 4 blows through to the wandering port 5 without undergoing a combustion stroke, it does not lead to improvement in charging efficiency.

On the other hand, as shown in FIG. 8, when the volume ratio C is set to 3.02 based on the present invention, the rise in pressure in the crank chamber 3 immediately after the scavenging port 4 is opened is suppressed, so that the scavenging The new type of outflow from the port 4 to the wandering port 5 is prevented, and the filling efficiency is improved. Furthermore, the new type of flow rate can be sufficiently ensured from immediately after the opening of the scavenging port 4 to near the bottom dead center of the piston to promote scavenging.

(Effects of the Invention) As described above, according to the present invention, in a two-stroke engine in which air compressed in the crank chamber by the forward movement of the piston flows into the cylinder through the scavenging port,
The ratio of the volume on the crank chamber side when the piston is at the bottom dead center to the stroke volume is set to approximately 3.5, which reduces pumping loss and increases charging efficiency, resulting in improved fuel efficiency and generation of 2-stroke engines. Torque can be improved.

[Brief explanation of drawings]

Fig. 1 is a sectional view of an ennon showing an embodiment of the present invention;
Figures ~@8 are diagrams showing experimental results, respectively. 1... 2-stroke engine, 2... cylinder, 3
...Crank chamber, 4...Scavenging port, 5...Exhaust port, 8...Piston.

Claims (1)

[Claims] In a two-stroke engine, a scavenging port closes in the middle of the cylinder, communicating this scavenging port with the crank chamber, and allowing air compressed in the crank chamber by the reciprocating motion of the piston to flow into the cylinder through the scavenging port. The ratio of the volume on the crank chamber side when the piston is at the bottom dead center is set to approximately 3.5.
stroke engine.