JPS6027729A - Crankcase reed valve type two-cycle engine - Google Patents

Abstract

PURPOSE:To raise the charging efficiency of a two-cycle engine, by employing such as arrangement that a connecting rod gives no resistance to the intake-air flow at the time of suction stroke by selecting the turning direction of a crankshaft such that a crank pin is moved on the side of an intake port at the time of expansion and scavenging strokes of a piston. CONSTITUTION:At the time of expansion and scavenging strokes of a piston 9 when the piston 9 is moved downward and a reed valve 17 at an intake port 13 is closed, the turning direction of a crankshaft 11 is so selected that a crank pin 12a is moved on the side of the intake port 13 with respect to the axis A of a cylinder 3a. By employing such an arrangement, intake-air flow is not affected at all by a connecting rod 10 when its big end 10b passes through the front of the intake port 13. Further, since drawing of intake air is started with opening of the reed valve 17 at the intake port 13 when the piston 9 begins to move upward, resistance to the intake-air flow by the big end 10b of the connecting rod 10 can be reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a crankcase reed valve type two-stroke engine that improves intake efficiency and achieves high output.

Conventionally, two-stroke engines that use reed valves as intake valves include a piston reed valve type that has a reed valve on the intake boat that opens on the cylinder side wall, and a crankcase type that has a reed valve on the intake boat that opens on the crankcase side wall. There is a reed valve type.

In order to make the engine run at high speed and increase output, it is necessary to enlarge the intake port to increase intake efficiency, but with a piston reed valve type, enlarging the intake port increases the area of the side wall of the cylinder that supports the side pressure of the piston. This decreases the piston's slapping sound and piston ring sound, and tends to cause disadvantages such as cylinder wall seizure due to cylinder distortion.

Although the crankcase reed valve type avoids the disadvantages of the piston reed valve type mentioned above, there are restrictions on the installation space and angle of the intake boat, and the large end of the connecting rod creates intake resistance at the front of the intake boat. There is a drawback that improvement in intake efficiency is hindered because the air passes through the air.

The present invention aims to solve the above-mentioned difficulties of the crankcase reed valve type two-stroke engine, improve intake efficiency, and enable high output. In a crankcase reed valve type two-stroke engine having an intake boat and an exhaust bow, the direction of rotation of the crankshaft is set so that the crank bin passes through the intake boat side during the expansion and scavenging strokes of the piston. In the second invention, in addition to the first invention, an auxiliary scavenging air is installed on the cylinder wall on the side facing the intake boat. To provide a crankcase reed valve type two-stroke engine which achieves the above object by providing an intake boat and forcibly sending intake air taken from the intake boat to an auxiliary scavenging port by a connecting rod as the crankshaft rotates.

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

Figure 1 shows crankcase reed valve type 2 according to the present invention.
A cycle engine is shown in which an engine body 1 has a cylinder head 2. A cylinder block 3 and a sealed crankcase 4 are successively joined together and installed horizontally, and a transmission case 5 is further connected to the crankcase 4. A cooling water passage 6 is provided in the cylinder head 2 and the cylinder block 3 to form a water jacket, and a spark plug 8 is attached to the cylinder head 2 facing the combustion chamber 7 above the cylinder 3a. The piston pin 9a of the piston 9 fitted in the cylinder 3a is connected to the connecting rod 1.
The crank pin 12a of the crank web 12, which is connected to the small end 10a of the connecting rod 10 and attached to the crankshaft 11 in the crankcase 4, is connected to the large end 10b of the connecting rod 10, and the reciprocating motion of the piston 9 causes the connecting rod 10 to The rotation is converted into rotation of the crankshaft 11 through the rotation of the crankshaft 11.

The intake boat 13 has an axis C that is substantially oriented toward the crankshaft 11 on a plane that is substantially perpendicular to a plane that includes the cylinder axis A and the crank axis B, and is approximately 456 degrees with respect to the cylinder axis A.
It is inclined toward the opposite side of the cylinder and opens into the crankcase 4, and an exhaust port 14 is opened at a predetermined position of the cylinder 3a on the same side as the intake boat 13. Cylinder 3a on a plane including cylinder axis A and crank axis B
Main scavenging ports 1-15.15 (Fig. 2), which communicate the crankcase 4 and a predetermined position of the cylinder 3a, are provided on the left and right side walls of the cylinder 3a, and are oriented toward the opposite exhaust port side of the cylinder 3a wall. On a plane including axis A and crank axis B,
Intake boat 13. relative to cylinder axis A. Exhaust port 1
An auxiliary scavenging boat 1 communicates between the crankcase 4 and a predetermined position of the cylinder 3a on the side wall of the cylinder 3a on the opposite side of the cylinder 3a.
6 is provided. That is, the intake boat t 3 ,
#ti ki boat】4. Main scavenging boat]5. The positional relationship of the auxiliary scavenging boats is shown in Figure 2.

The intake boat 3 is provided with two reed valves 17 that open toward the crankcase 4 side, and the inlet of the intake boat 13 is connected to the outlet of a slant carburetor 18 or a downdraft carburetor 18' depending on the installation space. The inlet of 18' is connected to an air cleaner case (not shown).

Here, in the present invention, the rotation direction of the crankshaft 11 is set to the first rotation direction during the expansion and scavenging stroke of the piston 9, that is, when the piston 9 moves downward.
The crank bin 12a is set so as to pass on the intake boat 13 side with respect to the axis A of the cylinder 3a, as shown by the arrow in the figure. The rotation of the crankshaft 11 is transmitted to a drive shaft (not shown) via a gear train within the mission case 5.

In the crankcase reed valve type two-stroke engine configured as described above, when the piston 9 moves upward and reaches near the top dead center shown in the figure, the spark plug 8 is ignited, and the cylinder 3a
The air-fuel mixture compressed inside is ignited, and the piston 9 moves into an expansion stroke and begins to move downward.

When the piston 9 begins to move downward, the crankcase 4
Since the pressure of the air-fuel mixture sucked into the engine increases, the riet valves 17 of the intake ports 1 to 13 are closed, the crankcase 4 is sealed, and the air-fuel mixture in the crankcase 4 begins to be compressed. The piston 9 moves downward and the combustion chamber 7 in the upper part of the cylinder 3a
When the piston 9 is moved further down and the main scavenging ports h15, 15 and the auxiliary scavenging port 16 are opened, the high pressure combustion gas starts to be discharged from the exhaust port 1 to the exhaust port 14. The compressed air-fuel mixture is sent into the cylinder 3a from the scavenging boats 15, 15, 16, and the combustion gas remaining in the cylinder 3a is expelled from the exhaust port 14, resulting in a scavenging stroke. In this scavenging stroke, the air-fuel mixture is fed into the cylinder 3a from the main scavenging boat 15.15 directed toward the opposite side of the exhaust boat on the wall of the cylinder 3a, and the air-fuel mixture is fed into the cylinder 3a from the auxiliary scavenging port 16 facing toward the exhaust port 1-14. The combustion gas is guided in the direction of the exhaust port 14 by the combustion gas, and has the effect of efficiently expelling the combustion gas to the exhaust port 14. When the piston 9 moves upward after passing through the bottom dead center and closes the main scavenging ports 15, 15 and the auxiliary scavenging port 16, and further closes the exhaust port 14, the scavenging and exhausting ends, and the cylinder 3
a is sealed and the air-fuel mixture is compressed as the piston 9 moves upward, resulting in a compression stroke.Meanwhile, the pressure inside the crankcase 4 decreases and the reed valve 17 of the intake boat 13 opens, allowing the air-fuel mixture to flow inside the crankcase 4. The same cycle is then repeated.

In the above operation, the direction of rotation of the crankshaft 11 is during the expansion and scavenging stroke of the screw I/N 9, that is, when the piston 9 moves downward and the riet valve 17 of the intake boat 13 is closed.
Since the crank pin 12a is set to pass through the intake port 1 to the intake port 13 side with respect to the axis A of the cylinder 3m, even if the large end tab of the connecting rod 10 passes through the front surface of the intake boat 13, the crank pin 12a is has no effect. Next, the large end tab of the connecting rod 10 passes through the front surface of the intake boat 13, and when the piston 9 begins to move upward, the reed valve 17 of the intake boat 13 is opened and intake begins, so the connecting rod 10
Intake resistance due to the large end 10b of the crankcase 4 is reduced, and the air-fuel mixture sucked into the crankcase 4 is forcibly fed into the auxiliary scavenging port 16 by the connecting rod 10 as the crankshaft 11 rotates. Therefore, even though it is a crankcase reed valve type two-stroke engine, intake efficiency can be improved, and high speed rotation and high output are possible.

FIG. 3 shows the reed valve 17 with respect to the axis A of the cylinder 3a shown in FIG.
The crank angle θ was set to 0 using an experimental device with
This is a graph showing the actual measurement of the intake air flow rate when air is sucked into the cylinder 3a at a constant pressure at each crank angle by fixing it in steps of 15 degrees from ° to 3Go6.
In the range around the crank angle of 90° where the connecting rod 10 of the piston 9 passes the front surface of the intake boat 13, the intake air flow rate decreases due to the resistance of the connecting rod 10, and in the range around the crank angle of 270° on the opposite side, the connecting rod 10 It has been shown that the intake air flow rate is increased by decreasing the resistance of the air.

When the crank angle is between about 0° and 180°, the reed valve 17 is closed and no intake air is produced, and when the crank angle is between about 1806° and 300°, it is the intake phase.

It has been proven that the intake efficiency is improved by setting the intake stroke to be the time when the connecting rod 10 is on the opposite side of the intake boat 13, such that the direction of rotation of the rank shaft is the same as in the present invention.

As explained above, according to the present invention, in a crankcase reed valve type two-stroke engine, the direction of rotation of the crankshaft is set so that the crank pin passes through the intake port 1 side during the expansion and scavenging strokes of the piston. In addition to this, by providing an auxiliary scavenging port on the cylinder wall on the side facing the intake boat, the connecting rod does not create intake resistance during the intake stroke of the piston, and the intake air is forced by the connecting rod as the crankshaft rotates. The intake air is sent to the auxiliary scavenging port, which improves intake efficiency even though it is a crankcase reed valve type two-stroke engine, making it possible to achieve high speed rotation and high output.

[Brief explanation of drawings]

The drawings show embodiments of the present invention, and FIG. 1 is a vertical cross-sectional view of a crankcase reed valve type two-cycle engine according to the present invention, and FIG. 2 is a cross-sectional view taken along the line ■-■ in FIG. 3
The figure is a graph showing an actually measured relationship between the crank angle and the intake air flow rate from the intake port, and FIG. 4 is a schematic diagram of the experimental apparatus. 1...Engine body, 4...Crank case, 9.
... Piston, 11... Crankshaft, L2a... Crank pin, 13... Intake port, 14... Exhaust port, 16... Auxiliary scavenging port, 17... Reed valve, A...・Cylinder axis, B...Crank axis. Applicant Honda Motor Co., Ltd. Agent Patent Attorney Toshihiko Watanabe

Claims (1)

[Claims] 1. In a crankcase reed valve type two-stroke engine that has an intake port and an exhaust port on the same side with respect to a plane containing the cylinder axis and the crank axis, the direction of rotation of the crankshaft is aligned with the expansion and scavenging of the piston. A crankcase reed valve type two-stroke engine, characterized in that a crank pin is set to pass through the intake boat side during a stroke. 2. In a crankcase reed valve type two-stroke engine that has an intake port and an exhaust port on the same side with respect to the plane containing the cylinder axis and the crank axis, the crank pin rotates in the direction of rotation of the crankshaft during the expansion and scavenging strokes of the piston. 1. A crankcase reed valve type two-stroke engine, characterized in that the intake air is set to pass through the boat side, and an auxiliary scavenging port is provided on the cylinder wall on the side facing the intake boat.