JPS6025606B2 - Scavenging device for crank chamber compression type 2-stroke engine - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a scavenging device for a crank chamber compression type two-stroke engine, and aims to improve output and fuel economy under partial load, and to improve startability.

Generally, in a crank chamber compression two-stroke engine, the striped airway surface mirror (effective cross-sectional area of the cross section) is constant.

Therefore, during partial load operation, the intake mixture is small and the pressure inside the crankcase is small, so the passage area designed for full load operation and the scavenging speed path are When the air-fuel mixture is allowed to flow into the cylinder, the scavenging flow rate is low, and sufficient scavenging action cannot be performed, and the turbulence necessary for effective combustion is not restricted. As a result, fuel consumption is insufficient, which tends to lead to a decrease in output and deterioration of fuel economy.
On the other hand, there are known decompression devices that release the pressure in the combustion chamber during startup and reduce the starting torque. However, if the pressure relief path to the combustion chamber is always open, the output will decrease during normal operation, and the fuel There is a drawback that the consumption rate is high, and if a dedicated opening/closing mechanism is provided as a countermeasure to this problem, the cost will increase. The present invention provides a rotary valve that can change the scavenging passage area in synchronization with the throttle coefficient so that as the throttle coefficient increases, the scavenging passage area increases. This makes it possible to obtain an optimal scavenging circuit area in the region of 1, and to improve output and fuel economy during partial load.

In addition, by providing a pressure relief passage that is closed by the rotary valve only when starting with the throttle fully closed or nearly fully closed, the starting torque is reduced, that is, the starting performance is improved, and the output and fuel efficiency are reduced during normal operation. We are trying to prevent this. The invention will now be explained in conjunction with the drawings. FIGS. 1 to 3 are longitudinal cross-sectional views of a crank chamber compression type two-stroke engine to which the present invention is applied, showing the engine at startup, at partial load operation, and at full load operation, respectively.

The two-stroke engine 1 shown in FIG. 1 is integrally equipped with a cylinder head 2, a cylinder 3, and a crankcase 4. A piston 5 is movably raised and lowered on the inner surface 12 of the cylinder 3. Rod 14,
The crank shaft 16 is connected to a crank ball 16 via a crank pin 15, and is rotatably supported by the crank case 4 by a bearing 17. The crank chamber 18 in the crank case 4 is sealed by a seal ring 19 installed between the crank case 4 and the crankshaft 16.
passes through a bridge air passage 6 provided within the wall thickness of the crankcase 4 and cylinder 3, and reaches the inner surface 1 of the cylinder wall at the scavenging pole 8.
Sekiguchi is on 2. An exhaust boat 7 is closed on the inner surface 12 of the cylinder wall between the scavenging poles 8, 8, and is communicated to the atmosphere through an exhaust pipe (not shown) having a muffler. In addition, an intake boat (not shown) is provided on the cylinder wall inner surface 12 facing the exhaust boat 7 or on the crankcase 4 facing the crank chamber 18, and this intake boat has a reed valve that allows flow only in the direction of the crank chamber 18. It communicates with the carburetor (both not shown) through a piston valve, or through a piston valve that opens and closes as the piston 5 moves up and down. A pressure relief hole 9 is closed in the inner surface 12 of the cylinder wall at a position higher than the exhaust boat 7, and this relief hole 9 communicates with the - side scavenging passage 6 via a pressure relief passage 10 and a scavenging rotary valve 11. The scavenging rotary valve 11 is a cylindrical body rotatably joined to a cylindrical valve seat 21 provided at the connection between the pressure relief circuit 10 and the scavenging passage 6, and is provided with an arc-shaped notch 22 in a part of the cylindrical surface. Rotary valve 11
The entire passage of the scavenging passage 6 on one side passes through the valve seat 21 near the scavenging boat 8. Therefore, at the time of starting as shown in FIG. The notch 22 connects the pressure relief passage 10 to the scavenging passage 6. An operating shaft 23 fixed to the center of the rotary valve 11 is provided with an arm 24 at a portion protruding outside the cylinder 3, and the arm 24 is connected to a throttle valve 26 via a cable 25.

27 is a return spring, 28 is a stopper, and 29 is a fulcrum of the pedal 26.

At the time of starting as shown in FIG. 1, the throttle pedal 26
Since the scavenging rotary valve 11 is not depressed, the scavenging rotary valve 11 stops at the position shown in FIG.
The scavenging passage 6 and scavenging boat 8 on the side where 1 is located are closed.

In this state, when the starter is operated to give starting rotation to the crankshaft 16, the piston 5 rises, and after passing through the upper part of the exhaust port 7, it moves into the combustion chamber 31 and reaches the scavenging passage. Fresh air (
The air-fuel mixture) starts to be compressed by the piston 5, but until the piston 5 passes upward through the pressure relief hole 9, the pressure relief hole 9 faces the combustion chamber 31 and is closed, so the compression pressure in the combustion chamber 31 decreases. are pressure relief hole 9, pressure relief passage 1
0, through the notch 22 to the scavenging passage 6, and the combustion chamber 31
The pressure rise becomes gradual, and the piston 5 rises easily. That is, the starting torque is reduced and the starting rotation of the crankshaft 16 becomes lighter, thereby improving starting performance. After the piston 5 passes upward through the pressure relief hole 9, the pressure inside the combustion chamber 31 increases, and an explosion occurs due to the spark supplied from the ignition plug 20 at a predetermined timing, and the piston 5 receives downward explosion pressure. Apply rotational force to the crankshaft 16. Scavenging is performed while idling operation is continued with the throttle pedal 26 not operated after startup and the throttle ratio kept fully open. - The tally valve 11 maintains the attitude shown in FIG. 1, so the compression in the fuel scale chamber 31 is appropriately released, and gentle idling rotation with low output and low vibration continues. Move throttle pedal 26 to arrow A
When the pedal is pressed a certain amount in the direction (partial load operation), the pedal 26
The movement is transmitted to the operating shaft 23 via the cable 25 and arm 24, and the rotary valve 11 rotates in the direction of arrow B.
The pressure relief passage 10' is immediately closed (FIG. 2), and the area of the scavenging passage 6 increases as the throttle opening increases from the opening state shown in FIG. 2. When the throttle pedal 26 is fully depressed and the throttle opening is fully opened, the rotary valve 11's opening 22 reaches the position where the rare air passage area 6 is maintained at its maximum, as shown in FIG. During partial load operation with a small throttle closing area, there is little air-fuel mixture sucked into the crank chamber 18 and the crank chamber pressure is also low, but the passage area of the scavenging passage 6 on the side where the rotary valve 11 is located is narrowed by the rotary valve 11. As a result, the scavenging air flow rate increases, and the scavenging air flow rate also increases due to the overall reduction in the area of the green air transport path in the scavenging passage 6 on the opposite side.
The scavenging air flow flowing into the combustion chamber 31 effectively drives out the exhaust gas in the combustion chamber 31, and also creates a moderate turbulence in the combustion chamber 31, promoting scavenging efficiency and atomization, and improving output and fuel economy at partial load. Improves sex.

When all the cargo is transferred together as shown in Fig. 3, a large amount of air-fuel mixture flows into the combustion chamber at a high flow rate from the scavenging passages 6, 6 on both sides, which have a large passage area and are designed for all-hands flow operation, to provide sufficient scavenging air. action takes place. As explained above, in the present invention, a pressure relief passage 1 is provided between one of the plurality of scavenging passages 6 and the inner surface 12 of the cylinder wall above the exhaust boat 7.
0, and a rotary valve 11 that operates in conjunction with the throttle pedal 26 or the throttle lever is provided at the connection between the pressure relief passage 10 and the scavenging passage 6, so that the pressure relief passage 10 communicates with the scavenging passage 6 only when the throttle is fully open or substantially fully closed. death,
Since the rare air passage area increases as the throttle function increases, the optimum scavenging passage area can be obtained in all areas from partial load to full load.
By increasing the flow velocity of the air-fuel mixture flowing into the combustion chamber 31 (cylinder) from the bridge air passage, a sufficient scavenging action can be performed, and a turbulent flow for effective combustion can be obtained.

As a result, output and fuel economy during partial load can be improved. Furthermore, since the relief passage 10 is closed at the time of starting with the throttle fully closed, it is possible to reduce the starting torque, that is, to improve starting performance, and since this pressure relief passage is blocked during normal operation, there is no reduction in output during normal operation. This has the advantage of preventing a decrease in fuel efficiency. Control of the area of the scavenging passage and opening and closing of the pressure relief passage 10 are performed in one system. Since this is done using the tally valve 11, the increase in the number of parts and cost can be kept to a minimum of 4.

[Brief explanation of the drawing]

Figures 1 to 3 show a crank chamber compression type 2 to which the present invention is applied.
This is a longitudinal cross-sectional view of a cycle engine, showing the times of startup, partial load operation, and full load operation, respectively. 6...Scavenging passage, 8...Exhaust boat, 10
...Pressure relief passage, 11...Women's rotary valve. Figure 1 Figure 2 Figure 3

Claims (1)

[Claims] 1. A pressure relief passage is provided between one of the multiple scavenging passages and the inner surface of the cylinder wall above the exhaust port, and a rotary valve that operates in conjunction with the throttle is provided at the connection between the pressure relief passage and the scavenging passage, and the throttle is fully closed. Alternatively, a scavenging device for a crank chamber compression two-stroke engine, characterized in that the pressure relief passage communicates with the scavenging passage only when the throttle is substantially fully closed, and the area of the scavenging passage increases as the throttle opening increases.