JPH05302521A - Scavenging device of two-cycle engine - Google Patents

Abstract

PURPOSE:To prevent any increase in an intake quantity into a crank case and blowby of exhaust air from a scavenging port by arranging a surge tank on the way of a scavenging passage, and respectively providing an intake air control valve and a scavenging control valve on the upstream and downstream of the surge tank in the scavenging passage. CONSTITUTION:A surge tank 16 is arranged on the way of a scavenging passage 15 which connects a crank case 12 to a cylinder 13. The scavenging passage 15 complies a first scavenging passage 31 which opens to a crank case 12, and a second scavenging passage 32 which opens to a scavenging port 26 drilled in the cylinder 13, and other ends of the respective scavenging passages 31, 32 are formed in funnel shapes which gradually expand radially so as to open it inside the surge tank 16. An intake control valve 28 is provided in the scavenging passage 31 and the scavenging control valve 29 is provided in the second scavenging passage 32, respectively, and the intake control valve 28 is openly operated across approximately all ranges along which a piston 14 makes its reciprocation. On the other hand, the scavenging control valve 29 is openly operated until an initial period when the piston 14 is reciprocated since the scavenging port 26 is opened.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a scavenging device for a two-cycle engine capable of improving the performance of a crankcase pump.

[0002]

2. Description of the Related Art In a two-cycle engine 1 shown in FIG. 10, the inside of a crankcase 4 is in a state where a piston 3 for compressing an air-fuel mixture in a cylinder 2 is moving upward (while returning from bottom dead center to top dead center). When the pressure becomes negative, the reed valve 5 opens, and the air-fuel mixture is sucked into the crankcase 4. Further, when the piston 3 descends (moves forward from the top dead center to the bottom dead center) due to the combustion of the air-fuel mixture, the air-fuel mixture in the crankcase 4 is guided into the cylinder 2 through the scavenging passage 6 and the scavenging port 7. Get burned.

In the two-cycle engine 1, the crankcase 4 functions as a crankcase pump by the reciprocating movement of the piston 3 as described above. Note that reference numeral 8 in FIG. 10 indicates an exhaust port, and reference numeral 9 indicates a crankshaft.

[0004]

Since the opening and closing of the scavenging port 7 is performed by the piston 3, the opening and closing timing of the scavenging port 7 is symmetrical with respect to the bottom dead center of the piston 3, as shown in FIG. become. Therefore, in the initial stage of the rising process of the piston 3, since the scavenging port 7 is opened, the negative pressure in the crankcase 4 is low and the reed valve 5 is not sufficiently opened, so that the air-fuel mixture in the crankcase 4 is not opened. Inhalation volume is low.

Further, since the scavenging port 7 is opened in the initial stage of the ascending process of the piston 3, the air-fuel mixture in the crankcase 4 is pumped into the cylinder 2 through the scavenging passage 6 and then in the cylinder 2. Exhaust gas may be blown back through the scavenging passage 6 due to the negative pressure in the crankcase 4.

The present invention has been made in consideration of the above circumstances, and increases the amount of intake air into the crankcase and prevents the exhaust gas from being blown back from the scavenging port to improve the efficiency of the crankcase pump. It is an object of the present invention to provide a scavenging device for a two-cycle engine, which can improve the engine.

[0007]

According to the present invention, the internal spaces of a cylinder accommodating a piston that reciprocates between a top dead center and a bottom dead center, and a crankcase in which this cylinder is installed have respective scavenging passages therebetween. In a scavenging device of a two-cycle engine in which the air-fuel mixture is communicated from the inside of the crankcase to the inside of the cylinder through the scavenging passage and the scavenging port, a surge tank is disposed in the middle of the scavenging passage, In the scavenging passage, an intake control valve is installed between the crankcase and the surge tank, and a scavenging control valve is installed between the surge tank and the cylinder. The opening operation is performed over substantially the entire section that moves forward from the point toward the bottom dead center, and the scavenging control valve is configured such that the piston moves during the forward movement. Open the air outlet, in which the piston toward the top dead center from the bottom dead center is controlled so as to be operated to open to the initial stage of backward.

[0008]

Therefore, according to the scavenging device for a two-cycle engine according to the present invention, the intake control valve is controlled so that the piston is operated to be closed in almost all sections during the backward movement from the bottom dead center to the top dead center. Therefore, in the crankcase, the negative pressure increases from the time when the scavenging port is still open at the initial stage of the piston return movement, the reed valve is opened, and intake air is guided into the crankcase. Therefore, the amount of intake air into the crankcase increases.

Further, the scavenging control valve is closed at the initial stage of the backward movement of the piston. This means that at the final stage of the scavenging process, where the scavenging opening is still open, the scavenging opening is closed by the scavenging control valve. Therefore, it is possible to prevent the exhaust gas from being blown back into the surge tank or the crankcase through the scavenging port and the scavenging passage in the final stage of the scavenging process.

The crankcase has a crankcase pump function of supplying the air-fuel mixture into the cylinder through the scavenging passage and the surge tank by the reciprocating motion of the piston. However, the amount of intake air into the crankcase and the exhaust gas blowing are increased. By preventing the return, the efficiency of the crankcase pump can be improved.

[0011]

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

FIG. 1 is a schematic sectional view showing an embodiment of a scavenging device for a two-cycle engine according to the present invention.
3 is a graph showing opening / closing operations of the intake control valve and the scavenging control valve of FIG. 1 with reference to a crankshaft rotation angle. FIG. 5 is a sectional view showing an actual two-cycle engine to which the scavenging device for the two-cycle engine of FIG. 1 is applied.

As shown in FIGS. 1 and 5, in a two-cycle engine 10, a cylinder 13 is installed in a crankcase 12 that rotatably accommodates a crankshaft 11.
A piston 14 is accommodated in the cylinder 13 so as to be capable of reciprocating between a top dead center and a bottom dead center, the crankcase 12 and the cylinder 13 are communicated with each other through a scavenging passage 15, and a surge tank 16 is provided in the scavenging passage 15. Are arranged.

The piston 14 and the crankshaft 11 are connected by a connecting rod (not shown), and the reciprocating motion of the piston 14 is converted into the rotary motion of the crankshaft 11. A cylinder head 17 is arranged above the cylinder 13, and an ignition plug 18 is installed on the cylinder head 17. When the piston 14 reaches the top dead center, the combustion chamber 19 is formed by being surrounded by the cylinder head 17 and the piston 14.

An intake passage 20 is formed in the crankcase 12, and the intake passage 20 is connected to an air cleaner 22 via an air tube 21. The air from the air cleaner 22 is sucked into the crankcase 12 as intake air. This intake air is controlled by a reed valve 23 arranged in the intake passage 20 and an intake throttle valve 24 arranged in the air tube 21.

That is, the reed valve 23 is the piston 1
In the process of 4 returning from the bottom dead center to the top dead center and compressing the air-fuel mixture in the cylinder 13, the inside of the crankcase 12 becomes a negative pressure, and this negative pressure causes the reed valve 23 to open.
Intake air is taken into the crankcase 12. Further, the combustion of the air-fuel mixture in the combustion chamber 19 compresses the intake air in the crankcase 12 while the piston 14 moves from the top dead center to the bottom dead center, and the inside of the crankcase 12 becomes a positive pressure. The reed valve 23 is closed. As described above, the crankcase 12 has a crankcase pump function of sucking intake air inside, compressing it, and discharging it into the surge tank 16.

On the other hand, the intake throttle valve 24 is closed when the engine is running at low speed, or when the engine brake is operated when the scavenging throttle valve 30 to be described later is closed for a long period of time, etc. The amount of intake air into the surge tank 16 is optimally adjusted, and the internal pressure in the surge tank 16 is prevented from becoming excessive when the engine brake is activated.

In the cylinder 13, one exhaust port 25 and a plurality of, for example, five scavenging ports 26 are formed. Exhaust port 25
Is connected to the exhaust pipe 27, and as shown in FIG.
The exhaust gas in the combustion chamber 19 and the cylinder 13 is exhausted. In addition, as shown in FIG. 2B, the scavenging port 26 also moves the piston 1 during the forward movement of the piston 14.
4, the air-fuel mixture is opened slightly later than the exhaust port 25, and the air-fuel mixture is introduced into the cylinder 13 in the exhaust process from the scavenging passage 15 (scavenging). The intake control valve 2 controls this scavenging.
8, scavenging control valve 29 and scavenging throttle valve 3
Implemented by 0.

The scavenging passage 15 is composed of a first scavenging passage 31 and a second scavenging passage 32, and the first scavenging passage 31 and the second scavenging passage 32 have a funnel shape whose diameter gradually increases on the surge tank 16 side. Formed in. The other end side of the second scavenging passage 32 is provided as a passage in the crankcase 12 and communicates with the inside of the crankcase 12. The other end of the second scavenging passage 32 is provided as a passage in the crankcase 12 and the cylinder 13,
It communicates with the scavenging port 26. An intake control valve 28 is provided in the first scavenging passage 31 and a scavenging control valve 29 is provided in the second scavenging passage 32. Further, as shown in FIG. 7, the scavenging throttle valve 30 is arranged in the second scavenging passage 32 on the upstream side of the scavenging control valve 29, that is, in the surge tank 16.

As shown in FIGS. 6 and 8, the intake control valve 28 and the scavenging control valve 29 are formed as through holes diametrically passing from the side peripheral surface of the cylindrical valve element 33 through the axial center thereof. The intake control valve 28 is provided at the center of the valve element 33 in the axial direction.
The scavenging control valves 29 are formed on both axial sides of the valve element 33, respectively. This valve element 33
Is connected to the crankshaft 11 via the valve gears 34 and 35, and is set to make 1/2 rotation per one rotation of the crankshaft 11.

As shown in (c) of FIGS. 2 and 3, the intake control valve 28 is operated to be opened in almost the entire section of the forward movement of the piston 14 and closed in the other sections. 2 and 4, the scavenging control valve 29 is opened at the same time as the piston 14 opens the scavenging port 26 during the forward movement, and is opened until the initial stage of the backward movement of the piston 14. The state is maintained and the closing operation is performed in other sections.

When the intake control valve 28 is opened, intake air (air) compressed in the crankcase 12 by the crankcase pump function is discharged into the surge tank 16. The fuel injector 3 installed in the surge tank 16 is added to the air discharged into the surge tank 16.
Fuel is injected from 6 to generate an air-fuel mixture in the surge tank 16. Further, by opening the scavenging control valve 29, the air-fuel mixture in the surge tank 16 is guided into the cylinder 13 through the second scavenging passage 32 and the scavenging port 26 (scavenging). The scavenging amount into the cylinder 13 is controlled by the scavenging throttle valve 30 and is determined according to the engine load.

According to the above embodiment, as shown in FIG. 2C, the intake control valve 28 is opened from the first stage of the forward movement of the piston 14, so that the crankcase pump shows the solid line in FIG. Crankcase 1 compressed like
The intake air in 2 is quickly introduced into the surge tank 16 without delay. Therefore, the intake air in the surge tank 16 is sufficiently compressed.

Further, as shown in FIG. 2 (c), since the intake control valve 28 is operated to be closed over substantially the entire section of the backward movement of the piston 14, the scavenging port 26 still remains at the initial stage of the backward movement of the piston 14. Crankcase 12 from the time it is opened
The inside becomes negative pressure. As a result, the reed valve 23 starts to open at substantially the same time as the closing operation of the intake control valve 28.
(E), that is, since the scavenging port 26 is conventionally opened, the negative pressure in the crankcase 12 is low, and the section in which the reed valve 23 is not opened is eliminated, so that the intake amount into the crankcase 12 is increased. it can.

Further, as shown in FIG. 2 (d), the scavenging control valve 29 is closed at the initial stage of the backward movement of the piston 14 since the scavenging port 26 is still open. Therefore, as shown by the chain double-dashed line in FIG.
At the final stage of the scavenging process before the scavenging port 26 is closed by the piston 14, the blowback flowing toward the crankcase 12 in the second scavenging passage 32 can be eliminated as shown by the solid line in FIG. .. Therefore, cylinder 1
It is possible to prevent the exhaust gas from flowing into the surge tank 16 from flowing back into the surge tank 16.

The crankcase 12 has the above-mentioned features because it quickly introduces intake air into the surge tank 16, increases the amount of intake air into the crankcase 12, and prevents exhaust gas from being blown back into the surge tank 16. The efficiency of the crankcase pump can be improved.

Further, since the surge tank 16 is interposed between the scavenging port 26 and the crankcase 12, pressure fluctuations in the cylinder 13 and pressure fluctuations due to the crankcase pump in the crankcase 12 are transferred to the surge tank 16. Therefore, the influence of the blowback flow in the scavenging passage 15 can be reduced. Therefore, the opening / closing timing of the scavenging port 26 and the control of the crankcase pump can be simplified.

Furthermore, by changing the length of the funnel shape in the surge tank 16 of the first scavenging passage 31 and the second scavenging passage 32, it is possible to optimally tune the intake air by the engine speed.

Further, since the intake control valve 28 and the scavenging control valve 29 are arranged in parallel in one valve element 33, each intake control valve 28 and the scavenging control valve 29 are arranged.
A complicated drive mechanism for individually activating the above is unnecessary, and the drive system of the intake control valve 28 and the scavenging control valve 29 can be made compact.

The intake control valve 28 and the scavenging control valve 29 may be plate valves, as shown in FIG.

[0031]

As described above, according to the scavenging device for a two-cycle engine according to the present invention, the surge tank is arranged in the middle of the scavenging passage, and the crankcase and the surge tank are provided in the scavenging passage. Between the intake control valve,
A scavenging control valve is installed between the surge tank and the cylinder, respectively, and the intake control valve is operated to open over substantially the entire section in which the piston moves forward from the top dead center to the bottom dead center. The control valve is controlled so that it is operated to open from the bottom dead center to the top dead center until the initial stage in which the piston retreats after the piston opens the scavenging port during the forward movement. Therefore, since the intake air can be sucked into the crankcase from the initial stage of the returning process of the piston, the intake amount into the crankcase can be increased, and the exhaust gas from the scavenging port in the final stage of the scavenging process can be increased. It is possible to prevent blowback. As a result, the efficiency of the crankcase pump of the crankcase can be improved.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view showing an embodiment of a scavenging device for a two-cycle engine according to the present invention.

FIG. 2 is a graph showing opening / closing operations of the intake control valve and the scavenging control valve of FIG. 1 with reference to a crankshaft rotation angle.

FIG. 3 is a graph showing the opening operation of the intake control valve of FIG. 1 in relation to the rate of change in crankcase internal pressure.

FIG. 4 is a graph showing the opening operation of the scavenging control valve of FIG. 1 in relation to the flow in the scavenging passage.

5 is a sectional view showing an actual two-cycle engine to which the scavenging device for the two-cycle engine of FIG. 1 is applied.

6 is a sectional view taken along line VI-VI of FIG.

7 is a sectional view taken along line VII-VII of FIG.

FIG. 8 is a perspective view showing the intake control valve and the exhaust control valve of FIG.

9 is a diagram showing another embodiment of the intake control valve and the exhaust control valve of FIG.

FIG. 10 is a schematic sectional view showing a conventional two-cycle engine.

[Explanation of symbols]

 10 2 cycle engine 12 Crank case 13 Cylinder 14 Piston 15 Scavenging passage 16 Surge tank 23 Reed valve 26 Scavenging port 28 Intake control valve 29 Scavenging control valve 31 First scavenging passage 32 Second scavenging passage

Claims (1)

[Claims] 1. A crankcase in which a piston that reciprocates between a top dead center and a bottom dead center is housed and a crankcase in which the cylinder is installed are communicated with each other through internal scavenging passages. In a scavenging device of a two-cycle engine in which an air-fuel mixture is supplied from inside to the inside of the cylinder through the scavenging passage and a scavenging port, a surge tank is arranged in the scavenging passage, and the crankcase is provided in the scavenging passage. An intake control valve is installed between the surge tank and the surge tank, and a scavenging control valve is installed between the surge tank and the cylinder.The intake control valve is configured such that the piston moves from top dead center to bottom dead center. The scavenging control valve is operated to open over substantially the entire forward movement section, and the scavenging control valve opens the scavenging port during the forward movement of the piston, and then the bottom dying occurs. A scavenging device for a two-cycle engine, characterized in that the scavenging device is controlled so as to be opened from a point to the top dead center until the initial stage of returning of the piston.