JP2001295652A - Stratified scavenging two-cycle engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To simplify the structure, reduce the size, and facilitate the opening control of a throttle valve in a mixture path and an air valve in an air path. SOLUTION: Spaces, formed through a partition wall 15 and adjacent to each other, are provided in a mixture path connected to a crankcase 3 and an air path 9 connected to a scavenging path 8, and a valve stem 25 is installed on generally the same level as the partition wall 15 to operate a butterfly valve 24, so that one side thereof through the valve stem 25 of a valve plate 26 acts as a throttle valve 27 and the other acts as an air valve 28. The opening control of the throttle valve 27 and the air valve 28 are performed by the single operation of the butterfly valve 24, so that the flow rate ratio becomes a specified fixed value.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a compression scavenging method in a crankcase, in which air is first introduced into a combustion chamber to discharge combustion gas during scavenging, and thereafter, an air-fuel mixture is introduced into the combustion chamber. More specifically, the present invention relates to a stratified scavenging two-stroke engine, more specifically to a stratified scavenging two-stroke engine provided with air-fuel ratio control means having a simple structure for controlling the flow rate of an air-fuel mixture while keeping the flow ratio of the air mixture substantially constant.

[0002]

2. Description of the Related Art When an air-fuel mixture in a combustion chamber ignites and explodes and a piston descends, an exhaust port is first opened to start discharging combustion gas, and then a scavenging port is opened and supplied to a crank chamber. In a two-cycle engine in which an air-fuel mixture is introduced into a combustion chamber and the remaining combustion gas is discharged, an air passage is connected to a scavenging passage connecting the crank chamber and the combustion chamber, and when the scavenging port is opened, the air passage is first opened. It is known that air is introduced to discharge combustion gas and then a mixture in a crankcase is introduced.

In a two-stroke engine of the crank chamber compression scavenging type which performs stratified scavenging, an output control throttle valve provided in a mixture passage connected to the crank chamber and air provided in an air passage. By opening and closing the air valve for flow control in conjunction with the opening and closing operation, a large amount of residual combustion gas is mixed into the air-fuel mixture, causing incomplete combustion or misfire, or significantly increasing the air-fuel ratio of the air-fuel mixture. Some proposals have been made so as not to fluctuate.

As one of them, it is disclosed in Japanese Unexamined Patent Application Publication No. Hei 9-1990 that, when a throttle valve and an air valve are arranged far apart from each other or are arranged in the cross direction even if they are close to each other. No. 125966 and JP-A-9-287521.

[0005] As another one, it is disclosed in Japanese Patent Application Laid-Open No. HEI 10-103605 that, when a throttle valve and an air valve are close to each other, they are arranged coaxially and integrated with each other.
No. 252565.

[0006]

The former proposal requires a large space for installation because a large or complicated link mechanism is used, and it is difficult to properly control the opening degree. Have a problem. Further, the latter proposal integrates a throttle valve and an air valve, each of which has a rotary flow control valve structure in which a cylindrical valve body is provided with a diametrical valve hole, and then installs fuel inside the throttle valve. The nozzle protrudes, a constant fuel chamber is disposed below the nozzle, and an accelerator lever is disposed above the air valve. That is, since this is a known rotary throttle valve type carburetor in which an air valve is provided in a throttle valve, it is inevitable that the entire structure becomes complicated and large.

[0007] For this reason, all of the above proposals require a large installation space, and may not be used for an engine whose installation space is extremely limited, such as a chain saw. Furthermore, in order to achieve a flow ratio corresponding to various requirements of the engine, the former one of the above proposals is extremely troublesome because the mounting angle and lever ratio of the link mechanism must be changed, and the latter one of the above proposals is also troublesome. Is also very troublesome because the diameter and phase of the valve hole must be changed.

According to the present invention, an air-fuel mixture passage having a throttle valve for output control is connected to a crank chamber, and an air passage having an air valve for flow rate control is connected to a scavenging passage communicating between the crank chamber and the fuel chamber. For the connected stratified scavenging two-stroke engine, the conventional air-fuel ratio control means has the above-mentioned conventional air-fuel ratio control means for making the opening and closing operations of the throttle valve and the air valve mutually related to make the flow ratio of the air-fuel mixture and the air substantially constant. A large installation space is required, it is difficult to respond to various demands of the engine, and it is difficult to properly control the opening degree of each of the means, and the structure is complicated and large. This was done to solve the problem.

[0009]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention provides a mixture passage and an air passage which are defined by partition walls and have sections adjacent to each other. The valve shaft is positioned on the same plane as the partition wall so that one of the valve shafts acts as a throttle valve that opens and closes the air-fuel mixture passage, and the other acts as an air valve that opens and closes the air passage. installed.

As described above, since the throttle valve and the air valve are formed by a single valve plate of a butterfly valve, an interlocking mechanism is not required, the structure is extremely simple and small, and the apparatus can be installed in a narrow place. In addition, the opening degree control for setting the flow rate ratio of the air-fuel mixture to the air to a predetermined value can be performed without using any special means.

In the above case, an opening is provided at the front and rear portions of the valve shaft of the partition wall so as to communicate the air-fuel mixture passage and the air passage, and when the valve plate is fully opened, the opening is closed to function as a part of the partition wall. There is.

In this case, the mixture and a part of the air mix with each other when the engine is idling and at a partial load,
In particular, part of the fuel is mixed into the scavenging air, so that the scavenging air introduced into the combustion chamber prior to the air-fuel mixture from the crankcase forms the air-fuel mixture, thereby improving idling and partial load operation. Can be maintained. In addition, during full load operation, only air and air-fuel mixture are introduced into the combustion chamber as before, so that it is possible to comply with exhaust gas regulations when fully opened and to comply with exhaust gas total amount regulations.

Further, in the above, the partition wall is divided into front and rear by the valve shaft, and the valve shaft is installed so that the air-fuel mixture passage and the air passage are mutually kept airtight so that the valve plate overlaps the partition wall when the valve plate is fully opened. In some cases.

[0014] In this case, the mixture passage and the air passage are always shut off from each other to perform the same layered scavenging as in the past, and also to comply with the exhaust gas regulation at the time of partial load, thereby easily complying with the exhaust gas total amount regulation. Can be.

Further, in the above, in addition to the airtight installation of the valve shaft, a closing wall for maintaining a closed state in a small opening range of the air valve may be provided in the air passage.

In this case, the air valve opens the air passage a little after the throttle valve starts opening the air-fuel mixture passage, and only the air-fuel mixture is introduced into the combustion chamber at the beginning of the acceleration operation, so that a good acceleration operation is performed. Can be done.

Referring to the drawings, an embodiment of the present invention will be described. In FIGS. 1 and 3, an engine 1 has a cylinder 2, a crank chamber 3, and a piston 4, and the cylinder 2 is an inlet of an exhaust passage 5. An exhaust port 5 a is open, and a suction port 6, which is an outlet of the mixture passage 6, is provided in the crank chamber 3.
The scavenging passage 8 is provided with a scavenging passage 8 which communicates between the crank chamber 3 and the combustion chamber 7 above the piston 4 of the cylinder 2. An air passage 9 is connected to the scavenging passage 8.

When the piston 4 starts rising from the bottom dead center, the volume of the crank chamber 3 increases, and the piston 4 closes the exhaust port 5a and the scavenging port 8a opened on the wall surface of the cylinder 2. Therefore, the crank chamber 3 and the scavenging passage 8
, The air-fuel mixture is sucked into the crank chamber 3 from the air-fuel mixture passage 6, and the air is sucked from the air passage 9 into the scavenging passage 8 and further into the crank chamber 3.

When the piston 4 reaches near the top dead center,
When the air-fuel mixture sent into the combustion chamber 7 in the previous stroke ignites and explodes, and the piston 4 starts descending, the crank chamber 3
Pressure starts to rise. On the other hand, when the exhaust port 5a and the scavenging port 8a are opened, the combustion gas in the combustion chamber 7 starts to be discharged into the exhaust passage 5, and the air in the scavenging passage 8 is blown out to the crank chamber 2 by the pressure of the crank chamber 3. The remaining combustion gas is discharged, and the air-fuel mixture in the crank chamber 3 is introduced into the combustion chamber 7 through the scavenging passage 8 following the air, and the piston 4 reaches the bottom dead center.

The rotation of the crankshaft 12 connected to the reciprocating piston 4 via the connecting rod 10 and the crank arm 11 by the above repetition is exactly the same as that of the conventional two-stroke engine.

The mixture passage 6 and the air passage 9 correspond to the engine 1
Are separated from each other toward the crank chamber 3 and the scavenging passage 8 in a section close to the other, but are separated by a partition wall 15 and extend parallel to and adjacent to each other in the other sections, and their inlet ends open to one air cleaner 16. ing.

A portion of the mixture passage 6 parallel to the air passage 9 has a venturi 17, and a main nozzle 19 for sending fuel sent from a diaphragm-type constant fuel chamber 18 provided below the venturi 17 to the venturi 17. In addition, an idle port 20 and a slow port 21 for sending out to the downstream side of the venturi 17 are opened, and this section constitutes a carburetor 22.

The mixture passage 6 and the air passage 9 are opened and closed by a single butterfly valve 24. The butterfly valve 24 is disposed with the valve shaft 25 positioned substantially on the same plane as the partition wall 15. One of the valve plates 26 sandwiching the valve shaft 25 opens and closes the mixture passage 6, and the other opens and closes. It operates to open and close the air passage 9. Therefore, the portion of the valve plate 26 that opens and closes the mixture passage 6 functions as a throttle valve 27 for output control, and the portion that opens and closes the air passage 9 functions as an air valve 28 that controls the flow rate of scavenging air.

An accelerator lever (not shown) and a return spring (not shown) are provided at one end of the valve shaft 25, from an idle position where each of the passages 6 and 9 is substantially closed to a fully open position which is located on substantially the same plane as the partition wall 15. The valve plate 26 is rotated. As described above, since the throttle valve 27 and the air valve 28 are formed by the valve plate 26 of one butterfly valve 24, an interlocking mechanism is not required, and the structure becomes extremely simple and small. can do. In addition, the flow rate ratio of the air-fuel mixture to the air is controlled by the air-fuel mixture passage 6 and the air passage 9, particularly, the butterfly valve 24.
Is set according to the passage area of the portion where is installed, and by the throttle valve 27 and the air valve 28 operating integrally,
The opening degree of the two passages 6, 9 can be controlled so that the flow rate ratio can be easily maintained at a predetermined value.

FIGS. 1 and 2 show claims 1 and 2.
The embodiment of the invention described in (1) is shown, and a partition wall 15 is shown.
Is formed in the front and rear portions of the valve shaft 25 to form an opening 29 for communicating the mixture passage 6 with the air passage 9. The opening 29 is provided when the throttle valve 27 and the air valve 28 are fully opened.
The outer peripheral edge of the valve plate 26 is closed by the partition wall 15.
Layered on.

FIG. 1 shows a state of the idling operation.
The mixture passage 6 and the air passage 9 communicate with each other through an opening 29 that is fully open. The fuel is sucked out from the idle port 20 located on the downstream side of the throttle valve 27, forms a mixture with the air flowing through the mixture passage 6, and is sent to the crank chamber 3. On the other hand, a part of the fuel flows into the air passage 9 from a portion downstream of the valve shaft of the opening 29 to form a lean mixture with the air flowing through the air passage 9 and is sent to the scavenging passage 8.

FIG. 2A shows a state of the partial load operation in which the throttle valve 27 and the air valve 28 are partially opened, and the fuel is sucked out from the main nozzle 19, the idle port 20, and the slow port 21 and mixed. An air-fuel mixture is formed with the air flowing through the air passage 6 and sent to the crank chamber 3. On the other hand, part of the fuel flows into the air passage 9 from both the upstream and downstream portions of the valve shaft 25 of the opening 29, forms a mixture with the air flowing through the air passage 9, and sends the mixture to the scavenging passage 8. Can be

As a result, scavenging is performed not with air but with a thin air-fuel mixture during the idling operation and in the partial load operation range, as compared with the case where the air-fuel mixture is introduced into the combustion chamber 7 after the air. Since the air-fuel mixture in the combustion chamber 7 is not diluted, idling and partial load operation can be favorably maintained without output shortage or the like.

When the throttle valve 27 and the air valve 28 are almost fully opened, the opening 29 becomes smaller, and the mixture passage 6 and the air passage 9
The air in each passage 6, without mixing with each other
9, the fuel gradually stops flowing into the air passage 9, and when fully opened, the valve plate 26 forms a part of the partition wall 15 as shown in FIG. 6, 9 are independent of each other.

As a result, at the time of full load operation, only the air is first introduced into the combustion chamber 7 to perform scavenging, followed by the introduction of the air-fuel mixture. In addition to this, it is possible to easily adapt to the exhaust gas total regulation, especially for a portable work machine that often operates at full throttle.

FIGS. 3 and 4 show an embodiment of the invention described in claims 1, 3 and 4. The partition wall 15 has openings at front and rear portions of the valve shaft 25. FIG. The air-fuel mixture passage 6 and the air passage 9 are always separated from each other by being divided into front and rear parts by the valve shaft 25 and provided with a sealing material 31 at a dividing part in contact with the valve shaft 25. . Further, the air passage 9 is provided with a closing wall 32 that maintains a closed state until the air valve 28 is opened from an idle position to a certain small opening. The closing wall 32 has an arc-shaped wall surface along the rotation locus of the outer periphery of the air valve 28.

According to this embodiment in which the mixture passage 6 and the air passage 9 are always isolated from each other and the valve shaft 25 is disposed on the same plane as the partition wall 15, the idle position shown in FIG. 4A through the partial load region shown in FIG.
While the throttle valve 27 and the air valve 28 rotate to the full load position shown in FIG. 3B, only the air-fuel mixture flows into the air-fuel mixture passage 6 and only the air flows into the air passage 9 to perform the same layered scavenging as in the conventional case. It is. Further, since it is possible to comply with the exhaust gas regulation at the time of partial load as compared with the first invention, it becomes easier to comply with the exhaust gas total amount regulation.

Further, in addition to this, the closing wall 3 having an arc-shaped wall surface along the rotation locus of the outer peripheral edge of the air valve 28.
According to the present embodiment in which the throttle valve 2 is provided in the small opening range, the throttle valve 2
The air valve 28 opens the air passage 9 slightly after the opening of the mixture passage 6 by the air passage 7. For this reason, only the air-fuel mixture is introduced into the combustion chamber 7 at the beginning of the acceleration operation, so that a favorable acceleration operation can be performed.

In the above two embodiments, the mixture passage 6 and the air passage 9 are vertically arranged. However, they may be arranged side by side and adjacent to each other. It becomes low and easy to install in a narrow place.

[0035]

As described above, according to the present invention in which the valve plate of one butterfly valve is used as a throttle valve and an air valve, the structure of the two valves is significantly simplified, and the interlocking mechanism is provided. It is possible to easily perform appropriate opening control by not using and opening and closing integrally.
And it can be installed in a narrow place. Further, the flow rate ratio between the air-fuel mixture and the air can be easily set to a required constant value.

Further, according to the present invention, in addition to the above, various other types of engines such as maintaining good idling and partial load operation, improving acceleration operation, and easily complying with exhaust gas regulations, etc. It can respond to requests.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view showing an embodiment of the present invention at an idle position.

FIGS. 2A and 2B are partial sectional views of the embodiment shown in FIG. 1, and FIG.

FIG. 3 is a vertical cross-sectional view showing another embodiment of the present invention at an idling position.

FIGS. 4A and 4B are partial cross-sectional views of the embodiment shown in FIG. 3 in a partial load region, and FIG.

[Explanation of symbols]

1 engine, 3 crank chamber, 5 exhaust passage, 6 mixture passage, 7 combustion chamber, 8 scavenging passage, 9 air passage,
15 partition wall, 22 carburetor, 24 butterfly valve, 25 valve shaft, 26 valve plate, 27 throttle valve, 28 air valve, 29
Opening, 31 sealing material, 32 partition,

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[Procedure amendment]

[Submission date] April 28, 2000 (200.4.2
8)

[Procedure amendment 1]

[Document name to be amended] Drawing

[Correction target item name] All figures

[Correction method] Change

[Correction contents]

FIG. 2

FIG. 4

FIG.

FIG. 3

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) F02M 9/12 F02M 9/12 B 13/04 13/04 B

Claims (4)

[Claims] An air-fuel mixture passage having a throttle valve for output control is connected to a crank chamber, and an air passage having an air valve for flow control is connected to a scavenging passage connecting the crank chamber and the combustion chamber. In the stratified scavenging two-cycle engine connected, the mixture passage and the air passage are partitioned by a partition wall and have sections adjacent to each other, and one butterfly valve sandwiches a valve shaft of a valve plate. The valve shaft is positioned on substantially the same plane as the partition wall such that one of the two functions as a throttle valve for opening and closing the mixture passage and the other functions as an air valve for opening and closing the air passage. A stratified scavenging two-stroke engine, wherein the engine is installed in a stratified scavenging two-cycle engine. 2. The partition wall has openings in front and rear portions of the valve shaft for communicating the mixture passage and the air passage,
2. The stratified scavenging two-stroke engine according to claim 1, wherein the valve plate closes the opening when fully opened and functions as a part of the partition wall. 3. 3. The valve shaft divides the partition wall back and forth, and is installed so as to keep the air-fuel mixture passage and the air passage mutually airtight, and the valve plate overlaps the partition wall when fully opened. The stratified scavenging two-stroke engine according to claim 1, wherein 4. The valve shaft is installed so as to divide the partition wall back and forth and keep the air-fuel mixture passage and the air passage airtight from each other, and the valve plate overlaps the partition wall when fully opened. 2. The stratified scavenging two-stroke engine according to claim 1, wherein the air passage further has a closing wall that maintains a closed state in a small opening range of the air valve. 3.