JP3031533B2 - Carburettor for two-stroke internal combustion engine - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention enables the amount of air-fuel mixture supplied to an engine via a throttle valve of a carburetor and the amount of air supplied to an engine via an air control valve to be set appropriately. The present invention relates to a carburetor for a two-stroke internal combustion engine which suppresses a blow-by phenomenon of an air-fuel mixture and obtains an appropriate air-fuel ratio.

[0002]

2. Description of the Related Art In a conventional two-stroke internal combustion engine of a crankcase compression type, an air-fuel mixture pressurized in a crankcase is supplied from a scavenging port to a cylinder or a combustion chamber so that combustion gas remaining in the cylinder is discharged to an exhaust port. When the scavenging of the combustion gas is performed satisfactorily, the air-fuel mixture flowing into the cylinder is discharged from the exhaust port to the atmosphere together with the combustion gas. I do.
The blow-by phenomenon of the air-fuel mixture is caused by hydrocarbons (H
C) will be contained in a large amount in the exhaust gas, and the amount of wastefully consumed fuel will increase.

If the closing timing of the exhaust port by the piston is advanced, the blow-by phenomenon can be suppressed, but the amount of combustion gas remaining in the cylinder increases, and irregular combustion such as incomplete combustion or misfire occurs. Hydrocarbons contained (H
There is a disadvantage that the amount of C) increases and the output of the engine decreases.

Therefore, Japanese Patent Application Laid-Open No. 7-139358 discloses
JP-A-7-189704, JP-A-7-26935
In a two-stroke internal combustion engine disclosed in, for example, Japanese Unexamined Patent Application Publication No. 6-205, an air passage is connected to a portion of a scavenging passage close to a scavenging port, a check valve is provided in the air passage, and an air flow rate in the air passage is controlled by a carburetor. The adjustment is made in conjunction with the operation of the throttle valve. According to the above-described two-stroke internal combustion engine, when the pressure of the crank chamber becomes negative when the piston rises, the air-fuel mixture flows from the carburetor into the crank chamber via the intake port, and at the same time, the air in the air passage pushes the check valve open. Flows into the scavenging passage or scavenging port. When the piston descends due to the explosion of the air-fuel mixture, the exhaust port opens near the bottom dead center, and the combustion gas is discharged. Subsequently, when the scavenging port is opened, first the air in the scavenging passage is supplied to the cylinder by the positive pressure of the crank chamber, and then the air-fuel mixture in the crank chamber is supplied to the cylinder.

However, in the above-described two-stroke internal combustion engine, only air is sucked into the cylinder through the scavenging port from the air passage,
The fuel becomes a mixture with air in the carburetor, is sucked into the crank chamber, and is ejected to the cylinder through the scavenging passage and the scavenging port.
That is, most of the air contributing to the output is sucked into the cylinder via the air control valve, the air passage, and the scavenging port.

Incidentally, the output of the engine is ultimately determined by the amount of air sucked into the cylinder. The output increases when the amount of air is large, and decreases when the amount of air is small. 2 above
In a stroke internal combustion engine, most of the air that contributes to the output of the engine does not pass through the carburetor, but flows through the air control valve, the air passage, and the scavenging port to the cylinder. Although the air becomes lean as a whole corresponding to the amount of air, the flow rate of the air-fuel mixture passing through the vaporizer becomes slow. In order to promote the mixing of fuel and air and increase the atomization of fuel, it is necessary to increase the flow rate of the air-fuel mixture passing through the vaporizer.

[0007]

SUMMARY OF THE INVENTION In view of the above-mentioned problems, it is an object of the present invention to supply air to a scavenging port via an air control valve, and to reduce the size of a throttle valve of a carburetor so that an air-fuel mixture passing through the throttle valve is reduced. To increase the flow rate of the fuel, to ensure an appropriate amount of air-fuel mixture supplied to the crankcase, and to increase the atomization of fuel.
It is an object of the present invention to provide a carburetor for an internal combustion engine.

[0008]

In order to solve the above-mentioned problems, according to the structure of the present invention, an air passage is connected to a portion of a scavenging passage communicating with a crank chamber and a scavenging opening which is close to the scavenging opening, and the air passage is connected to the scavenging opening. A first check valve for allowing air to flow to the scavenging passage, an air control valve for controlling the amount of air flowing from the air purifier to the air passage, and a second check valve to the crank chamber. 2 equipped with a vaporizer for supplying a mixture of air and fuel
In the stroke internal combustion engine, the opening area of the bench lily portion of the carburetor is set smaller than the opening area of the air control valve.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS In a two-stroke internal combustion engine of a crankcase compression type, a first step is to prevent a mixture blown from a scavenging port to a combustion chamber from flowing directly to an exhaust port.
The air passage provided with the check valve is connected to the scavenging passage, and an air control valve is provided to control the amount of air flowing to the air passage. The diameter of the intake path of the carburetor or the throttle valve is made smaller than the diameter of the air control valve, the flow rate of the air-fuel mixture passing through the bench lily is increased, and an appropriate amount of the air-fuel mixture is supplied to the crank chamber.
Increase fuel atomization.

[0010] The air control valve and the throttle valve are constituted by rotary type throttle valves, and the opening operation characteristics of both are made similar to increase the scavenging efficiency of the engine and obtain an appropriate air-fuel ratio.

[0011]

1 is a left side sectional view of a two-stroke internal combustion engine provided with a carburetor according to one embodiment of the present invention. The engine body A has a cylinder 32 coupled to an upper part of a crankcase 39,
A piston 34 is fitted to the cylinder 32 so as to be able to move up and down.
Arm 3 of crankshaft 38 supported by crankcase 39
8a, a piston 34 is connected by a connecting rod 42, and a combustion chamber 32 is provided between the upper end of the cylinder 32 and the piston 34.
a is partitioned. An ignition plug 31 is mounted on the head of the cylinder 32, and one exhaust port 35 and a plurality of scavenging ports 3, each of which is opened near the bottom dead center of the piston 34, are provided on the wall of the cylinder 32.
3 is formed. The exhaust port 35 communicates with the atmosphere via an exhaust muffler 44, and the scavenging port 33 communicates with the crank chamber 39a via a scavenging passage 33a.

The carburetor B is connected to the intake port 3 of the crankcase 39.
7, a second check valve (reed valve) 37a as an intake valve
Attached via a heat insulating tube 21 provided with Specifically, the carburetor B, the air control valve C, and the air purifier D are integrally attached to the crankcase 39 of the engine via the heat insulating pipe 21 by two attachment bolts (not shown). The carburetor B is fitted with a throttle valve 15 having a throttle hole so as to be rotatable and vertically movable in a cylindrical portion crossing the intake passage of the main body 16, and the throttle valve lever 10 is connected to a shaft portion 12 at the upper end of the throttle valve 15. You. A constant pressure fuel chamber 19 and an atmosphere chamber 17 are defined by a membrane 18 at a lower portion of the main body 16. The fuel in a fuel tank (not shown) is successively supplied to the constant pressure fuel chamber 19 by a fuel pump, and is constantly maintained at a constant pressure. A fuel nozzle 20 projects from the constant pressure fuel chamber 19 into a throttle hole of the throttle valve 15. A rod valve 14 protruding from the shaft portion 12 of the throttle valve 15 to the throttle hole,
The fuel nozzle 20 is inserted into the fuel nozzle 20 to adjust the degree of opening of the fuel injection hole. When the throttle valve lever 10 rotates against the force of the return spring, the opening of the throttle valve 15 increases, and at the same time, the throttle mechanism is formed by a cam mechanism formed between the throttle valve lever 10 and the upper end wall of the main body 16. The rod valve 14 rises together with 15, and the opening of the fuel injection hole of the fuel nozzle 20 increases.

According to the present invention, the scavenging passage 33a is externally provided.
To allow air to flow to the portion close to the scavenging port 33
The check valve (reed valve) 27 is provided on the wall of the cylinder 32. For this reason, the connection pipe 2 provided with the first check valve 27
6 has one end connected to a portion of the scavenging passage 33a close to the scavenging port 33, and the other end connected to the atmosphere via the air passage 25, the air control valve C, the intake passage 9, and the air purifier D.

An air control valve C is provided in the upper half of a block-shaped body 8 having an intake passage 9 in the same number as the number of scavenging ports 33, extending upward from the intake passage 9 and crossing the valve chamber 8a (FIG. 3). 7
Is provided. The upper end of the valve passage 7 is connected to the connecting pipe 6. As shown in FIG. 3, orthogonal to the intake path 9 of the main body 8,
That is, the rod-shaped valve element 5 is rotatably fitted into the cylindrical valve chamber 8a parallel to the crankshaft 38. The valve element 5 is a valve chamber 8a.
Is provided with a valve through-hole 5a that can communicate with a valve passage 7 that crosses the valve body 7. When the valve element 5 is rotated, the area of the valve passage 7 changes. The lower end of each valve passage 7 communicates with a passage 53 intersecting with the intake passage 9. The end of the passage 53 is closed by the lid 52. The air outlet of the air control valve C, that is, the connection pipe 6 is connected to a connection pipe 26 attached to the wall of the cylinder 32 by an air passage 25 (FIG. 2) formed of a pipe.

In the body 8 of the air control valve C, through holes 5 through which the above-mentioned mounting bolts are inserted are symmetrically positioned with respect to the intake passage 9.
4 are provided. The air control valve C is composed of a single rotary throttle valve. A retaining ring 51 is locked at one end of the valve element 5 fitted in the valve chamber 8a, and a lever 23 is connected to the other end of the valve element 5. Be combined. Return spring 22 wound around the outer end of valve body 5
Are locked at one end to the main body 8 and at the other end to the lever 23.

As shown in FIG. 1, the air purifier D is formed by connecting box-shaped cases 2 and 4 each having a two-piece structure with a filter 3 interposed therebetween. The sucked air is supplied to the filter 3, the case 4, the air control valve C
And the intake chamber 9 of the carburetor B, the heat insulating pipe 21, the second check valve 37a as an intake valve, and the crank chamber 39 through the intake port 37.
Flows to a. The air is separated from the air control valve C and flows to the scavenging port 33 via the air passage 25, the first check valve 27, and the scavenging passage 33a.

According to the present invention, the air-fuel mixture supplied to the engine changes according to the opening of the throttle valve 15 of the carburetor B, and the air supplied to the engine varies according to the opening of the air control valve C. The opening area of the air control valve C (the diameter of the valve hole 5a) is set to be larger than the opening area of the intake path of the carburetor B (the diameter of the throttle hole of the throttle valve 15). In other words, FIG.
As shown in (2), the opening of the air control valve C or the amount of air passing through the air control valve C is adjusted with respect to the opening of the throttle valve 15 or the amount of air passing through the throttle valve 15.

As shown in FIG. 4, an operation lever 61 for driving the throttle valve lever 10 of the carburetor B is supported by a support shaft 62 on the upper end wall of the main body 16. A pin 10a projecting upward from the throttle valve lever 10 is urged into engagement with the edge of the operation lever 61 by the force of the return spring. The operating lever 61 and the lever 23 of the air control valve C are linked and connected by one connecting rod 13. By selecting the connection point of the connection rod 13, that is, the adjustment hole 61a of the operation lever 61 or the adjustment hole 23a of the lever 23 of the air control valve C, the throttle valve 15 is selected.
The opening degree of the air control valve C with respect to the opening degree is adjusted. A mounting bracket 64 for fixing an outer tube of a remote control cable (not shown) is supported on a mounting plate 63a projecting upward from a support plate 63 supported on an upper end wall of the vaporizer main body 16,
The inner wire passing through the mounting bracket 64 is connected to the operation lever 6.
It is connected to a swivel 65 supported on one end.

Next, the operation of the carburetor for a two-stroke internal combustion engine according to the present invention will be described. The operation lever 61 is moved from the idle position shown in FIG.
When the operation lever 61 is rotated clockwise around
As a result, the pin 10a is pushed, and the throttle valve lever 10 is driven in the opening direction. At the same time, the connecting rod 13 is
, The lever 23 of the air control valve C is rotated, the air control valve C opens, and the amount of air sent to the scavenging port 33 increases.

During operation of the engine, the air-fuel mixture flows from the intake port 37 to the crank chamber 39a before the piston 34 reaches the top dead center.
And the air is filled from the connection pipe 26 into the scavenging passage 33 a and the scavenging port 33. On the other hand, a compressed air-fuel mixture exists in the cylinder 32 just before the piston 34 reaches the top dead center. When the compressed air-fuel mixture in the cylinder 32 is ignited by the ignition plug 31, the air-fuel mixture explodes inside the cylinder 32, and the piston 34 descends. Piston 3
When 4 descends, the air-fuel mixture in the crank chamber 39a is pressurized, and at the same time, the pressure in the crank chamber 39a is transmitted to the scavenging port 33 through the scavenging passage 33a, and the air in the scavenging port 33 is also pressurized.

When the piston 32 is further lowered, the exhaust port 35 starts to open, and the combustion gas in the cylinder 32 is released from the exhaust port 3.
5. Exhausted through the exhaust muffler 44 to the atmosphere. As soon as the exhaust port 35 opens, the scavenging port 33 starts to open, and the scavenging passage 33
a and the pressurized air of the scavenging port 33 flows into the cylinder 32, and the combustion gas remaining in the cylinder 32 is discharged to the exhaust port 35.
It performs a scavenging action that pushes out Next, the crank chamber 39a
Flows into the cylinder 32 via the scavenging passage 33a and the scavenging port 33. The air flowing into the cylinder 32 from the scavenging port 33 and the air-fuel mixture flowing from the crank chamber 39a into the cylinder 32 through the scavenging passage 33a and the scavenging port 33 are separated from each other by air, and the air flows first, and then mixed. Qi flows in.

Next, when the piston 34 moves to a stroke in which the piston 34 rises from the bottom dead center and reaches the vicinity of the top dead center, the crank chamber 39a
Is in a negative pressure state, the second check valve 37a of the intake port 37 opens, and the air-fuel mixture generated in the carburetor B is sucked from the intake port 37 into the crank chamber 39a. At the same time, the air-fuel mixture flowing into the scavenging port 33 in the previous stroke and remaining
It is sucked back to 9a. Further, the first check valve 27 is opened by the negative pressure of the crank chamber 39a, and the air flows from the air purifier D through the air control valve C, the air passage 25, the first check valve 27, and the scavenging passage 33a. It is sucked into the chamber 39a. Thus, when the piston 34 has almost reached the top dead center, the crank chamber 39a is filled with the air-fuel mixture, and the scavenging passage 33a and the scavenging port 33 are filled with only air.

As described above, in the present invention, only the air that has flowed into the cylinder 32 during the scavenging stroke flows out to the exhaust port 35 together with the combustion gas, and the air-fuel mixture that flows into the cylinder 32 after the air flows into the cylinder 32 Therefore, the scavenging efficiency is increased, the amount of unburned components (HC) contained in the exhaust gas is reduced, and the output of the engine is increased without waste of fuel.

As the throttle valve 15 opens to increase the amount of air-fuel mixture, the air control valve C linked to the throttle valve 15 also opens to increase the amount of air. The opening of the air control valve C is always kept larger than the opening of the throttle valve of the carburetor B, and an appropriate amount of air and air-fuel mixture is supplied to the cylinder over the entire operation range of the engine. That is, while the amount of the air-fuel mixture is substantially proportional to the opening of the throttle valve 15, the amount of air also changes substantially in proportion to the opening of the air control valve C linked to the throttle valve 15, and is supplied to the engine. The air-fuel ratio does not become too rich or too thin.

In the above-described embodiment, a film-type vaporizer frequently used in a portable work machine has been described, but the present invention is not limited to this type of vaporizer.

[0026]

As described above, according to the present invention, since the diameter of the throttle hole of the throttle valve of the vaporizer is smaller than the diameter of the valve hole of the air control valve, the flow rate of the air-fuel mixture passing through the vaporizer is reduced. As the air-fuel mixture becomes higher, atomization of the air-fuel mixture is promoted, and the improvement of the scavenging efficiency suppresses fuel blow-through, thereby improving fuel efficiency and purifying exhaust gas.

Since the throttle valve and the air control valve of the carburetor are composed of rotary type throttle valves having the same structure, the opening degree of the throttle valve and the opening degree of the air control valve with respect to the operation amount of the throttle valve change in the same manner. In addition, an appropriate air-fuel ratio can be easily maintained over the entire operation range of the engine, and the design of the fuel metering mechanism (fuel nozzle, rod valve, etc.) of the carburetor becomes easy.

[Brief description of the drawings]

FIG. 1 is a left side sectional view of a two-stroke internal combustion engine including a carburetor according to the present invention.

FIG. 2 is a plan sectional view of the two-stroke internal combustion engine.

FIG. 3 is a front sectional view of the air control valve of the carburetor, taken along line 3A-3A in FIG. 2;

FIG. 4 is a plan view showing an interlocking mechanism between a throttle valve and an air control valve of the carburetor.

FIG. 5 is a left side view of a lever of an air control valve of the carburetor.

FIG. 6 is a diagram showing opening operation characteristics of a throttle valve and an air control valve of the carburetor.

[Explanation of symbols]

A: Engine main body B: Vaporizer C: Air control valve D: Air purifier 5: Valve body 5a: Valve through hole 6: Connection pipe 7: Valve passage 8: Main body 9: Intake path 10: Throttle valve lever 1
2: Shaft 13: Connecting rod 14: Rod valve 15: Throttle valve 16: Vaporizer body 17: Air chamber 18: Membrane 1
9: constant pressure fuel chamber 20: fuel nozzle 21: heat insulating pipe 2
2: Return spring 23: Lever 23a: Adjustment hole 25:
Air passage 26: Connecting pipe 27: First check valve 31:
Spark plug 32: cylinder 32a: combustion chamber 33: scavenging port 33a: scavenging passage 34: piston 35: exhaust port 37: intake port 37a: second check valve (intake valve) 3
8: Crankshaft 38a: Arm 39: Crankcase 39a: Crankcase 42: Connecting rod 44: Exhaust muffler 51: Retaining ring 52: Lid 53: Passage 54: Through hole 6
1: Operation lever 61a: Adjustment hole 61b: Arm 62:
Support shaft 63: Support plate 63a: Vertical plate piece 64: Fixing bracket 65: Swivel

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Hitoshi Teramon 2-3-3 Shiba-koen, Minato-ku, Tokyo Inside Walbro Japan Co., Ltd. (72) Inventor Toshiro Onuma 2-3-3 Shiba-koen, Minato-ku, Tokyo No. 3 Japan Walbro Co., Ltd. (72) Inventor Takeshi Kobayashi 2-3-3, Shiba Park, Minato-ku, Tokyo Japan Co., Ltd. Walbro Co., Ltd. (56) References JP-A-7-269356 (JP, A) Japanese Utility Model 3-127032 (JP, U) Japanese Utility Model 4-271725 (JP, U) Japanese Utility Model 55-4518 (JP, Y2) (58) Fields investigated (Int. Cl. ⁷ , DB name) F02B 25/00-25/28 F02B 33/04

Claims (3)

(57) [Claims] An air passage is connected to a portion of a scavenging passage that communicates a crank chamber and a scavenging opening, the air passage being connected to a portion adjacent to the scavenging opening, and the air passage has a first check valve that allows air to flow to the scavenging passage. A two-stroke internal combustion engine having an air control valve for controlling the amount of air flowing from the air purifier to the air passage, and a carburetor for supplying a mixture of air and fuel to the crank chamber via a second check valve. A carburetor for a two-stroke internal combustion engine, wherein an opening area of a bench lily portion of the carburetor is set smaller than an opening area of the air control valve. 2. The method according to claim 1, wherein the amount of air-fuel mixture supplied to the engine changes according to the opening of a throttle valve of the carburetor, and the amount of air supplied to the engine changes according to the opening of the air control valve. The carburetor for a two-stroke internal combustion engine according to claim 1, wherein an opening area of the air control valve is set to be always larger than an opening area of a bench lily portion of the carburetor. 3. The carburetor for a two-stroke internal combustion engine according to claim 1, wherein the throttle valve of the carburetor and the air control valve are rotary throttle valves.