JP2003239807A - Butterfly throttle valve type carburetor for stratified scavenging internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an inexpensive butterfly throttle valve type carburetor for a stratified scavenging internal combustion engine with the same size as a conventional carburetor, in which phases of an air-fuel mixture throttle valve and an air throttle valve are easily set at optional angles required by the engine. <P>SOLUTION: An air-fuel mixture passage 22 and an air passage 42 horizontally piercing a carburetor body 25 are arranged in parallel with each other horizontally, and the air-fuel mixture throttle valve 20 and the air throttle valve 40 are respectively supported on valve stems 30 piercing both passages 22 and 42. An air limiting member 36 limiting air of the air passage 42 even when the air-fuel mixture throttle valve 20 is rotated a predetermined angle from a fully closed position is inserted in an entrance part of the air passage 42. A fuel pump 16 is provided in an upper part of the carburetor body 25, a constant pressure fuel feeding mechanism is provided in a lower part of the carburetor body 25, and a carburetor attaching bolt insertion hole 26 is provided between the air-fuel mixture passage 22 and the air passage 42. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention has substantially the same size as a conventional carburetor, and has a stratified structure in which a mixture throttle valve in a mixture passage is opened at a predetermined opening to open an air throttle valve in a scavenging air passage. The present invention relates to a butterfly type throttle valve carburetor for a scavenging internal combustion engine.

[0002]

2. Description of the Related Art In a stratified scavenging two-stroke internal combustion engine, in a low-load low-speed operation, the amount of air-fuel mixture blown from the crank chamber through the scavenging passage to the exhaust port is unburned, and therefore the amount of air-fuel mixture is emphasized. It is desired that only the air is supplied to the engine, and that the air from the air passage is supplied later than the air-fuel mixture in high-load high-speed operation.

A butterfly type throttle valve type carburetor for a stratified scavenging internal combustion engine disclosed in Japanese Patent Laid-Open No. 2001-295652 is provided with an air passage and an air passage partitioned by a partition wall in a carburetor body in parallel with each other. Two butterfly-type throttle valves are axially supported on the partition wall, the upper half of the butterfly-type throttle valve acts as an air valve that opens and closes the mixture passage, and the lower half of the butterfly-type throttle valve acts as a throttle valve that opens and closes the mixture passage. Is configured to work. However, in the above butterfly-type throttle valve type carburetor, the ratio of the air amount to the fuel is kept substantially constant regardless of the engine speed, so that it is particularly suitable for cold starting of an engine that requires a rich air-fuel mixture. I can not cope.

[0004]

In view of the above-mentioned problems, the object of the present invention is almost the same as that of the conventional carburetor, and the phases of the mixture throttle valve and the air throttle valve can be set to an arbitrary angle required by the engine. It is an object to provide a low-cost butterfly type throttle valve type vaporizer for stratified scavenging that can be easily set.

Another object of the present invention is for a stratified scavenging internal combustion engine in which the scavenging air passage is closed and the air in the air-fuel mixture passage is throttled when the engine is started, and a rich air-fuel mixture is supplied to the crank chamber to improve startability. It is to provide a butterfly-type throttle valve carburetor.

[0006]

In order to solve the above-mentioned problems, the structure of the present invention has a mixture passage and an air passage which traverse the carburetor main body and are arranged in parallel with each other in the carburetor main body. An air restricting member that supports the air-fuel mixture throttle valve and the air throttle valve respectively on the traversing valve shafts and that restricts the air in the air passage even if the air-fuel mixture throttle valve rotates from the fully closed position by a predetermined opening degree A fuel pump on the top of the carburetor body, a constant pressure fuel supply mechanism on the bottom of the carburetor body, and a carburetor mounting bolt insertion hole between the mixture passage and the air passage. Characterize.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION In the present invention, a mixture passage and a scavenging air passage are arranged in parallel in the carburetor body, and a carburetor mounting bolt insertion hole is provided between the mixture passage and the scavenging air passage. The air-fuel mixture throttle valve and the air throttle valve are supported by one valve shaft that crosses the air-fuel mixture passage and the scavenging air passage, and the opening degree of the air throttle valve can be arbitrarily set.

A fast idle mechanism is provided which increases the opening of the mixture throttle valve when the chioke valve is fully closed. For this reason, an air restriction member that restricts the flow of air with respect to the rotation of the air throttle valve in the opening direction is provided so that startability of the internal combustion engine and quick warm-up operation can be completed, and handling is simple. To

In addition, the valve shaft of the air-fuel mixture throttle valve and the valve shaft of the air throttle valve are separately provided, and have a predetermined play so that they can be interlocked. After the carburetor is attached to the internal combustion engine, the connecting portion of the valve shaft blocks the external atmosphere so as to prevent foreign matters from adhering to improve durability. The installation angle of the air throttle valve should be larger than the installation angle of the mixture throttle valve.Only the mixture throttle valve opens at first, and when the mixture throttle valve exceeds the specified opening, the air throttle valve interlocks with the mixture throttle valve. Then, the mixture throttle valve and the air throttle valve become parallel at the same time and fully opened.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS As shown in FIG. 1, a scavenging engine 1 equipped with a carburetor according to the present invention has a piston 4 fitted into a cylinder 2 having a spark plug 2a at its top end, and a combustion chamber above the piston 4. 7 is defined, and the crank chamber 3 is provided below the piston 4.
Is partitioned. An arm 11 that is rotatably supported and is integral with a crank shaft 12 and a piston 4 are connected to a wall portion of the crank chamber 3 by a connecting rod 10. An exhaust port 5 that opens near the bottom dead center of the piston 4 is provided in the left wall portion of the cylinder 2, and a scavenging passage 6 that connects the combustion chamber 7 and the crank chamber 3 is provided in the right wall portion of the cylinder 2. An air passage 9 having a check valve 8 open in the middle of the scavenging passage 6 and a mixture passage 9a having a check valve 8a opening to the crank chamber 3
Are arranged in parallel vertically on the right wall portion of the cylinder 2, and these passages 9 and 9a pass through the passages 14 and 15 of the heat insulating pipe 13 and the air passage 42 which laterally penetrates the carburetor main body 25 in the left-right direction.
And the mixture passage 22 respectively. Mixture passage 2
2, a mixture throttle valve 20 and a chain yoke valve 21 are provided on the valve shaft 30,
31 respectively supported. The air throttle valve 20 is supported by the valve shaft 30 in the air passage 42. The mixture throttle valve 20 is opened / closed by an operation rod or wire (not shown), and the air throttle valve 40 can be opened / closed arbitrarily.

A cover plate 18 is joined to the upper wall of the carburetor body 25 with the membrane 17 interposed therebetween, and as shown in FIG. 6, a pulsating pressure chamber 44 for introducing the pulsating pressure of the crank chamber 3 to the upper side of the membrane 17.
However, the pump chambers 45 are defined below the membrane 17, respectively. The fuel pump 16 sucks the fuel in a fuel tank (not shown) into the pump chamber 45 through the intake valve along with the vertical vibration of the membrane 17, and the fuel in the pump chamber 45 through the discharge valve and the inflow valve into a known constant pressure fuel chamber. Supply to 46. As shown in FIG. 6, in the constant pressure fuel supply mechanism, the cover plate 23 is coupled to the lower wall of the carburetor body 25 with the membrane 24 interposed therebetween, and the constant pressure fuel chamber 46 is provided above the membrane 24.
However, the air chambers 47 are defined below the membrane 24.
The inflow valve described above automatically opens when the amount of fuel in the constant pressure fuel chamber 46 becomes small, and the fuel is supplied from the fuel pump 16. The case 19 of the air purifier is connected to the right end of the carburetor body 25. The case 19 and the carburetor main body 25 are joined to the heat insulating pipe 13 by bolts that pass through a pair of upper and lower bolt insertion holes 26. The adiabatic tube 13 is connected to the engine wall by four bolts.

As shown in FIGS. 3 and 4, a lever 32 is connected to one end of the valve shaft 30, and as shown in FIG.
The lever 32 at one end and the carburetor main body 2 at the other end.
The air-fuel mixture throttle valve 20 is normally rotationally biased to the closed position shown in FIG. A bent piece 32a is formed at the end of the lever 32, and is configured to be engageable with a notch 33a at the tip of the lever 33 coupled to the valve shaft 31. A starting lever 34 is rotatably supported on the valve shaft 31, and a bent piece 34a provided on a side edge portion of the starting lever 34 is configured to be engageable with a lower edge portion of the lever 33. At the time of starting the engine, when the starting lever 34 is rotated clockwise from the position shown in FIG. 4, the lever 3 is moved by the bending piece 34a.
3 is also rotated clockwise and, as shown in FIG.
The lever 32 is rotated counterclockwise by 3. When the operating force applied to the starting lever 34 is released, the bent piece 32a is engaged with the cutout 33a, the chain yoke valve 21 is held in the closed position, and the mixture throttle valve 20 is held in the slightly idle fast idle position.

Thus, the optimum mixture for the idle operation of the engine is the through hole 21a of the chain yoke valve 21 of the mixture passage 22.
(FIG. 5), the mixture gas is supplied to the crank chamber 3 through the throttle valve 20 and the passages 15 and 9a. At this time, as shown in FIG.
The air throttle valve 40 in the air passage 42 is in the closed position. An annular air restricting member 36 is fitted to the outlet end of the air passage 42, an arc wall 36a in contact with the outer peripheral edge of the air throttle valve 40 is provided on the upper wall surface of the air restricting member 36, and the air passage of the carburetor main body 25 is also provided. An arcuate wall 36 a that contacts the outer peripheral edge of the air throttle valve 40 is also formed on the lower wall surface 42. In other words, the air-fuel mixture throttle valve 20 supported by the valve shaft 30 and the air throttle valve 40 rotate together, but the air throttle valve 40 moves from the closed position to the rotation angle α °. Keep 42 closed.

As shown in FIG. 5, one end of the valve shaft 31 is wound around the lever 33, and the other end thereof is located at the pin 73 of the carburetor body 25.
The force of the springs 74 that are respectively locked to the tee yoke valve 21 rotationally biases the chain yoke valve 21 to the fully open position shown in FIG. Figures 5 and 6
As shown in, the high-speed fuel injection hole 27 is projected from the constant pressure fuel chamber 46 to the bench lily portion 22a of the air-fuel mixture passage 22, and from the constant-pressure fuel chamber 46 near the closed position of the air-fuel mixture throttle valve 20 Also, a plurality of low-speed fuel injection holes 28 are opened to the upstream side portion, and a pilot injection hole is opened to the downstream side portion from the mixture throttle valve 20.

As described above, in idle operation of the engine,
Air is not supplied from the air passage 42 to the scavenging passage 6, but a rich air-fuel mixture is supplied to the crank chamber 3 from the air-fuel mixture passage 22, and the combustion gas in the combustion chamber 7 is exhausted during the downward stroke of the piston 4 shown in FIG. At the same time as being discharged from the mouth 5, the piston 4
The air-fuel mixture in the crank chamber 3 is supplied to the combustion chamber 7 through the scavenging passage 6 in accordance with the downward movement. In the idle operation of the engine, the amount of the air-fuel mixture in the crank chamber 3 flowing through the scavenging passage 6 and the combustion chamber 7 to the exhaust port 5 without being burned (blowing amount) is smaller than that in the high-speed operation. As the piston 4 rises, the scavenging passage 6 and the exhaust port 5 are closed, the mixture is compressed and ignited by the spark plug 2a, and the combustion pressure causes the piston 4 to descend again.

After the engine is warmed up, when the lever 32 together with the valve shaft 30 and the mixture throttle valve 20 is rotated counterclockwise in FIG. 3 against the force of the spring 30a, the mixture throttle valve 20 is rotated. Is increased, the bent piece 32a is disengaged from the notch 33a, and the force of the spring 74 of the valve shaft 31 causes the lever 33 to move.
Then, the starting lever 34 is returned to the fully open position shown in FIG. At this time, the air throttle valve 40 of the valve shaft 30 is also opened, and the air passage 42
The air is supplied to the crank chamber 3 through the passages 14 and 9 and the scavenging passage 6. During the ascending stroke of the piston 4, the scavenging passage 6
The air remaining in the combustion chamber 7 first enters the combustion chamber 7, flows out to the exhaust port 5 together with the combustion gas, and then the air-fuel mixture in the crank chamber 3 is supplied to the combustion chamber 7 through the scavenging passage 6. Since the air remaining in the scavenging passage 6 effectively expels the combustion gas in the combustion chamber 7 to the exhaust port 5, it is possible to prevent the air-fuel mixture from the crank chamber 3 from flowing to the exhaust port 5 without being burned.

The embodiment shown in FIGS. 8 to 13 is an air restricting member 3.
6, the valve shaft 30 of the air-fuel mixture throttle valve 20 and the valve shaft 50 of the air throttle valve 40 are divided, and the air-fuel mixture throttle valve 20 is rotated from the closed position to the starting position or the idle position. The air throttle valve 40 is configured so as not to rotate while stopped. A spring 51, which is weaker than the return spring 30a of the valve shaft 30 of the mixture throttle valve 20, is attached to the valve shaft 50 of the air throttle valve 40 between the carburetor body 25 and the lever 52 of the valve shaft 50. That is, the air throttle valve 40 is rotationally biased to the closed position shown in FIG. 10 by the force of the spring 51 wound around the valve shaft 50 and having one end engaged with the carburetor main body 25 and the other end engaged with the lever 52. . The air throttle valve 40 is set to have a larger installation angle than the air-fuel mixture throttle valve 20 when fully closed.

As shown in FIGS. 11 to 13, in the interlocking connecting mechanism 61 for connecting the valve shaft 30 and the valve shaft 50, the radial projection 63 formed on the inner end surface of the valve shaft 30 and the projection 63 rotate. Angle β
The groove 62 is formed in the inner end surface of the valve shaft 50 so that it can be freely rotated by only °. In this embodiment, the air restricting member 36 is not required and the air passage 42 can be constructed straight, so that the output of the internal combustion engine can be improved. When the valve shaft 30 is biased to the closed position by the force of the spring 30a, the valve shaft 50
Is urged to the closed position shown in FIG. 10 by the force of the spring 51, and the ridge 63 is in contact with the upper right wall of the groove 62 as shown in FIG. Now, when the air-fuel mixture throttle valve 20 of the valve shaft 30 is rotated counterclockwise by the rotation angle β ° to the idle position, as shown in FIG.
It only idles inside the groove 62 of 0 and does not give a rotational force to the valve shaft 50. Thus, in engine start-up and idle operation, that is, in fast idle operation, the air-fuel mixture throttle valve 20 in the air-fuel mixture passage 22 precedes the air throttle valve 40, and a preset arbitrary opening degree (indicated by a broken line in FIG. 9). Until the air throttle valve 40 in the air passage 42 is rotated to the position shown in FIG.
It maintains the fully closed position shown in. Since the valve shaft 30 of the air-fuel mixture throttle valve 20 and the valve shaft of the air throttle valve 40 are not offset from each other, the cost can be reduced by the simultaneous processing.

In the embodiment shown in FIGS. 14 to 17, the valve shaft 30 is used.
The valve shaft 50 and the valve shaft 50 are not coaxial and are arranged parallel to each other with a bias in the vertical direction, the front-back direction, or the diagonal direction, and the radius of rotation of the air-fuel mixture throttle valve 20 becomes larger than that of the air throttle valve 40 by a biased amount. When the throttle valve 20 precedes and rotates in the opening direction, the air throttle valve 40 smoothly rotates until it is fully opened. In the illustrated embodiment, the air passage 42 and the air throttle valve 4
0 is biased slightly above and behind the air-fuel mixture passage 22 and the air-fuel mixture throttle valve 20 (upstream of the air passage 42). The interlocking connecting mechanism 61 is an L-shaped push rod 68 connected to the valve shaft 30.
And a radial driven pin 67 connected to the valve shaft 50. When the valve shaft 30 is rotated from the closed position of the air-fuel mixture throttle valve 20 to the starting position or the idle position, the push rod 68 only comes into contact with the driven pin 67 and the valve shaft 50 is not rotated. When the valve shaft 30 is further rotated in the fully opening direction of the air-fuel mixture throttle valve 20, the driven pin 67 is pushed by the push rod 68 and the air throttle valve 40 opens the air passage 42. In the second and third embodiments, it is not necessary to provide the lever 32 having the bent piece 32a and the lever 33 having the notch 33a as shown in FIG. 3, and it is sufficient to connect the starting lever 34 to the valve shaft 31. .

In this embodiment, the interlocking connecting mechanism 61 is arranged at the center of the carburetor main body 25, and after the carburetor is attached to the engine, the flange surface of the carburetor main body 25, namely Since the interlocking connection mechanism 61 is closed, foreign matter and water do not enter the interlocking connection mechanism 61, and the durability is excellent.

[0021]

As described above, according to the present invention, the air-fuel mixture passage and the air passage that pass through the carburetor body are arranged in parallel with each other, and the air-fuel mixture throttle valve and the air throttle valve are respectively provided on the valve shafts that pass through both passages. The air limiting member that restricts the air in the air passage even when the mixture throttle valve rotates from the fully closed position by a predetermined opening is projected into the air passage, and the air limiting member is inserted into the outlet portion of the air passage. A fuel pump was installed above the carburetor body, a membrane type constant pressure fuel supply mechanism was installed below the carburetor body, and a carburetor mounting bolt insertion hole was provided between the mixture passage and the air passage. Since the air throttle valve rotates in the fully open direction ahead of the air throttle valve by the difference in rotational angle, both are fully opened at the same time, and one of them does not become insufficiently fully opened.

[Brief description of drawings]

FIG. 1 is a left side sectional view of a stratified scavenging internal combustion engine equipped with a butterfly throttle valve carburetor according to the present invention.

FIG. 2 is a front view showing a connecting portion between the engine and a heat insulating pipe.

FIG. 3 is a left side view showing a state of the butterfly type throttle valve carburetor during idle operation.

FIG. 4 is a left side view showing the state of the butterfly type throttle valve carburetor when the engine is stopped.

FIG. 5 is a plan sectional view of the butterfly-type throttle valve type carburetor.

FIG. 6 is a front sectional view of a throttle valve support portion of the butterfly type throttle valve carburetor.

FIG. 7 is a left side sectional view of an air passage of the butterfly type throttle valve carburetor.

FIG. 8 is a plan sectional view of a butterfly type throttle valve carburetor according to a second embodiment of the present invention.

FIG. 9 is a left side sectional view of a mixture passage of the butterfly type throttle valve carburetor.

FIG. 10 is a left side sectional view of an air passage of the butterfly type throttle valve carburetor.

FIG. 11 is a front cross-sectional view showing an interlocking connection mechanism between the valve shaft of the mixture throttle valve and the valve shaft of the air throttle valve.

FIG. 12 is a front sectional view showing an interlocking connection mechanism between the valve shaft of the mixture throttle valve and the valve shaft of the air throttle valve.

FIG. 13 is an exploded perspective view showing an interlocking connection mechanism between a valve shaft of a mixture throttle valve and a valve shaft of an air throttle valve.

FIG. 14 is a front sectional view of a butterfly throttle valve type carburetor according to a third embodiment of the present invention.

FIG. 15 is a plan sectional view of the butterfly type throttle valve carburetor.

FIG. 16 is a front sectional view showing an interlocking connection mechanism between the valve shaft of the mixture throttle valve and the valve shaft of the air throttle valve.

FIG. 17 is an exploded perspective view showing an interlocking connection mechanism between the valve shaft of the mixture throttle valve and the valve shaft of the air throttle valve.

[Explanation of symbols]

1: Engine 2: Cylinder 2a: Spark plug 3: Crank chamber 4: Piston 5: Exhaust port 6: Scavenging passage 7: Combustion chamber 8: Check valve 8a: Check valve 9: Air passage 9a: Mixture passage 10: Connecting rod 11: Arm 12: Crankshaft 13: Insulation pipe 14: Passage 15: Passage 1
6: Fuel pump 17: Membrane 18: Cover plate 19: Case 20: Mixture throttle valve 21: Chiyoke valve 21a: Through hole 22: Mixture passage 22a: Bench lily part 23: Cover plate 24: Membrane 25: Vaporizer body
26: Bolt insertion hole 27: High-speed fuel injection hole 28: Low-speed fuel injection hole 30: Valve shaft 30a: Spring 31: Valve shaft 3
2: Lever 32a: Bent piece 33: Lever 33a:
Notch 34: Starting lever 34a: Bending piece 36: Air restriction member 36a: Arc wall 40: Air throttle valve 42: Air passage
44: Pulsating pressure chamber 45: Pump chamber 46: Constant pressure fuel chamber
47: Atmosphere chamber 50: Valve shaft 51: Spring 52: Lever 61: Interlocking connection mechanism 62: Groove 63: Projection 67:
Driven pin 68: Push rod 73: Pin 74: Spring

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) F02M 1/02 F02M 1/02 A 3/06 3/06 A 11/10 11/10 17/34 17 / 34 E 19/00 19/00 GP R F term (reference) 3G006 AA01 AG01 BA01 BA02 3G065 AA02 EA08 EA11 FA05 HA03 KA05 KA23 KA32

Claims (8)

[Claims] 1. An air-fuel mixture passage and an air passage that pass through the carburetor main body are arranged in parallel to the carburetor main body, and the air-fuel mixture throttle valve and the air throttle valve are supported by valve shafts that traverse both passages, respectively.
An air restricting member that restricts the air in the air passage even if the mixture throttle valve rotates from the fully closed position by a predetermined degree is fitted to the outlet of the air passage, and a fuel pump is installed above the carburetor body to vaporize the air. A butterfly-type throttle valve carburetor for a stratified scavenging internal combustion engine, characterized in that a constant pressure fuel supply mechanism is provided in the lower part of the main body of the vessel, and a carburetor mounting bolt insertion hole is provided between the mixture passage and the air passage. 2. A butterfly type throttle valve type carburetor for a stratified scavenging internal combustion engine according to claim 1, wherein a pair of upper and lower carburetor mounting bolt insertion holes are arranged between the air-fuel mixture passage and the air passage. 3. A valve shaft of the air-fuel mixture throttle valve and a valve shaft of the air throttle valve are separately configured, and a return spring is locked between each valve shaft and the carburetor body to fully close the air throttle valve. The butterfly-type throttle valve carburetor for a stratified scavenging internal combustion engine according to claim 1, wherein the inclination angle at time is larger than the inclination angle when the mixture throttle valve is fully closed. 4. A return spring for arranging the valve shaft of the air-fuel mixture throttle valve and the valve shaft of the air throttle valve separately and offset from each other, each valve shaft rotatingly urging each throttle valve to a closed position. The butterfly-type throttle valve carburetor for a stratified scavenging internal combustion engine according to claim 1, wherein the inner end portions of the respective valve shafts, which are respectively opposed to each other, are connected so as to be interlocked with each other with a predetermined amount of free rotation. 5. A butterfly type throttle valve carburetor for a stratified scavenging internal combustion engine according to claim 4, wherein the valve shaft of the air throttle valve is arranged upstream of the valve shaft of the mixture throttle valve in the air passage. 6. The interlocking coupling mechanism between the valve shaft of the mixture throttle valve and the valve shaft of the air throttle valve has a carburetor attached to the internal combustion engine in a recess between the mixture passage and the air passage of the carburetor body. The butterfly throttle valve carburetor for a stratified scavenging internal combustion engine according to claim 1, wherein the butterfly carburetor is arranged so as to be shut off from the outside at the time. 7. A valve shaft of an air-fuel mixture throttle valve, wherein an L-shaped push rod is provided at the inner end portion of the valve shaft of the air-fuel mixture throttle valve, and a radial driven pin is provided at the inner end portion of the valve shaft of the air throttle valve. Has a larger radius of gyration than the valve shaft of the air throttle valve, and only the air-fuel mixture throttle valve rotates from the fully closed position of the air-fuel mixture throttle valve to a predetermined opening, and when the air-fuel mixture throttle valve exceeds the predetermined opening, the air-fuel mixture The butterfly throttle valve carburetor for a stratified scavenging internal combustion engine according to claim 1, wherein the air throttle valve rotates together with the throttle valve to a fully open position. 8. A mixture passage and an air passage are arranged in parallel with each other in the left-right direction, a chioke valve as a starting device is provided at an inlet portion of the mixture passage, and when the chioke valve is in a fully closed position, it interlocks with the chioke valve. The butterfly throttle valve carburetor for a stratified scavenging internal combustion engine according to claim 1, wherein the mixture throttle valve opens to a fast idle position.