JPH11324683A - Scavenge air passage for 2-cycle engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the degree of concentration separation of mixture in a cylinder, to reduce the blow-by of fuel, and to improve the fuel consumption and exhaust gas characteristics by holding the concentration separation results of the mixture by a bending part in the downstream side of the bending part. SOLUTION: Mixture flowing in a scavenge air passage 7 is separated according to the concentration in a bending part 9 by a centrifuging action so that a rich mixture and a lean mixture are so set as to flow in the direction for the combustion chamber in a place far from and near the exhaust port respectively. The scavenge air passage 7 in the downstream side of the bending part 9 is partitioned by a partition wall 10 to reinforce the orientation operation in an exit part. The curvature radius of the external inside wall of the bending part 9 is set to 1.1 times as large as the width H of the scavenge air passage right before the bending part from the viewpoint of the cylinder inside.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a two-stroke engine provided with a scavenging passage having a bent portion, and more particularly to a two-stroke engine in which the effect of centrifugal separation of the air-fuel mixture at the bent portion is enhanced.

[0002]

2. Description of the Related Art A conventional two-stroke engine having a scavenging passage having a bent portion is generally shown in FIG. 2 (internal combustion engine, July 1988).
A bent portion 9 'is formed at a predetermined position of the scavenging passage 7' leading from the crank chamber 4 'into the cylinder as shown in the drawing, p31). In the bent portion 9', the air-fuel mixture is separated into light and dark by centrifugal action of the flow. In a cylinder, a rich air-fuel mixture flows in a place far from the exhaust port and a lean air-fuel mixture flows in a direction near the exhaust port, thereby reducing fuel blow-through. However, since the radius of curvature R 'of the outside inner wall surface of the bent portion 9' is relatively small, even if turbulence occurs and the air-fuel mixture is separated into light and dark by centrifugal separation, mixing occurs on the downstream side of the bent portion 9 '. However, the degree of concentration separation of the air-fuel mixture in the cylinder became weak, and it was not possible to sufficiently reduce fuel blow-through.

[0003]

SUMMARY OF THE INVENTION It is an object of the present invention to increase the degree of density separation of an air-fuel mixture in a cylinder by maintaining the result of concentration separation of an air-fuel mixture by a bent portion as it is downstream of the bent portion. Therefore, it is intended to reduce fuel blow-through and improve fuel efficiency and exhaust gas characteristics.

[0004]

According to the present invention, the air-fuel mixture flowing in the scavenging passage is separated into dark and light by the centrifugal separation action at the bent portion, whereby the rich air-fuel mixture is located far from the exhaust port and close to the exhaust port. However, in a Schnille scavenging type two-stroke engine in which the lean mixture flows toward the combustion chamber, the scavenging passage downstream of the bent portion is divided by a separation wall to enhance the directing action at the scavenging passage outlet. The radius of curvature of the outer inner wall surface of the bent portion is 1.1 times or more the width of the scavenging passage immediately before the bent portion as viewed from the inside of the cylinder.

[0005]

FIG. 1 (a) shows one embodiment of a two-stroke engine according to the present invention.
Next, the scavenging passage 7 is opened, and the burned gas in the cylinder 1 is scavenged. The fresh air remaining in the cylinder 1 during this scavenging process is compressed with the rise of the piston 3 (at the same time, the air-fuel mixture is sucked into the crank chamber 4 through the carburetor 5 and the suction passage 6), and near the top dead center. It ignites and burns, producing explosive power. A bent portion 9 is formed at a predetermined position of the scavenging passage 7 leading from the crank chamber 4 into the cylinder, and the air-fuel mixture flowing in the scavenging passage 7 is separated into dark and light by the centrifugal separation action in the bent portion 9. Therefore, when the gas flows into the cylinder, the rich mixture flows toward the combustion chamber in a location far from the exhaust port (the portion where the exhaust passage 11 opens on the inner wall surface of the cylinder) and the lean mixture near the exhaust port. become. In the present invention, the scavenging method is the schneille scavenging method, in which the scavenging passage on the downstream side of the bent portion 9 is divided by a separation wall 10 (in the figure, it is divided into two, but may be divided into three). (Nozzle function). If the scavenging passage 8 extending from the inlet of the scavenging passage 7 to a predetermined portion that does not reach the bent portion 9 is formed in a groove shape without a partition wall from the crank chamber 4 (FIG. 2 has a partition wall), the structure and manufacturing are simplified. It's easy. Then, beyond the scavenging passage portion 8, the scavenging passage portion up to the bent portion 9 is covered by the spigot portion 2, and the spigot portion 2 forms a part of the inner wall surface of the scavenging passage. FIG. 1 (c) shows a view of the cylinder block as viewed from the bottom, and FIG. 1 (d) shows a view of the crankcase from the connecting surface AA ′ with the cylinder block (both showing only essential parts). In this case, in the scavenging passage on the crankcase side immediately before the coupling surface between the cylinder block and the crankcase, the inner wall surface 13 on the inner side with respect to the bending of the bent portion 9 is divided into the left and right dividing surfaces B-
If it is substantially perpendicular to B '(with an appropriate draft), it is convenient for casting (usually, the inner wall surface 13 is 1 mm).
Since it is parallel to 3 'and has an undercut shape, a sand core must be used.) Therefore, the inner wall surface of the scavenging passage on the cylinder block side connected to the inner wall surface 13 must be adjusted to its shape (see FIG. 1C). That is, 1
Reference numeral 2 denotes a smooth slope, which makes the flow in the scavenging passage smooth. In addition, in FIG.
It is also possible to form a part of the inner wall surface on the upstream side of the bent portion 9 by the connecting surface AA ′ between the cylinder block and the crankcase, which is shown in FIG.
FIG. 1 (e) shows only a main part of the crankcase viewed from the coupling surface AA '. The structure is simple, the manufacture is easy, and the advantage of cost reduction is produced. Returning again to FIG.
In the present invention, the radius of curvature R of the outer inner wall surface of the bent portion 9 is set to 1.1 of the width H when viewed from the inside of the cylinder of the scavenging passage 7 immediately before the bent portion.
There is a characteristic in that it is set to be twice or more (the term “immediately before the bent portion” means a position immediately upstream of the bent portion 9). The radius of curvature r of the inner inner wall surface of the bent portion 9 is made extremely small so that the attached liquid fuel can be put into the airflow again. When the radius of curvature ratio φ is φ = R /
FIG. 3 shows the result of an experiment defined as H and changing the value of φ. In the experiment, the scavenging passage 7 having the bent portion 9 was modeled with a transparent resin as shown in FIG. 3, and very fine powder (corresponding to non-gasified fuel particles) was blown into the inside with a blower and observed. FIG. 3A shows a case where φ = 0.5, the hatched portion indicates the flow of the powder, and since the radius of curvature R is small, a turbulent flow is generated downstream of the curvature portion 9, and the powder is formed at the bent portion 9. Even after centrifugation, they mix as they proceed downstream and are not clearly separated.
FIG. 3 (b) shows the case where φ = 1, and the density separation of the powder is also quite clear near the outlet of the scavenging passage 7, but it is not sufficient. FIG. 3 (c) is when φ = 1.1, and it was judged that the density separation of the powder was clear and sufficient. When oil was applied to the separation wall 10, the powder hardly adhered. The double shaded portion is a flow in a portion where the concentration of powder is high, and since there is a bent portion on the upstream side of the bent portion 9, the flow is as shown in the figure. Although the flow is in a low part, the powder flowing in the Z part flows while being separated into light and shade by the centrifugal separation action). FIG. 3D shows the condition when φ = 1.2, and FIG.
The results were even better than in the case of (1), and even if oil was applied to the separation wall 10, the powder hardly adhered. FIG. 3 (e) shows when φ = 1.4.
The separation of the density of the powder was very clear, and even if oil was applied to the separation wall 10, the powder did not adhere at all. From the above, it is considered that when φ = 1.1 or more, the separation of the density of the powder is clear even on the downstream side of the bent portion 9 and there is no mixing of both. This indicates that since the powder represents fuel particles that have not been gasified, the mixture is maintained at the outlet of the scavenging passage while the air-fuel mixture is separated at the bend portion 9. . Even when φ = 1.1 or more, when the powder squirts from the outlet of the scavenging passage as shown by the arrow in FIG. 3 (e), the powder tends to squirt slightly inclining from the direction of the inner wall surface of the scavenging passage. However, this is probably because the influence of the bent portion 9 remains slightly. In order to eliminate this, as shown in FIG. 3 (f), it is located downstream of the bent portion 9 of the scavenging passage, and is furthest from the exhaust port connected to the inner wall surface for orienting at the outlet of the scavenging passage. It is conceivable that the inner wall surface 14 is configured to gradually move away from the exhaust port as it goes toward the outlet. As is clear from the flow of the rich mixture in FIG.
As viewed from the inside of the cylinder, the separation wall 10 extends toward the outlet from a position a predetermined distance h away from the extension of the inner wall surface of the scavenging passage on the combustion chamber side immediately before the bent portion so that 0 does not collide with this flow. It is desirable to configure it in such a way. The radius of curvature R of the bent portion is the same as the inner wall surface 1 as shown in FIG.
Since 3 'is not perpendicular to the coupling plane BB', it is actually formed in the section P. Next, as shown in FIG. 4 (c), fresh air ejected from the outlet a near the inner wall surface that directs the farthest side from the exhaust port at the outlet of the scavenging passage collides with the cylinder inner wall surface and rebounds. The fresh air squirting from the outlet b except for the outlet a has to be pushed back, while trying to penetrate into the exhaust port. In this case, if there is no separation wall 10, the directing action at the outlet of the scavenging passage is weakened (the nozzle function is weak, and the fresh air to be ejected is easily diffused), and the flow ejected from the outlet a and repelled on the inner wall surface of the cylinder is reduced. I could not push it back enough and pierced the exhaust. By forming the separation wall 10, penetration into the exhaust port due to the rebound can be avoided, but fresh air flowing toward the combustion chamber still flows slightly inclined toward the exhaust port as shown in FIG. Can be Exit a to correct this
It is only necessary to attenuate the energy which is ejected from the cylinder and rebounds on the inner wall surface of the cylinder. As shown in FIGS. 4 (a) and 4 (b), the latter is the exhaust at the outlet of the scavenging passage as viewed from the arrow B of the former. A deflector 15 having an attenuating wall 16 for attenuating velocity energy by colliding a part of fresh air ejected from an outlet a near an inner wall surface orienting a side farthest from the mouth is formed at the top of the piston. As a result, the flow spouting from the outlet portion a and repelling on the inner wall surface of the cylinder is weakened, and the repulsive force of the fresh air spouting from the outlet portion b is relatively increased, so that the fresh air is correctly (vertically) along the inner wall surface of the cylinder. It flows toward the combustion chamber. In this case, as shown in FIG. 4 (d), the scavenging passage on the downstream side of the bent portion is divided into two by the separating wall 10, and the passage in the circumferential direction of the passage dividing portion 7b near the exhaust port is the passage on the far side. Division 7
The effect was greater when it was configured to be smaller than that of a. This may be because the orienting action of the passage dividing portion 7a is slightly weakened. Numeral 17 is a slope that smoothly connects to the piston top surface, and does not attenuate the velocity energy of the fresh air ejected from the outlet b (the fresh air ejected from the outlet b does not collide with the damping wall 16). In the embodiment shown in FIG. 4E, the scavenging passage immediately before the bend is narrowed in order to enhance the centrifugal action in the bend 9. In the present invention, when the bending angle of the bent portion 9 of the scavenging passage is set to approximately 90 °, the manufacture becomes easy considering the use of the core.

[0006]

According to the present invention, since the scavenging passage downstream of the bent portion 9 is divided by the separation wall 10, the directing action at the outlet portion is enhanced, and the exhaust port is repelled by fresh air rebounding on the inner wall surface of the cylinder. No fresh air flows through, and fresh air flows correctly (vertically) toward the combustion chamber along the cylinder inner wall surface (the deflector 15 shown in FIG. 4 is more effective). Further, in the present invention, since the radius of curvature R of the outer inner wall surface of the bent portion 9 is set to be 1.1 times or more the width H of the scavenging passage immediately before the bent portion as viewed from the inside of the cylinder, the flow is smooth, and the bent portions 9 and No turbulence occurs downstream of this. Therefore, the state where the centrifugal separation is performed at the bent portion 9 is maintained as it is, and no mixing occurs at the downstream side of the bent portion 9, and even if the mixture flows into the cylinder, the density separation becomes very clear. That is, as shown in FIG. 5, a mixture richer than the conventional one flows far from the exhaust port, and a mixture leaner than the conventional one flows toward the combustion chamber near the exhaust port. As a result, the rich mixture flows toward the combustion chamber in such a manner as to stick to the inner wall surface of the cylinder, so that the rich mixture is not carried away with the burned gas rushing to the exhaust port. If it is flowing, gas can enter during that time, so it is easy to carry it to the exhaust port.) Near the exhaust port, a far more lean air-fuel mixture than in the past is distributed, thus making it possible to greatly reduce fuel blow-through, thereby greatly improving fuel efficiency and exhaust gas characteristics. In the prior art shown in FIG. 2, the radius of curvature R 'of the bent portion 9' is relatively small, so that turbulence is generated and the effect is small. This is probably because the radius of curvature R 'was determined inadvertently and carelessness was neglected. In the present invention, it has been found that the size of the radius of curvature R has a great effect. In the present invention, the embodiments can be combined with each other (for example, the embodiment shown in FIG. 4E is provided with the deflector 15).

[Brief description of the drawings]

FIG. 1 is a diagram showing a scavenging passage of a two-stroke engine according to the present invention.

FIG. 2 is a diagram showing a scavenging passage of a conventional two-stroke engine.

FIG. 3 is a schematic view showing a flow in a scavenging passage.

FIG. 4 is a schematic view showing each embodiment of the present invention.

FIG. 5 is a schematic diagram for explaining the effect of the present invention.

[Explanation of symbols]

1 is a cylinder, 2 is a spigot part, 3 is a piston, 4 is a crank chamber, 5 is a carburetor, 6 is a suction passage, 7 is a scavenging passage, 7a and 7b are passage dividing portions, and 8 is a grooved portion of the scavenging passage. , 9 is a bent portion of the scavenging passage, 10 is a separation wall, 11 is an exhaust passage, 12 is a smooth slope, 13 and 13 'are inner wall surfaces, 1
4 is an inner wall, 15 is a deflector, 16 is a damping wall, 1
7 is a slope, a and b are outlets, 4 'is a crankcase, 7' is a scavenging passage, and 9 'is a bent portion.

Claims (10)

[Claims] 1. A scavenging process for scavenging burned gas by fresh air flowing into a cylinder, wherein a bent portion is formed at a predetermined position of a scavenging passage leading from the crankcase to the cylinder, and the scavenging passage is formed at the bent portion. The air-fuel mixture flowing through the interior is separated into dark and light by centrifugal separation, so that a rich air-fuel mixture far from the exhaust port and a lean air-fuel mixture near the exhaust port flow toward the combustion chamber. In the scavenging type two-stroke engine, the scavenging passage downstream of the bent portion is divided by a separating wall to enhance the directing action at the scavenging passage outlet portion, and the radius of curvature of the outer inner wall surface of the bent portion is changed immediately before the bent portion. A scavenging passage for a two-stroke engine, characterized in that the ratio is 1.1 times or more the width of the scavenging passage as viewed from inside the cylinder. 2. A scavenging passage on the downstream side of a bent portion, which is divided into two by a separation wall, wherein a circumferential length of a passage dividing portion closer to an exhaust port is smaller than that of a farther passage dividing portion. The scavenging passage of a two-stroke engine according to claim 1, wherein 3. A scavenging air for a two-stroke engine according to claim 1, wherein the scavenging passage extending from the inlet portion of the scavenging passage to a predetermined portion which does not reach the bent portion has a groove shape without a partition wall from the crank chamber. aisle. 4. The method according to claim 1, wherein the scavenging passage immediately before the bent portion is narrowed to enhance the centrifugal separation.
Scavenging passage of cycle engine. 5. A separation wall of a scavenging passage extending from a position at a predetermined distance from an extension of an inner wall surface of a scavenging passage on a combustion chamber side immediately before a bent portion when viewed from inside the cylinder, the separation wall of the scavenging passage extending toward the outlet. Item 2. A two-stroke engine according to any one of Items 1 to 4. 6. An attenuating inner wall surface that attenuates velocity energy by colliding a part of fresh air ejected from an outlet portion near an inner wall surface that directs a farthest side from an exhaust port at an outlet portion of a scavenging passage. The scavenging passage of a two-stroke engine according to any one of claims 1 to 5, wherein the deflector is formed on the top of the piston. 7. The bending angle of the bent portion of the scavenging passage is substantially 90.
The scavenging passage of the two-stroke engine according to any one of claims 1 to 6. 8. A scavenging passage which is located downstream of a bent portion of the scavenging passage,
8. The air purifier according to claim 1, wherein the inner wall surface furthest from the exhaust port connected to the inner wall surface for directing at the outlet portion of the scavenging passage gradually moves away from the exhaust port toward the outlet portion. A scavenging passage for a two-stroke engine according to any of claims 1 to 3. 9. The two-stroke engine according to claim 1, wherein a part of the inner wall surface upstream of the bent portion of the scavenging passage is formed by a coupling surface between the cylinder block and the crankcase. Scavenging passage. 10. A scavenging passage on a crankcase side immediately before a coupling surface between a cylinder block and a crankcase,
The scavenging passage of a two-stroke engine according to any one of claims 1 to 8, wherein an inner wall surface inside the bent portion is substantially perpendicular to a left-right divided surface of the crankcase.