JP2012107552A - Stratified scavenging two-stroke engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a stratified scavenging two-stroke engine which is simply structured to improve engine output and purify exhaust gas.SOLUTION: The stratified scavenging two-stroke engine 1 has a scavenging port 71 opening into a cylinder 2 for filling leading air through the side of the scavenging port 71 into a scavenging passage 7 connecting a combustion chamber R1 with a crank chamber R2, and includes a piston 5 inserted into the cylinder 2 in a reciprocatable manner, and having a recess 51 in the outer peripheral face opposed to the inner peripheral face of the cylinder, and an air passage 8 having an air port 81 provided in the inner peripheral face of the cylinder for supplying the leading air, and communicated with the scavenging passage 7 via the recess 51. The air passage 8 and the scavenging passage 7 are intercommunicated/isolated by the piston 5 in accordance with the reciprocatory movement of the piston 5, and the air port 81 partly opens to the combustion chamber R1 when the piston 5 is at a bottom dead center position.

Description

  The present invention relates to a stratified scavenging two-stroke engine.

  2. Description of the Related Art Conventionally, a stratified scavenging two-stroke engine having an air passage for introducing leading air for cylinder scavenging is known (for example, see Patent Documents 1 and 2). In this stratified scavenging two-stroke engine, the air passage is connected to the scavenging passage, and at the time of scavenging, first, the leading air filled in the scavenging passage scavenges the exhaust gas in the combustion chamber. For this reason, compared with a two-stroke engine that scavenges exhaust gas with an air-fuel mixture, the amount of air-fuel mixture that is exhausted with the exhaust gas during scavenging can be reduced.

US Pat. No. 6,918,359 US Pat. No. 6,662,766

However, in the stratified scavenging two-stroke engine described in Patent Documents 1 and 2, since the air passage is always in communication with the crankcase, the leading air and the air-fuel mixture in the crankcase flow backward in the air passage. In order to prevent this, it is necessary to provide a check valve such as a reed valve in the air passage. For this reason, there is a problem that the structure becomes complicated and the manufacturing cost increases.
In addition, demands for fuel consumption and exhaust gas are increasing year by year, and improvement of engine output that leads to fuel efficiency improvement and further exhaust gas purification are desired.

  An object of the present invention is to provide a stratified scavenging two-stroke engine capable of improving engine output and purifying exhaust gas with a simple structure.

  The present invention relates to a stratified scavenging two-stroke engine having a scavenging port opened in a cylinder and filling a scavenging passage communicating a combustion chamber and a crank chamber with leading air from the scavenging port side. A piston which is inserted in a reciprocating manner and has a concave portion on the outer peripheral surface facing the inner peripheral surface of the cylinder; and an air port for leading air supply provided on the inner peripheral surface of the cylinder; An air passage that communicates with the passage, and the air passage and the scavenging passage are blocked by the piston as the piston reciprocates, and the air port is located at the bottom dead center position. A part of which opens into the combustion chamber.

  In this invention, when the said piston exists in a bottom dead center position, it is preferable that the opening width of the reciprocating direction of the said air port is 1 mm or less.

  In the present invention, the air port is preferably formed in an L shape in plan view.

According to the stratified scavenging two-stroke engine of the present invention, the air passage and the scavenging passage are cut off by the piston as the piston reciprocates, so there is no need to provide a check valve in the air passage, and the structure is simple. Layered scavenging can be performed.
In addition, part of the air port opens to the combustion chamber when the piston is at the bottom dead center position, so that it is possible to ensure the flow of exhaust gas in a direction different from that of the exhaust port side, and combustion is possible compared to the conventional Turbulence tends to occur indoors. For this reason, since the air-fuel mixture passes through the combustion chamber R1 and is exhausted together with the exhaust gas during scavenging, the so-called air-blow amount of the air-fuel mixture can be reduced, so that the exhaust gas can be purified.
Furthermore, since it is not necessary to prevent the exhaust gas from flowing into the air passage, the opening width of the air port in the piston reciprocating direction can be increased. Accordingly, since the amount of the leading air flowing into the combustion chamber is increased as compared with the conventional case, the air-fuel ratio of the air-fuel mixture in the combustion chamber becomes closer to the stoichiometric air-fuel ratio, and the engine output is improved.

  In the present invention, if the opening width of the air port in the piston reciprocating direction is 1 mm or less when the piston is at the bottom dead center position, the amount of exhaust gas flowing from the air passage into the combustion chamber via the exhaust passage is reduced. It is possible to prevent the engine from becoming too much and effectively improve the engine output.

  In the present invention, if the air port is formed in an L shape in a plan view, the opening area of the air port can be secured while avoiding interference with the scavenging port. Therefore, the amount of leading air filled in the scavenging passage can be further increased.

1 is a longitudinal sectional view of a stratified scavenging two-stroke engine according to an embodiment of the present invention. II-II sectional view taken on the line of FIG. The figure for demonstrating operation | movement of a stratified scavenging 2 stroke engine. The schematic diagram for demonstrating operation | movement of a stratified scavenging 2 stroke engine. Schematic diagram for explaining the operation of the stratified scavenging two-stroke engine Schematic diagram for explaining the operation of the stratified scavenging two-stroke engine The figure for demonstrating the effect of this invention. The figure for demonstrating the effect of this invention.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
In the following description, for example, the expression indicating the direction of up, down, left, right, near side, or back side is used with reference to FIG. Moreover, the movement to the top dead center side of the piston 5 which will be described later is referred to as “up”, and the movement to the bottom dead center side of the piston 5 is referred to as “down”.

  1 and 2, a stratified scavenging two-stroke engine (hereinafter simply referred to as an engine) 1 is supported by a cylinder 2, a crankcase 3 provided on the lower side of the cylinder 2 in FIG. The piston 5 is connected to the crankshaft 31 via a connecting rod 4 and inserted into the cylinder 2 so as to be reciprocally movable. A combustion chamber R1 is formed by a cylinder inner space opposite to the crankcase 3 with the piston 5 as a boundary, and the crankcase 3 side space in the cylinder 2 and the inner space of the crankcase 3 define the crank chamber R2. Is formed.

  On the side of the cylinder 2, there are provided an intake passage 6 for supplying air-fuel mixture to the crank chamber R2, and an air passage 8 for supplying the leading air to the pair of scavenging passages 7 located above the intake passage 6, An exhaust passage 9 having an exhaust port 91 that opens to the inner peripheral surface of the cylinder 2 is provided on the opposite side of the passages 6 and 8 across the combustion chamber R1.

  The intake passage 6 includes an intake port 61 that opens on the inner peripheral surface of the cylinder 2. The intake port 61 opens and closes due to the reciprocating motion of the piston 5 (vertical movement in FIG. 1). When the piston 5 is raised, the intake port 61 is opened and the air-fuel mixture is sucked into the crank chamber R2.

  The scavenging passage 7 is provided at two locations facing the radial direction of the cylinder 2, and is provided at a position shifted by approximately 90 ° with respect to the intake passage 6 and the exhaust passage 9. The scavenging passage 7 includes a scavenging port 71 that opens to the inner peripheral surface of the cylinder 2. The scavenging port 71 opens as the piston 5 descends, and the scavenging passage 7 communicates the combustion chamber R 1 and the crank chamber R 2.

  The air passage 8 includes an air port 81 that is provided on the opposite side of the exhaust port 91 across the combustion chamber R1 and above the intake port 61 and opens to the inner peripheral surface of the cylinder 2. As shown in FIG. 3, the air port 81 is formed in an L shape in a plan view, and an opening area can be secured while avoiding interference with the scavenging port 71. Further, the upper end of the air port 81 is located above the lower end of the exhaust port 91, and the air port 81 opens slightly into the combustion chamber R1 when the piston 5 is at the bottom dead center position. Has been.

  On the other hand, a concave portion 51 having an L shape in plan view is provided on the outer peripheral surface of the piston 5. By making the recess 51 L-shaped in plan view, it is possible to ensure the height of the recess 51 in the piston reciprocating direction while avoiding interference with the piston pin insertion portion 52. The recess 51 communicates the air passage 8 and the scavenging passage 7 as the piston 5 rises, and the leading air in the air passage 8 is filled into the scavenging passage 7 from the scavenging port 71 side through the recess 51. The

  The engine 1 according to the present embodiment employs a piston valve type for an air-fuel mixture intake method and a method for filling the scavenging passage 7 with leading air. That is, the piston 5 controls the intake of the air-fuel mixture by opening and closing the intake port 61 on the outer peripheral surface thereof, and disconnects the air passage 8 and the scavenging passage 7 from each other at the outer peripheral surface and the recess 51.

Here, in the conventional piston valve type stratified scavenging two-stroke engine, when the piston 5 is at the bottom dead center position, the air port 81 is closed by the piston 5, so that the exhaust gas in the combustion chamber R 1 is reduced. The air passage 8 was prevented from flowing.
On the other hand, in the engine 1 according to the present embodiment, as described above, when the piston 5 is at the bottom dead center position, the air port 81 is configured to slightly open to the combustion chamber R1, and combustion is performed. The exhaust gas in the chamber R1 can be taken into the air passage 8.

Hereinafter, the operation and effects of the engine 1 will be described.
4 to 6 are schematic diagrams showing a cross section taken along line IV-IV in FIG. The leading air and air that is the basis of the air-fuel mixture sucked by the engine 1 passes through an air cleaner (not shown) and is sent to the intake passage 6 and the air passage 8. As shown in FIG. 4, the air sent to the air passage 8 becomes the leading air in the combustion chamber R <b> 1 by the fuel supply from the fuel supply device such as a carburetor and partly becomes an air-fuel mixture and flows through the air passage 8. Go. This air-fuel mixture is adjusted to a concentration higher than the stoichiometric air-fuel ratio depending on the situation.

  On the other hand, in the engine 1, the exhaust gas generated by the combustion of the air-fuel mixture in the combustion chamber R1 passes through the exhaust passage 91 (both shown in FIG. 1 to FIG. 3) and a part of the exhaust gas flows from the air port 81 into the air passage 8.

  Then, as shown in FIG. 5, when the piston 5 moves from the bottom dead center to the top dead center side, the pressure in the crank chamber R2 decreases and negative pressure is generated, and the intake port 61 is opened and the intake passage 6 is opened. The crank chamber R2 is in communication. For this reason, the air-fuel mixture in the intake passage 6 is sucked by the negative pressure in the crank chamber R2 and flows into the crank chamber R2. Further, the air passage 8 communicates with the scavenging port 71 through the recess 51 of the piston 5, and the exhaust gas and the leading air in the air passage 8 pass through the recess 51 from the air port 81 and scavenging from the scavenging port 71 side. The passage 7 is filled.

  Thereafter, as shown in FIG. 6, when the piston 5 descends and the scavenging port 71 and the exhaust port 91 are opened to the combustion chamber R1, the leading air and exhaust gas filled in the scavenging passage 7 are It flows into the combustion chamber R1 by the increased pressure in the crank chamber R2, and pushes the exhaust gas in the combustion chamber R1 into the exhaust passage 9. Next, the air-fuel mixture in the crank chamber R2 flows into the combustion chamber R1 through the scavenging passage 7. When the piston 5 rises and reaches near the top dead center, the air-fuel mixture in the combustion chamber R1 is ignited and burned, and thereafter the above cycle is repeated again.

  According to the engine 1 configured as described above, when the piston 5 is at the bottom dead center position, the upper end position of the air port 81 is increased so that the air port 81 opens into the combustion chamber R1, and the piston reciprocating direction is reached. Since the opening width of the air port 81 is increased, the opening area of the air port 81 is increased. Accordingly, the amount of the leading air filled in the scavenging passage 7 becomes larger than before, the amount of air flowing into the combustion chamber R1 during scavenging increases, and the air-fuel ratio of the air-fuel mixture in the combustion chamber R1 becomes the stoichiometric air-fuel ratio. Since it approaches, the output of the engine 1 improves.

  Further, when the piston 5 is at the bottom dead center position, the air port 81 opens into the combustion chamber R1, so that it is possible to ensure the flow of exhaust gas in the opposite direction to the exhaust port 91 side. Turbulence tends to occur in the combustion chamber R1. For this reason, since the air-fuel mixture passes through the combustion chamber R1 and is exhausted together with the exhaust gas during scavenging, the so-called air-blow amount of the air-fuel mixture can be reduced, so that the exhaust gas can be purified.

  Further, since the air port 81 is formed in an L shape in plan view, it is possible to secure an opening area while avoiding interference with the scavenging port 71. Furthermore, since the concave portion 51 of the piston 5 is L-shaped in plan view, the height of the concave portion 51 in the piston reciprocating direction can be increased while avoiding interference with the piston pin insertion portion 52. The communication continuation time between the rising air passage 8 and the scavenging passage 7 can be increased. Therefore, the amount of leading air filled in the scavenging passage 7 can be further increased.

  When the piston 5 is at the bottom dead center position, the opening width of the air port 81 in the piston reciprocating direction, that is, the width H of the position of the shoulder portion of the piston 5 indicated by the upper end position of the air port 81 shown in FIG. Is preferably 1 mm or less. If the opening width of the air port 81 becomes larger than that, the exhaust gas flows into the air passage 8 more than necessary, and the amount of exhaust gas flowing from the air passage 8 into the combustion chamber R1 through the scavenging passage 7 increases too much, and the engine 1 This is because the effect of improving the output may not be obtained.

  7 and 8 show the engine speed using the engine 1 of the present embodiment and a conventional stratified scavenging two-stroke engine in which the air port 81 is closed by the piston when the piston is near bottom dead center. The corresponding output and the result of measuring the THC concentration are shown. As shown in FIG. 7, it is recognized that the output of the engine 1 indicated by the A1 line is larger than the output of the conventional engine indicated by the A2 line, particularly in a region where the engine speed is high. Further, as shown in FIG. 8, in all engine speed ranges, it is recognized that the THC concentration of the engine 1 indicated by the B1 line is lower than the THC concentration of the conventional engine indicated by the B2 line.

It should be noted that the present invention is not limited to the above-described embodiments, and modifications, improvements, and the like within the scope that can achieve the object of the present invention are included in the present invention.
For example, in the embodiment, the air port 81 is formed in an L shape in plan view, but the shape of the air port 81 is not limited to this. In short, it is only necessary to secure an opening area while avoiding interference with the scavenging port 71, and the shape of the air port 81 may be a rectangle, a trapezoid, a circle, a parallelogram, or other shapes.

  In the embodiment, the concave portion 51 of the piston 5 is formed in an L shape in plan view, but the shape of the air port 81 is not limited to this. That is, it is only necessary that the air passage 8 and the scavenging passage 7 can be communicated with each other via the recess 51. The shape of the recess 51 depends on the position of the scavenging port 71 and the air port 81, the amount of leading air required for scavenging, and the like. It may be a rectangle, trapezoid, circle, parallelogram, U-shape or other shape.

  In the above embodiment, the scavenging passage 7 is provided at two locations facing the radial direction of the cylinder 2, and the air passage 8 is provided on the opposite side of the exhaust passage 9 across the combustion chamber R 1. If the air passage 8 and the scavenging passage 7 are cut off from each other and the air port 81 is opened to the combustion chamber R1 when the piston 5 is at the bottom dead center position, the passages 7 to 9 are arranged as follows. The invention is not limited to the above embodiment.

  INDUSTRIAL APPLICABILITY The present invention can be used as a layered scavenging type two-stroke engine for a chain saw, a portable working machine such as a brush cutter or a blower.

  DESCRIPTION OF SYMBOLS 1 ... Layered scavenging 2-stroke engine, 2 ... Cylinder, 5 ... Piston, 6 ... Intake passage, 7 ... Scavenging passage, 8 ... Air passage, 51 ... Recess, 71 ... Scavenging port, 81 ... Air port, R1 ... Combustion chamber, R2 ... Crank chamber.

Claims (3)

A stratified scavenging two-stroke engine having a scavenging port opened in a cylinder and filling a scavenging passage communicating with a combustion chamber and a crank chamber from the scavenging port side.
A piston that is reciprocally inserted into the cylinder and has a recess on the outer peripheral surface facing the inner peripheral surface of the cylinder;
An air port for leading air supply provided on the inner peripheral surface of the cylinder, and an air passage communicating with the scavenging passage through the recess,
The air passage and the scavenging passage are interrupted by the piston as the piston reciprocates,
A part of the air port opens into the combustion chamber when the piston is at a bottom dead center position. The stratified scavenging two-stroke engine according to claim 1,
A stratified scavenging two-stroke engine, wherein an opening width of the air port in a piston reciprocating direction is 1 mm or less when the piston is at a bottom dead center position. The stratified scavenging two-stroke engine according to claim 1 or 2,
The air port is formed in an L shape in a plan view.

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