JP5206286B2 - Two-cycle engine and engine tool provided with the same - Google Patents

Description

  The present invention relates to a two-cycle engine, particularly a two-cycle engine suitable for hand-held engine tools such as a brush cutter, a chain saw, and a blower, and an engine tool including the same.

  2. Description of the Related Art Conventionally, a reverse scavenging type two-cycle engine is known in which an air-fuel mixture in a crank chamber is supplied into a cylinder from a scavenging port on a cylinder side wall through a scavenging passage. As this scavenging passage, a passage provided in the cylinder block (for example, Patent Document 1), a groove extending in the cylinder axial direction on the side wall of the cylinder, and a space formed between the groove and the piston side wall are formed. is there.

JP 2000-179346 A

  However, when the scavenging passage is formed in the cylinder block, there is a problem that the manufacturing process becomes complicated because a complicated mold is used, and the manufacturing cost increases. In addition, when the scavenging passage in the cylinder block is replaced with the piston side wall and the groove on the cylinder side wall, when the piston descends and the combustion chamber and the scavenging passage are connected, the combustion gas in the combustion chamber passes through the scavenging passage into the crank chamber. When the piston descends and the pressure of the air-fuel mixture in the crankcase rises, the air-fuel mixture in the crankcase flows into the combustion chamber more than necessary and is easily blown out from the exhaust port without being burned. For this reason, there is a problem that the concentration of the mixed gas in the crankcase is lowered, the output of the engine is lowered, and the exhaust gas characteristics are deteriorated.

  The present invention has been made in view of the above-described problems, and an object of the present invention is to provide a two-cycle engine that can suppress a decrease in engine output and a deterioration in exhaust gas characteristics and can reduce manufacturing costs.

In order to solve the above problems, a two-cycle engine according to the first aspect of the present invention is:
A scavenging passage is formed between the intake port that communicates with the intake passage, the exhaust port that communicates with the exhaust passage, and the end of the bottom dead center side to the first predetermined position in the direction of the top dead center. A concave groove formed on the side wall;
In a two-cycle engine comprising a crankcase attached to an end of the cylinder at the bottom dead center side,
The cylinder extends from the bottom dead center side end of the cylinder to the top dead center direction to the second dead center side from the first predetermined position to cover the concave groove in the circumferential direction of the cylinder. And a scavenging passage are formed, and a rib is provided so as to be opposed to the side wall of the piston.

  Further, the crankcase is formed with a recess facing the bottom dead center side of the concave groove toward the top dead center and connected to the scavenging passage, and the through hole communicates with the recess. Yes.

A two-cycle engine according to the second aspect of the present invention is
An intake port communicating with the intake passage; an exhaust port communicating with the exhaust passage; and a cylinder formed on the side wall with a concave groove extending from the end on the bottom dead center side to the first predetermined position in the top dead center direction; ,
In a two-cycle engine comprising a crankcase attached to an end of the cylinder at the bottom dead center side,
The cylinder extends from the bottom dead center side end of the cylinder to the top dead center direction to the second predetermined position on the bottom dead center side from the first predetermined position, covers the concave groove in the circumferential direction of the cylinder, A rib disposed to face the side wall, a recess facing the bottom dead center side of the concave groove and opening toward the top dead center, and a recess connected to a passage formed by the rib and the concave groove; A through-hole formed in the rib connecting the chamber and the recess,
The crank chamber and the combustion chamber are communicated with each other by the concave groove, the side wall of the piston, the rib, the concave portion, and the through hole when the piston is near the bottom dead center.

  Moreover, it is preferable that the area of the said through-hole is smaller than the area of the opening formed in the side wall of the said cylinder by the said concave groove and the said piston when the said piston is in a bottom dead center.

  Further, the inner diameter of the rib at a position facing at least the piston is larger than the inner diameter of the cylinder.

  Further, the second predetermined position is located on the top dead center side with respect to the bottom dead center side end portion of the piston side wall facing the concave groove while the concave groove communicates with the combustion chamber. It is preferable.

  Furthermore, the concave groove extends to the inner wall side of the cylinder, extends from the bottom dead center side end of the cylinder in the top dead center direction to the second predetermined position, and at least one end of the concave groove in the circumferential direction. It is preferable that a widened portion extending beyond the portion is formed, and the rib closes the widened portion.

  The concave groove projects from the radial end of the concave groove toward the inner peripheral surface of the cylinder and extends from the bottom dead center side end to the top dead center side end so that the concave groove extends around the cylinder. A cylinder-side wall plate separated in a direction is provided, and the recess faces the cylinder-side wall plate and extends from the top dead center side end portion to the bottom dead center side end portion with the rib. Then, a wall plate on the crank chamber side that separates the recess in the cylinder circumferential direction may be provided, and the through hole may be provided corresponding to the recess separated by the wall plate on the crank chamber side.

  A plurality of the recessed grooves may be formed, a plurality of the recessed portions may be formed corresponding to the recessed grooves, and a through hole corresponding to each of the recessed portions may be formed in the rib.

  An engine tool according to a third aspect of the present invention includes these two-cycle engines.

  According to the present invention, a scavenging groove extending in the direction of the top dead center from the end of the bottom dead center side is formed on the side wall of the cylinder as a scavenging passage, and a rib having a through hole formed in the crankcase is a predetermined scavenging groove. Cover the area. For this reason, since a groove is simply formed in the cylinder block as a scavenging passage, processing is facilitated and the manufacturing cost can be greatly reduced, and the strength of the crankcase can be improved by the rib. Further, since the air-fuel mixture in the crank chamber is guided from the scavenging groove to the combustion chamber through the rib through-hole, the inflow amount of the air-fuel mixture can be regulated by the through-hole to suppress the inflow of excess air-fuel mixture into the combustion chamber. It is possible to reduce the amount of the air-fuel mixture discharged from the exhaust port and suppress the deterioration of the exhaust gas characteristic value.

  The best mode for carrying out the present invention will be described below with reference to the accompanying drawings. FIG. 1 is a cross-sectional view of a two-cycle engine (hereinafter referred to as engine) 1 of the present invention including a cylinder axis 10 at a position where an exhaust port 14 is divided into two. 2 is a cross-sectional view taken along the line II-II in FIG. 1, and FIG. 3 is a cross-sectional view corresponding to FIG. 1 in a state where the cylinder block and the crankcase 7 are assembled. 4 is a cross-sectional view taken along the line IV-IV of FIG. 3, FIG. 5 is a bottom view of the cylinder block, FIG. 6 is a perspective view of a half of the crankcase 7, and FIG. 8 is a sectional view taken along line VIII-VIII in FIG. 1, and FIG. 9 is a sectional view taken along line IX-IX in FIG. 10 is a cross-sectional view corresponding to FIG. 1 when the piston 2 is at the bottom dead center position, and FIG. 11 is a cross-sectional view corresponding to FIG. 1 when the piston 2 is at a position immediately after the start of the scavenging stroke. FIG. 12 is a view showing a brush cutter 1001 equipped with the engine 1 of the present invention.

  FIG. 12 shows a brush cutter 1001 equipped with the engine 1 of the present embodiment. A rotary blade 1003 is attached to the front ends of the brush cutter 1001 and the operating rod 1002, and the engine 1 is attached to the rear end. The output of the engine 1 is supplied to the rotary blade 1003 through a drive shaft that is inserted into the operation rod 1002. An operator grasps and operates a handle 1004 attached to the operation rod 1002.

  In FIG. 1, a crankcase 7 is attached to the cylinder block 3 of the engine 1. In the cylinder 4 of the cylinder block 3, the piston 2 moves up and down in FIG. 1 (the direction of the cylinder axis 10 in the vertical direction in the figure). Unless otherwise specified, the top dead center side is the top and the bottom dead center side is the bottom. FIG. 1 shows a state where the piston 2 is at the top dead center. The cylinder 4 has an ignition plug 19 attached to the upper end, and is connected to the crank chamber 12 in the crankcase 7 at the lower end. The piston 2 is connected via a piston pin 6 and a connecting rod 5 to a crankshaft 15 that is rotatably supported by the crankcase 7. A crank weight 8 is attached to the crankshaft 15.

  In the cylinder block 3, an exhaust port 9 for exhausting combustion gas from the cylinder 4 is formed on the side of the cylinder 4. Further, an intake port 13 for supplying air-fuel mixture to the crank chamber 12 is formed on the side of the cylinder 4 opposite to the exhaust port 9 with the cylinder 4 interposed therebetween. As shown in FIG. 3, a scavenging groove 11 that extends upward from the lower end of the cylinder 4 in the direction of the cylinder axis 10 is formed in the side portion of the cylinder 4. The scavenging groove 11 is divided by the partition plate 7 into an exhaust side scavenging groove 11 a close to the exhaust port 9 and an intake side scavenging groove 11 b close to the intake port 13. A pair of exhaust-side scavenging grooves 11 a and intake-side scavenging grooves 11 b are formed symmetrically with a plane that passes through the cylinder axis 10 and divides the exhaust port 9 into two equal parts in the circumferential direction of the cylinder 4. Further, as shown in FIG. 3, the circumferential width of the exhaust side scavenging groove 11a is smaller than the width of the intake side scavenging groove 11b. As shown in FIG. 4, the exhaust-side scavenging groove 11 a and the intake-side scavenging groove 11 b each open toward the cylinder side surface (the anti-exhaust port side) opposite to the exhaust port 9 when viewed in the direction of the cylinder axis 10. Furthermore, as shown in FIG. 5, the exhaust-side scavenging groove 11a and the intake-side scavenging groove 11b accommodate ribs 14 to be described later in the lower part, and have a certain width in the radial direction and in the circumferential direction. A widened portion 20 that extends beyond the circumferential end of the scavenging groove 11 is formed.

  As shown in FIG. 1, the upper end of the intake port 13 is located near the lower end of the piston 2 when the piston 2 is at the top dead center. Further, the lower end portion of the exhaust port 9 is located above the upper end portion of the intake port 13 and is located near the upper end of the piston 2 when the piston 2 is at the bottom dead center. The upper ends of the exhaust side scavenging groove 11a and the intake side scavenging groove 11b are located between the upper end and the lower end of the exhaust port 9 (first predetermined position).

  The crankcase 7 is composed of two parts. As shown in FIG. 6 showing one of the parts constituting the crankcase 7, the crankcase 7 is formed with an arc-shaped rib 14 in a top view protruding toward the widened portion 20 of the cylinder 4. In addition, ribs 14 are formed symmetrically with respect to a plane that passes through the cylinder axis 10 and is perpendicular to the crank axis 16 in the assembled state of the engine 1 on the other part of the crankcase 7. As shown in FIG. 7, the crankcase 7 has scavenging recesses 21 formed radially outward of the ribs 14, and the scavenging recesses 21 are located on the exhaust side scavenging recesses close to the exhaust port 9 by the crank-side partition plate 22. 21 a and an intake-side scavenging recess 21 b close to the intake port 13. As shown in FIG. 9, each of the ribs 14 is formed with a scavenging inlet hole 18 that allows the scavenging recess 21 and the crank chamber 12 to communicate with each other. The scavenging inlet hole 18 includes an exhaust side scavenging recess 21a, an intake side scavenging recess 21b, and an exhaust side scavenging inlet hole 18b communicating with the crank chamber 12, respectively. The area of the exhaust side scavenging inlet hole 18a is the area of the opening formed in the side part of the cylinder 4 by the exhaust side scavenging groove 11a and the upper end of the piston 2 when the piston 2 is at the bottom dead center as shown in FIG. Smaller than. Further, the area of the intake side scavenging inlet hole 18b is smaller than the area of the opening formed in the side part of the cylinder 4 by the intake side scavenging groove 11b and the piston 2 upper end when the piston 2 is at bottom dead center. The areas of the exhaust-side scavenging inlet hole 18a and the intake-side scavenging inlet hole 18b are different because the circumferential widths of the exhaust-side scavenging groove 11a and the intake-side scavenging groove 11b are different as described above. The passage formed by the scavenging groove 11 and the rib 14 or the side wall of the piston 2 and the passage cross-sectional area of the scavenging recess 21 are larger than the area of the scavenging inlet hole 18 at any location. There is no stop.

  In a state where the cylinder block 3 and the crankcase 7 are assembled, the rib 14 is accommodated in the widened portion 20 of the cylinder block 3 as shown in FIG. The inner diameter of the rib 14 is slightly larger than the inner diameter of the cylinder 4, and the rib 14 does not interfere with the vertical movement of the piston 2. Further, as shown in FIG. 2, the upper end portion of the rib 14 is lower (second predetermined position) than the upper ends of the exhaust-side scavenging groove 11a and the intake-side scavenging groove 11b, and the piston 2 is positioned downward. While the exhaust side scavenging groove 11a or the intake side scavenging groove 11b communicates with the combustion chamber 23 by moving, it is above the lower end of the side wall of the piston 2 facing the exhaust side scavenging groove 11a and the intake side scavenging groove 11b (second The upper end of the widened portion 20 is also formed in contact with the upper end of the rib 14. Further, the partition plate 17 formed on the cylinder block 3 and the crank side partition plate 22 formed on the crankcase 7 are in contact with each other, and the scavenging groove 11 separated into two also at the joint portion between the cylinder block 3 and the crankcase 7. And the scavenging recess 21 are separated. Therefore, the exhaust side scavenging groove 11a of the cylinder block 3 and the exhaust side scavenging recess 21a of the crankcase 7 communicate with each other, and the intake side scavenging groove 11b and the intake side scavenging recess 21b communicate with each other to form a scavenging passage.

  Next, the gas flow in one cycle of the engine 1 of the present embodiment will be described. The air-fuel mixture in the combustion chamber 23 is ignited by the spark plug 19 when the piston 2 comes near the top dead center. The air-fuel mixture in the combustion chamber 23 is combusted to become combustion gas, and becomes high temperature and high pressure, and pushes down the piston 2 from the top dead center toward the bottom dead center. When the piston 2 is lowered, the exhaust port 9 is first opened. When the exhaust port 9 is opened, the high-pressure combustion gas in the cylinder 4 flows out from the exhaust port 9. At the same time, as the piston 2 descends, the air-fuel mixture in the crank chamber 12 is compressed, and the pressure of the air-fuel mixture in the crank chamber 12 increases.

  When the piston 2 further descends, as shown in FIG. 11, the exhaust side scavenging groove 11a, the intake side scavenging groove 11b, and the combustion chamber 23 communicate with each other. At the beginning of communication, the pressure of the combustion gas in the combustion chamber 23 is higher than the pressure of the air-fuel mixture in the crank chamber 12, so that the combustion gas flows back into the exhaust side scavenging groove 11a and the intake side scavenging groove 11b. However, as described above, the exhaust-side scavenging groove 11 a and the intake-side scavenging groove 11 b are covered with the side walls of the piston 2 and the ribs 14 extending from the crankcase 7. Further, while the exhaust side scavenging groove 11a or the intake side scavenging groove 11b communicates with the combustion chamber 23, the upper end of the rib 14 is higher than the lower end of the piston 2 facing the exhaust side scavenging groove 11a and the intake side scavenging groove 11b. Located in. Therefore, the exhaust-side scavenging groove 11a and the intake-side scavenging groove 11b are upper openings defined by the upper end of the piston 2 and the boundary between the exhaust-side scavenging groove 11a and the side wall of the cylinder 4 of the intake-side scavenging groove 11b. It communicates with the combustion chamber 23, communicates with the exhaust-side scavenging recess 21a and the intake-side scavenging recess 21b at the lower end below, and opens between the piston 2 and the rib 14 and the exhaust-side scavenging recess 21a and the intake-side scavenging recess 21b. There is no communication with the combustion chamber 23 or the crank chamber 12 at other portions. The exhaust-side scavenging recess 21a and the intake-side scavenging recess 21b do not communicate with the crank chamber 12 except for the exhaust-side scavenging inlet hole 18a and the intake-side scavenging inlet hole 18b at the lower ends. For this reason, the combustion gas that has flowed back into the exhaust side scavenging groove 11a and the intake side scavenging groove 11b does not flow into the crank chamber 12 from other than the exhaust side scavenging inlet hole 18a and the intake side scavenging inlet hole 18b. Therefore, it is possible to suppress a decrease in the concentration of the air-fuel mixture in the crank chamber 12 due to the backflow. Further, since the regions above the ribs 14 of the exhaust side scavenging groove 11a and the intake side scavenging groove 11b are covered with the side walls of the piston 2, the air-fuel mixture in the exhaust side scavenging groove 11a and the intake side scavenging groove 11b is directly absorbed by the piston 2. It can be warmed to promote the vaporization of the fuel in the mixture.

  When the piston 2 further descends, the pressure in the crank chamber 12 becomes higher than the pressure in the combustion chamber 23, and the air-fuel mixture in the crank chamber 12 is exhausted from the exhaust side scavenging inlet hole 18a and the intake side scavenging inlet hole 18b, respectively. It flows into the cylinder 4 through the scavenging recess 21a, the intake-side scavenging recess 21b, the exhaust-side scavenging groove 11a, and the intake-side scavenging groove 11b. Here, as described above, the areas of the exhaust-side scavenging inlet hole 18a and the intake-side scavenging inlet hole 18b are respectively the exhaust-side scavenging groove 11a, the intake-side scavenging groove 11b, and the upper end of the piston 2 when the piston 2 is at bottom dead center. It is smaller than the area of each opening formed in the side part of the cylinder 4 by the part. Therefore, the amount of the air-fuel mixture flowing into the combustion chamber 23 can be regulated and the flow rate of the air-fuel mixture flowing into the combustion chamber 23 can be controlled. 9 can not only reduce the amount of the air-fuel mixture flowing out from the gas flow passage 9 but also adjust the flow velocity of the air-fuel mixture flowing into the combustion chamber 23 from each of the exhaust-side scavenging groove 11a and the intake-side scavenging groove 11b. The amount of the air-fuel mixture staying can be increased. Further, the exhaust-side scavenging groove 11a and the intake-side scavenging groove 11b open toward the counter-exhaust port side as viewed in the direction of the cylinder axis 10. For this reason, the air-fuel mixture that has flowed into the combustion chamber 23 is directed to the opposite side of the exhaust port 9, and it is possible to further suppress the air-fuel mixture from flowing out of the exhaust port 9.

  When the piston 2 reaches the bottom dead center and rises toward the top dead center as shown in FIG. 10, the respective communication portions of the exhaust side scavenging groove 11 a and the intake side scavenging groove 11 b and the combustion chamber 23 are gradually narrowed. And then the exhaust port 9 is also closed. At this time, since the crank chamber 12 expands to a negative pressure, the intake port 13 for supplying the air-fuel mixture opens and the air-fuel mixture is supplied to the crank chamber 12. And it shifts to the next cycle.

  As described above, in the engine 1 of the present embodiment, the scavenging grooves 11 (exhaust-side scavenging grooves 11 a and intake-side scavenging grooves 11 b) extending in the vertical direction are formed on the side wall of the cylinder 4 to form a scavenging passage, which is formed in the crankcase 7. The ribs 14 having the scavenging inlet holes 18 (the exhaust-side scavenging inlet holes 18 a and the intake-side scavenging inlet holes 18 b) cover a predetermined region of the scavenging groove 11. Therefore, the air-fuel mixture flowing from the crank chamber 12 is guided from the scavenging groove 11 to the combustion chamber 23 through the scavenging inlet hole 18. Further, the air-fuel mixture is prevented from flowing into the combustion chamber 23 through other than the scavenging inlet hole 18, and the inflow amount of the air-fuel mixture is regulated by the scavenging inlet hole 18. Accordingly, it is possible to suppress the inflow of excess air-fuel mixture into the combustion chamber 23, reduce the amount of air-fuel mixture discharged from the exhaust port 9, and suppress the deterioration of the exhaust gas characteristic value. Further, since it is only necessary to form a groove in the cylinder block 3 as a scavenging passage, processing is facilitated and manufacturing costs can be greatly reduced. Further, since the rib 14 is formed integrally with the crankcase 7, the number of parts does not increase and the configuration can be simplified. Further, the ribs 14 formed on the crankcase 7 can improve the strength of the crankcase 7. Further, since the scavenging inlet hole 18 that regulates the inflow amount of the air-fuel mixture into the combustion chamber 23 is formed in the crankcase 7, the scavenging inlet hole 18 having a desired diameter is formed in the machine to realize a desired inflow amount. Processing such as formation can be easily performed by processing, and the manufacturing cost can be reduced also from this point. Further, since the air-fuel mixture is directly heated by the side wall of the piston 2 in the scavenging groove 11, the fuel in the air-fuel mixture is vaporized, the combustion state during combustion is improved, and the deterioration of the exhaust gas characteristic value is further suppressed. You can also.

  Further, while the scavenging groove 11 and the combustion chamber 23 communicate with each other, the upper end of the rib 14 is located above the lower end of the piston 2 facing the scavenging groove 11. For this reason, even if the combustion gas flows backward from the combustion chamber 23 into the scavenging groove 11, the combustion gas can be significantly suppressed from flowing into the crank chamber 12 through the gap between the piston 2 and the rib 14. It is possible to suppress a decrease in the gas mixture concentration and to suppress a decrease in the output of the engine 1.

  Further, the area of the exhaust side scavenging inlet hole 18a and the intake side scavenging inlet hole 18b is such that the exhaust side scavenging groove 11a, the intake side scavenging groove 11b, and the piston 2 upper end when the piston 2 is at the bottom dead center. Smaller than the area of each opening formed. For this reason, resistance when flowing from the crank chamber 12 into the combustion chamber 23 increases, the amount of the air-fuel mixture can be regulated, and the flow rate of the air-fuel mixture flowing into the combustion chamber 23 can be controlled. Therefore, the amount of the air-fuel mixture remaining in the combustion chamber 23 can be increased, and at the same time, the amount of the air-fuel mixture flowing into the combustion chamber 23 and flowing out from the exhaust port 9 can be reduced, and the deterioration of the exhaust gas characteristic value can be suppressed.

  Further, since the inner diameter of the rib 14 is slightly larger than the inner diameter of the cylinder 4, the rib 14 does not interfere with the vertical movement of the piston 2, and the combustion in the combustion chamber 23 is caused by the gap between the rib 14 and the side wall of the piston 2. Leakage of gas into the crank chamber 12 is also suppressed. Further, since the rib 14 is accommodated in the widened portion 20 of the scavenging groove 11 of the cylinder block 3, the scavenging groove 11 can be easily and reliably closed.

  Further, the scavenging groove 11 and the scavenging recess 21 are separated by the partition plate 17 and the crank side partition plate 22 into an exhaust side scavenging groove 11a, an intake side scavenging groove 11b, an exhaust side scavenging recess 21a, and an intake side scavenging recess 21b, respectively. An exhaust-side scavenging inlet hole 18a and an intake-side scavenging inlet hole 18b are formed. For this reason, the flow in the exhaust side scavenging groove 11a and the intake side scavenging groove 11b (the exhaust side scavenging recess 21a and the intake side scavenging inlet hole 18b) can be adjusted separately, and the mixture or combustion in the combustion chamber 23 can be adjusted. An optimal flow of gas can be easily obtained.

  In the above-described embodiment, the scavenging groove 11 is separated by the exhaust-side scavenging groove 11a and the intake-side scavenging groove 11b, and the scavenging recess 21 is separated by the exhaust-side scavenging recess 21a and the intake-side scavenging recess 21b. However, this configuration is not necessarily required. For example, a pair of scavenging grooves and scavenging recesses, or three or more pairs of scavenging grooves and scavenging recesses may be provided across the cylinder. Appropriate selection can be made to obtain an optimal flow of the mixture or combustion gas.

  In the above-described embodiment, the area of the scavenging inlet hole 18 (exhaust side scavenging inlet hole 18a, intake side scavenging inlet hole 18b) is determined in accordance with the bottom dead center position of the piston 2. However, it is not always necessary to determine the correspondence with the bottom dead center position of the piston 2, so that the desired flow in the cylinder 2 can be obtained, corresponding to the shape of the scavenging groove 11, or appropriately determined from experiments or the like. Also good.

  Furthermore, in the above-described embodiment, the scavenging recess 21 (exhaust-side scavenging recess 21a, intake-side scavenging recess 21b) communicating with the scavenging groove 11 (exhaust-side scavenging groove 11a, intake-side scavenging groove 11b) is formed in the crankcase 7. However, the scavenging recesses 21 (exhaust-side scavenging recesses 21a and intake-side scavenging recesses 21b) may be omitted depending on the dimensions of the cylinder block 3, the crankcase 7, the piston 2, and the connecting rod 5. In this case, the scavenging inlet hole 18 (exhaust side scavenging inlet hole 18a, intake side scavenging inlet hole 18b) formed in the rib 14 is formed so as to communicate with the scavenging groove 11.

  Furthermore, in the above-described embodiment, the rib 14 is formed integrally with the crankcase 7, but the rib 14 may be formed as a separate body and held by the cylinder block 3 and the crankcase 7 from above and below. Even in such a configuration, the scavenging passage only needs to form a groove in the cylinder block, so that the manufacturing cost can be reduced and the through-hole can be easily formed. The effect of being able to suppress the inflow of the excess air-fuel mixture can be obtained. However, when the ribs 14 are formed separately, it is desirable to integrally form the ribs 14 because it is necessary to consider the effects of the ribs 14 dropping off due to the vibration of the engine 1 and resonance.

Sectional drawing in the position which includes the cylinder axis line of the 2-cycle engine of this invention, and divides an exhaust port into two. II-II sectional view taken on the line of FIG. Sectional drawing corresponding to FIG. 1 of the state which assembled | attached the cylinder block and the crankcase. FIG. 4 is a main part sectional view taken along line IV-IV in FIG. 3. The bottom view of a cylinder block. The perspective view of the half of the crankcase 7. FIG. The top view of the crankcase 7. FIG. VIII-VIII sectional view taken on the line of FIG. IX-IX sectional view taken on the line of FIG. Sectional drawing corresponding to FIG. 1 in case a piston is a bottom dead center. FIG. 2 is a cross-sectional view corresponding to FIG. 1 immediately after the start of a scavenging stroke. The perspective view which shows the brush cutter carrying the 2 cycle engine of this invention.

Explanation of symbols

1 Engine 2 Piston 3 Cylinder block 4 Cylinder 7 Crankcase 9 Exhaust port 10 Cylinder axis 11 Scavenging groove 11a Exhaust side scavenging groove 11b Intake side scavenging groove 12 Crank chamber 13 Intake port 14 Rib 18 Scavenging inlet hole 18a Exhaust side scavenging inlet hole 18b Inlet side scavenging inlet hole

Claims (10)

A scavenging passage is formed between the intake port that communicates with the intake passage, the exhaust port that communicates with the exhaust passage, and the end of the bottom dead center side to the first predetermined position in the direction of the top dead center. A concave groove formed on the side wall;
In a two-cycle engine comprising a crankcase attached to an end of the cylinder at the bottom dead center side,
The cylinder extends from the bottom dead center side end of the cylinder to the top dead center direction to the second dead center side from the first predetermined position to cover the concave groove in the circumferential direction of the cylinder. And a scavenging passage, and a rib disposed so as to be opposed to the side wall of the piston.   The crankcase is formed with a recess facing the bottom dead center side of the concave groove toward the top dead center, connected to the scavenging passage, and the through hole communicating with the recess. The two-cycle engine according to claim 1. An intake port communicating with the intake passage; an exhaust port communicating with the exhaust passage; and a cylinder formed on the side wall with a concave groove extending from the end on the bottom dead center side to the first predetermined position in the top dead center direction; ,
In a two-cycle engine comprising a crankcase attached to an end of the cylinder at the bottom dead center side,
The cylinder extends from the bottom dead center side end of the cylinder to the top dead center direction to the second predetermined position on the bottom dead center side from the first predetermined position, covers the concave groove in the circumferential direction of the cylinder, A rib disposed to face the side wall, a recess facing the bottom dead center side of the concave groove and opening toward the top dead center, and a recess connected to a passage formed by the rib and the concave groove; A through-hole formed in the rib connecting the chamber and the recess,
A two-cycle engine characterized in that the crank chamber and the combustion chamber are communicated with each other by the concave groove, the side wall of the piston, the rib, the concave portion, and the through hole when the piston is in the vicinity of bottom dead center. .   The area of the said through-hole is smaller than the area of the opening formed in the side wall of the said cylinder by the said concave groove and the said piston when the said piston is in a bottom dead center. The two-cycle engine according to any one of the above.   The two-cycle engine according to any one of claims 1 to 4, wherein an inner diameter of the rib at a position facing at least the piston is larger than an inner diameter of the cylinder.   The second predetermined position is located on a top dead center side with respect to a bottom dead center side end facing the concave groove on the piston side wall while the concave groove communicates with the combustion chamber. The two-cycle engine according to any one of claims 1 to 5, characterized in that: The concave groove extends on the inner wall side of the cylinder, extends from the bottom dead center side end of the cylinder in the top dead center direction to the second predetermined position, and has at least one end of the concave groove in the circumferential direction. A widened portion extending beyond is formed,
The two-cycle engine according to any one of claims 1 to 6, wherein the rib closes the widened portion. The concave groove projects from the radial end of the concave groove toward the inner peripheral surface of the cylinder and extends from the bottom dead center side end to the top dead center side end so that the concave groove extends around the cylinder. A wall plate on the cylinder side separated in the direction is provided,
A crank chamber that faces the cylinder-side wall plate and extends from the top dead center side end portion to the bottom dead center side end portion between the ribs and separates the concave portion in the cylinder circumferential direction. Side wall plates are provided,
The two-cycle engine according to any one of claims 2 to 7, wherein the through holes are respectively provided corresponding to recesses separated by a wall plate on the crank chamber side. A plurality of the concave grooves are formed,
A plurality of the concave portions are formed corresponding to the concave grooves,
The two-cycle engine according to any one of claims 2 to 7, wherein a through hole corresponding to each of the recesses is formed in the rib.   An engine tool comprising the two-cycle engine according to any one of claims 1 to 9.

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