JP2018028306A - Two-cycle engine and its manufacturing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a two-cycle engine which suppresses an increase of the number of part items, and can increase a flow-in amount of air into a scavenge passage, and its manufacturing method.SOLUTION: A two-cycle engine has first and second scavenge passage portions 26, 27 for making a combustion chamber and a crank chamber communicate with each other, and scavenge ports 26a, 27a of the scavenge passage portions 26, 27 are opened at an inner face of a cylinder 1. Scavenge passage upper parts 26c, 27c including the scavenge ports 26a, 27a, and an air passage 21 are die-molded of a molding mold piece P3 which moves in a radial direction of the cylinder 1. One portion of a penetration hole 40 in a peripheral direction at the inside of the radial direction between the scavenge passage upper parts 26c, 27c and the air passage 21 is blocked by a lid body.SELECTED DRAWING: Figure 7

Description

  The present invention relates to a method of manufacturing a cylinder of a two-cycle engine having a scavenging passage communicating a combustion chamber and a crank chamber and having a scavenging port of the scavenging passage open on an inner surface of the cylinder by molding. .

  In an air-leading two-cycle engine having a scavenging passage that communicates between a combustion chamber and a crank chamber, an intake passage is formed by an air-fuel mixture passage and an air passage. Here, an air passage, an upper portion of a scavenging passage including a scavenging port, and a through hole provided between the air passage and the upper portion of the scavenging passage are molded with a molding die piece that moves in the direction of the air passage. (For example, Patent Document 1). According to Patent Document 1, a cylinder of a two-cycle engine can be manufactured with excellent workability and productivity and at a low cost.

JP 2009-008043 A

  However, in the two-cycle engine of Patent Document 1, the communication path that introduces the air in the intake passage to the scavenging passage is formed so as to bend from the outside of the scavenging passage, so that the passage resistance tends to increase. In addition, a slide mold for forming a communication passage portion on the radially outer side of the scavenging passage and a lid member constituting the outer wall thereof are required.

  An object of the present invention is to provide a two-cycle engine that can suppress an increase in the number of parts and increase the amount of air flowing into a scavenging passage, and a method for manufacturing the same.

  In order to achieve the above object, a method for manufacturing a two-cycle engine of the present invention has a scavenging passage that communicates a combustion chamber and a crank chamber, and a scavenging port of the scavenging passage is open to the inner surface of the cylinder. A method of manufacturing a cylinder of a cycle engine by molding, wherein a scavenging passage upper portion including the scavenging port and an air passage are molded by a molding die piece that moves in a radial direction of the cylinder, and the scavenging passage upper portion and the air passage A portion on the radially inner side in the circumferential communication portion with the air passage is closed by a lid.

  According to this configuration, the slide mold and the lid member for forming the communication passage for introducing the air in the air passage into the scavenging passage are not necessary. Therefore, an increase in the number of parts can be suppressed. Further, since air from the air passage is introduced into the upper portion of the scavenging passage without going around radially outside the upper portion of the scavenging passage, the flow resistance can be suppressed and the amount of air flowing into the scavenging passage can be increased. .

  In the present invention, it is preferable to provide a pair of scavenging passages symmetrically about the axis of the air passage. According to this configuration, two sets of slide molds and lid members for forming the communication path are unnecessary. Therefore, the effect of suppressing the increase in the number of parts is great.

  In the present invention, it is preferable that the lid is provided with a closing portion that closes a part of the communication portion and an attachment portion that is attached to the cylinder. According to this configuration, since the structure of the lid is simplified, the manufacturing cost of the lid can be reduced. In this case, it is preferable that a scavenging guide surface that guides scavenging gas into the cylinder is formed in the closing portion. According to this configuration, air is smoothly guided into the cylinder by the scavenging guide surface.

  In the present invention, it is preferable that the cylinder and the vaporizer are connected by an insulator made of a heat shielding material, and the insulator forming a part of the air passage is inserted into a cavity formed by the mold piece. According to this configuration, since a part of the air passage can be formed using the insulator, the structure of the cylinder is simplified. In this case, it is preferable that an air guide surface for guiding air to the upper part of the scavenging passage is formed on the insulator. According to this configuration, the air is smoothly guided to the scavenging passage by the air guide surface.

  In this invention, it is preferable that the said cylinder is connected with the said crankcase by the fastening member inserted from the crankcase side. When a fastening member is inserted from the cylinder side and fastened to the crankcase, the fastening member insertion hole in the cylinder interferes with the molded piece. According to this configuration, interference between the fastening member insertion hole and the molded piece can be avoided. it can.

  The two-cycle engine of the present invention is a two-cycle engine having a scavenging passage that communicates between a combustion chamber and a crank chamber, and a scavenging port of the scavenging passage is open to an inner surface of a cylinder, and includes the scavenging port. The upper part of the scavenging passage and the air passage communicate with each other in the circumferential direction of the cylinder, and a part on the radially inner side of the communication part in the circumferential direction between the upper part of the scavenging passage and the air passage is closed by a lid. Yes.

  Since the two-cycle engine of the present invention is obtained by the manufacturing method of the present invention, the slide mold for the communication path and the lid member are not necessary. Therefore, an increase in the number of parts can be suppressed. Further, since air from the air passage is introduced into the upper portion of the scavenging passage without going around radially outside the upper portion of the scavenging passage, the flow resistance can be suppressed and the amount of air flowing into the scavenging passage can be increased. .

  According to the two-cycle engine of the present invention and the method for manufacturing the same, it is possible to suppress an increase in the number of parts and to increase the amount of air flowing into the scavenging passage.

1 is a front sectional view showing a two-cycle engine according to a first embodiment of the present invention. It is front sectional drawing which shows the cylinder and crankcase of the engine. It is sectional drawing along the III-III line of FIG. It is a front view which shows the cover body of the same engine. It is a front view which shows the crankcase. It is a longitudinal cross-sectional view which shows the outline of the shaping | molding die for casting the cylinder. It is sectional drawing along the VII-VII line of FIG. It is a plane sectional view of a mold piece which forms an air passage and a scavenging passage upper part. It is a side view of the same mold piece. It is the side view of the cylinder seen from the intake passage side after extracting the shaping | molding die piece. It is a side view of the cylinder seen from the intake passage side after closing a through hole with the lid. It is a horizontal sectional view of the important section of the cylinder after closing the through-hole.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings. In the following embodiments, a small two-cycle engine used for a brush cutter is illustrated.

  In FIG. 1, a cylinder 1 having a combustion chamber 1a formed therein is connected to an upper portion of a crankcase 2 forming a crank chamber 2a. The cylinder 1 and the crankcase 2 are each made of a metal such as an aluminum alloy, and are formed by a mold (mold). As shown in FIG. 5, the cylinder 1 is connected to the crankcase 2 by a fastening member 15 inserted from the crankcase 2 side. A carburetor 3 and an air cleaner 4 constituting an intake system are connected to one side (right side in FIG. 1) of the cylinder 1 shown in FIG. 1, and an exhaust system is constituted on the other side (left side in FIG. 1). The muffler 5 is connected. A fuel tank 6 is attached to the lower part of the crankcase 2.

  A cylinder bore 1b is formed inside the cylinder 1, and a piston 7 that reciprocates in the axial direction C1 is inserted into the cylinder bore 1b. A crankshaft 11 is rotatably supported by the crankcase 2 via a pair of crank bearings 10. A hollow crankpin 12 is provided at a position displaced from the axis of the crankshaft 11, and a large end bearing 14 and a space between the crankpin 12 and the hollow piston pin 13 provided on the piston 7 are provided. They are connected by connecting rods 18 via small end bearings 17. A crank web 19 is provided on the crankshaft 11, and a spark plug P is provided on the upper portion of the cylinder 1. An insulator 20 made of a heat shielding material is provided between the cylinder 1 and the vaporizer 3 for the purpose of heat insulation from the high temperature cylinder 1.

  In the insulator 20, a part of the air passage 21 that communicates with the cylinder 1 is formed on the upper side, and a part of the air-fuel mixture passage 22 that communicates with the cylinder 1 and is disposed in parallel with the air passage 21 on the lower side. Is formed. The air passage 21 and the mixture passage 22 form an intake passage 44. A scavenging inlet 22a for introducing the mixture M from the mixture passage 22 into the crank chamber 2a is formed in the peripheral wall of the cylinder 1, and an exhaust passage 23 having an exhaust port 23a that opens to the inner peripheral surface of the cylinder. Is formed. Exhaust gas (combustion gas) from the exhaust passage 23 is discharged to the outside through the muffler 5.

  Inside the cylinder 1 and the crankcase 2, a scavenging passage 25 that connects the combustion chamber 1 a and the crank chamber 2 a is provided. The scavenging passage 25 includes a first scavenging passage portion 26 and a second scavenging passage portion 27 into which both air-fuel mixture and air are introduced.

  In FIG. 2, the first and second scavenging ports 26a and 27a at the upper ends of the first and second scavenging passage portions 26 and 27 are set at positions slightly lower than the upper end of the exhaust port 23a. The upper end of the second air scavenging port 27a is set at a position higher than the upper end of the first scavenging port 26a for the air-fuel mixture. Thereby, in the scavenging stroke in which the piston 7 descends, scavenging by the air A is given priority over the air-fuel mixture M. Lower ends 26b, 27b of the first and second scavenging passage portions 26, 27 communicate with the crank chamber 2a. The lower end 26b of the first scavenging passage portion 26 is located away from the bearing 10, and the lower end 27b of the second scavenging passage portion 27 is located facing the bearing 10 from the axial direction. Thereby, the second scavenging passage portion 27 is longer than the first scavenging passage portion 26. The first and second scavenging ports 26 a and 27 a of the first and second scavenging passage portions 26 and 27 open to the inner surface of the cylinder 1.

  As shown in FIG. 3, the axial centers C2 and C3 of the exhaust passage 23 and the air passage 21 are substantially on the same line when viewed from the direction of the cylinder axial center C1. A pair of first and second scavenging passage portions 26 and 27 are provided symmetrically about the axis C3 of the air passage 21 or the axis C2 of the exhaust passage 23. The second scavenging passage portion 27 for air is formed closer to the exhaust port 23a than the first scavenging passage portion 26 for air-fuel mixture.

  Inside the cylinder 1, a communication passage 30 is formed for communicating the air A from the air passage 21 of the insulator 20 to the first and second scavenging passage portions 26 and 27. Specifically, the scavenging passage upper portions 26 c and 27 c including the first and second scavenging ports 26 a and 27 a and the air passage 21 are communicated with each other via the communication passage 30. The communication passage 30 connects the scavenging passage upper portions 26 c and 27 c and the air passage 21 in the circumferential direction of the cylinder 1.

  The insulator 20 is integrally formed with a protrusion 32 that extends into the cylinder 1 and forms a part of the wall surface of the communication passage 30. In the cylinder 1, the first recess 34 for forming the communication passage 30 is cast in a direction facing the exhaust port 23 a, that is, in a direction substantially parallel to the air passage 21. It is formed at the same time. A protrusion 32 extends into the first recess 34 to form a first side wall 33 of the communication path 30. That is, the first recess 34 constitutes a cavity into which the insulator 20 is inserted. The wall surface 33a of the first side wall 33 forms an air guide surface 33a that guides air to the scavenging passage upper portions 26c and 27c.

  A second side wall 38 that partitions the first scavenging passage portion 26 and the communication passage 30 is formed in the cylinder 1. A through hole 40 is formed in the second side wall 38, and a part of the through hole 40 is closed by a lid 50 described later. That is, the through hole 40 constitutes a circumferential communication portion between the scavenging passage upper portions 26 c and 27 c and the air passage 21, and a part of the through hole 40 (communication portion) on the radially inner side is closed by the lid body 50. ing. A portion of the through hole 40 that is not closed by the lid body 50 constitutes an air outlet port 42 that communicates the second scavenging passage portion 26 and the communication passage 30. The air outlet 42 is formed between the lid 50 and the outer wall of the cylinder 1.

  As shown in FIG. 4, the lid 50 is formed by pressing a plate material, and is generally U-shaped having a central base portion 50 a and two branch portions 50 b and 50 b. However, the method for forming the lid 50 is not limited to this. A mounting hole 51 is provided in the center of the base 50a. That is, the base portion 50 a constitutes an attachment portion that is attached to the cylinder 1.

  Further, the tips of the two branch portions 50b and 50b are bent to form flat portions 50c and 50c. As shown in FIG. 3, the flat portion 50 c constitutes a closing portion 53 that closes a part of the through hole 40 (FIG. 3) that is a communication portion. The flat portion 50c faces the scavenging passage upper portion 26c of the first scavenging passage portion 26, and a projection 50d protruding in a direction away from the base portion 50a is formed on the flat portion 50c. The projecting end surface 50e of the projection 50d is substantially flush with the inner surface of the first scavenging passage portion 26 to form a guide surface for guiding the air A and the air-fuel mixture M into the cylinder 1.

  A reed valve 36 is attached to the downstream outlet of the air passage 21 in the insulator 20. The reed valve 36 closes the air passage 21 when the pressure in the communication passage 30 connected to the air passage 21 rises above a predetermined value. That is, the air A from the air passage 21 is introduced into the scavenging passage upper portions 26c and 27c of the first and second scavenging passage portions 26 and 27 through the communication passage 30 and the air outlet port 42 by opening the reed valve 36. The

  The air-fuel mixture M from the air-fuel mixture passage 22 of the insulator 20 shown in FIG. 2 receives the negative pressure of the crank chamber 2a during the intake stroke in which the piston 7 rises, and the air-fuel mixture passage 22 provided on the inner peripheral surface of the cylinder 1. To the crank chamber 2a. On the other hand, the air A from the air passage 21 receives the negative pressure of the crank chamber 2a during the intake stroke in which the piston 7 ascends, and the first and second scavenging passage portions 26 and 27 from the communication passage 30 (FIG. 3). The gas is once introduced into the scavenging passage upper portions 26c and 27c.

  The air-fuel mixture M introduced into the crank chamber 2a from the air-fuel mixture passage 22 passes through the first and second scavenging passage portions 26 and 27 in the scavenging stroke in which the piston 7 shown in FIG. The gas is ejected obliquely upward from the scavenging ports 26a, 27a into the combustion chamber 1a. At this time, the air A stored in the scavenging passage upper portions 26c and 27c is jetted into the combustion chamber 1a before the air-fuel mixture M.

  Air A from the first and second scavenging ports 26a and 27a shown in FIG. 3 is jetted obliquely upward toward the combustion chamber 1a. Thereby, in particular, the air A from the second scavenging port 27a blocks the air-fuel mixture M, and the air blow-out of the air-fuel mixture M from the exhaust passage 23 to the outside is effectively suppressed.

  Next, the operation of the engine will be described. When the piston 7 in the cylinder 1 reaches near the top dead center in the intake stroke shown in FIG. 2, the inside of the cylinder 1 and the crank chamber 2a is in a negative pressure state. At this time, the air-fuel mixture M is directly introduced into the crank chamber 2a from the air-fuel mixture passage 22 that opens to the inner peripheral surface of the cylinder 1. The large-end bearing 14 and the small-end bearing 17 are lubricated by the introduced air-fuel mixture M.

  At this time, the first scavenging passage portion 26 directly communicating with the crank chamber 2a and the second scavenging passage portion 27 of air communicating with the crank chamber 2a via the bearing 10 also have negative pressure. The communication passage 30 in FIG. 3 connected to the second scavenging passage portions 26 and 27 has a negative pressure. As a result, the lead valve 36 attached to the outlet of the air passage 21 of the insulator 20 is opened, and the air A from the air passage 21 passes through the communication passage 30 and is once introduced into the first and second scavenging passage portions 26 and 27. Is done.

  As described above, when the lead valve 36 is opened due to the negative pressure in the crank chamber 2a of FIG. 2 during the intake stroke, the air A is always introduced into the first and second scavenging passage portions 26 and 27. For this reason, a sufficient amount of air for preventing blow-through is secured in both the scavenging passage portions 26 and 27.

  Subsequently, in the scavenging stroke, as shown in FIG. 3, the air A and the air-fuel mixture M are transferred from the first scavenging port 26 a of the first scavenging passage portion 26 and the second scavenging port 27 a of the second scavenging passage portion 27 to the combustion chamber. Introduced in 1a. At this time, first, air A is introduced from the second scavenging port 27a located at a high position, air A is introduced from the first scavenging port 26a with a slight delay, and then the air-fuel mixture M is introduced from both the scavenging ports 26a, 27a. It has come to be. Since the air A from the second scavenging port 27a is introduced into the combustion chamber 1a from the vicinity of the exhaust port 23a, the combustion gas is discharged from the exhaust port 23a by the air A from the second scavenging port 27a introduced earlier. . Therefore, the air-fuel mixture M can be prevented from being blown out from the exhaust port 23a.

Next, a method for manufacturing the cylinder of the two-cycle engine having the above configuration will be described.
As shown in FIG. 6, when the cylinder 1 is formed, the cylinder bore 1b and the two pairs of first and second scavenging passage portions 26 and 27 are arranged so that the inner die P1 with mesh hatching is moved downward along the cylinder axis C1. Are simultaneously molded by die cutting. The molding die P1 serving as the inner mold has a bore forming portion P11 that forms the cylinder bore 1b, and a scavenging passage forming portion P12 that forms the scavenging passage portions 26 and 27 excluding the scavenging ports 26a and 27a. The parts P11 and P12 are formed to be tapered toward the upper side in order to have a die cutting gradient.

  The bore forming portion P11 and the scavenging passage forming portion P12 do not communicate with each other in the radial direction of the cylinder 1, and in the space between them, passage walls (radially inner walls) 260, 270 of the scavenging passage portions 26, 27. Is molded. The outer surface of the cylinder 1 is formed by a divided outer mold P2 that moves in the front-rear direction X and the left-right direction Y that are hatched. Here, the front-rear direction X is a direction parallel to the axis of the crankshaft 11 (FIG. 1), and the left-right direction Y is a direction orthogonal to both the front-rear direction X and the cylinder axis C1.

  One of the divided types constituting the outer mold P2 forms the first scavenging port 26a and the second scavenging port 27a included in the scavenging passage upper portions 26c and 27c of the first scavenging passage portion 26 and the second scavenging passage portion 27. A mold piece P3 is included. The upper end surface P3a of the mold piece P3 is slightly inclined upward toward the cylinder axis C1 in accordance with the upper surfaces of the first scavenging port 26a and the second scavenging port 27a.

  FIG. 7 shows a cross-sectional view taken along line VII-VII in FIG. As is apparent from FIG. 7, the mold piece P3 forms an intake passage 44 including the air passage 21 and the air-fuel mixture passage 22, and scavenging passage upper portions 26c and 27c including the first and second scavenging ports 26a and 27a. To do. As shown in FIG. 8, the mold piece P3 is provided with an air passage forming portion 46 for forming the air passage 21 in the base portion 45, and protrudes from the air passage forming portion 46 so as to form the first and second scavenging air. A scavenging passage forming portion 48 for forming the ports 26a and 27a is provided.

  Further, as shown in FIG. 9, an air-fuel mixture passage forming portion 54 that forms the air-fuel mixture passage 22 and a recess forming portion 56 that forms the first recess 34 are provided in the base 45. The air passage forming portion 46 is thick and the scavenging passage forming portion 48 is thinner than the air passage forming portion 46, and a step 47 is provided between the air passage forming portion 46 and the scavenging passage forming portion 48. The scavenging passage forming portion 48 has a shape that gradually tapers toward the tip 48a. This scavenging passage forming portion 48 passes through the through hole 40 of FIG.

  After the cylinder 1 is molded, the mold piece P3 is moved outward in the radial direction F of the cylinder 1 in FIG. 7, that is, along the axis C3 of the air passage 21 of the cylinder 1 and is extracted and opened. Thereby, the first and second scavenging ports 26a and 27a and the intake passage 44 are integrally formed.

  At this stage, as shown in FIG. 10 viewed from the intake passage 18 side, the scavenging of the first scavenging passage portion 26 is formed around the through hole 40 corresponding to the stepped portion 47 (FIG. 11) of the mold piece P3. There is a stepped portion 58 between the passage upper portion 26 c and the air passage 21. A step surface 58a of the step portion 58 is exposed to the air passage 21 side.

  A part of the through hole 40 near the cylinder axis C1 is closed by a lid 50 as shown in FIG. That is, the closing member 50c of the lid 50 is brought into contact with the stepped surface 58a, and a fastening tool such as a screw body 60 inserted into the mounting hole 51 provided in the lid 50 shown in FIG. Screw into a screw hole 55a provided in 55. As a result, a part of the through hole 40 is closed by the closing part 50 c of the lid 50. In this manner, a part of the through hole 40 in the circumferential direction is closed by the lid 50, whereby an air outlet 42 is formed between the closed portion 50 c of the lid 50 and the outer wall of the cylinder 1.

  According to the above configuration, the slide mold and the lid member for forming the communication passage 30 for introducing the air in the air passage 21 of FIG. 3 into the second scavenging passage portion 26 are not necessary. Therefore, an increase in the number of parts can be suppressed. Further, the air A from the air passage 21 is introduced into the scavenging passage upper portions 26c and 27c without going around the radial outer sides of the scavenging passage upper portions 26c and 27c, so that the flow passage resistance is suppressed and the second scavenging passage portion. The inflow amount of air to the air outlet 27 can be increased.

  The through hole 40 has a simple structure that penetrates from the scavenging passage upper portions 26c, 27c of the first and second scavenging passage portions 26, 27 to the air passage 21 side. Therefore, a part of the through hole 40 can be easily closed with the lid 50 after the cylinder 1 is manufactured. As a result, the air outlet 42 can be easily formed, and the mold piece P3 can also have a simple shape as shown in FIGS.

  Since each of the scavenging passage portions 26 and 27 shown in FIG. 3 is provided in a pair symmetrically about the axis C3 of the air passage 21, two slide molds and lid members for forming the communication passage 30 are provided. No pair is required. Therefore, the effect of suppressing the increase in the number of parts is great.

  The lid 50 is provided with a closing portion 53 that closes a part of the through hole 40 and an attachment portion 50 a that is attached to the cylinder 1. As a result, the structure of the lid 50 is simplified, and the manufacturing cost of the lid 50 can be reduced. Furthermore, since the scavenging guide surface 50 e for guiding the air into the cylinder 1 is formed in the closing portion 53, the air is smoothly guided to the second scavenging passage portion 27.

  Moreover, since the closing part 53 is integrally formed in the lid 50 by pressing the plate material, an increase in the number of parts is suppressed. Furthermore, the lid 50 can be stably supported by contacting the step surface 58a. Further, since the step surface 58a becomes a sealing surface, the airtightness after the lid body 50 closes a part of the through hole 40 is improved.

  The insulator 20 that forms a part of the air passage 21 is inserted into the first recess 34 formed by the molding die piece P3 (FIG. 9). Thus, the structure of the cylinder 2 is simplified by forming a part of the air passage 21 using the insulator 20. Further, since the air guide surface 33a for guiding the air to the scavenging passage upper portions 26c, 27c is formed in the insulator 20, the air A is smoothly guided to the first and second scavenging passage portions 26, 27.

  The communication passage 30 is formed by a first recess 34 provided by molding the cylinder 1 and a protrusion 32 of the insulator 20 that enters the first recess 34. Since the first recess 34 of the cylinder 1 can be easily formed using a simple mold, the manufacturing cost can be kept low. Furthermore, the wide first recess 34 formed by casting in the cylinder 1 to form the communication path 30 is filled with the protrusion 32 integrally formed with the insulator 20 and becomes narrow. Thereby, the volume of the crank chamber 2a (FIG. 2) communicating with the first recess 34 is substantially reduced, so that a sufficient jet pressure of the air A can be ensured in the scavenging stroke.

  As shown in FIG. 5, the cylinder 1 is connected to the crankcase 2 by a fastening member 15 inserted from the crankcase 2 side. When the fastening member 15 is inserted from the cylinder 1 side and fastened to the crankcase 2, the fastening member insertion hole 1c and the molded piece P3 in the cylinder 1 interfere with each other. According to the above configuration, the fastening member insertion hole 1c and the molded piece Interference with P3 can be avoided.

  The present invention is not limited to the above-described embodiment, and various additions, modifications, or deletions can be made without departing from the gist of the present invention. Therefore, such a thing is also included in the scope of the present invention.

1 Cylinder 1a Combustion chamber 2 Crankcase 2a Crank chamber 3 Vaporizer 15 Fastening member 20 Insulator 21 Air passage 25 Scavenging passages 26a, 27a Scavenging ports 26c, 27c Upper portion of scavenging passage 30 Communication passage 33a Wall surface of first side wall (air guide surface)
34 First recess (cavity)
40 Through hole (communication part)
50 Lid 50a Base (Mounting part)
50e Scavenging guide surface 53 Closure part P3 Mold piece

Claims (8)

A method of manufacturing a cylinder of a two-cycle engine having a scavenging passage communicating with a combustion chamber and a crank chamber, the scavenging port of the scavenging passage being open on the inner surface of the cylinder by molding,
The upper part of the scavenging passage including the scavenging port and the air passage are molded by a molding die piece that moves in the radial direction of the cylinder,
A method for manufacturing a two-cycle engine, wherein a part inside the radial direction in a communication portion in a circumferential direction between the upper part of the scavenging passage and the air passage is closed by a lid.   2. The method for manufacturing a two-stroke engine according to claim 1, wherein a pair of the scavenging passages are provided symmetrically about the axis of the air passage.   3. The method for manufacturing a two-cycle engine according to claim 1, wherein the lid is provided with a closing portion for closing a part of the communication portion and an attachment portion attached to the cylinder.   The method for manufacturing a two-stroke engine according to claim 3, wherein a scavenging guide surface for guiding scavenging gas into the cylinder is formed in the closing portion.   5. The method for manufacturing a two-cycle engine according to claim 1, wherein the cylinder and the carburetor are connected by an insulator made of a heat shielding material, and the cavity formed by the mold piece is A method for manufacturing a two-cycle engine, wherein the insulator forming a part of an air passage is inserted.   6. The method for manufacturing a two-stroke engine according to claim 5, wherein an air guide surface for guiding air to the upper part of the scavenging passage is formed in the insulator.   The method for manufacturing a two-stroke engine according to any one of claims 1 to 6, wherein the cylinder is connected to the crankcase by a fastening member inserted from a crankcase side. A two-cycle engine having a scavenging passage communicating with a combustion chamber and a crank chamber, wherein a scavenging port of the scavenging passage is open on an inner surface of a cylinder;
The upper part of the scavenging passage including the scavenging port and the air passage communicate with each other in the circumferential direction of the cylinder,
A two-cycle engine in which a part on the radially inner side in the circumferential communication portion between the scavenging passage upper portion and the air passage is closed by a lid.

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