JP2006329152A - 2-stroke engine with lead valve stopper - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To effectively prompt flow of fuel air mixture in scavenging passage and then improve efficiency of scavenging and enhance output by simple configuration which only improves a stopper of a lead valve of a 2-stroke engine. <P>SOLUTION: The 2-stroke engine is provided with an intake passage 8 which introduces the fuel air mixture M from an intake port 4 to a crank chamber 7, an intake transverse scavenging passage 32 which introduces the fuel air mixture M in the crank chamber 7 through the intake passage 8 to a combustion chamber 3 and a lead valve 20 which is disposed in the intake passage 8 and approximates to the intake port 4. The 2-stroke engine is configured so that the stopper 28 which regulates opening of a lead strip 24 in the lead valve 20 is located in outside of the scavenging passage 32 so as to avoid adding a restriction to the scavenging passage 32. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a two-stroke engine provided with a stopper that restricts the maximum opening of a reed valve that is provided in an intake passage and prevents backflow of air-fuel mixture.

  Generally, a reed valve as a check valve is provided in an intake passage of a two-stroke engine (see, for example, Patent Document 1). In such a two-stroke engine, a reed valve is provided at a position as close as possible to the intake port in order to reduce the compression volume when the crank chamber is compressed by lowering the piston, and the air-fuel mixture in the crank chamber is used during the scavenging stroke. Is provided with a cross-intake scavenging passage for introducing the air into the combustion chamber via the downstream side of the reed valve of the intake passage.

JP 2001-234750 A

  The intake crossing scavenging passage increases the scavenging flow rate at medium and high speeds of the engine by restricting the passage area by the tip of a stopper that regulates the maximum opening of the reed valve. In general, it has been found that the scavenging flow rate becomes insufficient due to the restriction, and the scavenging efficiency of the combustion gas is lowered at 2,000 rpm to about 4,000 rpm during idling.

  The present invention has been made in view of the above-described conventional problems, and in a two-stroke engine, the configuration of only improving the reed valve stopper effectively promotes the flow of scavenging in a speed range from extremely low speed to low speed. The aim is to improve the scavenging efficiency and thereby improve the output.

  In order to achieve the object, a two-stroke engine according to the present invention includes an intake passage for introducing an air-fuel mixture from an intake port into a crank chamber, and an intake air for introducing the air-fuel mixture in the crank chamber into the combustion chamber through the intake passage. A stopper that regulates the opening of the lead piece in the reed valve is provided with a transverse scavenging passage and a reed valve that is disposed in the intake passage and is close to the intake port. It is located outside the scavenging passage to avoid it.

  According to this configuration, in the intake and compression strokes in which the piston rises, the reed valve lead piece opens due to the negative pressure generated in the crank chamber, and the air-fuel mixture is introduced into the crank chamber from the intake passage. As the crank chamber is pressurized during the exhaust and scavenging stroke, the lead piece closes the intake passage, and the air-fuel mixture in the crank chamber is introduced into the combustion chamber through the intake crossing scavenging passage to scavenge the combustion chamber. . At this time, since the stopper that regulates the maximum opening degree of the reed valve arranged close to the intake port is located outside the intake crossing scavenging passage so as to avoid the throttle, the intake crossing scavenging passage The scavenging flow through is promoted. As a result, the scavenging efficiency can be improved and the engine output can be improved, particularly in the speed range from the extremely low speed to the low speed of the engine having a slow scavenging flow rate.

  In the present invention, for example, the stopper may be configured such that a base end portion is supported by a valve body that supports the lead piece so as to be freely opened and closed, and a notch portion corresponding to the scavenging passage is formed at a distal end portion. . According to this configuration, the air-fuel mixture in the crank chamber can be smoothly flowed in the scavenging passage by the notch during the scavenging stroke, while the stopper is sufficiently long so that the tip of the lead piece contacts.

  In the present invention, it is preferable that a lightening hole having substantially the same width as the notch is formed in a portion of the stopper closer to the base end than the notch. According to this configuration, during the scavenging stroke when the lead piece is closed, the air-fuel mixture in the crank chamber can flow in the scavenging passage through the cutout portion and the cutout hole, so that a smooth flow of scavenging can be further promoted.

  In the present invention, preferably, an exhaust port is formed at a position approximately 180 ° away from the intake port in the cylinder about the cylinder axis, and the air-fuel mixture in the crank chamber is combusted between the intake port and the exhaust port. Another scavenging passage is introduced into the chamber. According to this configuration, the cross-sectional area of the intake air scavenging passage can be made small due to the presence of another scavenging passage, and the notch portion formed in the stopper can be small, so the contact area between the stopper and the lead piece Is sufficiently large to maintain the stopper function high.

  In the two-stroke engine of the present invention, a stopper for restricting the maximum opening of the reed piece in the reed valve disposed close to the intake port in the intake passage is avoided from adding a throttle to the intake crossing scavenging passage. With a simple configuration that is simply located outside the intake crossing scavenging passage, the scavenging efficiency can be improved and the output can be improved.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings.
FIG. 1 is a front sectional view of an intake / compression stroke in a two-stroke engine according to an embodiment of the present invention, and FIG. 2 is a front sectional view of an exhaust / scavenging stroke. In FIG. 1, a cylinder 1 is connected to an upper portion of a crankcase 2, and a piston 11 is inserted into a cylinder bore 1 a having a cylindrical inner peripheral surface provided in the cylinder 1 so as to be slidable in the direction of a cylinder axis C. ing. A combustion chamber 3 is formed by the cylinder 1, a cylinder head (not shown) connected to the upper portion of the cylinder 1, and the piston 11. An intake passage 8 communicating with the crank chamber 7 of the crankcase 2 is formed at one side of the cylinder 1 (right side in FIG. 1). The intake passage 8 allows an air-fuel mixture M supplied from an air-fuel mixture generating device (not shown) such as an air cleaner and a carburetor (or a fuel injection valve) constituting an intake system to be supplied from a front intake port 4 to a crank chamber 7. Introduce in. An exhaust port 10 that is an inlet of the exhaust passage 9 is opened on the other side portion (left side in FIG. 1) of the cylinder 1 that is separated from the intake port 4 about the cylinder axis C by about 180 °. A muffler (not shown) constituting an exhaust system is connected to the.

  A crankshaft 13 is supported inside the crankcase 2 via a bearing 12. The crankshaft 13 is provided with a crankpin 14 at a position displaced from the crankshaft center, and a connecting rod 18 connects the crankpin 14 and a piston pin 17 attached to the piston 11. A crank web 19 is provided on the crankshaft 13.

  A reed valve 20 is disposed in the intake passage 8 at a position close to the intake port 4. The reed valve 20 includes a valve body 21 having a valve hole 22 and a valve seat 23 that form a part of the intake passage 8, and a thin plate that opens and closes the valve hole 22 with a base end supported by the valve body 21. Shaped lead piece 24. The lead piece 24 is seated on the valve seat 23 in the closed position. The reed valve 20 is disposed at a position close to the intake port 4 when the air-fuel mixture M in the crank chamber 7 is compressed by the lowering of the piston 11 and includes a space communicating with the crank chamber 7. This is because the compression volume is made as small as possible to increase the compression efficiency of the air-fuel mixture M.

  The valve main body 21 is made of a metal material such as aluminum, and a cross section perpendicular to the flow path of the intake passage 8 is formed in an isosceles triangle, and a top portion protrudes downstream of the intake passage 8. As shown in FIG. 3, a plurality (two in this example) of valve holes 22 are provided side by side on both sides of the valve body 21 which are inclined. The lead pieces 24 are respectively arranged above and below so as to open and close the upper and lower valve holes 22. Two lead pieces 24 are formed by providing a slit 25b in a main body 25 made of, for example, a carbon plate, and each lead piece 24 opens and closes a corresponding valve hole 22. The main body 25 is provided with two screw insertion holes 25a.

  A pair of upper and lower reed valve stoppers 28 and 29 for restricting the maximum opening of the reed pieces 24 are provided outside the reed pieces 24. Each of the stoppers 28 and 29 is formed of, for example, a metal material such as iron or aluminum, and has a shape curved in a direction gradually separating from the valve seat surface 23a of the valve body 21 from the base end portion toward the tip end. is doing.

  4A and 4B are plan views showing the upper and lower stoppers 28 and 29, respectively. The stopper 28 on the upper side of FIG. 4A is provided with two screw insertion holes 28a at the base end, and an arc-shaped notch at the center of the tip corresponding to the cross-sectional shape of the intake transverse scavenging passage, which will be described later. 28b is formed. Further, the stopper 28 is formed with a lightening hole 28c having a width substantially the same as the width W of the notch 28b at a portion closer to the base end than the notch 28b. A pair of elongated holes 28d, 28d extending from the end portion toward the tip portion are formed. On the other hand, the stopper 29 on the lower side of FIG. 4B is the same as the existing one, and is a long hole-shaped hollow hole 29a extending from the base end portion toward the distal end portion in the central portion, A pair of triangular cutout holes 29b and 29b located on both sides of the hole 29a and a screw insertion hole 29c are formed. The stoppers 28 and 29 are reduced in weight by the lightening holes 28c, 28d, 29a, and 29b.

  As shown in FIG. 3, the valve body 21 is provided with a screw hole 21a, and the stoppers 28, 29 and the lead pieces 24, 24 are superposed at the base end portions thereof, so that the screw insertion holes 28a, 29c (FIG. 4 (b)) and 25a are screwed into the screw holes 21a and are fixed to the upper and lower surfaces of the valve body 21 in a cantilever manner.

  In the cylinder 1 of FIG. 1, a first scavenging passage 30 and a second scavenging passage 31 for introducing the air-fuel mixture M in the crank chamber 7 into the combustion chamber 3 are formed between the intake port 4 and the exhaust port 10. Has been. A communication passage 33 constituting a part (downstream portion) of a third scavenging passage 32 that is an intake crossing scavenging passage is formed in the cylinder 1 above the intake passage 8 shown in FIG. As shown in FIG. 5, the first and second scavenging passages 30, 31 are provided in pairs so that the communication passage 33 is located between the two second scavenging passages 31, 31. ing. As shown in FIG. 1, the upper ends of the first to third scavenging ports 30a, 31a, 32a, which are outlet openings to the cylinder bores 1a of the first to third scavenging passages 30, 31, 32, are connected to the exhaust port 10. The air-fuel mixture M, which is opened obliquely upward at a position slightly lower than the upper edge of the cylinder, is introduced into the combustion chamber 3 obliquely upward.

  As shown in FIG. 2, a circulation hole 11 a is provided in the peripheral wall of the piston 11. As indicated by a two-dot chain line in FIG. 2, the third scavenging passage 32 passes through the intake port 4 from the flow hole 11a, continues substantially across the intake passage 8, and continues to the communication passage 33. The third scavenging port 32a It is formed by the route to reach. A rib 34 is provided at the entrance of the communication passage 33 so as to protrude radially outward from the cylinder bore 1a. Thereby, the 3rd scavenging passage 32 is set to the suitable magnitude | size from which the passage area of the communicating path 33 can obtain moderate flow velocity. The width W of the notch 28b of the upper stopper 28 shown in FIG. 4 is substantially equal to the width of the communication passage 33 shown in FIG. 5, that is, the width of the third scavenging passage 32. Thus, the stopper 28 avoids adding a restriction to the third scavenging passage 32, and the third scavenging passage 32 is a smooth passage without a sudden passage area change in the flow direction.

Next, the operation of the two-stroke engine configured as described above will be described.
First, as shown in FIG. 1, when the piston 11 in the cylinder 1 rises toward the top dead center in the intake / compression stroke, the inside of the crank chamber 7 becomes negative pressure, and the upper and lower lead pieces 24, The air-fuel mixture M that has flown in the intake passage 8 is opened to the crank chamber 7 from the intake port 4 through the opened reed valve 20. Is done.

  In this intake / compression stroke, the air-fuel mixture M compressed in the combustion chamber 3 is ignited and burned, so that the piston 11 descends due to the expansion force of the combustion gas, and the exhaust / scavenging stroke shown in FIG. Move on. When the piston 11 descends toward the bottom dead center in the exhaust / scavenging stroke, the air-fuel mixture M in the crank chamber 7 passes through the first and second scavenging passages 30 and 31 and the first and second scavenging ports. By being introduced obliquely upward into the combustion chamber 3 from 30a, 31a, scavenging in the combustion chamber 3 is performed. In addition to this, in this two-stroke engine, the flow hole 11a of the piston 11 lowered near the bottom dead center communicates with the intake port 4 to form the third scavenging passage 32. The air-fuel mixture M is introduced through the third scavenging passage 32 from the third scavenging port 32b into the combustion chamber 3 in an obliquely upward direction. Thereby, scavenging in the combustion chamber 3 is further promoted.

  Since the cutout portion 28b provided in the upper stopper 28 shown in FIG. 5 corresponds to the passage cross-sectional shape of the third scavenging passage 32, the third scavenging passage 32 is not restricted by the stopper 28. . As a result, the flow of the air-fuel mixture (scavenging) M passing through the third scavenging passage 32 is restricted, particularly in the rotational speed range from 2,000 rpm when idling at a low scavenging speed to about 4,000 rpm at low speed. Is promoted than if present. Further, since the upper stopper 28 is provided with a lightening hole 28c formed with substantially the same width as the cutout portion 28b, a part of the air-fuel mixture M in the third scavenging passage 32 passes through the lightening hole 28c. Therefore, the flow of the air-fuel mixture M is further promoted. As a result, scavenging efficiency is improved and engine output is improved.

  In addition, in the upper stopper 28 shown in FIG. 4A, the cutout portion 28b and the cutout hole 28c can be combined to form a large cutout portion 28e as shown in FIG. Thus, the smooth flow of the air-fuel mixture M in the third scavenging passage 32 shown in FIG. 5 is further promoted. Although not included in the present invention, the opening degree is regulated by removing the upper stopper 28 in FIG. 1 and bringing the upper lead piece 24 into contact with the rib 34 at the inlet of the communication path 33. May be. In that case, since the stopper 28 does not exist, the third scavenging passage 32 is not restricted by the stopper 28 in the scavenging stroke.

It is front sectional drawing which shows the intake and compression stroke in the 2-stroke engine which concerns on one Embodiment of this invention. It is front sectional drawing which shows the exhaust_gas | exhaustion / scavenging process in a 2-stroke engine same as the above. It is a disassembled perspective view which shows a reed valve. (A), (b) is a top view which shows the stopper of an upper side and a downward side, respectively. It is sectional drawing along the VV line of FIG. It is a top view which shows the modification of a stopper.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Cylinder 3 Combustion chamber 4 Intake port 7 Crank chamber 8 Intake passage 10 Exhaust port 20 Reed valve 21 Valve body 24 Lead piece 28 Stopper 28b Notch 28c Meat removal hole 28e Notch 30 First scavenging passage (other scavenging passages)
31 Second scavenging passage (other scavenging passages)
32 3rd scavenging passage (intake crossing scavenging passage)
M Mixture C Cylinder axis

Claims (4)

An intake passage for introducing an air-fuel mixture from the intake port to the crank chamber;
An intake crossing scavenging passage for introducing the air-fuel mixture in the crank chamber into the combustion chamber through the intake passage;
A reed valve disposed in the intake passage and proximate to the intake port;
A two-stroke engine in which a stopper for regulating the opening of the lead piece in the reed valve is located outside the scavenging passage so as to avoid adding a throttle to the scavenging passage.   2. The two-stroke engine according to claim 1, wherein the stopper is supported by a valve body whose base end portion supports the lead piece so as to be freely opened and closed, and a notch portion corresponding to the scavenging passage is formed at a distal end portion.   The two-stroke engine according to claim 2, wherein a lightening hole having substantially the same width as the notch is formed in a portion of the stopper closer to the base end than the notch. 4. The exhaust port according to claim 1, wherein an exhaust port is formed at a position approximately 180 ° away from the intake port in the cylinder about the cylinder axis, and the air-fuel mixture in the crank chamber is placed between the intake port and the exhaust port. A two-stroke engine in which another scavenging passage to be introduced into the combustion chamber is formed.

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