JPH09287456A - Exhaust timing control device for two-stroke engine - Google Patents

Abstract

(57) [Abstract] [PROBLEMS] To provide an exhaust timing control device for a two-cycle engine capable of further improving engine performance by always maintaining an exhaust timing line formed by an exhaust control valve in a substantially horizontal straight line. thing. An exhaust timing control device for a two-cycle engine, in which first and second slide valves 11 and 12 (exhaust control valves) that operate according to engine rotation speed are used to open and close an upper portion of an exhaust port 2a to control exhaust timing. The upper surfaces of the first and second slide valves 11 and 12 forming the exhaust timing lines S ₁ and S ₂ are formed into a concave curved surface when viewed from the insertion direction of the first and second slide valves 11 and 12. According to the invention, the first and second slide valves 11,
12 Cylinder (piston) that has a concave curved surface and a cylindrical surface
Exhaust timing lines S ₁ and S ₂ formed as intersection lines with
Becomes a substantially horizontal straight line, and a large opening area is secured in the exhaust port 2a during blowdown when the piston descends and the exhaust port 2a begins to open. As a result, the exhaust pressure waveform becomes large and the engine performance is further improved. To be

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exhaust timing control device for a two-cycle engine, which controls exhaust timing according to engine speed.

[0002]

2. Description of the Related Art In a two-cycle engine in which the piston itself functions as an exhaust valve, the exhaust timing is determined by the upper edge position of the exhaust port opening on the inner peripheral surface of the cylinder. The exhaust timing depends on the engine speed. In order to improve the engine output as optimal, an exhaust control valve that opens and closes the upper part of the exhaust port is provided, and this exhaust control valve is opened and closed according to the engine speed to control the exhaust timing. Devices have been used for some time.

Here, an example of the exhaust timing control device is shown in FIG.

That is, FIG. 16 is a vertical sectional view of a cylinder body 101 of a two-cycle engine equipped with a conventional exhaust timing control device 110. The exhaust timing control device shown in the drawing is an angle inclined in the sliding direction of 110 and piston 108. A plate-shaped exhaust control valve (hereinafter,
A slide valve) 111 is moved to the upper part of the exhaust passage 102 near the exhaust port 102a to change the exhaust timing between the low rotation speed range and the high rotation speed range, thereby improving the engine output over the entire rotation speed range. Is intended.

By the way, in recent years, there has been a tendency to increase the opening area of the exhaust passage in order to improve the exhaust efficiency and improve the output of the engine. However, when the opening area of the exhaust passage becomes large, the width of the control valve increases accordingly. Also grows.

However, when the width of the control valve becomes large, the thermal strain of the control valve becomes large and the sliding resistance of the control valve becomes large.

Therefore, as shown in FIG. 17, two control valves 112 are provided above the exhaust passage 102 having a large opening area, and the amount of thermal strain of each control valve 112 is suppressed to a small value to reduce the sliding resistance thereof. Attempts have been made (eg
See JP-A-62-32216). FIG. 17 is a plan view schematically showing the relationship between the control valve 112 and the cylinder 104 and the exhaust passage 102, and the control valve 112 is slid in the direction of arrow C in the figure.

By the way, the front end face 1 of each control valve 112
Since 12a is an arc surface having a curvature equal to that of the cylinder 104, as shown in FIG. 17, the outer tips a, a of the control valve 112 are different from the inner tips b, b. It greatly protrudes by ΔL in the sliding direction (direction of arrow C in the drawing). For this reason, as shown in FIG. 18, even if the control valve 112 is retracted from the exhaust passage 102 and is in the fully open state, the outer tip portions a and a thereof project into the exhaust passage 102 to disturb the exhaust flow, and as a result, However, there is a problem that the exhaust resistance increases and the improvement of the engine output is hindered. still,
FIG. 18 is a view taken in the direction of the arrow X in FIG.
a Exhaust port.

Therefore, as shown in FIG. 19, it has been proposed to install a pair of left and right slide valves 121 so that their center lines in the width direction are inclined with respect to a plane perpendicular to the sliding direction of the piston. According to this, since the shape of the inner end surface of each slide valve 121 follows the shape of the inner wall of the exhaust passage 102, when each slide valve 121 withdraws from the exhaust passage 102 and is in a fully opened state, the outer tip thereof. The portion does not project into the exhaust passage 102, and the exhaust gas is exhausted through the exhaust passage 102.
Can flow smoothly.

[0010]

By the way, on the right side of FIG. 9 (the side labeled "conventional example"), there are two upper and lower slide valves (first Exhaust timing lines S ₁ 'and S ₂ ' of the slide valve and the second slide valve are shown respectively, but as shown in the figure, the exhaust timing line when the valve is fully opened (when the first and second slide valves are fully opened). (Upper edge of exhaust port) S ₀ '
Is a horizontal straight line, whereas the exhaust timing lines S ₁ 'and S ₂ ' of both slide valves are curves upwardly convex except when the valves are fully opened (when the first and second slide valves are operating). turn into. This is the exhaust timing line S ₁ ',
Since the upper surfaces of both slide valves forming S ₂ 'are both flat, an exhaust timing line S formed as an intersection of this flat surface and a cylinder (piston) which is a cylindrical surface.
_{Because 1} 'and S ₂ ' draw a curve.

Therefore, in terms of engine performance, it is best that the exhaust timing line is a horizontal straight line, and ideally the exhaust timing line moves up and down while maintaining a horizontal straight line as the engine speed changes. This is because the larger the exhaust port opening area at the time of blowdown at which the piston descends and the exhaust port starts to open, the larger the exhaust pressure waveform becomes, which contributes to the improvement of engine performance.

However, in the conventional exhaust timing control device, as described above, the exhaust timing line of the exhaust control valve is an upwardly convex curve except when the valve is fully opened. The highest,
As the piston descends, the timing at which the exhaust port begins to open becomes earlier.

Therefore, when the exhaust timing line is lowered to the required horizontal position, both ends of the exhaust timing line are lowered to a position lower than the horizontal position, and the exhaust port opening area becomes unnecessarily small and high. The performance cannot be obtained.

The present invention has been made in view of the above problems, and an object thereof is to keep the exhaust timing line formed by the exhaust control valve in a substantially horizontal straight line to further improve the engine performance. It is an object of the present invention to provide an exhaust timing control device for a two-cycle engine that can perform the operation.

[0015]

In order to achieve the above object, the invention according to claim 1 controls the exhaust timing by opening and closing the upper portion of the exhaust port by an exhaust control valve which operates according to the engine speed. In the exhaust timing control device for a cycle engine, a surface of the exhaust control valve forming an exhaust timing line is formed into a concave curved surface shape when viewed from the insertion direction of the exhaust control valve.

According to a second aspect of the present invention, in the first aspect of the invention, the exhaust control valve is a plate provided slidably at an angle inclined with respect to the cylinder radial direction in the piston sliding direction. It is characterized in that the slide valve is formed into a concave curved surface shape.

According to a third aspect of the present invention, in the first aspect of the invention, the exhaust control valve is constituted by a flap valve pivotably mounted on a cylinder body, and the upper surface of the flap valve and the cylinder. It is characterized in that the upper surface of the valve insertion hole of the body is molded into a concave curved surface.

Therefore, according to the present invention, since the surface forming the exhaust timing line of the exhaust control valve is formed into a concave curved surface, it is used as an intersecting line between the concave curved surface of the exhaust control valve and the cylinder (piston) which is a cylindrical surface. The formed exhaust timing line has a substantially horizontal straight line, and a large exhaust port opening area is secured during blowdown when the piston descends and the exhaust port begins to open.As a result, the exhaust pressure waveform becomes large and engine performance is further improved. Improvement is achieved.

[0019]

Embodiments of the present invention will be described below with reference to the accompanying drawings.

<First Embodiment> FIG. 1 is a vertical cross-sectional view of a cylinder body of a two-cycle engine equipped with an exhaust timing control device according to a first embodiment of the present invention. FIG. 2 is a view in the direction of arrow A in FIG. 3 and 4 are explanatory views of the operation of the drive mechanism of the exhaust control valve (slide valve), and FIGS. 5 to 7 are partial sectional views for explaining the operation of the exhaust timing control device.
FIG. 8 is a perspective view of the exhaust port as seen from the valve operating axis direction,
FIG. 9 is a diagram showing an exhaust timing line in comparison with a conventional one (a diagram in which the exhaust port is viewed in the horizontal direction from the inside of the cylinder).

As shown in FIG. 1, the two-stroke engine according to this embodiment has a cylinder body 1 and a center rib 1a.
The exhaust passage 2 and the scavenging passage 3 are divided into two parts on the left and right sides, and these exhaust passage 2 and the scavenging passage 3 open to the cylinder 4 as an exhaust port 2a and a scavenging port 3a, respectively. Here, the upper edge of each exhaust port 3a (the exhaust timing line S ₀ when the valve is fully opened) is located above the upper edge of the scavenging port 3a.

Water jackets 5, 6, and 7 are formed on the cylinder body 1.
A cylinder head (not shown) is attached to the upper part of the above, a crankcase (not shown) is attached to the lower part, and a piston 8 is vertically slidably fitted in the cylinder 4.

The cylinder body 1 is provided with the exhaust timing control device 10 according to the present invention.
The exhaust timing control device 10 has upper and lower two-stage plate-shaped first and second slide valves 11 and 12 which constitute an exhaust control valve provided above the exhaust passage 2.
The first and second slide valves 11 and 12 are provided for each of the two divided exhaust passages 2.

The first and second slide valves 11 and 12 are adapted to vary the exhaust timing by appearing and retracting independently from the exhaust passage 2 as will be described later. These are shown in FIG. A plane (horizontal plane) that is inclined downward in the sliding direction toward the axis center of the cylinder 4 in the sliding direction and is perpendicular to the sliding direction (vertical direction) of the piston 8 in the width direction as shown in FIG. Is inclined by a predetermined angle with respect to.

By the way, the shaft portion 11a of the first slide valve 11 is the flange portion 12a of the second slide valve 12.
Is slidably inserted in and held by the second slide valve 12
A cutout hole 11c is formed in a part of the hole.

Thus, the first and second slide valves 11, 1
Each of the two valve bodies 11b and 12b is closely and vertically stacked so as to be slidable independently of each other, but as shown in FIG. 8, when viewed from the sliding direction of both slide valves 11 and 12, The upper surface of the valve insertion hole 1b of the cylinder body 1 and the upper surface of the second slide valve 12 are centered on a point O above them and horizontally offset from the axial center line L of the cylinder 4 by e. It is formed into a concave curved surface of a convex arcuate curved surface under the radius R1, and the lower surface of the second slide valve 12 and the upper surface of the first slide valve 11 have a radius R2 (> R1) centered on the same point O. It is formed into a concave curved surface having a downwardly convex arcuate curved surface. Originally, the upper surface of the valve insertion hole 1b of the cylinder body 1 and the upper surface of the second slide valve 12 should have a geometrically elliptical (arc) shape, but in order to facilitate processing, an arc is used instead. And approximated.

By the way, the exhaust passage 2 of the cylinder body 1
A drive shaft 13, which is rotatably driven by a servo motor (not shown), is rotatably supported by bearings 14 (see FIG. 2) at both ends of the drive shaft 13 and is arranged long in the direction perpendicular to the plane of FIG. As shown in FIG. 2, an arm 13a for driving the pair of left and right first slide valves 11 is provided at the center of the drive shaft 13, and an arm 13b for driving each second slide valve 12 is provided at both ends. Each is integrally formed.

Here, the first and second slide valves 11, 1
The driving method of No. 2 will be described with reference to FIGS. 3 and 4.

As shown in FIG. 3, each first slide valve 11
A pin 15 is provided at the tip of the shaft portion 11b of the shaft 11b in a direction perpendicular to the axis, and the pin 15 is fitted in a fitting groove 12a-1 of a fork-shaped arm 12a formed in the drive shaft 13. .

Therefore, the drive shaft 13 is driven to drive the arm 13
When a is rotated in the direction of the arrow shown in the figure, the rotation of the arm 13a is converted into a reciprocating linear movement of the first slide valve 11 in the direction of the arrow shown in the figure, whereby the first slide valve 11 is opened and closed (FIG. 5). Through FIG. 7).

On the other hand, as shown in FIG. 4, a shaft portion 12d integrally provided on the flange portion 12a of the second slide valve 12 is provided.
A substantially rectangular notch hole 12d-1 is vertically formed therethrough, and a notch groove 12d-2 having an arcuate curved surface is formed therein, and each arm 13b formed on the drive shaft 13 is formed.
Is formed in an arcuate curved surface having the same curvature as the arcuate curved surface of the cutout groove 12d-2.

Then, as shown in FIG. 4 (a), the arm 13b rotates in the clockwise direction, and the top of the arm 13b is aligned with the notch groove 12d-2 formed in the shaft portion 12d of the second slide valve 12. In the fitted state, the second slide valve 12 moves to the right and is in the fully closed state (see FIG. 5), and from that state, the drive shaft 13 rotates in the opposite direction to the state shown in FIG. 4 (b). As shown in the figure, the second slide valve 12 remains stationary and remains fully closed until the arm 13b engages with the cutout hole 12d-1 of the second slide valve 12. Then, when the arm 13b is further rotated counterclockwise from the state shown in FIG. 4 (b),
The arm 13b causes the second slide valve 12 to move leftward and gradually open, and when the second slide valve 12 is opened in the state shown in FIG.
The slide valve 12 is fully opened (see FIG. 7).

Next, the operation of the exhaust timing control device 10 will be described with reference to FIGS.

When the two-cycle engine operates, the exhaust timing control device 10 is driven according to the rotation speed of the engine to control the exhaust timing.

That is, in the low rotation speed region where the engine rotation speed is lower than a predetermined value, the first and second slide valves 11 and 12 project into the exhaust passage 2 and the upper portion of the exhaust passage 2 as shown in FIG. The exhaust gas timing is determined by the exhaust timing line (hereinafter referred to as the first valve timing line S ₁ ) formed by the upper edge of the valve body 11b of the first slide valve 11 at this time. Is delayed. That is, in the expansion stroke, the piston 8 descends, and exhaust is started from the time when the top surface of the piston 8 reaches the first valve timing line S ₁ .

After that, when the engine speed increases beyond a predetermined value, the drive shaft 1 is driven by a servo motor (not shown).
3 is rotated counterclockwise in FIG. 5, and the arm 13b formed integrally with the drive shaft 13 is also rotated in the same direction, but as described above (see FIG. 4), the arm 13b is the second one.
Notch hole 12d formed in the shaft portion 12d of the slide valve 12
As shown in FIG. 6, the second slide valve 12 is kept fully closed until it is engaged with -1, and only the first slide valve 11 is gradually opened so that the exhaust timing is set to the second slide valve 12.
The exhaust timing is determined by the exhaust timing line formed by the upper edge of the valve body 12b (hereinafter referred to as the second valve timing line S ₂ ), and the exhaust timing is advanced as the engine speed increases. That is, in the expansion stroke, the piston 8
Of the second valve timing line S with the top surface of the piston 8 positioned above the first valve timing line S ₁
Exhaust is started from the point when it reaches ₂ , so the exhaust timing is advanced as described above.

When the engine speed further increases from the state shown in FIG. 6, the arm 13b of the drive shaft 13 is formed in the shaft portion 12d of each second slide valve 12 and the cutout hole 1 is formed.
2d-1 for engaging the first and second slide valves 1
1, 12 are moved integrally in the opening direction as the engine speed increases, and the exhaust timing is gradually advanced.

Thus, as shown in FIG. 7, the first and second
When the slide valves 11 and 12 are completely retracted from the exhaust passage 2 into the cylinder body 1, both slide valves 11 and 12 are fully opened, and the exhaust timing is the exhaust timing line S ₀ formed by the upper edge of the exhaust port 2a. The exhaust timing is the earliest. That is, since the piston 8 descends in the expansion stroke and exhaust is started from the time when the top surface of the piston 8 reaches the upper edge of the exhaust port 2a, the exhaust timing is further advanced.

As described above, the exhaust timing control device 1
The engine output can be improved by optimally controlling the exhaust timing in accordance with the engine speed by setting 0, but in the present embodiment, as shown in FIG. 8, sliding of both slide valves 11 and 12 is performed. Since the valve insertion hole 1b, the upper surface of the first slide valve 11 and the upper surface of the second slide valve 12 are formed in a concave curved surface convex downward when viewed from the moving direction, the valve insertion hole 1b and the first slide valve 11 are formed. Of the exhaust timing lines S ₀ , S ₁ and S _{2 which} are formed as intersections between the concave curved surface on the upper surface of the second slide valve 12 and the cylinder 4 (piston 8) which is a cylindrical surface. When viewed, it is in a substantially horizontal straight line shape as shown on the left side of FIG. 9 (the side labeled "the present invention"). Therefore, the piston 8
A large opening area is secured in the exhaust port 2a at the time of blowdown in which the exhaust port 2a starts to open and the exhaust port 2a starts to open. As a result, the exhaust pressure waveform is increased and the engine performance is further improved.

<Second Embodiment> Next, a second embodiment of the present invention will be described with reference to FIGS. FIG.
5 is a longitudinal sectional view of a cylinder body of a two-cycle engine including an exhaust timing device according to a second embodiment of the present invention, FIG. 11 is a view in a direction of arrow B in FIG. 10, FIG. 12 and FIG.
3 is a partial sectional view showing the operation of the exhaust timing control device,
14 is a perspective view of the exhaust port as seen from the direction of the valve insertion hole, and FIG. 15 is a view of the exhaust port as seen from the inside of the cylinder in the horizontal direction. In these figures, the same elements as those shown in FIGS. 1 to 9 are shown. Are denoted by the same reference numerals, and description thereof will be omitted below.

As shown in FIG. 10, an exhaust timing control device 20 according to the present embodiment is provided above the exhaust passage 2 of the cylinder body 1. The exhaust timing control device 20 is provided in each exhaust passage 2. A total of two flap valves 21, which are exhaust control valves that open and close, and a holder 2 that stores and holds each flap valve 21 in a freely openable and closable manner by a fulcrum pin 22.
3 is included.

Each of the holders 23 is incorporated into a valve insertion hole 1b formed in the cylinder body 1 so as to be inclined downward toward the center of the cylinder. It is fitted. A rod 25 is slidably inserted into each bush 24, and one end of the rod 25 has a long hole 25.
a is formed, and the flap valve 21 is provided in the long hole 25a.
The connecting pin 26 projecting from is engaged. The other end of the rod 25 extends to the outside of the holder 23, and a connecting pin 27 is inserted and held at the extended end.

On the other hand, the exhaust passage 2 of the cylinder body 1
A drive shaft 28, which is rotatably driven by a servomotor (not shown), is rotatably supported by bearings 29 (see FIG. 11) above the rod 25 and in the vicinity of the extending end of the rod 25. Two left and right cranks 30 are integrally formed in the middle of the drive shaft 28. A concave groove 30a is partially formed in each crank 30, and a coupling pin 27 inserted and held at the end of the rod 25 is engaged with the concave groove 30a. or,
A plate-shaped spring member 31 is connected to the end surface of each crank 30 by two screws 32 on the left and right, and a pair of left and right leaf springs 31a integrally formed on the spring member 31 abuts on the connecting pin 27. The rod 25 to the right in FIG. 10 (direction to close the flap 21 valve).

By the way, in the present embodiment, FIG.
As shown in FIG. 4, the cross section of the valve insertion hole 1b is inverted L
The upper surface of the flap valve 21 is formed into a concave curved surface having a downwardly convex arcuate curved surface shape.
The upper surface of is also formed in the same shape. The flap valve 21
The end surface 21a facing the cylinder is formed by machining into an arcuate curved surface along the cylinder 4.

Next, the operation of the exhaust timing control device 20 according to this embodiment will be described.

The drive shaft 28 is driven by a servo motor (not shown).
Is rotated by a predetermined angle, the drive shaft 28 is rotated by the cranks 30 of the bushes 2 of the rods 25.
4 is converted into a reciprocating linear motion, and the reciprocating linear motion of the rod 25 swings around the fulcrum pin 22 of each flap valve 21 to partially open and close the upper portion of the exhaust port 2a,
As a result, the exhaust timing is optimally controlled according to the engine rotation speed.

Thus, each flap valve 21 is opened and closed according to the engine rotation speed, and in the low rotation speed region where the engine rotation speed is lower than a predetermined value, the flap valve 21 is in the fully closed state as shown in FIG. At this time, the exhaust timing is determined by the exhaust timing line S ₁ (see FIG. 15) formed by the upper edge of the flap valve 21, and the exhaust timing is delayed. That is, in the expansion stroke, the piston 8 shown in FIG. 10 descends, and exhaust is started from the time when the top surface of the piston 8 reaches the exhaust timing line S ₁ .

After that, when the engine speed exceeds a predetermined value and increases, a drive shaft 2 is driven by a servo motor (not shown).
8 is rotated counterclockwise in FIG. 12, and the rotation of the drive shaft 28 is caused by the cranks 30 and the rods 25, respectively.
Is converted into a linear motion along the bush 24, and the linear motion of the rod 25 is converted into a swing motion around the fulcrum pin 22 of the flap valve 21, and the flap valve 21 is centered around the fulcrum pin 22 and the exhaust port 2a. Since the upper part of the engine begins to open partially, the exhaust timing is gradually advanced as the engine speed increases.

In the high engine speed range in which the engine speed exceeds a predetermined value, the flap valve 21 is completely retracted from the exhaust passage 2 into the cylinder body 1 as shown in FIG. The timing is determined by the exhaust timing line S ₀ (see FIG. 15) formed by the upper edge of the valve insertion hole 1b (exhaust port 2a), and the exhaust timing is the earliest. That is, in the expansion stroke, the piston 8 shown in FIG. 10 descends, and exhaust is started from the time when the top surface of the piston 8 reaches the exhaust timing line S ₀ (upper edge of the exhaust port 2a), so the exhaust timing is It can be accelerated.

As described above, also in this embodiment,
Although the engine output can be improved by optimally controlling the exhaust timing according to the engine rotation speed by the exhaust timing control device 20, in the present embodiment, as shown in FIG. 14, the valve insertion hole 1b is provided.
When viewed from the direction, the upper surface of the valve insertion hole 1b and the flap valve 2
Since the upper surface of No. 1 is formed in a downwardly convex concave curved surface, the exhaust timing line S formed as an intersection line between the concave curved surface of the upper surface of the valve insertion hole 1b and the cylinder 4 (piston 8) when the valve is fully opened. ₀ is shown in Fig. 1 when viewed from the horizontal direction.
As shown in FIG. 5, it becomes a substantially horizontal straight line. Therefore, a large opening area is secured in the exhaust port 2a during blowdown when the piston 8 descends and the exhaust port 2a begins to open.
As a result, the exhaust pressure waveform becomes large and the engine performance is further improved.

In the above embodiments, the case where the present invention is applied to the exhaust timing control device in which the exhaust control valve is provided in each of the exhaust passages divided into the left and right by the center rib is mentioned. Needless to say, the above is similarly applicable to an exhaust timing control device in which a single exhaust control valve is provided in a single exhaust passage.

[0052]

As is apparent from the above description, according to the present invention, the surface forming the exhaust timing line of the exhaust control valve is formed into a concave curved surface, so that the exhaust control valve has a concave curved surface and a cylindrical surface. The exhaust timing line formed as a line of intersection with the cylinder (piston) becomes a substantially horizontal straight line, and a large exhaust port opening area is secured during blowdown when the piston descends and the exhaust port begins to open, increasing the exhaust pressure waveform. As a result, the engine performance can be further improved.

[Brief description of drawings]

FIG. 1 is a vertical cross-sectional view of a cylinder body of a two-cycle engine including an exhaust timing control device according to a first embodiment of the present invention.

FIG. 2 is a view in the direction of arrow A in FIG. 1;

FIG. 3 is an operation explanatory view of a drive mechanism of an exhaust control valve (first slide valve).

FIG. 4 is an operation explanatory view of a drive mechanism of an exhaust control valve (second slide valve).

FIG. 5 is a partial cross-sectional view for explaining the operation of the exhaust timing control device according to the first embodiment of the present invention.

FIG. 6 is a partial cross-sectional view for explaining the operation of the exhaust timing control device according to the first embodiment of the present invention.

FIG. 7 is a partial cross-sectional view for explaining the operation of the exhaust timing control device according to the first embodiment of the present invention.

FIG. 8 is a perspective view of the exhaust port of the two-cycle engine including the exhaust timing control device according to the first embodiment of the present invention, as viewed from the inside of the cylinder in the valve operating axis direction.

FIG. 9 is a diagram showing an exhaust timing line in Embodiment 1 of the present invention in comparison with a conventional one (a diagram in which an exhaust port is viewed in a horizontal direction from the inside of a cylinder).

FIG. 10 is a vertical sectional view of a cylinder body of a two-cycle engine including an exhaust timing device according to a second embodiment of the present invention.

11 is a view in the direction of arrow B in FIG.

FIG. 12 is a partial cross-sectional view showing the operation of the exhaust timing control device according to the second embodiment of the present invention.

FIG. 13 is a partial cross-sectional view showing the operation of the exhaust timing control device according to the second embodiment of the present invention.

FIG. 14 is a perspective view of an exhaust port of a two-cycle engine including an exhaust timing control device according to a second embodiment of the present invention, as seen from a valve insertion hole direction.

FIG. 15 is a view of the same exhaust port of the two-cycle engine including the exhaust timing control device according to the second embodiment of the present invention as viewed horizontally from the inside of the cylinder.

FIG. 16 is a vertical cross-sectional view of a cylinder body of a two-cycle engine including a conventional exhaust timing control device.

FIG. 17 is a plan view schematically showing a relationship between a cylinder, an exhaust passage, and a control valve in a two-cycle engine including a conventional exhaust timing control device.

FIG. 18 is a view taken in the direction of arrow X in FIG.

FIG. 19 is a view similar to FIG. 18 showing another conventional example.

[Explanation of symbols]

1 Cylinder body 1b Valve insertion hole 2 Exhaust passage 2a Exhaust port 4 Cylinder 10, 20 Exhaust timing control device 11, 12 Slide valve (exhaust control valve) 21 Flap valve (exhaust control valve) S ₀ , S ₁ , S ₂ Exhaust timing line

Claims (3)

[Claims] 1. An exhaust timing control device for a two-cycle engine, wherein an exhaust control valve that operates according to an engine rotation speed opens and closes an upper portion of an exhaust port to control exhaust timing, wherein an exhaust timing line of the exhaust control valve is formed. An exhaust timing control device for a two-cycle engine, characterized in that the surface to be formed is formed into a concave curved surface shape when viewed from the insertion direction of the exhaust control valve. 2. The exhaust control valve is composed of a plate-shaped slide valve slidably provided at an angle inclined in the sliding direction of the piston with respect to the cylinder radial direction, and at least the upper surface of the slide valve is concave. The exhaust timing control device for a two-cycle engine according to claim 1, wherein the exhaust timing control device is formed into a curved surface. 3. The exhaust control valve is composed of a flap valve pivotably mounted on a cylinder body, and an upper surface of the flap valve and an upper surface of a valve insertion hole of the cylinder body are formed in a concave curved surface shape. The exhaust timing control system for a two-cycle engine according to claim 1.