JPH0357286B2 - - Google Patents

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to an exhaust timing control device for a two-stroke engine, and particularly relates to an exhaust timing control device for a two-stroke engine. The present invention relates to an exhaust timing control device for a two-stroke engine that is provided with a valve body that functions as the upper edge of the mouth.

[Conventional technology]

A conventional exhaust timing control device has a rotary valve body provided at the cylinder head side edge of an exhaust passage that opens into the inner circumferential surface of the cylinder. The valve body is
Its circumferential surface forms a drum shape along the inner circumferential surface of the cylinder, and the shape is cut in half along the axial direction. The valve body is rotatably provided in a recess formed in the cylinder head side edge of the exhaust passage so that the direction of its rotation axis is orthogonal to the axial direction of the cylinder. By rotating the valve body, the edge of the circumferential surface facing the inner surface of the cylinder moves in the axial direction of the cylinder, changing the opening height of the exhaust passage and changing the exhaust timing. Ta.

[Problem that the invention seeks to solve]

However, since the conventional exhaust timing control device for two-stroke engines has a valve body shaped like a drum, the diameter at both ends of the valve body is extremely large compared to the diameter at the middle part, and therefore the valve body itself has to be enlarged. I couldn't escape the trend. As a result, the recess for accommodating the valve body becomes correspondingly large, and the thickness of the cylinder body is reduced accordingly, which is disadvantageous in terms of strength. In particular, the wall thickness of the cylinder body sandwiched between the valve body and the inner peripheral surface of the cylinder is thin because the valve body is of a rotating type, which is also disadvantageous in terms of strength. Because of the above, there was a risk that the cylinder would suffer thermal deformation or the like. In addition, in the conventional exhaust timing control device for a two-stroke engine, the rotation axis of the valve body is arranged so as to be orthogonal to the axial direction of the cylinder, and when the valve body is assembled into the accommodating portion of the cylinder body, the valve body is placed in the center of the drum shape. A valve body divided into left and right parts is inserted from the side of the cylinder in a direction perpendicular to the axial direction of the cylinder. Therefore, in the case of a parallel multi-cylinder engine, there was a problem that each cylinder had to be separated so that adjacent cylinders would not get in the way when inserting and assembling the valve disc, making it impossible to use a multi-cylinder integrated cylinder. .

In view of this conventional situation, an exhaust system for a two-stroke engine using a plate-shaped slide valve as a valve body has been proposed by the same applicant as the present applicant (see Japanese Utility Model Application No. 51-39112).

As shown in FIG. 5, this proposed device is a two-stroke engine in which an exhaust port 102 that is opened and closed by a piston is provided on the wall of a cylinder 101, and an exhaust passage 103 is provided that slopes downward from the exhaust port 102. In the exhaust passage 10, a plate-shaped slide valve 104 for opening and closing is installed at the upper part of the exhaust port 102.
3, so as to slide horizontally in the radial direction of the cylinder toward the exhaust port 102, and by moving the slide valve 104 back and forth, the upper part of the exhaust port 102 closes when the engine is running at low speed and opens when the engine is running at high speed. This allows high output to be obtained both during high-speed and low-speed operation.

However, in this device, since the slide valve 104 is a horizontal slide, the following problems remain.

That is, as shown in FIG. 6B, which will be described later, the timing of the movement of the valve body and the timing of the exhaust do not correspond to each other, resulting in discontinuous exhaust timing, and the output characteristics of the engine change from on to off.
It should be close to off control [Figure 6 B-a,
(see b, c)], stroke L ₂ of slide valve 104
becomes larger and becomes larger as a whole [Figure B
-D], and the moment _M2 due to the exhaust pressure acting on the slide valve 104 becomes large, making it necessary to increase the valve thickness [see B-E in the same figure].

The present invention was made in view of these conventional problems.The purpose of the present invention is to be able to continuously change the exhaust timing, eliminate the drop in output during high-speed operation, prevent sliding failure of the valve body, and improve overall performance. An object of the present invention is to provide an exhaust timing control device for a two-stroke engine that can be made more compact.

[Means for Solving the Problems] In order to achieve the above object, the present invention provides a valve that functions as the upper edge of the exhaust port on the upper surface of the exhaust passage near the exhaust port, which has an exhaust port that opens into the inner circumferential surface of the cylinder. A valve body is provided, and a valve body is slidably inserted into a hole that opens near the exhaust port of the exhaust passage of the cylinder.
In the exhaust timing control device of a cycle engine,
The hole is formed at an angle with respect to the axis of the cylinder so as to descend toward the exhaust port, and the tip of the valve body is formed with an acute angle in its longitudinal cross section, so that the valve body can be easily moved during high-speed operation. When the valve body is retracted into the hole, the tip of the valve body is almost flush with the upper inner wall surface of the exhaust passage, and when the valve body protrudes from the hole into the exhaust passage during low-speed operation, the tip of the valve body is The piston is characterized by a structure in which the portion is close to the side wall surface of the piston.

[Effect]

With such a configuration, the valve body is fitted into the hole drilled at an angle with respect to the axis of the cylinder,
By sliding the valve body diagonally with respect to the axis of the cylinder, the exhaust timing is continuously changed.
It becomes possible to efficiently obtain high output over almost the entire operating range. Further, as the stroke of the valve body moving forward and backward becomes smaller, the moment due to the exhaust pressure acting on the valve body also becomes smaller, and the valve thickness can be reduced, thereby making it possible to make the valve body more compact as a whole.

Note that the above configuration and the salience of its effects will be more clearly understood from the following explanation.

FIGS. 6A and 6B are diagrams for explaining the functions of the diagonally sliding valve body in the present invention and the horizontally sliding valve body in the conventional device in comparison.

In addition, in FIG. 6A, 10 is a cylinder body, 30 is an exhaust passage, 34 is an exhaust port, 36 is a hole,
38 is a valve body, L ₁ is a stroke until the valve body 38 is completely immersed in the hole 36, and H is a portion that functions as the upper edge of the exhaust port that changes the exhaust timing, and indicates the opening degree of the exhaust port. When the upper edge of the piston passes H, the combustion gas pressure in the cylinder is suddenly lowered to determine the exhaust timing. l is the distance between the tip of the valve body and the inner peripheral surface of the cylinder, P is the exhaust pressure acting on the tip of the valve body, R ₁ is the length of the tip of the valve body from the opening of the hole 36 at the maximum protrusion position, M ₁ is the moment due to the exhaust pressure acting on the valve body 38.

In addition, in FIG. 6B, 101 is a cylinder;
102 is an exhaust port, 103 is an exhaust passage, 104 is a slide valve, 106 is a gap created between the tip of the slide valve and the inner wall surface of the exhaust passage, L ₂ , R ₂ , M ₂ are L ₁ R in the above figure A, Stroke, length, corresponding to ₁ M ₁
It's a moment.

In the present invention, as shown in FIG.
- As shown in (b), at a certain opening degree H, an interval l occurs. Therefore, the combustion gas flows out through the interval l even before the upper peripheral edge of the piston passes through H, so that the valve no longer functions as the upper edge of the exhaust port. Note that if the upper edge of the exhaust port could be moved vertically along the circumference of the piston, l would be 0, and there would be a one-to-one correspondence between the opening degree of the exhaust port and the exhaust timing, but creating such a structure would be extremely difficult and complicated. Become something. However, since the tip of the valve body is made into an acute angle, the streamline of the gas passing through the interval l bypasses the tip of the valve body and is pressed against the piston circumferential wall and contracts, reducing the passage area and restricting the flow rate. Ru. When the upper peripheral edge of the piston exceeds H, the flow rate increases and the pressure drops rapidly, so the relationship between the opening degree H and the exhaust timing corresponds within a certain range of the interval l, and when the valve body rises, the exhaust The timing becomes faster, and the exhaust timing can be changed continuously as shown in Figures A-B, and high output can be efficiently obtained over almost the entire operating range as shown in Figures A-C.

On the other hand, in the conventional device, the valve body is horizontally sliding as shown in Figure B-A, so even if the valve body moves back and forth, the opening degree H of the exhaust port does not change accordingly. As shown in Figure B, when the interval l exceeds a certain range, the upper edge of the exhaust port suddenly changes from H ₁ to H ₂ , so the exhaust timing becomes discontinuous.
As shown in Fig. 3, the engine output characteristics are similar to on/off control. With such output characteristics, the output changes suddenly at the Q point, which is not preferable because running is not smooth.

Furthermore, as is clear from Figure A-D and Figure B-D, the stroke of the valve body has a relationship of L ₁ <L ₂ ,
The valve body of the diagonal slide in the present invention has a stroke
L ₁ is small, making it more compact. Furthermore, when the valve body is retracted into the hole, its tip is almost flush with the upper inner wall of the exhaust passage, so a large amount of high-temperature exhaust gas can be removed. Even during high-speed operation when the exhaust flow is high, the valve body does not become an obstacle to the exhaust flow, so a drop in output is prevented, and carbon does not easily adhere to the valve body, so there is no possibility of sliding failure of the valve body. If there is an air gap 106 as shown in FIG.

Also, as is clear from Figure A-E and Figure B-E, the moment due to exhaust pressure acting on the valve body is
The relationship is M ₁ <M ₂ , and the diagonally sliding valve body according to the present invention has a small moment M ₁ , so the valve thickness can be reduced accordingly, and the stroke L ₁
Combined with the small size, the overall structure can be made even more compact.

〔Example〕

DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of an exhaust timing control device for a two-stroke engine according to the present invention will be described in detail below with reference to the accompanying drawings.

FIG. 1 is a sectional view showing the internal structure of the cylinder. In FIG. 1, numeral 10 is a cylinder body, a cylinder head 12 is attached to the upper part of the cylinder body 10, and a crank case 14 is attached to the lower part of the cylinder body 10. Furthermore, a piston 16 is slidably disposed inside the cylinder body 10, and a combustion chamber 18 is formed by a portion of the lower surface of the cylinder head 12, the inner peripheral surface of the cylinder body 10, and the upper surface of the piston 16. be done. 20, 22A, 22B are cylinder main bodies 10
Also shown is a cooling water jacket formed in the cylinder head 12, where cooling water jacket 22A and cooling water jacket 22B communicate with each other to form a common cooling water jacket. Cooling water jacket 20,2
2A and 22B are connected to a water pump, a radiator, etc. (not shown) via a connecting pipe 24, so that cooling water is circulated therethrough. Only a portion of the cooling water jackets 20, 22A, and 22B are shown in FIG. 1, and as shown in FIG. 2, the cooling water jacket 22B is provided over the entire circumference. Note that FIG. 2 is a plan view of the cylinder body 10 viewed from above with the cylinder head 12 removed from the top surface of the cylinder body 10. As shown in FIG.

Cylinder head 12 as shown in FIG.
A spark plug 26 is installed in the center of the
Furthermore, an intake passage 28 and an exhaust passage 30 are formed on the side surface of the cylinder body 10. Intake passage 2
8 is formed with an intake port 32 through which air-fuel mixture is supplied into the crankcase during the intake stroke. Furthermore, an exhaust port 34 is formed in the exhaust passage 30 and opens into the combustion chamber 18 . Further, scavenging ports 35, 35 are formed on the side surface of the cylinder body 10, as shown in FIG. 1, and the scavenging ports 35 are communicated with the inside of the crankcase 14 through a scavenging passage (not shown).

As shown in FIG.
A hole 36 in which a valve body (to be described later) is slidably arranged near the exhaust port 34 of
It is drilled at a 55° inclination. As shown in FIGS. 2 and 3, the hole 36 has a substantially rectangular cross section, that is, in this embodiment, the cross section has an elongated oval shape. Note that FIG. 3 is a plan view of a hole 36 formed in the cylinder body as seen from above with the valve body and cover described later removed. As shown in FIGS. 1 and 2, a plate-shaped valve body 38 is slidably inserted into the oval hole 36. As shown in FIGS. Although the cross-sectional shape of the valve body 38 is not shown, its cross section is formed into an oval shape corresponding to the shape of the hole 36 into which the valve body 38 is inserted. FIG. 4 is a drawing of the inner circumferential surface of the cylinder viewed from direction A in FIG. 1, and shows the shape of the tip 40 of the valve body 38. That is, the tip portion 40 is formed into a slightly curved concave shape, and this tip portion 40 is connected to the piston 16.
The exhaust passage 30 is formed to coincide with the outer peripheral surface of the exhaust passage 30 and to be substantially flush with the inner wall surface of the upper end of the exhaust passage 30 . Therefore, when the tip 40 of the valve body 38 is at its most retracted position within the hole 36 as shown in FIGS.
The distal end 40 of the valve body 38 is in contact with the outer peripheral surface of the piston at its most protruding position, as shown by the two-dot chain line in the figure. In this manner, the valve body 38 can change its position within the hole 36, thereby substantially changing the position of the upper edge of the exhaust port 34, thereby changing the exhaust timing.

In particular, in this embodiment, the valve body 3 is inserted into the hole 36, which is formed at an angle with respect to the axis of the cylinder, as described above.
8 is inserted and the valve body 38 slides diagonally with respect to the axis of the cylinder, so that the timing can be continuously changed, so that high output can be efficiently obtained over almost the entire operating range. In addition, the forward and backward stroke of the valve body 38 is smaller than that of the horizontally sliding valve body of the conventional device, and the moment due to the exhaust pressure acting on the valve body 38 is also reduced, making it possible to reduce the valve thickness. can be made more compact. In addition, during high-speed operation, the valve body 38 sinks into the hole 36 and the tip 40 of the valve body 38 smoothly connects with the inner wall surface of the exhaust passage 30, and during high-speed operation with a large exhaust flow rate, the valve body 38 becomes an obstacle to the exhaust flow. (Increase in exhaust resistance)
Therefore, a decrease in output is prevented, and the operability of the valve body 38 is maintained satisfactorily without causing poor sliding of the valve body 38 due to carbon deposition.

A shaft 42 is formed at the rear end of the valve body 38, and the end of the shaft 42 is connected via a link mechanism or the like to an actuator (not shown) that operates according to engine speed and output. That is, the valve body 38 slides according to the engine speed and output, and during high-speed operation, it is located at the most retracted position within the hole 36 as shown in FIGS. 1 and 4, and the exhaust port 34 is opened. The valve body 38 protrudes from the hole 36 into the exhaust passage 30 as the timing advances from high-speed operation to low-speed operation, and functions to substantially delay the opening timing of the exhaust port 34. Note that a seal 44 and a cover 46 are attached to the upper surface of the hole 36 to maintain airtightness.

The cylinder body 10, the cylinder head 12, and the crankcase 14 are connected to stud bolts 4 mounted on the crankcase as shown in FIG.
connected by 8. In the case of the conventional drum-shaped valve body, since the valve body passes through the cylinder body laterally, it is not possible to connect the cylinder head, cylinder body, and crankcase with a single through bolt. cylinder head and cylinder body,
Although the cylinder body and the crankcase were connected using separate bolts, in this embodiment, the stud bolt 48 was positioned so that its through hole 50 was located at the position of the valve body 38 as shown in FIG. Since the cylinder body 10, the cylinder head 12, and the crankcase 14 can be formed by removing them, a through bolt can be used to connect the cylinder body 10, the cylinder head 12, and the crankcase 14, thereby firmly connecting the three members. A cap nut 52 is fastened to the upper part of the stud bolt 48 as shown in FIG.

The operation of this embodiment is as follows. First, valve body 3
Since the shaft 42 of No. 8 is connected to an actuator (not shown) that operates according to the engine speed and output via a link mechanism, etc., the solid line shown in FIG. 2 from the position of
Move to the position indicated by the dotted chain line. That is, during high-speed operation, the valve body 38 is at the most retracted position within the hole 36, as shown by the solid line, and the opening timing of the exhaust port 34 is brought forward. In this case, the tip 40 of the valve body 38 is substantially flush with the inner wall surface of the exhaust passage 30 and is smoothly connected to the inner wall surface of the exhaust passage 30 . On the other hand, as the engine shifts to low-speed operation, the valve body 38, which was in the solid line position in FIGS. 1 and 4,
The distal end portion 40 gradually protrudes into the exhaust passage 30. When the valve body 38 protrudes into the exhaust passage 30 toward the position shown by the two-dot chain line, the position of the upper end of the exhaust port 34 is substantially lowered, and the exhaust timing is lowered.

As explained above, according to this embodiment, the valve body 38 is fitted into the hole 36 that is bored obliquely with respect to the axis of the cylinder. Since the exhaust timing can be changed continuously by sliding, high output can be obtained efficiently over almost the entire operating range. In addition, the forward and backward stroke of the valve body 38 is smaller than that of the horizontally sliding valve body of the conventional device, and the moment due to the exhaust pressure acting on the valve body 38 is also reduced, making it possible to reduce the valve thickness. can be made more compact. Further, in this embodiment, the valve body 38 is formed into a plate shape. Since it can be formed smaller than a conventional drum-shaped valve body, the housing portion for the valve body 38 formed in the cylinder 10 can be small, which is advantageous in terms of cylinder strength. In addition, in this embodiment, the valve body 38 does not perform rotational movement but an inclined linear movement, so the valve body 38
Cylinder body 1 sandwiched between 8 and the cylinder inner peripheral surface
0's flesh pressure will not become extremely thin. As a result, there is no risk of thermal deformation of the cylinder body 10. Furthermore, in this embodiment, the valve body 38 is not inserted and assembled from the side of the cylinder body 10, but only inserted from above, which facilitates assembly. Particularly in the case of a multi-cylinder engine, it can be assembled without interference from adjacent cylinders, making it possible to create a multi-cylinder integrated cylinder. Furthermore, since this embodiment uses a plate-shaped valve body 38 that slides diagonally with respect to the cylinder axis, the configuration is simple and the engine can be made compact.

〔Effect of the invention〕

According to the present invention, since the tip of the valve body is made into an acute angle, when the upper peripheral edge of the piston exceeds the tip, the exhaust gas flow rate increases rapidly and the pressure decreases. Timing is almost 1:1
In addition, the valve body is slidably inserted into the hole drilled at an angle to the axis of the cylinder, and the valve body slides in a direction oblique to the axis of the cylinder, so that the exhaust gas is The timing can be changed continuously, making it possible to efficiently obtain high output over almost the entire operating range. In addition, the forward and backward stroke of the valve body is smaller than that of a conventional valve body that slides in the horizontal direction, and the moment due to the exhaust pressure acting on the valve body is also smaller, making it possible to reduce the valve thickness, making the overall structure more compact. It is possible to aim for Furthermore, when the valve body is retracted into the hole, the tip is made to be almost flush with the upper inner wall surface of the exhaust passage, so the valve body does not obstruct the exhaust flow during high-speed operation, preventing a drop in output. Moreover, since carbon is difficult to adhere to the valve body, there is no possibility of sliding failure of the valve body.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing the internal structure of a cylinder to which an embodiment of the present invention is applied, FIG. 2 is a plan view of the cylinder shown in FIG. 1 with the cylinder head portion removed, and FIG. is a plan view showing the shape of the hole in which the valve body is inserted in the cylinder shown in FIG. 1 with the cover removed;
4 is a view taken in the direction of arrow A in FIG. 1, FIG. 5 is a vertical sectional view of the conventional example, and FIGS. 6 A and B show the valve body sliding in an oblique direction in the present invention and the conventional example. FIG. 4 is a diagram illustrating, in comparison, the action of a valve body that slides in the horizontal direction. 10... Cylinder body, 12... Cylinder head, 14... Crank case, 16... Piston, 30... Exhaust passage, 34... Exhaust port, 36...
...hole into which the valve body is inserted, 38...valve body, 40...
The tip of the valve body.

Claims (1)

[Claims] 1. A valve body functioning as an upper edge of the exhaust port is provided on an upper surface near the exhaust port of an exhaust passage having an exhaust port opening into the inner circumferential surface of the cylinder, and the valve body opens near the exhaust port of the exhaust passage of the cylinder. In an exhaust timing control device for a two-stroke engine which is slidably inserted into a hole, the hole is bored at an angle with respect to the axis of the cylinder so as to descend toward the exhaust port, and The tip of the valve body is formed with an acute angle in its longitudinal cross section, and when the valve body is retracted into the hole during high-speed operation, the tip of the valve body is almost flush with the upper inner wall surface of the exhaust passage. A two-stroke engine characterized in that, when the valve body protrudes from the hole into the exhaust passage during low-speed operation, the tip of the valve body approaches the side wall surface of the piston. Exhaust timing control device.