JPS63227922A - Exhaust timing control device for two-cycle engine - Google Patents

Abstract

PURPOSE:To obtain smooth operation of the captioned engine by moving a freely slidable valve body, which is installed on the top of an exhaust passage whose exhaust port is opened to the inner peripheral surface of a cylinder in the vicinity of the exhaust port, in such a manner that the tip of the valve body is projected until it agrees with the outer wall of the piston when the engine speed is low, although the valve body is set back from the surface when the engine speed is high. CONSTITUTION:An air intaking passage 28 and an exhaust passage 30 are formed on the side surface of the main body 10 of a two-cycle engine, and the exhaust passage 30 is opened to a combustion chamber 18 via an exhaust port 34. A plate-shaped valve body 38 is arranged in the vicinity of the exhaust port 34 in such a manner that the valve body 38 functions as an upper brim of this exhaust port 34. In this case, a hole 36, in which the valve body 38 is accommodated in a freely slidable manner, is made in such a manner that the hole is inclined with respect to the cylinder axis. In addition, the tip 40 of the valve body 38 is shaped into a slightly bent, recessed form. This valve body 38 is controlled to move in such a manner that when the engine speed is high the valve body 38 is sunken in the hole 36 so that the tip 40 of the valve body 38 becomes flush with the inner wall surface of the exhaust passage 30, while when the engine speed is low the valve body 38 is projected so that the tip 40 of the valve body 38 agrees with the outer peripheral surface of the piston.

Description

DETAILED DESCRIPTION OF THE INVENTION 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, and in particular, an exhaust passage having an exhaust port opening into the inner circumferential surface of a cylinder, which functions as an upper edge of the exhaust port on the upper surface near the exhaust port. The present invention relates to an exhaust timing control device for a two-stroke engine equipped with a valve body.

A conventional exhaust timing control device has a rotary dust valve body provided at the side edge of the cylinder head of an exhaust passage that opens on the inner circumferential surface of the cylinder. It is shaped like a drum along the surface, and 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 curve 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.

However, since the conventional exhaust timing control device for two-stroke engines has a valve body that is drum-shaped, 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 tends to become larger. I couldn't escape it. 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 disadvantageous in terms of mechanical strength. As a result of the above, there was a risk that the cylinder would undergo thermal deformation or the like. Furthermore, in the conventional exhaust timing control device for a two-stroke engine, the rotation axis of the valve body is arranged perpendicular to the axial direction of the cylinder, and when the valve body is assembled into the accommodating portion of the cylinder body, it is arranged in an hourglass shape. A valve body divided into left and right parts at the center 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 multi-cylinder engine, there is a drawback in that it is not possible to use a multi-cylinder integrated cylinder in which each cylinder has to be separated so that adjacent cylinders do not get in the way when inserting and assembling the valve body.

SUMMARY OF THE INVENTION An object of the present invention is to provide an exhaust timing control device for a two-stroke engine, which has no thin wall portion in the cylinder body, does not deform due to thermal stress, can be easily assembled into two cylinders, and is capable of forming a multi-cylinder integral cylinder. In the present invention, a hole is formed in the upper surface of the exhaust passage of the cylinder near the exhaust port, and the cross section is oblique with respect to the axis of the cylinder. The valve body is arranged in the exhaust passage, and the valve body is retracted into the hole during high-speed operation so that the tip of the valve body substantially coincides with the inner wall surface of the exhaust passage.

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 1O, and the upper surface of the piston 16. Ru.

20, 22A, 22B indicate cooling water jackets formed on the cylinder body 10 and the cylinder spatula +'12,
The cooling water jacket 22A and the cooling water jacket 22B communicate with each other to form a common cooling water jacket. The cooling water jackets 20.degree. 22A, 22B are connected to a water pump, a radiator, etc. (not shown) via a connecting pipe 24, so that the cooling water is circulated. 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. 1, a spark plug 26 is mounted in the center of the cylinder head 12, and an intake and air passage 28 and an exhaust passage 30 are formed on the side surface of the cylinder body 10. An intake port 32 is formed in the intake passage 28, from 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 . Also, the cylinder body 10
As shown in FIG. 1, a scavenging port 35, 35 is formed on the side surface of the crank case 14, and the scavenging port 35 communicates with the inside of the crankcase 14 through a scavenging passage (not shown).

As shown in FIG. 1, a hole 36 in which a valve body (described later) is slidably disposed is bored in the vicinity of the exhaust port 34 of the cylinder body 10 at an angle of 55° with respect to the axis of the cylinder. has been done. The hole 36 has an elongated oval cross section, as shown in FIGS. 2 and 3. Note that FIG. 3 is a plan view of a hole 36 drilled in the cylinder body, as seen from above, with the valve body and cover, which will be described later, removed. The oblong hole 36 has holes in FIGS. 1 and 2.
As shown in the figure, a plate-shaped valve body 38 is slidably inserted. Although the cross-sectional shape of the valve body 38 is not shown, this valve body 38
Its cross section is formed into an oval shape corresponding to the shape of the hole 36 into which it is inserted. FIG. 4 is a drawing of the inner circumferential surface of the cylinder seen from direction A in FIG.
The shape of is shown. That is, the tip 40 is formed in a slightly curved concave shape, and this tip 40 substantially matches the arc shape of the inner peripheral surface of the cylinder body 10 and also substantially matches the shape of the upper edge of the exhaust passage 30. It is formed to do so. Therefore, as shown in FIGS. 1 and 4, the tip 40 of the valve body 38 is located as shown by the solid line in the most retracted position within the hole 36, and is located at the upper edge of the exhaust passage 30. The distal end 40 of the valve body 38 forms a part of the circular shape of the cylinder at its most protruding position, as shown by the two-dot chain line in the figure. In this way, 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 timing of the exhaust timing.

A shaft 42 is formed at the rear end of the valve body 38 and is connected to the shaft 4 of the vagina.
The end of the engine 2 is connected to an actuator (not shown) that operates according to the engine speed and output via a link mechanism or the like.

That is, the valve body 38 slides depending on the engine speed and output, and during high-speed operation, the hole 36 closes as shown in FIGS. 1 and 4.
The valve body 38 is located at the most retracted position in the interior, so that the opening timing of the exhaust port 34 is earlier, and the valve body 38 is located at the most retracted position in the
protrudes into the exhaust passage 30 from the hole 36 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 confidentiality.

The cylinder body 10, cylinder head 12, and crankcase 14 are connected by stud bolts 48 implanted in the zinc case as shown in FIG. With conventional valves that use a drum-shaped valve body, the valve body passes through the cylinder body laterally, making it impossible to connect the cylinder head, cylinder body, and crankcase with a single through bolt. cylinder head and cylinder body,
The cylinder body and the crankcase were connected with separate bolts, but in this embodiment, space is taken up in the lateral direction. Since the cylinder head 12 can be formed by removing the position of 38, the cylinder body 10° and the cylinder head 12
, and a through bolt connecting the crankcase 14 can be used to firmly connect 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 the embodiment of the present invention constructed as described above is as follows. First, the shaft 42 of the valve body 38 is connected to an actuator (not shown) that operates according to the engine speed and output via a link mechanism, etc. 2 from the position of the solid line shown in
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 shape of the tip 40 of the valve body 38 substantially matches the upper edge of the exhaust passage 30 and forms a part of the upper edge of the exhaust passage 30 . On the other hand, as the engine shifts to low-speed operation, the first
The distal end portion 40 of the valve body 38, which was in the solid line position in the drawings and FIG. 4, gradually protrudes into the exhaust passage 30. Valve body 38
When the exhaust port 34 protrudes toward the position shown by the two-dot chain line in the exhaust passage 30, the position of the upper edge of the exhaust port 34 is substantially lowered, and the timing of the exhaust timing is lowered.

As explained above, according to the embodiment of the exhaust timing control device for a two-stroke engine according to the present invention, the valve body 38 is formed in a plate shape, and is formed smaller than a conventional drum-shaped valve body.

Therefore, the accommodating portion of the valve body 38 formed in the cylinder IOK can be small, which is convenient in terms of cylinder strength. Furthermore, in the embodiment according to the present invention, the valve body 38 does not rotate but performs an inclined linear motion, so that the wall thickness of the cylinder body 10 sandwiched between the valve body 38 and the inner circumferential surface of the cylinder becomes extremely thin. Never. As a result, there is no risk of thermal deformation of the cylinder body 1°. Further, in the embodiment according to the present invention, the valve body 38 is not inserted and assembled from the lateral direction of the cylinder body 10, but is only inserted from above, so that assembly is facilitated. 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 the embodiment according to the present invention uses a plate-shaped valve body 38 that slides obliquely with respect to the cylinder axis, the structure is simple and the engine can be made compact.

As explained above, according to the exhaust timing control device for a two-stroke engine according to the present invention, the valve body functioning as the upper edge of the exhaust port can be freely slid into the hole formed at an angle with respect to the axis of the cylinder. During high-speed operation, the valve body is retracted into the hole and is substantially aligned with the inner wall surface of the exhaust passage, so that the wall thickness of the cylinder near the valve body does not become thin and the valve body Since the body can be inserted from above, it can also be constructed as a multi-cylinder integral cylinder.

[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 removed, and FIG. The figure is a plan view showing the shape of the hole in which the valve body is inserted in the cylinder shown in Figure 1 with the cover removed, and Figure 4 is a view taken in the direction of arrow A in Figure 1. be. 10... Cylinder body, 12... Cylinder head,
14... Crank case, 30... Exhaust passage, 34
...Exhaust port, 36... Hole into which the valve body is inserted, 38.
... Valve body, 40... Tip of the valve body.

Claims (1)

[Claims] In an exhaust timing control device for a two-cycle engine, a valve body functioning as an upper edge of the exhaust port is provided on the upper surface near the exhaust port of an exhaust passage having an exhaust port opening on the inner circumferential surface of the cylinder.
A hole having an elongated cross section is opened near the exhaust port of the exhaust passage of the cylinder and is bored at an angle with respect to the axis of the cylinder, and the valve body is slidably disposed within the hole to facilitate high-speed operation. An exhaust timing control device for a two-stroke engine, characterized in that a middle valve body is retracted into a hole so that a tip end of the valve body substantially coincides with an inner wall surface of the exhaust passage.