JPH042777B2 - - 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 rotational 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 to be solved by the invention]

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 multi-cylinder engine, each cylinder must be separated so that adjacent cylinders do not get in the way when inserting and assembling the valve body, and a multi-cylinder integrated cylinder cannot be used.

In view of such conventional circumstances, an exhaust system for a two-stroke engine using a slide valve as a valve body has been proposed by the same applicant as the present applicant (see Japanese Utility Model Application Publication 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. A slide valve 104 for opening and closing the upper part of the exhaust port 102 is provided above the exhaust passage 103 so as to be slidable substantially in the radial direction of the cylinder toward the exhaust port 102. The upper part of the engine is closed when the engine is running at low speeds and opened when the engine is running at high speeds, making it possible to obtain high output at both high speeds and low speeds.

By the way, although this device is capable of controlling at low and high speeds, the control range is limited and there is a problem in that it is not possible to control over a wide range. Further, although heat radiation fins 105 are provided on the outer periphery of the cylinder, heat radiation near the slide valve accommodating portion is not necessarily good, and the problem remains that the temperature distribution in the cylinder may become uneven.

This point is also the same in the conventional example using the hourglass-shaped valve body mentioned at the beginning, and in this case, the upper edge of the exhaust port, which is sandwiched between the hourglass-shaped valve body and the inner peripheral surface of the cylinder, is thin. It is easy to heat and deform, but there was a problem in that even if you wanted to cool it, you could not bring the cooling water jacket close to it.

The present invention was made in view of these conventional problems.The purpose of the present invention is to enable exhaust timing control over a wide range, but also to prevent the cylinder body from deforming due to thermal stress without having any thin-walled parts. An object of the present invention is to provide an exhaust timing control device for a two-stroke engine that does not

[Means for solving problems]

In order to achieve the above object, the present invention provides an exhaust timing system for a two-stroke engine in which an exhaust passage having an exhaust port opening into the inner circumferential surface of the cylinder is provided with a valve body that functions as the upper edge of the exhaust port on the upper surface near the exhaust port. In the control device, a hole having a substantially rectangular cross section is opened near the exhaust port of the exhaust passage of the cylinder, and the hole is bored at an angle with respect to the axis of the cylinder so as to descend toward the exhaust port. A plate-shaped valve body is slidably inserted into the hole, and a plate-shaped valve body is inserted into the hole in the vicinity of the upper edge of the exhaust port, which is sandwiched between the valve body and the inner peripheral surface of the cylinder, over an area approximately equal to the width of the valve body. A cooling water jacket is extended, and the bottom surface of the cooling water jacket is formed substantially parallel to the slope of the valve body.

[Effect]

With this configuration, the valve body diagonally protrudes and retracts near the exhaust port in response to low-speed or high-speed engine operation, and the exhaust is controlled by the amount of protrusion, so the control range is wide. In addition, even if the valve body is placed, the wall thickness of the cylinder near the valve body does not become thinner, and the rigidity is high, so deformation is difficult to occur.
Moreover, since a cooling water jacket is provided near the valve body and the bottom surface of the cooling water jacket is formed to be approximately parallel to the slope of the valve body, the surface area of the inner surface of the jacket is inevitably large. The cooling of the cylinder is efficiently improved, and overheating of the valve body is also prevented, thereby further improving prevention of deformation.

〔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. In particular, in this embodiment, a cooling water jacket 22B is provided near the upper edge of the exhaust port, which is sandwiched between the valve body 38 and the inner peripheral surface of the cylinder, over an area approximately equal to the width of the valve body. As clearly shown in FIG. 1, the bottom surface of the cooling water jacket 22B near the inclined valve body 38 is formed almost parallel to the slope of the valve body 38, so that the cooling water jacket 22B
The surface area of the inner surface of the is inevitably large. Also,
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 an angle of 100 degrees. Hole 36 is the second
As shown in the drawings and FIG. 3, the cross section is approximately rectangular, that is, in this embodiment, the cross section is formed into 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 40 is formed in a slightly curved concave shape, and this tip 40 substantially matches the arcuate 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 like this. Therefore, as shown in FIGS. 1 and 4, the tip 40 of the valve body 38 is located at the most retracted position within the hole 36 as shown by the solid line, and is located at the upper edge of the exhaust passage 30. The tip 40 of the valve body 38, at its most protruding position, forms a part of the circular shape of the cylinder as shown by the two-dot chain line in the figure. In this manner, the valve body 38 changes its position within the hole 36, thereby substantially changing the position of the upper edge of the exhaust port 34, thereby allowing the timing of the exhaust timing to be varied over a wide range.

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 is located at the most retracted position within the hole 36 as shown in FIGS. The valve body 38 protrudes from the hole 36 into the exhaust passage 30 as the opening timing is made earlier and the speed goes 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 the embodiment according to 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. Move from the position indicated by the solid line to the position indicated by the two-dot 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 tip 40 of the valve body 38, which was in the solid line position in FIGS. 1 and 4, gradually protrudes into the exhaust passage 30. The valve body 38 is the exhaust passage 30
When the inner part protrudes toward the position shown by the two-dot chain line, 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 into a plate shape, and is smaller than a conventional drum-shaped valve body. Therefore, the accommodating portion of the valve body 38 formed in the cylinder 10 can be small, which is advantageous in terms of cylinder strength. Further, in the embodiment according to the present invention, the valve body 38 is not rotated but moves in an inclined linear motion, so that the wall thickness of the cylinder body 10 sandwiched between the valve body 38 and the inner peripheral surface of the cylinder becomes extremely thin. Never. Furthermore, overheating is prevented by the cooling water jacket 22B extending near the portion. As a result, there is no risk of thermal deformation of the cylinder body 10. 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.

〔Effect of the invention〕

According to the present invention, the valve body diagonally protrudes and retracts near the exhaust port in response to low-speed or high-speed operation of the engine, and the exhaust is controlled by the amount of protrusion, so the control range can be extended over a wide range. This allows for more fine-grained control of exhaust timing. Further, even when the valve body is disposed, the wall thickness of the cylinder near the valve body does not become thinner, and the rigidity is high, so deformation is unlikely to occur and it is safe. Moreover, since a cooling water jacket is provided near the valve body and the bottom surface of the cooling water jacket is formed to be approximately parallel to the slope of the valve body, the surface area of the inner surface of the jacket is inevitably large. ,
Cooling of the cylinder is efficiently improved, and overheating of the valve body is also prevented, further improving prevention of deformation.

[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. The figure 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; FIG. 4 is a view taken in the direction of arrow A in FIG. 1; FIG. 5 is a longitudinal sectional view of a conventional example. 10... Cylinder body, 12... Cylinder head, 14... Crank case, 22B... Cooling water jacket, 30... Exhaust passage, 34... Exhaust port, 36... Hole into which the valve body is inserted, 38... ... Valve body, 40... Tip portion of the valve body.

Claims (1)

[Claims] 1. In an exhaust timing control device for a two-cycle engine, in which 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 on the inner circumferential surface of the cylinder, A hole with a substantially rectangular cross section is opened near the exhaust port of the exhaust passage, and the hole is bored obliquely with respect to the axis of the cylinder so as to descend toward the exhaust port, and a plate-shaped valve is installed in the hole. The body is slidably inserted, and a cooling water jacket is provided near the upper edge of the exhaust port sandwiched between the valve body and the inner circumferential surface of the cylinder over an area approximately equivalent to the width of the valve body. An exhaust timing control device for a two-stroke engine, characterized in that a bottom surface of the cooling water jacket is formed substantially parallel to an inclination of the valve body.