JPH0561452B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION "Field of Industrial Application" The present invention relates to an exhaust timing control device for an engine, and particularly to an exhaust timing control device used in a two-stroke engine.

"Prior art and its problems" In a two-stroke engine, as a means to increase combustion gas filling efficiency, reflected waves in the exhaust passage are used to blow gas from the combustion chamber to the exhaust passage during scavenging (so-called blow-by gas). There is a known technology to push the fuel back into the combustion chamber.

When applying this technology to an actual engine, it is important to keep in mind that the exhaust reflected waves must be returned to the exhaust port after the scavenging port is closed and just before the exhaust port is closed. This is a point that should not be made.

By the way, the 2 installed on motorcycles and cars
In the case of a cycle engine, since the rotational speed is varied, at a certain rotational speed the reflected waves can be returned to the point where the exhaust port is on the verge of being blocked, and even if it is possible to increase the combustion gas filling efficiency, A phenomenon occurs in which this is no longer possible at other rotational speeds.

As a way to deal with such problems, Jikosho
Japanese Patent No. 47-36047 proposes a technique for changing the timing of opening and closing an exhaust port depending on the rotational speed of the engine.

In this technology, a support shaft is provided at the upper part of the inner wall of the exhaust passage at a position spaced downstream from the opening to the inner surface of the cylinder (exhaust port), and the support shaft is oscillated along the direction perpendicular to the length direction of the support shaft. It consists of a rod-shaped shank part that is movably attached and extends toward the opening, and an action part that is integrally attached to the swinging tip of the shank part and is curved in substantially the same manner as the inner wall surface of the cylinder. A control member (valve body) is provided in the lower part of the exhaust passage and near the opening,
A recess is formed to accommodate the operating portion of the control member.

According to the above-mentioned engine, the shank portion is operated to swing according to the rotational speed of the engine, and for example, when the engine rotates at a low speed, the operating portion is positioned above the opening of the exhaust passage to close the opening top. On the other hand, when the engine rotates at high speed, the operating portion is moved back from the opening of the exhaust passage and positioned in the recess at the bottom of the exhaust passage, thereby opening the upper part of the opening of the exhaust passage. In this way, the position of the upper edge of the opening of the exhaust passage can be substantially moved up and down depending on the rotational speed of the engine. The exhaust timing is controlled so that the exhaust reflected wave returns to the exhaust port after the exhaust passage is closed and just before the exhaust port closes, and the gas that has blown into the exhaust passage is pushed back into the cylinder to improve gas filling efficiency. The aim is to improve output across the entire rotation range.

"Problems to be Solved by the Invention" In the two-stroke engine described above, when opening the upper part of the exhaust passage to the cylinder, the rod-shaped shank is arranged so as to reach from the upper part of the exhaust passage to the lower part. When the shank portion is exposed to high-temperature exhaust gas, the temperature rises abnormally and there is a risk that the material may change and other problems may occur.

In order to solve the above problem, it is possible to make the entire control member into a plate shape with a predetermined thickness in order to increase the heat capacity of the shank part, but in this case, when the valve is opened, the control member is in the exhaust passage. Problems arise such as blocking the central portion and increasing the weight of the control member, which requires driving the control member with a larger driving force.

Additionally, since the center of the swing of the control member is exposed to the exhaust gas, carbon adheres between the control member and the inner surface of the exhaust passage at the center of the swing, affecting the swing operation of the control member. It is also assumed that they will be given.

``Object of the Invention'' The present invention has been made in view of the above circumstances, and is designed to make the valve body that opens and closes the upper part of the exhaust passage less susceptible to the effects of heat, and to suppress the adhesion of carbon at the swinging center of the valve body. However, it is an object of the present invention to provide an exhaust timing control device for a two-stroke engine that can operate the valve body with a small driving force.

"Means for Solving the Problem" In order to achieve the above-mentioned object, the exhaust timing control device according to the present invention includes a valve body storage recess that is provided in the upper part of the exhaust passage and stores the valve body when the valve is opened. On the other hand, the valve body is provided with an arm extending from the center of swing toward the inner surface of the cylinder, the swinging tip of the arm is provided with a collar extending upward, and a surface of the collar opposing the inner surface of the cylinder is provided. is a control surface that has almost the same curvature as the inner surface of the cylinder and is aligned with the inner surface of the cylinder, and further, the flange of the valve body is fitted into the inner surface of the cylinder of the valve body storage recess, and It has a structure in which a concave part is formed to form a bent gap between it and the brim part.

"Example" Hereinafter, an example of the present invention will be described in Figures 1 to 3.
This will be explained with reference to the figures.

FIG. 1 is a longitudinal sectional view of a two-stroke engine equipped with an exhaust timing control device according to the present invention, and FIG. 2 is a sectional view taken along the line - in FIG.

In the figure, numeral 1 is a cylinder block, 2 is a cylinder head, 3 is a piston slidably inserted into the cylinder, 4 is a scavenging passage, and 5 is an exhaust passage. A reinforcing rib 6 is provided at the center of the exhaust passage 5 in the left and right direction.
is provided extending from an opening (exhaust port) 5a to the inner surface of the cylinder to a predetermined location on the downstream side. The ribs 6 serve to reinforce the vicinity of the opening of the exhaust passage 5 to the inner surface of the cylinder, and also to prevent the piston ring from expanding radially outward and abutting against the upper or lower edge of the exhaust port 5a.

A recess 7 is formed in the upper part of the exhaust passage 5 and slightly downstream of the opening 5a to the inner surface of the cylinder for accommodating a valve body to be described later. A shaft 8 is rotatably provided in the recess 7 and extends in a direction perpendicular to the center line of the cylinder. The central portion of the shaft 8 has a rectangular cross section, and valve bodies 9, 9 for exhaust timing control are provided on both sides of the rib 6 so as to sandwich the rib 6 between them.

Both the valve bodies 9, 9 are symmetrical with respect to each other. As shown in FIG. 3, the valve body 9 has a shaft insertion portion 10 through which the shaft 8 is inserted, and one side (valve body 9) from the shaft insertion portion 10 to the inner surface of the cylinder when assembled to the cylinder block 1. It is composed of an extending arm portion 11 and a collar portion 12 provided at the swinging tip of the arm portion 11 and extending upward so as to be substantially orthogonal to the arm portion 11. A surface of the collar portion 12 facing the inner surface of the cylinder is a control surface 13 that is provided to have substantially the same curvature as the inner surface of the cylinder and is aligned with the inner surface of the cylinder. When the valve body 9 configured as described above is assembled into the cylinder block 1, there is a slight gap between the inner surface of the cylinder and the control surface 13.
They are assembled to form a gap.

The lower surface of the recess 7 has a shape corresponding to the upper surface of the valve body 9, that is, a recess 7a having a substantially triangular cross section, a flat portion 7b, and a recess 7c having an arcuate cross section are provided in this order from the opening side toward the downstream side. It has a similar shape.

When the flange 12 formed on the valve body 9 is fitted into the recess 7a,
Forming a bent gap between the collar portion 12 and the flange portion 12,
A labyrinth structure is formed, and an arcuate gap is formed between the arcuate recess 7c and the surface of the shaft insertion portion 10 of the valve body 9.

The valve bodies 9, 9 are connected to the shaft 8 according to the rotational speed of the engine.
It is designed to be driven and operated by a drive mechanism 20 via. The drive mechanism 20, as shown in FIG.
The engine consists of a motor (not shown) connected via a motor 2, and a controller (not shown) that rotates the motor in forward and reverse directions according to the rotational speed of the engine.

Further, the portion of the shaft 8 protruding from the cylinder block 1 and the wire guide 21 are connected to a wire case 23 attached to the cylinder block 1.
and is covered by a case cover 24 screwed onto the wire case 23. In addition, axis 8
On one end side, from the center to the end, there are a bush 25, a positioning knob 26, and a seal member 27.
are arranged in order. Also, Figures 1 and 2
In the figure, R indicates a passage for passing cooling water.

Thus, the exhaust timing control device configured as described above can improve the output characteristics of the engine over the entire rotation range by being operated based on the operating state of the engine.

That is, when the engine is being operated at low rotation speed, the shaft 8 is rotated in a predetermined direction to swing the valve body 9, causing the valve bodies 9 to protrude into the exhaust passage 5. By such movement of the valve bodies 9, 9, the control surface 13 is positioned midway above the opening 5a of the exhaust passage 5, and thereby the opening 5a of the exhaust passage 5 is positioned halfway up the opening 5a of the exhaust passage 5, as shown by the solid line in FIG. The upper part is closed, and the upper edge of the opening 5a is apparently lowered by a distance l from the lower edge of the control surface 13 of the valve bodies 9,9. Therefore, the exhaust port 5a, which is opened and closed by the movement of the piston 3, opens later and closes earlier as the control surface 13 is lowered by a distance l.

In this way, when the engine is running at low speed, the exhaust port 5a is opened late and closed late in response to the long vertical movement period of the piston 3, and as a result, the exhaust reflected wave is generated just before the exhaust port 5a is closed. is returned to the exhaust port 5a to improve combustion gas filling efficiency.

On the other hand, when the engine reaches a high rotation range,
The valve bodies 9, 9 are moved in the opposite direction to that described above and housed in the recess 7 as shown by the two-dot chain line in FIG. That is, in this case, in response to the shorter vertical movement period of the piston 3, the exhaust port 5a is opened earlier and closed later than in the case described above. Therefore, in this case as well, the exhaust reflected waves are returned to the exhaust port 5a just before the exhaust port 5a is closed, and as in the case described above, the combustion gas filling efficiency is improved by effectively utilizing the reflected waves.

In this way, the exhaust timing of the engine can be controlled by the valve bodies 9, 9.
The lower edge of the engine is used to improve output characteristics over the entire rotation range.

On the other hand, when exhaust gas flows into the exhaust passage 5, it is brought into contact with the control surface 13 of the valve body 9, and the flange portion 12 on which this control surface 13 is formed
is formed to be substantially perpendicular to the arm portion 11, so that the external force applied to the valve body 9 from the exhaust gas is directed approximately along the length direction of the arm portion 11. Therefore, even in a state where exhaust gas is acting on the control surface 13, an increase in the driving force of the valve body 9 is suppressed.

Moreover, when the exhaust gas that has come into contact with the control surface 13 of the valve body 9 attempts to blow through from the upper end surface of the control surface 13 to the upper part of the valve body 9, the flange portion 12 of the valve body 9
Since a bent space is formed between the valve body 9 and the recess 7a, a labyrinth effect suppresses the exhaust gas from blowing upward through the valve body 9.

Therefore, the shaft insertion portion 10 that exists behind it
The accumulation of carbon between the inner surface of the arc-shaped recess 7c is suppressed, and from this point of view, the valve body 9
The increase in operating force is suppressed.

The control method for the valve body 9 may be either step-type control such as two-position control, or continuous comparison control.

Further, in the above exhaust timing control device, since the entire valve body 9 is housed in the recess 7 provided in the upper part of the exhaust passage 5 when the valve is opened, it is not exposed to exhaust gas in a high temperature state. Not easily affected by heat.
Further, the valve body 9 is provided with a flange portion 12 at the swinging tip,
This ensures the necessary height h for the control surface 13, and achieves a lighter weight ratio compared to making the entire valve body into a plate shape with a thickness h, and allows the valve body 9 to be oscillated with a small driving force. It has the advantage of being able to be operated dynamically. In addition, in the above-mentioned valve body 9, the shaft insertion part 10 and the flange part 12 are connected by the arm part 11, and the structure is stronger than the conventional structure in which the operating part is supported by a rod-shaped shank part. It's increasing.

FIG. 4 shows another embodiment of the invention. In this embodiment, a plurality of through holes 31 are formed in the arm portion 11 of the valve body 9. The upper portions of these through holes 31 are chamfered, and edge portions E are formed between adjacent through holes 31.

If such a valve body 9 is used, carbon contained in the exhaust gas adhering to the upper surface of the valve body 9 can be removed.
As the valve body 9 swings, the carbon particles are finely divided by the edge portion E, and these small pieces of carbon can be discharged through the through hole 31 into the exhaust passage. That is, carbon that adheres to the upper surface of the valve body and prevents the valve from being closed can be quickly discharged to the outside, thereby stabilizing the operation of the valve body 9.

"Effects of the Invention" As explained above, according to the exhaust timing valve body device according to the present invention, the valve body is housed in the recess provided in the upper part of the exhaust passage when the valve is opened, so that high-temperature exhaust gas It is not exposed to heat and is not easily affected by heat.

In addition, the valve body is provided with a flange at the swinging tip, which secures the necessary height for the control surface, which reduces the weight of the valve body, allowing the valve to operate with a small driving force. He can manipulate his body.

Furthermore, by arranging the flange of the valve body upward, when exhaust gas collides with the control surface formed on the flange, the moment around the center of swing generated in the valve body is minimized. Also from this point of view, the driving force of the valve body can be reduced.

Furthermore, by forming a curved gap between the valve body storage recess and the valve body flange, a labyrinth effect is created between the two, thereby allowing exhaust gas to pass through the control surface into the valve body storage recess. It is possible to prevent carbon from flowing into the center of the valve body, and to prevent carbon from accumulating at the swinging center of the valve body, thereby ensuring smooth swinging operation of the valve body.

[Brief explanation of the drawing]

FIG. 1 is a longitudinal sectional view of a two-stroke engine equipped with an exhaust timing control device according to the present invention, FIG. 2 is a sectional view taken along the line - in FIG. 1, FIG. 3 is a perspective view of a valve body, and FIG. The figure is a perspective view showing another embodiment of the present invention. 1...Cylinder block, 2...Cylinder head, 4...Scavenging passage, 5...Exhaust passage, 5a...
(Exhaust port) opening, 7...valve body storage recess, 9...
...Valve body, 11...Arm part, 12...Brim part, 13...
... control surface, 20 ... drive mechanism, 31 ... through hole,
E...Edge part.

Claims (1)

[Claims] 1 Opening and closing the upper part of the opening of the exhaust passage communicating with the inside of the cylinder of a two-stroke engine to change the timing of communication between the inside of the cylinder and the exhaust passage by the piston slidably inserted into the cylinder. The exhaust timing control device includes: a valve body that is swingably attached to the upper part of the exhaust passage around an axis; and a valve body storage that is provided at the upper part of the exhaust passage and stores the valve body when the valve is opened. The valve body includes a recess and a valve body drive mechanism that opens and closes the valve body according to the rotational speed of the engine. The swinging tip of the arm is provided with a collar portion extending upward, and the surface of the collar portion facing the inner surface of the cylinder is provided with approximately the same curvature as the inner surface of the cylinder, and a control surface is aligned with the inner surface of the cylinder. A recess is formed on the inner surface of the cylinder of the valve body storage recess into which the flange is fitted and forms a bent gap between the flange and the flange. Exhaust timing control device for 2-stroke engine.