JPH0674737B2 - Exhaust timing control device for 2-cycle engine - Google Patents

Description

TECHNICAL FIELD The present invention relates to an engine exhaust timing control device, and more particularly, by opening and closing an upper portion (top dead center side) of an exhaust port in a two-cycle engine, The present invention relates to an exhaust timing control device in which an upper edge of an exhaust port is changed in a sliding direction of a piston to change a communication timing between an inside of a cylinder and an exhaust passage due to sliding of the piston.

"Prior Art" Generally, engines installed in vehicles are roughly divided into a low rotation type that emphasizes power characteristics in a low rotation range and a high rotation type that emphasizes power characteristics in a high rotation range. The former is designed so that the peak of the engine output can be obtained in the low revolution range, and the latter can be obtained in the high revolution range of the engine output.
In the former case, the output in the high rpm range reaches a peak, and in the latter case, the output in the low rpm range is lower than that of the former case. It has been studied to improve the power characteristics in a wide range from the low rotation range to the high rotation range by increasing the output in the low rotation range while maintaining the high output in the rotation range.

As one specific means for solving the problem, it is mentioned that the engine exhaust timing is changed between the low speed region and the high speed region. However, when this means is not applied to the two-cycle engine, the exhaust gas in the two-cycle engine is not applied. However, since it is performed by opening the exhaust port by the piston, in order to change the exhaust timing, it is necessary to move the upper edge of the exhaust port (that is, the edge on the top dead center side of the piston) in the sliding direction of the piston. There is.

Therefore, the present inventors have proposed the structure shown in FIG. 1 as one means for changing the upper edge of the exhaust port as described above.

In this proposal, as shown in FIG.
The upper part of the exhaust passage 2 (hereinafter, the upper side means the top dead center side of the piston, and the lower side means the lower dead center side of the piston). A shaft 3 is rotatably provided near the exhaust port 2a which is an opening to the inner surface of the cylinder 1 so as to be orthogonal to the center line of the cylinder 1, and a valve body 4 is integrally attached to the shaft 3 A recess 5 for accommodating the valve body 4 is formed in the upper portion of the exhaust passage 2 facing the body 4, and the recess 5 extends inwardly in the upper portion of the swing end of the valve body 4. In the state where the valve body 4 is projected from the recessed portion 4, a protrusion 6 that fills a gap between the swinging end portion of the valve body 4 and the upper edge portion of the exhaust port 2a is integrally formed, and the recessed portion 5 is In the case where the engine is operated at a low rotation speed, which has a configuration in which a deep bottom portion 5a for accommodating the protrusion 6 of the valve body 4 is continuously provided As shown in FIG. 1, the valve body 4 is swung about the shaft 3 and the upper end of the exhaust port 2a is closed by closing the upper part of the exhaust port 2a by the swing end. When the exhaust timing is delayed by moving the valve body 4 to the bottom dead center side by the distance L to the lower end of the swinging end portion, and when the engine speed reaches high speed, the valve body 4 is recessed.
It is housed inside and the upper portion of the exhaust port 2a is opened to accelerate the exhaust timing, thereby improving the output characteristics in the entire rotation range.

"Problems to be Solved by the Invention" The present invention aims to improve the following points, which are left for further improving the characteristics in the above-mentioned proposal.

That is, when exhausting (scavenging), a phenomenon occurs in which a part of the combustion gas discharged into the exhaust passage 2 slightly enters the recess 5 through the gap between the valve body 4 and the inner surface of the recess 5,
The carbon contained in the combustion gas stays in the recess 5 and adheres to and is fixed to the inner surface of the recess 5 and the upper surface of the valve body 4, and the adhered carbon causes the valve body 4 and the inner surface of the recess 5 to adhere to each other. The gap set between the two is filled, and the storage position of the valve body 4 is displaced from the predetermined position, or
The point is that the reciprocating inertial weight of the valve element 4 may increase.

"Means for Solving Problems" The present invention is intended to provide an exhaust timing control device for a two-cycle engine which can effectively eliminate the points to be improved in the above-mentioned proposal. In particular, a recess is formed in the upper wall of an exhaust passage having an exhaust port opening to the inner surface of the cylinder from the vicinity of the exhaust port toward the downstream side, and the recess is oscillated along a direction orthogonal to the cylinder. A valve body having an axis is swingably provided, and the valve body is swung in a direction in which it projects from the recess and in a direction in which it is stored, and the swing end portion opens and closes the upper portion of the exhaust port, thereby And an exhaust port, the exhaust timing control device is configured to change a communication timing between the exhaust port and the exhaust port, wherein a through hole communicating from an end face of the valve body to an upper surface of the valve body is formed at a swinging end portion of the valve body. .

[Operation] In the exhaust timing control device for a two-cycle engine according to the present invention, a part of the blow-through gas at the time of exhaust (scavenging) is blown into the recess through the through hole formed at the swing end of the valve body. The carbon adhering to the inner wall of the recess and the upper surface of the valve body is cleaned and removed by the blow-through gas before solidifying.

[Embodiment] An embodiment of the present invention will be described below with reference to FIGS. 2 and 3.

FIG. 2 is a longitudinal sectional view of a two-cycle engine equipped with an exhaust timing control device according to the present invention, and FIG. 3 is III-III of FIG.
It is arrow sectional drawing which follows the line.

In the figure, reference numeral 7 indicates a cylinder, and a cylinder block
7a and a cylinder head 7b attached to the cylinder block 7a to form a combustion chamber A. Reference numeral 8 denotes a piston slidably fitted in the cylinder 7,
Reference numeral 9 is a scavenging passage for sending the air-fuel mixture into the combustion chamber A, and 10 is an exhaust passage for discharging the combustion gas from the combustion chamber A. Inside the exhaust passage 10, there is provided a reinforcing rib 11 having a predetermined length from the exhaust port 10a which is an opening to the inside of the cylinder 7 toward the downstream side and extending along the length direction of the cylinder 7. As shown in FIG. 3, the exhaust passage 10 is provided so as to be divided into two in the circumferential direction of the cylinder 7. The rib 11 reinforces the vicinity of the exhaust port 10a of the exhaust passage 10, and when the piston 8 is slid, the piston ring 12 attached to the piston 8 spreads radially outward due to its elasticity. Functioning to prevent the exhaust port 10a from hitting the upper edge 10b or the lower edge 10c. Further, a water passage W for inserting cooling water is formed along the length direction of the rib 11 so as to suppress the temperature rise of the rib 11.

An exhaust timing control device 13 according to the present embodiment is provided above the exhaust passage 10 near the exhaust port 10a.

Next, the exhaust timing control device 13 will be described below.

The exhaust timing control device 13 has a recess 14 formed in the upper wall of the exhaust passage 10 from the vicinity of the exhaust port 10a toward the downstream side, and the shaft 15 extending in the recess 14 in a direction orthogonal to the cylinder 7. Is rotatably disposed, and a valve body 16 integrally provided on the shaft 15 and swingable by the shaft 15 is disposed, and a swing end portion of the valve body 16 is provided with a valve body 16 from its end face. A through hole 17 communicating with the upper surface of the shaft 15 is formed, and a drive mechanism (not shown) for reciprocally rotating the shaft 15 within a range of a predetermined angle corresponding to the operating state of the engine is connected to the shaft 15. The cylinder 7 has a schematic configuration, and the valve body 16 is swung in a direction in which it is projected from the recess 14 and a direction in which it is stowed by a drive mechanism, and the swing port end opens and closes the upper portion of the exhaust port 10a. The timing of communication between the inside of the vehicle and the exhaust port 10a is changed.

More specifically, as shown in FIG. 3, the two valve bodies 16 are arranged in the circumferential direction of the cylinder 7 with the ribs 11 interposed therebetween. It can be rocked. Also, each valve body 16
The oscillating end portion has a width such that it can cover the upper portion of the exhaust port 10a over the entire surface in the circumferential direction of the cylinder 7. A projecting portion 18 extending toward one side is formed over substantially the entire length of the swinging end portion. The projecting portion 18 and the swinging side end surface of the valve body 16 on the inner side of the cylinder 7 are made continuous. As a control surface 19 that is made substantially continuous with the inner surface of the cylinder 7 when the valve body 16 is swung to the projecting position.
The through hole 17 is formed so as to penetrate the hole 18. The size of the through hole 17 is set in consideration of the degree of improvement of the output characteristic in the low speed region of the engine.

On the other hand, the inner surface of the recess 14 has a shape corresponding to the upper surface of the valve body 16, and the valve body 1 is provided near the exhaust port 10a.
When 6 is swung to the storage position, the protrusion 18 of the valve body 16
Is formed with a deep bottom portion 14a having a triangular cross section. Then, from the deep bottom portion 14a toward the downstream side of the exhaust passage 10, a flat portion 14b in which the intermediate portion of the valve body 16 is housed,
Further, the valve body 16 has a shape in which a base portion 14c having a semicircular cross section for accommodating the swing center portion of the valve body 16 is sequentially provided.
In the state where 6 is accommodated, a minute gap is formed over the entire surface between the valve body 16 and the upper surface thereof.

Thus, according to the exhaust timing control device 13 of the present embodiment configured as described above, the valve body 16 is operated based on the operating state of the engine, thereby enhancing the output characteristics of the engine in the entire rotation range. , The inner surface of the recess 14 or the valve body
Suppresses the adhesion of carbon to 16.

That is, when the engine is operated at a low rotation speed, the shaft 15 is rotated in a predetermined direction and the valve body 16 is swung to project into the exhaust passage 10. Due to such movement of the valve body 16, the control surface 19 thereof is positioned above the exhaust port 10a, whereby the upper portion of the exhaust port 10a is closed as shown in FIG. The edge 10b is apparently lowered by the distance L to the lower edge of the control surface 19 of the valve body 16. Therefore, by lowering the upper edge 10b of the exhaust port 10a,
The opening timing of the exhaust port 10a by the piston 8, that is, the exhaust timing is delayed.

On the other hand, when the engine reaches the high speed range, the valve body 16 is moved in the opposite direction to the above and is housed in the recess 14. As a result, the upper portion of the exhaust port 10a is opened and the exhaust timing is advanced.

By such an operation, appropriate exhaust is performed in a wide range from the low speed range to the high speed range of the engine, and the output characteristics of the engine are improved in the entire speed range.

Then, while the above-mentioned exhaust action, that is, the scavenging action is being performed, the combustion gas is discharged to the exhaust passage 10, and a part thereof enters the recess 14 through the gap between the valve body 16 and the recess 14. It is conceivable that carbon in the combustion gas adheres to the inner surface of the recess 14 and the upper surface of the valve body 16. However, during the above-described exhaust (scavenging), part of the unburned gas is discharged as blow-through gas together with the combustion gas. Are blown into the concave portion 14 and the blow-by gas cleans the inner surface of the concave portion 14 and the upper surface of the valve body 16 so that carbon adhering to these is peeled off and the downstream side of the valve body 16 and the concave portion 14 The gas is discharged to the exhaust passage 10 through the gap between and.

Therefore, the protruding position and the storage position of the valve body 16 are maintained at the set values for a long period of time, and the increase of the reciprocating inertial mass of the valve body 16 is suppressed, so that the above-described control of the exhaust timing is accurately performed. .

It should be noted that the shapes, sizes, and the like of the respective constituent members shown in the above embodiment are examples, and can be variously changed based on design requirements and the like.

For example, the example in which the opening area is secured by making the cross-sectional shape of the through hole 17 flat is shown,
A plurality of independent through holes may be provided at intervals in the width direction of the valve body 16.

[Advantages of the Invention] As described above, the exhaust timing control device for a two-cycle engine according to the present invention is provided on the upper wall of the exhaust passage having the exhaust port opening to the inner surface of the cylinder, from the vicinity of the exhaust port to the downstream side. A valve body having a swinging axis line extending in a direction orthogonal to the cylinder is formed in the recessed portion so as to swing freely, and swings in a direction in which the valve body is projected from the recessed portion and in a storing direction. Then, by opening and closing the upper portion of the exhaust port by its swinging end,
An exhaust timing control device configured to change a communication timing between the inside of a cylinder and an exhaust port, wherein a swing hole of the valve body is formed with a through hole communicating from the end surface to the upper surface of the valve body. And when exhausting (scavenging),
Unburned gas discharged together with the combustion gas, that is, a part of the blow-through gas is blown into the recess from a through hole formed in the end face of the valve body, and the inner surface of the recess and the upper surface of the valve body are cleaned by the blow-through gas, It is possible to prevent carbon from adhering to these surfaces, which allows rocking of the valve element to be reliably performed within a set range, and
It is possible to suppress the increase in the reciprocating inertial mass of the valve element and to maintain stable control of the exhaust timing over a long period of time.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a vertical cross-sectional view showing a structural example of a conventional two-cycle engine equipped with an exhaust timing control device, and FIGS. 2 and 3 show an embodiment of the present invention. Fig. 2 shows a two-stroke engine, Fig. 2 is a longitudinal sectional view, and Fig. 3 is III in Fig. 2.
FIG. 6 is a cross-sectional view taken along the line III-III. 7 ... cylinder, 7a ... cylinder block, 7b ... cylinder head, 10 ... exhaust passage, 10a ... exhaust port, 10b ... upper edge, 13 ... exhaust timing control device, 14 ... recess, 15 ... … Axis, 16 …… Valve element, 17 …… Through hole, 18 …… Projection.

Claims (1)

[Claims] 1. A recess is formed in the upper wall of an exhaust passage having an exhaust port opening to the inner surface of a cylinder of a two-cycle engine from the vicinity of the exhaust port toward the downstream side, and the recess is orthogonal to the cylinder. A valve body having a swing axis line along the direction is swingably disposed, and the valve body is swung in a direction in which it projects from a recess and in a direction in which the valve body is stored, and the swing end portion causes the upper portion of the exhaust port to move upward. An exhaust timing control device for changing the timing of communication between the inside of the cylinder and the exhaust port by opening and closing the valve, the through-hole communicating from the end face to the upper face of the valve body at the swing end of the valve disc. An exhaust timing control device for a two-cycle engine, characterized in that: