JPH0549811B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an improvement in a variable exhaust timing two-stroke engine that is equipped with an exhaust valve and can adjust the exhaust timing and exhaust port opening area.

[Conventional technology]

Traditionally, two-stroke engines have been equipped with an exhaust valve in the exhaust port to improve output and combustion efficiency at high speeds, as well as improve torque and rotational stability at low speeds. The exhaust port is partially blocked to adjust the exhaust timing and the opening area of the exhaust port.

For example, as shown in FIGS. 5 and 6, a rotatable plate-shaped exhaust valve 53 is provided on the top dead center side of the exhaust port 52 of the cylinder 51, and a drive shaft 54 that is the rotation axis of the exhaust valve 53 is provided on the top dead center side of the exhaust port 52 of the cylinder 51. A pulley 56 on which a wire 55 is wound is attached to one end.
5 and pulley 56 to move the tip edge 53A of the exhaust valve 53 forward and backward into the opening surface of the exhaust port 52, thereby changing the opening area of the exhaust port 52 and The exhaust timing is changed by moving the edge of the top dead center side.

In addition, in the exhaust system for a two-stroke engine described in Japanese Patent Application Laid-open No. 59-101534, a rotary valve is used as the exhaust valve to control the exhaust timing, and a sub-exhaust port is provided adjacent to the main exhaust port. The opening area of the exhaust port is adjusted by opening and closing the sub-exhaust passage from the sub-exhaust port with a valve port formed in the rotary valve body.

[Problem that the invention seeks to solve]

Incidentally, in order to improve engine performance, it is desirable to increase the opening area of the exhaust port 52 to improve exhaust efficiency, especially at high engine speeds.

However, it is difficult to change the position of the top dead center side edge of the opening of the exhaust port 52 due to the exhaust timing, and the expansion of the exhaust port 52 is limited to the circumferential direction of the cylinder 51.

Therefore, in the rotatable plate-shaped exhaust valve 53 as described above, when the exhaust port 52 is expanded in the circumferential direction of the cylinder 51, the exhaust port 52 is expanded in the circumferential direction of the cylinder 51.
Since the difference in distance from the drive shaft 54 is large between both end portions 53B and the center portion 53C of the tip edge 53A corresponding to No. 2, the distance between both end portions 53B and the center portion 53
There is a possibility that the height of the end edge at C is different, and at both end portions 53B, the edge portion (commonly known as a knife edge) formed by the housing portion of the exhaust valve 53 and the inner wall of the cylinder 51 may become thin. There was a problem that expansion in the circumferential direction was restricted.

Further, even when using the rotary valve described above, although the area of the exhaust port is expanded by the auxiliary exhaust port, further expansion has similar problems. In other words, if an attempt is made to make the main exhaust port larger, the diameter of the rotary valve must become larger, making it difficult to process the valve port for the aforementioned sub-exhaust port. Furthermore, since exhaust gas flows through the hollow part formed in the cylinder block to accommodate and hold the rotary valve and the rotary sliding contact surface of the rotary valve itself, the rotary valve expands due to exhaust heat and slides into contact with the air conditioning part. There is a problem that the contact rotation tends to be uneven, and the existence of the sub-exhaust passage affects the intended exhaust timing control.

It is an object of the present invention to provide an exhaust timing that can always set the exhaust timing optimally and accurately, improve exhaust efficiency by adjusting the exhaust port opening area according to the rotation speed, and expand the total area of the exhaust port openings. The purpose of the present invention is to provide a variable two-stroke engine.

[Means for solving problems]

The present invention provides an exhaust valve that makes it possible to partially block off the top dead center side of the exhaust port to vary the exhaust timing, in an exhaust passage communicating with an exhaust port opened on the inner surface of the cylinder, and A sub-exhaust port is opened on the inner surface of the cylinder on the side of the port, the sub-exhaust port is communicated with the exhaust passage through a sub-exhaust passage, and means for opening and closing the exhaust passage according to the operation of the exhaust valve is provided. Further, the exhaust valve has a swing axis on the downstream side of the exhaust passage, and the exhaust timing can be varied at the tip edge on the cylinder side, and the opening exhaust valve on the exhaust passage side of the auxiliary exhaust passage is arranged so that the exhaust valve has a swing axis on the downstream side of the exhaust passage. This is a variable exhaust timing two-stroke engine characterized by being arranged in a position where the exhaust valve is closed by the side surface of the exhaust valve while being swung to the point side.

[Effect]

In this invention, at low rotation,
The exhaust valve partially blocks the exhaust port to delay the exhaust timing, and the side of the exhaust valve blocks the sub-exhaust passage to close the sub-exhaust port. On the other hand, at high engine speeds, the exhaust timing is accelerated by eliminating the partial blocking of the exhaust port by the exhaust valve, and the auxiliary exhaust passage is opened to allow the auxiliary exhaust port to communicate with the exhaust passage, effectively reducing the exhaust timing without changing the exhaust timing. Expand the exhaust port opening area and improve exhaust efficiency.

Here, in the present invention, since a swing type exhaust valve having a shaft on the exhaust downstream side is used, when the exhaust timing is set to a low speed and the sub-exhaust passage is closed, fresh air can be reliably prevented from blowing through. In addition, it is possible to reliably prevent problems such as effects on exhaust timing control due to expansion due to exhaust heat, and problems are less likely to occur even when the main exhaust port is enlarged in order to achieve high output.

〔Example〕

Hereinafter, one embodiment of the present invention will be described based on the drawings.

As shown in FIGS. 1 and 2, the variable exhaust timing two-stroke engine 10 of this embodiment has a piston 12 that reciprocates within a cylinder 11.
A plurality of scavenging ports 13 are provided on the inner surface of the cylinder 11.
and two exhaust ports 14 are opened.

The exhaust port 14 is communicated with the outside via an exhaust passage 15 passing through the block of the cylinder 11, and a plate-shaped exhaust valve 16 is provided in a recess 15A formed on the inner surface of the exhaust passage 15 on the top dead center side. It is rotatably provided.

Here, the exhaust valve 16 has one end fixed to an exhaust valve drive shaft 17, and the exhaust valve drive shaft 17 passes through the block of the cylinder 11 and is exposed to the outside, and a wire 18A is wound around the tip thereof. Pulley 18B is attached. Therefore, the exhaust valve 16 can be rotated by a servo motor (not shown) or the like via the wire 18A in accordance with the engine speed.

In addition, an exhaust port 1 is provided on the other end side of the exhaust valve 16.
A tip edge 16A is formed along the top dead center side edge of the exhaust valve 1.
6, it moves up and down in FIG. 2, advances and retreats into the exhaust port 14, and is configured to partially block the top dead center side of the opening surface, and the exhaust port 16A of the tip edge 16A is moved up and down in FIG. The maximum advance position into the port 14 is set to a position corresponding to the exhaust timing when the engine 10 is running at low speed.

Note that the exhaust valve 16 is provided with a vent hole 19 that communicates with both sides of the exhaust valve 16.
Alternatively, the recess 15 of the exhaust passage 15 that accommodates this
It is configured to prevent carbon and the like from adhering to A and the like.

On the other hand, as shown in FIG. 3, sub-exhaust ports 21 are opened on both sides of the exhaust port 14 on the inner surface of the cylinder 11. Furthermore, an opening 23 of the sub-exhaust passage 22 on the side of the exhaust passage 15 is formed on the side surface of the recess 15A of the exhaust passage 15, and can be opened and closed by the side surface 16B of the exhaust valve 16 rotating within the recess 15A. ing.

That is, as shown in FIG.
6 is housed in the recess 15A and L ₁ is the lower surface position in the state in which the auxiliary exhaust passage ₂₂ is advanced into the exhaust port 14.
The opening 23 is located above L ₂ in the figure,
The opening 23 is configured to be closed only when the exhaust valve 16 advances into the exhaust port 14.

In this embodiment configured in this manner, exhaust gas generated within the cylinder 11 as the engine 10 operates is exhausted to the outside via the exhaust port 14 and the exhaust passage 15 by scavenging air from the scavenging port 13. Here, the exhaust timing in the cylinder 11 is determined by the top dead center side edge of the exhaust port 14, but the exhaust valve 16 is rotated according to the rotation speed of the engine 10, etc.
The exhaust port 14 is partially blocked by A, and its edge position on the top dead center side is changed to maintain the optimum position at all times.
At this time, when the exhaust valve 16 is rotated toward the bottom dead center side, the opening 23 of the sub-exhaust passage 22 is opened on the side surface 16.
B, but is opened when rotated toward the top dead center side, opening the sub-exhaust port 21 and the sub-exhaust passage 22 to communicate the cylinder 11 and the exhaust passage 15, reducing the exhaust port opening area. Expand.

According to this embodiment, the following effects can be obtained.

That is, when the engine speed is high, the exhaust valve 16 is rotated toward the top dead center to advance the exhaust timing, and the auxiliary exhaust port 21 is opened to expand the exhaust port opening area, thereby increasing exhaust efficiency.

In addition, when the engine speed is low, the exhaust valve 16 is rotated toward the bottom dead center to delay the exhaust timing.
By closing the sub-exhaust port 21, the opening area of the exhaust port is reduced, and leakage of the air-fuel mixture from the scavenging port 13 to the outside can be prevented.

Therefore, according to this embodiment, the optimum exhaust timing and exhaust port opening area are always maintained by the exhaust valve 16, and the exhaust efficiency is improved to achieve high output at high rotation speeds and high output at low rotation speeds of the engine 10. Since contradictory factors such as high output can be satisfied at the same time, overall performance improvement can be achieved.

Furthermore, the auxiliary exhaust port 21, the auxiliary exhaust passage 22, and the opening 23 make it possible to expand the exhaust port opening area according to the state of the engine 10, without complicating the structure compared to conventional engines, and simplifying the manufacturing process. Inconveniences caused by increase or complexity can also be prevented.

In addition, since the distance from the center of rotation does not become excessive as in the case where the exhaust valve 16 and the exhaust port 14 are expanded in the circumferential direction of the cylinder 11,
The curvature of the trajectory of the tip edge 16A of the exhaust valve 16 can be reduced, and the knife edge shape formed at the top dead center side edge portion of the exhaust port 14 by the cylinder 11 and the recess 15A can be thickened.
It is possible to improve its own heat conduction efficiency, and it is also possible to arrange cooling water passages and the like.

Note that the present invention is not limited to the embodiments described above, but also includes the following modifications.

That is, the position of the sub-exhaust port 21 is not limited to the two locations on both sides of the exhaust port 14, but may be located at either one of the locations. Alternatively, a plurality of them may be arranged in each case, and these may be arranged at a position away from the exhaust port 14. However, if the configuration is as in the embodiment described above, the exhaust passage 22 can be shortened and the exhaust port opening surface can be expanded most effectively.

Furthermore, it is not particularly necessary that the top dead center side edge of the sub exhaust port 21 be located at approximately the same position as the top dead center side edge of the exhaust port 14.

Furthermore, the exhaust valve 16 is not limited to the shape shown in the embodiments described above, but may have any shape as long as it has a side 16B that can close the opening 23 of the sub-exhaust passage 22 during operation. This means that the opening 23 of 22 is placed in a position where it can be closed by such a side surface 16B.

Further, the mechanism for rotating the exhaust valve 16 and the exhaust valve drive shaft 17 is not limited to the wire 18A and the pulley 18B, but may be a structure using a transmission mechanism using gears, a structure directly connecting a solenoid or a motor, etc. Other details of shape,
Dimensions, etc. can be changed as appropriate in implementation.

〔Effect of the invention〕

As described above, according to the variable exhaust timing two-stroke engine of the present invention, the exhaust timing can always be optimally and accurately set, and the exhaust port opening area can be adjusted according to the rotation speed, etc., to improve exhaust efficiency. , and the total area of the exhaust port opening can be expanded.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view showing one embodiment of the present invention, FIG. 2 is a vertical cross-sectional view taken along the line - in FIG. 1, and FIG.
The figure is a developed view showing the inner surface of the cylinder of the above embodiment;
FIG. 4 is a partially broken perspective view showing the vicinity of the exhaust port of the embodiment, FIG. 5 is a cross-sectional view showing the conventional example, and FIG. 6 is a vertical cross-sectional view taken along the line - in FIG. be. 10...2-stroke engine with variable exhaust timing,
11...Cylinder, 14...Exhaust port, 15...
...Exhaust passage, 16...Exhaust valve, 16B...Side side of exhaust valve, 21...Sub-exhaust port, 22...
... Sub-exhaust passage, 23... Opening on the exhaust passage side of the sub-exhaust passage.

Claims (1)

[Scope of Claims] 1. An exhaust valve is provided in an exhaust passage communicating with an exhaust port opened on the inner surface of the cylinder to make it possible to partially block off the top dead center side of the exhaust port and to vary the exhaust timing. , a sub-exhaust port is opened on the inner surface of the cylinder on the side of the exhaust port,
A variable exhaust timing two-stroke engine, comprising means for communicating the sub-exhaust port with the exhaust passage through a sub-exhaust passage, and opening and closing the exhaust passage according to the operation of the exhaust valve, the exhaust The valve has a swing axis on the downstream side of the exhaust passage, and the exhaust timing can be varied at the tip edge on the cylinder side, and the opening on the exhaust passage side of the sub exhaust passage allows the exhaust valve to swing toward the bottom dead center side. 1. A variable exhaust timing two-stroke engine, characterized in that the engine is disposed in a position where the exhaust valve is closed by a side surface of the exhaust valve when the engine is in motion.