JPH0361608A - Exhaust device for two-cycle engine - Google Patents

Abstract

PURPOSE:To increase output over the whole revolution regions by installing an exhaust valve which changes the opening area at the upper edge part of an exhaust port in increase movement from the low speed operation to the high speed operation and successively closes a plurality of exhaust chamber inlets. CONSTITUTION:An exhaust valve 7 for vertically varying the opening area at the upper edge part of an exhaust port 5 in correspondence with the revolution speed of an engine is installed in the vicinity of the exhaust port 5 of an exhaust passage 6. When the engine changes operation from a low speed revolution region to a high speed revolution region, the opening area at the upper edge of the exhaust port 5 is varied in increase movement, and the inlets 9a and 9b of two exhaust chambers 8a and 8b are successively closed. Therefore, the exhaust timing proper for the revolution region and the equivalent pipe length to exhaust pipe can be obtained, and the mixed gas charging efficiency which is proper for the revolution region can be obtained, and blasting off is prevented. Therefore, the output can be increased uniformly over the whole revolution regions of the engine.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to an exhaust system for a two-stroke engine that makes it possible to increase output over the entire range from low speed rotation to high speed rotation.

[Prior art]

It is known that in order to increase the output of a two-stroke engine, it is sufficient to increase the charging efficiency of the mixed gas. In order to increase the filling efficiency of such a mixed gas, the exhaust timing may be adjusted so that it is slower in the low speed range and earlier in the high speed range, or by using the reflected waves of the exhaust pulsation waves to eliminate unburned gas. There are devices that prevent the mixed gas from blowing through the exhaust port.

Japanese Patent Application Laid-Open No. 60-252117 discloses a bypass hole that communicates with the cylinder and the exhaust passage above the exhaust port, and a bypass hole that communicates with the bypass hole in order to implement a method of increasing the filling efficiency of two mixed gases. This disclosure discloses a two-stroke engine that is provided with an exhaust chamber and an exhaust valve that opens and closes the bypass hole and the exhaust chamber depending on the engine rotation speed. With this configuration, in the low-speed rotation range, the exhaust valve closes the bypass hole, slows down the exhaust timing, and opens the exhaust chamber to lengthen the equivalent length of the exhaust pipe, allowing the reflected waves of the exhaust pulsation waves to blow through the air. On the other hand, in the high-speed rotation range, the exhaust valve opens the bypass hole to speed up the exhaust tie-up, and also closes the exhaust chamber to shorten the equivalent length of the exhaust pipe, allowing the reflected waves of the exhaust pulsation waves to cause blow-through. I'm trying to suppress it.

However, this two-stroke engine requires the use of a bypass hole with a small cross-sectional area to advance the exhaust timing in the high-speed rotation range, which not only causes power loss due to flow resistance but also becomes structurally complex. There was a problem. In addition, it is only possible to control rotation in both the low-speed rotation range and the high-speed rotation range, making it impossible to increase output evenly across the entire rotation range: low-speed rotation, medium-speed rotation, and high-speed rotation. There were drawbacks.

[Problem to be solved by the invention]

SUMMARY OF THE INVENTION In view of the above-mentioned conventional problems, it is an object of the present invention to provide an exhaust system for a two-stroke engine that has a simple structure and is capable of uniformly increasing the output over the entire rotation range of the engine.

[Means to solve the problem]

To achieve the above object, the present invention provides an exhaust valve in the vicinity of the exhaust port of the exhaust passage, which changes the opening area of the upper edge of the exhaust port in the vertical direction in response to the rotational speed of the engine, and also includes a plurality of exhaust chambers. The exhaust valve is configured to change the opening area of the upper edge of the exhaust port in the direction of expansion when the engine changes from a low speed rotation range to a high speed rotation range, and to open the exhaust valves so that the opening area of the exhaust port is changed in the direction of expansion. It is characterized by being configured to be closed in sequence.

〔Example〕

FIG. 1 shows a two-stroke engine according to an embodiment of the present invention, in which 1 is a cylinder and 2 is a piston. An intake port 3 that communicates with an intake passage 4 is opened at the lower part of the cylinder 1, and an exhaust port 5 that communicates with an exhaust passage 6 is opened at the upper side opposite to this.

A drum-shaped exhaust valve 7 that changes the opening area of the upper edge of the exhaust port 5 is provided near the exhaust port 5 . The exhaust valve 7 has a substantially horizontal axis of rotation in the direction across the exhaust passage 6, and is adapted to change the opening area of the upper edge of the exhaust port 4 in the vertical direction depending on the rotational speed of the engine. That is, the exhaust valve 7 closes the upper edge of the exhaust port as shown in the figure in the low speed rotation range, but as the rotation speed increases, it rotates counterclockwise to open the upper edge of the exhaust port. It has become.

Further, a plurality of exhaust chambers 8 are provided adjacent to the exhaust valve 7.
a, 8b...- are provided. In this embodiment, the number of exhaust chambers is two, but three or more may be provided. Further, in this embodiment, the volumes of the plurality of exhaust chambers are different from each other, and the exhaust chamber 8a is larger than the exhaust chamber 8b. The inlets 9a, 9b of these exhaust chambers 8a, 8b are connected to the exhaust valve 7.
By rotating counterclockwise, the exhaust chamber 8
The exhaust chambers 8a to 8b are closed sequentially.

The exhaust valve 7 configured as described above opens and closes the upper edge of the exhaust port 5 and opens and closes the exhaust chambers 8a and 8b according to the rotational speed of the engine as shown in the graph shown in FIG. , brings about the following effects.

When the engine is in a low speed rotation range, the exhaust valve 7 is in a state in which the upper edge of the exhaust port 5 is closed to the lowest position. Therefore, the exhaust timing at this time is delayed, increasing the efficiency of filling the mixed gas during low speed rotation. In addition, since the exhaust valve 7 at this time does not close the inlets 9a and 9b of the exhaust chambers 8a and 8b, the equivalent pipe length of the exhaust pipe is the longest, and the reflected wave of the exhaust pulsation wave is reflected from the unburned mixed gas. It acts to push back into the cylinder 1. Therefore, this exhaust pulsating wave also increases the filling efficiency of the mixed gas.

As the engine speed increases, the exhaust valve 7 gradually rotates counterclockwise, and in the middle speed range, only the inlet 9a of the exhaust chamber 8a is closed, and the upper edge of the exhaust port 5 is half opened. state. Therefore, the exhaust tie adjustment becomes faster than in the low speed rotation range, and the filling efficiency of the mixed gas is made suitable for this medium speed rotation range. In addition, since only the exhaust chamber 8a is closed, the reflected waves of the exhaust pulsating waves are also prevented from blowing in the middle speed rotation range.

Further, when the engine reaches a high-speed rotation range, the exhaust valve 7 is moved into the exhaust chamber 8a as well as the inlet 9b of the exhaust chamber 8b.
The exhaust port 5 is also closed, and the upper edge of the exhaust port 5 is left completely open. Therefore, the exhaust timing becomes even earlier. Additionally, the equivalent length of the exhaust pipe is shortened to accommodate the high-speed rotation range, thereby preventing unburned mixed gas from blowing through.

FIG. 5 shows the output curve of the two-cycle engine near the peak speed, where A is the curve of the engine according to the invention shown in FIG. 1, and B is the curve of the exhaust chamber 8a in the engine of FIG.

8b is not provided, C is a curve when only exhaust chamber 8a, which has a larger volume of the two exhaust chambers, is provided, and D is a curve when only exhaust chamber 8b, which has a smaller volume of the two exhaust chambers, is provided. This is the curve for the case. As is clear from these curves, the two-stroke engine according to the present invention has an increased output over the entire rotation range.

FIG. 2 shows a second embodiment of the invention.

In this embodiment, the inlet 9b of the exhaust chamber 8b having a smaller volume is separated from the inlet 9a of the exhaust chamber 8a having a larger volume than in the embodiment shown in FIG. Therefore, as shown in FIG. 6, the exhaust chamber 8a is not closed until the engine speed reaches a considerably high speed range.

FIG. 3 shows a third embodiment of the invention.

4. In this embodiment, a slit 5a is provided above the exhaust port 5 in the engine of the embodiment shown in FIG. As a result, as shown in FIG. 7, the opening of the exhaust port 5 is delayed to coincide with the completion of closing of the inlet 9a of the exhaust chamber 8a.

It goes without saying that in both the second and third embodiments, the output can be increased evenly over the entire rotation range of the engine, similarly to the embodiment shown in FIG. 1 described above.

〔Effect of the invention〕

As described above, the present invention allows the exhaust valve to change the opening area of the upper edge of the exhaust port in the direction of expansion when the engine changes from a low speed range to a high speed range, and to sequentially close the inlets of a plurality of exhaust chambers. Because of the configuration, the exhaust timing and the equivalent length of the exhaust pipe can be changed with a simple structure, and the output can be increased evenly over the entire rotation range of the engine.

[BRIEF DESCRIPTION OF THE DRAWINGS] FIG. 1 is a longitudinal sectional view of a two-stroke engine according to an embodiment of the present invention, FIG. 2 is a longitudinal sectional view of a two-stroke engine according to another embodiment, and FIG. 2 consisting of examples of
FIG. 4 is a vertical cross-sectional view of the cycle engine; FIG. 4 is a graph showing the engine rotational speed, the upper edge of the exhaust port due to the exhaust valve, and the opening and closing of the exhaust chamber in the engine of FIG. 1;
The figure shows the output curve of the same engine near its peak speed, and FIGS. 6 and 7 show the engine rotational speed and the upper edge of the exhaust port due to the exhaust valve in the engines of FIGS. 2 and 3, respectively. It is a graph showing opening and closing of an exhaust chamber. DESCRIPTION OF SYMBOLS 1... Cylinder, 2... Piston, 5... Exhaust port, 6... Exhaust passage, 7... Exhaust valve, 8a,
8b...exhaust chamber, 9a, 9b...inlet.

Claims (1)

[Claims] An exhaust valve that changes the opening area of the upper edge of the exhaust port in the vertical direction in response to the rotational speed of the engine is provided near the exhaust port of the exhaust passage, and the exhaust valve faces the inlets of a plurality of exhaust chambers. When the engine changes from a low speed rotation range to a high speed rotation range, the opening area of the upper edge of the exhaust port is changed in a direction of expansion, and the inlets of the plurality of exhaust chambers are sequentially closed. Device.