JPH0441922A - Exhaust device of two-cycle engine - Google Patents

Abstract

PURPOSE:To prevent fixing of tar an so on to between a valve and a storage recess part in an exhaust device of a two-cycle engine in which exhaust timing is controlled through arrangement of the valve in the storage recess part formed in the neighborhood of a main exhaust port by projecting a partition wall between an auxiliary exhaust passage and a main exhaust passage into the storage recess part. CONSTITUTION:A main exhaust port 3d and a pair of auxiliary exhaust ports 3e are opened at the part upper than a scavenge port 3c of a cylinder 3a in a two-cycle engine 1, and a storage recess part 11 is formed at the lower stream part adjacent to the main exhaust port 3d of a cylinder body 3 so that it crosses the upper part of a main exhaust passage 3f. And a valve 12 is rotatably inserted and arranged in the storage recess part 11 so as to make exhaust timing variable by rotating it according to an engine revolution number. In this case, a partition wall 3h forming a boundary between the main exhaust passage 3f and an auxiliary exhaust passage 3g is extended inward to a circular part 11b of the storage recess part 11 and projected into the circular part 11b. By this, exhaust gas is restrained from flowing from the main exhaust port 3d through a gap between the valve 12 and the storage recess part 11, and fixing of tar an so on is prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an exhaust system for a two-stroke engine, and particularly to an exhaust system for a two-stroke engine, in which an auxiliary exhaust passage is provided and the passage is opened and closed by an exhaust timing control valve body. This invention relates to improvements to the partition wall that forms the boundary between both exhaust passages.

[Conventional technology]

As an exhaust system for a two-stroke engine, a housing recess is formed in the exhaust passage, a valve body constituting the upper edge of the exhaust port is disposed within the recess, and the upper edge of the exhaust port is moved by rotating the valve body. There is a device that changes the position up and down, thereby making the exhaust timing variable. In addition, in order to increase the exhaust port area and improve exhaust efficiency, an auxiliary exhaust passage is provided that penetrates the housing recess and communicates the auxiliary exhaust port on the side of the exhaust port with the downstream portion of the valve body of the exhaust passage. Above exhaust i
There is a device which is provided on the side of the il passage and the auxiliary passage is opened and closed by the valve body (for example, Japanese Patent Application Laid-Open No. 59-10153).
(See Publication No. 4).

[Problem that the invention seeks to solve]

However, in the exhaust system described in the above-mentioned publication, the exhaust gas flows from the main exhaust port to the auxiliary exhaust passage using the gap between the accommodation recess and the valve body, and tar, etc. in the exhaust gas adheres to the gap due to high heat. In extreme cases, this may impede the operability of the valve body.

The present invention has been made in order to solve the above-mentioned conventional problems, and an object of the present invention is to provide an exhaust system for a two-stroke engine that can prevent the above-mentioned tar from sticking and ensure the operability of the valve body. It is said that

[Means for solving problems]

The present invention provides a housing recess that is formed in the vicinity of the main exhaust port opening on the inner surface of the cylinder of the main exhaust passage so as to be perpendicular to the main exhaust passage, and a valve that forms the upper edge of the main exhaust port within the housing recess. The upper edge height of the main exhaust port is moved up and down by the valve body to control the exhaust timing, and the main exhaust port passes through the housing recess in the direction of the main exhaust passage, and the main exhaust port is located inside the cylinder. A two-stroke engine, wherein an auxiliary exhaust passage is formed to communicate an auxiliary exhaust port opening at a side portion of the mouth with a portion downstream of the housing recess of the main exhaust passage, and the auxiliary exhaust passage is opened and closed by the valve body. The exhaust device is characterized in that a partition wall between the auxiliary exhaust passage and the main exhaust passage projects into the accommodation recess.

[Function] According to the exhaust device according to the present invention, the flow of exhaust gas from the main exhaust port to the auxiliary exhaust passage is suppressed by projecting the barrier toward the accommodation recess, and the flow of exhaust gas from the main exhaust port to the auxiliary exhaust passage is suppressed by causing the barrier to protrude toward the accommodation recess. During this period, tar and the like hardly stick, and therefore the operability of the valve body is not affected.

In addition, since the partition wall protrudes toward the housing recess, the boundary between the main exhaust 1ffi passage and the auxiliary exhaust ill is reinforced, and when the width of the exhaust port is increased to further improve exhaust efficiency. It is also possible to suppress the decrease in strength.

〔Example〕

Hereinafter, embodiments of the present invention will be described with reference to the drawings.

1 to 4 are diagrams for explaining an exhaust system for a two-stroke engine according to an embodiment of the present invention, and FIG.
The figure is a cross-sectional plan view, Figure 2 is a cross-sectional side view, Figure 3 is fa+,
(b) is a bottom view and side view of the valve body, and Figure 4 is I of Figure 3.
It is a sectional view taken along the line V-IV.

In the figure, reference numeral 1 denotes a two-stroke engine equipped with the exhaust system of this embodiment. In this engine 1, a cylinder body 3 is fixed with bolts on a crankcase 2, and a cylinder head 4 is mounted on the cylinder body 3 with head bolts. 5 indicates a structure in which the tightening is fixed. A combustion recess 4a that forms a combustion chamber 9 with the top surface of the piston 6 inserted into the cylinder 3a of the cylinder body 3 is formed in the bottom of the cylinder rad 4. A spark plug 10 is screwed into the combustion chamber 9 so that its electrode portion faces into the combustion chamber 9. The piston 6 is connected to a crankshaft 8 by a connecting rod 7, and a crank weight 8a of the crankshaft 8 is located within a crank chamber 2a of the crankcase 2. An intake port 2b for introducing outside air communicates with the crank chamber 2a, and the crank chamber 2a communicates with the cylinder 3a via a scavenging passage 3b and a scavenging port 3C.

In the portion above the scavenging port 3c of the cylinder 3a,
A main exhaust port 3d and a pair of auxiliary exhaust ports 3e are open, and the main exhaust port 3d is led out to the outside by a main exhaust passage 3f. Further, in the downstream portion of the cylinder body 3 adjacent to the main exhaust port 3d, a housing recess 11 is formed so as to cross the upper portion of the cough main exhaust passage 3f. The housing recess 11 is composed of a semicircular portion 11a formed by recessing the ceiling wall portion of the main exhaust passage 3f upward, and circular portions 11b formed on both sides of the semicircular portion 11a.

A valve body 12 is rotatably inserted into the accommodation recess 1. This valve body 12 is the semicircular portion 11a.
It consists of a timing variable part I2a located inside, and left and right shaft supports 12b12c formed on both sides thereof and rotatably supported by the circular part Ilb. In addition,
The left shaft support 12b is separate to ensure ease of assembly, and is connected to the variable timing portion 12a with a bolt 13. A rotation arm 14 is connected to the right shaft support 12C, and the rotation arm 12C is connected to the right shaft support 12C. A drive arm 15 is connected to the movable arm 14 . A drive mechanism (not shown) rotates the valve body 12 via the drive arm 159 and the rotation arm 14 in accordance with the engine speed.

The bottom surface 12d of the timing variable section 12a is shown in FIG.
As shown in bl, it is formed along the cross-sectional shape of the main exhaust passage 3f. Further, the upper edge 128 on the upstream side of the timing variable portion 12a is located at the cylinder 3 when viewed in the cylinder axial direction.
It is formed in an arc shape that roughly follows the inner peripheral surface of a (Fig. 1,
(see Figure 3 fa)), this upper edge 12e is the main exhaust port 3.
This will form the upper edge of d.

Auxiliary exhaust passages 3g are located on the left and right sides of the main exhaust passage 3f above.
is formed approximately parallel to the main exhaust passage 3f. This auxiliary exhaust passage 3g is a circular portion 11b of the housing recess 11.
The auxiliary exhaust port 3e is communicated with the downstream side 3j of the housing recess 11 of the main exhaust passage 3f. Further, the shaft supports 12b and 12c of the valve body 12 are formed with a notch 12f that communicates the auxiliary exhaust passage 3g with the downstream side 31.

A partition wall 3h forming a boundary between the main exhaust passage 3r and the auxiliary exhaust passage 3g extends inward of the circular portion 11b of the accommodation recess 11 and projects into the circular portion 11b. and valve body 1
2 timing variable part 12a and left and right shaft branches! 2b, 1
An escape groove 12g corresponding to the protruding shape of the partition wall 3h is formed at the boundary with the partition wall 2c, and the partition wall 3h is located within this escape groove 12g.

Next, the effects of this embodiment will be explained.

During the explosion stroke, the piston 6 descends, and the main exhaust hole 3d,
When the auxiliary exhaust port 3e starts to open, the exhaust gas flows into the main exhaust passage 3.
f and the auxiliary exhaust passage 3g to begin discharging outward. In this case, in the low rotation region, the valve body 12 rotates clockwise in FIG. While lowering the left and right shaft supports 12b1
2c closes the auxiliary exhaust passage 3g. As a result, in the low-speed operation range, the exhaust timing is delayed and the exhaust port area becomes narrower.

On the other hand, the valve body 12 is rotated counterclockwise in FIG. 2 so that its upper edge 12e rises as the rotation speed increases, and the auxiliary exhaust passage 3g is opened by the notch 12f. As a result, the exhaust timing becomes earlier in the high-speed operation range, and the exhaust port area becomes wider.

Here, as mentioned above, in the conventional exhaust system, the main exhaust port 3d
Exhaust gas flows through the gap between the valve body and the housing recess,
There was a risk that tar and the like would stick to this gap and impede the operability of the valve body.

In this embodiment, the partition wall 3h forming the boundary between the main exhaust passage 3f and the auxiliary exhaust passage 3g is made to protrude into the accommodation recess 11b, and the relief groove 12 in which the protrusion is accommodated in the valve body 12
Since the valve body 12 is formed with a groove 12, the flow of the exhaust gas described above can be suppressed to prevent tar and the like from sticking, and the operability of the valve body 12 can be ensured.

Further, in this embodiment, the partition wall 3h is extended, so that the necessary strength can be ensured even when the thickness of the barrier is reduced by widening the widths of the main and auxiliary exhaust ports 3d and 3e.

In the above embodiment, the exhaust bag W was described in which the exhaust timing was changed by rotating the valve body 12, but the present invention is directed to an exhaust device of a type in which the valve body is slid in the cylinder axial direction. It can also be applied to

〔Effect of the invention〕

As described above, according to the exhaust system for a two-stroke engine according to the present invention, the partition wall between the main exhaust passage and the auxiliary exhaust passage is made to protrude into the valve body housing recess, thereby preventing tar etc. from sticking in the exhaust gas. This has the effect of ensuring the operability of the valve body.

[Brief explanation of drawings]

1 to 4 are diagrams for explaining an exhaust system for a two-stroke engine according to an embodiment of the present invention, and FIG.
The figure is a cross-sectional plan view, Figure 2 is a cross-sectional side view, Figure 3 (a),
Figure 3 (bl is a bottom view and side view of the valve body, respectively, and Figure 4 is a cross-sectional view of Figure 3 (bl, taken along the line IV-IV). In the figure, l is a two-stroke engine, 3a is a cylinder, and 3d is a Main exhaust port, 3e is auxiliary exhaust port, 3f is main exhaust passage, 3g is auxiliary exhaust passage, 3h is partition wall, 31 is downstream side,
11 is a housing recess, and 12 is a valve body. Patent Applicant Yamaha Motor Co., Ltd. Agent Patent Attorney Tsutomu Shimofu Figure 3 (a) (b)

Claims (1)

[Claims] (1) A housing recess is formed in the vicinity of the main exhaust port opening on the inner surface of the cylinder of the main exhaust passage so as to be perpendicular to the main exhaust passage, and a valve body forming the upper edge of the main exhaust port within the housing recess. The valve body moves the upper edge height of the main exhaust port up and down to control the exhaust timing, and the main exhaust port extends through the housing recess in the direction of the main exhaust passage and is located on the inner surface of the cylinder. An auxiliary exhaust passage is formed that communicates an auxiliary exhaust port opening in a side part with a downstream part of the housing recess of the main exhaust passage, and the auxiliary exhaust passage is opened and closed by the valve body. An exhaust system for a two-stroke engine, characterized in that a partition wall between the auxiliary exhaust passage and the main exhaust passage projects into the housing recess.