JPH0378529A - Exhaust device of two-cycle engine - Google Patents

Abstract

PURPOSE:To easily ensure accurate action of a valve unit by guide-supporting the valve unit, which is advanced and retracted in an exhaust port to change the exhaust timing, to a shaft member additionally provided in a cylinder block. CONSTITUTION:When a link mechanism 25 is driven, a valve unit 21 is moved through a correlation pin 22, and a valve main unit 21b of this valve unit 21 is advanced and retracted for an exhaust port 11. For instance, when an engine is in a predetermined low speed region, the valve main unit 21b is protruded in the exhaust port 11. Consequently, height of each upper edge 11a' of each opening 11a in a side of a cylinder 12 of the exhaust port 11 is lowered respectively by a predetermined distance H with the exhaust timing delayed. Here the valve unit 21 is guide-supported by a plurality of shaft members 23. Each shaft member 23 is additionally provided in a guide member 20 held to a cylinder block 10. In this way, accurate action of the valve unit 21 is easily ensured.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an exhaust system for a two-stroke engine, and more particularly to an exhaust system that changes exhaust timing using a valve body.

[Conventional technology]

FIG. 3 conceptually shows this type of two-stroke engine. This two-stroke engine includes a valve body 4 at the upper edge of the cylinder 3 side opening 2a of the exhaust port 2 in the cylinder block 1.

The valve body 4 is slidably fitted into the cylinder block 1 and a valve body 4a disposed in a recess 5 opening into the excirst boat 2, with the valve body 4a being fixed to the lower end and having a valve body 4a fixed to the upper end. The shaft part 4b is provided with a link mechanism 6 that links with a drive means (not shown), and when the drive means is operated, the link mechanism 6 and the shaft part 4b are connected to each other.
The valve main body 4a is moved into and out of the exhaust port 2 via.

In such an engine, when the valve body 4a is moved forward and backward into the exhaust port 2, the upper edge 2a' of the cylinder 3 side opening 2a changes by a substantial distance A, which causes the reciprocating movement of the piston (not shown). Exhaust port 2 by
The opening timing, that is, the exhaust timing, can be changed.
It is possible to improve engine output over a wide rotation speed range from a low rotation speed range to a high rotation speed range.

[Problem to be solved by the invention]

By the way, since the valve body 4 in the above-mentioned exhaust system is always exposed to the exhaust port 2 through the valve body 4a, external forces such as pressure from the high temperature and high pressure burned gas passing through the exhaust port 2 are applied. will receive.

Therefore, in order to ensure accurate operation of the valve body 4 in this type of exhaust system, it is preferable to guide the valve body 4 by increasing the diameter of the shaft portion 4b or by increasing the number of shaft portions 4b.

However, in the conventional exhaust device described above, since the shaft portion 4b is also moved with the operation of the valve body 4a, this shaft portion 4b
If the diameter of the valve body 4 is increased or the number of valve bodies 4 is increased, the inertial weight of the valve body 4 will increase, and there is a risk that its operational response will be impaired.

SUMMARY OF THE INVENTION In view of the above-mentioned circumstances, an object of the present invention is to provide an exhaust system for a two-stroke engine that can ensure accurate operation without impairing the operational response of a valve body.

[Means to solve the problem]

In the exhaust system for a two-stroke engine according to the present invention, a valve body is movably disposed around the cylinder-side opening of the exhaust port in the cylinder block, and the exhaust timing is changed by moving the valve body forward and backward into the exhaust port. In the exhaust system for a two-stroke engine, the cylinder block is provided with a shaft member, and the valve body is guided by the shaft member.

[Operation] According to the above configuration, the valve body is guided by a shaft member that is separate from the valve body.

〔Example〕

EMBODIMENT OF THE INVENTION Hereinafter, the present invention will be described in detail based on drawings showing embodiments.

Fig. 1(a) and Fig. 1(b) conceptually show the main parts of a two-stroke engine to which an exhaust system according to the present invention is applied. It shows. Although not clearly shown in the figure, an exhaust port 11 formed in the cylinder block 10
The cylinder 12 side part is bifurcated, and the cylinder 12 has a pair of openings 11a, 11a.

These openings 11a and lla on the cylinder 12 side of the exhaust port 11 have a mutually symmetrical shape, and the height position of each upper edge 11a11a' is set to be suitable for the high rotation speed range of the engine. There is.

This two-stroke engine has an accommodation hole 13 in a portion of the cylinder block 10 located above the exhaust port 11. This accommodation hole 13 is formed from the outer surface 10a of the cylinder block 10 toward the exhaust port 11, and
Openings 11a, 11. on the cylinder 12 side. It opens near the upper edge of a, and a guide member 20 and a valve body 21 are accommodated therein.

As shown in FIG. 2, the guide member 20 is integrally formed with a bottom plate 20a having a cutout at the center of the tip and a standing plate 20b extending upward from the base end of the bottom plate 20a. An insertion hole 20c and a pair of fitting holes 20d are formed in the vertical plate 20b.
, 20d. The insertion hole 20c has a rectangular shape and is bored along the extending direction of the bottom plate 20g. The fitting holes 20d, 20d are formed along the extending direction of the upright plate 20b, and are arranged in parallel at intervals in the width direction of the guide member 20.

The valve body 21 includes a valve main body 21b having a distal end surface 21a having an arc shape and an oval shape when viewed from the side, and an outer end extending outward from the upper part of the proximal end surface of the valve main body 21b. Connecting pin 2
2 and a guide portion 21c. Valve body 21b
The tip portion is divided into left and right halves by a notch 21d formed in the center. The guide portion 21c is L when viewed from above.
It has a letter shape, and a pair of sliding holes 21e are provided at its base end.
.

21e is formed. The sliding holes 21e, 21e are vertically bored and are arranged in parallel with the same spacing as the fitting holes 20d, 20d formed in the guide member 20.

These guide member 20 and valve body 21 are
The guide portion 21c of the valve body 21 is inserted into the insertion hole 20c of the guide member 2o, and the shaft member 23.23 is inserted through the sliding holes 21e, 21e of the valve body 21 into the fitting holes 20d, 20d of the guide member 2o, respectively. It is made into a unit in advance by fitting the awn.

The guide member 20 and the valve body 21 in this state are moved by the shaft member 23.23 by the guide portion 21c of the valve body 21 sliding on the shaft member 23.
．． 23, and is relatively moved in the axial direction of these shaft members 23° 23 within the range of the insertion hole 20c.

These unitized guide member 20 and valve body 21
As shown in FIG.
After being accommodated in the accommodation hole 13 in a state where it faces toward the outside, it is held in the cylinder block 10 via the guide member 20 by fastening means such as screws (not shown).

Furthermore, the outer edge of the pin 22 is covered with a horseshoe-shaped plate 24, and a link mechanism 25 connected to a drive means (not shown) is linked to the link pin 22.

In the two-stroke engine configured as described above, when the link mechanism 25 is operated by the above-mentioned driving means (not shown), the valve body 21 is moved via the linking pin 22, and the valve body 21b of the valve body 21 is moved. It is moved forward and backward into the exhaust port 11.

At this time, as shown in FIG. 1(a), in the valve body 21 in the most retracted state, the valve body 21b is completely recessed into the accommodation hole 13, and its bottom surface 21f is inside the exhaust port 1. It is aligned with the wall surface 11b, and closes the opening 13a of the exhaust port 11 of the accommodation hole 13 together with the bottom plate 20a of the guide member 2o.

Now, when this two-stroke engine is being operated and the rotational speed is in a predetermined low rotational speed range, the above-mentioned driving means (not shown) is activated, and as shown in FIG. 1(b), the valve body 2
One valve body 21b projects into the exhaust port 11.

In this state, the valve body 21 opens the cylinder 12 side openings 11a and lla in the exhaust port 11.
This means that the height positions of the upper edges 11a' and 11a' have been lowered by a distance H, which ensures a suitable late exhaust timing in the low rotational speed range, and improves the engine output in the low rotational speed range. Ru.

On the other hand, when the engine speed increases from the above state and reaches a predetermined high speed range, the aforementioned driving means (not shown) is operated in the opposite direction, as shown in FIG. 1 (a). ), the valve body 21b of the valve body 21 is removed from the exhaust port 11.

In this state, the distance H
As a result, exhaust is started earlier, ensuring suitable exhaust timing in the high rotation speed range, and improving engine output in the high rotation speed range.

During this time, high temperature and high pressure burnt gas is passing through the exhaust port 11, so the valve body 21 receives external force such as pressure from this burnt gas. Since it is guided and supported by the shaft member 23° 23, the influence during its operation can be prevented as much as possible.

Moreover, since the plurality of shaft members 23.23 are provided on the guide member 20 held in the cylinder block 10, even if the diameter of these shaft members 23.23 is increased or the number of shaft members 23.23 is increased, the valve body The inertial weight of 21 is not affected and therefore its operational responsiveness is not impaired.

In the above embodiment, the guide member 20 is provided with the shaft member 23, and the guide member 20 is held by the cylinder block 10, so that the cylinder block 10 is provided with the shaft member 23, but the present invention In the exhaust system according to the above, the shaft member may be provided directly on the cylinder block 10. Further, since the valve body 21 and the guide member 20 are assembled in advance into a unit and held in the cylinder block 10, the valve body 21 can be easily assembled to the cylinder block 10. However, the present invention is not limited to this.

Further, in the above embodiments, a two-stroke engine mounted on a motorcycle and having a portion of the exhaust port 11 on the cylinder 12 side is bifurcated is illustrated, but the present invention is not limited to this.

〔Effect of the invention〕

As described above, according to the exhaust system for a two-stroke engine according to the present invention, since the valve body is guided by a shaft member that is separate from the valve body, accurate operation of the valve body is ensured. Therefore, even if the diameter of the shaft member is increased or the number of shaft members is increased, the inertial weight of the valve body does not increase, and its operational responsiveness can be ensured.

1(b) shows the state in which the valve body is protruded. Fig. 2 is an enlarged exploded perspective view conceptually showing the valve body applied to the exhaust system according to the present invention, and Fig. 3 conceptually shows the main parts of a two-stroke engine to which the conventional exhaust system is applied. FIG.

DESCRIPTION OF SYMBOLS 10... Cylinder block, 11... Exhaust port, 11a... Cylinder side opening, 12... Cylinder, 21... Valve body, 23... Shaft member.

Claims (1)

[Claims] In an exhaust system for a two-stroke engine, a valve body is movably disposed around the cylinder-side opening of an exhaust port in a cylinder block, and the exhaust timing is changed by moving the valve body forward and backward into the exhaust port, An exhaust system for a two-stroke engine, characterized in that the cylinder block is provided with a shaft member, and the shaft member guides the valve body.