JPH0814254B2 - Exhaust system for 2-cycle engine - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exhaust system for a two-cycle engine in which a piston itself acts as an exhaust valve.

[0002]

2. Description of the Related Art Conventionally, in a two-cycle engine, there is an exhaust device in which an auxiliary exhaust passage is provided in addition to the main exhaust passage, and the auxiliary exhaust passage is opened and closed by an auxiliary valve (for example, Japanese Patent Laid-Open No. 63-272916). reference). In this type of exhaust system, the auxiliary exhaust passage is closed at low speed and opened at high speed, and the cross-sectional area of the exhaust passage is made to be an area corresponding to the rotation speed of the engine, thereby improving the output at high speed.

On the other hand, at low speeds, a portion of the closed auxiliary exhaust passage, which is closer to the cylinder bore than the auxiliary valve (hereinafter referred to as "passage space"), functions as a combustion chamber of the engine, which operates at low speeds. Cause to reduce the output. Therefore, in the above-mentioned prior art, while setting the axis of the auxiliary valve parallel to the axis of the cylinder,
The passage space is reduced by providing the auxiliary valve close to the cylinder.

[0004]

However, in the above prior art, since the axis of the auxiliary valve is set parallel to the axis of the cylinder, when the auxiliary valve is brought close to the cylinder bore, it corresponds to the length of the auxiliary valve. Over the whole part,
The peripheral wall of the cylinder becomes thin. For this reason, in the above-described prior art, the auxiliary valve cannot be brought closer to the cylinder bore, and therefore the passage space cannot be sufficiently reduced, so that it may not be possible to sufficiently prevent the output from decreasing at low speed.

The present invention has been made in view of the above problems, and in a two-cycle engine equipped with an auxiliary valve for opening and closing the auxiliary exhaust passage, the passage space which is a part of the auxiliary exhaust passage is made small, The purpose is to sufficiently prevent the output from decreasing at low speed.

[0006]

In order to achieve the above object, the present invention provides a valve body of an auxiliary valve which is close to a cylinder bore, and from which the valve shaft portion projects only above the valve body.
The valve shaft is mounted on the cylinder so that it can rotate freely.
An input part that is supported and whose valve stem drives an auxiliary valve
Is a, as the input portion moves away from the cylinder bore than the valve body, by being inclined is disposed the axis of the auxiliary valve with respect to the axis of the cylinder.

[0007]

According to the present invention, since the valve body of the auxiliary valve is close to the cylinder bore, the passage space can be reduced, while the input portion for driving the auxiliary valve is located closer to the cylinder bore than the valve body. I'm moving away,
The peripheral wall of the cylinder is not thinned except in the vicinity of the valve body. Moreover, even if the valve body is brought close to the cylinder bore,
Since the valve shaft is not provided at the lower end of the valve disc, the auxiliary valve
Incline the bottom so that its lower surface follows the upper surface of the scavenging passage.
As a result, it was installed near the auxiliary exhaust passage.
The scavenging passage that does not interfere with the lower end of the auxiliary valve
Therefore, the scavenging passage can be formed into a smooth shape.

[0008]

An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 shows a vertical section of a two-cycle engine, 1 is a cylinder head, 2 is a cylinder, 3 is a scavenging passage, and 4 is a water jacket. The main exhaust port 5 communicates the inside of the cylinder 2 with the main exhaust passage 7 of FIG. The pair of auxiliary exhaust passages 9 connects the auxiliary exhaust port 8 on the side of the main exhaust port 5 and the main exhaust passage 7 as an auxiliary exhaust passage. That is, the cross-sectional area of the auxiliary exhaust passage 9 is formed smaller than that of the main exhaust passage 7. Reference numeral 2a denotes an exhaust vertical rib that divides the main exhaust passage 7 and the auxiliary exhaust passage 9 from each other. A resonance chamber 30 communicates with the main exhaust passage 7 at a low speed to prevent the output from decreasing at a low speed, but it is not necessarily provided in the present invention.

The rotary valve (auxiliary valve) 10 is
The auxiliary exhaust passage 9 is provided on the way and is rotationally driven in opposite directions by a drive device (not shown) via a transmission device 12 (see FIG. 4) in response to a change in the rotation speed of the engine. The exhaust passage 9 is opened and closed. The rotary valve 10 includes a valve passage 10a and a valve body 1
0b is formed on the columnar portion 10c in FIG. In this rotary valve 10, the valve body 10b has a cylinder bore 6
The axis Sv of the rotary valve 10 is inclined with respect to the axis Sc of the cylinder 2 so that the valve shaft portion (input portion) 10d that drives the rotary valve 10 to rotate is further away from the cylinder bore 6 than the valve body 10b. are doing.

The valve shaft portion 10d is, as shown in FIG.
A valve holder 11 fixed to the cylinder 2 is rotatably supported by screws 13 and the like. Valve holder 11
Has a cylindrical shape with large diameters at both ends, and a small diameter portion 11a in the middle faces the water jacket 4. The valve holder 11 has O-ring grooves 11b formed at the upper end and the lower end, and an O-ring 15 seals between the valve holder 11 and the cylinder 2. That is, the water jacket 4 is formed so as to surround the small diameter portion 11 a of the valve holder 11 and cools the rotary valve 10 via the valve holder 11. Incidentally, 31 is an oil seal.

The valve shaft portion 10d penetrates the cylinder 2 obliquely and protrudes above the cylinder 2 so that the cylinder 2
Above, is connected to the first or second pulleys 19 and 20 of the transmission device 12 via screws 14.

Next, the transmission device 12 will be described. The transmission device 12 includes the first and second drive cables 17 and 18 shown in FIG.
First and second pulleys 1 respectively engaged with the
It is composed of 9, 20 and the like, and transmits the rotational force of the motor to the valve shaft portion 10d of the rotary valve 10. Both pulleys 19 and 20 fixed to the valve shaft portion 10d give a rotational force to one rotary valve 10, respectively.

The drive cables 17 and 18 are the cable outers 17a and 18a and the cable inner 1 respectively.
7b and 18b, and columnar engagement members 34 are fixed to both ends of the inners 17b and 18b. The engagement members 34 are fitted into the notches 35 of the pulleys 19 and 20, so that the drive cables 17 and 18 are engaged with the pulleys 19 and 20. Outer 17
One ends of a and 18 a are fixed to the bracket 21 at the upper part of the cylinder 2.

As shown in FIG. 3, two cable guide grooves 23 are formed in the first and second pulleys 19 and 20, and one of them has the two pulleys 19 and 20 shown in FIG. Interlocking cable 2 so that it is in the opposite direction
2 is wrapped around. It should be noted that engagement members 34 that fit into the notches 35 are fixed to both ends of the interlocking cable 22.

Next, an example of the operation of the above configuration will be described. First, when the engine speed is low and the engine speed is low, both pulleys 19 and 20 of FIG. 4 are held at the positions shown, and the auxiliary exhaust passage 9 of FIG.
Closed by. Therefore, the exhaust gas G is exhausted only from the main exhaust passage 7, and as is well known, the cross-sectional area of the entire exhaust passage becomes small corresponding to a low speed, and a decrease in output at a low speed is prevented.

After that, when the rotational speed of the engine reaches a predetermined speed, the inner motor 1 shown in FIG.
7b is pulled in the direction of the arrow, and the first pulley 19 rotates. By this rotation, the second pulley 20 is rotated via the interlocking cable 22, and the inner 18b is pulled in the arrow direction. Due to the rotation of the two pulleys 19 and 20, the two valve shaft portions 10d rotate in the arrow direction, and the rotary valve 10 in FIG. 2 rotates to the fully open position. As a result, the auxiliary exhaust passage 9 communicates with the main exhaust passage 7, and exhaust is performed from both exhaust passages 7, 9. Therefore, when the engine speed is high and the engine speed is high, the cross-sectional area of all exhaust passages is large at the high speed and the output is improved as is well known.

In the above structure, since the passage space 9a in the auxiliary exhaust passage 9 closer to the cylinder bore 6 than the auxiliary valve 10 functions as a part of the combustion chamber of the engine at a low speed, the passage space 9a is made small so that the passage space 9a at a low speed. It is necessary to prevent output drop. Here, in this exhaust system, as shown in FIG. 1, the axis Sv of the rotary valve 10 is inclined with respect to the axis Sc of the cylinder 2 to bring the valve body 10b close to the cylinder bore 6, so that the passage space 9a is formed. (Fig. 2)
Can be made smaller. Therefore, it is possible to prevent the output from decreasing at a low speed.

On the other hand, the valve shaft portion 10d for driving the rotary valve 10 has the cylinder bore 6 rather than the valve body 10b.
Away from. Therefore, the cylinder 2 is not thinned in the portion other than the vicinity of the valve body 10d. Therefore, for example, the exhaust vertical rib 2a with which the rotary valve 10 of FIG. 2 is in sliding contact can also have a sufficient thickness in the upper portion of the cylinder 2. Further, since a large space is created between the valve shaft portion 10d and the cylinder bore 6 in FIG. 1, for example, a water jacket 4 as shown by a broken line can be provided above the cylinder 2 to sufficiently cool the engine. can do.

By the way, in this embodiment, the valve shaft portion 10d
The upper part of is rotatably supported by the valve holder 11, and the rotary valve 10 is supported by the cylinder 2. That is, no other valve shaft portion is provided at the lower end portion of the valve body 10b,
Also, tilt the rotary valve 10 to sweep the bottom surface.
Combined with the fact that it was along the upper surface of the air passage 3 ,
A scavenging passage 3 (shown by a broken line) provided near the auxiliary exhaust passage 9
Be) are less likely to interfere with the lower end of the rotary valve 10,
Therefore, the scavenging passage 3 can have a smooth shape.

In the above embodiment, the main exhaust passage 7 is inclined obliquely downward with respect to the axis Sc of the cylinder 2, and is inclined in a direction parallel to the upper end surface 2b of the cylinder 2. Therefore, by tilting the rotary valve 10, the entire rotary valve 10 can be shortened.

By the way, in this embodiment, a motor (not shown) is used as the drive source of the drive unit, but in the present invention, the drive unit may be a mechanical drive unit. As a mechanical drive device, when the rotational speed of the crankshaft becomes higher than a predetermined value due to the rotation of a governor (not shown) connected to the crankshaft, the steel ball tilts toward the dish-shaped spherical plate. There are known devices that move along. (See, for example, JP-A-60-249614).

[0022]

As described above, according to the present invention, since the axis of the auxiliary valve is inclined with respect to the axis of the cylinder to bring the valve element close to the cylinder bore, the passage space can be reduced. It is possible to prevent the output from decreasing at low speed. On the other hand, since the input part that drives the auxiliary valve is located farther from the cylinder bore than the valve body, it is possible to prevent the cylinder from becoming thin in the portion other than the vicinity of the valve body. A water jacket can be formed in the upper part between to sufficiently cool the engine. Also, place the valve element close to the cylinder bore.
Even if they come into contact with each other, the valve shaft is not provided at the lower end of the valve body.
Then, tilt the auxiliary valve so that its lower surface is the upper surface of the scavenging passage.
Along with the fact that the
The scavenging passage provided nearby interferes with the lower end of the auxiliary valve.
It is difficult to make the scavenging passage smooth.
Can be.

[Brief description of drawings]

FIG. 1 is a vertical sectional view of a two-cycle engine showing an embodiment of the present invention.

FIG. 2 is a cross-sectional view of the same plane.

FIG. 3 is a sectional view of a valve holder.

FIG. 4 is a plan view of a transmission device.

[Explanation of symbols]

2 ... Cylinder, 6 ... Cylinder bore, 7 ... Main exhaust passage, 9
... auxiliary exhaust passage, 10 ... auxiliary valve (rotary valve), 10b ... valve body, 10d ... input part (valve shaft part), 12
... transmission device, Sv ... auxiliary valve axis, Sc ... cylinder axis.

Claims (1)

[Claims] 1. A main exhaust passage communicating with the inside of a cylinder, an auxiliary exhaust passage connecting the inside of the cylinder and the main exhaust passage as an auxiliary exhaust passage, and an auxiliary valve opening and closing the auxiliary exhaust passage. , A drive device for driving the auxiliary valve in accordance with a change in the rotational speed of the engine 2
An exhaust system for a cycle engine, wherein the valve body of the auxiliary valve is close to a cylinder bore, and from the valve body,
The valve shaft portion is provided so as to project only above the valve shaft.
Is rotatably supported by the cylinder, and the valve shaft is
An input section for driving the auxiliary valve, and a two-cycle engine in which the axis of the auxiliary valve is inclined with respect to the axis of the cylinder so that the input section is farther from the cylinder bore than the valve body is. Exhaust system.