JPH0219283B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a starting pressure reducing device for a two-stroke engine equipped with an exhaust timing valve.

(Prior Art) Conventionally, some two-stroke engines are equipped with an exhaust valve.

In this device, an exhaust valve is provided at the upper part of the exhaust port side end of the exhaust passage extending from the exhaust port of the cylinder, and this exhaust valve is a movable wall that constitutes the upper edge of the exhaust port. The exhaust port is operated by a drive mechanism that is linked to the rotation of the engine, and the upper edge of the exhaust port is moved up and down in accordance with the rotation speed of the engine.

When the upper edge of the exhaust valve, ie, the exhaust port, is at a lower position, the exhaust timing is slow and suitable for low-speed operation of the engine, and when the upper edge of the exhaust port is at the upper position, the exhaust timing is early and suitable for high-speed operation of the engine.

The above-mentioned engine requires a pressure reducing device at the time of starting, since the compression ratio is higher when the exhaust valve is at the lowest position, that is, when the engine is in the starting state, than an engine without an exhaust valve.

Conventional pressure reducing devices consist of a communication passage that communicates the combustion chamber with the atmosphere, and a valve member that opens and closes the communication passage, and the valve member is operated manually or by interlocking with the accelerator. If an engine equipped with such an exhaust valve is equipped with a pressure reducing device, the structure will become complicated.

(Purpose) The present invention was made in view of the above circumstances, and
The purpose is to provide a two-stroke engine equipped with an exhaust valve with a starting pressure reducing device that does not require any manual operation and does not complicate the structure.

(Example) An example of carrying out the invention will be described with reference to the drawings. The drawing shows a two-stroke engine A, in which a is a cylinder, b is a piston, c is a cylinder head, 1 is a thermal combustion chamber, d is a crankcase, d ₁ is the crankcase cover, 2 is the crankshaft.

The cylinder a has a sleeve a ₁ cast therein, and has an exhaust port 3, an intake hole 4, and a scavenging hole 5 opened, and each of these ports 3, 4, and 5 is opened and closed as the piston b moves up and down. It's summery.

An exhaust valve 6 is provided to cross the exhaust passage 7 connected to the exhaust port 3, and is rotatably fitted and supported at the end of the upper surface of the exhaust passage 7 on the side of the exhaust port 3.

This exhaust valve 6 is composed of a single member,
It is formed into a substantially half-ring shape whose diameter gradually tapers along the inner wall of the cylinder a.

Further, the middle part of the exhaust valve 6, that is, the part constituting a part of the upper wall of the exhaust passage 7, has a semicircular cross section, and one of the lower edges of the middle part protrudes toward the exhaust port 3, and as the exhaust valve 6 rotates, Opening upper edge 3a of the exhaust port 3
It is designed to function as a movable wall.

That is, when the upper edge 3a of the opening is at the lower side, the exhaust port 3
The timing at which the opening opens and exhaust begins, that is, the exhaust timing is late, and is suitable for low-speed operation of the engine A. When the opening upper edge 3a is in the upper position, the exhaust timing is early, and the exhaust timing is suitable for high-speed operation of the engine A.

Reference numerals 8 and 9 denote support shaft portions protruding from both ends of the exhaust valve 6, that is, the large diameter portion 6a and the small diameter portion 6b, respectively. Supported for free movement.

The support shaft portion 8 of the large diameter portion 6a protrudes outward from the wall of the cylinder a, and is connected to the drive mechanism e.

The drive mechanism e drives the exhaust valve 6 in proportion to the rotational speed of the engine A, and the illustrated example employs a so-called governor mechanism that converts changes in the rotational speed of the engine A into displacement in the thrust direction.

Reference numeral 10 denotes a rotating shaft inserted into the crankcase cover _d1 , which is connected to the crankshaft 2 via gears 11 and 12 so as to rotate in conjunction with the crankshaft 2.

Since the rotational speed of the crankshaft 2 is the rotational speed of the engine A, the rotating shaft 10 interlocking with the crankshaft 2 rotates in proportion to the rotational speed of the engine A.

Reference numeral 13 denotes a rotating plate integrally formed at the upper end of the rotating shaft 11, and a plurality of spheres 15 are slidably engaged with the upper surface of the rotating plate via radial grooves 14.

The sphere 15 slides outward along the groove 14 due to the centrifugal force that acts as the rotating plate 13 rotates.
The operating frame 16 that engages with the upper surface of the sphere 15 is moved upward.

The operating frame 16 is formed into a substantially umbrella shape and engages with the spherical body 15 through its inclined surface, and is adapted to be displaced up and down as the spherical body 15 moves in and out.

Reference numeral 17 denotes a spring that urges the operating frame 16 downward, that is, toward the sphere 15 side.

A rod 18 is connected to the operating frame 16 so as to be rotatable and move up and down together with it, and its upper end is connected to the support shaft 8 of the large diameter portion 6a of the exhaust valve 6 via a lever 19. .

The lever 19 is connected to the rod 18 via an elongated hole 19a and a pin 20 that fits into the elongated hole 19a.
8. The vertical motion is converted into a rotational motion and transmitted to the exhaust valve 6, so that the valve 6 is rotated.

As the rotary plate 13 rotates with the rotation of the rotary shaft 10, centrifugal force acts on the sphere 15, and when the centrifugal force becomes larger than the spring force of the spring 17, the sphere 15 is released. direction and push up the operating frame 16.

Then, as the operating frame 16 moves upward, the rod 18
is displaced upward, and the exhaust valve 6 is rotated via the lever 19.

That is, an increase or decrease in the rotational speed of the rotating shaft 10, in other words, the rotational speed of the engine A, is detected as a displacement of the operating frame 16 in the thrust direction via the sphere 15, and the amount of rotation of the exhaust valve 6 is set according to the amount of displacement. be done.

Note that the drive mechanism e is not limited to a governor mechanism, but may include one in which the exhaust valve 6 is driven by a servo motor that electrically detects and drives the rotational speed of the engine A, or a crankshaft. The exhaust valve 6 may be driven in accordance with the discharge pressure of a water pump or an oil pump that rotates in conjunction with the exhaust valve 2.

The engine A is provided with a pressure reducing device that reduces the pressure inside the cylinder a at the time of starting the engine A.

This pressure reducing device includes a communication passage 22 that communicates a space 21 formed between a piston b in an upward stroke and a combustion chamber 1 in a cylinder a with the atmosphere, a valve member that opens and closes the communication passage 22, and a valve member that opens and closes the communication passage 22. It consists of a drive mechanism that drives the members in accordance with the rotational speed of the engine A.

The communication passage 22 is formed in the middle of the exhaust valve 6, and the valve 6 is connected to the upper opening edge 3a of the exhaust port 3.
is positioned at the lowest position, one end of which opens into the cylinder a, and the other end of which opens facing the exhaust passage 7.

The opening position of the communication passage 22 in the cylinder a corresponds to the upper edge of the exhaust port 3.

Note that the exhaust valve 6 in which the communication passage 22 is formed
As described above, since it is made of one piece, it is easier to process the communication passage 22 compared to a structure made by dividing it into two parts and connecting them, and the position of the communication passage 22 can be set freely. .

Accordingly, as the exhaust valve 6 rotates to move the opening upper edge 3a of the exhaust port 3 upward, the opening end of the communication passage 22 is displaced from inside the cylinder a toward the cylinder a side, and the opening end is displaced from the cylinder a wall. Blocked.

As a result, the communication passage 22 is closed, and the communication state between the space 21 above the piston b and the exhaust passage 7, that is, the atmosphere is cut off.

That is, the exhaust valve 6 is commonly used as a valve member that opens and closes the communication passage 22.

Therefore, the drive mechanism e of the exhaust valve 6 is also used as the drive mechanism for the valve member.

When the engine A equipped with such a pressure reducing device is started, when the crankshaft 2 is rotated by a starter (not shown), the piston b connected thereto moves up and down within the cylinder a. The sphere 15 in the drive mechanism e does not move outward, and the operating frame 16 and rod 18 do not move upward until the rotational speed of the engine A reaches the minimum required starting speed.

Therefore, the exhaust valve 6 does not rotate, the communication passage 22 opens, and the space 21 between the piston b and the combustion chamber 1 is communicated with the atmosphere until the piston b rises to the upper edge of the exhaust port 3.

As a result, the compression in the cylinder a during the compression process of the engine A is released, and the resistance that the crankshaft 2 receives through the piston b is reduced. In other words, the rotational torque necessary to rotate the crankshaft 2 is reduced. , the rotational speed of engine A increases rapidly.

When the rotational speed of the engine A increases beyond the required starting speed, the sphere 15 in the drive mechanism e moves outward, the operating frame 16 and the rod 18 rise, the exhaust valve 6 is rotated, and the communication passage 22 is closed. (Figure 3).

As a result, normal compression is performed in the cylinder a, and the engine A is started by the spark from the spark plug 23.

The communication passage 22 is designed to be closed even in a so-called idling state after the engine A is started, so that compression leakage does not occur.

Next, a second embodiment is shown in FIGS. 4 and 5.

In this embodiment, the communication passage 24 is connected to the exhaust valve 6.
It is composed of a passage 25 formed in the cylinder A wall, and passages 26 and 27 formed in the cylinder A wall.

One of the passages 26 and 27 in the cylinder a wall is connected to the exhaust port 3 on the inner surface of the cylinder a.
The other passage 27 opens at a position above the upper edge and extends outward from there, and the other passage 27 extends from the upper end of the cylinder a, perpendicular to the passage 26 and toward the exhaust valve 6.

Reference numeral 28 designates plugs that close the open ends of the passages 26 and 27 on the outer wall of the cylinder a.

On the other hand, one end of the passage 25 of the exhaust valve 6 matches the passage 27 in the wall of the cylinder a, and the other end is open facing the exhaust passage 7.

Therefore, in this embodiment, when the engine A is started, the exhaust valve 6 is close to the opening upper edge 3 of the exhaust port 3.
With valve a positioned at the lowest position, the passage 25 of the valve 6 and the passage 27 of the wall of the cylinder a meet to open the communication passage 24 (FIG. 4).

This state is maintained until the rotational speed of engine A reaches the required starting speed, as in the previous embodiment, and the compression in cylinder a is released and the rotational speed of engine A quickly increases.

Incidentally, since the opening position of the communication passage 24 in the cylinder a is set higher than that in the above embodiment, the compression release time is long and the pressure reduction effect is large.

When the rotational speed of the engine A increases beyond the required starting speed, the exhaust valve 6 rotates and the passage 25 of the valve 6 is separated from the passage 27 in the wall of the cylinder A, and the passage 27 is blocked by the exhaust valve 6. The communication path 24 is closed (FIG. 5).

As a result, normal compression is performed in the cylinder a, and the engine A is started by the spark from the spark plug 23.

Incidentally, when the engine A is in an idling state after starting, the communication passage 24 is closed as in the embodiment described above to prevent compression leakage.

The communication passage 24 of the second embodiment described above is constituted by a passage 25 formed in the exhaust valve 6 and passages 26 and 27 formed in the wall of the cylinder a.
Although a step of drilling the passages 26 and 27 separately from the passage 24 of the exhaust valve 6 is required, there is an advantage that the communication passage 24 can be laid out freely.

Furthermore, since the communication passage 22 of the first embodiment need only be bored in the exhaust valve 6, the processing is simple.

(Operations and Effects) The present invention is as described above, and by using the exhaust timing valve and its driving mechanism as the valve member of the pressure reducing device and its driving mechanism, a two-cycle engine equipped with an exhaust timing valve is manufactured. A pressure reducing mechanism can be provided to the engine without complicating its structure.

In addition, when the engine starts, the opening and closing operations of the valve member that opens and closes the communication passage are automatically controlled in accordance with the engine rotation speed, and when the engine rotation speed is less than the required starting speed, the valve member opens and the communication passage opens and closes. By opening the cylinder, the compression inside the cylinder is released, allowing the engine's rotational speed to quickly increase.

Then, when the rotational speed of the engine increases beyond the required starting speed, the valve member closes to close the communication passage, allowing normal compression to occur within the cylinder and starting the engine.

In the case where the communication passage is provided in the exhaust timing valve, the processing to form the communication passage only needs to be performed on the exhaust timing valve, so the processing is simple, and the communication passage can be formed in the same way as the exhaust timing valve. In the case where the valve is provided across the cylinder wall around the valve, there is an advantage that the communication passage can be laid out freely.

Therefore, it is possible to provide an excellent engine starting pressure reducing device that does not require any manual operation, and achieves the intended purpose.

[Brief explanation of drawings]

Fig. 1 is a partially cutaway side view showing the device of the present invention, Fig. 2 is an enlarged cross-sectional plan view of the same, Fig. 3 is an enlarged cross-sectional side view showing the communicating path in a closed state, and Fig. 4 is another embodiment. FIG. 5 is a sectional side view showing the communication passage in a closed state. In the figure, A... 2-cycle engine, a... cylinder, b... piston, 1... combustion chamber, 3...
Exhaust port, 6... Exhaust valve (exhaust timing valve), 7... Exhaust passage, e... Drive mechanism, 22...
...Communication path (first embodiment), 24...Communication path (second embodiment)
Example), 25, 26, 27... passage.

Claims (1)

[Claims] 1. An exhaust passage extends from the exhaust port of the cylinder toward the atmosphere, and an exhaust timing valve is provided at the upper part of the exhaust port side end of the exhaust passage, and the exhaust timing valve is connected to a movable wall that forms the upper edge of the exhaust port. In a two-stroke engine which is vertically displaced by a drive mechanism connected to the rotation of the engine, the exhaust timing valve is opened and closed by vertical displacement of the exhaust timing valve, and when the exhaust timing valve is in a lower position, the inside of the cylinder and the exhaust passage are communicated. A starting pressure reducing device that includes a communication passage that extends between the exhaust timing valve or the exhaust timing valve and the cylinder wall surrounding the valve.