JPH0531213Y2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] This invention relates to an exhaust system for an engine in which the piston itself acts as an exhaust valve, that is, a two-stroke engine.

[Conventional technology]

Conventionally, in two-stroke engines, an auxiliary exhaust passage has been provided in addition to the main exhaust passage, and the auxiliary exhaust passage is closed at low speeds and opened at high speeds, so that the cross-sectional area of the exhaust passage is adjusted to the engine rotational speed. There is an exhaust system that improves output at high speeds by making the area commensurate with the area (for example,
60-249614). An example of this is shown in FIGS. 6 and 7.

In FIG. 6, on both sides of the main exhaust port 22 of the main exhaust passage 21 communicating with the inside of the cylinder 20,
First and second auxiliary exhaust ports 23, 24 are provided. The first and second auxiliary exhaust ports 23 and 24 communicate with first and second auxiliary exhaust passages 25 and 26, which are provided on both sides of the main exhaust passage 21 and have a small passage area.
In other words, the auxiliary exhaust passages 25 and 26
0 and the main exhaust passage 21 are connected as an auxiliary exhaust passage.

The auxiliary exhaust passages 25, 26 are provided with rotary valves 27, 28. Reference numeral 29 indicated by a dashed line is a drive rod, which slides to the right as the rotational speed of the engine increases, opening the rotary valves 27 and 28 as shown in FIG.
This improves output at high speeds.

On the other hand, at low speed in FIG. 6, the rotary valve 2 in the auxiliary exhaust passages 25 and 26 is closed
A portion closer to the cylinder 20 than 7 and 28 functions as a part of the combustion chamber, resulting in a decrease in output.
For this reason, the rotary valves 27 and 28 are generally placed as close to the cylinder 20 as possible.

[The problem that the idea aims to solve]

However, in the above-mentioned prior art, while both the auxiliary exhaust passages 25 and 26 are being opened, the valve passages 27a and 28 of the rotary valves 27 and 28 are opened.
a is asymmetrical. For this reason, the flow of exhaust gas from both auxiliary exhaust passages 25 and 26 to the main exhaust passage 21 becomes asymmetrical as shown by arrows A and B, which causes turbulence in the flow of exhaust gas, which causes a decrease in output. .

Therefore, it is possible to form both rotary valves 27, 28 symmetrically with respect to each other, and to rotate both rotary valves 27, 28 in opposite directions by tilting the drive rod 30, as shown by the two-dot chain line in FIG. Conceivable. However, in this case, a portion of the drive rod 30 comes close to the cylinder 20, so that the wall thickness of the cylinder 1 cannot be maintained sufficiently. Alternatively, it becomes necessary to move the rotary valve 28 far away from the cylinder 20, which causes a reduction in output at low speeds.

This invention was made in order to solve the above-mentioned problems, and the purpose is to provide an exhaust system for a two-stroke engine that can maintain sufficient cylinder wall thickness and improve the output of the engine.

[Means to solve the problem]

In order to achieve the above object, this invention first provides first and second rotary valves that open the first and second auxiliary exhaust passages by rotating in response to an increase in the rotational speed of the engine.
First and second valve pinions are provided. The first valve pinion engages the drive rod, while the second valve pinion engages the drive rod via a pinion, thereby causing the first and second rotary valves to move in opposite directions. rotated to

[Effect]

According to this invention, since the first and second rotary valves rotate in opposite directions, that is, they rotate symmetrically, the flow of exhaust gas during rotation can be made symmetrical. Therefore, since there is little possibility that turbulence will occur in the flow of exhaust gas, it is possible to improve the output.

In addition, since the second valve pinion engages with the drive rod via the pinion, the first and second rotary valves are rotated in opposite directions, so unlike the conventional method, the drive rod does not have to be tilted. There is no. Therefore, there is no risk that the wall thickness of the cylinder will become thin. Furthermore, since there is no need to place the rotary valve far away from the cylinder, there is no risk of a decrease in output at low speeds.

〔Example〕

An embodiment of this invention will be described below with reference to the drawings.

In FIG. 1, first and second rotary valves 1 and 2 are provided in symmetrical positions in the middle of first and second auxiliary exhaust passages 25 and 26, respectively. Both rotary valves 1 and 2 have valve bodies 1 that are symmetrical and have the same shape.
a, 2a, and valve passages 1b, 2b,
As will be described later, the auxiliary exhaust passages 25 and 26, which are symmetrical to each other, are opened by rotating in opposite directions as the rotational speed of the engine increases.

In FIG. 2 showing a longitudinal section of FIG. 1, both the rotary valves 1 and 2 have the valve bodies 1a and 2a.
For example, the cylindrical portions 1c, 2c, the shaft portions 1d, 2d, and the valve pinions 1e, 2e are integrally formed. The rotary valves 1 and 2 have shaft portions 1d and 2d rotatably supported by the engine body 3, and rotate in both directions.

In FIG. 3, reference numeral 4 denotes a drive rod, which is moved by a drive device 5 to the left in a sliding hole 6 formed in the engine body 3 as the rotational speed of the engine increases. This drive rod 4 has
A first rack 4a that engages with the first valve pinion 1e and a second rack 4 that engages with the pinion 7.
b is engraved.

As shown in FIG. 2, the pinion 7 is rotatably supported on the engine body 3 by its shaft portion 7a, and the gear portion is formed long in the axial direction, and also engages with the second valve pinion 2e. are doing. In other words,
The second valve pinion 2e in FIG. 3 engages via a pinion 7 with the second rack 4b of the drive rod 4. Therefore, both valve pinions 1
e and 2e rotate in opposite directions. The second valve pinion 2e in FIG. 2 is formed, for example, at a lower position away from the position facing the drive rod 4 in the axial direction of the second rotary valve 2, and is prevented from interfering with the drive rod 4. .

In the driving device 5 shown in FIG. 3, when the rotational speed of the crankshaft exceeds a predetermined value due to the rotation of a governor (not shown) connected to the crankshaft, the steel balls are rotated by the slope of the dish-shaped spherical plate. This is a well-known device that moves along the vehicle (see the prior art cited above). Further, the drive device 5 may have a well-known structure that detects the rotational speed of the engine with a detector (not shown) and operates the actuator of the motor.

In addition, 8 is a low speed stopper, 9 is a high speed stopper, and at low speed or high speed, respectively,
This is for positioning the drive rod 4. The rest of the structure is the same as that of the conventional example shown in FIG. 6, and the same or corresponding parts are denoted by the same reference numerals, and detailed explanation thereof will be omitted.

Next, the operation of the above configuration will be explained.

First, when the engine speed is low, the drive rod 4 shown in FIG. 3 is held in the position shown in the drawing, and both auxiliary exhaust passages 25 and 26 shown in FIG. 1 are closed by the rotary valves 1 and 2. Therefore, exhaust is performed only from the main exhaust passage 21, and the cross-sectional area of the entire exhaust passage becomes small enough to be suitable for low speeds.

Thereafter, when the rotational speed of the engine reaches a predetermined speed, the drive rod 4 is gradually moved to the left by the drive device 5 shown in FIG. Along with this movement, the first valve pinion 1e and the pinion 7
are engaged with the first and second racks 4a and 4b, respectively, and are rotated counterclockwise. At this time, the second valve pinion 2e engages with the pinion 7 and is rotated clockwise. With these rotations, both rotary valves 1 and 2 in FIG.
As shown in FIG. 4, they rotate in opposite directions, that is, in the directions of arrows C and D, and begin to open both auxiliary exhaust passages 25 and 26.

Furthermore, as the rotational speed of the engine increases, the rotary valves 1 and 2 continue to rotate, and eventually the drive rod 4 shown in FIG. 3 comes into contact with the high-speed stopper 9. At this time of contact, both valve pinions 1
e, 2e and rotary valves 1, 2 in Fig. 5
stops rotating, and both auxiliary exhaust passages 2
5 and 26 are completely opened. Therefore, when the engine rotation speed is high, exhaust is exhausted from all exhaust passages 21, 25, and 26, so that the cross-sectional area of all the exhaust passages becomes large enough to correspond to the high speed.

In the above-mentioned configuration, since both rotary valves 1 and 2 shown in FIG. 4 rotate in opposite directions, the exhaust gas flow becomes symmetrical with respect to each other as shown by arrows E and F during rotation. Therefore,
Because there is less risk of turbulence in the exhaust flow,
It is possible to improve the output during the rotation of the rotary valves 1 and 2. Of course, the same effect can be obtained when shifting from high speed to low speed.

Also, the first valve pinion 1e in FIG.
As a result, both rotary valves 1 and 2 shown in FIG. 4 are rotated in opposite directions. Therefore, unlike the conventional case, the drive rod 4 in FIG.
Since there is no need to make the cylinder 20 oblique, the wall thickness of the cylinder 20 can be maintained sufficiently. Further, since there is no need to separate both valve pinions 1e and 2e, that is, the rotary valves 1 and 2 shown in FIG. 1 by a large distance from the cylinder 20, there is no fear that the output at low speeds will decrease.

By the way, the second valve pinion 2e in FIG.
must not engage directly with the drive rod 4. As a countermeasure for this, if the second valve pinion 2e is provided radially apart from the drive rod 4, the engine becomes slightly larger. In this embodiment, the second valve pinion 2e is provided, for example, below the drive rod 4, as shown in FIG. Therefore, since the shaft portion 2d, which has a smaller diameter than the second valve pinion 2e, faces the drive rod 4, the second rotary valve 2 can be disposed close to the drive rod 4 in FIG. There is no risk of the engine becoming larger.

Note that it is also possible to provide two exhaust passages 25 and 26 each in FIG. 1, and is included in this invention. Also, at low speed, the valve passage 1b,
It is also possible to provide a known resonance chamber which communicates with the main exhaust channel 21 via 2b.

[Effect of idea]

As described above, according to this invention, in an exhaust system for a two-stroke engine in which auxiliary exhaust passages are provided on both sides of a main exhaust passage, the output of the engine can be improved during rotation of the rotary valve. Further, since the wall thickness of the cylinder can be maintained sufficiently and there is no need to place the rotary valve far away from the cylinder, there is no fear that the output at low speeds will decrease.

[Brief explanation of the drawing]

Fig. 1 shows an embodiment of this invention; Fig. 2 is a planar sectional view of the engine at low speed; Fig. 3 is a longitudinal sectional view at low speed; Fig. 3 is a sectional view taken along the - line in Fig. 2; and Fig. 4 is a sectional view of the engine at low speed. FIG. 5 is a plan sectional view of the rotary valve during rotation, FIG. 5 is a plan sectional view at high speed, FIG. 6 is a plan sectional view of a conventional example at low speed, and FIG. 7 is a plan sectional view during rotation. 1...first rotary valve, 1e...first
Valve pinion, 2... Second rotary valve, 2e... Second valve pinion, 4... Drive rod, 7... Pinion, 20... Cylinder, 2
1... Main exhaust passage, 25... First auxiliary exhaust passage, 26... Second auxiliary exhaust passage.

Claims (1)

[Claims for Utility Model Registration] (1) A main exhaust passage that communicates with the inside of the cylinder, and a auxiliary exhaust passage that is provided on both sides of the main exhaust passage and connects the inside of the cylinder and the main exhaust passage. first and second auxiliary exhaust passages;
first and second rotary valves that are respectively provided in the first and second auxiliary exhaust passages and open the auxiliary exhaust passages by rotating in accordance with an increase in the rotational speed of the engine;
engaging with the first and second valve pinions provided on the first and second rotary valves, respectively, and the first valve pinion;
a drive rod that rotates the rotary valve; and a drive rod that engages with the drive rod and the second valve pinion to move the second rotary valve relative to the first rotary valve via the second valve pinion. An exhaust system for a two-stroke engine with a pinion that rotates in opposite directions. (2) The second valve pinion is formed at a location away from the position facing the drive rod in the axial direction of the second rotary valve. 2-cycle engine exhaust system.