JPH0557408B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an exhaust system for a two-stroke engine in which the piston itself acts as an exhaust valve.

[Prior Art] Conventionally, in two-stroke engines, there is an exhaust system in which an auxiliary exhaust passage is provided in addition to the main exhaust passage, and this auxiliary exhaust passage is opened and closed by an auxiliary valve (for example, Japanese Patent Laid-Open No. 60-249614 discloses reference). This exhaust system improves output at high speeds by closing the auxiliary exhaust passage at low speeds and opening it at high speeds, making the cross-sectional area of the exhaust passage commensurate with the rotational speed of the engine.

On the other hand, at low speeds, the portion of the closed auxiliary exhaust passage closer to the cylinder than the auxiliary valve functions as the combustion chamber of the engine, which causes a reduction in output at low speeds. For this reason, the auxiliary valve is provided close to the cylinder.

[Problems to be solved by the invention] By the way, in the above-mentioned prior art, the auxiliary valve is
It is opened and closed via a drive member inserted laterally into the cylinder block. For this reason, since the driving member is also provided close to the cylinder, for example, water jackets cannot be provided near the exhaust ports of both exhaust passages. Alternatively, the wall thickness of the cylinder becomes uneven. Therefore, the cooling of the cylinder becomes uneven.

Further, since the driving member and the auxiliary valve engage within the cylinder block, it is not easy to handle the driving member and its bearings, and various machining operations are required for the large cylinder block. Therefore, this causes a decrease in engine productivity.

The present invention has been made in view of the above-mentioned conventional disadvantages, and an object of the present invention is to provide an exhaust system for a two-stroke engine that can uniformly cool a cylinder block and improve cylinder productivity.

[Means for Solving the Problems] In order to achieve the above object, the present invention first sets the axial direction of the auxiliary valve in the sliding direction of the piston of the cylinder, so that the axial portion of the auxiliary valve is aligned with the cylinder block. It protrudes from the cylinder head through the cylinder head. The shaft is connected to a drive device above the cylinder head.

[Function] According to the present invention, since the driving device is connected to the auxiliary valve above the cylinder head, there is no need to install the driving device inside the cylinder block, so a water jacket can be installed.
Moreover, the inner thickness of the cylinder can be made uniform. Therefore, the engine can be cooled uniformly.

In addition, as mentioned above, since there is no need to install the drive device inside the cylinder block, there is no need to form an insertion hole in the cylinder block for installing the drive device, so machining of a large cylinder block is not necessary. becomes easier. Furthermore, since the auxiliary valve and the drive device are connected above the cylinder head, that is, outside the engine body, the drive device can be easily handled. Therefore, the productivity of the engine is improved.

[Example] Hereinafter, an example of the present invention will be described with reference to the drawings.

FIG. 1 shows a longitudinal section of a two-cylinder two-stroke engine, in which 1 is a cylinder head, 2 is a cylinder block, 3 is a piston, and 4 is a water jacket.
A main exhaust port 5 communicates the cylinder 6 with the main exhaust passage 7 shown in FIG. 9 is an auxiliary exhaust passage, which is an auxiliary exhaust port 8 on the side of the main exhaust port 5.
and the main exhaust passage 7 are connected as an auxiliary exhaust passage. That is, the cross-sectional area of the auxiliary exhaust passage 9 is smaller than that of the main exhaust passage 7. Note that 30 is a resonance chamber that communicates with the main exhaust passage 7 at low speeds to prevent a decrease in output at low speeds. Although only one side of the resonance chamber 30 is illustrated, it may be provided on both sides, and does not necessarily need to be provided.

Reference numeral 10 denotes a rotary valve (auxiliary valve), which is provided in the middle of the auxiliary exhaust passage 9, and is operated by a drive device 11, which will be described later, according to changes in the rotational speed of the engine.
(Fig. 5), the auxiliary exhaust passage 9
It opens and closes. This rotary valve 1
0, a valve passage 10a and a valve body 10b are formed in a cylindrical portion 10c in FIG. This rotary valve 10 has its axial direction set in the sliding direction of the piston 3 of the engine, and its shaft portion 10d.
is pivotally supported by the cylinder head 1 and cylinder block 2, and rotates in both directions around this shaft portion 10d. Shaft portion 10d of this rotary valve 10
protrudes from the cylinder block 2 through the cylinder head 1, and is connected to the transmission device 12 of the drive device 11 above the cylinder head 1. Note that 31 is a plain bearing, and 32 is an oil seal. Although not shown, the right engine is also provided with the rotary valve and transmission device.

The water jacket 4 is formed so as to surround the cylinder 6, as shown in FIGS. 1 and 2, to sufficiently cool the cylinder 6. Also,
Water jackets 4A shown in FIGS. 3 and 4 are also provided around both exhaust passages 7 and 9 through which high-temperature exhaust gas A is discharged.

The two-stroke engine is diagonally supported by a frame (not shown) of a motorcycle, as shown in FIG. 5, for example. In addition, in this figure,
13 is an exhaust pipe, and 14 is a reed valve case.

Next, the drive device 11 will be explained.

In FIG. 5, the drive device 11 includes a motor 15 capable of forward and reverse rotation, and the transmission device 12 described above.
The motor 15 is provided with a potentiometer 40 for detecting its rotation angle position. The transmission device 12 includes a pulley 16 connected to the motor 15 to rotate, first and second cables 17 and 18 that engage with the pulley 16, and a second cable that engages with the cables 17 and 18, respectively. The rotary valve 10 is made up of a first lever 19, a second lever 20 shown in FIG. The motor 15, potentiometer 40, and pulley 16 shown in FIG. 5 are assembled together to form a motor unit 33, which is fixed to the frame via a mount 34 of the motor unit 33.

The cables 17, 18 in FIG.
A cylindrical engagement member 34 is fixed to both ends of 18b. This engaging member 34 is connected to both levers 19 and 20.
or the notch 35 of the pulley 16 in FIG.
7, 18 and pulley 16 or lever 1 in Fig. 6
The above-mentioned engagement with 9 and 20 is made. One end of the outer parts 17a, 18a is fixed to a bracket 21 integrally formed with the cylinder head 1 shown in FIG. On the other hand, the other ends of the outer parts 17a and 18a are fixed to one of the plurality of fixing parts 36 provided in the motor unit 33.

In FIG. 6, the first and second levers 19, 20 are connected to each other via a first rod 22, and are connected via second and third rods 23, 24, respectively. 3 and a fourth lever 25, 26. Above 4
The three levers 19, 20, 25, and 26 each correspond to the shaft portion 10d of the rotary valve 10 in FIG.
It is screwed to and protrudes in the radial direction of this shaft portion 10d. Reference numeral 27 in FIG. 7 is a synthetic resin connector, which includes rods 22, 24 and levers 19, 26.
It is rotatably fixed by resin elasticity.

In FIG. 5, reference numeral 41 denotes a control means, which is composed of, for example, a microcomputer, and essentially controls the ignition timing of the engine. This control means 41 inputs the engine rotational speed signal a detected by the detector 42 and the rotational angle signal b of the motor 15 detected by the potentiometer 40, and according to the change in the engine rotational speed, Motor 1
Outputs a drive signal c to rotate 5.

Next, an example of the operation of the above configuration will be described.

First, when the engine speed is low, the levers 19, 20, 25, and 26 shown in FIG. 6 are held at the positions shown in the drawing, and the auxiliary exhaust passage 9 shown in FIG.
is closed by a rotary valve 10.
Therefore, the exhaust A 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 enough to be suitable for low speeds, and a decrease in output at low speeds is prevented.

Thereafter, when the rotational speed of the engine reaches a predetermined speed, this is detected by the detector 42 shown in FIG.
The rotational speed signal a is output to the control means 41. On the other hand, the rotation angle signal b of the motor 15 is input from the potentiometer 40 to the control means 41 . Based on these signals a and b, a drive signal c is output from the control means 41 to the motor 15, the motor 15 rotates by a predetermined angle, and the pulley 16 rotates. With this rotation, the inner 17b is pulled in the direction of the arrow, and the first lever 19 rotates as shown in FIG. This rotation causes the second lever 20 to rotate via the first rod 22, and the inner 18b is pulled in the direction of the arrow. At the same time, the second and first levers 2
0 and 19, the third and fourth levers 25 and 26 rotate via the second and third rods 23 and 24. Above four levers 1
9, 20, 25, and 26, the four shaft portions 10d rotate in the direction of the arrow, and the rotary valve 10 in FIG. 2 rotates approximately 90 degrees. As a result, the auxiliary exhaust passage 9 communicates with the main exhaust passage 7, and exhaust air is discharged from both exhaust passages 7 and 9. Therefore, when the engine rotational speed is high, the cross-sectional area of the entire exhaust passage becomes large enough to correspond to the high speed, and as is well known, the output is improved.

In the above structure, the shaft portion 10d of the rotary valve 10 shown in FIG. 1 projects from the cylinder head 1, and the shaft portion 10d is connected to levers 20 and 25 above the cylinder head 1, for example. Therefore, it is not necessary to arrange the drive device 11 inside the cylinder block 2. In other words, it is necessary to provide the drive rod in the cylinder block 2, which was conventionally provided at the position of point 0 in FIG. 3 and the two-dot chain line P in FIG. There is no. Therefore, for example, as shown in FIGS. 4 and 3, the water jacket 4A can be provided on the cylinder wall 2a on the side of the main exhaust passage 7 where the temperature is high, and as shown in FIG. The wall thickness can be made uniform. As a result, the engine is cooled uniformly. Incidentally, in an air-cooled engine, the effect of providing the water jacket 4A cannot be obtained, but the effect of smoothly transmitting the heat of the cylinder to the cooling fins is the same, and it goes without saying that it is included in this invention. .

Further, as described above, since there is no need to provide the drive rod at the position indicated by the two-dot chain line P, there is no need to provide an insertion hole in the cylinder block 2 into which the drive rod is inserted. Therefore, machining of the large cylinder block 2 becomes easy. Further, the rotary valve 10 shown in FIG. 1 and the drive device 11 shown in FIG. 5 are connected above the cylinder head 1, that is, outside the cylinder body. Therefore, the shape and arrangement of the drive device 11 can be freely determined, and its handling becomes easy.
In this way, the machining of the cylinder block 2 is facilitated, and the handling of the drive device 11 is also facilitated, thereby improving productivity.

By the way, in this embodiment, a motor 15 is used as the drive device 11. For this reason, in addition to simply controlling exhaust emissions at low speeds and high speeds, for example,
Complex control is possible, such as rotating the rotary valve 10 in Fig. 1 in forward and reverse directions during startup to remove carbon, or opening the rotary valve 10 during idling and then closing it at low speeds. be. Of course, in the present invention, the drive device 11 can also be a mechanical drive device. In addition, as a mechanical drive device, when the rotation speed of the crankshaft exceeds a predetermined value by the rotation of a governor (not shown) connected to the crankshaft, the steel balls are rotated on the slope of the dish-shaped spherical plate. There are known devices for moving along (see the prior art cited above).

Incidentally, in this embodiment, a plurality of rotary valves 10 are provided. Here, a pair of cables 17 and 18 are provided on the pulley 16 shown in FIG. 5, and the rotation of the pulley 16 causes the cable 1
7 and 18 operate in opposite directions to simultaneously rotate the plurality of rotary valves 10 in FIG. Therefore, since the position of the rotary valve 10 can be restrained by the two inners 17b, 18b, return springs for the inners 17b, 18b are not required. Note that if one of the cables 17 and 18 is made of a rod member, the rotary valve 10
Even in the case of a single return spring, the above-mentioned return spring becomes unnecessary.

[Effects of the Invention] As explained above, according to the present invention, the shaft portion of the auxiliary valve protrudes through the cylinder head and is connected to the drive device above the cylinder head, so that the cylinder block is uniformly distributed. This improves productivity.

[Brief explanation of the drawing]

1 is a vertical cross-sectional view of a cylinder showing an embodiment of the present invention, FIG. 2 is a cross-sectional view taken along the line -- in FIG. 1, FIG. 3 is a cross-sectional view taken along the line -- in FIG. Fig. 5 is an external view of the entire engine, Fig. 6 is a view taken along the - line of Figs. 1 and 5, and Fig. 7 is a sectional view taken along the - line of Fig. 6. . 1... Cylinder head, 2... Cylinder block, 3... Piston, 6... Cylinder, 7... Main exhaust passage, 9... Auxiliary exhaust passage, 10... Auxiliary valve (rotary valve), 11... Drive Device,
12... Transmission device, 15... Motor, 16... Pulley, 17, 18... Cable, 19, 20...
lever.

Claims (1)

[Scope of Claims] 1. A main exhaust passage that communicates with the inside of the cylinder, an auxiliary exhaust passage that connects the inside of the cylinder and the main exhaust passage as an auxiliary exhaust passage, and an auxiliary exhaust passage that opens and closes the auxiliary exhaust passage. A two-stroke engine exhaust system comprising a valve and a drive device that drives the auxiliary valve according to changes in engine rotational speed, the auxiliary valve having an axial direction in the sliding direction of the piston of the engine. set, the shaft of which protrudes from the cylinder block through the cylinder head,
An exhaust system for a two-stroke engine, which is connected to the drive device above the cylinder head. 2. The exhaust system for a two-stroke engine according to claim 1, wherein the auxiliary valve is a rotary valve that rotates in both directions around the shaft. 3. The above-mentioned drive device includes a motor, and a transmission device that is connected to the motor and the shaft of the rotary valve and transmits the driving force of the motor to the rotary valve to rotate the rotary valve. 2 as set forth in claim 2
Cycle engine exhaust system. 4. The transmission device includes a pulley connected to the motor, a cable engaged with the pulley, fixed to the shaft of the rotary valve, protruding in the radial direction of the shaft, and connected to the cable, 4. The exhaust system for a two-stroke engine according to claim 3, further comprising a lever that rotates the rotary valve by actuation of the cable. 5. According to claim 4, a plurality of the rotary valves are provided, and a pair of the cable and the lever are each provided, and the plurality of rotary valves are actuated in opposite directions by rotation of the pulley, thereby rotating the plurality of rotary valves. 2-cycle engine exhaust system.