JPH0543235Y2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] This 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 has been 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 a rotary valve (auxiliary valve) (for example, Japanese Patent Laid-Open No. 1983 −249614
(see publication). This exhaust system has an auxiliary exhaust passage,
It closes at low speeds and opens at high speeds, making the cross-sectional area of the exhaust passage commensurate with the engine's rotational speed, thereby improving output at high speeds.

By the way, in this type of exhaust system, a driving device such as a motor is provided outside the engine body, and on the other hand, the shaft portion of each rotary valve is made to protrude from the engine body, and the motor and each shaft portion are connected by a connecting member. There is one that rotates a rotary valve (for example, see Utility Model Application No. 105605/1983). In this prior art, the drive shaft for rotating the rotary valve is not provided in the cylinder block, which facilitates the installation of the water jacket.

[Problems to be solved by the invention] However, in these two-stroke engines, exhaust is also exhausted from the auxiliary exhaust passage in addition to the main exhaust passage, so the cylinder wall near both exhaust passages is connected to other parts of the cylinder wall. tends to reach high temperatures compared to On the other hand, the rotary valve is placed as close to the cylinder as possible in order to prevent a drop in output at low speeds, so a water jacket should be provided on the cylinder wall between the rotary valve and the cylinder. This causes the cylinder wall to become locally hot. Since this high-temperature portion is easily affected by heat, conventionally the clearance between the piston and the cylinder could not be made sufficiently small, which hindered improvement in engine performance.

This invention was developed in view of the above-mentioned conventional problems, and the purpose is to provide an exhaust system for a two-stroke engine that can suppress local high temperatures on the cylinder wall and improve engine performance. It is said that

[Means for Solving the Problems] In order to achieve the above object, this invention provides an exhaust system in which the shaft of the auxiliary valve protrudes from the engine body, in which the auxiliary valve is passed through the cylinder block and the cylinder head; A water jacket is introduced from the circumferential direction into the upper and lower parts of the auxiliary exhaust passage in the cylinder wall between the auxiliary valve and the cylinder, and the cylinder wall between the water jacket and the cylinder is locally made thinner. is formed.

[Operation] According to this invention, the water jacket is formed by entering the water jacket from the circumferential direction into the cylinder wall between the auxiliary valve and the cylinder, which tends to become hot, so that the cylinder wall is locally heated. It can suppress high temperatures.

By the way, by introducing the water jacket, the cylinder wall becomes locally thinned, but this thinned cylinder wall is reinforced by the cylinder block wall around the auxiliary valve.

[Example] An example of this invention will be described below with reference to the drawings.

Figure 1 shows a longitudinal section of a two-stroke engine mounted on a two-wheeled motor vehicle, for example, where 1 is a cylinder head, 2 is a cylinder block, 3 is a piston, and 4 is a cylinder head.
is a water jacket. A main exhaust port 5 communicates the cylinder 6 with the main exhaust passage 7 shown in FIG. An auxiliary exhaust passage 9 connects an auxiliary exhaust port 8 on the side of the main exhaust port 5 and the main exhaust passage 7 as an auxiliary exhaust passage. In other words,
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.

Reference numeral 10 denotes a cylindrical rotary valve, which is provided in the middle of the auxiliary exhaust passage 9, and is driven to rotate by a drive device 11 (FIG. 1), which will be described later, in response to changes in operating conditions such as engine rotational speed. It opens and closes the exhaust passage 9. This rotary valve 10 includes a valve passage 10a and a valve body 10.
b is formed in the cylindrical portion 10c of FIG. The 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 the cylinder block 2, so that the rotary valve 10 can rotate in both directions around the shaft portion 10d. Rotate. A shaft portion 10d of the rotary valve 10 projects from the cylinder block 2 through the cylinder head 1, and is connected to a drive device 11 above the cylinder head 1.

Although not shown, the drive device 11 rotates a motor depending on the engine speed, and rotates the rotary valves 10, 10 via operating members such as pulleys, cables, and rods. (For example, Jitsugan Sho 62-165015
(see issue). Therefore, an exhaust device (for example,
(Refer to Japanese Patent Application Laid-Open No. 60-249614), there is no need to provide the drive rod at the point 0, so the fourth
A water jacket 4a can be provided above the main exhaust passage 7, as shown in FIGS.

Next, the main parts of this idea will be explained. The water jacket 4 is formed to surround the cylinder 6 as shown in FIG.
is formed to have a substantially uniform thickness over the entire circumference of the cylinder 6. On the other hand, rotary valve 10
A water jacket 4b is inserted into the upper and lower parts of the auxiliary exhaust passage 9 in FIG. 5 from the circumferential direction as shown in FIG. The cylinder wall 12b is locally thinned to form a water jacket 4b.

As shown in FIG. 5, the water jacket 4b further enters the upper and lower corners 13 between the main exhaust passage 7 and the auxiliary exhaust passage 9 to form a water jacket 4d. On the other hand, both exhaust passages 7 and 9 in FIG.
Since the partition wall 14 between the two exhaust passages 7 and 9 needs to be provided as close as possible, the partition wall 14 is formed thin, so that no water jacket is provided in the partition wall 14 portion.

Further, the water jacket 4 is formed so as to surround the rotary valve 10 shown in FIG. 4, and the water jacket 4c in this area and the rotary valve 1
A cylindrical valve body portion 16 is formed by the cylinder lock wall between the valve body portion 15 and the hole 15 having a circular cross section in which the valve body 0 is accommodated.

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

First, when the engine speed is low, the rotary valve 10 is held at the position shown in FIG. 2, and the auxiliary exhaust passage 9 is closed by the 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, the drive device 11 (FIG. 1) is activated and the rotary valve 10 is rotated approximately 90 degrees. As a result, the auxiliary exhaust passage 9 communicates with the main exhaust passage 7,
Exhaust is carried out 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 configuration, at high speed, the main exhaust passage 7
In addition, since the exhaust A is also released from the auxiliary exhaust passage 9, the cylinder wall 12a in FIG. In contrast, this invention has a water jacket 4b on the cylinder wall 12a, which tends to become hot.
Since the cylinder wall 12a is inserted from the circumferential direction, it is possible to suppress the cylinder wall 12a from becoming locally heated. Therefore, thermal effects are reduced,
The clearance between the piston 3 (FIG. 3) and the cylinder 6 can be reduced, resulting in improved engine performance.

By the way, by inserting the water jacket 4b, the cylinder wall 12b between the water jacket 4b and the cylinder 6 becomes locally thin. However, since there is a cylinder block wall (valve box part 16) of the rotary valve 10 near the cylinder wall 12b in this part, the thin cylinder wall 12b is reinforced by the valve box part 16. It has the same strength as other parts.

Furthermore, since the cylinder wall 12b is made thinner as described above, the cylinder block 2 becomes lighter, so that the weight of the two-stroke engine, which should be lighter, can be reduced.

[Effects of the invention] As explained above, according to this invention, the water jacket is introduced from the circumferential direction into the cylinder wall between the auxiliary valve and the cylinder, which tends to become hot, so that the cylinder wall is locally heated. It is possible to suppress high temperatures during engine operation, thereby reducing the clearance between the piston and the cylinder, improving engine performance. Further, since the cylinder wall, which is locally thinned, is reinforced by the cylinder block wall around the auxiliary valve, there is no decrease in strength. Furthermore, since the cylinder walls are thinner, the two-stroke engine becomes lighter.

[Brief explanation of the drawing]

Fig. 1 is a longitudinal sectional view of a two-stroke engine showing an embodiment of this invention, Fig. 2 is a sectional view of the same plane, Fig. 3 is a sectional view taken along the - line in Fig. 2, and Fig. 4 is a sectional view of the two-stroke engine in Fig. 3. Fig. 5 is a sectional view taken along the - line in Fig. 3; 1... Cylinder head, 2... Cylinder block, 4b... Water jacket, 6... Cylinder, 7
...Main exhaust passage, 9...Auxiliary exhaust passage, 10...
Auxiliary valve, 10d...Shaft portion, 11...Driving device, 12, 12a, 12b...Cylinder wall.

Claims (1)

[Claims for Utility Model Registration] A main exhaust passage communicating with the inside of the cylinder, an auxiliary exhaust passage connecting the inside of the cylinder and the main exhaust passage as an auxiliary exhaust passage, and a main exhaust passage provided in the auxiliary exhaust passage. , a cylindrical auxiliary valve that opens and closes the auxiliary exhaust passage, and a drive device that drives the auxiliary valve according to changes in engine rotational speed, the shaft of the auxiliary valve passing through the cylinder block and the cylinder head. An exhaust system for a two-stroke engine, which protrudes above the cylinder head and is connected to the drive device above the cylinder head, the exhaust system comprising: a cylinder wall between the auxiliary valve and the cylinder; 2. The water jacket is formed by inserting the jacket from the circumferential direction and locally thinning the cylinder wall between the water jacket and the cylinder.
Cycle engine exhaust system.