JPS5813738B2 - Exhaust pipe for 2-stroke engine - Google Patents

Description

[Detailed Description of the Invention] Generally, two types of exhaust holes are opened on the inner surface of the cylinder.
Due to the structure of a cycle engine, some of the fresh air (scavenging air) in the cylinder flows out from the exhaust hole just before the piston closes the exhaust hole, but in order to prevent this fresh air from flowing out as much as possible, the exhaust pipe The positive pressure reflected from the constriction part is used to force fresh air that is about to flow out into the cylinder.

If you use the reflected waves from the exhaust pipe throttle, you can expect an increase in output, but in order to use the reflected waves, the exhaust hole opening time is long in the low-speed rotation range, so the reflected waves must be returned to the exhaust holes late. (i.e. the exhaust pipe length must be long),
On the other hand, if the rotational speed increases, the optimal exhaust pipe length must be shortened.

However, in the case of conventional exhaust pipes for two-stroke engines, the length of the exhaust pipe remains unchanged, so the fact is that the effect of pushing in fresh air by waves reflected from the exhaust pipe constriction is only achieved within a narrow range of engine speeds.

On the other hand, in a certain rotational speed range, reflected waves from the throttle section have an adverse effect, resulting in a decrease in output and torque, resulting in drawbacks such as poor acceleration and hesitation while the vehicle is running.

On the other hand, in a two-stroke engine, when the exhaust pipe length is not very short compared to the engine dimensions, the gas temperature at the exhaust pipe constriction part tends to be low in the low speed rotation range and increase as the speed reaches the high speed rotation range.

The present invention utilizes the above-mentioned tendency of the gas temperature in the exhaust pipe to drive the exhaust pipe restrictor in the longitudinal direction of the exhaust pipe using a temperature-sensitive expandable body that expands and contracts depending on the exhaust gas temperature, thereby automatically obtaining the optimum exhaust pipe length. One embodiment is shown in the drawings.

In the figure, a cylinder 2 has an intake hole 5, an exhaust hole 6, and a scavenging hole (not shown) opened on its inner surface, and each of these ports is opened and closed by a piston 1 fitted on the inner surface of the cylinder.

3 is a cylinder head, and 4 is a plug.

The exhaust pipe 7 directly connected to the exhaust hole 6 includes a diff user part 7a whose cross-sectional area first gradually increases according to the exhaust flow direction (arrow A), and a constricted part 7b whose cross-sectional area gradually decreases, and the constricted part 7b has a uniform cross-sectional area. an outer cylinder 8 with a circular cross section;
It is formed of a conical inner cylinder 9 that is slidable within an outer cylinder 8.

The present invention can be similarly applied to an exhaust pipe having an expansion part having the same diameter as the outer cylinder 8 at the boundary between the diffuser part 7a and the throttle part 7b.

The inner cylinder 9 has ribs 15, 1 extending radially on the outer periphery of the central part in the longitudinal direction and the tip on the side opposite to the engine (the right end in the figure), respectively.
6 (plate), the tip of each rib 15, 16 is slidably supported on the inner surface of the outer cylinder 8, and holds the inner cylinder 9 at the center of the outer cylinder 8.

14 is a sliding portion at the tip of the rib.

Reference numeral 10 denotes a bellows made of a heat-resistant metal plate, and the end on the engine side is fixed to the inner cylinder 9 in an annular portion 17 in an airtight manner.
The other end is attached to the retaining plate 13 integral with the outer cylinder 8, and the annular portion 1
8, it is fixed in an airtight manner.

12 is a space formed by the bellows 10 and the inner cylinder 9;
In the illustrated embodiment, the space 12 is filled with air and sealed.

19 is a gap provided on the outer periphery of the holding @ 13, 11 is a silencer,
20 is a tail pipe.

While the engine is running, exhaust gas flows through the differential user section 7a as indicated by the arrow A.
It flows while expanding in the direction, and promotes the scavenging action in the cylinder 2 due to the Kadenashi effect (suction action).

Exhaust gas flows from the differential user section 7a to the inner circumference 9 of the throttle section 7b.
It passes through the outer periphery, passes through the gap 19 and the muffler 11, and is emitted into the atmosphere from the tail pipe 20.

Mainly the inner cylinder 9 in the aperture part Tb plays the role of a reflector,
The reflected waves generated there travel in eight opposite directions and reach the exhaust hole 6 portion.

In order to utilize this reflected wave, as mentioned above, the opening time of the exhaust hole is long in the low speed rotation range, so the reflected wave must reach the exhaust hole 6 late (therefore, the exhaust pipe length must be long), and the As the number increases, the optimum exhaust pipe length must be shortened, but according to the present invention, the optimum exhaust pipe length is automatically set by the bellows 10 which is heated by the exhaust gas in the constriction portion 7b.

That is, the air in the space 12 within the bellows 10 senses the temperature of the constricted portion 7b, expands as the rotation becomes high speed, and pushes the conical inner cylinder 9 toward the engine (to the left in the figure).

In other words, the overall length of the exhaust pipe becomes shorter. Furthermore, in a low speed range, the air in the space 12 contracts, the conical inner cylinder 9 moves backward, and the overall length of the exhaust pipe becomes longer.

As described above, according to the present invention, the exhaust pipe length (equivalent pipe length) automatically changes depending on the rotation speed.

By appropriately selecting the length, spring constant, and effective diameter of the bellows 10, it is possible to maintain the optimum exhaust pipe length from low speed to high speed, resulting in a wider range of output over the entire operating range than with conventional engines. We can expect it to rise.

The temperature of the exhaust gas passing through the throttle part Tb ranges from, for example, approximately 150°C during idling to 400 to 500°C during high speed.
If bellows 10 is used, the distance will vary up to 100 m.
It is possible to obtain a lift of more than m and achieve the desired purpose.

When embodying the present invention, a warhead-shaped inner cylinder having a tip on the engine side may be used instead of the illustrated inner cylinder 9.

Further, a heat sensitive material having a large expansion coefficient such as ether, wax, etc. may be sealed in the bellows 10.

Of course, instead of the bellows 10, a temperature-sensitive expandable body having various structures that expands and contracts depending on the temperature of the exhaust gas flowing in the exhaust pipe can be used.

[Brief explanation of the drawing]

The figure is a longitudinal sectional view of an exhaust pipe according to the invention. 7...Exhaust pipe, 7a...Diff user section, 7b...Constriction section, 8...Outer cylinder, 10...Bellows (temperature-sensitive elastic body).

Claims (1)

[Claims] 1. In an exhaust pipe having a shape that has a diffuser section whose cross-sectional area first gradually increases in accordance with the direction in which the exhaust gas flows, and a constricted section whose cross-sectional area gradually decreases directly or directly or via an expansion section, the constricted section is A temperature-sensitive expansion/contraction system consisting of an outer cylinder with a similar cross-section and a conical or bullet-shaped inner cylinder that is slidably fitted into the outer cylinder and has its top facing toward the engine, and expands and contracts depending on the temperature of the exhaust gas flowing inside the exhaust pipe. The engine-side end of the body is fixed to the inner tube, and the other end is fixed to a part of the exhaust pipe, so that the inner tube moves toward the engine as the exhaust gas temperature rises.
Exhaust pipe for cycle engines.