JPS6320832Y2 - - Google Patents

Description

[Detailed explanation of the idea] The present invention relates to an improvement in an exhaust system for an internal combustion engine.

In an internal combustion engine, the mixed gas flows into the exhaust pipe by applying positive pressure of the pulsating wave of combustion gas reflected at the open end of the exhaust pipe to the exhaust hole at the end of the exhaust stroke in a certain set rotation range. This prevents leakage and improves the output of the engine.

Incidentally, the set rotation range is determined by the shape and dimensions of the exhaust pipe, but in the range outside this rotation range, a negative pressure wave acts on the exhaust hole, contrary to the above, and as a result, the mixed gas in the cylinder This has the disadvantage that it flows out into the exhaust pipe, causing a decrease in engine output.

The present invention has been developed to effectively eliminate such inconveniences, and its purpose is to provide a control mechanism that changes the volume of the subchamber branched in the middle of the exhaust pipe in accordance with the engine speed. To provide an exhaust system for an internal combustion engine, in which a positive pressure is always applied to an exhaust hole portion at the end of an exhaust process regardless of the rotation speed, thereby improving output over a wide rotation range. be.

A preferred embodiment of the present invention will be described below in detail with reference to the accompanying drawings.

Fig. 1 is a side view of a motorcycle equipped with an exhaust system according to the present invention, Fig. 2 is a schematic diagram of the exhaust system, and Fig. 3 is a side view of a motorcycle equipped with an exhaust system according to the present invention.
4 is a characteristic diagram of the control mechanism, FIG. 5 is a subchamber volume change characteristic diagram, and FIG. 6 is an engine output characteristic diagram.

In the motorcycle 1 shown in FIG. 1, 2 is a head pipe, and a stem shaft is inserted through the head pipe 2, and a handle 3 is fixed to the upper end of the stem shaft as shown. Further, the upper part of a front fork 4 is fixed to the stem shaft, and a front wheel 5 is rotatably supported at the lower end of the front fork 4.

Further, a fuel tank 6 and a seat 7 are arranged behind the head pipe 2, and below the fuel tank 6 there are two
A cycle engine 8 is mounted, and an exhaust pipe 9 extends from the engine 8.

On the other hand, the rear fork 10 is located approximately at the bottom of the center of the car body.
The front end of the rear fork 10 is pivotably mounted to be vertically swingable, and a rear wheel 11 serving as a driving wheel is rotatably supported at the rear end of the rear fork 10.

Incidentally, as shown in FIG. 2, a piston 13 is fitted into the cylinder 12 of the engine 8 so as to be able to swing freely, and the piston 13 is connected to a crankshaft (not shown) via a connecting rod 14. The cylinder 12 is provided with a scavenging port 15 and an exhaust port 16, an exhaust pipe 9 is connected to the exhaust port 16 as shown in the figure, and a subchamber 17 is branched off from the exhaust pipe 9 near the engine 8. ing. The subchamber 17 consists of a small-diameter cylindrical portion 17c connected to the exhaust pipe 9 and a large-diameter cylindrical portion 17b behind the small-diameter cylindrical portion 17c.

As shown in FIG. 3, a piston 18 is fitted in the subchamber 17 so as to be vertically slidable and airtight. The piston 18 has a small diameter part 18b at the front so that it can fit into the small diameter cylindrical part 17c of the subchamber 17, and a large diameter part 18a at the rear which fits into the large diameter cylindrical part 17b of the subchamber 17. It has a convex shape, and is configured such that when the piston 18 advances furthest toward the exhaust pipe 9, the end surface of the small diameter portion 18b is substantially flush with the inner wall surface of the exhaust pipe 9. The piston 18 also has a piston rod 1 that passes through the upper wall 17a of the subchamber 17.
The lower end of 9 is tied. The upper end of the piston rod 19 is connected to a centrifugal governor via an L-shaped bell crank 20. This centrifugal governor is known, and the explanation of its structure will be omitted here, but its displacement x is the engine speed Ne
It changes as shown in FIG. That is, in Fig. 4, the horizontal axis represents the engine speed Ne, and the vertical axis represents the displacement x.
In the rotation range of 0≦Ne≦Ne ₁ , x=0; in the rotation range of Ne ₁ <Ne≦Ne ₂ , the displacement x increases linearly in proportion to the rotation speed Ne, and Ne>
In the rotation range of Ne ₂ , x=x ₀ is maintained.

When the centrifugal governor is driven according to the displacement characteristics described above, the horizontal displacement x of the centrifugal governor is converted into a vertical displacement of the piston rod 19 via the bell crank 20, which causes the piston 18 to move into the subchamber 17. Move up and down inside. This vertical movement of the piston 18 causes the subchamber 17 to
The volume v changes as shown in FIG. 5 with respect to the engine speed Ne. That is, in FIG. 5, the horizontal axis represents the engine speed Ne, and the vertical axis represents the volume v of the subchamber 17.
In the rotation range of 0≦Ne≦Ne ₁ , v=vmaxNe ₁ <Ne≦Ne ₂ , v=vmaxNe 1 <Ne≦Ne 2
decreases continuously, and is adjusted to v=0 in the rotation range where Ne>Ne ₂ .

Incidentally, an air vent hole 21 is formed in the upper wall 17a of the subchamber 17 in order to allow the piston 18 to move up and down smoothly without resistance.

By the way, this two-stroke engine 8 is Ne>
In the high-speed range of Ne ₂ , the above-mentioned effect, that is, the effect of applying positive pressure to the exhaust port 16 at the end of the exhaust process to improve output, is set so that the subchamber 17 is installed in the exhaust pipe 9.
The output characteristics of the engine 8 in the case where the engine 8 is not provided is shown by curve A in FIG. In FIG. 6, the horizontal axis represents the engine rotational speed Ne, and the vertical axis represents the engine output P.

6th case when the above subchamber 17 is not provided
As is clear from the output characteristics shown by curve A in the figure, negative pressure acts on the exhaust port portion 16 in the low-speed rotation range, resulting in a decrease in output for the above-mentioned reason.

On the other hand, in the case where the subchamber 17 is provided, the volume v of this subchamber 17 is determined by the size v ₁ ,
The output characteristics when changing v ₂ (v ₁ > v ₂ ) are shown by curves B' and B'' in FIG. 6, respectively.As is clear from this, the smaller the volume v of the subchamber 17, the more The maximum point of P shifts to the high speed side. Therefore, according to the present invention, the volume v of the subchamber 17 is decreased as the rotational speed Ne increases as shown in FIG. 5, and in FIG. 6, for example, Ne=
v=v ₁ at Ne ₁ ′, v=v ₂ at Ne=Ne ₂ ′
By doing as follows, the maximum output at each rotation speed Ne can be obtained, and the output characteristic is shown by a curve B obtained by connecting the maximum output points at each rotation speed Ne. This means that positive pressure is always applied to the exhaust port 16 of the engine 8 at the end of the exhaust process over a wide rotation range, and therefore it is possible to improve the output over a wide rotation range and achieve smooth output characteristics. It will be done.

As is clear from the above explanation, according to the present invention, a control mechanism is provided that changes the volume of the subchamber branched in the middle of the exhaust pipe in accordance with the engine speed, so that the engine exhaust hole can be used at the end of the exhaust process. Positive pressure can always be applied to the engine, and output can be improved over a wide rotation range.

[Brief explanation of the drawing]

The drawings show one embodiment of the present invention; FIG. 1 is a side view of a motorcycle, FIG. 2 is a schematic diagram of the exhaust system of the motorcycle, and FIG. 3 is a cutaway side view of the main parts of the control mechanism. , Figure 4 is a characteristic diagram of the control mechanism, and Figure 5 is a characteristic diagram of the control mechanism.
The figure is a subchamber volume change characteristic diagram, No. 6
The figure is an engine output characteristic diagram. In the drawings, 1 is a motorcycle, 8 is an engine, 9 is an exhaust pipe, 15 is a scavenging port, 16 is an exhaust port,
17 is a subchamber, 18 is a piston, 19 is a piston rod, and 20 is a bell crank.

Claims (1)

[Scope of Claim for Utility Model Registration] (1) In an exhaust system for an internal combustion engine, which has a branched subchamber in the middle of an exhaust pipe, a small-diameter cylindrical portion that connects the subchamber to the exhaust pipe and a large-diameter cylindrical portion behind the small-diameter cylindrical portion. a piston that slides within the subchamber is formed into a convex shape consisting of a small diameter portion that fits into the small diameter cylindrical portion of the subchamber and a large diameter portion that fits into the large diameter cylindrical portion; The piston is provided with a control mechanism that makes the end face of the small diameter portion substantially flush with the inner wall surface of the exhaust pipe at the position where the piston protrudes most toward the exhaust pipe, and changes the volume of the subchamber according to the engine speed. An exhaust system for an internal combustion engine characterized by: (2) The exhaust system for an internal combustion engine according to claim 1, wherein the control mechanism includes a centrifugal governor.