JPH0126555Y2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to an exhaust system for a two-stroke engine for a motorcycle.

In a two-stroke engine, at the end of the exhaust stroke during high-speed rotation, the positive pressure of the pulsating waves of combustion gas reflected from the opening of the exhaust pipe is applied to the exhaust hole to reduce the mixture coming out of the exhaust pipe. The engine is designed to push the gas back into the cylinder to improve output, but the engine speed at which the output can be increased is limited to the high speed range if the shape and dimensions of the exhaust pipe are adapted to the high speed range; During rotation, a negative pressure wave acts on the exhaust hole and sucks out the mixed gas, resulting in a decrease in output.

Conventionally, in order to prevent the output from decreasing during low-speed rotation, an exhaust system has been known that includes a subchamber branched in the middle of an exhaust pipe and a valve body provided at the inlet of the subchamber so as to be openable and closable. In this exhaust system, by opening the valve body during low-speed rotation, the negative pressure in the exhaust hole caused by the pulsating waves of combustion gas at the end of the exhaust stroke is changed to positive pressure by the reflected waves from the subchamber, and the output is increased. By closing the valve body during high-speed rotation, the influence of the subchamber is eliminated and a decrease in output is prevented.

When installing such an exhaust system on a motorcycle,
In a motorcycle, many devices, parts, etc. are laid out in a frame of a predetermined size so that there is no extra space, so consideration must also be given to the layout of the subchamber. Generally speaking, the subchamber can be placed above the exhaust pipe and to the side of the fuel tank, or directly below the fuel tank, but in the former case, it will spoil the appearance of the vehicle body and the subchamber will In the latter case, problems arise such as the fuel tank hitting the rider's knees and restricting the rider's driving posture, and in the latter case, problems arise such as having to reduce the volume of the fuel tank.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide an exhaust system for a two-stroke engine for a motorcycle in which a subchamber is laid out by effectively utilizing the so-called dead space of the vehicle body without impairing the appearance.

To achieve this purpose, the exhaust system for a two-stroke motorcycle engine according to the present invention includes a down tube extending downward from a head pipe that rotatably supports a steering shaft, and at least two exhaust tubes branching from this down tube. In a motorcycle including a cradle pipe, a subchamber branched in the middle of the exhaust pipe is arranged in a position surrounded by the cradle pipe, the exhaust pipe of the two-cycle engine, and the crankcase. .

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a side view of a motorcycle according to the present invention, FIG. 2 is a side view including a partial cross section showing an embodiment of the present invention, and FIG. 3 is a front view thereof. In the figure,
1 is a head pipe that rotatably supports the steering shaft 2; 3 is a down tube extending downward from the head pipe 2; and 4, 4 are two cradle pipes that branch from the down tube 3 and extend further downward. A two-stroke engine 7 is attached to these two cradle pipes 4, 4 via brackets 5, 6.

In the exhaust system of the engine 7, a communication pipe 11 is provided between the exhaust hole 9 and the exhaust pipe 10 that communicate with the inside of the cylinder 8.
is removably provided and forms part of the exhaust pipe. A subchamber 13 is branched in the middle of the exhaust pipe and communicates with the communication pipe 11 via a support pipe 12 formed integrally with the communication pipe 11.
Furthermore, a valve body 15 is provided in the communication passage 14 between the communication pipe 11 and the subchamber 13 so that the communication passage 14 opens when the engine 7 rotates at low speed and closes when the engine 7 rotates at high speed. The valve body 15 is a butterfly valve provided on a rotating shaft 16 supported by the support tube 12. Gaskets 17 and 17 are interposed between the exhaust hole 9 and the exhaust pipe 10 and the communication pipe 11, respectively, so that the heat from the exhaust hole 9 and the exhaust pipe 10 is blocked by the gaskets 17 and 17. Therefore, unnecessary heat is not transferred to the bearing portion of the valve body 15, thereby improving durability and eliminating the need for means such as water cooling.

In FIGS. 2 and 3, the space surrounded by the communication pipe 11, which is a part of the exhaust pipe, the cradle pipes 4, 4, and the crankcase 18 of the engine 7 is a so-called dead space. The subchamber 13 is provided. According to this, the subchamber 13 is surrounded by the cradle pipes 4, 4, the communication pipe 11, the crankcase 18, and the bracket 5 that supports the engine 7, and these members prevent the subchamber 13 from becoming an obstacle. Since the subchamber 13 can be formed from a thin plate, the weight of the subchamber 13 can be reduced, and its durability and reliability can be improved. Further, since the volume of the subchamber 13 is within the range that can be laid out in the above-mentioned space, the subchamber 13 can be laid out without modifying the frame. Further, since the subchamber 13 is located immediately after the high temperature part of the exhaust pipe and is not exposed to the running wind and is not easily cooled, the temperature change in the subchamber 13 is small and the characteristics of the subchamber 13 are kept constant.

In the above embodiment, a case where the present invention is applied to a motorcycle has been described, but the present invention can also be applied to a tricycle, etc., which has two rear wheels and has a body structure similar to that of a motorcycle.

As described above, according to the present invention, a motorcycle includes a down tube extending downward from a head pipe rotatably supporting a steering shaft, and at least two cradle pipes branching from the down tube. Cradle pipe, 2
By installing a subchamber that branches off in the middle of the exhaust pipe in a position surrounded by the exhaust pipe and crankcase of the cycle, the dead space of the car body can be used effectively, and the shape and appearance of the finished car will not be compromised. The subchamber can be laid out without disturbing the rider's riding position, and the subchamber can be protected from obstacles by the engine, front fender, down tube, cradle pipe, and exhaust pipe. Furthermore, since the subchamber is located immediately after the high temperature part of the exhaust pipe and is not easily cooled, the temperature of the subchamber changes little and the characteristics of the subchamber are kept constant.

[Brief explanation of drawings]

FIG. 1 is a side view of a motorcycle according to the present invention, FIG. 2 is a side view including a partial cross section showing an embodiment of the present invention, and FIG. 3 is a front view thereof. Explanation of symbols of main parts, 1...Head pipe,
3...down tube, 4...cradle pipe, 7...2-stroke engine, 9...exhaust hole, 10
...Exhaust pipe, 11...Communication pipe, 13...Subchamber, 15...Valve body.

Claims (1)

[Scope of utility model registration request] In a motorcycle that includes a down tube extending downward from a head pipe that rotatably supports a steering shaft, and at least two cradle pipes branching from the down tube, the cradle pipe is branched in the middle of the exhaust pipe of a two-stroke engine. An exhaust system for a two-stroke engine, comprising a subchamber with a cradle pipe and a valve body provided at an inlet of the subchamber so as to be openable and closable, the exhaust system controlling opening and closing of the valve body according to the rotational speed of the engine, An exhaust system for a two-stroke engine for a motorcycle, characterized in that the subchamber is disposed at a position surrounded by an exhaust pipe and a crankcase of the engine.