JPS6224609B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an exhaust muffler for attenuating engine exhaust noise.

In engines installed in vehicles, the pulsation is suppressed by passing the exhaust consisting of the vibrating combustion gas through an exhaust pipe or an expansion chamber, etc., in order to dampen the loud noise caused by the vibrating combustion gas that accompanies the explosion inside the cylinder. ,
Through expansion and cooling, the pressure of the exhaust gas is lowered and released into the atmosphere. Silencers for reducing exhaust noise are classified into cavity type (expansion type), resonance type, sound absorption type, etc., and usually various combinations of these types are used to obtain the desired damping characteristics. In the hollow type, the cross-sectional area of a certain section of the pipe is increased to cause sound waves to interfere with each other to attenuate pulsation.

Vehicle engines generate particularly loud noises during high-speed rotations when the engine output is large, so mufflers are usually designed to have a large damping effect on high-frequency sounds during such high-speed rotations.

On the other hand, regarding the silencing effect of the above-mentioned cavity-type muffler, the larger the area ratio S=s ₂ /s ₁ of the cross-sectional area s ₂ of the expansion chamber and the cross-sectional area s ₁ of the exhaust pipe connected to the expansion chamber, the more the noise is muted. It is known that the effect is also great. However, the outer diameter of the expansion chamber cannot be increased unnecessarily due to limitations in the mounting space of the muffler, and the cross-sectional area _s1 of the exhaust pipe cannot be made too small in order to maintain high engine output performance. That is, the exhaust pipe is generally set to bring out the maximum output of the engine, and a cross-sectional area _s1 corresponding to the exhaust flow rate at this time is adopted. For this reason, it is possible to reduce the cross-sectional area of the exhaust pipe at low output and low-speed rotations when the exhaust flow rate is low, and by doing so, the area ratio S mentioned above can also be increased, improving the noise reduction effect during low-speed rotations. It becomes possible to do so.

From this point of view, it is conceivable to provide the exhaust pipe opening with a lid that opens and closes depending on the exhaust pressure. However, when the lid is in contact with the exhaust pipe opening in the closed state, during low-speed rotation with a large difference in exhaust pressure pulsation, a collision noise with the exhaust pipe opening is produced, which is a problem that becomes a new source of noise. In addition, with an opening/closing lid that can be opened and closed by pivoting on a pin or the like, if carbon adheres to the pivoting portion, there is a risk that the lid will not operate stably.

This invention was made based on this idea, and while maintaining a large silencing effect at high output and high rotation, it also exhibits an excellent silencing effect at low output and low rotation, and is stable. The object of the present invention is to provide an exhaust silencer with a reed valve that operates. In order to achieve this object, the present invention provides a reed valve that faces the exhaust pipe opening opening into the expansion chamber with a predetermined gap when the engine is stopped, so that the area of the exhaust pipe opening is determined by the engine output. It is configured to change accordingly. The present invention will be explained in detail below based on the drawings.

FIG. 1 is a partially omitted side view of a motorcycle to which an embodiment of the present invention is applied, and FIG. 2 is a partially sectional side view of a silencer thereof. 1 in Figure 1
is a power unit, and this power unit 1 is integrally formed by an engine 2, a power transmission mechanism using a centrifugal clutch (not shown), a rear wheel 3, etc., and its front end is pivoted to a frame 4. There is.
That is, this power unit 1 is movable up and down around its front end, and constitutes a so-called unit swing rear wheel suspension system. The rear wheel 3 is held by a rear arm (not shown) that also serves as a cover (not shown) for a drive chain (not shown) disposed on the left side of the vehicle body. Of course, this rear arm is also constructed integrally with the power unit 1. Further, on the right side of the rear wheel 3, an exhaust muffler 20, which will be described later and which is also integrally constructed with the power unit 1, is installed so as to form a pair with the rear arm, and a cover 5 is attached to the muffler 20. There is.

6 is a main stand attached to the power unit 1, and 7 is a reaction unit that resiliently supports the power unit. This reaction unit 7 is an integral combination of a buffer spring and a damper. 8 is a seat, 9 is a fuel tank, and 10 and 11 are mudguards.

Reference numeral 20 denotes an exhaust muffler, which is formed by forming a pair of left and right press molded products into a hollow shape and welding the outer peripheral flange portions. Inside this muffler 20, three expansion chambers are formed by two partition walls 21 and 22.
That is, a first expansion chamber 23 at the rear, a second expansion chamber 24 at the front, and a third expansion chamber 25 between these are formed. The first expansion chamber 23 has the largest volume, and an exhaust pipe 26 that guides exhaust from the exhaust port (not shown) of the engine 2 is located inside the partition wall 23.
2 and 21. By causing a portion of the end of the exhaust pipe 26 to protrude into the first expansion chamber 23 and appropriately selecting the length of this protruding portion, the damping characteristics of exhaust pulsation can be improved. The opening 27 of the exhaust pipe 26 is cut obliquely, and a reed valve 28 made of stainless steel faces the opening 27 at a constant distance from the opening 27. That is, this reed valve 28 is fixed by a rivet 30 to a bracket 29 fixed to the outer wall of the exhaust pipe 26 near the opening 27. Since the opening 27 is cut diagonally in this way, the area of the reed valve 28 that is hit by the exhaust gas exiting the exhaust pipe 26 increases, and the reed valve 28 becomes more flexible. Therefore, the reed valve 28 easily follows changes in the output of the engine 2, and the substantial opening area between the opening 27 and the reed valve 28 changes favorably. A sound absorbing material 31 made of glass wool is fixed to the inner wall of the first expansion chamber 23. This sound-absorbing material 31 has the effect of absorbing high-frequency noise particularly well and suppressing the emission of noise to the outside of the muffler 20.

The first expansion chamber 23 and the second expansion chamber 24 are defined by the partition wall 2
1 and 22 are communicated by a pipe 32 passing through both. The second expansion chamber 24 and the third expansion chamber 25 communicate with each other through a pipe 33 that penetrates the partition wall 22 . Further, one end of a tail pipe 34 opens in the third expansion chamber 25 , and the tail pipe 34 passes through the inside of the first expansion chamber 23 and the other end opens to the rear of the muffler 20 . Note that the pipe 33 has a smaller diameter than the pipe 32 and the exhaust pipe 26, and the tail pipe 34 has an even smaller diameter than the pipe 33.
As a result, when the exhaust gas passes through the third expansion chamber 25 from the first and second expansion chambers 23 and 24, and when it is led from the third expansion chamber 25 to the atmosphere, the exhaust passage is narrowed and pressure fluctuations are suppressed. . On the other hand, the inner diameter and length of the exhaust pipe 26 are determined so that the engine 2 produces maximum output.

When the exhaust gas from the engine 2 now flows into the exhaust pipe 26, this exhaust pressure acts on the reed valve 28. When the engine 2 is operating at low speed and low output, the exhaust pressure is low and the reed valve 28 hardly opens, and the substantial opening area of the opening 27 of the exhaust pipe 26 is the area between the opening 27 and the reed valve 28. Determined by the gap between. When the engine 2 is running at high speed and high output, the exhaust pressure also increases and the reed valve 28
automatically opens in the direction of arrow A in FIG. 2 and moves to the position indicated by the chain line, increasing the substantial opening area of the opening 27. That is, when the engine 2 rotates at low speed and has low output, the cross-sectional area s ₂ of the first expansion chamber 23 and the exhaust pipe 2
The area ratio S=s ₂ /s ₁ with respect to the substantial cross-sectional area s ₁ of 6 becomes large, and on the contrary, this area ratio S becomes small at high speed rotation and high output. Since the reed valve 28 is easily bent, the back pressure of the engine 2 increases only slightly even during high speed rotation and high output, and its output characteristics hardly deteriorate.

As a result, even if the muffler 20 is designed to effectively attenuate particularly loud and unpleasant noise during high-speed rotation and high output, the area ratio S becomes substantially large during low-speed rotation and low output. The damping effect becomes larger. Therefore, the noise can be significantly reduced even during low speed rotation and low output such as during idling, and the output characteristics at high output hardly deteriorate.

Furthermore, since the reed valve 28 has a constant gap with the exhaust pipe opening 27 even in the closed state, it does not collide with the opening 27 when vibrating due to exhaust pulsation.
Does not generate hitting sounds that become a new noise source. Further, since the reed valve 28 itself is elastically deformed and there is no movable member such as a shaft support portion such as a pin, the operation is not hindered even if carbon adheres to it, and a stable noise reduction effect can be achieved. Note that the reed valve 28 has an opening 27
Since there is no collision with other objects, there is no possibility of deterioration due to collisions under high heat.

3A and 3B are a side view and a rear view of the vicinity of the opening 27a showing another embodiment of the present invention. In this embodiment, a large number of small holes 40 are provided in the reed valve 28a, and by changing the number and area of the small holes 40, the amount of deflection of the reed valve 28a can be changed, and the output of the engine 2 can be changed. This makes it possible to achieve a delicate balance between the characteristics and the attenuation characteristics of the silencer 20.

FIGS. 4A and 4B are a side view and a rear view of the vicinity of the opening 27b showing still another embodiment of the present invention. In this embodiment, the opening 27b is cut so as to be perpendicular to the central axis of the exhaust pipe 26, and the reed valves 28b are held so as to face each other at a constant distance, leaving a portion of the opening 27b.

In addition to those shown in FIGS. 3 and 4, reed valves of various shapes and areas can be used in the present invention. For example, two reed valves may be arranged in a V-shape, or a plurality of reed valves having different hardnesses may be used to open the reed valves in sequence according to the engine output. In short, the configuration may be such that the substantial opening area of the exhaust pipe changes automatically in response to the rotational speed and output of the engine.

As described above, in this invention, a reed valve is provided at the opening in the expansion chamber of the exhaust pipe, and the opening area of the exhaust pipe is configured to change in accordance with the engine output, thereby effectively reducing noise at high output. Even if the muffler is designed to attenuate, at low power the cross-sectional area of the expansion chamber s ₂ and the effective cross-sectional area of the exhaust pipe s ₁
The area ratio S=s ₂ /s ₁ becomes larger, and the silencing effect becomes larger. Therefore, low speed rotation such as idling
Noise is extremely low even at low output. Furthermore, at high output, the reed valve is largely bent and there is little increase in back pressure, so the drop in engine output performance is slight and can be ignored. Furthermore, there is no knocking sound caused by the opening and closing of the exhaust pipe opening at low output. Furthermore, even if carbon adheres to it, the operation is not hindered and a stable sound damping effect can be achieved.

[Brief explanation of the drawing]

Fig. 1 is a partially omitted side view of one embodiment of the present invention, Fig. 2 is a partially sectional side view of the muffler, Figs. FIG. 7 is a side view and a rear view of the vicinity of a reed valve showing another embodiment of the invention. 2...Engine, 20...Exhaust silencer, 23...
...first expansion chamber, 26...exhaust pipe, 27...opening,
28...Reed valve.

Claims (1)

[Claims] 1. In an exhaust muffler having an expansion chamber, a reed valve is disposed at the exhaust pipe opening opening into the expansion chamber and faces with a predetermined gap when the engine is stopped, and the area of the exhaust pipe opening corresponds to the engine output. An exhaust muffler with a reed valve, characterized in that the exhaust muffler is configured to change according to