JPS6117211Y2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a muffler for an exhaust system installed in an automobile or other internal combustion engine, and particularly relates to an improvement in a muffler installed at the tail pipe end of the exhaust system.

Generally, an automobile or other internal combustion engine is equipped with an exhaust system, and the exhaust system is equipped with a muffler to keep exhaust noise low.

As is well known, this muffler is a can body with an expansion chamber, a resonance chamber, etc. provided inside, and an exhaust conduit is provided on the upstream side of the exhaust system to guide exhaust from the engine to the muffler. A tail pipe for discharging exhaust gas into the atmosphere communicates with the downstream side.

However, in such conventional noise reduction systems, the flow velocity of the exhaust gas discharged from the tail pipe differs significantly depending on the engine speed, so while this does not pose a problem at low engine speeds, when the engine speeds high, the flow rate at the end of the tail pipe changes significantly. Secondary noise due to the jet flow (hereinafter referred to as jet noise) is generated. Therefore, even if the main noise generated by the engine is effectively muffled with a muffler, new jet noise will occur unless some measure is taken at the end of the tail pipe that discharges the exhaust into the atmosphere. , there is a risk that the entire silencing system will not be able to achieve a sufficient silencing function.

Therefore, it may be possible to reduce the jet noise by changing the diameter of the end of the tail pipe, but in this case, if the tail pipe is made large in diameter, it will be possible to reduce the noise when the engine is running at high speeds, that is, when the displacement is large. Although it does work effectively because the exhaust flow velocity decreases, on the other hand, when the engine rotates at low speeds when there is no need to worry about jet noise, that is, when the displacement is small, resonance noise occurs and the silencing performance deteriorates. There's a problem.

Therefore, such conventional mufflers have a problem in that they cannot sufficiently muffle noise over a wide range from a low engine speed range to a high engine speed range.

In view of these points, it is an object of the present invention to provide an exhaust system muffling device that can sufficiently muffle noise in a wide range from low to high engine speeds, and has a simple structure and is easy to handle.

First, the silencing principle of the present invention will be explained.

Exhaust noise can be broadly divided into main noise caused by the explosion of fuel in the engine, acoustic noise caused by the acoustic characteristics of exhaust system components (characteristics due to the mounting position of the muffler, the internal structure, the shape of the exhaust system, etc.), and jet noise caused by the Karman flow that occurs depending on the flow velocity of the exhaust (the structure of the exhaust outlet inside the muffler,
There is secondary noise generated by the exhaust gas flow caused by the tail pipe diameter, tail pipe shape, etc.

No matter how good the structure of the muffler for muffling the main noise is, it is necessary to effectively reduce the secondary acoustic noise and jet noise to improve the muffling characteristics of the exhaust system. It won't make you do it.

By the way, the aforementioned main noise generated by the engine is
It is known that relatively high frequency noise is generated when the engine rotates at high speeds, and relatively low frequency noise is generated when the engine rotates at low speeds. Low-frequency noise may resonate with the system and cause resonance noise (a type of acoustic noise).

Figures 3 and 4 show the results of a bench test of exhaust noise measured immediately after the tail pipe with only the engine and exhaust system of the car taken out. That's what I did.

Figure 3 shows the actual exhaust noise measurement results.
FIG. 4 shows the measurement results of the so-called A characteristic (a characteristic that takes into account the characteristic that the human ear's sensitivity is low at low frequencies and high at high frequencies) corrected for noise perceived by the human ear.

That is, FIG. 3 shows the exhaust noise when the tail pipe diameter corresponding to the engine speed is 38.1 mm (dotted line), 45 mm (dotted line), and 50.8 mm (solid line). According to this, when the engine speed is medium or high, the larger the tail pipe diameter, the lower the noise, but when the engine speed is low (low frequency region), conversely, the tail pipe diameter becomes smaller. It can be seen that the higher the value, the louder the noise.

At high engine speeds (high frequency range),
One reason for the increase in noise is that jet noise is generated by the exhaust gas at the end of the tail pipe, and this jet noise increases in proportion to the exhaust flow velocity, so as the pipe diameter increases, the flow velocity increases. It falls and becomes lower. Also, the reason why the noise becomes louder even when the engine is running at low speeds (low frequency range) is because the low frequency components generate acoustic noise due to resonance in the exhaust system, and the acoustic noise due to this resonance is caused by the pipe diameter The larger the diameter, the easier it is to resonate, so the larger the pipe diameter, the larger the resonance.

In addition, the experimental results for characteristic A shown in Figure 4 show that exhaust noise increases in proportion to the engine speed over the entire range of engine speeds, and the larger the tail pipe diameter, the smaller the rate of increase. . That is,
At the same rotation speed, the larger the tail pipe diameter, the lower the exhaust noise.

Here, the reason why no increase in exhaust noise is observed in the low frequency region is because the human ear does not perceive low frequency noise.

The above are the results of the above-mentioned bench test, but when the actual vehicle is running, it is natural that not only the noise emitted from the exhaust gas mentioned above, that is, the noise given to the external environment, but also the noise given to the passengers inside the vehicle. I have to think about it. In addition, the noise that is applied to the external environment when the vehicle is actually running may resonate with the vehicle body itself, so it is affected by the vehicle body.
The acoustic noise described above will be different from the bench test.

The proportion of the secondary noise level of the exhaust system based on the rotational speed of the actual vehicle compared to the total exhaust noise varies depending on the engine displacement or tail diameter, but in the low to medium rotation range, the exhaust noise level is The proportion of acoustic noise is large, and the proportion of jet noise at the end of the tail pipe is large in the high rotation range. When the vehicle is actually running, the noise in the low frequency range that does not affect the human ear, as mentioned above, becomes a problem. The noise is transmitted to the vehicle floor through the mounts, and in some cases, it may resonate with the vibrations of the vehicle floor, producing so-called muffled noise in the vehicle interior.

Therefore, it is necessary to avoid expanding the diameter of the tail pipe, which increases resonance noise (acoustic noise) in the low frequency range that causes this muffled sound.

That is, the noise in the low to medium rotation range is relatively inoffensive, but the jet noise in the high rotation range is noisy, so the jet noise in the high rotation range is regulated by making the tail aperture large. If the tail aperture is made to vary small in the low to medium rotation range to prevent muffled noise, noise can be effectively prevented in the entire engine rotation range.

The present invention has been made based on this principle, and one embodiment of the present invention will be described below with reference to the drawings.

In FIG. 1, the tail pipe end 1 has a mounting portion 3a of a muffling inner cylinder 3, which forms a part of the muffling device 2 of the present invention.
is removably fitted on the outside, and the peripheral wall of this muffling inner cylinder 3 has a large number of small holes 4, 4 for allowing exhaust gas to pass through.
... are provided, and annular raised rings 5, 6 are formed by embossing at the front and back of the small hole forming portion where the small hole 4 is formed.

A sliding tube 8 provided with a small hole 7 corresponding to the small hole 4 is slidably fitted onto the small hole forming portion, and the inner wall of the sliding tube 8 is fitted with the raised rings 5 and 6 at the front and rear thereof. , thereby reducing the sliding frictional resistance of the sliding tube 8.

Further, a large-diameter noise-reducing outer cylinder 9 is provided to cover the noise-reducing inner cylinder 3 and the sliding cylinder 8, and this outer cylinder 9
A neck portion 9a is formed by swaging at the front portion of the slider 8, and the tip portion of the neck portion 9a is welded to the front end portion of the sliding tube 8.

An operating member 10 is provided on the neck portion 9a and the outer wall cylinder of the muffling inner cylinder 3 for rotating the sliding cylinder 8 and the muffling outer cylinder 9 together in the circumferential direction on the muffling interior. The actuating member 10 may be made of a bimetal that bends due to temperature changes in the exhaust gas, or a bimetal that can be elastically deformed to a certain extent but returns to its original shape as the temperature is increased, such as Nitinol (an alloy of nickel and titanium). Temperature deformable members made of shape memory metals such as (trade name) are used.

When a shape memory metal is used for this actuating member 10, for example, it is a flat plate with many small cuts made along the axial direction of the noise-reducing inner cylinder 3. Using a so-called net-like expanded actuator, one end corner of the actuating member 10 is fixed to the sound-deadening inner cylinder 3, and the other diagonal end corner of this corner is fixed to the sound-deadening outer cylinder 9.
It is conceivable that as the actuating member 10 is heated, it expands in the circumferential direction and rotates the sliding tube 8. In addition, any actuating member 10 may be used as long as the small hole 4 of the inner cylinder 3 and the small hole 7 of the sliding cylinder 8 can be made to match or deviate from each other. It may be possible to slide the actuating direction in the axial direction.

The inner wall of the mounting portion 3a of the noise-muffling inner cylinder is made smooth by homing and has a slit 11 in its axial direction, so that it can be easily mounted on the tail pipe end 1.

Next, the effect will be explained.

When the engine speed is low and the exhaust gas temperature is low (50 to 150 degrees Celsius), the flow rate of the exhaust gas is low, so the jet noise is also low. This jet noise can be effectively prevented by increasing the diameter of the muffling tube, but if the diameter is increased when the engine is running at low rotation speeds, muffled noise will become louder.

When the engine speed is low, the operating member 10 moves in the circumferential direction of the silencer inner cylinder 3 from the state shown in FIG. The positions of the small hole 7 of the cylinder 8 and the small hole 4 of the noise-muffling inner cylinder 3 are shifted, and the small hole 4 is closed.

Therefore, the exhaust gas is discharged to the outside from the pipe end of the muffler inner cylinder 3, and since the muffler inner cylinder 3 has a small diameter, generation of muffled noise is prevented.

As the engine speed increases, the temperature of the exhaust gas also rises, and as the flow velocity increases, the jet noise gradually increases. However, at this time, the actuating member 10 operates in accordance with the temperature change, and the small holes 7 of the sliding tube 8 are aligned with the small holes 4 of the muffling inner cylinder 3, so that the exhaust gas flowing inside the muffling inner cylinder 3 is controlled. A part of the flow is branched off and flows into the silencing outer cylinder 9.

Therefore, the flow velocity of the exhaust gas at the end of the tube is reduced, and the diameter of the muffling tube is increased, resulting in a reduction in jet noise.

When the engine speed is medium and the exhaust gas temperature is also medium, the positions of the small holes 4 and 7 are shifted depending on the temperature, leaving part of the small hole 4 open.

As shown in FIG. 2, a housing cylinder 12 having a large number of small openings 0, 0, etc. is provided on the inner wall of the sound-absorbing outer cylinder 9, and a sound-absorbing material such as glass wool is placed between the housing cylinder 12 and the inner wall of the sound-absorbing outer cylinder. If material 13 is filled,
It absorbs high frequencies when the engine speed increases, resulting in a significant reduction in noise.

As explained above, the present invention consists of fitting a sliding tube with a small hole corresponding to the small hole onto a sound-deadening inner tube having a small hole, and covering both tubes with a large-diameter sound-deadening outer tube. In addition, since the sliding tube is slid by an operating member that deforms due to temperature changes to open and close the small hole in the noise-muffling inner tube, noise, especially jet noise and muffled noise, can be effectively reduced over the entire range of engine speeds. Furthermore, if the noise-absorbing outer cylinder is lined with a sound-absorbing material, the noise-absorbing effect during high-speed rotation can be significantly increased.

[Brief explanation of the drawing]

Fig. 1 is a longitudinal cross-sectional view of the silencer of the present invention at high temperatures, Fig. 2 is a longitudinal cross-section of a silencer showing another embodiment of the present invention, Fig. 3 is a jet noise comparison graph,
FIG. 4 is an A characteristic comparison graph. 1... Tail pipe end, 2... Silencer, 3... Sound deadening inner cylinder, 4, 7... Small hole, 8... Sliding tube, 9...
Sound deadening outer cylinder, 10... Operating member, 13... Sound absorbing material.

Claims (1)

[Claims for Utility Model Registration] 1. A small hole 4 through which exhaust gas can pass is provided in the peripheral wall attached to the tail pipe end 1 through which exhaust gas is discharged into the atmosphere. a sliding cylinder 8 that is slidably engaged with the noise-reducing inner cylinder 3 and is provided with a small hole 7 corresponding to the small hole 4 of the noise-reducing inner cylinder 3;
A noise-reducing outer cylinder 9 is formed to cover the noise-reducing inner cylinder 3 and the sliding cylinder 8 and has a larger diameter than both cylinders. If the temperature of the exhaust gas is low, the positions of both the small holes 4 and 7 of the front air muffling inner cylinder 3 and the sliding cylinder 8 will shift, and the small hole 4 will be closed or partially opened. A silencer for an exhaust system, characterized in that it has an actuating member 10 made of a material that has a large amount of deformation in response to temperature changes, and is for sliding at least the sliding tube 8 so as to achieve the above-mentioned state. . 2. The silencer for an exhaust system according to claim 1, wherein the operating member is made of bimetal or shape memory metal. 3. The exhaust system muffling device according to claim 1 or 2, wherein the muffling outer cylinder has a sound absorbing material lined on the inner wall.