Noise reduction device having walls therein

Abstract

Disclosed is a noise reduction device, including a pipe-shaped body having an inlet and an outlet, and walls provided in the body to filter noise propagating from the inlet to the outlet, whereby the noise intensity exiting the outlet is less than the noise intensity entering the inlet, the quantity of walls and angle provided between the walls and body being variable to change the performance of noise reduction.

Description

PRIORITY

This application claims priority to an application entitled “NOISE REDUCTION DEVICE HAVING WALLS THEREIN” filed with the Korean Intellectual Property Office on Oct. 4, 2003 and assigned Serial No. 2003-0069765, the contents of which are hereby incorporated by reference.

FIELD OF THE INVENTION

The present invention relates to a noise reduction device, and more particularly to a noise reduction device which has an inlet and an outlet and is formed in the shape of a pipe, wherein walls are provided in the body thereof, thereby filtering some of the noise passing through the device, so that the noise in the outlet can be significantly reduced.

BACKGROUND OF THE INVENTION

Noise problems occur commonly in automobiles as well as machines used in plants. The demand for a noise reduction device, which has a structure that does not inhibit gas flow in a short-length device is present especially in noise generating mechanisms using internal combustion engines, such as motors, power generators, automobiles, etc. Thus, the following description will be provided, focusing on the internal combustion engine.

The internal combustion engine generates the strongest noise when the fuel is burned inside cylinders of the engines. Thus, mufflers are usually used in order to reduce the strong noise to a suitable level. The noise generated from burning fuel inside an engine is so strong and it is difficult to design a muffler in a to sufficiently reduce it to a desired level due to the limited size of the muffler.

If the muffler can be designed without any limitation on its size, the problem mentioned above should not occur. But mufflers are designed with considerable space limitations resulting in less than optimal performance.

FIG. 5 shows the muffler (10) of the passenger car model “AVANTE” made by Hyundai Motor Company, wherein the exhausting gas is arranged to be exhausted after taking a turn in the muffler (10). As a result, since the exhausting gas is arranged to flow in the reverse direction two times, the exhaust resistance is considerably increased, inhibiting the exhaust gas from completely discharging to the outside.

All mufflers, which are used as noise reduction devices for most internal combustion engines, have the same or similar shape as the muffler shown in FIG. 5. The reason that the muffler should be designed as shown in FIG. 5 is because of its compact size due to space limitations.

Therefore, in most noise generating mechanisms using internal combustion engines, exhaust gas remains in the engine due to exhaust resistance resulting in incomplete combustion and loss of power. A tuned muffler reduces noise and reduces lost power due to exhaust resistance.

Accordingly, noise generating mechanisms using internal combustion engines have a demand to reduce the noise to a suitable level within a small area, however, conventional technology for noise reduction does not satisfy the co-existing demands for noise reduction and a more complete flow of the exhaust gas out of the noise reduction device.

Conventional technology has used the muffler shown in FIG. 5 in order to effectively reduce the noise within a small area, however, in the case of using the conventional muffler as applied to an internal combustion engine, the power output is reduced and many pollutants are exhausted.

In addition, the conventional muffler has a structure incapable of discharging the condensed water completely leading to corrosion.

Further, in the case where noise generating mechanisms such as motors emit a lot of heat, it is difficult to exhaust the heat from the conventional muffler.

Accordingly, the object of the present invention is to provide an improved noise reduction device, which can reduce noise to a suitable level and more fully discharge the exhaust has to the atmosphere.

SUMMARY OF THE INVENTION

In order to achieve the above objects, the present invention provides a noise reduction device, which has an inlet and an outlet and is formed in the shape of a pipe, wherein walls are provided in the body thereof, thereby filtering some of the noise passing through the device, so that the noise at the outlet is significantly reduced.

In addition, in order to apply the present invention to automobiles, the noise reduction device is arranged with straight and angled sections.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the principles of the invention, wherein:

FIG. 1a shows a cross sectional view of a noise reduction device according to the present invention, and a vertical sectional view of the device, wherein both sides of the device are provided with walls;

FIG. 1b is a plan view of a muffler designed in accordance with the lower structure of the automobile according to the present invention;

FIG. 2a is a cross-sectional view of the present invention showing the noise being filtered by walls;

FIG. 2b shows a cross-sectional view of an angled section of the present invention showing noise dissipating as it hits the wall;

FIGS. 3a to 3d are line illustrations of different aspects of the present invention explained later in further detail;

FIG. 4a is a photograph showing the walls provided in the noise reduction device;

FIG. 4b is a photograph showing the sectional view of the walls provided in the device, wherein one end thereof is open so that exhaust resistance is not generated;

FIG. 4c is an illustration of the walls on two sides of the device showing the ease with which condensed water is discharged;

FIG. 4d is an embodiment of the present invention as applied to reducing bathroom noise;

FIG. 4e is an embodiment of the present invention as applied to reducing the noise from a helicopter's engine;

FIG. 5 is a diagram of a muffler from an “AVANTE” made by Hyundai Motor Company; and

FIG. 6 is an illustration of the present invention showing the sectional area of an outlet is designed to be smaller than that of an inlet to prevent secondary noise.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Reference will now be made in detail to the preferred embodiment of the present invention in conjunction with the accompanying drawings.

In FIG. 5, the conventional noise reduction device 10 used in the internal combustion engine is shaped so that the exhaust resistance is very high as described above. However, according to the present invention, the exhaust resistance is reduced significantly.

First, according to the present invention, as shown in FIGS. 1a, and 4b, the exhaust resistance of the exhaust gas is reduced to nothing. That is, passing the exhausting gas through the present invention is equal to a case wherein the exhausting gas passes through a a typical exhaust pipe of the prior art having an inner diameter as great as the empty space formed in the center of the present invention.

Someone might say that the resistance can be increased by the walls provided in the present invention, however, actually the space between the walls are packed with air, thus the exhaust gas does not enter the space because the space is considered full. That is, passing the exhaust gas through the present invention having walls is the same as the exhaust gas passing through a typical exhaust pipe. For easy understanding, it is synonymous to pouring sand into the empty space formed in the center of the present invention after filling the space between the walls 1 with sand.

Therefore, loss of power due to exhaust resistance of the exhaust gas is not generated in the present invention.

FIG. 2a shows an embodiment wherein the present invention is provided with a plurality of walls 1 inside the pipe 30 so that the noise is continuously blocked by the walls (1).

The exhaust gas and the noise are arranged to be exhausted from the left side to the right side. It can be anticipated that the noise in an outlet 12 will decrease due to absorption of the walls 1. The wall's arrangement, position, quantity and other characteristics can be varied depending on how much noise reduction is desired.

If the effect of noise reduction is too low, the muffler cannot be used as a noise reduction device, thus an appropriate method for installing the walls 1 in the present invention should be arranged in order to maximize the effect of noise reduction. The walls 1 are installed on the inner sides of the pipe. FIG. 4c shows a plurality of walls 1 provided on both inner sides of the pipe.

FIG. 2a is an illustration of noise propagating through a section of the pipe 30, wherein a plurality of walls 1 are provided perpendicularly in the present invention which show the sound transfer. However, FIGS. 3a to 3c, illustrate a second embodiment where the walls 1 are tilted at 45°. The principle for blocking the noise is the same, however, the angle reflecting the filtered noise to the center of the present invention is slightly different. FIG. 3c shows a graph optimizing the wall 1 angle in order to maximize the effect of noise reduction.

That is, as shown in FIG. 3c, when drawing a vertical line from an upper point of a wall 1 (hereinafter referred to as the “head 3”) to the body 13 of the present invention, the vertical line should meet a bottom point of an adjacent wall 1 (hereinafter referred to as the “root 2”). Assuming that the installing angle of the wall 1 is θ, the length of the wall is L, and the length between the “roots 2” is l, as in Equation (1).
L cos θ=l  {circle over (1)}

When Equation (1) is satisfied, the arrangement of the walls 1 is optimized. That is, when the value of L cos θ is equal to the value of l, it is the most preferable to prevent the filtered and reflected noise from directly proceeding to the outlet 12.

In this case, it is apparent from FIG. 3d that the noise filtered by the walls 1 and bumped against the body 13 of the present invention cannot directly proceed to the outlet 12. If a wall 1 is installed in a manner that a vertical line from the “head 3” of a wall 1 meets the middle portion of an adjacent wall 1, then as set forth in Equation (2):
l<L cos θ  {circle over (2)}

When the above condition is made, the noise bumped against the body 13 of the present invention and reflected from the body 13 cannot also directly proceed to the outlet 12, however, the intervals of the walls 1 are unnecessarily close. That is, in this case, the weight of the present invention increases without increasing the effect of noise reduction, thus that is not a preferable relation between the walls (1).
l>L cos θ  {circle over (3)}

In addition, when the above Equation (3) is satisfied, that is, the distance between a wall and an adjacent wall is far away from each other, some of the noise bumped against the body 13 of the present invention directly proceeds toward the outlet 12, thereby decreasing the effect of noise reduction.

As disclosed in the above, in order to maximize the effect of noise reduction by using the walls 1, the walls 1 should satisfy the Equation {circle over (1)}.

Accordingly, if the length of a wall 1 is lengthened, the number of walls 1 will decrease, and if the length of a wall 1 is shortened, the number of walls 1 will increase. FIG. 3b shows the relation between the length and the number of walls 1. In order to make the sectional area of the present invention smaller while maintaining an equal the sectional area of the exhaust exit, the length (L) of the wall 1 is shortened.

In order to use the present invention as a muffler for an automobile, the length of the wall 1 can be made as short as several millimeters. In this case, since the diameter of the present invention is only several millimeters bigger than that of a typical exhaust pipe, the present invention can be installed in accordance with the lower structure of the automobile as shown in FIG. 1b.

The noise passing through the present invention can be classified into two types, one is that which enters the space between the walls 1 after being filtered by the walls 1, and the other is that which goes straight through the center empty space of the present invention.

Since it is easy to illustrate an example for easy explanation and understanding, FIG. 2a is shown as the example wherein the walls 1 are installed perpendicularly against the body 13 of the present invention.

The two walls 1 opposed in the present invention are referred to as a set of walls 1. The noise passing through a set of walls 1 resounds in the present invention and then is filtered by an adjacent set of walls 1b.

While the noise appears to be reduced at the regular ratio as the noise passes through each set of walls 1, the ratio actually decreases. The reason is that sound waves strengthen during straight transmission rather than the property of spherical wave as the sound waves get away from the source of sound. The phenomenon is shown in FIG. 3d.

If the present invention is formed with a straight-line type and the actual strength of sound energy after reducing the sound pressure by using n sets of walls is defined as P_n, and the strength of sound energy after reducing the sound pressure by using each set of walls 1 is defined as α_k, then as set forth in Equation (4):
P_n=α₁ . . . α_k . . . α_n  {circle over (4)}

That is, as in the above Equation (4), the value of the sound pressure in the outlet 12 will be the value multiplied by the strength of the sound energy after being filtered by each set of walls 1. Let us refer to FIG. 3d, which shows the degree of noise being filtered by the walls 1. The noise is arranged to enter the present invention having the walls 1 from a typical exhaust pipe. A typical exhaust pipe does not interrupt the flow of the noise and allows the noise to be reflected after being bumped against its inner side, thus the noise enters the present invention, making spherical waves continuously. However, after reaching the present invention, the noise is filtered and reflected by the walls 1 of the present invention, thus the property of spherical wave is weakened and the property of straight transmission is strengthened. As a result, the ratio being filtered by the walls 1 is decreased as shown in FIG. 3d.

The noise can be largely reduced by the first set of walls 1 because the property of spherical wave is maintained strongly as if the source of sound were at the very front of the first set of walls 1. The ratio of the noise filtered by the first set of walls 1 can be different depending on the diameter D of the space passing the exhaust gas, the interval l between roots 2 of the walls 1 and the length of the wall 1 L as shown in FIGS. 3a, 3c, and 3d.

Assuming that the value of α₁ is 0.8, which can be obtained by adjusting the values of D and l.

If the value of α_k is equal to the value of α₁, $\begin{array}{c}{P}_n=0.8\dots 0.8\dots 0.8\\ ={0.8}^n\end{array}$

The above formula for noise reduction can only be made in the case of FIG. 2a. That is, according to the formula, the degree of noise reduction will be higher as the number of walls 1 is increased.

However, as shown in FIG. 3d, since the degree of noise reduction is actually decreased, the noise strength in the outlet 12 will be as follows:
P_n=0.8·0.89·0.92

Equation {circle over (4)} is the most suitable as the mathematical expression for the noise strength passing through the present invention without being filtered by the sets of walls 1, however, actually the value may be varied depending on the values of D and l. Also, since the condition α_k<α_(k+1) appears to be apparent from FIG. 3d, the ratio filtering the noise by using the sets of walls 1 decreases. Accordingly, if designing the present invention as a straight-line type the effect of noise is reduced.

That is, while noise, which is reflected by an inner surface of a typical exhaust pipe proceeds towards an outlet, it displays the property of spherical wave continuously. However, as the noise passes though the muffler according to the present invention is filtered by the walls 1 and bumped against the body 13 of the present invention and is thus deflected away from the outlet 12, the property of spherical wave is weakened and the property of straight transmission is strengthened, so that the ratio being filtered by the walls 1 is decreased. Thus, if designing the present invention as a straight-line type, the degree of noise reduction is decreased, in which case, the present invention will not be suitable for use in automobiles.

According to experiments, in a case that the walls 1 were attached on two sides of the present invention and the sectional area for expelling the exhaust gas through the present invention was 4 cm×⁴ cm and the length of the present invention was 60 cm, the quantity of the noise reduction was a little less than 20 dB. This is not suitable for the automobile since such a degree of noise in the automobile is too high.

On the other hand, in order to mount the present invention on the automobile, it cannot be made in a straight-line type due to the lower structure of the automobile.

Thus, a method for filtering the noise more effectively required for the part of the present invention where the property of straight transmission becomes strong as shown in FIG. 3d.

If the muffler is provided with shorter walls 1 as shown in vertical sectional view of FIG. 1a, the diameter of the present invention can be reduced by about 5 cm or as small as a typical exhaust pipe of an automobile. Thus the present invention can be applied in accordance with the lower structure of the automobile. Therefore, if forming curvatures 20 at the part where the property of straight transmission becomes strong as shown in FIGS. 1b and 2b, it will be an effective method for reducing the noise.

After the noise propagates about 30 cm into the pipe of the present invention, experiments show that the property of straight transmission becomes strong. FIG. 1a shows a cross sectional view of the present invention having a curvature 20 in order to improve the effect of noise reduction. The noise enters from the left side and proceeds to the right side. As disclosed in the above, while the noise in the usual exhaust pipe maintains the property of spherical wave, being reflected after being bumped against the inner side of the exhaust pipe, the noise entering into the present invention becomes strong in the property of straight transmission.

Therefore, as shown in FIG. 1a, 1f forming the curvatures 20 at the parts where the property of straight transmission becomes strong, most of the noise can be effectively blocked by the walls 1 in the curvatures 20. That is, the noise enters the space between the walls 1 in the curvature 20 and is blocked by the walls, which is different from the case of the exhaust gas (refer to FIG. 1a).

Accordingly, most of the noise is blocked by the walls 1 in the curvatures 20 and only the diffracted sound proceeds to the outlet 12. Although the property of straight transmission becomes strong, another noise having the property of spherical wave is generated at both ends of the proceeding surface, with the intensity of the sound energy dropping, which is the diffracted sound.

The diffracted sound becomes strong again in the property of spherical wave since it is newly generated. That is, the noise passing through the curvature 20 becomes strong in the property of spherical wave, thus the ratio of noise reduction by the walls 1 can be significantly increased.

Although it is not yet determined what the mathematical expression for how much the noise loses the sound energy in the moment when the noise is blocked by the wall 1 in the curvature 20, the obvious fact is that the noise intensity at the outlet 12 is equal to the noise intensity in the case of hearing the noise behind the soundproofing wall. Since the noise proceeding to the outlet 12 is only a diffracted sound, most of the noise is reechoed to the inlet 11 by being blocked by the walls 1 of the curvature 20 and cannot proceed to the outlet 12. Thus, the noise in the outlet 12 is heard as if the noise was heard behind a soundproof wall 1. Therefore, in order to improve the effect of noise reduction, straight portions 30 and curvatures 20 should be properly arranged when designing the muffler according to the present invention as shown in FIG. 1b.

The noise filtered by the walls 1 experiences a decrease in sound pressure, which will be discussed hereinafter in order to find out whether the filtered noise is found at the outlet 12. The filtered noise enters the space between the walls 1 and is bumped against the body 13 of the present invention and then is reflected toward the center of the present invention.

It is noticed from FIG. 3d that the noise strength filtered by the walls 1 is weaker than that of the noise proceeding that is not being filtered by the walls 1.

Also, referring to FIG. 3a, the noise, which is filtered by the walls 1 and reflected by the body of the present invention and then comes out to the center of the present invention, experiences space expansion at the center of the present invention and is weakened, thus only some of the noise proceeds to the outlet 12. Thus, the noise proceeding to the outlet 12 among the noise filtered by the walls 1 has a much weaker intnesity as compared with the noise not filtered by the walls 1.

Therefore, the effect of noise reduction can be obtained sufficiently by lowering the intensity of the noise not filtered by the walls 1 to the desired level. This also means that the noise intensity filtered by the walls 1 becomes very low at the point of the outlet 12 so that the filtered noise cannot influence the performance of the muffler according to the present invention.

As disclosed in the above, in order to reduce the noise effectively, Equation {circle over (1)} should be satisfied, and in order to improve the ratio of noise reduction, the curvatures 20 should be designed in the muffler.

If applying the present invention in accordance with the lower structure of automobiles or other applications, the effect of noise reduction can be sufficiently obtained.

As shown in FIG. 1a, if one curvature 20 is added to the muffler, the noise is reduced by about 15 dB. Thus, if several curvatures are applied to the muffler as shown in FIG. 1b, the effect of noise reduction will be significantly increased so that the muffler according to the present invention can be effectively used for the automobile.

As the length of the wall L is made several millimeters shorter as shown in the vertical sectional view of FIG. 1a and subsequently the diameter of the present invention is only several millimeters larger than that of a typical exhaust pipe, the noise can be reduced sufficiently by adding curvatures 20 to the automobile as shown in FIG. 1b.

Also, if the condensed water can be discharged, the life span of the muffler can be significantly extended. If the length of the wall is lengthened and both ends of the present invention have open ends 11′ as shown at the left side of FIG. 6, the secondary noise can be generated by the conflict between the last wall 1 and the exhaust gas being expelled to the atmosphere when the speed of the exhaust gas is high. For example, in case of 2000 cc CRDI diesel automobiles, if designing the wall to the dimensions of 4 cm×4 cm×1 mm and the sectional area for exhaust the gas is 4 cm×4 cm, the exhaust gas begins to bump against the walls 1 and to cause the secondary noise at RPM 2500, and the noise becomes louder at RPM 3000.

Accordingly, in case that the present invention is used for the automobile, the muffler should be designed in a manner that the size of the wall 1 is small and the secondary noise is not generated by the conflict the wall 1 and the exhausting gas. Thus, for this purpose, as shown in FIG. 6, the two ends 12a of the muffler are arranged to be narrower. Conversely, the sectional area of the inlet end 11′ of the muffler is arranged to be wider so that the speed of the exhaust gas is reduced. In case of 2000 cc CRDI diesel automobiles, when the sectional area of one end 11′ of the present invention was (4 cm×4 cm)×2, there was no secondary noise at RPM 3500.

The present invention can be applied to all the noise generating mechanisms. Particularly, the present invention is useful for noise reduction in the noise generating mechanisms using an internal combustion engine.

In addition, the present invention can be applied to apartments to reduce the noise between floors, for example, drainage pipes for bathroom. FIG. 4d shows a model for blocking the bathroom noise. While the noise proceeds in the direction of the arrows, it is blocked two times. The sound pressure of the noise is rapidly decreased by filtering two times and the filtered noise proceeds toward a ventilating opening between the floors. If attaching this type of noise reduction device to every floor, the bathroom noise is blocked four times by the walls 1, so that the noise becomes significantly weaker.

FIG. 4e is a model for reducing the noise from a helicopter's engine. If attaching this type of noise reduction device (a thin plate is sufficient for the device) to the engine, the noise can be reduced by over 10 dB without any influence on the output of power and aviation of the helicopter. If desired, the noise from propellers of a submarine can also be reduced. Therefore, the present invention can be applied to all kinds of sound sources.

It will be apparent to those skilled in the art that various modifications and variations can be made to the present invention without departing from the spirit and scope of the invention. The present invention covers the modifications and variations thereof provided they come within the scope of the appended claims and their equivalents.

Claims

1. A noise reduction device having an inlet and an outlet and formed in the shape of a pipe, comprising walls provided in a body thereof, thereby filtering some of the noise passing through the device and reducing noise at the outlet.

2. The noise reduction device as claimed in claim 1, wherein the body is arranged using straight sections and angled sections.

3. The noise reduction device as claimed in claim 1, wherein the quantity of walls and angles formed between the walls and body may vary to change the overall performance of the noise reduction device.

4. The noise reduction device as claimed in claim 1, wherein the wall is provided with protrusions and depressions.

5. A noise reduction device, comprising:

a pipe-shaped body having an inlet and an outlet; and

a plurality of walls provided in the body and partially protruding from the inner surface of the body towards the inner part of the body, to filter noise propagating from the inlet to the outlet, whereby the noise intensity exiting the outlet is less than the noise intensity entering the inlet.

6. The noise reduction device as claimed in claim 5, wherein the body is arranged using straight sections and angled sections.

7. The noise reduction device as claimed in claim 5, wherein the quantity of walls and angles formed between the walls and body may be varied to change the overall performance of the noise reduction device.