JPS6334283B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an exhaust silencing device for an internal combustion engine that uses a sound absorbing material.

Examples of sound absorbers used in absorption type silencers for general equipment include glass wool, rock wool,
Steel wool, ceramic porous bodies, metal porous bodies, etc. are well known.

However, when this type of porous sound absorber is used in an exhaust silencer for an internal combustion engine, the exhaust gas contains a large amount of soot or tar-like substances, which are the combustion residue components of fuels such as gasoline. A major drawback is that substances such as these adhere to the skeleton inside the sound absorber, causing the sound absorber to become clogged, resulting in a significant drop in sound absorption performance within a relatively short period of time, resulting in a very short lifespan as a sound muffling device. It was hot.

In other words, since conventional sound absorbers are inherently porous, they have air permeability. Since the flow resistance is determined by specific values representing the air permeability, such as the porosity, pore diameter, and thickness of the sound absorber, there is a slight difference between the pressure fluctuation waves in the exhaust gas passage and the space behind the sound absorber. The time delay (phase difference) is corrected. Therefore, a pressure difference Δp always occurs between the inside of the exhaust gas passage and the space behind the sound absorber. Due to this pressure difference Δp, a portion of the exhaust gas repeatedly flows into or out of the sound absorber, inducing a flow inside the sound absorber.

In addition, the particle size of soot contained in exhaust gas is
Since the diameter of the pores is approximately 100 to 1000 angstroms, which is extremely small compared to the pore diameter of the sound absorber, soot particles are guided into the interior of the sound absorber along with the exhaust gas by the above-mentioned flow.

Thereafter, the soot particles adhere to the skeletal surface of the sound absorber, and the particles adhere to each other and become coarse, thereby clogging the pores of the sound absorber.

In addition, moisture such as condensed water, tar-like substances, etc. can be considered as things that help soot adhesion. In order to solve the above problem, it is necessary to create a sound absorbing structure that prevents exhaust gas from flowing into the sound absorbing body. One conceivable way to do this is to first provide a non-permeable membrane on the surface of the sound absorber that comes into contact with the exhaust gas to completely block the flow. However, simply providing a coating on the surface of the sound absorber will also prevent the sound waves themselves from entering, so there is a risk that the sound absorbing ability will be significantly reduced.

The second method is to minimize the pressure difference between the inside of the exhaust gas passage and the space behind the sound absorber to create a sound absorbing structure that prevents flow from occurring inside the sound absorber.

In other words, by connecting the exhaust gas passage and the space behind the sound absorber and providing a communication port with extremely low flow resistance compared to the sound absorber, most of the exhaust gas that attempts to flow into or out of the sound absorber is absorbed through the communication port. If the exhaust gas is structured to flow into or out of the space on the back of the body, it will be difficult for exhaust gas to enter the sound absorbing body, thereby significantly reducing the deterioration in sound absorption performance due to clogging of the sound absorbing body.

For the above reasons, the present invention eliminates the drawbacks of conventional exhaust silencing devices for internal combustion engines using sound absorbers, provides good sound absorbing performance, and prevents deterioration of sound absorbing performance due to clogging with soot. The present invention aims to provide an exhaust silencing device for an internal combustion engine that is useful for improving engine output and fuel efficiency.

The present invention will be explained below with reference to the drawings.

First, FIG. 1 shows a conceptual diagram of an exhaust silencer for an internal combustion engine using a conventional cylindrical porous sound absorber.

A conventional sound damping device using a sound absorber mainly uses a cylindrical porous sound absorber 1 arranged almost linearly inside the device.
It is composed of a boundary wall 2 that divides the interior of the silencer, and a casing 3 of the silencer that houses these parts.

When such a silencer is used for an internal combustion engine, its performance as a sound absorber deteriorates significantly due to clogging with soot contained in the exhaust gas for the reasons mentioned above, making it impossible to use it over a long period of time. There is a big drawback.

FIG. 2 is a conceptual diagram for explaining one embodiment of an exhaust silencing device for an internal combustion engine, which was invented to eliminate the drawbacks of the conventional device described above. It has a structure in which a communication port 4 connecting the exhaust gas flow path and the back space of the sound absorber is provided in a part of the provided cylindrical porous sound absorber 1.

In addition, in one embodiment of the present invention shown in FIG.
Since the inside of the silencer is divided into a front chamber and a rear chamber by a boundary wall 2, each chamber is provided with the communication port 4 in a part of the porous sound absorber 1.

Therefore, by setting the resistance of the communication port 4 to be sufficiently small compared to the resistance to the flow of the sound absorber, most of the exhaust gas flowing into or out of the back space of the sound absorber is guided to the communication port 4. The flow of exhaust gas into the sound absorbing body is greatly reduced.

Therefore, less soot enters the sound absorbing body, and clogging of the sound absorbing body due to adhesion of soot is less likely to occur, so deterioration of sound absorption performance is almost eliminated. In the end, the provision of the communication port 4 results in an exhaust muffling device for an internal combustion engine that exhibits very little deterioration in muffling performance and can withstand long-term use.

Further, FIG. 3 shows another embodiment according to the present invention. As shown in the conceptual diagram above, if the interior of the silencer is divided into two or multiple chambers due to the presence of the boundary wall 2, only a part of the exhaust gas passage of the sound absorber 1 and the sound absorber on the front chamber side A communication port 4 connecting the rear space is provided, and communication pipes 5 connecting adjacent chambers are provided in a part of the boundary wall 2 that divides the interior of the silencer.

According to this structure, exhaust gas flows into or out of the space on the rear side of the sound absorber on the front chamber side through the communication port 4 that connects the exhaust gas flow path with the space, and the exhaust gas flows into or out of the space on the back side of the sound absorber on the rear chamber side. In this case, exhaust gas flows in or out through the communication pipe 5 provided in the boundary wall 2. Therefore, most of the exhaust gas flows in and out through the communication hole 4 and the communication pipe 5 without entering the sound absorber, so the amount of soot adhering to the skeleton inside the sound absorber decreases significantly, causing clogging of the sound absorber. It becomes difficult to do.

Therefore, the initial performance can be maintained over a long period of time without deterioration of the silencing performance, and the life of the silencing device is significantly extended.

In addition, the number and length of the communication pipes 5 provided in the boundary wall 2,
There are no particular limitations on the inner diameter, etc., and similar effects to those described above can be expected even if a communication port, that is, a communication portion is simply provided in the boundary wall 2.

FIG. 4 compares the performance deterioration of the internal combustion engine exhaust silencer according to the present invention with that of the conventional one.

The test method for both is exactly the same, and a domestically produced small passenger car (gasoline engine 4-cycle 4-cylinder 1600
cc) with each muffler installed, drive around town, measure the exhaust noise level under the same driving conditions using a measurement method based on DISD-1616, and subtract it from the initial (when not driving) exhaust noise level. The value is expressed as the amount of deterioration in the silencing performance, and only the overall value is shown in the figure.

In the figure, the solid line A represents the exhaust silencing device according to the present invention, and the broken line B represents the deterioration characteristics of the silencing performance of the conventional device. Note that the horizontal axis represents the distance traveled, and the vertical axis represents the amount of deterioration (OA value) in the silencing performance for each distance traveled.

As is clear from the figure, in the case of the conventional exhaust silencing system, the silencing performance decreases by about 5 dB after driving 20,000 km.
This poses a big problem in practice.

However, in the case of the silencer according to the present invention, it is approximately 1 dB when traveling 20,000 km, and approximately 1 dB when traveling 30,000 km.
There is a noise reduction deterioration of about 1.5 dB, which is not a problem in practice.

In addition, in order to visually check the amount of soot attached,
When the two exhaust silencers were dismantled after 10,000 km of driving, there was a clear difference in the amount of soot deposited, and the pores in the sound absorbing body of the present invention's silencer remained almost unchanged, whereas the conventional one It was confirmed that a large amount of soot had adhered to the skeleton of the sound absorber, causing almost complete clogging.

Further, at this time, significant soot was observed to adhere to the inner wall surface of the casing 3 of the silencer according to the present invention. This is considered to be because most of the soot flows in through the communication port 4 without adhering to the sound absorbing body, and adheres to and hardens on the inner wall surface of the casing, where the temperature is relatively low and condensed water is likely to occur.

Therefore, this phenomenon also confirms that the exhaust noise muffling device according to the present invention is less likely to have soot attached to its sound absorbing body.

As explained above, in the present invention, by providing a communication part in the porous sound absorber that connects the exhaust gas flow path and the space behind the sound absorber, deterioration of the sound deadening performance due to the adhesion of soot is prevented, and it can withstand long-term use. The present invention provides an exhaust silencing device for an internal combustion engine.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing an exhaust silencing device for an internal combustion engine using a conventional porous sound absorber, FIG. 2 is a configuration diagram showing an embodiment of the exhaust silencing device for an internal combustion engine according to the present invention, and FIG. Similarly, conceptual diagrams of other embodiments of the present invention are shown. FIG. 4 is a characteristic diagram showing the deterioration characteristics of the silencing performance with respect to the mileage when the conventional exhaust silencing device for an internal combustion engine and the exhaust silencing device for an internal combustion engine of the present invention are installed. In the figure, 1 is a cylindrical porous sound absorber, 2 is a boundary wall, and 3
4 indicates a housing, 4 indicates a communication port, and 5 indicates a communication pipe. Note that the same reference numerals in the figures indicate the same or corresponding parts.

Claims (1)

[Scope of Claims] 1. A cylindrical porous sound absorber that is housed in a housing and forms a space with the inner wall of the housing and forms a linear exhaust gas flow path; A surface of the porous sound absorber facing the exhaust gas flow path and a surface facing the space are exposed, and a communication hole for communicating the space with the exhaust gas flow path is provided in the cylindrical porous sound absorber. Exhaust silencer for internal combustion engines. 2. An internal combustion engine according to claim 1, wherein a boundary wall is provided to divide the space in the exhaust gas flow direction, and the boundary wall is provided with a communication hole for communicating the divided spaces. Exhaust silencer.