JPS6059410B2 - Silencer - Google Patents

Description

[Detailed Description of the Invention] A. Purpose of the Invention (Field of Industrial Application) This invention relates to a silencer that is installed in the exhaust system of an engine and that suppresses and silences the exhaust gas pulsatingly discharged from the engine. This invention can be used for expandable silencers.

(Prior art) Various types of silencers have been considered for attaching to automobile exhaust pipes to attenuate engine exhaust noise. It is not effective, and even if the same muffler is placed in a different position, the muffling effect will change.

In connection with this, the present inventor previously disclosed
Invented a method for installing a silencer described in Publication No. 8.

The method of the invention described above investigates where to install a muffler to obtain the best effect when installing it in the exhaust pipe of an engine, and obtains the relationship between the muffling effect and the position in which the muffler is installed relative to the exhaust pipe. It is something.

That is, Fig. 5 shows Fig. 2 of the above publication with some of the symbols changed.
As shown in the figure, when the muffler installation position is changed from scale O to scale 40 on the X-axis, the sound deadening effect is good in the valley part of figure a with vertical and horizontal lines, and the sound deadening effect is bad in the parts on both sides. The results are obtained so that the position of the silencer device with good noise reduction effect can be determined. If the muffler is attached to the exhaust pipe at a position corresponding to the valley of the vertical and horizontal lined figure a in FIG. 5, a good sound muffling effect can be obtained. The numerical value of the ratio of L1/L3 mentioned above was determined based on the above-mentioned previous invention corresponding to the valley bottom portion. Also,
In order to adjust the acoustically effective length of the exhaust pipe in an expandable muffler, there is an earlier invention (Japanese Patent Laid-Open No. 52-41567) in which a short circuit hole is bored in the side surface of the exhaust pipe in the muffler.

(Problems to be Solved by the Invention) When a silencer is installed in a car, it is often installed under the floor.

However, under the floor of a car are axles, propeller shafts,
Various parts such as a fuel tank and an exhaust purifier are attached to the silencer, which often prevents the silencer from being installed in the optimal position. Also, if you try to install a silencer that can be installed in the appropriate position on car A, on car O which is equipped with the same engine,
The position relative to the exhaust pipe may change, making it impossible to obtain a good muffling effect.

Therefore, even if a muffler is used for the same engine, it cannot be used in common with different car models and must be designed and rebuilt separately, which is uneconomical. Needless to say, it would be advantageous if both cars could use the same silencer with simple modifications. Structure of the Invention (Means for Solving the Problems) This invention provides a short circuit hole in the side surface of the part of the inlet side air conduit, the outlet side exhaust conduit, or both of the parts inserted into the outer cylinder of the muffler. By drilling, the acoustically effective length of one or both of the exhaust pipes (at the pipe end, the sound waves spread out in a spherical shape and are dissipated, or vice versa, so that the acoustically effective length of the pipe is reduced). When considering length, use the acoustically effective length, which is a correction to the actual length.

) to improve the silencing effect, and the relationship between both exhaust pipes at this time is the ratio of the acoustically effective lengths of both exhaust pipes: 40.074, 0.164, 0.258, 0. 34
4, 0.625, 1.00011.68λ7.66巳2
It is expressed as 5.000. (Function) First, the acoustically effective length of the inlet side exhaust pipe and the short circuit hole will be explained with reference to FIG.

As mentioned above, the propagation state of sound waves changes at the open end of the insertion tube, so when dealing with the acoustic properties of a silencer, the actual length of the insertion tube must be corrected to calculate the acoustically effective length. No.

Since this acoustically effective length is related to the thickness of the tube, the following calculation formula is used as a means of correction.

Note that the inlet side exhaust pipe 1 refers to the starting end of the exhaust pipe connected to the exhaust port end of the engine to the insertion end into the silencer outer cylinder 2, and the outlet side exhaust pipe 3 refers to the exhaust pipe connected to the exhaust port end of the engine to the insertion end into the silencer outer cylinder 2. from the insertion end of the exhaust pipe inserted into the air to the open end to the atmosphere.

First, to explain the inlet side exhaust pipe 1, let us assume that the length of the inlet side exhaust pipe 1 to the outer cylinder 2 is 11, the insertion length into the outer cylinder 2 is 12, and the inner diameter of the pipe 1 is D. The acoustically effective length of the inlet side exhaust pipe 1, indicated by the square in the figure, is as follows.

Here, α is an open end correction coefficient determined by the shape of the end of the exhaust pipe, and if the end of the circular pipe protrudes into the muffler as shown in FIG. 4, α=0. λ When the end plate is opened as shown in FIG. 3, α=0.41. The acoustically effective length L of the outlet side exhaust conduit 3 is determined in exactly the same manner. Next, an earlier invention (Patent Application No. 52-41567
No.) will be explained with reference to the description of the previous invention.

When a short circuit hole 4 is bored in the inlet-side exhaust pipe 1 within the outer cylinder 2 at a length 14 from the end plate 2a, the acoustically effective insertion length 1x of the exhaust pipe 1 into the outer cylinder 2 is ( However, K=0
．． 3160. ．． a=2.8539, b=7.0991,
13=1.

+αD).

This calculation formula is based on the results obtained by experimenting with the change in silencing effect by changing the position of the shunt hole in various ways, finding the effective acoustic length, and organizing the resulting diagram, which has a tendency to be a logistics curve.
And since its upward trend is opposite to the logistics curve, the well-known formula representing this curve, Y=point, is
This is an experimental formula created by the inventor by experimentally determining each constant using 1+e.

When the acoustically effective length L of the inlet side exhaust pipe 1 is determined from this equation, it becomes L=11+1x.

Since 14 can be changed arbitrarily within the range of O<14 x 12, by adjusting the position where the short circuit hole is drilled,
The acoustically effective length L1 of the inlet exhaust conduit 1 can be varied.

Regarding the outlet side exhaust conduit 3, the acoustically effective length L can be changed in exactly the same manner. Figure 6A, 6th
Figure B shows the difference in the silencing effect between the case where the short circuit hole 4 is provided in the exhaust pipe according to the present invention (Fig. 6A) and the case where the exhaust pipe is of the same length but without the short circuit hole (Fig. 6B). is shown in the graph of an experimental example, in which a microphone was placed toward the open end of the exhaust pipe on the outlet side of a silencer connected to the engine, and the intensity of the exhaust sound was measured, and the engine rotation speed (horizontal axis) was measured. The intensity of the ejection sound for each frequency (vertical axis), and the intensity of the ejection sound at each frequency (vertical axis) obtained by frequency analysis of this ejection sound are shown with the frequency as the horizontal axis.

The engine used in this experiment was a 4-stroke, 6-cylinder, 2
An experiment was conducted with a 000cc gasoline engine running at full load.

In addition, the muffler is an expanded type as shown in Figure 1, in which the outlet side exhaust pipe is touched, and a long pipe is used as the inlet side exhaust pipe, and a shunt hole is drilled in the same pipe. A silencer using an inlet exhaust conduit whose acoustically effective length was adjusted to 112 mm, which is the length of the silencer's outer cylinder, was used. Figure 6 A1
In FIG. 6B, solid lines 5a and 5b depict the intensity of the exhaust noise from the outlet side exhaust pipe with respect to the engine speed,
If the exhaust pipe on the inlet side is too long because there is no shorting hole (6th
In Figure B), the engine speed of solid line 5b is 345013.
There is a large peak in the discharge sound near 60014750r'Pm, but if a short-circuit hole is drilled in this inlet side exhaust pipe and its acoustically effective length is adjusted, the solid line 5a in Fig. 6A is obtained. It can be seen that the peak of the exhaust noise does not appear around this engine speed, and that the overall noise is reduced in this area.

This result agrees well with the calculated result. Figure 6 A1 Dotted lines 6a, 6b1 shown in Figure 6B, dashed line 7a,
7b1 Long dashed lines 8a, 8b and short dashed lines 9a, 9b are 1 obtained by frequency analysis of the ejection sound captured by the above microphone.
It shows the intensity of the next fundamental tone and the second, third, and fourth higher-order tones with respect to frequency (horizontal axis).

Figure 7 shows the insertion loss of the silencer (■NSellOnIj)
S.S. ．． It is abbreviated as IL.

Indicates the volume reduced by connecting a silencer. ), Figure 6A
．． ．． The results calculated for the same silencer as in B are shown in terms of sound intensity versus frequency, where the dotted line 10a is a graph with a short circuit hole provided, and the solid line 10b is a graph without a short circuit hole. In the case of the solid line 10b without a short circuit hole, IL is small at frequencies of 400 to 600 cycles, and there is a part where IL becomes negative (that is, the engine exhaust sound is magnified) around 450 cycles, but there is a short circuit. By drilling holes and changing the acoustically effective length of the inlet exhaust pipe,
This negative portion disappears, and moreover, IL becomes good around this area.

The above experimental examples and calculation examples show that the acoustically effective length of the exhaust pipe can be changed by providing a short circuit hole in the exhaust pipe.

According to the research of the present inventor, when the exhaust pipe is a circular pipe with an inner diameter of 40.3 mm, the above purpose can be achieved by drilling one or more short holes with a total area of about 25 to 300 wui. I understand that it can be achieved.

The fact that the effective lengths of the inlet and outlet exhaust pipes can be changed by drilling the short-circuit holes 4 in this way means that
If the same silencer is used and the short circuit hole 4 is drilled,
It is possible to move the silencer 2 closer to the inlet side or the outlet side.

The present invention shows the ratio of the acoustically effective lengths of the inlet-side and outlet-side exhaust pipes, which provides a good sound-dampening effect when the muffler mounting position is moved by drilling a short-circuit hole. Therefore, although the silencer can be installed on the first car with good sound deadening effect, it cannot be installed in the same way on the second car, and the mounting position is shifted, resulting in poor sound deadening effect. By changing the acoustically effective length so that the ratio of the lengths of the inlet and outlet exhaust conduits matches the above-mentioned ratio, it is possible to improve the silencing effect.

This invention provides the ratio of the acoustically effective lengths of both conduits, which is the target for drilling a shorting hole that improves the silencing effect, so the position of the shorting hole is adjusted to achieve this value. Once determined, a good sound deadening effect can be obtained, and it is possible to use a silencer manufactured by using the same materials except for the position of the short circuit hole on the first car and the second car. can be rationalized.

C. Effects of the invention (1) By drilling the short-circuit hole 4, the effective length of the exhaust pipe can be adjusted, so even if it is not possible to install the muffler in a position where the muffling effect is good, it is possible to change the position and install the muffler. You will be forced to mute the sound.

(2) Since it shows the ratio of the acoustically effective lengths of the inlet and outlet exhaust pipes, it is possible to quickly determine whether the silencer installation position is correct or not. (3) The muffler can be used more commonly.

[Brief explanation of the drawing]

FIG. 1 is a schematic vertical cross-sectional view illustrating an expandable muffler in which the ends of the inlet and outlet exhaust pipes are inserted into the outer cylinder, and FIG. Figure 1 is a schematic vertical cross-sectional view similar to Figure 1, Figures 3 and 4 are schematic vertical cross-sectional views showing the state of the end of the exhaust pipe, Figure 5 is a diagram showing Figure 2 of Japanese Patent Publication No. 51-4284, and Figure 6. A is a graph showing an experimental example when the acoustically effective length is adjusted by providing a shorting hole in a long inlet exhaust pipe, and Figure 6B shows an example of an inlet exhaust pipe of the same length without a shorting hole. FIG. 7 is a graph showing an example of an experiment in which a short circuit hole is provided to adjust the acoustic effective length, and a graph showing an example of calculation of insertion loss in the case where a short circuit hole is provided and the acoustic effective length is adjusted and when a short circuit hole is not provided. DESCRIPTION OF SYMBOLS 1... Inlet side exhaust pipe, 2... Outer cylinder, 2a... End plate, 3... Outlet side exhaust pipe, 4... Short circuit hole.

Claims (1)

[Claims] 1 Expandable silencer in which the end of the inlet exhaust pipe 1 is inserted into the outer cylinder through the end plate 2a of the outer cylinder 2, and the starting end of the outlet exhaust pipe 3 is inserted into the outer cylinder in the same way. , a short circuit hole 4 is bored in the exhaust pipe at a position of length l_4 from the end plate 2a inside the outer cylinder, and K is 0.3160 and a is 2.83.
59, b is 7.0991, and the acoustically effective length of the part inserted into the outer cylinder of the inlet side exhaust pipe 1 without the shorting hole is l_3, Find the acoustically effective length lx of the part from the formula ▲, which includes mathematical formulas, chemical formulas, tables, etc., and calculate the length lx of the inlet side, which is the sum of this length lx and the length l_1 of the inlet side exhaust pipe outside the outer cylinder. Ratio L_1/L_ of the acoustically effective length L_1 of the exhaust pipe and the acoustically effective length L_3 of the exit side exhaust pipe obtained in the same manner
3, allowing tolerance values before and after, 0.074, 0.164
, 0.258, 0.344, 0.625, 1.000,
A silencer characterized by having a value of 1.689, 7.666, or 25.000.