JP2003065025A - Pulsation reducing piping - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide pulsation reducing piping capable of reducing pulsation in a wider frequency band. SOLUTION: Two branch pipes 2, 3, whose end parts are formed with closed ends 2a, 2b, are provided on a main pipe (piping)/in a branched state, the length of one branch pipe 2 is formed shorter against the distance between the branch part 2b and the branch part 3b of the two branch pipes 2, 3 or odd number times thereof within the predetermined range, and the length of the other branch pipe 3 is formed longer against the distance between the branch part 2b and the branch part 3b or odd number times thereof within the predetermined range.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pulsation reducing pipe which suppresses the generation of pulsation in a pipe such as an exhaust pipe.

[0002]

2. Description of the Related Art Pulsations may occur in a system including piping such as an exhaust system. For example, in a pipe provided in an exhaust system of an engine, pulsation may be propagated due to periodic motion of a piston of the engine, which may cause noise, vibration, or the like.

In order to prevent such a pulsation, there is a means for absorbing a pulsating component by providing a resistor such as a split silencer. However, this means causes a large pressure loss. Therefore, there is a case where a means for providing the branch pipe 51 with respect to the pipe 50 as shown in FIG. 4 is adopted. The branch pipe 51 has a length of 1/4 of the wavelength of a sound wave that causes pulsation to be reduced, and the end portion 51a is a closed end. Thereby, the traveling wave 52 that does not enter the branch pipe 51,
The reflected wave 53 reflected at the end of the branch pipe is interfered with to prevent the pulsating component from propagating.

[0004]

However, in such a branch pipe, since the frequency band in which the effect is exerted is narrow,
If the frequency shifts due to a slight change in operating conditions, pulsation cannot be prevented. Further, there is a problem that the effect does not appear due to a slight difference between the design and the actual equipment.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a pulsation reducing pipe capable of reducing pulsation in a wider frequency band.

[0006]

According to a first aspect of the present invention, a pipe is provided with two branch pipes whose ends are closed ends, and one of the branch pipes has a length of It is configured such that the distance between the branch portions of the two branch pipes or an odd multiple of the distance is short within a predetermined range, and the length of the other branch pipe is the branch of the two branch pipes. It is characterized in that it is configured to be long within a predetermined range with respect to the distance between the portion and the branch portion or an odd multiple of the distance.

In the present invention, one branch pipe is short,
The other branch pipe is made longer. That is, assuming that the wavelength of the sound wave to be attenuated in the present invention is L and the predetermined range is α, the length of each branch pipe is (1/4) L * (2k + 1) ± α; k = 0, It can be represented as 1, 2, .... With such a configuration, an attenuation effect can be obtained in a wide frequency band.

According to a second aspect of the present invention, in the pulsation reducing pipe according to the first aspect, the length of the one branch pipe is the distance between the branch portions of the two branch pipes or the distance. 20% of the distance between the bifurcations with respect to an odd multiple of
The length of the other branch pipe is within 20% of the distance between the branch portions and the branch portion with respect to the distance between the branch portions of the two branch pipes. It is characterized by having a long configuration in the range of.

If the branch pipe is too short (or too long), the attenuation frequency band will be wide but sufficient attenuation cannot be obtained. In the present invention, a wide attenuation frequency band and a sufficient amount of attenuation can be obtained at the same time due to the above range.

According to a third aspect of the present invention, in the pulsation reducing pipe according to the first or second aspect, the distance between the branch portions is approximately ¼ wavelength of the sound wave to be attenuated. Is characterized by.

If the distance between the two branch pipes is too great, the damping effect of each branch pipe becomes completely independent, and the damping effect in the vicinity of the frequency of the sound wave to be attenuated is poor. In the present invention,
A desired attenuation effect can be obtained by setting the interval between the branch portions to be approximately ¼ wavelength of the sound wave to be attenuated.

The invention according to claim 4 is the invention according to claims 1 to 3.
In any one of the pulsation reducing pipes, the closed end of the branch pipe is a movable wall provided so as to be movable in the branch pipe longitudinal direction.

In the present invention, the length of the branch pipe is changed by moving the movable wall. As a result, the wavelength of the sound wave attenuated by the branch pipe changes.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, embodiments of the present invention will be described with reference to the drawings. FIG. 1 shows a pulsation reducing pipe according to this embodiment. In this pulsation reducing pipe, reference numeral 1 is a main pipe (pipe), and two branch pipes 2 and 3 are branched from the main pipe 1. The branch pipes 2 and 3 are parallel to the main pipe 1. The end portions 2a, 3a of each branch pipe 2, 3 are closed ends, and a branch portion 2 for the main pipe 1 is formed.
The interval L between b and 3b is approximately a quarter wavelength of the sound wave (pulsation) to be attenuated. The length of one branch pipe 2 is shorter than the distance L of the branch portion or an odd multiple thereof within 20% or less of the distance L of the branch portion.
Further, the length of the other branch pipe 3 is configured to be long within a range of 20% or less of the distance L of the branch portion with respect to the distance L of the branch portion or an odd multiple thereof. That is, the lengths of the branch pipes 2 and 3 are (1/4) L * (2k + 1) ± α; k = 0,1,
2, ..., 0 <α ≦ 0.2L.

Next, the operation of the branch pipe will be described.
FIG. 2 shows, as an example, the sound transmittance by the pulsation reducing pipe when a sound wave of a certain frequency F1 is set as an attenuation target. In the figure, the solid line A is the case where the pulsation reducing pipe according to the present embodiment is used, and the broken line B is the case where the conventional pulsation reducing pipe is used. As shown in the figure, in the pulsation reducing pipe of this example, the frequency band A attenuated by one branch pipe 2
1 and the frequency band A2 that is attenuated by the other branch pipe 3 are combined to obtain a wider attenuation frequency range than the conventional pulsation reducing pipe having a single branch pipe. Here, branch pipes 2, 3
The width of the frequency band in which the transmittance is reduced widens as the length of is deviated (lengthened or shortened) from ¼ of the wavelength or an odd multiple thereof, but the value of the central part of the attenuation region shown by the symbol A3 in the figure. Will be higher. Set the length of the branch pipes 2 and 3 to 1 / wavelength
4 or an odd multiple of 20% or more away from the center A3
Transmittance of 0.05 or more. Therefore, in the present application, the transmittance can be suppressed to 0.05 or less by setting the upper limit of the above value to 20%. The pulsation reduction frequency band of this example in FIG. 2 is not a combination of the damping effect when only the branch pipe 2 is provided and the damping effect when only the branch pipe 3 is provided. Since the distance between the branching portion 2b and the branching portion 3b is ¼ wavelength of the sound wave to be attenuated, in the vicinity of the frequency F1 to be attenuated, the attenuation effect of the branch pipes 2 and 3 is simply added. Also has a large damping effect. When the distance between the branch portion 2b and the branch portion 3b is increased, these effects are approximated to the sum of the damping effects of the branch pipe 2 and the branch pipe 3, and sufficient damping near the frequency F1 can be obtained. Disappear.

As described above, in the pulsation reducing pipe of this example,
The pulsation can be attenuated in a wider frequency band than the conventional pulsation reduction pipe shown by the broken line B. Therefore, even if the frequency is shifted, it is possible to sufficiently reduce the pulsation,
Further, even if there is a difference between the designed pulsation-reducible frequency and the actual pulsation-reducing frequency, the pulsation can be prevented because the frequency range in which attenuation is possible is wide.

Next, a second embodiment of the present invention will be described. The same components as those in the first embodiment will be designated by the same reference numerals and the description thereof will be omitted. In addition to the first embodiment, the present example further has the following configuration. In FIG. 3, reference numeral 10 is a closed end of the branch pipes 2 and 3. The closed end 10 is a movable wall 11 provided so as to be movable in the longitudinal direction of the branch pipes 2 and 3. The movable wall 11 is provided with a bar 15 having an outer peripheral wall formed with a thread groove 12 extending outward, and a guide member screwed to the bar 15 and fixed to the branch pipes 2 and 3. 16 are provided.

In the pulsation reducing pipe thus constructed, the movable wall 11 is moved in the longitudinal direction of the branch pipes 2 and 3 by rotating the rod 15, and the length of the internal space of the branch pipes 2 and 3 is increased. Can be changed. As a result, the attenuation frequency can be changed, so that it is possible to adjust the attenuation frequency when the designed attenuation frequency and the actual attenuation frequency when actually installed differ.

In the first embodiment, the branch pipe 2
Is short and the branch pipe 3 is long, but either branch pipe on the side closer to the sound source may be longer. In the above example, the branch pipes 2 and 3
Although the space required for installation is made small by making the pipe parallel to the main pipe 1, the direction of the branch pipe is not limited to this.

[0020]

As described above, in the pulsation reducing pipe of the present invention, the following effects can be obtained. According to the invention described in claim 1, since the two branch pipes are provided, the damping effect can be obtained in a wide frequency band. Therefore, it is possible to reduce the pulsation even when the frequency is deviated, and even when there is a difference between the designed pulsation reduction frequency and the actual pulsation reduction frequency, a wide frequency range in which the pulsation can be attenuated Therefore, pulsation can be prevented.

According to the second aspect of the present invention, the length of the branch pipe is the distance between the branch portions of the two branch pipes or an odd multiple of the distance, the branch portion and the branch portion. Distance of 2
Within the range of 0%, the composition is short or long. Therefore, a wide attenuation frequency band and a sufficient attenuation amount can be obtained at the same time.

According to the third aspect of the invention, the desired attenuation effect can be obtained by setting the interval between the branching portions to be approximately ¼ wavelength of the sound wave to be attenuated.

According to the invention of claim 4, the length of the branch pipe is changed by moving the movable wall. As a result, the damping frequency can be changed, so that the damping frequency can be adjusted, for example, when the designed damping frequency differs from the actual damping frequency when actually installed.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a pulsation reduction pipe shown as a first embodiment of the present invention.

FIG. 2 is a graph showing a relationship between frequency and sound transmittance in the same pulsation reducing pipe.

FIG. 3 is a sectional view showing a pulsation reducing pipe shown as a second embodiment of the present invention.

FIG. 4 is a diagram showing a configuration of a conventional pipe. It is a cross-sectional view of the machine.

[Explanation of symbols]

1 main pipe (piping) 2 branches 2a Closed end 2b Branch 3 branches 3a Closed end 3b Branch 11 movable wall

Claims (4)

[Claims] 1. A pipe is provided with two branch pipes whose ends are closed ends, and one of the branch pipes has a length which is equal to that of the two branch pipes. It is configured to be shorter than a distance or an odd multiple of the distance within a predetermined range, and the length of the other branch pipe is the distance between the branch portions of the two branch pipes or an odd multiple of the distance. The pulsation reducing pipe is characterized by having a long configuration within a predetermined range. 2. The pulsation reducing pipe according to claim 1, wherein a length of the one branch pipe is a distance between branch portions of the two branch pipes or an odd multiple of the distance, It is configured to be short within the range of 20% of the distance between the branch portions, and the length of the other branch pipe is the distance with respect to the distance between the branch portions of the two branch pipes. A pulsation reducing pipe having a long configuration within a range within 20% of a distance between branch portions. 3. The pulsation reducing pipe according to claim 1 or 2, wherein the distance between the branch portions is approximately ¼ wavelength of the sound wave to be attenuated. . 4. The pulsation reducing pipe according to claim 1, wherein the closed end of the branch pipe is a movable wall provided so as to be movable in a longitudinal direction of the branch pipe. Piping.