JP7637972B2 - Sound suppressor - Google Patents

Description

The present invention relates to a silencer that is inserted into the refrigerant pipes, exhaust pipes, etc. of vehicle air conditioners.

In vehicle air conditioners, mechanical noise from the compressor and noise caused by cavitation of the refrigerant are transmitted to the evaporator via the piping and then transmitted to the driver from the air outlet, or transmitted along the way to the driver via the vehicle body through the space in the engine compartment. For this reason, muffler-type silencers or internal insertion-type silencers are installed in the piping of vehicle air conditioners. Muffler-type silencers are large and heavy, and brazing increases costs, so internal insertion-type silencers have been widely adopted in recent years.

For example, Patent Document 1 describes a device in which a spiral fin is provided on the outer surface of an inner tube. This creates a phase difference due to the difference in the length of the inner and outer flow passages, which causes sound interference and creates a noise-dampening effect, but the only way to adjust the frequency at which the noise-dampening effect occurs is to change the difference in the length of the inner and outer flow passages, which is difficult to adjust.

Patent document 2 describes a silencer that is inserted into a tubular body, in which a resonator chamber is provided between the silencer and the body, and the flow path of the body is connected to the resonator chamber via a connecting channel. Patent document 3 describes a sound absorbing device in which the outer member surrounding the inner member is a bellows, a cavity is formed between the inner member and the outer member, and the opening of the inner member is open to the cavity. Both of these are of the resonance type, and the resonance frequency is determined by the shape of the resonator, so the frequency range in which the sound absorbing effect is achieved is narrow.

European Patent Publication EP2138750A1 Patent No. 5785173 specification JP 2005-84693 A

The present invention was made in consideration of the above-mentioned problems of the conventional technology, and aims to provide a noise suppression device that has a large transmission loss, is easy to adjust according to frequency, and has a wide frequency range in which it produces a noise suppression effect.

As a means for solving the above problems, the present invention provides
(1) A silencer that is inserted into a main pipe through which a fluid flows,
an inner pipe located inside the main pipe;
a spiral fin provided on an outer surface of the inner pipe and in contact with an inner surface of the main pipe;
a partition portion that partitions the spiral groove formed by the fin,
a side branch chamber surrounded by the fin and the partition portion is provided between the main pipe and the inner pipe,
The spiral groove is characterized in that an inlet/outlet communicating with the side branch chamber is provided at the upstream end or downstream end of the spiral groove.

(2) The partition portion is formed in a middle portion of the spiral groove,
The side branch chamber preferably includes a first side branch chamber upstream of the partition and a second side branch chamber downstream of the partition.

(3) The partition portion is formed at an upstream end or a downstream end of the spiral groove,
The side branch chamber is preferably formed upstream or downstream of the partition.

(4) The partition portion includes a first partition portion on the upstream side of the spiral groove and a second partition portion on the downstream side of the spiral groove,
A resonance chamber is provided between the first partition and the second partition,
The inner surface of the inner tube is preferably provided with an opening communicating with the resonating chamber.

(5) The spiral fin is composed of a plurality of fins,
the plurality of spiral grooves formed by the plurality of fins include a first spiral groove having the partition portion formed therein and a second spiral groove having no partition portion,
It is preferable that a secondary flow passage for a fluid flowing through the main pipe is formed between the main pipe and the inner pipe along the second spiral groove.

(6) It is preferable that an outer cylinder is provided to seal the fin.

According to the inventions of claims 1 to 3, sound waves that enter the side branch chamber from the upstream or downstream end of the spiral groove are reflected by the partition and return to the upstream or downstream end of the spiral groove, where they interfere with the sound waves in the inner tube in the opposite phase and are silenced. By changing the position of the partition, the frequency at which the sound silencing effect occurs can be adjusted.

According to the invention of claim 4, the energy of the sound waves that enter the resonating chamber from the opening on the inner surface of the inner tube is absorbed in the resonating chamber and silenced. This provides a combined sound silencing effect that combines the sound silencing effect of the side branch chamber in a wide frequency range with the sound silencing effect of the resonating chamber in a specific frequency range. In particular, by compensating for the frequency range in which it is difficult to obtain a sound silencing effect from the side branch chamber with the sound silencing effect of the resonating chamber, it is possible to obtain a sound silencing effect in a wider frequency range.

According to the invention of claim 5, among the multiple spiral grooves formed by the multiple fins, the second spiral groove without a partition is a secondary flow path between the secondary flow path and the main flow path inside the inner tube, which generates a phase difference in the sound waves, causing sound interference and creating a noise reduction effect. Therefore, a noise reduction effect is obtained that combines the noise reduction effect in a wide frequency range by the side branch chamber and the noise reduction effect due to the phase difference between the secondary flow path and the main flow path.

According to the invention of claim 6, the outer cylinder seals the side branch chamber and the resonating chamber, preventing leakage from the side branch chamber and the resonating chamber due to bending or vibration of the main tube, and maintaining the sound-deadening effect.

1 is a perspective view of a noise suppressor according to a first embodiment of the present invention, in which a part of a main pipe is cut away. FIG. 2 is a perspective view of the silencer of FIG. 1 as viewed from the upstream side. FIG. 2 is a perspective view of the silencer of FIG. 1 as viewed from the downstream side. FIG. 2 is a longitudinal sectional view of a main pipe into which the silencer of FIG. 1 is inserted. 2A and 2B are a perspective view and a front view showing a modified example of the silencer of FIG. 1 . FIG. 13 is a perspective view showing an example of the invention and a comparative example used in an analysis of the sound deadening effect. 1 is a graph showing analysis results of transmission loss for a comparative example (spiral 1) and an example of the invention (spiral 2). Graph showing the analysis results of transmission loss for the comparative example (spiral 1) and the invention example (spiral 2) in terms of average values in the low frequency range, high frequency range, and all frequency ranges. FIG. 5 is a perspective view of a silencer according to a second embodiment of the present invention. FIG. 10 is a longitudinal sectional view of a main pipe with the silencer of FIG. 9 inserted therein; FIG. 10 is a perspective view showing a modification of the silencer of FIG. 9 . FIG. 11 is a perspective view of a noise suppressor according to a third embodiment of the present invention, with a portion of the main pipe cut away.

An embodiment of the present invention will be described below with reference to the attached drawings.

First Embodiment
FIG. 1 shows a silencer 1 according to a first embodiment of the present invention. The silencer 1 is provided in a pipe through which a refrigerant of an air conditioner for a vehicle flows. Specifically, the silencer is inserted into a pipe (hereinafter referred to as a "main pipe") 2 on the outlet side of an evaporator or a compressor in an air conditioner for a vehicle, the air conditioner including a compressor, a condenser, an expansion valve, and an evaporator (not shown). The main pipe 2 is formed of a material having elasticity and flexibility, such as rubber or synthetic resin, but is not limited thereto, and a material having no flexibility, such as aluminum, may also be used. In the main pipe 2, a fluid (hereinafter referred to as a "refrigerant") flows from the upstream on the left side to the downstream on the right side in FIG. 1.

As shown in Figures 2 and 3, the silencer 1 includes an inner tube 3, fins 4, and a partition 5.

The inner pipe 3 has an outer diameter smaller than the inner diameter of the main pipe 2. The thickness of the inner pipe 3 is preferably as thin as possible to ensure a flow path. The length of the inner pipe 3 is arbitrary, but it is preferable that the length does not hinder the bending of the main pipe 2 at the location where the main pipe 2 is installed. The inside of the inner pipe 3 forms the main flow path 10 for the fluid flowing through the main pipe 2.

The fin 4 is composed of a first fin 4a and a second fin 4b having two helical stripes. The first fin 4a is provided on the outer surface of the inner pipe 3 and extends in a spiral shape with a predetermined pitch p from the upstream end of the inner pipe 3 to the downstream end. The second fin 4b extends in a spiral shape with the same pitch p as the first fin 4a from a position 180 degrees out of phase with the first fin 4a at the upstream end of the inner pipe 3 to the downstream end. The second fin 4b is located in the middle between two adjacent side surfaces of the first fin 4a. The height of the fin 4 is equal to the radial dimension from the outer surface of the inner pipe 3 to the inner surface of the main pipe 2. Therefore, the outer end surface of the fin 4 is in contact with the inner surface of the main pipe 2. The thickness of the fin 4 is preferably the same as the wall thickness of the inner pipe 3, but is not limited to this. The first fin 4a and the second fin 4b form a first groove 6a and a second groove 6b having two helical stripes between the main pipe 2 and the inner pipe 3. In this embodiment, the fins 4 have two rows, but they can also have one row or three or more rows.

The partition 5 is provided between the side of the first fin 4a of the first groove 6a and the side of the adjacent second fin 4b, and divides the first groove 6a into an upstream side and a downstream side. The position of the partition 5 is arbitrary, but determines the length of the side branch chambers 7a, 7b formed on the upstream side and downstream side of the partition 5. The height of the partition 5 is the same as the height of the fin 4. The thickness of the partition 5 is preferably the same as the thickness of the fin 4, but is not limited to this.

The silencer 1 is fixed inside the main pipe 2 by fastening a part of the fins 4, including the partition 5, from the outside of the main pipe 2 with a fixing member (not shown). The outer end faces of the first fin 4a and the second fin 4b and the outer end face of the partition 5 are in close contact with the inner surface of the main pipe 2 when the silencer 1 is inserted into the main pipe 2. This allows the side branch chambers 7a and 7b, which will be described later, to be sealed by the main pipe 2. As an alternative to the fixing means, the silencer 1 may be pressed in or a sealant may be used when inserting it into the main pipe 2.

As shown in FIG. 4, in the first spiral groove 6a formed between the main pipe 2 and the inner pipe 3 and by the first fin 4a and the second fin 4b, a first spiral side branch chamber 7a is formed on the upstream side of the partition 5, and a second spiral side branch chamber 7b is formed on the downstream side of the partition 5. The inlet/outlet 8a of the first side branch chamber 6a is located at the upstream end of the first groove 6a, and the inlet/outlet 8b of the second side branch chamber 7b is located at the downstream end of the second groove 6b.

The second spiral groove 6b formed between the main pipe 2 and the inner pipe 3 and by the first fin 4a and the second fin 4b forms a secondary flow path 9 from the upstream end to the downstream end of the inner pipe 3.

Next, the operation of the silencer 1 of this embodiment will be described.

As shown in FIG. 4, the refrigerant flowing through the main pipe 2 flows into the main flow path 10 inside the inner pipe 3 and into the spiral secondary flow path 9 outside the inner pipe 3 at the upstream end of the silencer 1, and flows out of the main flow path 10 inside the inner pipe 3 and the spiral secondary flow path 9 outside the inner pipe 3 at the downstream end. Sound generated from a sound source (not shown) on the upstream side of the silencer 1 (mechanical noise of the compressor and noise due to cavitation of the refrigerant) propagates downstream together with the refrigerant and enters the main flow path 10 inside the inner pipe 3 of the silencer 1 and the secondary flow path 9 outside the inner pipe 3. The sound source may be on the downstream side, in which case the silencing effect will be generated on the upstream side.

The sound waves propagating through the inner pipe 3 enter the first side branch chamber 7a from the inlet/outlet 8a at the upstream end of the inner pipe 3, and enter the second side branch chamber 7b from the inlet/outlet 8b at the downstream end of the inner pipe 3. They are reflected by the partitions 5 of the side branch chambers 7a and 7b and return to the inlets 8a and 8b, where they are in opposite phase to the sound waves in the inner pipe 3 and interfere with each other, resulting in silencing.

Here, assuming that the cross-sectional area of the main pipe 2 is S, the cross-sectional area of the side branch chambers 7a, 7b is Ss, the length of the side branch chambers 7a, 7b is l, the frequency of the sound wave is f, and the speed of sound is c, the transmission loss TL in the silencer 1 is expressed by Equation 1. The length l of the side branch chamber is the distance along the spiral from the inlets 8a, 8b to the partition section 5.

In addition to the sound deadening effect of the first side branch chamber 7a and the second side branch chamber 7b, the difference in flow path length between the main flow path 10 inside the inner tube 3 and the secondary flow path 9 outside the inner tube 3 creates a phase difference between the sound waves propagating through the main flow path 10 and the secondary flow path 9, causing sound interference and creating a sound deadening effect.

In the silencer 1 of this embodiment, the length of the first side branch chamber 7a and the second side branch chamber 7b can be adjusted by changing the position of the partition 5, thereby improving the noise reduction effect according to the frequency of the sound source.

In the silencer 1 of the first embodiment, the partition 5 is provided between the main pipe 2 and the inner pipe 3 and in the middle of the first spiral groove 6a formed by the first fin 4a and the second fin 4b. However, as shown in FIG. 5(a), the partition 5 may be provided at the upstream end of the first spiral groove 6a, or as shown in FIG. 5(b), the partition 5 may be provided at the downstream end.

In the silencer 1 of the first embodiment, as shown in FIG. 5(c), the inner surface of the upstream end of the inner tube 3 may be formed with a tapered surface 11a that narrows toward the downstream side. Similarly, the inner surface of the downstream end of the inner tube 3 may be formed with a tapered surface 11b that widens toward the downstream side. This can reduce the pressure loss of the refrigerant flowing from the main tube 2 through the inner tube 3 to the main tube 2.

To confirm the sound deadening effect of the silencer 1 of the first embodiment, the inventors performed acoustic analysis by computer simulation for the two analytical models shown in Figure 6.

In Figure 6, the comparative example (spiral 1) has two spiral fins 4a, 4b, but no partition and no side branch chamber. In contrast, the invention example (spiral 2) is the same as the silencer 1 of the first embodiment shown in Figure 2, and has a structure with side branch chambers 7a, 7b. Each analytical model had an outer diameter of 20 mm, an inner diameter of 8 mm, and a total length of 100 mm. For each analytical model, the transmission loss was calculated by changing the frequency of the sound source.

In this acoustic analysis, the medium was air with a temperature of 25°C, a pressure of 0.101325 MPa (standard atmospheric pressure), a density of 1.184 kg/m ³ , and a sound speed of 346.25 m/s. The target frequency at which the noise reduction effect can be obtained was set to 0 to 4000 Hz. If the length of the side branch is l and the sound speed is c, the theoretical value of the target frequency f was calculated using Equation 2. Specifically, the target frequencies of the first side branch chamber 7a and the second side branch chamber 7b were set to 421 Hz and 3785 Hz, respectively.

In the second groove 6b without a partition, when the length of the main flow path 10 is li and the length of the sub-flow path 9 is lo, the theoretical value of the target frequency f was calculated by Equation 3. Specifically, the target frequency of the second groove 6b was set to 1365 Hz.

Figure 7 shows the transmission loss when the frequency is changed from 0 to 8000 Hz. From Figure 7, it can be seen that the invention example (spiral 2) has a greater number of transmission loss peaks at 4000 to 8000 Hz than the comparative example (spiral 1), confirming that it has a greater sound deadening effect.

Figure 8 shows the average transmission loss at low frequencies from 0 to 4000 Hz, the average transmission loss at high frequencies from 4000 to 8000 Hz, and the average transmission loss at all frequencies. Figure 8 confirms that the example of the invention (spiral 2) has a larger transmission loss and a greater sound deadening effect than the comparative example (spiral 1).

Second Embodiment
9 and 10 show a noise suppressor 20 according to a second embodiment of the present invention.

The silencer 20 of the second embodiment has a first partition 5a and a second partition 5b on the outer surface of the inner pipe 3, a first side branch chamber 7a is formed between the first partition 5a on the upstream side and the upstream end of the inner pipe 3, a second side branch chamber 7b is formed between the downstream partition 5b and the downstream end of the inner pipe 3, and a resonance chamber 21 is formed between the first partition 5a and the second partition 5b. The configurations of the first side branch chamber 7a and the second side branch chamber 7b are the same as those of the first embodiment except for the length dimension, so the same reference numerals are used and the description is omitted.

The resonance chamber 21 is formed by a space surrounded by the inner surface of the main tube 2, the outer surface of the inner tube 3, the first fin 4a, the second fin 4b, the first partition 5a, and the second partition 5b. An opening 22 that communicates with the resonance chamber 21 is formed midway between the first partition 5a and the second partition 5b, penetrating the wall of the inner tube 3.

In the second embodiment of the silencer 20, in addition to the sound absorbing effects of the first side branch chamber 7a and the second side branch chamber 7b, the resonance chamber 21 also provides a sound absorbing effect. That is, the energy of the sound waves that enter the inner tube 3 is absorbed by the resonance chamber 21, and the sound is silenced.

Here, if the volume of the resonance chamber 21 is V, the cross-sectional area of the opening 22 is Sr, the length of the opening 22 is l, and the sound speed is c, then the resonance frequency ωr is expressed by Equation 4.

Therefore, by matching the resonant frequency of the resonant chamber 21 with the frequency of the incident sound, a sound deadening effect can be achieved for a specific frequency range, and combined with the sound deadening effect of the first side branch chamber 7a and the second side branch chamber 7b, the range of frequencies over which the sound deadening effect can be achieved can be widened.

In the second embodiment, the silencer 20 has a resonance chamber 21 between the first partition 5a and the second partition 5b, a first side branch chamber 7a between the first partition 5a and the upstream end of the inner pipe 3, and a second side branch chamber 7b between the second partition 5b and the downstream end of the inner pipe 3. However, as shown in FIG. 11(a), the first partition 5a may be provided at the upstream end of the inner pipe 3 and the second partition 5b may be provided downstream of the first partition 5a, with the resonance chamber 21 provided between the first partition 5a and the second partition 5b, and the side branch chamber 7 provided between the second partition 5b and the downstream end of the inner pipe 3. Also, as shown in FIG. 11(b), the second partition 5b may be provided at the downstream end of the inner pipe 3, the first partition 5a may be provided upstream of the first partition 5b, a resonance chamber 21 may be provided between the first partition 5a and the second partition 5b, and a side branch chamber 7 may be provided between the first partition 5a and the upstream end of the inner pipe 3. Also, by increasing the number of partitions, multiple resonance chambers may be provided.

Third Embodiment
FIG. 12 shows a noise suppressor 30 according to a third embodiment of the present invention.

The silencer 30 according to the third embodiment is formed by pressing the silencer 1 according to the first embodiment shown in FIG. 2 into an outer cylinder 31, so that the outer cylinder 31 seals each of the side branch chambers 7a, 7b.

The outer cylinder 31 is made of a synthetic resin such as nylon. The outer cylinder 31 may be made of a metal such as aluminum, but it is preferable to use a sealant or adhesive so that when the silencer 1 is inserted into the outer cylinder 31, the spiral fins 4a, 4b of the silencer 1 and the outer end surface of the partition 5 are in close contact with the inner surface of the outer cylinder 31.

The silencer 30 according to the third embodiment is inserted into the main pipe 2 that forms the refrigerant flow path with the outer tube 31 attached. In the silencer 30 according to the third embodiment, even if the main pipe 2 is bent when piping in the engine room, the outer tube 31 seals each side branch chamber, preventing leakage from the side branch chambers due to bending or vibration of the main pipe 2, and maintaining the sound absorbing effect.

The present invention is not limited to the above-described embodiment, and can be modified and changed within the scope of the invention as defined in the claims.
For example, the number of fins is not limited to two as in the above embodiment, and the position of the partition, i.e., the length of the side branch chamber, can also be changed as appropriate.

1...Silencer (first embodiment)
Reference Signs List 2: Main pipe 3: Inner pipe 4: Fin 4a: First fin 4b: Second fin 5: Partition 5a: First partition 5b: Second partition 6: Groove 6a: First groove 6b: Second groove 7: Side branch chamber 7a: First side branch chamber 7b: Second side branch chamber 8: Inlet/outlet 8a: First inlet/outlet 8b: Second inlet/outlet 9: Sub-flow passage 10: Main flow passages 11a, 11b: Tapered surface 20: Silencer (Second embodiment)
21... Resonance chamber 22... Opening 30... Silencer (third embodiment)
31...Outer cylinder

Claims (5)

A silencer that is inserted into a main pipe through which a fluid flows,
an inner pipe located inside the main pipe;
a spiral fin provided on an outer surface of the inner pipe and in contact with an inner surface of the main pipe;
a partition portion that partitions the spiral groove formed by the fin,
a side branch chamber surrounded by the fin and the partition portion is provided between the main pipe and the inner pipe,
an inlet/outlet communicating with the side branch chamber is provided at an upstream end or a downstream end of the spiral groove ;
A silencer comprising: an outer cylinder that seals the fins; the outer cylinder being in contact with an inner surface of the main pipe . The partition portion is formed in a middle portion of the spiral groove,
2. The silencer according to claim 1, wherein the side branch chamber comprises a first side branch chamber located upstream of the partition and a second side branch chamber located downstream of the partition. The partition portion is formed at an upstream end or a downstream end of the spiral groove,
2. The noise suppressor according to claim 1, wherein the side branch chamber is formed on the upstream side or the downstream side of the partition portion. the partition portion includes a first partition portion on the upstream side of the spiral groove and a second partition portion on the downstream side of the spiral groove,
A resonance chamber is provided between the first partition and the second partition,
2. The silencer according to claim 1, wherein an opening is provided on the inner surface of the inner tube so as to communicate with the resonance chamber. The spiral fin is composed of a plurality of fins,
the plurality of spiral grooves formed by the plurality of fins include a first spiral groove having the partition portion formed therein and a second spiral groove having no partition portion,
5. The silencer according to claim 1, wherein a secondary flow passage for a fluid flowing through the main pipe is formed between the main pipe and the inner pipe along the second spiral groove.

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