Skirted muffler for compressed gas systems

Abstract

The present application relates to a muffler (1) for a compressed air system, comprising: a housing (2) having an inlet opening (3) for a compressed air flow; a chamber (4); the silencing device (5) is arranged in the cavity (4); a grille (6) comprising at least two channels (7) through which the compressed air flow is adapted to exit the chamber (4); and a skirt (8) arranged downstream of the grille (6) wherein the skirt (8) is adapted to guide compressed gas out of the channels (7) of the grille (6). The skirt (8) serves to terminate the propagation of noise in the radial direction.

Description

Technical Field

[0001] The invention relates to a silencer for a system for handling compressed gases, such as a system working with compressed air, in particular for commercial vehicles. For example, pneumatic brakes require compressed air. Background Art

[0002] Systems that work with compressed gases, such as compressed air systems, are able to release large amounts of compressed gas into the environment in a short period of time. This decompression of the gas can generate noticeable noise. However, noise emissions must be kept below acceptable levels, so silencers for compressed gas systems are often necessary.

[0003] In commercial electric vehicles, most of the noise is generated by the mixing of high-speed air flow with the ambient air.

[0004] In the prior art, document WO 2019 / 063350 A1 is known, which discloses a noise damper for a compressed air system, which has an air intake channel and a chamber for accommodating a sound-absorbing material. In this case, the air intake channel and the chamber are separated perpendicularly to the compressed air flow by a partition, which has a plurality of openings in the peripheral area of ​​the compressed air flow to introduce compressed air into the chamber. This noise damper has a sound-absorbing function for the noise generated by the flow of compressed air (for example, in a valve that releases compressed air).

[0005] For electric commercial vehicles equipped with pneumatic brake systems, extremely low noise is essential. Currently, according to ISOR362, EEC92 / 97 and ECE R51 standards, the valve components through which compressed air flows should meet the maximum noise requirement of 72dB(A) at a distance of 7m.

[0006] However, for an electric commercial vehicle with pneumatic brakes, whose electric motor is very quiet compared to other engines, the maximum noise value of 72 dB(A) at a distance of 7 m is still too high.

[0007] Therefore, there is a need for a new type of silencer that can reduce noise emissions to less than 68dB(A) at a distance of 7m from the vehicle, or more preferably less than 60dB(A). In commercial electric vehicles, the largest part of the noise is generated by the mixing of high-speed airflow with ambient air. This noise (and noise generated by other situations) is regularly propagated in all directions.

[0008] However, if the noise has already been generated, the noise damper according to the prior art does not provide a solution to deal with the noise. Summary of the invention

[0009] Therefore, the technical problem of the present application is to provide an improved silencer which is able to reduce the propagation of noise leaving the silencer.

[0010] The technical problem of the application is solved by a silencer according to claim 1 and by the use of a silencer according to claim 16. Further advantageous embodiments of the application are subject matter of the dependent claims.

[0011] The silencer for a compressed air system according to the present application comprises: a housing having an inlet opening for a compressed air flow; a chamber; a silencer arranged in the chamber; and a grille comprising at least two channels through which the compressed air flow is suitable for leaving the chamber.

[0012] Furthermore, the silencer comprises a skirt arranged downstream of the grille and adapted to guide the compressed gas out of the passage of the grille. The diameter of the skirt is more preferably at least as large as the diameter of the grille, and optimally the skirt and the grille have substantially the same or even the same diameter.

[0013] The effect of the skirt is that if noise is already generated, its propagation is terminated radially, as the noise waves are reflected back towards the centre of the flow, but the noise is largely inaudible to those away from the silencer.

[0014] In other words, the skirt drives the generated noise in the direction of the flow, rather than in the direction of the observer, thus acting as a barrier. Therefore, the propagation of noise in the radial direction (of the muffler / grille) is terminated, because the skirt reflects the noise waves to the center of the airflow leaving the grille, i.e. the flow smoothes the noise propagation.

[0015] If the muffler and skirt are oriented in a ground direction (ie pointing in the direction of the ground), the noise may be directed primarily toward the ground, rather than toward the ears of an observer (eg, at a distance of 7 m from the muffler).

[0016] Furthermore, the skirt has an effect on mixing, since less mixing energy is generated. The skirt reduces the surface for mixing (of compressed air and ambient air) (the surface is usually tapered around the compressed air, i.e. a high-speed fluid), thereby reducing the surface for generating turbulence. Therefore, the skirt is particularly effective in situations where noise is already generated.

[0017] Furthermore, since the grid generates many individual jets, the skirt is adapted to terminate mixing between the high-speed flow and the ambient air in areas where the jets are not fully developed.

[0018] Preferably, the skirt has a cylindrical or polygonal, preferably hexagonal cross section, or a combination of different cross sections. Such a cross section is most effective for achieving the effect of the skirt.

[0019] Preferably, the skirt has a constant cross-sectional area over its length, or the cross-sectional area increases or decreases in the downstream direction over the length of the skirt.

[0020] The cross section is the area through which the airflow flows when passing through the skirt.

[0021] In case of an increase in the cross-sectional area over the length scale of the skirt, the skirt acts as a diffuser. In case of a decrease in the cross-sectional area over the length scale of the skirt, the skirt acts as a mixer. The shape can be adapted to the flow cone formed in the mixing area of ​​the compressed air and the ambient air.

[0022] Preferably, the length of the skirt is between 2 mm and 200 mm. The preferred minimum length is at least 5 mm, further more preferably at least 10 mm, further more preferably at least 20 mm, and most preferably at least 50 mm. Such a length has been shown to be most effective for achieving the effect of the skirt.

[0023] Preferably, the cross-sectional area of ​​the skirt at the inlet of the skirt is larger than the sum of the cross-sectional areas of all the channels of the grille at their respective outlets. In other words: the total cross-sectional area covered by the skirt is larger than the total cross-sectional area of ​​all the channels. In this case, the skirt can most effectively drive the generated noise in the direction of the flow. Furthermore, this ensures that the flow velocity in the skirt is not increased, which could cause additional noise.

[0024] Preferably, the length of the at least two channels is between 3 mm and 200 mm. The preferred minimum length is at least 4 mm, even more preferably at least 5 mm, further more preferably at least 7 mm, and most preferably at least 10 mm. A channel having a length of at least 3 mm ensures a uniform flow of gas, thereby reducing turbulence in the mixing region where the high pressure gas mixes with the ambient air. Therefore, a channel having at least 3 mm can effectively reduce the noise generated by the mixing of the air flowing out of the chamber with the muffler. Therefore, a channel having at least 3 mm helps to avoid noise generated by turbulence. The longer the channel, the stronger the effect of flow homogenization.

[0025] Preferably, the cross-sectional areas of the at least two channels respectively decrease from the inlet of the channel to the smallest diameter portion, and then increase from the smallest diameter portion toward the outlet of the channel.

[0026] The specific shape of the channels (the cross-sectional area of ​​at least two channels decreases from the channel inlet to the smallest diameter portion inside the channel and then increases again from the smallest diameter portion toward the channel outlet) simulates a nozzle, which usually has optimized flow characteristics. This nozzle shape can reduce the flow rate.

[0027] The specific configuration of the cross-sectional area of ​​at least two of the passages is streamlined, which reduces separation vortices and drag vortices that may form behind the grille. Such streamlined passages reduce the drag caused by the grille and also reduce flow resistance that affects, for example, the operating speed of a pneumatic valve. In addition, such streamlined passages can reduce the size and intensity of the vortex behind the grille (which is formed when the compressed air mixes with the ambient air), thereby reducing the noise energy generated by turbulence.

[0028] Thus, in particular by reducing the turbulence intensity in the grid, turbulent wakes (eddies) which are formed by the wakes generated by the separation of air through the grid can be effectively reduced.

[0029] This channel length and shape helps to direct the internally generated noise into the direction of the flow rather than the direction of the observer (e.g. at a distance of 7m).

[0030] Preferably, the effective surface ratio is between 60% and 90%, more preferably above 80%. The effective surface ratio is defined as the cross-sectional area covered by the channels (i.e. where flow through the grid can occur) divided by the total cross-sectional area of ​​the grid. The greater the number of channels and the smaller their size, the higher the stiffness. The optimal effective surface ratio depends on the available surface, channel length and stiffness requirements.

[0031] Preferably, the sound-absorbing device comprises a fibrous material, more preferably a polyethylene fiber mesh. Such a fibrous material is suitable for attenuating noise that has been generated, such as noise originating from a valve.

[0032] Preferably, the cross-section of at least two channels is polygonal, more preferably hexagonal (i.e., forming a honeycomb structure). The hexagon can also be divided by other shapes. For such hexagonal channels, the effective flow surface is optimal because the remaining area covered by the solid grid structure (dead area may appear after leaving the channel) is minimized. Therefore, the ratio of the channel area to the area covered by the solid (i.e., the grid) increases. Therefore, this structure makes the ratio of the effective flow area to the total grid area the highest. Therefore, the optimal outflow area is available for the flow of compressed air on the grid area.

[0033] Alternatively, the cross section of at least two passages is circular. In addition, by this shape, a very uniform flow can be guaranteed.

[0034] Preferably, the cross-sectional area of ​​the smallest diameter portion (eg approximately midway along the length scale of the channel) is between 80% and 95%, preferably more than 85%, of the cross-sectional area of ​​the channel inlet and / or the channel outlet.

[0035] This geometric constraint mimics the shape of a nozzle. Through this channel shape, the flow velocity of the compressed gas is reduced. This geometric constraint results in low resistance at the inlet and low wake at the outlet.

[0036] Furthermore, due to the nozzle shape, the mixing point / area (of pressurized gas and ambient gas) is towards the grid, and the size of the separation wake is reduced. In addition, the flow core (the flow velocity distribution in each channel leaving the grid) becomes wider, resulting in a very uniform flow with less turbulence and thus less noise.

[0037] In one embodiment, the inlet of the channel and the outlet of the channel have the same cross-sectional area, which results in a uniform flow. The cross-sectional area is the area through which the air flows at the inlet, outlet, or somewhere in between.

[0038] Preferably, the cross-sectional area of ​​the channel at the channel inlet is larger than the cross-sectional area at the smallest diameter portion and at the channel outlet, and the cross-sectional area of ​​the channel at the channel outlet is larger than the cross-sectional area at the smallest diameter portion.

[0039] With this nozzle design, a very uniform flow is ensured.

[0040] In this case, the channel acts as a flow mixer, concentrating the flow at the outlet of the channel.

[0041] Alternatively, the cross-sectional area of ​​the channel at the channel outlet is larger than the cross-sectional area at the smallest diameter portion and at the inlet of the channel, wherein the cross-sectional area of ​​the channel at the channel inlet is larger than the cross-sectional area at the smallest diameter portion.

[0042] This nozzle design is a diffuser and, in particular, by moving the mixing zone (of pressurized air and ambient air) away from the grille, also results in a very rapid pressure drop, but without generating noise.

[0043] One inventive use of the silencer is in a brake system, preferably a brake system of a commercial vehicle, more preferably a brake system of an electric commercial vehicle. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] In the following, advantageous embodiments of the present application will be described in more detail with reference to the accompanying drawings.

[0045] Figure 1 A silencer with a skirt is shown - Figure 1 In a), the skirt acts as a flow mixer. Figure 1 In b), the skirt acts as a diffuser.

[0046] Figure 2 The flow velocity distribution when a skirt is used downstream of the grille channels is shown. Figure 2 a) shows this flow distribution directly downstream of the grid, Figure 2 b) shows the development of the flow velocity distribution throughout the skirt.

[0047] Figure 3 The overall structure of the silencer according to the present invention is shown. Figure 3 a) to Figure 3 d) shows different embodiments, in particular regarding the shape of the channels.

[0048] Figure 4 The grid structure with channels is shown in more detail - Figure 4 a) to 4d) and Figure 4 f) to 4i) show different shapes of the channels and Figure 4 e) shows the Figure 4 d) Isometric view of the structure.

[0049] Figure 5 The physical background of the flow resistance of objects of different shapes is shown.

[0050] Figure 6 The velocity distribution, wake and vortex are shown. Figure 6 a) A silencer according to the prior art is shown here, and Figure 6 b) and Figure 6 c) shows the effect of channel length and shape on flow. DETAILED DESCRIPTION

[0051] Figure 1 A silencer 1 is shown which comprises a skirt 8 located downstream of a grille 6. The silencer 1 comprises a housing 2 with an inlet opening 3 through which compressed air can flow in. Inside the silencer 1 there is a chamber 4 which is filled with a silencer 5, in this case a fibrous material. In the end of the silencer 1 in the flow direction there is a grille 6 which has several channels 7. Figure 1 In a), the skirt has a cross-sectional area (and diameter) that decreases gradually in the flow direction and acts as a flow collector; in Figure 1 In b), the skirt has a cross-sectional area (and diameter) which increases gradually in the flow direction and thus acts as a diffuser.

[0052] Figure 2 The flow velocity distribution when a skirt 8 is used downstream of the channels 7 of the grid 6 is shown.

[0053] Figure 2 a) shows such a flow profile directly downstream of the grille 6. Here, it can be seen that individual conical flow cores are formed at the outlet of the channels 7 of the grille. Between these flow cores, wake separation occurs. The skirt 8 acts as a barrier and reflects the noise into the middle of the flow. Almost no noise can reach an observer or receiver (e.g. a microphone) radially spaced from the skirt 8.

[0054] Figure 2b) shows the development of the flow velocity distribution within the entire skirt 8. Here, it can be seen that the individual flow cores form a developed flow core downstream of the skirt 8. In this area, there is no longer turbulence. Almost no noise can reach an observer or receiver (such as a microphone) radially spaced from the skirt 8.

[0055] exist Figure 3 In the figure, the general structure of a silencer 1 according to the invention is described. The silencer 1 comprises a housing 2 with an inlet opening 3, through which compressed air can flow in. Inside the silencer 1, there is a chamber 4, which is filled with a silencer 5, in this case a fibrous material. At the end of the silencer 1 in the flow direction, there is a grid 6, which has several channels 7. Each channel 7 has an inlet 7a, a portion with the smallest diameter 7b and an outlet 7c. The cross-sectional area decreases from the inlet 7a to the portion with the smallest diameter 7b and then increases again to the outlet 7c.

[0056] exist Figure 3 In a), the channels 7 have a polygonal shape. The cross section of the wall 7d between the channels 7 has a rhombus shape.

[0057] exist Figure 3 b), the channel 7 has a circular shape, wherein the cross-sectional areas (and diameters) of the inlet 7a and the outlet 7c of the channel 7 are substantially the same. The cross-sectional area of ​​the wall 7d between the channels 7 has a quasi-elliptical shape.

[0058] Figure 3 c) shows an embodiment in which the cross-sectional area (and diameter) of the inlet 7a of the channel 7 is larger than the cross-sectional area (and diameter) of the smallest diameter portion 7b of the channel 7 and the cross-sectional area (and diameter) of the outlet 7c. Here, the cross-sectional area (and diameter) of the outlet 7c of the channel 7 is larger than the cross-sectional area (and diameter) of the smallest diameter portion 7b of the channel 7. The cross-sectional area of ​​the wall between the channels 7 is in the shape of an elongated teardrop.

[0059] exist Figure 3 d) shows an embodiment in which the cross-sectional area (and diameter) of the outlet 7c of the channel 7 is larger than the cross-sectional area (and diameter) of the smallest diameter portion 7b of the channel 7 and the cross-sectional area (and diameter) of the inlet 7a. Here, the cross-sectional area (and diameter) of the inlet 7a of the channel 7 is larger than the cross-sectional area (and diameter) of the smallest diameter portion 7b of the channel 7. The cross-sectional area of ​​the wall between the channels 7 has a carrot shape.

[0060] Figure 4 a) shows a top view of a grid 6 with several channels 7a, which have a hexagonal shape. Figure 4 b) shows the same structure, but with Figure 4 a) The hexagon is larger in comparison. Figure 4c) shows a larger channel 7a (still hexagonal, but with a larger cross-sectional area). Figure 4 d) shows a structure where the walls of the channels are tapered but still have a hexagonal shape. Figure 4 e) shows the Figure 4 d) isometric view of a grid 6, again with hexagonal channels 7. The walls 7d separating the channels 7 are very thin in this embodiment (e.g., between 1 and 4 mm). A thickness below 1 mm would result in insufficient structural strength, while a thickness above 4 mm would excessively reduce the cross-sectional area available for flow.

[0061] Figure 4 f) shows a grid 6 with a diamond-shaped cross-sectional area of ​​the channels 7, also maximizing the cross-sectional area available for flow. Figure 4 g) and 4h) show a grid 6 in which the cross-sectional area of ​​the channels 7 is triangular, also maximizing the cross-sectional area available for flow. Figure 4 i) shows a grid 6 in which the channels 7 are arranged in a star shape. In this case, channels 7 with a pentagonal cross-sectional area are used.

[0062] Figure 5 The physical background of the flow resistance of objects O with different shapes is shown. Figure 5 In a), there is a thin wall, and it can be seen that there is a dead volume behind the object O, and eddies are also generated. Figure 5 In b), the object O has a spherical or ball shape. It can be seen that there is still dead volume, but it is different from Figure 5 Compared with a), less eddy current is generated. Figure 5 c), the object O has a combined shape, which is a water drop shape (the wider part faces the direction of the flow). Figure 5 Compared with a) and 5b), the dead volume and turbulence are much less. Figure 5 d) shows a very thin object that is elongated in the flow direction. It can be seen that there is almost no dead volume and no eddies are generated. Figure 5 d) has the smallest flow resistance.

[0063] Figure 6 a) shows the flow through the channels 7 of the grille 6 of a silencer according to the prior art. The fluid can flow through the silencer 5 and it can be seen that resistance is created before reaching the grille 6 with the channels 7. Since the grille 6 and the channels 7 are very thin, vortices are created in the flow in each channel 7 and the confluence zone is located directly downstream of the grille 6. In the confluence zone, the compressed air and the ambient air mix.

[0064] The velocity profile of the flow leaving the channel 7 is cone-shaped. Between the cones, wake separation occurs. This causes vortices and thus high turbulence. The mixing of compressed air and ambient air generates noise.

[0065] exist Figure 6 b), a thicker grille 7 is shown (with Figure 4 a)). It shows that there is less drag and less eddy in the flow. Nevertheless, there is still wake separation in the merging area, but the noise can be reduced.

[0066] Figure 6 c) shows an elongated grid 6 (similar to Figure 6 b)), however, its shape is such that the cross-sectional area of ​​the passage decreases gradually from the inlet to the smallest diameter, but then gradually increases again, like the structure of a nozzle. It can be seen that this embodiment has less resistance and a little wake separation in the confluence area, but it can be seen that the flow core is very wide, so less turbulence is generated and almost no noise.

[0067] Reference numerals list

[0068] 1 Silencer

[0069] 2 Housing

[0070] 3 Entrance opening

[0071] 4 Chambers

[0072] 5. Silencer

[0073] 6 Grille

[0074] 7 channels

[0075] Entrance to channel 7a

[0076] 7b Smallest diameter part

[0077] Exit of channel 7c

[0078] 7d Channel wall

[0079] 8 Skirt

[0080] O Object

[0081] B. Braking system

Claims

1. A silencer (1) for a compressed air system, comprising: a housing (2) having an inlet opening (3) for a compressed gas flow, Chamber (4), a muffler (5), which is arranged in the chamber (4), a grille (6) comprising at least two channels (7) through which the compressed air flow is adapted to leave the chamber (4), and a skirt (8) arranged downstream of the grille (6), wherein the skirt (8) is suitable for guiding the compressed gas out of the channels (7) of the grille (6).

2. The muffler according to claim 1, wherein: The skirt (8) has a cylindrical or polygonal, preferably hexagonal, cross section, or a combination of different cross sections.

3. The silencer according to claim 1 or 2, wherein: The skirt (8) has a constant cross-sectional area or has a cross-sectional area that increases or decreases in the downstream direction over the length scale of the skirt (8).

4. A silencer according to any one of the preceding claims, wherein: The length of the skirt (8) is between 2 mm and 200 mm, preferably at least 5 mm, more preferably at least 10 mm, more preferably at least 20 mm, most preferably at least 50 mm.

5. A silencer according to any one of the preceding claims, wherein: The cross-sectional area of ​​the skirt (8) at the inlet of the skirt (8) is greater than the sum of the cross-sectional areas of all channels (7) at their respective outlets (7c).

6. A silencer according to any one of the preceding claims, wherein: The length of the at least two channels (7) is between 3 mm and 200 mm, preferably at least 4 mm, more preferably at least 5 mm, even more preferably at least 7 mm, most preferably at least 10 mm.

7. A silencer according to any one of the preceding claims, wherein: The cross-sectional areas of the at least two channels (7) decrease from the channel inlet (7a) to the smallest diameter portion (7b), and then increase from the smallest diameter portion (7b) toward the channel outlet (7c).

8. The silencer (1) according to any one of the preceding claims, wherein: The grid (6) has an effective surface ratio between 60% and 90%, preferably above 80%.

9. The silencer (1) according to any one of the preceding claims, wherein: The noise reduction device (5) comprises a fiber material.

10. The silencer (1) according to any one of the preceding claims, wherein: The cross-sections of the at least two channels (7) are polygonal, preferably hexagonal.

11. The silencer (1) according to any one of the preceding claims, wherein: The cross-section of the at least two channels (7) is circular.

12. The silencer (1) according to any one of the preceding claims, wherein: The cross-sectional area of ​​the smallest diameter portion (7b) of the at least two channels (7) is between 80% and 95%, preferably above 85%, of the cross-sectional area of ​​the inlet (7a) and / or outlet (7c) of the at least two channels.

13. The silencer (1) according to any one of the preceding claims, wherein: The inlets (7a) of the at least two channels (7) and the outlets (7c) of the at least two channels have the same cross-sectional area.

14. The silencer (1) according to any one of claims 1 to 12, wherein: The cross-sectional area of ​​the at least two channels (7) at the inlet (7a) of the at least two channels is larger than the cross-sectional area at the minimum diameter portion (7b) and at the outlet (7c) of the at least two channels, and wherein the cross-sectional area of ​​the at least two channels (7) at the outlet (7c) of the at least two channels is larger than the cross-sectional area at the minimum diameter portion (7b).

15. The silencer (1) according to any one of claims 1 to 12, wherein: The cross-sectional area of ​​the at least two channels (7) at the outlets (7c) of the at least two channels is larger than the cross-sectional area at the smallest diameter portion (7b) and at the inlets (7a) of the at least two channels, and wherein the cross-sectional area of ​​the at least two channels (7) at the inlets (7a) of the at least two channels is larger than the cross-sectional area at the smallest diameter portion (7b).

16. Use of a silencer (1) according to any one of claims 1 to 15 for a brake system, preferably a brake system (B) of a commercial vehicle.

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