Improved compressed gas system silencer

Abstract

The present application relates to a muffler (1) for a compressed air system, comprising: a housing (2) with an inlet opening (3) for a flow of compressed gas, a chamber (4), a muffling device (5) arranged in the chamber (4), a grille (6) comprising at least two channels (7) through which the flow of compressed gas is adapted to exit the chamber (4), where the at least two channels (7) have a length of at least 3 mm, the cross-sectional areas of the at least two channels (7) each decrease from the inlet (7a) of the channel to the minimum diameter portion (7b) and then increase from the minimum diameter portion (7b) to the outlet (7c) of the channel. Such a silencer (1) is suitable for effectively reducing the noise generated by the mixing of air, in particular compressed air, with ambient air.

Description

Technical Field

[0001] The invention relates to a silencer for a system for handling compressed gases, such as a system operating 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 ambient air.

[0004] In the prior art, document WO 2019 / 063350 A1 is known, which discloses a silencer for a compressed air system, which has an air inlet channel and a chamber for accommodating a sound-absorbing material. In this case, the air inlet channel and the chamber are separated perpendicularly to the compressed air flow by a partition, and in the peripheral area of ​​the compressed air flow, the partition has a plurality of openings to introduce compressed air into the chamber. This silencer 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 which is capable of reducing noise emissions to below 68 dB(A) at a distance of 7 m from the vehicle, or more preferably below 60 dB(A). Summary of the invention

[0008] The technical problem underlying the present application is therefore to provide an improved silencer which is able to perform improved sound attenuation and thus to achieve lower noise values ​​than existing systems.

[0009] In particular, externally generated noise, such as that generated by valves that discharge compressed air to the atmosphere, should be suppressed, since the most significant part of the noise is generated by the mixing of the (high-speed flowing) compressed air with the ambient air.

[0010] The object of the invention is achieved by a silencer according to claim 1 and by the use of a silencer according to claim 16. Further advantageous embodiments of the invention are the subject matter of the dependent claims.

[0011] The silencer for a compressed air system according to the present application comprises: a housing with 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 adapted to leave the chamber. The length of the at least two channels is at least 3 mm. The cross-sectional area of ​​the at least two channels decreases from the inlet of the channel to the smallest diameter portion in the channel, and then increases from the smallest diameter portion to the outlet of the channel.

[0012] Therefore, there are a plurality of channels in the grid. Channels having a length of at least 3 mm ensure a uniform flow of the gas and thus reduce turbulence in the mixing zone where the high pressure gas mixes with the ambient air.

[0013] Therefore, a passage of at least 3 mm can effectively reduce the noise generated by the mixing of air flowing out of the chamber and the silencer. Therefore, a passage of at least 3 mm helps to avoid turbulence generating noise.

[0014] The specific shape of the channels (the cross-sectional area of ​​at least two channels decreases from the inlet of the channel to the smallest diameter portion in the channel and then increases from the smallest diameter portion to the outlet of the channel) simulates a nozzle, which generally has optimized flow characteristics. This nozzle shape can reduce the flow velocity.

[0015] The specific streamlined structure of the cross-sectional area of ​​at least two channels reduces the separation vortex and drag vortex that may be formed behind the grille. Such streamlined channels reduce the drag generated by the grille and also reduce the flow resistance that affects the operating speed of pneumatic valves, etc. In addition, such streamlined channels can reduce the size and intensity of the vortex behind the grille (formed when the compressed air mixes with the ambient air) and thus reduce the noise energy generated by turbulence.

[0016] Thus, turbulent wakes (eddies) can be effectively reduced, in particular by reducing the turbulence intensity in the grid, said turbulence being formed by the wakes generated by the separation of air through the grid.

[0017] Such channel length and shape helps to direct the internally generated noise in the direction of the flow rather than in the direction of an observer (eg 7m away).

[0018] Preferably, the length of at least two channels is between 4 mm and 200 mm. The preferred minimum length is at least 5 mm, further preferably at least 7 mm, most preferably at least 10 mm.

[0019] The longer the channel, the better the air flow uniformity.

[0020] Preferably, the effective surface area ratio of the grille is between 60% and 90%, more preferably above 80%. The effective surface area ratio refers to the cross-sectional area covered by the channels (i.e. the area where the airflow can pass through the grille) divided by the total cross-sectional area of ​​the grille. A larger number of channels with smaller size have higher rigidity. The optimal effective surface area ratio depends on the available surface area, channel length and rigidity requirements.

[0021] 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 from a valve.

[0022] 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 (the area where the gas may form a dead volume 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 allows the highest ratio of effective flow area to be achieved over the total grid area. Therefore, the optimal outflow area can be used for the flow of compressed air over the grid area.

[0023] Alternatively, at least two channels have a circular cross section. This shape can also ensure a very uniform flow.

[0024] Preferably, the cross-sectional area of ​​the smallest diameter portion (eg approximately in the middle of the channel length) is 80% to 95%, preferably above 85%, of the cross-sectional area of ​​the channel inlet and / or channel outlet.

[0025] Such a geometric constraint mimics the shape of a nozzle. Through a channel of such shape, the flow velocity of the compressed gas is reduced. This geometric constraint results in low resistance at the inlet and small wake at the outlet. Moreover, due to the nozzle shape, the mixing point / area (of pressurized gas and ambient gas) moves towards the grid and the size of the separation wake is reduced. Furthermore, the flow core (the velocity profile of the gas flow leaving each channel of the grid) is widened, resulting in a very uniform gas flow with less turbulence and, therefore, less noise.

[0026] In one embodiment, the channel inlet and the channel outlet have the same cross-sectional area, which results in uniform flow. The cross-sectional area refers to the area through which the air flows when it flows at the inlet, outlet, or somewhere in between.

[0027] Preferably, the channel cross-sectional area at the channel inlet is larger than the channel cross-sectional area at the smallest diameter portion and outside the channel, and the channel cross-sectional area at the channel outlet is larger than the channel cross-sectional area at the smallest diameter portion.

[0028] With this nozzle design, a very uniform flow is guaranteed.

[0029] In this case, the channel acts as a flow concentrator, causing the air flow to converge at the channel outlet.

[0030] Alternatively, the channel cross-sectional area at the channel outlet is larger than the channel cross-sectional area at the smallest diameter portion and at the channel inlet, wherein the channel cross-sectional area at the channel inlet is larger than the channel cross-sectional area at the smallest diameter portion.

[0031] This nozzle design is a diffuser which also allows very rapid decompression, but without generating noise, in particular by moving the mixing zone (of pressurized air and ambient air) away from the grille.

[0032] Furthermore, the silencer preferably comprises a skirt arranged downstream of the grille, the skirt being 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 most preferably the diameters of the skirt and the grille are substantially the same or even the same.

[0033] The effect of the skirt is that, if noise is already generated, its propagation in the radial direction is terminated, since the noise waves are reflected back to the center of the airflow and are largely inaudible to persons at a certain distance from the silencer.

[0034] In other words, the skirt directs the generated noise into the direction of the airflow, rather than towards the observer, thus acting as a barrier. Thus, the propagation of noise in the radial direction (of the muffler / grille) is terminated, since the skirt reflects the noise waves back towards the center of the airflow leaving the grille, i.e., streamlines the noise propagation.

[0035] If the muffler and the skirt are oriented in the ground direction (ie pointing in the direction of the ground), the noise may be directed mainly to the ground and not to the ears of an observer (eg 7 m from the muffler).

[0036] 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 mixing surface is usually tapered around the compressed air, i.e. high-speed air flow), and thus reduces the surface for generating turbulence. Therefore, the skirt is particularly effective in situations where noise is already generated.

[0037] Furthermore, the skirt is adapted to terminate the mixing of the high-speed airflow with the ambient air in the area where the jet has not yet fully developed, since the grille would generate many individual jets.

[0038] Preferably, the cross section of the skirt is cylindrical or polygonal, preferably hexagonal, or a combination of different cross sections. Such a cross section is most effective for achieving the effect of the skirt.

[0039] Preferably, the skirt has a constant cross-sectional area over its length, or its cross-sectional area increases or decreases over the length of the skirt in the downstream direction.

[0040] Likewise, the cross-sectional area refers to the area through which the airflow flows as it passes through the skirt.

[0041] In case the cross-sectional area increases over the length of the skirt, the skirt acts as a diffuser. In case the cross-sectional area decreases over the length of the skirt, the skirt acts as a flow collector. The shape can be adapted to the flow cone formed in the mixing area of ​​the compressed air and the ambient air.

[0042] Preferably, the length of the skirt is between 2 mm and 200 mm. The preferred minimum length is at least 5 mm, even more preferably at least 10 mm, and even more preferably at least 20 mm, most preferably at least 50 mm. These lengths have proven to be most effective in achieving the effect of the skirt.

[0043] 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 is most effective in directing the generated noise into the direction of the airflow. In addition, this ensures that the airflow velocity in the skirt is not increased, which might otherwise generate additional noise.

[0044] The use of the silencer according to the invention is for use in a brake system, preferably for a brake system of a commercial vehicle, more preferably for a brake system of an electric commercial vehicle. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] Advantageous embodiments of the present application will be described in more detail below with reference to the accompanying drawings.

[0046] Figure 1 The overall structure of the silencer according to the present invention is shown. Figure 1 a) to Figure 1 d) shows a different embodiment, which differs in particular in the shape of the channels.

[0047] Figure 2 The structure of the grid with channels is shown in more detail - Figure 2 a) to Figure 2 d) and Figure 2 f) to Figure 2 i) shows different channel shapes, Figure 2 e) shows the Figure 2d) isometric view of the structure.

[0048] Figure 3 The physical background of the flow resistance of objects of different shapes is shown.

[0049] Figure 4 The velocity profile, wake and vortex are shown. Figure 4 a) shows a silencer according to the prior art, Figure 4 b) and Figure 4 c) shows the effect of channel length and shape on airflow.

[0050] Figure 5 Shown is a muffler with a skirt - in Figure 5 a), the skirt acts as a flow collector; Figure 5 In b), the skirt acts as a diffuser.

[0051] Figure 6 The velocity profile is shown when a skirt is used downstream of the channels of the grille. Figure 6 a) shows the velocity profile just downstream of the grille, Figure 6 b) shows the further development of the velocity profile within the entire skirt. DETAILED DESCRIPTION

[0052] exist Figure 1 In the embodiment of the present invention, the overall structure of the silencer 1 is described. The silencer 1 comprises a housing 2 with an inlet opening 3, through which compressed air can flow. In the silencer 1, there is a chamber 4, which is filled with a silencer 5, which is a fiber material in this embodiment. In the end of the silencer 1 in the flow direction, there is a grille 6, which has a plurality of 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 until the outlet 7c.

[0053] exist Figure 1 In a), the channel 7 is polygonal in shape. The cross section of the wall 7d between the channels 7 is rhombus-shaped.

[0054] exist Figure 1 b), the channel 7 is circular, 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 is quasi-elliptical.

[0055] Figure 1c) 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 and the outlet 7c of the channel 7. 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.

[0056] exist Figure 1 d), an embodiment is shown, 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 and the inlet 7a of the channel 7. 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 is carrot-shaped.

[0057] Figure 2 a) shows a top view of a grid 6 with a plurality of hexagonal channels 7a. Figure 2 b), the same structure is shown, but with a hexagonal Figure 2 a) is larger. Figure 2 In c), a further larger channel 7a is shown (still hexagonal, but with a larger cross-sectional area). Figure 2 d) shows a structure where the walls of the channels are tapered, but still hexagonal. Figure 2 e) shows the Figure 2 d) isometric view of a grille 6, which also has hexagonal channels 7. In this embodiment, the walls 7d separating the channels 7 are very thin (e.g., between 1 and 4 mm). A thickness of less than 1 mm would result in insufficient structural strength, while a thickness of more than 4 mm would excessively reduce the cross-sectional area available for airflow.

[0058] Figure 2 f) shows a grille 6 with channels 7 having a diamond-shaped cross-sectional area, which also maximizes the cross-sectional area available for airflow. Figure 2 g) and Figure 2 h) shows a grille 6 with channels 7 having a triangular cross-sectional area, which also maximizes the cross-sectional area available for airflow. Figure 2 i) shows a grid 6, the channels 7 of which are arranged in a star shape. In this case, channels 7 with a pentagonal cross-sectional area are used.

[0059] Figure 3 The physical background of the flow resistance of objects O of different shapes is shown. Figure 3 In a), there is a thin wall, and it can be seen that there is a dead volume behind the object O, and a vortex is also generated. Figure 3In b), the object O has the shape of a ball or sphere, and it can be seen that there is still dead volume, but it is different from Figure 3 a) produces less vortex than the Figure 3 In c), the object O is in a combined shape, a teardrop shape (the wider part faces the flow direction). Figure 3 a) and Figure 3 Compared to b), there is much less dead volume and vortexing. Figure 3 d) shows a very thin object that is long in the flow direction. It can be seen that there is almost no dead volume and no vortex is generated. Therefore, Figure 3 d) has the smallest flow resistance.

[0060] Figure 4 a) shows the airflow 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 airflow in each channel 7 and a merging zone is just downstream of the grille 6. In the merging zone, the compressed air and the ambient air mix.

[0061] The velocity profile of the air flow leaving the channel 7 is conical.

[0062] Wake separation occurs between the cones. This causes vortices and thus high turbulence. The mixing of compressed air with ambient air creates noise.

[0063] exist Figure 4 b), a thicker grid 7 is shown (with Figure 4 a). You can see that there is less drag, less eddy currents in the airflow. There is still wake separation in the merging region, but the noise is reduced.

[0064] Figure 4 c) shows a long strip of grille 6 (with Figure 4 b) is similar, but its shape is that the cross-sectional area of ​​the channel decreases from the inlet to the smallest diameter part and then increases again, that is, a nozzle-like structure. It can be seen that the resistance is further reduced in this embodiment, and there is a small amount of wake separation in the merging area, but it can be seen that the flow core is very wide, so less turbulence is generated, resulting in almost no noise.

[0065] Figure 5 An embodiment is shown in which the silencer 1 has a skirt 8. All other parts are the same as Figure 1 The same as in. Figure 5 In a), the cross-sectional area (and diameter) of the skirt decreases along the flow direction, acting as a flow collector; Figure 5In b), the cross-sectional area (and therefore the diameter) of the skirt increases in the direction of flow, thus acting as a diffuser.

[0066] Figure 6 The flow velocity profile is shown when a skirt 8 is used downstream of the channels 7 of the grid 6 .

[0067] Figure 6 a) shows the velocity profile just 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. Wake separation occurs between these flow cores. The skirt 8 acts as a barrier, reflecting the noise into the middle of the airflow. Very little noise can reach an observer or receiver (e.g. a microphone) radially spaced from the skirt 8.

[0068] Figure 6 b) shows the further development of the flow velocity profile within the entire skirt 8. Here, it can be seen that the individual flow cores form a further developed flow core downstream of the skirt 8. In this area, there is no longer turbulence. Very little noise can reach an observer or receiver (e.g. a microphone) radially spaced from the skirt 8.

[0069] Reference numerals

[0070] 1 Silencer

[0071] 2 Housing

[0072] 3 Entrance opening

[0073] 4 Chambers

[0074] 5. Silencer

[0075] 6 Grille

[0076] 7 channels

[0077] Entrance to channel 7a

[0078] 7b Smallest diameter part

[0079] Exit of channel 7c

[0080] 7d Channel wall

[0081] 8 Skirt

[0082] O Object

[0083] B. Braking system

Claims

1. A silencer (1) for a compressed air system, comprising: a housing (2) with an inlet opening (3) for a compressed gas flow; Chamber (4); A silencer (5) disposed in the chamber (4); a grid (6) comprising at least two channels (7) through which the compressed air flow is adapted to leave the chamber (4), wherein at least two channels (7) have a length of at least 3 mm, The cross-sectional areas of 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) to the channel outlet (7c).

2. The silencer (1) according to claim 1, wherein: The length of the at least two channels (7) is between 4 mm and 200 mm, preferably at least 5 mm, more preferably at least 7 mm, most preferably at least 10 mm.

3. The silencer (1) according to claim 1 or 2, wherein: The effective surface area ratio of the grid (6) is between 60% and 90%, preferably above 80%.

4. The silencer (1) according to any one of claims 1 to 3, wherein: The sound-absorbing device (5) comprises a fibrous material.

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

6. The silencer (1) according to any one of claims 1 to 4, wherein: At least two channels (7) have circular cross-sections.

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

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

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

10. The silencer (1) according to any one of claims 1 to 7, wherein: The cross-sectional area of ​​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 the cross-sectional area of ​​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).

11. The silencer (1) according to any one of the preceding claims, wherein: The silencer (1) further comprises a skirt (8) arranged downstream of the grille (6), wherein the skirt (8) is adapted to guide the compressed gas out of the channel (7) of the grille (6).

12. The muffler according to claim 11, wherein: The cross section of the skirt (8) is cylindrical or polygonal, preferably hexagonal; or a combination of different cross sections.

13. The silencer according to claim 11 or 12, wherein: The skirt (8) has a constant cross-sectional area, or its cross-sectional area increases or decreases over the length scale of the skirt (8) towards the downstream direction.

14. The silencer according to any one of claims 11 to 13, 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, even more preferably at least 20 mm, most preferably at least 50 mm.

15. The silencer according to any one of claims 11 to 14, 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).

16. Use of the 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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