GB2572644A

GB2572644A - An attenuator for a fluid duct

Info

Publication number: GB2572644A
Application number: GB1805786.9A
Authority: GB
Inventors: Reucroft Laurence
Original assignee: Jaguar Land Rover Ltd
Current assignee: Jaguar Land Rover Ltd
Priority date: 2018-04-06
Filing date: 2018-04-06
Publication date: 2019-10-09
Anticipated expiration: 2038-04-06
Also published as: GB2572644B; GB201805786D0

Abstract

An attenuator 100 comprises a fluid duct 110 having a wall 112, an inlet 114 and an outlet 116. An enclosure 120 surrounds at least a portion of the fluid duct and defines a chamber 122. The fluid duct has at least one perforation 130 to provide fluid communication between the fluid duct and the chamber. At least an area of the fluid duct containing a majority of the total area of the perforation is located within a first portion of the fluid duct. The first portion extends over less than or equal to 25% of the total length of the fluid duct surrounded by the enclosure. The perforation is at a relative axial position between the fluid duct and the enclosure to provide an acoustic transmission line of predetermined length. A motor vehicle exhaust system (80, fig 1) comprises the attenuator, where the fluid duct is an exhaust pipe and one of the axial length of the chamber, an axial position of the chamber relative to the exhaust pipe, or the axial position of the perforation is predetermined based on the acoustic characterisation of the exhaust system. A motor vehicle (50, fig 1) comprises the attenuator or exhaust system.

Description

AN ATTENUATOR FOR A FLUID DUCT

TECHNICAL FIELD

The present invention relates to an attenuator for a fluid duct and particularly, but not exclusively, the air exhaust duct of an internal combustion engine of a vehicle. Aspects of the invention relate to an attenuator, to a motor vehicle exhaust system and to a motor vehicle.

BACKGROUND

Vehicle engines require an exhaust duct to remove combustion gases from the engine. The size, shape and routing of this duct is determined by the maximum engine air flow requirement, and by space and packaging requirements for other vehicle equipment.

Air flow confined in the exhaust duct tends to generate noise and may also generate vibration of the vehicle structure via the mountings of the duct. The frequency range of such noise and vibration tends to be restricted to relatively low frequencies, and at certain frequencies the air in the duct and/or the duct itself may resonate so as to amplify noise and vibration.

Noise and vibration associated with the exhaust duct can be noticeable to occupants of the vehicle, and it would be desirable to provide attenuation. Insulation and muffling provide one possible solution, but the increase in overall duct size may be difficult to accommodate in a congested vehicle architecture. Furthermore it may be impossible to insulate the duct over the entire length thereof.

Attenuators are used on fluid ducts so as to reduce or cancel unwanted noises. One such example are exhaust resonators. Exhaust resonators are used for reducing the amount of noise emitted by the exhaust system of an internal combustion engine (see W02004029561 for an example).

What is required is a compact device for attenuating noise and vibration over a targeted frequency band, which is economical to manufacture, and which can fit with the vehicle architecture. Furthermore this compact device should be able to be tuned without substantial change of overall size and position within the vehicle architecture.

The present invention aims to address one or more of the above problems.

SUMMARY OF THE INVENTION

Aspects and embodiments of the invention provide an attenuator, a motor vehicle exhaust system and a motor vehicle as claimed in the appended claims.

According to an aspect of the invention, there is provided an attenuator comprising: a fluid duct having a wall, an inlet and an outlet; and an enclosure surrounding at least a portion of the fluid duct, and defining a chamber. The fluid duct comprises at least one perforation to provide fluid communication between the fluid duct and the chamber. At least an area of the fluid duct containing a majority of the total area of the at least one perforation is located within a first portion of the fluid duct. The first portion extends over less than or equal to 25% of the total length of the fluid duct surrounded by the enclosure.

The first portion of the fluid duct may be located closer to a first end of the enclosure than to a second end of the enclosure.

The first portion of the fluid duct may be located within a second portion of the fluid duct, the second portion extending from the first end of the enclosure towards the second end of the enclosure. The second portion extends over less than or equal to 45% of the total length of the fluid duct surrounded by the enclosure.

The fluid duct may be substantially unperforated between the first portion of the fluid duct and the second end of the enclosure.

The at least one perforation may comprise at least one first perforation, each of the at least one first perforation being provided at a first relative axial position between the fluid duct and the enclosure, so as to provide an acoustic transmission line of predetermined length within the chamber.

All, or substantially all, perforations between the duct and the chamber may be provided at or near the same relative axial position. Where multiple perforations are provided, these may be provided in a group, the group being at, or centred on, the relative axial position. The fluid duct may be substantially unperforated within the enclosure except at (or near) a single axial position. If other perforations are provided at other axial positions, the benefits of the present technique can still be achieved where substantially all, or at least a majority of, the fluid communication between the fluid duct and the enclosure is provided via perforations at the single axial position.

An acoustic transmission line is essentially a duct which acts as a guide for sound waves and is used to transmit sound from one end of the duct to the other. The length of an acoustic transmission line is tuned according to the wavelength of the sound to be transmitted. In use, the air contained in the chamber resonates at its natural frequency. The chamber is tuned, i.e. its length, volume etc. is selected, so that the natural frequency of the air contained in the chamber is such that it cancels out the frequency of the noise in the exhaust gas which is required to be cancelled.

The length of the chamber may be tuned to be one quarter of the wavelength of the frequency to be attenuated.

The enclosure may have a tapered wall and an annular end wall so as to define a tapered chamber. In embodiments of the invention wherein the first portion of the fluid duct is located closer to a first end of the enclosure than to a second end of the enclosure, the annular end wall may be located at the first end of the enclosure to provide a tapered transmission line. Alternatively, the annular end wall may be located at the second end of the enclosure to provide an expanding transmission line.

For a given wavelength to be cancelled, a shorter tapered or expanding transmission line resonator is required compared with a conventional resonator chamber of constant cross-section. This means that the resonator can be packaged within a smaller space within a vehicle. The tapered chamber is also effective over a larger frequency span than a chamber of constant cross-section. Furthermore, the expanding chamber provides a larger cancellation effect at the tuned frequency relative to a chamber of constant cross-section of the same length.

The annular end wall may be a first annular end wall and the enclosure may further comprise a second annular end wall, the second annular end wall being located at the other of the first or second end of the enclosure to the end of the enclosure at which the first annular end wall is located.

The enclosure may have a taper ratio, wherein the taper ratio is within the range of less than or equal to 20 and greater than 1, less than or equal to 10 and greater than 1, or less than or equal to 15 and greater than 5.

A plurality of perforations may be provided, distributed circumferentially about the fluid duct.

Each perforation of the plurality of perforations may be spaced circumferentially equidistantly from each adjacent perforation. Alternatively, the plurality of perforations may be provided as at least one circumferential group of perforations, the circumferential group extending about a portion of the circumference of the pipe.

In embodiments of the invention in which the at least one perforation comprises at least one first perforation, the at least one perforation may further comprise at least one further perforation providing fluid communication between the fluid duct and the chamber, each of the at least one further perforation being provided at a respective further relative axial position between the fluid duct and the enclosure, so as to provide an acoustic transmission line of predetermined length within the chamber.

At least one of the at least one perforation may comprise an elongate slot.

An insulating material may be provided within the enclosure. The insulating material may be arranged to extend over less than or equal to two-thirds of the length of the chamber. The insulating material is provided to dampen any remaining sound, not cancelled by the chamber - typically to damp higher harmonics resulting from the first half wave and every second resonance thereafter.

The insulating material may be arranged to extend from a first end of the chamber towards a second end of the chamber. The insulating material may be arranged to fill the entire volume of the length of the chamber over which it extends. Alternatively, the insulating material may be arranged to partially fill the volume of the length of the chamber over which it extends.

According to another aspect of the invention, there is provided a motor vehicle exhaust system comprising an attenuator as hereinbefore described.

According to another aspect of the invention, there is provided a motor vehicle exhaust system comprising an attenuator as hereinbefore described, wherein the fluid duct is an exhaust pipe, and wherein one of the axial length of the chamber, an axial position of the chamber relative to the exhaust pipe, or the axial position of the at least one perforation is predetermined based upon the acoustic characterization of the motor vehicle exhaust system in use.

According to another aspect of the invention, there is provided a motor vehicle comprising the attenuator or motor vehicle exhaust system as hereinbefore described.

Within the scope of this application it is expressly intended that the various aspects, embodiments, examples and alternatives set out in the preceding paragraphs, in the claims and/or in the following description and drawings, and in particular the individual features thereof, may be taken independently or in any combination. That is, all embodiments and/or features of any embodiment can be combined in any way and/or combination, unless such features are incompatible. The applicant reserves the right to change any originally filed claim or file any new claim accordingly, including the right to amend any originally filed claim to depend from and/or incorporate any feature of any other claim although not originally claimed in that manner.

BRIEF DESCRIPTION OF THE DRAWINGS

One or more embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

Figure 1 is a side elevation of a motor vehicle;

Figure 2 is a schematic isometric view of the attenuator of the present invention;

Figure 3 is a schematic cross sectional view of the attenuator of Figure 2;

Figure 4 is a schematic cross sectional view of an attenuator in accordance with an alternate embodiment; and

Figure 5 is a schematic side elevation of fluid duct in accordance with an alternate embodiment.

DETAILED DESCRIPTION

A motor vehicle 50 is provided with a bonnet 60 arranged at a front end of the motor vehicle 50, and an underside 70 extending between the front end and a rear end of the motor vehicle 50. An engine (not shown in Figure 1) is housed under the bonnet 60. An exhaust system 80 connects the engine to an exhaust outlet 90 adjacent the rear end of the motor vehicle 50. The exhaust system 80 extends in part along the underside 70.

Referring to Figures 2 and 3 the attenuator 100 comprises a fluid duct 110 and an enclosure 120.

The fluid duct 110 is a cylindrical pipe 111. The pipe 111 has a wall 112, an inlet 114 and an outlet 116. The pipe 111 has longitudinal axis 118 which extends between the inlet 114 and the outlet 116.

The pipe 111 is provided with a plurality perforations 130 provided at a single axial position along the longitudinal axis 118. The perforations 130 are circumferentially arranged about the pipe 111. Each perforation is spaced equidistantly from each adjacent perforation. In an alternate embodiment, the plurality of perforations 130 are provided as at least one group of perforations 130, the or each group extending about a portion of the circumference of the pipe. In yet a further alternate embodiment, the at least one perforation 130 comprises an elongate slot.

The enclosure is frustoconical. The enclosure 120 has a tapered wall 124, a first annular end wall 126 and a second annular end wall 128.

The enclosure 120 is arranged co-axially with the pipe 111 and surrounds the pipe

111. The first annular end wall 126 is arranged between the inlet 114 and the second annular end wall 128, and the second annular end wall 128 is arranged between the first annular end wall 126 and the outlet 116. The skilled person will realize that the pipe 111 forming the fluid duct 110 of the exhaust system 80, will in reality be far longer than shown in the schematic of Figure 3. In fact, the fluid duct 110 will extend from an engine (typically at the front of the vehicle) towards an exhaust outlet 90 (typically at the rear of the vehicle - as described above). The first annular end wall 126 and the second annular end wall 128 are of different sizes.

The enclosure 120 is arranged with the pipe 111 such that the perforations 130 are arranged proximate the first annular end wall 126. The term ‘proximate the first annular end wall’ should be construed to mean closer to the first annular end wall than the second annular end wall 128. For example, the perforations 130 may be arranged within the first 50% of the distance between the first annular end wall 126 and the second annular end wall 128. Alternatively, the perforations 130 may be arranged within the first 10%, 20%, 30% or 40% of the distance between the first annular end wall 126 and the second annular end wall 128.

The enclosure 120 is fluidly sealed relative to the pipe 111. The enclosure 120 defines a tapered chamber 122. In an alternate embodiment, an insulating material is provided within the chamber 122. The insulating material may be arranged to fill approximately two-thirds of the length of the chamber 122.

The perforations 130 provide fluid communication between the pipe 111 and the chamber 122. The perforations 130 are provided at a single relative axial position between the pipe 111 and the enclosure 120. The at least one perforation 130 is provided adjacent the larger of the first and second annular end walls 126, 128 to provide a tapered transmission line.

The distance between the perforations 130 and first annular end wall 126 of the enclosure 120 is L This arrangement provides an acoustic transmission line of length L within the chamber 122.

The enclosure 120 has a taper ratio defined as the cross-sectional area of the annulus formed by the larger of the first annular end wall 126 or the second annular end wall 128 divided by the cross-sectional area of the annulus formed by the smaller of the first annular end wall 126 or the second annular end wall 128.

The taper ratio is within the range of less than or equal to 20 and greater than 1. In an alternate embodiment the taper ratio is within the range of less than or equal to 10 and greater than 1 .In a further alternate embodiment the taper ratio is within the range of less than or equal to 15 and greater than 5.

The fluid duct 110 is arranged to receive exhaust gases from an engine of a vehicle 50 as part of a vehicle exhaust system 80. The attenuator 100 is positioned, for example on the underside 70 of the vehicle so that the fluid duct 110 is the exhaust pipe 111 of the exhaust system 80. One of the axial length of the chamber 122, an axial position of the chamber 122 relative to the exhaust pipe 111, and the axial position of the at least one perforation 130 is predetermined based upon the acoustic characterization of the motor vehicle exhaust system 80 in use.

A further embodiment is shown in Figure 4. Similar reference numerals have been used to identify features in common with embodiments described with respect to Figures 2 and 3, the reference numbers being prefixed with a 2 to denote they relate to the further embodiment.

The attenuator 200 of Figure 4 is substantially similar to the attenuator 100 of Figures 2 and 3, such that only substantial differences shall be described.

The attenuator 200 is arranged with the first annular end wall 226 arranged proximate the inlet 214 and the second annular end wall 228 arranged proximate the outlet 216, however, the at least one perforation 230 is provided adjacent the smaller of the first and second annular end walls 126, 128 to provide an expanding transmission line.

A further embodiment of a fluid duct 310 is shown in Figure 5. Similar reference numerals have been used to identify features in common with embodiments described with respect to Figures 2, 3 and 4, the reference numbers being prefixed with a 3 to denote they relate to the further embodiment.

The fluid duct 310 is a cylindrical pipe having a longitudinal axis 318. The pipe is provided with perforations 330a, 330b, 330c, circumferentially arranged about the pipe. The perforations comprise a plurality of first perforations provided at a first relative axial position between the fluid duct and the enclosure, and a plurality of further perforations provided at respective further relative axial position between the fluid duct and the enclosure. In the embodiment of figure 5, the perforations comprise a plurality of first perforations 330a provided at a first relative axial position between the fluid duct and the enclosure, and a plurality of second and third perforations 330b, 330c provided at second and third relative axial position between the fluid duct and the enclosure respectively.

It will be appreciated that although the attenuator 300 is depicted as being arranged such that the perforations 330a, 330b, 330c are proximate the first annular end wall 326, the attenuator 300 could alternatively be arranged such that the perforations 330a, 330b, 330c are proximate the second annular end wall 328. The term ‘proximate the first annular end wall’ should be construed to mean closer to the first annular end wall than the second annular end wall, that is all of the plurality of 10 perforations 330a, 330b, 330c are arranged closer to the first annular end wall than the second annular end wall. The term ‘proximate the second annular end wall’ should be construed to mean the inverse.

Claims

1. An attenuator, comprising:

a fluid duct having a wall, an inlet and an outlet; and an enclosure surrounding at least a portion of the fluid duct, and defining a chamber; wherein the fluid duct comprises at least one perforation to provide fluid communication between the fluid duct and the chamber; wherein at least an area of the fluid duct containing a majority of the total area of the at least one perforation is located within a first portion of the fluid duct; wherein the first portion extends over less than or equal to 25% of the total length of the fluid duct surrounded by the enclosure.

2. The attenuator according to claim 1, wherein the first portion of the fluid duct is located closer to a first end of the enclosure than to a second end of the enclosure.

3. The attenuator according to claim 2, wherein the first portion of the fluid duct is located within a second portion of the fluid duct, the second portion extending from the first end of the enclosure towards the second end of the enclosure; wherein the second portion extends over less than or equal to 45% of the total length of the fluid duct surrounded by the enclosure.

4. The attenuator according to claim 2 or claim 3, wherein the fluid duct is substantially unperforated between the first portion of the fluid duct and the second end of the enclosure.

5. The attenuator according to any preceding claim, wherein the at least one perforation comprises at least one first perforation, each of the at least one first perforation being provided at a first relative axial position between the fluid duct and the enclosure, so as to provide an acoustic transmission line of predetermined length within the chamber.

6. The attenuator according to any preceding claim, wherein the enclosure has a tapered wall and an annular end wall so as to define a tapered chamber.

7. The attenuator according to claim 6, when dependent on claim 2, wherein the annular end wall is located at the first end of the enclosure to provide a tapered transmission line.

8. The attenuator according to claim 6, when dependent on claim 2, wherein the annular end wall is located at the second end of the enclosure to provide an expanding transmission line.

9. The attenuator according to claims 7 or claim 8, wherein the annular end wall is a first annular end wall and the enclosure further comprises a second annular end wall, the second annular end wall being located at the other of the first or second end of the enclosure to the end of the enclosure at which the first annular end wall is located.

10. The attenuator according to any of claims 6 to 9, wherein the enclosure has a taper ratio, wherein the taper ratio is within the range of less than or equal to 20 and greater than 1, less than or equal to 10 and greater than 1, or less than or equal to 15 and greater than 5.

11. The attenuator according to any preceding claim, wherein a plurality of perforations are provided, distributed circumferentially about the fluid duct.

12. The attenuator according to claim 11, wherein each perforation of the plurality of perforations is spaced circumferentially equidistantly from each adjacent perforation.

13. The attenuator according to claim 11, wherein the plurality of perforations are provided as at least one group of perforations, the or each group extending about a portion of the circumference of the fluid duct.

14. The attenuator according to any of claims 6 to 13, when dependent on claim 5, wherein the at least one perforation comprises at least one further perforation providing fluid communication between the fluid duct and the chamber, wherein each of the at least one further perforation is provided at a respective further relative axial position between the fluid duct and the enclosure, so as to provide an acoustic transmission line of predetermined length within the chamber.

15. The attenuator according to any preceding claim, wherein at least one of the at least one perforation comprises an elongate slot.

16. The attenuator according to any preceding claim, wherein an insulating material is provided within the chamber.

17. The attenuator according to claim 16, wherein the insulating material is arranged to extend over less than or equal to two-thirds of the length of the chamber.

18. The attenuator according to claim 16 or claim 17, wherein the insulating material is arranged to extend from a first end of the chamber towards a second end of the chamber.

19. A motor vehicle exhaust system comprising the attenuator according to any of claims 1 to 18.

20. A motor vehicle exhaust system comprising an attenuator according to any of claims 1 to 18, wherein the fluid duct is an exhaust pipe, and wherein one of the axial length of the chamber, an axial position of the chamber relative to the exhaust pipe, or the axial position of the at least one perforation is predetermined based upon the acoustic characterization of the motor vehicle exhaust system in use.

21. A motor vehicle comprising the attenuator according to any of claims 1 to 18, or a motor vehicle exhaust system according to claim 19 or claim 20.