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1. WO2019059942 - ACOUSTIC VOLUME IN HOT-END OF EXHAUST SYSTEMS

Note: Text based on automatic Optical Character Recognition processes. Please use the PDF version for legal matters

[ EN ]

ACOUSTIC VOLUME IN HOT-END OF EXHAUST SYSTEMS

BACKGROUND OF THE INVENTION

[0001] An exhaust system conducts hot exhaust gases generated by an engine through various exhaust components to reduce emissions, improve fuel economy, and control noise. Short exhaust systems, such as those encountered with hybrid vehicles or rear engine vehicles for example, often have insufficient volume and/or length to achieve a desired tailpipe noise level in combination with acceptable back pressure levels. Further, as gasoline particulate filter (GPF) technology emerges into the market, corresponding increases in exhaust system back pressure will need to be offset in order to avoid adverse effects on fuel economy or performance.

[0002] In addition to addressing issues raised by the introduction of GPF technology, other emerging powertrain technologies are requiring the industry to provide even more stringent noise reduction. The frequencies that need to be attenuated are being pushed to lower and lower frequencies not previously having to have been addressed. One traditional solution to attenuate such frequencies is to provide more internal volume; however, due to tight packaging constraints, the area required for such volume is not available. Another solution to attenuate these lower frequencies is to use valves; however, valves drive a higher back pressure at lower revolutions-per-minute, which is not desirable. As such, there is a need for unique acoustic solutions that are more efficient from a volume perspective and have less impact from a back pressure aspect.

SUMMARY OF THE INVENTION

[0003] In one exemplary embodiment, a vehicle exhaust system includes a component housing defining an internal cavity, a first exhaust gas treatment element positioned within the internal cavity, a second exhaust gas treatment element positioned within the internal cavity and axially spaced from the first exhaust gas treatment element by a gap, and a resonator volume in communication with the internal cavity.

[0004] In a further embodiment of the above, the resonator volume is formed between an outer surface of the component housing and an inner surface of a resonator housing that at least partially surrounds the component housing, and the system further includes at least one resonator connection in communication with the resonator volume, wherein the resonator connection is located at the gap.

[0005] In a further embodiment of any of the above, the resonator volume is formed between an outer surface of the component housing and an inner surface of a resonator housing that at least partially surrounds the component housing, and the system further includes an inlet cone positioned at one end of the component housing and an outlet cone positioned at an opposite end of the component housing. The system also includes at least one resonator connection in communication with the resonator volume, and wherein the at least one resonator connection is located at one of the inlet and outlet cones.

[0006] In a further embodiment of any of the above, the resonator volume is enclosed within a resonator housing and further including at least one connection of the resonator housing to the component housing.

[0007] In a further embodiment of any of the above, the resonator housing is located externally of the component housing.

[0008] In a further embodiment of any of the above, the at least one resonator comprises a plurality of resonator connections in communication with a resonator volume.

[0009] In a further embodiment of any of the above, the resonator volume is in parallel with the first and second gas treatment elements.

[0010] In another exemplary embodiment, a vehicle exhaust system includes a first housing defining an internal cavity, at least one exhaust gas treatment element positioned within the internal cavity, a resonator volume spaced radially outwardly of the at least one exhaust gas treatment element, and a resonator connection to provide communication between the resonator volume and the internal cavity.

[0011] In a further embodiment of any of the above, a second housing defines the resonator volume, and wherein the resonator connection is either located internally within the second housing or externally of the second housing.

[0012] In another exemplary embodiment, a vehicle exhaust system includes a component housing defining an internal cavity, an inlet coupled to an upstream end of the component housing, an outlet coupled to a downstream end of the component housing, a first exhaust gas treatment element positioned within the internal cavity, and a second exhaust gas treatment element positioned within the internal cavity and separated from the first exhaust gas treatment element by a gap. The system further includes a resonator

volume in communication with the internal cavity and a plurality of resonator connections in communication with the resonator volume.

[0013] In a further embodiment of any of the above, the second exhaust gas treatment element is axially spaced from the first exhaust gas treatment element by the gap such that the first and second exhaust gas treatment elements are coaxial, and wherein the plurality of resonator connections comprises at least a first resonator connection located at the gap and a second resonator connection located at the inlet or outlet.

[0014] In a further embodiment of any of the above, the resonator volume is external to the component housing.

[0015] In a further embodiment of any of the above, the second exhaust gas treatment element is in parallel with the first exhaust gas treatment element such that the first and second exhaust gas treatment elements are non-coaxial, and wherein the plurality of resonator connections comprises at least a first resonator connection located at the gap and a second resonator connection located at the inlet or outlet.

[0016] These and other features of this application will be best understood from the following specification and drawings, the following of which is a brief description.

BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 schematically illustrates a vehicle exhaust system and shows standing pressure waves generated by the system.

[0018] Figure 2 shows one example of a hot end component of the system of Figure 1 and which includes the subject invention.

[0019] Figure 3 shows another example embodiment.

[0020] Figure 4 shows another example embodiment.

[0021] Figure 5A shows another example embodiment.

[0022] Figure 5B shows another example embodiment.

[0023] Figure 5C shows another example embodiment.

[0024] Figure 6A shows another example embodiment.

[0025] Figure 6B shows another example embodiment.

[0026] Figure 6C shows another example embodiment.

[0027] Figure 7 shows another example embodiment.

DETAILED DESCRIPTION

[0028] Figure 1 shows a schematic representation of a vehicle exhaust system 10 as a long pipe that conducts hot exhaust gases generated by an engine 12 through various exhaust components to reduce emission and control noise as known. The various exhaust components can include one or more of the following: pipes, filters, valves, catalysts, mufflers etc. The exhaust system 10 includes a hot end 14 that is located immediately downstream of the engine 12 and a cold end 16 that is downstream of the hot end 14. The long pipe is considered closed at an engine end 18 and open at an opposite end 20 where, after passing though the various exhaust components, the engine exhaust gas exits the exhaust system 10 to atmosphere.

[0029] Exhaust components at the hot end 14 can include, for example, exhaust gas treatment elements such as a diesel oxidation catalyst (DOC), a diesel particulate filter (DPF), a gasoline particulate filter (GPF), and a selective catalytic reduction (SCR) catalyst that are used to remove contaminants from the exhaust gas as known. Exhaust gases pass through these components and enter the cold end 16 where the exhaust gas exits the system 10 via a tailpipe. The described exhaust components can be mounted in various different configurations and combinations dependent upon vehicle application and available packaging space.

[0030] As discussed above, Figure 1 shows the exhaust system schematically illustrated as a long pipe that is closed at the engine end 18 and open at the opposite end 20 to atmosphere. Acoustic waves will travel from their source, which is the engine 12, down the pipe and then the exit to atmosphere. When the acoustic wave encounters a boundary of some form, e.g. an impedance change, then some fraction of the wave will be reflected back the way it came and the remaining fraction will continue. In the case of a closed-open pipe such as shown in Figure 1 , this reflection occurs at the exit of the pipe. The reflected wave interferes with the incident wave and at certain frequencies, which are a function of the length of the pipe, constructively interfere to increase the level of the wave and also to make the wave appear stationary. Such waves are called standing waves and in the case of a closed-open pipe the frequencies of such waves may be calculated with the equation below.

[0031] Fn = (nc)/(4L) where:

[0032] fn = resonant frequency of standing wave n (Hz)

[0033] n = ordinal number of standing wave

[0034] c = speed of sound (m/s)

[0035] L = length of closed-open pipe (m)

[0036] The chart of Figure 1 shows the first three standing pressure waves for a closed-open pipe of 4 meters in length. In this example, the resonances occur at 22, 65 and 108 Hz. As shown, for each standing wave the pressure is a maximum (anti-node) at the closed engine end 18 and a minimum (node) at the open end 20 to atmosphere. The ideal place for a Helmholtz resonator is at a pressure anti-node. As such, the best position for a resonator is at the engine outlet; however, Helmholtz resonators are not traditionally used in the hot end 14 of exhaust systems 10. The subject invention provides a Helmholtz resonator in the hot end 14 to provide improved acoustic benefits over the same resonator as placed in the cold end 16 as the subject resonator is closer to the anti-node for all system acoustic resonances.

[0037] It has been shown through testing and simulations that a Helmholtz Resonator, such as an acoustic volume of the order of 2 to 4 L in communication with the exhaust flow via a neck pipe for example, that is positioned in the hot end 14 between a turbo outlet and a converter, or between converter after-treatment elements, provides an acoustic benefit about twice that of a similar amount of volume applied in the cold end 16 (downstream of the after-treatment) with no impact on back pressure. From a tailpipe noise perspective, positioning the Helmholtz resonator as close as possible to the engine 12 provides the best acoustic performance.

[0038] The subject invention proposes packaging one or more Helmholtz Resonators at one of three locations in the hot end 14 of the system 10. For example, the resonator(s) could be located after the manifold or turbo outlet but before the converters, between the converters; and/or after the converters. Various example configurations are discussed below and shown in the accompanying figures.

[0039] Figure 2 shows one example of a hot end component 30 that is situated downstream of the exhaust manifold and turbocharger. The hot end component 30 includes a component housing 32 that defines an internal cavity 34. A first exhaust gas treatment element 36 is positioned within the internal cavity 34 and a second exhaust gas treatment element 38 is positioned within the internal cavity 34 downstream and axially spaced from the first exhaust gas treatment element 36 by a gap 40. A resonator volume 42 enclosed

within a resonator housing 43 is in communication with the internal cavity 34. The resonator housing 43 at least partially surrounds the component housing 32.

[0040] An inlet cone 44 directs flow into the first exhaust gas treatment element 36. The inlet cone 44 receives hot engine exhaust gases from an inlet pipe 46. An outlet cone 48 directs treated exhaust gas flow exiting the second exhaust gas treatment element 38 into an outlet pipe 50. In this example, the component housing 32 defines a center axis A and the inlet cone 44, first exhaust gas treatment element 36, second exhaust gas treatment element 38, and outlet cone 48 are coaxial with the center axis A.

[0041] At least one resonator connection 52 is in communication with the resonator volume 42 within the resonator housing 43. The component housing 32 comprises a center housing portion 54 that encloses the first 36 and second 38 gas treatment elements, an inlet portion 56 that is positioned at one end of the center housing portion 54 to surround the inlet cone 44, and an outlet portion 58 that is positioned at an opposite end of the center housing portion 54 to surround the outlet cone 48. At least one resonator connection 52 is in communication with the resonator volume 42. In the example shown in Figure 2, the resonator connection 52 comprises a Helmholtz neck that is positioned at the gap 40 and is in communication with Helmholtz resonator volume 42. Optionally, or in addition to, the connection point of the resonator connection 52 could be at the inlet 44 or outlet 48 cone as indicated with dashed lines in Figure 2.

[0042] In each of these different configurations, the configuration is sealed such that there is no net flow in the Helmholtz resonator. Hot engine exhaust gas flows in through the inlet pipe 46, expands and slows down as the gas travels through inlet cone 44, passes through the first exhaust gas treatment element 36, and then expands into the gap 40 between the first 36 and second 48 exhaust gas treatment elements. The Helmholtz resonator connection 52 and resonator volume 42 are in parallel with the flow connected at the gap 40. The exhaust gas then contracts and passes through the second exhaust gas treatment element 38 and then expands into the outlet cone 48 before contracting and exiting through the outlet pipe 50.

[0043] The exhaust gas pressure pulsations from the engine travel down through the exhaust system 10 and are modified as they travel through the mechanisms of restriction, reflection, and absorption. When the pulsations reach the gap 40 they cause the exhaust gas in the resonator neck/connection 52 to start moving. For low frequencies this gas can be

considered as a lumped mass. The lumped mass of gas in the resonator neck 52 compresses or rarifies the exhaust gas in the surrounding resonator volume 42. As the lumped mass of gas compresses the resonator volume 42, the volume pressure increases. As the lumped mass of gas rarifies, the volume pressure decreases. The result of this pressure is to push the lumped mass in the opposite direction to which it is travelling. In this way, the resonator volume 42 is acting as a spring and provides a spring-mass system with a tuned frequency. As there is no net flow through the Helmholtz resonator, and as the resonator neck 52 comprises a side-branch arrangement, the impact on back pressure is negligible.

[0044] In the example shown in Figure 2, the resonator volume 42 is formed between an inner surface of the resonator housing 43 and an outer surface of the component housing 32. The resonator volume 42 is concentric with the center axis A such that the resonator housing 43 and resonator volume 42 completely and entirely surrounds an outer circumference of the first 36 and second 38 gas treatment elements. Figure 3 shows an example that is similar to Figure 2 but which comprises an offset configuration. In this example, the resonator volume 42' is offset relative to the component housing 32 such that the resonator housing 43 and resonator volume 42' only partially surrounds an outer circumference of the first 36 and second 38 gas treatment elements.

[0045] Figure 4 shows another example configuration. In this example, a resonator volume 60 is removed from the component 30 and is connected to the component housing 32 by at least one pipe 62. The resonator volume 60 is enclosed within a resonator housing 64 and the pipe 62 connects the resonator housing 64 to the component 30. As such, the resonator housing 64 and volume 60 are located externally of the component housing 32.

[0046] In the example shown in Figure 4, the pipe 62 connects the resonator housing 64 to the inlet portion 56 of the component housing 32. The pipe 62 also optionally connects to the outlet portion 58; however, the inlet portion 56 is preferred as it is located closer to the engine 12. Optionally, or in addition to, an additional pipe or a branch from the pipe 62 could connect the volume 60 to the center housing portion 54 and one of the inlet 56 or outlet 58 portions. Figure 5A shows an example where the external volume 60 is connected to the inlet pipe 46. Figure 5B shows an example where the external volume 60 is connected to the center housing portion 54 and is in communication with the gap 40. Figure

5C shows an example where the external volume 60 is connected to the outlet pipe 50.

[0047] Figures 6A-6C show examples of an internal resonator volume 70 that is in series with the first 36 and second 38 exhaust gas treatment elements. Figure 6A shows an example where the volume 70 is upstream of the first exhaust gas treatment element 36. Figure 6B shows an example where the volume 70 is upstream of the second exhaust gas treatment element 38 and downstream of the gap 40. Figure 6C shows an example where the volume 70 is downstream of the second exhaust gas treatment element 38.

[0048] In another example shown in Figure 7, the first 36 and second 38 gas treatment elements are enclosed within a common housing 80. In this configuration, the first 36 and second 38 exhaust gas treatment elements are non-coaxial and parallel with each other, and are connected by a gap 82 such that exhaust gas exits the first exhaust gas treatment element 36, enters the gap 82, and then enters the second exhaust gas treatment element 38. A plurality of resonator volumes 84 are provided within the housing 80. A plurality of resonator connections 86 are also provided. The housing 80 includes a baffle 88 with an inlet resonator volume 90 coupled to an inlet pipe 92 and an outlet resonator volume 94 coupled to an outlet pipe 96. The housing 80 also includes a second baffle 98 to define a resonator volume at the gap 82.

[0049] Possible locations for the resonator connections 86 are at the inlet resonator volume 90, at the outlet resonator volume 94, and at the resonator volume at the gap 82. The resonator connection 86 associated at the gap 82 can be at a location between the elements 36, 38, at an exit from the first exhaust gas treatment element 36, and/or at an entrance to the second exhaust gas treatment element 38. The resonator connections 86 can be used in any number, and in any combination, as needed to provide the desired acoustic effect.

[0050] The subject invention combines a tuning element with the primary function of acoustic attenuation with a component in the hot end 14 of the exhaust system 10 at a location that is much closer to the pressure anti-node at the engine exhaust outlet than traditional configurations. This provides improved acoustic efficiency with negligible back pressure impact resulting in tailpipe noise / acoustic volume improvement.

[0051] Although an embodiment of this invention has been disclosed, a worker of ordinary skill in this art would recognize that certain modifications would come within the scope of this invention. For that reason, the following claims should be studied to determine the true scope and content of this invention.