Patent Application
20210262374
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.
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 space 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 always acceptable. 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.
In one exemplary embodiment, a vehicle exhaust system includes a component housing defining an internal cavity and at least one exhaust gas treatment element positioned within the internal cavity. A resonator volume is connected in parallel with the internal cavity via at least one resonator element and insulating material is located within the resonator volume.
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.
In a further embodiment of any of the above, an inlet cone is positioned at one end of the component housing and an outlet cone is positioned at an opposite end of the component housing, and wherein the at least one resonator element is located at one of the inlet and outlet cones.
In a further embodiment of any of the above, the at least one resonator element comprises a Helmholtz neck or a perforated portion of at least one of the inlet and outlet cones.
In a further embodiment of any of the above, there is no net flow out of the resonator volume.
In a further embodiment of any of the above, a second exhaust gas treatment element is positioned within the internal cavity and axially spaced from the first exhaust gas treatment element by a gap, and wherein the component housing is located in a hot end of the vehicle exhaust system and is immediately downstream of an engine or turbocharger.
In a further embodiment of any of the above, the at least one resonator element comprises at least one of a Helmholtz neck and perforated portion of the component housing.
In a further embodiment of any of the above, the component housing comprises a center housing portion that encloses the at least one gas treatment element, an inlet portion positioned at one end of the center housing portion, and an outlet portion positioned at an opposite end of the center housing portion, and wherein the at least one resonator element comprises at least one of a pipe or a perforated portion associated with at least one of the center housing portion, inlet portion, and outlet portion.
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 completely surrounds the component housing, and wherein the insulating material completely fills the resonator volume.
In a further embodiment of any of the above, the resonator element is located in the inlet portion.
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 completely surrounds the component housing, and wherein the insulating material only partially fills the resonator volume and is positioned at a location of the at least one resonator element.
In a further embodiment of any of the above, the resonator element is located in the inlet portion and including a perforated baffle positioned at a location between the inlet portion and the center housing portion to separate the resonator volume into an inlet volume at the inlet portion and a remaining volume, and wherein the insulating material only fills the inlet volume.
In a further embodiment of any of the above, the resonator element is located in the inlet portion and including a perforated baffle positioned at a location between the inlet portion and the center housing portion to separate the resonator volume into an inlet volume at the inlet portion and a remaining volume, and wherein a first portion of the insulating material fills the inlet volume and a second portion of the insulating material comprises a layer of insulating material that is attached to an inner surface of the center housing portion.
In a further embodiment of any of the above, the inlet portion comprises an inlet cone having an upstream end connected to an inlet pipe and a downstream end connected to the center housing portion, and wherein the downstream end has a greater outer dimension than the upstream end, and wherein the outlet portion comprises an outlet cone having an upstream end connected to the center housing portion and a downstream end connected to an outlet pipe, and wherein the upstream end has a greater outer dimension than the downstream end.
In a further embodiment of any of the above, a resonator housing is separate from the component housing and provides the resonator volume, and wherein the at least one resonator element comprises a pipe that connects the component housing to the resonator housing, and wherein the insulating material completely fills the resonator volume.
In a further embodiment of any of the above, a resonator housing is separate from the component housing and provides the resonator volume, and wherein the at least one resonator element comprises a pipe that connects the component housing to the resonator housing, and wherein the insulating material only partially fills the resonator volume and is located at a connection to the pipe.
In another exemplary embodiment, a vehicle exhaust system includes at least one exhaust gas treatment element and a component housing defining an internal cavity. The component housing comprises a center housing portion that encloses the at least one exhaust gas treatment element, an inlet cone positioned at an upstream end of the center housing portion, and an outlet cone positioned at a downstream end of the center housing portion. The component housing is located in a hot end of the vehicle exhaust system and is immediately downstream of an engine or turbocharger. A resonator volume is connected in parallel with the internal cavity via at least one resonator element, and there is no net flow out of the resonator volume. Insulating material is located within the resonator volume.
In a further embodiment of any of the above, the at least one resonator element comprises at least one of a pipe and a perforated portion of the component housing.
In a further embodiment of any of the above, a resonator housing is separate from the component housing and provides the resonator volume, and wherein the at least one resonator element comprises a pipe that connects the component housing to the resonator housing, and wherein the insulating material at least partially fills the resonator volume.
In a further embodiment of any of the above, a resonator housing completely surrounds the component housing such that the resonator volume is provided between an inner surface of the resonator housing and an outer surface of the component housing, and wherein the insulating material at least partially fills the resonator volume.
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.
Exhaust gas operational temperatures at the hot end 18 are typically higher than exhaust gas operational temperatures at the cold end 20 due to the proximity of the engine 12. In one example, exhaust gas operational temperatures at the hot end can be within a range of 750-950 degrees Celsius. Under certain conditions, the operational temperatures may exceed 1000 degrees Celsius. In the cold end 20, as it is located further downstream of the engine 12 than the hot end 18, exhaust gas operational temperatures are lower, and in one example, are typically less than 650 degrees Celsius.
Exhaust components 24 at the hot end 18 can include, for example, exhaust gas treatment elements such as a diesel oxidation catalyst (DOC), a diesel particulate filter (DPF) and a selective catalytic reduction (SCR) catalyst or a gasoline particulate filter (GPF) and one or several three way catalysts (TWC) that are used to remove contaminants from the exhaust gas as known. Exhaust components 26 in the cold end 20 typically include, for example, noise attenuation components such as mufflers, resonators, etc. Exhaust gases pass from the hot end 18 into the cold end 20 and exit the exhaust system 10 via the tailpipe 22. The described exhaust components can be mounted in various different configurations and combinations dependent upon vehicle application and available packaging space.
It has been shown through testing and simulations that a Helmholtz Resonator, such as an acoustic volume of the order of two to four liters in communication with the exhaust flow via a neck pipe for example, that is positioned in the hot end 18 between a turbocharger outlet and an after-treatment element, or between after-treatment elements, provides an acoustic benefit about twice that of a similar amount of volume applied in the cold end 20 (downstream of the after-treatment section of the exhaust system 10) with little or 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.
The subject disclosure packages one or more Helmholtz resonators at various locations in the hot end 18 of the system 10. For example, the resonator(s) could be located immediately after the exhaust manifold or turbocharger outlet but before the after-treatment elements, between the after-treatment elements, and/or immediately after the after-treatment elements. Various example configurations are discussed below and shown in the accompanying figures.
A resonator volume 42, enclosed within a resonator housing 44, is coupled to be in parallel with the internal cavity 34 via a resonator element 46 that comprises a Helmholtz resonator, for example. In one example, the resonator housing 44 extends around the component housing 32. The resonator housing 44 can completely surround, or partially surround, the component housing 32. The resonator housing 44 can also be coaxial with the component housing 32 or offset (non-coaxial) from the component housing 32.
In one example, additional material 48 is located within the resonator volume 42. The additional material 48 can comprise, for example, fibrous material that is used for sound absorption and/or insulation. Any type of such material can be used; however, the material should be able to withstand high exhaust gas temperatures and corrosive/harsh environmental conditions. Examples of such materials are poly-crystalline wool (PCW), refractory ceramic fibers (RCF), alkaline silicate fibers, silica fibers, high temperature glass fibers, or glass fibers.
As such, the subject disclosure provides a dampened resonator comprising a parallel resonator volume 42 with fibrous material 48 that is closely situated next to a resonator element 46. Using the fibrous material dampens and broadens the Helmholtz resonance making the attenuation weaker but broader, which in certain conditions is preferable to providing a strong but sharp attenuation. Additionally, the fibrous material lowers an outer shell skin temperature and improves heat retention in the exhaust gas treatment element, which provides for improved emissions performance.
The component housing 32 receives exhaust gases from an inlet pipe 50 and directs treated exhaust gases to the cold end 20 via an outlet pipe 52. In one example, the component housing 32 includes 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 and that connects to the inlet pipe 50, and an outlet portion 58 that is positioned at an opposite end of the center housing portion 54 and connects to the outlet pipe 52. In one example, the inlet 56 and outlet 58 portions comprise inlet and outlet cones.
In one example, the component housing 32 defines a center axis A and the inlet portion 56, first exhaust gas treatment element 36, second exhaust gas treatment element 38, and outlet portion 58 are coaxial with the center axis A.
In one example, the resonator housing 44 extends around the component housing 32 such that the resonator volume 42 is enclosed between an inner surface 60 of the resonator housing 44 and an outer surface 62 of the component housing 32. In one example, the resonator housing 44 includes a center housing portion 64 that surrounds the center housing portion 54 of the component housing 32, an inlet portion 66 that is positioned at one end of the center housing portion 64 to surround the inlet cone of the component housing 32, and an outlet portion 68 that is positioned at an opposite end of the center housing portion 64 to surround the outlet cone of the component housing 32. Thus, in this example, the resonator housing 44 generally matches a shape of the component housing 32. The housing 32, 44 can have any cross-sectional shape including circular, oval, elliptical, polygonal, etc.
As such, in some disclosed embodiments, the inlet portions 56, 66 and the outlet portions 58, 68 comprise inlet and outlet cones. The inlet cone 56 of the component housing 32 has an upstream end connected to the inlet pipe 50 and a downstream end connected to the center housing portion 54 wherein the downstream end has a greater outer dimension than the upstream end. The inlet cone 66 of the resonator housing 44 has an upstream end connected to the inlet pipe 50 and/or inlet cone 56 and a downstream end connected to the center housing portion 64 wherein the downstream end has a greater outer dimension than the upstream end. The outlet cone 58 of the component housing 32 has an upstream end connected to the center housing portion 54 and a downstream end connected to the outlet pipe 52 wherein the upstream end has a greater outer dimension than the downstream end. The outlet cone 68 of the resonator housing 44 has an upstream end connected to the center housing portion 64 and a downstream end connected to the outlet pipe 52 and/or outlet cone 58 wherein the upstream end has a greater outer dimension than the downstream end.
The at least one resonator element 46 couples the resonator volume 42 with the internal volume of the internal cavity 34 in a parallel configuration. In one example, the resonator element 46 comprises at least one of a perforated portion of the component housing 32 and a Helmholtz neck or pipe.
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 location of the resonator element 46 they cause the exhaust gas in the resonator element 46 to start moving. For low frequencies this gas can be considered as a lumped mass. The lumped mass of gas in the resonator element 46 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 resonator, and as the resonator element 46 comprises a side-branch arrangement, the impact on back pressure is negligible. This lack of flow in the resonator volume is also beneficial for retention of the insulating material 48. There will also be a positive effect on convection into the main gas volume. The fibrous material will work to broaden the tuned frequency of the resonator.
In the example of
One purpose of the material 48 is to absorb noise and the absorption will be particularly effective at high frequencies. Use of the material 48 will also broaden the attenuation of the Helmholtz resonator, which is tuned to much lower frequencies. It will provide an additional benefit of thermally insulating the resonator housing 44 from the heat of the first 36 and second 38 gas treatment elements. This thermal insulation will also result in an increase in the temperature of the component housing 32 and the substrate material of the first 36 and second 38 gas treatment elements such that the material can retain heat more effectively during less strenuous driving.
If additional retention is needed for the material 48, a perforated grid 72 on the neck 70 can be used. The perforated grid 72 comprises a flat structure with a plurality of openings and may cover an open end of the neck 70.
In the examples shown in
As discussed above, a resonator volume 42 that is closely coupled to the engine is more efficient and effective than the same volume added to a muffler in the middle or rear of the exhaust system. Typically, 3 or 4 liters added to the hot end is about as effective as 6 to 8 liters in the cold end. The subject disclosure uses necks or perforated housing portions to provide an acoustic volume in the hot end that forms a Helmholtz resonator. The neck dimensions (length and diameter) and acoustic volume determine a tuned frequency. When a volume surrounds a perforated portion, the perforates are the neck of the Helmholtz resonator. The perforates can be tuned more broadly than the neck configuration.
As Helmholtz resonators are tuned to lower frequencies (by making the neck of the resonator to have a smaller diameter or a longer length) their resonances become increasingly sharp. This makes them useful over a decreasingly small engine speed range. The use of the additional material in the acoustic volume provides a damping effect and reduces the sharpness effect. The use of the additional material also provides thermal benefits in addition to acoustic benefits. The material can be used to hold substrates in place, to insulate the substrates such that the substrates heat up quickly (good for light-off) and retains temperatures with less heat input, and to reduce external temperatures of components.
Thus, the subject disclosure combines a tuning resonator element 46 for acoustic attenuation in a component in the hot end 18 of the exhaust system 10 with fibrous material 48 that is located within the resonator volume 42 to provide further acoustic and/or thermal benefits. This combination results in improved acoustic efficiency with negligible back pressure impact resulting in tailpipe noise/acoustic volume improvement.
Although various embodiments have 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.
