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 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.
In one exemplary embodiment, a method of forming an acoustic volume in a vehicle component includes providing a vehicle frame member that includes a hollow cavity, forming an internal shell that is completely sealed and which includes at least one connection point, and locating the internal shell within the hollow cavity. At least one exhaust system component is connected to the internal shell at the connection point to provide at least one acoustic volume.
In another exemplary embodiment, a vehicle exhaust system includes a first component that receives exhaust gas output from an engine, a first exhaust assembly fluidly coupled to the first component to define a hot end of a vehicle exhaust system, and a second exhaust assembly fluidly coupled to the first exhaust assembly to define a cold end of the vehicle exhaust system, wherein an exhaust gas temperature at the hot end is higher than at the cold end. A frame member includes a hollow cavity. An internal shell is completely sealed and includes at least one connection point, wherein the internal shell is received within the hollow cavity to provide an internal acoustic volume. A neck connects to the connection point of the internal shell such that the internal acoustic volume is in parallel to the hot end of the vehicle exhaust system.
In a further embodiment of the above, the method includes forming the internal shell by blow molding.
In a further embodiment of any of the above, the internal shell is formed from a plastic or composite material.
In a further embodiment of any of the above, the frame member comprises a support beam configured to at least partially support the engine and that connects to at least one additional vehicle frame member.
In a further embodiment of any of the above, the frame member comprises at least first and second outer shells that enclose the hollow cavity.
In a further embodiment of any of the above, the first and second outer shells comprise metal stampings.
In a further embodiment of any of the above, the first component comprises an exhaust manifold or turbocharger, and wherein the first exhaust assembly includes one or more of a catalytic converter, diesel oxidation catalyst, or a particulate filter, and wherein the second exhaust assembly comprises one or more mufflers coupled to one or more tailpipes.
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 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), a three-way catalyst (TWC), 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 cold end 16 can include components such as mufflers, valves, and one or more tailpipes, for example. The described exhaust components can be mounted in various different configurations and combinations dependent upon vehicle application and available packaging space.
As discussed above,
Fn=(nc)/(4L) where:
fn=resonant frequency of standing wave n (Hz)
n=ordinal number of standing wave
c=speed of sound (m/s)
L=length of closed-open pipe (m)
The chart of
It has been shown through testing and simulations that a Helmholtz Resonator, such as an acoustic volume of the order of 2 to 4 liters (L) connected in parallel 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
The subject invention proposes a method for forming one or more Helmholtz Resonators so that they can be packaged at one of various locations in the hot end 14 of the system 10. The difficulty with this proposal; however, is that there is very little packaging space available at the hot end 14 of the system. In order to overcome this packaging issue, it is proposed to use an already existing vehicle component as the Helmholtz volume. One example of such a volume is found in application Ser. No. 15/874,288, which was filed on Jan. 18, 2018 and which is assigned to the assignee of the present application and incorporated herein.
As shown in
The vehicle frame member 30 provides an internal acoustic volume 52 that is enclosed within the frame member 30. The internal acoustic volume 52 is fluidly coupled in parallel to the hot end 14 of the exhaust system 10 with a connecting pipe or neck 54. In one example, the vehicle frame member 30 comprises an engine sub-frame that extends underneath the engine 12 to support the engine 12 and possibly a vehicle transmission 56 or gearbox. The engine 12 and transmission 56 are schematically shown in
In one example shown in
In the example shown in
In each of these different configurations, the internal acoustic volume 52 is sealed and in parallel with the exhaust flow through the exhaust system such that there is no net flow in the Helmholtz resonator. Hot engine exhaust gas flows into the component 36 through the inlet pipe 46, expands and slows down as the gas travels through inlet cone 44, passes through the exhaust gas treatment element 42, then contracts and passes through the outlet cone 48 before exiting into the outlet pipe 50. The neck 54 connects the internal acoustic volume 52 in parallel with the flow through the component 36 to provide the Helmholtz resonator.
The exhaust gas pressure pulsations from the engine 12 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 flexible neck 54 they cause the exhaust gas in the resonator neck/connection to start moving. For low frequencies this gas can be considered as a lumped mass. The lumped mass of gas in the resonator neck 54 compresses or rarifies the exhaust gas in the internal acoustic volume 52. As the lumped mass of gas compresses this volume 52, 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 engine sub-frame volume 52 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 in parallel with the exhaust system, and as the resonator neck 54 comprises a side-branch arrangement, the impact on back pressure is negligible.
In each of these example configurations, the hollow cavity that defines the internal acoustic volume 52 is completely sealed and airtight. The subject invention provides a method for achieving this sealed volume. In one example, the method of forming the acoustic volume includes providing the vehicle frame member 30 with a hollow cavity 80 as shown in
In one example, the internal shell 82 is formed by a blow molding process and the connection point 84 comprises at least one opening 86 resulting from the blow molding process. In one example, the internal shell 92 is formed from a plastic or composite material.
In one example, the vehicle frame member 30 is provided as at least first 30a and second 30b outer shells that enclose the hollow cavity 80. In one example method, the first 30a and second 30b outer shells are attached to each other to define a space for the hollow cavity 80. Next, the internal shell 82 is formed by blow molding material directly into the hollow cavity 80 to form the internal shell 82 after the frame has been assembled. One advantage with this configuration is that the internal volume is defined by the inner surfaces of the frame shells to maximize the volume and to ensure that the volume is completely leak-free.
In another example, the vehicle frame member 30 is provided as at least first 30a and second 30b outer shells that enclose the hollow cavity 80 and the internal shell 82 is formed prior to attaching the first 30a and second 30b outer shells to each other. One advantage with this configuration is that a plurality of internal shells 82 can be formed for various shapes/sizes and then a desired shape/size can be selected at a vehicle assembly location for incorporation into the frame.
Another example method includes providing the vehicle frame member 30 as a solid structure. The solid structure is then modified by machining, for example, to form one or more hollow cavities 80. The cavity 80 should be formed to be a shape/size that is not detrimental to the overall structural integrity of the frame member. An internal shell 82 can then be blow molded or inserted into each cavity 80 to form the one or more acoustic volumes. One advantage with this configuration is that an existing component can be modified without requiring a new frame member to be installed.
In another example, the vehicle frame member is comprised of a composite material with an internal hollow cavity that forms the acoustic volume. This hollow cavity can then be connected in parallel to the exhaust system component to form a parallel acoustic volume. Optionally, this composite vehicle frame member can be surrounded by a protective cover to prevent damage and/or puncture of the frame member into the hollow cavity. In one example, this protective cover can comprise metal stampings as discussed above that are placed around the composite material, which would then form an inner shell.
In one optional example, instead of forming a single acoustic volume in the frame member 30, a plurality of acoustic volumes can be formed in the vehicle frame member 30. Each acoustic volume could have a corresponding internal shell 82 that would be received within the hollow cavity 80 of the frame member 30.
As such, a leak-free volume is ensured within a space formed between frame outer shells of an engine sub-frame, cradle, or vehicle frame structure by using a plastic or composite internal shell that is received within such space. The internal shell can be blow molded into the space between the frame outer shells which ensures the leak-free volume because the only entrance to the internal volume is via the injection point. Additional advantages with this is that the internal shell is then being protected by the structure of the frame outer shells themselves. The opening or hole left by the blow molding process can then be used to form the connection location for the neck 54 which connects the volume of the internal shell 82 to the rest of the vehicle exhaust system.
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. Further, by including an acoustic volume within the already existing engine sub-frame structure, packaging problems are significantly reduced.
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.